Modeling and Analysis of DFIG Operation under Unbalanced Gnd Voltage and Non-linear Load Conditions

Abstract

This thesis presents the modeling and analysis of doubly fed induction generator (DFIG) operations under unbalanced grid voltage in the normal and non-linear load conditions. For the simulations, a novel control strategy for wind power generation system is also applied. The oscillations of the DFIG electromagnetic torque and power in the stator side are fully described in the unbalanced grid voltage. Besides, the harmonic current components in the network which come from non-linear loads are also analyzed. A current controller, proportional-resonant (PR) controller, implemented in the stationary reference frame is proposed to mitigate the negative sequence current components in both grid side converter (GSC) and rotor side converter (RSC). To provide enhanced operation, the RSC is controlled to mitigate the stator active power and the rotor current oscillations at double supply frequency under unbalanced grid voltage while the GSC is controlled to mitigate ripples in the dc-link voltage and compensate harmonic components of the network currents. Simulation results using Psim simulation program are presented for a 2 MW DFIG wind generation system to explain the operations of DFIG under normal conditions and confirm the effectiveness of the proposed control strategy during unbalanced gird voltage and non-linear load conditions.