Brushless DC motor high-resistance connection fault identification method and system

Abstract

The invention discloses a brushless direct current motor high-resistance connection fault identification method and system, and belongs to the field of brushless direct current motors, and the method mainly comprises the steps: S1, capturing current values and time points before and after phase current commutation through employing a box diagram outlier detection principle in combination with a phase current commutation rule; s2, estimating the commutation process time of the phase current; and S3, transversely comparing the commutation time difference and the commutation current amplitude between each phase of current, and judging whether the brushless direct current motor has a high-resistance connection fault or not according to a comparison result. According to the invention, based on the commutation time difference, high-resistance connection detection and fault phase positioning of the brushless direct current motor can be accurately realized.

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 of brushless DC motors. Background Art

[0002] Brushless DC motors eliminate the brush problem and have the advantages of compact structure, high efficiency, low cost, easy maintenance, wide speed adjustment range, and long service life. They are widely used in industrial automation, aerospace and other fields. The stator winding is an important part of the brushless DC motor and is easily affected by environmental factors, resulting in winding failure. Among them, the high-resistance connection failure of the stator winding is one of the common faults, which will cause thermal overload of the stator winding, accelerate the deterioration of the insulation performance of the stator winding, and eventually lead to an open circuit failure in the brushless DC motor. Therefore, accurately identifying the high-resistance connection failure of the brushless DC current and then carrying out planned power outage maintenance work is conducive to ensuring the safe and stable operation of the motor.

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

[0004] 1) Motor voltage drop measurement method: During the operation of the motor, the voltage between the circuit and each phase terminal of the motor is measured to identify and locate the high resistance connection fault.

[0005] 2) Infrared thermal imaging method: Use an infrared camera 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 identify and locate high-resistance connection faults by detecting the characteristic signal distribution in the phase current.

[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 group to identify and locate high-resistance connection faults.

[0008] The above four types of motor high-resistance connection fault identification methods each have their own advantages and disadvantages:

[0009] 1) The motor voltage drop measurement method is simple in principle and low in cost, but the motor voltage drop may also be caused by factors such as temperature and material fatigue, and the measurement error of the voltage drop is related to the driving 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), so it is not very feasible in actual application scenarios.

[0011] 3) The signal injection method requires injecting a specific signal current into the motor, and usually requires adding a signal injection loop. It is an invasive 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 the addition of additional hardware circuits and phase neutral points to achieve the measurement of the zero-sequence voltage component. It is an intrusive detection technology, which is not very convenient to detect and may also affect the normal operation of the motor. In addition, the zero-sequence component characteristics of high-resistance connection faults and turn-to-turn short-circuit faults are similar, and the conventional zero-sequence component method is difficult to accurately distinguish between the above two faults.

[0013] At present, these four types of fault identification methods are widely used in the high-resistance connection fault diagnosis of permanent magnet synchronous motors or asynchronous motors. However, there are certain gaps between the mechanical structure and drive mode of brushless DC motors and permanent magnet synchronous motors. Conventional fault identification methods are difficult to directly apply to brushless DC motors, and there are few reports on the 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 the 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 objective 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 difference sequence of phase current according to the phase current discrete sampling sequence;

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

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

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

[0026] S16. Find the element values ​​in the last column of the standardized matrix that exceed the corresponding upper and lower limits of the outliers, so as to establish the 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 limit of outliers for 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 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+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 inflection point currents of the three phase currents are taken for horizontal comparison. If the maximum inflection point current of any phase current is less than Lim2 times the currents 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 point before and after the phase current commutation according to the phase current commutation law and the box plot outlier detection principle;

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

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

[0042] In some embodiments, 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.

