This paper proposes a new control strategy of effective fifth and seventh harmonic elimination in the stator output voltage at the point of common coupling for a stand-alone doubly fed induction generator (DFIG) feeding a three-phase diode rectifier. This load regularly causes such harmonic distortions, which harmfully affect the performance of other loads connected to the DFIG. In order to allow the DFIG to deliver a pure sinusoidal stator output voltage, these harmonics must be rejected. The proposed elimination method is investigated based on the rotor current controller employing a proportional integral and a resonant controller, which is implemented in the fundamental reference frame. In this frame, both positive seventh and negative fifth voltage harmonic can be eliminated by using only single resonant compensator tuned at six multiples of synchronous frequency in the rotor current controller.
The control scheme is developed in the rotor-side converter for the control and operation of the DFIG. Simulations and experimental results with 2.2-kW DFIG feeding a nonlinear load are shown to verify prominent features of the proposed control method.Index Terms-Doubly fed induction generator (DFIG), nonlinear loads, resonant controller, stand-alone system, wind turbine system.
NOMENCLATUREv s , v r Induced stator voltage and rotor voltage. v P Stator output voltage at the point of common coupling. v N S The nonlinear voltage drop on the internal stator impedance. V dc DC-link voltage. i s , i r , i m s Stator current, rotor current, and stator magnetizing current. λ s , λ r Stator and rotor fluxes. L s , L r , L m Stator, rotor, and mutual inductances. R s , R r Stator and rotor resistences. ω s , ω r , ω sl Synchronous, rotational rotor, and slip speeds. θ s , θ r , θ sl Synchronous, rotational rotor, and slip angles. σ Total leakage factor. d/dt, Δ Differential operator and error value.