The increasing penetration of RESs in modern power systems introduces significant challenges to frequency stability due to their intermittent nature and reduced system inertia. These issues result in larger frequency deviations and degraded system reliability. To address these challenges, this paper proposes a novel cascade controller, namely 2DOF-FOPIDN-(1+I \(\vphantom{0}^\lambda\) D \(\vphantom{0}^\mu\) ), for effective LFC in interconnected power systems integrated with ESSs. The ESS configuration includes battery, flywheel, ultra-capacitor, and superconducting magnetic energy storage systems to provide fast power support and virtual inertia. The controller parameters are optimally tuned using the Human Conception Optimizer (HCO) algorithm based on the ITAE criterion. The proposed approach is evaluated on a two-area interconnected power system while incorporating key nonlinearities, including GDB, GRC, and boiler dynamics, to reflect practical operating conditions and ensure realistic system representation. Simulation results demonstrate that the proposed method significantly enhances system performance, achieving up to 94.61% reduction in settling time and 71.29% improvement in performance index under nonlinear conditions. Additionally, under RES integration, frequency deviation and overshoot are reduced by up to 67.05% and 85.48%, respectively. These results confirm that the proposed controller provides improved stability, reduced oscillations, and enhanced robustness, making it a promising solution for modern renewable-integrated power systems.
