A method and system for identifying high-resistance connection faults of a brushless DC motor

Abstract

The present invention discloses a method and system for identifying high-resistance connection faults in brushless DC motors, belonging to the field of brushless DC motors. The method mainly comprises: S1, combining the phase current commutation pattern and utilizing the box plot outlier detection principle to capture the current values ​​and time points before and after the phase current commutation; S2, estimating the commutation process time of the phase current; and S3, horizontally comparing the commutation time differences and commutation current amplitudes between the phase currents, and determining whether the brushless DC motor has a high-resistance connection fault based on the comparison results. Based on the commutation time differences, the present invention can accurately detect high-resistance connections and locate the faulty phase in a brushless DC motor.

Description

Technical Field

[0001] The present invention relates to the field of brushless DC motors, and in particular to a method and system for identifying high-resistance connection faults in brushless DC motors. Background Art

[0002] Brushless DC motors eliminate the issues associated with brushes and offer advantages such as compact structure, high efficiency, low cost, easy maintenance, a wide speed adjustment range, and a long service life. They are widely used in fields such as industrial automation and aerospace. The stator winding, a crucial component of a brushless DC motor, is susceptible to environmental factors, leading to winding failures. High-resistance connection failures in the stator winding are a common fault. These can cause thermal overload in the stator winding, accelerate insulation deterioration, and ultimately lead to open-circuit failures in the brushless DC motor. Therefore, accurately identifying high-resistance connection failures in the brushless DC motor and enabling planned power outages for maintenance can help ensure safe and stable motor operation.

[0003] Currently, the common identification methods for motor high-resistance connection faults are:

[0004] 1) Motor voltage drop measurement method: During motor operation, high-resistance connection faults can be identified and located by measuring the voltage between the circuit and each phase terminal of the motor.

[0005] 2) Infrared thermal imaging method: Use infrared cameras to monitor the temperature distribution in the motor power circuit in real time, and identify high-resistance connection faults by comparing the hot spots of different components.

[0006] 3) Signal injection method: Inject characteristic signals into the running motor and detect the characteristic signal distribution in the phase current to identify and locate high-resistance connection faults.

[0007] 4) Zero-sequence component method: By detecting the zero-sequence voltage or current component of the motor, analyzing its time-frequency domain spectrum characteristics, constructing a fault indicator or establishing a linear equation system to identify and locate high-resistance connection faults.

[0008] The above four methods for identifying motor high-resistance connection faults each have their own advantages and disadvantages:

[0009] 1) The motor voltage drop measurement method is simple in principle and low in cost. However, the motor voltage drop may also be caused by factors such as temperature and material fatigue. In addition, the measurement error of the voltage drop is related to the drive mode of the brushless DC motor, so the accuracy of fault identification is difficult to guarantee.

[0010] 2) Infrared thermal imaging is safer and faster, but it is expensive, requires infrared camera equipment, and may be affected by ambient thermal conditions and motor load (or stator current), making it difficult to implement in actual application scenarios.

[0011] 3) The signal injection method requires injecting a specific signal current into the motor, which usually requires adding a signal injection loop. It is an intrusive detection technology. On the one hand, the signal characteristic current may affect the normal operation of the motor and cause additional losses. On the other hand, the reliability and safety of the signal injection loop require special attention.

[0012] 4) The zero-sequence component method often requires additional hardware circuitry and phase neutral points to measure the zero-sequence voltage component. This is an intrusive detection technique, inconvenient, and may affect the normal operation of the motor. Furthermore, the zero-sequence component characteristics of high-resistance connection faults and turn-to-turn short-circuit faults are similar, making it difficult to accurately distinguish between these two faults using the conventional zero-sequence component method.

