Voltage source inverter single-tube open-circuit fault diagnosis method based on second derivative

Abstract

The invention relates to the technical field of inverter fault diagnosis. The invention provides a voltage source inverter single-tube open-circuit fault diagnosis method based on a second derivative. The method comprises the steps of calculating an absolute value of a second derivative of each phase in three-phase current output by an inverter when the inverter operates; comparing the calculated absolute value of the second derivative of each phase with a set threshold value, and judging whether the inverter has an open-circuit I-type fault or an open-circuit II-type fault; and when the judgment result is yes, judging whether the inverter has a single-tube open-circuit fault or not by utilizing the symbolic characteristics of the second derivative of each phase in the three-phase current output by the inverter, and positioning a fault power tube. According to the invention, two types of single-tube open-circuit faults can be diagnosed, and the diagnosis reliability is improved.

Description

Technical Field

[0001] This invention relates to the technical field of inverter fault diagnosis, and more specifically, to a method for diagnosing single-transistor open-circuit faults in voltage source inverters based on the second derivative. Background Technology

[0002] Three-phase voltage source inverters, as core components of modern motor drive systems and renewable energy conversion systems, play a crucial role in achieving efficient energy conversion and precise control. However, during actual inverter operation, power semiconductor switching devices are prone to open-circuit faults. These faults not only severely degrade system output performance and increase the stress load on healthy devices, but may also trigger system-level failures, threatening the safety and stability of the equipment. Therefore, developing efficient and reliable open-circuit fault diagnosis technologies is of great significance for ensuring the stable operation of inverter systems.

[0003] To address open-circuit faults, researchers have proposed various diagnostic methods, primarily including techniques based on output voltage and current signal analysis, intelligent diagnostic methods based on artificial intelligence, and algorithms based on observers and fault mode recognition. These methods all achieve the detection and localization of open-circuit faults by extracting characteristic signals under fault conditions.

[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 high computational load 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 simultaneously. These problems restrict the widespread application of inverter fault diagnosis technology in practical industrial systems.

[0005] Therefore, we urgently need to develop a novel fault diagnosis method that features low computational complexity, high reliability, and accurate identification of Type I and Type II open-circuit faults. Such research will not only help improve the operational safety and reliability of inverter systems but also have significant practical implications for promoting the application of intelligent motor drive systems and new energy equipment. Summary of the Invention

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

[0007] The purpose of this invention is to propose a single-transistor open-circuit fault diagnosis method for voltage source inverters based on the second derivative.

[0008] To achieve the above objectives, the present invention provides a method for diagnosing single-transistor open-circuit faults in voltage source inverters based on the 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 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 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 calculated absolute value of the second derivative of each phase with a set threshold value. A comparison is made to determine whether the voltage source inverter has experienced a Type I or Type II open-circuit fault. If the determination result is yes, step S3 is executed. A Type I fault occurs when the power transistor is conducting; a Type II fault occurs when the power transistor is idle. Step S3: Using the sign characteristic of the second derivative of each phase of the three-phase current output by the voltage source inverter, it is determined whether the voltage source inverter has experienced a single-transistor open-circuit fault, and the faulty power transistor is located. A single-transistor open-circuit fault refers to the faulty power transistor located on the upper switching transistor. S 1. Lower switch transistor S 4. Upper switch tubeS 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.

[0009] Preferably, step S1 specifically includes: step S1.1: when the voltage source inverter is running, acquiring the three-phase current output by the voltage source inverter; step S1.2: calculating the second derivative of each phase of the three-phase current using a differential method, and obtaining 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.

[0010] Preferably, before step S2, the method further includes: determining the set threshold. The value of; wherein, 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; where the set threshold is determined by equation (2). for: (3) In equation (3), for The maximum value.

[0011] Preferably, (4).

[0012] Preferably, step S2 specifically includes: step S2.1: taking the absolute value of the second derivative. With the set threshold Compare; when When, execute step S2.2; when When that time comes, 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 experienced an open-circuit Type I fault or a Type II fault.

