Thesis

Control design and stability assessment of VSC-HVDC networks for large-scale offshore wind integration

Downloadable Content

Download PDF
Creator
Rights statement
Awarding institution
  • University of Strathclyde
Date of award
  • 2011
Thesis identifier
  • T12916
Qualification Level
Qualification Name
Department, School or Faculty
Abstract
  • This thesis investigates the use of voltage source converter high-voltage direct current (VSC-HVDC) transmission systems for large-scale integration of offshore wind farms into the Scottish power network, and reinforcement or replacement of the existing high voltage ac links between Scotland and England to increase transmission capacity, without affecting the power and voltage stability of both networks. To achieve these objectives, several multi-tasking controllers for VSC-HVDC transmission that use neutral-point clamped converter are developed as a platform in Simulink, and used throughout the research work presented in the thesis. The main controllers implemented in this thesis are, active power, de voltage, ac current in synchronous reference frame, ac voltage and frequency control. Regarding the use of VSC-HVDC for offshore wind farm integration, two control approaches for the offshore-side converter were investigated. In the first approach, the wind farm-side converter injects all the wind power into the de side without assigning a direct power command and establishes a stiff ac bus at the wind farm network main hub (bus). In the second approach, the wind farm-side converter uses an assigned power command to inject the wind power into the de side while the wind turbines use their pitch control to regulate active power production so as to guarantee power balance between the offshore ac network and the de side. The advantages and shortcomings of both approaches are highlighted and their influence on network stability assessed. Two possible HVDC configurations were investigated to accommodate future offshore wind power into Scottish networks without significantly compromising the overall system stability and reliability, paying special attention to Grid Code compliance. The two configurations investigated are two independent point-to-point HVDC networks and a multi-terminal HVDC network. The viability of the both configurations is evaluated in steady-state and transient conditions. This evaluation includes flexibility of power dispatch, provision of ancillary services to Scottish networks and potential improvement in system stability. For completeness of the work, the small-signal stability of the multi-terminal HVDC network configuration when used to connect offshore wind farms was explored using eigenvalue Techniques. This thesis also investigated two possible connection scenarios to increase the transmission capacity of the links between England and Scotland, by reinforcing the existing HVAC links with parallel HVDC links (hybrid connection), or replacement of the current HVAC links by two independent point-to-point HVDC links. The benefits and drawbacks of both connection scenarios are highlighted. These include the benefits to frequency control in the Scottish network in the event of severe disturbance in the English network. The impact of both connection scenarios on the network stability were assessed during steady-state and transient conditions.
Advisor / supervisor
  • Anaya-Lara, Olimpo
  • Lo, Kwok Lun
Resource Type
DOI
EThOS ID
  • uk.bl.ethos.549415

Relations

Items

Thumbnail Title Date Uploaded Visibility Actions
file details PDF of thesis T12916 2026-11-04 Public Download