Droop transient control strategy considering transient power angle stability and fault current limitation of a grid-connected inverter

There are issues of transient power angle instability and fault overcurrent in droop-controlled inverters in fault conditions. Thus a transient control strategy that considers both transient power angle stability and fault current limiting is proposed. First, the mechanism of transient power angle instability in droop-controlled inverters and the transient characteristics of fault currents are analyzed. The impact of the reactive power control loop on transient stability and the relationship among transient power angle, short-circuit current, and inverter output voltage are quantitatively analyzed. Second, to achieve transient power-angle stability and fault current limiting, a comprehensive control approach is proposed, one which introduces a dynamic compensation term for transient power-angle in the active power control loop and adapts the voltage reference command value in the reactive power control loop. Finally, simulation experiments are conducted to validate the proposed control strategy. It not only suppresses the continuous increase of power angle caused by unbalanced power during fault processes and mitigates fault overcurrent but also increases reactive power during fault periods to facilitate fault voltage recovery. Consequently, the proposed strategy enables the safe and stable operation of droop-controlled inverters during grid faults. © 2023 Power System Protection and Control Press. All rights reserved.