A method for determining asynchronous motor fault based on current vector modulus

Abstract

The present invention discloses a method for diagnosing asynchronous motor faults, which transforms the three-phase current of the motor stator to the dq axis rotating at a three-phase synchronous speed. The dq component of the current is mainly direct current, and the comprehensive vector length of the stator current is also direct current. Faults such as stator turn-to-turn short circuit, rotor bar breakage, rotor eccentricity, and bearing damage are reflected in the pulsating changes of the dq current and vector length. According to the pulsating frequency, it is easy to identify the motor fault. Since the motor is usually powered by an inverter, the three-phase current on the motor stator has a lot of harmonic content. After the motor fails, the three-phase AC current contains both harmonics generated by the inverter or frequency converter power supply and harmonics generated after the fault. It is not easy to distinguish these harmonics. The method provided by the present invention overcomes this shortcoming and has the advantages of convenient detection and simple algorithm. The present invention uses the current component and the comprehensive current vector length I under the synchronous rotating coordinate system dq0. l As a characteristic quantity, the result of asynchronous motor fault diagnosis is more accurate.

Description

Technical Field

[0001] The invention relates to the technical field of motor state monitoring, in particular to a method for motor fault diagnosis, which is a fault diagnosis method based on dq axis DC components and current comprehensive vectors. Background Art

[0002] As a transmission machine, asynchronous motors are widely used in power plants, steel mills, ships and other industrial and defense fields, and their safe operation is crucial. Asynchronous motors are generally in a state of continuous operation for a long time and in a harsh working environment, so failures are inevitable. Asynchronous motor failures not only damage the motor itself, but also affect the entire transmission system. If they are not discovered and repaired in time, accidents and downtime will occur, resulting in economic losses and even casualties.

[0003] At present, the "periodic maintenance (such as minor maintenance every six months and major maintenance every year)" method is usually adopted to avoid asynchronous motor shutdown due to accidents. However, due to the existence of maintenance cycles, asynchronous motors may fail or have accidents within the maintenance cycle, and the "periodic maintenance" method is powerless to prevent this. This is what is called "missed inspection" on the construction site; on the other hand, when the maintenance cycle comes, the asynchronous motor may not have any faults, or even be in good condition. The "periodic maintenance" method will cause what is called "over-inspection" on the construction site. "Misinspection" will lead to accidents and shutdowns of asynchronous motors, and the losses are self-evident. "Over-inspection" will lead to unnecessary maintenance costs and downtime.

[0004] The emergence, development and application of asynchronous motor fault detection and diagnosis technology have gradually transformed the traditional post-maintenance and periodic maintenance methods into predictive maintenance methods.

[0005] Statistics show that asynchronous motor failures mainly include stator winding inter-turn short circuit failure, rotor bar broken failure and bearing failure, with the probability of occurrence being approximately 6%, 30%, 10% and 40% respectively. These failures are progressive and become accidents after going through the occurrence and development stages.

[0006] There have also been a lot of research and applications on motor drive system faults, such as rolling bearing, gear and shaft faults. In recent years, with the development of computer simulation technology, the literature on fault diagnosis theory modeling, simulation analysis, etc. for broken bars, eccentricity, bearings, etc. has gradually increased. The scope of application has also gradually expanded to fields such as frequency conversion, DC and AC servo motors.

[0007] Regardless of how the motor stator electrical signal is obtained, its frequency component is mainly the power supply frequency, and the real fault signal component is very weak. Therefore, how to extract the weak fault signal and eliminate the useless power supply frequency component is the basis for the asynchronous motor fault detection and diagnosis method to be widely used.

