Efficient and Parameter Robust Phase-Shift-Modulation Strategy for LCR-DAB Converter

Loosely-coupled-resonant dual-active-bridge (LCR-DAB) converter substitutes a high-frequency (HF) transformer for inductive power transfer (IPT) coils. An air gap between the IPT coils is advantageous in achieving high-voltage isolation, the key technical barrier of medium-voltage (MV) solid-state-transformer (SST) systems. Owing to weak magnetic coupling between IPT coils, the LCR-DAB converter requires resonant compensations. This makes the LCR-DAB converter unique characteristics compared to conventional transformer-coupled DAB converters. Conventional modulation strategies should be revisited for the LCR-DAB converter. In this paper, the well-known phase-shift modulation (PSM) is investigated for LCR-DAB converters. Input impedance, output power, and efficiency of the LCR-DAB converter are analyzed with respect to operating frequency and phase-shift angle. Based on the analysis, an efficient and parameter-robust PSM strategy for LCR-DAB converters is proposed. In addition, a novel MV-isolated coil design for the LCR-DAB converter is presented. The proposed modulation strategy was evaluated by PLECS simulation results.