Abstract: In order to suppress the harmonics of switching frequency and system resonant peak in weak power grid, a harmonic mixed damping control strategy for LLCL grid-connected inverter in weak power grid is proposed.First the LLCL type and LCL type amplitude frequency characteristics of the filter are analyzed, and then based on the active damping method to add the passive damping method, through the active damping of k value and R value set in the passive damping, under the condition of no more loss, the effect of active damping method by control delay is reduced, combining the advantages of two methods.Finally, the simulation results show that the proposed control strategy has good harmonic suppression effect, and the total harmonic distortion rate is reduced by 1.18% compared with the active damping method, and it has good stability and adaptability under different weak power networks.

Key words: LLCL filter, mixed damping control strategy, active damping method, passive damping method, weak grid