KR100928551B1 - Capacitance Measuring Displacement Sensor Structure and It's Transducer for Radial Active Magnetic Bearing - Google Patents

Abstract

The present invention relates to a cylindrical radial displacement measurement system of magnetic bearings using capacitance and a method of determining whether there is a failure, and more particularly, to establish a double shielded displacement measurement sensor to improve accuracy compared to conventional systems. Cylindrical radial displacement measuring system using magnetic capacitance, which can provide robust characteristics to surge noise, etc., and also improves the function of the transducer so as to determine the presence and failure of magnetic bearing, and It relates to a method of determining whether there is a failure.

To this end, the present invention includes a rotor for providing a virtual ground, and four cylindrical sensor electrode faces spaced apart from the circumferential surface of the rotor with a gap therebetween; A guard electrode surrounding the sensor electrode surface and disposed outside thereof; A signal ground plane disposed outside of the guard electrode for grounding of the sensing signal; A stator body disposed outside the signal ground plane for a power grounding role; A transducer connected to each sensor electrode surface and a sensor electrode; A magnetic bearing controller which receives the signal of the transducer and controls the magnetic bearing; A magnetic bearing driver and a motor drive inverter for driving the magnetic bearing; It provides a cylindrical radial displacement measurement system of the magnetic bearing using the capacitance characterized in that it comprises a and a method of determining the failure thereof.

Magnetic Bearing, Cylindrical, Radial, Displacement Measurement, System, Failure, Sensor Electrode, Guard Electrode, Signal Cell, Transducer, Capacitance

Description

Capacitance Measuring Displacement Sensor Structure and It's Transducer for Radial Active Magnetic Bearing}

The present invention relates to a cylindrical radial displacement measurement system of magnetic bearings using capacitance and a method of determining whether there is a failure, and more particularly, to establish a double shielded displacement measurement sensor to improve accuracy compared to conventional systems. Cylindrical radial displacement measuring system using magnetic capacitance, which can provide robust characteristics to surge noise, etc., and also improves the function of the transducer so as to determine the presence and failure of magnetic bearing, and It relates to a method of determining whether there is a failure.

As feedback sensors for controlling magnetic bearings, leakage flux sensors, inductive sensors, and capacitive sensors are widely used, and in particular, capacitive sensors have strong advantages such as magnetic field noise. Among them, cylindrical capacitive sensors are rotors. Since there is an advantage of reducing the shape error of the, it can be applied more suitably in a rotating body such as a magnetic bearing.

The conventional cylindrical capacitive displacement sensor structure using capacitance is as shown in FIG.

As shown in FIG. 1, the conventional cylindrical magnetic bearing displacement measuring sensor using capacitance has four cylindrical sensor electrode surfaces 110, 111, 112, and 113, a guard electrode 120 surrounding the sensor electrode surfaces, and serves as a virtual ground. It is composed of a stator body 300 that serves as a ground of the rotor 200 and the sensor signal.

Each of the sensor electrode surfaces 110, 111, 112, and 113 and the guard electrode 120 may be integrally fixed to the inner diameter of the stator body 300 by molding means 140 (eg, an epoxy resin). The inner surface of the sensor electrode surface is maintained at a constant distance from the rotor 200.

In this case, the sensor electrode 160 is connected to each of the sensor electrode surfaces 110, 111, 112, and 113, and each sensor electrode 160 is connected to the transducer 500 so as to transmit a signal.

In addition, a magnetic bearing controller 600 for receiving a signal from the transducer 500 to control the magnetic bearing is connected to the output side of the transducer 500, the output side of the magnetic bearing controller 600 of the magnetic bearing The magnetic bearing driver 700 for driving is connected to enable signal transmission.

Meanwhile, reference numeral 800 in FIG. 1 designates a motor driving inverter.

