JPH01150015A - Magnetic bearing controller - Google Patents

Abstract

PURPOSE:To prevent divergent vibration so as to aim at stabilization of a high speed rotation by providing, in a feedback system a notch filter having a function which decreases or increases a central frequency proportionally to the number of rotation under measurement. CONSTITUTION:The signal of a position sensor 3 for measuring the displacement of a rotary body is adjusted in a position feedback gain 4 to a signal having the required dimension, introduced into notch filters 7B, 7F having a property in which a gain falls at a specific central frequency so as to cut the component of proper frequency having unstabilizing force. This signal is reformed in a shape adequate to an electromagnet 6 for generating magnetic force for floating the rotary body, in a control circuit 5. Meantime, the signal of a rotation speed meter 8 is input to a subtracter 11, and an adder 12 together with a preset value 10 via gains 9B, 9F and is input to the notch filter 7B, 7F. Accordingly, divergent frequency is prevented so that stable high speed rotation can be maintained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a magnetic bearing control device applied to active magnetic bearings used in turbomolecular pumps, oil-free compressors, turbines, spindles for machine tools, etc. Regarding.

[Conventional technology]

A magnetic bearing using an electromagnet is used as a means for keeping a rotating body floating. This magnetic bearing has less loss than conventional fluid-lubricated bearings, allows for a dryer bearing, and a cleaner atmosphere, making it particularly useful in vacuum conditions.

A pair of magnetic bearings that function as journal bearings. As a means for setting the floating position of the rotating body 1 using the magnetic bearings 2a and 2b, the floating position of the rotating body 1 is measured, and the magnetic bearing 2a is set based on the measurement signal.

There is a means for determining the current value to be passed through the electromagnet (not shown) provided in the electromagnet 2b and determining the magnitude of the magnetic force generated from the electromagnet.

FIG. 5 is a block diagram of a control system showing this means.

In the figure, 3 is a position sensor, 4 is a feedback gain of 1
．． 5 is a control circuit, and 6 is an electromagnet.

Considering the simplest position feedback system in which the control circuit 5 is composed of only proportional elements (P elements), the transfer function between the input current I of the electromagnet 6 and the magnetic force F which is the output is the coil,
Due to the resistance and inductance of the iron core, etc., the system becomes a first-order lag system as shown below.

F/I -Km/ (1+Tm-3) ・= (1
) Here, Km is the gain of the electromagnet 6, Tm is the time constant of the electromagnet 6, and S is the Laplace operator. Therefore, the transfer function from the measured displacement of the position feedback system to the force F to the rotating body 1, which is a floating object, is as follows.

F/D-K f IIKp ・Km / (1+Tm-8) ... (2) Here,
Kf is position feedback gain 4, Kp is control circuit 5
shows the proportional gain of , respectively.

In order to see the frequency characteristics of (force F)/(displacement D) of the position feedback system, we set the Laplace operator 5-j2πf,
(2) Substitute into equation. Here, f is the frequency [Hz], and is ]j--r-. (Force F)/(Displacement D) is a complex number and is written as follows.

F/D-Kr (f) +j-Ki (f) ... (3) (3
) In the equation, the real part of (force F)/(displacement D) means stiffness that depends on frequency f, and the imaginary part means damping that depends on frequency f. The imaginary part of the first-order lag as in equation (2) is always negative, and it becomes a destabilizing force on the floating object that is opposite to damping.

FIG. 6 is a diagram showing the relationship between (force F)/(displacement D), that is, the value of the imaginary part of equation (3), and frequency f.

The broken line A shown in FIG. 6 corresponds to equation (2),
The above state is shown. Damping of the natural frequency fc consisting of the rotating body 1 and the position feedback system, especially the rotating body 1
If the frequency fmfc shown in FIG. 6 is larger than the attenuation of , the natural frequency will oscillate divergently, making it impossible to operate.

