A Reduced Component Count Single-stage Electrolytic Capacitor-less Battery Charger with Sinusoidal Charging

Transcription

1 A Reduced Component Count Single-stage Electrolytic Capacitor-less Battery Charger with Sinusoidal Charging Byeongwoo Kim, Minjae Kim and Sewan Choi Department of Electrical and Information Engineering Seoul National University of Science and Technology Seoul, Korea Contact Abstract This paper proposes a new single-stage electrolytic capacitor-less ac-dc converter with sinusoidal charging for Etery chargers. The proposed converter has simple circuit structure with reduced component count. It achieves ZVS turn-on of all switches and ZCS turn-off of all diodes. Requiring no input filter due to CCM operation and bulky electrolytic capacitors, and having no low frequency component in the transformer the proposed converter is able to achieve high power density. A 2-kW prototype of the proposed converter has been built and tested to verify the validity of the proposed operation. Keywords single-stage; battery charger; on-board charger; EV charger; electrolytic capacitor-less; I. INTRODUCTION On-board battery chargers, considered as a critical equipment in driving range extension of electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs), should have high efficiency and high power density because of limited space and high fuel economy requirements[1]. In general, the on-board charger has two-stage structure composed of an ac-dc converter for power factor correction (PFC) and an isolated dc-dc converter for battery charge [2]- [4]. The two-stage structure has advantages of wide line regulation and high power factor, but has limitations in improving efficiency due to double power conversion and reducing cost due to high component count. Several singlestage structures [5]-[8] have been proposed for some low power applications where PFC circuit and isolated dc-dc converter are integrated to possibly achieve cost reduction and efficiency improvement. In the meanwhile, dc-link electrolytic capacitors are not considered suitable as an automotive part due to large volume and short life expectancy. It was reported in [9] [11] that low frequency ripple currents do not have an obvious adverse effect on efficiency and lifetime of the lithium-ion batteries. Several electrolytic capacitor-less single-stage structures with sinusoidal charging have been proposed for the lithium-ion battery charger where low frequency ripple is allowable at the output [12]-[13]. Electrolytic capacitor-less single-stage structure based on DCM operation eliminate low frequency components in the transformer. But, the aforementioned electrolytic capacitor-less single-stage structures have not only cost of high component count but also high conduction losses at the DCM operation. Hence is not suited to high power application. This paper proposes a new single-stage electrolytic capacitor-less ac-dc converter with sinusoidal charging for Etery chargers. The proposed converter has the following features: 1) simple circuit structure with reduced component counts while providing interleaving effect; 2) small conduction losses and no input filter required due to CCM operation; 3) elimination of low frequency component in the transformer; 4) removal of bulky electrolytic capacitor; 5) ZVS turn-on of all switches and ZCS turn-off of all diodes; 6) simple control with soft start-up capability. A 2- kw prototype of the proposed converter has been built and tested to verify the validity of the proposed operation. II. PROPOSED CONVERTER A. Circuit Configuration Fig. 1 shows the circuit diagram of the proposed singlestage interleaved soft-switching on-board battery charger. The primary side circuit of the proposed converter acts as not only ac-dc converter for PFC but primary circuit of the isolated dc-dc converter. Two current-fed half-bridge converters are interleaved in such a way that the twice fundamental frequency component generated from the grid side is cancelled and does not appear at the primary winding voltage and current of the transformer, thereby making the magnetizing current small unlike the conventional singlestage AC-DC converter [11]-[12]. A small film capacitor is used to clamp voltage spikes caused by leakage inductance of the transformer. Fig 1. Circuit diagram of the proposed converter.

2 1:n Fig 2. Operational waveforms and operating states of the proposed converter. Fig 3. Voltage and current waveforms and harmonic amplitude spectra.

