Three-Phase High-Power and Zero-Current-Switching OBC for Plug-In Electric Vehicles

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1 Energies 015, 8, ; doi: /en Aricle OPEN ACCESS energies ISSN Three-Phase High-Power and Zero-Curren-Swiching OBC for Plug-In Elecric Vehicles Cheng-Shan Wang 1, Wei Li 1,, Zhun Meng 1,, Yi-Feng Wang 1, * and Jie-Gui Zhou 1 School of Elecrical Engineering and Auomaion, Tianjin Universiy, Tianjin 30007, China; s: cswang@ju.edu.cn (C.-S.W.); liweiju@homail.com (W.L.); quakermaser@homail.com (Z.M.) The Third Railway Survey and Design Insiue Group Corporaion, Tianjin 30051, China; zhou.jiegui@163.com These auhors conribued equally o his work. * Auhor o whom correspondence should be addressed; wayif@ju.edu.cn; Tel.: ; Fax: Academic Edior: Joeri Van Mierlo Received: 4 May 015 / Acceped: 3 June 015 / Published: 30 June 015 Absrac: In his paper, an inerleaved high-power zero-curren-swiching (ZCS) onboard charger (OBC) based on he hree-phase single-swich buck recifier is proposed for applicaion o plug-in elecric vehicles (EVs). The muli-resonan srucure is used o achieve high efficiency and high power densiy, which are necessary o reduce he volume and weigh of he OBC. This sudy focuses on he border condiions of ZCS convering wih a baery load, which means he variaion ranges of he oupu volage and curren are very large. Furhermore, a novel hybrid conrol mehod combining pulse frequency modulaion (PFM) and pulse widh modulaion (PWM) ogeher is presened o ensure a driving frequency higher han 10 khz, and his will reduce he unexpeced inner resonan power flow and decrease he oal harmonic disorion (THD) of he inpu curren under a ligh load a he end of he charging process. Finally, a prooype is esablished, and experimens are carried ou. According o he experimenal resuls, he conversion efficiency is higher han 93.5%, he THD abou 4.3% and power facor (PF) 0.98 under he maximum power oupu condiion. Besides, a hree-sage charging process is also carried ou he experimenal plaform. Keywords: onboard charger; buck converer; zero-curren-swiching; elecric vehicle

2 Energies 015, Inroducion Due o he environmenal and energy crises, more and more researchers are paying aenion o novel energy vehicles, such as elecric vehicles (EVs) and hybrid elecric vehicles (HEVs). I is widely known ha baery chargers play a criical role in he developmen of EVs, and he charging ime and lifeime of baeries are closely relaed o he characerisics of he chargers. A baery charger mus be efficien and reliable, wih low cos, low volume and low weigh, as well as high-power oupu capabiliy [1 5]. Mos of he chargers can be divided ino wo ypes: onboard chargers (OBCs) and off-board chargers (FBCs). Generally, FBCs are locaed in charging saion, which are suiable for fas charging. However, he expensive consrucion cos and limied locaions (mosly in big ciies) have limied he wide applicaion of FBCs. Differen from FBCs, OBCs mean aking he chargers wih he vehicles and hus having relaively higher flexibiliy, which makes i possible o ge charged hrough a socke. Thereby, he OBCs are supposed o be a beer alernaive for cusomers. However, OBCs have some specific limiaions, since he added charger will increase he volume, weigh and cos, as well as he charging ime, which is oo long for normal usage. Therefore, novel OBCs wih low volume, high efficiency, high power densiy and high power capabiliy are needed [3]. From he perspecive of srucure, OBCs are classified ino wo ypes: a single-sage opology and a muli-sage opology. The muli-sage (mosly wo-sage) srucures are commonly used a presen due o heir favorable feaures. A simplified srucure of he wo-sage OBC using digial signal processor (DSP) or microconroller uni (MCU) as conroller is shown in Figure 1. The wo-sage srucure has he advanages of a wide adjusable oupu volage range and high flexibiliy of he oupu load. To saisfy he requiremens of he conversion efficiency, sof swiching echnology is widely used in he DC/DC converer. The mos commonly-used opologies are he phase shifed zero-volage-swiching (ZVS) opology [6 10] and he resonan ank wih wo inducors and a capacior (LLC) resonan opology [11 13]. The shifed ZVS opology can achieve a relaively high oupu power level, which is more han a dozen kilowas wih an efficiency beween 95% and 97%. However, i also has some drawbacks, such as a limied sof swiching range and being sensiive o he parasiic parameers of swich devices and he leakage inducance of he ransformer. All of hese problems will increase he design difficuly. The LLC resonan opology has disadvanages, such as a low power raing and a rigorous design of he ransformer and inducor because of he parasiic parameers. In addiion, he wide frequency range of he LLC srucure increases he difficuly of he design process for he inpu elecromagneic inerference (EMI) filer. Figure 1. Simplified block diagram of a universal single-phase onboard charger (OBC); power facor correcion (PFC). Compared wih he wo-sage srucure, he single-sage srucure will reduce he number of devices and circui complexiy, so i is easier o ge low volume, high efficiency and high power densiy. Furhermore,

3 Energies 015, o realize rapid charging for EVs, hree-phase AC/DC converers are widely used in he single-sage charging srucure. A large number of hree-phase AC-DC converers have been developed o improve power facor correcion (PFC), o reduce THD and EMI of he AC inpu and o regulae DC oupu, which are addressed as he hree-phase improved power qualiy AC-DC converers (IPQCs). Concerning opologies, hese circuis can be classified ino five caegories: buck, boos, buck-boos, mulilevel and muli-pulse [14]. The oupu volage of he boos IPQCs is higher han he peak inpu volage, which will resul in a high oupu volage or a decrease of he inpu volage o saisfy he oupu requiremen. Therefore, his kind of converer is usually used o provide a consan, regulaed DC oupu volage [14,15]. Furhermore, here are many problems hindering he buck-boos IPQCs from high-power applicaions, such as he sorage capacior selecion and he reversed oupu volage polariy. Therefore, he boos and buck-boos IPQCs are no suiable for he single-sage OBC applicaion. The buck IPQCs wih high-frequency swiching devices are exensively used in baery charging for auomoive applicaions [16]. These circuis can reduce he filer size and weigh and enhance he efficiency of he sysem. Several opologies, such as using a single swich wih a diode bridge recifier [17], hree swiches wih a dual diode, shown in Figure a [18], and six swiches wih free-wheeling diodes, shown in Figure b [19], are used o improve he power facor, o reduce he harmonic currens of AC inpu and o ge a well-filered oupu DC volage. (a) (b) Figure. Three-phase AC-DC buck converers: (a) hree-swich buck converer; (b) six swich wih free-wheeling diode buck converer. To enhance he efficiency and swiching frequency of buck IPQCs, Rober W. Erickson and Yungaek Jang proposed a new zero-curren-swiching (ZCS) hree-phase high qualiy recifier, which is illusraed in Figure 3 [15,0,1]. In his hree-phase ZCS buck circui, coninuous inpu and oupu currens, a high power facor and low harmonic recificaion are achieved. By he usage of a muli-resonan scheme, he swich operaes in ZCS mode, and he diodes operae in ZVS mode; herefore, his circui is suiable for he high-frequency implemenaion wih insulaed gae bipolar ransisor (IGBT) [1].

