A method for diagnosing open-circuit faults in inverters of AC servo systems

Abstract

The present invention relates to an AC servo system inverter open circuit fault diagnosis method, which belongs to the field of fault diagnosis. First, the AC three-phase current data before the servo motor reaches the highest yaw speed is collected as window data, and the current vector modulus and current vector phase in the window data are obtained through Clark transformation. Secondly, the standard deviation of the current vector modulus in the window is used to construct an open circuit fault identification feature F based on the current vector modulus standard deviation to realize the identification of the open circuit fault. Finally, the current vector phase feature is used to construct the open circuit fault phase positioning feature P. M and the open circuit fault power device positioning characteristic DP M , achieving open-circuit fault location. This invention requires no sample training and is easy to apply in practice. It can detect single-device and two-device open-circuit faults using only the three-phase current on the AC side of the AC servo system inverter. It offers high fault diagnosis accuracy and has important engineering application value in reducing the operation and maintenance costs of AC servo systems.

Description

Technical Field

[0001] The invention belongs to the field of fault diagnosis and relates to a method for diagnosing open-circuit faults of an inverter of an AC servo system. Background Art

[0002] Voltage source inverters are currently widely used in motor drives. According to statistics, approximately 38% of faults in AC servo systems in the industrial sector are caused by power device failures. The inverter is one of the core power modules, and most inverters use insulated gate bipolar transistors (IGBTs). These components can withstand high rated voltages and currents, and can withstand over 10 times the short-circuit current. Excessive electrical and thermal stress can damage IGBTs, and IGBT failures can be broadly categorized as open-circuit and short-circuit. Unlike short-circuit failures, open-circuit failures do not generate excessive current under most operating conditions in AC servo systems, eliminating the need for corresponding protection detection circuits. Furthermore, open-circuit failures do not directly cause the AC servo system to shut down, and therefore may remain undetected for a long time after they occur. However, open-circuit failures can affect the normal operation of other components, causing secondary damage to the inverter or other system components, or even system downtime, resulting in high repair costs. Therefore, studying the open circuit fault diagnosis method of the AC servo system inverter not only provides technical support for its condition maintenance, but also has very important practical significance and can effectively reduce the downtime of the AC servo system.

[0003] To address these issues, existing technologies have proposed the use of machine learning and neural network algorithms for inverter open-circuit fault diagnosis. For example, the Chinese invention, published with publication number CN115902688A, utilizes a TS fuzzy neural network to address the multi-causal coupling, ambiguity, and uncertainty between inverter open-circuit fault characteristics and fault types, improving the accuracy of online diagnosis of open-circuit faults in three-phase, two-level inverters. However, machine learning and neural networks inherently require high data volumes, requiring a large amount of data for sample training. The methods are complex, computationally intensive, and place high demands on hardware equipment, making it difficult to balance hardware costs with diagnostic efficiency. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an AC servo system inverter open circuit fault diagnosis method. Based on the modulus and phase interval of the current vector, the proposed method can reduce the dependence on the number of samples while maintaining the accuracy of the diagnostic results. The method is simple, has a small amount of computation, and is more suitable for practical engineering applications.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A method for diagnosing an open-circuit fault of an AC servo system inverter comprises the following steps:

[0007] S1. Collecting AC three-phase current data for T cycles before the servo motor reaches its maximum speed, using the AC three-phase current data as window data, obtaining two-phase currents in a two-phase stationary coordinate system through Clark transformation, and obtaining a current vector modulus and a current vector phase within the window data based on the two-phase currents;

[0008] S2. Determine whether an open circuit fault exists. If so, locate the open circuit fault.

[0009] Specifically include:

[0010] S21, calculating the standard deviation of the current vector modulus;

[0011] S22, constructing an open circuit fault identification feature F;

[0012] S23, determining a judgment result according to the open circuit fault identification feature F;

[0013] S3. Complete open circuit fault location according to the current vector phase characteristics; the open circuit fault location includes open circuit fault phase location and open circuit fault power device location;

[0014] Specifically include:

[0015] S31, construct open circuit fault phase positioning feature value P M , complete the open circuit fault phase positioning;

[0016] S32, construct open circuit fault power device positioning feature DP M , complete the positioning of open circuit fault power devices.

