A Voltage Balancing Method for Series-Connected SiC MOSFETs Based on Active Clamping Modules Operating Under Hard Switching Conditions

This article proposes a voltage balancing method for series-connected SiC mosfets operating under hard-switching conditions, utilizing active clamping modules (ACMs), which consist of an auxiliary switch and a clamping capacitor, to achieve the voltage balancing. The charging mechanisms of ACM capacitors are analyzed, which correspond to switching asynchrony and commutation process, and mathematical models are established. A control strategy is introduced that employs feedback-based turn-off timing adjustment to eliminate switching asynchrony and controls auxiliary switches to implement voltage difference-driven discharge to recover the charge introduced during the commutation process. The effectiveness of this method is verified through experiments in a 1-kV boost converter, where the six series-connected SiC mosfets exhibited effective voltage balancing during both the startup and steady-state phases. The measured voltage imbalance degree of the series-connected SiC mosfets is less than 3% under both full-load and no-load conditions, which confirms the effectiveness of the proposed method.