Integrating Offshore Wind Power and Multiple Oil and Gas Platforms to the Onshore Power Grid using VSC-HVDC Technology

Abstract

This thesis investigates the possibilities of integrating oil and gas platforms and offshore wind power to the onshore power grid. The main motivation for this is to reduce the large greenhouse gas emissions associated with traditional oil and gas platforms. The oil and gas industry is responsible for 25 % of total greenhouse gas emissions from Norway. The major part of these emissions originates from the power generation on the platforms. By supplying the oil and gas platforms with renewable energy from the onshore power grid in combination with offshore wind power there will be little or no use for power generation on the platforms and greenhouse gas emissions can be greatly reduced. The feasibility of a hypothetical power system in the North Sea consisting of five oil and gas platforms and one offshore wind farm with a common connection to the onshore power grid is studied. The connection to the onshore grid is realized through a High Voltage Direct Current (HVDC) transmissions system based on Voltage Source Converter (VSC) technology The main goal of this thesis is to gain understanding of the system dynamics and the control of VSC-HVDC transmission system, offshore wind power, as well as offshore power systems.A dynamic simulation model of the system and a control system has been developed using SimPowerSystems in MATLAB®/Simulink. In order to save computation time aggregated models are used. The load on the platforms consists of a passive load, a fixed speed induction motor, and a constant power load representing variable speed drives on the platform. The wind farm consists of a wind turbine and a permanent magnet synchronous machine operating at variable speed using a back-to-back VSC. The converters in the VSC-HVSC transmission system and the wind farm are modeled using average models. Simulations are performed on system disturbances that are thought to be critical for the operation of the system. The simulation cases represent large and partly exaggerated disturbances in order to test the limitations of the system. The simulation results showed that the developed control system was able to keep the voltage and frequency variations within the grid code in IEC 61892 even during large disturbances. It was concluded that the system handles variations in the load very well and that the system configuration studied in this thesis is regarded as a feasible way of integrating oil and gas platforms and offshore wind power to the onshore grid. However more detailed studies are recommended including short circuit analysis.