[0017] Furthermore, in S1, when the three-phase windings of the servo motor stator are star-connected, the three-phase currents satisfy i A +i B +i C = 0, i in the two-phase stationary coordinate system after coordinate transformation using Clark transformation α and i β for:

[0018]

[0019] At this time, the current vector is:

[0020] I s =i α +ji β =|I s |e jθ (2)

[0021] satisfy:

[0022]

[0023] Among them, |I s | is the current vector magnitude, θ is the current vector phase, and θ∈[0,2π].

[0024] Furthermore, in S2, the standard deviation of the current vector modulus in the window is:

[0025]

[0026] Where σ is the standard deviation, |I s | k is the current vector modulus at time k, μ is the mean current vector modulus in the window, and N is the amount of data in one acquisition window length;

[0027] When the current sampling period in the window is T s When , the number of window data N is:

[0028]

[0029] Where p is the number of pole pairs of the servo motor, ω m is the rotor mechanical angular velocity.

[0030] Furthermore, in S2, based on the change of the current vector modulus before and after the open circuit fault occurs in the inverter, the open circuit fault identification feature F is constructed as follows:

[0031]

[0032] Wherein, σ is the standard deviation of the current vector modulus, k1 is the open circuit fault identification threshold; when F=1, an open circuit fault occurs in the inverter.

[0033] Furthermore, in S23, when F=0, it is determined that no fault exists, and the process returns to S1 to re-collect window data.

[0034] Furthermore, in said S31, said open circuit fault phase location characteristic quantity P M for:

[0035]

[0036] Where θ is the current vector phase; θ M is the fault phase location criterion; M=A, B, C; when P M = 0, it means that θ is not in the interval θ M Inverter M phase has no fault; when P M =1, it means that θ is in the interval θ M An open circuit fault occurs in phase M of the inner inverter.

[0037] Further, in said S32, said open circuit fault power device positioning characteristic value DP M for:

[0038]

[0039] Among them, when DP M =0, inverter M phase has no fault; when DP M =-1, the device on the M-phase bridge arm fails; when DP M =-2, the upper and lower components of the M-phase bridge arm fail simultaneously; DP M =1, the device under the M-phase bridge arm is faulty; S M is the auxiliary fault location feature, which is expressed as:

[0040]

[0041] When P M =0, S M Always 0, the inverter M phase is in a fault-free state; when P M =1, S M The value of varies with the current vector phase interval;

[0042] D M is the fault phase location characteristic when the inverter M phase has an open circuit fault, D M The expression is:

[0043]

[0044] Among them, θ M(·) Indicates the positioning criteria of a power device when phase M fails.

[0045] The beneficial effects of the present invention are:

[0046] The AC servo system inverter open circuit fault diagnosis method based on current vector modulus and phase interval proposed in this scheme can realize single-device and two-device open circuit faults (a total of 21 fault types) by only using the three-phase current on the AC side of the AC servo system inverter, and has high diagnostic accuracy; at the same time, compared with the existing AC servo system inverter fault diagnosis method based on machine learning, the present invention does not require sample training while maintaining diagnostic accuracy, reduces dependence on data, and the method is simple and has a small amount of calculation. It can provide technical support for the operation, maintenance and repair of the AC servo system inverter, and has important engineering application value for reducing the operation, maintenance and repair costs of the AC servo system and improving the repair efficiency.

[0047] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0049] Figure 1 This is a flow chart for diagnosing open circuit faults in power devices of AC servo system inverters;

[0050] Figure 2 This is the AC servo system inverter circuit topology diagram;

[0051] Figure 3 The current vector modulus and current vector phase diagram when VT3 and VT4 have open circuit faults;

[0052] Figure 4 This is the open circuit fault identification result when VT3 and VT4 fail;

[0053] Figure 5 This is the open circuit fault location result when VT3 and VT4 fail. DETAILED DESCRIPTION

[0054] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0055] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0056] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0057] See also Figures 1 to 5 This paper presents a method for open-circuit fault diagnosis of an AC servo system inverter based on the current vector magnitude and phase interval. The object is a two-level AC servo system inverter. The method mainly includes three steps: data acquisition, fault identification, and fault location.

