Improved Vector Control of Brushless Doubly Fed Induction Generator under Unbalanced Grid Conditions for Offshore Wind Power Generation

Brushless doubly fed induction generators (BDFIGs) are promising alternatives to doubly fed induction generators due to high reliability and low maintenance cost for the absence of brushes and slip rings. As a typical application in offshore wind energy generation, a feedforward method is applied to the grid-voltage oriented vector control to make the active and reactive power decoupled. Another challenge in practice is how to meet the demanding requirements of grid codes. The dynamic behavior of BDFIG is analyzed in detail under unbalanced grid conditions with the proposal of four different targets. To deal with these issues, an improved vector control strategy based on the proportional-integral resonant controller (PI + R) in a single synchronous reference frame is developed. The stability and robustness of the proposed control scheme under parameters uncertainties and variations are discussed as well. The advantage of this control strategy is that it is simple and fast in transient response. The effectiveness of the proposed control strategy is validated by the experiment results of a 3-kW prototype machine.