Dynamic Voltage Restorer Based on Three-Phase Inverters Cascaded Through an Open-End Winding Transformer

This paper investigates a dynamic voltage restorer (DVR) composed of two conventional three-phase inverters series cascaded through an open-end winding (OEW) transformer, denominated here DVR-OEW. The DVR-OEW operating with either equal or different dc-link voltages is examined. The proposed topology aims to regulate the voltage at the load side in the case of voltage sags/swells, distortion, or unbalance at the grid voltage. A suitable control strategy is developed, including space-vector analysis, level-shifted PWM and its equivalent optimized single-carrier PWM, as well as the operating principles and characteristics of the DVR. Comparisons among the DVR-OEW and conventional configurations, including a neutral-point clamped converter-based DVR, are furnished. The main advantages of the DVR-OEW compared to the conventional topologies lie on: 1) reduced harmonic distortion, 2) reduced converter losses, and 3) reduced voltage rating of the power switches. Simulated and experimental results are presented to validate the theoretical studies.