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This paper proposes an enhanced Second-Order Sliding Mode Control (SOSMC) strategy based on a sigmoid function (S-SOSMC) for robust operation of two-stage grid-connected photovoltaic (PV) systems. The S-SOSMC is comprehensively applied to maximum power point tracking (MPPT), DC-link voltage regulation, and grid-side current control. The controller's superiority is rigorously validated through MATLAB/Simulink simulations under diverse challenging conditions, including rapid irradiation changes, step variations in power references, grid voltage sags/swells, and a two-phase grid fault. Compared to conventional PI and standard SOSMC, the proposed S-SOSMC demonstrates consistently superior performance: it achieves faster MPPT convergence (0.009 s) with minimal power oscillation, provides stable DC-link voltage with reduced overshoot during transients, and ensures high-quality grid current injection. Crucially, the S-SOSMC maintains the lowest total harmonic distortion (THD) across all tests, culminating in a remarkable 76.29 % reduction compared to conventional methods and a further 23.5 % improvement over standard SOSMC under variable irradiation. The controller also exhibits exceptional robustness, enabling rapid system recovery and minimal harmonic distortion during grid faults. These results conclusively establish the S-SOSMC as a highly effective solution for enhancing the dynamic performance, power quality, and resilience of grid-connected PV systems.
Guerbouz et al. (Thu,) studied this question.