Adaptive super-twisting terminal sliding mode control and LVRT capability for switched reluctance generator based wind energy conversion system

Abstract

Wind Energy Conversion systems (WECS) based on the Switched Reluctance Generator (SRG) devoid of rotor windings and permanent magnets are becoming more and more an attractive generator in wind energy market. Currently, the applicability of this machine in the WECS is now possible thanks to the mitigation of its drawbacks, mainly its high torque fluctuations and its low power factor. In this paper, an Adaptive Super Twisting Terminal Sliding Mode (AST-TSM) control is proposed for SRG-based WECS interfaced to the grid via a full-scale back-to-back converter. The main purpose of the proposed scheme is controlling the generator speed in order to achieve a Maximum Power Point Tracking (MPPT) with better performances. The second issue addressed consists of exploring the Low Voltage Ride Through (LVRT) capability of SRG-based WECS for compliance with recent grid code requirements. In modern grid codes, wind farms are only allowed to be connected to the grid if they have the capacity to remain in service during a short grid disturbance. As a matter of fact, under grid faults, the main tasks of the LVRT method consist in feeding the required reactive power into the grid in order to facilitate the recovery of the grid voltage. In this work, the investigated LVRT scheme, classified as a software method, is responsible for swapping the back-to back converter duties without external devices under grid voltage sags. Thereby, the generated power is stored as kinetic form, preventing strong overvoltage on the DC-bus. The proposed AST-TSM control scheme and the adopted LVRT method are substantiated by simulation results. All simulation case studies show that the AST-TSM control achieves good performance and extreme robustness as compared with the Proportional Integral (PI) and Integral Backstepping (IBC) controllers. Furthermore, the proposed controller is able to improve the suppression of chattering effect when its parameters are adjusted carefully. Also, simulation under grid faults conditions has proven that the LVRT method is effective for SRG-based WECS.