An Investigation into the Performance of Magnetically Geared Devices for Marine Hydrokinetic and Wind Applications

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Wind and rotary based marine hydrokinetic energy conversion devices often rely on a mechanical gearbox to increase their speed so as to match the requirements of the electromagnetic generator. However, mechanical gearboxes are creating reliability concerns and the maintenance of the gearbox can significantly add to the levelized cost of energy. Alternative approaches such as using a direct-drive generator become impractical at higher power levels due to their inherently low torque-per-volume capability. This research will investigate the theoretical and practical performance capabilities of using magnetically geared generation devices. A magnetic gearbox offers a number of advantages over traditional mechanical gearboxes in that a magnetic gearbox creates speed change without any physical contact, it does not require gear lubrication and has an inherent overload torque limiting capability. By coupling a magnetic gearbox to a generator the reliability of the generator system can be significantly improved and the volumetric size could potentially be comparable to its mechanically geared equivalent. By improving reliability a magnetically geared generator could reduce the levelized cost of wind and ocean power conversion. This could increase the utilization of renewable energy resources and consequently help reduce the emission of airborne pollutants associated with the combustion of fossil fuels. The primary goals of this research are to (1) develop modeling tools to understand the scaling and cost/performance trade-offs of axial magnetic gears and radial magnetic gear topologies. (2) Construct and test a stator driven continuously variable magnetic gear and an axially driven direct-drive magnetically geared generator. (3) Experimentally assess the efficiency of the proposed magnetic gear devices over a wide speed and torque range. The practical performance trade-offs between axial and radial flux-focusing magnetic gear designs when using ferrite and rare-earth magnets will be determined in the context of cost. The power flow, efficiency and power factor characteristics will be characterized with respect to existing technology. This research will lead to a greater understanding of the energy conversion process when using magnetic gears, continuously variable magnetic gears and magnetically geared direct-drive electrical machines. The techniques required to achieve very high mass and volumetric torque densities when using flux focusing magnetic gear topologies will be carefully defined. The power flow and control equations for the integration of a continuously variable magnetic gear into the grid will be derived. Both undergraduate and graduate students will assist with this research. Underrepresented students will be actively involved in this research. Outreach activities and yearly summer research experiences for local high-school students will take place. The research results will be disseminated in leading journals, conferences, and workshops in order to benefit the scientific and industrial community.