4 Energies 015, Figure 3. New hree-phase muli-resonan zero-curren-swiching buck recifier. In view of he aforemenioned advanages, his hree-phase ZCS buck opology is adoped and opimized in his aricle. Alhough his opology can saisfy he requiremen of single-sage OBC in general, he baery characerisics and he ZCS boundary condiion of he muli-resonan ank, as well as heir influence on each oher have o be considered. Moreover, he oupu volage and curren flucuaions should be carefully considered for differen baery sauses. Many charging sraegies for EV baeries have been proposed [ 6]. Comprehensively considering he life cycle of baeries and he feasibiliy of he conrol mehods, he hree-sage charging sraegy is seleced in his aricle. Then, his aricle sudies he influence beween he realizaion of ZCS and he baery parameers or saus changes and solves he problem of he large inpu curren ripple and he useless large resonan curren wihin he ank when he driving frequency is exremely low under ligh load condiions. In addiion, an inerleaved srucure is used o improve he power level of he OBC sysem in his paper, which can reduce he charging curren ripple and inducor size, and i also reduces he curren sress on oupu capaciors [1,7,8]. Finally, a prooype plaform was buil o verify he feasibiliy of he proposed opology. Besides, he SiC Schoky diodes were applied o promoe he power level and he sysem efficiency [9,30]. The srucure of his aricle is organized as follows. The operaing saes and principles are shown in Secion. Secion 3 explains he process of he sysem design, he ZCS border condiions, he impac caused by he baery load and he novel PWM and PFM combined conrol sraegy. Secion 4 presens he simulaion and experimenal resuls o evaluae he proposed converer. Finally, Secion 5 concludes he work carried ou in his aricle.. Sysem Inroducion The proposed inerleaved hree-phase muli-resonan ZCS OBC is shown in Figure 4. I is composed of he inpu filer inducors La, Lb, Lc, Las, Lbs, Lcs, inpu resonan capaciors Cr1, Cr, Cr3, Crs1, Crs, Crs3, unconrolled recifier bridges D1 D6 and Ds1 Ds6, resonan inducors Lr and Lrs, oupu resonan capaciors Cd and Cds, fly-wheel diodes Dd and Dds, oupu filer inducor Lf and Lfs and oupu filer capacior Cf. In his opology, Cr1 Cr3, Cd and Lr consiue a resonan ank, and he resonance cycle of his is fixed. Therefore, he PFM conrol sraegy wih a consan urn on ime is adoped, and he oupu volage will increase wih he driving frequency increasing while oher circui parameers remain he same.

5 Energies 015, Figure 4. The proposed OBC. Due o he srucures of he wo inerleaved channels being compleely he same, he following analysis is based on he single-channel srucure. This opology is esablished on he basis of he hree-phase single-swich recifier [16], in which he oupu volage is conrollable from zero o he peak AC inpu line volage. Only one IGBT in each channel needs o be conrolled in his srucure. In he proposed opology, Cr1 Cr3, Cd and Lr consiue a muli-resonan ank, which can guaranee he IGBTs S1 and S working in ZCS mode and diodes Dd and Dds operaing in ZVS mode. Moreover, by he usage of he muli-resonan scheme and he inerleaved srucure, his converer can improve he power level and achieve high qualiy inpu curren and almos uniy power facor; which can reduce he inpu and oupu side ripples and decrease he volume of he circui. The operaing waveforms of he inpu side resonan capacior vcr and IGBT curren is are shown in Figure 5. The volage vcr can be divided ino four pars: during T1, IGBT is urned off, and Cr is charged wih inpu curren; during T, Cr,Lr and Cd form a resonan ank, unil vcr decreases o zero; vcr remains zero during T3; during T4, Cr is charged wih a curren of inpu line curren iin minus he IGBT curren is. While he average value of vcr is he same as he inpu volage during each swiching cycle, and peak value of vcr is proporional o he inpu curren. If inerval T1 is much longer han he sum of T, T3 and T4, he inpu curren will follow he inpu volage waveform. The deails of he working process and conrol sraegy will be analyzed below. Figure 5. The waveforms of he inpu side capacior volage vcr and insulaed gae bipolar ransisor (IGBT) currenis.

6 Energies 015, Operaing Saes Boh of he inerleaved channels adop same conrol sraegy, bu hold a phase shif of π in driving signal from each oher. Assuming ha he hree-phase inpu volages are symmerical and balanced, i is sufficien o consider a 30-degree inerval of he AC inpu. The 30-degree inerval where va > 0 > vc > vb is inroduced. In order o simplify he algorihm, we choose he operaing poin a π/ o analyze he operaing process of each period. VPM and IPM represen he peak inpu phase volage and curren, respecively. A he poin of π/, boh va and ia reach he peak value of he phase volage and curren, and vb = vc = 0.5vA, va = VPM. Similarly, ib = ic= 0.5iA, ia = IPM. A his poin, he inpu side resonan capacior Cr and Cr3 are charged and discharged enirely synchronously, and diodes of phase B and C of he unconrolled recifier are urned on and off synchronously, oo. Therefore, he following analysis of Cr3 is negleced. Since he driving frequency is much higher han he inpu volage frequency, so during one swiching cycle he inpu volage and curren can be considered as a consan value. The ideal operaing waveforms of he OBC is shown in Figure 6, and he equivalen circuis of each inerval are shown in Figure 7. Figure 6. Ideal waveforms of he charger mode. (a) (b) Figure 7. Con.

