A stability criterion research on the energy storage inverter under the off-grid condition is conducted. First

this paper describes the concept of the cascade system and that of output impedance and input impedance based on the topology of an energy storage inverter with load. A quasi proportional-resonant (PR) controller is adopted to control the inverter

set up its mathematical model and get the inverter’s output impedance. Based on the MATLAB simulation model

the influence of variation of the inverter's output impedance on the system stability is analyzed by simulation under the condition of variation of the load level

controller parameters and filter parameters

respectively. Corresponding conclusions are drawn which can provide theoretical support and guiding experience for actual system design. This work is supported by National High Technology Research and Development Program of China (863 Program) (No. 2014AA052004).