Active Gate Driver With Turn-off Delay Control for Voltage Balancing of Series–Connected SiC MOSFETs

Connecting semiconductor switches in series is a way to increase the voltage rating of a power electronic converter. However, if two switches are directly connected without any special effort, an uneven voltage between the switches can occur due to nonidentical characteristics of them. A significant voltage imbalance may destroy the switches, and both thermal and loss imbalance also lead to the unstable system. Since a silicon carbide (SiC) metal–oxide–semiconductor field–effect transistor (mosfet) has a faster switching speed and higher voltage blocking capability than silicon (Si) devices, existing voltage balancing methods for Si devices may not be suitable. This article proposes a voltage balancing method that controls turn-off delay time of the switch by adding one bipolar junction transistor (BJT) on a gate turn-off path. Depending on the base voltage of the BJT, turn-off resistance and delay time are actively changed which mitigates the imbalance problem. The theoretical analysis of the proposed method has been discussed in detail based on the classical mosfet model. Both the simulations and experiments have been performed to verify the theory and the validity of the proposed method where the voltage imbalance is reduced from 22.4% to 3.2% as well as reducing the switching loss at the entire voltage and load conditions.