Adaptive Balancing of Series-Connected SiC MOSFETs Based on Active Clamping and Comparison Circuitry

This paper proposes a control method for balancing the voltages of series-connected SiC MOSFETs based on active clamping and comparison circuitry. Each SiC MOSFET is paired with an active clamping module (ACM), which comprises an auxiliary switch and a capacitor. Equal voltage distribution across the SiC MOSFETs is achieved by maintaining balance among the voltages of the ACM capacitors. This voltage balance is achieved through a local comparison circuit with the threshold set at the blocking voltage of the SiC MOSFET in its OFF state. When the ACM capacitor voltage exceeds this threshold, the auxiliary switch is triggered on during the dead time, and the excess energy of this capacitor is recycled back to the DC bus. The proposed adaptive balancing process maintains all ACM capacitor voltages at the threshold without requiring system-level coordination or communication between ACMs, thus simplifying the control circuits. The method does not affect the SiC MOSFETs’ switching speed and enables zero-voltage switching on for the auxiliary switches. Comprehensive operating principles and key parameter designs are provided for both DC transformer (DCT) and Voltage Source Converter (VSC) applications. A high-voltage power module, incorporating six SiC MOSFETs in series, was constructed to demonstrate the effectiveness of the proposed approach. Tests on a DCT and a VSC incorporating this high-power module validated the efficacy of the proposed voltage balancing method.