Analysis and Design of a Novel Thyristor-Based Circuit Breaker for DC Microgrids

DC microgrids have attracted increasing concern in industrial applications due to a simple and efficient integration with renewable energy sources, battery energy storage, and variable speed generators and motors. However, extensive application of dc architecture is still restricted by fault protection challenges posed by the absence of natural current zero-crossing. This paper has proposed a novel thyristor-based dc circuit breaker with a one-shot triggering commutating circuit, which maintains a compact size as no additional power supply is required to precharge the commutating capacitors. Considering di/dt limitation of the triggering thyristor in the commutating circuit, a saturable inductor is utilized to avoid hot spot failure in the thyristor. Moreover, saturation characteristic of the inductor allows a sharp-rising commutating current which can provide zero-crossing for the main thyristor with a shorter delay. A real-time analog protecting unit is also introduced to interrupt fault current accurately and rapidly. Furthermore, detailed breaker topology analysis and circuit design guidelines are provided through mathematical modeling. Finally, the proposed breaker design method is verified by simulation studies over two cases and further validated by a 400 V/4 kW laboratory prototype.