JP4000969B2 - Control type magnetic bearing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control type magnetic bearing device used for a turbo molecular pump or the like.
[0002]
[Prior art]
In this type of magnetic bearing device, the rotating body is supported in a non-contact manner by a plurality of sets of control type magnetic bearings and rotated by an electric motor driven by an inverter. In addition, power is supplied from a commercial AC power supply (200 V), which is an external power supply, to an inverter, a magnetic bearing drive circuit, and a power supply unit that supplies power (DC) to a main control unit that controls these. The power supply unit rectifies and smoothes the alternating current from the commercial power supply and supplies it to an inverter or the like.
[0003]
[Problems to be solved by the invention]
However, in the conventional magnetic bearing device, when the input voltage from the power supply unit to the inverter fluctuates due to fluctuations in the voltage of the external power supply, the motor current (current that actually flows through the electric motor) fluctuates accordingly. Since the rotational speed of the motor fluctuates, there is a problem that the exhaust performance of the pump cannot be kept constant.
[0004]
In a main control unit of a conventional magnetic bearing device, for example, in a PI control calculation unit, a current value supplied to the motor is calculated from the difference between the target rotation speed value of the motor and the detected rotation speed value, and this calculated current value is used as a current command value. Is output to the inverter. For this reason, even if the current command value output to the inverter is constant, if the input voltage from the power supply unit to the inverter varies, the motor current varies.
[0005]
In order to solve this, hardware such as a constant voltage circuit may be added to the main control unit. However, this increases the size of the apparatus and increases the manufacturing cost.
[0006]
An object of the present invention is to provide a control type magnetic bearing device that solves the above-described problems, can suppress fluctuations in motor current due to fluctuations in input voltage from a power supply unit, and can reduce the size and cost of the apparatus. There is.
[0007]
[Means for Solving the Problems and Effects of the Invention]
A control type magnetic bearing device according to the present invention includes a plurality of sets of control type magnetic bearings that support a rotating body in a non-contact manner, an electric motor that rotates the rotating body, a magnetic bearing drive circuit that drives the magnetic bearing, and an electric motor that drives the motor. Control type magnetic bearing comprising: an inverter to be operated; a magnetic bearing drive circuit; a main control unit for controlling the inverter; and a power supply unit connected to an external power source to supply power to the magnetic bearing drive circuit, the inverter and the main control unit In the apparatus, the main control unit has a digital processing means capable of a software program, and the digital processing means controls the current command value output to the inverter in accordance with the input voltage value from the power supply unit. It is characterized by this.
[0008]
For example, an MPU (microprocessor), a digital signal processor or the like is used as the digital processing means capable of software programming. In this specification, a digital signal processor refers to dedicated hardware that can input a digital signal and output the digital signal, can be software-programmed, and can perform high-speed arithmetic processing. Hereinafter, this is abbreviated as DSP.
[0009]
Input voltage values from the power supply unit in the main control unit and the inverter are equal to each other. For this reason, the main control unit controls the inverter according to the input voltage value from the power supply unit, thereby controlling the inverter according to the input voltage value from the power supply unit to the inverter.
[0010]
The main control unit controls the inverter so that the motor current does not fluctuate even if the input voltage value from the power supply unit fluctuates.
[0011]
According to the control type magnetic bearing device of the present invention, the current command value output to the inverter is controlled according to the input voltage value from the power supply unit, so that even if the input voltage value from the power supply unit varies, As a result, fluctuations in the motor current can be suppressed. Therefore, fluctuations in the motor rotation speed due to fluctuations in the input voltage value can be suppressed. For example, when applied to a turbo molecular pump, the pumping performance of the pump can be kept constant. Moreover, the main control unit has digital processing means that can be programmed with software, and the inverter is controlled by this digital processing means, so it can be handled only by changing software, and hardware such as a constant voltage circuit is added. There is no need to do. For this reason, it is possible to reduce the size and cost of the apparatus.
[0013]
The main control unit, for example, calculates the current value to be supplied to the motor from the difference between the motor rotation speed target value and the rotation speed detection value, and even if the input voltage value from the power supply unit fluctuates, the motor current value is The current command value output to the inverter is controlled so as to be equal to the calculated value. That is, when the input voltage value decreases, the current command value is increased with respect to the current calculation value, and when the input voltage value increases, the current command value with respect to the current calculation value is decreased. For the same current calculation value, for example, the current command value is linearly decreased as the input voltage value increases.
