Numerical Modelling and Analysis of a New Rotor Cooling Technique for Axial Flux Permanent Magnet Machines

  • Ahmad Syahid Fawzal

    Student thesis: Doctoral ThesisDoctor of Philosophy


    An efficient thermal management is essential for an electrical machine because it determines its durability and performance; particularly the continuous power output. Without good thermal management, the operational temperature will exceed the machine’s temperature threshold limit, which may possibly lead to catastrophic failure.

    YASA Motors Ltd. specialise in the design and development of high efficiency electric motors specifically aimed at the automotive industry. However, the current Yokeless and Segmented Armature (YASA) machine has limited performance due to the sealed or confined design that limits the heat transfer on the rotors and the permanent magnets. Therefore, this thesis presents a new cooling technique for the YASA machine but which can also be adapted to any Axial Flux Permanent Magnet (AFPM)design in order to maximise its continuous performance f or automotive and motorsports applications.

    The work begins with a detailed review on the issues of thermal challenges for electrical machines (i.e. efficiency, reliability and performance), the derivation of an AFPM machine and then the heat sources from which the electric machine losses are produced. Utilising the Computational Fluid Dynamics (CFD), the losses of a 50kW sealed YASA machine has been studied in order to understand the thermal characteristics and thermal distribution.

    The novel secondary cooling strategy of the rotor has been implemented by attaching several fan designs on the rotor including other design iteration to assess its cooling performance. The idea is to allow the fan to drive the coolant (air) in the machine and become a heat exchanger at the same time. At this stage, only a single side of the rotor has studied under secondary cooling design, while the other side remained sealed. In order to aid the design assessment, a novel dimensionless number named Cooling Performance Index (CPI) has been proposed. The CPI number helps in comparing the cooling performance, apart from the comparison in the flow and thermal characteristics of each design change.

    The dual rotor cooling technique for the YASA machine is subsequently presented, where the backward curve fan has been selected as the best option based on its higher CPI number. The air outlet of the non-drive-end rotor that has an attached fan, was channelled to the drive-end to cool the other side of the rotor. The CFD analysis prove that the dual rotor cooling technique is able to maintain the rotors and magnets temperature with an increase up to 300% (150kW) continuous power compared to the 50kW on the existing sealed machine.

    The work presented here is not limited to the YASA machine case; rather it can be extrapolated to any other disc-type AFPM machine.

    Date of Award2018
    Original languageEnglish
    Awarding Institution
    • Coventry University
    SupervisorKonstantinos Gyftakis (Supervisor), Remus Cirstea (Supervisor), Mike Dickison (Supervisor) & Mike Blundell (Supervisor)

    Cite this