[0013] At present, these four types of fault identification methods are widely used in the diagnosis of high-resistance connection faults of permanent magnet synchronous motors or asynchronous motors. However, the mechanical structure and drive mode of brushless DC motors are somewhat different from those of permanent magnet synchronous motors. Conventional fault identification methods are difficult to directly apply to brushless DC motors, and there are few reports on research on high-resistance connection fault identification methods for brushless DC motors. Summary of the Invention

[0014] The purpose of the present invention is to overcome the technical problems existing in the prior art and provide a method and system for identifying high-resistance connection faults of brushless DC motors. Based on the mapping relationship between phase current commutation time and high-resistance connection faults, combined with the phase current commutation law, the box plot outlier detection principle is used to capture the phase current "inflection point", that is, the current value and time point before and after commutation, and then the commutation time difference and commutation current amplitude between the phase currents are horizontally compared to realize high-resistance connection detection and fault phase location of the brushless DC motor.

[0015] The object of the present invention is achieved through the following technical solutions:

[0016] In a first aspect, a method for identifying a high-resistance connection fault of a brushless DC motor is provided, comprising the following steps:

[0017] S1. Combined with the phase current commutation law, the box plot outlier detection principle is used to capture the current value and time point before and after the phase current commutation;

[0018] S2, estimating the commutation process time of the phase current;

[0019] S3. Compare the commutation time differences and commutation current amplitudes between the phase currents horizontally, and determine whether a high-resistance connection fault occurs in the brushless DC motor based on the comparison results.

[0020] In some embodiments, step S1 specifically includes:

[0021] S11, using a current sensor to obtain a discrete sampling sequence of phase current of the brushless DC motor;

[0022] S12. Calculating a time sequence difference sequence of phase currents according to the phase current discrete sampling sequence;

[0023] S13, selecting an integer number of time series difference values ​​from the time series difference value sequence to form a matrix;

[0024] S14, standardizing the matrix using Z-Score transformation to obtain a standardized matrix;

[0025] S15. Based on the outlier detection principle of the box plot, the upper and lower quartiles of the elements in any row of the standardized matrix are calculated in sequence, and the upper and lower limits of the outliers in any row of the standardized matrix are calculated;

[0026] S16. Find the element values ​​in the last column of the normalized matrix that exceed the corresponding upper and lower limits of the outliers, and thereby establish an inflection point matrix of the phase current.

[0027] Preferably, in step S11, the sampling period T=k·T0, and the sampling frequency is f s , so the number of discrete sampling of phase current N=T×f s , where T0 is the phase current period, and the coefficient k is a positive integer greater than 2.

[0028] Preferably, the upper and lower limits of the outliers of any row of the normalized matrix are calculated by the following formula:

[0029]

[0030] in, represents the upper bound on the number of outliers in any row of the normalized matrix, and represents the lower bound of the outlier value of any row of the normalized matrix, represents the upper quartile of any row of the standardized matrix, Represents the lower quartile of any row of the normalized matrix.

[0031] In some embodiments, step S2 specifically includes:

[0032] The first twelve inflection points of the phase current inflection point matrix are taken, and the time difference between two adjacent inflection points is calculated to obtain a time difference sequence.

[0033] In some embodiments, step S3 specifically includes:

[0034] Arrange the elements of the time difference sequence of the three phase currents in descending order to form a comprehensive time difference sequence. If the mean of the first six elements in the comprehensive time difference sequence is greater than 1 + Lim1 times the mean of the remaining twelve elements, it is considered that the brushless DC motor may have a high-resistance connection fault;

[0035] When a high-resistance connection fault may occur in the brushless DC motor, the maximum current values ​​of the inflection points of the three phase currents are taken for horizontal comparison. If the maximum current value of the inflection point of any phase current is less than Lim2 times the current of the remaining two phases, it is considered that a high-resistance connection fault has occurred in that phase.

[0036] Preferably, the value of Lim1 is 0.1-0.5.

[0037] Preferably, the value of Lim2 is 0.5-1.