[0008] For the amplitude modulation of electrical signals, the most basic analysis method is to use the sideband analysis method of amplitude spectrum or refined spectrum. Due to the instability of the sideband, Hilbert transform can also be used to obtain the envelope spectrum and instantaneous frequency spectrum of the electrical signal for analysis. Among them, the envelope spectrum can remove the main power frequency with a large amplitude in the electrical signal, highlight the fault characteristic frequency, and the expression form of the spectrum is the same as the conventional vibration signal spectrum, which is convenient for analysis and comparison; the instantaneous frequency spectrum is more suitable for extracting the frequency modulation component in the current signal. Hilbert transform demodulation spectrum analysis also has disadvantages. For the modulation signal demodulation spectrum exceeding the carrier frequency, additional demodulation frequency components will be generated. This phenomenon is called overmodulation. The additional frequency components appearing in the demodulation spectrum are called overmodulation folded frequency components. Some scholars use square demodulation method or quadratic frequency shift demodulation method to solve the problem, but the fault characteristic frequency will be displaced in the spectrum, and additional harmonic components will appear, which is not conducive to the identification and diagnosis of spectrum characteristics. Summary of the invention

[0009] In order to solve the problems of the prior art, the purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for determining the fault of an asynchronous motor based on the current vector modulus, using the current component and the comprehensive current vector length I under the synchronous rotating coordinate system dq0. l As a characteristic quantity, the result of asynchronous motor fault diagnosis is more accurate, and it has the advantages of convenient detection and simple algorithm.

[0010] In order to achieve the above invention purpose, the present invention adopts the following technical solution:

[0011] A method for determining asynchronous motor fault based on current vector modulus, the operation steps are as follows:

[0012] (1) Obtain the three-phase stator current i of the asynchronous motor to be detected sa 、i sb 、i sc ;

[0013] (2) Change i sa 、i sb 、i sc The current component i is transformed to the synchronous rotating coordinate system dq0 sd 、i sq ;

[0014] (3) for i sd 、i sq Perform spectrum analysis;

[0015] (4) Change i sa 、i sb 、i sc Transformed to the current component i in the two-phase stationary αβ0 coordinate systemsα 、i sβ ;

[0016] (5) Calculate the value of i sα 、i sβ The modulus length of the comprehensive current vector formed;

[0017] (6) Perform spectrum analysis on the current vector modulus;

[0018] (7) The fault type of the asynchronous motor to be monitored is determined based on the results of the above spectrum analysis.

[0019] Preferably, the specific operation steps of step (2) are:

[0020] i in the synchronously rotating dq0 coordinate system sd 、i sq Use the following formula to obtain:

[0021]

[0022] where θ e is the synchronous electrical angle.

[0023] Preferably, the specific operation steps of step (3) are:

[0024] The DC current component in the synchronous rotating coordinate system is subjected to discrete Fourier transform, and the calculation formula is:

[0025]

[0026] Where: I dq is the current in the frequency domain, k is the ordinal number on the frequency axis, n is the ordinal number on the time axis, and N is the length of the sampled current.

[0027] Preferably, the specific operation steps of step (4) are:

[0028] i in the two-phase stationary αβ0 coordinate system sα 、i sβ Use the following formula to obtain:

[0029]

[0030] Preferably, the specific operation steps of step (5) are:

[0031] The calculation formula for the modulus of the current vector is: Where: |I l | is the current vector modulus length.

[0032] Preferably, the specific operation steps of step (6) are:

[0033] Perform discrete Fourier transform on the current vector modulus, and the calculation formula is: Where: I L is the current vector modulus in the frequency domain, k is the ordinal number on the frequency axis, n is the ordinal number on the time axis, and N is the length of the sampled current.

[0034] Preferably, the specific operation steps of step (7) are:

[0035] When the component of the stator current under the synchronous rotating coordinate axis is DC and has no obvious pulsation change, and the vector length of the stator current is a fixed value, the motor has no fault;

[0036] When the component of the stator current under the synchronous rotating coordinate axis has a pulsation of twice the fundamental frequency, and the vector length of the stator current also has a pulsation of twice the fundamental frequency, the motor has a turn-to-turn short circuit fault;

[0037] When the component of the stator current under the synchronous rotating coordinate axis exists 2ksf 1 The frequency pulsation, the vector length of the stator current also exists 2ksf 1 When the frequency pulsates, the motor has a broken rotor bar failure;

