Analysis, Modeling, and Experiments of a Nonlinear Inductor-Based Fault Current Commutation Strategy for a Hybrid DC Circuit Breaker

Mediumvoltage dc (MVdc) power system offers a potent solution for high power density, agility, and robustness required by electric ships with escalating power needs. However, the dc power systems suffer from short-circuit fault managing issues. To solve the issue, a hybrid dc circuit breaker (dcCB) has been developed, featuring a novel piezoelectric actuated fast mechanical switch (FMS) and a sequential metal-oxide varistor (MOV) insertion scheme. A key innovation is its nonlinear inductor-based fault current commutation strategy, designed for fast fault current extinguishment and ensuring arc-less operation of the FMS. Using the saturation phenomenon properly, the inductor with variable inductance can hold current around zero to enable arc-less opening of the FMS without slowing down the fault current commutation speed. The article analyzes the features of the nonlinear inductor and presents a fractal RL circuit to model the frequency-related inductance variance and the saturation phenomenon in the time domain. Based on the model of the circuit breaker, including the nonlinear inductor, a genetic algorithm (GA)-based multiobjective optimization method is developed to design the fault current commutation circuit (FC3). Experimental results with 4-kV dc voltage are presented to confirm the accuracy of the model of the nonlinear inductor and the optimized design method.