Series-Resonant Topology for Highly Efficient Bidirectional Power Conversion System

Abstract

This paper proposes series-resonant topology for highly efficient bidirectional power conversion system. Firstly, highly efficient bidirectional resonant dc/dc converter over wide range of battery voltages is introduced. It operates as a pulse-width-modulation (PWM) full-bridge series-resonant converter in the forward direction and a PWM half-bridge resonant-boost converter in the backward direction. One advantage of the proposed converter is that it has wide voltage gain range in the backward operation. Also, it requires only six active switches. To achieve high efficiency, SiC MOSFETs are used for two bottom switches in the primary side, because only these switches suffer hard switching turn-off in both forward and backward directions. Since it operates with fixed-frequency and with PWM control, the magnetic components and passive filters can be optimally designed with respect to the volume and the loss. Thus, the proposed converter achieves low cost, high conversion ratio, and high efficiency over wide range of battery voltages.

Secondly, bidirectional resonant dc/dc converter with minimum switching loss over a wide range of battery voltages is proposed. It operates as a PWM T-type resonant-boost converter in the forward direction and a PWM T-type resonant-buck converter in the backward direction. It can then achieve a wide range of voltage gains in the backward operation. By employing a bidirectional switch on the secondary side of the transformer, we can achieve almost zero voltage switching at the turn-off instants, thereby incurring little switching loss at all active switches. Also very little instantaneous reactive current flows through the circuit under wide variations of battery voltages. The proposed converter can achieve a wide range of voltage gains in both directions and high efficiency over a wide range of battery voltages.

The highly efficient series-resonant converters are achieved by a full-bridge and a half-bridge structure with PWM modulation. Detailed analysis of the converter operation is presented along with the design procedure. A 3.3 kW/400 V prototype of the proposed converter has been built to operate for 250-415 V primary source voltages and tested to demonstrate its circuit design.