Variable Turn-OFF Gate Voltage Drive for Voltage Balancing of High-Speed SiC MOSFETs in Series-Connection

Active gate drive with high accurate and self-adaptive closed-loop control is a promising approach to solving the imbalanced voltage problem of series-connected silicon carbide (SiC) mosfet s. However, due to the inherent time propagation mismatching between Si- and SiC-based devices, behavior adjustment through Si-based ICs during the switching transient takes at least tens of nanoseconds, which limits the minimum allowable turn- off time of each series unit. In this article, a novel active gate drive with a variable gate voltage regulator (GVR) is proposed. It uses a single P-channel mosfet to determine the connection timing of a precharged capacitor in series with the input capacitance in which way the switching transient of each device in the stack is adjustable. It is more advantageous when applied to the low-power SiC mosfet applications with relatively smaller external gate resistors. Two sampling and voltage balancing control circuits based on different processors are proposed for the GVR to adapt to different switching frequencies and costs. Its operational principle and design guidelines are specified and its performance on voltage balancing control is experimentally verified. Analytical assessment on switching losses and costs, compared with the previous work, is provided.