Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-09-12
2002-09-24
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
Reexamination Certificate
active
06455966
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic bearing device for use with a motor-combined structure, and more particularly to a magnetic bearing device having magnetic bearings which supports a rotatable shaft that is rotated by a motor armature mounted on the rotatable shaft and a motor stator disposed around the motor armature.
2. Description of the Related Art
FIG. 1
of the accompanying drawings shows a conventional magnetic bearing device for use with a motor-combined structure. As shown in
FIG. 1
, the motor-combined structure has a rotatable shaft
11
that is rotated by a revolving magnetic field generated by a motor stator
13
which is disposed around a motor armature
12
mounted centrally on the rotatable shaft
11
. The motor armature
12
and the motor stator
13
make up a motor. The magnetic bearing device has magnetic bearings
14
A,
14
B disposed around the rotatable shaft
11
one on each side of the motor stator
13
. Each of the magnetic bearings
14
A,
14
B comprises a magnetic member
15
fixed to the rotatable shaft
11
and electromagnets
16
for producing magnetic fluxes to apply magnetic attractive or repulsive forces to the magnetic member
15
to levitate and hold the rotatable shaft
11
in a predetermined position.
Displacement sensors
17
A,
17
B for detecting a positional displacement of the rotatable shaft
11
are disposed respectively near the magnetic bearings
14
A,
14
B. The displacement sensors
17
A,
17
B supply detected positional displacement signals to a magnetic bearing controller
18
. In the magnetic bearing controller
18
, a displacement sensor signal detector
18
A detects the detected positional displacement signals from the displacement sensors
17
A,
17
B, and a compensating circuit
18
B generates a signal for levitating and supporting the rotatable shaft
11
in a desired target position from an output signal from the displacement sensor signal detector
18
A. The signal generated by the compensating circuit
18
B is amplified by a driver
18
C, which supplies the amplified signal to the electromagnets
16
. The rotatable shaft
11
is levitated and supported in the desired target position based on positional displacements of the rotatable shaft
11
that are detected by the sensors
17
A,
17
B.
The magnetic bearing controller
18
is supplied with electric power directly from a commercial three-phase AC power supply
20
, and the motor stator
13
is supplied with electric power from the AC power supply
20
via a switch
21
.
The magnetic bearing controller
18
converts the supplied electric power to electric power for generating control forces to act on the rotatable shaft
11
. The converted electric power is supplied from the magnetic bearing controller
18
to the electromagnets
16
.
When the conventional magnetic bearing device starts to operate, the magnetic bearing controller
18
is activated to control the magnetic bearings
14
A,
14
B to levitate the rotatable shaft
11
. Thereafter, the switch
21
is closed to supply electric power from the AC power supply
20
to the motor stator
13
. The motor armature
12
fixedly mounted on the rotatable shaft
11
starts rotating under a revolving magnetic field generated by the motor stator
13
. A certain period of time after the motor armature
12
starts rotating, the rotatable shaft
11
rotates at a rated rotational speed.
If the voltage of the electric power supplied to the AC power
20
varies for some reason while the motor is in operation, then the motor is subject to a change in the voltage of the electric power supplied thereto which is commensurate with the variation of the voltage of the electric power supplied to the AC power supply
20
. Specifically, because the motor stator
13
is connected to the AC power supply
20
via the switch
21
, the motor directly undergoes the variation of the voltage of the electric power supplied to the AC power supply
20
. When the voltage applied to the motor stator
13
varies, the drive torque applied to rotate the motor armature
12
also varies. The variation of the drive torque causes a variation of unbalanced magnetic forces produced between the motor armature
12
and the magnetic poles of the motor stator
13
. The variation of unbalanced magnetic forces is transmitted through the rotatable shaft
11
to the magnetic bearings
14
A,
14
B.
In view of possible variations of unbalanced magnetic forces produced between the motor armature
12
and the motor stator
13
due to changes in the power supply voltage applied to the motor, the magnetic bearing controller
18
is arranged to change its output characteristics in order to prevent such variations from adversely affecting the levitation control performed thereby. Specifically, if the voltage from the AC power supply
20
changes, then the magnetic bearing controller
18
adjusts its output characteristics to provide control characteristics depending on the power supply voltage or changes control characteristic settings based on the supplied voltage.
Inasmuch as the motor armature of the motor is integrally fixed to the rotatable shaft, the motor operates normally when the motor armature rotates at the rated rotational speed, and the magnetic levitation control characteristics of the magnetic bearing device are determined on the assumption that unbalanced magnetic forces produced between the motor armature and the motor stator are substantially constant when the motor armature rotates at the rated rotational speed. If the unbalanced magnetic forces produced between the motor armature and the motor stator are changed, then the magnetic levitation control characteristics of the magnetic bearing device vary, possibly resulting in a control failure in the worst case.
If a power supply voltage that is available to the installation site for the magnetic bearing device cannot be specified, or if it is assumed that the voltage applied to the magnetic bearing device is variable over a certain wide range for the purpose of using the magnetic bearing device in numerous applications, then control characteristics of the magnetic bearing device tend to vary as a result of a variation of the unbalanced magnetic forces produced in the motor. However, it is tedious and time-consuming to adjust or modify the magnetic bearing device each time when control characteristics of the magnetic bearings vary.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a magnetic bearing device for stably controlling magnetic bearings at all times without having to readjust control characteristics of magnetic bearings and change settings thereof.
To achieve the above object, there is provided in accordance with the present invention a magnetic bearing device for use with a motor-combined structure, comprising magnetic bearings for supporting a rotatable shaft out of contact therewith, a motor for rotating the rotatable shaft, a common power supply for supplying electric power to the magnetic bearings and the motor, and a motor drive power supply for limiting variations of the electric power supplied to the motor to at most a predetermined level with respect to variations of electric power supplied to the common power supply.
The motor drive power supply controls the voltage of electric power to be supplied to the motor. Even if the voltage of electric power supplied to the common power supply varies over a certain range, the motor drive power supply can hold variations of the voltage of the electric power to be supplied to the motor within a predetermined range. Regardless of variations of the voltage of the electric power supplied to the common power supply, therefore, the motor is supplied with electric power at a substantially constant voltage. Consequently, unbalanced magnetic forces produced between a motor armature and a motor stator of the motor can be held at a constant level or less at all times. The magnetic bearings which levitate and support the rotatable shaft can be controlled stably
Barada Toshimitsu
Komai Masakazu
Nakazawa Toshiharu
Ooyama Atsushi
Sekiguchi Shinichi
Armstrong Westerman & Hattori, LLP
Ebara Corporation
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