Second derivative-based open-circuit fault diagnosis method for voltage source inverter with one open switch

Abstract

The present application relates to the technical field of inverter fault diagnosis, and provides a voltage source inverter single tube open circuit fault diagnosis method based on second derivative. The method comprises the following steps: calculating the absolute value of the second derivative of each phase of the three-phase current output by the inverter during operation of the inverter; comparing the calculated absolute value of the second derivative of each phase with a set threshold value to determine whether the inverter has an open circuit type I fault or type II fault; when the result is yes, the sign characteristic of the second derivative of each phase of the three-phase current output by the inverter is used to determine whether the inverter has a single tube open circuit fault, and the fault power tube is located. The present application can diagnose two types of single tube open circuit faults, and improves the reliability of diagnosis.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inverter fault diagnosis, and in particular, relates to a voltage source inverter single tube open circuit fault diagnosis method based on second derivative. BACKGROUND

[0002] Three-phase voltage source inverters are the core components of modern motor drive systems and renewable energy conversion systems, playing a crucial role in achieving efficient energy conversion and precise control. However, during the actual operation of the inverter, power semiconductor switching devices are prone to open circuit faults. Such faults not only lead to serious degradation of system output performance, increasing the stress load of healthy devices, but also may cause system-level faults, threatening the safety and stability of equipment. Therefore, developing efficient and reliable open circuit fault diagnosis technology is of great significance to ensure the stable operation of the inverter system.

[0003] For open circuit fault problems, researchers have proposed a variety of diagnostic methods, mainly including techniques based on output voltage, current signal analysis, intelligent diagnosis methods based on artificial intelligence, and algorithms based on observers and fault pattern recognition. These methods all extract feature signals in fault states to achieve detection and positioning of open circuit faults.

[0004] However, existing open circuit fault diagnosis techniques still have certain limitations. On the one hand, many methods rely on complex signal processing or machine learning models, resulting in large diagnostic computation and poor real-time performance, making them unsuitable for engineering applications; on the other hand, existing methods are insufficient in terms of diagnostic accuracy and robustness, making it difficult to effectively identify both Type I and Type II open circuit faults. These problems restrict the widespread application of inverter fault diagnosis technology in actual industrial systems.

[0005] Therefore, we urgently need to develop a new fault diagnosis method with low diagnostic computation complexity, high reliability, and the ability to accurately identify both Type I and Type II open circuit faults. Such research not only helps to improve the operational safety and reliability of inverter systems, but also has important practical significance for promoting the application of intelligent motor drive systems and new energy equipment. SUMMARY

[0006] The present application aims to at least solve one of the problems in the prior art or related art.

[0007] The present application aims to at least solve one of the problems in the prior art or related art.

[0008] In order to achieve the above object, the technical scheme of the present application provides a voltage source inverter single tube open circuit fault diagnosis method based on second derivative, the voltage source inverter is a two-level voltage source inverter; the two-level voltage source inverter is a three-phase bridge inverter circuit, and the power supply of the three-phase bridge inverter circuit is a direct current power supply V dc , and the output end of the three-phase bridge inverter circuit is connected to a three-phase motor; the three-phase bridge inverter circuit is composed of three independent A-phase, B-phase and C-phase bridge arms, the A-phase bridge arm comprises upper switch tube S 1 and anti-parallel diode Z 1, lower switch tube S 4 and anti-parallel diode Z 4; the B-phase bridge arm comprises upper switch tube S 2 and anti-parallel diode Z 2, lower switch tube S 5 and anti-parallel diode Z 5; the C-phase bridge arm comprises upper switch tube S 3 and anti-parallel diode Z 3, lower switch tube S 6 and anti-parallel diode Z 6; the midpoint a 、 b 、 c of each bridge arm is connected to the corresponding phase of the three-phase motor as an alternating current output end; the current output by the midpoint a 、 b 、 c is respectively i a 、 i b , and i c ; the fault diagnosis method comprises the following steps: step S1: when the voltage source inverter is running, the absolute value of the second derivative of each phase of the three-phase current output by the voltage source inverter is calculated respectively; step S2: the calculated absolute value of the second derivative of each phase is compared with a set threshold value to determine whether the voltage source inverter has an open circuit type I fault or type II fault; when the determination result is yes, step S3 is executed; wherein the type I fault is a fault occurring when the power tube is in the process of being turned on; the type II fault is a fault occurring when the power tube is in an idle state; step S3: the sign characteristic of the second derivative of each phase of the three-phase current output by the voltage source inverter is used to determine whether the voltage source inverter has a single tube open circuit fault and to locate the fault power tube; wherein the single tube open circuit fault refers to the open circuit of the upper switch tube S 1, lower switch tube S 4, upper switch tubeS 2, lower switch tube S 5, upper switch tube S 3, and lower switch tube S 6, only one power tube has type I fault or type II fault.

