Low voltage ride-through capability enhancement using optimal super twisting sliding mode control for grid-tied pv systems

Abstract

This paper addresses the critical issue of enhancing the low-voltage ride-through (LVRT) capability of grid-tied photovoltaic power (GTPVP) systems, particularly in compliance with modern grid codes (GCs) during grid faults. It proposes a novel control strategy using super-twisting sliding mode control (STSMC) for a 100-MW PV system, with the gains of the STSMC optimized through a Newton-Raphson-based optimizer (NRBO). The NRBO is also employed as a maximum power point tracker to regulate PV voltage based on a STSMC. Additionally, the STSMCs are integrated into the voltage source inverter for optimal control of various parameters, including the DC-link voltage, active, and reactive currents. Furthermore, the effectiveness of the NRBO-STSMC is validated through comparative analysis against other methods, such as particle swarm optimization (PSO)-tuned STSMC, NRBO-based conventional SMC, and NRBO-tuned proportional-integral (PI) controllers. A MATLAB/Simulink model was utilized for optimization and simulation, demonstrating that the NRBO-STSMC achieved superior performance, with the lowest integral of time-weighted absolute error values and higher efficiency, for both DC-DC and DC-AC converters. It minimizes voltage overshoot at the point of common coupling and ensures stable power injection during severe grid faults. In contrast, the NRBO-SMC method shows significant overshoots, while the NRBO-PI method faces oscillations and poor power balance. The study concludes that the proposed NRBO-STSMC successfully complies with the IEEE 1547 LVRT grid code during the grid fault. It provides a robust, highly efficient, and stable control solution for the LVRT issue of GTPVP systems, proving essential for meeting the demands of modern GCs.