[0038] When the component of the stator current under the synchronous rotating coordinate axis exists kf outer The frequency pulsation, the vector length of the stator current also exists kf outer When the frequency pulsates, the motor has a bearing outer track failure;

[0039] When the component of the stator current under the synchronous rotating coordinate axis exists kf inner The frequency pulsation, the vector length of the stator current also exists kf inner When the frequency pulsates, the motor has a bearing track failure;

[0040] When the component of the stator current under the synchronous rotating coordinate axis exists kf ball The frequency pulsation, the vector length of the stator current also exists kf ball When the frequency pulsates, the motor has a bearing ball failure;

[0041] When the component of the stator current under the synchronous rotating coordinate axis exists kf r The frequency pulsation, the vector length of the stator current also exists kf r When the frequency pulsates, the motor has a mixed eccentricity fault;

[0042] Where k is an integer, s is the slip rate, f 1 、f outer 、f inner 、f ball They are the fundamental frequency, the characteristic frequency of the outer track of the bearing, the inner track of the bearing and the ball when they fail, fr is the rotation frequency of the motor.

[0043] Compared with the prior art, the present invention has the following obvious outstanding substantive features and significant advantages:

[0044] 1. Compared with the traditional sensor-based detection method, the present invention has the advantages of convenient detection and simple algorithm;

[0045] 2. The present invention overcomes the problem that the fault diagnosis of asynchronous motors fails due to the presence of a large number of harmonics in the stator current caused by the inverter or frequency converter power supply;

[0046] 3. The present invention uses the current component and the comprehensive current vector length I under the synchronous rotating coordinate system dq0 l As a characteristic quantity, the result of asynchronous motor fault diagnosis is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 Flowchart for motor fault diagnosis.

[0048] Figure 2 This is the matlab / simulink simulation model for three-phase asynchronous motor turn-to-turn short-circuit fault detection.

[0049] Figure 3 This is the matlab / simulink simulation model for detecting broken rotor bar faults in a three-phase asynchronous motor.

[0050] Figure 4 This is the matlab / simulink simulation model for three-phase asynchronous motor bearing fault detection.

[0051] Figure 5 This is the simulation result when an asynchronous motor has a turn-to-turn short circuit fault.

[0052] Figure 6 This is the simulation result when an asynchronous motor has a broken rotor bar fault.

[0053] Figure 7 These are the simulation results when a mixed eccentricity fault occurs in an asynchronous motor.

[0054] Figure 8 This is the simulation result when the asynchronous motor has an outer track fault.

[0055] Fig. 9 This is the simulation result when the asynchronous motor has an inner track fault.

[0056] Fig.10 This is the simulation result when a ball failure occurs in an asynchronous motor. DETAILED DESCRIPTION

[0057] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0058] The above scheme is further described below in conjunction with specific implementation examples. The preferred embodiments of the present invention are described in detail as follows:

[0059] Embodiment 1:

[0060] In this embodiment, a method for determining an asynchronous motor fault based on a current vector modulus is provided, and the operation steps are as follows:

[0061] (1) Obtain the three-phase stator current i of the asynchronous motor to be detected sa 、i sb 、i sc ;

[0062] (2) Change i sa 、i sb 、i sc The current component i is transformed to the synchronous rotating coordinate system dq0 sd 、i sq ;

[0063] (3) for i sd 、i sq Perform spectrum analysis;

[0064] (4) Change i sa 、i sb 、i sc Transformed to the current component i in the two-phase stationary αβ0 coordinate system sα 、i sβ ;

[0065] (5) Calculate the value of i sα 、i sβ The modulus length of the comprehensive current vector formed;

[0066] (6) Perform spectrum analysis on the current vector modulus;

[0067] (7) The fault type of the asynchronous motor to be monitored is determined based on the results of the above spectrum analysis.