[0009] Preferably, the step S1 specifically comprises: step S1.1, acquiring three-phase currents output by the voltage source type inverter when the voltage source type inverter is running; and step S1.2, calculating a second derivative of each phase of the three-phase currents by using a differential method, and obtaining an absolute value of the second derivative of each phase of the three-phase currents at k time instant ; wherein the absolute value corresponds to a formula as follows:

[0010] (1)

[0011] In formula (1), is a current value of any phase of the three-phase currents at k time instant ; k is a first derivative of any phase of the three-phase currents at time instant k ; is a first derivative of any phase of the three-phase currents at -1 time instant; is a time interval between two discrete current points

[0012] , in a carrier cycle. Preferably, before the step S2, further comprising: determining a value of the set threshold ; wherein a formula for determining the value of the set threshold

[0013] is as follows: (2)

[0014] In formula (2), is a current value of any phase of the three-phase currents at k time instant ; is an amplitude of any phase of the three-phase currents after a current normalization operation, and the value is 1; is an angular frequency of any phase of the three-phase currents output by the voltage source type inverter; is an initial phase of any phase of the three-phase currents output by the voltage source type inverter; k is a first derivative of any phase of the three-phase currents at time instant k ;a second derivative of the voltage at the time instant t; wherein the set threshold value is determined by equation (2) is:

[0015] (3)

[0016] in equation (3), is a maximum value.

[0017] Preferably, (4).

[0018] Preferably, the step S2 specifically comprises: a step S2.1 of comparing an absolute value of the second derivative of the voltage at the time instant t with the set threshold value; when the absolute value of the second derivative of the voltage at the time instant t is greater than the set threshold value, performing a step S2.2; when the absolute value of the second derivative of the voltage at the time instant t is less than the set threshold value, performing a step S2.3; wherein the second derivative of the voltage at the time instant t is a second derivative of the voltage at the time instant t; the set threshold value is determined by equation (2) is a second derivative of any one of the three-phase currents at the time instant t; the step S2.2 of determining that the voltage source inverter has an open-circuit type I fault or type II fault; the step S2.3 of determining that the voltage source inverter does not have an open-circuit type I fault or type II fault. k

[0019] Preferably, the step S3 specifically comprises: a step S3.1 of performing a step S3.2 when the second derivative of the A-phase of the three-phase currents output by the voltage source inverter is greater than , the second derivative of the B-phase of the three-phase currents is greater than , and the second derivative of the C-phase of the three-phase currents is greater than ; performing a step S3.3 when the second derivative of the A-phase of the three-phase currents output by the voltage source inverter is greater than , the second derivative of the B-phase of the three-phase currents is greater than , and the second derivative of the C-phase of the three-phase currents is greater than ; performing a step S3.4 when the second derivative of the A-phase of the three-phase currents output by the voltage source inverter is greater than , the second derivative of the B-phase of the three-phase currents is greater than , and the second derivative of the C-phase of the three-phase currents is greater than ; performing a step S3.5 when the second derivative of the A-phase of the three-phase currents output by the voltage source inverter is greater than , the second derivative of the B-phase of the three-phase currents is greater than , and the second derivative of the C-phase of the three-phase currents is greater than ; performing a step S3.6 when the second derivative of the A-phase of the three-phase currents output by the voltage source inverter is greater than , the second derivative of the B-phase of the three-phase currents is greater than , and the second derivative of the C-phase of the three-phase currents is greater than​​​​​ when the second order derivative of the A-phase of the three-phase current outputted by the voltage source inverter the second order derivative of the B-phase of the three-phase current and the second order derivative of the C-phase of the three-phase current is executed; step S3.2: it is determined that the voltage source inverter has a single tube open circuit fault, and it is determined that the fault power tube is the upper switch tube S 1; step S3.3: it is determined that the voltage source inverter has a single tube open circuit fault, and it is determined that the fault power tube is the upper switch tube S 4; step S3.4: it is determined that the voltage source inverter has a single tube open circuit fault, and it is determined that the fault power tube is the upper switch tube S 2; step S3.5: it is determined that the voltage source inverter has a single tube open circuit fault, and it is determined that the fault power tube is the upper switch tube S 5; step S3.6: it is determined that the voltage source inverter has a single tube open circuit fault, and it is determined that the fault power tube is the upper switch tube S 3; step S3.7: it is determined that the voltage source inverter has a single tube open circuit fault, and it is determined that the fault power tube is the upper switch tube S 6.

[0020] Preferably, the second order derivative-based voltage source inverter single tube open circuit fault diagnosis method further comprises: step S4: according to the corresponding number of the upper switch tube S 1, the lower switch tube S 4, the upper switch tube S 2, the lower switch tube S 5, the upper switch tube S 3 and the lower switch tube S 6, the fault power tube is coded; step S5: directly outputting an integer from 1 to 6 to display the corresponding fault power tube.

