Circulating Current and ZVS-on of a Dual Active Bridge DC-DC Converter: A Review
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paper_title: Research on voltage and power balance control for cascaded modular solid-state transformer

paper_content:

The solid-state transformer (SST) is one of the key elements in power electronic-based microgrid systems. The single-phase SST consists of a modular multilevel ac-dc rectifier, a modular dual active bridge (DAB) dc-dc converter with high-frequency transformers, and a dc-ac inverter stage. However, due to dc bus voltage and power unbalancing in each module, the modular SST often presents instability problems making its design difficult and causing unpredictable behavior. Moreover, the unbalanced dc-link voltages increase the stress of the semiconductor devices, and also cause high harmonic distortions of grid current, therefore, necessitating the use of a bigger ac filter. This paper presents a novel single-phase d-q vector-based common-duty-ratio control method for the multilevel rectifier, and a voltage feedforward and feedback based controller for the modular DAB converter. With the proposed control methods, the dc-link voltage and power in each module can be balanced. In addition, the low-distortion grid current, unity power factor, and bidirectional power flow can be achieved. Simulation and experimental results are presented to validate the proposed control methods.
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paper_title: A Modular-Designed Three-Phase High-Efficiency High-Power-Density EV Battery Charger Using Dual/Triple-Phase-Shift Control

paper_content:

In this paper, an enhancement-mode GaN high-electron mobility transistor (HEMT)-based 7.2-kW single-phase charger was built. Connecting three such single-phase modules to the three-phase grid, respectively, generates a three-phase ∼22-kW charger with the $>{\text{97}}\% $ efficiency and $>{\text{3.3}}-{\rm{kW}/ \rm{L}}$ power density, superior to present Si-device-based chargers. In addition to GaN HEMTs with fast-switching transitions yielding high efficiency, the proposed charger employs the dc/dc stage to control the power factor and power delivery simultaneously, yielding little dc-bus capacitance and thereby high power density. To secure the soft switching for all switches within full voltage and power ranges, a variable switching frequency control with dual phase shifts was adopted at high power, and a triple phase shift was employed to improve the power factor at low power. Both control strategies accommodated the wide input range (80–260 VAC) and output range (200–450 VDC). A closed-loop control for the three-phase charger was realized to minimize the output current ripple and balance the power among three single-phase modules. Experimental results validated this design.
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paper_title: Future electronic power distribution systems a contemplative view

paper_content:

Although it has long been argued that electronic power converters can help improve system controllability, reliability, size, and efficiency, their penetration in power systems is still quite low. The often-cited barriers of higher cost and lower reliability of the power converters are quite high if power electronics is used as direct, one-to-one, replacement for the existing electromechanical equipment. However, if the whole power distribution system were designed as a system of controllable converters, the overall system cost and reliability could actually improve, as is currently the case at low power levels within computer and telecom equipment. Starting from the example of a computer power system, the paper contemplates possible future ac and dc electronic power distribution system architectures, especially in the presence of renewable energy sources. The proposed nanogrid-microgrid-…-grid structure achieves hierarchical dynamic decoupling of generation, distribution, and consumption by using bidirectional converters as energy control centers. This is illustrated by the description and simulation of static and dynamic operation of a dc nanogrid in a hypothetical future sustainable home. Several ideas for modeling, analysis, and system-level design of such systems, including power flow control, protection, stability, and subsystem interactions, are presented.
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paper_title: BP Statistical review of world energy 2014

paper_content:

BP Statistical review of world energy 2014 : 63rd edition. BP, June 2014, 48 p. http://www.bp.com/en/global/corporate/about-bp/energy-economics/statistical-review-of-world-energy.html Discours de Christof Ruhl, economiste en chef de BP, a l'occasion de l'edition 2014 du rapport : Introduction: the last ten years The purpose of this review has always been to provide objective data on global energy developments; and to chronicle changes in global energy markets year by year, in as rigorous a fa...
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paper_title: A Bidirectional DC–DC Converter for an Energy Storage System With Galvanic Isolation

paper_content:

This paper addresses a bidirectional dc-dc converter suitable for an energy storage system with an additional function of galvanic isolation. An energy storage device such as an electric double layer capacitor is directly connected to a dc side of the dc-dc converter without any chopper circuit. Nevertheless, the dc-dc converter can continue operating when the voltage across the energy storage device drops along with its discharge. Theoretical calculation and experimental measurement reveal that power loss and peak current impose limitations on a permissible dc-voltage range. This information may be useful in design of the dc-dc converter. Experimental results verify proper charging and discharging operation obtained from a 200-V, 2.6-kJ laboratory model of the energy storage system. Moreover, the dc-dc converter can charge the capacitor bank from zero to the rated voltage without any external precharging circuit.
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paper_title: Comprehensive Conceptualization, Design, and Experimental Verification of a Weight-Optimized All-SiC 2 kV/700 V DAB for an Airborne Wind Turbine

paper_content:

This paper details the design, implementation, and experimental verification of a minimum weight input series output parallel structured dual active bridge (DAB) converter for an airborne wind turbine system. The main power components of the DAB converter, particularly the bridge circuits, the actively cooled high-frequency transformer and inductor, and the cooling system, which largely contribute to the total system weight, are designed and realized based on multiobjective considerations, i.e., with respect to weight and efficiency. Furthermore, the design includes all necessary considerations to realize a fully functional prototype, i.e., it also considers the auxiliary supply, the control for a stable operation of the system, which also comprises an input filter, over the specified operating range, and the start-up and shut down procedures. These considerations show the complex interactions of the various system parts and reveal that a comprehensive conceptualization is necessary to arrive at a reliable minimum weight design. Experimental results validate the proposed design procedure for a realized lightweight DAB hardware prototype with a rated power of $ \mathrm {6.25~\,kW}$ . The prototype weighs $ \mathrm {1.46~\,kg}$ , i.e., features a power-to-weight ratio of $ \mathrm {4.28~\,kW{/}\,kg}$ ( $ \mathrm {1.94~\,kW{/}\,lb}$ ), and achieves a maximum full-load efficiency of 97.5%.
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paper_title: Dual active bridge based battery charger for plug-in hybrid electric vehicle with charging current containing low frequency ripple

paper_content:

High power density is strongly preferable for the on-board battery charger of Plug-in Hybrid Electric Vehicle (PHEV). Wide band gap devices, such as Gallium Nitride HEMTs are being explored to push to higher switching frequency and reduce passive component size. In this case, the bulk DC link capacitor of AC-DC Power Factor Correction (PFC) stage, which is usually necessary to store ripple power of two times the line frequency in a DC current charging system, becomes a major barrier on power density. If low frequency ripple is allowed in the battery, the DC link capacitance can be significantly reduced. This paper focuses on the operation of a battery charging system, which is comprised of one Full Bridge (FB) AC-DC stage and one Dual Active Bridge (DAB) DC-DC stage, with charging current containing low frequency ripple at two times line frequency, designated as sinusoidal charging. DAB operation under sinusoidal charging is investigated. Two types of control schemes are proposed and implemented in an experimental prototype. It is proved that closed loop current control is the better. Full system test including both FB AC-DC stage and DAB DC-DC stage verified the concept of sinusoidal charging, which may lead to potentially very high power density battery charger for PHEV.
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paper_title: Open data in power grid modelling : new approaches towards transparent grid models

paper_content:

In order to analyse the mid- and long-term impacts of energy related policies, different modelling approaches can be derived. However, the results of even the best energy system model will highly depend on the underlying input data. First, in this contribution the importance and availability issues of grid data in the context of energy system modelling are highlighted. Second, this paper focuses on power grid modelling based on open and publicly available data from OpenStreetMap using open source software tools. Two recent approaches developed to build electrical transmission network models using openly available data sources are presented and discussed. The proposed methods provide transparent assumptions, simplifications and documentation of grid modelling. This results in the ability of scientists and other stakeholders to validate, discuss or reproduce the results of energy system models. Thus the new open approaches offer a unique opportunity to increase transparency, comparability and reproducibility of results in energy system modelling.
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paper_title: High-Efficiency Bidirectional DAB Inverter Using a Novel Hybrid Modulation for Stand-Alone Power Generating System With Low Input Voltage

paper_content:

This paper proposes a high-efficiency bidirectional dual-active-bridge (DAB) inverter using a novel hybrid modulation for a stand-alone power generating system with a low input voltage. The proposed DAB inverter consists of a DAB dc–dc converter and a synchronous rectifier (SR) for unfolding. The DAB dc–dc converter transforms the low dc voltage into a rectified sine wave that pulsates twice the grid frequency. The rectified sine wave unfolds into the grid voltage by SR. The proposed hybrid modulation combines a phase shift control and a variable frequency control. The variable frequency control converts the nonlinear function of the phase shift angle into a linear function and controls the output power. This leads to a simple closed-loop control for the sinusoidal current waveform, a low harmonic distortion, and a high-voltage conversion ratio without an increase of the transformer turn ratio. Since the proposed DAB inverter has only a single power conversion stage, it has a simple structure, high power density, and low cost. It also has a high efficiency of 94.2% by a zero-voltage switching (ZVS) turn on of the switches in two full bridges (FBs). The operation principle of the proposed DAB inverter using this hybrid modulation is analyzed and verified. Experimental results for a 1-kW prototype are obtained to show the performance.
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paper_title: Power Electronic Traction Transformer-Low Voltage Prototype

paper_content:

Recently, a world's first ever power electronic traction transformer (PETT) for 15 kV, 16 2/3Hz railway grid, has been newly developed, commissioned, and installed on the locomotive, where it is presently in use. This marks an important milestone in the traction world. The design and development of the PETT are described in this paper, where a low-voltage (LV) PETT prototype is presented. It has been designed for the purposes of control hardware and software commissioning, thus serving a role of an analogue simulator. In this paper, emphasis is placed on the overall system requirements, from where control system has been developed, implemented, and successfully commissioned. The development of a 1.2MVA medium-voltage PETT prototype will be reported separately in accompanying paper.
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paper_title: Design and Implementation of a Two-Stage Grid-Connected High Efficiency Power Load Emulator

paper_content:

The need to reduce the time consumption in developing and implementing power converters, and to improve the effectiveness of the test equipment, continues to grow. This trend is further accelerated through the development of electricity-based technology, such as the electric or hybrid vehicle. As the price of energy continues to increase, regenerative test equipment used for validating power converters are gaining importance and attention. This paper focuses on the development of a two-stage regenerative power load emulator. This type of intelligent load requires a connection to the network interface, which, for some applications, should be bidirectional and must possess a galvanic isolation. The development of such grid-connected unit that processes ac-dc conversion is treated in this paper. A 5 kW prototype is used as a base to model, simulate, design, implement, and test such a system. The stability of the interconnection between the two conversion stages is established and tested in real-time applications. The prototype was tested at 180, 220, and 260 V RMS. The measured efficiency is higher than 90%, and the power factor is 0.99 over a wide range of operation.
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paper_title: A Modular Multilevel DC-Link Front-to-Front DC Solid-State Transformer Based on High-Frequency Dual Active Phase Shift for HVDC Grid Integration

paper_content:

This paper proposes a modular multilevel dc-link dc solid-state transformer (MADCT) based on high-frequency dual active phase shift for HVDC grid integration. The proposed MADCT employs one arm of modular multilevel converter as HVDC active front-end interface and dual active bridge as high-frequency power transfer link, which brings many advantages and makes the operation of MADCT quiet different with traditional dc transformers. Compared with the traditional dc transformer schemes, the MADCT not only has good modularity and flexibility but also has good fault handling capacity. Especially, the performances of current stress, power transfer capacitor, and efficiency are improved. The topology, operation principle, voltage, current, power performances, and control and parameter design are presented and analyzed comprehensively in this paper. At last, a MADCT prototype is built and the experimental results verify the correctness and effectively of the proposed solution.
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paper_title: A Distributed Architecture Based on Microbank Modules With Self-Reconfiguration Control to Improve the Energy Efficiency in the Battery Energy Storage System

paper_content:

