Impact of high penetration of solar PVS on harmonics in LV distribution networks

Abstract

Present trend of using solar photovoltaic (PV) technology for generating electricity has marked a rapid growth in the number of grid connected solar PV systems which has been reported to make a considerable impact on the power quality in the grid. With comparison of power quality (PQ) problems such as voltage unbalance, local voltage rise and voltage fluctuations, the increase of network harmonic levels has been identified as a potential PQ concern with the grid connected solar PVs. PV inverters are source of harmonics that produces low order and high order harmonics at the switching frequency and its side bands. Low order harmonics present at the inverter output due to the inability of producing pure sinusoidal waveform. Varying solar irradiance, inverter characteristics, inverter capacity, multi-inverter interactions and background harmonic level are examples of factors which influence the amount of harmonic generation of a PV system. This research focuses on the effect of high levels of harmonic injection and propagation of current harmonics in distribution network with solar PV integrations. A methodology is discussed in this thesis to achieve the aforementioned matter with the detailed modeling of PV inverters in a typical distribution network using PSCAD/EMTDC simulation platform. From the analysis of simulation results, the current harmonics injected by single phase inverters has been found substantial and influential with regard to the energy transmission and increase losses with compared to the three phase inverters. Unbalance occurred due to single phase inverters results in triplen harmonics to propagate to the upstream grid via the distribution transformer. Moreover, current harmonics superimposition were recorded as a result of multi-inverter operation. It was found that the Point of connection (POC) of the PV inverter affects the voltage harmonic levels at the inverter output.