DC Microgrid Protection: Using the Coupled-Inductor Solid-State Circuit Breaker

Since the great debate between Thomas Edison and Nikola Tesla, our nation's power system has operated on alternating current (ac). This was chosen over direct current (dc) because of the need to increase voltage with ac transformers to a high value using transformers for long-distance power transmission. The system has served its purpose well, but now, many energy sources, such as solar panels, fuel cells, and batteries, supply dc voltage. Also, dc/dc power converters are commonly used to transform voltage and to interface these dc sources with a larger system. Because of this, local dc power systems (or microgrids) have become popular topics in research literature. It also turns out that interfacing a wind power generator to a dc system is simpler than interfacing it to an ac system because ac/dc conversion is needed for the former and ac/dc/ac conversion is needed for the latter. Although energy sources and power conversion are readily available for dc power systems, some highperformance applications require fast-acting dc circuit breakers, which are currently in the experimental phase. This article discusses options for high-performance dc circuit breakers and specifically details the coupled-inductor dc breaker. This breaker is demonstrated for fault protection in a notional dc microgrid.