Improved Sliding Mode Control for a Standalone PMSG-Based Wind Energy Conversion System with Battery Backup

In this study, four advanced control schemes, Field-Oriented Control (FOC), Backstepping Control (BSC), Classical Sliding Mode Control (CSMC), and an Improved Sliding Mode Control (ISMC), are designed, implemented, and evaluated within a standalone Permanent Magnet Synchronous Generator (PMSG)-based WECS supplying an irrigation water pumping load. The proposed ISMC is explicitly formulated to suppress the chattering effect inherent in conventional sliding mode control while preserving robustness against system uncertainties and external disturbances. To ensure continuous and reliable operation during wind intermittency, a battery energy storage system is integrated, and a coordinated energy management strategy is developed to regulate power flow among the PMSG, battery, and pumping system. To objectively assess the effectiveness of each control strategy, a unified simulation framework is established in MATLAB/Simulink. The evaluation focuses on both steady-state and dynamic performance indices, namely the Total Harmonic Distortion (THD) of the PMSG three-phase stator currents and the convergence characteristics of the controlled variables. The results indicate that the proposed ISMC achieves superior harmonic suppression, yielding a THD reduction of 52% compared with FOC, 72% compared with CSMC, and 36% compared with BSC. These improvements directly reflect the enhanced switching behavior and reduced control-induced oscillations achieved by the ISMC formulation. In addition, convergence time analysis demonstrates a pronounced enhancement in transient response, with the ISMC reducing settling time by approximately 99% relative to FOC, 95% relative to CSMC, and 51% relative to BSC. This accelerated convergence confirms the effectiveness of the proposed control law in rapidly enforcing system trajectories onto the desired sliding surface. Collectively, the quantitative improvements in harmonic quality and dynamic response translate into improved power regulation and operational stability of the standalone WECS. Consequently, the proposed ISMC not only enhances current waveform quality and transient performance but also contributes to a more reliable and efficient integration of renewable energy and storage components in PMSG-based wind-driven pumping applications.