Improved operation of DFIG and FSIG-based wind farms during network unbalance

This paper investigates the modeling and control of doubly fed induction generator (DFIG) and fixed speed induction generator (FSIG) based wind farms under unbalanced conditions. A DFIG model suitable for analyzing unbalanced operation is developed, and used to assess the impact of an unbalanced supply on DFIG and FSIG operation are illustrated. Network voltage unbalance can cause unequal heating on the stator windings due to the unbalanced current, extra mechanical stresses due to the torque oscillations, and output power fluctuations. These problems are particularly serious for the FSIG based wind farm without power electronic interface to the grid. A control strategy for improving the stability of a wind energy system containing both DFIG and FSIG based wind farms during network unbalance is proposed. The simulation results implemented in MATLAB/Simulink show that the proposed DFIG control system can not only improve its own performance, but it can also improve the stability of the FSIG system with the same grid connection point during network unbalance.