Digital control cannot avoid control delay in spite of its high reliability and flexible control

which can change the stability of the system. A discrete accurate mathematical model of the LCL-typed grid-connected inverter is developed and the direct digital method is adopted with the digital delay elements such as computation

sampling taken into account. The system stability with single-loop control based on grid-side current is comparatively analyzed in continuous domain and discrete domain

which accounts for the influence of the digital delay on the system stability. Thus the stability influence of the frequency ratio range of the sample and resonance based on grid-side current control is mainly analyzed when the digital delay is set one-step delay and the frequency ratio range is obtained

meanwhile the parameters of the controller are designed. Simulation and experiment proves the correctness and effectiveness of the proposed method.