Fault Recovery of Grid-Forming Inverter by Droop Coefficient Modifier

Current limiting is necessary for the ride-through during fault conditions with grid-forming inverters, and the grid-forming inverter is crucial for inverter-based resources (IBR’s) dominated power system. Current limiting not only shifts the power angle curve but also decreases the critical clearing time. During faults, there is a considerable mismatch between the nominal power and the measured power, which causes a large deviation of the virtual power angle from its initial value. Depending on the fault duration, the grid forming inverter (GFM) inverter takes a certain time to return to a steady state and if the fault is not cleared before the critical clearing time, the system loses synchronism with the infinite bus. Reduction of the P-f droop coefficient limits the virtual power angle to its steady state value so after fault clearance, it takes less time for fault recovery. In this work, current is limited by reducing the current reference, and for this, a d-q component current limiter is used. The point of common coupling (PCC) voltage is measured and used to calculate the droop coefficient modifier. This is due to the fact that the reference voltage generated by the outer power control loop does not vary significantly during faults. A droop-controlled grid forming (GFM) inverter is connected to an infinite bus. The results are simulated for both symmetrical and asymmetrical in the Simulink environment of MATLAB to highlight the performance and advantages of the proposed method.