An advanced control and protection integration scheme for microgrids

Abstract

The increasing trend in integrating intermittent distributed energy resources (DERs) into AC microgrids presents operational challenges in stability and protection. In islanded microgrids with power electronic interfaces, protection poses a major challenge due to the reduced level of short circuit currents resulting from inverter output capabilities. However, traditional protection schemes that are utilized in distribution systems are no longer appropriate to protect the microgrid in the presence of different levels of fault currents. This paper develops an integrated control and protection framework based on state observer and fault current limiter (FCL) devices. The state observer has been developed to detect and identify the faults that occur within multiple protection zones. In addition, controlled switches, consisting of FCLs, have been utilized to limit the fault currents and provide rapid switching during the faults, thereby improving system reliability. An adaptive control and protection integration scheme proposed in this paper has been applied to islanded microgrid configuration and is demonstrated to be an effective means to protect the system and maintain the voltage and frequency within an acceptable range with the capability of power continuity during both transient and persistent faults.