Enhanced FRT control strategies for VSC-HVDC connected offshore wind farms

  • Antonio Luque

Student thesis: Doctoral Thesis


The EU has a binding target of 20% of energy to come from renewables by 2020, with an associated CO2 emissions reduction target of 20% (relative to 1990) and a 20% reduction in energy usage by the same date. This is the so-called 20/20/20 target. The UK target is for 15% of energy to be sourced from renewables by this date. For this target to be met, over 30% of electricity will need to be generated from renewables and it is anticipated that 31GW of this will come from wind power, with 13 GW onshore and 18GW offshore, by 2020. At present 6 GW of wind power have been installed onshore and 3.5+ GW offshore. To increase offshore capacity by at least a factor of five in 5 years, whilst minimising the cost of energy, presents very significant design, operational and logistical challenges. As the offshore infrastructure is established and connected big challenges are introduced such as the development of reliable and cost effective wind farm electrical collectors and offshore transmission systems, and the design and implementation of enhanced controls to enable wind farms to support power system operation and maintain system stability.The objective of this thesis is to present, discuss and solve technical barriers for offshore grids. This research is based on simulation studies of control structures of Doubly-fed Induction Generator (DFIG) and Fully-Rated Converter (FRC) wind turbine generators, and VSC-HVDC offshore transmission systems. Simulation results validate the enhancements achieved in the control strategies of both wind turbine generators and VSC-HVDC. These enhanced controls enable the VSC-HVDC connected wind farms to comply with Grid Code requirements such as Fault Ride-Through and provision of voltage and frequency support. The thesis also discusses the pros and cons of installing modifications in the control system of the point-to-point HVDC converters. Furthermore, this research includes a mathematical analysis of the specific conditions of the VSC converters and the AC and DC transmission lines which need to be established in order to ensure the efficient performance of wind farms, and thus to comply with Grid Codes requirements.;Matlab/Simulink software - specifically the SimPowerSystem tool for transient simulation - is used to model and examine a series of proposed scenarios. To achieve the objectives of this thesis and thus to investigate and provide an explanation of the operational system of the DFIG/FRC wind turbines, their interconnection to the offshore cluster substation (VSC converter) and the HVDC connection, basic models have been designed, analysed and tested. A variety of modifications in the control system of the power converters have been applied in order to obtain a better dynamic response in each scenario (single point connection with basic point-to-point connection or more complex offshore scenarios which incorporate several offshore wind farms connected to one offshore cluster substation). These new models (wind turbines and VSC-HVDC) have been compared with the basic models to facilitate the analysis of both systems.
Date of Award8 May 2018
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde & EPSRC (Engineering and Physical Sciences Research Council)
SupervisorOlimpo Anaya-Lara (Supervisor) & Adam Dysko (Supervisor)

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