An Isolated Phase-Shift-Controlled Quasi-Switched-Capacitor DC/DC Converter With Gallium Nitride Devices

This paper presents the circuit analysis and design guidelines of an isolated voltage-fed phase-shift-controlled quasi switched-capacitor (QSC) dc/dc circuit. The circuit under study is friendly toward the adoption of gallium nitride (GaN) devices by reducing the voltage stress on the devices and mitigating the circulating energy in the circuit. Compared to the conventional halfand full-bridge-based circuits, the phase-shift-controlled QSC circuit can reduce the voltage stress of high-voltage-side devices to 2/3 of the dc bus voltage. The reduced voltage stress can greatly extend the short-circuit withstand time of GaN devices and, thus, improve the reliability of the overall circuit. In a manner similar to a dual-active-bridge circuit, the circuit under study has low circulating energy since it achieves soft switching operation merely with the energy stored in the transformer's leakage inductance. In this paper, the operation principle, soft switching analysis, and design guidelines of the circuit are presented. A 1-kW, 400-48-V, 500-kHz switching frequency prototype with GaN devices was built and tested to verify the circuit analysis.