Control of DFIG for rotor current harmonics elimination

Unbalanced stator conditions cause rotor current harmonics and torque pulsations in Doubly-Fed Induction Generators (DFIG) which are used widely in wind energy systems. From a hardware perspective, current control techniques to minimize the rotor current harmonics include rotor-side converter injected voltage compensation and grid-side converter compensation. From a software perspective, the current controllers either adopt synchronous reference frame for controller design or adopt positive synchronous (qd⁺) negative synchronous reference frames (qd^-) to decompose the harmonics in rotor currents and control them separately. This paper develops a proportional resonance (PR) control strategy in the stationary reference frame (alphabeta) to minimize rotor current harmonics and torque pulsations. The main advantages of the proposed method are (i) only one transformation (abc/alphabeta) is required and (ii) harmonic filters are not required. The proposed control strategy is compared with the proportional integral (PI) control strategyin qd⁺ and qd^- and the proportional integral and resonant (PIR) control strategy in qd⁺. Simulations performed in Matlab/Simulink are presented to illustrate the effectiveness of the proposed control strategy.