Research Article Photovoltaic Power System with an Interleaving Boost Converter for Battery Charger Applications

Transcription

1 Inernaional Journal of Phooenergy Volume 212, ricle ID , 15 pages doi:1.1155/212/ Research ricle Phoovolaic Power Sysem wih an Inerleaving Boos Converer for Baery Charger pplicaions Sheng-Yu Tseng 1 and Cheng-Tao Tsai 2 1 Deparmen of Elecrical Engineering, Chang-Gung Universiy, Taoyuan 3332, Taiwan 2 Deparmen of Elecrical Engineering, Naional Chin-Yi Universiy of Technology, Taiping 411, Taiwan Correspondence should be addressed o Cheng-Tao Tsai, csai@ncu.edu.w Received 2 June 212; cceped 11 Sepember 212 cademic Edior: Tapas Mallick Copyrigh 212 S.-Y. Tseng and C.-T. Tsai. This is an open access aricle disribued under he Creaive Commons ribuion License, which permis unresriced use, disribuion, and reproducion in any medium, provided he original work is properly cied. This paper proposes a phoovolaic (PV) power sysem for baery charger applicaions. The charger uses an inerleaving boos converer wih a single-capacior urn-off snubber o reduce volage sresses of acive swiches a urn-off ransiion. Therefore, acive swiches of he charger can be operaed wih zero-volage ransiion (ZVT) o decrease swiching losses and increase conversion efficiency. In order o draw he maximum power from PV arrays and obain he opimal power conrol of he baery charger, a perurbaion-and-observaion mehod and microchip are incorporaed o implemen maximum power poin racking (MPPT) algorihm and power managemen. Finally, a prooype baery charger is buil and implemened. Experimenal resuls have verified he performance and feasibiliy of he proposed PV power sysem for baery charger applicaions. 1. Inroducion Due o he coninuous growh of he global energy demand for developing indusry, i increases sociey awareness of environmenal impacs from he widespread uilizaion of fossil fuels, leading o he exploraion of renewable energy sources, such as PV arrays, wind energy, and so on. One of hese sources is PV arrays energy, which is clean, quie, and mainenance-free. However, due o he insabiliy and inermien characerisics of PV arrays, i canno provide a consan or sable power oupu. Thus, a power converer (dc/dc converer or dc/ac converer) and MPPT algorihm are required o regulae is oupu power. Several MPPT algorihms have been proposed [1 1]. Some of he popular MPPT algorihms use perurbaionand-observaion mehod [1 3], incremenal conducance mehod [4], consan volage mehod [5, 6], β mehod [7], sysem oscillaion mehod [8, 9], and ripple correlaion mehod [1]. The perurbaion-and-observaion mehod requires he measuremen of only a few parameers, hus i faciliaes an MPPT conrol. s a resul, i is ofen applied o he PV arrays for enhancing power capaciy. ypical PV power sysem is shown in Figure 1. The PV arrays usually need a baery charger o increase is uiliy rae. The research of his paper is only focused on PV arrays for baery charger applicaions. For charger design, many charging mehods have been developed, such as he consan rickle curren (CTC), consan curren (CC), consan volage (CV), hybrid CC/CV [11], and reflex charging mehods [12 15]. The CTC mehod has a disadvanage ha i has a longer charging ime, he CC and CV are he simples mehods o baery charger, bu boh of hem resul in he siuaions of undercharge and overcharge. The hybrid CC/CV mehod can improve charging efficiency and charging ime, bu i has a disadvanage of difficul conrol. To reduce he charging ime of he baeries, he reflex charging mehod is adoped in his paper. The mehod consiss of a high posiive pulse-charging curren followed by a high curren, shor ime negaive pulse-discharging curren, and a res period. high posiive pulse-charging curren can reduce he charging ime and a negaive pulsedischarging curren is o reduce inernal cell pressure and emperaure of baeries. res period can provide he baeries wih a reflex ime in charging process.

