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Partially rated soft open points for electricity distribution networks

Abdelrahman, Mohamed 2021. Partially rated soft open points for electricity distribution networks. PhD Thesis, Cardiff University.
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Abstract

The connection of multiple Distributed Generators (DGs) to medium voltage (MV) distribution networks requires careful control of the power flow in order to maintain the voltages and currents within limits. At present, the operation of distribution networks is passive. New devices are required to provide distribution network operators with the means of controlling the power flow and improving the utilisation of existing distribution networks. In this thesis, various topologies of Soft Open Points (SOPs) to be used in MV distribution networks were examined. The following points were addressed: 1) The benefits of a multi-terminal back-to-back (B2B) SOP were quantified and compared with a two-terminal SOP and with no SOPs. An optimisation problem was solved to determine the setpoints of the SOPs to achieve multiple control objectives separately. The three-terminal B2B SOP enabled the distribution network to host more DGs and achieved lower energy losses than the two-terminal SOP. However, B2B SOPs have not been widely deployed in MV distribution networks as they are too expensive. 2) The operation of a Transformer-less Unified Power Flow Controller (UPFC) in distribution networks was investigated. It offered power flow control with the complete removal of interfacing transformers. However, its ability to control reactive power is limited by the converter’s current ratings. A small-scale experimental setup was used to test the performance of the Transformer-less UPFC in response to control signals to step changes in active and reactive power. 3) The well-established conventional UPFC, that has been demonstrated in some transmission systems, was improved for use in MV distribution networks. The Improved UPFC provides similar performance to the conventional UPFC with no need for an interfacing series transformer. The series converter was protected against immediate overvoltage and overcurrent applied when faults occur on the distribution network using a fast-acting protection circuit. A model of a two-busbar distribution network was used for the investigation, supported by simulations and some experimental tests. The results showed that SOPs with a series connection can provide power flow control similar to that of B2B SOPs with lower rating converters and size.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Soft Open Points, Distribution networks , Power flow control, Distribution-level power electronics , Unified Power Flow Controller, Voltage source converters
Last Modified: 13 Apr 2022 09:46
URI: https://orca.cardiff.ac.uk/id/eprint/148991

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