Comparative Evaluation of a Triangular Current Mode (TCM) and Clamp-Switch TCM DC-DC Boost Converter

Transcription

1 IEEE Proceedings of he IEEE Energy Conversion Congress & Expo (ECCE USA ), Milwakee, WI, USA, Sepember -, Comparaive Evalaion of a rianglar Crren Mode (CM) and Clamp-Swich CM - Boos Converer O Knech, D Boris, J W Kolar his maerial is pblished in order o provide access o research resls of he Power Elecronic Sysems aboraory / D-IE / EH Zrich Inernal or personal se of his maerial is permied However, permission o reprin/repblish his maerial for adverising or promoional prposes or for creaing new collecive works for resale or redisribion ms be obained from he copyrigh holder By choosing o view his docmen, yo agree o all provisions of he copyrigh laws proecing i

2 Comparaive Evalaion of a rianglar Crren Mode (CM) and Clamp-Swich CM - Boos Converer O Knech, D Boris and J W Kolar Power Elecronic Sysems aboraory, EH Zürich, Swizerland, knech@lemeeehzch Absrac For he power managemen of a wireless power ransfer sysem for implanable mechanical hear pmps, an addiional boos - converer sage is needed in order o conrol he power delivered o he implan Pariclarly, baery powered and implanable medical devices pose special demands on he efficiency and/or power densiy of he employed converers Accordingly, sof-swiching and/or high swiching freqencies ms be argeed Modlaion schemes ha allow for Zero- Volage-Swiching (ZVS) sch as rianglar Crren Mode (CM) offer a highly efficien operaion, b sffer from a large operaing freqency variaion, which is mainly limied by he digial conrol herefore he Clamp-Swich CM () converer can be employed which allows also for he conrol of he swiching freqency variaion In his paper, he and he CM converer are compared regarding he power conversion efficiency and he power densiy of he converer Since he converer is no well known in he lierare, he converer is analysed in deail and a modlaion scheme is explained ha allows for ZVS for all swiches in he enire range of operaion In addiion, he reqiremens for ZVS and a conrol scheme (ie iming calclaions) are provided for he converer in order o limi he maximm swiching freqency he modlaion and conrol scheme are verified wih a hardware prooype Finally, he performance of he converer is measred and compared o he performance of he converer operaed in CM mode he measremens show ha he converer offers similar performance compared o he CM operaion a lower indcor power densiy, b has he advanage of a significanly redced swiching freqency variaion In applicaions, where a very high power densiy is needed, he CM converer operforms he converer in erms of efficiency Index erms boos converer, clamp swich, rianglar crren mode (CM), zero volage swiching (ZVS) I INRODUCION Indcive Power ransfer (IP) echnology has proven o be a promising solion for powering medical implans wiho he need for a galvanic conac As par of he Zrich Hear Projec, a prooype of a highly efficien IP sysem has been bil [] in order o spply elecrical power o an implanable blood pmp, sch as a ef Venriclar Assis Device (VAD), replacing he percaneos driveline which is sed in oday s sae-of-he-ar implanable Mechanical Circlaory Sppor Sysems (MCSS) and which imposes a severe risk of infecion o he paien he basic srcre of he power managemen of his ranscaneos Energy ransfer (E) sysem is shown in Fig he E sysem s main power spply is a rechargeable baery pack which is carried by he paien he power is fed o he IP sysem which consiss of an inverer sage, he energy ransfer coils and a synchronos recifier sage on he secondary side In addiion, an implaned backp baery allows for a emporary compleely nehered operaion of he VAD he ypical coninos average power consmpion of crren sae-ofhe-ar VADs is in a range of -7 W wih peak power consmpion of p o W [], [3] However, he maximm power ransfer capabiliy of he E sysem has o be in a range of p o -3 W dring he charging process of he implaned backp baery he opimizaion of he IP sysem in [] has shown ha i is beneficial o operae he IP sysem a a higher inp and op volage U, and U, han he ypical nominal baery pack op volage of V herefore, an addiional boos converer is placed in beween he primary baery and he inverer circi Similarly, a bidirecional - converer is needed on he secondary side as charging conroller for he implaned backp baery, which is able o operae eiher in bck or boos mode, depending on he direcion of he power flow (ie bck-mode