JP3677826B2 - Magnetic bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic bearing device which can reduce the time during which a rotating shaft is decelerated in the event of power failure. SOLUTION: This magnetic bearing device includes a brushless dc motor 1 which drives and rotates a rotating shaft; magnetic bearing means 13, 14 for levitating the rotating shaft magnetically; a magnetic bearing control circuit 6 for controlling the magnetic bearing means; and a forced brake circuit 3 which involves a resistance that is connected in series with the brushless dc motor during power failure. If power is normally supplied from a power supply, the motor controls magnetic levitation using the magnetic bearing means 13, 14 driven under control of the magnetic bearing circuit 6 In the event of power failure, the resistance 31 of the forced brake circuit 3 is connected in series to the motor 11 to convert current flowing through the motor into heat by means of the resistance to perform heated breaking, by means of which the deceleration time of the rotating shaft is reduced.

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic bearing device, and more particularly to a magnetic bearing device used for a high-speed rotating device such as a vacuum pump such as a turbo molecular pump or a high-speed spindle for machine tools.
[0002]
[Prior art]
High-speed rotating equipment such as vacuum pumps such as turbo molecular pumps are required to be oil-free in order to obtain a good vacuum, and support high-speed rotating bodies such as high-speed spindles for machine tools in a non-contact manner. Is required to do. Therefore, magnetic bearings have been developed in place of conventional bearings using oil lubrication. This magnetic bearing can reduce the vibration which generate | occur | produces by rotating and rotating a rotating shaft non-contactingly.
[0003]
Conventionally, this magnetic bearing device, for example, in the turbo molecular pump shown in FIG. 2, includes radial magnetic bearings 21 and 22 provided with electromagnets in the radial direction of the rotating body, and thrust bearings 23 provided with electromagnets in the axial direction. Displacement sensors such as radial sensors 24 and 25 and a thrust sensor 26 provided at substantially the same position as the electromagnet to detect the state of the rotating body are installed to constitute a feedback control system, and the current flowing through each electromagnet is adjusted to adjust the electromagnet The suction force is adjusted to support the rotating body at the center position.
[0004]
The electromagnets are arranged so as to face each other with the rotation shaft interposed therebetween. By passing an excitation current determined by PID control or the like through each excitation magnet through the excitation amplifier, the rotation shafts are attracted to each other by the opposing electromagnets. Is controlled to an appropriate position. Thereby, magnetic levitation control is performed.
[0005]
FIG. 9 is a schematic block diagram of a conventional magnetic bearing device. In FIG. 9, the inverter circuit 4 controls the phase of the DC voltage obtained from the rectifier circuit 1 connected to the AC power source, the smoothing capacitor, and the stabilized power source 2 and applies it to the induction motor 16, and this inverter circuit 4 performs motor control in response to a control signal from the inverter control circuit 5 that inputs a detection signal of the rotation sensor 17. The electromagnet 14 of the magnetic bearing means that supports the rotating shaft of the motor 16 is controlled by the magnetic bearing control circuit 6 that inputs the shaft displacement signal of the displacement sensor 13. Electric power for driving the inverter control circuit 4 and the magnetic bearing control circuit 6 is supplied by a DC voltage obtained through the DC / DC conversion circuit 7.
[0006]
When a power supply abnormality such as a power failure occurs in such a magnetic bearing device, the supply of driving power to the magnetic bearing control circuit 6 is stopped, and magnetic levitation control and motor control become difficult. It will be supported by friction. Conventionally, in order to maintain this magnetic levitation control and motor control, the magnetic bearing control circuit 6 and the inverter control circuit 5 are backed up by regenerative power generated by using the motor as a generator and a backup battery (not shown). Yes. The brake control circuit 8 performs braking of the motor by performing regenerative braking that regenerates energy of the rotating shaft to the control circuit side and exothermic braking that consumes energy exceeding the regenerative amount.
[0007]
[Problems to be solved by the invention]
The conventional magnetic bearing device has a problem that it takes a long time to decelerate the rotating shaft when a power supply abnormality occurs.
[0008]
FIG. 10 is a schematic diagram illustrating a deceleration state in a conventional magnetic bearing device. When electric power obtained by using a motor as a generator is used as a power source for a magnetic bearing control circuit or a motor control circuit when a power supply is abnormal, when the rotating shaft is rotating at high speed (section B in FIG. 10). Sufficient electric power can be obtained for each control, but when the speed is low (section C in FIG. 10), the generated electric power decreases and the motor control and magnetic levitation control cannot be maintained, and the rotating shaft is supported by the protective bearing. become. The braking in the section B in FIG. 10 is mainly a regenerative braking in which the energy of the rotating body is returned to the control circuit side, and after the generated power can no longer be obtained (section C in FIG. 10), the small friction caused by the protective bearings. Deceleration is performed by resistance. The deceleration due to the frictional resistance of the protective bearing takes a long time, and during this time, the protective bearing is deteriorated by friction and the replacement time of the protective bearing is advanced. A one-dot chain line in FIG. 10 indicates a deceleration state when regenerative braking is maintained.
