Enhanced sliding mode control with a cascaded sliding surface for load frequency control in two-area islanded microgrid

Islanded microgrids often struggle to maintain frequency stability due to fluctuating loads and the intermittency of renewable energy sources. In highly dynamic microgrid environments, conventional load frequency control (LFC) techniques such as standard Sliding Mode Control (SMC) can face challenges in handling nonlinearities, which may limit their performance under disturbances. This paper introduces an enhanced SMC approach using a Cascaded Sliding Surface that combines PID and fractional-order PID (FOPID) components, thus strengthening the dynamic response and improving disturbance rejection. Controller parameters are optimized using three evolutionary algorithms: Genetic Algorithm (GA), Differential Evolution (DE), and Particle Swarm Optimization (PSO), enabling systematic and objective performance tuning. To validate the effectiveness of the proposed controller, it is benchmarked against PID, FOPID, cascaded PID-FOPID, and conventional SMC under load variations, noisy wind/solar irradiation perturbations, nonlinearities, and parameter uncertainties. The simulation results and robustness tests confirm that the enhanced SMC controller achieves superior frequency regulation, with the lowest overshoot, undershoot, settling time, and ITAE values among all tested controllers for both single-area (SAMG) and two-area (TAMG) islanded microgrids, ensuring stable operation under diverse and realistic conditions.