JP3049448B2 - Electromagnetic bearing control device and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control apparatus and method for stably lifting a rotor in an electromagnetic bearing.

[0002]

2. Description of the Related Art An electromagnetic bearing control device detects a radial position of a rotor and supplies a current corresponding to the detected signal to a coil of the electromagnetic bearing, thereby holding the rotor at a neutral position. In general, a PID circuit is used as a circuit for controlling the current supply. However, in the PID circuit, the noise of the detection signal is often amplified or the bending vibration of the rotor is excited due to the increase of the high frequency gain by the differentiating circuit. Have been.

Further, a motion model of the rotor including the behavior of bending vibration is created, and a state estimator such as a Kalman filter or an observer is constructed based on modern control theory.
A method of forming a feedback circuit of the estimated state quantity has been proposed. As applications of such modern control theory, Yukio Ozaki et al., "Stabilization control using observer of flexible structure type magnetic levitation system", IEICE Linear Drive Research Group, LD88-32, pp. 21- There are 29 pages, in which a stable levitation of the rotor is realized by the configuration of the minimum dimension observer in consideration of the bending primary vibration of the beam.

[0004]

However, in the above-mentioned prior art, if there are many unstable bending vibration modes due to small internal damping of the rotor, the number of notch filters or the number of dimensions of the bending mode model is increased. It has to be prepared, and there is a disadvantage that the load on the control circuit is increased.

More specifically, FIG. 7 shows an example of the frequency characteristic of a control circuit constituted by using the same-dimensional observer considering the first-order bending mode of the rotor. The horizontal axis represents frequency, and the vertical axis represents gain. Has become. As can be seen from the figure, the phase is delayed by 90 degrees in the high frequency region due to the primary delay characteristics of the observer (equivalent to inserting a low-pass filter in the PID circuit to prevent high frequency noise). If the phase is delayed by 90 degrees in the high-frequency region as described above, the mode becomes unstable when the internal attenuation of the second or subsequent bending mode is small. Or increase the notch filter.

An object of the present invention is to provide an electromagnetic bearing control device and method capable of compensating for high stability in a high-order bending mode even if the number of dimensions of the control circuit is small.

[0007]

To achieve the above object, the present invention provides a position detecting sensor for detecting a radial displacement of a rotor, a reference position signal generator for outputting a reference position signal of the rotor, Control means for controlling an exciting current to an electromagnet supporting the rotor based on a deviation between a detection signal from the position detection sensor and a reference position signal from the reference position signal generator. A plurality of natural frequencies for a bending mode of the rotor in the apparatus.
In the frequency range between adjacent natural frequencies ,
A means for delaying the phase characteristic of the control signal in the means by 180 degrees or more is provided.

The means is a second-order low-pass filter, and the resonance frequency component of the output of the low-pass filter is attenuated by the anti-resonance characteristic of the rotor.

Furthermore, the transfer function of the control means has a high frequency.
The phase in the region is 270 degrees behind.

Further, the present invention is to together when detecting the displacement in the radial direction of the rotor, on the basis of the deviation between the reference position of the rotor that has been set in advance and the displacement, to the electromagnet for supporting the rotor An electromagnetic bearing control method for controlling an exciting current, wherein a plurality of unique
In the frequency domain between adjacent natural frequencies ,
The purpose is to delay the phase characteristic of the signal for controlling the exciting current by 180 degrees or more.

[0011]

According to the above configuration, since the phase characteristic is delayed by 180 degrees or more in the high frequency region, the phase characteristic acts to give a positive attenuation to the higher-order bending mode, and the stability of the higher-order bending mode can be enhanced.

Further, by increasing the stability of the higher-order bending mode, the loop gain can be increased as a whole, and the rigidity of the electromagnetic bearing can be increased.

[0013]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the overall configuration of the electromagnetic bearing control device of the present invention. In the figure, reference numeral 1 denotes a rotor, one end of which is levitated and held by electromagnets 2a and 2b provided to face each other at a predetermined interval, and the other end is supported by a ball bearing 14. The rotor 1 is driven to rotate by a rotation mechanism (not shown). Further, a pair of electromagnets is also provided in a direction perpendicular to the paper surface, and has a circuit configuration that functions similarly to the illustrated electromagnetic bearing control system.

