Modeling, Design, and Evaluation of Active $\mathrm{\text{} d }v/\mathrm{\text{} d }t$ Balancing for Series-Connected SiC MOSFETs

Abstract

Series connection of SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MOSFET</small> s 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{\text{} d }v/\mathrm{\text{} d }t$</tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{\text{} d }v/\mathrm{\text{} d }t$</tex-math></inline-formula> control is derived to unveil the linear correlation between the control voltage and the device <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{\text{} d }v/\mathrm{\text{} d }t$</tex-math></inline-formula> during the turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> 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 <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MOSFET</small> s 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.