JPH05306715A - Control method for magnetic bearing - Google Patents

Abstract

PURPOSE:To prevent the stable state from being deteriorated by the displacement of a rotor by installing a dynamic compensator for compensating the time constant of a magnet which varies according to the floated position of the rotor, on the basis of the signal of a displacement sensor for detecting the floating-up position of the rotor, between a controller and an electric power compensator. CONSTITUTION:A control system for a magnetic bearing is constituted of a displacement sensor which is constituted of a sensor head 6 fixed in the vicinity of an electromagnet 3 and a diaplacement converter 10, comparator 11, controller 9, compensation instruction devices 12 and 13 each of which generates a time constant compensation instruction according to the displacement signal of a rotor, dynamic compensators 14 and 15, and electric current amplifiers 7 and 8. Even if each floating-up position of the electromagnet 3 and the rotor 1 changes and the time constsnt of the electromagnet 3 varies, the compensation instruction devices 12 and 13 operate according to the floating-up position of the rotor 1, and the dynamic compensators 14 and 15 are given with each instruction, and the time constant is varied, and the transmission characteristic of the whole of the dynamic compensators 14 and 15, electric current amplifiers 14 and 15, and electromagnets 2 and 3 is kept constant. Accordingly, even if the local characteristic of the electromagnet 3 part changes drastically, the whole characteristic can be kept constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a suction control type magnetic bearing for non-contact bearing.

[0002]

2. Description of the Related Art A conventional suction control type magnetic bearing will be described with reference to FIG. In the figure, reference numeral 1 is a rotor which is supported by a magnetic attraction force in a non-contact manner to be rotatable, and is opposed to the rotor via a constant gap, and two electromagnets 2 and 3 are fixed to a fixing portion (not shown). Coils 4,
5 is wound, and currents are supplied by current amplifiers 7 and 8, respectively. On the other hand, the sensor head 6 fixed near the electromagnet and the displacement converter 10 constitute a displacement sensor to detect the displacement of the rotor 1 with respect to the electromagnets 2 and 3. The comparator 11 compares the command value X ₃ designating the displacement of the rotor 1 with the signal X _{f of the} displacement sensor, and the controller 9 receives this and gives a command to the current amplifiers 7, 8. In such a configuration, when the rotor 1 is positioned below the position designated by the command value X _s , the displacement signal of the rotor 1 detected by the displacement sensor including the sensor head 6 and the displacement converter 10 is received, The comparator 11 and the controller 9 work to give a large command to the current amplifier 7 to increase the current of the coil 4 to increase the magnetic attraction between the electromagnet 2 and the rotor 1 and to give a small command to the current amplifier 8. It is applied to reduce the current of the coil 5 to reduce the magnetic attraction force between the electromagnet 3 and the rotor 1 to pull up the rotor 1. On the other hand, when the rotor 1 is located above the position designated by the command value X _s , the comparator 11 and the controller 9 operate in response to the displacement signal of the rotor 1 detected by the displacement sensor, and the current amplifier 8 operates. A large command is given to increase the current of the coil 5, the magnetic attraction between the electromagnet 3 and the rotor 1 is increased, and a small command is given to the current amplifier 7 to reduce the current of the coil 4 to reduce the current of the electromagnet 2 and the rotor 1. It acts to reduce the magnetic attraction force between the rotors 1 and lower the rotor 1. The same structure as described above is also provided in the horizontal direction in the drawing to form one radial bearing, and supports the rotor 1 in a non-contact manner.

