Microgrid Stability Definition, Analysis, and Examples

The voltage and frequency of microgrid systems are changed when imbalances occur between power generation and demand. Thus, an important issue for systems is the operation in islanded mode. To solve this problem, a robust controller can be used to improve the stability responses of voltage and frequency. Accordingly, this study develops a novel adaptive fuzzy proportional-integral-derivative (AFPID) controller to regulate the voltage and frequency oscillations of islanded microgrids. The controller has two parts that operate in parallel to ensure the proper performance against uncertainties. The first part is a simple PID controller with constant gains that are obtained in nominal operation, and the second part is a fuzzy logic-based online mechanism for tuning PID gains against uncertainties. The non-dominated sorting improved differential evolution (NSIDE) algorithm is applied in the design of the AFPID controller to avoid the need for trial-and-error attempts and overcome the challenges presented by fuzzy design. The Analytical Hierarchy Process (AHP) mechanism is used in the optimization process that involves the optimal tuning of gains, membership functions and rule bases to ensure excellent decision making regarding solutions. The combination of fuzzy theory features and the NSIDE algorithm is intended to guarantee robust voltage/frequency control in islanded microgrids and simplicity in terms of process and structure. Ultimately, the data of the Himmerlands Elforsyning power system in Aalborg, Denmark is utilized to compare the effectiveness of the proposed AFPID controller, the conventional fuzzy PID controller and the classical PID controller against different disturbances and load uncertainties. The comparison is based on the integral of squared time multiplied by square error, maximum overshoot, maximum undershoot and settling time. Simulation results demonstrate that the proposed AFPID controller is robust against disturbances and load uncertainties; thus rendering it is an excellent choice for application in the actual islanded microgrids.