JPH08303461A - Magnetic bearing controller - Google Patents

Abstract

PURPOSE: To provide a magnetic bearing controller in which stabilization in the natural frequency range is achieved. CONSTITUTION: In a magnetic bearing controller provided with a position sensor 1 for detecting the floating position of a target shaft, a gain circuit 2 for receiving the output of the position sensor 1, and a control circuit 3 for receiving the output of the gain circuit 2 and sending an exciting signal to an electromagnet 4 for floating the target shaft, a lag filter 7 is provided between the gain circuit 2 and the control circuit 3.

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 applied to a magnetic bearing used for a high speed rotating body such as a turbo molecular pump or a turbine.

[0002]

2. Description of the Related Art A magnetic bearing using an electromagnet is known as a means for floatingly holding a rotating body. This magnetic bearing has a smaller loss than the conventional fluid lubrication bearing, and the dryness of the bearing and the cleanliness of the atmosphere are removed, and it is a useful bearing especially in a vacuum state.

In this magnetic bearing, as a means for setting the levitation position of the rotating body, the levitation position of the levitation object is measured, the current value to be flown to the electromagnet is determined based on the measurement signal, and the magnitude of the magnetic force generated from the electromagnet is determined. There is a means to determine.

FIG. 6 is a block diagram of a control system of the means. The thrust position sensor 1 is the position (displacement) of the floating object.
An eddy current displacement meter or the like is an example of such a sensor for measuring. Gain circuit (position feedback gain) 2
Is for multiplying the magnitude of the signal obtained by the thrust position sensor 1 by a required magnitude. The control circuit 3 comprises a signal processing circuit for inputting the signal obtained by the position feedback gain 2 into the electromagnet 4 in an appropriate form. As this signal processing circuit, for example, PID (proportional,
There are integration and differentiation circuits, phase compensation circuits, and their combination circuits. The electromagnet 4 is a coil wound around an iron core, and generates a magnetic force for levitation in accordance with the current input from the control circuit 3.

Considering the simplest position feedback system in which the control circuit 3 is composed of only proportional elements (P elements),
The transfer function between the input 1 and the output magnetic force F of the electromagnet 4 is
The following 1 depending on the resistance and inductance of the coil, iron core, etc.
It becomes the next delay system.

F / I = Km / (1 + Tm · S) (1) where Km is the gain of the electromagnet 4, Tm is the time constant of the electromagnet 4, and S is the Laplace operator. Therefore, the transfer function from the measured displacement D of the position feedback system to the force F on the floating object is as follows.

F / D = Kf · Kp · Km / (1 + Tm · S) (2) However, I = Kf · Kp · D.

Here, Kf is the proportional gain of the position feedback gain 2, and Kp is the proportional gain of the control circuit 3. Position feedback system (force F) / (displacement D)
In order to see the frequency characteristic of, the Laplace operator S is changed to S = j2
It is set to πf and is substituted into the equation (2). Here, f is a frequency and j = √−1. (Force F) / (Displacement D) is a complex number, and is set as follows.

F / D = Kr (f) + j · Ki (f) (3) The real part of (force F) / (displacement D) in equation (3) means the rigidity depending on the frequency f. However, the imaginary part means attenuation depending on the frequency f. In the first-order lag as shown in equation (2), the imaginary part is always negative, and the floating object has a destabilizing force opposite to the damping.

FIG. 7 is a diagram showing the relationship between (force F) / (displacement D), that is, the value of the imaginary part of the equation (3) and the frequency f. The dotted line A corresponds to the equation (2) and shows the above-mentioned state. When the value at the frequency f = fc shown in the figure is larger than the damping of the natural frequency fc composed of the floating object and the position feedback system, especially the material damping of the floating material, the natural frequency vibrates divergently, I can't drive.

