抄録
The Virtual Synchronous Generator (VSG) is an inverter control structure that supports power system stability by imitating a synchronous machine. Because of the restriction of inverter power and current, the VSG performance under disturbances should be evaluated and enhanced. In this paper, the response of the VSG unit to symmetrical and unsymmetrical voltage sags is assessed. A theoretical analysis that traces the trajectory of the state variable of the system during voltage sags is presented. The analysis confirms the effect of the characteristics of symmetrical and unsymmetrical voltage sags on the severity of their consequences. In addition, it is detected that two types of transients appear that must be mitigated: one is the transients during the voltage sag and the other one is the transients after voltage recovery. To prevent overcurrent during voltage sags, voltage amplitude control and output power control are implemented, and to suppress the transients after voltage recovery, virtual inertia control is implemented. The experimental results from a 10kVA VSG-controlled inverter confirm the effectiveness of the additional controllers.
