WindSurf- A self-starting, active-pitch, vertical-axis wind turbine

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Conventionally designed wind turbines only operate efficiently in steady, uninterrupted air. However, most users want to access wind in urban areas or near industrial units where the nature of the wind is more turbulent and swirling. Conventional designs do not work efficiently with the swirling, variable nature of wind at such sites. In this project Swift Energy present a radical re-design of a vertical axis wind turbine, with key technological improvements that will allow efficient operation in small-footprint, urban sites. Such sites have the added advantage that they are close to consumers, minimising transmission losses. WindSurf is a vertical axis, active pitching wind turbine. Swift's patented control technology uses servomotors to continually alter blade pitch, which allows self-starting in wind speeds as low as 3m/s, and optimised energy capture in free and turbulent wind streams. Edinburgh's role in this project is to produce an optimised design of the electrical generator for the WindSurf rated at 16kW, taking into account the environment in which it will be operating. A direct drive generator will be used to eliminate the gearbox, which will improve reliability and efficiency. Both of these contribute to LCOE: reliability through increased availability and reduced OPEX; and improved efficiency will enhance annual energy yield. An air-cored permanent magnet generator will be designed and built that is optimised for the structure of the Swift wind turbine. In order to achieve such an optimised design an integrated design approach is required, which links electromagnetic design, with structural design and thermo-fluid design. Edinburgh has built up 10 years of experience in the integrated design of direct drive permanent magnet air-cored generators for wind and marine renewable energy applications. Air-cored machines eliminate undesirable magnetic attraction forces that try to close the gap, and thus this topology benefits manufacture, assembly and structural design. A vertical axis wind turbine allows the electromagnetic design of the machine to have a large diameter, out near the blades. A large diameter will result in high airgap velocity and thus have a positive impact on torque density (Nm/kg), reducing the amount of active material, which is the most expensive part of the machine. A novel structural arrangement will be developed for integration into the turbine, which where possible makes best use of the existing structural material, again to minimise material usage and thus cost. A modular design approach will be adopted to ease manufacture and assembly of the generator, but also to make O&M easier. By positioning the generator close to the blades, we will investigate we will investigate methods of "scooping" air from the turbine onto the generator to assist with cooling. Effective cooling will benefit the torque density and the overall performance of the machine. Numerical modelling tools will be used in the design process, such as ANSYS for structural analysis, StarCCM for thermo-fluid analysis, and Infolytica for electromagnetic design. An existing analytical design tool will be refined based on the structural and CFD modelling in order to assist SWIFT in the future design and production of their turbine. Multi-body modelling using SIMPACK will be combined with structural modelling to investigate the impact of environmental loads on the generator in terms of airgap deflection. Once the design is finalised, the machine will be built under subcontract to Fountain Design Ltd, with whom we have worked in the past to build prototype generators. The machine will be tested at the University of Edinburgh on its wind-emulator test rig to verify performance and the design tools developed. A thorough integrated design approach with manufacturing and production techniques in mind supported by laboratory testing will ensure that SWIFT can move towards commercialisation.