Abstract: Aiming at the problem that the inherent resonance of LCL filter, filter parameters and impedance fluctuation in weak power network will seriously damage the stability of grid-connected system, a super spiral sliding mode based control strategy for LCL grid-connected inverter under weak power grid is proposed. Firstly, according to the grid-connected system model, the super-twisting sliding mode observer is constructed, and the filter capacitor voltage and the output current on the inverter side are estimated,eliminating the need for additional sensors and reducing costs. Secondly, a super-twisting sliding mode controller with non-singular fast terminal sliding mode control (NFTSMC) is used to quickly track the reference current and reduce the dynamic steady-state error of the grid-connected system, as well as to improve the global robustness of the grid-connected system against external disturbances and parameter uncertainties. Finally, the simulation results show that the system shows strong robustness when the filter parameters are perturbated and the grid impedance changes, and the THD value of the grid-connected current is maintained at about 0.5%.

    Key words: super-twisting sliding mode control; non-singular fast terminal sliding mode control; super-twisting sliding mode observer;parameter perturbation; impedance variation