[0058] S1, collect the AC three-phase current data i before the servo motor reaches the maximum speed for T cycles M (M=A, B, C), the AC three-phase current data is used as window data, and the two-phase current in the two-phase stationary coordinate system is obtained through Clark transformation, and the current vector modulus and current vector phase in the window data are obtained according to the two-phase current.

[0059] When the three-phase winding of the servo motor stator is star-connected, the three-phase current satisfies i A +i B +i C = 0, i in the two-phase stationary coordinate system after coordinate transformation using Clark transformation α and i β for:

[0060]

[0061] At this time, the current vector is:

[0062] I s =i α +ji β =|I s |e jθ (2)

[0063] Among them, |I s | is the current vector modulus, θ is the current vector phase, θ∈[0,2π], and:

[0064]

[0065] S2. Determine whether an open circuit fault exists. If an open circuit fault exists, locate the open circuit fault.

[0066] Specifically include:

[0067] S21, calculating the standard deviation of the current vector modulus;

[0068] The standard deviation of the current vector magnitude within the window is:

[0069]

[0070] Where σ is the standard deviation, |I s | k is the current vector modulus at time k, μ is the mean current vector modulus in the window, and N is the amount of data in one acquisition window length;

[0071] When the current sampling period in the window is T s When , the number of window data N is:

[0072]

[0073] Where p is the number of pole pairs of the servo motor, ω m is the rotor mechanical angular velocity.

[0074] S22, constructing an open circuit fault identification feature F;

[0075] Since the current vector modulus suddenly increases after the inverter has an open-circuit fault compared to when the fault occurred, the open-circuit fault identification feature F is constructed as:

[0076]

[0077] Where σ is the standard deviation of the current vector modulus, and k1 is the open circuit fault identification threshold.

[0078] S23. Determine the judgment result based on the open circuit fault identification feature F; when F=0, no open circuit fault occurs in the inverter, that is, the judgment result is that there is no fault, and it is necessary to return to step S1 and re-collect window data; when F=1, an open circuit fault occurs in the inverter, and the open circuit fault is located.

[0079] S3. Complete open circuit fault location according to the current vector phase characteristics; the open circuit fault location includes open circuit fault phase location and open circuit fault power device location.

[0080] Specifically include:

[0081] S31. Constructing open circuit fault phase location feature quantity P using current vector phase feature M , complete the open circuit fault phase positioning;

[0082] The open circuit fault phase positioning characteristic quantity P M for:

[0083]

[0084] Where θ is the current vector phase; θ M is the fault phase location criterion; phase M=A, B, C; when P M = 0, it means that θ is not in the interval θ M Inverter M phase has no fault; when P M =1, it means that θ is in the interval θ M An open circuit fault occurs in phase M of the inner inverter.

[0085] S32, constructing the open circuit fault power device positioning feature DP using the current vector phase feature M , complete the positioning of open circuit fault power devices.

[0086] Constructed fault location feature DP M :

[0087]

[0088] Among them, when DP M =0, inverter M phase has no fault; when DP M =-1, the device on the M-phase bridge arm fails; when DP M =-2, the upper and lower components of the M-phase bridge arm fail simultaneously; DP M =1, the device under the M-phase bridge arm is faulty; S M is the auxiliary fault location feature, which is expressed as:

[0089]

[0090] When P M =0, S M Always 0, the inverter M phase is in a fault-free state; when P M =1, S M The value of varies with the current vector phase interval;

[0091] D M is the fault phase location characteristic when the inverter M phase has an open circuit fault, D M The expression is:

[0092]

[0093] Among them, θ M(·) Indicates the positioning criteria of a power device when phase M fails.

[0094] Combine Figure 1The proposed open circuit fault diagnosis method and implementation steps are described in detail. Taking the actual wind turbine yaw inverter as an example, its circuit topology is shown in the following figure. Figure 2 As shown, under this circuit topology, the open circuit fault types of the yaw inverter are shown in Table 1, and the fault phase location criteria and the fault power device location criteria are shown in Tables 2 and 3.