[0009]
When a backup battery is used as the power supply for the control circuit when the power supply is abnormal, the magnetic bearing control and the motor control are maintained even after the power supply is abnormal, but it takes a long time to decelerate because there is no braking means. In addition, it is necessary to prepare a large capacity battery separately.
[0010]
Accordingly, an object of the present invention is to solve the problems of the conventional magnetic bearing device described above and to provide a magnetic bearing device capable of shortening the speed of rotation of the rotating shaft when a power supply abnormality occurs.
[0011]
[Means for Solving the Problems]
The magnetic bearing device of the present invention supports a brushless DC motor that rotationally drives a rotating shaft, magnetic bearing means that magnetically floats the rotating shaft, a magnetic bearing control circuit that controls the magnetic bearing means, and supports the rotating shaft when a magnetic bearing is abnormal By providing a protective bearing that performs this operation and a forcible brake circuit including a resistor connected in series with the brushless DC motor when the power supply is abnormal, the speed of the rotating shaft is reduced when the power supply abnormality occurs.
[0012]
A brushless DC motor is a motor that can convert rotational energy of a rotating shaft into an induction current in a coil on the stator side, and the present invention thermally converts this induced current by a resistance in a forced brake circuit to perform a braking action. Exothermic braking is performed.
[0013]
In the first embodiment of the present invention, the forced brake circuit includes a relay circuit that connects a brushless DC motor and a resistor in series when the voltage applied to the motor is equal to or lower than a set voltage. Exothermic braking can be performed to convert the energy of the motor into heat.
[0014]
In the second embodiment of the present invention, the forced brake circuit includes a current braking means for flowing a power equal to or greater than the regenerative power to the control circuit to the resistor, thereby enabling regenerative braking and exothermic braking.
[0015]
The third embodiment of the present invention is provided with a backup battery for driving the magnetic bearing control circuit, whereby magnetic levitation control of the rotating shaft can be performed even during operation of the forced brake circuit.
[0016]
In a fourth embodiment of the present invention, the magnetic bearing control circuit is driven by electric power obtained by using a brushless DC motor as a generator.
[0017]
When electric power is normally supplied from the power source, the motor is magnetically levitated by magnetic bearing means driven by control of the magnetic bearing circuit. When a power supply abnormality occurs, the supply of drive power from the power supply to the motor stops. The motor continues to rotate due to the inertial force, and conversely acts as a generator to generate electric power. When the rotational speed is high and the generated power is sufficient, the magnetic bearing control circuit is driven by the generated power. When the rotational speed decreases and the generated power becomes insufficient, the magnetic bearing control circuit stops the magnetic levitation control.
[0018]
At this time, by connecting the resistance of the forced brake circuit and the motor in series, the current flowing through the motor is converted into heat by the resistance to perform heat braking. This shortens the speed of the rotation of the rotating shaft.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Configuration of Embodiment of the Present Invention) FIG. 1 is a schematic block diagram of an embodiment of a magnetic bearing device of the present invention. The configuration shown in FIG. 1 is substantially the same as the configuration shown in FIG. 9 except that a forced brake circuit 3 is provided in place of the brake control circuit 8, a brushless DC motor 11 is used as a motor, and an induction motor 16 The configuration differs in that the rotation sensor 17 is changed to the hall sensor 12 in accordance with the change from the brushless DC motor 11 to the brushless DC motor 11.
[0020]
In FIG. 1, an inverter circuit 4 controls the phase of a DC voltage obtained from a rectifier circuit 1 connected to an AC power source, a smoothing capacitor, and a stabilized power source 2 and applies it to a brushless DC motor 11. The circuit 4 receives the control signal from the inverter control circuit 5 that inputs the detection signal of the hall sensor 12 and performs motor control. Note that the rotation sensor 17 is changed to the Hall sensor 12 in order to detect the rotation position of the permanent magnet of the brushless DC motor 11. The electromagnet 14 of the magnetic bearing means that supports the rotating shaft of the brushless DC motor 11 is controlled by a magnetic bearing control circuit 6 that receives the shaft displacement signal from the displacement sensor 13 and outputs a control signal. Electric power for driving the inverter control circuit 5 and the magnetic bearing control circuit 6 is supplied by a DC voltage obtained through the DC / DC conversion circuit 7.
[0021]
Between the stabilized power supply 2 and the inverter circuit 4, there is a forced brake circuit 3 in which a resistor 31 and a current control element 32 are connected in series to the power supply, and a relay 33 is connected in parallel to the current control element 32. Provided.
