Current-based direct power control of a DFIG under unbalanced grid voltage

Abstract

A novel current-based direct power control (CB-DPC) strategy for a grid-connected doubly-fed induction generator (DFIG) is proposed. The reported control scheme is applicable to DFIG-based variable-speed wind turbines that operate under unbalanced network voltages. The required DFIG rotor voltage for pre- cise regulation of the stator active and reactive output powers and accurate elimination of their inherent pulsations are directly obtained using a nonlinear integral sliding-mode control (ISMC) scheme. Compared with other control methods, the proposed strategy is simpler since it is not based on the sym- metrical components theory, does not need multiple synchronous coordinate transformations, and only requires DFIG voltage and current values as its inputs. Constant switching frequency of the rotor-side converter (RSC) is achieved by means of space vector pulse-width modulation (SVPWM) technique. Uncertainties in the parameters of the generator are included in the design. A compensation strategy is also proposed for tracking error mitigation of the powers that occur due to elimination of the chattering phenomena in the ISMC scheme. Simulation results on a 2MW DFIG under different operating conditions are presented to validate the effectiveness and robustness of the proposed method.