Thermal management of an axial flux permanent magnet machine considering heat pipes

[摘要] ENGLISH ABSTRACT: Axial Flux Permanent Magnet (AFPM) machines have become attractive because of significantimprovements in permanent magnets over the past decade, improvements in power electronicdevices, and the ever increasing need for more efficient machines in electric vehicle systems. Incomparison with the cylindrical radial flux motor, the AFPM machine is better in a number ofaspects: short frame; compact construction; high efficiency; brush less construction; good startingtorque and high-power density. The common modes of failure and typical operating conditionsof AFPM machines are discussed further. The focus of this research project is a prototype AFPMmachine developed by the Electrical Engineering Department of The University of Stellenbosch.The machine considered has a power rating of 300 kW and an operating efficiency of 95 % at aspeed of 2300 rpm. This specific machine is used as an example to illustrate the thermalcharacteristics of geometrically similar AFPM machines.The thermal characterization was achieved with the use of two numerical computer models.Firstly a fluid model was specially developed and experimentally verified. The objective of thefluid model was to calculate the mass flow rate of air through any geometrically similar AFPMmachine. The fluid model was further used to investigate the effects of different magnetthickness and axial gaps between the stator and the rotor plates on the mass flow rate of airthrough the machine. The fluid model was verified with experimental testing that was done on ahalf-scale Perspex model. During the experimental testing the magnet thickness was variedbetween 2.5 mm, 5.0 mm, and 7.5 mm along with axial gaps of 6.5 mm, 7.5 mm, 8.5 mm, and9.5 mm. The fluid model showed a correlation to within 10 % of the experimental mass flowrates. The results of these tests showed that the magnet thickness and axial gap between thestator and the rotor plates had no significant effect on the mass flow rate of air. The fluid modelwas based on one-dimensional, steady-state, and incompressible flow.The second numerical computer model was a thermal model. This model was used to calculatethe transient temperature response of the AFPM machine. The model was based on a twodimensionaltransient finite difference solution technique. Experimental temperatures taken fromthe prototype AFPM machine were used to verify the thermal model. Correlations between theexperimental and theoretical temperatures were within 5.8 % of each other. The thermal modelwas used to investigate the effect of geometrical changes on the temperatures in the AFPMmachine. It was found that these geometrical changes had no significant effect on thetemperatures in the AFPM machine. It was also established that increasing the air mass flow rate over about I kg/s had no further effect on lowering the temperatures. The stator was alsoidentified as being the most critical component as it reached its maximum temperature limitbefore any other component. Heat pipes were considered as an alternative thermal managementtechnique. The location of the heat pipe was limited to the stator. Further simulations were doneto investigate the effect of the heat pipe properties on the amount of heat removed from thestator.Recommendations were made concerning the thermal management of the current and possiblefuture prototype AFPM machines. It was recommended that a further more detailed investigationinto the use of heat pipes be considered. This recommendation is substantiated by the fact that inthis research project only one type of heat pipe was considered and its location was limited towithin the stator.

[发布机构] Stellenbosch University