2 2 Inernaional Journal of Phooenergy Uiliy line DC/DC DC/C PV arrays converer (MPPT) C dc V dc inverer Charger (MPPT) V B Discharger Figure 1: Block diagram of a ypical PV power sysem. I L L 1 D 1 1 D S3 V i M 1 I DS1 L S D S1 D S2 2 C O RL Lossless urn-off snubber Figure 2: Topology of basic boos converer wih a passive lossless urn-off snubber. The basic swiching power converers have six circui srucures, such as buck, boos, buck-boos, Cuk, Sepic, and Zea converers. In order o obain coninuous inpu curren for baery charger, he basic boos converer is widely used. However, i is operaed under high swiching frequencies resuling in high swiching losses, noises, and componen sresses. These drawbacks reduce power seriously and deeriorae in he performances of he basic boos converer. In order o alleviae he problems described previously, sof-swiching echnologies are inroduced ino he basic boos converer o reduce swiching losses. Sofswiching echnologies can be classified as passive and acive sof-swiching echnologies. The passive echnologies use only passive componens o perform sof-swiching operaion [16 18].Theaciveechnologiesaddoneormore acive swiches along wih oher passive componens o he basic swiching power converers o perform sof-swiching operaion [19, 2]. For cos consideraions, he proposed baery charger wih passive sof-swiching echnologies is more aracive a low power level applicaions. basic boos converer wih a passive lossless urn-off snubber for baery charger applicaions is usually adoped, as shown in Figure 2 [18], because i has a simple srucure. However, he basic boos converer has a disadvanage ha is oupu ripple curren will swing over a wide range resuling in a low baery life. In order o reduce oupu ripple curren and increase power level, wo ses of boos converers are incorporaed wih an inerleaving fashion, as shown in Figure 3 [21]. lhough inerleaving boos converer wih wo ses of passive sof-swiching circuis can also achieve sof-swiching feaures, heir componen couns and cos are increased significanly. To overcome he previously discussed drawbacks, an inerleaved boos converer wih a singlecapacior urn-off snubber for baery charger applicaions is proposed, as shown in Figure 4. The proposed baery charger requires only a resonan capacior which is associaed wih inducors L 1 and L 2 o reduce swiching losses of acive swiches. 2. Conrol lgorihm of he Proposed Charger Inorderoachieveanopimalpowerconrolofbaery charger, an MPPT algorihm and a power managemen uni are needed. These conrol algorihms are described as follows Topology of Baery Charger. The proposed charger includes an inerleaving boos converer and a conroller, as shown in Figure 5. Moreover, he conroller adops microchip o implemen MPPT of PV arrays and baery

3 Inernaional Journal of Phooenergy 3 I L21 L 21 F D 21 V CS21 21 B D S23 D S22 L S21 D S21 22 C VCS22 I L11 L 11 G D 11 V CS11 D CS11 D S13 DS12 V PV L S11 D S11 12 E V CS12 Figure 3: Topology of wo ses of boos converers operaed in an inerleaving fashion. I L2 L 2 I D2 D 2 I D I DS1 I DS2 I D1 D 1 Figure 4: Topology of he proposed inerleaving boos converer wih a single-capacior urn-off snubber for baery charger applicaions. charging managemen. Therefore, he conroller of he proposed baery charger can be divided ino hree unis. They are MPPT operaion, baery managemen, and power managemen unis. The MPPT operaion uni can implemen he MPPT of PV arrays. The charging algorihm of baery charger is conrolled wih reflex charging mehod by baery managemen uni o reduce he charging ime. In order o achieve he bes energy uilizaion of he PV arrays, an MPPT wih perurbaion-and-observaion mehod is inegraed ino an MPPT operaion uni. Since he MPPT and charging algorihm mus be associaed o implemen opimal conrol of baery charger, he power managemen uni is needed. To achieve opimal sabiliy and safey for he proposed baery charger, he funcions of under-volage, over-curren, and over-emperaure proecion circuis are required. ll of he proecion signals are also realized on a microchip MPPT lgorihm. Oupu characerisic variaions of PV array depend on climaic condiions, such as emperaure of PV arrays and insolaion of sun. Is P-V curves a differen insolaion of he sun are shown in Figure 6.FromFigure 6,i can be seen ha each insolaion level has a maximum power P max,wherep max 1 is he maximum power a he larges insolaion of sun while P max 3 is he one a he leas insolaion of sun. Three maximum power poins P max 1 P max 3 can be conneced by a sraigh line. Operaional area on he righ hand side of he sraigh line is defined as B area, while he one on he lef hand side is defined as area. Since oupu load conneced in PV arrays increases, oupu volage of PV arrays decreases. Therefore, when working poin of PV arrays locaes in area, oupu load mus decrease o make he working poin o approach he maximum power poin of PV arrays. On he oher hand, when working poin of PV arrays places on B area, oupu load mus increase. Their operaion condiions are shown in Figure 7. Figure 7(a) shows he working poin locaed on area, while Figure 7(b) illusraes he one locaed on B area. When working poin locaes on area, he working poin is changed from 1 o maximum power poin P max a poin 6 hrough 2, 3, 4,and 5, as shown in Figure 7(a). When working poin locaes on B area, he working poin is changed from B 1 o maximum power poin P max a poin B 6 hrough B 2, B 3, B 4,andB 5, as shown in Figure 7(b). ccording o differen operaional area o increase or decrease oupu load, working poin of PV arrays can be shifed o MPP. In order o exrac maximum power of PV arrays, a simple perurbaion-and-observaion mehod is adoped. Is flow char is shown in Figure 8. In he MPPT flow char, V n and I n are, respecively, new volage and curren of PV arrays, V P and P P separaely represen is old volage and power value, and P n (= V n I n )ishenewpowervalueofpv