for charging he baery) he design of he implaned - converer is pariclarly challenging becase of he limied available volme and he need for a very high power conversion efficiency in order o limi he heaing of he srronding isse o a safe level In his work, he focs is on he realizaion of he primary side boos converer, where he main objecive is he achievemen of a high power conversion efficiency in order o allow for an exension of he rnime of he main baery Common realizaions of qasi-resonan boos converers, ha allow for Zero-Volage-Swiching (ZVS) are known in he lierare as Synchronos Condcion Mode (SCM) [], [] or rianglar Crren Mode (CM) [] [] operaion However as will be discssed in Secion II, hese modlaion schemes show limiaions regarding he power conversion efficiency or operabiliy herefore, a second ZVS converer opology comprising an indcor clamp swich [9], [] and fearing a limied swiching freqency variaion is analysed in deail and compared o he CM operaion In addiion, a modlaion scheme [] of he Clamp-Swich CM () converer is presened in Secion III ha allows for ZVS of all swiches in he enire range of operaion, ie in he inp or op volage and power range he fndamenal design consideraions and he iming calclaions [] needed for he operaion of he converer are provided in Secion IV In Secion V he realized hardware prooype of he C- CM converer is presened and is performance is compared o he CM operaion sing experimenal resls Conclding remarks are given in Secion VI II CONVERER EVAUAION he very basic srcre of he boos converer ha can be operaed eiher in hard-swiched or sof-swiched SCM or CM operaion is shown in Fig (b) In hard-swiched operaion, he indcor crren is always posiive and he swich experiences a hard rn-on when he posiive indcor crren is commaed from he body diode of swich o he low-side swich As a resl, he losses in he swich are increased significanly Sof-swiching of he converer can be achieved if he indcor crren has a negaive vale a he end of he ime inerval off If he negaive indcor crren is able o deliver enogh charge dring he dead-ime inerval o flly discharge he parasiic op capaciance of he swich and charge he op capaciance of, he swich can rn on wih negligible

3 U Ba, exernal implaned U, C,, U, AC AC AC C, k, Boos-Converer Inverer Recifier Bck-Converer VAD M U Ba, () P max CM 3 D () P max (b) C I,min () (c) on P max off P min P min SCM C (d) I,min () I,min (e) on off cl P min Figre : Basic power managemen concep of he ranscaneos Energy ransfer (E) sysem (b) Sandard boos converer opology and (c) he indcor waveforms for Synchronos Condcion Mode (SCM) and rianglar Crren Mode (CM) operaion (d) Clamp-Swich CM () boos converer opology and (e) he associaed indcor crren waveforms power loss he indcor crren waveform of he CM and SCM operaion of he converer are shown schemaically in Fig (c) for minimm and maximm op power In he SCM operaion, he indcor peak-o-peak crren ripple is consan and independen of he op power As a resl, he swiching freqency can be kep a a consan vale, b he converer sffers from a low power conversion efficiency a ligh load condiions de o he high RMS indcor crren A beer performance is offered by he CM operaion where he minimm indcor crren I,min is kep a a consan vale, large enogh o ensre ZVS he op power is hen conrolled by varying he on-ime inerval on of he swich As a resl, he RMS indcor crren is redced a par load operaion, b he swiching freqency increases significanly Assming a consan inp volage and a lossless operaion, he variaion of he swiching freqency can be expressed wih n f,cm fmax f min (Pmax I,min) (,max ),min () (P min I,min) (,min ),max he freqency variaion depends on he op power and op volage variaion [,min,,max] and can be very large, depending on he range of operaion he maximm swiching freqency f max occrs a minimm op power and maximm volage conversion raio and is mainly limied by he ime delays in he measremen and conrol circi, as he swiching ime inervals need o be calclaed and synchronized o he zero-crossings of he indcor crren In order o address his drawback, an addiional clamp-swich is inrodced in parallel o he indcor, comprising an ani-series connecion of he wo swiches 3 and enabling bidirecional volage blocking, as i is shown in Fig (d) Noe ha he onsae resisance of he clamp-swiches can be higher compared o he swiches and, since hey do no have o direcly condc he load crren Hence, a swich wih lower parasiic op capaciance can be sed