(2) The resonant inductor current i Lr can be defined as, II. PROPOSED CONVERTER

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1 A High Powe Density Soft Switching Bidiectional Convete Using Unified Resonant Cicuit Ratil H Ashique, Zainal Salam, Mohd Junaidi Abdul Aziz Depatment of Electical Engineeing, Univesity Technology Malaysia, Joho Bahu, Malaysia atil.eee05@gmail.com Abstact This pape poposes a high efficiency bi-diectional convete with high powe handling capability. Soft switching technique is endowed with all powe switches by using an auxiliay unified esonant cicuit. Zeo voltage switching (ZS) and zeo cuent switching (ZCS) modes ae implemented fo all powe switches in boost opeation. Fo buck mode of opeation, ZS and ZCS ae executed fo most of the powe switches. oltage stesses fo all of the powe switches ae significantly educed. Additionally, the poposed convete has a high step up and step down gain compaed to a conventional bi-diectional convete. The cicuit is simulated in PSPICE and pefomance paametes ae measued and veified. Keywods Bi-diectional convete(bdc), zeo voltage switching(zs), zeo cuent switching(zcs), zeo voltage tansition(zt). I. INTRODUCTION BDC s have thei access today fom home UPS to moden spacecaft systems. Being an insepaable and obligatoy pat of the enegy stoage systems of apid gowing FCE, HE and E s aound the wold, BDC s ae equied to shape fo high gain, high efficiency and high powe density to adopt the coming futue. Reseaches widely investigated isolated and non-isolated bi-diectional convetes pimaily fo high gain and high efficiency [1-8]. In non-isolated class of BDC s, multilevel concept and coupled inducto based designs ae adopted to attain a vey high gain cicuit [9-13]. Soft switching techniques ae applied in a lage numbe of isolated and non-isolated designs to build vey high efficiency cicuits. Howeve high efficiency non-isolated cicuits having high powe densities ae aely poposed. This pape poposes a soft switching high efficiency non-isolated bidiectional convete which is capable of handling lage amount of powe. As an added advantage, the step up and step down gain fo the poposed cicuit is also highe than the conventional BDC. II. PROPOSED CONERTER A. Configuation and Opeation The poposed convete is a modified vesion of conventional ZT convete. The modification is intoduced in tems of high powe handling capability and implementing soft switching technique. The efficiency is inceased significantly compaed to a conventional BDC. Fou powe switches MS1-MS4 and five auxiliay low powe switches AS1-AS5 ae used in the design. A sub-cicuit A shown in Fig.1 is utilized in the buck mode of opeation to educe voltage stess on switches MS3 and MS4. The sub-cicuit is futhe utilized in achieving soft switching conditions fo MS1 and MS2 in the buck mode of opeation. The esonance between esonant inducto L and C a ae utilized to execute ZS switching of MS1 and MS2. On the othe hand, C b is designed to esonate with L to achieve ZCS switching of MS3 and MS4. B. Boost Mode In boost mode of opeation the auxiliay switches AS4 and AS5 ae pemanently off and the sub-cicuit A in Fig.1 has no effect in the cicuit opeation. Hence A is omitted in the following boost mode opeational states analysis. The PWM switching of the powe and auxiliay switches ae shown in Fig.2. 1) Mode 1(t0-t1): The esonant capacito is full chaged at the beginning of this mode. This mode stats with tuning on the switch AS1 in the esonant cicuit. The esonant inducto cuent i 1 inceases until it becomes equal to the inducto cuent i L.The esonant cuent ciculates between the esonant inducto and esonant capacito. Hence the voltage acoss the switches MS1 and MS2 becomes zeo at the end of this state and the switches can be tuned on at ZS condition. The inducto cuent i L inceases maintaining the slope di/dt as in equation (2). The body diodes of switches MS1 and MS2 ae tuned on at the end of this state caying the esidue of esonant inducto cuent i L. The state of the esonant capacito (C ) voltage at t 1 and inducto cuent (i L ) ae chaacteized in the equations (1) and (2) espectively. The esonant fequency can be obtained fom equation (5). The snubbe capacitos will dischage to zeo though this mode. C (1) L C The esonant inducto cuent i L can be defined as, Fig.1. Poposed bi-diectional convete (2)

