Negative-Sequence Virtual Circuit Breaker in Islanded Inverter-Based Microgrids

Unbalanced loads in islanded inverter-based microgrids induce voltage and current imbalances, posing significant challenges to the operation of critical equipment and sensitive loads. To address this issue, conventional circuit breakers, strategically placed between microgrids, play a key role in fault isolation during unbalanced conditions. However, they exhibit weaknesses in effectively addressing power quality issues, frequency variations, and power supply interruptions to specific loads. To solve these limitations, this article introduces the new concept of a negative-sequence virtual circuit breaker. Microgrid inverters are responsible for implementing this concept, which consists of eliminating negative-sequence voltages and currents at the point of-common-coupling between microgrids without altering positive-sequence voltages and currents. This last issue allows the entire electrical system to operate on a single frequency, guaranteeing the loads’ supply. The compensators responsible for implementing the proposed concept are unilateral bandpass filters with complex coefficients. The primary advantage of these compensators over conventional integral compensators is their ability to offer plug-and-play operation. The effectiveness of the proposed concept has been verified through experimental tests in a laboratory setup.