Design of Fully Soft-Switched Semi-Dual Active DC-DC Converter for Battery Charging Application

Semi-dual active bridge converter (SDABC), a unidirectional variant of dual active bridge converter, is popular for battery charging applications. However, it suffers an efficiency dip at different charging instants of the constant current-constant voltage (CC-CV) charging profile, especially at low voltage-medium power conditions of CC mode and high voltage-low power conditions of CV mode. These dips are due to the loss of soft switching at these charging instants. To address this, a design-based approach focusing on transformer turns ratio and leakage inductance is proposed in this digest. The proposed design methodology achieves zero-voltage switching (ZVS) under low voltage-medium power conditions by properly selecting leakage inductance and under high voltage-low power conditions by carefully choosing the turns ratio. In addition, the discontinuous conduction property of SDABC is explored to reduce transformer circulating current at light loads, thereby enhancing efficiency by reducing conduction loss. Analytical results demonstrate that the proposed design enables soft switching across the CC-CV profile and improves efficiency. Validation with a 1.5 kW laboratory-developed hardware prototype of OBC charging 96 V battery shows a 61 % efficiency improvement at the start of CC mode and an improvement of 66 % at 30 % loading at CV mode with the proposed design compared to the conventional design.