Permanent magnet motor interphase short circuit fault diagnosis method

Abstract

The invention relates to the technical field of permanent magnet motor fault diagnosis, in particular to a permanent magnet motor phase-to-phase short circuit fault diagnosis method. In order to solve the defects in the prior art, the invention provides a novel permanent magnet motor phase-to-phase short circuit fault diagnosis method, which comprises the following steps of: 1) acquiring corresponding vibration effective values Kn of a normal motor at different rotating speeds fn; and 2) phase short diagnosis: if the instantaneous value of the motor stator current is over-current and the three-phase current is unbalanced, acquiring fn and K, and performing phase short judgment by comparing K with 5 * Kn and a frequency spectrum. According to the inter-phase short-circuit fault diagnosis method for the permanent magnet motor, the time consumption of the whole calculation process on an embedded system is at the ms level, the diagnosis algorithm has timeliness, the diagnosis method is effective, and meanwhile online fault diagnosis can be achieved.

Description

Technical Field

[0001] This invention relates to the field of permanent magnet motor fault diagnosis technology, specifically a method for diagnosing phase-to-phase short-circuit faults in permanent magnet motors. Background Technology

[0002] The main faults of permanent magnet motors are insulation, bearing, and magnet failures. Approximately 40% of these faults are related to insulation. The stator insulation system of traction variable frequency motors is primarily affected by electrical, thermal, and mechanical aging processes, especially the high switching frequency and voltage levels of the inverter. The transient overvoltages caused by the high du / dt rapid and frequent switching of the inverter accelerate the aging of the stator winding insulation. When an insulation short-circuit fault occurs, the internal short-circuit current increases sharply, torque pulsation significantly increases, and the system loses its operational stability. Phase-to-phase short-circuit faults are particularly destructive and harmful, especially for rail transit motors, where their danger severely impacts train safety and can lead to serious accidents such as derailment and fires.

[0003] Stator insulation failure is an internal electrical asymmetry fault in the motor. Besides causing abnormalities in the circuit, it also significantly affects the magnetic circuit in the air gap. The net magnetic pull per unit area is no longer zero, leading to a sharp increase in motor vibration. This is especially true for high-power, high-speed permanent magnet motors in rail transit. When a phase-to-phase short circuit occurs, the motor's torque secondary pulse increases significantly, resulting in unstable motor speed, excessive vibration, and unstable operation. Furthermore, the sudden accumulation of localized energy and a rapid temperature spike can cause localized insulation burn-out. Phase-to-phase short circuits are undoubtedly one of the most serious faults for permanent magnet motors. Therefore, when a phase-to-phase short circuit occurs, timely diagnosis, location, and early warning are crucial. Immediately taking measures such as stopping operation or activating three-phase short-circuit protection can reduce the probability of the fault escalating into insulation and core burn-out, and prevent damage to other mechanical equipment in the transmission chain due to abnormal motor vibration. Therefore, the earlier the diagnosis and protection, the more effective the mitigation of the hazards of a permanent magnet motor short circuit, ensuring stable and safe motor operation and protecting personal and property safety.

[0004] Existing technology 1: For example, Chinese patent CN111123104B "A method for diagnosing permanent magnet motor winding faults without prior knowledge". This invention discloses a method for diagnosing permanent magnet motor winding faults without prior knowledge. First, the fundamental amplitude of the zero-sequence voltage is extracted using coordinate transformation theory to identify the winding state. Then, high-frequency currents with the same amplitude but different frequencies are injected sequentially into the converter of the permanent magnet motor, and the fault type is distinguished according to the amplitude of the high-frequency response signal in the zero-sequence voltage. Finally, corresponding fault degree and fault location diagnosis methods are adopted for different types of winding faults. However, this method requires the permanent magnet motor converter to inject high-frequency currents with the same amplitude but different frequencies sequentially to assist in the diagnosis of phase short. This diagnosis method cannot perform uninterrupted real-time diagnosis during motor operation and requires modification of the drive control algorithm of the motor converter, increasing design risk.