for he clamp-swiches For nidirecional power flow, he clamp-swich can be implemened wih only one swich 3 and diode D A maximm op power, he operaion corresponds o he CM operaion Hence, he indcor crren has a rianglar shape wih a negaive indcor crren I,min ha allows for ZVS of he wo main swiches and However, a ligh load operaion, he clampswich allows o inrodce a free-wheeling sae for he indcor crren afer he rn-off of he swich and hence, sreches he swiching period as i is shown in Fig (e) As a resl, he swiching freqency variaion is redced significanly, which relaxes he reqiremens for he conrol circi and allows o operae he converer a a higher swiching freqency in he enire range of operaion when compared o he CM converer, implemened for he same maximm swiching freqency he clamp-swich converer opology is implemened eg in he Picor Cool-Power ZVS Bck Reglaor Series provided by Vicor and is explained briefly in [9] However, he realizaion of he clampswich iself is no shown and he sof-swiching is shown only for he swiches and and no ZVS modlaion scheme for he fll converer is described herefore, in he following secion, he operaion of he is explained in deail and a new modlaion scheme [] is shown which garanees sof-swiching for all swiches III MODUAION SCHEME he deailed operaing principle of he proposed modlaion of he converer in boos operaion is shown in Fig he indcor crren and swich-node volage waveforms belonging hereo are shown in Fig 3 Saring wih he firs ime inerval [, ], swich is condcing and he indcor crren rises linearly he clamp swich is in on-sae and he body diode of swich 3 is in blocking sae and prevens a shor circi of he inp capacior C As soon as he indcor crren reaches he vale I,, swich rns off and he indcor crren charges he parasiic op capaciance of swich, while discharging he op capaciances of and 3 Dring [, ], he volage sw rises nil he body diode of swich 3 sars o condc In [, 3] he indcor volage is clamped o he diode forward volage drop DF and swich 3 can be rned on a nearly zero volage a 3 he ime inerval [ 3, ] is an inermediae sep, where he indcor crren is free-wheeling hrogh he clamp swiches his sep is imporan in order o reverse he volage blocking capabiliy of he clamp swiches, before he indcor crren sars decreasing and reverses is direcion a ime In pracice, he ime inerval [ 3, ] ms be as shor as possible in order o minimize he power loss in he clamp swiches A, swich is rned off and dring [, ]

4 [, ] [, ] [, 3 ] [ 3, ] [, ] [, ] [, 7 ] [ 7, ] [, 9 ] C sw [ 9, ] [, ] [, ] C sw C sw Figre : Operaing saes of he proposed ZVS modlaion scheme for a fll swiching cycle [, ] he indcor crren charges he parasiic op capaciance of he swiches and and frher discharges he op capaciance of As soon as he parasiic op capaciance of swich is flly discharged, he ani-parallel diode sars o condc in and clamps he volage across he swich o DF as shown in he ime inerval [, ] As a resl, a ime, swich can be rned on a zero volage Noe ha he diode of swich is in blocking sae and prevens a shor circi of he converer s inp and op erminal In he ime inerval [, 7] he indcor crren is spplied o he op and is decreasing he zero-crossing of he indcor crren a ime is deeced and is sed o deermine he rn-off ime delay of swich ha is needed in order o generae he reqired negaive indcor crren I, o achieve ZVS of he swiches in he remaining ime inervals A 7, swich is rned off and he negaive indcor crren discharges he parasiic op capaciance of he swiches and, while charging he op capaciance of swich dring [ 7, ] When he volage sw reaches a vale of ( + DF) a, he aniparallel diode of swich sars o condc As a resl, swich can be rned on a zero volage a he ime 9 Dring he ime inerval [ 9, ], he indcor crren is free-wheeling in negaive direcion hrogh he clamp-swich In his ime inerval here is no energy delivered from he inp o he op and can herefore be sed as a degree of freedom o conrol he swiching period and he amon of power delivered o he load In he clamping ime inerval, he indcor crren amplide is coninosly decreasing de o he power losses in he clamp swiches and in he indcor his has o be aken ino accon if he clamping ime inerval is very large, becase he crren amplide cold fall below a minimm vale, where ZVS of swich canno be achieved anymore in he following ime inervals A, swich 3 is rned off and he negaive indcor crren conines discharging he parasiic op capaciance of swich nil he swich-node volage sw reaches zero