[0003]

However, such a conventional method has a problem in stabilizing the control system because the attraction force F of the electromagnet has a remarkable nonlinear characteristic with respect to the command. .. Among the non-linear characteristics, the static non-linearity of F∝ (I / X) ² generated between the attractive force F, the gap X, and the current I is determined by the method disclosed in Japanese Patent Publication No. 12970/1989. Linearization compensation is done and the problem is solved. However, on the other hand, among the non-linear characteristics, the inductance L of the electromagnet portion changes according to the gap, so that the response of the current to the command of the current amplifier is different when the rotor is in the central portion and when it is displaced. Therefore, even if the control parameters are adjusted so that the control characteristics are best when the rotor 1 is in the center, the deviation of the rotor causes one of the electromagnets to have a smaller time constant and a better current rise. However, the other electromagnet has a large time constant and the rise of the current is deteriorated, so that the characteristics of the entire control system are changed and the initial stability is impaired.

[0004]

In order to solve the above problems, the present invention provides a dynamic compensator consisting of an approximate differentiator whose time constant changes according to the floating position of the rotor in front of the current amplifiers 7 and 8. It was.

[0005]

With this configuration, even if the flying positions of the electromagnet and the rotor change and the time constant of the electromagnet changes,
The compensation commander operates according to the floating position of the rotor to give a command to the dynamic compensator to change its time constant, so that the transfer characteristics of the dynamic compensator, the current amplifier and the electromagnet are constant. Therefore, even if the local characteristics of the electromagnet portion change significantly, the overall characteristics can be kept constant, so that instability due to rotor deviation can be prevented and the initial stability can be maintained. You can do it.

[0006]

EXAMPLES Specific examples of the present invention will be described below with reference to FIGS. FIG. 1 is a configuration diagram of a specific embodiment of the present invention, FIG. 2 is an explanatory diagram of elements used in the embodiment, and FIG. 3 is a diagram explaining an operation. In this case, the compensation of the static non-linearity of the magnet is treated as included in the controller 9. In FIG. 1, only the points different from FIG. 4 will be described. Dynamic compensators 14 and 15 are provided between the controller 9 and the current amplifiers 7 and 8, and time constant compensation commands are given from the compensation command devices 12 and 13, respectively. The difference is. The compensation command device generates a time constant compensation command in accordance with the rotor deviation signal. FIG. 2 shows an embodiment of the compensation commander 12 (or 13) and the dynamic compensator 14 (or 15). The compensation commander 12 (or 13) includes three adders / subtractors and one divider. It consists of Here undergo deflection signal X _f of the rotor when the constant X ₀ and an addition (or subtraction) is sought air gap x between the magnets and the rotor are then added to the x _00, it is divided then k ₁ and , And k ₂ is further subtracted to obtain the time constant compensation command k ₃ . Dynamic compensator 14 (or 15)
Consists of three resistors, one capacitor, one operational amplifier and one multiplier, and constitutes a proportional plus approximate differentiator. Since the signal obtained by multiplying the input signal I _s1 and the time constant compensation command k ₃ by the multiplier is given to the capacitor, the transfer characteristic of the dynamic compensator 14 (or 15) is as follows.

[Equation 1] Here, the sign of G ₁₄ (or G ₁₅ ) is inverted and a negative sign is added, but for ease of explanation, it is omitted because an inverter is added to the controller 9. In addition, the compensation command device 12
The transfer characteristic of (or 13) is as follows.

[Equation 2]

[Equation 3] Is. Now, the transfer characteristics of the electromagnet and the current amplifier as a whole are expressed as follows. First, the inductance L of the electromagnet is

[Equation 4] Is expressed as Next, the current I is I = I ₀ sin2πft
And its maximum slope | dI / dt |
= 2πfI ₀ is set equal to E / L. E / L is the rate of increase in current when the voltage E is applied to the coil ignoring resistance. That is, if the frequency at which the sinusoidal current is not distorted is f and the time constant for this is defined as T = 1 / 2πf, the following equation is obtained.

[Equation 5] Therefore, when the frequency characteristics of the current amplifiers 7 and 8 are negligible as compared with the magnet, the transfer characteristics of the electromagnet and the current amplifier are as follows.

