Research on Control Strategy for Doubly-fed Generation System under Unbalanced Voltage Condition

Due to the distribution characteristics of wind resources,many wind turbines are installed in remote areas,where the power grid is usually weak and the unbalanced voltage condition often occurs.The unbalanced voltage condition should be taken into account in the control system,otherwise it will cause active and reactive power fluctuations.The models of doubly fed induction generator and grid-side converter under unbalanced voltage are presented based on the symmetrical component theory.The impact of negative sequence voltage on the conventional vector control is analyzed.According to the analysis results,a novel double fed wind generation(DFWG) vector control method based on the proportional resonant(PR) regulator is presented.Theoretical analysis and simulation results show that the proposed strategy is very effective to minimize the torque,reactive power and dc-link voltage fluctuations in unbalanced network.