Therefore, in order to provide a damping effect to (force F)/(displacement D) of the position feedback system, a differential element (D element) or a phase compensation element is provided in the control circuit 5 in parallel with the proportional element (P element). Here, we will take the differential element as a representative example. When the differential element is realized as a circuit in the control circuit 5, it becomes 1 as follows.
This is a form in which a second-order delay system is added.

(Differential element) -Kcl -S/ (1+Td -S)・
...(4) where Kd is the gain of the differential element and Td is the time constant. (Force F)/( of the position feedback system with only differential elements
The displacement D) is expressed by the following formula.

F/D-K f ΦKd -Km @S/ l(1+T
d-S)(1+Tm-5)1...(5) Since the numerator of equation (5) is the first order of S and the denominator is the second order of S, the imaginary part of equation (5) is shown in Figure 6. It will look like the dashed line B shown in . That is, it has a damping effect on the rotating body 1 in a low frequency range, and a destabilizing effect in a high frequency range. In order to maintain the position of the rotating body 1, the control circuit 5 needs to have both a proportional element and a differential element. The (force F)/(displacement D) of the position feedback system of the control circuit 5 is expressed as F/
D-Kf Working (Kp+Kd-S/ (1+Td-S))-K
m/(1+Tm-8)-(6),
It becomes like the solid line C shown in FIG. 6, and has the same characteristics as described above. By placing the natural frequency fc of the rotating body 1 and the position feedback system in a low frequency range that has a damping effect, stability can be ensured and operation can be performed without generating vibrations.

A magnetic bearing having such characteristics is used as the bearing 2a of the rotating body 1.
, 2b, and when the rotating body 1 is levitated, the result shown in Fig. 7 (
A) (b) The following phenomena occur.

The rotating body 1 shown in FIG. 7(a) is shown in FIGS. 7(b), (c) (
d) It has a natural frequency on the infinite side as shown in (e) (f) ~. (b) CC) in Fig. 7 is the natural frequency at which the rotating body 1 exhibits a rigid mode with almost no bending;
)(f) ~ is the natural frequency at which the rotating body 1 exhibits an elastic mode of bending.

The higher the order of the natural frequency, the more the rotating body 1 exhibits a mode of bending. Furthermore, the damping caused by the material of the rotating body 1 itself acts as a destabilizing effect for natural frequencies below the rotational speed, and acts as a damping effect for natural frequencies above the rotational speed.

Therefore, it is necessary that the position feedback system of the magnetic bearings 2a, 2b has a natural frequency lower than the rotational speed in a frequency range that has a damping effect of (force F)/(displacement D). However, the natural frequency of the rotating body 1 is
) (e) (f) Since there are infinite numbers as shown in ~, there is always a natural frequency in the frequency region that has the destabilizing effect of (force F)/(displacement D). Therefore, if the destabilizing effect of the position feedback system of the magnetic bearings 2a and 2b is greater than the damping of the natural frequency of the rotating body 1 itself, the instability will occur, the vibration will increase divergently, and it will be difficult to rotate the body. become unable.

Therefore, a notch filter having characteristics as shown in FIG. 2 whose center frequency is matched to the frequency that causes divergent vibration is usually provided between the position feedback gain 4 and the control circuit 5.

[Problem that the invention seeks to solve]

The notch filter shown in FIG. 2 is one in which the gain is reduced only in a certain frequency range, and the destabilizing force corresponding to the divergent frequency is not fed back. However, in an actual rotating body, the natural frequency at rest is divided into two due to the gyroscopic effect, as shown in FIG. One of these has the property that it increases with the number of rotations, and the other decreases with the number of rotations. Therefore, when the natural frequency reaches a certain rotational speed, the gain of the notch filter falls outside the narrow range, causing divergent vibrations again, and the rotation cannot be increased.

In this way, in order to maintain the position of the rotating body, conventional devices measure the position of the rotating body, feed back the signal, and generate force using an electromagnet.
This force becomes a destabilizing force that causes the rotating body to vibrate. And PID in the control circuit.