[0021] The beneficial effects of the present application are:

[0022] (1) In view of the problem that in the existing open-circuit fault diagnosis method of the inverter, different diagnosis strategies are designed for different types of open-circuit faults (for example, type I fault and type II fault), the application proposes to use the second-order difference method to construct a unified fault diagnosis framework, which can effectively diagnose type I and type II open-circuit faults at the same time, thereby improving the reliability and universality of the diagnosis. The second-order difference can sensitively capture the mutation and nonlinear change of the current signal, and these changes are important characteristics of the open-circuit fault of the switching tube. By performing second-order difference processing on the collected current signal, whether it is a type I fault caused by loss of the drive signal or a type II fault caused by failure of the power device itself, it will cause significant and identifiable characteristic changes in the second-order difference signal. This unified framework avoids the complexity of designing different diagnosis logics for different fault types, simplifies the diagnosis process, and improves the reliability of the diagnosis system.

[0023] (2) In view of the problem that under variable frequency operating conditions, the frequency of the inverter output current is constantly changing, which may affect the performance of the traditional fault diagnosis method based on fixed frequency characteristics, the application proposes to use the size of the current second-order difference for fault diagnosis, and use the sign of the second-order difference for fault positioning. Research shows that even under variable frequency operating conditions, when the switching tube has an open-circuit fault, the amplitude of the current second-order difference will still increase significantly, while under normal operation or only frequency change, the change of the amplitude of the second-order difference is relatively small. Therefore, by setting a suitable threshold to detect whether the amplitude of the second-order difference exceeds the normal range, the open-circuit fault can be effectively diagnosed. Further, the application also proposes to use the sign of the second-order difference to locate the specific switching tube that has failed. By analyzing the sign pattern of the second-order difference at a certain time or in a certain current cycle after the fault occurs, the power switch that has an open-circuit fault can be accurately identified. Since the second-order difference method mainly focuses on the degree and direction of current change, it is not sensitive to the absolute amplitude and frequency change of the current signal, so it can well solve the problem of fault diagnosis and positioning under variable frequency operating conditions, and improve the adaptability of the fault diagnosis method in practical application.

[0024] Additional aspects and advantages of the application will become apparent in the following description, or will be learned by practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 a schematic flow chart of a second-order derivative-based single tube open-circuit fault diagnosis method for a voltage source inverter according to an embodiment of the application is shown;

[0026] Figure 2 a topological schematic diagram of a two-level voltage source inverter according to an embodiment of the application is shown;

[0027] Figure 3aA schematic diagram of the current characteristics of a type I open-circuit fault in a voltage source inverter according to an embodiment of the present invention is shown.

[0028] Figure 3b A schematic diagram of the current characteristics of a type II open-circuit fault in a voltage source inverter according to an embodiment of the present invention is shown. Detailed Implementation

[0029] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0030] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0031] Figure 1 A schematic flowchart illustrating a single-transistor open-circuit fault diagnosis method for a voltage source inverter based on the second derivative, according to an embodiment of the present invention, is shown. The inverter is a two-level voltage source inverter; such as... Figure 2 As shown, the two-level voltage source inverter is a three-phase bridge inverter circuit, and the power supply for the three-phase bridge inverter circuit is a DC power supply. V dc The output of the three-phase bridge inverter circuit is connected to the three-phase motor; the three-phase bridge inverter circuit consists of three independent A-phase, B-phase, and C-phase bridge arms, with the A-phase bridge arm including the upper switching transistor. S 1 and anti-parallel diode Z 1. Lower switch transistor S 4 and anti-parallel diodes Z 4; Phase B bridge arm includes the upper switch tube S 2 and anti-parallel diodes Z 2. Lower switch transistor S 5 and anti-parallel diodes Z 5; Phase C bridge arm includes the upper switch tube S 3 and anti-parallel diodes Z 3. Lower switch transistor S 6 and anti-parallel diodes Z 6; Midpoint of each bridge arm a , b , c As AC output terminals, they are connected to the corresponding phases of the three-phase motor; midpoint a , b , c The output currents are respectively i a ,i b ,and i c .

[0032] like Figure 1 As shown, this method for diagnosing single-transistor open-circuit faults in voltage source inverters based on second derivatives includes:

[0033] Step S1: When the voltage source inverter is running, calculate the absolute value of the second derivative of the three-phase current output by the voltage source inverter for each phase. ;in, For any one of the three-phase currents in k The second derivative at time t;

[0034] Step S2: Calculate the absolute value of the second derivative of each phase. Each with a set threshold The comparison is performed to determine whether the voltage source inverter has experienced an open-circuit Type I or Type II fault; if the determination result is yes, step S3 is executed; wherein, Type I fault is a fault that occurs when the power transistor is in the on state; and Type II fault is a fault that occurs when the power transistor is in the idle state.

[0035] Step S2 specifically includes: Step S2.1: Calculate the absolute value of the second derivative. With set threshold Compare; when When, execute step S2.2; when When the voltage source inverter has experienced an open circuit type I fault or a type II fault, proceed to step S2.3; Step S2.2: Determine whether the voltage source inverter has experienced an open circuit type I fault or a type II fault; Step S2.3: Determine whether the voltage source inverter has experienced an open circuit type I fault or a type II fault.

