Influence of Multiple Air Gaps on the Performance of Electrical Machines With (Semi) Halbach Magnetization

Abstract

The ever increasing necessity to improve torque density while simultaneously maintaining high efficiency is a constant point of concern for electrical machine designers. This is mainly driven by the need for direct-drive solutions in evermore applications. This paper presents a general mesh-free description of the magnetic field distribution in multiple air-gap electromagnetic machines, although the tool is also useful for single air-gap machines, actuators, and other magnetic devices. The used method is based on transfer relations and Fourier theory, which can provide the magnetic field solution for a wide class of 2-D boundary value problems. This technique is in this paper applied to the rotary multiple air-gap machine with slotless (without slots but with and without rotor back-iron) armature. The presented analysis is compared to finite-element analysis for the multiple-layer winding, which shows the applicability of this method for future optimization. It is shown that multiple air-gap machines make better use of the volume and for short axial lengths where a single-side bearing configuration can be utilized provides a means to improve the achievable torque density.

Winding topologies of flux-switching motors for in-wheel traction

“…On the other hand, toroidal windings can potentially allow higher current density due to the large area of exposed coils. Concerning the efficiency, the superior topology is dependent on the motor dimension, where in the toroidal winding topology, conductors outside the stator yoke do not contribute to the torque production in case of a single air gap motor (Paulides et al, 2011).…”

Design of a 600kW ring-type direct-drive Flux-Switching Permanent Magnet machine for aerospace main propulsion

“…Due to the limitations of hard and soft magnetic materials and the air-cooling constraint, aiming for unconventionally high values of airgap shear stress using a high current loading is not viable: For permanent magnet machines this value surpasses 50kPa only with difficulty ( [7], [8]). Instead a machine construction that makes optimal use of the available airgap force density must be pursued by emphasizing in the following principles:…”

Multiple-airgap iron-cored direct-driven permanent magnet wind generators

“…Such machines, also sometimes referred to as multiple-air-gap (MAG) machines, are known for many decades. There have been published numerous papers, for example [4], [5], [6], [7], and filed many patent applications, which will be referred to further in this paper.…”