Phase-Shifted Full-Bridge DC-DC Converter with High Efficiency and High Power Density Using Center-Tapped Clamp Circuit for Battery Charging in Electric Vehicles

In this paper, a phase-shifted full-bridge (PSFB) converter employing a new center-tapped clamp circuit is proposed to achieve high efficiency and high power density in electric-vehicle battery charger applications. By using a simple center-tapped clamp circuit, which consists of two diodes and one capacitor, many limitations in conventional PSFB converters are solved. The proposed center-tapped clamp circuit provides the clamping path and allows the secondary voltage stress to be clamped to the secondary-reflected input voltage. This results in a greatly reduced conduction loss in the secondary full-bridge rectifier (FBR) due to the low-forward-voltage drop of low-voltage-rated diodes, and the resistor-capacitor-diode snubber loss is eliminated. In addition, the circulating current in the primary side is removed without any duty-cycle loss. Furthermore, the turn-off switching loss in the FBR is substantially reduced due to the decreased reverse-recovery current and the reduced reverse voltage. With these advantages, high efficiency can be achieved. Besides, the size of the output inductor is considerably reduced with the aid of clamping voltage, resulting in a high power density with saving the cost. In order to confirm the effectiveness of the proposed converter, a 3.3-kW prototype was tested. Experimental results show that the proposed converter achieves high efficiency over the entire conditions with high power density.