In the conventional cylindrical capacitive displacement sensor structure, when the rotor stator body 300 serves as a ground of a sensing signal by the sensor electrode surfaces 110, 111, 112, and 113 and the sensor electrode 160, the transducer 500 may be used. Although there is less leakage between the sensor electrode and the sensor electrode 160, the accuracy of the sensor measurement is improved, but since the sensing signal ground and the power ground 310 are made in the stator body 300 in the same manner, a rotator system including magnetic bearings. Motor driving inverter 700, magnetic bearing driver 800, rotating machine (not shown), power transformer and filter (not shown), rectifier (not shown), ground wire (not shown), etc. There is a disadvantage that is vulnerable to noise.

In brief description of the sensing operation of the conventional cylindrical capacitive displacement sensor, a pulsed voltage of several tens of kHz to several thousand kHz is applied to each of the sensor electrode surfaces 110, 111, 112, and 113 and the guard electrode 120 based on the ground of the rotor stator body 300. The charge and discharge current is generated in the air gap 150 between each of the sensor electrodes 110, 111, 112, and 113 and the rotor 200 forming the virtual ground, thereby measuring the discharge current generated to obtain the capacitance.

Although a high bandwidth switching measurement can be obtained through such a high speed switching technique, the switch element constituting the transducer 500 and its internal components act as a large stress.

In particular, the stator frame, that is, the ground of the stator body 300 is connected to a power ground that is commonly connected to other rotors or power converters in the industrial field, and therefore is always exposed to surge noise. Each component in the transducer 500 may be destroyed or malfunction, resulting in inaccurate measurement of the displacement and thus unstable magnetic bearing system.

The present invention has been made to solve the above-mentioned problems of the conventional displacement measuring sensor, a rotor for providing a virtual ground, a sensor electrode surface spaced apart from the circumferential surface of the rotor, this sensor electrode surface And a guard electrode disposed to surround the sensing electrode, and a signal ground plane disposed outside of the guard electrode for grounding of the sensing signal, so that the sensing signal is electrically disconnected from the power ground line through which the noise passes. In the functional structure of the transducer for displacement measurement, it is possible to reduce the noise effect transmitted from an accompanying inverter, a rotator, a magnetic bearing driver, and the like. After this has been removed, the power outage is differentially amplified and compared to improve the accuracy of the sensor. It is an object of the present invention to provide a cylindrical radial displacement measurement system of a magnetic bearing using a capacity.

Another object of the present invention is to improve the function of the transducer, by comparing the displacement measurement results measured in the two coordinate axes in the 45 ° rotation conversion relationship, the power failure can easily determine the presence and failure location of the magnetic bearing sensor The present invention provides a method for determining a failure of a cylindrical radial displacement measuring system of a magnetic bearing using a capacity.

One embodiment of the present invention for achieving the above object is:

A rotor providing a virtual ground; Four cylindrical sensor electrode surfaces spaced apart from the circumferential surface of the rotor with a gap therebetween; A guard electrode surrounding the sensor electrode surface and disposed outside thereof; A signal ground plane disposed outside the guard electrode and surrounding the sensor electrode surface and the guard electrode surface to present a reference of the measurement signal; A stator body disposed outside the signal ground plane serving as a ground of the power device; A transducer connected to a sensor electrode, a guard electrode, a signal ground, and a shielded cable of each of the sensors; A magnetic bearing controller which receives the signal of the transducer and controls the magnetic bearing; A magnetic bearing driver and a motor drive inverter for driving the magnetic bearing; It provides a cylindrical radial displacement measurement system of a magnetic bearing using the capacitance, characterized in that configured to include.

In one preferred embodiment, the transducer comprises: a capacitance measuring circuit for measuring actual capacitance by receiving a detection signal measuring capacitance between each sensor electrode surface and the rotor; An offset adjuster for removing the DC component of the measured capacitance; A differential amplifier for differentially amplifying four-way displacement information of each capacitance from which the DC component is removed; Characterized in that configured to include.

In a preferred embodiment, a low pass filter and a notch filter are connected between the signal ground line of the transducer and the power ground line connected to the stator body.

