The microgrid concept integrates Renewable Energy Systems (RES) to the Electrical Power System (EPS) as a means to produce clean energy, meet consumer energy demands and preserve the depleting fossil fuels reserves. These RES are usually interfaced to the grid using power electronic converters (such as Voltage Source Converters) to achieve the required control and conversion of power. Nevertheless, Voltage Source Converters (VSCs) produce both current and voltage harmonics which negatively impact on the Power Quality (PQ) of a microgrid and may cause damage or malfunctions of equipment. This thesis focuses on the impact of VSC harmonics on the power quality of a microgrid. It also investigates various factors that affect the harmonics generated by VSCs with the aim of predicting their impact on the PQ of the microgrid. The PQ of the microgrid is represented as a measure of the level of harmonic distortion of the voltage and current at the Point of Common Coupling (PCC) to the grid. The harmonic mean was used as a measure to determine if the VSCs harmonic level meets the IEEE Standard 519 harmonic limits. The level of harmonic distortion of many VSCs can be significantly affected and difficult to predict in the presence of uncertainties, which may arise due to design parameter choice or system parameter changes. This necessitates the use of statistical techniques to quantify VSC harmonic distortion level in the presence of uncertainties. A common statistical approach is to employ Monte Carlo Simulation (MCS), although accurate it is time consuming and burdensome for systems containing a large number of variables. This thesis utilizes the Univariate Dimension Reduction (UDR) technique formulated from an enhanced Unscented Transform (UT) equation in predicting the harmonic distortion level of large numbers of VSCs in a microgrid, when some system or design parameters are only known within certain constraints. The UDR technique drastically reduce the computation time and burden associated with the MCS approach and avoids assumptions that leads to system simplification required to implement other analytical methods. Various microgrid configuration and statistical distributions similar to practical system variations of RES are considered in order to achieve a good evaluation of the UDR performance in predicting the VSC harmonics. The UDR performance was also evaluated experimentally using a practical microgrid lab containing 3 VSCs. The MCS approach was used as a benchmark for the predicted UDR results. In all cases the UDR predicted results were obtained with significant time saved as compared to the MCS approach and the UDR results showed a good match with the MCS approach.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:689869 |
| Date | January 2016 |
| Creators | Ivry, Preye Milon |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.nottingham.ac.uk/33041/ |
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