Even if processing such as phase compensation is performed, it still has a large destabilizing power in the low frequency region. Therefore, in a rotating body having an infinite number of natural frequencies, the natural frequency always exists in a region where a destabilizing force occurs, and the magnetic bearing generates divergent vibrations. Furthermore, in a rotating body, the rotational speed changes due to the gyroscopic effect, and with the notch filter known as a conventional countermeasure, the above-mentioned vibration occurs again when the rotation becomes high speed, making it impossible to rotate stably.

Therefore, the present invention has the ability to follow changes in the natural frequency due to the gyroscopic effect, reduces the destabilizing force in the medium and high frequency range generated by magnetic bearings, prevents divergent vibrations, and maintains stable An object of the present invention is to provide a magnetic bearing control device that can maintain high-speed rotation.

[Means for solving problems]

In order to solve the above-mentioned problems and achieve the object, the present invention takes the following measures. In other words, signals such as position information from the rotating body are fed back, and PID (proportional, integral,
In a device that controls actively used magnetic bearings, it is configured to perform control such as differentiation) and phase compensation, and has the function of decreasing or increasing the center frequency in proportion to the rotational speed being measured. A notch filter was installed in the feedback system.

[Effect]

By taking such measures, the following effects are achieved. In other words, a notch filter that can change the center frequency depending on the rotational speed is installed in the feedback system, which reduces the destabilizing force of the magnetic bearing by responding to changes in the natural frequency caused by the gyroscopic effect not only when it is not rotating, but also when it is rotating. Therefore, divergent vibrations can be prevented even during high-speed rotation, and stable high-speed rotation can be obtained.

〔Example〕

FIG. 1 is a block diagram showing the configuration of a magnetic bearing control device that is an embodiment of the present invention. The position sensor 3 is a sensor for measuring the position (displacement) of the rotating body 1, which is a floating object,
An example is an eddy current displacement meter. The position feedback gain 4 is for proportionally multiplying the magnitude of the signal obtained by the position sensor 3 to a required magnitude. Notch filter 7, . 7. has a gain-frequency characteristic in which the gain decreases at the center frequency fc as shown in Figure 2, and cuts off the natural frequency component that has the potential to destabilize the signal input from the position feedback gain 4. do. Note that the center frequency fc is adapted to match the input from the subtracter 11 or the adder 12. The control circuit 5 includes a signal processing circuit for inputting the signal obtained by the position feedback gain 4 to the electromagnet 6 in an appropriate form. Examples of this signal processing circuit include a PID (proportional-integral-integral) circuit, a phase compensation circuit, and a combination thereof. The electromagnet 6 has a coil wound around an iron core, and generates magnetic force for levitating the rotating body in response to a current manually input from the control circuit 5.

The rotational speed meter 8 measures the rotational speed of the rotating body 1 and provides it to a gain 9B and a gain 9F. Gain 9B and Gain 9F
, proportionally multiplies the signal from the revolution counter 8 and supplies it to a subtracter 11 and an adder 12. The set value 10 always outputs a certain numerical value to the subtracter 11 and the adder 12. The subtracter 11 subtracts the human power from the gain 98, and the set value is 10.
The input from the two is used as an addition value, and the two are subtracted, and the result is output to the notch filter 7B. The notch filter 7B matches the center frequency fc with the manual value from the subtracter 11. The adder 12 adds the input from the gain 9F and the human power from the set value 10, and outputs the result to the notch filter 7F. The notch filter 7F makes the center frequency fc match the input value from the adder 12.

Next, the operation of the apparatus having the above configuration will be explained. In FIG. 8, the third natural frequency f3 when not rotating is the magnetic bearing 2a, 2
It is about to be destabilized by b.

The notch filter 7F corresponds to the natural frequency f3F, which increases with rotation due to the gyroscopic effect, and the notch filter 7B corresponds to the natural frequency f3B, which decreases.

Due to the rotation speed due to this gyro effect, changes in the natural frequency can be predicted by calculation and are approximately constant.

