Unlike in low-speed machines, frequency-dependent phenomena in very-high-speed machines ¿ skin- and proximity effect, eddy currents ¿ may greatly influence copper losses. To alleviate these phenomena, parallel or stranded conductors are commonly used. Goal of the paper is to distinguish dominant causes of copper losses in slotless PM machines and, based on modeling, to establish a method for optimization of stator conductors ¿ number of parallel wires/strands within a phase conductor and their diameter ¿ for a minimum copper loss. Effectiveness of the modeling and optimization approach is evaluated using finite-element simulations.@en

Asymmetric rotor displacement in permanent magnet machines brings about unbalanced magnetic force between the rotor and stator. Prediction of the unbalanced force is important in design of spindle drives because it helps assessing eventual spindle runout. Additionally, maximum anticipated unbalanced force sets stiffness requirements for bearings of soft-mounted high-speed machines. Good modelling of the distorted flux density in the machine with an eccentric rotor is essential for accurate force estimation. In the paper a simple method for estimating unbalanced force in slotless PM machines is presented and effectiveness of the model is compared with models based on conformal mapping.@en

Abstract Permanent magnet (PM) machines are considered the most suitable machine type for very high-speed applications. Still, due to the growing demand for ever higher rotational speeds, PM machines are approaching their limits. The focus of this paper are dierent factors that lie behind inherent speed limitations of permanent magnet machines. The limits - thermal, elastic and rotordynamical - are defined, classified and correlated to basic machine parameters.@en

The I/f control is an open-loop method of control of PM machines in which the reference current is set proportionally to the electrical frequency while the voltage is generated through a current regulator. A realization of the method for control of a very high-speed synchronous PM motor is presented in the paper. To add necessary damping to the system, the controller uses modulation of the electrical frequency in the way which is frequently utilized in the V/f method for high-speed PM machines. Adequate current reference is obtained based on measurements of the no-load voltage and speed decay. Stable speed control is achieved throughout the whole speed range.@en

High-speed permanent magnet rotors need a non-magnetic enclosure so as to ensure structural integrity of the rotor at elevated speeds. Optimal design of the enclosure is the focus of this paper. Analytical modelling of mechanical stress in the rotor is presented. The model distinguishes between influences of enclosure geometry and fitting on the stress, while also considering rotational speed and operating temperature. Through analytical modelling, a relatively simple approach of optimizing the enclosure is achieved. This optimization approach was used in the design of a carbon fibre enclosure of an unconventional high-speed rotor with a disc shape. It is shown that a planar analytical model of stress with isotropic material assumption is sufficiently good for structural optimization of a permanent magnet rotor. (6 pages)@en

Abstract This paper focuses on integration of a permanent magnet motor with active magnetic bearings for driving a high-speed micro-milling spindle. A new concept of supporting a short rotor with a slotless PM motor embedded by 5DOF bearings is conceived. In the concept, the bearings and motor functions remain independent. A 100 W, 200000 rpm motor compatible with magnetic bearings was designed and manufactured. An additional setup with aerostatic bearings was also constructed for testing of the motor.@en

In this paper, the design of a very high-speed motor for magnetically levitated micromilling spindle is presented. The target speed of the motor is 300.000 rpm. Slotless permanent magnet motor was chosen as a favorite for high-speed applications due to its compatibility with active magnetic bearings. A 500W permanent magnet motor is designed to fit an existing setup with magnetic bearings. Optimization procedure for the motor with an objective of minimum stator loss is presented.

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