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Active magnetic bearings (AMBs) provide reliable solution for high-speed rotors, where oil-free and reliable operation are crucial. In high-power applications benefits of AMBs, compared to traditional rolling element bearings or fluid film bearings, are highly valued. Typical AMB rotors comprise two radial AMBs, which are designed with compressor or generator wheels integrated on the rotor. AMB dimensions and locations are carefully selected for each new application. The system design is being iterated such that the nodes of the lowest frequency rotor bending modes are sufficiently far away from the AMB and sensor nodes to ensure robust AMB control. The design is very challenging and cost sensitive. This work focuses on electromagnetic design, modeling, and control of fully levitated AMB-rotor with three radial AMBs. The additional bearing ensures that the same design can be reused with different applications and regardless of the changes in locations of nodes of the first bending mode. The control plant is modeled based on flexible rotor dynamics; while bearing inductances and forces are modeled with 2-D and 3-D finite element method (FEM) electromagnetic simulations. The presented multi-input multi-output (MIMO) model-based control is coupled and centralized with three actuator-sensor pairs for radial suspension. The control design is verified in simulations using nonlinear engineering models. Additionally, experimental identification results are included. [ABSTRACT FROM AUTHOR]

The article addresses coupled loss and thermal analyses of a bearingless drive with an operating speed range of 17 000–32 000 rpm. The drive is a part of a high-temperature heat pump system integrated in a high-speed compressor. This drive system comprises two bearingless motor units and an axial active magnetic bearing. The drive can be positioned horizontally or vertically. The positioning is directly related to the force necessary to raise and suspend the rotor. Furthermore, the amplitude of the suspension current has a significant effect on the motor winding and iron losses. The iron losses, eddy current losses in the magnets, and losses in the bandage are investigated by three-dimensional (3-D) and 2-D finite-element analysis. The influence of segmentation of the magnets on losses is analyzed. Friction losses of the coolant are calculated analytically, and all the losses obtained from the electromagnetic analysis are represented as distributed heat sources and coupled with the 3-D thermal field analysis. The temperature fields are modeled under different motoring and suspension current conditions and evaluated for horizontal and vertical positions of the motor. As a precaution, demagnetization of the magnets is also considered. [ABSTRACT FROM AUTHOR]