Surface-mounted permanent magnet motor local field loss fault detection method

Abstract

The invention belongs to the technical field of motor fault detection, and relates to a surface-mounted permanent magnet motor local field loss fault detection method. Comprising the following steps: firstly, for a surface-mounted integer slot permanent magnet motor in operation, establishing a rotor magnetomotive force expression under a local field loss fault and expanding the rotor magnetomotive force expression into Fourier series; secondly, designing a detection coil of which the pitch is equal to two times of the polar distance, extracting a fractional harmonic magnetic field signal generated during a local field loss magnetic fault, and solving the back electromotive force of the local field loss magnetic fault when the local field loss magnetic fault occurs; and finally, carrying out harmonic analysis on the counter electromotive force of the detection coil, and judging whether a local field loss fault occurs or not by comparing the magnitude of a plurality of harmonic amplitudes. The method does not need to change the original structure of the motor, does not affect the normal operation of the motor, avoids shutdown loss, can rapidly recognize the sudden local field loss fault, is simple in structure, is low in manufacturing cost, is not limited by the power and rotating speed of the motor, is suitable for various types of permanent magnet motors, is precise in recognition of different field loss degrees, and is friendly to an application environment.

Description

Technical Field

[0001] This invention belongs to the field of motor fault detection technology and relates to a method for detecting local demagnetization faults in surface-mounted permanent magnet motors. By analyzing and calculating the rotor magnetomotive force, the operating and structural state of the motor can be deduced, which is used for detecting local demagnetization faults in surface-mounted permanent magnet motors. Background Technology

[0002] Currently, electric motors are used in almost all electrical applications. In some cases, the operating status of a motor must be analyzed and determined using information from its electric or magnetic fields. Surface-mounted permanent magnet motors, with their outstanding advantages such as high torque density, high power factor, and high efficiency, are widely used in high-performance drive applications. However, under extreme conditions such as strong current impulses and long-term operation in high-temperature environments, permanent magnets are susceptible to strong magnetic field disturbances and high-temperature degradation, leading to localized demagnetization faults. This fault directly results in a decrease in rated output torque and increased torque pulsation. Therefore, to ensure reliable motor operation, it is necessary to analyze and extract the characteristics of localized demagnetization faults in permanent magnet motors, transforming complex electromagnetic field signals and voltage signals into quantifiable diagnostic indicators. This provides a theoretical basis for fault diagnosis and crucial support for distinguishing localized demagnetization faults from other similar faults.

[0003] Chinese patent (publication number: CN116930755A) discloses an online detection method for uneven demagnetization faults in permanent magnet motors. Vector control (FOC) is applied to a surface-mounted permanent magnet synchronous motor (SPMSM) to ensure stable and normal operation. The current differential of the current sensor (Rogowski coil) is read to obtain the current differential under both effective and zero vector conditions. The stator inductance is obtained based on the current differential under effective and zero vector conditions. Fault characteristic harmonic analysis is performed based on the current differential under zero vector conditions and the stator inductance to achieve online detection of uneven demagnetization faults in the permanent magnet motor. This invention utilizes motor current differential analysis (MCDA) to detect fault characteristic harmonics contained in the current differential, thereby assisting in the diagnosis of uneven demagnetization faults. MCDA has stronger anti-interference capabilities against load fluctuations, a lower probability of false diagnosis, and can better quantitatively reflect the degree of uneven demagnetization faults.

[0004] Chinese Patent (Publication No.: CN108051739A) discloses a method and system for monitoring rotor demagnetization faults in permanent magnet synchronous motors. The method includes: detecting the actual port voltage of one or more detection coils arranged within the permanent magnet synchronous motor and the operating speed of the permanent magnet synchronous motor; for each of the one or more detection coils, calculating the effective value of a predetermined harmonic component in the actual port voltage of that detection coil; calculating an online monitoring value for that detection coil based on the effective value of the predetermined harmonic component in the actual port voltage of that detection coil; comparing the online monitoring value of that detection coil with an alarm value corresponding to the operating speed of that detection coil to obtain a comparison result; and determining whether a rotor demagnetization fault has occurred in the permanent magnet synchronous motor based on the comparison result of the one or more detection coils. This patent proposes using novel detection coils to monitor rotor demagnetization faults in permanent magnet synchronous motors in real time, and the proposed monitoring method has high sensitivity and reliability for detecting rotor demagnetization faults in permanent magnet synchronous motors.

