Microgrid Protection and Control Schemes for Seamless Transition to Island and Grid Synchronization

Microgrid transitions to islanded mode and grid synchronization can be designed either as seamless transitions or as a black-start. Secure and reliable seamless transition represents one of the most challenging engineering tasks during the microgrid design phase. Existing literature has several shortcomings - proposed microgrids are either ungrounded or not effectively grounded; DER transformer configurations are not properly implemented; communications within the microgrid do not reflect realistic time delays and there is very little discussion of the impact of relay protection settings on the proposed microgrid protection. This paper presents a new microgrid protection and control scheme that enables seamless islanding and grid synchronization using the point of common coupling (PCC) breaker relays, battery energy storage system (BESS) inverter controller and remote input/output mirror bits based communications approach (85RIO). All schemes have been implemented in the field within the electric utility's microgrid installed on the 12.47kV distribution feeder. The results presented in this paper are based on approximately 9,000 islanding and grid synchronization transitions.