On finding optimal machines and comparison of axial and radial flux propulsion machines

Report, 2021

Permanent magnet synchronous motors are often used in drive trains for electric and hybrid vehicles. At the Division of Electrical Engineering at Chalmers University of Technology, several works on different machine types as traction motor have been done. Radial flux machines of different sizes, axial and transversal machines have been investigated. Together with the department of Environmental Systems Analysis, the different motors have also been objects for LCA calculations. A method for calculating the axial flux machine is investigated. The 3D-analysis is replaced by five 2D-calculations for different radii. The resulting torque is estimated correctly with the 2D approximation but there are bigger differences to the eddy current losses. The method is used for analysis of an axial flux machine with central stator and two rotor discs. A method for finding a useful machine for propulsion is tested where maximum torque, field weakening, and high efficiency are key parameters. A radial flux machine with 8-poles is compared to the best axial flux machines. To find a good size, pole number etc., a method with randomised parameters and a multitude of calculations are done. The selection of machine constructions is done based on data from a few operational points. Afterwards, some selected machines, that in steps are changed towards better performance, are evaluated both in terms of mapped efficiency and calculated performance during WLTP, US06 and other drive cycles. The best investigated axial flux machine can produce 20 % lower losses than the reference machine, in the low-speed drive cycles, if grain-oriented laminations are used in the stator teeth. At higher speed drive cycles, the losses are 20 % higher than from the radial flux machine. If a thinner lamination will be used, the losses could be lowered in the high-speed region. The weight of the axial flux machine can be lower than of the radial flux machine, but if the efficiency shall be better or equal, the weight of the axial flux machine will be higher.