MODELING AND CONTROL OF GRID CONNECTED DOUBLY FED INDUCTION GENERATOR

Abstract

Wind energy is one of the most promising and fastest growing energy resources in the world. Now a day this energy is an essential ingredient of socio-economic development and economic growth. In the recent days, the increased emphasis is being given on the harnessing of renewable/non conventional energy sources. Wind energy conversion systems are employed to generate electrical power from mechanical power derived from the wind. Wind energy conversion systems may operate at fix speed or at variable speed. Operating the wind turbine at variable speed has some attractive advantages like reduced mechanical stress in the gear box, increased annual energy capture, the need for costly blade control mechanism is avoided, improved controllability. This dissertation work is oriented towards investigating the performance characteristics of variable speed constant frequency (VSCF) wind generation systems. In the presented work a DFIG variable speed constant frequency (VSCF) wind generation system has been simulated in MATLAB/Simulink software with an algorithm to track peak power points of wind turbine and a control scheme has been implemented to control active and reactive power injected into the grid. The doubly fed induction generator is used as wind generator for its variable speed operation and four-quadrant active and reactive power capabilities. This report provides a vector-control scheme for the PWM converter which is used for controlling the DFIG, results in independent control of active and reactive power of the doubly fed induction generator. The control system generates the pitch angle command and the voltage command signals for rotor side and grid side converter respectively in order to control the power of the wind turbine, the DC bus voltage and the reactive power or the voltage at the grid terminals. The mathematical model of the machine written in an appropriate d-q reference frame is established to investigate simulations. In order to control the power flowing between the stator of the DFIG and the grid, a decoupled control of active and reactive power is synthesized using PI controllers. It provides decoupled regulation of the active and reactive power and it is suitable for both electric energy generation and drive applications.