As shown in Fig. 2, the model of DFIG frequency converter system consists of rotor-side converter, grid-side converter, the dc link and the corresponding converter control. In this chapter, it is assumed that the grid-side converter is ideal and the dc link voltage between the converters is constant during analysis. This decouples the grid-side converter from the rotor-side converter. The rotor-side converter is assumed to be a voltage-controlled current source, and the stator flux-oriented control strategy is employed to implement the decoupled control of the real and reactive power outputs of DFIG. The overall converter control system consists of two cascaded control loops, i.e. the inner control and the outer control. The inner control loop implements the rotor current control, and the outer control loop implements the power control (Tapia et al., 2006).
In order to implement the decoupled control of the real and reactive power outputs of DFIG, two new variables, Udr, Uqr are introduced which are defined as:
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