A novel inverter voltage support strategy based on phase-separated reactive power injection under complex grid faults

Abstract When the grid voltage experiences a drop, various current injection strategies can be employed to support three-phase three-wire inverters. However, under complex grid fault conditions—such as when voltage sag and swell occur simultaneously—the effectiveness of existing voltage support strategies becomes limited and is often accompanied by considerable active power fluctuations. To address this issue, this paper proposes a Phase-Separated Reactive Power Injection (PSRPI) strategy to enhance voltage support at the point of common coupling (PCC) during asymmetrical voltage sags. The first contribution of this work is improving voltage support capability by injecting phase-separated reactive currents according to the proposed PSRPI strategy tailored to the depth of voltage sags or swells in each phase. The second contribution involves leveraging the coupling relationship between active power fluctuations and reactive current to limit the reactive current magnitude, thereby reducing the adverse impact of power fluctuations on the inverter. Furthermore, a current saturation strategy is implemented to prevent over current risks under deep voltage sags and ensure reliable over current protection. Simulation and experimental results demonstrate that, under voltage sag conditions, the proposed control strategy increases the positive-sequence voltage at the PCC by 15.1% and reduces the negative-sequence voltage by 20.31%. Under voltage swell conditions, the elevated fault voltage is reduced by 2.8%. Furthermore, under different asymmetric fault types, the proposed strategy achieves a maximum positive-sequence voltage improvement of 20.65% and a maximum negative-sequence voltage reduction of 7.49%, outperforming the comparative control strategies.