Hard-Switching 650-V GaN HEMTs in an 800-V DC-Grid System With No-Diode-Clamping Active-Balancing Three-Level Topology

For any voltage above 600-V dc, it is usually recommended to use 900-1200-V SiC MOSFETs instead of GaN high-electron-mobility transistors (HEMTs), given presently commercial GaN HEMTs have the maximum voltage rating up to 650 V. This paper is an attempt of employing 650-V E-mode GaN HEMTs to build a three-level bidirectional dc/dc converter, with the input as an 800-V battery, the output as the ~400-V dc grid, and half of the switches working at the hard-switching mode. The active-balancing control instead of using clamping diodes in the conventional neutral-point clamping topology is adopted, aiming at higher efficiency. Simulation based on the double-pulse test results shows that such a design strategy with GaN has a better efficiency over the conventional 1200-V SiC MOSFETbased buck/boost converter. Two bottom-cooled GaN HEMTs are in parallel to enhance the power capability and efficiency, which require the special focus on the parasitic parameters. The effects of parasitics, especially the stray inductance in the current commutating loop and the gate drive loop during switching transitions, have been comprehensively analyzed in this paper. Experimental results under 800-V bus voltage are presented to verify the proposed solution.