Angle Resetting Control for Virtual Synchronous Generator with Limits of Frequency

Due to the narrow operational domain of the Voltage Source Converter (VSC), it is necessary to implement frequency limitations to prevent damage to the equipment and to maintain the stability of the system. This paper provides new insights for rationally setting frequency limits to ensure the transient stability of Virtual Synchronous Generator (VSG). First, the grid-connected VSG dynamic model with frequency restrictions and subsystem switched model are developed. It is shown that the system's frequency-limited trajectories leave away from boundaries at two specified points which are fixed irrespective of the switching times. According to the Lyapunov theory, if the leaving bound points have less energy than that of the Unstable Equilibrium Points (UEP), the limited system can remain stable. As a result, the stability of the system can be ensured by adjusting the upper and lower boundaries of the frequency. Moreover, since the energy of the SEP only has kinetic energy, which is minimal among all the leaving bound points, resetting the angle of VSG to its SEP once the limits of frequency are reached can ensure the system always stabilize at the initial period of the angle.