ANALYSIS OF A WIND TURBINE GENERATION SYSTEM

Abstract

Wind turbine technology is one of the fastest developing renewable technologies_ The development started in the 1980s with a few tens of kilowatt power rating wind turbines and has grown to today's megawatt range wind turbines. In the earlier times wind power production did not have any serious impacts on the power system operation and control, but now it plays an active part in the grid since the wind power penetration level is increasing rapidly. The technology used in wind turbines was in the beginning based on squirrel-cage induction generators directly connected to the grid. By that, power pulsations in the wind are almost directly transferred to the grid and also the efficiency is less because it can operate only at particular speed. But the introduction of new types of generators and power electronics to wind energy network has made the system more efficient. Different types of generators used in variable speed operations are squirrel cage induction generator, wound rotor induction generator, synchronous generator. The predominant ones among these are Doubly Fed Induction Generator which is a type of wound rotor induction generator and permanent magnet synchronous generator employing permanent magnet on the rotor as field. In this thesis, Doubly Fed Induction Generator is studied in detail along with AC-DC-AC converter operating in both super synchronous and sub synchronous modes. The AC-DC- AC converters used here use the PWM techniques for better performance. The scheme allows the speed of the wind turbine to be varied to obtain more efficient turbine operation at different wind speeds. The rating of the converter is proportional to the maximum rated slip value, typically about ± 30 per cent, where positive slip applies to sub synchronous rotor speeds. In comparison, a variable-speed, constant-frequency system using a synchronous generator would require a frequency converter rated at full generator power. The simulation work is carried out in the matlab software.