[0005] Chinese Patent (Publication No.: CN109239599A) discloses a method for diagnosing demagnetization faults in permanent magnet synchronous motors. This method establishes a sample library by conducting experiments on different types of demagnetization faults, extracts the back electromotive force (EMF) of coil elements, and calculates the back EMF after a demagnetization fault and the residual back EMF under healthy conditions as fault characteristic quantities. Simultaneously, it establishes a sample library and energy range library of demagnetization fault characteristic quantities through relevant formula conversions. The method acquires the coil back EMF signal in real time, and analyzes the correlation between the measured fault characteristic quantities and the fault characteristic quantities in the lookup table based on the magnitude of the back EMF residual signal. By analyzing the energy of the back EMF residual signal and the correlation coefficient results, the method can diagnose demagnetization faults and the degree of demagnetization. It can also distinguish between uniform demagnetization and localized demagnetization, and can quickly and accurately locate the faulty magnetic pole when a localized demagnetization fault occurs in the motor, effectively improving the accuracy of diagnosing demagnetization faults in permanent magnet synchronous motors. The most significant inventive aspect of this patent is the use of the coil back EMF residual as a fault characteristic quantity to achieve demagnetization fault diagnosis. The working principle is as follows: Any coil element on the stator of the designated motor is used as a detection coil to acquire the back EMF data of the coil element after one revolution of the motor. In a healthy permanent magnet state, the coil back EMF changes sinusoidally. In the event of a demagnetization fault, when the demagnetizing pole passes through the designated coil element, the waveform of the coil back EMF changes.

[0006] None of the existing demagnetization fault diagnosis methods mentioned above can reliably diagnose local demagnetization faults in surface-mounted permanent magnet motors. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the existing technology and to design a method for detecting local demagnetization faults in surface-mount permanent magnet motors. By analyzing and calculating the information of the motor magnetomotive force, it is possible to effectively determine whether a local demagnetization fault has occurred in the permanent magnet motor, thus providing a more reliable and effective new approach for diagnosing local demagnetization faults in surface-mount permanent magnet motors.

[0008] To achieve the above-mentioned objectives, the present invention relates to a method for detecting partial demagnetization faults in surface-mount permanent magnet motors, the fault detection process of which includes the following steps:

[0009] (1) Derivation of rotor magnetomotive force: For a surface-mounted integer slot permanent magnet motor in operation, the rotor magnetomotive force under a local demagnetization fault is composed of the normal rotor magnetomotive force minus the magnetomotive force generated by one magnetic pole. The result is expressed as follows:

[0010] ;

[0011] In the formula: F p (θ,t) represents the magnetomotive force generated by all permanent magnets under normal conditions. Due to the sinusoidal pole clipping treatment performed on the permanent magnets, the generated magnetomotive force is a sine wave; F one_pole (θ,t) represents the magnetomotive force generated by a single magnetic pole, F. pm The amplitude of the sinusoidal magnetomotive force is given by θ, where A is the degree of demagnetization (where A = 1 indicates no demagnetization and A = 0 indicates complete demagnetization), θ is the rotor position, p is the number of pole pairs, and ω is the sine magnetomotive force amplitude. m Where t is the mechanical angular frequency, and t is time;

[0012] F one_pole (θ,t) can be expanded into a Fourier series:

[0013] ;

[0014] The coefficients for each item are:

[0015] ;

[0016] (2) Design of the detection coil: Design a detection coil with a pitch equal to twice the pole pitch to extract the fractional harmonic magnetic field signal generated during a local demagnetization fault; when a local demagnetization fault occurs, the back electromotive force of the detection coil contains only fractional harmonics, the expression of which is:

[0017] ;

[0018] Where, N sc The number of turns of the probe coil, μ0 is the free permeability, and l ef R represents the axial length of the stator core, g0 is the air gap length, and R is the axial length of the stator core. sWhere ω is the stator inner diameter, ω is the electric angular velocity, and n is the harmonic order;

[0019] (3) Diagnosing demagnetization fault: Perform harmonic analysis on the back electromotive force of the detection coil, and determine whether a local demagnetization fault has occurred by comparing the magnitude of the fractional harmonics; when the number of pole pairs of the motor is even, the motor has a local demagnetization fault when the amplitude of the 1 / 2 harmonic is greater than the amplitude of the 3 / 2 harmonic; when the number of pole pairs of the motor is odd, the motor has a local demagnetization fault when the amplitude of the (p+1) / 2p harmonic is greater than the amplitude of the (3p+1) / 2p harmonic.

[0020] This invention uses a detection coil as a sensor to extract fault signals, thereby diagnosing local demagnetization faults in surface-mounted permanent magnet motors. This avoids the structural increase caused by selecting additional sensors and diagnoses local demagnetization faults by judging the magnitude of fractional harmonic amplitudes.

