Thesis

Novel hybrid HVDC system for resilient and efficient operation of offshore wind farms

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Awarding institution
  • University of Strathclyde
Date of award
  • 2024
Thesis identifier
  • T16990
Person Identifier (Local)
  • 201780298
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Qualification Name
Department, School or Faculty
Abstract
  • As strategies to achieve Net-Zero targets are proposed by various countries worldwide, offshore wind power generation has attracted the attention of industry and academia as its advantages, like higher, less-turbulent wind speeds, no use of continental land space and energy capture capacity make it more attractive than other renewable energy solutions. However, the connection of large, distant offshore wind farms is a current challenge pressing the wind industry hard. High-Voltage Direct Current transmission is the type of connection favoured for these cases. At present, HVDC using voltage source converters (VSC), has been used. To reduce the cost and land space, the diode rectifier based HVDC solution has been proposed for offshore wind farms. In this thesis, a novel hybrid converter topology is proposed for the offshore substation (wind farm) converter. The topology structure of the hybrid converter is a VSC and a 12-pulse diode rectifier (12P-DR) in a series connection. This thesis research focuses on the modelling and control of an offshore wind farm connected with an HVDC system based on this hybrid deployment converter. Due to the control capabilities of the VSC used in the hybrid converter, two control strategies were designed and assessed. In addition, the 6-pulse diode rectifier (6P-DR) is used in the hybrid converter to reduce the complex structure of the transformer on the offshore side. The first control strategy uses the VSC converter of the hybrid converter (Hybrid-VSC) as a grid forming converter to perform the AC voltage control at the PCC point. The second control strategy uses the grid-side converter of the PMSG wind turbine to establish the offshore AC voltage. Also, a harmonics compensation controller based on Synchronous Reference Frames (SRF) tuned by PI controller is proposed in the hybrid converter to reduce the harmonic content of the hybrid topology. The harmonic compensation structure provides an easy-to-tune harmonics compensation control strategy. An additional research contribution is the use of an advanced power electronics device, the Vienna rectifier, in the hybrid converter in order to reduce the harmonic components on the offshore side. This topology uses one switching device per phase, which reduces power losses and produces a low harmonic sinusoidal current output. The Vienna rectifier-based system uses a backup ancillary services control mode that retains harmonic-free power transfer capabilities, even in the case of a switch failure, by using the VSC converter harmonic compensation capabilities. Finally, A fast harmonics controller based on the Two Degrees of Freedom Internal Model controller (2DF-IMC) is used in the hybrid converter to reduce the harmonics compensation time. A fast harmonics controller is used in the hybrid converter and compared with the SRF-PI harmonics compensation controller. The results of this work demonstrate the performance and feasibility of the hybrid topology and pave the way for its implementation in offshore projects, providing cost reductions and increasing efficiency.
Advisor / supervisor
  • Anaya-Lara, Olimpo
Resource Type
DOI

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file details PDF of thesis T16990 2024-06-19 Public Download