Effects of high levels of harmonic penetration in distribution networks with photovoltaic inverters

The rapid increase of the grid-connected solar photovoltaic (PV) has been reported to make a considerable impact on the power quality (PQ) in the grid. This paper discusses the generation and propagation of significant current/voltage harmonics which are caused by PV inverters in distribution networks. The impact made by high switching frequencies and different operating scenarios are studied by detailed modelling of PV inverters in a typical low voltage (LV) distribution network using PSCAD/EMTDC simulation platform. It was found that the PV inverter systems inject high frequency current harmonics at the switching frequency or associated side bands. Low order current harmonics are also significant due to the inability of switching control system of PV inverter to produce perfectly sinusoidal output. It is found that the amount of harmonics depend on the inverter control strategy, background distortion present at the point of connection (POC) and the percentage of inverter loading. Further, harmonic voltage distortion is found to be mainly dependent on the impedance of the distribution network where weak networks lead to give rise to higher voltage distortions. Moreover, harmonic resonances are significant due to the interaction of the inverter output impedance and the grid inductance. The current harmonics injected by single phase inverters have been found substantial and influential with regard to the energy transmission and increase losses.