This paper presents the optimization of axial-flux induction motors (AFIMs) for electric vehicles application by solving the Maxwell's equations inside five subdomains. It allows a detailed modelling and accurate steady-state performance prediction of the AFIMs in a very short time (under 1 sec). The analytical model is verified against 2D finite-element analysis. Different design options of the AFIM are considered and then optimized based on the proposed analytical model with the aim of minimizing the motor's volume and satisfy a set of predefined performance parameters for operation in a nominal point and also over a driving cycle. For operation in a nominal point, three power levels and for the driving cycle based operation, three driving cycles are considered. In each operation state, maximum torque per ampere (MTPA) constraint is enforced by changing the number of winding turns per slots. Alternatively, similar optimizations are performed without MTPA constraint by considering the number of winding turns as a variable. It is observed that driving cycle based motor designs benefit from a volume reduction and also ensures feasibility of all operating conditions. Enforcing the MTPA in design leads to a wider torque-speed operating range and simpler operation in the expense of additional volum

In some applications such as electric vehicles, electric motors should operate in a wide torque and speed ranges. An efficiency map is the contour plot of the maximum efficiency of an electric machine in torque-speed plane. It is used to provide an overview on the performance of an electric machine when operates in different operating points. The electric machine losses in different torque and speed operating points play a prominent role in the efficiency of the machines. In this paper, an overview about the change of various loss components in torque-speed envelope of the electric machines is rendered to show the role and significance of each loss component in a wide range of torque and speeds. The research gaps and future research subjects based on the conducted review are reported. The role and possibility of the utilization of the computational intelligence-based modeling of the losses in improvement of the loss estimation is discussed.

This paper presents research work on a 12-slot ten-pole tapered axial-flux permanent-magnet machine utilizing amorphous magnetic material in the stator core. Novel loss separation techniques are described, including mechanical loss and locked-rotor tests. Mechanical loss estimation is based on a combination of experimental tests and 3-D finite-element model analysis using an uncut stator. The locked-rotor test is introduced to separate the stator and rotor losses by eliminating the uncertainty associated with mechanical loss. High rotor yoke losses were identified in the baseline design. The rotor design was modified and a significant improvement in efficiency was demonstrated.

Efficiency maps (EffMs) illustrate the maximum efficiencies of electric machines over a range of torque-speed operating points. This paper reviews the available techniques for efficiency map calculation and gives a general understanding of EffM modelling and interpretation for traction motors. It shows the accuracy versus calculation effort trade-off for different methods. The process of efficiency map calculation for sample induction motor and permanent magnet synchronous machines is explained. Calculation of EffMs using commercial software is also covered. Finally, possible future research opportunities in this field are suggested.

Consideration of the overload (OL) performance of electric machines designed for EVs enables increasing the power density of the propulsion system. This paper aims to show the characteristics and advantages of the optimal IMs which have the capability of handling OL. A subdomain model (SDM) with the capability of the saturation prediction is developed and validated using experimental data. A lumped thermal model is developed to predict the transient temperature variation of the IMs. The thermal model is validated using the Motor-CAD transient thermal analysis. The fast speed and accuracy of the applied SDM allows to select twelve variables in a large search space for the optimization purpose. Initially, an optimization procedure is proposed to design three IMs over three different driving cycles. The optimal designs are validated from the electromagnetic and thermal aspects by the finite element analysis. IMs are then designed optimally with consideration of the OL capability. A transient thermal analysis is carried out to validate the designs. The optimal designs with and without consideration of OL are compared in terms of the machine parameters and geometry to understand how dimensions and equivalent circuit parameters of the IMs vary according to the driving cycles. The comparison allows more intuition about the consideration of OL capability in design.

This paper investigates the accuracy of the estimation of efficiency maps for permanent magnet (PM) machines using the stator resistance, d- and q-axis flux-linkages versus the corresponding axis current and the iron loss versus speed characteristic. The ultimate goal is to apply this approach to experimental measurements but this paper performs initial investigation using only finite-element data. Detailed FE data for 50-kW surface and interior PM machines is used to determine the “actual” or exact efficiency map and hence the accuracy of using approximations. The paper examines the effect on the torque-speed capability curve when ignoring cross-saturation effects. It also examines the modelling of the variation of iron losses as a function of load in the constant torque and power regions. A novel approach based on scaling the no-load losses as a function of load is proposed and shown to give promising results. Finite-element results from two other machines are also provided which show good correspondence.