JPH0988955A - Controller of magnetic bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent control from being unstabilized by a variation in voids between a rotator and an electromagnet as well as to make it so as not to cause an increase in cost. SOLUTION: A magnetic bearing 2a is equipped with four electromagnets 5a, 6a, 7a and 8a supporting a rotator 1 in a noncontact manner owing to magnetic force. A controller 4a of this magnetic bearing 2a is equipped with two pairs of position sensors 11a, 12a, 13a and 14a being set up so as to hold the rotator 1 between and outputting each void signal in proportion to size in a void with the rotator 1, and an electromagnet control circuit 9a controlling a supply current to respective electromagnets 5a to 8a on the basis of each void signal out of these position sensors 11a to 14a, respectively. The electromagnet control circuit 9a addeds respective void signals to the paired position sensors 11a and 12a, and this void signal added value is compared with the specified void value, and on the basis of this compared result, each supply current to the respective electromagnets 5a to 8a is compensated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic bearing control device, and more particularly to a magnetic bearing control device provided with a plurality of electromagnets that support a rotating body in a non-contact manner by magnetic force.

[0002]

2. Description of the Related Art Magnetic bearings of this type include a radial magnetic bearing that supports a rotating body in the radial direction and an axial magnetic bearing that supports the rotating body in the axial direction.

The radial magnetic bearing has a pair of first electromagnets arranged so as to sandwich the rotating body from both sides in the first radial direction, and a rotating body sandwiched from both sides in a second radial direction orthogonal to the pair of first electromagnets. And a pair of second electromagnets disposed in the first and second electromagnets, and the controller controls the first and second radial positions of the rotor to a predetermined neutral position. The axial magnetic bearing is provided with a pair of electromagnets arranged so as to sandwich the flange formed on the rotating body from both sides in the axial direction, and the controller controls the axial position of the rotating body to a predetermined position. Controlled to neutral position. The rotating body thus supported by the radial magnetic bearing and the axial magnetic bearing is rotated at a high speed by a high frequency motor or the like.

The control device for the radial magnetic bearing is arranged so as to sandwich the rotating body from both sides in the first radial direction in the vicinity of the first electromagnet, and adjusts the size of the gap in the radial direction with the rotating body. A pair of first position sensors that respectively output proportional air gap signals, arranged in the vicinity of the second electromagnet so as to sandwich the rotor from both sides in the second radial direction, and in the same radial direction with the rotor. In the first radial direction of the rotating body by calculating the difference between the air gap signals of the pair of second position sensors and the pair of first position sensors which respectively output air gap signals proportional to the size of the air gap of A first radial displacement calculation circuit for calculating a displacement, and a second radial displacement for calculating a displacement of the rotating body in a second radial direction by calculating a difference between air gap signals of the pair of second position sensors. Performance Circuit, a supply current calculation circuit (PID control circuit) for calculating a supply current to the first and second electromagnets based on displacements of the rotating body in the first and second radial directions, and calculation results of the supply current calculation circuit An electromagnet drive circuit (power amplifier) that supplies a current to each electromagnet based on

Centrifugal force due to rotation acts on the rotating body,
In addition, the temperature rises due to iron loss and wind loss. For this reason,
The outer diameter of the rotating body changes during use, which changes the size of the air gap between the rotating body and the radial magnetic bearing even when the position of the rotating body is constant. By the way, in the conventional radial magnetic bearing control device, the relationship between the displacement of the rotor and the current supplied to each electromagnet is set to be optimum when the size of the air gap is a predetermined value. It does not change even when the angle changes. Therefore, when the change in the air gap becomes large, the control of the magnetic bearing becomes unstable.
The reason will be described with reference to FIG.

FIG. 4 shows the current I flowing through the electromagnet on the horizontal axis.
It is the graph which showed the attraction force F by an electromagnet on the vertical axis.
In FIG. 4, F1 is a curve representing the attraction force of one of the pair of electromagnets, F2 is a curve representing the attraction force of the other pair of magnets, and F is the total attraction force of the attraction forces of the pair of electromagnets. It is usually straight. Further, FIG. 4 (a) is a graph when the gap between the rotating body and the electromagnet is relatively large, and FIG. 4 (b) is a graph when the gap is relatively small. Assuming that the amount of change in current is ΔI and the amount of change in attraction force is ΔF, ΔF / ΔI changes due to changes in the air gap, and increases as the air gap becomes smaller. This ΔF / ΔI corresponds to the spring constant K in the one-degree-of-freedom control system. Here, if the control constant of the control device is set to be optimum in the state of FIG. 4 (a), when it becomes as shown in FIG. 4 (b), the control target is different from that at the time of setting. Therefore, if the change in the size of the void becomes large, the control becomes unstable.