4 4 Inernaional Journal of Phooenergy M 1 Charger V B M 1 MPPT operaion uni Power managemen uni Baery managemen uni V B Conroller Figure 5: Block diagram of baery charger. P Increase load area P max1 P max2 P max3 B area V Figure 6: Plo of P-V curvesforpvarraysadifferen insolaions of sun. arrays. ccording o flow char of MPPT using perurbaionand observaion-mehod, he firs sep is o read new volage V n and curren I n of PV arrays, and hen o calculae new PV power P n. The nex sep is o judge he relaionship of P n and P P. ccording o he relaionship of P n and P P and procedures of MPPT flow char, he procedure eners o judge he relaionship of V n and V P. When he relaionship of V n and V P is decided, operaional area of working poin can be specified. ccording o conrol algorihm of MPPT, when he working poin of PV arrays is locaed in area, power sysem conneced in PV arrays o supply load power mus decrease oupu power o close he disance beween working poin and MPP of PV arrays. On he oher hand, when he operaing poin is locaed in B area, PV power energy mus be increased o approach maximum power poin of PV arrays. Finally, he procedure of MPPT flow char is reurned o he firs sep o judge nex maximum power poin of PV arrays Power Managemen. The proposed charger is wih a reflex charging mehod o reduce charging ime, since he charging volage and curren of baeries mus be limied for proecing baery life. The concepual waveforms of charging curren and volage of baery charger wih a reflex charging mehod are shown in Figure 9. Figure 9(a) shows reflex charging waveforms of baery charger under minimum baery volage V B(min),isV B(min) is expressed as undercharge condiion of baery volage. Figure 9(b) shows reflex charging waveforms of baery charger under maximum baery volage V B(max),isV B(max) is expressed as overcharge condiion of baery volage. ccording o V B(min) and (max) or V B(max) and (min), he power limiaion curve of baery charger can be obained, as shown in Figure 9. When he maximum power P PV(max) of PV arrays is larger or less han P max 1, he power operaion poin of PV arrays is raced as shown in Figure 1. s menioned previously,he charging and discharging power of he proposed charger will be limied by power curve o exend baery life. 3. Derivaion and Operaional Principle of he Proposed Charger In order o describe he meris of he proposed baery charger, is opology derivaion and operaional principles are briefly described as follows Derivaion of he Proposed Charger. To reduce swiching losses, a lossless urn-off snubber is insered in a basic boos converer as shown in Figure 2. When swich M 1 is urned on, capaciors 1 and 2 are charged hrough inducor L s and diode D S2 in a resonan manner. he end of he resonan inerval, capaciors 1 and 2 are charged o and are clamped a unil swich M 1 is urned off. When swich M 1 is urned off, he charges sored

5 Inernaional Journal of Phooenergy 5 P area P max B area P area P max B B 6 51 B 5 B 41 B 4B3B2 B area B 31 B 21 B 11 B 1 Curve C 3 Curve C 2 Curve C 1 V area Curve C 3 Curve C 2 Curve C 1 V (a) (b) Figure 7: Illusraion of PV arrays operaed in (a) area and (b) B area for MPPT. Sar Read V n, I n Calculae P n = V n I n No Judge P n <P P No Judge P n >P P Yes Yes Judge V n = V P No No Judge V n <V P Yes No Judge V n >V P Yes Yes area B area B area area Decrease Increase Increase Decrease load load load load (ΔI) (ΔI) (ΔI) (ΔI) Replace V P = V n P P = P n Figure 8: Flow char of MPPT using perurbaion-and-observaion mehod for PV arrays sysem.

