Abstract
This paper presents a fault ride-through control strategy for grid-tied virtual synchronous generator (VSG) under two main grid fault conditions, grid voltage sag fault and unintentional grid outage fault. Considering the overcurrent issue of VSG during the grid voltage sag fault, mechanism on overcurrent issue and the relationship among power angle, voltage amplitude, active power and reactive power are analyzed. Based on the analysis, a control strategy based on direct power angle and voltage amplitude control is proposed. Compared to the common control strategy based on additional inner current loop, the proposed VSG requires no add extra voltage or current sensors. For the grid outage fault, detailed analysis on the relationship among power angle, active power and frequency has been conducted, and it is found that the power angle is related to the output active power when the converter operates on grid-tied condition; under unintentional islanding conditions, the power angle is related to the voltage frequency. Based on the found, a detection method based on small frequency disturbance is proposed. Simulation studies on a prototype VSG system are presented to demonstrate the validity of the proposed control strategy.
