Characterization of network harmonic impedance for grid connection studies of renewable plants

The impedance of a grid as a function of the frequency, or grid harmonic impedance, indicates the nature of the distortion and, especially, of the resonances that may appear in the system due to the presence of harmonic sources. Modelling this impedance is fundamental to be able to perform grid connection studies of renewable generation plants. However, usually the necessary information is not available, and the impedance is represented in a very simplified way. This paper analyses the different methods proposed in the literature to model the grid harmonic impedance and selects the most suitable for its implementation in PowerFactory simulation software, widely used in the industry for this type of studies. The selected method allows obtaining an equivalent network model that reproduces the harmonic behaviour of the network, without having to model the complete network in detail. A case study that applies the method to analyse the harmonic distortion at the POI of an offshore wind farm is presented.