6 6 Inernaional Journal of Phooenergy Real power curve V B(min) P 1 (=V B(min) (max)) Power limiaion curve (max) Real power curve V B(max) P 2 (=V B(max) (max)) Power limiaion curve (max) T T1 T 2 T S T S Charging ime T T 1 T 2 T S T S Charging ime (a) (b) Figure 9: Concepual waveforms of charging curren, volage and power for baery charger wih reflex charging mehod (a) under he minimum baery volage V B(min) and (b) under he maximum baery volage V B(max). P max1 (=V B (max) ) Real power curve P max1 (=V B (max) ) P PV(max) Real power curve P PV(max) Power curve Power curve T T 1 T 2 T S T S Charging ime T T 1 T 2 Charging ime T S T S (a) (b) Figure 1: Concepual power waveforms of PV arrays and baery charging power: (a) P PV(max) P max 1 and (b) P PV(max) P max 1. in capaciors 1 and 2 are discharged o oupu load hrough diodes D S1 and D S3,respecively.Thus,swichM 1 is urned off wih zero-volage ransiion (ZVT). s menioned previously, alhough i can achieve he sof-swiching feaure, is oupu curren ripple is relaively large for high curren and low oupu volage applicaions. Therefore, o reduce oupu curren ripple, an inerleaving scheme is usually adoped. In he following, he proposed inerleaving boos converer wih a single-capacior snubber is derived. Two lossless urn-off snubbers are used in an inerleaving boos converer o reduce swiching losses, as shown in Figure 3. To simplify circui of Figure 3, volages of capaciors 12 and 22 are replaced wih dc volages 12 and 22, respecively. When volages of capaciors 12 and 22 are replaced wih dc volages, he energies sored in capaciors 12 and 22 do no need o discharge heir charges. Thus, diodes D S11 and D S21 can be removed, as shown in Figure 11(a). If volage 12 or 22 is equal o ( ), nodes, C, and E will have he same poenial. Thus, hey canbemergedasnode,asshowninfigure 11(b).Basedon he operaional principle of an inerleaving boos converers and he urn-off snubber, operaional saes of diode D 11 (or D 21 ) is he same as diode D S23 (or D S13 ) excep ha he operaional duraion of he urn-off snubber is operaed wihin resonan mode. Since he duraion of resonan mode is much shorer han a period of he proposed converers, nodes F and D (or G and B) can be combined as he same node H (or I), as shown in Figure 11(c). Iwillnoaffec is original operaional principle. Because inducor currens I L11 and I L21 are unidirecional in he derived converer, inducors L 11 and L S21 conneced wih diode D S22 in series can be combined and replaced by inducor L 1. Similarly, inducors L 21 and L S11 and diode D S12 can be also merged as inducor L 2, as shown in Figure 11(d). InFigure 11(c), since capaciors 11 and 21 and diodes D 11 and D S23 or D 21 and D S13 are, respecively, conneced in parallel, hey can be, respecively, incorporaed as capacior and diode D 1 or D 2.FromFigure 11(d), i can be observed ha he derived boos converer requires only a resonan capacior,which is associaed wih inducors L 1 and L 2 o funcion as a lossless urn-off snubber, reducing swiching losses and componen couns significanly. Therefore, Figure 11(d) is proposed for baery charger applicaions Operaional Principle of he Proposed Charger. In Figure 4, he proposed baery charger wih a single-capacior urnoff snubber can achieve a ZVT feaure for acive swiches. Operaional modes of he proposed charger are divided

7 Inernaional Journal of Phooenergy 7 C R I L21 L 21 F D 21 B 21 D S23 D S22 L S21 I L11 L 11 C D V G CS22 11 D 11 D S13 D S12 L S11 O L E 12 I L21 L 21 F D 21 L S21 D S22 21 D S23 B I L11 L 11 G D 11 LS11 D S12 11 D S13 D (a) (b) I L21 L 21 H D 21 I L2 L 2 I D2 D2 I D L S11 D S12 D S13 IPV I L11 11 L 11 L S21 D S22 I 21 D 11 D S23 C O R L I DI D 1 VO (c) (d) Figure 11: Derivaion of he proposed baery charger wih a single-capacior urn-off snubber. ino en modes, as illusraed in Figure 12, and heir key waveforms are illusraed in Figure 13.In he following,each operaional mode is described briefly. Mode 1 (Figure 12(a); < 1 ). Before, diode D 2 is in freewheeling, and inducor curren I L2 is equal o diode curren I D2. =,swichm 1 is urned on. The equivalen circui a his ime inerval is shown in Figure 12(a), from which i can be found ha swich curren I DS1 is equal o he sum of capacior curren and inducor curren I L1. Since he inerval of 1 is very shor, inducor curren I L1 is approximaely equal o zero and capacior volage is close o zero. Thus, swich curren I DS1 is approximaely equal o capacior curren. During his ime inerval, he curren is abruply increased up o inducor curren I L2, and I D2 is abruply decreased down o zero. Mode 2 (Figure 12(b); 1 < 2 ). ime 1,capacior curren is equal o inducor curren I L2, and diode D 2 is reversely biased. his ime inerval, snubber capacior resonaes wih inducor L 2, and swich curren I DS1 is jus equal o he sum of resonan inducor curren I L2 (= ) and inducor curren I L1. he same ime, capacior curren reaches is maximum value which can be expressed as follows: = V i Z O, (1) where Z O is he characerisic impedance of L 2 - or L 2 - nework, which is equal o L 1 /C s or L 2 /C s. Mode 3 (Figure 12(c); 2 < 3 ). When = 2,capacior volage is equal o, and diode D 2 sars freewheeling hrough inducor L 2. he same ime, swich M 1 is sill in he on sae. The swich curren I DS1 is now equal o inducor curren I L1 which increases linearly, while inducor curren I L2 is decreased linearly. Mode 4 (Figure 12(d); 3 < 4 ). ime 3,swich M l is urned off. Because inducor curren I L1 mus be coninuous, capacior sars o discharge for susaining a coninuous inducor curren. Thus, swich M 1 can be urned off wih ZVT. Mode 5 (Figure 12(e); 4 < 5 ). When ime reaches 4, he volage across capacior is discharged oward zero,

8 8 Inernaional Journal of Phooenergy I L2 L 2 I D2 D2 I D I L2 L 2 I D2 D 2 I D I DS1 I DS2 C O R L I DS1 I DS2 (a) Mode 1 ( < 1 ) I L2 L 2 I D2 D2 I D (b) Mode 2 ( 2 < 3 ) I L2 L 2 I D2 D 2 I D (c) Mode 3 ( 3 < 4 ) I L2 L 2 I D2 D 2 I D (d) Mode 4 ( 4 < 5 ) I L2 L 2 I D2 D 2 I D (e) Mode 5 ( 5 < 6 ) I L2 L 2 I D2 D 2 ID (f) Mode 6 ( 6 < 7 ) I L2 L 2 I D2 D 2 I D (g) Mode 7 ( 7 < 8 ) (h) Mode 8 ( 8 < 9 ) Figure 12: Coninued.

