Method for testing an igbt module and testing device therefor

Abstract

This invention discloses a testing method and apparatus for IGBT modules. The IGBT module is connected to a DC bus and an inductor box. A temperature outer loop generates a reference current value based on the deviation between the target test junction temperature and the actual junction temperature. An inner current loop adjusts the PWM duty cycle based on the deviation between the actual output current and the reference current value, thereby controlling the IGBT module to apply a converted DC voltage to the inductor box. This makes the actual junction temperature of the IGBT module approach the target test junction temperature. Based on the actual junction temperature data and actual output current data during the testing process, the IGBT module test results are output to achieve power cycle testing of the IGBT. The dual closed-loop control achieves accurate simulation of the IGBT module junction temperature, and the connection between the IGBT module and the inductor box reproduces the thermal stress of the IGBT module under actual operating conditions, thus more accurately determining the power cycle test results of the IGBT module under actual operating conditions.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a testing method and testing apparatus for IGBT modules. Background Technology

[0002] With the widespread application of power semiconductor modules, represented by IGBTs (Insulated Gate Bipolar Transistors), in power conversion and distribution in new energy vehicles, industrial drives, and smart grids, IGBT modules are crucial for ensuring the stable operation and efficient output of these systems. Therefore, the long-term reliability of IGBT modules has become a key performance indicator. In actual operating conditions, each IGBT within an IGBT module faces complex and variable load conditions and harsh thermal environments. These factors directly and significantly impact the performance and lifespan of the IGBT module. Therefore, power cycle testing of IGBT modules is an indispensable step in verifying their design lifespan and screening for potential defects. Summary of the Invention

[0003] The purpose of this invention is to provide a testing method and device for IGBT modules. It achieves accurate simulation of the junction temperature of the IGBT module through dual closed-loop control, and reproduces the thermal stress of the IGBT module under actual operating conditions by connecting the IGBT module with the inductor box, thereby more accurately determining the power cycle test results of the IGBT module under actual operating conditions.

[0004] To address the aforementioned technical problems, this invention provides a testing method for an IGBT module, wherein the input terminal of the IGBT module is connected to a DC bus, and the output terminal of the IGBT module is connected to an inductor box; the method includes: The reference current value is determined based on the junction temperature deviation between the target test junction temperature and the actual junction temperature of the IGBT module. The duty cycle of the PWM modulation signal is adjusted based on the current deviation between the actual output current of the IGBT module and the reference current value. Based on the PWM modulation signal, each IGBT in the IGBT module is controlled so that the IGBT module applies the DC voltage on the DC bus to the inductor box after voltage transformation, so that the actual junction temperature of the IGBT module is the target test junction temperature; The actual junction temperature data and actual output current data of each IGBT in the IGBT module are determined during the control process, and the IGBT module test results are output based on the actual junction temperature data and the actual output current data.

[0005] Preferably, before determining the actual junction temperature data and actual output current data during the control process of each IGBT in the IGBT module, the method further includes: Set the preset test duration; The test begins when the control of the IGBTs in the IGBT module is started. If the duration of the test on the IGBT module reaches the preset test duration, the test is terminated, and the process proceeds to the step of determining the actual junction temperature data and actual output current data during the control of each IGBT in the IGBT module.

[0006] Preferably, before determining the actual junction temperature data and actual output current data during the control process of each IGBT in the IGBT module, the method further includes: Before the duration reaches the preset test duration, determine whether there is a faulty IGBT in the IGBT module that has a short circuit or open circuit. If present, then the IGBT module is determined to have a failure anomaly.

[0007] Preferably, before determining the reference current value based on the junction temperature deviation between the target test junction temperature and the actual junction temperature of the IGBT module, the method further includes: Static parameter tests are performed on each IGBT in the IGBT module to obtain the initial static parameters of each IGBT. The initial static parameters include the collector-emitter initial saturation voltage drop and the gate initial threshold voltage.