[0068] This embodiment uses the current component and the comprehensive current vector length Il under the synchronous rotating coordinate system dq0 as characteristic quantities, so that the results of asynchronous motor fault diagnosis are more accurate, with the advantages of convenient detection and simple algorithm. The method transforms the three-phase current of the motor stator to the dq axis rotating at a three-phase synchronous speed. The current dq component is mainly DC, and the comprehensive vector length of the stator current is also DC. Faults such as stator turn short circuit, rotor broken bar, rotor eccentricity, bearing damage, etc. are reflected in the pulsating changes of dq current and vector length. According to the pulsating frequency, it is easy to identify the motor fault. Since the motor is usually powered by an inverter, the three-phase current on the motor stator has a lot of harmonic content. After the motor fails, the three-phase AC current has both harmonics generated by the inverter or frequency converter power supply and harmonics generated after the fault. It is not easy to distinguish these harmonics. The method of this embodiment overcomes this shortcoming and improves efficiency.

[0069] Embodiment 2:

[0070] This embodiment is basically the same as the first embodiment, except that:

[0071] In this embodiment, the specific operation steps of step (2) are as follows:

[0072] i in the synchronously rotating dq0 coordinate system sd 、i sq Use the following formula to obtain:

[0073]

[0074] where θ e is the synchronous electrical angle.

[0075] In this embodiment, the specific operation steps of step (3) are as follows:

[0076] The DC current component in the synchronous rotating coordinate system is subjected to discrete Fourier transform, and the calculation formula is:

[0077]

[0078] Where: I dq is the current in the frequency domain, N is the sequence length of the sampled current, n is the ordinal number on the time axis, and k is the ordinal number on the frequency axis.

[0079] In this embodiment, the specific operation steps of step (4) are as follows:

[0080] i in the two-phase stationary αβ0 coordinate system sα 、i sβ Use the following formula to obtain:

[0081]

[0082] In this embodiment, the specific operation steps of step (5) are as follows:

[0083] The calculation formula for the modulus of the current vector is: Where: |I l | is the current vector modulus length.

[0084] In this embodiment, the specific operation steps of step (6) are:

[0085] Perform discrete Fourier transform on the current vector modulus, and the calculation formula is: Where: I L is the current vector modulus in the frequency domain, and N is the length of the sampled current.

[0086] In this embodiment, the specific operation steps of step (7) are:

[0087] When the component of the stator current under the synchronous rotating coordinate axis is DC and has no obvious pulsation change, and the vector length of the stator current is a fixed value, the motor has no fault;

[0088] When the component of the stator current under the synchronous rotating coordinate axis has a pulsation of twice the fundamental frequency, and the vector length of the stator current also has a pulsation of twice the fundamental frequency, the motor has a turn-to-turn short circuit fault;

[0089] When the component of the stator current under the synchronous rotating coordinate axis exists 2ksf 1 The frequency pulsation, the vector length of the stator current also exists 2ksf 1 When the frequency pulsates, the motor has a broken rotor bar failure;

[0090] When the component of the stator current under the synchronous rotating coordinate axis exists kf outer The frequency pulsation, the vector length of the stator current also exists kf outer When the frequency pulsates, the motor has a bearing outer track failure;

[0091] When the component of the stator current under the synchronous rotating coordinate axis exists kf inner The frequency pulsation, the vector length of the stator current also exists kf inner When the frequency pulsates, the motor has a bearing track failure;

[0092] When the component of the stator current under the synchronous rotating coordinate axis exists kf ball The frequency pulsation, the vector length of the stator current also exists kf ball When the frequency pulsates, the motor has a bearing ball failure;

[0093] When the component of the stator current under the synchronous rotating coordinate axis exists kf r The frequency pulsation, the vector length of the stator current also exists kfr When the frequency pulsates, the motor has a mixed eccentricity fault;

[0094] Where k is an integer, s is the slip rate, f 1 、f outer 、f inner 、f ball They are the fundamental frequency, the characteristic frequency of the outer track of the bearing, the inner track of the bearing and the ball when they fail, f r is the rotation frequency of the motor.

