High Power Quality Voltage Control of Smart Transformer-fed Distribution Grid

Unlike the conventional Uninterruptible Power Supply (UPS), which generally is connected to the scheduled critical loads (data centers, chemical plants and hospitals), the Smart Transformer (ST) experiences a complicated distribution grid with high penetration of Distributed Generator (DG) and nonlinear loads, leading to ST-fed distribution grid suffering from more power quality issues, due to harmonic interaction among DG, nonlinear loads and ST. Based on the CIGRE LV 50Hz distribution grid model, this paper systematically studies the impact of distribution grid integrated with DGs and nonlinear loads on grid voltage power quality by comparing various voltage FeedForward (FF) (reference and measured voltage FF), various current FeedBack (FB) (filter inductor and capacitor current FB), and various current controller (proportional and proportional plus resonant controller). In order to satisfy the standard EN50160 requirement on voltage quality, an improved voltage control strategy is proposed to improve grid voltage quality. The simulation results based on the CIGRE model clearly validate the effectiveness and feasibility of the proposed voltage control strategy.