A Capacitor-Current-Feedback Positive Active Damping Control Strategy for LCL-Type Grid-Connected Inverter to Achieve High Robustness

To guarantee system stability, proportional capacitor-current-feedback (CCF) active damping control has been widely used in LCL -type grid-connected inverter. However, when digital control is adopted in a grid-side current-controlled inverter, proportional CCF active damping will show negative damping characteristic in frequency band higher than one-sixth of the sampling frequency ( f s /6), causing poor robustness in weak grid. In this article, an unstable second-order phase lead compensator is proposed to insert into the CCF path for eliminating the negative effect resulting from the digital control delay. In doing so, the positive damping region is extended to almost Nyquist frequency ( f s /2), which achieves high robustness against grid impedance variation. To ensure system stability, the discrete rule is investigated for the proposed compensator and system performance is analyzed when the LCL resonance frequency changes in the range of (0, f s /2) in discrete domain, a particularly simple and practical design is further presented for the proposed compensator and the current regulator. Finally, the effectiveness of the proposed strategy and parameters design is verified by the experimental results.