Removal of Instantaneous Reactive Power From High-Conversion-Ratio Bidirectional Resonant Converter With Balanced Capacitor Voltage

This article presents bidirectional operation of a resonant converter that features high step-up/down capability, high efficiency, and balanced capacitor voltage. When transferring power in the backward direction, the original converter may suffer from significant reverse current due to large fluctuation of the resonant capacitor voltage. By applying the right amount of phase in the pulsewidth-modulation signal, we can remove the instantaneous reactive power generated during the backward operation. We first derive the nominal duty ratio of the secondary side in terms of the backward voltage gain, then derive the threshold load level, above which the instantaneous reactive power appears, and compute the required amount of phase shift to remove it. We also analyze the sensitivity of the required amount of phase with regard to resonant tank parameters. A 400-W prototype converter has been built to demonstrate the performance of the proposed converter.