An Adaptive Current Limiting Strategy for Grid-Forming Inverters Under Symmetrical Grid Faults

When the grid voltage drops, the grid-forming converter (GFM) may experience problems such as short circuit overcurrent and power angle instability, which affect the stable operation of GFM. Virtual synchronous generator (VSG), as a control method of GFM, utilizes the flexible and adjustable characteristics of VSG parameters to propose an adaptive current limiting strategy for grid type inverters under symmetrical voltage drops in the power grid. The fault current during voltage drop on the grid side includes steady-state and transient impulse components. By improving the reactive power voltage control loop to adjust the output voltage reference value, the voltage difference between the grid and the fault current can be reduced, thereby suppressing the steady-state component of the fault current. Introduce variable virtual reactance to suppress the transient surge component of current in the early stage of faults. If the active power reference value is not adjusted after taking current limiting measures, there is a risk of power angle instability, and an increase in power angle will also increase the fault current. By improving the active frequency control loop and introducing an active power adaptive adjustment coefficient, the power angle deviation during faults can be suppressed to ensure the transient power angle stability of GFM. The proposed current limiting strategy enables GFM to effectively suppress short-circuit overcurrent at different voltage drops, ensuring stable power angle during faults and achieving safe and stable operation of GFM during power grid faults. Verify the effectiveness and correctness of the proposed adaptive current limiting strategy through simulation.