2 i L Fig.2. PWM switching of boost mode of opeation il + fl The esonant capacito cuent i C is opposite to the inducto cuent i L and can be defined as, (4) Ca ic fc f a 1 L C a 2) Mode 2(t1-t2): Duing this shot peiod the switch snubbe capacitances CS1 and CS2 ae dischaged though the body diodes of MS1 and MS2 to futhe assist ZS switching. 3) Mode 3(t2-t3): At t 2, the switches MS1 and MS2 ae tuned on in ZS condition. The inducto cuent i L inceases to the end of this mode. To futhe assist smooth tansition, the switches MS1 and MS2 ae suppoted by snubbe capacitances CS1 and CS2.The voltage acoss the esonant capacito emains zeo in this mode. At the end of this mode the switch MS1 and MS2 ae tuned off. The slope of the cuent i L can be defined by the following equation, dil (6) L 4) Mode 4(t3-t4): This mode epesents a shot time peiod in between the switching of main and auxiliay switches. The inducto cuent (i L ) is positive. Resonant capacito (C ) along with snubbes CS1 and CS2 ae chaged in this mode. The slope of i L is inceasing and can be descibed as in (7). (7) Ca 5) Mode 5(t4-t5): (3) (5) Switches AS1 and AS2 ae tuned on at t 4 to stat this mode. Consequently, the esonant cuent stats to flow in between the esonant inducto (L ) and esonant capacito (C ).The powe switch MS3 expeiences zeo voltage dop at the end of this mode. Hence a ZS condition fo MS3 is achieved. The esonant cuent (i ) can be descibed in equation (3) and (4). At t 5, AS1 and AS2 ae tuned off to end this mode. The inducto cuent continues to incease accoding to (6). Snubbe capacitos CS3 and CS4 ae chaged wheeas CS1, CS2 along with the esonant capacito C ae dischaged at the end of this mode. 6) Mode 6(t5-t6): This mode povides a dead time in between the switching of AS1, AS2 and MS3.The dead time is povided to assist the ZS switching of MS3.The inducto cuent continues to incease accoding to equation (6).CS1,CS2 ae chaged in contay to the dischaging of CS3 and CS4 at t 6. 7) Mode 7(t6-t7): At t 6, switch MS3 is tuned on in ZS condition. The auxiliay switch AS3 is also tuned on simultaneously to activate the seconday esonant cicuit. Resonant cuent stats to flow in between L and C b. CS1 and CS2 ae dischaged at the end of this mode. CS4 ae chaged to assist ZS switching of MS4 at t 7. At t 7, AS3 is tuned off. The esonant cuent i L can be expessed as in equation (8). (8) Cb il fl 8) Mode 8(t7-t8): This mode stats by tuning on MS4 in ZS condition. The slope of inducto cuent becomes negative and can be defined as, (9) OUT Whee, i o is the output cuent and C is the integal constant. CS1 and CS2 ae chaged in this mode. 9) Mode 9(t8-t9): In this shot time peiod, switch AS1 is tuned on to enegize esonant inducto L and esonant capacito C b. This mode ends by tuning off AS1. Inducto cuent emains constant in this mode. 10) Mode 10(t9-t10): Fo ZCS switching of MS3 and MS4 the switch AS3 is tuned on at t 8 to attain a esonance among the snubbe capacitos CS1-CS4, esonant capacito C b and esonant inducto L. L is enegized and C b is chaged by the dischaging of capacitos CS1 and CS2 though the gate diodes of MS1 and MS2. CS4 is also chaged along with C b. The esonant fequency in this mode is geneally highe than that in mode 1.The esonant cuent (i ) though L is defined in (8). This mode ends by tuning off the switches MS3, MS4 at t 8 in ZCS condition. The switch AS2 is tuned off slightly befoe MS3 and MS4.The slope of inducto cuent i L emains negative as in the pevious mode. 11) Mode 11(t10-t11): A dead time (t10-t11) is inseted in this mode. The snubbe capacitos CS1 and CS2 ae chaged to assist ZS switching

3 of MS1 and MS2 in mode 1. The gate diodes of MS3 and MS4 ae on and CS3 and CS4 ae dischaged at the end of this mode. (g) Mode 7 (a) Mode 1 (h) Mode 8 (b) Mode 2 (i) Mode 9 (c) Mode 3 (j) Mode 10 (d) Mode 4 (k) Mode 11 (e) Mode 5 (l) Mode 12 Fig.3. Opeational states fo boost mode (f) Mode 6 C. Buck Mode: In buck mode of opeation the sub-cicuit A is activated and diection of powe flow is evesed. PWM switching of the switches ae shown in Fig.4. The opeational states of the cicuit in Fig.5 ae descibed below. 1) Mode 1(t0-t1):

