Improved Modulation Strategy for Single-Phase Single-Stage Isolated AC–DC Converter Considering Power Reversion Zone

In this article, an improved modulation strategy for the single-phase single-stage isolated bidirectional ac-dc converter is proposed. The modulation of ac side cycloconverter is based on the unipolar idea to reduce the switching quantity and the ac side current ripple and provide the bidirectional current flow path. The dc side H-bridge converter is driven by the pulsewidth modulation signals cooperatively to speed up the transformer current and thus to eliminate the voltage spike. Furthermore, the power reversion zone (PRZ) of the converter is verified. The action of the proposed modulation strategy in PRZ is analyzed for the first time. It reveals that the reverse current overshoot is caused in ac-to-dc direction and the voltage spike is caused in dc-to-ac direction. An online switching scheme of the proposed modulation strategies in two power directions is proposed to solve these problems. The detailed experimental results verify the correctness and reliability of the proposed modulation strategy.