# Adoption of Multiphase and Variable Flux Motors in Automotive Applications
## 5 Conclusions  
In this paper, three different motor technologies are compared: multiphase, variable flux, and conventional 3-phase motors. As a result, the benefits and drawbacks of each technologies are identified. First, a literature review is conducted to identify their characteristics, advantages, and drawbacks. This review is complemented by FEM simulations of 3-phase, DTP, 3-phase VF, and DTP VF motors, which demonstrate their characteristics. The main contribution is that both technologies have been implemented in a single motor  
Figure 13: Overall summary of motor performances. to evaluate and quantify their impact together, obtaining higher torque and constant power values, lower torque ripples, and higher efficiencies in the whole working range. According to the literature review, MP motors have inherent advantages, such as reduced torque ripple, higher torque capability, power segmentation, and the need of a smaller DC-link capacitance in the inverter, increasing the power density of the whole system. Torque levels are improved around 3% just by increasing the phase number, and torque ripple reduces from around 20% until 60% in the mentioned articles, which is a significant improvement. Power losses are also decreased: the copper loss decrease thanks to higher winding factors could benefit from 3% higher efficiencies in a driving cycle, and iron and rotor (magnet and iron) losses reduced around 25% and 50%, respectively. Moreover, there are additional degrees of freedom when controlling the motor, which could be used to enhance its performance even more. Concerning VF motors, HE motors have good controllability and flux-weakening performance, but the need for additional coils and converters makes the manufacturing process more complex and more expensive, which is a significant drawback for EVs. Moreover, in the cases that slip rings are used to transfer energy to the rotor, there is more need for maintenance. VFMMs are a very interesting choice, but the high magnetising currents require an oversized inverter, which is the major challenge to introduce this technology to EVs. Last, among mechanically flux-varying motors, the ones that use the centrifugal force of the rotor are identified as the most attractive, as they do not require additional actuators. However, the complex flux-varying technologies can elevate the manufacturing costs. Regarding the FEM simulations, the following general conclusions are obtained. All the comparative indicators are given with respect to the reference three-phase motor. * The DTP winding improved the maximum torque capability by 4.3% thanks to the higher winding factor. This also reduces the copper losses in the low speed region between 6% and 8%, and magnet and rotor losses between 25% and 50%, although they are not significant. At maximum speed, the need for higher flux-weakening currents increased copper losses between 3% and 8%, but stator iron losses reduced between 1% and 4%, which could be thanks to the more sinusoidal MMF. Last, rotor losses reduced around 25% for the same reason but magnet losses increased between 1% and 3% because of the larger flux-weakening current. Regarding torque ripple, it was reduced more than 40% at all the working points. * The VF rotor had the same performance at low speed, as in the FE-MS the magnets were fully magnetised, same as in the three-phase motor. Therefore, the benefits came at high speeds when FW-MS was used to weaken magnet flux. This improved the maximum-speed power capability by 7.1% as less amount of current was used to weaken magnet flux. The smaller current and magnetic fields also reduced all losses, accounting for 23% and 38% total loss reductions in the high-speed working points, which was a significant improvement. Furthermore, torque ripple was also reduced at these points by 25% and 43% for the same reason. * The DTP VF motor exhibited advantages of both DTP and VF motors, being the best candidate among all the motors analysed. The maximum torque was increased by 4.3% and the power at maximum speed by 7.3%.