Quantitative Comparisons of Outer-Rotor Permanent Magnet Machines of Different Structures/Phases for In-Wheel Electrical Vehicle Application

Abstract

As one of the key components, low-speed direct-drive in-wheel machines with high compact volume and high torque density are important for the traction system of electric vehicles (EVs). This paper introduces four different types of outer-rotor permanent magnet motors for EVs, including one five-phase SPM machine, one three-phase IPM machine with V-shaped PMs, one seven-phase axial flux machine (AFM) of sandwich structure and finally one hybrid flux (radial and axial) machine with a third rotor with V-shaped PMs added to the AFM. Firstly, the design criteria and basic operation principle are compared and discussed. Then, the key properties are analyzed using the Finite Element Method (FEM). The electromagnetic properties of the four fractional slot tooth concentrated winding in-wheel motors with similar dimensions are quantitatively compared, including air-gap flux density, electromotive force, field weakening capability, torque density, losses, and fault tolerant capability. The results show that the multi-phase motors have high torque density and high fault tolerance and are suitable for direct drive applications in EVs.

In-Wheel Motor Drive Systems for Electric Vehicles: State of the Art, Challenges, and Future Trends

“…Therefore, IWM-DEVs have not been utilized in mass-produced commercial EV/HEV, and further research is necessary to overcome this challenge. In order to design a motor as suitable as IWM, the following requirements must be considered [15][16][17][18]:…”

“…Additionally, incorporating a multi-phase design can further improve fault tolerance. Certain OR-PMSM models include sub-motors to increase fault tolerance, and various techniques have been implemented to mitigate parasitic effects, such as eddy currents and NVH [17,26]. Two topologies based on the radial flux outer-rotor PMSM are shown in Figure 5, surface mounted PMSM with outer rotor (Figure 5a) and V-shaped IPM-PMSM (Figure 5b).…”

Rotating Electrical Machines: Types, Applications and Recent Advances

“…The small-size Rotating Electrical Motors are used in in-wheel systems like Moto/Scooters, because of improved torque which increases acceleration in slope conditions (Gong, et al, 2022). The switched Reluctant Motors are widely used in three-wheelers because they are efficient in reducing windage loss of the wheelers (Seshadri, & Natesan, 2023).…”

Design, Analysis of a Seven-Phase Fault-Tolerant Bi-Harmonic Permanent Magnet Machine With Three Active Air Gaps for In-Wheel Traction Applications

“…Four types of motors are compared in [26]，including one 3-phase IPM machine with V-shape PMs [5], one 5-phase SPM machine [27], one 7-phase AFM of sandwich structure [28] and finally one hybrid flux (radial and axial) machine with a third rotor with V-shape PMs added to the AFM. The results show that the multi-phase AFM have higher torque density and higher fault tolerance, and are very suitable for direct drive applications.…”