Performance evaluation of control strategies for grid connected wind power generator

Abstract

South Africa is currently experiencing a significant load-shedding situation because of rising electricity demand. The renewable energy power producer (RPP) sector is growing rapidly to become an important source of power in South Africa and nations across the globe. Companies within this sector provide a variety of clean energy sources, including wind, solar, hydroelectric, biomass and geothermal. Despite its ability to support the power system and conserve the environment that sustains life, the rising usage of renewable distributed generators (RDGs) poses power quality problems in the overall distribution network, such as the voltage instability at buses, the increase in voltage/current harmonics distortions, etc. The technical requirements for connecting RDGs to the power system have been defined in standard grid code to ensure the safe, secure and proper functioning of the overall power system. The specifications defined in the grid code include the limit of voltage variations (i.e., +/-1 pu), the limit of frequency variations (i.e., +/-5%), and the limit of current/voltage harmonic distortions (i.e., total harmonic distortion voltage (THDv) of 0.1% and total harmonic distortion current (THDi) of 5%), and a power factor limit of Pf = (0.9-0.95). Additionally, RDGs must remain connected throughout a fault condition and assist in voltage recovery. In this dissertation, control strategies for grid connected wind energy conversion system (WECS) are investigated for dynamic performance evaluation. This work focuses on the doubly fed induction generator (DFIG) – based WECS incorporating a proportional integral (PI) controller; the permanent magnet synchronous generator (PMSG) – based WECS incorporating a PI controller; DFIGb-based WECS incorporating a voltage source converter (VSC) with a fuzzy-logic controller, the proportional integral derivative (PID), and fuzzy-PID controller. A comparative analysis of the different WECS topologies was further conducted in terms of the steady-state error, the percentage overshoot, and the settling time of the voltage/current or power output signals and dc-link voltage signals.The VSC was selected as compared to the line-commutated converters (LCCs) because of the commutation that is not dependent on voltage and current AC signals. The grid-side converter was applied to regulate DC-link voltage and reactive power to their reference values. The rotor side converter provided rotor speed regulation on the DFIG to control the power output signal. The vector control method was used for the dynamic performance analysis. The simulations were done using MATLAB/SIMULINK. From the simulation results, it was found that the DFIG-based WECS incorporating a fuzzyPID controller performed efficiently compared to the other topologies of WECS.