Flexible Voltage Support Control of Three-Phase Four-Leg Inverter with Active and Reactive Power Oscillation Optimization Under Typical Double-Line-to-Ground Faults

Owing to the existence of zero-and negative-sequence voltage during grid faults, supporting the power grid and restraining active and reactive power oscillation (RPO) have become two main fault-tolerant requirements of distributed generation (DG). This paper presents a flexible voltage support control strategy without RPO in the four-leg inverter system relies on appropriate value of defined coefficient E, which can support the power grid, optimize the active power oscillation (APO) flexibly and limit the injected current to the allowed maximum by calculating the appropriate reference currents according to the equivalent impedance and the voltage sag characteristics under typical double-line-to-ground (DLG) faults. In this paper, it is assumed that the grid impedance is known, the proposed fault-tolerant control scheme requires calculating the grid impedance angle. The availability of the proposed strategy is verified by the simulation and experimental result.