The increased deployment of renewable energy in existing power networks has jeopardized rotational inertia, resulting in system degradation and instability. To address the issue, this paper proposes a demand response strategy for ensuring the future reliability of the electrical power system. In addition, a modified fuzzy logic control topology-based two-degree-of-freedom (fractional order proportional integral)-tilt derivative controller is designed to regulate the frequency within a demand response framework of a hybrid two-area deregulated power system. The test system includes thermal power plants, renewable energy sources (such as wind, parabolic trough solar thermal plant, biogas), and electric vehicle assets. To adaptively tune the controller's coefficients, a quasi-opposition-based harris hawks optimization (QOHHO) algorithm is developed. The effectiveness of this algorithm is compared to other optimization algorithms, and the stability of the system is evaluated. The results demonstrate that the designed control algorithm significantly enhances system frequency stability in various scenarios, including uncertainties, physical constraints, and high penetration of renewables, compared to existing work. Additionally, an experimental assessment through OPAL-RT is conducted to verify the practicality of the proposed strategy, considering source and load intermittencies.