Novel Bidirectional High-Frequency Isolated Direct AC/AC Converter With Unipolar Phase-Shifted Modulation Strategy

This article introduces a novel bidirectional high-frequency isolated direct ac/ac converter with unipolar phase-shifted modulation strategy based on double dc modulation indexes. The main idea of topological construction is that the non-isolated two-level nondifferential bipolar direct ac/ac converter is combined to the bidirectional phase-shifted full-bridge converter, which inherits the advantages of no commutation problem, zero voltage switching, simple control, bipolar output voltage gains, et al. The operating principles of this converter and the design considerations for the key parameters are given in detail. Moreover, the application in voltage sag/swell compensation is simply analyzed. Thanks to the high-frequency isolation capability, it satisfies needs of distribution networks in terms of sensitive loads protection, voltage resilience control without applying the bulky line frequency transformers. Finally, the feasibility of this proposed topology is verified by the various experimental results of the prototype.