A Modular Switching Position With Voltage-Balancing and Self-Powering for Series Device Connection

Medium-voltage converters, especially those making use of SiC devices, require high common-mode voltage immunity and resilience against associated high dv/dt across multiple isolation barriers. A truly modular and common-mode immune switching position could be beneficial for these applications. The design of a modular switching position is presented here for a series connection of power semiconductors with voltage-balancing and self-powered-gate capabilities. The designs of the voltage-balancing and self-powered circuits are described, followed by simulations and testing of a 3.3-kV switching position formed by two 1.7-kV SiC MOSFETs in series. Testing results demonstrate the ability of the proposed switching position to balance the voltage across series-connected MOSFETs even if the gate signals of the series-connected devices are not perfectly synchronized while powering themselves directly from the OFF-state voltage across them. In addition, a startup circuit for the switching position is proposed and experimentally confirmed.