In this chapter, two special PI controllers are designed to implement the decoupled control of the real and reactive power outputs of DFIG. The block diagrams of rotor-side converter including the inner and outer control loops expressed in d and q axes are given in Fig.4 and Fig.5. In the rotor current control loop, Tr'=Xr'/R, Tr' is the time constant of rotor circuit; Idrref, Iqrref are the rotor current references in d and q axes, respectively; K2 and T2 are the control parameters of PI controller. In the power control loop, Psref, Qsref are the real and reactive power references; Kl, Tl are the control parameters of PI controller. It should be noted that the specific values of Kl, Tj, K2 and T2 can be determined through pole placement method (Tapia et al., 2006).
In accordance with Fig. 4, the corresponding stator real power control model can be described as fW - KT (^ - ^) = K1 (Ps - Psref) (30)
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