A Review of Multilevel Inverter Based Active Power Filter
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paper_title: A New Neutral-Point-Clamped PWM Inverter

paper_content:

A new neutral-point-clamped pulsewidth modulation (PWM) inverter composed of main switching devices which operate as switches for PWM and auxiliary switching devices to clamp the output terminal potential to the neutral point potential has been developed. This inverter output contains less harmonic content as compared with that of a conventional type. Two inverters are compared analytically and experimentally. In addition, a new PWM technique suitable for an ac drive system is applied to this inverter. The neutral-point-clamped PWM inverter adopting the new PWM technique shows an excellent drive system efficiency, including motor efficiency, and is appropriate for a wide-range variable-speed drive system.
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paper_title: Trends in active power line conditioners

paper_content:

Active power line conditioners, which are classified into shunt and series ones, have been studied with the focus on their practical installation in industrial power systems. In 1986, a combined system of a shunt active conditioner of rating 900 kVA and a shunt passive filter of rating 6600 kVA was practically installed to suppress the harmonics produced by a large capacity cycloconverter for steel mill drives. More than one hundred shunt active conditioners have been operating properly in Japan. The largest one is 20 MVA, which was developed for flicker compensation for an arc furnace with the help of a shunt passive filter of 20 MVA. In this paper, the term of "active power line conditioners" is used instead of that of "active power filters" because active power line conditioners would cover a wider sense than active power filters. The primary intent of this paper is to present trends in active power line conditioners using PWM inverters, paying attention to practical applications. >
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paper_title: A general circuit topology of multilevel inverter

paper_content:

A generalized circuit topology of multilevel voltage source inverters which is based on a direct extension of the three-level inverter to higher level is proposed. The circuit topologies up to five-level are presented. The proposed multilevel inverter can realize any multilevel pulsewidth modulation (PWM) scheme which leads to harmonic reduction and provides full utilization of semiconductor devices like GTOs, especially in the high power range where high voltage can be applied. The capacitor voltage balancing problem is discussed and a circuit remedy for such a problem is given. >
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paper_title: Imbricated Cells Multi-Level Voltage-Source Inverters for High Voltage Applications

paper_content:

SummaryIn the field of High Voltage Power Conversion, various techniques have been developped to use series-connected switches.Plain series connection of switches is the first solution and its drawbacks are now well-known (static and dynamic voltage sharing difficulties that require selecting paired switches or using sophisticated control techniques, high dV/dts generated by the synchronous commutation of all the switches, output waveform that does not benefit from the increased number of switches...).The “neutral point clamped” technique introduced in the early 80s improves voltage sharing and dV/dts, and gives a three-level output waveform.More recently a new multilevel topology has been introduced; compared to former techniques, it really solves the problem of voltage sharing and dV/dts, and gives a three-level output waveform with cancellation of the harmonic at the switching frequency.In this paper, it is shown that this technique can be easily generalized to voltage-source inverter legs with any num...
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paper_title: Active Power Filter Based on Four-leg Hybrid-Clamped Technique

paper_content:

Parallel active power filter based on four-leg hybrid-clamped converter topology is proposed in this paper. The detailed description is given on the balancing principle of capacitors' voltages with four-leg hybrid-clamped technique. An independent leg operating as a clamping leg brings better performance and easy control. For levels larger than live, this topology is a better choice when the ability of voltage balance and simple control are considered. The simulation and experiment of active power filter based on this topology show good performance of voltage balance and compensation.
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paper_title: Extended operation of flying capacitor multilevel inverters

paper_content:

Recent research in flying capacitor multilevel inverters (FCMIs) has shown that the number of voltage levels can be extended by changing the ratio of the capacitor voltages. For the three-cell FCMI, four levels of operation are expected if the traditional ratio of the capacitor voltages is 1:2:3. However, by altering the ratio, the inverter can operate as a five-, six-, seven-, or eight-level inverter. According to previous research, the eight-level case is referred to as maximally distended (or full binary combination schema) since it utilizes all possible transistor switching states. However, this case does not have enough per-phase redundancy to ensure capacitor voltage balancing under all modes of operation. In this paper, redundancy involving all phases is used along with per-phase redundancy to improve capacitor voltage balancing. It is shown that the four- and five-level cases are suitable for motor drive operation and can maintain capacitor voltage balance under a wide range of power factors and modulation indices. The six-, seven-, and eight-level cases are suitable for reactive power transfer in applications such as static var compensation. Simulation and laboratory measurements verify the proposed joint-phase redundancy control.
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paper_title: A power line conditioner based on flying capacitor multilevel voltage source converter with phase shift SPWM

paper_content:

In this paper, a new power line conditioning system is proposed. This system is constructed by a flying capacitor multilevel VSC (voltage source converter) and two reactors. The phase-shift SPWM (sinusoidal pulse width modulation) switching scheme is applied to control the switching devices of this converter. Due to this multilevel VSC and the switching scheme applied to this converter, the system is applicable to distribution systems or industrial applications. The reactive power compensation, harmonic suppression and load balancing functions of the power line conditioner are analyzed. A novel and effective startup procedure is proposed to start up the system. System simulation is carried out to verify the theoretical analysis results.
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paper_title: An active power filter implemented with a three-level NPC voltage-source inverter

paper_content:

This paper presents an active power filter implemented using a three-level neutral point-clamped voltage-source inverter. The active power filter can compensate current harmonics and reactive power in medium voltage distribution systems. The paper presents the principles of operation and design criteria for both the power and control circuits. Finally, the viability of the proposed scheme is shown with computer simulation using Matlab.
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paper_title: Multilevel inverter, based on multi-stage connection of three-level converters scaled in power of three

paper_content:

A multi-stage inverter using three-state converters is being analyzed for multipurpose applications, such as active power filters, static VAr compensators and machine drives for sinusoidal and trapezoidal current applications. The great advantage of this kind of converter is the minimum harmonic distortion obtained. The drawbacks are the isolated power supplies required for each one of the stages of the multiconverter. In this paper this problem has been overcome by using isolated, bidirectional DC power supplies, which are fed from a common power source. This solution becomes practical because only one converter of the chain, called Master, takes more than 80% of the total active power required by the system. The rest of the converters, called "Slaves", need very low power, and then those DC supplies are small. Another configuration with common DC supply and output transformers is displayed, and simulation results for different applications are shown and compared with similar results obtained with conventional PWM converters. The control of this multi-converter is being implemented using DSP controllers, which give flexibility to the system.
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paper_title: Multilevel converters for large electric drives

paper_content:

Traditional two-level high-frequency pulse width modulation (PWM) inverters for motor drives have several problems associated with their high frequency switching which produces common-mode voltage and high voltage change (dV/dt) rates to the motor windings. Multilevel inverters solve these problems because their devices can switch at a much lower frequency. Two different multilevel topologies are identified for use as a power converter for electric drives: a cascade inverter with separate DC sources; and a back-to-back diode clamped converter. The cascade inverter is a natural fit for large automotive all-electric drives because of the high VA ratings possible and because it uses several levels of DC voltage sources which would be available from batteries or fuel cells. The back-to-back diode clamped converter is ideal where a source of AC voltage is available such as a hybrid electric vehicle. Simulation and experimental results show the superiority of these two power converters over PWM-based drives.
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paper_title: A hybrid multilevel inverter for shunt active filter using space-vector control

paper_content:

In this paper, a current active power filter using a hybrid asymmetric multilevel inverter is presented and analyzed. The control proposed is based on a vector-control technique, generating an optimized switching pattern. The hybrid multilevel inverter increases the voltage levels number, reducing the harmonics associated to the commutation frequency. The hybrid multilevel inverter is structured by two cascaded-inverters, and the DC link voltage between the stages has the relation 1:3, generating 9 voltage levels. The signal reference is generated using a variant of the single-phase d-q Theory, allowing a fast transient response and stability. Simulated waveforms prove the viability of the control scheme and the multilevel active current filter proposed.
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paper_title: A novel control algorithm for cascade shunt active power filter

paper_content:

In this paper a novel control scheme of cascade shunt active power filter (CSAPF) is presented. This work is motivated by the fact that the compensation ability of traditional active power filter is limited by the voltage capability of the power devices. While the converter with cascade topology has been put into practical use for years especially in high voltage and high power drives. The application of such converter to active power filter is hindered by the problem of voltage unbalance of separate DC capacitors that leads to system instability. This paper deals with the design and implementation of a new digital controller for CSAPF. Finally experimental results obtained from a laboratory system developed in this paper are presented to verify the viability and effectiveness of the proposed control algorithm.
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paper_title: Hybrid Control Scheme for a Single-Phase Shunt Active Power Filter Based on Multilevel Cascaded Inverter

paper_content:

This paper presents a hybrid control scheme for a single-phase shunt active power Alter (SAF) based on a multilevel cascaded inverter. The multilevel-cascaded inverter has better characteristics than other topologies. In this topology, extra capacitors and clamping diodes are not needed to reproduce the same number of levels that other multilevel topologies. In order to improve the time response and behavior of SAF, a Passivity- based controller (PBC) is proposed and designed in this work. The focus of this controller is to increase the operation region of the shunt active Alter with respect to linear controller designed around an operation point. The current controller is performed by PBC and the voltage regulations are carried out by PIs. The proposed control scheme is verified by simulation and experimental tests.
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paper_title: Dynamic performance and control of a static VAr generator using cascade multilevel inverters

paper_content:

A cascade multilevel inverter is proposed for static VAr compensation/generation applications. The new cascade M-level inverter consists of (M-1)/2 single-phase full bridges in which each bridge has its own separate DC source. This inverter can generate an almost sinusoidal waveform voltage with only one time switching per cycle. It can eliminate the need for transformers in multipulse inverters. A prototype static VAr generator (SVG) system using an 11-level cascade inverter (21-level line-to-line voltage waveform) has been built. The output voltage waveform is equivalent to that of a 60-pulse inverter. This paper focuses on the dynamic performance of the cascade inverter based SVG system. Control schemes are proposed to achieve a fast response which is impossible for a conventional static VAr compensator (SVC). Analytical, simulation and experimental results show the superiority of the proposed SVG system.
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paper_title: Cascade multilevel inverters for utility applications

paper_content:

Cascade multilevel inverters have been developed by the authors for utility applications. A cascade M-level inverter consists of (M-1)/2 H-bridges in which each bridge has its own separate DC source. The new inverter: (1) can generate almost sinusoidal waveform voltage while only switching one time per fundamental cycle, (2) can eliminate transformers of multipulse inverters used in conventional utility interfaces and static VAr compensators, and (3) makes possible direct parallel or series connection to medium- and high-voltage power systems without any transformers. In other words, the cascade inverter is much more efficient and suitable for utility applications than traditional multipulse and pulse width modulation (PWM) inverters. The authors have experimentally demonstrated the superiority of the new inverter for reactive power (VAr) and harmonic compensation. This paper summarizes features, feasibility, and control schemes of the cascade inverter for utility applications including utility interface of renewable energy, voltage regulation, VAr compensation, and harmonic filtering in power systems. Analytical, simulated, and experimental results demonstrate the superiority of the new inverters.
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paper_title: A power line conditioner using cascade multilevel inverters for distribution systems

paper_content:

A power line conditioner (PLC) using a cascade multilevel inverter is presented for voltage regulation, reactive power (VAr) compensation and harmonic filtering in this paper. The cascade M-level inverter consists of (M-1)/2 H-bridges in which each bridge has its own separate DC source. This new inverter: (1) can generate almost an sinusoidal waveform voltage with only one time switching per line cycle; (2) can eliminate transformers of multipulse inverters used in the conventional static VAr compensators; and (3) makes possible direct connection to the 13.8 kV power distribution system in parallel and series without any transformer. In other words, the power line conditioner is much more efficient and more suitable to VAr compensation and harmonic filtering of distribution systems than traditional multipulse and pulse width modulation (PWM) inverters. It has been shown that the new inverter is specially suited for VAr compensation. This paper focuses on feasibility and control schemes of the cascade inverter for voltage regulation and harmonic filtering in distribution systems. Analytical, simulated and experimental results show the superiority of the new power line conditioner.
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paper_title: Hybrid multilevel power conversion system: a competitive solution for high power applications

paper_content:

Use of multilevel inverters is becoming popular in recent years for high power applications. Various topologies and modulation strategies have been investigated for utility and drive applications in literature. Trends in power semiconductor technology indicate a trade-off in the selection of power devices in terms of switching frequency and voltage sustaining capability. New power converter topologies permit modular realization of multilevel inverters using a hybrid approach involving integrated gate commutated thyristors (IGCT) and insulated gate bipolar transistors (IGBT) operating in synergism. This paper is devoted to the investigation of a hybrid multilevel power conversion system typically suitable for high performance, high power applications. This system designed for 4.16 kV, /spl ges/100 hp load comprises of a hybrid seven-level inverter, a diode bridge rectifier and an IGBT rectifier per phase. The IGBT rectifier is used on the utility side as a real power flow regulator to the low voltage converter and as a harmonic compensator for the high voltage converter. The hybrid seven-level inverter on the load side consists of a high voltage, slow switching IGCT inverter and a low voltage, fast switching IGBT inverter. By employing different devices under different operating conditions, it is shown that one can optimize the power conversion capability of entire system. A detailed analysis of a novel hybrid modulation technique for the inverter, which incorporates stepped synthesis in conjunction with variable pulse width of the consecutive steps is included. In addition, performance of a multilevel current regulated delta modulator as applied to the single phase full bridge IGBT rectifier is discussed. Detailed computer simulations accompanied with experimental verification are presented in the paper.
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paper_title: A Generalized Design Principle of a Uniform Step Asymmetrical Multilevel Converter For High Power Conversion

paper_content:

This paper is focused on a general design principle of a uniform step multilevel converter, with K series-connected full bridges inverters per phase. A new design terminology is proposed and analytical relationships are established. The DC-voltage sources supplying partial inverters are supposed to be rationally unbalanced. The corresponding “Asymmetrical” topology provides more flexibility to the designer, and can generate a large number of levels (any odd number from 2K+1 to 3K) without increasing the number of H-bridges. Simulation results and experimental tests shown the reliability of the design approach suggested.
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paper_title: DC bus ripple minimization in cascaded H-bridge multilevel converters under staircase modulation

paper_content:

Cascade connected H bridge multilevel converters are becoming an attractive topology for very high power applications. Due the single phase loading of the individual bridges, the DC link capacitors required in these converters are faced with a heavy stress. The problem is particularly acute with stair-case type modulation strategies. This paper presents an approach for equalizing the power drawn from each H bridge within less than one cycle period with the aim of reducing capacitor sizing. The presented approach is based on rearranging the switching strategies focusing on the redundancies in synthesizing output voltage of H bridge multilevel converters. The proposed approach also holds nearly the same degree of freedom in selecting conduction angles and attains similar levels of harmonic performance as with conventional switching angle selection approaches. The analysis presented in this paper is also confirmed by simulation.
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paper_title: Minimizing network harmonic voltage distortion with an active power line conditioner

paper_content:

Active power line conditioner (APLC) is a type of active filter that compensates for power system waveform distortion. The objective is to develop and illustrate a procedure for calculating the APLC injection current needed to minimize voltage harmonic distortion throughout a power network. The procedure is intended for use with APLC frequency domain correction in networks that are experiencing periodic harmonic distortion. The injection currents are determined using nonlinear optimization theory. The chief contribution lies in developing a simple procedure for finding the Fourier series of the optimum APLC injection current waveform. The procedure is intended to apply in any of the following situations: (1) one single-phase APLC in a single-phase network; (2) one single-phase APLC in a three-phase network; or (3) one three-phase APLC in a balanced three-phase network. >
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paper_title: A study on the theory of instantaneous reactive power

paper_content:

A new definition of instantaneous reactive power is presented. This definition has a clear physical meaning that includes both the conventional instantaneous reactive power and the instantaneous power of a zero-phase component. A simple control algorithm for the active filter derived from the new definition is described. Simulations verified the control algorithm. >
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paper_title: Generalized instantaneous reactive power theory for three-phase power systems

paper_content:

A generalized theory of instantaneous reactive power for three-phase power systems is proposed in this paper. This theory gives a generalized definition of instantaneous reactive power, which is valid for sinusoidal or nonsinusoidal, balanced or unbalanced, three-phase power systems with or without zero-sequence currents and/or voltages. The properties and physical meanings of the newly defined instantaneous reactive power are discussed in detail. A three-phase harmonic distorted power system with zero-sequence components is then used as an example to show reactive power measurement and compensation using the proposed theory.
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paper_title: An active filter used for harmonic compensation and power factor correction: A control technique

paper_content:

The paper deals with the analysis of an active power filter with two legs for three-phase systems. Although the converter topology is not symmetric, a suitable control of the power switches allows the achievement of balanced currents. The control technique for the compensation of the harmonics and reactive power of the load is derived directly from the mathematical model of the converter. The reference signals of the currents are used for the space vector modulation (SVM) both for balanced and unbalanced voltages of the dc-link capacitors. Numerical simulations validate the proposed control showing the capabilities of the active filter in reducing the total harmonic distortion and reactive powers in supplying of the source currents.
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paper_title: A control structure for fast harmonics compensation in active filters

paper_content:

Shunt active filters are a means to improve power quality in distribution networks. Typically, they are connected in parallel to disturbing loads in order to reduce the injection of nonsinusoidal load currents into the utility grid. The high power active filter investigated in this paper is based on a PWM controlled voltage source inverter. Its inner current control is realized with a deadbeat controller that allows fast tracking of stochastically fluctuating load currents. For the mitigation of stationary load current harmonics, an outer control loop is required that compensates for the persistent phase error caused by the delay of the inner loop. The outer loop developed in this paper is based on integrating oscillators tuned to the major load current harmonics. Mathematically, they are equivalent to I-controllers in rotating reference frames. Some of these oscillators are located within a closed control loop. For frequencies where the feedback would excite grid resonances they are placed in a prefilter with phase shifting elements. Since all oscillators share a common feedback full selectivity of the harmonic analysis is achieved. For every harmonic the degree of compensation can be adjusted individually. In addition to the oscillators, a direct path is provided that feeds forward the load current to the inner control loop. Thus, load current transients can be tracked with the full speed of the dead-beat controller. The direct path does not affect the harmonic analysis performed by the oscillators.
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paper_title: Instantaneous Reactive Power Compensators Comprising Switching Devices without Energy Storage Components

paper_content:

The conventional reactive power in single-phase or three- phase circuits has been defined on the basis of the average value concept for sinusoidal voltage and current waveforms in steady states. The instantaneous reactive power in three-phase circuits is defined on the basis of the instantaneous value concept for arbitrary voltage and current waveforms, including transient states. A new instantaneous reactive power compensator comprising switching devices is proposed which requires practically no energy storage components.
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paper_title: A general circuit topology of multilevel inverter

paper_content:

A generalized circuit topology of multilevel voltage source inverters which is based on a direct extension of the three-level inverter to higher level is proposed. The circuit topologies up to five-level are presented. The proposed multilevel inverter can realize any multilevel pulsewidth modulation (PWM) scheme which leads to harmonic reduction and provides full utilization of semiconductor devices like GTOs, especially in the high power range where high voltage can be applied. The capacitor voltage balancing problem is discussed and a circuit remedy for such a problem is given. >
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paper_title: Imbricated Cells Multi-Level Voltage-Source Inverters for High Voltage Applications

paper_content:

SummaryIn the field of High Voltage Power Conversion, various techniques have been developped to use series-connected switches.Plain series connection of switches is the first solution and its drawbacks are now well-known (static and dynamic voltage sharing difficulties that require selecting paired switches or using sophisticated control techniques, high dV/dts generated by the synchronous commutation of all the switches, output waveform that does not benefit from the increased number of switches...).The “neutral point clamped” technique introduced in the early 80s improves voltage sharing and dV/dts, and gives a three-level output waveform.More recently a new multilevel topology has been introduced; compared to former techniques, it really solves the problem of voltage sharing and dV/dts, and gives a three-level output waveform with cancellation of the harmonic at the switching frequency.In this paper, it is shown that this technique can be easily generalized to voltage-source inverter legs with any num...
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paper_title: Multilevel converters-a new breed of power converters

paper_content:

Multilevel voltage source converters are emerging as a new breed of power converter options for high-power applications. The multilevel voltage source converters typically synthesize the staircase voltage wave from several levels of DC capacitor voltages. One of the major limitations of the multilevel converters is the voltage unbalance between different levels. The techniques to balance the voltage between different levels normally involve voltage clamping or capacitor charge control. There are several ways of implementing voltage balance in multilevel converters. Without considering the traditional magnetic coupled converters, this paper presents three recently developed multilevel voltage source converters: (1) diode-clamp, (2) flying-capacitors, and (3) cascaded-inverters with separate DC sources. The operating principle, features, constraints, and potential applications of these converters are discussed.
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paper_title: Multilevel converters for large electric drives

paper_content:

Traditional two-level high-frequency pulse width modulation (PWM) inverters for motor drives have several problems associated with their high frequency switching which produces common-mode voltage and high voltage change (dV/dt) rates to the motor windings. Multilevel inverters solve these problems because their devices can switch at a much lower frequency. Two different multilevel topologies are identified for use as a power converter for electric drives: a cascade inverter with separate DC sources; and a back-to-back diode clamped converter. The cascade inverter is a natural fit for large automotive all-electric drives because of the high VA ratings possible and because it uses several levels of DC voltage sources which would be available from batteries or fuel cells. The back-to-back diode clamped converter is ideal where a source of AC voltage is available such as a hybrid electric vehicle. Simulation and experimental results show the superiority of these two power converters over PWM-based drives.
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paper_title: Multicarrier PWM strategies for multilevel inverters

paper_content:

Analytical solutions of pulsewidth-modulation (PWM) strategies for multilevel inverters are used to identify that alternative phase opposition disposition PWM for diode-clamped inverters produces the same harmonic performance as phase-shifted carrier PWM for cascaded inverters, and hybrid PWM for hybrid inverters, when the carrier frequencies are set to achieve the same number of inverter switch transitions over each fundamental cycle. Using this understanding, a PWM method is then developed for cascaded and hybrid inverters to achieve the same harmonic gains as phase disposition PWM achieves for diode-clamped inverters. Theoretical and experimental results are presented in the paper.
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paper_title: Study on shunt active power filter based on cascade multilevel converters

paper_content:

A shunt active power filter (APF) based on cascade multilevel converters with carrier phase shifted sinusoidal pulse width modulation (CPS-SPWM) is presented. The main sections of the shunt APF such as switching modulation strategy, harmonic and reactive current detection, AC side control and DC side control are discussed. Simulated results are given that verify this APF can compensate the harmonic and reactive current correctly and validly.
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paper_title: Optimized modulation techniques for the generalized N-level converter

paper_content:

A balancing control strategy that allows the voltage differences among the DC link capacitors of the generalized n-level power converter to be minimized is presented. The case n=3 is treated, but the technique can be generalized to larger n values. The balancing algorithm does not achieve correct voltage sharing of the capacitors under all operating conditions, but it provides a great improvement. This strategy appears to be very promising in single-phase applications, for which nonredundant switching configurations do not affect the capacitor voltage balance. >
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paper_title: A new modulation strategy for improved DC bus utilization in hard and soft switched multilevel inverters

paper_content:

Multilevel inverters provide an attractive solution for high power, high voltage applications. While the multilevel topology permits higher voltages using devices of lower ratings, the DC link voltage balancing problem is a serious drawback which limits the applicability of multilevel topologies for motor drives. So far, redundant state selection has been the only method for regulating the capacitor voltages which results in a limited voltage capability. A new control strategy to improve the DC bus utilization, while generating low THD voltages is introduced. The proposed scheme is independent of the type of multilevel inverter topology and can be used for both hard and soft switching inverters. Simulation results are presented to demonstrate the validity of control scheme.
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paper_title: Seven-level shunt active power filter

paper_content:

In this work, the seven-level cascaded type inverter is used as a shunt active power filter to exploit multilevel inverter advantages. The capacitor voltage control technique used as a harmonic current extraction method for the two-level inverter is extended to the seven-level shunt active power filter. A predictive current controller based on the supply current (not the active filter current) is applied. Phase-shifted space vector modulation for the multilevel inverter is used as a PWM technique. The proposed seven-level shunt active power filter is validated by simulation.
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paper_title: A new predictive control strategy for active power filters

paper_content:

A new control strategy for active power filters based on dynamic programming control is presented. This method replaces an active power filter with an ideal controllable current source whose waveform is optimally determined beforehand. This new control technique is very suitable for suppressing harmonics of nonlinear loads. In addition other parameters such as power factor can also be controlled.
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paper_title: Space vector pulse width modulation of three-level inverter extending operation into overmodulation region

paper_content:

Multilevel voltage-fed inverters with space vector pulse width modulation have established their importance in high power high performance industrial drive applications. The paper proposes an overmodulation strategy of space vector PWM of a three-level inverter with linear transfer characteristic that easily extends from the undermodulation strategy previously developed by the authors for neural network implementation. The overmodulation strategy is very complex because of large number of inverter switching states, and hybrid in nature, that incorporates both undermodulation and overmodulation algorithms. The paper describes systematically the algorithm development, system analysis, DSP based implementation, and extensive evaluation study to validate the modulator performance. The modulator takes the command voltage and angle information at the input and generates symmetrical PWM waves for the three phases of an IGBT inverter that operates at 1.0 kHz switching frequency. The switching states are distributed such that the neutral point voltage always remains balanced. An open loop volts/Hz controlled induction motor drive has been evaluated extensively by smoothly varying the voltage and frequency in the whole speed range that covers both undermodulation and overmodulation (nearest to square-wave) regions, and performance was found to be excellent. The PWM algorithm can be easily extended to vector-controlled drive. The algorithm development is again fully compatible for implementation by a neural network.
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paper_title: A two-level inverter based SVPWM algorithm for a multilevel inverter

paper_content:

Implementation of space vector modulation for multilevel inverters is complex and computationally intensive due to difficulty in determining the location of reference vector, calculation of on-times and determination of switching state vectors. This paper proposes a simple space vector PWM algorithm for a multilevel inverter based on standard two-level inverter and its implementation. Since the pro-posed multilevel space vector modulation method uses the basic two-level modulation to calculate the on-times, computation process for n-level inverter becomes simpler and easier. The main advantage of the proposed methodology is that it uses a simple mapping process to achieve the multilevel space vector modulation. The effectiveness of the algorithm has been verified by simulation and experiments, on a 3-level inverter.
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paper_title: Optimized space vector switching sequences for multilevel inverters

paper_content:

Previous work has shown that space vector modulation and carrier modulation for two-level inverters achieve the same phase leg switching sequences when appropriate zero sequence offsets are added to the reference waveforms for carrier modulation. This paper presents a similar equivalence between the phase disposition (PD) carrier and space vector modulation strategies applied to diode clamped, cascaded N-level or hybrid multilevel inverters. By analysis of the time integral trajectory of the converter voltage, the paper shows that the optimal harmonic profile for a space vector modulator occurs when the two middle space vectors are centered in each switching cycle. The required zero sequence offset to achieve this centring for an equivalent carrier based modulator is then determined. The results can be applied to any multilevel converter topology without differentiation. Discontinuous behavior is also examined, with the space vector and carrier based modulation methods shown to similarly produce identical performance. Both simulation and experimental results are presented.
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Title: A Review of Multilevel Inverter Based Active Power Filter

Section 1: INTRODUCTION
Description 1: This section introduces the importance of maintaining power quality in electrical systems, highlights the limitations of passive filters, and explains the advantages and challenges of active power filters, particularly in high voltage applications.

Section 2: TOPOLOGIES OF MULTILEVEL INVERTERS
Description 2: This section discusses the different topologies of multilevel inverters, including Diode Clamped, Flying Capacitor, and Cascade H-bridge, along with their configurations and operational principles.

Section 3: CONTROL STRATEGIES
Description 3: This section describes various control strategies for active power filters, detailing the steps involved in signal conditioning, estimation of compensating signals, and the generation of firing signals for switching devices.