[0036] Step S3: Using the sign characteristic of the second derivative of each phase in the three-phase current output by the voltage source inverter, determine whether a single-transistor open-circuit fault has occurred in the voltage source inverter, and locate the faulty power transistor; wherein, a single-transistor open-circuit fault refers to a fault in the upper switching transistor. S 1. Lower switch transistor S 4. Upper switch tube S 2. Lower switch transistor S 5. Switch on top S 3 and the lower switch transistor S In case 6, only one power transistor experiences a Type I or Type II fault.

[0037] Step S4: Based on the upper switching transistor S 1. Lower switch transistor S 4. Upper switch tube S 2. Lower switch transistor S5, upper switch S 3 and lower switch S 6 corresponding number, the fault power tube is coded;

[0038] Step S5: directly output the integer from 1 to 6 to display the corresponding fault power tube.

[0039] In the embodiment, in view of the problem that in the existing open-circuit fault diagnosis method of the inverter, different diagnosis strategies are designed for different types of open-circuit faults (for example, type I fault and type II fault), the application proposes to adopt a second-order difference method to construct a unified fault diagnosis framework, which can effectively diagnose type I and type II open-circuit faults at the same time, thereby improving the reliability and universality of diagnosis. The second-order difference can sensitively capture the mutation and nonlinear change of the current signal, and these changes are important characteristics of the open-circuit fault of the switch tube. By performing second-order difference processing on the collected current signal, whether it is a type I fault caused by loss of the drive signal or a type II fault caused by failure of the power device itself, it will cause significant and identifiable characteristic changes in the second-order difference signal. This unified framework avoids the complexity of designing different diagnosis logics for different fault types, simplifies the diagnosis process and improves the reliability of the diagnosis system.

[0040] Further, in view of the problem that under variable frequency operating conditions, the frequency of the inverter output current is constantly changing, which may affect the performance of the traditional fault diagnosis method based on fixed frequency characteristics, the application proposes to use the size of the second-order difference of the current for fault diagnosis, and use the sign of the second-order difference for fault positioning. Research shows that even under variable frequency operating conditions, when the switch tube has an open-circuit fault, the amplitude of the second-order difference of the current will still increase significantly, while under normal operation or only frequency change, the change of the amplitude of the second-order difference is relatively small. Therefore, by setting a suitable threshold to detect whether the amplitude of the second-order difference exceeds the normal range, the open-circuit fault can be effectively diagnosed. Further, the application also proposes to use the sign of the second-order difference to locate the specific switch tube that has a fault. By analyzing the sign pattern of the second-order difference at a certain time or in a certain current period after the fault occurs, the power switch that has an open-circuit fault can be accurately identified. Since the second-order difference method mainly focuses on the degree and direction of current change, it is not sensitive to the absolute amplitude and frequency change of the current signal, so it can well solve the problem of fault diagnosis and positioning under variable frequency operating conditions, and improve the adaptability of the fault diagnosis method in practical application.

[0041] In an embodiment of the application, the step S1 specifically comprises: step S1.1: collecting three-phase currents output by the voltage source inverter when the voltage source inverter is running; and step S1.2: calculating the second-order derivative of each phase of the three-phase currents by using a difference method, and obtaining the second-order derivative of each phase of the three-phase currents at each sampling point.k absolute value of the second derivative of the time ; wherein the absolute value of the second derivative of the time The corresponding formula is:

[0042] (1)

[0043] In formula (1), is the current value of any one phase of the three-phase current at the time t; k is the first derivative of any one phase of the three-phase current at the time t; is the first derivative of any one phase of the three-phase current at the time t-1; k is the second derivative of any one phase of the three-phase current at the time t; is the second derivative of any one phase of the three-phase current at the time t-1; k is the time interval between two discrete current points , in a carrier cycle.

[0044] In an embodiment of the present application, before step S2, further comprising: determining the value of the set threshold ; wherein the formula for determining the value of the set threshold is as follows:

[0045] (2)

[0046] In formula (2), is the current value of any one phase of the three-phase current at the time t; k is the amplitude of any one phase of the three-phase current after the current normalization operation, and the value is 1; is the angular frequency of any one phase of the three-phase current output by the voltage source inverter; is the initial phase of any one phase of the three-phase current output by the voltage source inverter; is the first derivative of any one phase of the three-phase current at the time t; is the second derivative of any one phase of the three-phase current at the time t; wherein the set threshold k is determined by formula (2) as follows: k

[0047] (3)

[0048] In formula (3), is the maximum value of .

