A Fault Detection and Diagnosis Method for RC-IGBT

Abstract

The present invention discloses an RC-IGBT fault detection and diagnosis method, belonging to the technical field of IGBT fault detection. The present invention applies pulse signals with different frequencies (low frequency, medium frequency, high frequency) to the RC-IGBT tube, analyzes the voltage signals between the collector and the emitter, constructs a distortion value sequence, and then combines the distortion time deterioration coefficient and the distortion frequency deterioration coefficient at low frequency, medium frequency, and high frequency to obtain the RC-IGBT fault diagnosis value, improving the accuracy of RC-IGBT fault diagnosis.

Description

Technical Field

[0001] The present invention relates to the technical field of IGBT fault detection, and particularly relates to a method for detecting and diagnosing RC-IGBT faults. Background Art

[0002] RC-IGBT (Reverse Conducting Insulated Gate Bipolar Transistor) is a key power semiconductor device in modern power electronic systems, and is widely used in fields such as high-voltage converters, motor drives, and new energy power systems. Traditional IGBT fault detection methods mainly rely on static parameter measurement and simple electrical characteristic analysis, and these methods have many limitations. Existing technologies usually adopt single-parameter monitoring, such as DC parameter measurement, switching loss analysis, or temperature characteristic detection. These methods are difficult to accurately reflect the actual working state and potential faults of RC-IGBT, as well as its response to different switching frequencies.

[0003] Traditional methods mainly rely on a single parameter, such as static parameter measurement (such as drain-source saturation voltage VCE(sat)) or DC parameter analysis. These methods cannot comprehensively capture the dynamic characteristic changes of the device. When RC-IGBT operates in a complex working environment, a single parameter is difficult to accurately reflect its actual performance degradation. Therefore, the existing technology has the problem of low accuracy in diagnosing RC-IGBT faults. Summary of the Invention

[0004] Aiming at the above deficiencies in the prior art, a method for detecting and diagnosing RC-IGBT faults provided by the present invention solves the problem of low accuracy in diagnosing RC-IGBT faults in the existing technology.

[0005] In order to achieve the above object of the invention, the technical solution adopted by the present invention is: A method for detecting and diagnosing RC-IGBT faults, comprising the following steps:

[0006] S1. Apply three pulse signals with low frequency, medium frequency, and high frequency to the gate of the RC-IGBT tube respectively, and collect the voltage signal between the collector and emitter of the RC-IGBT tube;

[0007] S2. Calculate the distortion value for each switching cycle in the voltage signal, and construct a distortion value sequence;

[0008] S3. Calculate the distortion time deterioration coefficient for the distortion value sequence;

[0009] S4. Take the mean value of each distortion value sequence to obtain the distortion mean value, and calculate the distortion frequency deterioration coefficient;

[0010] S5. Based on the distortion mean values corresponding to low frequency, medium frequency, and high frequency, and with the correction of the distortion time deterioration coefficient and the distortion frequency deterioration coefficient, obtain the RC-IGBT fault diagnosis value.

[0011] Further, in S1, the frequency range of the low frequency is 0.1 kHz to 1 kHz, the frequency range of the intermediate frequency is 1 kHz to 20 kHz, and the frequency range of the high frequency is 20 kHz to 100 kHz.

[0012] Further, S2 includes the following sub - steps:

[0013] S21. Extract the high - level vibration value, low - level vibration value, rising - edge steepness value, and falling - edge steepness value according to each switching period in the voltage signal;

[0014] S22. Calculate the distortion value according to the high - level vibration value, low - level vibration value, rising - edge steepness value, and falling - edge steepness value;

[0015] S23. For the same voltage signal, construct a distortion - value sequence with the distortion values as elements in the order of occurrence in time.