and he diode of swich sars o condc as shown in ime inerval [, ] he indcor crren is rising and swich ms be rned on before he crren zero crossing o allow for ZVS of Similar o he analysis provided in [] for CM operaion, an - Zi-diagram (phase diagram) shown in Fig 3(b) is sed o reveal he basic crieria ha ms be me in order o achieve sof-swiching of he swiches afer he resonan ransiions In his represenaion, consan parasiic op capaciances are assmed for he swiches herefore, as explained in [], he resonan ransiion ime and he reqired crrens o enable ZVS can be calclaed wih good approximaion sing he charge eqivalen capaciance of he swiches For he hardware prooype described in Secion V, each swich is composed of a Gallim Niride (GaN) Field Effec ransisor (FE) placed in parallel wih an addiional Schoky diode o lower he volage drop across he swich in diode condcion mode he oal capaciance C o of he swich is herefore given by he sm of he swich op capaciance C oss and he Schoky diode jncion capaciance C j Fig shows he oal capaciance given by he employed GaN FE EPCC and he Schoky diode MBRHSF, as well as he oal sored charge Q o and he charge eqivalen capaciance which can be calclaed sing [], C Q,eq(V ) V V C o(v)dv () he resonan ransiion in he ime inervals [ 7, ] and [, ] can be described in he -Zi-diagram as a circle wih he cener a

5 i() I, I, Z i() Z I, 3 I,min SW() R () sw Si() s s s3 s R 9 Z I, (b) Z I,min 7 Figre 3: ypical waveforms of he indcor crren i and swich-node volage sw and he swiching saes o (b) -Zi-diagram, showing he scaled indcor crren Z i () wih respec o he swich-node volage sw () q R (Z I, ) + ( ), wih Z CQ,eq,o (3) As shown in Fig (b), dring he ime inerval [7, ] he capaciance C is charged from V o ( ), neglecing he forward volage drop DF of he Schoky diode he capaciances C and C are discharged from o and from ( ) o V, respecively Assming he same non-linear capaciance Co for each swich, he oal delivered charge and he associaed charge eqivalen capaciance can be calclaed wih QC, R Co, (v)dv R R QC, R Qo,c QC, + QC, + QC, QC, Co, (v)dv Co, (v)dv Co, (v)dv Qo,c Qo,c Uo,c ( ) () Qo,d Co,3 (v)dv QC, + QC, + QC,3 and he charge eqivalen capaciance can be calclaed wih CQ,eq,o,d Qo,d Qo,d Uo,d Volage (V) 3 C3 i (c) i C sw C C i C sw C i i (b) [7, ] c Coss Cj Co d sw i 7 [, ] () QC,3 3 iance and sored charge (b) Illsraion of he crren flow dring he resonan volage ransiion in ime inerval [7, ] and (c) in ime inerval [, ] R R Co, (v)dv Co, (v)dv R Co, (v)dv, () R QC, 3 3 Figre : oal swich op capaciance, charge-eqivalen capac- Similar consideraions can be made for he ime inerval [, ] In his case, a he end of he clamping inerval, he resonan ransiion is iniiaed wih he rn-off of swich 3 he swiching sae of he converer and he flow of he crren in he parasiic capaciances is shown in Fig (c) he capaciance C is frher discharged from o V and he capaciances C and C3 are charged from ( ) o and from V o, respecively he oal delivered charge is hen given by QC, Qo Co CQ,eq i and CQ,eq,o,c 7 3 Charge (nc) r Capaciance (nf) sw and i and a radis given by (7) Hence, he oal charge eqivalen capaciance associaed wih he oal resonan ransiion from 7 o can be calclaed wih CQ,eq,o Qo,c + Qo,d () he absole minimm indcor crren I, a he ime insan 7, reqired for sof-swiching of he swich a he ime can hen be calclaed sing (3) and () I, p ( ), Z for (9) In his case, he criical operaing poin, where sof-swiching of cold be los, is a he minimm op volage, regardless of he power delivered o he load he ime inerval c 7 of he resonan ransiion can hen be calclaed sing he geomeric relaions depiced in he -Zi-diagram and he eqaion for he radis R given in (3), c I, Z,c arcan ω,c h + π i, ()

6 wih he characerisic impedance and he resonan freqency calclaed wih he charge eqivalen capaciance given in (), Z,c and ω,c () C Q,eq,o,c CQ,eq,o,c he peak negaive indcor crren can hen be calclaed wih I,min R (Z,cI,) + ( ) () Z,c Z,c Similar o he previos case, he ime inerval d of he resonan ransiion can be calclaed sing eqaion (), sbsied wih he charge eqivalen capaciance from (7) and is given by d ω,d arcsin ( ) (3) I,min Z,d De o he large indcor crren I, a ime, he ime inervals [, ] and [, ] are very shor and can be negleced in he general case he criical operaing poin where sof-swiching of cold be los is a he maximm op volage and very low op power Noe ha he modelling of he resonan ransiion sing he charge eqivalen capaciance is an