A position detecting sensor 3 is provided in the vicinity of the rotor 1, detects a radial displacement of the rotor 1, and sends a detection signal to a control circuit 5 via a converter 4. The control circuit 5 determines the difference between the reference position signal from the reference position signal generator 6 and the detection signal from the converter 4
This is a signal processing circuit that generates a control signal.

A control signal from the control circuit 5 is sent to an electromagnetic drive circuit 7, and the electromagnetic drive circuit 7 is configured to supply an exciting current to the electromagnets 2a and 2b in accordance with the control signal.

Next, the internal configuration of the control circuit 5 will be described. The control circuit 5 includes an observer circuit 8, a regulator circuit 9, an integrator 10, a gain adjuster 11, a secondary low-pass filter 12, and a low-pass filter feedback circuit 13.

The observer circuit 8 has a mathematical model of the rotor 1 therein and estimates a state quantity of the rotor 1 that cannot be directly measured by the position detection sensor 3. If a mathematical model of the rotor 1 is shown, a known configuration method can be used.

Here, how to make a mathematical model of the rotor 1 will be described. The displacement of the electromagnetic bearing point of the rotor 1 is x ₂ , the displacement of the rotor 1 at a point other than the electromagnetic bearing point is vector x ₁ , the electromagnet 2
Let u be the force that a and 2b exert on the rotor 1.
The equation of motion can be expressed as follows.

[0019]

(Equation 1)

The above equation (1) can be obtained by finite element analysis. However, as it is, the number of dimensions is large,
Since it is not suitable for forming the observer circuit 8, it is necessary to reduce the dimension appropriately.

Now, it is assumed that the behavior of the rotor 1 is represented by a combination of a rigid body motion and a bending vibration as shown in FIG.
That is, as shown in FIG. 5 and FIG. 6, the mode δ when the unit displacement is given to the electromagnetic bearing point and the free vibration mode φ when the electromagnetic bearing point is constrained,

[0022]

(Equation 2)

It is assumed to be expressed as follows. Where s
Is a weight value of the mode φ. In addition, the vibration modes after the secondary bending are ignored.

According to the equation (2), the equation (1) becomes a reduced-order equation as follows.

[0025]

(Equation 3)

[0026] Since only the displacement x ₂ of the electromagnetic bearing point of the rotor 1 can be observed, the state equation of modern control theory format is as follows.

[0027]

(Equation 4)

[0028]

(Equation 5)

Here, k is an observer gain vector, which is a parameter for specifying the pole of the observer.

If the above equation (5) is converted to a transfer function description, the observer circuit 8 can be realized by an operational amplifier. Further, if the data is converted into a discrete time system, it can be realized by a digital processing device such as a digital signal processor. Here, the observer circuit 8 is of the fourth order, but if there is room in the circuit configuration, (2)
By considering the second and subsequent modes of bending in the equation, it is possible to realize a more accurate observer circuit.

The state quantity estimated by the observer circuit 8 becomes an input signal of the regulator circuit 9. The regulator circuit 9 is a circuit that weights and adds each state quantity and outputs a signal. The weight applied to each state quantity is set to a value that stably supports the rotor 1 by the optimal regulator theory or the pole arrangement method. The rotor 1 is connected to the regulator circuit 9.
Compensates for the stability up to the first-order bending mode modeled.

As shown in FIG. 7, the input / output characteristics of the above-described compensating circuit based on the same-dimensional observer and the state feedback rule are of a first-order type in which the phase is delayed by 90 degrees in a high frequency region. If such a compensation circuit is used as it is as a stabilizing compensator, a higher-order bending mode is likely to oscillate due to phase lag.

Therefore, in the present embodiment, a second-order low-pass filter 12 is further provided in the control circuit 5 to constitute a third-order lag-type circuit system as a whole so that the high-frequency phase characteristic is delayed by 270 degrees. Thereby, the control circuit 5 works so as to give a positive damping to the higher-order bending mode. Further, since the gain characteristic is also reduced, the force for exciting the higher-order bending mode is also reduced.

When the frequency of the pole of the secondary low-pass filter 12 is represented by ωF, the attenuation ratio is represented by ζF, the input signal is represented by υ, and the output signal is represented by z, the secondary low-pass filter 12 is described by the following equation.

[0035]

(Equation 6)

The integrator 10 controls the rotor 1 due to gravity or the like.
It is provided to compensate for steady-state deviation. The gain adjuster 11 adjusts the integral compensation amount to be optimal.