[0049] In an embodiment of the present application, (4). ​​​​

[0050] In one embodiment of the present application, the step S3 specifically comprises: step S3.1: when the second order derivative of the A-phase in the three-phase current output by the voltage source inverter is the second order derivative of the B-phase in the three-phase current and the second order derivative of the C-phase in the three-phase current , step S3.2 is performed; when the second order derivative of the A-phase in the three-phase current output by the voltage source inverter is the second order derivative of the B-phase in the three-phase current and the second order derivative of the C-phase in the three-phase current , step S3.3 is performed; when the second order derivative of the A-phase in the three-phase current output by the voltage source inverter is the second order derivative of the B-phase in the three-phase current and the second order derivative of the C-phase in the three-phase current , step S3.4 is performed; when the second order derivative of the A-phase in the three-phase current output by the voltage source inverter is the second order derivative of the B-phase in the three-phase current and the second order derivative of the C-phase in the three-phase current , step S3.5 is performed; when the second order derivative of the A-phase in the three-phase current output by the voltage source inverter is the second order derivative of the B-phase in the three-phase current and the second order derivative of the C-phase in the three-phase current , step S3.6 is performed; when the second order derivative of the A-phase in the three-phase current output by the voltage source inverter is the second order derivative of the B-phase in the three-phase current and the second order derivative of the C-phase in the three-phase current , step S3.7 is performed; step S3.2: it is determined that the voltage source inverter has a single tube open circuit fault, and it is determined that the faulty power tube is the upper switch tube S 1; step S3.3: it is determined that the voltage source inverter has a single tube open circuit fault, and it is determined that the faulty power tube is the upper switch tube S 4; step S3.4: it is determined that the voltage source inverter has a single tube open circuit fault, and it is determined that the faulty power tube is the upper switch tube S 2; step S3.5: it is determined that the voltage source inverter has a single tube open circuit fault, and it is determined that the faulty power tube is the upper switch tube S 5; step S3.6: it is determined that the voltage source inverter has a single tube open circuit fault, and it is determined that the faulty power tube is the upper switch tube S 3; step S3.7: it is determined that the voltage source inverter has a single tube open circuit fault, and it is determined that the faulty power tube is the upper switch tube S 6.

[0051] In one embodiment of the present application, the fault diagnosis method further comprises: step S4: according to the upper switch tube S 1, the lower switch tube S 4, the upper switch tube S 2, the lower switch tube S 5, the upper switch tube S 3 and the lower switch tube S 6, the corresponding number is encoded for the fault power tube; step S5: directly output the integer from 1 to 6 to display the corresponding fault power tube.

[0052] The following will demonstrate the second derivative-based single-tube open-circuit fault diagnosis method of the voltage source inverter of the present application with a specific embodiment. The inverter is a two-level voltage source inverter; the inverter is a three-phase bridge inverter circuit, and the power supply of the three-phase bridge inverter circuit is a direct current power supply V dc , and the output end of the three-phase bridge inverter circuit is connected to a three-phase motor; the three-phase bridge inverter circuit is composed of three independent A-phase, B-phase and C-phase bridge arms, the A-phase bridge arm includes the upper switch tube S 1 and the anti-parallel diode Z 1, the lower switch tube S 4 and the anti-parallel diode Z 4; the B-phase bridge arm includes the upper switch tube S 2 and the anti-parallel diode Z 2, the lower switch tube S 5 and the anti-parallel diode Z 5; the C-phase bridge arm includes the upper switch tube S 3 and the anti-parallel diode Z 3, the lower switch tube S 6 and the anti-parallel diode Z 6; the midpoint a , b , c of each bridge arm is connected to the corresponding phase of the three-phase motor as the alternating current output end; the midpoint a , b , c outputs the current i a , i b , and i c .

[0053] The implementation steps of the second derivative-based single-tube open-circuit fault diagnosis method of the voltage source inverter of the present application are as follows:

[0054] (1) Step S1: when the voltage source inverter is running, the absolute value of the second derivative of each phase of the three-phase current output by the voltage source inverter is calculated respectively;

[0055] Step S1, specifically comprising: step S1.1: collecting three-phase currents output by the voltage source inverter when the voltage source inverter is running; step S1.2: calculating the second derivative of each phase of the three-phase currents by using a difference method, and obtaining the absolute value of the second derivative of each phase of the three-phase currents at k time; ; wherein the absolute value corresponding formula is:

[0056] (1)

[0057] In formula (1), is the current value of any phase of the three-phase currents at k time; is the first derivative of any phase of the three-phase currents at k time; is the first derivative of any phase of the three-phase currents at (- k -1) time; is the time interval between two discrete current points , in a carrier cycle.

[0058] In this step S1, when the voltage source inverter occurs open-circuit type I fault or type II fault, the first derivative of the output fault phase current has a jump discontinuity at the fault point, thereby causing the second derivative of the fault phase current to suddenly increase. This feature can be used for inverter open-circuit fault diagnosis. Therefore, we need to calculate the second derivative of each phase of the three-phase currents by using a difference method, and obtain the absolute value of the second derivative of each phase of the three-phase currents at k time to further diagnose the two fault types, i.e., to perform the next step S2.

[0059] Step S2: comparing the calculated absolute value of the second derivative of each phase with a set threshold value , to determine whether the voltage source inverter occurs open-circuit type I fault or type II fault; when the determination result is yes, performing step S3; wherein the type I fault is a fault occurring when the power tube is in the process of being turned on; the type II fault is a fault occurring when the power tube is in an idle state;

[0060] Before step S2, further comprising: determining the value of the set threshold value ; wherein the formula for determining the value of the set threshold value is as follows:

[0061] (2)

[0062] In equation (2), For any one of the three-phase currents in k The current value at that moment; The amplitude of any one phase of the three-phase current after current normalization is 1. The angular frequency of any one phase of the three-phase current output by the voltage source inverter; The initial phase of any one phase of the three-phase current output by the voltage source inverter; For any one of the three-phase currents in k The first derivative at time t; For any one of the three-phase currents in k The second derivative at time t; where the set threshold is determined by equation (2). for:

[0063] (3)

[0064] In equation (3), for The maximum value. (4).