This paper proposes a new distributed battery energy architecture based on the microbank module (MBM) for dc microgrids. The benefits of the proposed architecture include: 1) no voltage sharing problem and no overcharge/overdischarge problem; 2) high compatibility and reliability; 3) high energy utilization efficiency; 4) reduced volume and weight of the battery management system (BMS). The proposed MBM consists of a microbidirectional dc/dc converter, a micro-BMS and a cell bank. Moreover, taking advantage of the battery recovery effect, a self-reconfiguration discharge strategy is also proposed to further enhance the battery performance and discharge efficiency of the new battery energy storage system (BESS). To optimize the proposed control, an efficiency analytical model considering the battery recovery effect is proposed using the curve fitting method. Owing to the bidirectional capability, soft switching capability and high efficiency, the dual active bridge (DAB) converters are chosen as the microbidirectional dc/dc converters. A hybrid modulation strategy with variable switching frequency combining the conventional phase-shift modulation and triangular current modulation is proposed for the DAB converter to reduce the dominant loss and improve the efficiency in wide load range based on the minimum loss model. A 1.5-kW experimental testing platform consisting of four MBMs and four 12 V/100 Ah lithium battery modules was built to verify the proposed architecture with the control and the proposed model. The experimental results show that the discharge time of the proposed distributed BESS is increased significantly under wide operation condition with the self-reconfiguration control. The discharge efficiency of the BESS is improved by 7.1% with the idling time of 5 min under the power level of 1.5 kW.
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paper_title: A three-phase soft-switched high power density DC/DC converter for high power applications

paper_content:

Three DC/DC converter topologies suitable for high-power-density high-power applications are presented. All three circuits operate in a soft-switched manner, making possible a reduction in device switching losses and an increase in switching frequency. The three-phase dual-bridge converter proposed is shown to have the most favorable characteristics. This converter consists of two three-phase inverter stages operating in a high-frequency six-step mode. In contrast to existing single-phase AC-link DC/DC converters, lower turn-off peak currents in the power devices and lower RMS current ratings for both the input and output filter capacitors are obtained. This is in addition to smaller filter element values due to the higher-frequency content of the input and output waveforms. Furthermore, the use of a three-phase symmetrical transformer instead of single-phase transformers and a better utilization of the available apparent power of the transformer (as a consequence of the controlled output inverter) significantly increase the power density attainable. >
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paper_title: The Future Renewable Electric Energy Delivery and Management (FREEDM) System: The Energy Internet

paper_content:

This paper presents an architecture for a future electric power distribution system that is suitable for plug-and-play of distributed renewable energy and distributed energy storage devices. Motivated by the success of the (information) Internet, the architecture described in this paper was proposed by the NSF FREEDM Systems Center, Raleigh, NC, as a roadmap for a future automated and flexible electric power distribution system. In the envisioned “Energy Internet,” a system that enables flexible energy sharing is proposed for consumers in a residential distribution system. The key technologies required to achieve such a vision are presented in this paper as a result of the research partnership of the FREEDM Systems Center.
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paper_title: Overview of Dual-Active-Bridge Isolated Bidirectional DC–DC Converter for High-Frequency-Link Power-Conversion System

paper_content:

High-frequency-link (HFL) power conversion systems (PCSs) are attracting more and more attentions in academia and industry for high power density, reduced weight, and low noise without compromising efficiency, cost, and reliability. In HFL PCSs, dual-active-bridge (DAB) isolated bidirectional dc-dc converter (IBDC) serves as the core circuit. This paper gives an overview of DAB-IBDC for HFL PCSs. First, the research necessity and development history are introduced. Second, the research subjects about basic characterization, control strategy, soft-switching solution and variant, as well as hardware design and optimization are reviewed and analyzed. On this basis, several typical application schemes of DAB-IBDC for HPL PCSs are presented in a worldwide scope. Finally, design recommendations and future trends are presented. As the core circuit of HFL PCSs, DAB-IBDC has wide prospects. The large-scale practical application of DAB-IBDC for HFL PCSs is expected with the recent advances in solid-state semiconductors, magnetic and capacitive materials, and microelectronic technologies.
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paper_title: A review of bidirectional dual active bridge converter

paper_content:

To have a systematic synthesis and galvanic isolation, it is common to use a full-bridge bidirectional DC-DC converter which is sometimes called dual active bridge. A comparative evaluation of full-bridge based bidirectional DC-DC converter is presented in this paper. Basic operation, control algorithm, advantages and disadvantages of several types of bidirectional converters are explained.
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paper_title: Voltage Balance Control Based on Dual Active Bridge DC/DC Converters in a Power Electronic Traction Transformer

paper_content:

In this paper, a voltage balance control strategy based on dual active bridge (DAB) dc/dc converters in a power electronic traction transformer (PETT) is proposed. Based on this strategy, the output-parallel DAB converters can be equivalent to an input-series-output-parallel system. Furthermore, a PETT starting control method is put forward, which can effectively avoid risks of overcurrent and overvoltage in the PETT starting process. In order to carry out the controller design and system stability analysis, three different kinds of mathematical models of DAB converters are set up. The first model is related to a single DAB converter, the second model reflects the equivalent relation between an output-parallel DAB system and a single DAB converter in terms of the output-voltage control loop, and the third model indicates that the voltage balance control system based on DAB converters is a multiinput-multioutput system. Due to the nonzero off-diagonal elements of the controlled plant, there is a mutual effect between different control loops, which is defined as “interaction” in the multivariable feedback control theory. The stability of the voltage balance control system is made up of two parts, including the stability of each single-input-single-output (SISO) control loop and the influence of the interaction on the system stability. The research is carried out to measure the intensity of the interaction in this paper, and a criterion directly based on the controlled plant is proposed to predict the influence of the interaction, which can obviously simplify the system stability analysis. Considering the particular traction onboard application, a new control structure toward the voltage balance controller is introduced. Based on the new structure, the controller is designed and the stability of the SISO system is analyzed. Finally, a five-cell PETT prototype with rated power of 30 kW is taken to carry out further research, and the experiment results verify the effectiveness and correctness of the proposed algorithms.
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paper_title: Medium-Voltage Solid-State Transformer: Technology for a Smarter and Resilient Grid

paper_content:

The most important impact of power electronics on our society in the last 50 years has been the elimination of the 60-Hz ac power delivery system for consumer electronic products. Central to this achievement is the use of silicon (Si) power devices and pulsewidth modulation (PWM) techniques in delivering regulated ac and dc powers to low-voltage (LV) loads such as light-emitting diodes and computers. These solid-state power electronic converters have provided our society numerous benefits, including high-quality power and substantial energy savings. They also form the core technology for integrating renewable energies such as wind and solar into our power grid. Figure 1 shows a typical power delivery architecture commonly found in computer supplies and data centers. The incoming universal ac grid power is converted by a power factor correction circuit to 400 V dc before it is stepped down to a lower voltage dc intermediate bus, such as 12 V, and then it powers the digital loads at voltages as low as 1 V by a point-of-load converter. Si power metal-oxide-semiconductor field-effective transistor (MOSFET) transistors from 20 V to 700 V are almost exclusively used in this application with switching frequencies from tens of kilohertz to one megahertz. Emerging devices based on gallium nitride (GaN) heterojunction field effect transistors reduce the switching and conduction losses when compared with Si power MOSFETs and are, therefore, poised to compete in these applications, driven by the need for higher energy efficiency and higher power density.
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paper_title: A Bidirectional Isolated DC–DC Converter as a Core Circuit of the Next-Generation Medium-Voltage Power Conversion System

paper_content:

This paper describes a bidirectional isolated dc-dc converter considered as a core circuit of 3.3-kV/6.6-kV high-power-density power conversion systems in the next generation. The dc-dc converter is intended to use power switching devices based on silicon carbide (SiC) and/or gallium nitride, which will be available on the market in the near future. A 350-V, 10-kW and 20 kHz dc-dc converter is designed, constructed and tested. It consists of two single-phase full-bridge converters with the latest trench-gate insulated gate bipolar transistors and a 20-kHz transformer with a nano-crystalline soft-magnetic material core and litz wires. The transformer plays an essential role in achieving galvanic isolation between the two full-bridge converters. The overall efficiency from the dc-input to dc-output terminals is accurately measured to be as high as 97%, excluding gate drive and control circuit losses from the whole loss. Moreover, loss analysis is carried out to estimate effectiveness in using SiC-based power switching devices. Loss analysis clarifies that the use of SiC-based power devices may bring a significant reduction in conducting and switching losses to the dc-dc converter. As a result, the overall efficiency may reach 99% or higher
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paper_title: A novel ZVS DC/DC converter for high power applications

paper_content:

This paper presents a novel ZVS PWM DC/DC power converter for high power applications. By using two active switches on the secondary side of a transformer, the proposed converter achieves not only ZVS of the active switches in the entire load range, but also soft commutation of the output rectifier diodes. Simulation results and experimental results of a 2.8 kW 200 kHz DC/DC converter are presented.
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paper_title: BP Statistical review of world energy 2014

paper_content:

BP Statistical review of world energy 2014 : 63rd edition. BP, June 2014, 48 p. http://www.bp.com/en/global/corporate/about-bp/energy-economics/statistical-review-of-world-energy.html Discours de Christof Ruhl, economiste en chef de BP, a l'occasion de l'edition 2014 du rapport : Introduction: the last ten years The purpose of this review has always been to provide objective data on global energy developments; and to chronicle changes in global energy markets year by year, in as rigorous a fa...
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paper_title: A three-phase soft-switched high power density DC/DC converter for high power applications

paper_content:

Three DC/DC converter topologies suitable for high-power-density high-power applications are presented. All three circuits operate in a soft-switched manner, making possible a reduction in device switching losses and an increase in switching frequency. The three-phase dual-bridge converter proposed is shown to have the most favorable characteristics. This converter consists of two three-phase inverter stages operating in a high-frequency six-step mode. In contrast to existing single-phase AC-link DC/DC converters, lower turn-off peak currents in the power devices and lower RMS current ratings for both the input and output filter capacitors are obtained. This is in addition to smaller filter element values due to the higher-frequency content of the input and output waveforms. Furthermore, the use of a three-phase symmetrical transformer instead of single-phase transformers and a better utilization of the available apparent power of the transformer (as a consequence of the controlled output inverter) significantly increase the power density attainable. >
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paper_title: Operation, design and control of dual H-bridge-based isolated bidirectional DC-DC converter

paper_content:

The operation, design and control of an isolated bidirectional DC - DC converter for hybrid electric vehicle energy management applications are discussed. Different operation modes and boundary conditions are distinguished by phase-shift angle and load conditions. The absolute and relative output voltage ripple was derived. The dead-band effect and safe operational area are further investigated. The relations between output power and leakage inductance and switching frequency are also presented. The proposed converter was simulated and a prototype was built and tested. Experiments on the converter's steady state and transient operations validated the design and simulation.
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paper_title: FRS-DAB Converter for Elimination of Circulation Power Flow at Input and Output Ends

paper_content:

Dual active bridge (DAB) converter is the most suitable converter to transfer high power with bidirectional power flow capability and isolation. However, it has the drawbacks of circulation power flow (CPF) and limited range of zero voltage switching (ZVS). To overcome these drawbacks, several modulation strategies have been proposed; however, the CPF can be eliminated either at input or output voltage ends. In order to eliminate the CPF at both input and output sides, a novel front and rear end switch DAB (FRS-DAB) bidirectional dc–dc converter has been proposed in this paper. It has the advantages of lower current stress, extension of ZVS range, higher power transfer capacity, and improved efficiency compared to the conventional DAB converter. The paper presents the detailed operating modes and analysis of power flow control for the proposed FRS-DAB converter. The operation and analytical results of the proposed converter have been verified through the experimental results using an FPGA Spartan 3AN processor.
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paper_title: Eliminate Reactive Power and Increase System Efficiency of Isolated Bidirectional Dual-Active-Bridge DC–DC Converters Using Novel Dual-Phase-Shift Control

paper_content:

This paper proposes a novel dual-phase-shift (DPS) control strategy for a dual-active-bridge isolated bidirectional DC-DC converter. The proposed DPS control consists of a phase shift between the primary and secondary voltages of the isolation transformer, and a phase shift between the gate signals of the diagonal switches of each H-bridge. Simulation on a 600-V/5-kW prototype shows that the DPS control has excellent dynamic and static performance compared to the traditional phase-shift control (single phase shift). In this paper, the concept of ldquoreactive powerrdquo is defined, and the corresponding equations are derived for isolated bidirectional DC-DC converters. It is shown that the reactive power in traditional phase-shift control is inherent, and is the main factor contributing to large peak current and large system loss. The DPS control can eliminate reactive power in isolated bidirectional DC-DC converters. In addition, the DPS control can decrease the peak inrush current and steady-state current, improve system efficiency, increase system power capability (by 33%), and minimize the output capacitance as compared to the traditional phase-shift control. The soft-switching range and the influence of short-time-scale factors, such as deadband and system-level safe operation area, are also discussed in detail. Under certain operation conditions, deadband compensation can be implemented easily in the DPS control without a current sensor.
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paper_title: A novel ZVS DC/DC converter for high power applications

paper_content:

