Finite Element Design of Bearingless Permanent Magnet Motors

In high performance applications with high demands on speed range, lifetime, cleanness or tightness, magnetic bearing systems can provide substantial advantages to classical drive systems using ball or sliding bearings. Some of these applications like pumps, blowers or fans require only three actively controlled degrees of freedom and can be supported by four coil bearingless permanent magnet motors. In these cases three degrees of freedom are passively stabilized by the tensible force of permanent magnets. Depending on the particular application an interior or exterior rotor design of the bearingless motor may be advantageous. A finite element analysis is used to show the interactions between the current density distributions of the stator and the excitation fields of the rotor. Different permanent magnet magnetization forms are examined. It is shown that the results of the interior rotor design differ significantly from the results achieved by exterior rotor design.