Extended High Efficiency Operation of Semi - Active Half-Bridge DC-DC Converter

The semi-active half-bridge converter (SAHBC) is a promising option for cost-competitive electric vehicle (EV) charging systems. However, the conversion efficiency of SAHBC is poor at part load conditions. This is attributed to the small duration of current supply to the output and large duration of circulating current in the transformer. This paper proposes an efficiency improvement technique to address this issue. The proposed technique is a combination of design of SAHBC and strategic changes in its switching frequency. The design of SAHBC selects the turns ratio and leakage inductance. Whereas, the switching frequency of SAHBC is strategically increased to enhance the duration of output current transfer. This increase in switching frequency is easily implementable due to complete ZVS and ZCS operation of the power devices. A step-by-step methodology for the proposed technique and its application to a 2.4 kW EV charger are included in the paper. The presented analysis shows that the proposed technique achieves up to 9.3 % improvement in conversion efficiency at part load conditions. The operation of proposed technique is also validated with the help of a 2.4 kW laboratory prototype.