Harmonic Emissions Assessment of Distributed Photovoltaic Systems in Low Voltage Network

The inherent nature of power-electronic circuits inside on-grid PV inverters of Distributed Photovoltaic installations has brought new challenges of maintaining the harmonic voltage levels throughout the network within acceptable limits. Having the harmonic currents spectrum of each inverter already certified ‘individually’ does not ensure the compliance of accumulated spectrums from multiple of these inverters connected in parallel. As such, the accumulated harmonic current emissions from parallel PV inverters of certain Distributed Photovoltaic installations should be assessed in terms of their impact on the harmonic voltage levels throughout the network it's connected to. This work presents a detailed investigation and analysis to simulate and assess the levels of accumulated harmonic currents from a photovoltaic system with parallel PV inverters. The work contains derivations to generate emission limits based on the installed capacity of Distributed Photovoltaic installation and background harmonic voltage levels of the network. Furthermore, additional parameters have been considered, including the line impedance, topology of the point of connection, vector sum of harmonic orders, and others. The work presents an actual case study to assess the harmonic currents and voltages of a certain installation, based on which its integration approval with the grid has been decided by the network planners/operators.