Akira Chiba

Super high speed electrical machines - summary

There is increasing interests in super-high-speed motors and generators in industry applications such as microgas turbines, compressors, blowers, pumps, hybrid electric vehicles, turbo-molecular pumps, machine tool spindle drives, information storage disk drives and etc. In this paper, the state of the art survey of super-high speed electrical machines presented. Recent development of high speed and power ranges are summarized. Various structures of electrical machines, including induction, permanent magnet, claw pole, homopolar, axial gap synchronous and switched reluctance machines, are reviewed from the point of view of high rotational speed characteristics. Emerging technologies such as bearingless operation and intelligent controls are introduced in other papers of the panel session

Radial force in a bearingless reluctance motor

A four-pole reluctance synchronous machine with additional two-pole windings was constructed. The additional winding currents produce the radial force to act as a magnetic bearing. Expressions for the machine inductance functions are given. Inductance functions with respect to the eccentric displacement of the rotor were measured. The contribution of these inductances to the radial force production is established.

Characteristics of a bearingless induction motor

A bearingless induction motor with additional windings in the stator slots is proposed. Additional two-pole windings were wound with the conventional four-pole windings to produce radial magnetic forces. These forces, which control the position of the rotor shaft, are produced when magnetic fluxes from the two-pole windings cause an imbalance in the revolving magnetic field of the four-pole windings. Inductance functions were measured to derive the machine inductance matrix expression, and from this matrix the radial force and current relationships were found. Control circuits were designed and fabricated for a test machine. This test machine was successfully driven by the control circuits. A bearingless induction motor was successfully operated at speeds up to 6000 r/min. >

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 closed-loop operation of super high-speed reluctance motor for quick torque response

The authors examine operating modes of the cageless reluctance motor and propose a new control method for quick torque response. It is shown that the control of sinusoidal phase current in magnitude with fixed current phase angle provides a simple means for achieving quick torque response and efficient operation. The flux linkage, current, torque. and the rated voltage of the inverter are calculated for a reluctance motor. A performance comparison is made between the proposed control method and the field-oriented control method. Analysis and computer simulation show that substantial improvements in dynamic response and efficiency are achieved for a reluctance motor when operated with constant current phase angle compared with operation at constant direct axis current or constant flux. Test data from a 24000 r/min. 1.3 kW reluctance motor drive system are provided. >

Efficiency Improvements of Switched Reluctance Motors With High-Quality Iron Steel and Enhanced Conductor Slot Fill

In this paper, a comparison of efficiencies is put forward for a set of test machines constructed from several different types of low-loss magnetic steels. These are laminated amorphous alloys, 6.5% high silicon steel, and general-purpose low-loss silicon steel. Efficiency and characteristics are compared by experiment. The test switched reluctance motors are shown to have more than 95% efficiency at an output of about 2 kW. The effectiveness of an enhanced winding slot fill factor is also evaluated. The use of the high silicon steel is more practical at improving the efficiency as opposed to the use of increased slot fill factor.

Optimal design of rotor circuits in induction type bearingless motors

A design procedure of optimal rotor circuits is proposed considering a thickness of divided coil end conductors. If the conductor thickness is increased, rotor bar length is also increased, which results in an increased secondary rotor resistance. On the contrary, if the conductor thickness is decreased, a significant resistance is caused in coil end circuits, which also results in the increased secondary resistance. It is shown that there is an optimal design point to minimize the secondary resistance. The optimal design point is analytically derived. Test results indicated a validity of the proposed optimal design procedure.

A new control method of bearingless switched reluctance motors using square-wave currents

Bearingless switched reluctance motors have the combined characteristics of synchronous motors and magnetic bearings. Radial force production for rotor shaft magnetic suspension is explained with differential stator windings composed of the motor main windings and radial force windings. In this paper, a new control method with square-wave currents in the motor main windings is proposed. Under every condition, from no load to full load, stable operation is realized by opportunely controlling the advanced current phase angle /spl theta//sub m/, and the current pulse width /spl theta//sub m/ with the new control method. The rotational torque produced by the radial force winding currents is also considered in the new control method. It is shown in experimental results that a proposed method is very effective for stable operation at no load.

No load characteristics of a bearingless induction motor

This study involves a bearingless induction motor constructed with additional two-pole stator windings. These additional windings can be used to produce radial forces on the rotor shaft. The two-pole winding currents were regulated by radial position control loops to maintain the rotors position near the stator center. The voltage and current relationships of the two-pole windings were derived from a machine inductance model and equivalent circuits. The influence of secondary circuits was also taken into account. The theoretical values of current, voltage, and radial force were compared with the experimental results. It was found that the two-pole windings need only about 2% of the volt-ampere requirements of the main motor windings.<<ETX>>

Analysis of No-Load Characteristics of a Bearingless Induction Motor

This paper presents the design and analysis of a bearingless squirrel-cage induction motor. There are two sets of stator windings. The main winding is a four-pole arrangement, while the control winding is a two-pole type. The latter is utilized to produce radial forces on the rotor shaft. The two-pole winding currents are regulated by radial position sensors and control strategies in order to maintain the rotor shaft position near the air gap center. The voltage and current relationships of the two-pole windings were derived from the machine inductance model and equivalent circuits. The influences of the secondary rotor circuits were also taken into account. The theoretical values of current, voltage, and radial force were compared with the experimental results. It was found that the two-pole windings need only about 2 percent of the voltampere (VA) requirements of the main motor windings.