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电动车
充电器
研究
设计
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电动车充电器研究与设计,电动车,充电器,研究,设计
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Abstract-In order to reduce size of bidirectional DC-DC converter, conventional topologies using hard switching method operate with high frequency. As switching frequency is getting higher, switching loss is increased. Conventionally an auxiliary circuit is implemented by using soft switching method in order to overcome this drawback,. The switch of the auxiliary circuit, however, is operated as hard switching. In this paper, high efficient bi-direction DC-DC converter is proposed. The suggested auxiliary circuit consists of one resonant inductor and two capacitors. Loss reduction is induced from both switches since the switches operate under ZVS turn-on and off condition. Main characteristic of the proposed topology is not only operated with soft switching method but has simple structure. The efficiency of proposed bidirectional soft switching DC-DC converter is verified by experimental results. Index TermsBidirectional converter, soft switching, electric vehicles, distributed power system, non-isolated converter, zero-voltage-switching, high-efficiency, resonant networks. I. INTRODUCTIONDue to the rapidly increasing economy and enormous demand for energy, the global energy crisis has been aggravated. To deal with this energy problem, researches on environmental friendly system such as the electric vehicles and distributed power system 1-3 have been carried out. In these applications, an energy storage system like a battery system must be needed to save and use energy. Thus, a bidirectional DC-DC converter (BDC) which allows transfer power between two DC sources becomes an important topic of power electronics. The BDC is categorized into an isolated converter 4-6 and a non-isolated converter 7-8. The demands of BDC are smaller size, lighter weight and higher efficiency etc. In order to minimize the size of BDC, the switching frequency must be increased. However, the increase of switching frequency results in higher switching losses. To solve this problem, many soft switching technology that employ resonant networks widely used in the DC-DC converters. This paper proposes a high-efficiency bidirectional soft switching DC-DC converter (BSDC). The proposed converter is based on a bidirectional half-bridge type buck-boost topology. Compared to the half-bridge topology, it has added a resonant inductor, two resonant capacitors and two parallel capacitors. The proposed converter has no additional switch for soft switching of the main switch. The proposed converter can achieve zero voltage switching (ZVS) for all switches by using resonant circuit. This paper presents the BDCs operational principle and theoretical analysis in detail. A 3kW prototype has been implemented, and experimental results are given to verify the proposed BSDC. II. CONVENTIONAL CONVERTERThe half-bridge type BDC shown in Fig. 1 is made to operate with bidirectional power transfer The bidirectional converter is never turned-on simultaneously. Switch S1 is main switch while bidirectional converter is operated in boost mode, the main switch is S2 while that converter is operated in buck mode. Fig. 1. Conventional half-bridge type BDC.The disadvantage of this topology is the inductor current has lots of ripple with a high peak. This drawback is the cause of efficiency reduction in topology using hard switching. The following approach is the way to resolve that problem 8. 1)Reduce the turn-off loss using soft switching method. 2)Use the additional filter to input and output. 3)Decrease of ripple current using interleaved technique. 4)Use the resonant technique. 5)Use the auxiliary circuit to assist the switches to operate with soft switching as the ZVT converter. But these techniques are complex, costly and difficult to control. High-Efficiency Bidirectional Soft Switching DC-DC Converter Jun-Gu Kim*, Seung-Won Park*, Young-Ho Kim*, Yong-Chae Jung*, and Chung-Yuen Won* * School of Information and Communication Engineering, Sungkyunkwan University, South-Korea * Department of Electronic Engineering, Namseoul University, South-Korea 2905The 2010 International Power Electronics Conference978-1-4244-5393-1/10/$26.00 2010 IEEEIII. DESCRIPTION OF THE PROPOSED CONVERTERFig. 2 shows the proposed BSDC in this paper. Compared to Fig. 1, the auxiliary circuit consists of a resonant inductor, two resonant capacitors and two parallel capacitors. Through using these components, both switches are performed as ZVS turn-on or turn-off without switching loss. Fig. 2. Circuit configuration of the proposed BSDC.Proposed BSDC has two operation modes. Boost mode is that the BSDC transfers the power from VLow to VHigh, and the other mode(boost mode) is that BSDC. In the Boost mode, the switch S2 is operated as a main switch, and S1 is used as a auxiliary switch. On the other hand, the switch S1 is performed as a main switch, and S2is operated as an auxiliary switch in the Buck mode. When the current flows through anti-parallel diodes, both switches are turned on. Also, MOSFET has small conduction loss