Another embodiment of the present invention for achieving the above object comprises the steps of: detecting capacitance between four cylindrical sensor electrode surfaces and a rotor; Calculating an actual capacitance in the capacitance measuring circuit based on the detected capacitance measuring signal; Removing the DC component of the calculated capacitance in the offset adjuster; Differentially amplifying, in the differential amplifier, four-way displacement information of the capacitance from which the DC component has been removed; Displacement measured in two coordinate axes in a 45 ° rotation conversion relationship by extracting displacement information in a desired direction from four-direction displacement information ( X ₁ , Y ₁ , X ₂ , Y ₂ ) obtained by differential amplification by the differential amplifier. Comparing the values [ X ₁ , Y ₁ ] ^T and [ X ₂ , Y ₂ ] ^T ; The present invention provides a method for determining a failure of a cylindrical radial displacement measuring system of a magnetic bearing using capacitance, characterized in that it is possible to determine a failure state and a failure position of a magnetic bearing sensor.

In another preferred embodiment, the displacement values [ X ₁ , Y ₁ ] ^T and [ X ₁ , Y ₁ ] ^T measured at two coordinate axes in a 45 ° rotation conversion relationship are obtained from Equations 1 and 2 below. It features.

Equation 1

Equation 2

In Equation 1, C ₁ , C ₂ , C ₃ , and C ₄ represent capacitances measured by the respective sensors, and X ₁ and Y ₁ represent displacements of the rotor 200 in the X ₁ - Y ₁ coordinate system. And X ₂ and Y ₂ represent rotor displacements in X ₂ - Y ₂ axial directions.

Equation 2 above represents the displacement [ X ₁ , Y ₁ ] ^{T as seen} from the X ₂ - Y ₂ coordinate system [ X ' ₁ , Y' ₁ ] ^T.

In another preferred embodiment, if the value of [ X ' ₁ , Y' ₁ ] ^{T and} the value of [ X ₂ , Y ₂ ] ^T coincide with very small errors according to Equations 1 and ₂ , the sensor is normal. It is determined by the state, and if there is a mismatch while having a large error, it is characterized by determining that a specific sensor has failed.

Through the above problem solving means, the present invention can provide the following effects.

Compared with the cylindrical radial displacement measurement system of the magnetic bearing using the capacitance, it is possible to improve the measurement accuracy, robust to noise, etc., and to provide reliability against failure.

That is, the system is electrically disconnected from the power ground through which noise passes through a sensor structure including a rotor providing a virtual ground, a sensor electrode surface, a guard electrode surface, and a signal ground surface for grounding a sensing signal. It provides an advantage that it can withstand the noise transmitted from the inverter, rotator, etc. constituting.

In addition, in the functional structure of the transducer connected to each sensor electrode surface, the capacitance value measured by the four sensors stops the offset adjuster, the DC component is removed, and then differentially amplified and compared, thereby improving the accuracy of the sensor. have.

In addition, by comparing the displacement measurement results measured in the two coordinate axes in the 45 ° rotation conversion relationship, it is possible to easily determine whether the magnetic bearing sensor has a failure and the location of the failure.

As a result, the cylindrical radial displacement sensor system using the capacitance of the present invention improves the precision of the displacement sensor system, is robust against noise such as surge, and increases the reliability of sensor failure, thereby ultimately expanding the magnetic bearing system. Can contribute to dissemination.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As is well known, the cylindrical radial displacement measuring sensor and the transducer connected thereto play an important role in stabilizing the magnetic bearing system by feeding back the displacement information of the rotor to the controller of the magnetic bearing.

For the reliability and performance of magnetic bearing systems, displacement measuring sensors and transducers require high displacement accuracy, high reliability against failure, and robust characteristics that can withstand noise, and also have high displacement accuracy and robust noise structure. And, it is required to be able to easily grasp the presence and failure of the sensor failure location.

Therefore, the first aspect of the present invention is composed of a signal ground plane disposed for the grounding of the sensing signal on the outside of the guard electrode, so that the sensing signal is electrically disconnected from the power ground line through which the noise passes, thereby accompanying the entire rotor system This is to reduce the effects of noise transmitted from an inverter, a rotor, a magnetic bearing driver and the like.

