A Zero Current Switching Hybrid Circuit Breaker for DC Grid Applications

The increasing demand for development and utilization of renewable energy sources has led to a growing interest in DC transmission and distribution systems. However, lack of a proper protection system remains as the main hurdle for the faster adoption of DC systems. The conventional mechanical circuit breakers (MCB) used in the AC system become ineffective due to the absence of natural zero crossings in the DC current waveform. Fast and arc less fault current interruption can be achieved by using solid-state circuit breakers (SSCB). However, the on-state resistance offered by the semiconductor devices hurts the steady-state efficiency of the power system. The hybrid circuit breakers are formed by combining mechanical and power semiconductor switches. The general idea is to make use of the efficient steady state (ON-time) characteristics of an MCB with the fast and smooth dynamic characteristics of a solid-state circuit breaker. However, the fault interruption speed of the HCB is often limited by the reaction time of the mechanical disconnector switch. This paper introduces a new zero current switching hybrid circuit breaker (HCB) that provides an ultra-fast load side fault protection independent of the reaction time of the mechanical disconnector switch. The proposed circuit breaker topology is validated experimentally by developing a 400V/25A prototype in the laboratory.