Superjunction MOSFETs in Voltage-Source Three-Level Converters: Experimental Investigation of Dynamic Behavior and Switching Losses

The superjunction MOSFETs with low RDS(on) and fast-switching speed are expected to achieve high efficiency and high-switching-frequency operation in three-phase voltage-source converters. In this letter, experimental measurements of MOSFET switching behavior and losses in a mixed-technology (silicon MOSFET, silicon superjunction-MOSFET, and silicon carbide diode) three-level neutral-point-clamped phase-leg circuit are presented. The effects of superjunction MOSFETs' nonlinear output capacitance and silicon MOSFET intrinsic diode reverse recovery are identified, acting to limit the achievable switching speed and efficiency. A significant high voltage is observed across the superjunction MOSFET occurring under no-load conditions. This letter has revealed that the superjunction MOSFETs cannot be directly used in voltage-source converters (e.g., to replace IGBTs) to achieve higher switching speed due to its nonlinear output capacitance, which creates significant high voltage across the inner device and extra losses.