approximaion only B as shown in Fig, he oal charge of he GaN FEs and he parallel Schoky diode does no show a high non-lineariy Hence, he eqaions ()- (3) allow for an accrae modelling of he operaion of he converer dring he resonan volage ransiions and a relaive error of less han % was obained for ime inervals c and d when compared o a circi simlaion he minimm negaive indcor crren I, reqired o achieve ZVS can be prediced sing eqaion (9) However, a relaive error of p o % was obained for he specificaions and range of operaion sed for he prooype converer Based on he operaing principle shown in his secion, he conrol scheme of he converer was derived similar o [] as presened in he following secion IV BOOS OPERAION For CM operaion, he on-ime of he swich is he only degree of freedom available in order o conrol he power delivered o he load B for he modlaion, he clamping ime inerval [ 9, ] is an addiional degree of freedom which is sed o conrol he swiching freqency variaion of he converer In order o minimize he RMS indcor crren, i is beneficial o emlae CM operaion a he nominal op power, where he clamping ime inerval is se o zero his implies ha he operaing freqency is sill allowed o vary in a cerain range de o variaions of he inp or op volage However, for consan erminal volages b varying op power, he clamping ime inerval is sed o conrol he average inp crren, while mainaining a consan swiching freqency A consan swiching freqency cold also be mainained despie a variaion of he erminal volages, b in his case, he adjsmen of he clamping ime-inerval wold lead o an increase of he indcor RMS crren and is herefore no desirable he digial conrol circi can be implemened as illsraed in Fig he operaion of he converer is deermined by he ime inervals on, off and cl In order o se he negaive indcor crren I,min, he zero crossing of he crren needs o be sensed For he converer prooype, he indcor crren was measred direcly a he indcor sing a mω resisor in he indcor crren pah However, i is recommended o measre he crren i a he resisor R cm depiced in Fig in order o deermine he zero crossing of he,min,, on on C 3 GD DSP off cl on, off, cl FPGA GD GD ref i R cm ref i R on Figre : Realizaion of he conrol srcre and recommended implemenaion of he indcor crren zero crossing deecion sing a crren measremen resisor a he low-side swich indcor crren dring ime inerval on, which has he advanage of a redced power loss and a significan simplificaion of he measremen circi A a rising indcor crren, as soon as he crren zero crossing is deeced, he swich is held in on-sae nil o he end of he ime inerval on his ensres a synchronizaion of he indcor crren o he desired minimm and maximm vale sch ha he reqired average inp crren is achieved he oal on-ime of swich can be calclaed for a desired average inp crren I in and inp volage sing ( ) on ( ) Pmax I in I,min + I,min + I,min, () and herefore, assming ha he indcor crren sars rising always from he desired negaive vale I,min, he remaining on-ime on is esimaed wih on on I,min () he remaining ime inervals off and cl can hen be calclaed wih ( ) off on and cl p,pmax on off, () sing he swiching period p evalaed for he nominal op power P max, calclaed wih p,pmax (Pmax/ I,min) ( ) on (7) Noe ha he eqaions ()-(7) assme a lossless operaion of he converer and he resonan ransiion imes are negleced In a pracical design, hese eqaions can be evalaed sing a Digial Signal Processor (DSP) or he iming inervals can be calclaed in advance for a defined range of operaion and dring operaion, he iming vales are inerpolaed sing a look-p able An FPGA is sed in addiion o keep rack of he iming and o conrol he gae signals Noe ha an pdae of he iming vales is needed only when a change of he load condiions is deeced or de o a change of he op volage reference herefore, he pdae freqency is limied o he conroller bandwidh, which is sally mch slower han he swiching freqency As a resl of his conrol scheme, he swiching freqency variaion is independen of he variaion of he op power and can be expressed wih n f,c fmax,c f min,c,min,max (,max ) (,min ) ()

