State feedback control of brushless Doubly-Fed wind power generator under symmetrical drop of grid voltage

In the dynamics of grid-connected operation of brushless doubly fed generators (BDFG), when the grid voltage dips, it is equivalent to adding a reverse voltage source at the parallel node suddenly. By deriving the expressions of the transient current of power winding (PW), control winding (CW), and rotor winding (RW) of BDFG in the complex frequency domain under natural state, it is concluded that the overshoot and oscillation time are affected by the generator parameters, the drop degree and phase of the grid voltage, and the rotor speed. Then, a state feedback control strategy is proposed, and a state model with PW, CW, and RW current as state variables is constructed. State variables are added to the input through the feedback matrix, the parameters of system matrix of the generator are changed, that is, the equivalent parameters of the generator are changed. The pole distribution diagram shows that under the state feedback strategy, the poles shift significantly to the left compared with the poles with traditional control, so it could make the system accelerate convergence, reduce the amplitude. Finally, the feasibility of the state feedback algorithm was verified using tests on an experimental platform.