Aggregate harmonic fingerprint models of PV inverters. Part 2: Operation of parallel-connected units

This paper is the second part of a two-part series on the development of aggregate frequency domain models (FDMs) of photovoltaic inverters (PVIs). The first-part paper presents measurement-based harmonic fingerprint models (HFMs) of individual PVIs, which require a large number of tests, in order to accurately represent power-dependent changes of PVIs harmonic characteristics. Part 1 paper also presents two suitable modifications of harmonic admittance matrices (HAMs), which allow for accurate representation of PVIs harmonic emission at different operating powers with significantly reduced number of required measurements. This paper evaluates operation of parallel-connected PVI units, investigating whether the correct aggregate HFM can be obtained from their individual HFMs, by summing-up the corresponding HAM elements. The paper compares the results for the aggregate HFMs obtained using individual HFMs from measurement-based and two modified HAM approaches, which are illustrated using an example of two parallel-connected PVIs. The presented HFM-based aggregation approach is specifically aimed for the analysis of networks with a large number of PVIs operating at different powers, as it allows for accurate and computationally efficient determination of their aggregate models and subsequent evaluation of their aggregate impact and effects on the grid and other connected equipment.