Advanced Modulation Techniques and Topological Innovations in High-Frequency Link Inverters: A Comprehensive Review

High-Frequency Link inverters (HFLIs) have attracted significant research attention owing to their compact design, high power density, and high efficiency. HFLI systems achieve power conversion by integrating a High-Frequency Transformer (HFT) between a full-bridge (FB) inverter and cycloconverter. The coupling of HFT between the primary and secondary sides of the converter poses challenges for devising appropriate modulation strategies. The voltage stress on the secondary-side cycloconverter switches arises from the abrupt changes in the output filter inductor current. Another cause of voltage stress is the resonance between the switch output capacitance and the HFT leakage inductance. Given these challenges, examining and investigating modulation strategies in depth is essential. Existing review studies have primarily concentrated on topological configurations and their operational principles, with little attention paid to the modulation strategies. This review examines the topological designs of single-phase HFLI, followed by an in-depth analysis of the modulation strategies, operational principles, and switching signal generation logic diagrams. The limitations of each modulation strategy and their solutions are presented. The primary side modulation (PSM) and secondary side modulation (SSM) strategies are comprehensively reviewed for the operation of the HFLI. A comparative analysis of existing HFLIs in terms of switching frequency, soft-switching capability, modulation strategies, power rating, and efficiency is discussed. Recommendations on various modulation strategies are also provided. This review study is valuable for academic and industry-oriented researchers investigating HFLI.