JP3206264B2 - Control method of magnetic bearing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a magnetic bearing for supporting a rotating body in a non-contact manner.

[0002]

2. Description of the Related Art The hardware of Conventional Example 1 as a conventional technique will be described with reference to a general circuit configuration shown in FIG. FIG.
FIG. 2 is a block diagram illustrating an entire circuit configuration of a magnetic bearing control system. In FIG. 3, 1 and 9 are A / D (analog →
The digital signals are converted into analog signals from the displacement sensor 8 and the position command by the (digital) converter, and are input to the digital control unit 3. In the digital control unit 3, the displacement sensor 8
Based on the signals from the position command and the position command, that is, after deriving the position deviation obtained by subtracting the current position detected by the displacement sensor 8 from the position command in the mixer 2a, the digital calculator 2 calculates the current command Iref. This current command I
ref is converted into an analog signal by a D / A (digital-to-analog) converter 4 and input to a current amplifier 5. In the current amplifier 5, a current proportional to the current command Iref is caused to flow through the electromagnet 6 for the magnetic bearing, so that the rotating body 7 floats in a non-contact manner and is controlled. Next, FIG. 4 shows a flowchart of an operation for performing the magnetic bearing control of the above-described conventional example 1. In this control method, the process is started (step 401), and parameters for control calculation are initialized (step 402).
Then, the A / D converters 1 and 9 take in the position command and the data of the position sensor [Step 403], whereby the digital calculator 2 calculates the current command Iref [Step 40].
Four ]. In this calculation, the current command Iref has already been linearized. Further, after calculating the current command Iref,
It is checked whether the absolute value | Iref | of the current command is within the output limit of the current amplifier 5 [Step 405].
], If it is within the range of the output limit [NO in step 405], it is output to the D / A converter 4 according to the instruction [step 406] [step 408], and if it is outside the range of the output limit [step 405] YES], the current command Iref is replaced with a value corresponding to the maximum positive or negative current of the current amplifier 5 [Step 407] and output to the D / A converter 4 [Step 408]. Thereafter, the control returns to the point B by a timer interrupt, and a control loop is formed. Further, as a conventional example 2, there is JP-A-2-42210. This is a magnetic bearing device including a control coil that supports the rotating body in a vertical direction, and current control means that increases a control current in accordance with an increase in the distance between the control coil and the rotating body. When the separation distance between the control coil and the rotating body is shorter than a predetermined distance, the magnetic bearing device includes gain control means for controlling a control current with a gain larger than the predetermined distance,
In a high frequency region of the rotating body, the control by the gain control unit is stopped, and a frequency response unit that controls the control current with a substantially constant gain over the entire length of the controllable separation distance,
The magnetic bearing device according to the preceding item, wherein the current control means is provided.

[0003]