[0038] In a second aspect, a brushless DC motor high-resistance connection fault identification system is provided, comprising:

[0039] The inflection point capture module is used to capture the current value and time points before and after the phase current commutation based on the phase current commutation law and the box plot outlier detection principle;

[0040] Commutation time calculation module, used to estimate the commutation process time of phase current;

[0041] The high-resistance connection fault judgment module is used to horizontally compare the commutation time difference and commutation current amplitude between the phase currents, and judge whether the brushless DC motor has a high-resistance connection fault based on the comparison results.

[0042] In some embodiments, the inflection point capture module includes a current sensor, which is used to obtain a discrete sampling sequence of phase currents of the brushless DC motor.

[0043] It should be further explained that the technical features corresponding to the above options can be combined or replaced with each other to form a new technical solution if there is no conflict.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) Based on the mapping relationship between phase current commutation time and high-resistance connection fault, the present invention combines the phase current commutation law and uses the box plot outlier detection principle to capture the phase current "inflection point", that is, the current value and time point before and after commutation. Then, the commutation time difference and commutation current amplitude between the phase currents are compared horizontally, which can realize the high-resistance connection detection and fault phase location of the brushless DC motor.

[0046] (2) The present invention only relies on the phase current sensor of the brushless DC motor, and does not require the addition of other sensors or measurement points. It is simple to operate, highly feasible, and does not affect the normal operation of the brushless DC motor.

[0047] (3) The present invention uses the box plot outlier detection principle to accurately capture the phase current inflection point. Compared with conventional rigid threshold judgment, it does not require complex parameter adjustment and has higher accuracy and versatility.

[0048] (4) The present invention inverts the health status of the brushless DC motor by detecting the change in the commutation time of the phase current. The characteristics of the commutation time difference are obvious and the fault differentiation is high, which is conducive to improving the accuracy of high-resistance connection fault identification of the brushless DC motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 A simplified flow chart of a method for identifying a high-resistance connection fault of a brushless DC motor according to an embodiment of the present invention;

[0050] Figure 2 This is a specific process of identifying a high-resistance connection fault according to an embodiment of the present invention. DETAILED DESCRIPTION

[0051] The technical solutions of the present invention are described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present application generally described and shown in the drawings herein can be arranged and designed in various different configurations. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0052] It should be noted that the defects existing in the solutions in the above-mentioned prior art are the results obtained by the inventor after practice and careful research. Therefore, the discovery process of the above-mentioned problems and the solutions proposed in the embodiments of this application below for the above-mentioned problems should be the contributions made by the inventor to this application in the process of invention and creation, and should not be understood as technical contents known to technical personnel in this field.

[0053] In response to the technical problems pointed out in the background technology, the embodiments provided by the present invention are as follows:

[0054] Reference Figure 1 A method for identifying high-resistance connection faults in brushless DC motors is proposed. Combining the phase current commutation law of the brushless DC motor, the box plot outlier detection principle is used to capture the phase current "inflection point", that is, the current value and time point before and after the commutation, and then the commutation process time of any phase current is estimated. The commutation time difference and commutation current amplitude between the phase currents are then compared horizontally, thereby realizing high-resistance connection detection and fault phase location of the brushless DC motor. Figure 2 The specific steps are as follows:

[0055] S1. Use the current sensor to obtain the discrete sampling sequence of the i-phase (i=a, b, c) current of the brushless DC motor Among them, the sampling period T = k·T0 (T0 is the phase current period, the coefficient k is a positive integer greater than 2), the sampling frequency is f s , so N = T × f s.

[0056] According to the discrete sampling value x of phase i current i , calculate the time difference sequence D of phase i current i .

[0057]

[0058] From the time difference sequence D i Select L time series differences to form the matrix Bx i .

[0059]

[0060] In particular, the parameter L is a positive integer, which is determined according to the actual situation of the brushless DC motor; Bx i (m,p) represents the matrix Bx i The value of the element in row m and column p.

