Control of doubly fed induction generator based wind energy conversion system

Abstract

The doubly fed induction generator (DFIG) is widely used in today’s wind energy conversion industry. The DFIG is essentially a wound rotor induction generator in which the rotor circuit can be controlled by external devices to achieve variable speed operation. This machine stands out for its flexibility and robustness, which make it an ideal device for efficient wind energy exploitation. This thesis modifies a vector-control scheme for DFIG operating as a variable-speed generator. The controller is developed in the d-q axis frame and can be used to control both active and reactive power output separately. The new speed control scheme simplifies and improves Maximum Power Point Tracking (MPPT) control over conventional PI control schemes. The machine model, control system and the modified scheme are simulated and the results are discussed. To implement the control scheme, a new position-sensorless estimation scheme for slip angular velocity is also presented in this thesis.