[0014]
In this way, even if the input voltage value fluctuates, the motor current for the same current command value can be prevented from fluctuating.
[0015]
The control type magnetic bearing device according to the present invention also includes a plurality of sets of control type magnetic bearings that support the rotating body in a non-contact manner, an electric motor that rotates the rotating body, a magnetic bearing drive circuit that drives the magnetic bearing, and an electric motor. Control type comprising: an inverter for driving the motor; a magnetic bearing drive circuit and a main control unit for controlling the inverter; and a power supply unit connected to an external power supply to supply power to the magnetic bearing drive circuit, the inverter and the main control unit In the magnetic bearing device, the main control unit has digital processing means capable of software programming, and the digital processing means allows the upper limit value of the current command value to be output to the inverter in accordance with the voltage input value from the power supply unit. It is characterized by being changed.
[0016]
The main control unit changes the upper limit value of the current command value so that the motor current, that is, the maximum value of the motor current becomes the same when the upper limit value is output as the current command value even if the input voltage value fluctuates. That is, when the input voltage value decreases, the current command value upper limit value is increased, and when the input voltage value increases, the current command value upper limit value is decreased. For example, the current command value upper limit value is linearly decreased as the input voltage value increases.
[0017]
According to the control type magnetic bearing device of the present invention, even if the input voltage value fluctuates, the maximum value of the motor current can be made constant and the fluctuation of the maximum value of the motor current can be suppressed.
[0018]
For example, the main control unit calculates a current value supplied to the electric motor from the difference between the rotation speed target value and the rotation speed detection value of the electric motor, and sets the current calculation value from the control calculation unit to a predetermined upper limit value. There is provided a command value output unit that outputs a current command value by limiting to the following values, and an upper limit value changing unit that changes an upper limit value in the command value output unit in accordance with an input voltage value from the power supply unit.
[0019]
Also in this case, as described above, even if the input voltage value fluctuates, the maximum value of the motor current can be made constant and the fluctuation of the maximum value of the motor current can be suppressed.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to a turbo molecular pump will be described with reference to the drawings.
[0021]
FIG. 1 shows a schematic configuration of a turbo molecular pump.
[0022]
The turbo molecular pump includes a machine main body (1) constituting a pump main body and a controller (2) constituting a pump control unit as control means.
[0023]
The machine body (1) includes a rotating body (pump rotor) (3) constituting a pump, a displacement detector (4), a control type magnetic bearing (5), for example, a built-in type electric motor (6) which is an induction machine, and A rotation speed sensor (7) is provided as a rotation speed detection means.
[0024]
The controller (2) is provided with a displacement calculation circuit (8), a magnetic bearing drive circuit (9), an inverter (10), a DSP board (11) and a power supply unit (12). The DSP board (11) A main control unit (13), an AD converter (14), and a DA converter (15) are provided.
[0025]
Although not shown, the magnetic bearing (5) includes a set of control-type axial magnetic bearings that support the rotating body (3) in a non-contact manner in the axial direction of the rotating body (3) at one axial position of the rotating body (3). In addition, two sets of control type radial magnetic bearings that support the rotating body (3) in a non-contact manner in two radial control axis directions orthogonal to each other at two locations in the axial direction of the rotating body (3) are included. The axial magnetic bearing includes a pair of electromagnets (axial electromagnets) arranged so as to sandwich the rotating body (3) from both sides in the axial control axis direction. Each radial magnetic bearing includes a pair of electromagnets (radial electromagnets) arranged so as to sandwich the rotating body (3) from both sides in the radial control axis direction for each radial control shaft.
[0026]
Although not shown, the displacement detection unit (4) includes an axial displacement detection unit and a radial displacement detection unit. The axial displacement detection unit includes one axial displacement sensor that detects the displacement of the rotating body (3) in the axial control axis direction. The radial displacement detector includes a pair of radial displacement sensors arranged to sandwich the rotating body (3) from both sides in the radial control axis direction for each radial control shaft in each radial magnetic bearing portion. The displacement calculation circuit (8) calculates the displacement in the axial control axis direction of the rotating body (3) from the output of the axial displacement sensor for the axial control axis, and outputs the output of a pair of radial displacement sensors for each radial control axis. The displacement of the rotating body (3) in the radial control axis direction is calculated based on the above, and displacement signals corresponding to these displacement calculation values are output to the main control unit (13) via the AD converter (14). The displacement detector (4) and the displacement calculation circuit (8) constitute a displacement detector that detects the displacement of the rotating body (3).
