Comparison of Transient Angle Stability Between Virtual Synchronous Generator and Droop-controlled Inverter

Inverters using virtual synchronous generator (VSG) or droop control may lose synchronization with the grid due to transient angle instability under severe symmetrical grid faults, especially when they are connected to weak grid. To investigate the angle stability of microgrid and improve inverters’ transient angle stability, transient Angle stability of inverters using VSG and droop control in grid connected system are compared in this paper. The equivalence of swing equation between these two control strategies is present. Then, the principle of transient angle stability is explained by using equal area criterion (EAC). To evaluate the effect of parameters of inverter on the angle stability, domain of attraction for VSG and droop-controlled inverter are compared based on Lyapunov function. Finally, experiments are carried out to draw the conclusion: Droop-controlled inverter can lose synchronization with the grid faster than VSG during the period of fault and resynchronize faster than VSG after fault for its very low inertia. While the VSG can change its angle stability higher or lower than droop-controlled inverter flexibly by changing its inertia and damping.