[0021] The detection method of the present invention is for a surface-mounted integer slot permanent magnet motor in operation. It establishes an expression for the rotor magnetomotive force when a certain magnetic pole on the rotor side experiences a uniform demagnetization fault, expands it into a Fourier series, and derives the magnetomotive force data of the rotor with a local demagnetization fault.

[0022] The detection method of the present invention involves designing a detection coil with a pitch equal to twice the pole pitch based on the derived magnetomotive force data, and then solving for the back electromotive force of the detection coil.

[0023] The detection method of the present invention analyzes the amplitude of each harmonic of the back electromotive force and determines whether a local demagnetization fault has occurred by comparing the magnitudes of the fractional harmonics.

[0024] The motor involved in this invention is an integer slot motor, or a fractional slot motor with a slot pitch equal to twice the pole pitch.

[0025] Compared with existing technologies, this invention has the following advantages: it does not require modification of the original structure of the motor, does not affect the normal operation of the motor, and avoids downtime losses; it can capture magnetic field changes in real time, quickly identify sudden local demagnetization faults, and its response speed is better than some offline detection methods; its detection coil design has a simple structure and low manufacturing cost, and can be directly installed at the stator slot of the motor without complex hardware support; it is not limited by motor power or speed, is suitable for small and large permanent magnet motors, has accurate identification of different degrees of demagnetization, and is environmentally friendly. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the magnetomotive force of a rotor with a localized loss of magnetomagnetism fault, as described in this invention.

[0027] Figure 2 This is a schematic diagram illustrating the principle of the detection coil arrangement structure involved in this invention.

[0028] Figure 3 This is a schematic diagram of the back EMF harmonic composition in the detection coil involved in the present invention.

[0029] Figure 4 and Figure 5 This is a schematic diagram showing the results of applying the present invention to on-site fault detection and diagnosis. Detailed Implementation

[0030] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0031] Example 1:

[0032] This embodiment relates to a method for detecting localized demagnetization faults in a surface-mounted permanent magnet synchronous motor when a uniform demagnetization fault occurs in one pole. The specific process for fault diagnosis includes the following steps:

[0033] (1) Deriving the rotor magnetomotive force:

[0034] For a surface-mounted integer-slot permanent magnet motor in operation, the rotor magnetomotive force under a partial demagnetization fault is composed of the normal rotor magnetomotive force minus the magnetomotive force generated by one magnetic pole, and the result is expressed as (e.g.) Figure 1 (as shown)

[0035] ;

[0036] In the formula: F p (θ,t) represents the magnetomotive force generated by all permanent magnets under normal conditions. Due to the sinusoidal pole clipping treatment performed on the permanent magnets, the generated magnetomotive force is a sine wave; F one_pole (θ,t) represents the magnetomotive force generated by a single magnetic pole, F. pm ω is the amplitude of the sinusoidal magnetomotive force, A is the degree of demagnetization (where 1 represents no demagnetization and 0 represents complete demagnetization), θ is the rotor position, p is the number of pole pairs, and ω is the amplitude of the sinusoidal magnetomotive force. m Where t is the mechanical angular frequency, and t is time;

[0037] F one_pole (θ,t) can be expanded into a Fourier series:

[0038] ;

[0039] The coefficients for each item are:

[0040] ;

[0041] (2) Design of the detection coil: Design a detection coil with a pitch equal to twice the pole pitch, and arrange it as follows: Figure 2 As shown, the fractional harmonic magnetic field signal generated during a local demagnetization fault is extracted (e.g., Figure 3(As shown); when a local demagnetization fault occurs, the back EMF of the detection coil contains only fractional harmonics, and its expression is:

[0042] ;

[0043] Where, N sc The number of turns of the probe coil, μ0 is the free permeability, and l ef R represents the axial length of the stator core, g0 is the air gap length, and R is the axial length of the stator core. s Where ω is the stator inner diameter, ω is the electric angular velocity, and n is the harmonic order;

[0044] (3) Diagnosing demagnetization fault: Perform harmonic analysis on the back electromotive force of the detection coil, and determine whether a local demagnetization fault has occurred by comparing the magnitude of the fractional harmonics; when the number of pole pairs of the motor is even, the motor has a local demagnetization fault when the amplitude of the 1 / 2 harmonic is greater than the amplitude of the 3 / 2 harmonic; when the number of pole pairs of the motor is odd, the motor has a local demagnetization fault when the amplitude of the (p+1) / 2p harmonic is greater than the amplitude of the (3p+1) / 2p harmonic.

[0045] This embodiment uses a detection coil as a sensor to extract fault signals, thereby diagnosing local demagnetization faults in surface-mounted permanent magnet motors. This avoids the structural increase of additional sensors and diagnoses local demagnetization faults by judging the magnitude of fractional harmonic amplitudes.