[0027]
The main control unit (13) is a DSP which is a digital processing means capable of a software program, and controls the magnetic bearing drive circuit (9), the inverter (10) and the like as will be described later.
[0028]
The power supply unit (12) is connected to a 200V commercial power supply (16), which is an external power supply, and rectifies and smoothes the alternating current from the power supply (16) to convert the direct-current power into a magnetic bearing drive circuit (9) and an inverter (10). To the main control unit (13).
[0029]
The main control unit (13) calculates the excitation current value for each electromagnet of the magnetic bearing (5) based on the displacement signal input from the AD converter (14), and outputs the corresponding excitation current signal to the DA converter. Output to the magnetic bearing drive circuit (9) via (15).
[0030]
The magnetic bearing drive circuit (9) includes a plurality of power amplifiers corresponding to the electromagnets of the magnetic bearing (5), and generates an excitation current proportional to the excitation current signal output from the DA converter (15). Supply to the corresponding electromagnet of 5). Thereby, the rotating body (3) is supported in a non-contact manner at a predetermined target position.
[0031]
The motor (6) rotationally drives the rotating body (3) supported in a non-contact manner by the magnetic bearing (5). The rotational speed sensor (7) is for detecting the rotational speed of the rotating body (3). For example, a constant number (for example, one) of pulse signals per rotation of the rotating body (3) is supplied to the main controller. Output to (13). As will be described in detail later, the main control unit (13) calculates the rotational speed of the rotating body (3) from the pulse signal of the rotational speed sensor (7), and based on this, the rotational speed of the motor (6) is calculated. A current command signal for control is output to the inverter (10). The inverter (10) controls the rotational speed of the motor (6) based on the current command signal from the main controller (13), for example, by the PWM method. Thereby, in the steady operation state, the rotation speed of the rotating body (3) is kept substantially constant.
[0032]
The main control unit (13) also samples the input voltage value from the power supply unit (12) at regular intervals (for example, 5 seconds) and outputs a current command to the inverter (10) according to the input voltage value. Control the value.
[0033]
FIG. 2 is a functional block diagram showing an example of the function of the motor control unit (motor rotational speed control part) of the main control unit (13). Next, an example of the rotational speed control of the motor (6) by the motor control unit will be described with reference to this figure.
[0034]
The motor control unit performs PI control of the rotation speed of the motor (6), and includes a PI control calculation unit (30) having a proportional operation unit (17) and an integration operation unit (18).
[0035]
In FIG. 2, D1 is a rotation speed target value set in the motor control unit, and D2 is a rotation speed detection value of the motor (6) detected by the rotation speed sensor (7).
[0036]
In the motor control unit, first, in the target value limiting unit (31), the rotation speed target value is compared with the settable maximum rotation speed D3max and the settable minimum rotation speed D3min, and a value D4 in which D1 is limited between D3max and D3min. Is input to the subtraction unit (19) as the target rotational speed value. In the subtracting section (19), a difference D5 between the rotational speed target value D4 and the rotational speed detected value D2 is calculated and input to the proportional operation section (17) and the integral operation section (18). The proportional operation unit (17) outputs a proportional output value D6 proportional to the difference D5 and inputs it to the addition unit (20). In the integral operation unit (18), an integral output value D7 proportional to the integral value of the difference D5 is output. The integral output value D7 is compared with the maximum allowable integral output value D8max and the minimum allowable integral output value D8min in the integral output limiter (32). Input to the adder (20). The allowable maximum integrated output value D8max is a positive value, and the allowable minimum integrated output value D8min is a negative value. Usually, the absolute values of both are equal to each other. In the adder (20), the sum D10 of the proportional output value D6 and the integral output value D9 is calculated. This D10 is a current calculation value and is output from the calculation unit (30).
[0037]
In the case of acceleration, in the current value limiting unit (34) of the first command value output unit (33), the current calculation value D10 is the upper limit allowable maximum current value D11max and the acceleration allowable minimum current value D11min. A value D12 obtained by limiting D10 between D11max and D11min is input to the adder (21). This D12 is a current command value at the time of acceleration. In the adding unit (21), D12 and the constant value D13 are added, and the added value D14 is output from the command value output unit (33) to the inverter (10) as a current command signal.