[0065] Step S2 specifically includes: Step S2.1: Calculate the absolute value of the second derivative. With set threshold Compare; when When, execute step S2.2; when When that happens, proceed to step S2.3; where, For any one of the three-phase currents in k The second derivative at time; Step S2.2: Determine whether the voltage source inverter has an open-circuit Type I fault or a Type II fault; Step S2.3: Determine whether the voltage source inverter has not had an open-circuit Type I fault or a Type II fault.

[0066] In step S2, when the inverter is operating normally under frequency conversion and load conditions, the second derivative of the three-phase current will be within a certain range. When either type of open-circuit fault occurs, the second derivative of the faulty phase will exceed the original range. Therefore, a threshold value can be set. Fault diagnosis is performed. Furthermore, the amplitude of the three-phase current output by the voltage source inverter varies with the load it carries, causing the second derivative of the current to also change. To ensure detection accuracy, the threshold value would need to vary with the current amplitude, resulting in a significant computational burden. Therefore, we normalized the three-phase current output by the voltage source inverter. The normalized current avoids the influence of current amplitude variations on the threshold value.

[0067] (3) Step S3: using the sign characteristics of the second derivative of each phase of the three-phase current output by the voltage source inverter, determining whether the voltage source inverter has a single tube open circuit fault, and locating the fault power tube; wherein the single tube open circuit fault refers to the I type fault or the II type fault of only one power tube in the upper switch tube S 1, lower switch tube S 4, upper switch tube S 2, lower switch tube S 5, upper switch tube S 3 and lower switch tube S 6.

[0068] Step S3, specifically comprising: step S3.1: when the second derivative of phase A of the three-phase current output by the voltage source inverter is , the second derivative of phase B of the three-phase current is , and the second derivative of phase C of the three-phase current is , step S3.2 is executed; when the second derivative of phase A of the three-phase current output by the voltage source inverter is , the second derivative of phase B of the three-phase current is , and the second derivative of phase C of the three-phase current is , step S3.3 is executed; when the second derivative of phase A of the three-phase current output by the voltage source inverter is , the second derivative of phase B of the three-phase current is , and the second derivative of phase C of the three-phase current is , step S3.4 is executed; when the second derivative of phase A of the three-phase current output by the voltage source inverter is , the second derivative of phase B of the three-phase current is , and the second derivative of phase C of the three-phase current is , step S3.5 is executed; when the second derivative of phase A of the three-phase current output by the voltage source inverter is , the second derivative of phase B of the three-phase current is , and the second derivative of phase C of the three-phase current is , step S3.6 is executed; when the second derivative of phase A of the three-phase current output by the voltage source inverter is , the second derivative of phase B of the three-phase current is , and the second derivative of phase C of the three-phase current is , step S3.7 is executed; step S3.2: determining that the voltage source inverter has a single tube open circuit fault, and determining that the fault power tube is the upper switch tube S 1; step S3.3: determining that the voltage source inverter has a single tube open circuit fault, and determining that the fault power tube is the upper switch tube S4; Step S3.4: Determine that the voltage source inverter has a single tube open circuit fault, and determine that the fault power tube is the upper switch tube S 2; Step S3.5: Determine that the voltage source inverter has a single tube open circuit fault, and determine that the fault power tube is the upper switch tube S 5; Step S3.6: Determine that the voltage source inverter has a single tube open circuit fault, and determine that the fault power tube is the upper switch tube S 3; Step S3.7: Determine that the voltage source inverter has a single tube open circuit fault, and determine that the fault power tube is the upper switch tube S 6.

[0069] In this step S3, when the A phase S 1 type I fault or type II fault occurs, the first derivative of the A phase will experience a drop. That is: the second derivative of the A phase The second derivatives of the other two phases , . Similarly, when the A phase S 4 fault occurs, the second derivative of the A phase The second derivatives of the other two phases , The sign of the second derivative can be used to locate the fault switch tube of the two open circuit faults. Using a unified second derivative framework for fault diagnosis and location only needs to calculate the second derivative once. This reduces the computational complexity.

[0070] In order to further improve the anti-interference performance of fault diagnosis, improve the accuracy of fault diagnosis, carry out fault diagnosis anti-interference design, as shown in formula (10). When the second derivative of the current of a certain phase at two consecutive points is greater than, a fault warning is given, and the two points of the second derivative of the phase are opposite in sign to the second derivatives of the other two phases. It is considered to be a fault phase.

[0071] (10)

[0072] In order to visually show the fault switch tube, the present application encodes the fault according to the switch tube number, and outputs an integer of 1-6 to display the fault switch, that is, the next step step S4 and step S5.