7 Energies 015, (c) (d) (e) (f) (g) (h) (i) (j) Figure 7. Con.

8 Energies 015, (k) (l) Figure 7. Equivalen circuis of each inerval. (a) 0 1; (b) 1 ; (c) 3; (d) 3 4; (e) 4 5; (f) 5 6; (g) 6 7; (h) 7 8; (i) 8 9; (j) 9 10; (k) 10 11; (l) The parameers are defined as follows: vcr1 vcr3 and icr1 icr3 are he volage and curren of resonan capaciors Cr1 Cr3, respecively; vcd and icd are he volage and curren of he resonan capacior Cd, respecively; vlr and ilr are he volage and curren of he resonan inducor Lr, respecively; Iou is he oupu curren; Vou is he oupu volage; icf is he curren of Cf. Since he wo paralleled channels use he same conrol sraegy, he single channel will be inroduced in he following heoreical analysis and calculaion pars. The inpu and oupu curren for each channel are he half of he oal circui and can be defined as 0.5IPM and 0.5Iou. The capaciance values of Cr1 Cr3 are he same and can be represened as Cr. Figure 7a illusraes he volage and curren reference direcions of he devices for he following analysis, and he reference direcions of Cr1 Cr3 are exacly he same. Inerval I (0 3): D1 D6, S1 and Dd are off. Cr1 Cr3 are charged by he inpu curren. During his inerval, Lr provides he oupu curren. Cd is discharged wih ilr, and Cf is also charged. This inerval ends when vcd decreases o zero and Dd is urned on. The sae equaions of his inerval are: d vcr1( ) Cr 0.5IPM d d vcr ( ) Cr 0.5IPM d d vcd ( ) Cd icd() d d ilf ( ) VLf () Lf d icd ()= ilr () ilf () 0.5 Iou i() vcd ()+ vlr () vlf () Vou vs() vcd() vcr1() vcr() (1) In Equaion (1), i() represens he flucuaion componen of he freewheel curren hrough Cd, Lr and Lf. From he perspecive of he curren analysis, i() can be ignored, while in he volage analysis, i() will cause a decided change of VLf(). Moreover, VLr() can be considered as a consan value in his inerval, in view of he fac ha compared o Lf, he value of Lr is very small. Inerval II (3 ~ 7): Dd is on, and D1 ~ D6 and S1 are off. The oupu curren is sill supplied by Lr. The only difference beween Inerval I and Inerval II is ha he curren flows hrough Dd, raher han

9 Energies 015, he resonan capacior Cd. This inerval ends when he swich S1 is urned on. The sae equaions of his inerval are: d vcr1( ) Cr 0.5IPM d d vcr ( ) Cr 0.5IPM d ilr () idd() ilf () 0.5 Iou i() vs() vcr1() vcr() () Inerval III (7 8): D1, D5, D6, S1 and Dd are on, and he oher diodes are off. Cr1 Cr3 and Lr form a resonan ank, unil he inducor curren increases o zero. The sae equaions of his inerval are: d vcr1( ) Cr icr1 () d d vcr ( ) Cr icr () d d ilr ( ) Lr vlr() d icr1()=- icr() is() ilf () ilr() vlr () vcr1()- vcr() icr1() is () 0.5IPM (3) Inerval IV (8 10): D1, D5, D6 and S1 are on, and D D4 and Dd are off. Cd, Cr and Lr form a resonan ank. This inerval ends unil he volage of Cr decreases o zero. The sae equaions of his inerval are: d vcr1( ) Cr icr1 () d d vcr ( ) Cr icr () d icr1() icr () is() ilf () ilr() d i ( ) d Lf ( ) Lr i Lr vcd() Lf Vou vcr1() vcr() d d 0.5 IPM icr1( ) is ( ) (4) Inerval V (10 11): D1 D6 and S1 are on, and Dd is off. Lr and Cd form a resonan ank. This inerval ends when he curren is1 reduces o he inpu curren 0.5IPM. If is1 < 0.5IPM, hen he curren icr1 > 0, and he inpu capacior begins o charge, indicaing ha his inerval ends. The sae equaions of his inerval are: d ilr ( ) Lr vcd() 0 d d vcd ( ) Cd icd() ilr() d is() ilf () ilr() d ilf ( ) Lf Vou 0 d (5)

10 Energies 015, Inerval VI (11 1): D1, D5, D6 and S1 are on, and D D4 and Dd are off. Cr, Cd and Lr form a resonan ank. This inerval ends when he curren is1 decreases o zero. Afer his ending poin, S1 can realize urning on of ZCS. The sae equaions of his inerval are: d vcr1( ) Cr icr1 () d d vcr ( ) Cr icr () d icr1() - icr() is() ilf () ilr() d ilr ( ) Lr vcd() vcr1()- vcr() d 0.5 IPM icr1( ) is ( ) (6).. Operaing Analysis This secion will carry ou a furher analysis of he operaing principle during each inerval. From he sae Equaions (1) (6), he curren and volage expressions of S1, Lr, Cr and Cd can be calculaed. Then, he saring and ending poin of each inerval are confirmed, which will be used o deermine he ZCS boundary and o provide he basis for he circui design. By solving Equaion (1), he expressions of he main power devices of Inerval I are lised as: I PM vcr1() Cr I PM vcr() vcr3() 4Cr Iou vcd ()= VCd T 0 Cd I V V I icd () ilr () ilf () Iou vlf () VCd V T 0 ou LC f d 3I PM Iou vs() VCd T 0 4Cr Cd ou Cd T 0 ou ou ilf () C11 Lf 4LfCd (7) As analyzed above, Inerval I will end when vcd decreases o zero, so he ending momen T1 and C11 can be deduced as: V T1 = I Cd T 0 ou C d (8) Iou C11= ILf (9) T 0 Then, he value of each elecric parameer a he ending ime of Inerval I can be derived as:

11 Energies 015, VCd 0 T1 IPM VCd C T 0 d VCr1 T1 IouCr IPM VCd C T 0 d VCr V T Cr3 1 T1 IouCr 3IPM VCd C T 0 d VS T 1 IouCr I V V V C I V C I Lf ( ) T1 4 Lf Iou Lf Cd Iou ICd I T Lr ILf 1 T 1 T1 VLf V T ou 1 ou Cd T 0 ou Cd T 0 d ou Cd T 0 d C 11 (10) Similarly, by solving Equaions () (6), he expressions of Inervals II VI can be obained. For Inerval II, he expressions of he main devices of can be lised as: I PM vcr1() ( + T 1) Cr VCr1() vcr() vcr3() 3 vcr1( ) vs () vlf () Vou Iou Vou ilf () C1 Lf idd () ilf () ilr () (11) For he duraion of Inerval II, T and he final value of each elecric parameer can be inferred as: T DTs T1 (1) I ou C1= ILf (13) T1 IPM DTS VCr1 T Cr1 IPM DTS VCr VCr3 T T 4Cr1 3IPM DT S VS (14) T 4Cr1 Vou ILf ILf ( DTS T1 ) T T Lf IDd I T Lf ILr T T For Inerval III, he expressions of he main devices can be lised as:

12 Energies 015, vcr1() C31sin3C3cos3 icr1() C31Cr3cos3C3Cr3sin3 I PM is() C31Cr3 cos3c3cr3 sin3 I PM Iou ilr () C31Cr3 cos3c3cr3 sin3 vlr () LC r 31Cr3 sin3lc r 3Cr3 cos3 (15) By subsiuing he final value of Inerval II ino Equaion (15), he parameers can be shown as: 3 α3 (16) L r C r I C31= Crα3 C = V Cr1 T 3 Cr1 T For he duraion of Inerval III, T3 and he final value of each parameer can be deduced as: T arcsin[ M ] M N 3 3 I I ou g r3 31 r 3 31 r r 3 I I ou g C C C C C C C C C 3 Cr 3 C31 C3 1 M 3 3 VCr1 C 3 31M3 C3N T 3 ICr1 C 3 31Cr3N3 C3Cr T 3M3 I PM IS C T 3 31Cr3N3 C3Cr3M3 I I I C C N C C M VLr LC T 3 r 31Cr3 M3 LC r 3Cr3 N3 PM ou Lr T 3 31 r r 3 3 (17) (18) (19) For Inerval IV, he volage and curren expressions of he main devices can also be deduced by solving Equaion (4). They can be lised as: ilr() C41sin4 icd () C41 sin4 vl r() C41Lr4cos4 C41 vcd () 1cos4 Cd4 C 41 vcr1( ) C41Lr 4cos4 1cos 4 3 Cd 4 C41Cr1 C41Cr1LC r d 4 icr1() sin4 3Cd I PM C41Cr1 C41Cr1LC r d 4 is () sin 4 3Cd I PM C41Cr1 C41Cr1LC r d4 3C41C d ilf () sin4 3Cd (0)

13 Energies 015, The parameers of Equaion (0) can be deermined by he final value of Inerval III. α 4 Lr Lf 4Lf Lr (1) CLL C 41 V d f r Lr T 3 r α 4 () For he duraion of Inerval IV, T4 and he final value of each elecric parameer can be derived as: L 4 arccos N 4 T4 N M LC r d4 1 N 4 4 (3) IL r C 4 41M T 4 ICd C 4 41M T 4 VLr C T 4 41Lr4N4 C41 VCd 1N4 T 4 Cd4 C V C L N 1N 41 Cr1 T 4 41 r Cd4 C41Cr1 C41Cr1LC r d 4 ICr1 M T 4 4 3Cd I PM C41Cr1 C41Cr1LC r d 4 IS M T 4 4 3Cd I PM C41Cr1 C41Cr1Lr d d ILf T 4 3Cd C C C M 4 (4) For Inerval V, according o he above operaing saes analysis, we can deduce he expressions of he elecrical parameers as: ilr () C51 sin5c5 cos5 vcd () C51Lr 5 cos5c5lr 5 sin5 ilr () icd () Vou ilf () C53 Lf vlr () C5Lr 5 sin5c51lr 5 cos5 V is () C sin C cos C ou Lf (5) The parameers in Equaion (5) are lised as: α 5 1 L C r d (6)

14 Energies 015, C C C 51 Cd T =V ICd T 4 = C =I d 5 Lf T 4 (7) Since his inerval ends when is1 reduces o 0.5IPM and from Equaions (5) (7), he ime lengh of his inerval T5 can be deduced as: T arcsin[ M ] M N 5 5 I I I I C ( ) C C C C ( ) ( ) PM ou 4 ou PM C51 C5 1 M 5 5 Then, we can ge he final value of each elecric parameer as: (8) ILr C 5 51M5 C5N T 5 VCd C 5 51Lr5 N5 C T 5Lr5M5 ICd C T 5 51M5 C5N5 Vou ILf T T5 5 ILf L T4 f VLr C T 5 5Lr 5M5 C51Lr 5N5 V I C M C N T I ou S T Lf L T 4 f (9) For Inerval VI, we can deduce he expressions of he elecrical parameers as: icr1() C616 C616 vcr1() Cr1 C616 3 ilf () VouC6 6LC f d I PM is () C616 I PM C616 3 ilr () icd () VouC C 6LC f d C616 vlr () Lr ( Vou C616 ) LC f d C616 C616 vcd () Lr ( Vou C616 ) Cd 3LfCd (30) Lr Lf 4Lf Lr α6 (31) CLL d f r C C 61 6 V L α I Lr T 5 r Lf T 5 6 (3) From Equaions (30) (3), he ime lengh of his inerval T6 is:

15 Energies 015, T 6 I PM (33) C α 61 6 Then, we can ge he final value of each parameer as: I PM ICr1 T 6 C616 VCr1 T 6 Cr1 C616 3 ILf T 6 6 VouT6 C T 6 6LC f d IS 0 T 6 I C I I T V T C T C C616 VLr L ( 6 r Vou C616 T6 ) T LC f d C616 C616 VCd T 6 6 Lr ( Vou C616 T6 ) T Cd 3LfCd PM Lr T6 Cd T6 6 ou LC f d (34) 3. Sysem Design In his secion, based on he analysis above and he baery charging requiremens, he hardware parameers and conrol sraegy are designed. The design mainly focuses on he ZCS realizaion when considering he differences of baery parameers and charging condiions ZCS Condiion Analysis The sysem canno realize ZCS under wo condiions, which are: (1) The circui parameers do no saisfy he ZCS requiremen. () The circui parameers are appropriae, bu he driving signal is mismached Mismach of Circui Parameers To realize ZCS, he previous sage should provide he condiions o obain he nex sage. From he ideal waveforms in Figure 6 and he operaing analysis above, we can deduce he consrain expressions. Inerval I and II should be long enough o guaranee energy sorage, for he resonan inducor curren o be posiive. This can be expressed as, a he end of Inerval III, he volage of vcr is posiive. V C M C N (35) Cr1 T Cr mus be compleely discharged when he resonan inducor curren is posiive. This can be expressed as: I Lr C T 4 41M4 0 (36) During Inerval V and Inerval VI, Lr and Cd form a resonan ank. Only if Cd have enough energy, he resonan inducor curren can reach oupu curren 0.5Iou, and is can reach zero o realize ZCS. I can be described as:

16 Energies 015, V C L N C L M (37) Cd 5 51 rα5 5 5 rα5 5 0 T C α C α V T L ( V C α T ) 0 (38) Cd T 6 6 r ou Cd 3LfCd Figure 8 shows he working waveforms wih mismached circui parameers, where he converer canno realize ZCS. We can see ha he oupu side resonan capacior is enirely discharged before is decreases o zero. Thus, is fails o drop down o zero, and ZCS canno be realized Mismach of he Driving Signal Figure 8. Typical waveforms wih mismach circui parameers. ZCS can only be realized when he circui and he driving signal are mached. The condiion ha opimizes he circui parameers wih an improper driving signal is discussed below, and he ypical waveforms are shown in Figure 9. Figure 9a shows he waveforms when Ton is shorer han he minimum allowable value, and Figure 9b shows he waveforms when Ton is longer han he maximum allowable value. (a) (b) Figure 9. Theoreical waveforms wih mismach driving signal. (a) Ton is oo shor and (b) Ton is oo long Regarding he ideal waveforms of he proposed converer, which are shown in Figure 6, ZCS can only be realized during a specified period. Addiionally, if he drive signal urns o zero before is1 decreases o zero, ZCS will no be realized obviously, and his consrain is expressed as Equaion (39).