4 Fig.4. PWM switching in buck mode of opeation At t0 the auxiliay switch AS1 and AS2 is tuned on. The esonant cuent stats to flow in L and C a. The body diodes of MS1 and MS2 ae tuned on and the slope of inducto cuent i L is negative and can be defined as in equation (10). At the end of this mode Auxiliay switches ae tuned off. OUT (10) 2) Mode 2(t1-t2): This mode epesents a dead time between t1 and t2. The time diffeence is kept extemely shot aound 0.2% of switching time T S. The body diodes of MS1 and MS2 ae tuned off. The inducto cuent deceases as in the pevious mode. 3) Mode 3(t2-t3): At t3, MS3 is tuned on in ZS condition. The auxiliay switch AS5 is also tuned on simultaneously with MS3. A small cuent flows though the esisto R1 intoducing a small voltage dop acoss R1. The inducto cuent deceases having a negative slope as in (10). 4) Mode 4(t3-t4): This mode stats by tuning on MS4 at t3. The inducto cuent continues to incease accoding to the slope in (11). The snubbe capacitos CS1 and CS2 ae chaged. H (11) OUT 5) Mode 5(t4-t5): In this shot time peiod the esonant inducto is enegized by tuning on AS1. At the end of this mode AS1 is tuned off. i L continues to incease as in the pevious mode. 6) Mode 6(t5-t6): At t6, auxiliay switch AS3 is tuned on. The esonant cuent flows in between L and C b. At the end of this mode MS3 and MS4 is tuned off in ZCS condition. 7) Mode 7(t6-t7): A dead time is inseted in this mode. The body diode of MS4 is tuned on and CS3 is chaged. The slope of inducto cuent i L becomes negative as in (12). Ca (12) OUT 8) Mode 8(t7-t8): AS1 is tuned on at the beginning of this mode. Resonant cuent flows in between L and C a to facilitate ZS switching of MS1 and MS2. The gate diodes of MS1, MS2 ae on and CS1 and CS2 ae dischaged. 9) Mode 9(t8-t9): At the beginning of this mode C a is dischaged along with CS1 and CS2. 10) Mode 10(t9-t10): MS1 and MS2 ae tuned on at t9. The inducto cuent stats to decease at the end of this mode accoding to (10). 11) Mode 11(t10-t11): At t10, body diodes of MS1, MS2 and MS3 ae tuned on. CS3 is dischaged though the body diode of MS3. CS4 is chaged in this shot time peiod. Inducto cuent continues to decease. (a) Mode 1 (b) Mode 2 (c) Mode 3 (d) Mode 4

5 (k) Mode 11 Fig.5. Opeational states fo buck mode (e) Mode 5 (f) Mode 6 (g) Mode 7 (h) Mode 8 (i) Mode 9 (j) Mode 10 III. SIMULATION RESULTS The cicuit is simulated in PSPICE and pefomance paametes ae measued. The specifications and value of the cicuit paametes ae tabulaized in TABLE I fo the simulation. The summaized switching and voltage stess conditions of the switches fo boost and buck mode of opeation is shown in TABLE II. In Fig.6 and Fig.7 the voltage and cuent at vaious switching states fo boost and buck mode of opeation ae shown. TABLE I. CIRCUIT PARAMETERS BOOST/BUCK MODE PARAMETER ALUE f S(switching fequency) 100KHz f (esonant fequency) 200KHz D1,D2,D3,D4,D5(boost mode) 0.05,0.30,0.05,0.02,0.5 D1,D2,D3,D4(buck mode) 0.1,0.5,0.05,0.3 L/ OUT 50/100 I OUT 10 A H/ OUT 50/20 I OUT 40A L 500uH L 0.8uH C a 800nF C b 800nF C1 50uF C2 100uF R1 50Ω. TABLE II. SWITCHING STATES BOOST MODE SWITCH STATE OLTAGE STRESS MS1 ZS,ZCS Reduced MS2 ZS,ZCS Reduced MS3 ZS,ZCS Reduced MS4 ZS,ZCS Reduced BUCK MODE MS1 ZS,ZCS Reduced MS2 ZS,ZCS Reduced MS3 ZS,ZCS Lagely educed MS4 - Lagely educed

