T. Fukao

Improved analysis of a bearingless switched reluctance motor

Bearingless switched reluctance motors, which can control rotor radial positions with magnetic force, have been proposed. Bearingless switched reluctance motors have combined characteristics of switched reluctance motors and magnetic bearings. Production of radial force for rotor shaft magnetic suspension is explained with differential stator windings. Mathematical relations between motor currents and radial force are derived by considering cross coupling and fringing fluxes. Theoretical relationships are verified with experimental results at partial overlap positions.

Radial force and torque of a bearingless switched reluctance motor operating in a region of magnetic saturation

Bearingless switched reluctance motors, which can control rotor radial positions with magnetic force, have been proposed. These motors are characterized by integration of switched reluctance motors and magnetic bearings. It is essential for a control system to consider magnetic saturation in real time in order to realize stable operation at a full torque load. Thus, this paper proposes a method for fast calculation of radial force and torque of a bearingless switched reluctance motor operating in a region of magnetic saturation. It is shown experimentally that the proposed method is effective in calculating the radial force and the torque under conditions of magnetic saturation.

A Novel Magnetic Suspension-Force Compensation in Bearingless Induction-Motor Drive With Squirrel-Cage Rotor

This paper presents an improved analysis of magnetic force compensation in a bearingless induction motor with a squirrel-cage rotor. The expressions for air-gap flux linkages are derived. Simulation blocks of suspension force are constructed. A novel control system, which compensates the delay and direction error in suspension force generation for a squirrel-cage rotor, is proposed. The efficacy of the proposed control system is established by both simulation and experiment

Radial force and speed detection for improved magnetic suspension in bearingless motors

In this paper, radial forces and speeds are detected and used in negative feedback loops to enhance damping factors and response speed in bearingless induction motors. Radial forces and speeds are calculated from the detected radial force fluxes. Both radial force and torque generating fluxes are detected from search coil fluxes wound around stator teeth. The effectiveness on improving damping of radial positioning is shown both theoretically and experimentally.

A deeply-buried permanent magnet bearingless motor with 2-pole motor windings and 4-pole suspension windings

-Various permanent magnet bearingless motors, which can control rotor radial positions with magnetic force actively, have been proposed and developed. These bearingless motors are characterized by integration of permanent magnet motors and magnetic bearings. However, these bearingless motors cannot generate suspension force effectively, because suspension flux necessary for generating the suspension force passes through permanent magnets which have large magnetic reluctance. Accordingly, this paper proposes a novel deeply-buried permanent magnet bearingless motor with 2-pole motor windings and 4-pole suspension windings. In the proposed motor, the suspension flux does not pass through the permanent magnets. Thus, the proposed motor is shown to generate suspension force effectively. In addition, a control method of the proposed motor and its drive system are theoretically analyzed, and it is shown experimentally that the proposed drive system is effective in realizing stable operation of magnetic suspension. Keywords--permanent magnet motors, magnetic bearings, bearingless motors, magnetic suspension.

Development of homo-polar type bearingless motors

The authors have proposed bearingless motors, that is, magnetic bearings combined with motors in the same stator. It is possible to reduce their shaft length compared with a conventional motor with magnetic bearings, and achieve higher rotational speed. Bearingless motors generate radial force by adding n/spl plusmn/2-pole flux on n-pole motor flux to make the flux distribution unbalanced. Several types of bearingless motors have already proposed, and most of them require to take variations of motor flux into account to control radial position stably. In this paper, homo-polar type bearingless motors are proposed and their radial force is analyzed. The rotor of a homo-polar motor has two cores with salient poles, each core is magnetized in a single pole. The important characteristics that the radial force doesnt vary in accordance with the rotor angle nor the motor torque current is derived from analysis. It is confirmed by experiments that the radial position can be controlled nearly independently from the rotational angle and torque.

An airgap flux oriented vector controller for stable magnetic suspension during high torque acceleration in bearingless induction motors

A bearingless induction machine has the combined characteristics of an induction motor and magnetic bearings. It is known that the magnetic suspension of the rotor becomes unstable at over load operation, particularly in transient conditions. A novel airgap flux oriented vector control scheme has been proposed to operate the bearingless induction motor during the high torque acceleration period. It has been found that there is an optimal flux orientation for complete decoupling in radial force generation. Test results in a laboratory bearingless induction motor validates the performance efficacy of proposed controller at overload conditions.

A novel magnetic suspension force compensation in a bearingless induction motor with a squirrel cage rotor

This paper presents an improved analysis of magnetic force compensation in a bearingless induction motor with a squirrel cage rotor. The expressions for rotor flux linkage are derived. Simulation blocks of suspension force are constructed. A novel control system, which compensates the delay and direction error in suspension force generation for a squirrel cage rotor is proposed. The efficacy of the proposed control system is established by both simulation and experiment.