Research on Control for Grid-Connected Brushless Doubly-Fed Power Generation System Under Different Quantities

Brushless doubly-fed induction generator (BDFIG) promises significant advantages such as high reliability and low maintenance costs, which shows commercial promise for power generation system. 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 grid-connected mode usually uses the power winding (PW) synchronous and orientation frame since PW is connected to the grid; however, in stand-alone mode, control winding (CW) current orientation is widely used for its unique advantages. This paper compares PW-flux orientation, CW-current orientation and PW-flux-CW-current dual orientation methods, and the control system is designed. In order to adopt the same orientation strategy with stand-alone mode to maintain the advantages of CW-current orientation and avoid the switching of orientation strategy with different operation modes, this paper adopts CW-current orientation control method after comparison of the three orientations in grid-connected mode. With CW-current orientation, the large CW current can be limited at a safety level once the overload or Low-Voltage Ride Through (LVRT) happened as it oriented on the control winding, which significantly increased security and stability of the system. Finally, the proposed control strategy is verified by the experimental results.