9 Inernaional Journal of Phooenergy 9 I L2 L 2 I D2 D2 I D I L2 L 2 ID2 D 2 I D I DS1 M 1 I DS2 M2 (i) Mode 9 ( 9 < 1 ) (j) Mode 1 ( 1 < 11 ) Figure 12: Operaional modes of he proposed baery charger over one swiching cycle. and diode D 1 sars freewheeling. During his ime inerval, diodes D 1 and D 2 are in freewheeling hrough inducors L 1 and L 2,respecively. Mode 6 (Figure 12(f); 5 < 6 ). ime 5, diode D 1 is sill in freewheeling, bu diode D 2 sops freewheeling because inducor curren I L2 drops o zero. In his momen, swich M 2 is urned on. Inducor curren I L1 is equal o he sum of diode curren I D1 and capacior curren. ddiionally, because he swich curren I DS2 will flow hrough he lowimpedance pah of capacior, diode curren I D1 will be dominaed by he swich curren I DS2. Tha is, wihin his ime duraion, capacior curren is approximaely equal o he swich curren I DS2.Capaciorcurren is abruply increased up o inducor curren I L1,andI D1 is abruply decreased down o zero. Mode 7 (Figure 12(g); 6 < 7 ). ime 6, diode D 1 is reversely biased, and resonan nework formed by capacior and inducor L 1 sars resonaing. The swich curren I DS2 is equal o he sum of inducor curren I L1 (= )and inducor curren I L2, and capacior is reversely charged. Mode 8 (Figure 12(h); 7 < 8 ). = 7, he capacior volage goes down o. The ime inerval lass approximaely a quarer of he resonan cycle. he same ime, capacior curren reaches is maximum value, which can be expressed by (1). During his mode, diode D 1 sars freewheeling, and inducor curren I L2 is increased linearly. Mode 9 (Figure 12(i); 8 < 9 ). ime 8,swichM 2 is urned off. Since he inducor curren I L2 mus be in smooh ransiion, capacior volage will drop o mainain a coninuous inducor curren. When = 9, capacior volage drops o zero. Mode 1 (Figure 12(j); 9 < 1 ). During his ime inerval, diodes D 1 and D 2 are in freewheeling hrough inducors L 1 and L 2, and heir currens I D1 and I D2 are decreased linearly. When swich M l is urned on again a he end of Mode 1, a new swiching cycle will be recycled. 4. Conrol and Design of he Proposed Charger In order o achieve opimal conrol of he proposed charger, he MPPT operaion algorihm of PV arrays and reflex charging algorihm of baery mus be considered. In he following, conrol and design of he proposed charger are described Conrol of he Proposed Charger. The proposed charger consiss of an inerleaving boos converer and conroller. The conroller adops microchip of CY8C27443 made by Cypress Company. Block diagram of he proposed charger is shown in Figure 14.InFigure 14, he CY8C27443 microchip is divided ino hree unis: MPPT, baery managemen, and power managemen unis. In MPPT uni, he perurbaionand-observaion mehod is adoped o race maximum power poin of PV arrays. The maximum power P P of PV arrays can be decided. Moreover, baery managemen uni has four inpu signals (V B, V B(max),,and(max) )wherev B is he baery volage, V B(max) is he se maximum baery volage, is he baery charging curren, and (max) is he se maximum baery charging curren. ccording o four inpu signals, P B (= V B )andp B(max) (= V B (max) ) can be calculaed. The P B represens he presen charging power of baery, while P B(max) is he se maximum charging power. In addiion, when V B is equal o or greaer han V B(max), proecion judgmen makes oupu signal S P from low o high value. The S P is sen o PWM generaor for shudown PWM generaor o avoid baery overcharge. In power managemen uni, a comparaor is used o judge relaionship of P P and P B(max). When P P (=P PV(max) )isgreaer han P B(max), signal S 1 is high and swich selecor is operaed o se P se = P B(max). When P P is equal o or less han P B(max), signal S 1 is low and swich selecor is operaed o se

10 1 Inernaional Journal of Phooenergy V GS1 V GS2 V DS1 I DS1 V DS2 I DS2 I D1 I D2 I L1 I L Figure 13: Key waveforms of he proposed baery charger operaing over one swiching cycle.

