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.