3 B. Operational Principle Fig.2 shows operational waveforms and operating states of the proposed converter during positive half cycle of the grid voltage. The operation of the proposed converter can be divided into five modes, as shown in Fig. 2. Two interleaved half bridge converters are operated with 180 degree phase shift each other in order to reduce the input current ripple. Fig. 3 shows the principle of eliminating the low frequency component in the transformer. The gate signals for switches are obtained by comparing reference voltage v r with carrier signal v tri. The duty cycles of switches are varied to shape the grid current into sinusoidal waveform, and at the same, to convert capacitor voltage v to chopped voltages v ag and v bg. It is seen from the harmonic spectra that transformer primary voltage v ab does have only switching frequency component while voltages v ag and v bg do have both low and switching frequency components, which results in small magnetizing current. The transformer primary voltage v ab is sum of two voltage v ag and v bg and its low frequency component becomes zero, as follows, feedforward (FFD) control is used to increase the inner loop gain at 120 Hz, and a start-up duty is added to achieve soft start-up without large overshoot. Fig. 5 shows the soft startup waveform of the proposed converter. v pri,2 (t) = v ag,2 (t) + v bg,2 (t) (1) α + β = χ. (1) (1) A small film capacitor Co is used to absorb high frequency switching ripple component of rectified current i rec, thereby injecting sinusoidal like current into the battery. It is also seen from Fig. 3 that the proposed converter achieves ZVS turn on of all switches and ZCS turn off of all diodes. In fact, the soft switching can be achieved under the whole voltage and load range by proper design of magnetizing inductance of the transformer. The reference voltage v r is expressed by the following equation, Vm vr () t = 1 sin( ωt) (2) Fig 5. α Start-up + β = waveform χ. of (1) the proposed (1) converter. Vbat III. EXPERIMNETAL RESULTS C. Control Algorithm Fig. 4 shows the control block diagram of the proposed converter which is almost the same as that of conventional PFC with CC-CV charging. It consists of an outer double loop controller for CC-CV charging and an inner loop current controller. Due to absence of the dc link voltage control the proposed converter saves one sensor and one compensator compared to the two-stage battery charger. A Fig 4. Control block diagram of the proposed converter with start-up duty To verify the operating principle of the proposed converter, a 2kW prototype was built according to the following specification: P o =2kW, V g =220VAC, =400V, n p :n s =1:1, f s =50kHz,, =350μH, =20μH, C C =45uF and =20uFFig. 5 shows the experimental waveforms of the proposed converter. Fig. 6(a) shows the proposed converter achieves the soft start-up waveform. It can be seen from Fig. 6(a) that the input current, input voltage and output voltage has no large overshoot. Fig. 6(b) shows that the input current is almost sinusoidal and in phase with the input voltage. Fig. 6(c) shows the transformer voltage and FFT waveform, it is seen from FFT of primary winding voltage of the transformer that low frequency component is absent in the transformer. It can be seen from Fig. 6(d), 6(e) and 6(f) that the proposed converter achieves ZVS turn on of switches and ZCS turn off of diodes. The measured power factors and efficiencies according to the load variation are shown in Fig. 7. The power factor and efficiency are measured using Yokogawa WT3000. The maximum power factors are 0.99 at 1.8kW and 0.98 at 2kW. The maximum efficiency is 94.5% at 2kW.

4 Fig 6(a). Soft start-up waveform Fig 6(b). Input current, input voltage and output voltage Fig 6(d). Switch S1 current and voltage Fig 6(e). Switch S2 current and voltage Fig 6(f). Diode D5 and D6 current and voltage Fig 6(c). Transformer voltage and FFT waveform