11 Inernaional Journal of Phooenergy 11 Inerleaving boos converer I L2 L 2 I D2 D 2 I D I CS C O R L Conroller (CY8C27443) Perurb and observe mehod (MPPT ) P P PWM generaor ΔP Error amplifier P se B Swich selecor S 1 Comparaor P P and P B(max) S P P B P B(max) Proecion judgemen Calculae P B = V B Calculae P B (max) = V B (max) V B(max) V B (max) MPPT uni Power managemen uni Baery managemen uni Figure 14: Block diagram of he proposed baery charger. P se = P B.TheP se and P B are sen o error amplifier o aain error value ΔP. When PWM generaor aains ΔP, ΔP and riangle waves inside PWM generaor aain PWM signals M 1 and M 2 via he comparaor. The inerleaving boos converer can change charging curren according o PWM signals M 1 and M Design of he Proposed Charger. To realize he proposed sof-swiching charger sysemaically, design of inducor L 1 or L 2 and he snubber are presened as follows Design of Inducor L 1 or L 2. Since he proposed charger is operaed a he boundary of coninuous conducion mode (CCM) and disconinuous conducion mode (DCM), he relaionship beween V i and can be aained wih vol-second balance principle. Thus, ransfer funcion M(= / ) can be expressed as M = 1 1 D, (2) where D is duy raio of he proposed charger. When duy raio D is deermined by he relaionship beween and, inducor L 1 or L 2 can also be expressed as L 1 = L 2 = D(1 D) 2 T S, (3) where T S is he swiching cycle of he proposed charger and is oupu curren Design of Snubber Capacior. In he proposed charger, capacior resonaes wih inducor L 1 or L 2 o smooh ou swich volage a urn-off ransiion. The energy sored in can be deermined as W CS = (4) To compleely eliminae he swich urn-off loss, he energy sored in capacior mus be a leas equal o he urn-off loss W S off. ccording o swiching loss calculaion of swich, W S off can be expressed by W S off = S off 2 I DP, (5) where S off is he falling ime of swich a urn-off ransiion, represens oupu volage and I DP is swich curren a urn-off ransiion of swich. Therefore, capacior can be deermined as I DP S off. (6) The peak curren of capacior should be limied o being less han he peak values of I DS1 and I DS2,soi will no increase he curren raings of swiches M 1 or M 2. To eliminae urn-off loss W S off compleely a differen operaion condiions, he ime S off is approximaely equal o 2 ns in pracical design consideraions.

12 12 Inernaional Journal of Phooenergy V DS I DS Turn-off ZVT V DS I Turn-off DS ZVT - ZVT (a) (V DS1 :5V/div,I DS1 :5/div,ime:1μs/div) V DS I DS Turn-off ZVT - Figure 16: (V DS1 :5V/div,I DS1 :5/div,ime:1μs/div). Measured volage and curren waveforms of swich in he inerleaved boos converer wih wo ses of urn-off snubbers. I L (b) (V DS1 :5V/div,I DS1 :5/div,ime:1μs/div) Figure 15: Measured volage and curren waveforms of (a) swich M 1, and (b) swich M 2 in he proposed converers. 5. Measuremens and Resuls (a) (I L :1/div, :5/div,ime:1μs/div) To verify he analysis and discussion, a PV sysem used o charge 48 V baery wih he following specificaions was implemened: (i) inpu volage V i :34 42V dc (PV arrays), (ii) oupu volage :44 54 V dc (4 ses of 12 V baery conneced in series), (iii) oupu maximum curren (max) :1, (iv) oupu maximum power P O(max) : 54 W. I L1 I L2 From (6), value of snubber capacior can be calculaed as 37 nf where I DP is 1 and is 54 V. In our design sample, a capacior wih 39 nf is adoped. The componens of power sage in he proposed boos converers are deermined as follows: (i) M 1, M 2 : IRFP25, (ii) D 1, D 2 : MVUR156, (iii) C O : 47 μf, (iv) L 1, L 2 :3μH, (v) :39nF, (vi) inducor core: EE-35. The measured volage and curren waveforms of he acive swiches wih he proposed single-capacior snubber (as shown in Figure 4) and wih wo ses of urn-off snubbers (as shown in Figure 3) are shown in Figures 15 and 16, respecively. lhough we can observe ha each power swich is urned off wih ZVT feaure, here sill exis significan differences. Compare wih Figures 15 and 16, we can see (b) (I L1, I L2 :1/div, :5/div,ime:1μs/div) Figure 17: Measured waveforms of inducor curren I L and charging curren of (a) single boos converer and (b) he proposed inerleaving boos converer. ha he rise volage curves of Figure 15 are smooher han hose of Figure 16. The reason of his is ha inerleaving boos converer wih wo ses of urn-off snubbers, causes an abrup energy on acive swiches and resuls in more swiching losses. Figure 17(a) shows measured inducor curren and charging curren of he single boos converer wih a urn-off snubber, and Figure 17(b) shows measured inducor curren and charging curren of he proposed inerleaved boos converer wih a single-capacior urn-off snubber. From Figure 17, i can be seen ha he proposed converer wih a single-capacior urn-off snubber has a lower ripple charging curren. To make a fair comparison, he hardware componens of he proposed charger and hard-swiching boos charger

