Like synchronous generators

transient instability also occurs to droop-controlled inverters when subjected to large disturbances. Owing to the current limitation

the voltage loop of the inverter is out of work during the disturbance and the inverter turns to operating in the current source mode. The mechanism of the virtual power angle curves deviating during the transient process because of the limited voltage tracking performance

which reduces the stability margin

is further analyzed. To this end

a current feed-forward control method based on estimating the output current is proposed to improve the voltage tracking performance so that the transient stability is improved. Besides

to deal with the loss of equilibrium points during the transient process

a transient synchronous control method is proposed. It helps the inverter to reach a proper equilibrium point when the voltage loop is out of commission and prevents the inverter from transient instability. Finally

simulations on a single-machine-infinite-bus system verify the effectiveness of the proposed control methods. This work is supported by National Key Research and Development Program of China(No. 2016YFB0900104)

National Natural Science Foundation of China(No. 51577168)

and Yunnan Electric Power Company(No. yndw(2016)000303DD00124).