7 Main Power Connecor Inp Indcor Capacior Connecor Gae Driver Clamp Swiches Main Swiches oad Connecor 3 mm (b) FPGA Axiliary Power Spply Vale 7 µh 3 x µm 9 N7 x EEP mm W/cm3 7 mm Parameer Indcance iz Wire rns Core Maerial Core oal Air Gap Power Densiy Vale 39 µh 3 x µm 9 N7 ER / mm W/cm3 mm Op Capacior DSP 7 mm Parameer Indcance iz Wire rns Core Maerial Core oal Air Gap Power Densiy 7 mm mm (c) Figre : Hardware prooype of he converer inclding he conrol board (b)-(c) Realizaion and echnical specificaions of he indcors (9) If he converer is designed for he same maximm swiching freqency as for CM operaion, he indcance vale needed for he converer is mch smaller compared o he indcance vale needed for CM operaion he raio of he indcance needed for he and CM converer for his pariclar case is given mainly by he op power range and can be calclaed wih C Pmin I,min,CM n CM Pmax I,min,C () On he oher hand, if he converer is designed for he same minimm swiching freqency as for CM operaion wih he same range of op volage and op power, he reqired indcance vale is he same for boh modes of operaion In order o verify he proposed operaion of he converer, a hardware prooype was bil and is presened in he following secion ogeher wih experimenal resls V H ARDWARE P ROOYPE & M EASUREMENS Fig shows he hardware prooype of he converer As menioned in he previos secions, he EPCC GaN FEs are sed for he prooype, operaed wih he half-bridge gae-driver M3 As shown in Fig, a boo-srap power spply was sed also for he clamp swich gae drivers which allows for a very simple and compac design of he addiional for-qadran swich he converer is conrolled wih a DSP/FPGA conrol board comprising a exas Insrmens MS3F33 DSP and a aice FXP-E FPGA he conrol board is no opimized for his converer and cold be designed wih significanly redced fooprin and power loss he prooype is designed according o he specificaions given by he applicaion for an inp volage of V and an op volage range of - V In order o direcly compare he and CM operaion of he converer, he same indcor is sed for boh modes of operaion, sch ha boh converer have he same minimm swiching freqency he hardware realizaion and he echnical specificaions of he indcors are shown in Fig (b) and (c) he indcor shown in Fig (b) is (b) - Pmax Pmin 7 ime (µs) Pmax Pmin Uo 3 V Uo 3 V 3 ZVS ZVS - 7 ime (µs) (c) Uo V Po W sw 3 ZVS ZVS 3 ime (µs) i Crren (A) (,max ),max fmax (Pmax I,min ) - Volage (V) Crren (A) Accordingly, he indcance vale can be deermined sing (7) sch ha a specified maximm swiching freqency fmax is no exceeded for he specified range of operaion, Crren (A) sed for he performance evalaion of he converer - Figre 7: -(b) Measred indcor crren waveforms of he prooype converer in operaion and CM mode respecively (c) Measred converer swich-node volage sw and indcor crren i indicaing ZVS operaion bil sing wo EEP core ses wih he EPCOS N7 maerial he indcor is designed for high-efficiency operaion wih a minimm converer swiching freqency of khz and has herefore a raher low peak power densiy of W/cm3 he second indcor shown in Fig (c) is bil sing an ER / core se in order o achieve a high peak indcor power-densiy of W/cm3, and is designed sch ha he swiching freqency reaches a maximm vale of fmax MHz in CM mode For he measremens, he op power range is se o -3 W and he op volage is se o V, 3 V and V he converer was operaed in open-loop and he inp volage was kep in a range of - V he indcor crren waveform for minimm and maximm op power for an op volage of 3 V is shown in Fig 7 and (b) for and CM operaion respecively Sof-swiching of he swiches - was achieved a any poin of operaion and is shown in Fig 7(c) as an example for minimm op power and an op volage of V Fig -(c) show he measred and calclaed indcor crren characerisics, he swiching freqency and he iming vales on, off and cl se by he DSP o operae he converer in mode Fig (d)-(f) show he same measred and calclaed parameer for he converer operaed in CM mode he indcor shown in Fig (b) was sed for he measremens and he peak negaive indcor crren i,min was se o -7 A for boh modes of operaion sch ha he oal dead-ime needed for he ime inervals [7, 9 ] and [, ] was