[0005] Existing technology 2: such as Chinese patent CN116136568A "A method and device for predicting short circuit faults in permanent magnet motors": This invention provides a method and device for predicting short circuit faults in permanent magnet motors. By analyzing the influencing factors of short circuit current through high-dimensional correlation analysis, it provides data support for forming a fault tree in a fault diagnosis expert system and also provides a foundation for using big data technology for fault prediction. The method includes: acquiring the current change trend of the fundamental current component within a set time period under the current actual operating conditions of the traction system; predicting short-circuit faults of the permanent magnet motor based on the current change trend in response to the difference between the first and second high-dimensional correlation coefficients meeting a preset condition; wherein, the first high-dimensional correlation coefficient is calculated based on the joint distribution function constructed between the current between the inverter and the isolation contactor and various influencing factors, and the second high-dimensional correlation coefficient is calculated based on the joint distribution function between various influencing factors related to the current obtained by the Pair-Copula method. However, this method not only targets the current change trend within a set time period, but also constructs the first high-dimensional correlation coefficient based on the joint distribution function constructed between the current between the inverter and the isolation contactor and various influencing factors, and constructs the second high-dimensional correlation coefficient based on the Pair-Copula method. The method also relies on big data technology, making it complex, computationally expensive, and unable to guarantee the timeliness of diagnosis. Summary of the Invention

[0006] In order to address the deficiencies of the prior art, this invention provides a new method for diagnosing phase-to-phase short-circuit faults in permanent magnet motors.

[0007] This invention is achieved using the following technical solution:

[0008] When a phase-to-phase short circuit occurs in the stator winding of a permanent magnet motor, an imbalance immediately arises between the three phase windings. This causes a momentary overcurrent in the motor, a sudden increase in the motor's back electromotive force, and triggers an inverter IGBT drive fault. However, simply identifying the motor overcurrent and IGBT drive fault is insufficient to accurately pinpoint the phase-to-phase short circuit fault, as system overload, grounding, and inverter power module failures can all trigger both motor overcurrent and IGBT drive faults.

[0009] However, when a permanent magnet motor experiences a short circuit, the air gap magnetic flux density changes, and the resultant force of the magnetic pull per unit area is no longer zero, causing abnormal vibration in the motor. After a phase-to-phase short circuit, the magnetic field generated by the imbalance of the air gap magnetic flux density acts on the rotor at twice the relative speed, causing secondary torque pulsation in the motor, and the motor's vibration exhibits fault characteristics at twice the electrical frequency.

[0010] Therefore, by performing feature fusion analysis on the stator current, vibration, and speed signals of the motor, the fault characteristics of phase short circuits are extracted. The fault characteristics are monitored in real time until the fault warning threshold is reached, and a warning is issued. The warning result is promptly sent to the traction motor control unit, which then takes three-phase short circuit protection measures to prevent the fault from escalating.

[0011] The study investigates the fault mechanism of the characteristic changes in the operating signal after a phase short circuit in a motor. When a phase short circuit fault occurs in the stator coil of a permanent magnet synchronous motor, the three-phase symmetry of the stator winding is disrupted, which will cause the following effects: stator current overcurrent; a significant increase in the three-phase imbalance in the stator current; and at the same speed, the vibration of the short-phase motor has a large amplitude at the even-order harmonics of the stator frequency, which is much larger than that of a normal motor.

[0012] Based on the above research results on the fault mechanism of phase short, the following fault diagnosis algorithm for permanent magnet motors is designed.

