Impact of Photovoltaic Integration on Voltage Variation of Electricity Distribution Network

Ruifeng Yan (2012). Impact of Photovoltaic Integration on Voltage Variation of Electricity Distribution Network PhD Thesis, School of Information Technol and Elec Engineering, The University of Queensland.

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Author Ruifeng Yan
Thesis Title Impact of Photovoltaic Integration on Voltage Variation of Electricity Distribution Network
School, Centre or Institute School of Information Technol and Elec Engineering
Institution The University of Queensland
Publication date 2012-02
Thesis type PhD Thesis
Supervisor Professor Tapan Kumar Saha
Dr Mithulananthan Nadarajah
Total pages 298
Total colour pages 80
Total black and white pages 218
Language eng
Subjects 090608 Renewable Power and Energy Systems Engineering (excl. Solar Cells)
090607 Power and Energy Systems Engineering (excl. Renewable Power)
Abstract/Summary Global warming has become a serious concern all over the world. Many nations have already taken actions to reduce greenhouse gas emissions. One of these measures is to encourage renewable energy generation through government subsidy, especially for small-scale solar systems at a residential level. As a result, more and more photovoltaic (PV) panels are being installed in power networks. This certainly will have a positive impact on environment; however, at the same time PV systems may cause network operational problems that have never been encountered before. PV systems as small generator units have their own unique characteristics. They are distributed generators (DGs) scattered into distribution networks, and their power generation is significantly affected by natural conditions (e.g. ambient temperature, sun radiation and sunlight incident angle). These properties make them behave differently from the fossil fuel based generators which can produce controllable power and force one-way downstream power flow. Consequently many problems have been brought into traditional networks, for example voltage rise, reverse current flow, islanding detection, protection device malfunction, generation variability and transient stability. Most PV systems are integrated at a power distribution level, and this is also the installation tendency in the future. Distribution networks have never been balanced due to asymmetrical upstream sources, non-transposed lines and uneven phase loads, thus analysis of PV integration impacts should take network imbalance into account. In steady states, unbalanced loads and PV power have unequal contributions to voltage drops of each phase. Moreover, during cloud coverage phases of unbalanced networks have different voltage variation sensitivities to PV power swings. Therefore, it is possible that an unbalanced network may suffer extremely low voltages of a phase and unacceptable voltage imbalance at certain buses. These voltage problems are exacerbated with increase in PV penetration levels, which are the situations that may be confronted in the near future. Even for low PV penetration, some power utilities have already experienced similar voltage issues and started to reject further grid-connected PV applications. This research investigates these voltage problems of PV integration into an unbalanced distribution network. Methodologies and theories have been proposed for unbalanced network analysis with and without considering PV power fluctuations. Based on these developed technical tools, solutions are recommended to mitigate PV integration impacts so more PV units can be accommodated into power networks. In this research, a single-phase PV model is first addressed to pave the way to the study at a network level. Then in the IEEE 13 bus system the related voltage problems, which can hardly be explained by using balanced system theories, are raised. In order to solve the problems, theories are developed to analyse the causes for unbalanced voltage variations in an unbalanced distribution system including unbalanced sources, lines, PVs and loads. After understanding the reasons of the problems, an economical solution – network reconfiguration is proposed to improve voltage performances. This method utilizes the characteristics of the unbalanced network itself and does not require extra compensation devices. The proposed methodologies and solution are further validated in a larger and more comprehensive unbalanced distribution network – the IEEE 123 bus system. Around the world, not all countries can afford or have the freedom to have all three phases present in each residential area. There are many places having the similar network structures to the IEEE 13 and 123 bus systems, which have already been or will be heavily integrated with PV systems. Also, there are engineers who experience the similar concerns on their own networks that suffer the comparable problems to those of the IEEE 13 and 123 bus systems with PVs. This research provides a number of technical tools to analyse unbalanced networks and identify the reasons for voltage imbalance. Then the network reconfiguration solution may further be applied to improve the performance of networks. Even for those networks, which do not have serious unbalance issues, this research also presents general guidelines for future planning and network enhancement.
Keyword photovoltaic
unbalanced distribution network
cloud transient
unbalanced voltage variation sensitivity
Additional Notes Printed in colour: 26, 32-33, 52, 55, 63-64, 68-70, 72-73, 76-78, 86-88, 91-93, 113, 118-119, 122-123, 131-132, 134-135, 139, 142, 145-146, 160, 167, 169-172, 187, 208-210, 213, 216-217, 220-223, 231, 233-235, 237, 242, 246, 249, 260, 262-263, 265, 268, 270, 272, 276-278, 281-283, 287, 290, 292-293, 295-298 Printed in Landscape: 202-203 Printed on both sides for all

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Created: Thu, 05 Apr 2012, 14:48:01 EST by Ruifeng Yan on behalf of Library - Information Access Service