Decoupled control of active and reactive power for a grid-connected doubly-fed induction generator

In this paper, a novel control strategy by internal model control based on the inverse system theory is proposed for the DFIG, which guarantees a sufficient stability region in the state space, and decouples the active and reactive stator current allowing the independent control of the active power and reactive power of DFIG. First, a nonlinear mathematical model of DFIG is developed with state variables in d-q axis. Then the alpha order inverse system of DFIG is derived. Put the alpha order inverse system in front of the original system, a pseudo linear system can be obtained. The IMC (internal model control) is used for the pseudo linear system. This control strategy is able to decouple the coupling effect of the d-q current control, and have good ability to ride through both symmetrical and unsymmetrical voltage sags. The simulation results verified the validity of the proposed control strategy.