[0013] A method for diagnosing phase-to-phase short-circuit faults in a permanent magnet motor includes the following steps:

[0014] 1) Obtain the normal motor at f n (n = 1, 2, 3, ..., n) The effective vibration value K corresponding to different rotational speeds n This forms a vibration-speed relationship table (since the vibration of a normal motor changes with different speeds, and the normal vibration values ​​of different motors are different, it is difficult to define the normal and abnormal states of a motor solely from the threshold of the effective vibration value. Therefore, it is necessary to obtain the effective vibration values ​​of a normal motor within different speed ranges):

[0015] ① Initialize the vibration-speed relationship table so that K n (n = 1, 2, 3, ..., n) are all equal to 0;

[0016] ②At regular intervals t, acquire the motor speed data and the corresponding instantaneous vibration acceleration data within the time interval Δt.

[0017] ③ Calculate the coefficient of variation f_cv of the motor speed f during the time interval Δt.

[0018]

[0019] in, T=Δt×F s F s The sampling rate for rotational speed data;

[0020] ④ If f_cv≥0.5%, continue for time t and obtain the motor speed data f within the time interval Δt. If f_cv<0.5%, then calculate ff sequentially. n The absolute value of f is taken as the smallest of the absolute values. n If there are multiple minimum values, then the minimum value f is taken. n ;

[0021] ⑤ Calculate the effective value K of the vibration corresponding to the instantaneous acceleration during the current time interval Δt;

[0022] ⑥ If K > 0, then update K in the "Vibration-Speed ​​Relationship Table" based on the f obtained in step ④. n In the corresponding vibration effective value unit, otherwise keep the original value;

[0023] ⑦ When K1 to K10 are all greater than 0, then the phase shortening diagnosis begins;

[0024] 2) The diagnostic steps for phase shortening are as follows:

[0025] I. Determine whether the instantaneous value of the motor stator current is normal and whether the three-phase current is balanced;

[0026] If the instantaneous value of the motor stator current is normal and the three-phase current is balanced, then return to step 1). If the instantaneous value of the motor stator current is normal but the three-phase current is unbalanced, then continue to judge whether the instantaneous value of the motor stator current is normal and whether the three-phase current is balanced.

[0027] If the instantaneous value of the motor stator current is overcurrent and the three-phase current is balanced, then continuously check whether the instantaneous value of the motor electronic current is normal and whether the three-phase current is balanced. If the instantaneous value of the motor stator current is overcurrent and the three-phase current is unbalanced, then perform subsequent phase short diagnosis.

[0028] II. During phase short diagnosis, the motor speed data and corresponding instantaneous vibration acceleration data within the time interval Δt are acquired at regular intervals t, and ff is calculated sequentially. n The absolute value of f is taken as the smallest of the absolute values. nIf there are multiple minimum values, then the minimum value f is taken. n ;

[0029] III. Calculate the effective value K of the vibration acceleration within the current time interval Δt;

[0030] IV. In the "Vibration-Speed ​​Relationship Table" obtained in step 1), find the value of f obtained in step II. n Corresponding K n Compare K obtained in step III. If K > 5 × K n Directly issue a short-term warning if 2×K n >K, return to step I, and continue to determine whether there is an overcurrent and whether there is an imbalance in the three phases. If 2×K n ≤K≤5×K n Then calculate the vibration spectrum function Vib_fft(f) corresponding to K obtained in step III;

[0031] V. In the vibration spectrum, calculate the sum of energy fsum within the frequency band from the rotation frequency to 8 times the rotation frequency, i.e., f r Up to 8×f r Sum of squared spectral amplitudes within the frequency band Where f r =f n / 60; respectively extract 1 / 2 / 4 / 6 / 8 times the frequency f r The energy of the frequency band, i.e., calculating i×f r Sum of squared spectral amplitudes within ±3Hz band

[0032] , where i = 1, 2, 4, 6, 8;