Set the slope as follows.

d f3 F / d N-α, d f3 B
/dN--β...(7) Here, the output of the set value 10 is f3, the gain 9B is β,
Set the gain 9F to α. When the motor is not rotating, the output of the revolution counter 8 is "0". Therefore, f3 is input to both the notch filter 7B and the notch filter 7F, and the center frequency fc of the notch filter 7B and notch filter 7F becomes f3. In this manner, during non-rotation, the signal from the position feedback gain 4 has the destabilizing component, the natural frequency f3, cut off, and is stable without divergent vibrations.

As the rotation increases, an output from the rotation counter 8 is generated. If the output of this rotational speed counter 8 is, for example, N, the input of the notch filter 7B is f3-βN1.
The input of F becomes f3+αN, and the notch filters 7s, 7
The center frequencies fc of p are f3-βN and f3+α, respectively.
N, and the signal from position feedback gain 4 is f
The natural frequencies of 3-βN and f3+αN are each cut. The center frequency of the notch filter at this time f3-β
N, f3+αN is the natural frequency f3 which is the destabilizing component
B, almost coincides with f3F.

Therefore, it can be considered that the natural frequency f3B+f3F has been cut.

FIG. 3 is a diagram showing the damping characteristics of the magnetic bearing at this time. As shown in the figure, the natural frequencies f3B and f, which are destabilizing forces,
The destabilizing power of 3F is reduced.

In this way, according to this embodiment, the destabilizing force of the magnetic bearing is reduced not only during non-rotation but also in response to natural frequency changes due to the gyro effect during rotation, and divergent vibrations are suppressed even during high-speed rotation. can be prevented and stable high-speed rotation can be obtained.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, attention was paid to the third natural frequency f3, but the same applies to the fourth natural frequency f4+the fifth natural frequency f5.

In addition, when dealing with a plurality of natural frequencies, the number of sets of notch filters corresponding to the number of notch filters and associated circuits should be provided somewhere between the position feedback gain 4 and the control circuit 5. Good.

〔Effect of the invention〕

According to the present invention, signals such as position information from a rotating body are fed back to control PID (proportional, integral, differential), phase compensation, etc., and the magnetic bearing is actively used. In the device, its center frequency is
Since the feedback system is equipped with a notch filter that has the function of decreasing or increasing the rotational speed in proportion to the rotational speed being measured, a magnetic bearing is generated so that it can follow changes in the natural frequency due to the gyroscopic effect. It is possible to provide a magnetic bearing control device that can reduce the destabilizing force in the medium and high frequency range, prevent divergent vibrations, and maintain stable high-speed rotation.

[Brief explanation of the drawing]

Figures 1 to 3 are diagrams showing one embodiment of the present invention. Figure 1 is a block diagram showing the configuration, Figure 2 is a diagram showing the characteristics of the notch filter, and Figure 3 is a diagram showing the characteristics of the notch filter. It is a figure showing the attenuation characteristic of. FIGS. 4 to 8 are diagrams showing conventional examples,
Fig. 4 is a diagram showing the basic configuration, Fig. 5 is a block diagram showing the configuration of the control system, Fig. 6 is a diagram showing the damping characteristics of the magnetic bearing,
FIGS. 7(a) to 7(f) are diagrams showing the rotating body and the natural frequency, and FIG. 8 is a diagram showing the relationship between the rotation speed and the natural frequency of the rotating body. 1...Rotating body, 2a, 2b...Magnetic bearing, 3...
Position sensor, 4...Position feedback gain, 5.
... Control circuit, 6... Electromagnet, 7s, 7p... Notch filter, 8... Revolution meter, 9s l 9p...
Gain, 10...Set value, 11...Subtractor, 12.
...Adder. Applicant's agent Patent attorney Takehiko Suzue (frequency) Figure 2 + Figure 5 Figure 7 Figure 8

Claims (1)

[Claims] Feedback signals such as position information from the rotating body,
In devices that control actively used magnetic bearings that are configured to perform ID (proportional, integral, differential) control, phase compensation, etc., the center frequency decreases in proportion to the rotational speed being measured. A magnetic bearing control device characterized in that a notch filter having a function of increasing the notch is provided in the feedback system.