6 (a) (b) (c) Fig.6.Switching at boost mode (a) MS1/MS2 (b) MS3 (c) MS4 (a) (b) Fig.7. Switching at buck mode(a) MS1/MS2 (b) MS3 As evident fom Fig.6, Fig.7 and TABLE II, switches MS1 and MS2 have ZS and ZCS mode of switching fo both boost and buck mode of opeation. ZS and ZCS switching ae also possible fo switch MS3 in both mode of opeations. In addition, fo all powe switches MS1-MS4, the voltage stess is educed moe than 50% compaed to a conventional bidiectional convete. I. CONCLUSION The poposed convete is capable of handling vey high powe compaed to a conventional ZT bidiectional convete. In addition, the switching stess fo the powe switches ae educed lagely compaed to a conventional bidiectional convete. ZS and ZCS mode of opeation fo all powe switches ae achieved in boost mode of opeation. Fo buck mode of opeation ZS and ZCS ae achieved fo MS1, MS2 and MS3. A moe detail expeimental analysis will be pesented in anothe vesion of this pape in nea futue. ACKNOWLEDGMENT The authos wish to acknowledge the Ministy of Education Malaysia (MOE) fo poviding the eseach fund unde the Reseach Univesity Gant Scheme, ote Numbe Q.J G11. The gant is managed by the Reseach Management Cente, Univesiti Teknologi Malaysia, Joho Bahu, Malaysia. REFERENCE [1] A. Mizaei, A. Jusoh, Z. Salam, E. Adib, and H. Fazanehfad, "A novel soft switching bidiectional coupled inducto Buck-Boost convete fo battey dischaging-chaging," in Applied Powe Electonics Colloquium (IAPEC), 2011 IEEE, 2011, pp [2] M. Ahmadi, M. R. Mohammadi, E. Adib, and H. Fazanehfad, "Family of non-isolated zeo cuent tansition bi-diectional convetes with one auxiliay switch," Powe Electonics, IET, vol. 5, pp , [3] E. Adib and H. Fazanehfad, "Soft switching bidiectional DC DC convete fo ultacapacito batteies inteface," Enegy Convesion and Management, vol. 50, pp , [4] M. R. Mohammadi and H. Fazanehfad, "New family of zeovoltage-tansition PWM bidiectional convetes with coupled inductos," Industial Electonics, IEEE Tansactions on, vol. 59, pp , [5] E. Adib and H. Fazanehfad, "Family of zeo cuent zeo voltage tansition PWM convetes," IET Powe Electonics, vol. 1, pp , [6] Z. Salam, A. Aziz, and M. Junaidi, "The Design and Development of a High Pefomance Bi-diectional Invete Fo Photovoltaic Application," [7] Z. Salam, M. Ramli, L. Toh, and C. Nge, "An isolated bidiectional invete using high fequency cente-tapped tansfome," in Powe Electonics, Machines and Dives, 2004.(PEMD 2004). Second Intenational Confeence on (Conf. Publ. No. 498), 2004, pp [8] M. Mahdavi, A. Emani, and H. Fazanehfad, "A new zeo cuent switching esonant Buck convete," in 2011 Intenational Confeence on Applied Electonics, ed, [9] L. Matinez-Salameo, J. Calvente, R. Gial, A. Poveda, and E. Fossas, "Analysis of a bidiectional coupled-inducto Cuk convete opeating in sliding mode," Cicuits and Systems I: Fundamental Theoy and Applications, IEEE Tansactions on, vol. 45, pp , [10] R.-Y. Duan and J.-D. Lee, "High-efficiency bidiectional DC-DC convete with coupled inducto," Powe Electonics, IET, vol. 5, pp , [11] R.-J. Wai and R.-Y. Duan, "High step-up convete with coupledinducto," Powe Electonics, IEEE Tansactions on, vol. 20, pp , [12] Y.-P. Hsieh, J.-F. Chen, L.-S. Yang, C.-Y. Wu, and W.-S. Liu, "High-convesion-atio bidiectional dc dc convete with coupled inducto," Industial Electonics, IEEE Tansactions on, vol. 61, pp , [13] P. Das, S. A. Mousavi, and G. Moschopoulos, "Analysis and design of a nonisolated bidiectional ZS-PWM DC DC convete with coupled inductos," Powe Electonics, IEEE Tansactions on, vol. 25, pp , 2010.

A New Buck-Boost DC/DC Converter of High Efficiency by Soft Switching Technique

A New Buck-Boost DC/DC Converter of High Efficiency by Soft Switching Technique A New Buck-Boost D/D onvete of High Efficiency by Soft Switching Technique Dong-Kul Kwak, Seung-Ho Lee, and Do-Young Jung Pofessional Gaduate School of Disaste Pevention, Kangwon National Univesity, 45-711,