A load-independent reconfigurable resonant DC–DC converter with current-driven synchronous rectification for electric vehicle charging without bidirectional switches

Abstract

In this paper, a control-free battery charger based on an isolated resonant DC-DC converter is proposed for constant current (CC) and constant voltage (CV) charging of electric vehicle (EV) batteries. The proposed converter employs a current-driven synchronous rectifier (SR) and fea- tures load-independent output as well as a reduced number of switching components. Both CC and CV modes are intended to operate at a fixed resonant frequency with the help of LCC and LC resonant tanks, respectively. In the proposed converter, mode transition from CC to CV charging is carried out by reconfiguring the resonant tank without changing the switching frequency. The reconfiguration is realized by using a single auxiliary MOSFET to allow a smooth transition be- tween the charging modes without requiring a bidirectional switch. In the CV mode, the auxiliary switch acts as a semi-synchronous rectifier (S-SR) and increases the efficiency. Additionally, in the CC mode, the current-driven SR technique is implemented to extract the switching timing directly from the resonant tank inductor current. As a result, by eliminating the external gate driver, a low-cost and simple implementation is achieved. A 1 kW prototype of the proposed converter with output voltages ranging from 250 to 450 V and an input voltage of 400 V is tested to validate the theoretical analysis and acceptable operation of the converter. The experimental results indicate a peak efficiency of 98.7%, which can be attributed to the reduced number of switching components, operation at resonant frequency, zero-voltage switching (ZVS), and zero-current switching (ZCS) operation of the proposed converter over a wide output voltage range under load fluctuations.