[0013] Preferably, 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. When the voltage source inverter experiences a single-transistor open-circuit fault, proceed to step S3.7; Step S3.2: Determine that the voltage source inverter has experienced a single-transistor open-circuit fault, 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.

[0014] Preferably, the method for diagnosing single-transistor open-circuit faults in voltage source inverters based on second derivatives further 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 is used to encode the faulty power transistor; Step S5: Directly output integers from 1 to 6 to display the corresponding faulty power transistor.

[0015] The beneficial effects of this invention are: (1) To address the problem in existing inverter open-circuit fault diagnosis methods that require different diagnostic strategies for different types of open-circuit faults (e.g., Type I and Type II faults), this invention proposes a unified fault diagnosis framework using the second-order differential method. This framework can simultaneously and effectively diagnose both Type I and Type II open-circuit faults, thereby improving the reliability and versatility of the diagnosis. The second-order differential method can sensitively capture abrupt changes and nonlinear variations in the current signal, which are key characteristics of open-circuit faults in switching transistors. By performing second-order differential processing on the acquired current signal, both Type I faults caused by the loss of the drive signal and Type II faults caused by the failure of the power devices themselves will cause significant and identifiable feature changes in the second-order differential signal. This unified framework avoids the complexity of designing different diagnostic logics for different fault types, simplifies the diagnostic process, and improves the reliability of the diagnostic system.

[0016] (2) To address the issue that the frequency of the inverter output current changes continuously under variable frequency operation, potentially affecting the performance of traditional fault diagnosis methods based on fixed frequency characteristics, this invention proposes using the magnitude of the second-order differential current for fault diagnosis and utilizing the sign of the second-order differential for fault location. Research shows that even under variable frequency operation conditions, when an open-circuit fault occurs in the switching transistor, the second-order differential current amplitude still increases significantly, while during normal operation or when only the frequency changes, the change in the second-order differential amplitude is relatively small. Therefore, by setting an appropriate threshold to detect whether the second-order differential amplitude exceeds the normal range, open-circuit faults can be effectively diagnosed. Furthermore, this invention also proposes using the sign of the second-order differential to locate the specific switching transistor that has experienced a fault. By analyzing the sign pattern of the second-order differential at a specific moment or within a specific current cycle after the fault occurs, the power switch experiencing an open-circuit fault can be accurately identified. Since the second-order difference method mainly focuses on the drasticness and direction of current changes and is not sensitive to changes in the absolute amplitude and frequency of the current signal, it can effectively solve the problem of fault diagnosis and location under variable frequency operating conditions, thus improving the adaptability of fault diagnosis methods in practical applications.

[0017] Additional aspects and advantages of the invention will become apparent from the description which follows, or may be learned by practice of the invention. Attached Figure Description

[0018] Figure 1 A schematic flowchart of a single-transistor open-circuit fault diagnosis method for voltage source inverters based on second derivatives according to an embodiment of the present invention is shown. Figure 2 A topology diagram of a two-level voltage source inverter according to an embodiment of the present invention is shown; Figure 3a A 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. 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

[0019] 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.

[0020] 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.

[0021] Figure 1 A schematic flowchart of 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; the midpoint... a , b , c The output currents are respectively i a , i b ,and i c .

[0022] like Figure 1 As shown, this method for diagnosing single-transistor open-circuit faults in voltage source inverters based on second derivatives includes: 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; 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. 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.

[0023] 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.

[0024] 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.

[0025] In this embodiment, addressing the problem in existing inverter open-circuit fault diagnosis methods that design different diagnostic strategies for different types of open-circuit faults (e.g., Type I and Type II faults), this invention proposes a unified fault diagnosis framework using the second-order differential method. This framework can simultaneously and effectively diagnose both Type I and Type II open-circuit faults, thereby improving the reliability and versatility of the diagnosis. The second-order differential method can sensitively capture abrupt changes and nonlinear variations in the current signal, which are key characteristics of open-circuit faults in switching transistors. By performing second-order differential processing on the acquired current signal, both Type I faults caused by drive signal loss and Type II faults caused by power device failure will exhibit significant and identifiable characteristic changes in the second-order differential signal. This unified framework avoids the complexity of designing different diagnostic logics for different fault types, simplifies the diagnostic process, and improves the reliability of the diagnostic system.