[0061] Use Z-Score transformation to transform matrix Bx i Perform standardization to obtain the standardized matrix PB i .

[0062]

[0063]

[0064] Furthermore, according to the outlier detection principle of the box plot, the standardized matrix PB is calculated in turn. i The upper and lower quartiles of the elements in any m-th row (m=1,2,…,NL) and Thus the normalized matrix PB i The lower and upper bounds of outliers in any m-th row and

[0065]

[0066] Find the normalized matrix PB i The last column element PB i (m,L) exceeds the corresponding outlier upper and lower limits and The element value of the i-phase current is used to establish the inflection point matrix TP i .

[0067] Specifically, if or It is believed that PB i Bx corresponding to (m,L) i There is an inflection point at (m, L), that is, the current discrete value It is the inflection point of phase i current.

[0068]

[0069] In the above formula, is the timing position of the inflection point of the i-phase current, is the corresponding inflection point current value, is the number of inflection points of phase i current.

[0070] S2. Take the i-phase current inflection point matrix TP i The first 12 inflection points of , calculate the time difference between two adjacent inflection points, and obtain the time difference sequence Dt i .

[0071]

[0072] S3. The time difference sequence Dt of the three-phase currents a, b, and c a ,Dt b With Dt c The element values ​​are arranged in descending order to form a comprehensive time difference sequence DT. If the mean of the first 6 elements in the comprehensive time difference sequence DT is greater than (1+Lim1) times the mean of the remaining 12 elements, it is considered that the brushless DC motor may have a high-resistance connection fault, that is:

[0073] mean{DT(1:6,1)}>(1+Lim1)×mean{DT(7:18,1)}

[0074] In the above formula, mean{} represents the function of taking the mean; Lim1 represents the time difference threshold, which is generally set to 0.1~0.5.

[0075] When a high-resistance connection fault may occur in the brushless DC motor, the maximum inflection current values ​​of the three-phase currents a, b, and c are taken for horizontal comparison. If the maximum inflection current value of the F-th phase current (F∈{a,b,c}) is less than Lim2 times the currents of the remaining two phases, it is considered that a high-resistance connection fault has occurred in the F-th phase, that is:

[0076]

[0077] In the above formula, max{} represents the function of taking the maximum value; Lim2 represents the current difference threshold, which is generally 0.5 to 1.

[0078] In summary, by combining the phase current commutation law of the brushless DC motor and using the box plot outlier detection principle to accurately capture the phase current "inflection point", the commutation process time of any phase current is estimated. The commutation time differences and commutation current amplitudes between the phase currents are then compared horizontally to realize high-resistance connection detection and fault phase location of the brushless DC motor.

[0079] In another exemplary embodiment, based on the same inventive concept as the method, a brushless DC motor high-resistance connection fault identification system is provided, comprising:

[0080] The inflection point capture module is used to capture the current value and time points before and after the phase current commutation based on the phase current commutation law and the box plot outlier detection principle;

[0081] Commutation time calculation module, used to estimate the commutation process time of phase current;

[0082] The high-resistance connection fault judgment module is used to horizontally compare the commutation time difference and commutation current amplitude between the phase currents, and judge whether the brushless DC motor has a high-resistance connection fault based on the comparison results.

[0083] It should be noted that each module in the system implements functions corresponding to each step in the method, which will not be described in detail here.

[0084] Furthermore, the inflection point capture module includes a current sensor, and the current sensor is used to obtain a discrete sampling sequence of phase current of the brushless DC motor.

[0085] The above specific implementation methods are detailed descriptions of the present invention. It cannot be considered that the specific implementation methods of the present invention are limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, they can make several simple deductions and substitutions without departing from the concept of the present invention, which should be regarded as falling within the scope of protection of the present invention.

