Investigation of UPQC for Sag Compensation in Wind Farms to Weak Grid Connections

Abstract

In the last years, the wind power generation incorporated into standard grids has been increased significantly. This situation forced the revision of grid connection code requirements, to guarantee the reliability in systems with high wind power penetration. In case of events like voltage sags, wind farms must keep connected to power system avoiding power imbalance and even system collapse. For induction generator based wind farms connected to weak grids, such sag may lead to wind farm outage. Several strategies have been proposed in the literature, but often for full or partial amplitude voltage restoration, without caring phase jump associated to voltage sags. In this work a voltage sag compensation strategy is proposed for voltage magnitude restoration with phase jump compensation, and compared with a magnitude only restoration strategy. These strategies were implemented using a Unified Power Quality Compensator UPQC. A model of wind farm with induction generators connected to a weak grid system, including a detailed UPQC compensator was developed on simulation software. Then simulations were conducted in order to compare the proposed compensation strategy with previous methods. Results show a better wind farm performance in proposed strategy than that found in magnitude only compensation schemes. Also, the power rating of the compensators used in the proposed strategy is similar than the one that would be required in classical strategies. Thus, considering the improvement in performance, the proposed strategy is recommended in retrofitting the existing installed fixed speed induction generators based wind farms.