Design and Validation of a 100 kW, 60 kHz, High Efficiency, Loosely-Coupled-Resonant Dual-Active-Bridge Converter

A novel loosely-coupled-resonant dual-active-bridge (LCR-DAB) converter substitutes a high-frequency (HF) transformer for inductive power transfer (IPT) coils. The primary and secondary sides of the LCR-DAB converter can be separated over several centimeters for high-voltage isolation, which is the critical challenge of medium-voltage (MV) solid-state transformer (SST) systems. In this study, input impedance, zero-voltage switching (ZVS) region, output power, and efficiency of the LCR-DAB are investigated concerning operating frequency and phase-shift angle. Based on the analysis, an efficient and parameter-robust operating frequency for LCR-DAB converters is proposed. In addition, novel loosely coupled coil design guidelines for LCR-DAB converters are presented. A 1 kV, 100 kW, 60 kHz LCR-DAB test bed was fabricated for experimental evaluations. The measured coil-to-coil and dc-to-dc efficiencies were 99% and 97.3% over a 3-cm air gap. The parameter robustness and the coils' insulation performance were also evaluated.