[0016] Further, the calculation formula for the high - level vibration value in S21 is: , where V H is the high - level vibration value, H i is the i - th voltage value in the high - level part of the switching period, H steady is the high - level steady - state value, i is a positive integer, N H is the number of voltage values in the high - level part of the switching period, and | | is the absolute - value operation;

[0017] The calculation formula for the low - level vibration value in S21 is: , where V L is the low - level vibration value, L i is the i - th voltage value in the low - level part of the switching period, L steady is the low - level steady - state value, H L is the number of voltage values in the low - level part of the switching period;

[0018] The calculation formula for the rising - edge steepness value in S21 is: , where K R is the rising - edge steepness value, V R,E is the end - point voltage value of the rising edge in the switching period, V R,S is the start - point voltage value of the rising edge in the switching period, △t R is the interval time from the start point to the end point of the rising edge;

[0019] The calculation formula for the falling - edge steepness value in S21 is: , where K F is the falling - edge steepness value, V F,S is the start - point voltage value of the falling edge in the switching period, V F,Eis the end voltage value at the falling edge during the switching period, and △t F is the time interval from the start to the end of the falling edge.

[0020] Further, the formula for calculating the distortion value in S22 is: , where θ is the distortion value, V H is the vibration value at high level, V L is the vibration value at low level, K R is the steepness value of the rising edge, K F is the steepness value of the falling edge, K R,th is the steepness standard value of the rising edge, K F,th is the steepness standard value of the falling edge.

[0021] Further, S3 includes the following sub-steps:

[0022] S31. Take the last consecutive M distortion values and the first consecutive M distortion values in the distortion value sequence, where M is a positive integer;

[0023] S32. Take the average of the last consecutive M distortion values to obtain the end distortion average value;

[0024] S33. Take the average of the first consecutive M distortion values to obtain the start distortion average value;

[0025] S34. Take the ratio of the end distortion average value to the start distortion average value as the distortion time deterioration coefficient.

[0026] Further, S4 includes the following sub-steps:

[0027] S41. Take the average of each distortion value sequence to obtain the distortion average value;

[0028] S42. Calculate the first distortion frequency deterioration value according to the difference between the distortion average value corresponding to the intermediate frequency and the distortion average value corresponding to the low frequency;

[0029] S43. Calculate the second distortion frequency deterioration value according to the difference between the distortion average value corresponding to the high frequency and the distortion average value corresponding to the intermediate frequency;

[0030] S44. Add the first distortion frequency deterioration value and the second distortion frequency deterioration value to obtain the distortion frequency deterioration coefficient.

[0031] Further, the formula for calculating the first distortion frequency deterioration value in S42 is: , where μ1 is the first distortion frequency deterioration value, tanh is the hyperbolic tangent function, θ M is the distortion average value corresponding to the intermediate frequency, θ L is the distortion average value corresponding to the low frequency;

[0032] The formula for calculating the deterioration value of the second distortion frequency in S43 is as follows: , where μ2 is the deterioration value of the second distortion frequency, and θ H is the distortion mean value corresponding to the high frequency, and θ M is the distortion mean value corresponding to the medium frequency.

[0033] Furthermore, S5 includes the following sub-steps:

[0034] S51. Multiply the distortion mean value at low frequency by the distortion time deterioration coefficient to obtain the fault value at low frequency;

[0035] S52. Multiply the distortion mean value at medium frequency by the distortion time deterioration coefficient to obtain the fault value at medium frequency;

[0036] S53. Multiply the distortion mean value at high frequency by the distortion time deterioration coefficient to obtain the fault value at high frequency;

[0037] S54. Calculate the RC-IGBT fault diagnosis value based on the correction of the distortion frequency deterioration coefficient according to the fault values at low frequency, medium frequency, and high frequency.

[0038] Furthermore, the formula for calculating the RC-IGBT fault diagnosis value in S54 is as follows: , where G is the RC-IGBT fault diagnosis value, y L is the fault value at low frequency, y M is the fault value at medium frequency, y H is the fault value at high frequency, and γ is the distortion frequency deterioration coefficient.

[0039] In summary, the beneficial effects of the present invention are as follows:

[0040] 1. By applying three kinds of pulse signals of low frequency, medium frequency, and high frequency to the RC-IGBT tube, the present invention comprehensively captures the voltage signal characteristics of the device in different frequency operating states. Compared with the traditional single-parameter detection method, the present invention can more accurately reflect the dynamic characteristic changes of the RC-IGBT, significantly improving the accuracy and reliability of fault detection.

