A soft-switched three-port bidirectional converter for fuel cell and supercapacitor applications

This paper presents a zero-voltage-switching (ZVS) three-port bidirectional converter for fuel cell and supercapacitor applications. A simple and effective method to extend the soft-switching range is proposed, especially for the three-port active-bridge topology. By continuously adjusting the duty cycle on the supercapacitor side H-bridge according to the supercapacitor voltage level, soft-switching conditions are achieved over the full operating range due to the equivalent volt-second products applied to the transformer over half the switching period. Detailed analysis is provided for both the two-port and the three-port converters. Furthermore, a dual PI-loop based control strategy is proposed to achieve constant output voltage and precise power flow management, as well as soft-switching. The converter is implemented and tested.