13 Inernaional Journal of Phooenergy 13 V B 1 9 (a) (V B :1V/div, :3/div) V B η (%) v Load (%) Wih wo urn-off snubbers Wih he proposed single-capacior Wih hard-swiching circui (b) (V B :1V/div, :3/div) Figure 19: Comparison among efficiencies of he discussed inerleaving boos converer wih a single-capacior urn-off snubber, hard swiching, and wo ses of urn-off snubbers from ligh load o heavy load. Figure 18: Baery volage V B and charging curren under sepload changes beween 2% and 1% of full load of he discussed inerleaving boos converers wih (a) hard swiching (b) a singlecapacior urn-off snubber. V B LeCroy are kep as he same as possible. Figure 18 shows he plos of oupu volage and curren waveforms of he wo kinds of chargers under sep-load changes beween 2% and 1% wih, respecively, rae of 1 khz and a duy raio of 5%. From Figure 18, i can be observed ha alhough he proposed charger uses less componen couns, i yields almos he same dynamic performance as hose wih complicaed configuraions. The comparisons beween he efficiencies of he proposed charger and heir counerpars are illusraed in Figure 19. I can be observed ha he proposed charger canno always yield higher efficiencies han he ohers under various operaing condiions. I has a rend ha, a higher oupu load, he proposed charger and he ones wih wo urn-off snubbers can yield higher efficiency, while a lower ones, he discussed charger wih wo ses of urn-off snubbers yields lower efficiency han he ohers. The reasons behind his are ha a a fixed power level, a higher oupu load level will resul in higher swich currens and he urn-off losses W S off will be much higher han he sum of he exra conducion loss W ES and swiching loss W S on. Figure 2 shows he measured waveforms of baery volage V B and charging curren wih pulse curren charging mehod under repeiive rae of 1 s and duy raio of 5 ms, as shown in Figure 14. Figure 2(a) shows hose waveforms under P PV(max) = 5 W, while Figure 2(b) illusraes hose waveforms P PV(max) = 1 W. From Figure 2, i can be seen ha maximum pulse charging curren (max), respecively, is limied 1 (abou.15 C) and (a) (V B : 5 V/div, : 1 /div, ime: 5 ms/div) V B (b) (V B : 5 V/div, : 2 /div, ime: 5 ms/div) LeCroy Figure 2: Measured waveforms of baery volage V B and charging curren wih pulse curren charging mehod: (a) (max) = 1 and(b) (max) = 2. 2 (abou.3 C), where baery adops lead-acid baery and capaciy of each baery is 12 V/7 h and oal baery volage is 5 V. Measured waveforms of volage,curren and power P PV of PV arrays wih perurbaion-and-observaion mehod are used o implemen MPPT. Figure 21(a) shows hose waveforms under maximum power poin P PV(max) a 1 W, while Figure 21(b) depics hose waveforms under

