Disturbance Observer-Aided SSA-TID Control for Frequency Stabilisation in Hybrid Renewable Power Systems

Power systems with high renewable energy (RE) penetration are increasingly vulnerable to frequency instabilities caused by the stochastic nature of RE sources and load-generation imbalances. Additional challenges such as communication delays in phasor measurement units (PMUs), nonlinearities like governor deadband (GDB) and generation rate constraints (GRC) and cross-coupling between load frequency control (LFC) and automatic voltage regulation (AVR) loops further impair system stability. This paper proposes an efficient control framework that combines a fractional-order tilt-integral-derivative (TID) controller, optimised using the salp swarm algorithm (SSA), with a continuous-time disturbance observer (DO) for real-time estimation and rejection of aggregate disturbances. Unlike traditional approaches that rely solely on complex feedback controllers, the integration of the DO improves robustness against nonlinearities and disturbances while maintaining a low-order control structure. The controller parameters are optimised over a nonlinear time-delay model of a two-area hybrid power system, considering both inter-area coupling and dynamic uncertainties, using SSA, genetic algorithm (GA), particle swarm optimisation (PSO) and Archimedes optimisation algorithms (AOA). The proposed SSA-TID-DO controller achieved the lowest objective function value (IAE = 0.2367), clearly outperforming SSA-TID (0.4082), SSA-PID (0.6413), PSO-TID (0.4434), GA-TID (0.4515) and AOA-TID (0.4435) controllers. The results highlight the effectiveness and practicality of the proposed strategy for robust frequency regulation in RE-dominated power systems.