High-Torque Electric Machines: State of the Art and Comparison

Abstract

The state of the art of high-torque electric motors has been reviewed in this paper. This paper presents a literature review of high-torque density electric machines based on their airgap classifications, which brings a unique consideration to new design ideas to increase torque density. Electric machines are classified into three main groups based on their airgap configuration, i.e., (1) machines with a constant airgap, (2) machines with a variable airgap, and (3) machines with an eccentric airgap. This paper also presents the modeling of a high-torque airgap-less electric motor based on the concept of eccentric airgap. The torque density of this motor has been compared to motors available in the literature review. Among electrical motors with no permanent-magnet, airgap-less electric motors take the lead in terms of torque density, which is almost five times greater than the next motor, “in-wheel for electric vehicle”.

Mechanical and Vibration Analysis of a High-Speed Outer Rotor Electric Motor

“…This configuration is advantageous for various applications, from electric vehicles to industrial tools, making studying its design and performance crucial for technological advancements [1], [2]. In outer rotor motors, surface-mounted permanent magnets (SPMs) can provide higher torque density than regular PMs [3]. Examples of recent work on outer rotor motors include [4], which investigates the effect of axial length over pitch-pole ratio in outer rotor brushless DC (BLDC) motors, and [5], which reports on the design and optimization of hub BLDC motors.…”

“…Zhang et al [2] developed a retaining sleeve that can work in megawatt PM machines at high speeds of 22,000 rpm. Sanchez et al [3] discussed the limits of highspeed inner rotor PM motor designs, the dynamic stability limit of PM motors, and how the dynamic stability is related to rotor geometry. Yu et al [20] performed rotodynamic analysis for a cantilever outer rotor motor with very high tip speeds and analyzed the modes of vibration.…”

Circular Economy Aspects of Permanent Magnet Synchronous Reluctance Machine Design for Electric Vehicle Applications: A Review

“…Alternative electric motor technologies for BEVs are also available. Still, PMSMs are the most dominant in the case of BEVs and hybrid vehicles because of their 20 times higher torque density than a switched reluctance machine or 200 times higher torque density than an asynchronous machine [7]. Hybrid vehicles are still preferred, but the EV sector is growing rapidly [8].…”