Axial Suspension Position Control Method of Magnetic Levitation Motor Based on Axial Magnetic Bearing Current

Abstract

The present invention belongs to the technical field of magnetic levitation bearings, and particularly relates to a method for controlling the axial suspension position of a magnetic levitation motor based on the current of an axial magnetic bearing, comprising the following steps: establishing two arrays in a control algorithm respectively for storing the current signals in the coils of the axial magnetic bearings on both sides; calibrating the axial displacement sensor and storing the calibration data before controlling the rotor to levitate, and then performing static levitation; sampling the current in the coils of the axial magnetic bearings in each control cycle and storing it in the array; calculating the average values of the current signals in the two arrays respectively, and performing a difference operation on the two average values; when the absolute value of the difference between the average values is less than a set threshold, the process of self-seeking the suspension center position ends; when the absolute value of the difference between the average values is greater than the threshold, it is judged whether the adjusted suspension position reference value exceeds the adjustment range. When it exceeds the adjustment range, the process of self-seeking the suspension center position ends. When it does not exceed, the suspension position reference value is adjusted.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetic levitation bearings, and particularly relates to a method for controlling the axial suspension position of a magnetic levitation motor based on the current of an axial magnetic bearing. Background Technique

[0002] The active magnetic levitation bearing system suspends the rotor in the middle of the stator magnetic poles through a controllable electromagnetic force, so it has the advantages of no friction, no lubrication, no pollution, high speed, long life, etc. At present, the active magnetic levitation bearing has been used as an advanced mechatronic product and has been applied to a certain extent in the industrial field, such as gyroscopes, high-speed motors, bearingless motors, aeroengines, artificial heart pumps, and distributed generation systems.

[0003] The magnetic levitation motor is a high-speed permanent magnet synchronous motor using magnetic levitation bearings as supports. The magnetic levitation bearings support the rotor, and the high-speed motor drives the rotor to rotate at high speed. A thrust disk is usually installed on the rotor of the magnetic levitation motor, and two axial magnetic levitation bearings are arranged on both sides of the thrust disk in the stator. During the assembly process of the magnetic levitation motor, it is usually necessary to adjust the axial protection gap to ensure that when the rotor is normally suspended, the thrust disk is in the middle of the magnetic levitation bearings of the bearings, so as to avoid the excessive wind friction loss and the possible rubbing between the thrust disk and the magnetic bearings caused by thermal expansion and other reasons during normal operation.

[0004] In the prior art, due to the existence of machining and assembly errors, it is difficult to ensure that the center of the protection bearing protection gap coincides with the center of the axial air gap between the axial magnetic levitation bearings. Therefore, after calibrating the axial displacement sensor based on the axial gap of the protection bearing, after suspension, the thrust disk will be in the middle of the protection gap, rather than in the middle of the axial magnetic levitation bearings. When it is difficult to ensure that the thrust disk is suspended at the center position of the axial magnetic levitation bearing after calibrating the displacement sensor, the thrust disk is too close to the stator of the axial magnetic levitation bearing, which will lead to an increase in wind friction loss, cause the thrust disk and the axial magnetic levitation bearing to heat up, and further increase the risk of rubbing, affecting the stability of the control system. Summary of the Invention

[0005] In view of the above deficiencies, the purpose of the present invention is to provide a method for controlling the axial suspension position of a magnetic levitation motor based on the current of an axial magnetic bearing.

[0006] The present invention provides the following technical solutions:

[0007] A method for controlling the axial suspension position of a magnetic levitation motor based on the current of an axial magnetic bearing, comprising the following steps:

[0008] S1. The magnetic levitation bearing controller adds a self-finding axial center position control module;

[0009] S2. In the control algorithm, establish two arrays respectively used to store the current signals in the coils of the axial magnetic bearings on both sides;

[0010] S3. Calibrate the axial displacement sensor and store the calibration data before controlling the rotor to levitate, and then perform static levitation according to the central position calibrated by the axial displacement sensor;

[0011] S4. Sample the currents in the axial magnetic bearing coils on both sides in each control period and store them in the corresponding arrays; the values in the arrays are updated according to the principle of first-in first-out;

[0012] S5. Calculate the average values of the current signals in the two arrays respectively, and perform a subtraction operation on the two average values;

[0013] S6. When the absolute value of the difference between the average values is less than the set threshold, the process of self-seeking the levitation center position ends; when the absolute value of the difference between the average values is greater than the threshold, proceed to the next step;

[0014] S7. Judge whether the adjusted levitation position reference value exceeds the adjustment range. When it exceeds the adjustment range, the process of self-seeking the levitation center position ends. When it does not exceed, proceed to the next step;

[0015] S8. Adjust the levitation position reference value, and then return to S4.

[0016] Specifically, the threshold is 100 mA.

[0017] Specifically, in S8, within each control period, the levitation position reference value is adjusted by 2 μm towards the side with a smaller average value of the current signal in the axial magnetic bearing coil.

[0018] Specifically, in S7, 25% of the set axial protection gap is set as the maximum adjustment range.