[0041] 2. By introducing the distortion value sequence, the distortion time deterioration coefficient, and the distortion frequency deterioration coefficient, the present invention realizes the comprehensive performance evaluation of the RC-IGBT at low, medium, and high frequencies. Through the comprehensive analysis of multi-frequency signals, the actual operating state of the device can be more comprehensively described, overcoming the limitations of the traditional method that only relies on a single frequency or a single parameter.

[0042] 3. In each switching cycle of the voltage signal, the present invention calculates the distortion value to reflect the distortion condition of the signal in one switching cycle. The constructed distortion value sequence reflects the distortion conditions of the signals in each switching cycle of the voltage signal. Then, the distortion time deterioration coefficient is calculated for the distortion value sequence to reflect the distortion deterioration condition of the RC-IGBT tube over time. Next, the distortion frequency deterioration coefficient is calculated to reflect the distortion deterioration condition of the RC-IGBT tube with frequency change. Based on the distortion mean values at low frequency, medium frequency, and high frequency, and with the correction of the distortion time deterioration coefficient and the distortion frequency deterioration coefficient, the accuracy of RC-IGBT fault diagnosis is improved. Description of the Drawings

[0043] Figure 1 is a flowchart of a method for RC-IGBT fault detection and diagnosis;

[0044] Figure 2 is a signal schematic diagram of one switching cycle in the desired voltage signal;

[0045] Figure 3 is a signal schematic diagram of one switching cycle in the voltage signal when the RC-IGBT fails. Detailed Embodiments

[0046] The following describes the detailed embodiments of the present invention to facilitate those skilled in the art of the present technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the detailed embodiments. For those of ordinary skill in the art of the present technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are within the scope of protection.

[0047] As Figure 1 shown, a method for RC-IGBT fault detection and diagnosis includes the following steps:

[0048] S1. Apply three kinds of pulse signals with low frequency, medium frequency, and high frequency to the gate of the RC-IGBT tube respectively, and collect the voltage signal between the collector and the emitter of the RC-IGBT tube;

[0049] S2. Calculate the distortion value for each switching cycle in the voltage signal and construct a distortion value sequence;

[0050] S3. Calculate the distortion time deterioration coefficient for the distortion value sequence;

[0051] S4. Take the mean value of each distortion value sequence to obtain the distortion mean value, and calculate the distortion frequency deterioration coefficient;

[0052] S5. Based on the distortion mean values corresponding to low frequency, medium frequency, and high frequency, and with the correction of the distortion time deterioration coefficient and the distortion frequency deterioration coefficient, obtain the RC-IGBT fault diagnosis value.

[0053] In this embodiment, in S1, the frequency range of the low frequency is 0.1 kHz to 1 kHz, the frequency range of the medium frequency is 1 kHz to 20 kHz, and the frequency range of the high frequency is 20 kHz to 100 kHz.

[0054] The low-frequency band (0.1 - 1 kHz) represents the basic operating frequency of the RC-IGBT in industrial control and power systems, reflects the static characteristics and basic switching performance of the device, can capture the most basic performance degradation signals of the device, and simulates low-speed conversion and load regulation conditions.

[0055] The medium-frequency band (1 - 20 kHz) corresponds to the actual operating frequencies of most industrial frequency converters and motor drive systems, is in the critical conversion interval of switching losses and dynamic performance, can reflect the performance changes of the RC-IGBT under complex operating conditions, and simulates medium-load and medium-speed operating conditions.

[0056] The high-frequency band (20 - 100 kHz) represents the high-speed switching characteristics of modern power electronic systems, reflects the dynamic response of the RC-IGBT under extreme operating conditions, captures sensitive signals of internal microscopic defects and performance degradation of the device, and simulates high-frequency application scenarios such as new energy and high-speed rail traction.

[0057] In the present invention, a pulse signal is applied to the gate of the RC-IGBT tube to make the RC-IGBT tube conduct when at a high level and turn off when at a low level, and the switching performance of the RC-IGBT tube is tested.