In the second aspect of the present invention, in the case of a two-dimensional displacement sensor having four sensor electrodes, a failure occurs in only one sensor, in order to affect the feedback of the magnetic bearing and make the system unstable and improve reliability of the failure. Considering the fact that adding additional sensors increases the price of the sensor system, in order to provide a sensor system for self-diagnosis without additional addition of sensors, the function logic of the transducer is improved to improve the four sensors. From the information detected by the two-dimensional displacement sensor having an electrode surface, that is, the capacitance information between the four sensor plates (sensor electrode surface) and the rotating shaft (rotor), a displacement is obtained in two rectangular coordinate systems spaced at 45 ° intervals. By comparing the measured values obtained from each coordinate axis, it is possible to determine whether the magnetic bearing sensor is faulty and the fault position. The.

As a system of the present invention for this purpose, a cylindrical radial displacement measuring system configuration of a magnetic bearing comprising a cylindrical radial displacement measuring sensor and a transducer using capacitance is as shown in FIG.

As shown in FIG. 2, the cylindrical magnetic bearing displacement measuring sensor according to the present invention includes four rotors 200 spaced apart from each other with a rotor 200 providing a virtual ground and a circumferential surface of the rotor and a space 150 therebetween. Cylindrical sensor electrode surfaces 110, 111, 112, and 113, guard electrodes 120 surrounding the sensor electrode surfaces 110, 111, 112, and 113 and disposed outside thereof, and signal ground planes 130 disposed outside the guard electrodes for grounding of the sensing signal. And a stator body 300 disposed outside the signal ground plane 130 to serve as a power ground.

In this case, each of the sensor electrode surfaces 110, 111, 112, 113, the guard electrode 120, and the signal ground surface 130 are integrally formed with the inner diameter of the stator body 300 by molding means 140 (for example, epoxy resin). The inner surface of each sensor electrode surface is maintained at a constant distance from the rotor 200 with the gap 150 therebetween.

In addition, the sensor electrode 160 is connected to each of the sensor electrode surfaces 110, 111, 112, and 113, and each sensor electrode 160 is connected to the transducer 500 so as to transmit a signal.

In addition, a magnetic bearing controller 600 that receives the signal of the transducer 500 to control the magnetic bearing is connected to the output side of the transducer 500, the drive of the magnetic bearing on the output side of the magnetic bearing controller 600 The magnetic bearing driver 800 for the signal transmission is connected, the reference numeral 700 in FIG. 2 indicates a motor drive inverter.

In the configuration of the displacement measurement system of the present invention, since the power source and the signal source are separated from each other, a complete noncontact can be achieved, thereby providing a stable and robust advantage in disturbances such as external noise in the form of surge.

That is, unlike the conventional grounding of the power supply and the signal power is made in the stator body 300, as the ground of each sensor electrode surface (110, 111, 112, 113) is made in the signal ground plane 130, The signal power is separated from each other, resulting in a complete non-contact, thus releasing the noise effects transmitted to the power ground line from the inverter, rotor, magnetic bearing driver, etc. included in the overall rotor system configuration.

In addition, the signal ground of the transducer 500 and the power ground connected to the stator body 300 of the rotor are connected to each other through a filter 311 (low pass and notch filter), thereby facilitating the measuring operation of the transducer. In doing so, it is possible to block noise such as surge from being transmitted to the transducer 500.

FIG. 3 is a functional block diagram of a transducer connected to a cylindrical radial displacement measurement sensor using capacitance according to the present invention, wherein the transducer 500 includes four cylindrical sensor electrode surfaces 110, 111, 112, and 113 and a rotor 200. Capacitive for measuring actual capacitance based on the detection signal of the capacitive displacement sensor 100 measuring the capacitance between the electrodes, that is, the capacitance measurement signal transmitted from the sensor electrode surfaces 110, 111, 112, and 113 and the sensor electrode 160. Measuring circuit 510; An offset adjuster 520 which serves to remove the DC component of the capacitance; And a differential amplifier 530 which differentially amplifies four-way displacement information.