8 Indcor Crren (A) 3 V 3 V V calc,rms,max,min Freqency (khz) Op Power (W) (b) Op Power (W) (c) Op Power (W) Indcor Crren (A) on (s) V 3 V V calc 7 V V V 3 V 3 V V V 3 calc,max calc 3 V 3,RMS,min V (d) Op Power (W) (e) Op Power (W) (f) Op Power (W) Freqency (khz) V 3 V V on (s) off (s) off (s) 3 Op Power (W) 3 Op Power (W) cl (s) cl (s) 3 Op Power (W) 3 Op Power (W) Figre : Measred and calclaed minimm, maximm and RMS indcor crren vales of he prooype converer (b) Measred and calclaed swiching freqency and (c) on-, off- and clamping-ime inervals of he converer (d)-(f) show he same parameer measred for he converer operaed in CM mode no larger han ns, which allows o neglec he dead-imes for he iming calclaions in he open-loop operaion of he converer For he CM converer, he minimm indcor crren cold generally be chosen lower compared o he converer, becase of he redced swich capaciance ha needs o be charged o allow for ZVS As expeced, a maximm op power, he peak indcor crren in mode is similar o he CM operaion and he operaing freqency measremen in Fig (b) confirms he consan swiching freqency of he converer a a fixed inp and op volage As discssed in Secion IV, his comes a he expense of a higher peak and RMS indcor crren a low op power when compared o he CM operaion he swiching freqency of he CM converer varies by a facor of, whereas he operaing freqency of he converer varies only by facor of 7 and is in good agreemen wih he resl obained wih eqaion () As prediced by he eqaions ()-(7), he clamping-ime inerval cl shown in Fig (c) approaches zero a he nominal op power of 3 W which corresponds o he CM operaion he inp and op power of he converer was calclaed based on he measremen of he erminal volage and crren sing Agilen 3A mlimeer he power loss and he achieved - efficiency of he and CM converer is shown in Fig 9 he consan power loss cased by he crren and volage measremen circi of he converer is measred separaely and amons o 37 mw he consan power loss cased by he DSP/FPGA board is 99 mw, where he DSP accons approximaely for 7 % of he losses hese consan power losses can be redced significanly (down o -3 mw), sing a more siable conroller and are herefore no inclded in he power loss and efficiency measremen As indicaed in Fig 9(b) and (d), a consan power loss of p o 3 mw cold be acceped for he conrol circi in order o achieve a minimm efficiency of 9 % in he enire range of operaion he and CM converer show almos he same efficiency a minimm and maximm op power From he increased swiching freqency of he CM converer a low op power, i cold be expeced ha he power losses are higher compared o he operaion he measremens show ha his is no he case becase as he swiching freqency of he CM converer increases, he RMS indcor crren decreases linearly wih decreasing op power, which compensaes for he increased AC losses in he indcor core and winding In order compare he degradaion of he performance wih increasing power densiy of he converer, he swiching freqency variaion and he - efficiency was measred for boh converer operaing modes wih he indcor shown in Fig (c) Fig depics he measred swiching freqency variaion he operaing freqency of he CM converer varies from 7 khz o MHz by a facor of 9 he converer insead has a maximm swiching freqency of khz and he freqency varies only by a facor of he resl of he efficiency measremen is shown in Fig (b) for boh prooype indcors Again, he consan power loss of he DSP/FPGA board is no inclded in his measremen Addiionally, he negaive peak indcor crren was increased o -7 A in order o achieve ZVS wihin he ns oal dead-ime wih he redced indcance vale Again, he wo converer show very similar efficiencies However, for he wors case operaing poin which is a an op volage of V and an op power of 3 W, he efficiency of he converer is decreasing wih a seeper slope compared o he CM operaion as he power densiy of he indcor is increased As explained in Secion IV, he emlaes CM operaion a maximm op power Hence, he clamping ime inervals are redced o 3 ns b are no compleely omied for he measremen in order o mainain he same modlaion scheme for he enire range of operaion, which is he main reason why he measred efficiency of he converer is lower han he efficiency of he CM converer a maximm op power as i is shown in Fig (b)

9 9 V 3 V 7 9 V incl consan V 9 power loss 3 V of 3 mw V Op Power (W) (b) Op Power (W) 9 V CM 3 V 7 9 V 9 CM 9 3 incl consan V 9 power loss 3 V of 3 mw V (c) Op Power (W) (d) Op Power (W) Power oss (W) Power oss (W) Efficiency Efficiency Figre 9: -(b) Measred power loss and - efficiency of he C- CM converer a variable op power and differen op volages (c)- (d) Measred converer performance wih CM operaion Noe ha hese measremens do no inclde he consan power loss of he DSP/FPGA board VI CONCUSIONS In his paper he converer is explained in deail and a ZVS modlaion scheme is provided ha allows for sof-swiching of all swiches In addiion, he condiions for ZVS operaion are idenified and a conrol scheme is proposed ha allows for a significan redcion of he swiching freqency variaion, while mainaining a low RMS