[0033] VI. Compare the magnitudes of fd and fsum. If fd > 0.3 × fsum, directly implement phase short circuit warning and protection. Otherwise, return to step I and continue to determine whether the current is overcurrent and whether there is a three-phase imbalance. When the motor has an overcurrent alarm, but the effective value of the vibration does not reach the fault alarm of direct phase-to-phase short circuit, further analysis can be performed on the vibration spectrum. In the vibration spectrum, extract the energy of the 1 / 2 / 4 / 6 / 8 times the frequency band respectively, and calculate the sum of the energy of each frequency band, fd. Then calculate the sum of the energy in the frequency band up to 8 times the frequency band, fsum. Compare the magnitudes of fd and fsum. If fd is greater than 30% of fsum, directly implement phase short circuit warning and protection. Otherwise, continue to determine whether the current is overcurrent and whether there is a three-phase imbalance.

[0034] Furthermore, n is 10, f1~f 10 20% × f in sequence v 40%×f v 60%×f v 80%×fv f v f v +20%×(f max -f v ), f v +40%×(f max -f v ), f v +60%×(f max -f v ), f v +80%×(f max -f v ), f max .

[0035] The beneficial effects of this invention are as follows: The permanent magnet motor phase-to-phase short circuit fault diagnosis method of this invention takes milliseconds for the entire calculation process on an embedded system. The diagnosis algorithm is timely and the diagnosis method is effective. At the same time, online fault diagnosis can be realized. Attached Figure Description

[0036] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a flowchart of the method for obtaining the vibration-speed relationship table in the present invention;

[0039] Figure 2 This is a flowchart of step 2) in the method described in this invention. Detailed Implementation

[0040] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0041] In this description, it should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. It should also be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joint" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0042] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0043] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0044] Based on the construction of a permanent magnet motor phase-short test platform, the motor's rated speed is 1200 r / min, and its maximum speed is 2000 r / min. During normal motor operation, the motor speed fn (n = 1, 2, 3, ..., 10) is controlled to be 240, 480, 720, 960, 1200, 1360, 1520, 1680, 1840, and 2000 r / min, respectively. The running time at each speed is no less than 2 minutes, and this speed variation test is repeated for 5 cycles. The specific fault diagnosis method includes the following steps:

[0045] 1) Obtain the normal motor speeds from f1 to f 10 The effective vibration value K at different rotational speeds n (n = 1, 2, 3, ..., 10), forming a vibration-speed relationship table, such as Figure 1 As shown:

[0046] ① Initialize the vibration-speed relationship table so that K1, K2, ..., K 10 All values ​​are equal to 0. The vibration-speed relationship is shown in Table 1 below.

[0047] Serial Number rotational speed RMS value of vibration 1 <![CDATA[f1=20%*f v ]]> <![CDATA[K1 <!-- 4 -->]]> 2 <![CDATA[f2=40%*f v ]]> <![CDATA[K2]]> 3 <![CDATA[f3=60%*f v ]]> <![CDATA[K3]]> 4 <![CDATA[f4=80%*f v ]]> <![CDATA[K4]]> 5 <![CDATA[f5=f v ]]> <![CDATA[K5]]> 6 <![CDATA[f6=f v +20%*(f max -f v )]]> <![CDATA[K6]]> 7 <![CDATA[f7=f v +40%*(f max -f v )]]> <![CDATA[K7]]> 8 <![CDATA[f8=f v +60%*(f max -f v )]]> <![CDATA[K8]]> 9 <![CDATA[f9=f v +80%*(f max -f v )]]> <![CDATA[K9]]> 10 <![CDATA[f 10 =f max ]]> <![CDATA[K 10 ]]>

[0048] ② Acquire the motor speed data f and the corresponding instantaneous vibration acceleration data within a 1-second time interval every 10 seconds;

[0049] ③ Calculate the coefficient of variation f_cv of the motor speed f within a 1-second time interval.

