Family of isolated bidirectional resonant converters with duty-cycle control and automatic power flow transition

This study proposes a family of duty-cycle controlled bidirectional resonant converters and its uniform modulation schemes. This family of converters is composed of a current-fed stage, a transformer with LC resonant tank and a voltage-fed stage. Therefore, high-voltage gain and low-current ripple can be achieved. With the proposed uniform modulation schemes, automatic forward and backward mode transition is realised. Furthermore, the voltage gain is only determined by the duty cycle, independent of load and power flow direction, thus simple control can be adopted and voltage can be regulated in a wide range. Zero-voltage switching of all switches can be achieved over a wide load range. The operation principle and analysis of one of the converters are presented as an example. Design considerations are provided. Experimental results are shown to verify the theoretical analysis.