indcor crren he effor for he conrol of he CM and converer is similar and he addiional clamp-swich and boo-srap gae drive do no consie a significan increase of circi complexiy in he case of a low volage applicaion he redced swiching freqency variaion of he converer helps o relax he reqiremens for he conrol circi and for he applicaion a hand where a high power conversion efficiency is desired, he C- CM and CM converer achieve boh similar performance a a lower power densiy of he indcor However, for applicaions where a very high power densiy is needed, he CM converer shows a sperior performance in erms of efficiency and power densiy compared o he converer, mainly becase of he redced amon of swiches needed for CM operaion On he oher hand, for example in applicaions where Elecromagneic Inerference (EMI) ms be redced, he converer simplifies he filer design de o he decreased swiching freqency variaion Fre work will also inclde a comparison of he and CM converer o he convenional hard-swiched boos converer De o he significan improvemens in modern wide-band-gap semicondcor devices, he swiching losses in a hard-swiched converer are no he main decisive facor which deermines he mos siable converer opology or modlaion scheme and in low power applicaions, he consan power loss generaed by he conrol circi has a significan impac on he ocome of he comparison beween sof-swiched and hard-swiched converers herefore a carefl, applicaion specific analysis of he converer opologies and modlaion schemes is mandaory in order o reveal he advanages and limiaions of each opology Freqency (MHz) CM 3 Op Power (W) Efficiency (%) U o V P o 3 W CM 9 U o V P 9 o 3 W U 9 o V P o W 93 Op 3 7 Volage (V) (b) Indcor Power Densiy (W/cm 3 ) Figre : Measred swiching freqency variaion of he and CM converer wih he indcor shown in Fig (c) (b) Measred - efficiency of he and CM converer wih respec o he power densiy of he wo indcors shown in Fig (b) and (c) Noe ha he efficiency does no inclde he power losses of he DSP/FPGA board ACKNOWEDGMEN he ahors graeflly acknowledge he financial sppor by he Bagaren fondaion his work is par of he Zrich Hear projec nder he mbrella of Universiy Medicine Zrich/Hochschlmedizin Zürich Frher hanks goes o Andrés Cao for he design of he hardware prooype in he corse of his semeser projec REFERENCES [] O Knech, R Bosshard, and J W Kolar, High-efficiency ranscaneos energy ransfer for implanable mechanical hear sppor sysems, IEEE rans Power Elecron, vol 3, no, pp 3, [] Pirbodaghi, C Coer, and K Borqe, Power consmpion of roary blood pmps: plsaile verss consan-speed mode, Arif Organs, vol 3, no, pp, [3] M S Slagher and J Myers, ranscaneos energy ransmission for mechanical circlaory sppor sysems: hisory, crren sas, and fre prospecs, J Card Srg, vol, no, pp 9, [] D M Sable, F C ee, and B H Cho, A zero-volage-swiching bidirecional baery charger/discharger for he NASA EOS saellie, in Proc 7h IEEE App Power Elecron Conf and Expo (APEC), 99, pp [] J S ai, B York, A Koran, Y Cho, B Whiaker, and H Miwa, High-efficiency design of mliphase synchronos mode sof-swiching converer for wide inp and load range, in Proc In Power Elecron Conf (IPEC),, pp 9 [] C P Henze, H C Marin, and D W Parsley, Zero-volage swiching in high freqency power converers sing plse widh modlaion, in Proc 3rd IEEE App Power Elecron Conf and Expo (APEC), 99, pp 33 [7] S G Yoon, J M ee, J H Park, I K ee, and B H Cho, A freqency conrolled bidirecional synchronos recifier converer for HEV sing sper-capacior, in Proc 3h IEEE Annal Power Elecron Specialiss Conf (PESC),, pp 3 [] C Marxg, F Krismer, D Boris, and J W Kolar, Ulrafla inerleaved rianglar crren mode (CM) single-phase PFC recifier, IEEE rans Power Elecron, vol 9, no, pp 73, [9] C R Swarz, High performance ZVS bck reglaor removes barriers o increased power hroghp in wide inp range poin-of-load applicaions,, Jan [Online] Available: hp://wwwvicorpower com/docmens/whiepapers/picor/wp HighPerfomanceZVSpdf [] Meier, Design, Opimizaion and Implemenaion of a Bidirecional - 3kW / Converer, Maser s hesis, Dep Elec Eng, Swiss Federal Ins echnol Zrich (EHZ), [] D Boris and J W Kolar, / Konverer nd Verfahren zr Seerng eines weich schalenden bidirekionalen / Konverers (in German), Swiss Paen Applicaion CH /, Jan 3, [] F Krismer, Modeling and opimizaion of bidirecional dal acive bridge - converer opologies, PhD disseraion, Dep Elec Eng, Swiss Federal Ins echnol Zrich (EHZ), Zrich, Swizerland,