[0095] Table 1 - Yaw inverter open circuit fault types

[0096]

[0097]

[0098] Table 2 - Fault phase location criteria

[0099]

[0100] Table 3 - Faulty power device location criteria

[0101]

[0102] Collect the three-phase current data of the inverter AC side T cycles (generally T>200) before the servo motor reaches the maximum speed. M (M=A, B, C) is used as the window data. After Clark transformation of the three-phase current using formula (1), the current vector modulus |I is obtained by formula (3) and formula (4). s | and current vector phase θ; use formula (5) to calculate the standard deviation of the current vector modulus in the window, and use the open circuit fault identification feature F to construct the open circuit fault, as shown in formula (7), to achieve the identification of the open circuit fault; according to the current vector phase calculated by formula (4), combined with the open circuit fault phase location criterion (Table 2) and the open circuit fault location criterion (Table 3), the open circuit fault phase location feature P is constructed. M and the fault power device location characteristic DP M , thus realizing the open circuit fault diagnosis of yaw inverter, Table 1 shows the open circuit fault types of yaw inverter. Figure 2 The effectiveness of the present invention is illustrated by taking the simultaneous open circuit failure of VT3 and VT4 power devices at 4s as an example.

[0103] Step 1: Current data acquisition. Collect the three-phase current signal data of the AC side of the wind turbine yaw inverter. M (M=A, B, C) is used as the window data, and the current vector modulus value |I is obtained by Clark transformation. s | and the current vector phase θ. For example, when Figure 2When the power devices VT3 and VT4 of the yaw inverter have an open circuit fault, the process is as follows: Clark transform is performed on the collected three-phase current data according to formula (1) to obtain the two-phase current i in the two-phase stationary coordinate system. α and i β , and then the current vector |I is obtained by equations (3) and (4) respectively. s | and the current vector phase θ see Figure 3 As shown, it can be seen that compared with the case without fault, both the current vector and the current vector phase change significantly at 4s.

[0104] Step 2: Open circuit fault identification. The open circuit fault identification feature F is constructed by calculating the standard deviation σ of the current vector modulus value to identify the open circuit fault. The process is: using the current vector modulus value obtained in S1, the standard deviation σ of the current vector modulus value is calculated by formula (5), where the window length is selected according to formula (6), where p = 4, ω m =360r / min, T s =5000Hz, we can get N t ≈87. Afterwards, the open circuit fault identification feature F is constructed as shown in formula (7), and the open circuit fault identification threshold k1=10 is set. When F=0, it represents the normal operation of the inverter; when F=1, it represents the open circuit fault of the inverter. When the yaw system operates under the open circuit fault of power devices VT3 and VT4, the standard deviation σ of the current vector modulus suddenly changes and is greater than the threshold k1=10. The fault identification feature F=1, and the identification time is T F , accounting for 25% of a current cycle T, see Figure 4 shown.

[0105] Step 3: Open circuit fault location. This includes fault phase location and fault power device location. The process is as follows: Based on the current vector phase obtained in the first step, the fault phase location criteria and fault power device location criteria in Table 2 and Table 3 are combined, where θ thr is the defined phase threshold, and θ thr ∈[0,π / 6], in practice, considering the influence of current noise and measurement error, θ thr The smaller the better, in this invention, θ thr =π / 48. Construct the open circuit fault phase location feature value P as shown in formula (8) M , when P M =0 means θ is not in the interval θ M Inverter M phase has no fault; when P M =1 means θ is in the interval θ M The M phase of the inner inverter has an open circuit fault. When the M phase of the yaw inverter has an open circuit fault, it is necessary to use the fault location feature DP M, as shown in formula (9), the faulty power device is located. M =0 means inverter M phase has no fault; when DP M =-1 represents a device failure on phase M; DP M =-2 means that the upper and lower components of phase M fail at the same time; DP M =1 indicates a device failure in phase M.

