Control and Modulation Methods of Single- and Three-Phase Transformerless AC-DC Converters for Suppressing Leakage Current

This thesis presents a pivotal advancement in next-generation power electronics, specifically addressing the critical challenges of transformerless AC-DC power conversion: leakage current and electromagnetic interference (EMI). As the industry shifts toward transformerless architectures for higher efficiency and power density, addressing the inherent disadvantages in safety and reliability becomes paramount. Distinguishing itself from conventional approaches, this research establishes a unified framework for analyzing common-mode voltage (CMV) across frequency domains. It proposes innovative control strategies, including active CMV control and extended vector PWM, to simultaneously suppress the low- and high- frequency leakage current. Significantly, this work bridges the gap between advanced theory and industrial application, by validating on a full-scale 11 kW grid-connected system. The system achieved a peak efficiency of 99.4% and a power density of 4 kW/L, while strictly complying with IEC 61851 safety and CISPR EMI standards. Consequently, this research simultaneously achieves the three core values required by industrial power conversion systems: high efficiency, high power density, and high reliability. By offering a unified approach that is scalable to multi-level and parallel systems, it serves as an essential reference for researchers and engineers designing next-generation power conversion systems such as electric vehicle chargers, renewable energy systems, and microgrids.