Impact on Renewable Energy Sources on Harmonic Levels in the Future UK Power Grid: Modelling, Assessment and Mitigating Solutions

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The UK is committed to reducing its greenhouse gas emissions by at least 80% by 2050, relative to 1990 levels. Meeting this target will require a significant shift in the way energy is used (for example, through electrification of heat and transport) and generated. To reduce our dependency on fossil fuels, significant levels of Renewable Energy Sources (RESs) will need to be integrated into the power grid. RESs include energy sources that do not rely on fossil fuels and nuclear energy, such as solar, wind, tidal and wave. Some sources of renewable energy have been successfully incorporated (for example, pumped-hydro), and they are generally not classified as 'RESs' as this term refers to devices that are connected to the grid by means of power converters. While the benefits of RESs are undisputable and their installation should be facilitated, the integration of large amounts of these devices requires the development of new paradigms and methods to maintain a reliable and safe power system. RESs have certain characteristics that differentiate them from traditional sources: they are less controllable than traditional energy sources, they cause unintended power flow patterns, and they impact voltage and current waveforms and the overall power quality of electricity. This proposal will focus on the study of harmonic propagation in the UK power grid due to RESs. Harmonics are current and voltage components at frequencies multiple of the fundamental, and they are generated by the operation of the power converters. While low harmonic levels are tolerated and do not impact grid operation, increasing harmonic levels have detrimental effects including: increased losses, reduced efficiency, misoperation and reduced lifetime of equipment, and nuisance protection tripping. While the costs of harmonics are not easy to determine because of their long-term effect, it has become accepted by the power grid operators and users that increasing harmonic levels are detrimental for efficient grid operation. More importantly, they may compromise the future integration of RESs. This proposal aims at assessing the harmonic impact of RESs in the future power grid. Carrying out this assessment requires the development of accurate models of both RESs and of the power system. At the same time, these models requires some form of simplification because of the number of components involved. Previous research has focused on either detailed power converter models, or the use of a large power system model with simplified converter representation. This NIA aims at combining both aspects in a model which is able to represent correctly harmonic generation from RESs, the transfer of harmonics between voltage levels, and the representation of statistical variations of harmonic levels in the system, for varying levels of penetration of RESs. This research will involve close collaboration with two industrial partners, National Grid and Measurable Ltd, and with the University of Texas at Austin. The impact of this research will be widespread: the models developed will help the academic community in understanding the best approaches to study harmonic behaviour of large energy systems. This work will assist the system operator in assessing the impact of new RESs on the power system. Furthermore, this research will inform the future developments of power quality standards and of harmonic mitigating solutions. The ultimate goal of this project is to minimise the occurrence of harmonic problems in the future power grid, allowing for a smooth and clean integration of increasing amounts of RESs, not only in the UK, but on a global scale. Furthermore, it will benefit the UK as a whole in terms of maintaining the operations and efficiency of this ubiquitous infrastructure, whilst helping the government to meet targets for reducing CO2 emissions.