Therefore, (force F) / of the position feedback system
In order to have a damping effect on (displacement D), a differential element (D element) or a phase compensation element is provided in parallel with the proportional element (P element) in the control circuit 3. Because of the static position retention,
These elements advance the phase in the time direction. Here, the differential element is taken as an example. When the differential element (D element) is realized as a circuit in the control circuit 3, a first-order delay is added as follows.

(Differential element) = Kd · S / (1 + Td · S) (4) Here, Kd is a gain of the differential element, and Td is a time constant. (Force F) / of position feedback system with only differential element
(Displacement D) is given by the following equation.

F / D = Kf · Kd · Km · S / {(1 + Td · S) · (1 + Tm · S)} (5) The numerator of the equation (5) is the first order of S and the denominator of S is Since it is quadratic, the imaginary part of the equation (5) is as shown by the alternate long and short dash line B. That is, it has a damping effect on the floating object in the low frequency region, and has a destabilizing effect in the high frequency region. In order to maintain the position of the floating object, the control circuit 3 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 3 is F / d = Kf · {Kp + Kd · S / (1 + Td · S)} · Km / (1 + Tm · S) .... ( 6), and becomes like a solid line C, and has almost the same characteristics as the one-dot chain line B described above. If the natural frequency fc composed of the floating object and the position feedback system is placed in a low frequency region having a damping effect, stability can be ensured and operation can be performed without generating vibration.

A magnetic bearing having such characteristics is shown in FIG.
Considering the case where the rotor 5 is used as a bearing of the rotor 5 having a plurality of stages of blades having different dimensional specifications and the rotor 5 is levitated, the following phenomenon is exhibited.

Since the rotor 5 has a plurality of blade natural frequencies in the thrust direction as shown in (a) to (c),
There is always a natural frequency in the frequency region having a destabilizing action of (force F) / (displacement D). Therefore, if the destabilizing action of the position feedback system of the magnetic bearing 6 becomes larger than the material damping of the blade having this natural frequency, it becomes unstable, and the vibration diverges once the natural frequency is excited or resonated. It becomes large and cannot be levitated.

[0016]

As described above, in order to maintain the position of the floating object in the conventional device, the position of the floating object is measured by the thrust position sensor 1, the signal is fed back, and the electromagnetic force 4 is applied. It is supposed that the force is generated from this, but this force becomes the destabilizing force that vibrates the floating object.
Even if the control circuit 3 performs processing such as PID and phase compensation, it still has a large destabilizing force in the high frequency region.

Therefore, in a levitating object having a plurality of natural frequencies such as a rotating body having a plurality of stages of blades having different dimensional specifications, the natural frequency always exists in the frequency region which is the destabilizing force. Therefore, there is a problem that once the natural frequency is excited or resonated, divergent vibration is generated by the magnetic bearing 6.

[0018]

The present invention employs the following means to solve the above-mentioned problems.

That is, a position sensor for detecting the levitation position of the target shaft, a gain circuit for receiving the output of the position sensor, and a control circuit for receiving the output of the gain circuit and sending an excitation signal to the levitation electromagnet of the target bearing. In the magnetic bearing control device having the above, a lag filter is provided between the gain circuit and the control circuit.

[0020]

In the above invention, in the post-lag filter in which the gain is applied to the output of the position sensor, only a certain band of the frequency band which becomes unstable only by the PDI or PI control circuit or the like has the phase delayed by the delay filter. The signal in this band is delayed by about 180 ° from the original state.
Then, it is sent to the control circuit, subjected to PDI or PI processing, and output.

Therefore, the polarity is reversed at the unstable portion. That is, it is stabilized in the frequency band in which the destabilizing force is exerted.

In this way, the levitation position of the target shaft can be stably maintained even in the previously destabilized band.

[0023]

【Example】

(1) The first embodiment of the present invention will be described with reference to FIGS.

The parts described in the conventional example are designated by the same reference numerals, and the description thereof will be omitted. The parts relating to the present invention will be mainly described.

