Detailed Analysis of FDPWM1 Scheme With Trapezoidal High-Frequency Currents for Isolated Single-Stage AC-DC Converters

Isolated AC-DC topologies based on the dual parallel voltage-sourced converters (DP-VSCs) arrangement are well suited for single-stage power processing. This work focuses on a family of DP-VSC based single-stage AC-DC converters that deliberately multitask a high-frequency transformer (HFT) such that the primary side windings carry both low and high frequency (HF) currents. The low frequency components correspond to the ac grid currents that do not generate any core flux while the HF currents are exploited for power transfer via transformer action. Quasi-square HF differential voltages can be synthesized across the primary HFT windings to yield HF trapezoidal currents, all the time guaranteeing zero common-mode winding voltages. Recently, the authors proposed a discontinuous pulse-width modulation scheme, termed FDPWM1, that satisfies all these objectives to allow use of a compact 3-limb HFT in comparison to prior art that relied on collectively bulkier three single-phase HFT units. Building upon our previous work that introduced FDPWM1, this article presents an in-depth analysis of its performance characteristics across a broad range of operating points. The key contributions of this work include a comprehensive analysis of HF voltage waveform variations, HF trapezoidal currents waveform generation, HF power transfer mechanism, and soft-switching capabilities for isolated AC-DC applications. Results are experimentally validated using a 250 V$_{{dc}}$, 121V$_{ac}$, 0.75 kW prototype with 40 kHz HFT.