Analysis of an innovative design of an axial flux Torus-machine

Abstract: The high compactness of axialflux permanent magnet (AFPM) machines compared with theconventional induction, DC and radial flux permanent magnet(RFPM) machines, renders this machine-topology particularlysuitable to be integrated in a system for hybrid electricvehicles (HEVs). Indeed, due to the limited space inside thevehicle, the considerable reduction in volume and weightoffered by AFPM machines is of major importance. In particular,the limited axial length of AFPM machines is an important issuefor HEVs. Furthermore, AFPM machines present high efficiencydue to the absence of rotor currents. However, in order to besuitable for traction applications, the AFPM machine has tooperate at high-torque and high-speeds.A particular type of AFPMmachine, the so-called Torus-machine, has been investigated andan innovative design has been analyzed in order to fulfill thehigh-speed requirements. In fact, the machine has been designedto work in field-weakening operations and, to this purpose, themachine stator is provided with teeth and slots so as toincrease the field-weakening capability. A further improvementof the field weakening capability of the machine is obtained bythe addition of rotor saliency.A general analysis of theequations, which describe the machine parameters, is presented.Next the design of a 30kW, 4000 r/min Torus-machine has beeninvestigated on the basis of volume and performancerequirements. Furthermore, the performance of a machine havingthe previously calculated parameters but without rotor saliencyhas been investigated and the results have been compared. FEMcalculations based on the software programs Flux-2D and Flux-3Dhave been examined and most of the results present satisfactoryagreement with the analytical calculations. Moreover, asimplified thermal model of the machine has been developed inorder to predict the temperature rise in the winding atdifferent operating conditions.ABB Corporate Research,Västerås, Sweden, has manufactured a prototype of themachine. The measurements performed on the parameters of theprototype validate the analytical results. Furthermore, themachine thermal test agrees satisfactorily with the thermalmodel for the no load condition.