[0106] Depend on Figure 5 It can be seen that the current vector phase θ belongs to the interval θ A and interval θ B , fault phase location characteristic quantity P A and P B The sudden change to 1 indicates that phase A and phase B have faults. Further, according to Table 3, the current vector phase θ belongs to the interval θ A(1) and interval θ B(-1) At this time, the fault power device positioning feature D AN and D BN like Figure 5 ; Finally, calculate the fault location feature DP M , where DP A =1, DP B =-1, DP C =0, indicating that the inverter phase A lower arm power device VT4 and the phase B upper arm power device VT3 are simultaneously faulty, phase C is in a normal state, and the fault location time is one current cycle T. In summary, it can be seen that the AC servo system inverter open circuit fault diagnosis method based on current vector modulus and phase interval proposed in the present invention can accurately and effectively obtain the open circuit fault result.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for diagnosing open circuit faults in an AC servo system inverter, characterized in that: The following steps are involved: S1. Collecting AC three-phase current data for T cycles before the servo motor reaches its maximum speed, using the AC three-phase current data as window data, obtaining two-phase currents in a two-phase stationary coordinate system through Clark transformation, and obtaining a current vector modulus and a current vector phase within the window data based on the two-phase currents; S2. Determine whether an open circuit fault exists. If so, locate the open circuit fault. Specifically include: S21, calculating the standard deviation of the current vector modulus; S22, constructing an open circuit fault identification feature F; S23, determining a judgment result according to the open circuit fault identification feature F; S3. Complete open circuit fault location according to the current vector phase characteristics; the open circuit fault location includes open circuit fault phase location and open circuit fault power device location; Specifically include: S31, construct open circuit fault phase positioning feature value P M , complete the open circuit fault phase positioning; S32, construct open circuit fault power device positioning feature DP M , complete the open circuit fault power device positioning, in the S31, the open circuit fault phase positioning feature value P M for: Where θ is the current vector phase; θ M is the fault phase location criterion; M=A, B, C; when P M = 0, it means that θ is not in the interval θ M Inverter M phase has no fault; when P M =1, it means that θ is in the interval θ M An open circuit fault occurs in the M phase of the inner inverter; In said S32, said open circuit fault power device positioning characteristic value DP M for: Among them, when DP M =0, inverter M phase has no fault; when DP M =-1, the device on the M-phase bridge arm fails; when DP M =-2, the upper and lower components of the M-phase bridge arm fail simultaneously; DP M =1, the device under the M-phase bridge arm is faulty; S M is the auxiliary fault location feature, which is expressed as: When P M =0, S M Always 0, the inverter M phase is in a fault-free state; when P M =1, S M The value of varies with the current vector phase interval; D M is the fault phase location characteristic when the inverter M phase has an open circuit fault, D M The expression is: Among them, θ M(·) Indicates the positioning criteria of a power device when phase M fails.

2. The AC servo system inverter open circuit fault diagnosis method according to claim 1, characterized in that: In S1, when the three-phase winding of the servo motor stator is star-connected, the three-phase current satisfies i A +i B +i C = 0, i in the two-phase stationary coordinate system after coordinate transformation using Clark transformation α and i β for: At this time, the current vector is: I s =to α +ji β =|I s e jθ (6) satisfy: Among them, |I s | is the current vector magnitude, θ is the current vector phase, and θ∈[0,2π].

3. The AC servo system inverter open circuit fault diagnosis method according to claim 2, characterized in that: In S2, the standard deviation of the current vector modulus in the window is: Where σ is the standard deviation, |I s | k is the current vector modulus at time k, μ is the mean current vector modulus in the window, and N is the amount of data in one acquisition window length; When the current sampling period in the window is T s When , the number of window data N is: Where p is the number of pole pairs of the servo motor, ω m is the rotor mechanical angular velocity.

4. The AC servo system inverter open circuit fault diagnosis method according to claim 1, characterized in that: In S2, based on the change of the current vector modulus before and after the open circuit fault occurs in the inverter, the open circuit fault identification feature F is constructed as follows: Wherein, σ is the standard deviation of the current vector modulus, k1 is the open circuit fault identification threshold; when F=1, an open circuit fault occurs in the inverter.

5. The AC servo system inverter open circuit fault diagnosis method according to claim 4, characterized in that: In S2, in S23, when F=0, it is determined that no fault exists, and the process returns to S1 to re-collect window data.

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