[0073] (4) Step S4: According to the corresponding number of the upper switch tube S 1, the lower switch tube S 4, the upper switch tube S 2, the lower switch tube S 5, the upper switch tube S 3 and the lower switch tube S 6, the fault power tube is encoded.

[0074] (5) Step S5: Directly output integers from 1 to 6 to display the corresponding faulty power transistor; wherein, the faulty power transistor and its corresponding directly output code are shown in Table 1; based on the fault characteristics in Table 1, directly output integers from 1 to 6 to display the corresponding faulty power transistor. When When it is - / 0, it represents the second derivative of phase A in the three-phase current output by the voltage source inverter. When less than 0 or equal to 0, it also represents the second derivative of phase A in the three-phase current output by the voltage source inverter. hour.

[0075] Table 1. Faulty power transistors and their corresponding direct output codes

[0076] .

[0077] In this specific implementation, when determining whether a Type I or Type II open-circuit fault occurs in a voltage source inverter, we can also analyze the characteristics of the open-circuit fault output current. The analysis of the open-circuit fault output current characteristics specifically includes: Step B1: Plotting the open-circuit fault output current waveform; wherein, the open-circuit fault output current waveform includes Type I open-circuit fault output current waveforms and Type II open-circuit fault output current waveforms; Type I faults occur when the power transistor is conducting; Type II faults occur when the power transistor is idle; Step B2: Summarizing the characteristics of the open-circuit fault output current; Step B3: Analyzing the diagnostic blind zone; wherein, the diagnostic blind zone is the area near the current commutation point when an open-circuit Type I fault occurs.

[0078] Plot the output current waveform during an open-circuit fault as follows: Figure 3a and Figure 3b As shown. Figure 3a As shown, when a Type I open-circuit fault occurs in a voltage source inverter, the current in the faulty phase will rapidly drop to 0 and remain there for a period of time, before returning to normal in the second half of the cycle; as Figure 3b As shown, when a Type II open-circuit fault occurs in a voltage source inverter, the current of the faulted phase remains unchanged until the second half of the cycle, and the current will remain at 0 for the entire half-cycle.

[0079] In summary, the voltage source inverter single tube open circuit fault rapid online diagnosis method based on the second order difference method of the application aims at the problem that different diagnosis strategies may need to be designed for different types of open circuit faults (for example, type I and type II faults) in the existing inverter open circuit fault diagnosis method, the application proposes to adopt the second order difference method to construct a unified fault diagnosis framework, which can effectively diagnose type I and type II open circuit faults at the same time, thereby improving the reliability and universality of diagnosis. The second order difference can sensitively capture the mutation and nonlinear change of the current signal, and these changes are important characteristics of the open circuit fault of the switching tube. By performing second order difference processing on the collected current signal, whether it is a type I fault caused by loss of the drive signal or a type II fault caused by failure of the power device itself, it will cause significant and identifiable characteristic changes in the second order difference signal. This unified framework avoids the complexity of designing different diagnosis logics for different fault types, simplifies the diagnosis process, and improves the reliability of the diagnosis system.

[0080] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for diagnosing single-transistor open-circuit faults in a voltage source inverter based on the second derivative, wherein the voltage source inverter is a two-level voltage source inverter; the two-level voltage source inverter is a three-phase bridge inverter circuit, and the power supply for the three-phase bridge inverter circuit is a DC power supply. V dc The output of the three-phase bridge inverter circuit is connected to a three-phase motor; the three-phase bridge inverter circuit consists of three independent A-phase, B-phase, and C-phase bridge arms, with the A-phase bridge arm including an upper switching transistor. S 1 and anti-parallel diode Z 1. Lower switch transistor S 4 and anti-parallel diodes Z 4; Phase B bridge arm includes the upper switch tube S 2 and anti-parallel diodes Z 2. Lower switch transistor S 5 and anti-parallel diodes Z 5; Phase C bridge arm includes the upper switch tube S 3 and anti-parallel diodes Z 3. Lower switch transistor S 6 and anti-parallel diodes Z 6; Midpoint of each bridge arm a , b , c As AC output terminals, they are respectively connected to the corresponding phases of the three-phase motor; the midpoint a , b , c The output currents are respectively i a , i b ,and i c Its characteristics are, The fault diagnosis method includes: Step S1: When the voltage source inverter is running, calculate the absolute value of the second derivative of each phase of the three-phase current output by the voltage source inverter. Step S2: Compare the absolute value of the second derivative of each phase obtained from the calculation with a set threshold. A comparison is made to determine whether the voltage source inverter has experienced an open-circuit Type I fault or a Type II fault; if the determination result is yes, step S3 is executed; wherein, the Type I fault is a fault that occurs when the power transistor is in the on state; the Type II fault is a fault that occurs when the power transistor is in the off state; Step S3: Using the sign characteristic of the second derivative of each phase in the three-phase current output by the voltage source inverter, determine whether a single-transistor open-circuit fault has occurred in the voltage source inverter, and locate the faulty power transistor; wherein, the single-transistor open-circuit fault refers to the faulty power transistor in the upper switching transistor. S 1. Lower switch transistor S 4. Upper switch tube S 2. Lower switch transistor S 5. Switch on top S 3 and the lower switch transistor S In case 6, only one power transistor experiences a Type I or Type II fault.