[0026] Furthermore, addressing the issue that the constantly changing frequency of the inverter output current under variable frequency operation may affect the performance of traditional fault diagnosis methods based on fixed frequency characteristics, this invention proposes using the magnitude of the second-order differential current for fault diagnosis and utilizing the sign of the second-order differential for fault location. Research shows that even under variable frequency operation conditions, when an open-circuit fault occurs in the switching transistor, the second-order differential current amplitude still increases significantly, while the change in the second-order differential amplitude is relatively small during normal operation or when only the frequency changes. Therefore, by setting an appropriate threshold to detect whether the second-order differential amplitude exceeds the normal range, open-circuit faults can be effectively diagnosed. Furthermore, this invention also proposes using the sign of the second-order differential to locate the specific switching transistor that has experienced a fault. By analyzing the sign pattern of the second-order differential at a specific moment or within a specific current cycle after the fault occurs, the power switch experiencing an open-circuit fault can be accurately identified. Since the second-order difference method mainly focuses on the drasticness and direction of current changes and is not sensitive to changes in the absolute amplitude and frequency of the current signal, it can effectively solve the problem of fault diagnosis and location under variable frequency operating conditions, thus improving the adaptability of fault diagnosis methods in practical applications.

[0027] In one embodiment of the present invention, step S1 specifically includes: step S1.1: when the voltage source inverter is running, acquiring the three-phase current output by the voltage source inverter; step S1.2: calculating the second derivative of each phase of the three-phase current using a differential method, and obtaining 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 ink 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.

[0028] In one embodiment of the present invention, before step S2, the method further includes: determining a set threshold. The value; where 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; where the set threshold is determined by equation (2). for: (3) In equation (3), for The maximum value.

[0029] In one embodiment of the present invention, (4).

[0030] In one embodiment of the present invention, 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 the second derivative of phase A in the three-phase current output by the voltage source inverter is... The second derivative of phase B in a three-phase current And the second derivative of phase C in the three-phase current. When the second derivative of phase A in the three-phase current output by the voltage source inverter is... The second derivative of phase B in a three-phase current And the second derivative of phase C in the three-phase current. When the second derivative of phase A in the three-phase current output by the voltage source inverter is... The second derivative of phase B in a three-phase current And the second derivative of phase C in the three-phase current. When the second derivative of phase A in the three-phase current output by the voltage source inverter is... The second derivative of phase B in a three-phase current And the second derivative of phase C in the three-phase current. When the second derivative of phase A in the three-phase current output by the voltage source inverter is... The second derivative of phase B in a three-phase current And the second derivative of phase C in the three-phase current. When the fault occurs, 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.

[0031] In one embodiment of the present invention, the fault diagnosis method further 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 is used to encode the faulty power transistor; Step S5: Directly output integers from 1 to 6 to display the corresponding faulty power transistor.

[0032] The following specific embodiment will demonstrate the single-transistor open-circuit fault diagnosis method for voltage source inverters based on the second derivative of the present invention. The inverter is a two-level voltage source inverter; the 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; the midpoint... a , b , c The output currents are respectively i a , i b ,and i c .

[0033] The implementation steps of the single-transistor open-circuit fault diagnosis method for voltage source inverters based on the second derivative of the present invention are as follows: (1) 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 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 a 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 ; where absolute value The corresponding formula is: (1) In equation (1), For any one of the three-phase currents ink The current value at that moment; For any one phase of the three-phase current in k The first derivative at time t; For any one phase of the three-phase current in ( k The first derivative at time -1); For two discrete current points within one carrier cycle , The time interval between them.

