Research on stability of grid-connected LCL-filtered inverter with capacitor current feedback active damping control

For grid-connected LCL-filtered inverter, the inherent resonance of LCL filter endangers the stability so that the inverter is hard to be controlled. To solve the resonance, the capacitor-current-feedback active damping (AD) is welcomed. However, the digital control delay was not seriously considered in the previous studies. The research on the stability with such control considering the digital control delay is lacking. Thus, this paper aims to provide a deep analysis of the capacitor-current-feedback AD in a digitally-controlled inverter. A stable region is derived. It is proved that the stable region for the capacitor-current-feedback AD is closely related to the sampling and computation delay, the control frequency, the resonance frequency and the capacitor-current-feedback factor. Several suitable approaches are then proposed to improve the performance with the capacitor-current-feedback AD. The experimental results verify the presented research.