Aggregate harmonic fingerprint models of PV inverters. part 1: Operation at different powers

This paper is the first part of a two-part series on the development of aggregate frequency domain models of PV inverters (PVIs). The developed PVI models are expressed in the form of harmonic admittance matrix (HAM) of a coupled Norton model, also known as the harmonic fingerprint model (HFM). The development of accurate measurement-based HFMs requires considerable amount of measurements, which further increase in case of PVIs, as they typically exhibit strong power- dependent changes in harmonic emission. The authors propose a novel approach, which significantly reduces the number of measurements, as it requires only two sets of measurements at a single operating power: one with the fundamental voltage component, and another with individual voltage harmonics added one by one to the fundamental component. These two sets of measurements are used to calculate a “reference HAM”, which is then multiplied by two coefficients calculated from the power-dependent changes of the PVIs total subgroup current harmonic distortion, THDSj. The presented methodology is illustrated and validated using a comprehensive laboratory tests with three different PVIs and it can be easily applied to other types of power electronic devices with similar characteristics.