[0038]
In the case of deceleration, in the current value limiting unit (36) of the second command value output unit (35), D10 is compared with the allowable maximum current value D11max and the allowable minimum current value D15min during deceleration, which is the lower limit value. a value D16 obtained by limited between D15min is input to the summing unit (22). This D16 is a current command value at the time of deceleration. In the adding section (22), D16 and the constant value D13 are added, and the added value D17 is output from the command value output section (35) to the inverter (10) as a current command signal.
[0039]
On the other hand, the input voltage value D18 from the power supply unit (12) is input to the integrating unit (23) of the upper limit value changing unit (37). In the integrating unit (23), a product D20 of D18 and a constant value D19 is calculated, and this product D20 is input to the subtracting unit (24). In the subtracting section (24), a difference D22 between D20 and a constant value D21 is calculated and input to the integrating section (25). In the integrating unit (25), the product of D22 and a constant value D23 is calculated. This integrated value is the allowable maximum current value D11max, and is output from the upper limit value changing unit (37) to the current value limiting units (34) and (36).
[0040]
The upper limit value D11max calculated by the upper limit value changing unit (37) as described above is expressed by the following equation (1).
[0041]
D11max = D23 × (D21−D19 × D18) (1)
Since D23, D21 and D19 are constant values, when these are a, b and c, respectively, the above equation (1) becomes the following equation (2).
[0042]
D11max = a * (bc-D18) (2)
This equation (2) indicates that the upper limit value D11 decreases linearly as the input voltage value D18 increases.
[0043]
When the upper limit value is output as the current command value to the inverter (10), the motor current becomes maximum. The above constants a, b and c are determined so that the motor current, that is, the maximum value of the motor current is the same when the upper limit value D11max is output as the current command values D12 and D16 even if the input voltage value D18 varies. It is done. By doing so, even if the input voltage value fluctuates, the maximum value of the motor current can be made constant and the fluctuation of the maximum value of the motor current can be suppressed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a control type magnetic bearing device showing an embodiment in which the present invention is applied to a turbo molecular pump.
FIG. 2 is a functional block diagram showing an example of motor rotation speed control processing in the main control unit.
[Explanation of symbols]
(3) Rotating body
(5) Magnetic bearing
(6) Electric motor
(7) Rotational speed sensor
(9) Magnetic bearing drive circuit
(10) Inverter
(12) Power supply
(13) Main control unit
(16) Commercial power supply
(30) Control calculation part
(33) (35) Command value output section
(37) Upper limit change section

Claims (3)

Multiple sets of control-type magnetic bearings that support a rotating body in a non-contact manner, an electric motor that rotates the rotating body, a magnetic bearing drive circuit that drives the magnetic bearing, an inverter that drives the electric motor, a magnetic bearing drive circuit, and an inverter In a control type magnetic bearing device comprising: a main control unit that controls the power supply; and a power supply unit that is connected to an external power source and supplies power to the magnetic bearing drive circuit, the inverter, and the main control unit.
The main control unit has digital processing means capable of a software program, and the digital processing means controls the current command value output to the inverter in accordance with the input voltage value from the power supply unit. Control type magnetic bearing device. Multiple sets of control-type magnetic bearings that support a rotating body in a non-contact manner, an electric motor that rotates the rotating body, a magnetic bearing drive circuit that drives the magnetic bearing, an inverter that drives the electric motor, a magnetic bearing drive circuit, and an inverter In a control type magnetic bearing device comprising: a main control unit that controls the power supply; and a power supply unit that is connected to an external power source and supplies power to the magnetic bearing drive circuit, the inverter, and the main control unit.
The main control unit has a digital processing means capable software program, by the digital processing means in accordance with the voltage value input from the power supply unit, and changes the upper limit value of the current command value output to the inverter to that control type magnetic bearing device characterized in that. The main control unit calculates a current value to be supplied to the electric motor from the difference between the rotation speed target value and the rotation speed detection value of the electric motor, and sets the current calculation value from the control calculation unit to a predetermined upper limit value or less. A command value output unit that outputs a current command value by limiting to a value, and an upper limit value changing unit that changes an upper limit value in the command value output unit according to an input voltage value from a power supply unit, The control type magnetic bearing device according to claim 2 .

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