This paper presents a novel ZVS PWM DC/DC power converter for high power applications. By using two active switches on the secondary side of a transformer, the proposed converter achieves not only ZVS of the active switches in the entire load range, but also soft commutation of the output rectifier diodes. Simulation results and experimental results of a 2.8 kW 200 kHz DC/DC converter are presented.
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paper_title: Improved Boundary Operation for Voltage-Fed Semi-DAB With ZVS Achievement and Nonactive Power Reduction

paper_content:

An improved boundary operation is proposed for the voltage-fed semi dual active bridge converter for applications needing only unidirectional power flow capability. The leakage inductor current works in boundary mode under most operating conditions. The operating principle and comparison with conventional single-phase-shifted control are presented in detail. The nonactive power can be suppressed under most working conditions and the conduction loss for output MOSFETs can be reduced significantly. All the power switches can achieve zero-voltage switching (ZVS) while the output side rectifying diodes can obtain zero-current switching in most operating conditions. The parameter design including the compensated value and the dead-time selection is given. The ZVS achievement can be obtained with reduced nonactive power and the closed loop implementation can be simplified. The effectiveness of the control strategy has been validated by the experimental results of 1-KW hardware prototype.
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paper_title: FRS-DAB Converter for Elimination of Circulation Power Flow at Input and Output Ends

paper_content:

Dual active bridge (DAB) converter is the most suitable converter to transfer high power with bidirectional power flow capability and isolation. However, it has the drawbacks of circulation power flow (CPF) and limited range of zero voltage switching (ZVS). To overcome these drawbacks, several modulation strategies have been proposed; however, the CPF can be eliminated either at input or output voltage ends. In order to eliminate the CPF at both input and output sides, a novel front and rear end switch DAB (FRS-DAB) bidirectional dc–dc converter has been proposed in this paper. It has the advantages of lower current stress, extension of ZVS range, higher power transfer capacity, and improved efficiency compared to the conventional DAB converter. The paper presents the detailed operating modes and analysis of power flow control for the proposed FRS-DAB converter. The operation and analytical results of the proposed converter have been verified through the experimental results using an FPGA Spartan 3AN processor.
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paper_title: A Dual Active Bridge Converter With an Extended High-Efficiency Range by DC Blocking Capacitor Voltage Control

paper_content:

A Dual active bridge (DAB) converter can achieve a wide high-efficiency range when its input and output voltages are equal, assuming a 1:1 turns ratio for its isolation transformer. If its input or output voltage is doubled, efficiency of the DAB will drop significantly, because of the introduction of the hard switching and high circulating power. Thus, a new modulation scheme has been proposed, whose main idea is to introduce a voltage offset across the dc blocking capacitor connected in series with the transformer. Operational principle of the proposed modulation has been introduced, before analyzing its soft-switching area and circulating power mathematically. The final modulation scheme is not difficult to implement, but can help the DAB achieve soft switching, low circulating power, and thereby high efficiency, even with its input or output voltage doubled. These features have been verified by experimental results obtained with a 1.2-kW prototype.
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paper_title: Hybrid-Bridge-Based DAB Converter With Voltage Match Control for Wide Voltage Conversion Gain Application

paper_content:

This paper proposes a voltage match (VM) control for hybrid-bridge-based dual active bridge (DAB) converter in wide voltage conversion gain applications. With the addition of an auxiliary half-bridge circuit, the topology becomes an integration of a half-bridge and a full-bridge DAB converter. Unlike other pulse width modulation generation method for DAB converters, this converter utilizes four-level voltage at one port of the transformer to obtain matched voltage waveforms within the range of twice the minimum conversion gain. Wide conversion gain, decoupling of the two power control variables and wide zero-voltage switching (ZVS) ranges can be achieved with the proposed VM control. Full load ranges of ZVS for the six main power switches can be achieved and the two auxiliary switches can also operate in a wide ZVS range. In addition, the power control is done only using two control variables and its implementation is very simple, only needing a divider and a conventional voltage regulator. These characteristics and benefits of the proposed control are verified by experimental results from a 1-kw converter prototype.
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paper_title: A Dual Active Bridge Converter With an Extended High-Efficiency Range by DC Blocking Capacitor Voltage Control

paper_content:

A Dual active bridge (DAB) converter can achieve a wide high-efficiency range when its input and output voltages are equal, assuming a 1:1 turns ratio for its isolation transformer. If its input or output voltage is doubled, efficiency of the DAB will drop significantly, because of the introduction of the hard switching and high circulating power. Thus, a new modulation scheme has been proposed, whose main idea is to introduce a voltage offset across the dc blocking capacitor connected in series with the transformer. Operational principle of the proposed modulation has been introduced, before analyzing its soft-switching area and circulating power mathematically. The final modulation scheme is not difficult to implement, but can help the DAB achieve soft switching, low circulating power, and thereby high efficiency, even with its input or output voltage doubled. These features have been verified by experimental results obtained with a 1.2-kW prototype.
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paper_title: Power Characterization of Isolated Bidirectional Dual-Active-Bridge DC–DC Converter With Dual-Phase-Shift Control

paper_content:

Compared to the traditional single-phase-shift control, dual-phase-shift (DPS) control can greatly improve the performance of the isolated bidirectional dual-active-bridge dc-dc converter (IBDC). This letter points out some wrong knowledge about transmission power of IBDC under DPS control in the earlier studies. On this basis, this letter gives the detailed theoretical and experimental analyses of the transmission power of IBDC under DPS control. And the experimental results showed agreement with theoretical analysis.
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paper_title: Switching strategy for isolated dual-active-bridge converter

paper_content:

The operating characteristics of a dual-active-bridge (DAB) converter are generally poor when using the single-phase-shift (SPS) control strategy while working with a light load or when the input voltage and the output voltage are not matched with the transformer ratio. To improve DAB operating characteristics when working under such undesirable conditions, a novel one-side single half-bridge pulse-width-modulation plus phase-shift (HPPS) switching strategy is proposed in this study. The operational principle of the strategy is demonstrated, and a suitable power mathematical model is also established. Based on this model, a detailed contrast analysis is conducted to compare HPPS control with SPS control, and includes zero-voltage-switching range comparison, circulating power comparison and root-mean-square current value comparison. A laboratory prototype is constructed, and the validity and feasibility of the proposed HPPS control strategy is verified by the experimental results.
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paper_title: Efficient high-frequency soft-switched power converter with signal processor control

paper_content:

DC/AC high-power, high-density converter structures and topologies are evaluated. The direct DC-low frequency-AC structure with the dual active bridge (DAB) topology is selected together with insulated gate bipolar transistor (IGBT) switches at 100 kHz, 20 kVA. A novel control strategy for the DAB and series-loaded resonant converters is introduced. It gives the possibility of fixed-frequency, zero voltage switching in the entire converter output V-I-plane. Design equations are presented. A method for comparing topologies by mapping stress levels in the output V-I plane is demonstrated. Experimental results from a small-scale model are shown, with good correspondence to simulation waveforms. The converter will be driven by an IBM PC/MS Windows based control system, of which the core is a 32-b digital signal processor connected to a programmable gate array holding all switch control circuitry. >
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paper_title: Universal High-Frequency-Link Characterization and Practical Fundamental-Optimal Strategy for Dual-Active-Bridge DC-DC Converter Under PWM Plus Phase-Shift Control

paper_content:

This letter first develops a universal steady-state model to simply and accurately describe the analytical expressions for the high-frequency-link (HFL) electrical quantities of isolated dual-active-bridge (DAB) dc–dc converter under PWM plus phase-shift control. Second, a universal reactive power interaction among the HFL electrical quantities is present; using this interaction, the circulating current characteristic of DAB can be described accurately by HFL power factor. On this basis, a practical HFL fundamental-optimal strategy is proposed to decrease the circulating current and increase the efficiency. At last, experimental results verify the correctness of the universal model and the effectiveness of the fundamental-optimal strategy.
---
paper_title: BP Statistical review of world energy 2014

paper_content:

BP Statistical review of world energy 2014 : 63rd edition. BP, June 2014, 48 p. http://www.bp.com/en/global/corporate/about-bp/energy-economics/statistical-review-of-world-energy.html Discours de Christof Ruhl, economiste en chef de BP, a l'occasion de l'edition 2014 du rapport : Introduction: the last ten years The purpose of this review has always been to provide objective data on global energy developments; and to chronicle changes in global energy markets year by year, in as rigorous a fa...
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paper_title: Extended-Phase-Shift Control of Isolated Bidirectional DC–DC Converter for Power Distribution in Microgrid

paper_content:

This paper points out a phenomenon of power backflow in traditional phase-shift (TPS) control of isolated bidirectional full-bridge DC-DC converter (IBDC), and analyzes the effects which backflow power act on power circulating flow and current stress. On this basis, the paper proposes a novel extended-phase-shift (EPS) control of IBDC for power distribution in microgrid. Compared with TPS control, EPS control not only expands regulating range of transmission power and enhances regulating flexibility, but also reduces current stress and improves the system efficiency. The operation principle of EPS control and the operation modes of IBDC are analyzed in the paper. By establishing mathematical models of transmission power, backflow power, and current stress, the paper comparatively analyzes control performances of TPS and EPS control. At last, experimental results verify the excellent performance of EPS control and correctness of the theoretical analysis.
---
paper_title: Optimal Phase-Shift Control to Minimize Reactive Power for a Dual Active Bridge DC–DC Converter

paper_content:

In a dual active bridge (DAB) dc–dc converter, modulating the phase-shift ratios can suppress reactive power and increase the efficiency under non-unity voltage gain conditions. Derivation of the optimal phase-shift ratios to achieve the minimum reactive power is challenging because a DAB can operate in four different scenarios (forward/backward, buck/boost) and each scenario has five operating modes. This paper first introduces a transformation in which different DAB operating scenarios (forward/backward, buck/boost) can be equivalent to one another; then optimization of only one scenario (forward/buck) is required. Next, for the five modes in forward/buck scenario, based on a graphical method, this paper proves that each operating point of Modes 1, 2, and 5 can be mapped into that of Mode 3 with lower conduction losses, and only two modes require detailed analysis. The optimization process of these two modes are derived step-by-step. Global optimal phase-shift signals that minimize the reactive power under four different DAB operating scenarios (forward/backward, buck/boost) are presented. A simple table and control block diagram are presented for practical implementation of global reactive-power minimization control. Experimental comparison with other modulation schemes verifies the efficiency improvement of the proposed control method.
---
paper_title: A Power Efficiency Improvement Technique for a Bidirectional Dual Active Bridge DC–DC Converter at Light Load

paper_content:

Bidirectional dc-dc converters, which make possible the bidirectional transmission of power, have become indispensable in recent years due to the diversification of the power supply network, including the use of batteries. Of these, the dual active bridge (DAB) dc-dc converter features a simple mechanism and symmetric circuit architecture, making possible the equal transmission of power in both directions. Because of these advantageous characteristics, DAB dc-dc converters are in wide use. However, this circuit has the intrinsic problems that, during light-load conditions, switching surges occur and power efficiency decreases. This paper proposes digitally controlled operation as a new method to resolve these problems and reports on an experiment that was carried out using a 1-kW system. In addition, for both buck and boost modes, output power characteristic equations were derived through application of the extended state-space averaging method, and a loss-included circuit analysis was carried out for the circuit used in the experiment. It was thereby demonstrated that circuit loss was smaller for the proposed operation than that for conventional operation. In the loss-included circuit analysis, for both proposed and conventional operations, equivalent circuits that approximated circuit loss as a single resistance were used. As a result, it was confirmed that, with the operation proposed in this paper, without the use of a snubber circuit, switching surges could be reduced significantly and also that, during light load, there was a power efficiency improvement of up to 16%. In addition, a loss-included circuit analysis with a single equivalent resistance has been done. The resistance value is assigned with the averaged circuit total resistance. By the analysis, a relation between phase difference and output power is obtained. The results were confirmed with the experiment.
---
paper_title: Minimum-Current-Stress Scheme of Dual Active Bridge DC–DC Converter With Unified Phase-Shift Control

paper_content:

To reduce current stress and improve efficiency of dual active bridge (DAB) dc–dc converters, various control schemes have been proposed in recent decades. Most control schemes for directly minimizing power losses from power loss modeling analysis and optimization aspect of the adopted converter are too difficult and complicated to implement in real-time digital microcontrollers. Thus, this paper focuses on a simple solution to reduce current stress and improve the efficiency of the adopted DAB converter. However, traditional current-stress-optimized (CSO) schemes have some drawbacks, such as inductance dependency and an additional load-current sensor. In this paper, a simple CSO scheme with a unified phase-shift (UPS) control, which can be equivalent to the existing conventional phase-shift controls, is proposed for DAB dc–dc converters to realize current stress optimization. The simple CSO scheme can overcome those drawbacks of traditional CSO schemes, gain the minimum current stress, and improve efficiency. Then, a comparison of single-phase-shift (SPS) control, simple CSO scheme with dual-phase-shift (CSO-DPS) control, simple CSO scheme with extended-phase-shift (CSO-EPS) control, and simple CSO scheme with UPS (CSO-UPS) control is analyzed in detail. Finally, experimental results verify the excellent performance of the proposed CSO-UPS control scheme and the correctness of theoretical analysis.
---
paper_title: Fundamental Duty Modulation of Dual-Active-Bridge Converter for Wide-Range Operation

paper_content:

This paper proposed a modulation scheme for the dual-active-bridge (DAB) converter to reduce rms current in wide-range operating conditions. The operating principle of the proposed fundamental duty modulation (FDM) is formulated based on the fundamental component analysis of the DAB converter. By modulating the PWM signals in the fundamental component domain, the optimal operation is implemented with a simple controller structure not requiring an operating mode classification, offline calculation, or current information. Operating characteristics including rms current level and ZVS characteristics are analyzed to compare loss breakdowns of the proposed scheme to those of recent related works. The proposed FDM achieves high efficiency under wide operation conditions due to reduced conduction level and wide ZVS range. Experimental results are obtained under various voltage gain and load conditions to confirm the operation of the proposed modulation scheme. A thorough experimental comparison with other sophisticated modulation schemes has verified the efficiency improvement of FDM.
---
paper_title: Novel Dual-Phase-Shift Control With Bidirectional Inner Phase Shifts for a Dual-Active-Bridge Converter Having Low Surge Current and Stable Power Control

paper_content:

To transmit constant powers particularly at light load, the isolated dual active bridge (DAB) with conventional dual-phase-shift (DPS) control exhibits large variations of currents, losses, and efficiencies if there is a small change of outer phase shift ratio, which is caused by the change of command to adjust power transmission. This is mainly because of the narrow operation region of outer phase shift ratio if the conventional DPS modulation is used. To solve this problem, a novel DPS control with bidirectional inner phase shifts for the DAB is developed to reduce the current surge in the high-frequency transformer, which can stabilize the output power with high efficiency. From the analysis of operation modes and power characteristics of the proposed DPS control, it is shown that due to wider operation region of outer phase shift ratios compared with the conventional DPS control in which the inner phase shifts of both the primary and secondary H-bridges are in the same direction, lower surge current can be obtained in the change of phase shift command, which results in stable power transmission particularly at light load without scarifying the efficiency. Moreover, the DAB of using the proposed DPS control can transmit bidirectional energy with the inner and outer shift ratios of 0-1. For experimental verifications, the test results are also presented in this paper.
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paper_title: Unified Triple-Phase-Shift Control to Minimize Current Stress and Achieve Full Soft-Switching of Isolated Bidirectional DC–DC Converter

paper_content:

This paper presents a comprehensive analysis of the current-stress optimization and soft-switching operation of the isolated bidirectional dual active bridge (DAB) dc–dc converter with the unified triple-phase-shift (UTPS) control. On this basis, the current-stress-optimized modulation scheme is proposed for DAB, which leads to the minimum current stress with the required transmission power and voltage conversion ratio in the whole load range. Moreover, the full soft-switching operation is achieved for the converter simultaneously. Distinct from the previous modulation schemes, the proposed optimized modulation scheme is deduced from a unified analysis of TPS where all effective switching modes are investigated. A novel algorithm based on the Karush–Kuhn–Tucker (KKT) conditions is originally proposed to derive closed-form solutions for the global optimal control parameters. This paper also presents a typical closed-loop control strategy for DAB with TPS control and detailed descriptions about the closed-loop operation. A laboratory prototype is applied, and the experimental results validate that the current-stress optimization and efficiency improvement are realized by applying the optimized modulation scheme. The experimental results also verify the effectiveness of the closed-loop control strategy for DAB with TPS control.
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paper_title: Unified Boundary Trapezoidal Modulation Control Utilizing Fixed Duty Cycle Compensation and Magnetizing Current Design for Dual Active Bridge DC–DC Converter

paper_content:

The unified boundary trapezoidal modulation (TZM) control utilizing fixed duty cycle compensation and magnetizing current design for dual active bridge dc-dc converter is proposed in this paper. The fixed duty cycle compensation and magnetizing current design are first introduced to achieve the zero voltage switching (ZVS) of the power switches, which cannot be ensured with the conventional TZM control. As a result, all the power switches of dual active dc-dc converter can achieve ZVS and four switches can be turned off with very low current. Besides, based on the revealed power transfer characteristic, the power control variables including the duty cycles and phase-shift ratio can be unified without lookup tables or operation region division. With the proposed boundary TZM control, circulating current losses can be reduced and nonactive power is significantly suppressed according to the mathematic analysis, resulting in decrease of the conduction loss. A 1.6-kW laboratory prototype is built to verify the theoretical analysis and effectiveness of the proposed control.
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paper_title: Minimum-Reactive-Power Scheme of Dual-Active-Bridge DC–DC Converter With Three-Level Modulated Phase-Shift Control

paper_content:

This paper presents a novel reactive-power minimization method under the three-level modulated phase-shift control to improve the efficiency for a wide operation condition. First, in order to unify all operation modes, a mathematic model of the dual-active-bridge converter with the three-level modulated phase-shift control by a harmonic analysis method is obtained. Then, the detailed analysis of the odd-order harmonic components of the active and reactive powers varied with the multiple control dimensions is presented. The soft-switching boundaries with respect to the voltage ratio and unified active power are specified. On this basis, a novel optimal three-level phase-shift (OPS) control strategy for minimizing reactive power is proposed. Experimental results of reactive power and operation efficiency among the proposed OPS method, and other methods are compared to verify the effectiveness of the OPS algorithm.
---
paper_title: Efficiency Characterization and Optimization of Isolated Bidirectional DC–DC Converter Based on Dual-Phase-Shift Control for DC Distribution Application

paper_content:

Compared to the traditional single-phase-shift control, dual-phase-shift (DPS) control can greatly improve the performance of the isolated bidirectional dc–dc converter (IBDC). This paper gives a detailed switching characteristic analysis of IBDC under DPS control, establishes a power loss model to predict the dissipated power for each power component, and analyzes the efficiency-optimized characteristic across the whole range. On this basis, an efficiency-optimized switching strategy is proposed and the corresponding control scheme is designed and implemented. At last, an experimental prototype was implemented to verify the feasibility of the proposed switching strategy and correctness of the theoretical analysis. The experimental results show that the proposed method can minimize the power loss and maximize the system efficiency, and these performances are particularly effective for operation conditions with high voltage conversion ratio.
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paper_title: Review of Energy Storage System Technologies in Microgrid Applications: Issues and Challenges

paper_content:

A microgrid (MG) is a local entity that consists of distributed energy resources (DERs) to achieve local power reliability and sustainable energy utilization. The MG concept or renewable energy technologies integrated with energy storage systems (ESS) have gained increasing interest and popularity because it can store energy at off-peak hours and supply energy at peak hours. However, existing ESS technology faces challenges in storing energy due to various issues, such as charging/discharging, safety, reliability, size, cost, life cycle, and overall management. Thus, an advanced ESS is required with regard to capacity, protection, control interface, energy management, and characteristics to enhance the performance of ESS in MG applications. This paper comprehensively reviews the types of ESS technologies, ESS structures along with their configurations, classifications, features, energy conversion, and evaluation process. Moreover, details on the advantages and disadvantages of ESS in MG applications have been analyzed based on the process of energy formations, material selection, power transfer mechanism, capacity, efficiency, and cycle period. Existing reviews critically demonstrate the current technologies for ESS in MG applications. However, the optimum management of ESSs for efficient MG operation remains a challenge in modern power system networks. This review also highlights the key factors, issues, and challenges with possible recommendations for the further development of ESS in future MG applications. All the highlighted insights of this review significantly contribute to the increasing effort toward the development of a cost-effective and efficient ESS model with a prolonged life cycle for sustainable MG implementation.
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paper_title: Closed Form Solution for Minimum Conduction Loss Modulation of DAB Converters

paper_content:

An optimal modulation scheme that enables minimum conduction and copper losses is presented for a bidirectional dual active bridge (DAB) dc-dc converter. The considered converter system is employed for an automotive application and comprises of a high voltage (HV) port with port voltage V1, 240V ≤ V1 ≤ 450 V, and a low voltage (LV) port with port voltage V2, 11 V ≤ V2 ≤ 16 V; the rated output power is 2 kW. The closed-form expressions for the optimal control parameters are derived and implementation details are presented in order to facilitate the direct application to a given DAB converter. The paper further details the properties of the presented modulation scheme with respect to switching losses. Experimental results confirm a considerable increase of the converter efficiency achieved with the proposed optimal modulation scheme, compared to the efficiency obtained with conventional phase shift modulation. The efficiency increase is most distinct at V1=450V and V2 = 11V with an increase from 78.6% to 90.6% at 1 kW output power and from 85.9% to 90.7% at rated output power as compared to conventional phase shift modulation.
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paper_title: Hybrid Modulation for Dual-Active-Bridge Bidirectional Converter With Extended Power Range for Ultracapacitor Application

paper_content:

In order to actively control the power flow between the load and ultracapacitor, a dual-active-bridge converter can be utilized. Conventional phase-shift modulation (PSM) has difficulties in working with a wide range of source voltage levels and load power levels. In addition, a traditional PI controller does not provide satisfactory behavior as the relation between the control variable and output voltage is nonlinear. In this paper, a hybrid modulation scheme is proposed to extend the power range of operation from 100% to 16.67% instead of 100% to 58.33% that is achieved by conventional PSM. A feedback-linearized controller is also designed to achieve a better dynamic response under various load conditions. The details of the modulation principle and controller design are given, and the experimental results verify the proposed modulation and control scheme.
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paper_title: Modeling and Analysis of a Dual-Active-Bridge-Isolated Bidirectional DC/DC Converter to Minimize RMS Current With Whole Operating Range

paper_content:

The triple phase shift (TPS) modulation scheme, which provides three control freedoms, is of great importance for the optimized operation of a dual active bridge (DAB) isolated bidirectional dc/dc converter. First of all, this paper introduces an accurate, universal model to describe the analytic expressions of the DAB converter under TPS control. Based on this, six operating modes of the DAB converter are further discussed. Afterwards, the concept of global optimal condition (GOC) equations is proposed to derive the closed form of analytic expressions of an optimal modulation scheme that makes the DAB converter operate with minimized root-mean-square (rms) current during whole power range with different operating modes. According to the GOC equations, the physical explanation of the proposed modulation scheme is further given in details, and the complex interaction among the control variables, the transferred power, and rms current is revealed. The real-time optimization process of the proposed method is also specified. Finally, the proposed methods are applied to a laboratory prototype. The experimental results confirm the theoretical analysis and practical feasibility of the proposed strategies.
---
paper_title: Current-Stress-Optimized Switching Strategy of Isolated Bidirectional DC–DC Converter With Dual-Phase-Shift Control

paper_content:

By establishing the mathematical model of the current stress of the isolated bidirectional dc-dc converter (IBDC), this paper comparatively analyzes the performances of IBDC under traditional single-phase-shift control and dual-phase-shift (DPS) control. On this basis, this paper proposes a current-stress-optimized switching strategy for IBDC with DPS control, and the corresponding control scheme is designed and implemented. The current-stress-optimized switching strategy can minimize the current stress, improve the system efficiency, and increase system power capability, and these performances are particularly effective for operation conditions with high voltage conversion ratio and light load. At last, experimental results verify the excellent performance of the current-stress-optimized switching strategy and correctness of the theoretical analysis.
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paper_title: Eliminate Reactive Power and Increase System Efficiency of Isolated Bidirectional Dual-Active-Bridge DC–DC Converters Using Novel Dual-Phase-Shift Control

paper_content:

This paper proposes a novel dual-phase-shift (DPS) control strategy for a dual-active-bridge isolated bidirectional DC-DC converter. The proposed DPS control consists of a phase shift between the primary and secondary voltages of the isolation transformer, and a phase shift between the gate signals of the diagonal switches of each H-bridge. Simulation on a 600-V/5-kW prototype shows that the DPS control has excellent dynamic and static performance compared to the traditional phase-shift control (single phase shift). In this paper, the concept of ldquoreactive powerrdquo is defined, and the corresponding equations are derived for isolated bidirectional DC-DC converters. It is shown that the reactive power in traditional phase-shift control is inherent, and is the main factor contributing to large peak current and large system loss. The DPS control can eliminate reactive power in isolated bidirectional DC-DC converters. In addition, the DPS control can decrease the peak inrush current and steady-state current, improve system efficiency, increase system power capability (by 33%), and minimize the output capacitance as compared to the traditional phase-shift control. The soft-switching range and the influence of short-time-scale factors, such as deadband and system-level safe operation area, are also discussed in detail. Under certain operation conditions, deadband compensation can be implemented easily in the DPS control without a current sensor.
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paper_title: Pwm control of dual active bridge: Comprehensive analysis and experimental verification

paper_content:

The dual active bridge (DAB) topology is ideally suited for high power dc-dc conversion. This paper presents a comprehensive analysis and experimental results with PWM control of the DAB. The PWM control is in addition to phase shift modulation between the two H-bridges. The analysis includes PWM of one bridge at a time and of both bridges simultaneously. In the latter, five distinct modes arise based on the choice of PWM and load condition. The possibilities are analyzed for optimizing power density and efficiency for low load operation. An optimum PWM scheme is proposed that extends the soft-switching range, reduces rms and peak currents at low loads, and results in significant size reduction of the transformer. Experimental results are presented with a 10 kW prototype.
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paper_title: Symmetrical multilevel converters with two quadrant DC-DC feeding

paper_content:

In the technology sector of power electronics and control, the multilevel converter technology is still a rather new research area, but the application possibilities in the field of power drives and energy will demand more solutions with this promising technology. In the future, more converter systems will be realized with the multilevel topology. Up to now, multilevel converters have only been used in very particular applications, mainly due to the high costs and complexity of the multilevel converter system. The high costs are due to the fact that the latest technology on semiconductors, magnetic material for inductor and transformer cores and control system technology had to be used. But nowadays new developments in the fields of power semiconductors such as the IGBT, IGCT and perhaps in the future SiC switches as well as improvements of the performance of magnetic cores used in medium frequency transformers will favor the multilevel converters for many other application fields. It can be noted that the industrial trend is moving away from heavy and bulky passive components towards power converter systems using more and more semiconductor elements controlled by powerful processor systems integrating intelligent multi-task control algorithms. The presented work is a contribution to the large field of multilevel converters. It shows a certain kind of multilevel converter in a single phase and a three-phase configuration, called the series-connected four-quadrant converters (SCFQ). The two specialties of the presented converter type are a) that all the multilevel converter steps are fed by an identical DC voltage and b) that every multilevel converter step is realized with an individual AC-DC converter or four-quadrant converter. This type of multilevel converter is called multilevel converter with symmetrical feeding. In this work, a general theoretical development has been done for the use of this multilevel converter type. A special type of DC-DC converter is presented, in order to feed the individual four-quadrant converters of the multilevel converter with a constant DC voltage. All the developments and methods used are based on mathematical expressions. Various simulations using the latest software simulation tools are accomplished and are used to study different cases. The feasibility of the developments is underlined with a series of experimental results with all types of the used converters, which have been realized in the framework of this thesis. The main application for the multilevel converter presented in this work is the frontend power converter in locomotives. Instead of using a heavy low-frequency transformer to reduce the high-voltage from the catenary to a supportable voltage for the semiconductors, a multilevel converter concept is used. The multilevel converter is directly coupled to the catenary. There are many advantages compared to the existing solutions. In the same context, a novel solution of a multilevel converter has been developed for a locomotive usable on different power lines. The converter allows not only the operation on the high AC voltage power line (15kV), but also can be coupled to a medium-voltage DC power line (3kV). Three different configuration types of the locomotive converter have been developed and tested in a complex simulation environment. Besides the locomotive application, there are many more interesting applications for the symmetrical multilevel converter, e.g. in the fields of energy transmission (FACTS, static VAR compensators, electronic high-voltage transformers, etc.) and industrial drives. But certainly in the future with the availability of cheap semiconductors adapted to the needs of the multilevel converter, even more applications in lower power fields will be realized.
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paper_title: Universal High-Frequency-Link Characterization and Practical Fundamental-Optimal Strategy for Dual-Active-Bridge DC-DC Converter Under PWM Plus Phase-Shift Control

paper_content:

This letter first develops a universal steady-state model to simply and accurately describe the analytical expressions for the high-frequency-link (HFL) electrical quantities of isolated dual-active-bridge (DAB) dc–dc converter under PWM plus phase-shift control. Second, a universal reactive power interaction among the HFL electrical quantities is present; using this interaction, the circulating current characteristic of DAB can be described accurately by HFL power factor. On this basis, a practical HFL fundamental-optimal strategy is proposed to decrease the circulating current and increase the efficiency. At last, experimental results verify the correctness of the universal model and the effectiveness of the fundamental-optimal strategy.
---
paper_title: Optimal Phase-Shift Control to Minimize Reactive Power for a Dual Active Bridge DC–DC Converter

paper_content:

In a dual active bridge (DAB) dc–dc converter, modulating the phase-shift ratios can suppress reactive power and increase the efficiency under non-unity voltage gain conditions. Derivation of the optimal phase-shift ratios to achieve the minimum reactive power is challenging because a DAB can operate in four different scenarios (forward/backward, buck/boost) and each scenario has five operating modes. This paper first introduces a transformation in which different DAB operating scenarios (forward/backward, buck/boost) can be equivalent to one another; then optimization of only one scenario (forward/buck) is required. Next, for the five modes in forward/buck scenario, based on a graphical method, this paper proves that each operating point of Modes 1, 2, and 5 can be mapped into that of Mode 3 with lower conduction losses, and only two modes require detailed analysis. The optimization process of these two modes are derived step-by-step. Global optimal phase-shift signals that minimize the reactive power under four different DAB operating scenarios (forward/backward, buck/boost) are presented. A simple table and control block diagram are presented for practical implementation of global reactive-power minimization control. Experimental comparison with other modulation schemes verifies the efficiency improvement of the proposed control method.
---
paper_title: Minimum-Current-Stress Scheme of Dual Active Bridge DC–DC Converter With Unified Phase-Shift Control

paper_content:

To reduce current stress and improve efficiency of dual active bridge (DAB) dc–dc converters, various control schemes have been proposed in recent decades. Most control schemes for directly minimizing power losses from power loss modeling analysis and optimization aspect of the adopted converter are too difficult and complicated to implement in real-time digital microcontrollers. Thus, this paper focuses on a simple solution to reduce current stress and improve the efficiency of the adopted DAB converter. However, traditional current-stress-optimized (CSO) schemes have some drawbacks, such as inductance dependency and an additional load-current sensor. In this paper, a simple CSO scheme with a unified phase-shift (UPS) control, which can be equivalent to the existing conventional phase-shift controls, is proposed for DAB dc–dc converters to realize current stress optimization. The simple CSO scheme can overcome those drawbacks of traditional CSO schemes, gain the minimum current stress, and improve efficiency. Then, a comparison of single-phase-shift (SPS) control, simple CSO scheme with dual-phase-shift (CSO-DPS) control, simple CSO scheme with extended-phase-shift (CSO-EPS) control, and simple CSO scheme with UPS (CSO-UPS) control is analyzed in detail. Finally, experimental results verify the excellent performance of the proposed CSO-UPS control scheme and the correctness of theoretical analysis.
---
paper_title: Fundamental Duty Modulation of Dual-Active-Bridge Converter for Wide-Range Operation

paper_content:

This paper proposed a modulation scheme for the dual-active-bridge (DAB) converter to reduce rms current in wide-range operating conditions. The operating principle of the proposed fundamental duty modulation (FDM) is formulated based on the fundamental component analysis of the DAB converter. By modulating the PWM signals in the fundamental component domain, the optimal operation is implemented with a simple controller structure not requiring an operating mode classification, offline calculation, or current information. Operating characteristics including rms current level and ZVS characteristics are analyzed to compare loss breakdowns of the proposed scheme to those of recent related works. The proposed FDM achieves high efficiency under wide operation conditions due to reduced conduction level and wide ZVS range. Experimental results are obtained under various voltage gain and load conditions to confirm the operation of the proposed modulation scheme. A thorough experimental comparison with other sophisticated modulation schemes has verified the efficiency improvement of FDM.
---
paper_title: A Four-Degrees-of-Freedom Modulation Strategy for Dual-Active-Bridge Series-Resonant Converter Designed for Total Loss Minimization

paper_content:

This paper proposes a four-degrees-of-freedom modulation scheme to mitigate the conduction and switching losses in a dual-active-bridge (DAB) series-resonant converter. Under wide-range variations in the voltage gain and output current, the increased reactive power and root-mean-square tank current can contribute significantly to the conduction loss in a DAB converter, while the occurrence of hard switching leads to a switching loss and an increased device stress. The proposed modulation scheme utilizes internal, external phase shifts, and switching frequency as modulation parameters to achieve zero reactive power, minimum-tank-current, and complete soft-switching operation. Analysis of the proposed modulation scheme is given for both buck- and boost-mode operations. The proposed modulation scheme is validated by means of a 1-kW experimental prototype of a DAB series-resonant converter operating at 100 kHz, designed to interface a supercapacitor with a rated output voltage of 48 V to a 250-V dc bus. The effectiveness of the proposed topology for charging/discharging a supercapacitor under wide-range variations in the voltage gain and output current is verified by simulations and experimental results. A maximum efficiency of 97.7% is recorded from the experimental prototype (The experimental setup used for measuring converter's efficiency is shown in the supplementary material).
---
paper_title: Unified Triple-Phase-Shift Control to Minimize Current Stress and Achieve Full Soft-Switching of Isolated Bidirectional DC–DC Converter

paper_content:

This paper presents a comprehensive analysis of the current-stress optimization and soft-switching operation of the isolated bidirectional dual active bridge (DAB) dc–dc converter with the unified triple-phase-shift (UTPS) control. On this basis, the current-stress-optimized modulation scheme is proposed for DAB, which leads to the minimum current stress with the required transmission power and voltage conversion ratio in the whole load range. Moreover, the full soft-switching operation is achieved for the converter simultaneously. Distinct from the previous modulation schemes, the proposed optimized modulation scheme is deduced from a unified analysis of TPS where all effective switching modes are investigated. A novel algorithm based on the Karush–Kuhn–Tucker (KKT) conditions is originally proposed to derive closed-form solutions for the global optimal control parameters. This paper also presents a typical closed-loop control strategy for DAB with TPS control and detailed descriptions about the closed-loop operation. A laboratory prototype is applied, and the experimental results validate that the current-stress optimization and efficiency improvement are realized by applying the optimized modulation scheme. The experimental results also verify the effectiveness of the closed-loop control strategy for DAB with TPS control.
---
paper_title: Minimum-Reactive-Power Scheme of Dual-Active-Bridge DC–DC Converter With Three-Level Modulated Phase-Shift Control

paper_content:

This paper presents a novel reactive-power minimization method under the three-level modulated phase-shift control to improve the efficiency for a wide operation condition. First, in order to unify all operation modes, a mathematic model of the dual-active-bridge converter with the three-level modulated phase-shift control by a harmonic analysis method is obtained. Then, the detailed analysis of the odd-order harmonic components of the active and reactive powers varied with the multiple control dimensions is presented. The soft-switching boundaries with respect to the voltage ratio and unified active power are specified. On this basis, a novel optimal three-level phase-shift (OPS) control strategy for minimizing reactive power is proposed. Experimental results of reactive power and operation efficiency among the proposed OPS method, and other methods are compared to verify the effectiveness of the OPS algorithm.
---
paper_title: Modeling and Analysis of a Dual-Active-Bridge-Isolated Bidirectional DC/DC Converter to Minimize RMS Current With Whole Operating Range

paper_content:

The triple phase shift (TPS) modulation scheme, which provides three control freedoms, is of great importance for the optimized operation of a dual active bridge (DAB) isolated bidirectional dc/dc converter. First of all, this paper introduces an accurate, universal model to describe the analytic expressions of the DAB converter under TPS control. Based on this, six operating modes of the DAB converter are further discussed. Afterwards, the concept of global optimal condition (GOC) equations is proposed to derive the closed form of analytic expressions of an optimal modulation scheme that makes the DAB converter operate with minimized root-mean-square (rms) current during whole power range with different operating modes. According to the GOC equations, the physical explanation of the proposed modulation scheme is further given in details, and the complex interaction among the control variables, the transferred power, and rms current is revealed. The real-time optimization process of the proposed method is also specified. Finally, the proposed methods are applied to a laboratory prototype. The experimental results confirm the theoretical analysis and practical feasibility of the proposed strategies.
---
paper_title: Pwm control of dual active bridge: Comprehensive analysis and experimental verification

paper_content:

The dual active bridge (DAB) topology is ideally suited for high power dc-dc conversion. This paper presents a comprehensive analysis and experimental results with PWM control of the DAB. The PWM control is in addition to phase shift modulation between the two H-bridges. The analysis includes PWM of one bridge at a time and of both bridges simultaneously. In the latter, five distinct modes arise based on the choice of PWM and load condition. The possibilities are analyzed for optimizing power density and efficiency for low load operation. An optimum PWM scheme is proposed that extends the soft-switching range, reduces rms and peak currents at low loads, and results in significant size reduction of the transformer. Experimental results are presented with a 10 kW prototype.
---
paper_title: Fundamentals of Power Electronics

paper_content:

Preface. 1. Introduction. I: Converters in Equilibrium. 2. Principles of Steady State Converter Analysis. 3. Steady-State Equivalent Circuit Modeling, Losses, and Efficiency. 4. Switch Realization. 5. The Discontinuous Conduction Mode. 6. Converter Circuits. II: Converter Dynamics and Control. 7. AC Equivalent Circuit Modeling. 8. Converter Transfer Functions. 9. Controller Design. 10. Input Filter Design. 11. AC and DC Equivalent Circuit Modeling of the Discontinuous Conduction Mode. 12. Current Programmed Control. III: Magnetics. 13. Basic Magnetics Theory. 14. Inductor Design. 15. Transformer Design. IV: Modern Rectifiers and Power System Harmonics. 16. Power and Harmonics in Nonsinusoidal Systems. 17. Line-Commutated Rectifiers. 18. Pulse-Width Modulated Rectifiers. V: Resonant Converters. 19. Resonant Conversion. 20. Soft Switching. Appendices: A. RMS Values of Commonly-Observed Converter Waveforms. B. Simulation of Converters. C. Middlebrook's Extra Element Theorem. D. Magnetics Design Tables. Index.
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paper_title: BP Statistical review of world energy 2014

paper_content:

BP Statistical review of world energy 2014 : 63rd edition. BP, June 2014, 48 p. http://www.bp.com/en/global/corporate/about-bp/energy-economics/statistical-review-of-world-energy.html Discours de Christof Ruhl, economiste en chef de BP, a l'occasion de l'edition 2014 du rapport : Introduction: the last ten years The purpose of this review has always been to provide objective data on global energy developments; and to chronicle changes in global energy markets year by year, in as rigorous a fa...
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paper_title: ZVS Soft Switching Boundaries for Dual Active Bridge DC–DC Converters Using Frequency Domain Analysis

paper_content:

Dual active bridge (DAB) converters offer an unmatched capability to transfer energy in either direction between two dc sources, while also providing galvanic isolation and high conversion efficiency. However, to operate at higher efficiencies, the bridges must operate with zero voltage switching (ZVS) over as wide an operating range as possible. The conventional approach to determine ZVS operation uses time domain analysis with ideal ac coupling inductances, which only approximately identifies the ZVS boundaries. This paper proposes a new approach using harmonic decomposition of the bridge switching patterns, which gives an explicit theoretical solution under all operating conditions, while also accommodating more complex ac coupling structures, practical impedance nonidealities, and the switching impact of dead-time and device capacitance. The methodology is confirmed by matching analytical predictions with experimental results for selected DAB systems.
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paper_title: Variable-Frequency Phase Shift Modulation of a Dual Active Bridge Converter

paper_content:

In this paper, a variable-frequency modulation method for a dual active bridge converter is introduced. The proposed method ensures zero-voltage switching over a wide power range with a minimal circulating current. Unlike previously presented modulation schemes, this modulation method can also be used for half-bridge variants of a traditional dual active bridge converter. The modulation method is given in a closed form, which makes it easy to apply in practice. Further, the phase drift phenomenon is discussed, and a simple phase drift compensation scheme is presented. Finally, a detailed analysis of the proposed modulation method is provided and its feasibility is verified by measurements.
---
paper_title: Efficiency-Optimized High-Current Dual Active Bridge Converter for Automotive Applications

paper_content:

An efficiency-optimized modulation scheme and design method are developed for an existing hardware prototype of a bidirectional dual active bridge (DAB) dc/dc converter. The DAB being considered is used for an automotive application and is made up of a high-voltage port with port voltage V1, 240 V ≤ V1 ≤ 450 V, and a low-voltage port with port voltage V2, 11 V ≤ V2 ≤ 16 V; the rated output power is 2 kW. A much increased converter efficiency is achieved with the methods detailed in this paper: The average efficiency, calculated for different voltages V1 and V2, different power levels, and both directions of power transfer, rises from 89.6% (conventional phase shift modulation) to 93.5% (proposed modulation scheme). Measured efficiency values, obtained from the DAB hardware prototype, are used to verify the theoretical results.
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paper_title: Universal High-Frequency-Link Characterization and Practical Fundamental-Optimal Strategy for Dual-Active-Bridge DC-DC Converter Under PWM Plus Phase-Shift Control

paper_content:

This letter first develops a universal steady-state model to simply and accurately describe the analytical expressions for the high-frequency-link (HFL) electrical quantities of isolated dual-active-bridge (DAB) dc–dc converter under PWM plus phase-shift control. Second, a universal reactive power interaction among the HFL electrical quantities is present; using this interaction, the circulating current characteristic of DAB can be described accurately by HFL power factor. On this basis, a practical HFL fundamental-optimal strategy is proposed to decrease the circulating current and increase the efficiency. At last, experimental results verify the correctness of the universal model and the effectiveness of the fundamental-optimal strategy.
---
paper_title: BP Statistical review of world energy 2014

paper_content:

BP Statistical review of world energy 2014 : 63rd edition. BP, June 2014, 48 p. http://www.bp.com/en/global/corporate/about-bp/energy-economics/statistical-review-of-world-energy.html Discours de Christof Ruhl, economiste en chef de BP, a l'occasion de l'edition 2014 du rapport : Introduction: the last ten years The purpose of this review has always been to provide objective data on global energy developments; and to chronicle changes in global energy markets year by year, in as rigorous a fa...
---
paper_title: Fundamental Duty Modulation of Dual-Active-Bridge Converter for Wide-Range Operation

paper_content:

This paper proposed a modulation scheme for the dual-active-bridge (DAB) converter to reduce rms current in wide-range operating conditions. The operating principle of the proposed fundamental duty modulation (FDM) is formulated based on the fundamental component analysis of the DAB converter. By modulating the PWM signals in the fundamental component domain, the optimal operation is implemented with a simple controller structure not requiring an operating mode classification, offline calculation, or current information. Operating characteristics including rms current level and ZVS characteristics are analyzed to compare loss breakdowns of the proposed scheme to those of recent related works. The proposed FDM achieves high efficiency under wide operation conditions due to reduced conduction level and wide ZVS range. Experimental results are obtained under various voltage gain and load conditions to confirm the operation of the proposed modulation scheme. A thorough experimental comparison with other sophisticated modulation schemes has verified the efficiency improvement of FDM.
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paper_title: Minimum-Reactive-Power Scheme of Dual-Active-Bridge DC–DC Converter With Three-Level Modulated Phase-Shift Control

paper_content:

This paper presents a novel reactive-power minimization method under the three-level modulated phase-shift control to improve the efficiency for a wide operation condition. First, in order to unify all operation modes, a mathematic model of the dual-active-bridge converter with the three-level modulated phase-shift control by a harmonic analysis method is obtained. Then, the detailed analysis of the odd-order harmonic components of the active and reactive powers varied with the multiple control dimensions is presented. The soft-switching boundaries with respect to the voltage ratio and unified active power are specified. On this basis, a novel optimal three-level phase-shift (OPS) control strategy for minimizing reactive power is proposed. Experimental results of reactive power and operation efficiency among the proposed OPS method, and other methods are compared to verify the effectiveness of the OPS algorithm.
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paper_title: Applying Variable-Switching-Frequency Variable-Phase-Shift Control and E-Mode GaN HEMTs to an Indirect Matrix Converter-Based EV Battery Charger

paper_content:

An indirect matrix converter is employed directly converting the grid ac to the battery voltage, with the dual-active-bridge taking care of the power factor correction and power delivery simultaneously. Such circuit is regarded as one candidate of the high-efficiency and high-power-density electric vehicle on-board chargers, if the double-frequency current ripple to the battery is tolerated. Instead of optimizing the overall charger, this paper is focused on adopting variable switching frequency with multiple phase shifts to accommodate the wide input range (80–260 $V_{\mathrm{ ac}}$ ) and output range (200 V–450 $V_{\mathrm{ dc}}$ ). In addition to the phase shift between the transformer primary-side and secondary-side voltage, one extra phase shift is added to the primary-side H-bridge when the instantaneous input voltage is higher than the reflected output, otherwise, to the secondary side. The goal is to secure zero-voltage-switching for all switches at all voltage range. Such control strategy is further optimized incorporating with the switch parasitic capacitance and dead-band settings. To further enhance the charger performance, GaN HEMTs are equipped to the on-board charger aiming at higher efficiency and higher power density than Si devices. Experimental results indicated that such charger with proposed control strategy embraces the peak efficiency of >97% at 7.2 kW and a power density of ~4 kW/L.
---
paper_title: Overview of Dual-Active-Bridge Isolated Bidirectional DC–DC Converter for High-Frequency-Link Power-Conversion System

paper_content:

High-frequency-link (HFL) power conversion systems (PCSs) are attracting more and more attentions in academia and industry for high power density, reduced weight, and low noise without compromising efficiency, cost, and reliability. In HFL PCSs, dual-active-bridge (DAB) isolated bidirectional dc-dc converter (IBDC) serves as the core circuit. This paper gives an overview of DAB-IBDC for HFL PCSs. First, the research necessity and development history are introduced. Second, the research subjects about basic characterization, control strategy, soft-switching solution and variant, as well as hardware design and optimization are reviewed and analyzed. On this basis, several typical application schemes of DAB-IBDC for HPL PCSs are presented in a worldwide scope. Finally, design recommendations and future trends are presented. As the core circuit of HFL PCSs, DAB-IBDC has wide prospects. The large-scale practical application of DAB-IBDC for HFL PCSs is expected with the recent advances in solid-state semiconductors, magnetic and capacitive materials, and microelectronic technologies.
---
paper_title: Modeling and Analysis of a Dual-Active-Bridge-Isolated Bidirectional DC/DC Converter to Minimize RMS Current With Whole Operating Range

paper_content:

The triple phase shift (TPS) modulation scheme, which provides three control freedoms, is of great importance for the optimized operation of a dual active bridge (DAB) isolated bidirectional dc/dc converter. First of all, this paper introduces an accurate, universal model to describe the analytic expressions of the DAB converter under TPS control. Based on this, six operating modes of the DAB converter are further discussed. Afterwards, the concept of global optimal condition (GOC) equations is proposed to derive the closed form of analytic expressions of an optimal modulation scheme that makes the DAB converter operate with minimized root-mean-square (rms) current during whole power range with different operating modes. According to the GOC equations, the physical explanation of the proposed modulation scheme is further given in details, and the complex interaction among the control variables, the transferred power, and rms current is revealed. The real-time optimization process of the proposed method is also specified. Finally, the proposed methods are applied to a laboratory prototype. The experimental results confirm the theoretical analysis and practical feasibility of the proposed strategies.
---
paper_title: Variable-Frequency Phase Shift Modulation of a Dual Active Bridge Converter

paper_content:

In this paper, a variable-frequency modulation method for a dual active bridge converter is introduced. The proposed method ensures zero-voltage switching over a wide power range with a minimal circulating current. Unlike previously presented modulation schemes, this modulation method can also be used for half-bridge variants of a traditional dual active bridge converter. The modulation method is given in a closed form, which makes it easy to apply in practice. Further, the phase drift phenomenon is discussed, and a simple phase drift compensation scheme is presented. Finally, a detailed analysis of the proposed modulation method is provided and its feasibility is verified by measurements.
---
paper_title: Pwm control of dual active bridge: Comprehensive analysis and experimental verification

paper_content:

The dual active bridge (DAB) topology is ideally suited for high power dc-dc conversion. This paper presents a comprehensive analysis and experimental results with PWM control of the DAB. The PWM control is in addition to phase shift modulation between the two H-bridges. The analysis includes PWM of one bridge at a time and of both bridges simultaneously. In the latter, five distinct modes arise based on the choice of PWM and load condition. The possibilities are analyzed for optimizing power density and efficiency for low load operation. An optimum PWM scheme is proposed that extends the soft-switching range, reduces rms and peak currents at low loads, and results in significant size reduction of the transformer. Experimental results are presented with a 10 kW prototype.
---
paper_title: Optimized Operation of Current-Fed Dual Active Bridge DC–DC Converter for PV Applications

paper_content:

The current-fed dual active bridge (CF-DAB) dc–dc converter gains growing applications in photovoltaic (PV) and energy storage systems due to its advantages, e.g., a wide input voltage range, a high step-up ratio, a low input current ripple, and a multiport interface capability. In addition, the direct input current controllability and extra control freedom of the CF-DAB converter make it possible to buffer the double-line-frequency energy in grid-interactive PV systems without using electrolytic capacitors in the dc link. Therefore, a PV system achieves high reliability and highly efficient maximum power point tracking. This paper studies the optimized operation of a CF-DAB converter for a PV application in order to improve the system efficiency. The operating principle and soft-switching conditions over the wide operating range are thoroughly analyzed with phase-shift control and duty-cycle control, and an optimized operating mode is proposed to achieve the minimum root-mean-square transformer current. The proposed operating mode can extend the soft-switching region and reduce the power loss, particularly under a heavy load and a high input voltage. Moreover, the efficiency can be further improved with a higher dc-link voltage. A 5-kW hardware prototype was built in the laboratory, and experimental results are provided for verification. This paper provides a design guideline for the CF-DAB converter applied to PV systems, as well as other applications with a wide input voltage variation.
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paper_title: A new ZVS bidirectional DC-DC converter for fuel cell and battery application

paper_content:

This paper presents a new zero-voltage-switching (ZVS) bidirectional dc-dc converter. Compared to the traditional full and half bridge bidirectional dc-dc converters for the similar applications, the new topology has the advantages of simple circuit topology with no total device rating (TDR) penalty, soft-switching implementation without additional devices, high efficiency and simple control. These advantages make the new converter promising for medium and high power applications especially for auxiliary power supply in fuel cell vehicles and power generation where the high power density, low cost, lightweight and high reliability power converters are required. The operating principle, theoretical analysis, and design guidelines are provided in this paper. The simulation and the experimental verifications are also presented.
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paper_title: High-Efficiency Current-Fed Dual Active Bridge DC–DC Converter With ZVS Achievement Throughout Full Range of Load Using Optimized Switching Patterns

paper_content:

For current-fed dual active bridge bidirectional dc–dc converters, all the possible switching patterns are summarized in view of the combinations of both side pulse-width modulation duty cycles and phase-shift angle. A control strategy is proposed for the current-fed dual active bridge converter to operate with the optimized patterns. The equivalent duty cycle of the secondary side is smaller than that of the primary side by a fixed value, which is optimized based on the soft-switching achievement and the circulating current minimization. The closed-loop control is easy to be implemented since there are only two independent variables, one-side duty cycle and the phase-shift angle. With the proposed control, zero-voltage switching can be achieved for all power switches throughout full range of load even at no-load condition. The typical working modes with the proposed control are given. The optimal design of the system parameters including the fixed time delta and dead time is illustrated. The converter has a very good performance, not only under steady states but also in transients. The conversion efficiency is high. The effectiveness of the proposed control is verified by the experimental results of a 1-kW laboratory prototype.
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paper_title: Improvement of light load efficiency of Dual Active Bridge DC-DC converter by using dual leakage transformer and variable frequency

paper_content:

Dual Active Bridge (DAB) topology performs very well for converter output/input ratio close to transformer ratio. However, if a considerable deviation from the transformer ratio is required the conversion efficiency drops significantly. The approach presented in this paper uses variable AC link reactance to improve the DAB performance during operation at light load. The variable reactance is obtained by using a variable frequency in combination with so-called dual leakage transformer. Simple phase-shift control is used, and the switching frequency is varied in order to minimize the peak transformer current. In addition to that, the dual leakage transformer proposed in this paper has a winding configuration yielding a high leakage inductance at low currents and low leakage inductance at high currents. A fully operational prototype was built, demonstrating a power density of 7.1 kW/Liter with forced air cooling, and a peak efficiency at rated 4 kW load equal to 96.6 %. The presented variable reactance approach resulted in more than 10 % efficiency improvement over the conventional DAB design in the most critical point.
---
paper_title: High-Frequency Transformer Isolated Bidirectional DC–DC Converter Modules With High Efficiency Over Wide Load Range for 20 kVA Solid-State Transformer

paper_content:

This paper presents the design of new high-frequency transformer isolated bidirectional dc-dc converter modules connected in input-series-output-parallel (ISOP) for 20-kVA-solid-state transformer. The ISOP modular structure enables the use of low-voltage MOSFETs, featuring low on-state resistance and resulted conduction losses, to address medium-voltage input. A phase-shift dual-half-bridge (DHB) converter is employed to achieve high-frequency galvanic isolation, bidirectional power flow, and zero voltage switching (ZVS) of all switching devices, which leads to low switching losses even with high-frequency operation. Furthermore, an adaptive inductor is proposed as the main energy transfer element of a phase-shift DHB converter so that the circulating energy can be optimized to maintain ZVS at light load and minimize the conduction losses at heavy load as well. As a result, high efficiency over wide load range and high power density can be achieved. In addition, current stress of switching devices can be reduced. A planar transformer adopting printed-circuit-board windings arranged in an interleaved structure is designed to obtain low core and winding loss, solid isolation, and identical parameters in multiple modules. Moreover, the modular structure along with a distributed control provides plug-and-play capability and possible high-level fault tolerance. The experimental results on 1 kW DHB converter modules switching at 50 kHz are presented to validate the theoretical analysis.
---
paper_title: High-Frequency-Link-Based Grid-Tied PV System With Small DC-Link Capacitor and Low-Frequency Ripple-Free Maximum Power Point Tracking

paper_content:

This paper proposes a grid-tied photovoltaic (PV) system consisting of modular current-fed dual-active-bridge (CF-DAB) dc–dc converter with cascaded multilevel inverter. The proposed converter allows a small dc-link capacitor in the three-phase wye-connected PV system; therefore, the system reliability can be improved by replacing electrolytic capacitors with film capacitors. The low-frequency ripple-free maximum power point tracking (MPPT) is also realized in the proposed converter. First of all, to minimize the influence resulting from reduced capacitance, a dc-link voltage synchronizing control is developed. Then, a detailed design of power mitigation control based on CF-DAB dynamic model is presented to prevent the large low-frequency voltage variation propagating from the dc-link to PV side. Finally, a novel variable step-size MPPT algorithm is proposed to ensure not only high MPPT efficiency, but also fast maximum power extraction under rapid irradiation change. A downscaled 5-kW PV converter module with a small dc-link capacitor was built in the laboratory with the proposed control and MPPT algorithm, and experimental results are given to validate the converter performance.
---
paper_title: Applying Variable-Switching-Frequency Variable-Phase-Shift Control and E-Mode GaN HEMTs to an Indirect Matrix Converter-Based EV Battery Charger

paper_content:

An indirect matrix converter is employed directly converting the grid ac to the battery voltage, with the dual-active-bridge taking care of the power factor correction and power delivery simultaneously. Such circuit is regarded as one candidate of the high-efficiency and high-power-density electric vehicle on-board chargers, if the double-frequency current ripple to the battery is tolerated. Instead of optimizing the overall charger, this paper is focused on adopting variable switching frequency with multiple phase shifts to accommodate the wide input range (80–260 $V_{\mathrm{ ac}}$ ) and output range (200 V–450 $V_{\mathrm{ dc}}$ ). In addition to the phase shift between the transformer primary-side and secondary-side voltage, one extra phase shift is added to the primary-side H-bridge when the instantaneous input voltage is higher than the reflected output, otherwise, to the secondary side. The goal is to secure zero-voltage-switching for all switches at all voltage range. Such control strategy is further optimized incorporating with the switch parasitic capacitance and dead-band settings. To further enhance the charger performance, GaN HEMTs are equipped to the on-board charger aiming at higher efficiency and higher power density than Si devices. Experimental results indicated that such charger with proposed control strategy embraces the peak efficiency of >97% at 7.2 kW and a power density of ~4 kW/L.
---
paper_title: An Improved Modulation Scheme of Current-Fed Bidirectional DC–DC Converters For Loss Reduction

paper_content:

Current-fed bidirectional dc–dc converters have attracted much attention in battery energy storage system applications due to their zero-voltage-switching performances and greater degree of control freedom. However, high efficiency cannot be achieved for both light and heavy load ranges with the present modulation schemes for a current-fed bidirectional dc–dc converter, especially with low battery voltages. A new modulation scheme is proposed to improve the conversion efficiency over a wide load range and with variations in the battery voltage. The relationship between the duty cycle of the secondary full bridge and the phase-shift angle was investigated to lower the power losses with the wide load variations. Based on the operation mode analysis, the control loop with the proposed pulse wide modulation plus phase-shift modulation scheme was developed. Comparisons of the switch conduction loss and the core loss in the series inductor for the previous modulation schemes and the proposed modulation scheme were carried out. The results show that lower power losses occur with the proposed scheme. The experimental results verify the theoretical analysis and effectiveness of the proposed modulation scheme on loss reduction.
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paper_title: Variable-Frequency Phase Shift Modulation of a Dual Active Bridge Converter

paper_content:

In this paper, a variable-frequency modulation method for a dual active bridge converter is introduced. The proposed method ensures zero-voltage switching over a wide power range with a minimal circulating current. Unlike previously presented modulation schemes, this modulation method can also be used for half-bridge variants of a traditional dual active bridge converter. The modulation method is given in a closed form, which makes it easy to apply in practice. Further, the phase drift phenomenon is discussed, and a simple phase drift compensation scheme is presented. Finally, a detailed analysis of the proposed modulation method is provided and its feasibility is verified by measurements.
---
paper_title: Improvement of light load efficiency of Dual Active Bridge DC-DC converter by using dual leakage transformer and variable frequency

paper_content:

Dual Active Bridge (DAB) topology performs very well for converter output/input ratio close to transformer ratio. However, if a considerable deviation from the transformer ratio is required the conversion efficiency drops significantly. The approach presented in this paper uses variable AC link reactance to improve the DAB performance during operation at light load. The variable reactance is obtained by using a variable frequency in combination with so-called dual leakage transformer. Simple phase-shift control is used, and the switching frequency is varied in order to minimize the peak transformer current. In addition to that, the dual leakage transformer proposed in this paper has a winding configuration yielding a high leakage inductance at low currents and low leakage inductance at high currents. A fully operational prototype was built, demonstrating a power density of 7.1 kW/Liter with forced air cooling, and a peak efficiency at rated 4 kW load equal to 96.6 %. The presented variable reactance approach resulted in more than 10 % efficiency improvement over the conventional DAB design in the most critical point.
---
paper_title: High-Frequency Transformer Isolated Bidirectional DC–DC Converter Modules With High Efficiency Over Wide Load Range for 20 kVA Solid-State Transformer

paper_content:

This paper presents the design of new high-frequency transformer isolated bidirectional dc-dc converter modules connected in input-series-output-parallel (ISOP) for 20-kVA-solid-state transformer. The ISOP modular structure enables the use of low-voltage MOSFETs, featuring low on-state resistance and resulted conduction losses, to address medium-voltage input. A phase-shift dual-half-bridge (DHB) converter is employed to achieve high-frequency galvanic isolation, bidirectional power flow, and zero voltage switching (ZVS) of all switching devices, which leads to low switching losses even with high-frequency operation. Furthermore, an adaptive inductor is proposed as the main energy transfer element of a phase-shift DHB converter so that the circulating energy can be optimized to maintain ZVS at light load and minimize the conduction losses at heavy load as well. As a result, high efficiency over wide load range and high power density can be achieved. In addition, current stress of switching devices can be reduced. A planar transformer adopting printed-circuit-board windings arranged in an interleaved structure is designed to obtain low core and winding loss, solid isolation, and identical parameters in multiple modules. Moreover, the modular structure along with a distributed control provides plug-and-play capability and possible high-level fault tolerance. The experimental results on 1 kW DHB converter modules switching at 50 kHz are presented to validate the theoretical analysis.
---
paper_title: BP Statistical review of world energy 2014

paper_content:

BP Statistical review of world energy 2014 : 63rd edition. BP, June 2014, 48 p. http://www.bp.com/en/global/corporate/about-bp/energy-economics/statistical-review-of-world-energy.html Discours de Christof Ruhl, economiste en chef de BP, a l'occasion de l'edition 2014 du rapport : Introduction: the last ten years The purpose of this review has always been to provide objective data on global energy developments; and to chronicle changes in global energy markets year by year, in as rigorous a fa...
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paper_title: A Novel ZVS Range Enhancement Technique of a High-Voltage Dual Active Bridge Converter Using Series Injection

paper_content:

In this paper, a novel technique is proposed to extend the region of zero voltage switching (ZVS) of a dual active bridge (DAB) dc–dc converter using an auxiliary series injection transformer. The series voltage injection by the series transformer helps us to maintain ZVS by controlling the reactive power flow through the main converter of the DAB. A model for the series compensation is developed to compute the phase angle of the series voltage to obtain the optimum efficiency over the entire region of operation. The proposed technique is validated through simulations and the corresponding converter loss reduction is presented. The system is implemented on a high-voltage hardware with $6$ kV- $270$ V DAB using 10-kV SiC mosfet -based converter in the primary and 1200-V SiC mosfet on the secondary side of the transformer and the corresponding results are presented.
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paper_title: Extension of Soft-Switching Region of Dual-Active-Bridge Converter by a Tunable Resonant Tank

paper_content:

Hard-switching-induced switching loss can contribute significantly to the power loss of an isolated bidirectional dual-active-bridge (DAB) dc–dc converter operating at high frequency. An $LC$ -type series resonant DAB converter based on a switch-controlled-inductor (SCI) is proposed to mitigate the loss arising from hard switching under wide-range variations in output voltage and current. Zero-voltage switching is achieved at the primary side (high voltage), while at the secondary side (low voltage), zero-current switching is preferred to reduce excessive ringing due to circulating current and switching loss. In order to achieve reduced conduction loss, a nominal operating point is chosen where the root-mean-square resonant tank current is the minimum. To validate the proposed topology and modulation scheme, an $LC$ -type series resonant DAB converter based on SCI operating at 100 kHz is designed to interface a 400-V dc bus to a supercapacitor-based energy storage. Simulation and experimental results validate the effectiveness of the proposed topology for charging/discharging a supercapacitor with an output voltage variation of between 10 and 48 V and a maximum rated power of 480 W. A maximum efficiency of 94.6% is achieved using the proposed topology and modulation scheme.
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paper_title: Maintaining Continuous ZVS Operation of a Dual Active Bridge by Reduced Coupling Transformers

paper_content:

A major advantage of the dual active bridge (DAB) dc–dc converter is its ability to operate under zero voltage switching (ZVS) conditions to reduce switching losses. However, when the ac link coupling transformer is conventionally designed to minimize its magnetizing current, nonideal switching conditions almost invariably lead to hard switching operation at particular power transfer levels and dc–dc voltage ratios. This paper presents a mathematically based design approach for a coupling transformer with a reduced magnetizing inductance that creates just sufficient ac link circulating current to maintain continuous ZVS operation over the converter's entire specified operating range without incurring significant additional losses. The required magnetizing inductance reduction is found to be a function of the inherent transformer leakage inductances, switching dead-time, and device parasitic capacitances. The analysis approach is validated by matching experimental results.
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paper_title: A series compensation enabled ZVS range enhancement of a dual active bridge converter for wide range load conditions

paper_content:

A novel ZVS range control technique using an auxiliary series transformer for a Dual Active Bridge (DAB) DC-DC converter is proposed. The auxiliary transformer fed with an additional H-bridge at the secondary, adds a phase-controlled voltage in series with the main converter voltage either at the primary or secondary. This addition helps to control the reactive power flowing through the main converters of the DAB. Hence the power-factor of the main converters can be controlled in such a way that the DAB can maintain ZVS even at light loads. Also it operates at minimum reactive power at higher loads while it still operates in ZVS and thus results in higher efficiency on both extremes. The series transformer carries dominantly reactive power since the compensation angle is most often near quadrature. For medium/high power DAB, the cost and additional losses associated with the series circuit can be neglected due to significant efficiency improvement. The external inductor can be eliminated by using a series transformer designed with enough leakage inductance hence saving the additional magnetic cost. The proposed technique is validated with simulations followed by experiment on a hardware implementation. The technique is also simulated for a medium voltage DAB system with actual switching and magnetic data to bring out the efficiency improvements.
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paper_title: Different purpose design strategies and techniques to improve the performance of a Dual Active Bridge with phase-shift control

paper_content:

This paper addresses the performance of the bidirectional Dual Active Bridge (DAB) converter. One of the advantages of the DAB is the possibility to achieve Zero Voltage Switching (ZVS) operation in all the switches of this converter. However, the ZVS operation range can be lost for light loads, especially if high voltage is required in at least one of the DAB ports and the phase-shift control is used to regulate the power processed by the converter. Theoretically simple averaged model is presented for the DAB converter. Using the study presented in this paper, the boundaries of ZVS operation can be easily evaluated. The proposed models and analysis of the ZVS boundaries allow the proposal and evaluation of two different design strategies with different purposes: on the one hand, increasing the ZVS operation range and, on the other, improving efficiency at full load. Moreover, some techniques are presented for increasing the ZVS operation range and improving the efficiency of the DAB at full load (both using phase-shift control) employing the aforementioned analysis to obtain certain design criteria and conclusions. Finally, the proposed models, design strategies and techniques to improve the performance of the DAB are experimentally tested using a 1kW prototype with input and output voltages of 48V and 400V, respectively.
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paper_title: A Modified Dual Active Bridge Converter With Hybrid Phase-Shift Control for Wide Input Voltage Range

paper_content:

By inserting a small inductor between the transformer center tap and the midpoint of two split output capacitors in the dual active bridge (DAB) topology, this paper proposes a modified DAB converter for wide-input applications. A hybrid phase-shift (HPS) control scheme is proposed to allow all power switches to achieve practical ZVS over the full operating range; thereby, significantly minimizing the switching losses and alleviating electromagnetic interference. Moreover, the proposed control scheme does not significantly increase the conduction losses in comparison with the extended phase-shift (EPS) control. Therefore, the modified DAB can operate efficiently. The topology derivation and description are first presented. Then, the EPS and triple phase-shift (TPS) modulations are applied, and the corresponding operating principles and characteristics, including the soft-switching, power transfer, and root-mean-square current, are investigated in detail. To achieve practical ZVS operation of all switches over full operating range, while minimizing the conduction losses, the EPS and TPS are combined, and an HPS control scheme is proposed. Finally, experimental results from a 1.4-kW converter prototype with 200–400-V input and 400-V output are presented to verify the feasibility and advantages of the converter and control.
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paper_title: A Soft Switching Three-phase Current-fed Bidirectional DC-DC Converter With High Efficiency Over a Wide Input Voltage Range

paper_content:

In this paper, a three-phase current-fed dual-active-bridge (DAB) bidirectional DC-DC converter is presented. Compared to the voltage source DAB converter, the proposed converter allows low RMS current and maintains zero voltage switching (ZVS) in the whole operating range by keeping the ratio between primary side and secondary side DC-link voltage constant, leading to high efficient energy conversion over a wide input voltage range. In addition, the ZVS conditions can be maintained using small DC inductors and the input current ripple still remains small because of high DC inductor current ripples being alleviated by three-phase interleaving structure. Furthermore, the proposed topology with Y-Y connected transformers is proven to have better current sharing capability compared with other three-phase topologies with different transformer connections. The operation mode analysis, soft switching conditions, and hardware design guidelines are derived in this paper. A 6-kW hardware prototype with input voltage range of 24~48 V and rated 288 V output voltage is developed and tested in the laboratory. The experimental results verified that the proposed converter could maintain high efficiency over a wide input voltage and power range.
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paper_title: Design and evaluation of a reconfigurable stacked active bridge dc/dc converter for efficient wide load-range operation

paper_content:

This paper presents the design and implementation of a large-step-down soft-switched dc-dc converter based on the active bridge technique which overcomes some of the limitations of the conventional Dual Active Bridge (DAB) converter. The topology comprises a double stacked-bridge inverter coupled to a reconfigurable rectifier through a special three-winding leakage transformer. This particular combination of stages enable the converter to run in an additional low-power mode that greatly increases light-load efficiency by reducing core loss and extending the zero-voltage switching (ZVS) range. The converter is implemented with a single compact magnetic component, providing power combining, voltage transformation, isolation, and energy transfer inductance. A 175 kHz, 300 W, 380 V to 12 V GaN-based prototype converter achieves 95.9% efficiency at full load, a peak efficiency of 97.0%, an efficiency above 92.7% down to 10% load and an efficiency above 79.8% down to 3.3% load.
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paper_title: Dual-Transformer-Based DAB Converter With Wide ZVS Range for Wide Voltage Conversion Gain Application

paper_content:

A control strategy is proposed for the dual-transformer-based dual-active-bridge converter to achieve wide zero-voltage switching (ZVS) range for wide voltage conversion gain range application. The phase-shift control is adopted for the dual-transformer-based converter with minimum power switches employing half bridge output, and a control law is proposed to achieve wide ZVS range and reduce the current-related loss. With the proposed method, four switches of the converter can achieve full range of ZVS. The other two switches can achieve full-range ZVS under positive power flow, while a slightly reduced ZVS region under reverse power flow. Unlike the methods employing three control degrees of freedom, the proposed method only utilizes two decoupled control variables, making the controller easy to be implemented, more reliable, and independent of the converter parameters. In addition, the design of turns ratios for the two transformers is also optimized based on the control law and loss analysis. The effectiveness of the converter with the proposed control is verified by experimental results from a 1-kW prototype.
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paper_title: A Four-Degrees-of-Freedom Modulation Strategy for Dual-Active-Bridge Series-Resonant Converter Designed for Total Loss Minimization

paper_content:

This paper proposes a four-degrees-of-freedom modulation scheme to mitigate the conduction and switching losses in a dual-active-bridge (DAB) series-resonant converter. Under wide-range variations in the voltage gain and output current, the increased reactive power and root-mean-square tank current can contribute significantly to the conduction loss in a DAB converter, while the occurrence of hard switching leads to a switching loss and an increased device stress. The proposed modulation scheme utilizes internal, external phase shifts, and switching frequency as modulation parameters to achieve zero reactive power, minimum-tank-current, and complete soft-switching operation. Analysis of the proposed modulation scheme is given for both buck- and boost-mode operations. The proposed modulation scheme is validated by means of a 1-kW experimental prototype of a DAB series-resonant converter operating at 100 kHz, designed to interface a supercapacitor with a rated output voltage of 48 V to a 250-V dc bus. The effectiveness of the proposed topology for charging/discharging a supercapacitor under wide-range variations in the voltage gain and output current is verified by simulations and experimental results. A maximum efficiency of 97.7% is recorded from the experimental prototype (The experimental setup used for measuring converter's efficiency is shown in the supplementary material).
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Title: Circulating Current and ZVS-on of a Dual Active Bridge DC-DC Converter: A Review

Section 1: INTRODUCTION
Description 1: Introduce the growth in renewable energy and the need for technologies such as energy storage systems (ESSs) and micro-grids. Highlight the importance of isolated bidirectional dc-dc (IBDC) converters with a focus on the dual active bridge (DAB) topology. Mention the issues of large circulating current and loss of zero voltage switching (ZVS-on), which affect efficiency.

Section 2: CIRCULATING CURRENT SUPPRESSION
Description 2: Explain the concept of circulating current in a DAB and its impact on efficiency. Discuss various methods for suppressing circulating current, categorized into hardware methods and duty cycle methods.

Section 3: HARDWARE METHODS
Description 3: Detail hardware modifications such as replacing bidirectional power switching devices with unidirectional diodes, using blocking capacitors, and implementing hybrid bridges to suppress circulating current.

Section 4: DUTY CYCLE METHODS
Description 4: Describe modulation techniques like dual phase shift (DPS) and triple phase shift (TPS) to control duty cycles and suppress circulating current. Discuss the criteria for optimizing these phase shifts to minimize circulating current.

Section 5: ZVS-ON
Description 5: Discuss the importance of zero voltage switching (ZVS-on) to reduce switching losses. Review the ZVS-on range using single phase shift (SPS) modulation and methods to expand this range.

Section 6: ZVS-ON RANGE USING SPS
Description 6: Explain the ZVS-on boundary conditions with SPS modulation under ideal and practical conditions. Present the challenges in maintaining ZVS-on at different voltage gains and load conditions.

Section 7: METHODS TO EXPAND THE ZVS RANGE
Description 7: Review various methods to extend the ZVS-on operating range, including frequency modulation, current fed DAB converters, and adjusting inductances or adding auxiliary circuits.

Section 8: CONCLUSION
Description 8: Summarize the problems of circulating current and loss of ZVS-on in DAB converters. Compare the effectiveness of hardware and control methods for mitigating these issues, and discuss the potential of current fed DAB converters and optimization strategies for high and low frequency applications.