By making the control circuit 5 of a third-order lag type, the higher-order bending mode is stabilized, but the eigenvalues of the rotor 1 are usually close to each other. Thus, a circuit that slowly retards the phase will destabilize any of the bending modes from low to high. Therefore, it is preferable that the secondary low-pass filter 12 has a sharp characteristic around a sharply resonating phase. That is, the characteristic of the control circuit 5 is a characteristic that sharply resonates between the natural frequencies of the primary bending and the secondary bending of the rotor 1 as shown in FIG. 2, and the phase characteristic is in a frequency range between the primary bending and the secondary bending. Is reversed. Further, in order to prevent the control circuit 5 itself from becoming unstable, its resonance frequency is set to the anti-resonance point of the rotor system (point fp shown in FIG. 3) so that the resonance frequency component is not input to the control circuit 5. To

If the control circuit 5 is considered as a series combination of three transfer functions for each characteristic, it can be understood as shown in FIG. That is, a notch filter for attenuating the bending first-order mode and a so-called phase lead / lag circuit (first-order delay type)
By preparing a second-order low-pass filter and a second-order low-pass filter, the control circuit 5 can be realized completely equivalently.

The electromagnetic bearing control device according to the present embodiment can be used for a pump, a centrifugal compressor, and the like.

[0040]

As described above, according to the present invention,
By providing a means for delaying the phase characteristic of the control signal in the control means by 180 degrees or more, positive attenuation can be given to the higher-order bending mode of the rotor, and the gain characteristic also decreases. Can hardly occur.

Further, since the stability of the high-order bending mode is high, the feedback amount of the bearing can be increased, so that high rigidity can be achieved.

Further, by realizing a sharp phase inversion using the anti-resonance point of the rotor, it is possible to prevent the stability of the low-order mode from being impaired for stabilizing the high-order bending mode. .

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing an electromagnetic bearing control device of the present invention.

FIG. 2 is a graph showing frequency characteristics of a control circuit.

FIG. 3 is a graph showing gain characteristics of a rotor and a numerical model thereof.

FIG. 4 is a diagram illustrating mode synthesis.

FIG. 5 is a diagram of a certain mode serving as a basis for mode synthesis.

FIG. 6 is a diagram of another mode serving as a basis for mode synthesis.

FIG. 7 is an explanatory diagram showing an exploded transfer function of the control circuit.

FIG. 8 is a graph showing frequency characteristics of a conventional control circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rotor main body 2a, 2b Electromagnet 3 Position detection sensor 4 Converter 5 Control circuit 6 Reference position signal generator 7 Electromagnetic drive circuit 8 Observer circuit 9 Regulator circuit 10 Integrator 11 Gain adjuster 12 Secondary low-pass filter 13 Low-pass filter feedback circuit 14 Ball bearing

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Ikuhiro Saito 502 Kandachicho, Tsuchiura-shi, Ibaraki Machinery Research Laboratory, Hitachi, Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) F16C 32/04

Claims (4)

(57) [Claims] 1. A position detection sensor for detecting a radial displacement of a rotor, a reference position signal generator for outputting a reference position signal of the rotor, a detection signal from the position detection sensor and a reference position signal from the reference position signal generator. Control means for controlling an exciting current to an electromagnet supporting the rotor based on a deviation from the reference position signal of the rotor, wherein a plurality of natural frequencies for a bending mode of the rotor are provided.
In the frequency range between adjacent natural frequencies ,
An electromagnetic bearing control device, comprising: means for delaying a phase characteristic of a control signal in the means by 180 degrees or more. 2. The electromagnetic bearing control device according to claim 1, wherein said means is a secondary low-pass filter, and a resonance frequency component of an output of said low-pass filter is attenuated by anti-resonance characteristics of said rotor. Electromagnetic bearing control device. 3. The electromagnetic bearing control device according to claim 1, wherein a phase of a transfer function of said control means in a high frequency region.
Is an electromagnetic bearing control device which is delayed by 270 degrees . 4. A method for detecting radial displacement of a rotor.
To, on the basis of the deviation between the reference position of the rotor that has been set in advance and the displacement, in the electromagnetic bearing control method for controlling the exciting current to the electromagnet for supporting the rotor, a plurality against bending mode of the rotor The exciting current is controlled in a frequency region between adjacent natural frequencies of the natural frequencies.
A method for controlling an electromagnetic bearing, wherein a phase characteristic of a signal to be controlled is delayed by 180 degrees or more.