College of Information Engineering, Xiangtan University, Xiangtan 411105, China

The influence of control delay in digital control on system stability is inevitable for LCL-typed grid inverter. The deficiency of robustness in the digital grid-current single-loop control is discovered, and an active damping method is needed to enhance the damping. But the inner loop control delay is brought about by the digital capacitive current feedback, which makes the equivalent virtual impedance of capacitive current feedback no longer retain its pure resistance characteristic while increasing the difficulty in stabilizing the system. So a method of combining duty cycle prediction with increased zero-pole to compensate for control delay is proposed. The control delay is effectively compensated by the duty cycle obtained by predictive control algorithm with the increased zero-pole, which eliminates the one beat and half of beat control delay generated by calculation, sampling and zero-order holder, respectively. And the active damping method is enabled to effectively enhance damping. The design of the method is simple and the stability of the system is enhanced. The effectiveness and feasibility of the proposed method are proved by simulation and experiment.