Highly Efficient and Cost-Effective Dual Quasi-Resonant Bidirectional DC/DC Converter

This article proposes a bidirectional dual quasi-resonant dc/dc converter (BQRC) that aims to achieve high efficiency and cost-effectiveness with a high-conversion ratio. When transferring the power in the backward direction, the existing converter with conventional switching modulation does not work because single-diode rectification at the primary side disrupts the expected power flow mechanism. To solve this problem, the diagonal pairs of primary-side switches and secondary-side bidirectional switches were modulated complementarily with a fixed duty ratio of 0.5 and the secondary-side half-bridge switches with a variable duty ratio. This approach enables power delivery in the backward direction while achieving a high-conversion ratio, low-component count, and almost zero voltage switching turn-off, which makes the converter highly efficient and cost-effective. Furthermore, in this topology, nomagnetizing current flows through the external resonant inductor during backward operation, so the core size of the resonant inductor can be reduced. Consequently, even though the primary-side and secondary-side circuit structures differ, symmetric operations are achieved for power flow in both directions. To demonstrate the viability of this approach, a 400-W prototype was designed and tested, capable of converting a 40-60-V input voltage to a 380-V output.