Coherency-based Coordination Scheme to Mitigate Adverse Dynamic Interaction of Grid-Forming Inverters

Due to the better frequency response and transient stability, grid-forming inverters (GFMIs) have shown themselves as a promising solution for the future grid with high penetration of power electronic converters. However, in a network composed of multiple GFMIs using virtual synchronous generator (VSG) as the primary controller, the disturbance from pulse loads or plugin loads may introduce undesired frequency and active power dynamics and oscillations. These adverse dynamics can increase the rate of change of frequency (ROCOF) in some of the buses and disturb transient stability. In this paper, a coherency-based coordination scheme is proposed to eliminate these adverse frequency dynamics and improve frequency nadir in a network comprising fleet of VSG-based GFMIs. The proposed coherency-based coordination selects a coordinative frequency trajectory using the VSG control loop. The proposed coordinative scheme then calculates coordinative coefficients based on which the VSGs start to inject power while maintaining a coherent dynamic response and mitigating adverse dynamic interactions and oscillations. Simulation results for different values of load change in multiple buses are presented to validate the effectiveness of the proposed coordination scheme.