Microgrid control overview

A microgrid (MG) is always prone to the uncertainties of its demand variation and generation of its non-dispatchable renewable sources, particularly when operating in the islanded mode. Such events can push voltage and/or frequency of the MG beyond their desired range of operation. This chapter reviews the control and management techniques to retain the voltage and frequency of such MGs within a predefined safe zone. Suitable real time, corrective, and preventive controllers are discussed on the generation and demand side, which aim to satisfy various objectives at different time instances. First, the necessity of such controllers and mechanisms is explained in both grid-tied and islanded modes and during the transition between these modes. Then, islanding detection and its impact on MG management are briefly discussed. Afterwards, the MG's control architecture is outlined, and the existing approaches in the literature are described briefly. Finally, three case studies on different aspects of MG control are reported to show the applicability and criticality of such services for MG operation. The emphasis of the case studies is on the islanded MG operation because frequency and voltage issues are more pronounced for those types of MGs. In particular, a new generalised droop-based controller is explained in Section 2.4.1 as an example of advanced power-sharing strategies for voltage and frequency regulation with the plug-and-play feature. In Section 2.4.2, the primary frequency control problem is tackled from the demand control perspective, where demand response (DR) resources are altered to provide frequency and voltage regulation within a short period of time. Finally, a corrective and preventive controller is outlined and explained in Section 2.4.3. The corrective controller takes action immediately after the occurrence of an event that violates the voltage or frequency by defining the least cost solution among available options. In the preventive controller, generation and load demand forecast are used to predict unexpected events in very short horizons that can lead to voltage/frequency violations and take suitable actions beforehand.