This paper builds a unified model from the perspective of active power and power angle to compare the stability of virtual synchronous generator (VSG) and current-controlled inverter (CCI) when connected to weak grid. Under the unified model, the effect of grid strength on the stability and dynamic response of CCI and VSG is analyzed. It is found that VSG better damps active power perturbation while CCI will have right half plane poles (RHP) under weak grid, which result in stronger stability of VSG than CCI under weak grid. Then an active power feedforward control is proposed to improve the stability of CCI under weak grid. Through feedforward the input of active power controller to the amplitude command of AC voltage control, the low frequency oscillation of CCI under weak grid is well suppressed. Simulation validates the theoretical analysis and effectiveness of the proposed control.

current-controlled inverter,stability analysis,VSG,weak grid