Delay-resilient super-twisting sliding mode control for frequency regulation in multi-area power systems under time-varying delays

Load frequency control (LFC) is essential in power systems (PSs) to maintain frequency stability under load variations, external disturbances, and communication constraints. In modern PSs, time-varying communication delays and increasing disturbances pose significant challenges to conventional LFC methods. To address these issues, this paper proposes a modified super-twisting sliding mode control (SMC) scheme with a new delay-resilient sliding surface for LFC in multi-area PSs subject to external disturbances and time-varying communication delays. Unlike existing SMC-based LFC approaches that mainly compensate delays via observers or conservative control laws, the proposed method explicitly embeds delayed state dynamics into the sliding surface design, enabling inherent resilience to delay-induced instability. Based on this sliding surface, a proposed super-twisting SMC law is developed to ensure finite-time convergence of the sliding variable while effectively mitigating chattering effects. Sufficient conditions for robust asymptotic stability of the closed-loop system are derived using Lyapunov functionals and formulated as linear matrix inequalities. The effectiveness of the proposed approach is validated through extensive simulations on single-area, two-area, and IEEE 39-bus PSs under fixed and time-varying delays as well as load disturbances. The results demonstrate faster convergence, reduced frequency deviations, and improved robustness compared with existing first-order and second-order SMC-based LFC methods.