Research on Control-Winding-Current Orientation Control for Grid-Connected Brushless Doubly Fed Induction Generation System

Compared with the traditional doubly-fed induction generator (DFIG), the brushless doubly-fed induction generator (BDFIG) eliminates the slip rings and brush gear, which has the benefit of low maintenance costs and high reliability. It thus promises broad application prospects in power generation. The whole generation system should operate in both stand-alone mode and grid-connected mode to provide uninterrupted and continuous power to critical loads. The two operating modes have different control structures due to separate control targets, increasing the control complexity of the power generator system. This article proposes the control winding (CW) current-oriented vector control method for BDFIG in grid-connected mode, which has unique advantages in stand-alone mode. First, the modified variables are obtained under the CW-current rotating frame; Second, the power expression of the system is deduced according to the modified variables; Third, the angle of CW was chosen as a new control degree of freedom based on phase-angle control to realize power control. The proposed control strategy analyzed the control principle of CW-current amplitude and angle control in detail. This method adopts the same orientation strategy with stand-alone mode, which avoids the switching of orientation strategy in different operation modes, thus simplifying the system design a lot. Moreover, considering the same criteria GSC control, reactive power compensation, the control during grid voltage recovery and so on, the large CW-current can be limited at a safety level once the overload or grid faults happened, which can easily achieve Low-Voltage-Ride-Through (LVRT) and significantly increased security and stability of the system. Finally, the proposed control strategy is verified by the experimental results.