High-Efficiency Voltage Balancer Having DC-DC Converter Function for EV Charging Station

Due to the recent proliferation of electric vehicles, high-power charging stations are being actively studied. Among the main types of charging stations, bipolar dc-bus-fed ones outperform the ac-bus-fed ones because of easier interfacing with distributed generation and fewer conversion stages. Bipolar dc-bus-fed charging stations generally require voltage balancing control (VBC) between the dc-bus voltages; hence, they use a three-level (TL) dc-dc converter that serves as a fast charger while balancing the dc-bus voltages. However, the VBC range of the TL converter is limited by its output load power, which can cause voltage imbalance of the bipolar dc-bus. To address this problem, this paper proposes a high-efficiency voltage balancer (VB) having dc-dc converter function. The proposed VB has the ability of the dc-dc converter and can serve as a fast charger. Moreover, this VB has no limitations on the VBC range, unlike the TL converter, and features lower voltage and current stresses on the switches as well as higher conversion ratio and efficiency compared to the conventional VB with dc-dc converter function. The key features of the proposed and conventional schemes are compared, and simulated and experimental results are presented to demonstrate the effectiveness of the proposed VB.