On-line Measurement of Grid Impedance for Large Capacity Grid-tied Inverter Based on Multiple-sinusoidal Signal Injection
This paper focuses on the impedance measurement technology of large capacity grid-tied inverter based on multiple-sinusoidal disturbance signal injection.In this paper,multiple-sinusoidal signal is selected as the voltage disturbance,designed by referring to the Gerchberg-Saxton phase recovery algorithm in the spatial light field theory.Clip function,as one of the key elements,can determine the clipping speed as well as the clipping capability of the time domain wave crest of the disturbance signal.In order to improve the above performance,an inverse tangent function is proposed to replace the logarithmic clip function in the conventional algorithm,with the simulation results suggesting that the clip performance of the phase recovery algorithm is substantially improved.Then,the Gauss-Newton nonlinear least square method is used to carry out curve fitting on the information of characteristic harmonic frequency points of the collected disturbance signal to obtain the current grid impedance following by disturbance signal injected into the grid through the inverter.In the end,the experiments of impedance measurement under multiple weak grid scenarios are conducted on the established RT-Lab platform of a 1.5 MW grid-tied inverter,and the experimental results verify the effectiveness and accuracy of this scheme.
large capacity grid-tied invertergrid impedance measurementmulti-sinusoidal signaldisturbance signal designcurve fit
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