International Journal of Electrical and Computer Engineering (IJECE) Vol. 15, No. 4, August 2025, pp. 3583~3592 ISSN: 2088-8708, DOI: 10.11591/ijece.v15i4.pp3583-3592  3583 Journal homepage: http://ijece.iaescore.com Load frequency control for integrated hydro and thermal power plant power system Vu Tan Nguyen 1 , Thinh Lam-The Tran 1 , Dao Huy Tuan 1 , Dinh Cong Hien 2 , Vinh Phuc Nguyen 1 , Van Van Huynh 3 1 Faculty of Electrical and Electronics Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam 2 Major Projects/Field Operations/Commissioning Department, North Oil Company, Doha, Qatar 3 Modeling Evolutionary Algorithms Simulation and Artificial Intelligence, Faculty of Electrical and Electronics Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam Article Info ABSTRACT Article history: Received Aug 14, 2024 Revised Mar 26, 2025 Accepted May 24, 2025 Persistent electrical supply requires the power systems to be stable and reliable. Against varying load conditions, control strategies such as load frequency control (LFC) is a key mechanism to protect its stability. Traditional control strategies for LFC often face challenges due to system uncertainties, external disturbances, and nonlinearities. This paper presents an advanced approach to control load frequency and enhancing LFC in power systems by using sliding mode control (SMC). SMC offers powerful stability and robustness versus nonlinearities and perturbation, making it a promising approach for addressing the limitations of conventional control methods. We contemporary a comprehensive analysis of the SMC approach tailored for LFC, including the strategy and employment of the control algorithm. The proposed method makes use of a sliding/gliding surface to enable the system trajectories to be continuous on this surface despite parameter variations and external disturbances. Simulation results demonstrate significant improvements in frequency stability and system performance compared to conventional proportional-integral-derivative (PID) controllers. The paper also includes a comparative analysis of SMC with other modern control techniques, highlighting its advantages in terms of robustness and adaptability. Keywords: Integral sliding mode control Integral sliding surface Load frequency control Sliding mode control Three-area interconnected power system This is an open access article under the CC BY-SA license. Corresponding Author: Van Van Huynh Modeling Evolutionary Algorithms Simulation and Artificial Intelligence, Faculty of Electrical and Electronics Engineering, Ton Duc Thang University 19 Nguyen Huu Tho Str., Tan Phong ward, District 7, Ho Chi Minh City, Vietnam Email: huynhvanvan@tdtu.edu.vn 1. INTRODUCTION Load frequency control (LFC) is a critical component in upholding the stability and efficiency of modern power systems (PS), particularly in the context of multi-area interconnected networks. As PS evolves to incorporate diverse energy sources, including recent advances in energy generation plants such as wind power generation, solar power generation, or even biodiesel fuel, and as the complexity of these systems increases, effective control strategies become more essential. Recent advancements in control theory have significantly enhanced the performance of LFC systems. Among these, sliding mode control (SMC) and its variations, such as greater order of SMC and observer-based methods, have garnered substantial attention for their robustness and effectiveness. These approaches are particularly valuable in managing the dynamic