Double Voltage Rectification Modulation for Bidirectional DC/DC Resonant Converters for Wide Voltage Range Operation

It is difficult to achieve wide voltage range for fullbridge-based bidirectional resonant dc/dc converter due to the large resonant current caused by the small magnetizing inductance. A half-bridge modulation was proposed to extend the output voltage range by offering an additional step-down voltage step of 0.5 normalized gain. But in backward operation, the converter cannot provide the two-times step-up voltage gain to match the forward 0.5 step-down voltage gain, which disables the converter to truly work hidirectionally with large voltage range. This paper proposes a double voltage rectification (DVR) modulation on the rectification side to achieve twice the voltage gain for the backward direction to effectively widen the operation voltage range, which matches the ratio of the two dc port voltages where the half-bridge modulation is used in the forward direction. In the DVR modulation, the operation of the input-side resonant tank is the same as that of the conventional modulation. The switches on the input side still turn ON with zero-voltage switching (ZVS), and the body diodes on the rectification side still turn OFF with zero-current switching. Moreover, the turning ON and OFF of the MOSFETs on the rectification side are also ZVS, which causes no additional losses and guarantees high-frequency operation. The rotational operation of the rectification-side switches improves the thermal balance condition, enlarging the power capacity and improving the reliability of the converter. A smooth transition method between the two modulations is also proposed, which still guarantees ZVS turning oN for the rectification-side switches. The symmetrical CLLLC resonant converter is taken as an example to illustrate the operation principle and features of the proposed modulation. And other bidirectional resonant converters for the DVR modulation are also presented. Finally, a 3-kW bidirectional CLLLC resonant converter prototype with 100-kHz resonant frequency is built to verify the proposed modulation.