variable frequency drive variable frequency drive termed frequency drive variable speed drive drive micro drive drive type speed drive electro mechanical drive systems control motor speed varying motor input frequency voltage applications ranging small largest mill drives world electrical energy consumed electric motors industrial applications especially energy savings load service global market penetration applications relatively small lack penetration highlights significant energy efficiency improvement opportunities new installations decades power electronics technology reduced cost size improved performance advances switching devices drive simulation control techniques control hardware software available number different medium voltage system description operation variable frequency drive device drive system consisting following main sub systems motor main drive controller assembly drive operator interface electric motor system usually phase induction motor types single phase motors phase motors usually preferred types motors offer advantages situations phase induction motors suitable purposes generally economical motor choice motors designed fixed speed operation elevated voltage stresses imposed induction motors supplied require motors designed definite purpose fed duty accordance requirements controller controller solid state power electronics conversion system consisting distinct sub systems bridge direct current link voltage source drives generic sub section far common type drives drives drives convert line input output applications common bus solar applications drives drives basic drive phase pulse wave bridge drive link consists output provides stiff input filtered voltage converted quasi voltage output active switching elements drives provide higher power factor lower distortion phase controlled current source csi load drives generic sub section drive controller phase having single phase input phase output controller advances exploited dramatic increases voltage current ratings switching frequency solid state power devices past decades introduced gate past decades come dominate switching device variable applications suited volts drive control motor characteristics require voltage magnitude output motor adjusted match required load linear relationship example motors linear relationship suitable wide ranging applications control sub optimal high performance applications involving low speed demanding dynamic speed regulation positioning reversing load requirements control drives operate mode programmed suit special multi point paths drive control platforms control direct control adjust motor voltage magnitude angle reference frequency precisely control motor magnetic mechanical space pulse width increasingly popular straightforward method vary drives motor voltage current frequency control quasi variable pulse width output constructed intersections saw toothed carrier signal signal variable operating frequency voltage current operation motors rated speed base speed possible limited conditions require power rating motor called field weakening motors means operating rated rated speed permanent motors limited field weakening speed range constant wound motors induction motors wider speed range example rpm pole induction motor supplied limited speed rpm power higher speeds induction motor limited lowering motor rated power typically produced rated speed wound motors run higher speeds rolling mill drives base speed mechanical strength limits maximum speed motor embedded overall operation controller basic programming provided user inaccessible user programming display variable function block parameters provided control protect monitor motor driven equipment basic drive controller include optional power components accessories follows connected upstream circuit breaker isolation filter line passive filter connected link braking braking connected downstream output wave filter filter operator interface operator interface provides means operator start stop motor adjust operating speed additional operator control functions include reversing switching manual speed adjustment automatic control external process control signal operator interface includes display indication lights meters provide information operation drive operator interface display unit provided controller shown photograph display cable connected mounted short distance controller provided input output connecting push buttons switches operator interface devices control signals serial communications port available allow adjusted monitored controlled computer drive operation referring accompanying chart drive applications categorized single quadrant quadrant quadrant chart defined follows forward accelerating quadrant positive speed braking forward braking quadrant positive speed negative reverse accelerating quadrant negative speed braking reverse braking quadrant negative speed positive applications involve single quadrant loads operating quadrant variable pumps fans certain constant loads certain applications involve quadrant loads operating quadrant speed positive changes case fan faster natural mechanical losses sources define quadrant drives loads operating iii speed positive negative directions certain high performance applications involve quadrant loads speed direction elevators hilly regeneration occur drive link bus voltage smaller magnitude motor voltage starting motor initially applies low frequency voltage avoiding high current associated direct line starting start applied frequency voltage increased controlled rate accelerate load starting method typically allows motor develop rated drawing rated current low speed range adjusted produce steady starting right speed motor cooling result speed decreases prolonged low speed operation significant usually possible separately fan ventilation stopping sequence opposite starting sequence frequency voltage applied motor controlled rate frequency approaches zero motor shut small braking available help load little faster stop motor simply switched allowed coast additional braking obtained adding braking circuit controlled dissipate braking energy quadrant active end able brake load applying reverse energy line benefits energy savings fixed speed motor load applications supplied direct line power save energy operated variable speed means energy cost savings especially pronounced variable fan pump applications load power vary square cube respectively speed change gives large power reduction compared fixed speed operation relatively small reduction speed example speed motor load speed power reduction accordance affinity laws define relationship load united_states estimated electrical energy supply motors variable fan pump loads eighteen percent energy million motors saved efficient energy improvement technologies total installed base motors provided drives estimated drive technology adopted newly installed motors energy consumption breakdown global population motor installations shown following table control performance drives bring process quality improvements industrial commercial applications acceleration flow monitoring pressure speed temperature tension fixed speed loads subject motor high starting current times load current drives instead gradually ramp motor operating speed mechanical electrical stress reducing maintenance repair costs extending life motor driven equipment variable speed drives run motor specialized patterns minimize mechanical electrical stress example curve pattern applied application acceleration control reduces backlash occur accelerating performance factors tending favor use drives drives include requirements continuous operation low speed quadrant operation regeneration frequent acceleration routines need motor protected hazardous area following table compares drives according certain key parameters high frequency injection types ratings generic drives classified according following generic voltage source drive image drive output bridge stores energy bus supply stiff voltage input vast majority drives type voltage output current source csi drive image csi drive output bridge stores