[0058] In this embodiment, S2 includes the following sub-steps:

[0059] S21: Extract the high-level vibration value, low-level vibration value, rising-edge steepness value, and falling-edge steepness value according to each switching cycle in the voltage signal;

[0060] S22: Calculate the distortion value according to the high-level vibration value, low-level vibration value, rising-edge steepness value, and falling-edge steepness value;

[0061] S23: For the same voltage signal, in the order of occurrence in time, use the distortion value as an element to construct a distortion value sequence.

[0062] The high-level vibration value reflects the stability of the switching device in the high-level state and reveals the influence of parasitic parameters such as parasitic inductance and capacitance; the low-level vibration value characterizes the electrical characteristics of the device in the on state, reflects the leakage current and switching losses, and reveals the degradation degree of the PN junction and the gate oxide layer; the falling-edge steepness value reflects the turn-on speed and switching performance of the device and directly reflects the carrier injection and transport ability; the rising-edge steepness value reflects the turn-off speed and switching performance of the device and reveals the carrier recombination and drive-away characteristics.

[0063] During a switching cycle of the voltage signal, the high-level vibration value, low-level vibration value, rising-edge steepness value, and falling-edge steepness value are extracted, and the distortion value is calculated, which can reflect the distortion situation of the signal in one switching cycle.

[0064] In this embodiment, the calculation formula for the high-level vibration value in S21 is: , where V H is the high-level vibration value, H i is the i-th voltage value in the high-level part of the switching cycle, H steady is the high-level steady-state value, i is a positive integer, N H is the number of voltage values in the high-level part of the switching cycle, and | | is the absolute value operation.

[0065] In this embodiment, the calculation formula for the low-level vibration value in S21 is: , where V L is the low-level vibration value, L i is the i-th voltage value in the low-level part of the switching cycle, L steady is the low-level steady-state value, H L is the number of voltage values in the low-level part of the switching cycle.

[0066] As Figure 2 shown, when the RC-IGBT tube is normal, the high-level part and the low-level part are stable. As Figure 3 shown, in one switching cycle, there are a large number of oscillation signals in the high-level part and the low-level part, seriously deviating from the low-level steady-state value and the high-level steady-state value.

[0067] In this embodiment, the high-level steady-state value is the bus voltage of the RC-IGBT tube, and the low-level steady-state value is the ground voltage.

[0068] In this embodiment, the calculation formula for the rising-edge steepness value in S21 is: , where K R is the rising-edge steepness value, V R,E is the end voltage value of the rising edge in the switching cycle, V R,S is the start voltage value of the rising edge in the switching cycle, △t R is the interval time from the start to the end of the rising edge.

[0069] The end voltage value of the rising edge is the last voltage value in the rising-edge segment signal, and the start voltage value of the rising edge is the first voltage value in the rising-edge segment signal.

[0070] In this embodiment, the calculation formula for the falling-edge steepness value in S21 is: , where K F is the falling-edge steepness value, VF,S is the starting voltage value at the falling edge during the switching period, V F,E is the ending voltage value at the falling edge during the switching period, △t F is the time interval from the start to the end of the falling edge.

[0071] The starting voltage value of the falling edge is the first voltage value in the falling edge signal, and the ending voltage value of the falling edge is the last voltage value in the falling edge segment signal.

[0072] The steepness values of the rising edge and the falling edge of the present invention directly reflect the switching speed and stability of the IGBT. By monitoring the changes of these values, potential faults or performance degradation can be detected in a timely manner, thereby improving the accuracy of fault diagnosis.

[0073] In this embodiment, the formula for calculating the distortion value in S22 is: , where θ is the distortion value, V H is the high-level vibration value, V L is the low-level vibration value, K R is the steepness value of the rising edge, K F is the steepness value of the falling edge, K R,th is the steepness standard value of the rising edge, K F,th is the steepness standard value of the falling edge, | | is the absolute value operation.