17 Energies 015, Besides, if he drive signal remains on afer he volage vs1 increases o zero, S1 will be urned on again, and ZCS will no be realized eiher; he consrain expression is shown in Equaion (40). Ton T6 (39) Ton T6 T 3I g Iou T ( Vou - T ) 0 Cr Cd (40) ZCS Boundary Based on he above analysis and he consrains shown in Equaions (35) (40), he Ton range and ZCS boundary can be obained, when he parameers of he resonan devices vary under he maximum power oupu condiion (380-V inpu line volage, 400-V oupu volage, 8-Ohm load resisance). Figure 10a,b illusraes he minimum and maximum Ton value o realize ZCS, respecively. The driving frequency o saisfy he maximum oupu power wih resonan device parameers changing is shown in Figure 11. (a) (b) Figure 10. Minimum and maximum Ton value o realize zero-curren-swiching (ZCS). (a) minimum Ton and (b) maximum Ton. Figure 11. Driving frequency f o realize maximum oupu power.

18 Energies 015, ZCS and Baery In his secion, he cooperaive conrol beween ZCS realizaion and he hree-sage baery charging mehod is sudied, and he negaive influence of baery charging saus on ZCS realizaion is analyzed. Furhermore, a new mehod is presened o limi he minimum driving frequency when he baery is in a differen saus of charging. In order o opimize he charge cycles and lifeime of EV baeries, we adop he hree-sage charging mehod. The hree sages are: consan curren sage, consan volage sage and floaing volage sage. During he consan curren sage, he open-circui volage of he baery is abou 300 V, and i is charged by a consan curren of 50 A. The baery volage increases wih he charging process. When he volage increases o 400 V, his sage ends, and he consan volage sage begins. In he consan volage sage, he charging volage is 400 V, and he charging curren will decrease; his sage ends when he curren is below 5 A. The floaing volage sage is acually a low consan volage sage o ensure a small charging curren, o make sure ha he baery is ruly sauraed o exend he service ime. During his sage, he charging volage is 350 V. The charging process and parameer seings are shown in Figure 1 and Table 1. Resriced by he experimenal condiions, we use resisor load o simulae he baeries, and he equivalen resisor value is also shown in Figure 1 and Table 1. Figure 1. Three-sage charging process. Table 1. Three-sage charging parameers. Sage I ou (A) V ou (V) R load (Ohm) Consan curren Consan volage Floaing volage During he whole process of charging, he flucuaion range of he load equivalen resisance is very large. Jus as he parameers shown in Table 1, a he end of he consan curren sage, he charging power is he greaes a 0 kw. A he end of he floaing volage process, he minimum charging power

19 Energies 015, is 0.7 kw. If we use he PFM conrol sraegy during he whole process, he driving frequency variaion range is very large. We selec a poin of he floaing volage sage as an example. If he equivalen resisor is 100 Ohm, he driving frequency should be 5.5 khz o ge a volage oupu of 350 V. The simulaion waveforms are shown in Figure 13. From Figure 13c, i can be seen ha a his working poin, he power swich S works under he ZCS condiion, while, he driving frequency is very low, so he urn off ime is much longer han he resonan period of he resonan ank: Lr, Cr and Cd. Therefore, before S1 urns on, he resonan componens will begin he nex resonan cycle. Reacive power will be circulaing in he ank, which will reduce he sysem efficiency and increase he THD of he inpu curren. (a) (b) (c) Figure 13. Simulaion waveforms of he floaing volage charging sage. (a) inpu phase volage and inpu phase curren; (b) resonan capaciors volage and resonan inducor curren and (c) volage and curren of IGBT and gae signal. To solve he menioned problem, we proposed a new conrol sraegy. The complee conrol mehod of he sysem should be as follows: ake he PFM conrol sraegy a he beginning of he charging process (he conducion ime is consan), and saisfy he oupu requiremens by adjusing he frequency. If he PFM frequency is lower han 10 khz, conver i o he PWM conrol sraegy, keep he fixed driving frequency a 10 khz and saisfy he oupu requiremens by adjusing he conducion ime Ton. The charging process conrol flow char is shown in Figure 14. By using he proposed conrol sraegy, he minimum frequency is se a 10 khz, and he frequency flucuaion will be reduced. Alhough he PWM sraegy canno guaranee ZCS realizaion, under he condiion of a ligh load, he conducion losses increase grealy, are greaer han he swiching losses and seriously affec he sysem efficiency. Thus, using he PWM conrol sraegy can conribue o he improvemen of he sysem s efficiency. Wha is more, his sraegy can reduce he unexpeced resonance on he resonan devices and power swiches caused by a sharp drop of he driving frequency under a ligh load, which will lead o he increase of he inpu curren THD.

20 Energies 015, Opimized Parameers Figure 14. Charging process conrol flow char. Considering he fac ha he oupu volage and curren are changing during he whole charging process, we chose a se of circui parameers ha can ensure ZCS in he whole load range, as shown in Table. Table. Main componens of he prooype. Componen Inpu filer inducors L a L c Resonan inducor L r Oupu filer inducor L f Inpu side resonan capaciors C r1 C r3 Oupu side resonan capacior C d Oupu filer capacior C f Unconrolled recifier diodes D 1 D 6 Fly-wheel diode D d Power swich S 1 Value mh 50 μh 800 μh 0.65 μf 0.44 μf 860 μf C3D5170H C3D5170H IGW5T10 3 in parallel As shown in Table 3, he power devices are seleced a he maximum oupu curren and volage, which are 50 A and 400 V, respecively. From he inerval analysis and Equaions (7) (34), we can