In FIG. 1, the output of the thrust shaft position sensor 1 is sent to an electromagnet 4 through a gate circuit (position feedback gain) 2, a lag filter 7, and a PID control circuit 3 in this order.

The lag filter 7 is a first-order low-pass filter in which an amplifying element 8 and R and C are combined as shown in FIG.

FIG. 3 is a diagram showing a gain-phase characteristic of the delay filter 7. As shown in the figure, the gain of the filter 7 is constant in the entire frequency range, and only the phase is 0 ° to −2.
It gradually lags the frequency to π (360 °). The frequency f _{0 at} which the phase becomes −π (−180 °) is the center frequency, and the center frequency and the amount of phase change are changed by adjusting the resistor R and the capacitor C. The center frequency f ₀ is set near the natural frequency which is destabilized by the bearing 6.

Next, the operation of the apparatus of this embodiment thus constructed will be described. The signal from the position sensor 1 enters the lag filter 7 via the gain circuit 2, is delayed only in phase, and is input to the control circuit 3.

The (force F) / (displacement D) of the magnetic bearing is (3)
The lag filter 7 is expressed by the following equation.

V2 / V1 = exp [-jθ (f)] (7) where V1 is the input voltage, V2 is the output voltage, and exp
Is the exponential function and θ is the phase.

Thus, (force F) / of this new magnetic bearing
(Displacement D) is expressed by the equation (8).

F / D = {K _R (f) + j · K _I (f)} · exp [−jθ (f)] = {K _R (f) cos θ (f) + K _I (f) sin θ (f) } + J {K _I (f) cos θ (f) −K _R (f) sin θ (f)} (8) The imaginary part of F / D near the frequency f ₀ at which θ (f) is around −π. Was negative but becomes positive due to the delay.

Thus, the damping characteristic of the magnetic bearing is as shown by the solid line D in FIG. 4, and the portion of the frequency band f _{c1 to} f _c2 is changed to the stabilizing force. Therefore, when the natural frequency of the shaft 5 [(a) to (c) part] is set to be included in the above frequency band, the natural frequency is stabilized, and even if the natural frequency is excited or resonated, it is divergent. The generation of vibrations is prevented.

(2) A second embodiment of the present invention is shown in FIG. In this example, as the delay filter 7, an amplification element 8 as shown in FIG. 5 and a second-order low-pass filter in which R and C are combined are used. The action and effect are almost the same as above.

Although the above is used for the thrust bearing 6,
It may be used for the radial bearing 6a.

[0036]

As described above, according to the present invention, the phase of the signal of the thrust position sensor is delayed by the lag filter and input to the control circuit. It is possible to provide a magnetic bearing control device that can change a stabilizing force to a stabilizing force (damping force), prevent divergent vibration from occurring, and stably float and hold a target shaft.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram of a delay filter of the same embodiment.

FIG. 3 is an explanatory view of the operation of the embodiment.

FIG. 4 is an explanatory view of the operation of the embodiment.

FIG. 5 is a circuit diagram of a delay filter according to a second embodiment of the present invention.

FIG. 6 is a configuration block diagram of a conventional example.

FIG. 7 is an operation explanatory view of the conventional example.

FIG. 8 is an explanatory diagram of a bearing portion of the conventional example.

[Explanation of symbols]

 1 Thrust position sensor 2 Gain circuit 3 Control circuit 4 Electromagnet 5 Rotating shaft 6 Thrust magnetic bearing 6a Radial magnetic bearing 7 Lag filter 8 Amplifying element C Capacitor element R Resistive element V1, V2 Filter input voltage and output voltage

Claims (1)

[Claims] 1. A position sensor for detecting a levitation position of a target shaft, a gain circuit for receiving an output of the position sensor, and a control circuit for receiving an output of the gain circuit and sending an excitation signal to a levitation electromagnet of the target shaft. A magnetic bearing control device having: a magnetic bearing control device, wherein a lag filter is provided between the gain circuit and the control circuit.