[0095] Compared with the traditional sensor-based detection method, the method of this embodiment has the advantages of convenient detection and simple algorithm; the method of this embodiment overcomes the problem that the asynchronous motor fault diagnosis fails due to the presence of a large number of harmonics in the stator current caused by the power supply of the inverter or frequency converter.

[0096] Embodiment three:

[0097] This embodiment is basically the same as the above embodiment, with the following features:

[0098] In this embodiment, if Figure 1 The flowchart of a motor fault diagnosis method according to the present embodiment is shown, and the method comprises the following steps:

[0099] Step 1: Get the three-phase stator current i sa 、i sb 、i sc ;

[0100] Step 2: i sa 、i sb 、i sc The current component i is transformed to the synchronous rotating coordinate system dq0 sd 、i sq ;

[0101]

[0102] Step 3: Perform discrete Fourier transform on the DC current component in the synchronous rotating coordinate system. The calculation formula is:

[0103]

[0104] Step 4: i sa 、i sb 、i sc The current component i transformed to the two-phase stationary coordinate system αβ0 sα 、i sβ :

[0105]

[0106] Step 5: According to isα 、i sβ Calculate the magnitude of the current vector:

[0107] Step 6: Perform discrete Fourier transform on the current vector modulus, and the calculation formula is:

[0108] Step 7: Determine the type of fault based on the diagnosis results:

[0109] When the component of the stator current under the synchronous rotating coordinate axis is DC and has no obvious pulsation change, and the vector length of the stator current is a fixed value, the motor has no fault;

[0110] When the component of the stator current under the synchronous rotating coordinate axis has a pulsation of twice the fundamental frequency, and the vector length of the stator current also has a pulsation of twice the fundamental frequency, the motor has a turn-to-turn short circuit fault;

[0111] When the component of the stator current under the synchronous rotating coordinate axis exists 2ksf 1 The frequency pulsation, the vector length of the stator current also exists 2ksf 1 When the frequency pulsates, the motor has a broken rotor bar failure;

[0112] When the component of the stator current under the synchronous rotating coordinate axis exists kf outer The frequency pulsation, the vector length of the stator current also exists kf outer When the frequency pulsates, the motor has a bearing outer track failure;

[0113] When the component of the stator current under the synchronous rotating coordinate axis exists kf inner The frequency pulsation, the vector length of the stator current also exists kf inner When the frequency pulsates, the motor has a bearing track failure;

[0114] When the component of the stator current under the synchronous rotating coordinate axis exists kf ball The frequency pulsation, the vector length of the stator current also exists kf ball When the frequency pulsates, the motor has a bearing ball failure;

[0115] When the component of the stator current under the synchronous rotating coordinate axis exists kf r The frequency pulsation, the vector length of the stator current also exists kf r When the frequency pulsates, the motor has a mixed eccentricity fault;

[0116] Where k is an integer, s is the slip rate, f 1 is the supply frequency, f outer 、f inner 、f ballare the characteristic frequencies of the outer track of the bearing, the inner track of the bearing and the ball when they fail, f r is the rotation frequency of the motor.

[0117] Figure 2 to Figure 4 For the faulty motor open-loop system simulation model built on Matlab / Simulink simulation software, the fault diagnosis method is built according to the design steps introduced above.

[0118] Figures 5 to 10 The dq-axis DC component and the modulus length of the current comprehensive vector obtained by simulation are analyzed by spectrum analysis of the simulation results, and the conclusions are shown in the following table:

[0119]

[0120] Compared with the traditional sensor-based detection method, the method of this embodiment has the advantages of convenient detection and simple algorithm; the method of this embodiment overcomes the problem that the stator current has a large number of harmonics caused by inverter or frequency converter power supply, which leads to the failure of asynchronous motor fault diagnosis; the method of this embodiment uses the current component under the synchronous rotating coordinate system dq0 and the comprehensive current vector length I l As a characteristic quantity, the result of asynchronous motor fault diagnosis is more accurate.

