Voltage Balancing Control Method Using Variable Capacitors with Simple Turn-on Adjusting Function for Multi-Stage FET Bidirectional Converter

摘要

This paper proposes a voltage balancing control method using variable capacitors with simple turn-on adjusting function for multi-stage FET bidirectional converter. The proposed voltage balancing control circuit is composed of a feedback circuit using photocouplers and a delay circuit using variable capacitors with turn-on adjusting diodes. The proposed voltage balancing circuit can reduce the drain-source voltage unbalance which occur during the turn-on and turn-off period of series-connected FETs. The theoretical discussion includes analyzing the unbalanced drain-source voltage in seriesconnected FETs using a simplified converter. Also, the principal of the proposed voltage balancing control method is clarified. The experimental results show that the proposed voltage balancing control method can reduce the drain-source voltage difference Δvds of series-connected FETs from 36 V to 11 V (69% reduction in Δvds) during the turn-off and from 22 V to 11 V (50% reduction in Δvds) during the turn-on period. The multistage FET bidirectional converter can achieve a maximum power conversion efficiency of 99.2%.