Investigation of Mechanical Loss Components and Heat Transfer in an Axial-Flux PM Machine

Abstract

This paper investigates components of mechanical loss together with heat transfer effects in an axial-flux PM motor. The mechanical loss components generated within electrical machines are well known, however, their prediction or derivation has not been widely reported in the literature. These, together with the electromagnetic loss sources and heat transfer effects are crucial and must be accounted for when considering high-power-density, high-speed and/or compact machine designs. This research is focused on separating the mechanical loss components to gain a more in depth understanding of the effects and their importance. Both experimental and theoretical techniques have been employed in the analysis of a machine demonstrator. In particular, hardware tests with dummy rotors have been performed to measure the bearing and windage/drag loss components. These have been supplemented with CFD analysis to theoretically evaluate the aerodynamic effects occurring within the mechanical air-gap accounting for loss and heat transfer. It has been identified that the analysed hardware demonstrator suffered from bearing loss significantly higher than that suggested by the bearing manufacturer. This has been attributed to design of the mechanical assembly accommodating bearings, which resulted in inappropriate bearing preload. The excessive bearing loss had a significant detrimental effect on the machine thermal behaviour. In contrast, the aerodynamic effects have been found to have less pronounced effects here, due to fully enclosed and naturally cooled machine construction.Index Terms-Axial-flux PM machine, mechanical loss, heat transfer, computational fluid dynamics, thermal equivalent circuit, bearing loss, windage loss.

Development of Correlations for Windage Power Losses Modeling in an Axial Flux Permanent Magnet Synchronous Machine with Geometrical Features of the Magnets

“…More importantly, the results were verified with the numerical simulations by Wrobel et al [21] as well as the experimental data by Howey et al [24]. This verification can give us trust in the CFD modeling used in this study.…”

“…He showed that an increase in the magnet groove depth from 2 to 18 mm can noticeably raise the windage losses (up to 60 W) through the generator with the rotor diameter of 220 mm, gap size distance of 2 mm and the angular velocity of 1500 rpm. Wrobel et al [21] also performed CFD simulations to assess the windage losses in an AFPMSM. They investigated the aerodynamic effects occurring within the air-gap.…”

Investigation of Heat Loss from the Finned Housing of the Electric Motor of a Vacuum Pump

“…It can be mentioned that in some studies on self-ventilated electric motors, in the absence of air flow measurements, it was assumed that the flow velocity of air in the channels was equal to 75% of the peripheral speed of the fan rotor [12]. The results of the heat exchange on electric motor confirmed that the heat is mainly transferred by conduction from the stator/winding assembly to the housing [13].…”

Nonlinear Dynamic Model of PMBLDC Motor Considering Core Losses

“…The reasons for the difference between the simulated and the tested efficiency maps of the ferrite magnet prototype has been explored, and they are 1) The simplified windage and friction loss model used in the dynamic model cannot expect to be accurate, especially when the motor is operating with an efficiency more than 90 %. The windage loss characterisation of the PMBLDC motor requires a detailed study using nonmagnetic dummy rotors and computational fluid dynamic models [23], [24]. The lack of mechanical loss characterisation prevents the extraction of electromagnetic losses other than the conduction loss from the test data.…”