5 Fig 7(a). Measure power factor of the proposed converter Fig 7(b). Measure efficiency of the proposed converter IV. CONCLUSION In this paper, a new single-stage electrolytic capacitorless ac-dc converter with sinusoidal charging for Etery chargers is proposed. The proposed converter has simple circuit structure with reduced component count while providing interleaving effect at the input. It can be designed to achieve ZVS turn-on of all switches and ZCS turn-off of all diodes without regard to voltage and load variation. The proposed converter does not require input filter and bulky electrolytic capacitors. Also, in spite of single stage structure the transformer does not have low frequency component. Therefore, the proposed battery charger is able to achieve high power density. Experimental results from a 2kW prototype are provided to validate the proposed concept. The maximum power factors are 0.99 at 1.8kW and 0.98 at 2kW. The maximum efficiency is 94.5% at 2kW. Hybrid Vehicles," in IEEE Transactions on Power Electronics, vol. 28, no. 5, pp , May J. Clerk Maxwell, A Treatise on Electricity and Magnetism, 3rd ed., vol. 2. Oxford: Clarendon, 1892, pp [2] D. S. Gautam, F. Musavi, M. Edington, W. Eberle and W. G. Dunford, "An Automotive Onboard 3.3-kW Battery Charger for PHEV Application," in IEEE Transactions on Vehicular Technology, vol. 61, no. 8, pp , Oct K. Elissa, Title of paper if known, unpublished. [3] B. Singh, B. N. Singh, A. Chandra, K. Al-Haddad, A. Pandey and D. P. Kothari, "A review of single-phase improved power quality AC- DC converters," in IEEE Transactions on Industrial Electronics, vol. 50, no. 5, pp , Oct Y. Yorozu, M. Hirano, K. Oka, and Y. Tagawa, Electron spectroscopy studies on magneto-optical media and plastic substrate interface, IEEE Transl. J. Magn. Japan, vol. 2, pp , August 1987 [Digests 9th Annual Conf. Magnetics Japan, p. 301, 1982]. [4] T. H. Kim, S. J. Lee and W. Choi, "Design and control of the phase shift full bridge converter for the on-board battery charger of the electric forklift," Power Electronics and ECCE Asia (ICPE & ECCE), 2011 IEEE 8th International Conference on, Jeju, 2011, pp [5] R. Zhang and H. S. h. Chung, "A TRIAC-Dimmable LED Lamp Driver With Wide Dimming Range," in IEEE Transactions on Power Electronics, vol. 29, no. 3, pp , March [6] S. Dusmez, X. Li and B. Akin, "A Fully Integrated Three-Level Isolated Single-Stage PFC Converter," in IEEE Transactions on Power Electronics, vol. 30, no. 4, pp , April [7] Jung-Goo Cho, Chang-Yong Jeong, Hong-Sik Lee and Geun-Hie Rim, "Novel zero-voltage-transition current-fed full-bridge PWM converter for single-stage power factor correction," in IEEE Transactions on Power Electronics, vol. 13, no. 6, pp , Nov [8] W. Y. Choi, "Single-stage battery charger without full-bridge diode rectifier for light electric vehicles," in Electronics Letters, vol. 47, no. 10, pp , May [9] M. Uno and K. Tanaka, "Influence of High-Frequency Charge Discharge Cycling Induced by Cell Voltage Equalizers on the Life Performance of Lithium-Ion Cells," in IEEE Transactions on Vehicular Technology, vol. 60, no. 4, pp , May [10] L. R. Chen, S. L. Wu, D. T. Shieh and T. R. Chen, "Sinusoidal- Ripple-Current Charging Strategy and Optimal Charging Frequency Study for Li-Ion Batteries," in IEEE Transactions on Industrial Electronics, vol. 60, no. 1, pp , Jan [11] M. Kwon, S. Jung and S. Choi, "A high efficiency bi-directional EV charger with seamless mode transfer for V2G and V2H application," 2015 IEEE Energy Conversion Congress and Exposition (ECCE), Montreal, QC, 2015, pp [12] S. Li, J. Deng and C. C. Mi, "Single-Stage Resonant Battery Charger With Inherent Power Factor Correction for Electric Vehicles," in IEEE Transactions on Vehicular Technology, vol. 62, no. 9, pp , Nov [13] J. Y. Lee, Y. D. Yoon and J. W. Kang, "A Single-Phase Battery Charger Design for LEV Based on DC-SRC With Resonant Valley- Fill Circuit," in IEEE Transactions on Industrial Electronics, vol. 62, no. 4, pp , April [14] Byeongwoo Kim, Minjae Kim and S. Choi, "Single-stage electrolytic capacitor-less AC-DC converter with high frequency isolation for EV charger," 2016 IEEE 8th International Power Electronics and Motion Control Conference (IPEMC-ECCE Asia), Hefei, China, 2016, pp REFERENCES [1] M. Yilmaz and P. T. Krein, "Review of Battery Charger Topologies, Charging Power Levels, and Infrastructure for Plug-In Electric and