It should be noted that the temperature sensor and the rotation speed sensor are used to determine the temperature change of the rotating body and the change of the outer diameter due to the centrifugal force, that is, the change of the air gap, and based on this, the current supplied to the electromagnet can be corrected. For example, although the above problem is eliminated, in this case, a temperature sensor and a rotation speed sensor are required in addition to the position sensor, which increases the cost.

The object of the present invention is to solve the above problems,
It is an object of the present invention to provide a control device for a magnetic bearing which can prevent control from becoming unstable due to a change in the gap between the rotating body and the electromagnet, and at which the cost is not increased.

[0009]

In a magnetic bearing control device according to the present invention, in a magnetic bearing having a plurality of electromagnets for supporting a rotating body in a non-contact manner by magnetic force, the rotating body is arranged so as to sandwich the rotating body. At least one pair of position sensors that respectively output a gap signal corresponding to the size of the gap between the body and the body, and electromagnet control means that controls the supply current to each electromagnet based on the gap signal from each position sensor. In the magnetic bearing control device, the electromagnet control means adds the air gap signals of the pair of position sensors, compares the air gap signal added value with a predetermined reference air gap value, and based on the comparison result. It is characterized in that the current supplied to each electromagnet is corrected.

The air gap signal addition value obtained by adding the air gap signals of the pair of position sensors corresponds to the size of the air gap between the rotating body and the electromagnet. Then, by correcting the current supplied to each electromagnet based on the result of comparison between the air gap signal added value and the reference air gap value, the current supplied to the electromagnet is corrected by the change in the size of the air gap, and the control becomes uncontrollable. It can be prevented from becoming stable. Moreover,
Since the size of the air gap between the rotating body and the electromagnet is calculated from the air gap signal of the position sensor required to detect the displacement of the rotating body, a temperature sensor or rotation speed sensor is used in addition to the position sensor originally required. There is no need to do so, and there is no increase in cost.

For example, the pair of position sensors each output a gap signal proportional to the size of the gap with the rotating body, and the current supplied to each electromagnet is steady regardless of the gap signal. The constant current supplied to the reference air gap value is added to the control current that changes according to the air gap signal, and the electromagnet control means changes the steady current to the reference air gap value as the air gap signal addition value becomes larger than the reference air gap value. The steady-state current is corrected so that the steady-state current becomes smaller than the reference gap value as the gap signal addition value becomes smaller than the reference gap value.

Alternatively, for example, the pair of position sensors each output a gap signal proportional to the size of the gap with the rotating body, and the current supplied to each electromagnet is related to the gap signal. The stationary current that is supplied steadily and the control current that changes according to the air gap signal are added, and the electromagnet control means controls the control current as the air gap signal addition value becomes larger than the reference air gap value. The control current is corrected so that the absolute value of the control current becomes smaller than the value of the reference air gap value as the absolute value becomes larger than the value of the reference air gap value and the air gap signal added value becomes smaller than the reference air gap value. There is.

