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.
