Year

2022

Degree Name

Doctor of Philosophy

Department

School of Electrical, Computer and Telecommunications Engineering

Abstract

Small and large scale solar photovoltaic energy generating systems have been observed to take a leading place in power systems around the world which are aiming to move away from the use of fossil fuels. Technical and other challenges associated with such systems have become the focus areas of discussion and investigation in recent years. Among a range of technical challenges, power quality issues associated with the power electronic converters, especially the harmonics, are an important aspect in order to ensure that their stipulated limits are maintained. While harmonics caused by small-scale inverters, for example, those used in rooftop systems, are managed through their harmonic current emission compliance requirements, the harmonics caused by large scale inverters used in solar farms need to be managed at network levels which is essentially the responsibility of the network owners and operators. To be successful in this management process, the relevant generator connection requirements and system standards, relevant data provided by inverter manufacturers, pre-connection and post-connection studies and procedures require attention. With regard to limits associated with harmonic voltage levels at medium, high and extra high voltage (MV, HV and EHV) levels, well-established international standards exist, whereas the pre-connection study procedures which have existed for many years are now being challenged, noting the increase in the number and capacity of inverter based resources (IBRs).

With regard to pre-connection harmonic compliance studies associated with power electronic based grid integrated resources or devices, the most well-known approach is the use of equivalent frequency domain models of the systems on either side of the point of connection or the grid interface. The grid is often represented by an equivalent harmonic impedance together with a corresponding background harmonic voltage. The power electronic based resources or the devices are represented by Thevenin or Norton models at the harmonic frequencies of interest, which are provided by their vendors where the approaches or the conditions under which these models are determined are not comprehensively known. It is however understood that the parameters of such equivalent circuits are mostly determined based on site tests and represent worst case harmonic performance, which do not necessarily correspond to rated power output. There is also the anecdotal understanding that such models are determined based on mathematical or simulation modelling. The most significant concern associated with such frequency domain models is their suitability for representation of the actual harmonic behaviour at a given point in time, thus posing the question of their fidelity which forms the backbone of the work presented in this thesis.

FoR codes (2008)

0906 ELECTRICAL AND ELECTRONIC ENGINEERING

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.