A Voltage Support Scheme for Distributed Generation With Minimal Phase Current Under Asymmetrical Grid Faults

In the event of grid faults, the disconnection of a large capacity distributed generation (DG) may compromise grid stability. To address this challenge, grid codes in many countries have incorporated fault ride-through capability that requires the DG to remain connected to the grid for a stipulated time and regulate the voltage at the point of common coupling (PCC). A voltage support scheme (VSS) aims at restoring the PCC voltage within stipulated limits by injecting suitable currents. To restore the voltage under asymmetrical faults, a conventional VSS requires unequal current injection. As the phase current of the highest amplitude hits the rating of the inverter, the voltage support capability of the DG is compromised. The VSS proposed in this article aims to minimize the highest phase current while maintaining the same voltage support at PCC. The reduction in the highest phase current, in turn, provides reserve voltage support capability. The proposed scheme works well for all types of grid impedances, and the optimum points are found to be independent of the grid impedance. This independence of the optimum points simplifies the implementation of the proposed VSS. The simulation and experimental results demonstrate the effectiveness of the proposed VSS.