Abstract
The rapid expansion of electric vehicle (EV) fleets necessitates ultra-efficient, compact, and bidirectional fast-charging infrastructure capable of seamless vehicle-to-grid (V2G) and grid-to-vehicle (G2V) power transfers. Conventional silicon-based power conversion stages are constrained by thermal bottlenecks, low switching frequencies, and compromised power densities. This paper presents the design, optimization, and experimental validation of a high-efficiency bidirectional DC-DC converter utilizing 650 V enhancement-mode Gallium Nitride (GaN) High-Electron-Mobility Transistors (HEMTs). Based on an optimized Dual Active Bridge (DAB) architecture integrated with a customized high-frequency planar transformer, the proposed converter utilizes an adaptive extended phase-shift (EPS) modulation strategy to achieve zero-voltage switching (ZVS) across the entire battery voltage spectrum (400 V to 800 V). A 10 kW, 300 kHz experimental prototype was designed with an ultra-low-inductance layout and Kelvin-source gate driving circuits to mitigate high-frequency switching transients and parasitic ringing. Experimental results demonstrate a peak conversion efficiency of 98.85% in G2V mode and 98.72% in V2G mode, alongside a volumetric power density of 6.4 kW/L. The dynamic transition between charge and discharge modes occurs in under 1.8 ms, validating the topology's suitability for frequency regulation and grid-supportive fast-charging applications.