[0074] In the present invention, the higher the high-level vibration value and the low-level vibration value, and the more the steepness value of the rising edge deviates from the steepness standard value of the rising edge, and the more the steepness value of the falling edge deviates from the steepness standard value of the falling edge, the greater the distortion value.

[0075] The steepness standard value of the rising edge and the steepness standard value of the falling edge can be obtained by referring to the technical manual of the RC-IGBT tube. For a typical RC-IGBT tube, the specific values of the steepness standard value of the rising edge and the steepness standard value of the falling edge are usually in the following ranges: the steepness standard value of the rising edge: 5000 - 15000 V / μs, for high-performance IGBTs: up to 10 - 20 kV / μs, for low-power IGBTs: about 2 - 5 kV / μs, the steepness standard value of the falling edge: 3000 - 10000 V / μs, for high-performance IGBTs: up to 8 - 15 kV / μs, for low-power IGBTs: about 1 - 4 kV / μs.

[0076] In this embodiment, S3 includes the following sub-steps:

[0077] S31. Take the last consecutive M distortion values and the first consecutive M distortion values in the distortion value sequence, where M is a positive integer;

[0078] S32. Take the average of the last consecutive M distortion values to obtain the last distortion average;

[0079] S33. Take the average of the first consecutive M distortion values to obtain the starting distortion average value.

[0080] S34. Use the ratio of the ending distortion average value to the starting distortion average value as the distortion time deterioration coefficient.

[0081] The present invention compares the ending distortion value with the starting distortion value to reflect whether the distortion situation deteriorates over time.

[0082] In this embodiment, S4 includes the following sub-steps:

[0083] S41. Take the average of each distortion value sequence to obtain the distortion average value.

[0084] S42. Calculate the first distortion frequency deterioration value according to the difference between the distortion average value corresponding to the intermediate frequency and the distortion average value corresponding to the low frequency.

[0085] S43. Calculate the second distortion frequency deterioration value according to the difference between the distortion average value corresponding to the high frequency and the distortion average value corresponding to the intermediate frequency.

[0086] S44. Add the first distortion frequency deterioration value and the second distortion frequency deterioration value to obtain the distortion frequency deterioration coefficient.

[0087] In this embodiment, the formula for calculating the first distortion frequency deterioration value in S42 is: , where μ1 is the first distortion frequency deterioration value, tanh is the hyperbolic tangent function, θ M is the distortion average value corresponding to the intermediate frequency, θ L is the distortion average value corresponding to the low frequency;

[0088] The formula for calculating the second distortion frequency deterioration value in S43 is: , where μ2 is the second distortion frequency deterioration value, θ H is the distortion average value corresponding to the high frequency, θ M is the distortion average value corresponding to the intermediate frequency.

[0089] The present invention calculates the first distortion frequency deterioration value according to the difference between the distortion average value corresponding to the intermediate frequency and the distortion average value corresponding to the low frequency to reflect the deterioration situation of the RC-IGBT tube from the low frequency to the intermediate frequency, and then calculates the second distortion frequency deterioration value according to the difference between the distortion average value corresponding to the high frequency and the distortion average value corresponding to the intermediate frequency to reflect the deterioration situation of the RC-IGBT tube from the intermediate frequency to the high frequency.

[0090] When calculating the deterioration value of the distortion frequency in the present invention, the difference of the distortion mean value is cubed to enhance the difference situation, and the positive and negative of the difference are not changed. The hyperbolic tangent function is set so that the deterioration value of the distortion frequency is within the range of -1 to 1. When the deterioration value of the distortion frequency is greater than 0, the state of the RC-IGBT tube deteriorates further as the frequency increases. When the deterioration value of the distortion frequency is less than 0, the state of the RC-IGBT tube improves as the frequency increases.

[0091] In this embodiment, S5 includes the following sub-steps:

[0092] S51. Multiply the distortion mean value at low frequency by the distortion time deterioration coefficient to obtain the fault value at low frequency;

[0093] S52. Multiply the distortion mean value at medium frequency by the distortion time deterioration coefficient to obtain the fault value at medium frequency;

[0094] S53. Multiply the distortion mean value at high frequency by the distortion time deterioration coefficient to obtain the fault value at high frequency;

[0095] S54. Calculate the RC-IGBT fault diagnosis value based on the correction of the distortion frequency deterioration coefficient according to the fault value at low frequency, the fault value at medium frequency, and the fault value at high frequency.