[0034] In step S1, when a Type I or Type II open-circuit fault occurs in the voltage source inverter, the first derivative of the output fault phase current exhibits a jump discontinuity at the fault point, resulting in a sudden increase in the value of the second derivative of the fault phase current. This characteristic can be used for inverter open-circuit fault diagnosis. Therefore, we need to calculate the second derivative of each phase of the three-phase current using a differential method, and obtain the value of the second derivative of each phase of the three-phase current. k The absolute value of the second derivative at time t To further unify the diagnosis of these two fault types, the next step S2 is executed.

[0035] (2) Step S2: Compare the absolute value of the second derivative of each phase with the 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. Before step S2, the method further includes: determining the set threshold. The value; where 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; where the set threshold is determined by equation (2). for: (3) In equation (3), for The maximum value. (4).

[0036] 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 time comes, 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.

[0037] 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.

[0038] (3) 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 the voltage source inverter has a single-transistor open-circuit fault, 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.

[0039] 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 the second derivative of phase A in the three-phase current output by the voltage source inverter is... The second derivative of phase B in a three-phase current And the second derivative of phase C in the three-phase current. When the second derivative of phase A in the three-phase current output by the voltage source inverter is... The second derivative of phase B in a three-phase current And the second derivative of phase C in the three-phase current. When the second derivative of phase A in the three-phase current output by the voltage source inverter is... The second derivative of phase B in a three-phase current And the second derivative of phase C in the three-phase current. When the second derivative of phase A in the three-phase current output by the voltage source inverter is... The second derivative of phase B in a three-phase current And the second derivative of phase C in the three-phase current. When the second derivative of phase A in the three-phase current output by the voltage source inverter is... The second derivative of phase B in a three-phase current And the second derivative of phase C in the three-phase current. When the fault occurs, 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.

[0040] In step S3, when phase A S When a Type I or Type II open-circuit fault occurs, the first derivative of phase A will experience a drop. That is, the second derivative of phase A... The other two phases of second derivative , Similarly, phase AS 4. Second derivative of phase A during fault. The other two phases of second derivative , The sign of the second derivative can be used to locate faulty switching transistors in two types of open-circuit faults. Using a unified second derivative framework for fault diagnosis and location only requires calculating the second derivative once, thus reducing computational complexity.

[0041] To further improve the anti-interference performance and accuracy of fault diagnosis, an anti-interference design for fault diagnosis is implemented, as shown in Equation (10). When the second derivative of the current at two consecutive points of a phase is greater than 1, a fault warning is issued. Furthermore, if the second derivatives at the two points of the phase have opposite signs to the second derivatives of the other two phases, the phase is considered to be faulty.

[0042] (10) To visually identify the faulty switch, this invention encodes the fault based on the switch number and displays the faulty switch by outputting an integer from 1 to 6, which corresponds to the next steps S4 and S5.

[0043] (4) Step S4: According to the upper switch tube 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 is used to encode the faulty power transistor.

[0044] (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.

[0045] Table 1. Faulty power transistors and their corresponding direct output codes .

[0046] 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.

[0047] 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.

[0048] In summary, the rapid online diagnosis method for single-transistor open-circuit faults in voltage source inverters based on the second-order differential method addresses the problem that existing open-circuit fault diagnosis methods may require different diagnostic strategies for different types of open-circuit faults (e.g., Type I and Type II faults). This invention proposes a unified fault diagnosis framework using the second-order differential method, which can simultaneously and effectively diagnose both Type I and Type II open-circuit faults, thereby improving the reliability and versatility of the diagnosis. The second-order differential method can sensitively capture abrupt changes and nonlinear variations in the current signal, which are key characteristics of open-circuit faults in the switching transistor. By performing second-order differential processing on the acquired current signal, both Type I faults caused by drive signal loss and Type II faults caused by power device failure will cause significant and identifiable characteristic changes in the second-order differential signal. This unified framework avoids the complexity of designing different diagnostic logics for different fault types, simplifies the diagnostic process, and improves the reliability of the diagnostic system.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

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 time comes, 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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