However, in the conventional example 1, when the disturbance applied to the magnetic bearing is large (for example, the unbalance of the rotating body is large), as shown in FIG. , A sine wave having a large amplitude synchronized with the rotation frequency of the rotating body (solid line 51 in FIG. 5, actually discrete). At this time, the current command I
Since ref exceeds the output limit of the current amplifier 5, an output limit (dotted line 52 in FIG. 5) is provided in advance for the current command Iref so that an excessive signal does not enter the current amplifier 5. Therefore, the current i flowing through the electromagnet 6 for magnetic bearing has a saturated waveform similar to the current command Iref having the output limit, and the control system loses its linearity and becomes unstable, and eventually becomes uncontrollable. It falls into an abnormal state called touchdown of the rotating body. As described above, in the magnetic bearing according to Conventional Example 1, the means for detecting the above-described inconvenient phenomenon increases even if the unbalance of the rotating body increases due to a sudden load change or the like during rotation of the rotating body. There was no problem, so the rotating body eventually touched down. Further, the second conventional example is a means for setting the control gain of the system so as to increase the efficiency by reducing the control current from the positions of the rotating body and the control coil. This is because if the distance between the rotating body and the control coil becomes longer, the control tends to return to its original state, requiring an excessive force, and the current is likely to be saturated, but the current is not saturated by reducing the control gain. Even if the current is not saturated, the magnetic bearing device does not know any instantaneous transient cause, and it is considered that the imbalance based on the root cause cannot be corrected. By the way, when the vibration increases due to the unbalance of the rotating body generated during the operation support of the rotating body by the magnetic bearing, an excessive current (generally, a sine wave synchronized with the rotating frequency) is intended to control the vibration. ) Flows into the bearing electromagnet. However, if the current is too large, the current amplifier has an output limit, so the peak value of this sine wave will reach the limit value, resulting in a saturated waveform, and non-linear control will cause the magnetic bearing to oscillate. is there. Therefore, in the present invention, when this current exceeds the limit, the degree of saturation is determined in the digital arithmetic unit, and an alarm is output and an emergency stop is performed. It is an object of the present invention to provide a method for controlling a magnetic bearing to prevent the occurrence of a magnetic field.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is directed to a rotating body provided at both ends of a rotating shaft provided in a rotating body so that the rotating body is magnetically supported through a gap. The electromagnet for bearings arranged side by side, a displacement sensor for detecting the displacement of the rotating body, and a position command and a position deviation based on a detection signal of the displacement sensor are derived, and then a current command given to the electromagnet for bearing is digitally calculated. In a magnetic bearing control device including a digital control unit and a current amplifier that flows a current according to the current command, a current command to the current amplifier calculated by the digital control unit is monitored, and the current command is set to the current amplifier. When the time exceeding the value of the output limit exceeds a preset period, an alarm output is output or the rotation of the rotating body is stopped.
That is, according to the present invention, the current command calculated by the digital calculator is constantly monitored, and if the current command exceeds the range of the current limit continuously for each sampling period, the number of times is counted, and the ratio is determined by the rotation of the rotating body. If the number of times of sampling is larger than the number of times of sampling in the cycle, the control method is to output an alarm or to stop the rotation in an emergency.

[0005]

