A medium voltage DC power system is a promising solution for a range of applications; however, it still suffers from challenges with short-circuit fault management. A hybrid dc circuit breaker with a piezoelectric actuated fast mechanical switch has been developed to overcome this challenge. To limit and clear fault currents as fast as possible while achieving arc-less opening of the mechanical switch, a nonlinear inductor-based fault current commutation strategy was developed. In this paper, the relationships between the frequency-related features and parameters of the nonlinear inductor are analyzed and a fractal equivalent circuit model of the nonlinear inductor for time-domain simulations is presented. Based on the model, an optimal design procedure is applied to design the circuit parameters and evaluate the impacts of the number of magnetic cores on the performances and parameter selection of the fault current commutation circuit. A setup for 12 kV system has been built and results with 3 kV dc voltage are presented that verifies the model with optimal design procedure and effectiveness of the nonlinear inductor-based commutation strategy.