For example, the electromagnet control means calculates displacement of the rotating body by calculating the difference between the air gap signals of the pair of position sensors, and the supply current to each electromagnet based on the displacement of the rotating body. A supply current calculating means for calculating, an electromagnet driving means for supplying a current to each electromagnet based on the calculation result of the supply current calculating means, and a gap signal for adding the gap signals of the pair of position sensors and outputting a gap signal addition value. Adding means, reference air gap value generating means for outputting a reference air gap value corresponding to the air gap signal addition value in a predetermined reference state, and comparison / correction calculation for calculating a correction value by comparing the air gap signal addition value and the reference air gap value. The electromagnet driving means is configured to correct the current supplied to each electromagnet based on the calculation result of the comparison / correction calculation means. The supply current calculation means outputs a steady current value and a control current value for each electromagnet to the electromagnet drive means, and the electromagnet drive means
A current obtained by adding the steady current value and the control current value is supplied to each electromagnet. The relationship between the displacement of the rotating body and the steady current value and the control current value in the supply current calculation means is constant regardless of the air gap signal addition value. The comparison / correction calculation means, for example, sets a correction coefficient for the steady current that becomes larger than 1 as the air gap signal added value becomes larger than the reference air gap value and becomes smaller than 1 as the air gap signal added value becomes smaller than the reference air gap value. It is calculated and output to the electromagnet driving means. Then, the electromagnet driving means obtains a corrected steady current value by multiplying the steady current value from the supply current calculation means by the correction coefficient from the comparison / correction calculation means, and adds this and the control current value from the supply current calculation means. The supplied current is supplied to each electromagnet. Alternatively, the comparison / correction calculation means calculates a current correction coefficient similar to the above, and outputs it to the electromagnet driving means. Then, the electromagnet driving means obtains a corrected control current value by multiplying the control current value from the supply current calculation means by the correction coefficient from the comparison / correction calculation means, and adds this and the steady current value from the supply current calculation means. The supplied current is supplied to each electromagnet.

[0014]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a shaft-shaped rotating body (1) and a rotating body (1).
There are shown two sets of radial magnetic bearings (2a) and (2b) for supporting the rotor in the radial direction in a non-contact manner, and a high frequency motor (3) for rotating the rotating body (1) at a high speed. In the following description, the axial direction (front-back direction) of the rotating body (1) is the Z-axis direction, and one radial direction (vertical direction) orthogonal to the Z-axis is orthogonal to the X-axis direction, the Z-axis and the X-axis. The other radial direction (left-right direction) is the Y-axis direction. The two sets of radial magnetic bearings (2a) and (2b) are arranged at a predetermined distance in the front-rear direction, and the motor (3) is arranged between them. The rotating body (1) is axially supported in a non-contact manner by an axial magnetic bearing, but its illustration is omitted.

FIG. 2 shows an example of the front radial magnetic bearing (2a) and its controller (4a), and FIG. 3 shows an example of the rear radial magnetic bearing (2b) and its controller (4b). It is shown.
Note that, in FIGS. 1, 2, and 3, the same portions are denoted by the same reference numerals. In addition, the front magnetic bearing (2a) and control device (4a) and the rear magnetic bearing (2b) and control device
In (4b), the same numerals are used for the corresponding parts, and the subscript a is attached to the front part and the subscript b is attached to the rear part.

Next, referring to FIG. 2, the front magnetic bearing (2
The a) and the control device (4a) will be described.

The front magnetic bearing (2a) is a pair of X-axis electromagnets arranged so as to sandwich the rotating body (1) from both sides in the X-axis direction.
(5a) and (6a), and a pair of Y-axis electromagnets (7a) and (8a) arranged so as to sandwich the rotating body (1) from both sides in the Y-axis direction.

The front side control device (4a) is an X-axis electromagnet (5a) (6a)
A pair of X-axis position sensors (11a) (12a) arranged so as to sandwich the rotating body (1) from both sides in the X-axis direction near the Y-axis, and in the Y-axis direction near the Y-axis electromagnets (7a) (8a). A pair of Y-axis position sensors (1
3a) and (14a), and an electromagnet control circuit (9a) as electromagnet control means. The electromagnet control circuit (9a) includes an X-axis displacement calculation circuit (15a) and Y
Axial displacement calculation circuit (16a), PID control circuit (17), X-axis electromagnet drive circuit (18a) composed of a power amplifier, and Y
Axial electromagnet drive circuit (19a), air gap signal addition circuit (20a) as air gap signal addition means consisting of an adder, reference air gap value generator (21a) as reference air gap value generation means, and comparison /
A comparison / correction calculation circuit (22a) is provided as correction calculation means.

