Analysis of a Gate Voltage-Based Fault Current Commutation Strategy to Enable Zero-Current Opening of a Mechanical Switch in a Hybrid Dc Circuit Breaker

Although medium voltage dc (MVdc) power system is promising to provide flexible, robust, and highly power dense power distribution systems for various applications, the dc power systems suffer from short-circuit fault management issues. To solve the issue, a hybrid dc circuit breaker with piezoelectric actuated fast mechanical switch (FMS) and sequential metal oxide varistors insertion scheme has been developed. In the hybrid dc circuit breaker, to commutate fault current from the FMS to solid-state switches and then, keep zero current through the FMS, a gate voltage-based fault current commutation strategy was developed. The method regulates the current through FMS by adjusting the gate voltage of IGBTs and, thus, the voltage across the solid-state branch without switching of the IGBTs. The paper formulates a model of the de circuit breaker based on the gate voltage-based fault current commutation strategy. From the model, a sufficient condition for enabling the zero-current opening capability is identified, consequently determining the adjustment range of gate voltage-based method, i.e., the limits of voltage across the series of IGBTs. In addition, an analytical solution of the current through FMS is obtained and design guidelines for the gate voltage controller parameters are provided. The analytical solution matches SPICE simulation with detailed IGBT model very well, which verifies the effectiveness of gate voltage-based fault current commutation.