An Integrated Automatic Control System for Distributed Generation Hierarchical Islanding

The penetration of distributed generation causes unintentional islanding, failure of re-closing, unsynchronized re- closing, etc. Existing anti-islanding techniques can be susceptible to common mode tripping, which could decrease the stability of total system and increase the requirement for secure spinning reserve. The strategy of hierarchical islanding of DG is described in this paper, which includes Mini Islanding and Substation Islanding. The main purposes of hierarchical islanding are to achieve stable islanding and utilize the DG contribution to system availability under conditions of major system disturbance. Substation Islanding is the first choice. When the inter-ties faults occur, the Substation Island is split from the grid and achieves stable islanding. If the stable islanding can not be obtained, the Substation Island would split into several Mini Islands. A hierarchical distributed control system integrated splitting, realtime load shedding and resynchronization is introduced to maintain stability of hierarchical islanding.