14 14 Inernaional Journal of Phooenergy LeCroy LeCroy P PV P PV (a) ( :5V/div, :2/div,P PV : 1 W, ime: 1 ms/div) (b) ( :5V/div, :2/div,P PV : 1 W, ime: 1 ms/div) Figure 21: Measured waveforms of volage, curren and Power P VP of PV arrays wih perurbaion- and-observaion mehod o implemen MPPT: (a) P PV(max) = 1 W, and (b) P PV(max) = 2 W. P PV(max) a 2 W. From Figure 21, i can be found ha racking ime of PV arrays from zero o he maximum power poin is abou 4 ms. 6. Conclusions In his paper, an inerleaving boos converer wih a passive snubber for baery charger applicaions is proposed. The proposed charger wih a single-capacior snubber o reduce volage sresses of acive swiches a urn-off ransiion. Therefore, he conversion efficiency of he proposed charger can be increased significanly. In order o draw maximum power from he PV energy, a simple perurbaion-andobservaion mehod is incorporaed o realize maximum power conversion. To verify he meris of he proposed charger, he operaional principle, seady-sae analysis, and design consideraions have been described in deail. ddiionally, from he experimenal efficiency of he proposed charger, i has been shown ha he proposed charger can yield higher efficiency a heavy load condiion. n experimenal prooype for a baery charger applicaion (54 W, 54 V dc /1 ) has been buil and evaluaed, achieving he efficiency of 88% under full load condiion. Therefore, he proposed inerleaving boos converer is relaively suiable for baery charger applicaions. References [1] S.L.Brunon,C.W.Rowley,S.R.Kulkarni,andC.Clarkson, Maximum power poin racking for phoovolaic opimizaion using ripple-based exremum seeking conrol, IEEE Transacions on Power Elecronics, vol. 25, no. 1, pp , 21. [2] V. garwal, R. K. ggarwal, P. Paidar, and C. Paki, novel scheme for rapid racking of maximum power poin in wind energy generaion sysems, IEEE Transacions on Energy Conversion, vol. 25, no. 1, pp , 21. [3]. M. Subiyano and S. Hussain, Hopfield neural nework opimized fuzzy logic conroller for mximum power poin racking in a phoovolaic sysem, Inernaional Journal of Phooenergy, vol. 212, ricle ID , 13 pages, 212. [4] M. Taherbaneh,. H. Rezaie, H. Ghafoorifard, K. Rahimi, and M. B. Menhaj, Maximizing oupu power of a solar panel via combinaion of sun racking and maximum power poin racking by fuzzy conrollers, Inernaional Journal of Phooenergy, vol. 21, ricle ID 31258, 13 pages, 21. [5] X. Weidong and W. G. Dunford, modified adapive hill climbing MPPT mehod for phoovolaic power sysems, in Proceedings of he IEEE 35h nnual Power Elecronics Specialiss Conference (PESC 4), vol. 3, pp , June 24. [6] K. Kobayashi, H. Masuo, and Y. Sekine, n excellen operaing poin racker of he solar-cell power supply sysem, IEEE Transacions on Indusrial Elecronics, vol. 53, no. 2, pp , 26. [7] S. Jain and V. garwal, new algorihm for rapid racking of approximae maximum power poin in phoovolaic sysems, IEEE Power Elecronics Leers, vol. 2, no. 1, pp , 24. [8] H.S.H.Chung,K.K.Tse,S.Y.R.Hui,C.M.Mok,andM. T. Ho, novel maximum power poin racking echnique for solar panels using a SEPIC or Cuk converer, IEEE Transacions on Power Elecronics, vol. 18, no. 3, pp , 23. [9] B. M. T. Ho and H. S. H. Chung, n inegraed inverer wih maximum power racking for grid-conneced PV sysems, PEC, vol. 3, pp , 24. [1] D. Casadei, G. Grandi, and C. Rossi, Single-phase single-sage phoovolaic generaion sysem based on a ripple correlaion conrol maximum power poin racking, IEEE Transacions on Energy Conversion, vol. 21, no. 2, pp , 26. [11]..-H. Hussein and I. Baarseh, review of charging algorihms for nickel and lihium baery chargers, IEEE Transacions on Vehicular Technology, vol. 6, no. 3, pp , 211. [12] F. Savoye, P. Vene, M. Mille, and J. Groo, Impac of periodic curren pulses on Li-Ion baery performance, IEEE Transacions on Indusrial Elecronics, vol. 59, no. 9, pp , 212. [13] L. R. Chen, Design of duy-varied volage pulse charger for improving Li-ion baery-charging response, IEEE Transacions on Indusrial Elecronics, vol. 56, no. 2, pp , 29. [14] Y. C. Chuang and Y. L. Ke, High efficiency baery charger wih a buck zero-curren-swiching pulse-widh-modulaed converer, Ineracive Elecronic Technical Specificaion, vol. 1, pp , 28. [15] L. R. Chen, C. M. Young, N. Y. Chu, and C. S. Liu, Phaselocked bidirecional converer wih pulse charge funcion for 42-V/14-V dual-volage PowerNe, IEEE Transacions on Indusrial Elecronics, vol. 58, no. 5, pp , 211. [16] J. Yun, H.-J. Choe, Y.-H. Hwang, Y.-K. Park, and B. Kang, Improvemen of power-conversion efficiency of a DC DC

15 Inernaional Journal of Phooenergy 15 boos converer using a passive snubber circui, IEEE Transacions on Indusrial Elecronics, vol. 59, no. 4, pp , 212. [17] C.. Gallo, F. L. Tofoli, and J.. C. Pino, passive lossless snubber applied o he CDC inerleaved boos converer, IEEE Transacions on Power Elecronics, vol. 25, no. 3, pp , 21. [18] C. Munoz, Sudy of a new passive lossless urn-off snubber, CIEP, pp , [19] B. R. Lin and H. Y. Shih, ZVS converer wih parallel connecion in primary side and series connecion in secondary side, IEEE Transacions on Indusrial Elecronics, vol. 58, no. 4, pp , 211. [2] T.-F. Wu, Y.-D. Chang, C.-H. Chang, and J.-G. Yang, Sofswiching boos converer wih a flyback snubber for high power applicaions, IEEE Transacions on Power Elecronics, vol. 27, no. 3, pp , 212. [21] Y.K.Luo,Y.P.Su,Y.P.Huang,Y.H.Lee,K.H.Chen,andW.C. Hsu, Time-muliplexing curren balance inerleaved currenmode boos DC-DC converer for alleviaing he effecs of righ-half-plane zero, IEEE Transacions on Power Elecronics, vol. 27, no. 9, pp , 212.

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