energy series connection supply stiff current input csi drives operated step output step drive image largely obsolete step drives csi type referred variable voltage drives pulse pam drives square wave drives drives step drive output bridge bus series connection supply quasi step voltage current input induction motor load drive drive special csi case output bridge stores energy link circuit supply stiff quasi step current output second bridge excited machine matrix image intermediate link energy storage operates phase current source anti parallel connected bridges pulse configuration phase acting convert fixed line frequency voltage alternating voltage variable load frequency drives based fed slip recovery system fed slip recovery system feeds slip power supply power supply network speed motor controlled adjusting current control platforms drives use following control platforms control field oriented control control direct control load power characteristics variable frequency drives categorized following load power characteristics variable fan pump applications constant positive displacement pump applications constant power machine tool traction applications available power ratings available voltage current ratings covering wide range single phase multi phase motors low voltage drives designed operate output equal motor application drives available ratings order economic considerations typically favor medium voltage drives lower power ratings different drive table accordance voltage current combination ratings different drive controllers switching devices given voltage rating greater equal following standard nominal motor voltage ratings generally manufacturer rated switching applications step placed drive motor load drives typically rated motor applications greater drives historically required considerably application design effort required drive applications power rating drives reach range different drive involved different rating performance power quality reliability requirements drives machines detailed lastly useful relate terms following classifications terms machines shown table terms detailed shown tables application considerations line note output easily filtered carrier frequency related filter supply near currents motor load bridge converts line voltage voltage output super imposing non linear half phase current creating current distortion voltage distortion line input loads relatively small comparison large stiff power system available electric power company effects distortion grid acceptable limits furthermore low voltage networks caused single phase equipment computers partially cancelled phase bridge 5th 7th proportion non linear load compared total load non linear load compared power supply relatively large load negative impact power available power company customers grid power company voltage distorted losses loads normal fixed speed motors increased condition lead shorter operating life compensation affected negatively particular cause resonance conditions levels order limit voltage distortion owners load required install equipment reduce distortion acceptable limits alternatively utility adopt solution installing equipment affected large equipment high power installations distortion reduced supplying multi pulse bridge multiple phase shifted possible replace standard bridge directional switching device bridge standard uses switching device output motor referred designations including active active supply unit active end quadrant operation control suitable input line current nearly inherently energy quadrant mode grid braking needed efficiency drive improved drive frequently required brake motor techniques exploit use passive active filters connected common bus branch load bus passive filters involve design low pass filter traps trap tuned required frequency 5th 7th 11th 13th pulse number common practice power companies customers impose distortion limits based standards example standard limits customer connection point maximum individual frequency voltage fundamental voltage total distortion general power supply system switching frequency switching frequency drive uses default switching frequency setting reducing drive switching frequency carrier frequency reduces heat generated carrier frequency times desired output frequency establish switching intervals carrier frequency range common low voltage volts higher carrier frequency produces better wave higher switching losses decreasing overall power conversion efficiency noise drives noise feature turned introduce random variation switching frequency acoustic noise range frequencies lower peak noise intensity long lead effects carrier frequency output voltage causes rapid rise times transmission line effects considered transmission line cable motor different tend reflect motor cable resulting produce equal twice bus voltage times rated line voltage long cable runs putting high stress cable motor eventual failure note standards phase motors rated adequately protect long lead systems 3rd generation rise time maximum recommended cable distance motor feet solutions caused long lead lengths include cable distance lowering carrier frequency installing filters duty rated motors rated withstand pulse trains rise time equal peak magnitude installing low pass wave filters lowering carrier frequency note noise noticeably increased carrier frequencies noticeable note selection carrier frequency drives involves balancing noise heat motor stress common mode voltage induced motor bearing current damage smooth motor operation factors obtained low pass wave filter filter motor bearing currents drives inherently associated high frequency common mode currents cause trouble motor high frequency find path earth bearing transfer metal electrical discharge sparking occurs bearing ball bearing race time based sparking causes erosion bearing race seen pattern large motors stray provides paths high frequency currents pass motor shaft ends leading circulating type bearing current poor grounding motor lead shaft ground bearing currents small motors poorly grounded driven equipment susceptible high frequency bearing currents prevention high frequency bearing current damage uses approaches good grounding practices bearing currents common mode currents example soft magnetic called good grounding practices include use shielded symmetrical geometry power cable supply motor installation shaft grounding bearing bearing currents interrupted installation specially designed shielded induction motors high frequency bearing soft magnetic phases giving high frequency common mode motor bearing currents approach use instead standard level drives level drives matrix fed motor cables high frequency current spikes interfere facilities fed motor cables shielded symmetrical geometry design routed away signal cables dynamic braking generated drive causes induction motor run speed slip load drives motor faster speed motor acts generator converting mechanical power electrical power power returned drive link element link connected electronic power switch braking controls dissipation power heat set cooling fans prevent dynamic braking braking energy transforming heat contrast drives recover braking energy energy line capital cost drives relatively high drives drives capacity recover braking energy load moving faster designated motor speed load return power system matrix csi drives inherently allow return energy load line voltage source require additional return energy supply regeneration useful value recovered energy large compared extra cost system system requires frequent braking starting widely speed control loads required examples belt drives manufacturing stop minutes stopped parts assembled correctly belt moves crane motor stops frequently braking required slow load lowering plug hybrid electric vehicles types image historical systems solid state devices available variable frequency drives machines obtained patents early 20th century example patent states generator finds useful application supplying current induction motors driving cars locomotives mechanism driven variable speeds
Variable-frequency drive