[0019] The beneficial effect of the present invention is that during static levitation, if the thrust disk is in the middle of the axial magnetic levitation bearing, due to the complete symmetry of the two axial magnetic levitation bearings on both sides, when the air gaps are the same and there is no axial force, the currents flowing through the two axial magnetic bearing coils should be equal. The present invention can adjust the levitation position of the thrust disk based on the current flowing through the axial magnetic levitation bearing coil in real time, so as to ensure that the thrust disk is at the center position of the axial magnetic bearing stator during static levitation. Description of the Drawings

[0020] Figure 1 is the flow chart of the present invention;

[0021] Figure 2 is the cross-sectional view of the magnetic levitation motor.

[0022] The labels in the figure are: axial magnetic levitation bearing 102, thrust disk 103, radial magnetic levitation bearing 104, motor stator 105, displacement sensor 106, protection bearing 107, axial protection gap 108, axial air gap 109, rotor 110. Detailed implementation mode

[0023] As Figure 2 shown, inside the magnetic levitation motor, the rotor 110 is supported by the radial magnetic levitation bearing 104, and the high-speed motor drives the rotor 101 to rotate at high speed. A thrust disk 103 is installed on the rotor 110, and two axial magnetic levitation bearings 102 are arranged on both sides of the thrust disk 103 in the motor stator 105. A displacement sensor 106 and a protection bearing 107 are also installed inside the motor stator 105. An axial protection gap 108 is formed between the protection bearings 107, and an axial air gap 109 is formed between the axial magnetic levitation bearings 102.

[0024] As Figure 1 shown, a method for controlling the axial suspension position of a magnetic levitation motor based on the current of an axial magnetic bearing is characterized by including the following steps:

[0025] S1. The magnetic levitation bearing controller adds a self-seeking axial center position control module;

[0026] S2. In the control algorithm, two arrays are established to store the current signals in the coils of the axial magnetic bearings on both sides respectively;

[0027] S3. Before controlling the rotor to levitate, calibrate the axial displacement sensor and store the calibration data, and then perform static levitation according to the center position calibrated by the axial displacement sensor;

[0028] S4. Sample the current in the coils of the axial magnetic bearings on both sides in each control cycle and store it in the corresponding array; the values in the array are updated according to the principle of first in first out;

[0029] S5. Calculate the average values of the current signals in the two arrays respectively, and perform a difference operation on the two average values;

[0030] S6. When the absolute value of the difference between the average values is less than the set threshold, the process of self-seeking the levitation center position ends; when the absolute value of the difference between the average values is greater than the threshold, go to the next step; specifically, the threshold is 100 mA;

[0031] S7. Judge whether the adjusted suspension position reference value exceeds the adjustment range; specifically, set 25% of the axial protection gap as the maximum adjustment range; when it exceeds the adjustment range, the process of self-seeking the levitation center position ends, and when it does not exceed, go to the next step;

[0032] S8. Adjust the suspension position reference value, and then return to S4; specifically, in each control cycle, the suspension position reference value is adjusted 2 μm to the side with a smaller average value of the current signal in the coil of the axial magnetic bearing.

[0033] When the absolute value of the difference in the average value is 63 milliamperes, since it is less than the threshold value at this time, no adjustment is required at this time, and the process of finding the floating center position by itself ends.

[0034] When the absolute value of the difference in the average value is 163 milliamperes, since it is greater than the threshold value at this time, it is determined whether the adjusted floating position reference value exceeds the adjustment range. If it exceeds the adjustment range, the process of finding the floating center position by itself ends; if it does not exceed, the floating position reference value is adjusted 2 micrometers to the side where the average value of the current signal in the axial magnetic bearing coil is smaller, and then the currents in the axial magnetic bearing coils on both sides are sampled continuously. The difference in the average value of the current signals is compared with the threshold value, and then it is determined whether to adjust.

[0035] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for controlling the axial suspension position of a magnetic levitation motor based on the current of an axial magnetic bearing, characterized in that, It includes the following steps: S1. Add a self-seeking axial center position control module to the magnetic levitation bearing controller; S2. Establish two arrays in the control algorithm, which are respectively used to store the current signals in the axial magnetic bearing coils on both sides; S3. Before controlling the rotor to levitate, calibrate the axial displacement sensor and store the calibration data, and then perform static levitation according to the center position calibrated by the axial displacement sensor; S4. Sample the currents in the axial magnetic bearing coils on both sides in each control cycle and store them in the corresponding arrays; the values in the arrays are updated according to the principle of first in first out; S5. Calculate the average values of the current signals in the two arrays respectively, and perform a difference operation on the two average values; S6. When the absolute value of the difference between the average values is less than the set threshold, the process of self-seeking the levitation center position ends; when the absolute value of the difference between the average values is greater than the threshold, proceed to the next step; S7. Judge whether the adjusted levitation position reference value exceeds the adjustment range. When it exceeds the adjustment range, the process of self-seeking the levitation center position ends. When it does not exceed, proceed to the next step; S8. Adjust the levitation position reference value. In each control cycle, the levitation position reference value is adjusted by 2 microns towards the side with the smaller average value of the current signal in the axial magnetic bearing coil, and then return to S4.

2. The axial suspension position control method of the magnetic levitation motor based on the axial magnetic bearing current according to claim 1, characterized in that: The threshold is 100 mA.

3. The axial suspension position control method of the magnetic levitation motor based on the axial magnetic bearing current according to claim 1, wherein: In S7, 25% of the set axial protection gap is set as the maximum adjustment range.

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