A Frequency Trajectory Planning Control for Grid-forming Inverter

Due to the limited inertia damping of standalone power system, frequency deviation and rate of change of frequency (RoCoF) are vulnerable to disturbances, so it is necessary to improve frequency stability through proper control strategies. Limited by disturbance calculation and inertia/damping evaluation, the typical strategies such as droop control and virtual synchronous generator (VSG) cannot ensure frequency safety under large disturbance conditions. To solve these problems, the frequency trajectory planning control (FTP) is proposed to assist in controlling inertia/damping. FTP control autonomously detects the system frequency during normal operation. When the system frequency indicators have the risk of triggering frequency related relays, FTP function is enabled by frequency deviation and/or RoCoF, and actively plans a frequency trajectory that complies with national standards to limit the frequency trajectory in the safe area. Finally, the experimental results under different working conditions verified the effectiveness and advancement of the FTP control.