[0050]

[0051] in, T = F s F s The sampling rate for rotational speed data;

[0052] ④ If f_cv≥0.5%, continue for time t and then obtain the motor speed data f within a 1s interval. If f_cv<0.5%, then calculate ff sequentially. n The absolute value of f is taken as the smallest of the absolute values. n If there are multiple minimum values, then the minimum value f is taken. n ;

[0053] ⑤ Calculate the effective vibration value K corresponding to the vibration acceleration within the current 1-second time interval;

[0054] ⑥ If K > 0, then update K in the "Vibration-Speed ​​Relationship Table" based on the f obtained in step ④. n In the corresponding vibration effective value unit, otherwise keep the original value;

[0055] ⑦ When K1~K 10 If all values ​​are greater than 0, then phase short diagnosis begins, and the phase short algorithm start flag fd_start = 1; otherwise, fd_start = 0.

[0056] After five cycles of operation under varying speed conditions, phase short circuit diagnosis begins. During the operation of the motor at any speed, an isolation contactor is connected between two phases. By closing the isolation contactor, a phase short circuit fault is pre-simulated between two phases of the motor stator winding. At the same time, the motor's three-phase current, instantaneous vibration acceleration, and speed are collected to verify the phase short circuit diagnosis algorithm.

[0057] 2) When the flag fd_start = 1, the phase short algorithm starts. The phase short diagnosis steps are as follows: Figure 2 As shown

[0058] If the instantaneous value of the motor stator current is overcurrent and the three-phase current is unbalanced, then subsequent phase short diagnosis should be performed.

[0059] II. During phase short diagnosis, the motor speed data and corresponding instantaneous vibration acceleration data for a 1-second time interval are acquired every 10 seconds, and ff is calculated accordingly. n The absolute value of f is taken as the smallest of the absolute values. n If there are multiple minimum values, then the minimum value f is taken. n ;

[0060] III. Calculate the effective value K of the vibration acceleration within the current 1-second time interval;

[0061] IV. In the "Vibration-Speed ​​Relationship Table" obtained in step 1), find the value of f obtained in step II. n Corresponding K n Compare K obtained in step III with K n .

[0062] Scenario 1: During the test, at low speeds of 240 and 480 r / min, a closed isolating contactor was used to short-circuit two phases of the motor stator winding. The phase-to-phase short-circuit diagnostic algorithm calculated K to be approximately 4.5 × K1 and 4.9 × K2, respectively, satisfying 2 × K. n <K<5×K n Calculate the vibration spectrum function Vib_fft(f). From the vibration spectrum, sum the energy of the 1st, 2nd, 4th, 6th, and 8th times the rotational frequency band, respectively, i.e., calculate i×f. r The sum of squares of the spectral amplitude within the ±3Hz band, fd, where i = 1, 2, 4, 6, 8, and the rotation frequency f. r =f n / 60, that is

[0063]

[0064] In the vibration spectrum, calculate the sum of energy fsum within the frequency band from the rotation frequency to eight times the rotation frequency, i.e., f r Up to 8×f r Sum of squared spectral amplitudes within the frequency band Where f r =f n / 60; Compare the magnitudes of fd and fsum. If both fd / fsum are greater than 30%, then perform phase short warning and protection processing directly.

[0065] Scenario 2: During the test, at speeds of 720, 960, 1200, 1360, 1520, 1680, 1840, and 2000 r / min, a closed isolating contactor is used to short-circuit two phases of the motor stator winding. The phase-to-phase short-circuit diagnostic algorithm calculates K to be approximately 13.5×K3, 16.9×K4, 17×K5, 21.6×K6, 30.1×K7, 22.5×K8, 28.9×K9, and 31.6×K1000 respectively. 10 All satisfy K > 5 × K n It can directly carry out short-term early warning and protection measures.

[0066] The above experiments verify that the phase short circuit diagnosis algorithm is effective and can diagnose phase-to-phase insulation short circuit faults in real time.

[0067] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered within the protection scope of the claims.

