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For a salient-pole machine, the values of the inductances measured by the locked rotor test can lead to appreciable error if the windings produce mmf harmonics. In practice, the effects of winding harmonics cause considerable divergence from values of the ideal machines. In the case of a reluctance-synchronous machine, the discrepancy is even larger because the axis reactance ratio is higher than that of a conventional synchronous machine.In this paper, the amplitude of the second harmonic term of the self-inductance is defined to be independent of the corresponding amplitude of the mutual inductance, which represents the effects of space harmonics. Therefore, expressions for the direct-and quadrature-axis inductances of the machine with space harmonics can be derived only for three-phase machines.Inductance variations of several cageless reluctance-synchronous machines for high-speed drives were measured. Based on the results of the measurements, the direct-and quadrature-axis inductances are predicted using derived expressions. In addition, these are also predicted by the conventional method and compared with the machine parameters ohtained by the load tests. The proposed method is found to predict accurate machine parameters.

Super high speed and high power electric machines are required for turbomolecular pumps and spindle drives. High rotational speed and high power drives can be achieved with bearingless motors. In this paper, a bearingless motor with principles of permanent magnet type synchronous motors is proposed. High power factor and high efficiency can be expected in permanent magnet type bearingless motors. The proposed bearingless motor is a 4-pole permanent magnet synchronous motor, in which additional 2-pole windings are wound together with 4-pole motor windings in stator slots. With currents of 2-pole windings, radial magnetic forces are produced to support a rotor shaft. Principles of radial force production of surface-mounted permanent magnet bearingless motors are analyzed mathematically. It was found that radial forces are efficiently produced by employing thin permanent magnets on the surface of rotor iron. A test machine was built to measure inductance functions as well as relationships between voltages and currents. I . INTRODUCIION Magnetic bearings have been applied to high speed motors such as machine tools and turbomolecular pumps [1][2]. The advantages of magnetic bearings are no mechanical contacts, no lubrication and no wear. However, these high speed motors with magnetic bearings require rather long axial shaft length because magnetic bearings are in considerable size, and are arranged in the both ends of the motor. Therefore, critical speeds are decreased, which results in difficulties in increasing rotational speeds. One of the solutions to realize high rotational speed and high power drives can be bearingless motors[3-71. Bearingless motors are hybrids of magnetic bearings and electric motors. Radial force windings are wound together with conventional motor windings to produce magnetic forces. Bearingless motors have advantages over conventional high speed motors with magnetic bearings as follows; (a)The motor shaft IenEth can be short, i.e., critical speed is high, if the output power is equal. (b)High power can be achieved if shaft lengths are the same. (c)DC exciting current of conventional magnetic bearings is not needed. Induction and synchronous reluctance type bearingless motors have been proposed by the authors[5][6]. The bearingless motors proposed by the authors have additional sets of 2-pole windings in 4-pole motor stators to produce radial forces. The principles of the proposed bearingless motors are applicable not only to induction and synchronous reluctance machines but also to various types of super high speed motors. Recently, permanent magnet synchronous machines have been developed for super high speed applications with improved mechanical robustness of rotor structures[8][9]. Permanent magnet synchronous motors have considerably possibilities in super high speed applications. A permanent magnet type bearingless motor has been reported to be constructed[7]. However, optimal structure of rotor magnet thickness, as well as inductance functions have not yet made clear. Voltage and curre...