[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 the commutation, and then horizontally compares the commutation time difference and commutation current amplitude between the phase currents, so as to 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 need to add 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 utilizes the box plot outlier detection principle to realize accurate capture of the phase current inflection point. Compared with the 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 beneficial 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 shown in an embodiment of the present invention;

[0050] Figure 2 The specific process of high-resistance connection fault identification shown in the embodiment of the present invention. DETAILED DESCRIPTION

[0051] The technical solution of the present invention is clearly and completely described 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 described and shown in the accompanying drawings can be arranged and designed in various 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 the present application for the above-mentioned problems below should all be the contributions made by the inventor to the present 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 view of 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 of brushless DC motors is proposed. Combining the phase current commutation law of brushless DC motors, 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. Then, the commutation time difference and commutation current amplitude between the phase currents are compared horizontally, thereby realizing the high-resistance connection detection and fault phase location of brushless DC motors. Figure 2 The specific steps are as follows:

[0055] S1. Use the current sensor to obtain the i-phase (i=a, b, c) current discrete sampling sequence of the brushless DC motor Among them, the sampling period T = k·T0 (T0 is the phase current period, and the coefficient k is a positive integer greater than 2), and 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 the mth row and pth column.

[0061] Using Z-Score transformation on matrix Bx i Standardize and 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 upper and lower limits 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, 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 element values ​​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 value; Lim1 represents the time difference threshold, which is generally 0.1 to 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-phase current (F∈{a,b,c}) is less than Lim2 times of the remaining two-phase currents, it is considered that a high-resistance connection fault has occurred in the F-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, combined with the phase current commutation law of the brushless DC motor, the box plot outlier detection principle is used to accurately capture the phase current "inflection point", and then the commutation process time of any phase current is estimated. Then, the commutation time difference and commutation current amplitude between the phase currents are horizontally compared to realize the 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 point before and after the phase current commutation according to the phase current commutation law and the box plot outlier detection principle;

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

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

[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 capturing 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 determined 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, several simple deductions and substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for identifying high-resistance connection fault of 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 point 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, characterized in that: The step S1 specifically includes: S11, using a current sensor to obtain a discrete sampling sequence of phase current of the brushless DC motor; S12, calculating a time difference sequence of phase current according to the phase current discrete sampling sequence; S13, selecting an integer number of timing difference values ​​from the timing difference value sequence to form a matrix; S14, standardizing the matrix using Z-Score transformation to obtain a standardized matrix; S15. According to the outlier detection principle of the box plot, the upper and lower quartiles of the elements of any row of the standardized matrix are calculated in sequence, and the upper and lower limits of the outlier values ​​of any row of the standardized matrix are calculated; S16. Find the element values ​​in the last column of the standardized matrix that exceed the corresponding upper and lower limits of the outliers, so as to establish the 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, characterized in that: In step S11, the sampling period T=k·T0, 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.

4. The method for identifying a high-resistance connection fault of a brushless DC motor according to claim 2, characterized in that: The upper and lower limits of outliers for any row of the normalized matrix are calculated by the following formula: in, represents the upper bound on the number of outliers in any row of the normalized matrix, and represents the lower limit of outliers for 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 high-resistance connection fault of a brushless DC motor according to claim 2, characterized in that: The 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, characterized in that: The 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+Lim1 times the mean of the remaining twelve elements, it is considered that the brushless DC motor may have a high-resistance connection fault. When a high-resistance connection fault may occur in the brushless DC motor, the maximum inflection point currents of the three phase currents are taken for horizontal comparison. If the maximum inflection point current of any phase current is less than Lim2 times the currents of the remaining two phases, it is considered that a high-resistance connection fault has occurred in that phase.

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

5.

8. The method for identifying high-resistance connection fault of a brushless DC motor according to claim 6, characterized in that: The value of Lim2 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 point before and after the phase current commutation according to the phase current commutation law and the box plot outlier detection principle; A commutation time calculation module is used to estimate the commutation process time of the phase current; The high-resistance connection fault judgment module is used to horizontally compare the commutation time difference and the commutation current amplitude between the phase currents, and judge whether the brushless DC motor has a high-resistance connection fault according to the comparison result.

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, and the current sensor is used to obtain a discrete sampling sequence of phase current of the brushless DC motor.

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