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

Abstract

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 powerdependent 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, THDS I . 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.

Extended coupled Norton model of modern power‐electronic devices for large‐scale harmonic studies in distribution networks

“…1 a ) by observing the change in harmonic currents (sensitivity) as a response on a change in harmonic voltages (e.g. [19]). This applies to the ECNM parameterisation in the same way, but requires the additional step of separating the diagonal elements of the FCM into the circuit‐based part and the respective residual part (cf.…”

Circular regression models of modern harmonic producing sources

“…As it can be deduced from (14), the final circular regression model is represented by both cosine and sine terms. According to (12), the estimated mean direction is given as…”

“…The measurement approach is quite similar to the one used for FCM models, yet the post-processing part does not require complex mathematical equations. The idea was further developed in [12] for aggregate models of PV inverters.…”

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

“…The two HAM modifications presented in Part 1 paper allow to obtain two corresponding HFMs for individual PVIs with a significant reduction of required measurements, [1]. Both modifications use only one "reference HAM", multiplied by two coefficients calculated from power-dependent changes of PVIs total subgroup current harmonic distortion, THDS I .…”

“…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 main motivation for this work, as discussed in Part 1 paper [1], is a strong increase of the numbers of various types of PVIs over the recent years, which is anticipated to continue, if not to grow further, in the future. For example, the total installed PV capacity in the UK exhibited an extraordinary increase from around 30 MW in 2010, to around 12.6 GW at the end of 2017, of which around 54% (6.8 GW) are PV installations with rated power, P rated , less than 5 MW and around 20% (2.5 GW) are highly dispersed small PVI units with P rated less than 4 kW, typically connected to residential low voltage (LV) networks, [2].…”