Primary and Secondary Frequency Control in an Autonomous Microgrid Supported by a Load-Shedding Strategy

This paper proposes a frequency control strategy for an islanded inverter-based microgrid which based on the priority of supply, has got two distinct types of loads, namely sensitive and deferrable. The proposed strategy consists of primary and secondary levels of generation control supported by a load-shedding scheme. The primary control regulates the output power of the distributed generator (DG) units to be proportional to their ratings while secondary control has got the duty of frequency restoration after each load change. Functionality of these two levels is demonstrated to be independent of each other. Both controls are in distributed forms which have no need of communication infrastructure. Moreover, the proposed load-shedding strategy is activated occasionally to restore frequency despite the limitation of secondary control since the sensitive loads always demand high power quality. The performance of the proposed control scheme is verified by using digital time-domain simulation studies in the MATLAB/SIMULINK software environment.