21 Energies 015, calculae he volage and curren sresses of he main power devices in he circui and finally deermine he device ype as follows. Componen Table 3. Volage and curren sress of he main power devices. Peak Volage (V) Volage RMS (V) Peak Curren (A) Curren RMS (A) Value D 1 D C3D5170H D d C3D5170H S IXBH4N170A 3 in parallel L a L c L r L f C d C r1 C r Design of he Inducors Besides he power swiches and diodes seleced above, he design of he inducors is very criical for he sysem design. Through he heoreical analysis above, he currens of inpu filer inducors La Lc and he oupu filer inducor Lf are sine wave shaped inpu curren and non-oscillaory DC oupu curren, respecively. Thus, he FeSi circular magneic rings (PPF306060) are chosen o be he magneic cores of he inpu and oupu filer inducors. Since he currens of he resonan inducors are a high-frequency resonan curren wih an exremely high peak value, a specially designed air gap is needed for he high frequency peak energy sorage, and E-shaped magneic cores (EE110) are seleced for he resonan inducors Inpu Filer Inducor According o he heoreical analysis and simulaion resuls, he inpu filer inducance is mh; he peak inducor curren is 3 A; and he RMS curren is 16 A. We choose he magneic core PPF and use hree cores in parallel. The inducance can be deermined by he relaive permeabiliy and he effecive core parameers as: 4πN A L (41) e In Equaion (41), μ represens relaive permeabiliy; N represens he number of urns; A represens he effecive cross-secion area; e represens he mean magneic pah lengh. From he parameers shown in he daashee of PPF306060, i can be compued ha N = Resonan Inducor According o he heoreical analysis and simulaion resuls, he resonan inducance is 50 μh, and he peak inducor curren and RMS curren are 65 A and 3 A, respecively. The inducor core is seleced as EE110, and he maerial is PC-40 (MnZn power ferrie maerial). The urns of his inducor can be calculaed as:

22 Energies 015, LI p N AB (4) From he daashee, Ae = 196 mm and Bmax = 0.39 T. Thus, he urns can be deduced: N = Oupu Filer Inducor According o he simulaion resuls, he oupu filer inducance is 800 μh; he peak inducor curren is 7 A; and he RMS curren is 5 A. We also choose he magneic core PPF and use hree cores in parallel. The number of urns can be calculaed in he same way as Equaion (41), and he parameers of his core are exacly he same as hose of he inpu filers; finally, N = Loss Disribuion In his secion, he power losses of he power swiches, power diodes, inducors and capaciors a 50 A and 400 V oupu are esimaed Power Swiches When calculaing he power swich losses in he maximum power oupu condiion, in view of he ZCS saus of he power swiches, we ignore he swiching losses and only consider he conducion losses. The losses can be calculaed by he following expression. e max Pcond DVCESAT IC (43) In Equaion (43), D represens he duy raio, VCESAT represens he drop volage of he swich and IC represens he average curren flow hrough he swich. In he maximum power oupu condiion, he driving frequency is abou 35 khz, so D is abou The curren of each swich can be approximaed o a sine wave, shown in Equaion (44), from zero o π. According o he daashee of he swich, VCESAT a his poin is.1 V. I C (0.5 ou 41) sin I C 3 π L C r d (43) From Equaions (43) and (44), he power loss of each power swich is: P cond I d60w 15 0 C (44) Thus, he oal power loss of he 6 IGBTs is: PS = 6 Pcond = 360 W Unconrolled Recifier Bridge Diodes Jus like he IGBTs, only conducion losses of he unconrolled recifier bridge diodes are considered: Pf DVf I f (45) Vf VT I f RT RT T VT T ( ) ( ) (46)

23 Energies 015, According o he parameers shown in he daashee and he operaing poin of he diodes, we can ge ha he power loss of each diode in he unconrolled recifier is 5 W. Therefore, he oal power losses of 1 unconrolled recifier diodes in he maximum power oupu condiion can be shown as: PDBir = 1 Pf = 300W Fly-Wheel Diodes The calculaing formula of fly-wheel diodes is he same as hose of he recifier diodes shown in Equaions (46) and (47). Based on he inerval analysis above, he curren of he fly-wheel diodes is half of he oupu curren. Thus, we can calculae he power loss for each fly-wheel diode o be abou 7 W. The oal power loss of he wo fly-wheel diodes in he maximum power oupu condiion is 14 W. The power dissipaion of all he diodes in he OBC is: PD = PDBir + PDFly = 314 W Resonan and Filer Capaciors The losses of he capaciors include wo pars: dielecric loss and meal loss. The calculaing expression is shown in Equaions (48) and (49). P UIsin θ (47) an an 0 f Cn RESR (48) In Equaions (48) and (49), RESR represens equivalen series resisance, anθ0 represens he dielecric dissipaion facor and anθ represens he dissipaion facor. For he inpu side resonan capaciors, he daashee gives ha he anθ is lower han 0.001, so we selec he maximum value as he dissipaion facor. Considering ha he dissipaion angle is oo small, he sine value can be approximaed o he angen value. Consequenly, he power losses of he six inpu side resonan capaciors can be calculaed as: PCr = 6 (70 V 5 A 0.001) = 40.5 W. The oupu side resonan capaciors use he same calculaion and approximaion mehod as he inpu side resonan capaciors. We use wo 0.-μF capaciors in parallel for each channel. The dissipaion facor is lower han Thus, he power losses of he four oupu side resonan capaciors can be calculaed as: PCd = 4 (500 V 5 A ) = 6 W. Using he same calculaion and approximaion mehod, he power losses of he oupu filer capaciors can be calculaed. We use wo 430-μF capaciors in parallel for each channel, and he daashee gives ha he dissipaion facor is lower han 0.00 a he operaing poin. Therefore, he power loss of he oupu filer capaciors is: PCf = (400 V 10 A 0.00) = 16 W. Therefore, he oal power losses of he capaciors in he OBC can be calculaed as: PC = PCd + PCr + PCf = 6.5 W Resonan and Filer Inducors The power losses of he inducor can be divided ino wo pars: core loss and winding loss. For he magneic core PPF306060, he core loss can be decided by he flux densiy and working frequency. The flux densiy can be calculaed by he following expression.