As described above, the cylindrical radial displacement measurement system of the magnetic bearing using the capacitance of the present invention includes the sensor electrode surface (110, 111, 112, 113) and the guard electrode surface 120, and the signal electrode surface, that is, the signal ground surface 130 In general, the capacitance between the sensor electrode surfaces 110, 111, 112, and 113 and the rotor 200 is designed to be several pF to several hundred pF.

delete

On the other hand, since the differential amplifier 530 using the differential amplifier circuit is used in the displacement measuring system of the present invention, the final measured displacement is not proportional to the capacitance itself but to the amount of change in the capacitance.

Therefore, in order to obtain accurate displacement information, it is necessary to remove a DC component having a relatively large value from the measured charge amount and extract only an AC component proportional to the rotor displacement.

In order to extract only such an AC component, the offset adjuster 520 serves to remove the DC component of the capacitance.

The differential amplifier 530 extracts the displacement information in the desired direction from the differential information X ₁ , Y ₁ , X ₂ , and Y ₂ obtained by differential amplification, and the displacement information is a sensor for diagnosing a failure. By comparing the displacement values [ X ₁ , Y ₁ ] ^T and [ X ₂ , Y ₂ ] ^T which are output to the output terminal 540 and measured in two coordinate axes in a 45 ° rotation conversion relationship, the presence of a failure of the magnetic bearing sensor and The fault location can be determined.

Here, the logic for determining the presence or absence of a failure of the magnetic bearing sensor and the failure location will be described in detail.

4 is a conceptual diagram of sensor output stage logic capable of determining whether a magnetic bearing sensor has a failure and a failure position.

The displacement values [ X ₁ , Y ₁ ] ^T and [ X ₂ , Y ₂ ] ^T measured at two coordinate axes in a 45 ° rotation conversion relationship are obtained from the following equation.

However, in the above formula, C ₁ , C ₂ , C ₃ , and C ₄ represent the capacitance measured by each sensor.
Gain1 is a value determined by the design dimension of the capacitance sensor (exact equation is Gain1 = 1/2 * ε ₀ * A, where ε ₀ is the dielectric constant of air and A is one electrostatic Cross-sectional area of the capacitive sensor).
In addition, Gain2 = k * Gain1, where k is a correction constant for correcting a displacement magnitude.

X ₁ and Y ₁ represent the displacement of the rotor 200 in the X ₁ - Y ₁ coordinate system, and X ₂ and Y ₂ represent the displacement of the rotor 200 in the X ₂ - Y ₂ coordinate system.

이 된다.In this case, the displacement [ X ₁ , Y ₁ ] ^T in X ₂ - Y ₂ coordinate system [ X ' ₁ , Y' ₁ ] ^T is

Becomes

는 45°좌표축 회전 변환행렬을 나타낸다.
위의 수식에 의거, [X' ₁, Y' ₁] ^T 의 값과 [X ₂, Y ₂] ^T 의 값이 일치하면 센서를 정상 상태로 판별하고, 불일치할 경우에는 센서가 고장난 것으로 판별한다. The above equation converts the X ₁ - Y ₁ coordinate system displacement [ X ₁ , Y ₁ ] ^T by 45 ° to obtain a value [ X ' ₁ , Y' ₁ ] ^T seen in the X ₂ - Y ₂ coordinate system. Represents a formula.
Rot (45 °) =

Denotes a 45 ° coordinate axis rotation transformation matrix.
According to the above formula, if the value of [ X ' ₁ , Y' ₁ ] ^{T and} the value of [ X ₂ , Y ₂ ] ^T coincide, the sensor is regarded as a normal state. .

Here, the operation principle of the capacitance measuring circuit 510 for measuring capacitance between the four cylindrical sensor electrodes 110, 111, 112, and 113 and the rotor 200 will be described with reference to FIG. 5.