[0022]
(Operation of the embodiment of the present invention) When the motor performs normal rotation, AC power from a power source is obtained by a rectifier circuit 1, a smoothing capacitor, and a stabilized power source 2, and this DC voltage is converted into an inverter circuit. The phase is controlled by 4 and supplied to the brushless DC motor 11 for driving. The magnetic bearing control circuit 6 sends a control signal to the electromagnet 14 of the magnetic bearing means to control the magnetic levitation of the rotating shaft. At this time, the inverter control circuit 5 and the magnetic bearing control circuit 6 are driven by the DC voltage from the stabilized power source obtained through the DC / DC conversion circuit 7.
[0023]
Next, motor braking in the case of emergency stop due to power failure will be described. FIG. 3 is a flowchart for explaining the first braking action of the embodiment of the present invention, FIG. 4 is a diagram for explaining the operation of the forced brake circuit, and FIG. 5 is a diagram showing the time variation of the rotational speed of the rotary shaft of FIG. The first braking action of motor braking will be described using FIG.
[0024]
The inverter control circuit 5 and the magnetic bearing control circuit 6 are supplied with power from the power source through the DC / DC conversion circuit 7 and perform normal rotation. The section A in FIG. 5 shows this normal rotation state (step S1).
[0025]
When the supply of power from the power supply side is stopped due to a power supply abnormality or the like, the power supply voltage is lowered, and the motor 11 side induces a voltage and conversely functions as a generator. The inverter control circuit 5 and the magnetic bearing control circuit 6 receive power supply from the motor side instead of the power source. When this voltage is a voltage sufficient for driving the inverter control circuit 5 and the magnetic bearing control circuit 6, motor control and magnetic levitation control are performed with this electric power. (Steps S2, 3).
[0026]
A section B in FIG. 5 shows the rotation state of the rotating shaft at this time. The braking in the section B is performed by regenerative braking and exothermic braking. FIG. 4A shows the operation of the forced brake circuit 3 in the section B. In the section B, the relay 33 in the forced brake circuit 3 is turned off, and only the current control element 32 is driven. The inverter control circuit 5 diverts the electric power generated from the motor side to the motor side and the forced brake circuit 3 side. Regenerative braking is performed by returning to the motor side, and exothermic braking is performed by flowing the resistance 31 through the forced brake circuit 3. This diversion is performed by the current control element 32 in the forced brake circuit 3, and control is performed so that the electric power exceeding the amount returned to the motor side flows through the resistor 31 (step S4).
[0027]
When the rotation of the rotating shaft advances and the generated voltage drops below a voltage sufficient for driving the inverter control circuit 5 and the magnetic bearing control circuit 6 (step S2), the inverter control circuit 5 and the magnetic bearing control circuit 6 Since supply is lost, inverter control and magnetic levitation control are stopped (step S5). The section C in FIG. 5 shows the rotation state of the rotating shaft at this time. At this time, the relay 33 of the forced brake circuit 3 is turned on and the motor and the resistor 31 are connected in series, and the current induced on the motor side flows into the resistor 31 and is converted into heat. Is called. FIG. 4B shows the flow of current in the forced brake circuit at this time (step S6). At this time, since the magnetic levitation control is stopped, the rotating shaft is supported by the protective bearing 15 and is also braked by this friction.
[0028]
Therefore, in the section C, rapid deceleration is performed by heat braking by resistance and friction braking by the protective bearing.
[0029]
Next, the second braking action of motor braking will be described. FIG. 6 is a flowchart for explaining a second braking action according to the embodiment of the present invention, and FIG. 8 is a diagram showing a change with time in the rotational speed of the rotating shaft.
[0030]
The inverter control circuit 5 and the magnetic bearing control circuit 6 are supplied with power from the power source through the DC / DC conversion circuit 7 and perform normal rotation. Section A in FIG. 8 shows this normal rotation state (step S11).
[0031]
When the supply of power from the power supply side is stopped due to a power supply abnormality or the like, the inverter control circuit 5 and the magnetic bearing control circuit 6 cannot receive power supply from the power supply side. Thereby, inverter control and magnetic levitation control are performed (step S12).
[0032]
When the voltage generated on the motor side is a voltage at which regenerative braking can be performed (section B in FIG. 8), braking of the rotating shaft is performed by regenerative braking and exothermic braking as in step S4 ( Step S13, 14).
[0033]
When the rotation of the rotating shaft progresses and the generated voltage falls below the voltage at which regenerative braking can be performed (step S13), the inverter control circuit 5 turns on the relay 33 of the forced brake circuit 3 and connects the resistor 31 in series with the motor. Then, heat braking is performed by the resistor 31 (step S15). A section C in FIG. 8 shows the rotation state at this time, and the inverter control circuit 5 and the magnetic bearing control circuit 6 are driven by the backup battery to continue the motor control and the magnetic levitation control.