2. The method for diagnosing single-transistor open-circuit faults in voltage source inverters based on second derivatives according to claim 1, characterized in that, Step S1 specifically includes: Step S1.1: When the voltage source inverter is running, collect the three-phase current output by the voltage source inverter; Step S1.2: Calculate the second derivative of each phase of the three-phase current using the differential method, and obtain the second derivative of each phase of the three-phase current. k The absolute value of the second derivative at time t Wherein, the absolute value The corresponding formula is: （1） In equation (1), For any one of the three-phase currents in k The current value at that moment; For any one of the three-phase currents in k The first derivative at time t; For any one of the three-phase currents in ( k The first derivative at time -1); For two discrete current points within one carrier cycle , The time interval between them.

3. The method for diagnosing single-transistor open-circuit faults in voltage source inverters based on second derivatives according to claim 1, characterized in that, Before step S2, the method further includes: determining the set threshold. The value; Among them, the set threshold is determined. The formula upon which the value is based is as follows: （2） In equation (2), For any one of the three-phase currents in k The current value at that moment; The amplitude of any one phase of the three-phase current after current normalization is 1. The angular frequency of any one phase of the three-phase current output by the voltage source inverter; The initial phase of any one phase of the three-phase current output by the voltage source inverter; For any one of the three-phase currents in k The first derivative at time t; For any one of the three-phase currents in k The second derivative at time t; The set threshold is determined by equation (2). for: （3） In equation (3), for The maximum value.

4. The method for diagnosing single-transistor open-circuit faults in voltage source inverters based on second derivatives according to claim 3, characterized in that, （4）。 5. The method for diagnosing single-transistor open-circuit faults in voltage source inverters based on second derivatives according to claim 2, characterized in that, Step S2 specifically includes: Step S2.1: Calculate the absolute value of the second derivative. With the set threshold Compare; when When, execute step S2.2; when When that happens, proceed to step S2.3; where, For any one of the three-phase currents in k The second derivative at time t; Step S2.2: Determine whether the voltage source inverter has experienced an open-circuit Type I fault or a Type II fault; Step S2.3: Determine that the voltage source inverter has not experienced an open-circuit Type I or Type II fault.

6. The method for diagnosing single-transistor open-circuit faults in voltage source inverters based on second derivatives according to claim 5, characterized in that, Step S3 specifically includes: Step S3.1: When the second derivative of phase A in the three-phase current output by the voltage source inverter... The second derivative of phase B in a three-phase current And the second derivative of phase C in the three-phase current. When, execute step S3.2; when the second derivative of phase A in the three-phase current output by the voltage source inverter... The second derivative of phase B in a three-phase current And the second derivative of phase C in the three-phase current. When, execute step S3.3; when the second derivative of phase A in the three-phase current output by the voltage source inverter... The second derivative of phase B in a three-phase current And the second derivative of phase C in the three-phase current. When, execute step S3.4; when the second derivative of phase A in the three-phase current output by the voltage source inverter... The second derivative of phase B in a three-phase current And the second derivative of phase C in the three-phase current. When, execute step S3.5; when the second derivative of phase A in the three-phase current output by the voltage source inverter... The second derivative of phase B in a three-phase current And the second derivative of phase C in the three-phase current. When, execute step S3.6; when the second derivative of phase A in the three-phase current output by the voltage source inverter... The second derivative of phase B in a three-phase current And the second derivative of phase C in the three-phase current. At that time, proceed to step S3.7; Step S3.2: Determine that a single-transistor open-circuit fault has occurred in the voltage source inverter, and determine that the faulty power transistor is the upper switching transistor. S 1; Step S3.3: Determine that a single-transistor open-circuit fault has occurred in the voltage source inverter, and determine that the faulty power transistor is the upper switching transistor. S 4; Step S3.4: Determine that a single-transistor open-circuit fault has occurred in the voltage source inverter, and determine that the faulty power transistor is the upper switching transistor. S 2; Step S3.5: Determine that a single-transistor open-circuit fault has occurred in the voltage source inverter, and determine that the faulty power transistor is the upper switching transistor. S 5; Step S3.6: Determine that a single-transistor open-circuit fault has occurred in the voltage source inverter, and determine that the faulty power transistor is the upper switching transistor. S 3; Step S3.7: Determine that a single-transistor open-circuit fault has occurred in the voltage source inverter, and determine that the faulty power transistor is the upper switching transistor. S 6.

7. The method for diagnosing single-transistor open-circuit faults in voltage source inverters based on second derivatives according to claim 6, characterized in that, Also includes: Step S4: Based on the upper switching transistor S 1. Lower switch transistor S 4. Upper switch tube S 2. Lower switch transistor S 5. Switch on top S 3 and the lower switch transistor S The number corresponding to 6 was used to encode the faulty power transistor; Step S5: Directly output an integer from 1 to 6 to display the corresponding faulty power transistor.

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