Claims

1. A method for diagnosing phase-to-phase short-circuit faults in a permanent magnet motor, characterized in that, Includes the following steps: 1) Obtain the normal motor at f n (n = 1, 2, 3, ..., n) The effective vibration value K corresponding to different rotational speeds n This forms a vibration-speed relationship table: ① Initialize the vibration-speed relationship table so that K n (n = 1, 2, 3, ..., n) are all equal to 0; ②At regular intervals t, acquire the motor speed data and the corresponding instantaneous vibration acceleration data within the time interval Δt. ③ Calculate the coefficient of variation f_cv of the motor speed data f during the time interval Δt. in, T=Δt×F s F s The sampling rate for rotational speed data; ④ If f_cv≥0.5%, continue for time t and obtain the motor speed data f within the time interval Δt. If f_cv<0.5%, then calculate ff sequentially. n The absolute value of f is taken as the smallest of the absolute values. n If there are multiple minimum values, then the minimum value f is taken. n ; ⑤ Calculate the effective value K of the vibration corresponding to the instantaneous acceleration during the current time interval Δt; ⑥ If K > 0, then update K in the "Vibration-Speed ​​Relationship Table" based on the f obtained in step ④. n In the corresponding vibration effective value unit, otherwise keep the original value; ⑦ When K1~K n If all values ​​are greater than 0, then a short-term diagnosis begins; 2) The diagnostic steps for phase shortening are as follows: I. Determine whether the instantaneous value of the motor stator current is normal and whether the three-phase current is balanced; If the instantaneous value of the motor stator current is normal and the three-phase current is balanced, then return to step 1). If the instantaneous value of the motor stator current is normal but the three-phase current is unbalanced, then continue to judge whether the instantaneous value of the motor stator current is normal and whether the three-phase current is balanced. If the instantaneous value of the motor stator current is overcurrent and the three-phase current is balanced, then continuously check whether the instantaneous value of the motor electronic current is normal and whether the three-phase current is balanced. If the instantaneous value of the motor stator current is overcurrent and the three-phase current is unbalanced, then perform subsequent phase short diagnosis. II. During phase short diagnosis, the motor speed data and corresponding instantaneous vibration acceleration data within the time interval Δt are acquired at regular intervals t, and ff is calculated sequentially. n The absolute value of f is taken as the smallest of the absolute values. n If there are multiple minimum values, then the minimum value f is taken. n ; III. Calculate the effective value K of the vibration acceleration within the current time interval Δt; IV. In the "Vibration-Speed ​​Relationship Table" obtained in step 1), find the value of f obtained in step II. n Corresponding K n Compare K obtained in step III. If K > 5 × K n Directly issue a short-term warning if 2×K n >K, return to step I, and continue to determine whether there is an overcurrent and whether there is an imbalance in the three phases. If 2×K n ≤K≤5×K n Then calculate the vibration spectrum function Vib_fft(f) corresponding to K obtained in step III; V. In the vibration spectrum, calculate the sum of energy fsum from the rotational frequency to 8 times the rotational frequency, which is the sum of the squares of the spectral amplitudes from fr to 8×fr. Where fr = fn / 60; extract the energy of the frequency bands at 1 / 2 / 4 / 6 / 8 times the turnaround frequency fr, respectively, that is, calculate the sum of squares of the spectral amplitude within the i×fr±3Hz frequency band. Where i = 1, 2, 4, 6, 8; VI. Compare the magnitudes of fd and fsum. If fd > 0.3 × fsum, directly perform phase short-circuit warning and protection. Otherwise, return to step I and continue to determine whether the current is overcurrent and whether there is an imbalance in the three phases.

2. The method for diagnosing phase-to-phase short-circuit faults in a permanent magnet motor according to claim 1, characterized in that, n is 10, f1~f 10 20% × f in sequence v 40%×f v 60%×f v 80%×f v f v f v +20%×(f max- f v ), f v +40%×(f max- f v ), f v +60%×(f max- f v ), f v +80%×(f max- f v ), f max .

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