New analytical assessment for fast and complete pre-fault restoration of grid-connected FSWTs with fuzzy-logic pitch-angle controller

Abstract

Fixed speed wind turbines (FSWTs) are still commonly used due to simplicity, robustness, and the life extension programs implemented by leading WT manufacturers. However, due to the sluggish behavior of squirrel cage induction generator (SCIG) during transient and abnormal conditions, complete and fast pre-fault restoration of grid connected FSWTs has become a necessity to maintain high power quality and avoid further instability degradation. This study provides a new analytical tool to maintain stability and assess the response of FSWTs during and post fault conditions. The SCIG’s global asymptotic stability in the sense of the Lyapunov function (LF) is given whereas the stability boundaries are established via the eigenvalues of the LF and its derivative matrices. The outcomes of LF analysis provide a comprehensible stability mapping for FSWTs equipped with pitch angle control (PAC). The study considers fuzzy logic controller (FLC) and other PAC maneuvering schemes. Moreover, the performance assessment criteria based on voltage quality and WT efficiency are presented to further validate the LF analysis results. Different scenarios under various operating conditions for actual wind speed data of the onshore Zafarana wind farm (WF) with FSWT in the Suez Gulf region of Egypt are simulated using MATLAB/Simulink® platform. Based on the results, an improved reliable strategy for driving PAC schemes based on Lyapunov decision-making is proposed. This strategy presents a recommended system for the designers and manufacturers of WT and utility operators to maintain and analyze the stability of FSWTs using Lyapunov stability boundaries as a guideline.