Abstract

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.