[0121] The above describes the embodiments of the present invention in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made according to the purpose of the invention. Any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principle of the technical solution of the present invention should be equivalent replacement methods. As long as they meet the purpose of the invention and do not deviate from the technical principles and inventive concepts of the present invention, they belong to the protection scope of the present invention.

Claims

1. A method for determining an asynchronous motor fault based on current vector modulus, characterized in that: The operation steps are as follows: (1) Obtain the three-phase stator current i of the asynchronous motor to be detected sa 、i sb 、i sc ; (2) Change i sa 、i sb 、i sc The current component i is transformed to the synchronous rotating coordinate system dq0 sd 、i sq ; (3) for i sd 、i sq Perform spectrum analysis; the specific steps are: The DC current component in the synchronous rotating coordinate system is subjected to discrete Fourier transform, and the calculation formula is: Where: I dq is the current in the frequency domain, N is the sequence length of the sampled current, n is the ordinal number on the time axis, and k is the ordinal number on the frequency axis; (4) Change i sa 、i sb 、i sc Transformed to the current component i in the two-phase stationary αβ0 coordinate system sα 、i sβ ; (5) Calculate the value of i sα 、i sβ The modulus length of the comprehensive current vector is calculated as follows: Where: |I l | is the current vector modulus; (6) Perform spectrum analysis on the current vector modulus. The specific steps are as follows: Perform discrete Fourier transform on the current vector modulus, and the calculation formula is: Where: I l is the current vector modulus in the frequency domain, and N is the length of the sampled current; (7) The fault type of the asynchronous motor to be monitored is determined based on the results of the above spectrum analysis.

2. The method for determining asynchronous motor fault based on current vector modulus according to claim 1 is characterized in that: The specific operation steps of step (2) are as follows: i in the synchronously rotating dq0 coordinate system sd 、i sq Use the following formula to obtain: where θ e is the synchronous electrical angle.

3. The method for determining asynchronous motor fault based on current vector modulus according to claim 1, characterized in that: The specific operation steps of step (4) are as follows: i in the two-phase stationary αβ0 coordinate system sα 、i sβ Use the following formula to obtain:

4. The method for determining asynchronous motor fault based on current vector modulus according to claim 1, characterized in that: The specific operation steps of step (7) are as follows: When the component of the stator current under the synchronous rotating coordinate axis is DC and has no obvious pulsation change, and the vector length of the stator current is a fixed value, the motor has no fault; When the component of the stator current under the synchronous rotating coordinate axis has a pulsation of twice the fundamental frequency, and the vector length of the stator current also has a pulsation of twice the fundamental frequency, the motor has a turn-to-turn short circuit fault; When the component of the stator current under the synchronous rotating coordinate axis pulsates at a frequency of 2ksf1, and the vector length of the stator current also pulsates at a frequency of 2ksf1, a rotor bar breakage fault occurs in the motor; When the component of the stator current under the synchronous rotating coordinate axis exists kf outer The frequency pulsation, the vector length of the stator current also exists kf outer When the frequency pulsates, the motor has a bearing outer track failure; When the component of the stator current under the synchronous rotating coordinate axis exists kf inner The frequency pulsation, the vector length of the stator current also exists kf inner When the frequency pulsates, the motor has a bearing track failure; When the component of the stator current under the synchronous rotating coordinate axis exists kf ball The frequency pulsation, the vector length of the stator current also exists kf ball When the frequency pulsates, the motor has a bearing ball failure; When the component of the stator current under the synchronous rotating coordinate axis exists kf r The frequency pulsation, the vector length of the stator current also exists kf r When the frequency pulsates, the motor has a mixed eccentricity fault; Where k is an integer, s is the slip rate f1, f outer 、f inner 、f ball They are the fundamental frequency, the characteristic frequency of the outer track of the bearing, the inner track of the bearing and the ball when they fail, f r is the rotation frequency of the motor.

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