Claims

1. A method for identifying high-resistance connection faults in a brushless DC motor, characterized in that: The following steps are involved: S1. Combined with the phase current commutation law, the box plot outlier detection principle is used to capture the current value and time points before and after the phase current commutation; S2, estimating the commutation process time of the phase current; S3. Compare the commutation time differences and commutation current amplitudes between the phase currents horizontally, and determine whether a high-resistance connection fault occurs in the brushless DC motor based on the comparison results.

2. The method for identifying a high-resistance connection fault of a brushless DC motor according to claim 1, wherein: Step S1 specifically includes: S11, using a current sensor to obtain a discrete sampling sequence of phase currents of the brushless DC motor; S12. Calculating a time sequence difference sequence of phase currents according to the phase current discrete sampling sequence; S13, selecting an integer number of time series difference values ​​from the time series difference value sequence to form a matrix; S14, standardizing the matrix using Z-Score transformation to obtain a standardized matrix; S15. Based on the outlier detection principle of the box plot, the upper and lower quartiles of the elements in any row of the standardized matrix are calculated in sequence, and the upper and lower limits of the outliers in any row of the standardized matrix are calculated; S16. Find the element values ​​in the last column of the normalized matrix that exceed the corresponding upper and lower limits of the outliers, and thereby establish an inflection point matrix of the phase current.

3. The method for identifying a high-resistance connection fault of a brushless DC motor according to claim 2, wherein: Sampling period in step S11 , the sampling frequency is , so the number of discrete sampling of phase current is ,in, is the phase current period, coefficient k Take a positive integer greater than 2.

4. The method for identifying a high-resistance connection fault of a brushless DC motor according to claim 2, wherein: The upper and lower limits of outliers in any row of the normalized matrix are calculated as follows: ,in, represents the upper bound on the number of outliers in any row of the normalized matrix, represents the lower bound of the outlier value of any row of the normalized matrix, represents the upper quartile of any row of the standardized matrix, Represents the lower quartile of any row of the normalized matrix.

5. The method for identifying a high-resistance connection fault of a brushless DC motor according to claim 2, wherein: Step S2 specifically includes: The first twelve inflection points of the phase current inflection point matrix are taken, and the time difference between two adjacent inflection points is calculated to obtain a time difference sequence.

6. The method for identifying a high-resistance connection fault of a brushless DC motor according to claim 5, wherein: Step S3 specifically includes: Arrange the time difference sequence elements of the three phase currents in descending order to form a comprehensive time difference sequence. If the mean of the first six elements in the comprehensive time difference sequence is greater than 1+ the mean of the remaining twelve elements Lim1 times, it is considered that the brushless DC motor may have a high-resistance connection fault; Lim1 represents the temporal difference threshold; When a high-resistance connection fault may occur in the brushless DC motor, the maximum current values ​​of the three phase currents are taken for horizontal comparison. If the maximum current value of the inflection point of a phase current is less than that of the remaining two phase currents, Lim2 times, it is considered that a high-resistance connection fault has occurred in this phase; Lim2 Represents the current difference threshold.

7. The method for identifying a high-resistance connection fault of a brushless DC motor according to claim 6, wherein: described Lim1 The value is 0.1~0.

5.

8. The method for identifying a high-resistance connection fault of a brushless DC motor according to claim 6, wherein: described Lim2 The value is 0.5~1.

9. A brushless DC motor high-resistance connection fault identification system, characterized in that: include: The inflection point capture module is used to capture the current value and time points before and after the phase current commutation based on the phase current commutation law and the box plot outlier detection principle; Commutation time calculation module, used to estimate the commutation process time of phase current; The high-resistance connection fault judgment module is used to horizontally compare the commutation time difference and commutation current amplitude between the phase currents, and judge whether the brushless DC motor has a high-resistance connection fault based on the comparison results.

10. The brushless DC motor high-resistance connection fault identification system according to claim 9, characterized in that: The inflection point capture module includes a current sensor, which is used to obtain a discrete sampling sequence of phase currents of the brushless DC motor.

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