[Equation 6] Here, K _i is the amplification ratio of the current amplifier, and Is is the current command. As can be seen from the equations (4) and (5), the dynamic characteristics of the current amplifier and the electromagnet as a whole change depending on the floating position of the rotor. A dynamic compensator 14 (or 15) and a compensation commander 12 (or 13) are used as shown in FIG.
If Is, then the overall transfer characteristic I / Is including these
Is from equations (1) to (5)

[Equation 7] Therefore, it becomes constant regardless of the deviation of the rotor.
The above is again shown in the frequency vs. gain diagram for the electromagnet 2 as follows. Since X = −X ₀ in the state where the rotor 1 is displaced to the upper side and contacts the electromagnet 2, (4)
From the formula, the time constant of the magnet is

[Equation 8] And the dynamic characteristics are as shown by the broken line in FIG. At this time, the dynamic compensator characteristic G ₁₄ is calculated from the equations (1) and (2).

[Equation 9] And becomes like the broken line in FIG. Therefore, the dynamic characteristics of the dynamic compensator 14, the current amplifier 7, and the electromagnet 2 are as shown in FIG. Next, the rotor 1 is displaced downward,
Since X = + X _o when in contact with the electromagnet 3, the time constant of the magnet is calculated from the equation (4).

[Equation 10] And the dynamic characteristics are as shown by the solid line in FIG. At this time, the dynamic compensator characteristic G ₁₄ is calculated from the equations (1) and (2).

[Equation 11] And becomes like the solid line in FIG. Therefore, the dynamic characteristics of the dynamic compensator 14, the current amplifier 7, and the electromagnet 2 are as shown in FIG. Although it has been shown above that the dynamic characteristics of the entire magnet 2 are constant, it goes without saying that the same holds true for the magnet 3 as well. Although FIG. 3 shows the case where T ₂ <T ₁ <t, t <T2 <T
Even in the case of 1, as a result, the overall dynamic characteristics can be made constant. Although the compensation commander and the dynamic compensator using the analog arithmetic element have been shown as examples above, a digital circuit is used to obtain the same function, and
It goes without saying that it can be realized by using a computer.

[0007]

As described above, according to the present invention, even if the rotor is deviated to change the dynamic characteristics of the current amplifier and the electromagnet as a whole, the compensation commander and the dynamic compensator apparently cause the overall movement of the rotor. The characteristics can be kept constant. For this reason, what was originally intended to stabilize the entire control system can be maintained in a stable state without being damaged by the deviation of the rotor, and there is an effect of improving the quality and performance of the magnetic bearing.

[0008]

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram of an embodiment of a compensation commander and a dynamic compensator.

FIG. 3 is a dynamic characteristic diagram of the example.

FIG. 4 is a block diagram of a conventional magnetic bearing control device.

[Explanation of symbols]

 1 Rotor 2,3 Electromagnet 4,5 Coil 6 Sensor head 7,8 Current amplifier 9 Controller 10 Displacement converter 11 Comparator 12,13 Compensation commander 14,15 Dynamic compensator

Claims (3)

[Claims] 1. A rotor, an electromagnet having a coil wound around an outer periphery of the rotor and wound with a coil, a current amplifier for supplying a current to the electromagnet, and a controller for giving a command to the current amplifier. In a magnetic bearing comprising a displacement sensor for detecting the floating position of the rotor and giving a detection signal to the controller, a dynamic bearing for compensating for a time constant of a magnet which changes corresponding to the floating position of the rotor based on the signal of the displacement sensor. A method of controlling a magnetic bearing, characterized in that a dynamic compensator is provided between the controller and the power amplifier. 2. The method of controlling a magnetic bearing according to claim 1, wherein the dynamic transfer compensator, the current amplifier, and the electromagnet are compensated so that the transfer characteristics thereof are substantially constant regardless of the floating position of the rotor. 3. The compensating command of the dynamic compensator is obtained by the compensating command device based on the displacement signal of the rotor.
A method for controlling a magnetic bearing as described.