[0034]
Therefore, in the section C, it rotates in a non-contact state by magnetic levitation control, and is decelerated by exothermic braking by resistance.
[0035]
In the second braking action, since the rotating shaft is not supported by the protective bearing when the power supply is abnormal, the effect of reducing the deterioration of the protective bearing becomes large.
[0036]
Next, the third braking action of motor braking will be described. FIG. 7 is a flowchart for explaining a third braking action according to the embodiment of the present invention.
[0037]
The third braking action supplies drive power for motor control and magnetic levitation control by switching between generated power and a backup battery. The inverter control circuit 5 and the magnetic bearing control circuit 6 are supplied with power from the power source through the DC / DC conversion circuit 7 and perform normal rotation. Section A in FIG. 8 shows this normal rotation state (step S21).
[0038]
When the supply of power from the power supply side is stopped due to a power supply abnormality or the like, the inverter control circuit 5 and the magnetic bearing control circuit 6 cannot receive power supply from the power supply side, so the motor 11 side can be used as a generator. It is driven using the power that is generated. When this voltage is a voltage sufficient for driving the inverter control circuit 5 and the magnetic bearing control circuit 6, motor control and magnetic levitation control are performed with this electric power. (Steps S22 and S23). In this section B, the rotating shaft is braked by regenerative braking and exothermic braking as in step S4 (step S24).
[0039]
When the rotation of the rotating shaft progresses and the generated voltage drops below a voltage sufficient for driving the inverter control circuit 5 and the magnetic bearing control circuit 6 (step S22), the inverter control circuit 5 and the magnetic bearing control circuit 6 are not shown. Electric power is supplied from the backup battery, thereby performing motor control and magnetic levitation control (step S25). Further, the inverter control circuit 5 turns on the relay 33 of the forced brake circuit 3 to connect the resistor 31 in series with the motor, and performs heat-generating braking by the resistor 31. Section C in FIG. 8 shows the rotation state at this time (step S26).
[0040]
Therefore, in the section C, it rotates in a non-contact state by magnetic levitation control, and is decelerated by exothermic braking by resistance.
[0041]
In the third braking action, the effect of reducing the deterioration of the protective bearing is increased as in the second braking action, and the use time of the backup battery is shorter than that in the second braking action. The backup battery can be small.
[0042]
It should be noted that, in place of the relay in the forced brake circuit, an element that maintains the ON state even when power is not supplied can be used.
[0043]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a magnetic bearing device that can shorten the speed of rotation of the rotating shaft when a power supply abnormality occurs.
[Brief description of the drawings]
FIG. 1 is a schematic block diagram of an embodiment of a magnetic bearing device of the present invention.
FIG. 2 is a schematic view of a turbo molecular pump.
FIG. 3 is a flowchart illustrating a first braking action according to the embodiment of the present invention.
FIG. 4 is a diagram illustrating the operation of a forced brake circuit according to the present invention.
FIG. 5 is a diagram showing a change with time in the rotational speed of the rotary shaft according to the embodiment of the present invention.
FIG. 6 is a flowchart illustrating a second braking action according to the embodiment of the present invention.
FIG. 7 is a flowchart for explaining a third braking action of the embodiment of the present invention.
FIG. 8 is a diagram showing a change over time in the rotational speed of the rotating shaft according to the embodiment of the present invention.
FIG. 9 is a schematic block diagram of a conventional magnetic bearing device.
FIG. 10 is a schematic diagram illustrating a deceleration state in a conventional magnetic bearing device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Rectification circuit, 2 ... Stabilized power supply, 3 ... Forced brake circuit, 4 ... Inverter circuit, 5 ... Inverter control circuit, 6 ... Magnetic bearing control circuit, 7 ... DC / DC conversion circuit, 8 ... Brake control circuit, 11 DESCRIPTION OF SYMBOLS ... Brushless DC motor, 12 ... Hall sensor, 13 ... Displacement sensor, 14 ... Electromagnet, 15 ... Protective bearing, 16 ... Induction motor, 17 ... Rotation sensor, 31 ... Resistance, 32 ... Current control element, 33 ... Relay.

Claims (1)

A brushless DC motor that rotationally drives the rotating shaft, a magnetic bearing means that magnetically levitates the rotating shaft, a magnetic bearing control circuit that controls the magnetic bearing means, a protective bearing that supports the rotating shaft in the event of an abnormal magnetic bearing,
With a forced brake circuit including a resistor connected in series with a brushless DC motor in case of power failure,
The forced brake circuit includes a current braking means for causing a power component greater than regenerative power to flow through the resistor when the applied voltage to the motor is equal to or higher than the set voltage, and a brushless DC motor and resistor when the applied voltage to the motor is equal to or lower than the set voltage. And a relay circuit for connecting them in series.

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