Flexible power flow control for brushless doubly fed induction generator

This thesis presents the brushless doubly fed induction generator (BDFIG) system for wind energy conversion. The system is proposed as an advanced solution to the traditional doubly fed induction generator (DFIG) to reduce the maintenance cost and improve the system reliability of the wind turbine system. The proposed BDFIG employs two cascaded induction machines to eliminate the brushes and copper rings in DFIG. The dynamic model of BDFIG with two machines' rotors electromechanically coupled in the back-to-back converter is developed. The independent control of the active and reactive power flow is achieved by means of a four-quadrant power converter under the closed-loop stator flux oriented control scheme. In the proposed control strategy, the generator speed tracks well the reference speed, thus the maximum power extraction is achieved. The experiment was done on a 2kW BDFIG system. Simulations and experimental results from the experimental system verify the proposed system model and control design.