A Nonlinear Inductor-Based Fault Current Commutation Strategy to Enable Zero-Current Opening of the Mechanical Switch in a Hybrid DC Circuit Breaker

Medium voltage dc (MVdc) power system is a promising solution to provide high power dense, agile, and robust power distribution systems that are necessary for all-electric naval ships with increasing power and energy demands. However, all the promising DC power systems suffer from short-circuit fault managing issues. To solve the issue, a hybrid dc circuit breaker with novel piezoelectric actuated fast mechanical switch (FMS) and sequential MDV insertion scheme has been developed. To extinguish fault current as fast as possible and achieve arc-less opening of the mechanical switch, a novel nonlinear inductor-based fault current commutation strategy was developed. By utilizing the saturation phenomenon properly, the inductor with variable inductance can hold current around zero to enable arc-less open of the FMS without slowing down the fault current commutation speed. The paper provides a model to describe the nonlinearities of the inductor, including the frequency-related inductance variance and the saturation phenomenon. Based on the model of the nonlinear inductor, a genetic algorithm based multi-objective optimal design method has been employed to minimize the fault current commutation time and maximize the zero-current period. Experimental results with 8 kA peak current are presented to confirm the accuracy of the model of the nonlinear inductor and the optimal design method.