Improved composite control of grid-connected inverter

The LCL filter is a third-order system of a low damping, where resonanceis easy to occur. Aiming at the issue, this paper adopts a dual-loop control strategy with the grid-connected current feedback and the capacitor current feedback to control the grid-connected current, and then designs a novel repetitive controller, which possesses a modified self-adaptive internal model and is plugged in the system. This repetitive controller is combined with the traditional PI control to form a new improved composite control scheme, thus improving the working stability of the LCL filter, minimizing the current harmonic distortion and increasing the performance of the grid-connected inverter. Finally, the feasibility and superiority of the improved scheme are verified by simulations and experiments. Besides, whether the voltage frequency of power systems changes or not, the improved scheme can effectively avoid the resonance of grid currents and can achieve a high in-grid power factor. ©, 2015, South China University of Technology. All right reserved.