[0008] Preferably, after determining whether there is a faulty IGBT with a short circuit or open circuit in the IGBT module before the duration reaches the preset test duration, the method further includes: If not, after the duration reaches the preset test duration, static parameter tests are performed on each IGBT in the IGBT module to obtain the current static parameters of each IGBT. The current static parameters include the current collector-emitter saturation voltage drop and the current gate threshold voltage. The first rate of change of the collector-emitter saturation voltage drop of each IGBT is determined based on the current collector-emitter saturation voltage drop and the initial collector-emitter saturation voltage drop of each IGBT. The second rate of change of the gate threshold voltage of each IGBT is determined based on the current gate threshold voltage and the initial gate threshold voltage of each IGBT. IGBTs that exhibit the condition that the first rate of change is greater than the first threshold and / or the second rate of change is greater than the second threshold are identified as failed IGBTs.

[0009] Preferably, before determining the reference current value based on the junction temperature deviation between the target test junction temperature and the actual junction temperature of the IGBT module, the method further includes: The dynamic parameters of each IGBT in the IGBT module are tested using a dual-pulse test circuit to obtain the initial turn-on loss and initial turn-off loss of each IGBT.

[0010] Preferably, after determining whether there is a faulty IGBT with a short circuit or open circuit in the IGBT module before the duration reaches the preset test duration, the method further includes: If not, after the duration reaches the preset test duration, the dynamic parameters of each IGBT in the IGBT module are tested through the dual-pulse test circuit to obtain the current turn-on loss and current turn-off loss of each IGBT. The change in activation loss is determined based on the difference between the current activation loss and the initial activation loss and a first ratio of the initial activation loss; The change in turn-off loss is determined based on the difference between the current turn-off loss and the initial turn-off loss and a second ratio of the initial turn-off loss; IGBTs that exhibit a change in turn-on loss exceeding the third threshold and / or a change in turn-off loss exceeding the fourth threshold are classified as failed IGBTs.

[0011] Preferably, adjusting the duty cycle of the PWM modulation signal based on the current deviation between the actual output current of the IGBT module and the reference current value includes: During each switching cycle, the peak value of the three-phase output current of the IGBT module is detected and used as the actual output current; The difference between the actual output current and the reference current value is defined as the current deviation; The current deviation is calculated using a PI method to determine the target control voltage; The duty cycle of the PWM modulation signal is adjusted based on the target control voltage.

[0012] To address the aforementioned technical problems, this invention provides a testing apparatus for IGBT modules, comprising: Memory, used to store computer programs; A processor, used to implement the steps of the test method for the IGBT module as described above when executing a computer program.

[0013] Preferably, it also includes an IGBT module, a programmable voltage source, and an inductor box; The output terminal of the programmable voltage source is connected to the DC bus to provide DC bus voltage; The input terminal of the IGBT module is connected to the DC bus, and the output terminal of the IGBT module is connected to the inductor box; the control terminal of the IGBT module is connected to the processor.

[0014] This application provides a testing method and apparatus for IGBT modules. The IGBT module is connected to a DC bus and an inductor box. A temperature outer loop generates a reference current value based on the deviation between the target test junction temperature and the actual junction temperature. A current inner loop adjusts the PWM duty cycle based on the deviation between the actual output current and the reference current value, thereby controlling the IGBT module to apply the converted DC voltage to the inductor box. This makes the actual junction temperature of the IGBT module approach the target test junction temperature. Based on the actual junction temperature data and actual output current data during the testing process, the IGBT module test results are output to achieve power cycle testing of the IGBT. The dual closed-loop control achieves accurate simulation of the IGBT module junction temperature, and the connection between the IGBT module and the inductor box reproduces the thermal stress of the IGBT module under actual operating conditions, thus more accurately determining the power cycle test results of the IGBT module under actual operating conditions. Attached Figure Description

[0015] To more clearly illustrate the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 A flowchart illustrating a testing method for an IGBT module provided in this application; Figure 2 A schematic diagram of the structure of a test system for an IGBT module provided in this application; Figure 3 A schematic diagram of the structure of a test device for an IGBT module provided in this application; Figure 4 A schematic diagram of the d-axis equivalent circuit of the motor control system provided in this application; Figure 5 A schematic diagram of the q-axis equivalent circuit of the motor control system provided in this application; Figure 6 This is a schematic diagram of the structure of a computer-readable storage medium provided in this application. Detailed Implementation

[0017] The core of this invention is to provide a testing method and device for IGBT modules. It achieves accurate simulation of the junction temperature of IGBT modules through dual closed-loop control, and reproduces the thermal stress of IGBT modules under actual operating conditions by connecting the IGBT module with the inductor box, thereby more accurately determining the power cycle test results of IGBT modules under actual operating conditions.