[0096] Since three pulse signals are applied in the present invention, corresponding to 3 voltage signals and 3 distortion value sequences, therefore, multiply the distortion mean value corresponding to low frequency by the distortion time deterioration coefficient corresponding to low frequency to obtain the fault value at low frequency; multiply the distortion mean value corresponding to medium frequency by the distortion time deterioration coefficient corresponding to medium frequency to obtain the fault value at medium frequency; multiply the distortion mean value corresponding to high frequency by the distortion time deterioration coefficient corresponding to high frequency to obtain the fault value at high frequency. When the distortion time deterioration coefficient is greater than 1, as the working time increases, the state of the RC-IGBT tube deteriorates further. Therefore, it has an enhancing effect on the distortion mean value and the obtained fault value is larger. When the distortion time deterioration coefficient is less than 1, as the working time increases, the state of the RC-IGBT tube improves. Therefore, it has a weakening effect on the distortion mean value and the obtained fault value is smaller.

[0097] In this embodiment, the formula for calculating the RC-IGBT fault diagnosis value in S54 is: , where G is the RC-IGBT fault diagnosis value, y L is the fault value at low frequency, y M is the fault value at medium frequency, y H is the fault value at high frequency, and γ is the distortion frequency deterioration coefficient.

[0098] The present invention synthesizes the fault values at low frequency, medium frequency and high frequency, and further improves the accuracy of fault diagnosis based on the compensation of the distortion frequency deterioration coefficient.

[0099] The present invention applies three kinds of pulse signals of low frequency, medium frequency and high frequency to the RC-IGBT tube to comprehensively capture the voltage signal characteristics of the device in different frequency operating states. Compared with the traditional single-parameter detection method, the present invention can more accurately reflect the dynamic characteristic changes of the RC-IGBT, and significantly improve the accuracy and reliability of fault detection.

[0100] The present invention introduces the distortion value sequence, the distortion time deterioration coefficient and the distortion frequency deterioration coefficient to realize the comprehensive performance evaluation of the RC-IGBT at low, medium and high frequencies. Through the comprehensive analysis of multi-frequency signals, the actual operating state of the device can be more comprehensively characterized, overcoming the limitations of the traditional method that only relies on a single frequency or a single parameter.

[0101] The present invention calculates the distortion value in each switching cycle of the voltage signal to reflect the distortion of the signal in one switching cycle. The constructed distortion value sequence reflects the distortion of the signals in each switching cycle of the voltage signal, and calculates the distortion time deterioration coefficient for the distortion value sequence to reflect the distortion deterioration of the RC-IGBT tube over time. Then, the distortion frequency deterioration coefficient is calculated to reflect the distortion deterioration of the RC-IGBT tube with frequency change. According to the distortion means at low frequency, medium frequency and high frequency, and based on the correction of the distortion time deterioration coefficient and the distortion frequency deterioration coefficient, the accuracy of RC-IGBT fault diagnosis is improved.

