Modelling and simulation of a grid connected doubly fed induction generator for wind energy conversion system

Abstract

The Doubly Fed Induction Generator (DFIG) based wind turbine with variable speed variable-pitch control scheme is the most popular wind power generator in the wind power industry. This machine can be operated either in grid connected or standalone mode. A thorough understanding of the modelling, control, and dynamic as well as the steady state analysis of this machine in both operation modes is necessary to optimally extract the power from the wind and accurately predict its performance. In this thesis, first a three phase PWM voltage source converter models expressed in the ABC and the DQO synchronous reference frame with its control schemes are developed and analysed. Then a DFIG-based wind turbine model connected to a constant voltage and frequency grid is developed in the Matlab/Simulink software in detail and its corresponding generator and turbine control structure is implemented. A thorough explanation of this control structure as well as the steady state behaviour of the overall wind energy conversion system which includes the aerodynamic models of the wind turbine, the DFIG models and the three-phase two-level PWM voltage source converter models are presented. A developed control schemes are also necessary to achieve useful output power from the WECS. These control schemes include the generator-side converter control, the grid-side converter control, the pitch angle control and the maximum power point tracking control. The grid-side converter controller is used to maintain the constant voltage across the capacitor and produce a unity power factor operation of the grid. The generator-side converter controller is used to regulating the torque, active power and reactive power.