Enhanced Cocharge Operation Scheme in Bidirectional PhaseShift Full-Bridge Converters with Eliminated Voltage Overshoot and Reduced Freewheeling Current

For high power density, high efficiency, wide voltage range, and low current ripple in isolated bidirectional DC/DC converters for battery charging applications, the phase-shift full-bridge (PSFB) converter is employed in this paper. However, the PSFB converter exhibits significant voltage overshoot on the transformer's secondary side, increasing the voltage stress on the secondary-side switches. Additionally, it generates a large freewheeling current, leading to extra conduction losses and larger transformer sizes, which compromise both efficiency and power density. This paper proposes an enhanced operating method to eliminate voltage overshoot while reducing freewheeling current. A simplified model is developed to analyze and predict the voltage overshoot under the proposed operation, offering insights into circuit behavior and design guidelines for bidirectional PSFB converters.