Load Frequency Control in Isolated Microgrids with Pumped Hydroelectric Energy Storage

Low inertia levels in modern power systems and the slow response of thermal power plants make the use of energy storage systems increasingly important for maintaining frequency stability. In this study, the integration of a pumped hydro energy storage (PHES) system into a thermally based single-area isolated microgrid is proposed in order to improve frequency response performance. In addition, a PI controller based on the Glider Snake Optimization (GSO) algorithm is proposed as a novel approach to ensure effective load frequency control. In the first stage, the proposed GSO method is compared with a conventional optimization technique, namely the Genetic Algorithm (GA), under a 0.01 pu step load perturbation in the isolated microgrid. The obtained results demonstrate that the proposed GSO method provides a superior frequency response with an undershoot of 6.647 E-03 pu, an overshoot of 2.946 E-03 pu, a settling time of 3.82 s and an objective function value of 0.0198. In the second stage, the PHES system is integrated into the isolated microgrid considering two different operating modes: generation mode and pumping mode. When the PHES operates in generation mode, improvements of 9.95% and 40.77% are achieved in undershoot and overshoot values, respectively. Moreover, the settling time is reduced by 22.8%, while the steady-state error decreases by 96.92%. In the pumping mode, an additional load effect of Ppump =0.05 pu is assumed in the system. Under this condition, only an 11% reduction in settling time is observed, while no significant improvement is achieved in other performance criteria. The obtained results indicate that the PHES system significantly enhances frequency stability in generation mode, whereas in pumping mode the system remains stable but the overall performance is slightly degraded compared to the base case.