Modeling and Coordinated Control Design for Brushless Doubly Fed Induction Generator-Based Wind Turbine to Withstand Grid Voltage Unbalance

In this project, Wind turbines must be able to withstand a certain level of grid voltage unbalance without tripping, according to grid codes. Existing controls for brushless doubly-fed induction generator (BDFIG)-based wind turbines under grid unbalance, on the other hand, have numerous issues, such as difficulty in realising decoupling control, involvement with flux or current estimations, and complex control structure. Furthermore, the existing Studies have primarily focused on the control of the machine side converter (MSC), but the coordinated control of MSC and grid side converter (GSC), as well as the overall control objectives of the BDFIG wind turbine system have not been addressed thus far. To address these issues and improve control capability, this paper proposes a coordinated control strategy that takes MSC and GSC into account. First, the improved control objectives for the overall BDFIG wind turbine system are established. Second, for MSC and GSC, simple single current closed-loop controllers are designed that do not involve any flux or current estimations. Meanwhile, all disturbances and cross-coupling terms on the dq axes are derived and used for feed forward control in current loops to achieve decoupling control and improve system dynamic response. The results show that the proposed control can effectively achieve the overall wind turbine system's control objectives while providing excellent dynamic and stable performance under grid voltage unbalance.

Keywords: Brushless doubly-fed induction generator (BDFIG), voltage unbalance, decoupling control, wind turbine, sequence decomposition.