The X-axis position sensor (11a) (12a) is composed of the rotating body (1).
A gap signal proportional to the size of the gap in the X-axis direction between and is output. The Y-axis position sensors (13a) and (14a) respectively output air gap signals proportional to the size of the air gap with the rotating body (1) in the Y-axis direction. X-axis displacement calculation circuit (15a)
By calculating the difference between the air gap signals of the pair of X-axis position sensors (11a), (12a), the displacement of the rotating body (1) in the X-axis direction is calculated, and the calculation result is output. Y-axis displacement calculation circuit (16a)
Calculates the displacement of the rotating body (1) in the Y-axis direction by calculating the difference between the air gap signals of the pair of Y-axis position sensors (13a) (14a), and outputs the calculation result. PID control circuit (17)
Is the displacement of the rotating body (1) in the X-axis direction, which is the output of the X-axis displacement calculation circuit (15a), and the displacement of the rotating body (1) in the Y-axis direction, which is the output of the Y-axis displacement calculation circuit (16a). And based on each electromagnet
The current supplied to (5a) (6a) (7a) (8a) is calculated and the calculation result is output. The control circuit (17) outputs a steady current value and a control current value for each of the electromagnets (5a) to (8a). The steady current value is a constant positive value regardless of the displacement of the rotating body (1). The control current value changes positively and negatively around 0 due to the displacement of the rotating body (1). Further, the relationship between the displacement of the rotating body (1) and the steady-state current value and the control current value in the control circuit (17) is constant regardless of the air gap signal added value described later.
Each electromagnet drive circuit (18a) (19a), based on the steady current value and the control current value from the control circuit (17), each electromagnet (5a) ~ (8a)
To supply current. The air gap signal addition circuit (20a) adds the air gap signals of the pair of X-axis position sensors (11a) (12a) and outputs the air gap signal addition value. This air gap signal added value is the size of the air gap between the X-axis position sensors (11a) (12a) and the rotor (1), that is, the air gap between the X-axis electromagnets (5a) (6a) and the rotor (1). It corresponds to the size. Also, since there is no directionality in the radial dimension change of the rotating body (1) due to centrifugal force or temperature change, the above-mentioned air gap signal addition value is obtained by the Y-axis electromagnet (7a) (8
It corresponds to the size of the gap between a) and the rotating body (1). Therefore, only by adding the air gap signals of the X-axis position sensors (11a) (12a), the X-axis electromagnets (5a) (6a) and the Y-axis electromagnets (7a)
The size of the gap between (8a) and the rotating body (1) can be calculated. The reference air gap value generation circuit (21a) outputs a reference air gap value corresponding to the air gap signal addition value in a predetermined reference state.
The comparison / correction calculation circuit (22a) is the gap signal addition circuit (20a)
The air gap signal addition value from the reference air gap value generation circuit (21a) is compared to calculate the correction coefficient for the current supplied to each electromagnet (5a) to (8a), and this is calculated. Circuit (18
a) Output to (19a). The correction coefficient is 1 when the air gap signal added value is equal to the reference air gap value, becomes larger than 1 as the air gap signal added value becomes larger than the reference air gap value, and becomes 1 as the air gap signal added value becomes smaller than the reference air gap value. Get smaller. Each electromagnet drive circuit (18a) (19a) is controlled by the control circuit (1a) based on the correction coefficient from the comparison / correction calculation circuit (22a).
The supply current value from 7) is corrected and the corrected current is supplied to each electromagnet (5a) to (8a). There are various ways to correct the supply current value.For example, the steady current value from the control circuit (17) is multiplied by the correction coefficient to correct the steady current value, and this and the control current from the control circuit (17) are corrected. The value is added and supplied as a supply current. Alternatively, in some cases, the control circuit
The control current value from (17) is multiplied by the correction coefficient to correct the correction current value, and this and the steady current value from the control circuit (17) are added and supplied as the supply current. Furthermore, both the steady current value and the control current value may be multiplied by a correction coefficient at a predetermined ratio to correct both the steady current value and the control current value at the same time.

As described above, the electromagnets (5a) to (8a) and the rotating body
By correcting the current supplied to the electromagnets (5a) to (8a) according to the change in the air gap with (1), control is not possible even if the air gap changes due to the radial dimension change of the rotating body (1). It never stabilizes.

