DESIGN AND ANALYSIS OF PERMANENT MAGNET-TYPE BEARINGLESS MOTORS

Magnetic bearings have been applied to high speed and high power elect ric machines for machine tools, turbomolecular pumps, etc, Bearingless motors can be expected to realize high speed and high power ratings b ecause magnetic bearing functions are integrated into high-speed motor s, which results in a simplified structure with short shaft length. In this paper, permanent magnet type bearingless motors, having built-in capability to achieve high power factor and high efficiency, are prop osed. The shaft is suspended and centered by electromagnetic forces pr oduced by currents in the additional radial force windings of the stat or slots. At first the relationships of these radial forces, currents and voltages are derived analytically, Moreover, the relationships bet ween radial forces and permanent magnet thickness are found. The optim al permanent magnet thickness is determined. The ratio of radial force over current as well as the peak air-gap flux density are discussed. These relationships are confirmed by prototype machines.