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Thermal management of the permanent magnets in a totally enclosed axial flux permanent magnet synchronous machine

Elevated magnet temperature in Axial Flux Permanent Magnet Synchronous Machines (AF PMSM) adversely affects torque production, material cost, and the risk of demagnetisation. These machines show promise in applications requiring high power density, however the factors which affect magnet temperature have rarely been investigated. This is therefore the focus of the thesis. A multiphysics numerical model was formulated which predicted the loss, flow, and temperature fields within an AF PMSM. A criterion for estimating the relative importance of the fluctuating component of a periodic heat source on the temperature response of a device was proposed and validated. In this work it was used to justify a steady state, rather than transient, thermal analysis. Thermometric and electrical measurements were taken from an instrumented AF PMSM to validate the numerical predictions. A novel magnet loss measurement technique was implemented; losses were determined by measuring the initial temperature rise rate of the magnets. This was achieved via a calibration relating temperature rise to voltage constant. It was found that 99% of the heat generated in the magnets was convected to the inner cavity of the machine, due to the inner cavity's recirculating flow structure this heat was dissipated to the casing and core. As a proportion of all heat entering the inner cavity 56-62% left to the casing while 28-41% left to the core. Magnet hot spots were found to be up to 13% greater than the mean temperature rise. Their location was influenced by the distribution of losses and the direction of shaft rotation. Temperature gradients within the inner cavity caused the magnet's trailing edge to incur a 10% greater temperature rise than the leading edge. As increasing temperature decreases the coercivity of magnet materials these findings are a crucial contribution to the understanding of devices where local demagnetisation is of concern.
Date January 2014
CreatorsMalloy, Adam
ContributorsMartinez-Botas, Ricardo
PublisherImperial College London
Source SetsEthos UK
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation

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