Page - 140 - in Hybrid Electric Vehicles

(I) The optimization procedure provided solutions over the examined range of poles number and the final topologies are investigated and compared to each other from several aspects. The designer has the opportunity to evaluate the derived results from many points of view (i.e. technical, economical, etc.) and finally select the appropriate in-wheel SPMSM topology. (II) The motors efficiency has been found high enough, as it varies from 94 to 95.5%. This feature, especially when is combined with the lowest possible current, is of great im- portance for HEV’s energy management. Concerning this, Motor A seems to be a more suitable choice for the case study. (III) All topologies exhibit high power to mass ratio over 1 kW/kg, since their mass range is from 12.5 to 14.8 kg. In the case of Motor C, the ratio is increased by 22%. Thus, if mo- tor’s total mass is the primary objective, this motor prevails. Despite their relatively low weight, all configurations present durability and do not suffer from mechanical stresses. (IV) The volume of NdFeB magnets is small, which will lead to a reasonable motor’s cost. (V) The current density constraint has been fulfilled. However, concerning the short axial length of the machine (30 mm) and its placement into a totally enclosed environment the implementation of a cooling system, which has been also proposed and optimized here, is more than essential. More details about the cooling system’s characteristics and its performance are going to be provided later in this chapter. (VI) During the adopted design approach, a large amount of motor features were also de- termined, as they significantly affect its operation. Some of great importance estimated quantities are airgap flux density, torque and phase-back emf curve’s shape, as well as their corresponding harmonics, cogging torque, torque angle and magnetic field distri- bution. For completeness purposes, these quantities are depicted in Figures 7–11, indica- tively for Motor C and Motor D. As it can be seen from Figure 7, the values of flux densi- ty developed over the different parts of both configurations are found within acceptable limits. Despite the low volume and especially active length of the motor, non-saturable operation has been detected for all the finally proposed topologies. Moreover, the airgap flux density and the phase-back emf, as depicted in Figures 8 and 9, respectively, pres- ent low harmonic content. The proper selection of windings configurations along with the specification of permanent magnets parameters through the proposed approach contribute to this feature. The airgap flux is of great importance of the torque pulsation. The small amplitude of its third, fifth and seventh harmonic in both cases resulted in the low value of motors torque ripple. The torque ripple for Motor C was found equal to 3.3%, while the same parameter for Motor D was equal to 2.4%. The above can also be validated by the observation of Figure 10, in which the torque and its harmonic content is presented. A very low cogging torque and relatively torque angle is also achieved, as it can be seen from Figure 11. These parameters are essential for this kind of traction application, as their low value can ensure a high quality and safe driving performance. (VII) The calculation of crucial HEV’s parameters, such as fuel consumption, permits a better ap- proximation of the optimal configuration. For example, Motor A seems to have a significant Hybrid Electric Vehicles140