A Capacitor-Current-Feedback Active Damping Control Strategy With Phase Lead Compensation for LCL-Type Grid-Connected Inverter

Capacitor-current-feedback (CCF) active damping is widely used to deal with the hazard of LCL filter resonance in the grid-connected inverter based on either phase lead or lag compensation, and the effect of active damping on open-loop of the control system can be evaluated directly by its equivalent impedance. However, the principle of phase compensation for active damping is not clear, and it is difficult to point out how to regulate the compensator to achieve the desired effect of virtual impedance. This paper presents a comprehensive investigation of active damping control of the LCL-type grid-connected inverter. Firstly, the effect of digital control delay on unstable poles of CCF active damping and the principle of phase compensation are identified by analyzing the frequency response of the inverter system. Subsequently, the designs of CCF active damping with phase lead compensation and proportional resonance regulator are studied to guarantee the performance of the inverter system, where a novel solution is given to find the frequencies of phases with -180 degrees crossings, which is essential to the design of control parameters. Finally, the effectiveness of the proposed method has been validated by the experimental results.