Since the present invention is such a method of controlling a rotating bearing, touchdown during rotation of the rotating body is completely prevented, and rotation of the rotating body can be stopped without damaging the device. Thus, the reliability of the control system is improved.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. The overall configuration block diagram of the control system of the magnetic bearing representing the hardware of one embodiment of the present invention is the same as that of FIG. FIG. 1 is a flowchart showing software of a magnetic bearing control method according to an embodiment of the present invention. First, when the control of the magnetic bearing of the rotating shaft of the rotating body is started [Step 101], initialization, that is, parameters such as a sampling period T, a filter (not shown) time constant, and a control gain, which will be described later, for the control calculation are constant. Initial setting is performed [Step 102]. Next, f / V
[Frequency → voltage] A rotation speed signal of the rotating body and data of the displacement sensor 8 passed through a converter (not shown) are input to the A / D converter 1 and a position command is input to the A / D converter 9. [Step 103]. Then, in the digital arithmetic unit 2 (in one embodiment of the present invention, for example, a personal computer or a CPU board is applied), the number of samplings n during one-half rotation of the rotating body is calculated from the rotating speed of the rotating body. [Step 104]. Here, FIG. 2A is a diagram of a current command to the current amplifier representing the number of samplings n.
The horizontal axis indicates the passage of time, and the vertical axis indicates the current command Iref. The range from 0 to Iref limit on the vertical axis indicates the range of the positive current limit, and the range from 0 to thalf on the horizontal axis indicates the time period of 1/2 rotation of the rotating body. One sampling period T for detection is created. The calculation is as follows: n = 1 / (2 × f × T) where f is the rotation frequency of the rotating body and hertz (Hz) T is the sampling period. Further, a current command Iref is calculated from the position command and the data of the displacement sensor 8 [Step 105]. If the absolute value | Iref | of this current command is within the output limit of the current amplifier 5, [NO in Step 106] ), The counter value (count) of the limit over is set to 0, and the current command Iref is output to the D / A converter 4 as it is [step
107] Then, the D / A converter 4 performs D / A conversion and outputs the result [Step 113], returns to the point A, and repeats the following calculation. However, due to disturbance applied to the magnetic bearing, the absolute value | Iref |
If the value exceeds the value [YES in step 106], the counter value (count) of the limit over is increased by one [step 108], and the current command is supplied during the counter value (count) ≦ () n. The positive or negative maximum output (MAX) value of the current amplifier 5 is output to the D / A converter 4 as Iref [step 112]. Then, the D / A converter 4 performs D / A conversion and outputs the result (step 113), returns to the point A, and repeats the following calculation. Further, in the determination of step 109, the absolute value of the current command | Iref |> current amplifier limit [YES]
], The counter (not shown) calculates the absolute value | Ir of the current command.
ef | is continuously limited by each sampling.
Only when the value exceeds imt, the number of times of sampling is counted, and this count value is compared with the number of times of sampling n during 1/2 rotation of the rotating body calculated in advance. Then, as shown in FIG. 2 (a), the absolute value | Iref | of the current command continuously exceeds the output limit Iref limit, and the counter value (count) is equal to or greater than the ratio set for the number of samplings n. [For example, counter value (count)>
(1/3) n] [when YES in step 109], it is determined that the nonlinearity of the control system due to the saturation of the current command Iref is large, and an alarm is output or the rotation of the rotor is stopped in an emergency. [Step 110], this control is temporarily terminated [Step 111]. However, FIG. 2 (b)
As shown in (1), when the absolute value | Iref | of the current command intermittently falls below the value of the limit Iref limt while the counter value (count) is increasing, the process proceeds to step 107, where the counter value (count) is incremented. Is returned to 0, and the lowered current command Iref is output to the D / A converter 4 as it is. Note that the set value counter value (count), which is the ratio set as described above,>
(1/3) n is a value until the rotating body can be stably controlled, which is obtained by an experiment or the like.
/ 3) and the like are adjusted according to the characteristics of the magnetic bearing, such as the specification and the number of revolutions. In each of steps 107 and 112, after output to the D / A converter 4, the flow returns to point A by a timer interrupt from step 113.
This control loop is formed again and the operation is performed.

[0007]

As described above, according to the present invention, even if the unbalance of the rotating body is increased due to disturbance or the like and the control system becomes unstable, the rotating body is stopped before touching down. Therefore, the device is not damaged, and a special effect of significantly contributing to the improvement of the stability of the control system can be obtained.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a control process according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a current command of a current amplifier according to the present invention.

FIG. 3 is a configuration block diagram of an entire control system as hardware according to an embodiment of the present invention.

FIG. 4 is a flowchart showing a conventional control method.

FIG. 5 is a diagram for explaining a current command of a conventional current amplifier.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 A / D converter 2 Digital arithmetic unit 3 Digital control part 4 D / A converter 5 Current amplifier 6 Electromagnet for magnetic bearings 7 Rotating body 8 Displacement sensor 9 A / D converter f Rotating body rotation frequency (Hz) T sampling Cycle (time) n Number of sampling times Iref Current command

Claims (1)

(57) [Claims] An electromagnet for bearings disposed at both ends of a rotating shaft provided in a rotating body so that the rotating body is magnetically supported via an air gap and arranged in parallel at each end, and a displacement for detecting a displacement of the rotating body. A sensor, a digital control unit that digitally calculates a current command given to the bearing electromagnet after deriving a position deviation based on a position command and a detection signal of the displacement sensor, and a current amplifier that flows a current according to the current command. In the magnetic bearing control device provided, the current command to the current amplifier calculated by the digital control unit is monitored, and when the time when the current command exceeds the value of the output limit of the current amplifier exceeds a preset period. A method for controlling a magnetic bearing, comprising: outputting an alarm output or stopping rotation of a rotating body.