Research on Coordinated Compensation Using Multi-Tap Transformer and DVR

In recent years, frequent voltage sag events have significantly impacted high-quality grid operation. To address the limitations of conventional compensation methods-specifically, the inability of multi-tap transformers (MTT) to achieve full voltage sag compensation and the high cost of large-capacity dynamic voltage restorers (DVRs)-this study proposes a hybrid compensation system (MTT-DVRs) combining MTT and DVR technologies. The topology of the MTT-DVR system is analyzed, and the fundamental principles of coordinated compensation are established. Aiming to minimize the active power output of the DVR, two compensation strategies are investigated: full compensation and in-phase compensation. For these strategies, a mathematical model for selecting the optimal transformer ratio <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$k$</tex> of the MTT is developed. A coordinated control strategy is proposed based on the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$d q$</tex> fundamental synchronous rotating coordinate transformation method and resonant filters. This strategy enables the MTT to compensate for the majority of voltage sags while the DVR handles residual voltage deviations and harmonic elimination. Finally, simulation results verify the effectiveness of the proposed MTT-DVR system.