Abstract: With the wide application of new energy grid connection technology，a large number of power

electronic devices are connected to the power grid，and the power quality is affected by harmonic interaction. Aiming at the harmonic interaction problem of multi-inverter grid-connected system，the multi-input and multi-output model was used to analyze the harmonic coupling characteristics. Firstly，the model of several parallel three-phase LCL gridconnected inverter systems which is based on the small signal equation of the inverter and the harmonic state space （HSS）theory was built. Secondly，the theoretical equation of harmonic coupling coefficient was derived by the HSS model of multiple inverters，and the coupling diagram of harmonic components was drawn，so as to analyze the harmonic coupling characteristics in the grid-connected system of multiple inverters，that is，the transfer process of each harmonic between the AC side and the DC side. Finally，the effectiveness of the mathematical model was verified by contrasting the results of HSS model with the results of simulation experiments and RTLAB experiment.

      Key words: harmonic state space（HSS）；harmonic interaction；LCL grid-connected inverter；DC voltage

disturbance