FIG. 5 shows a voltage pattern applied to each of the sensor electrode surfaces 110, 111, 112, and 113 and the guard electrode surface 120, and a pattern of charge / discharge currents generated at that time, and the sample period T is proportional to the magnitude of the capacitance.

Referring to the operation principle, a gap between the sensor electrode surfaces 110, 111, 112, 113 and the rotor 200 acting as a virtual ground by applying a DC voltage to the sensor electrode surfaces 110, 111, 112, 113 and the guard electrode surface 120 at the same time ( 150 to form an electrostatic field of uniform density.

Thus, after a certain time when the electrostatic field is completely formed, the guard electrode surface 120 is short-circuited with the signal ground surface 130, so that the amount of charge accumulated on the guard electrode surface is zero.

Thereafter, the sensor electrode surfaces 110, 111, 112, and 113 and the signal ground plane 130 are short-circuited. At this time, the amount of charge accumulated on the sensor electrodes 110, 111, 112, and 113 is detected to obtain a corrected capacitance. Can be obtained by

6 is a circuit diagram of an internal block diagram of a transducer in a radial displacement measurement system configuration using capacitance according to the present invention.

The transducer 500 measures capacitance based on a capacitance measurement signal of a capacitance displacement sensor 100 measuring capacitance between four cylindrical sensor electrodes 110, 111, 112, and 113 and the rotor 200. A capacitance measuring circuit 510; An offset adjuster 520 which serves to remove the DC component of the capacitance; And a differential amplifier 530 for differentially amplifying four-way displacement information. The circuit for integrating the discharge current of the capacitance measuring circuit 510 uses an integrator using OP-Amp, and the offset adjuster 520. The inverted amplifier circuit of the OP-Amp is used, and the differential amplifier 530 is also configured using the OP-Amp.

As described above, the cylindrical radial displacement sensor system using the capacitance according to the present invention separates the ground of the sensing signal to improve the accuracy of the sensing signal, and can withstand noise such as surge, and also the function of the transducer. Newly improved can easily identify the failure of the magnetic bearing sensor can increase the reliability of the failure.

1 is a configuration diagram showing a displacement measuring system of a conventional cylindrical magnetic bearing using capacitance;

2 is a block diagram showing a cylindrical radial displacement measurement system using the capacitance according to the present invention,

3 is a functional block diagram of a transducer in the configuration of a cylindrical radial displacement measurement system using capacitance in accordance with the present invention;

4 is a conceptual diagram illustrating logic capable of determining a failure state and a failure position of a magnetic bearing sensor in a cylindrical radial displacement measurement system configuration using capacitance according to the present invention;

5 is an operation principle of the capacitance measurement circuit of the transducer in the configuration of the cylindrical radial displacement measurement system using the capacitance according to the present invention, the voltage pattern and the charge / discharge current pattern applied to each sensor electrode surface and the guard electrode surface Graph representing,

6 is a circuit diagram showing an example of the configuration of the transducer in the configuration of the cylindrical radial displacement measurement system using the capacitance according to the present invention.

<Explanation of symbols for the main parts of the drawings>

110, 111, 112, 113: sensor electrode surface 120: guard electrode

130: signal ground plane 140: molding means

150: void 160: sensor electrode

200: rotor 300: stator body

311: filter (low pass filter and notch filter)

500: transducer 510: capacitance measurement circuit

520: offset adjuster 530: differential amplifier

540: sensor output stage 600: magnetic bearing controller

700: motor drive inverter 800: magnetic bearing driver

Claims (6)