24 Energies 015, B 0.4NI l (50) Pcore 0.4B f V (51) where B represens flux densiy (kg); μ represens relaive permeabiliy; N represens he number of urns; l means magneic pah lengh (cm); I represens peak magneic curren (A); f represens he working frequency (khz) and V represens he volume of he magneic core (cm 3 ). The winding loss is he hea loss caused by he coil resisance, and i can be calculaed by Ohm s law, shown in following expression. Pwind I R (5) From Equaions (50) (5), we can ge he power losses of he six inpu filer inducors and he wo oupu filer inducors, respecively, as: PLin = 6 (Pcore + Pwire) = 7 W; PLf = (Pcore + Pwire) = 4 W. For he resonan inducor, he winding loss is very small compared o he core loss. The core is designed as PC-40 EE110, where Ve = 336,40 mm 3. According o he daashee, he core loss per volume is obained as: Pcv = W/mm 3 a 60 C. As a resul, he core losses of wo resonan inducors are: PLr ( VePcv) 69 W (53) Thus, he oal power losses of he inducors in he sysem can be shown as: PL = PLr + PLin + PLf = 365 W. Finally, based on he calculaion resuls shown in Equaions (43) (53), he conversion efficiency a he 0-kW oupu condiion can be deduced as: Pou % 100% 94.8% P P P P P (54) ou S D C L A power loss disribuion under a 0-kW load is shown in Figure 15. I can be concluded ha he dissipaion of his OBC mainly cenralizes a he IGBTs, resonan inducors and bridge diodes. Addiionally, his will be verified in he experimen secion. 4. Simulaion and Experimen Figure 15. Power loss disribuion. In order o verify he efficiency, PFC and THD of he proposed opology and he accuracy of he heoreical analysis above, we esablished a simulaion model. Furhermore, a hardware plaform was buil for he experimenal research.

25 Energies 015, Simulaion Resul Simulaion a Maximum Oupu Power Figure 16 illusraes he simulaion waveforms of he proposed opology a he maximum oupu power (50-A curren and 400-V volage). There are wo parallel inerleaved channels in he circui, and he driving signals have a 180-degree phase shif from each oher. Figure 16a shows he waveforms of he inpu line curren wih is AC phase volage and oupu volage. Figure 16b shows he deails of he IGBT volage and curren. Figure 16c shows he volage waveforms of he resonan capaciors Cr and Cd and he curren of he resonan inducor Lr. (a) (b) (c) Figure 16. Simulaed waveforms under 0-kW maximum oupu power: (a) inpu curren, inpu and oupu volage; (b) volage and curren of IGBT; (c) volage of resonan devices. The simulaion resuls indicae ha he proposed opology can realize he maximum oupu power a 34.5 khz; he measured THD of he inpu curren is 3.5%, and PF is Besides, he deailed waveforms of he resonan componens are consisen wih he heoreical analysis resuls. The volage and curren waveforms of he IGBT show ha he buck swiches can realize ZCS a he maximum oupu power Simulaion of he Proposed Conrol Sraegy In order o verify he effeciveness of he proposed conrol sraegy, wo groups of simulaions under a low-power condiion wih radiional PFM conrol and he proposed hybrid PFM conrol mehod are compared in Figure 18. Take he charging process ending poin for example, for which he oupu volage and curren are 350 V and A, respecively. For hese wo groups of simulaions, he inpu and oupu condiions are he same: 380-V inpu line volage, 350-V oupu volage and -A oupu curren. Figure 17a shows he inpu volage and curren of phase a under a 5-kHz driving frequency and a 15-μs urn on ime. Ia1 is he inpu curren of a single channel, and Ia is he inpu curren of phase a. The resuls indicae ha he inerleaved srucure will reduce he inpu curren ripple obviously. However, Ia under he PFM conrol sraegy has a grea flucuaion, and he THD is abou 41.%. Figure 17b shows he inpu volage and curren of phase a under a 10-kHz driving frequency and a 5.8-μs urn on ime. I can be seen ha he proposed conrol sraegy eliminaes he phase shif beween Va and Ia, and he THD of

26 Energies 015, Ia decreases o 5.1%. Therefore, by adoping he new proposed hybrid PFM conrol mehod, he qualiy of he inpu curren waveform can be improved obviously. (a) (b) Figure 17. Simulaed waveforms: (a) PFM; (b) he proposed hybrid PFM conrol sraegy Simulaion under Imbalanced Curren Condiion Besides he simulaions based on equally-shared inpu currens for he wo parallel circuis above, he condiion under an imbalanced curren is also simulaed. In his siuaion, he resonan inducors Lr and Lrs are se o be 50 μh and 0 μh separaely, and he oupu is 0 kw. The simulaion waveforms of he wo paralleled channels use he same driving signals wih a 180-degree phase shif from each oher and are shown in Figure 18a. A his ime, he driving frequency of boh channels is 35 khz. In Figure 18a, 0. Va and inpu curren Ia are compared o illusrae PF of he sysem, Vou, and he conras beween Ia1 and Ia is also shown in Figure 18a. By calculaion, we can ge he RMS value, THD and PF of Ia1, Ia and Ia, as shown in Table 4. (a) (b) Figure 18. Simulaed waveforms under he imbalanced curren condiion: (a) wo channels wih a synchronous drive; (b) he curren sharing conrol sraegy.

27 Energies 015, Alhough he curren imbalance has no effec on he PF and THD of he circui, i will cause he uneven disribuion of hea, which will limi he increase of he sysem power. Therefore, a curren sharing conrol sraegy can be used: he curren of wo paralleled circuis can be equally shared by adjusing he driving frequency of he wo paralleled circuis respecively when he circui parameers are no exacly he same. The simulaion resuls using he curren sharing conrol sraegy are shown in Figure 18b. Addiionally, he saisic parameers are also shown in Table 4. Table 4. Simulaion resuls conras under balanced and imbalanced curren. Resonan Inducor (μh) Driving Frequency (khz) Inpu Curren RMS (A) THD (%) PF L r L rs f 1 f I a I a1 I a I a I a1 I a I a I a1 I a Experimen Resul To verify he performance of he proposed opology, a prooype based on he previous sudy is buil. Freescale MCU is used as he monolihic digial conroller. Figure 19 is he phoo of he prooype Maximum Oupu Power Experimen Figure 19. Prooype of he proposed opology. Resriced by experimenal condiions, he maximum oupu power experimen can only be done a 8.5 kw. The experimen resul of a 00-V oupu a a 6-Ohm load is presened in Figure 0. Figure 0a shows he inpu line volage, inpu phase a curren and oupu curren. Figure 0b shows he envelope of he IGBT volage vs, IGBT curren is, resonan inducor Lr curren ilr and oupu curren of he single channel 0.5iou. Figure 0c is he enlarged waveforms of Figure 0b, from which we can see ha he IGBT realized ZCS and was compleely consisen wih he heoreical analysis waveforms shown in Secion 3. Figure 0d is he hermal image, and he maximum emperaure is abou 46.8 degrees cenigrade in he seady sae. The concree daa of his experimen are as follows: inpu line volage: 30 V; driving frequency: 30 khz; urn on ime Ton: 15 μs; oupu volage: 00 V; load resisance: 6 Ohm; inpu curren THD: 4.3%; PF: 0.98 and efficiency: 93.7%.