since its RDS(on) is low. Energy storable battery or Super-capacitor is used as VLow source. The voltage source, VHigh, is connected to the DC-Bus of power electronics system such as grid connected inverter. A. Boost Mode of Operation Fig. 3. Theoretical voltage and current for boost mode operation. Fig. 3 shows key waveforms of the proposed converter during the one switching period in boost mode. The one switching cycle is divided into 8 stages. It can be shown that the current pattern of ico2 is equal to that of iLr in the Fig. 3. Fig. 4 shows the stages of the operation. Fig. 4. Equivalent circuits of the proposed converter during one switching period at boost mode. 2906The 2010 International Power Electronics ConferenceMode 1 (t0tt1)When the gate signal of switch S2 is turned off, mode 1 is activated. While the switch S2 is turned off, the current used to flow through the switch, is started to flow through Cr2, and S2 is turned off during ZVS condition. Since the current flows through Cr1 as well, the flowing current makes switch S1 turning on with ZVS condition in mode 2. This mode is the first resonant mode, and following equations are presented. 11112( )cos()sin=+rrrrCrCoCoVtVVtZ IIt (1) 11222( )cos()sin=+rrrrCrCoCoVtVVtZ IIt (2) 2111( )()cossin=+CorrrLrrVitIIIttZ (3) Mode 2 (t1tt2)When the voltage of Cr2 is equal to that of VHigh, mode 2 is begun. The inductor current iL and resonant inductor current iLr flows along anti-parallel diode. When the switch S1 receives gate signal, the current flowing through the resonant inductor is decreased. The current of resonant redactor is represented as (4). This mode is finished when the current became zero. 12( )=+OLrrVittIL (4) Mode 3 (t2tt3)When the direction of resonant inductor current is changed due to the current flowing through main inductor, mode 3 is started. In mode 3, main inductor current is getting decreased, and it can be represented as (5). On the other hand, resonant inductor current is increased, and the corresponding equation (6) is given as well. When the amount of current iL and iLr becomes equal to each other, this mode is finished. 2( )=+OLVi ttIL (5) 1( )=OLrVittL (6) Mode 4 (t3tt4)Mode 4 is started when the amount of main inductor current iL is equal to that of resonant inductor current ILr.This mode is maintained until the gate signal of S1 is turned off. In this mode, when current is flowing through anti-parallel diode, switch S1 is turned on under ZVS condition. Output voltage is determined depending on the condition of gate signal. The equations (7) and (8) are corresponding to the main inductor current and resonant inductor current respectively. 2( )=+OLVi ttIL (7) 1( )=OLrVittL (8) Mode 5 (t4tt5)Mode 5 is the second resonant mode, and this mode is activated when the switch S1 is turned off. The current flowed along S1 passes through Cr1 when S1 is turned off. Therefore, switch S1 is turned off with zero voltage condition. The difference between mode 1 and mode 5 is the opposite direction of a resonant loop. Equations from (9) to (11) explain the voltage and current of each resonant component changed based on time. 11144( )cos()sin=+CrOOrrrrVtVVtZ IIt (9) 22144( )cos()sin=+CrOOrrrrVtVVtZ IIt (10) 1444( )()cossin=+OLrrrrrVitIIIttZ (11) Mode 6 (t5tt6)This mode begins when the voltage level of Cr1 is equal to that of VHigh. The current flows through anti-parallel diode due to the continuity of resonant inductor current. When turn-on gate signal is applied to switch S2, the switch is turned on under ZVS condition. 5( )=+INLrVi ttIL (12) 25( )=+OLrrrVittIL (13) Mode 7 (t6tt7)When the current level of main inductor is equal to that of resonant inductor, mode 7 is started. Since the switch S2 is in on-state, main inductor current is getting increased, and corresponding equation (14) is given. The resonant inductor current is decreased with the slope came from (15). When this mode is finished. 6( )=+INLrVi ttIL (14) 26( )=+OLrrrVittIL (15) 2907The 2010 International Power Electronics ConferenceMode 8 (t7tt8)From mode 6 to 8, main inductor current is increased with the slope of (16). The resonant inductor current is increased with opposite direction compared to previous mode, and corresponding equation is (17). When switch S2 is turned off, this mode is finished. 7( )=+INLrVi ttIL (16) 2( )=OLrrVittL (17) B. Buck Mode of Operation The buck mode operation, is also able to be classified into 8 stages like as boost mode operation. In order to compare buck mode with boost mode, voltage polarity and current direction are fixed because of an accuracy analysis of waveform. So, main inductor current flows continuously even its level is below zero. On the basis of zero current level, the current flows to the opposite direction compared with that of boost mode. Particularly, when the buck mode is analyzed, the role of switches are changed, but analysis method is similar to that of boost mode. In buck mode, switch S1 and S2 is operated as a main switch and auxiliary switch, respectively. Fig. 5 shows key waveforms of the proposed converter during the one switching period in buck mode. Fig. 5. Theoretical voltage and current for buck mode operation.It can be shown the current pattern