Active Gate-Driver With dv/dt Controller for Dynamic Voltage Balancing in Series-Connected SiC MOSFETs

Series connection of individual semiconductors is an effective way to achieve higher voltage switches. However, the inherent unequal dynamic voltage sharing problem needs to be solved, even when well-matched gate drivers and semiconductors are used. A majority of the existing voltage balancing schemes are developed for slow-switching silicon (Si)-based semiconductors, and are also associated with a significant amount of additional losses in the control circuit or on the switches. In this paper, a novel method is proposed for balancing the dynamic voltages among series-connected silicon carbide (SiC) MOSFETs with high dv/dt rates. The method takes advantage of a small capacitor to provide additional current to the gate of the MOSFETs at turn-off, meaning the switching speed (and thus, the device voltage after turn-off) is controlled. The proposed method generates negligible losses in the control circuit, and also does not significantly increase the switching losses of the semiconductors. Experimental results are provided to prove the effectiveness of the proposed voltage balancing scheme on two SiC MOSFETs inside a module connected in series. In order to do so, an active gate driver is designed embedding the active dv/dt control scheme as well as other essential functionalities needed for operation of SiC MOSFETs.