A Load Adaptive Control Approach for a Zero-Voltage-Switching DC/DC Converter Used for Electric Vehicles

This paper presents a load adaptive control approach to optimally control the amount of reactive current required to guarantee zero-voltage switching (ZVS) of the converter switches. The proposed dc/dc converter is used as a battery charger for an electric vehicle (EV). Since this application demands a wide range of load variations, the converter should be able to sustain ZVS from full-load to no-load condition. The converter employs an asymmetric auxiliary circuit to provide the reactive current for the full-bridge semiconductor switches, which guarantees ZVS at turn-on times. The proposed control scheme is able to determine the optimum value of the reactive current injected by the auxiliary circuit in order to minimize extra conduction losses in the power MOSFETs, as well as the losses in the auxiliary circuit. In the proposed approach, the peak value of the reactive current is controlled by controlling the switching frequency to make sure that there is enough current to charge and discharge the snubber capacitors during the deadtime. In addition, some practical issues of this application (battery charger for an EV) are discussed in this paper. Experimental results for a 2-kW dc/dc converter are presented. The results show an improvement in efficiency and better performance of the converter.