A rotor 200 providing a virtual ground; Four cylindrical sensor electrode surfaces (110,111,112,113) spaced apart from each other with a circumferential surface of the rotor (200) therebetween; A guard electrode 120 surrounding the sensor electrode surfaces 110, 111, 112, and 113 and disposed outside thereof; A signal ground surface 130 disposed outside the guard electrode 120 and surrounding the sensor electrode surfaces 110, 111, 112, and 113 and the guard electrode surface to present a reference of a measurement signal; A stator body 300 disposed outside the signal ground plane 130 serving as a ground of the power device; A transducer (500) connected to the sensor electrodes (160), guard electrodes (120), signal grounds and shielded cables of the sensors; A magnetic bearing controller 600 which receives the signal of the transducer 500 and controls the magnetic bearing; A magnetic bearing driver 800 and a motor driving inverter 700 for driving the magnetic bearing; Cylindrical radial displacement measurement system of a magnetic bearing using the capacitance, characterized in that configured to include. The method of claim 1, wherein the transducer 500 is: A capacitance measuring circuit 510 for receiving a detection signal measuring capacitance between the sensor electrode surfaces 110, 111, 112, and 113 and the rotor 200 to measure actual capacitance; An offset adjuster 520 for removing the DC component of the measured capacitance; A differential amplifier 530 which differentially amplifies four-way displacement information of each capacitance from which the DC component is removed; Cylindrical radial displacement measurement system of a magnetic bearing using the capacitance, characterized in that configured to include. The capacitance of claim 1 or 2, wherein a low pass filter and a notch filter 311 are connected between the signal ground line of the transducer 500 and the power ground line connected to the stator body 300. Cylindrical radial displacement measuring system of a magnetic bearing using a. Detecting the capacitance between the four cylindrical sensor electrodes (110, 111, 112, 113) and the rotor (200); Calculating an actual capacitance in the capacitance measuring circuit 510 based on the detected capacitance measuring signal; Removing at the offset adjuster 520 the DC component of the calculated capacitance; Differentially amplifying, in the differential amplifier 530, four-way displacement information of the capacitance from which the DC component has been removed; The differential amplifier 530 extracts displacement information in a desired direction from the displacement information ( X ₁ , Y ₁ , X ₂ , Y ₂ ) obtained by differential amplification at the two coordinate axes in a 45 ° rotation conversion relationship. Comparing the measured displacement values [ X ₁ , Y ₁ ] ^T and [ X ₂ , Y ₂ ] ^T ; Method for determining the failure of the cylindrical radial displacement measurement system of the magnetic bearing using the capacitance characterized in that it is possible to determine the failure and the location of the failure of the magnetic bearing sensor through. The method according to claim 4, The displacement values [ X ₁ , Y ₁ ] ^T and [ X ₁ , Y ₁ ] ^T measured at two coordinate axes in a 45 ° rotation transformation relationship are obtained from the capacitances 1 and 2 below. Method for determining the failure of the cylindrical radial displacement measuring system of the magnetic bearings used. Equation 1

Equation 2

In Equation 1, C ₁ , C ₂ , C ₃ , and C ₄ represent capacitances measured by the respective sensors, and X ₁ and Y ₁ represent displacements of the rotor 200 in the X ₁ - Y ₁ coordinate system. X ₂ and Y ₂ represent the displacement of the rotor 200 in the X ₂ - Y ₂ coordinate system. Gain1 is a value determined by the design dimension of the capacitive sensor (exact equation is Gain1 = 1/2 * ε ₀ * A, where ε ₀ is the dielectric constant of air and A is one electrostatic Cross-sectional area of the capacitive sensor). In addition, Gain2 = k * Gain1, where k is a correction constant for correcting a displacement magnitude. Equation 2 above converts the X ₁ - Y ₁ coordinate system displacement [ X ₁ , Y ₁ ] ^T by 45 ° to convert the value [ X ' ₁ , Y' ₁ ] ^T seen in the X ₂ - Y ₂ coordinate system. The equation to be obtained is shown. Rot (45 °) =

Denotes a 45 ° coordinate axis rotation transformation matrix. The method according to claim 5, According to Equation 1 and Equation 2, if the value of [ X ' ₁ , Y' ₁ ] ^{T and} the value of [ X ₂ , Y ₂ ] ^T coincide, the sensor is determined to be in a normal state. Method for determining whether there is a failure of the cylindrical radial displacement measuring system of the magnetic bearing using the capacitance characterized in that it is determined.

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