Second-order sliding mode voltage-regulator for improving MPPT efficiency of PMSG-based WECS

Abstract

Driven by the rapidly growing use of wind power, the maximum power extraction of wind energy conversion systems (WECS) has become a significant issue. However, due to the stochastic nature of the wind, employing a nonlinear controller to provide a good tracking performance can be a viable option. In this study, a voltage mode Second-Order Sliding Mode Controller (SO-SMC) is proposed to capture maximum power from the WECSs. Optimum voltages to track are determined via a mechanical sensorless maximum power point tracker (MPPT) approach and these are transferred to the controller. In the proposed method, second-order surface is based on PID type sliding surface. The voltage-mode SO-SMC structure has not been implemented before as a voltage regulator for PMSG-based WECSs consisting of Rectifier and Boost Converter (BC). It is guaranteed that the system can be operated at maximum power point for all wind conditions thanks to the switching of the BC with only a control signal produced by the controller. The proposed method is validated by two different scenarios with different behaviors, that are realistic and step change wind speed profiles ranging from 5 m/s to 12 m/s. In addition, a conventional sliding mode (C-SMC) voltage regulator is designed and performance comparisons are made at these wind speed profiles in terms of output voltage fluctuation, steady-state error and maximum captured average power in steady-state and MPPT efficiency. From these results, it is proven that the proposed controller has a superior performance and it increases efficiency in the extraction of maximum power from WECS with the fast and robust voltage tracking. While MPPT efficiency was increased up to approximately 0.7% for the wind speed profile having the step variations, an increase up to about 1.05% was observed for the realistic wind speed profile.