Calculation of Eddy Current Loss in Surface Permanent Magnet Rotor Due to Suspension Flux in High Power Bearingless Motors

This paper presents how to reduce eddy current losses of the rotor permanent magnet in high power bearingless motors. It has four-pole surface permanent magnet rotor and 36-slot stator core with two set of three-phase distributed windings. When the rotor pole number is defined as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$P_{t}$</tex>, the number of poles <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$P_{s}$</tex> of the suspension winding is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$P_{t}+2$</tex> or <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$P_{t}-2$</tex> according to a principle of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$P\pm 2$</tex> poles. In this paper, the eddy current loss due to the suspension flux is discussed. It is seriously high compared to that of the motor winding flux because the relative speed between the rotor rotational speed and the rotating field of the suspension flux is large. In 3D-FEM analysis, the eddy current loss in the permanent magnet is calculated and compared in two cases of two- and six-pole suspension windings. In addition, the total efficiency is shown when the rated torque and radial load are applied.