[0046] Example 2:

[0047] This embodiment relates to a specific application example. In the Special Electric Drive System Laboratory of Marine Equipment at Qingdao University, a six-phase sinusoidal pole-cutting surface-mounted permanent magnet synchronous motor with a rated power of 10kW and a rated speed of 600rpm was selected as the test object. The rotor of the test object has a total of 8 permanent magnets, one of which is not magnetized.

[0048] (1) Test method: The motor control mode is vector control. Under no-load operation at a speed of 600 rpm, the port induced voltage of the detection coil is measured using an oscilloscope. The measured port induced voltage is as follows: Figure 4 As shown;

[0049] (2) Data processing: The measured data were subjected to Fourier decomposition. The Fourier decomposition results are as follows: Figure 5 As shown; the measured amplitude of the 1 / 2 harmonic is 1.03473V, and the amplitude of the 3 / 2 harmonic is 0.590487V. The amplitude of the 1 / 2 harmonic is greater than that of the 3 / 2 harmonic.

[0050] (3) Conclusion: This embodiment verifies the correctness of the theory in Embodiment 1, and the test results achieve the purpose of the invention; Appendix Figure 4 and 5The results of the embodiments were displayed.

Claims

1. A method for detecting partial demagnetization faults in surface-mounted permanent magnet motors, characterized in that, Includes the following steps: (1) Derivation of rotor magnetomotive force: For a surface-mounted integer slot permanent magnet motor in operation, the rotor magnetomotive force under a local demagnetization fault is composed of the normal rotor magnetomotive force minus the magnetomotive force generated by one magnetic pole. The result is expressed as: ； In the formula: F p (θ,t) represents the magnetomotive force generated by all permanent magnets under normal conditions. Due to the sinusoidal pole clipping treatment performed on the permanent magnets, the generated magnetomotive force is a sine wave; F one_pole (θ,t) represents the magnetomotive force generated by a single magnetic pole, F. pm The amplitude of the sinusoidal magnetomotive force is given by θ, where A is the degree of demagnetization (where A = 1 indicates no demagnetization and A = 0 indicates complete demagnetization), θ is the rotor position, p is the number of pole pairs, and ω is the sine magnetomotive force amplitude. m Where t is the mechanical angular frequency, and t is time; F one_pole (θ,t) can be expanded into a Fourier series: ； The coefficients for each item are: ； (2) Design of the detection coil: Design a detection coil with a pitch equal to twice the pole pitch to extract the fractional harmonic magnetic field signal generated during a local demagnetization fault; when a local demagnetization fault occurs, the back electromotive force of the detection coil contains only fractional harmonics, the expression of which is: ； Where, N sc The number of turns of the probe coil, μ0 is the free permeability, and l ef R represents the axial length of the stator core, g0 is the air gap length, and R is the axial length of the stator core. s Where ω is the stator inner diameter, ω is the electric angular velocity, and n is the harmonic order; (3) Diagnosing demagnetization fault: Perform harmonic analysis on the back electromotive force of the detection coil, and determine whether a local demagnetization fault has occurred by comparing the magnitude of the fractional harmonics; when the number of pole pairs of the motor is even, the motor has a local demagnetization fault when the amplitude of the 1 / 2 harmonic is greater than the amplitude of the 3 / 2 harmonic; when the number of pole pairs of the motor is odd, the motor has a local demagnetization fault when the amplitude of the (p+1) / 2p harmonic is greater than the amplitude of the (3p+1) / 2p harmonic.

2. The method for detecting partial demagnetization faults in a surface-mount permanent magnet motor according to claim 1, characterized in that, For a surface-mounted integer slot permanent magnet motor in operation, an expression for the rotor magnetomotive force when a certain magnetic pole on the rotor side experiences a uniform demagnetization fault is established, and expanded into a Fourier series to derive the magnetomotive force data of the rotor with a local demagnetization fault.

3. The method for detecting partial demagnetization faults in a surface-mount permanent magnet motor according to claim 1, characterized in that, Based on the derived magnetomotive force data, a detection coil with a pitch equal to twice the pole pitch is designed, and then the back electromotive force of the detection coil is solved.

4. The method for detecting partial demagnetization faults in a surface-mount permanent magnet motor according to claim 1, characterized in that, The amplitudes of each harmonic of the back electromotive force are analyzed, and the magnitudes of the fractional harmonics are compared to determine whether a local demagnetization fault has occurred.

5. The method for detecting partial demagnetization faults in a surface-mount permanent magnet motor according to claim 1, characterized in that, The motor has an integer number of slots, or a fractional slot motor with a slot pitch equal to twice the pole pitch can be selected.

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