A novel low-loss control strategy for bidirectional DC-DC converter

Bidirectional DC-DC converter with phase-shift control is commonly used for hybrid electric vehicle and fuel-cell vehicle applications. This converter is characterized by simple circuit topology and soft-switching implementation without additional devices. Despite these advantages, the efficiency is poor at light load condition because of high switching and conduction losses caused by high RMS inductor current. To achieve zero-voltage switching (ZVS) for all power MOSFETs, a constant offset inductor current is maintained to conduct the antiparallel body diodes before MOSFETs turn on. A control strategy of combining duty ratio and phase-shift modulation is proposed to reach the constant offset current. By reaching the constant offset current, the RMS inductor current can be reduced significantly, and ZVS can be achieved in all load variation ranges, resulting in high efficiency. A 2.5-kW prototype is implemented to verify the control scheme, and a minimum efficiency of 97.3% is achieved at light load condition. Copyright (c) 2017 John Wiley & Sons, Ltd.