28 Energies 015, (a) (b) (c) (d) Figure 0. Experimenal resuls (30-V inpu line volage, 00-V oupu, 6-Ohm load resisance): (a) inpu volage, inpu and oupu curren; (b) envelop of resonan volage and curren; (c) enlarged waveform of resonan volage and curren; (d) hermal image Three-Sage Charging Process Experimen The hree-sage charging process is implemened by equivalen experimens, in which several variable high-power resisors are used as he load. In order o avoid overheaing, he charging process is only fulfilled a he low-power level. The experimenal parameers of hree-sage charging are shown in Table 5. Figure 1a shows he collecor-emier (C-E) volage and curren of he IGBT and he oupu curren a a 70-V inpu line volage. The driving frequency reached he upper limi of 40 khz, and he oupu curren is 9. A. Figure 1b shows he same parameers a a 90-V inpu line volage; a his ime, he driving frequency is 9 khz, and he oupu curren is 10 A. Comparing hese experimenal resuls, i can be concluded ha he proposed conrol mehod can saisfy he requiremens of consan curren charging by adjusing he driving frequency, and even when he load or frequency changes, his circui sill can realize ZCS. Table 5. Three-sage charging process parameer seing. Sage Oupu Volage (V) Oupu Curren (A) Load Resisance (Ohm) Consan curren Consan volage Floaing volage Noe: In his able, - means ha a ha sage, his value is no a parameer ha needs o be conrolled.

29 Energies 015, (a) (b) Figure 1. Experimenal resuls under consan curren charging: (a) 70-V line in; (b) 90-V line in. Two groups of experimenal resuls under he consan volage sage are also compared in Figure. Figure a shows he C-E volage and curren of he IGBT and oupu curren a a 90-V inpu line volage. The driving frequency reached he upper limi of 40 khz, and he oupu volage is V. Figure b shows he same parameers a a 110-V inpu line volage. The driving frequency is 5 khz, and he oupu volage is 10.1 V. Consan volage charging and ZCS are realized. (a) (b) Figure. Experimenal resuls under he consan volage charging sage (a) V ou; (b) 110 V ou. The experimenal resuls of floaing charging sage are shown in Figure 3. Figure 3b is he enlarged waveforms of Figure 3a. I also shows he C-E volage and curren of he IGBT and oupu curren a a 10-V inpu line volage; a his condiion, he driving frequency is 5 khz and he oupu curren.5 A, and he load resisance is 40 Ohm. In his case, ZCS is also realized in he possible load range. Figure 4 shows he experimenal waveforms in he process of charging sae swiching. Figure 4a shows he waveforms of he ransformaional ransiion from he consan curren sage o he consan volage sage. During his inerval, he oupu curren iou urns o 8 A from 10 A in.5 ms. Figure 4b shows he swiching poin from he consan volage charging sage o he floaing volage charging sage, where iou urns from 8 A down o.5 A wihin 3. ms. I can be concluded ha he buil OBC plaform can realize he swiching of hree charging sages smoohly wihou obvious overshoo and oscillaion.

30 Energies 015, (a) (b) Figure 3. Experimen resuls under he floaing volage charging sage. (a) (b) Figure 4. Experimenal resuls under he mode ransiion poin. Afer a series of experimens, he efficiency, THD and PF of his OBC plaform under differen oupu powers are obained and shown in Figure 5. I is shown ha, wih he power increases, he efficiency says in a sable range beween 93.5% and 94.0%. A he maximum oupu condiion, he THD is abou 4.3%, and PF is abou (a) (b) Figure 5. Measured efficiency, oal harmonic disorion (THD) and PF curves: (a) efficiency; (b) THD and PF. 5. Conclusions This paper proposed a hree-phase inerleaved high-efficiency and high power facor ZCS OBC for EV applicaion. By using he muli-resonan srucure, he buck swich can realize ZCS and can achieve

31 Energies 015, a high-qualiy inpu curren waveform wih high PF and low THD. The ZCS consrain condiions were deduced under a baery load. A hybrid PFM conrol mehod based on he baery load requiremens during he hree-sage charging process is also proposed. This mehod combines he PFM and PWM sraegy and keeps he driving frequency in a range of 10 khz 40 khz, o avoid he power losses caused by he reacive power ransmission and resonance a a low frequency. The performance of he proposed charger has been verified hrough experimenal resuls based on he buil prooype plaform. Due o he power upper limi of he AC source, he maximum oupu power experimen was done a 8.5 kw only. The efficiency is above 93.5%, and THD and PF remain around 4.3% and 0.98, respecively. Moreover, simulaions and experimenal resuls were verify he heoreical analysis. I is shown ha he proposed inerleaved hree-phase high-power ZCS buck recifier is suiable for high-frequency and high-efficiency OBC applicaions. Acknowledgmens This research was suppored by he Naional Naural Science Foundaion of China (Gran: ) and suppored by Tianjin Municipal Science and Technology Commission (Gran: 14ZCZDGX00035). The auhors would also like o hank he anonymous reviewers for heir valuable commens and suggesions o improve he qualiy of he paper. Auhor Conribuions Cheng-Shan Wang, Wei Li and Yi-Feng Wang designed he main pars of he sudy, including he circui simulaion model, opology innovaion and simulaion developmen. Zhun Meng helped in he hardware developmen and experimen. Jie-Gui Zhou were also responsible for wriing he paper. Conflics of Ineres The auhors declare no conflic of ineres. References 1. Yilmaz, M.; Krein, P.T. Review of baery charger opologies, charging power levels, and infrasrucure for plug-in elecric and hybrid vehicles. IEEE Trans. Power Elecron. 013, 8, Hawkins, T.R.; Gausen, O.M.; Srømman, A.H. Environmenal impacs of hybrid and elecric vehicles A review. In. J. Life Cycle Assess. 01, 17, Haghbin, S.; Lundmark, S.; Alaküla, M.; Carlson, O. Grid-conneced inegraed baery chargers in vehicle applicaions: Review and new soluion. IEEE Trans. Ind. Elecron. 013, 60, Chan, C.C.; Chau, K.T. An overview of power elecronics in elecric vehicle. IEEE Trans. Ind. Elecron. 1997, 44, Mapelli, F.L.; Tarsiano, D.; Mauri, M. Plug-in hybrid elecric vehicle: Modeling, prooype realizaion, and inverer losses reducion analysis. IEEE Trans. Ind. Elecron. 010, 57, Musavi, F.; Edingon, M.; Eberle, W.; Dunford, W.G. Evaluaion and efficiency comparison of fron end AC-DC plug-in hybrid charger opologies. IEEE Trans. Smar Grid 01, 3,