Mechanical design of rotors for permanent magnet high speed electric motors for turbocharger applications

Realization of electrically boosted turbochargers requires electric motors capable of operating at very high speeds. These motors often use a permanent magnet rotor with the magnets retained within an interference fit external sleeve. Whilst it is possible to model such systems numerically, these models are an inefficient tool for design optimization. Current analytical models of rotors typically consider the stresses induced by the shrink fit of the sleeve separately from the stresses generated by centripetal forces due to rotation. However, such an approach ignores the frictional interaction between the components in the axial direction. This paper presents an analytical model that simultaneously accounts for interaction between the magnet and outer sleeve in both the radial and axial directions at designed interference and with the assembly subjected to centripetal and thermal loads. Numerical models presented show that with only moderate coefficients of friction and rotor lengths; axial load transfer between magnet and sleeve takes place over a short distance at the ends of the assembly. The paper then demonstrates how the analytical model aids definition of a feasible set of rotor designs and selection of an optimum design

Comparative analysis of inductances of air-gap windings

Inductance value of an electrical machine is important for high-speed electrical drives. In this paper, a comparative analysis of inductances of toroidal, skewed and concentrated air-gap windings has been performed. Analytical approach of inductance calculation, using Biot-Savart’s law and method of images, is applied to toroidal and concentrated windings. The analytical method of inductance calculation is verified by FEM 3D. Additionally, comparison of the conductor length of the windings is performed

Comparative analysis of inductances of air-gap windings

Inductance value of an electrical machine is important for high-speed electrical drives. In this paper, a comparative analysis of inductances of toroidal, skewed and concentrated air-gap windings has been performed. Analytical approach of inductance calculation, using Biot-Savart’s law and method of images, is applied to toroidal and concentrated windings. The analytical method of inductance calculation is verified by FEM 3D. Additionally, comparison of the conductor length of the windings is performed

Analysis of rotor eddy current losses in slotless high-speed permanent magnet machines

Rotor eddy current losses are one of the main reasons of permanent magnet demagnetization in high-speed permanent magnet machines. In this paper the rotor eddy current losses of high-speed permanent magnet machines with different slotless windings have been analysed. The analysis of the losses was performed using 2D and 3D analytical models. In the study, test machines with different windings and the same torque production capability have been analysed. Presented paper shows the dependency of rotor eddy current losses on sine- and square-wave PWM supply voltages and rotor sleeve properties. Several recommendations for reduction of rotor eddy current losses in high-speed permanent magnet machines are given

3D modeling of armature field of helical (Faulhaber) winding including rotor Eddy currents

Helical (Faulhaber) windings are widely used in low-power permanent magnet machines. The paper presents an analytical model of the armature reaction field of a machine with a helical winding, which takes into account induced eddy-currents in the rotor. The eddy-current losses are calculated applying the Poyting vector. The model has been verified by FE

Inductance calculation of high-speed slotless permanent magnet machines

Purpose – The purpose of this paper is to give a simple, fast and universal inductance calculation approach of slotless-winding machines and comparison of inductances of toroidal, concentrated and helical-winding machines, since these winding types are widely used among low-power PM machines. Design/methodology/approach – Harmonic modeling approach is applied to model the magnetic field of the windings in order to calculate the synchronous inductances. The method is based on distinction between electromagnetic properties of different regions in the machine where each region is represented by its own governing equation describing the magnetic field. The governing equations are obtained from Maxwell’s equations by introducing vector potential in order to simplify the calculations. Findings – Results of the inductances of toroidal, concentrated and helical-winding slotless PM machines, which have the same torque and dimensions, obtained by the proposed analytical method are in good agreement with 3D FEM, where the relative difference is smaller than 15 percent. However, the calculation time of the analytical method is significantly less than in 3D FEM: seconds vs hours. Additionally, from the results it is concluded that the toroidal-winding machine has the highest inductance and DC resistance values among considered machines. Helical-winding machine has lowest inductance and DC resistance values. Inductance of concentrated-winding machine is between inductance of helical and toroidal windings; however, DC resistance of the concentrated windings is comparable with resistance toroidal windings. Originality/value – In this paper the inductance calculation based on harmonic modeling approach is extended for toroidal and helical-winding machines which makes the method applicable for most of the slotless machine types

Force and torque calculation methods for airgap windings in permanent magnet machines

Methods for force and torque calculations in permanent magnet (PM) machines with airgap windings are studied. Both analytical and numerical methods are applied to calculate the Lorentz force. The presented methods are applicable to various winding types and allow evaluating the geometry quickly. For a comparison of the methods a rhombic winding has been selected as a test case