Research on Control Strategy for LCL-Type Three-Phase Grid-Connected Inverters Based on Variable Universe Fuzzy PI Control

In the new energy grid connected system, due to the PI control parameters in traditional grid connected inverters are fixed, the system faces a high risk of instability when severe power fluctuations occur caused by the sudden changes in external energy. To solve this problem, this paper establishes a small-signal model of LCL grid-connected inverters and analyzes the stability region of the external loop control parameters of the system under different output active conditions. And a variable universe fuzzy PI control strategy is designed, which combines the advantages of fuzzy control and PI control, automatically adapts to power fluctuations by dynamically adjusting the domain, and improves control performance. The time-domain simulation results verify the effectiveness of this strategy, proving that compared to traditional PI control, the designed method performs better in shortening power adjustment time, reducing overshoot, and lowering the total harmonic distortion (THD) of current.