JPH05141421A - Control circuit for magnetic bearing - Google Patents

Abstract

PURPOSE:To enhance rigidity and a damping characteristic of a bearing by connecting a proportional circuit between a sensor circuit and a compensating circuit or between a compensating circuit and current amplifiers, and returning a signal output from the proportional circuit in a positive or a negative output to an input of the proportional circuit through a low pass filter secondary or further. CONSTITUTION:A displacement sensor 2 detects a displacement in the circumferential direction of a rotor as a voltage signal in forming a pair with a sensor converter 4. The obtained displacement signal is compared with a target value signal, to be input into a compensating circuit 5 as a target deviation signal (e). The compensating circuit 5 compensates stable lifting of the rotor. A signal obtained by returning an output from the compensating circuit 5 and an output from a proportional circuit 8 through a secondary low pass filter 9 is additionally input into the proportional circuit 8. Power amplifiers 7a, 7b control a current supplied to a magnetic bearing on the basis of the output from the proportional circuit 8, divided into a positive and a negative output by a switcher. Consequently, a gain is increased at a frequency not higher than a cut-off frequency of the filter 9 so that a high frequency gain can be relatively restrained, thus enhancing rigidity and a damping characteristic of the bearing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic levitation type rotor control device supported by magnetic bearings.

[0002]

2. Description of the Related Art A magnetic bearing of interest is an active magnetic bearing that supports a rotor in the air by the attractive force of electromagnets that face each other with the rotor in between. In order to stably support the rotor, it is necessary to constantly monitor the position of the rotor by a displacement sensor and control the electromagnetic force based on the displacement signal so that the rotor is stably supported. The compensation circuit is generally based on PID control.

FIG. 2 is a conceptual diagram of a radial bearing. 1 is a rotor, 2 is a displacement sensor, 3a and 3b are electromagnets, 4 is a displacement sensor converter, 5 is a compensation circuit, 6 is a switcher, 7
Reference numerals a and 7b are power amplifiers (current amplifiers).

[0004] Incidentally, the one related to the basic technology of this type of magnetic bearing is "Dynamics of electromagnetic force application equipment (Corona Publishing Co., Ltd., July 25, 1990, pp. 159-17.
6) ”

[0005]

In the compensating circuit for the magnetic bearing described above, if the phase lead amount or gain of the compensating circuit is increased in order to improve the rigidity or damping of the bearing, the higher order mode of the rotor becomes unstable. It may be oscillated and cause oscillation. This is because the gain of the open loop transfer function exceeds 0 dB in the higher-order mode portion of the rotor existing in the phase delay region.

In order to avoid such uncontrollability, it is sufficient to have a means capable of increasing the amount of phase advance and the gain for the low frequency mode while keeping the high frequency gain low.
Alternatively, a means for attenuating the high frequency gain without degrading the low frequency control performance may be used.

As a technique corresponding to the latter expression of the above demand, a method of attenuating a high frequency gain by a low pass filter has been conventionally performed, but the low pass filter is difficult to use because it also causes a phase delay. In Japanese Patent Laid-Open No. 21025/1990, the output of the compensator is input to a low-pass filter (second or higher) and a proportional circuit, and the signal obtained by adding the outputs of these circuits is input to a current amplifier to reduce the phase delay. We are devising a circuit that suppresses high frequency gain while keeping it to a minimum. In addition, as a technique corresponding to the latter expression of the above requirement, Nikkei Mechanical (198
4.10.22, p102 / 110) discloses a control circuit for increasing the phase advance at a specific frequency.

An object of the present invention is to provide a circuit which suppresses high frequency gain by a circuit configuration different from that of Japanese Patent Laid-Open No. 21025/1990.

[0009]

In order to achieve the above object, in the present invention, a proportional circuit is connected between a sensor circuit and a compensation circuit or between a compensation circuit and a current amplifier in a controller of a magnetic bearing device. Further, the output signal of the proportional circuit is positively fed back to the input of the proportional circuit through a second-order or higher-order low-pass filter.

[0010]

According to the object of the present invention, a proportional circuit is connected between the sensor circuit and the compensating circuit or between the compensating circuit and the current amplifier, and the output signal of the proportional circuit is passed through a low-pass filter of the second or higher order to obtain the proportional circuit. By positively feeding back to the input, the gain increases at low frequencies below the cutoff frequency of the low-pass filter, and the gain at relatively high frequencies is suppressed.