[0102] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A fault detection and diagnosis method for RC-IGBT, characterized in that, Including the following steps: S1. Apply three kinds of pulse signals with low frequency, medium frequency and high frequency to the gate of the RC-IGBT tube respectively, and collect the voltage signal between the collector and emitter of the RC-IGBT tube; S2. Calculate the distortion value for each switching cycle in the voltage signal and construct a distortion value sequence; S3. Calculate the distortion time deterioration coefficient for the distortion value sequence; S4. Take the average value of each distortion value sequence to obtain the average distortion value, and calculate the distortion frequency deterioration coefficient; S5. Based on the average distortion values corresponding to low frequency, medium frequency and high frequency, and the correction of the distortion time deterioration coefficient and the distortion frequency deterioration coefficient, obtain the RC-IGBT fault diagnosis value; The specific content of S2 is: Extract the high-level vibration value, low-level vibration value, rising edge steepness value and falling edge steepness value according to each switching cycle in the voltage signal, and calculate the distortion value; For the same voltage signal, in the order of time occurrence, use the distortion value as an element to construct a distortion value sequence; The calculation formula for the high-level vibration value is: , where V H is the high-level vibration value, H i is the i-th voltage value in the high-level part of the switching period, H steady is the high-level steady-state value, i is a positive integer, N H is the number of voltage values in the high-level part of the switching period, and | | is the absolute value operation; The calculation formula for the low-level vibration value is: , where V L is the low-level vibration value, L i is the i-th voltage value in the low-level part of the switching period, L steady is the low-level steady-state value, H L is the number of voltage values in the low-level part of the switching period; The calculation formula for the rising edge steepness value is as follows: , where K R is the rising edge steepness value, V R,E is the end voltage value of the rising edge in the switching period, V R,S is the starting voltage value of the rising edge in the switching period, △t R is the interval time from the start to the end of the rising edge; The calculation formula for the steepness value of the falling edge is as follows: , where K F is the steepness value of the falling edge, V F,S is the starting voltage value of the falling edge in the switching period, V F,E is the ending voltage value of the falling edge in the switching period, △t F is the interval time from the starting point to the ending point of the falling edge; The formula for calculating the distortion value is as follows: , where θ is the distortion value, K R,th is the steepness standard value of the rising edge, K F,th is the steepness standard value of the falling edge, and | | is the absolute value operation; The said S3 includes the following sub-steps: S31. Take the last continuous M distortion values and the first continuous M distortion values in the distortion value sequence, where M is a positive integer; S32. Take the average value of the last continuous M distortion values to obtain the average value of the last distortion; S33. Take the average value of the first continuous M distortion values to obtain the average value of the first distortion; S34. Take the ratio of the average value of the last distortion to the average value of the first distortion as the distortion time deterioration coefficient; The said S4 includes the following sub-steps: S41. Take the average value of each distortion value sequence to obtain the average distortion value; S42. Calculate the first distortion frequency deterioration value according to the difference between the average distortion value corresponding to medium frequency and the average distortion value corresponding to low frequency; S43. Calculate the second distortion frequency deterioration value according to the difference between the average distortion value corresponding to high frequency and the average distortion value corresponding to medium frequency; S44. Add the first distortion frequency deterioration value and the second distortion frequency deterioration value to obtain the distortion frequency deterioration coefficient; The formula for calculating the first distortion frequency deterioration value in S42 is as follows: , where μ1 is the first distortion frequency deterioration value, tanh is the hyperbolic tangent function, and θ M is the average distortion corresponding to the intermediate frequency, and θ L is the average distortion corresponding to the low frequency; The formula for calculating the second distortion frequency deterioration value in S43 is as follows: , where μ2 is the second distortion frequency deterioration value, and θ H is the distortion mean value corresponding to the high frequency, and θ M is the distortion mean value corresponding to the medium frequency; The said S5 includes the following sub-steps: S51. Multiply the average distortion value at low frequency by the distortion time deterioration coefficient to obtain the fault value at low frequency; S52. Multiply the average distortion value at medium frequency by the distortion time deterioration coefficient to obtain the fault value at medium frequency; S53. Multiply the average distortion value at high frequency by the distortion time deterioration coefficient to obtain the fault value at high frequency; S54. Based on the fault values at low frequency, medium frequency and high frequency, and the correction of the distortion frequency deterioration coefficient, calculate the RC-IGBT fault diagnosis value; The formula for calculating the fault diagnosis value of the RC-IGBT in S54 is as follows: , where G is the fault diagnosis value of the RC-IGBT, and y L is the fault value at low frequency, y M is the fault value at medium frequency, and y H is the fault value at high frequency. γ is the distortion frequency deterioration coefficient.

2. The RC-IGBT fault detection and diagnosis method according to claim 1, wherein, In S1, the frequency range of low frequency is 0.1kHz to 1kHz, the frequency range of medium frequency is 1kHz to 20kHz, and the frequency range of high frequency is 20kHz to 100kHz.

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