Modeling, Design, and Evaluation of Active dv/dt Balancing for Series-Connected SiC MOSFETs

Series connection of SiC MOSFETs provides an effective alternative to achieving higher blocking voltage with simpler circuit topologies. However, the voltage imbalance during the switching transient remains a critical issue. Recently, an active dv/dt control approach utilizing a controllable equivalent Miller capacitor has been proved to be an effective, low-loss, and compact solution. This article renders an improved control circuit with comprehensive modeling and analysis. First, the original circuit is modified with an additional bipolar-junction-transistor and pulsed control signal so that the external capacitor can be fully reset every switching cycle. Second, a simplified model of the active dv/dt control is derived to unveil the linear correlation between the control voltage and the device dv/dt during the turn- OFF transient. Third, a feedback control model is described by difference equations for stability analysis, offering parameter selection guidelines for the control process. Fourth, experimental results with two series-connected SiC MOSFETs under 1.5-kV dc-link voltage are demonstrated to validate the open-loop control model and closed-loop stability. Finally, the control method is expanded to eight series-connected devices under 6 kV to prove its scalability and potential for medium-voltage high-current applications.

Automated summary

This article presents an improved control circuit for series connection of SiC MOSFETs, which achieves higher blocking voltage and resolves the voltage imbalance issue during switching transient. The proposed control method has been validated through modeling, analysis, and experimental results, demonstrating its potential for medium-voltage high-current applications.