[0011]

FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, 11 is a magnetic bearing main body, the outline of which is shown in the block diagram of FIG. That is, the rotor is levitated and held by the electromagnetic force acting between the electromagnets 3a and 3b formed of the laminated core and the coil and the electromagnet fitted to the rotor 1 and the opposing laminated sleeve.

Reference numeral 2 denotes a displacement sensor, which is paired with the sensor converter 4 to detect the circumferential displacement of the rotor as a voltage signal. The displacement signal is compared with the target value signal and becomes a target deviation signal e, which is input to the compensation circuit 5. The compensating circuit 5 is a circuit for compensating the stable levitation of the rotor, and is composed of a PID control circuit or a phase lead / lag circuit.

A signal obtained by feeding back the output of the compensation circuit 5 and the output signal of the proportional circuit through the secondary low-pass filter 9 is added to the proportional circuit 8.

The power amplifiers 7a and 7b control the supply current of the magnetic bearing based on the output signal of the proportional circuit 8 which is divided into positive and negative by the switcher.

In the proportional circuit 8, the gain of the proportional circuit is kp, and the transfer function of the secondary low-pass filter 9 is

[0016]

[Equation 1]

Then, the total transfer function of the circuit composed of the proportional circuit and the second-order low-pass filter is

[0018]

[Equation 2]

It becomes In the above equation, the zero point is the pole of the second-order low-pass filter.

In Expression 2, kl> 0 (where kp · k
l <1), that is, when the output signal of the second-order low-pass filter is positively fed back, as shown in FIG. 3, the pole has a frequency lower than the zero point, and the high frequency gain is lower than the low frequency gain. Get lower. Therefore, the gain can be reduced for higher-order modes with a small stability margin,
Improves stability.

In the equation 2, kl <0, that is,
When the output signal of the secondary low-pass filter is negatively fed back, the pole has a frequency higher than the zero point as shown in FIG. 4, and the phase advance locally increases in the frequency range between the zero point and the pole. By adjusting the area of this phase lead to the critical speed of the rotor, stable passage of the critical speed can be realized.

Further, two different circuits for different purposes are separately constructed and connected in series,
It is possible to realize a control circuit that achieves both prevention of higher-order mode oscillation and stable passage of dangerous speed.

[0023]

By suppressing the high frequency gain of the control signal of the magnetic bearing according to the present invention, the stability margin of the higher order mode is increased, so that the bearing rigidity or damping property can be improved more than before.

Further, according to the present invention, if a phase lead is locally applied to the eigenmode of the rotor in the control signal of the magnetic bearing, the damping characteristic of the eigenmode is improved, the vibration is reduced, and the control current is also reduced.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram of a radial bearing.

FIG. 3 is a Bode diagram of the circuit of the present invention.

FIG. 4 is a Bode diagram of the circuit of the present invention.

[Explanation of symbols]

1 ... Rotor, 2 ... Displacement sensor, 4 ... Sensor converter, 5 ...
Compensation circuit, 6 ... Switcher, 7a, 7b ... Power amplifier, 8 ... Proportional circuit, 9 ... Secondary low-pass filter, 11 ...
Magnetic bearing body.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshima Minor 603 Jinritsu-cho, Tsuchiura-shi, Ibaraki Hiritsu Manufacturing Co., Ltd. Tsuchiura Plant (72) Inventor Mitsuho Yoneyama 603 Jinritsu-cho, Tsuchiura-shi, Ibaraki Hiritsu Manufacturing Co., Ltd. Inside the Tsuchiura Factory (72) Inventor Naofumi Sakanashi 603, Jinrachicho, Tsuchiura City, Ibaraki Prefecture

Claims (1)

[Claims] 1. A displacement sensor for detecting a displacement of an electromagnet and a rotor arranged so as to exert a force in a direction opposite to the rotor, a compensation circuit for processing an output signal of the displacement sensor, and the compensation. In a control device for a magnetic bearing device, comprising a current amplifier for controlling an electromagnetic force of the electromagnet based on an output signal of the circuit, a proportional relation is provided between a sensor circuit and the compensation circuit or between the compensation circuit and the current amplifier. A control device for a magnetic bearing, characterized in that a circuit is connected and an output signal of the proportional circuit is fed back positively or negatively to an input of the proportional circuit through a second-order or higher-order low-pass filter.