The rear magnetic bearing (2b) and its control device (4
Since the configuration of b) is almost the same as that of the front side, the description is omitted. In the above embodiment, the front electromagnet (5a)
(6a) (7a) (8a) to calculate the value of the current supplied to the rotating body
(1) Using the displacements of the rear side X-axis and Y-axis directions, in order to calculate the value of the current supplied to the rear side electromagnets (5b) (6b) (7b) (8b), the rotor (1) Since the so-called cross control that uses the displacement in the X-axis and Y-axis directions on the front side is also performed, the control device on the front side
One common PID control circuit (17) is used by (4a) and the control device (4b) on the rear side. However, the electromagnets (5a) to (8
In the case where the control of a) and the control of the electromagnets (5b) to (8b) on the rear side are completely independent, the front control device (4a) and the rear control device (4b) are separated. PID control circuit is used.

The temperature change of the rotating body (1) depends on the front magnetic bearing (2a).
The portion and the rear magnetic bearing (2b) are not necessarily the same. Therefore, in each of the two sets of magnetic bearings (2a) and (2b), the electromagnets (5a) to (8a) are calculated based on the air gap signal addition value.
The supply current to (5b) to (8b) is corrected.

In the above embodiment, the position sensor that outputs a gap signal proportional to the size of the gap between the rotating body and the position sensor is used. A position sensor that outputs a gap signal that is inversely proportional to the size of the gap may be used as the position sensor. However, in that case, the supply current value becomes smaller than the value for the reference air gap value as the air gap signal added value becomes larger than the reference air gap value, and the supply current becomes smaller as the air gap signal added value becomes smaller than the reference air gap value. The supply current value needs to be corrected so that the value is larger than the reference air gap value.

[Brief description of drawings]

FIG. 1 is a side view of a rotating body and two sets of radial magnetic bearings showing an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an example of a set of radial magnetic bearings and a control device therefor.

FIG. 3 is a configuration diagram showing an example of another set of radial magnetic bearings and a control device therefor.

FIG. 4 is a graph showing the relationship between the current supplied to the electromagnet and the attractive force of the electromagnet.

[Explanation of symbols]

 (1) Rotating body (2a) X-axis magnetic bearing (2b) Y-axis magnetic bearing (4a) X-axis controller (4b) Y-axis controller (5a) (5b) (6a) (6b) X-axis electromagnet (7a) ) (7b) (8a) (8b) Y-axis electromagnet (9a) X-axis electromagnet control circuit (9b) Y-axis electromagnet control circuit (11a) (11b) (12a) (12b) X-axis position sensor (13a) (13b) ) (14a) (14b) Y-axis position sensor

Claims (3)

[Claims] 1. A magnetic bearing including a plurality of electromagnets for supporting a rotating body in a non-contact manner by magnetic force, and a gap signal corresponding to a size of a gap between the rotating body and the rotating body. A controller for a magnetic bearing, comprising: at least one pair of position sensors that respectively output the position sensor; and electromagnet control means that controls a supply current to each of the electromagnets based on an air gap signal from each of the position sensors. The electromagnet control means adds the air gap signals of the pair of position sensors, compares the air gap signal added value with a predetermined reference air gap value, and corrects the current supplied to each of the electromagnets based on the comparison result. A control device for a magnetic bearing, which is characterized in that 2. The pair of position sensors each output a gap signal proportional to the size of the gap between the position sensor and the rotating body, and the current supplied to each electromagnet is related to the gap signal. A stationary current that is supplied steadily and a control current that changes according to the air gap signal are added, and the electromagnet control means uses the steady current as the air gap signal addition value becomes larger than the reference air gap value. The steady current is corrected so that the steady current becomes smaller than the value for the reference air gap value as the current becomes larger than the value for the reference air gap value and the air gap signal addition value becomes smaller than the reference air gap value. The control device for the magnetic bearing according to claim 1, wherein the control device is provided. 3. The pair of position sensors each output an air gap signal proportional to the size of the air gap between the rotor and the rotating body, and the current supplied to each electromagnet is related to the air gap signal. A stationary current that is constantly supplied and a control current that changes depending on the air gap signal are added, and the electromagnet control means controls the air gap signal as the air gap signal addition value becomes larger than the reference air gap value. The absolute value of the current becomes larger than the value for the reference air gap value, and the absolute value of the control current becomes smaller than the value for the reference air gap value as the air gap signal added value becomes smaller than the reference air gap value. 2. The magnetic bearing control device according to claim 1, wherein the control device corrects an electric current.