of ico2 is equal to that of iLr in the Fig. 5. Fig. 6 shows the stages of the operation. Fig. 6. Equivalent circuits of the proposed converter during one switching period at buck mode. 2908The 2010 International Power Electronics ConferenceIV. EXPERIMENTAL RESULTSIn order to verify the performance of the proposed BSDC. The experimental set-up is implemented as shown in Fig. 7. Fig. 7(a) depicts the hardware of stand-along PVPCS without boost converter, and Fig. 7(b) shows proposed bi-directional topology. Fig. 7. Prototype of the proposed BSDC. Stand-alone PVPCS is required a bidirectional power conversion system and an energy storage system such as battery and super-capacitor. The system efficiency of energy conversion system is able to be improved through using proposed topology. Consider battery voltage, VLowwas set up 200V, and VHigh was set up 400V for DC-bus voltage as well. The capacity of main inductor L is 1mH, and the ferrite core is used. Resonant inductor Lr is a PQ core and its capacity is 60uH. ICEL companys 10uF and 5uF capacitors are used as resonant capacitors, Cr1, Cr2, Co1 and Co2respectively. Power switch is IFN70N60Q2 made by IXYS. Peripheral circuit implies gate drive and sensor circuit. Bidirectional converters switching frequency is 30kHz. On the basis of boost mode experiment, each mode was compared with fixed voltage polarity and current direction. Fig. 8 shows the waves of bidirectional converter under boost mode, and Fig. 11 corresponds to the voltage and current waves of the converter under buck mode. Depends on the switch condition, iL was increased or decreased as well, and the current was continuous. The current waveform is shown in Fig. 8(a). Resonant inductor current iLr, was alternated based on 0A. The current and voltage of main switch is shown in Fig. 8(b). Switch was turned off under ZVS condition, and the wave can be shown in the enlarged figure. Also, when current is flowing through anti-parallel diode, S2 received gate signal to be ZVS turn-on. Fig. 8(c) shows voltage and current waves of an auxiliary switch. TABLE 1. EXPERIMENTAL PARAMETERS.Symbol Meaning Value PPower 3kW LMain Inductor 1mH LrResonant Inductor 60uH Cr1, Cr2Resonant Capacitor 10nF VHighHigh-side Voltage 400V VLowLow-side Voltage 200V fswSwitching Frequency 30kHz (a) Measured waveforms of inductor and resonant inductor current. (b) Measured drain voltage and current of main switch. (c) Measured drain voltage and current of auxiliary switch. Fig. 8. Boost mode of operation. 2909The 2010 International Power Electronics Conference(a) Measured waveforms of inductor and resonant inductor current. (b) Measured drain voltage and current of main switch. (c) Measured drain voltage and current of auxiliary switch. Fig. 9. Buck mode of operation. In the buck mode, the current waves of L and Lr are shown in Fig. 9(a). Compared to boost mode, because the direction of L and Lrcurrent is opposite, it was confirmed that current polarity was changed. Fig. 9(b) and (c) shows the voltage and current waves of switch respectively. Similar to boost mode, both switches were turned on and off under ZVS condition. Although the role of both switches S1 and S2 was altered, its wave form was similar to that of Fig. 9(b) and (c). Fig. 10. Experimental efficiency graph. The efficiency graphs of conventional half-bridge type BDC and BSDC are presented in Fig. 10. The efficiency was measured by WT-3000. In order to measure the efficiency of proposed converter under same condition with conventional converter, the proposed converters efficiency was measured first. Then, the utility factor of half-bridge type BDC was measured. With the lowest capacity light load, the minimum efficiency was 88%, and as the capacity of load was getting higher, the utility factor was getting increased. Compared with conventional converter, it is shown that the proposed BSDC has a high efficiency as shown in Fig. 10. Proposed converter has a higher efficiency than any other converters mentioned other papers. In boost mode, maximum 97.6% efficiency is obtained and 97.48% efficiency can be acquired in the buck mode as well. V. CONCLUSIONThis paper proposes a high-efficiency bidirectional soft switching DC-DC converter. The proposed converter is based on a bidirectional half-bridge type buck-boost topology. Compared to the half-bridge topology, it has a resonant inductor, two resonant capacitors and two parallel capacitors additionally. The proposed converter has no additional switch for soft switching of the main switch. The proposed converter can achieve zero voltage switching for all switches by using resonant circuit. Proposed converter Can achieve higher efficiency than any other converters mentioned in the other papers. In Boost Mode, maximum 97.6% efficiency rate is obtained and 97.48% efficiency can be acquired in the buck mode as well. 808284868890929496981003006009001200150018002100240027003000Efficiency(%)Power (W)Proposed BSDC -BoostConventional BDC - BoostProposed BSDC -BuckConventional BDC - Buck2910The 2010 International Power Electronics ConferenceVI. ACKNOWLEDGMENTThis work is outcome of the fostering project of the Spec
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