Fukuzo Nakamura

Characteristics of a permanent magnet type bearingless motor

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.<<ETX>>

Inductances of cageless reluctance-synchronous machines having nonsinusoidal space distributions

A method for the analysis of a cageless reluctance-synchronous machine with nonsinusoidal space distributions is described. First, general equations for inductances are derived from the winding and permeance distributions in the air gap, which are assumed to have space harmonics. It is shown how the amplitude of ascending order decreases more rapidly for the inductance harmonic than for the harmonic of the permanence or the magnetomotive force. Second, the fundamental components of the inductances that vary with the angular position of the rotor are found to be influenced by the space harmonics. Thus, the variations of the self-inductance and mutual inductance are assumed to be purely sinusoidal with no harmonics. On the basis of this mathematical model, simple equations are derived for the general direct and quadrature-axis inductances. Finally, these equations are used in the single-phase standstill method for measuring the parameters of a 1.3 kW test machine, and it is shown that the measured values agree fairly well with the equations.<<ETX>>

A radial position control of induction type bearingless motor considering phase delay caused by the rotor squirrel cage

A squirrel cage induction type bearingless motor which has conventional four-pole stator windings and additional two-pole stator windings for the radial position control of the rotor has been proposed. The squirrel cage rotor windings can be seen as not only four-pole windings but also as two-pole windings. An equivalent circuit for one phase at the two-pole winding terminals is shown. The frequency response characteristics of effective current components in the radial force production are calculated. A phase lead-lag compensator is designed, and its effectiveness was shown.<<ETX>>

A rotor design of a permanent magnet-type bearingless motor considering demagnetization

The characteristics of a surface-mounted permanent magnet-type bearingless motor have reported by the authors. Thin permanent magnets are employed to generate radial forces efficiently. However, thin permanent magnets have a crisis of demagnetization because not only q-axis fluxes but also additional radial force fluxes exist in the motor magnetic field. The maximum q-axis and radial force currents limited by the demagnetization have been already made clear for a particular machine configuration using the finite element method. However, these results are not theoretically verified. In this paper, a limitation of demagnetization is analytically derived. The maximum current is found as a parameter of a permanent magnet thickness.

A novel strategy for microcomputer-based control of a single-phase output cycloconverter

A novel control algorithm using a time process chart that is capable of accurate control of cycloconverters is developed. This algorithm is obtained by making a straight-line approximation in a newly contrived phase plane. In spite of its rather simple procedures, this algorithm is capable of highly accurate control that is comparable to that of the conventional analog scheme. A six-pulse noncirculating current-type cycloconverter is controlled with a small-scale interface and a high-speed control program. Experimental results confirm the validity and usefulness of the proposed method. As far as the processing time is concerned, this method could be used to control a system with a larger pulse number, such as a 12 or 24-pulse system. >