An interconnection protection design for the interface of alternating current microgrids

The interface of AC microgrids plays an important part in implementing the flexible operation modes. It always manages the disconnection and reconnection between microgrids and the host distribution networks. This study proposes a new protection design interconnection protection (IP), for the interface of microgrids especially the multiple and large-scale ones. IP is intended to decouple interconnected subsystems to prevent disturbances or faults from damaging the both subsystems. IP can be classified into facility IP, circuit IP, and utility IP corresponding to the microgrid served. The deployments, features, and protection schemes of different IPs are analyzed according to the operation characteristics and requirements of the typical microgrid in IEEE Std 1547.4. Facility IP detects faults and disturbances by monitoring the power quality at the point of common coupling. Circuit IP and utility IP have alternative schemes, for example, current differential protection, distance protection, and overcurrent protection. A fault-direction-judgment overcurrent method is proposed for their overlap protection zone. Besides, a time-grading method is used to ensure the coordination of the IPs in the large-scale microgrid. The effectiveness of the proposed designs and protection schemes are demonstrated by the simplified microgrid in IEEE Std 1547.4. (C) 2014 AIP Publishing LLC.