Comparison of Permanent Magnet Rotor Designs for Different Vehicle Classes and Driving Scenarios: A Simulation Study

The most important magnet layouts in rotors of hybrid permanent-magnet synchronous machines (PMSM) for electric vehicles are compared in a variety of characteristics. The effect of different rotor designs on the vehicle performance and energy consumption is evaluated for a small battery electric vehicle (BEV) for different drive cycles. With electromagnetic and mechanical Finite Element Method (FEM) calculations as well as a longitudinal vehicle simulation platform, the

• Torque, power, ripple, and noise characteristics
• The energy consumption in a small passenger vehicle
• The suitability for high-speed applications of the electric machine (EM) are simulated and compared.

Five rotor types are included in the study, which represent the most seen designs in popular electric vehicles: V-Shape, Straight type, multilayer U-Shape, Spoke type, and Spoke+Straight type.

As the methodical approach, the electric motor from the Toyota Prius 2004 is taken as base design and only the magnet arrangement in the rotor is varied. The rotors are equal in length, diameter, material selection, and magnet mass, only the arrangement of the magnets is varied. Hence a change in the performance of the EM can only be due to the magnet arrangement.

It can be shown that noticeable differences between the designs exist and that the choice of the rotor plays an important role. The differences mainly result from the characteristic magnet flux shape in the air gap together with the different reluctances of each individual design. An evaluation of the results reveals that all types have their advantages and disadvantages without one design standing out very much in all disciplines. In the overall rating, the V-Shape slightly leads the ranking. It has the broadest area of high efficiency and, thus, the best energy consumption in a mixed driving scenario of a small BEV. Its energy consumption is 3.5% better than with the worst design, which is the Spoke type in this context. The Spoke type in turn has the highest peak power and torque, being 11%/13.5% better than the worst design in these disciplines. A disadvantage of the Spoke type is its low mechanical resilience against centrifugal forces, making this design not well suited for high-speed EM applications. The multilayer U-Shape design has the least torque production herein, while it has very low iron losses and noise (63% less cogging torque and 73% lower torque ripple than with the worst design) due to its particularly low air gap flux harmonics. This makes this design better suitable for high-speed EM where iron losses get more dominant over copper losses. The Straight type is the most versatile rotor design, having no very bad discipline and a good overall rating.