The Stability of LCL-Type Grid-Tied Inverter Based on Repetitive Control and Grid Voltage Feed-Forward

The grid voltage feed-forward can improve the dynamic performance of the repetitive controller (RC), but it will seriously weaken the stability under non-ideal grid conditions. This article focuses on the stability and dynamic characteristics of a grid-tied inverter with RC and grid voltage feed-forward. The internal model filter of RC uses an infinite impulse response (IIR) filter to improve the steady-state performance. First, an equivalent digital control model with RC and feed-forward is established, the parameters of RC are designed, and the system's stability is analyzed based on the small gain theorem. Then, it is verified that the stability of RC in the presence of grid impedance can be weakened by the feed-forward term, thus a better feed-forward scheme is required. In addition, the solution for weak grid condition is proposed, and different feed-forward algorithms are compared from various perspectives, which is concluded that the improved proportional and first-order differential feed-forward scheme has a better performance. Finally, the validity of the controller is verified by the experimental prototype of a single-phase $LCL$ -type grid-tied inverter.