Harmonic degradation analysis method for parameter-unknown grid-connected inverter based on impedance fitting

The invention discloses a harmonic degradation analysis method for a parameter-unknown grid-connected inverter based on impedance fitting, and the method comprises the following steps: S1, collecting frequency response data of the grid-connected inverter, converting the frequency response data into time domain data, and calculating an initial order and an initial pole through a matrix pencil algorithm; S2, updating a pole, estimating a residue, a first term and a constant term by using vector matching, and performing impedance fitting to obtain a frequency response fitting value; S3, calculating the relative error percentage of the frequency response fitting value and the actually measured frequency response data, comparing the relative error percentage with a given threshold value, if the relative error percentage is greater than the given threshold value, updating the initial parameter, repeating S2 to form iteration until the relative error percentage is less than the given threshold value, and outputting