Parametric excitation for rapid converter-based PV module broadband impedance estimation

Broadband impedance spectroscopy (BIS) characterization of electrochemical devices using power electronic converters has received recent attention as a more cost effective, time-reducing, and online alternative to frequency response analyzers. Although the benefits of this system have been demonstrated, there are still linearity drawbacks to the induction of the excitation signal, using a converter as an excitation source, that this paper seeks to address. The second order frequency response of the converter, as well as the first order small signal response of electrochemical devices, both contribute to the amplification at low frequencies and attenuation at high frequencies of the induced excitation signal. This causes non-uniformity in the crest factor, which compromises the system linearity and impedance measurements. This study demonstrates how parametrizing the excitation signal, can improve the reliability of BIS characterization of PV modules when making use of a power electronic converter as the excitation source. The experimental results show how the induced signals meet the criteria for an LTI system, whereas the impedance of the PV module shows smaller parameter errors when benchmarked against an FRA, compared to conventional excitation signal design.