Design and Control Method of ZVT Interleaved Bidirectional LDC for Mild-Hybrid Electric Vehicle

Abstract

In this paper, design and control method ZVT Interleaved Bidirectional LDC(IB-LDC) for mild-hybrid electric vehicle is proposed. The IB-LDC is composed of interleaved buck and boost converters employing an auxiliary inductor and auxiliary capacitors to achieve zero-voltage-transition. Operating principle of IB-LDC according to operation mode is introduced and mathematically analyzed in buck and boost mode. Moreover, PFM and phase control are proposed to reduce circulating current for low power range. Passive components design such as main inductor, auxiliary inductor and capacitors is suggested, considering ZVT condition and maximizing efficiency. Furthermore, a 600W prototype of ZVT IB-LDC for MHEVs is built and tested to verify validity.

Fig. 1. Speed profile of vehicle in urban area

Fig. 2. IB-LDC for MHEVs

Fig. 3. Equivalent circuit diagrams of buck and boost mode

Fig. 4. Key waveforms of buck mode operation

Fig. 5. Key waveforms of boost mode operation

Fig. 6. Waveform of the auxiliary inductor and outputcurrent

Fig. 7. Switching frequency variation depending on dutyand output power

Fig. 8. Key waveforms of zero-current mode

Fig. 9. Equivalent circuit diagrams of zero-current mode

Fig. 10. Control block diagram of ZVT IB-LDC forMHEVs

Fig. 11. Inductance variation with respect to fs

Fig. 12. Current waveforms of main and auxiliary inductor

Fig. 13. Switch of current and voltage

Fig. 14. Resonant voltage variation depending on La and Ca

Fig. 15. The switching loss of ZVT IB-LDC

Fig. 16. The current shape flowing the switches

Fig. 17. The ratio of loss in MOSFET switches

Fig. 18. Experimental set for ZVT IB-LDC

Fig. 19. Experimental waveforms in buck mode operation.(a) Gate signals G1 and G2, switch currents is1 andis2. (b) Gate signals Vgs1 and Vgs2, switch voltagesvs1 and vs2. (c)Gate signal Vgs1, switch voltage vs1,output current IL1 and auxiliary inductor currentiLa. (d) Output currents IL1, IL2 and current ofauxiliary inductor iLa

Fig. 20. Experimental waveforms in boost mode operation.(a) Gate signals G1 and G2, switch currents is1 andis2. (b) Gate signals Vgs1 and Vgs2, switch voltagesvs1 and vs2. (c) Gate signal vgs1, switch voltage vs1,output current IL1 and auxiliary inductor currentiLa. (d) Output currents IL1, IL2 and current ofauxiliary inductor iLa

Fig. 21. Experimental waveforms in zero-current operation.(a) Zero-current mode without phase control. (b)Zero-current mode with phase control

Fig. 22. Measured efficiency at different output powers

Fig. 23. The losses of conventional IB-LDC

Fig. 24. The losses of ZVT IB-LDC with PFM

Fig. 25. The total loss of conventional and ZVT IB-LDCwith PFM

Table 1. Experiment parameters