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Please refer to Figure 1 , Figure 1 The flowchart illustrates a testing method for an IGBT module provided in this application. The input terminal of the IGBT module is connected to a DC bus, and the output terminal of the IGBT module is connected to an inductor box. The method includes: S11: Determine the reference current value based on the junction temperature deviation between the target test junction temperature and the actual junction temperature of the IGBT module; In electric vehicle applications, inverters, such as IGBT modules, are core components. The IGBTs within these modules are crucial for power conversion and distribution, ensuring stable operation and high-efficiency output for electric vehicles. However, in actual electric vehicle operation, IGBT modules and their internal IGBTs face complex and variable load conditions and harsh thermal environments. These factors directly and significantly impact their performance and lifespan. Therefore, factory reliability testing of IGBT modules is particularly important.

[0020] Traditional power cycling testing methods involve placing the module under test (DUT) in an ideal environment and simulating heat exchange between its arms. Specifically, a programmable voltage source controls the gate voltage of each IGBT in the DUT module to drive it into a fully on or fully off switching state. Simultaneously, a programmable current source injects a constant high-current DC current into the collector and emitter circuits of the IGBTs during the heating phase. This constant DC current flowing through the IGBTs generates conduction losses, causing the junction temperature to rise rapidly to a set peak value. During the cooling phase, the gate voltage is removed, the current source is cut off, and the IGBT module cools down using the cooling system. By repeatedly performing this cycle of heating with current flow and cooling with current flow interruption, and by monitoring the saturation voltage drop and junction temperature changes of the IGBTs in real time, the module's lifespan is ultimately assessed based on failure criteria.

[0021] However, while the aforementioned traditional DC power cycling test method can effectively simulate the mechanical stress generated by thermal expansion and contraction of packaging materials, it still has significant shortcomings when dealing with the complex operating conditions of modern power electronic devices. First, the heating process of this method relies solely on the conduction losses of the IGBT. In actual inverter applications, the module operates in a high-frequency pulse width modulation mode, and its losses include both conduction and switching losses. The presence of switching losses makes the internal heat distribution of the chip more complex and closer to real-world operating conditions. Second, in traditional tests, the anti-parallel diode hardly participates in heating. However, in actual inductive load circuits, the current carried by the diode during freewheeling and the losses it generates have a significant impact on the overall thermal coupling effect and failure modes of the module. Furthermore, since a real high-voltage bus is not applied, the traditional method cannot simulate the electric field stress and overvoltage impact experienced by the device when the inductive load is turned off, making it difficult to reproduce the special failure mechanisms triggered by electrical stress coupling.

[0022] In this embodiment, during power cycle testing, a control benchmark reflecting the actual thermal state of the IGBT module, i.e., the target test junction temperature, is first determined. The actual junction temperature of the IGBT module is acquired in real time and compared with the preset target test junction temperature to calculate the junction temperature deviation. This junction temperature deviation serves as the input to the outer temperature loop, and after processing by the temperature controller, a reference current value is output. However, the reference current value is not the final control quantity but rather serves as the control target for the subsequent inner current loop. Based on this, by introducing temperature closed-loop control, the system can dynamically adjust the current command according to the actual thermal state of the IGBT module, thereby accurately simulating junction temperature fluctuations under actual operating conditions and avoiding junction temperature deviations caused by fixed current loading.

[0023] It should be noted that the actual junction temperature is determined in the following way: First, the short-circuit current of the IGBT in the IGBT module refers to the current flowing through the IGBT when the IGBT module enters the short-circuit condition under specific test conditions. There is a definite functional relationship between the amplitude of the short-circuit current and the junction temperature of the IGBT module. That is, as the junction temperature increases, the short-circuit current shows a decreasing trend. Therefore, the short-circuit current can be used as a temperature-sensitive electrical parameter to characterize the junction temperature.

[0024] Based on the above principles, this embodiment first calibrates the short-circuit current-junction temperature characteristics of the IGBT module before starting the power cycle test. Specifically, under different case temperature conditions, such as 25°C, 75°C, and 125°C, a preset short-circuit test pulse is applied to the IGBT module. For example, the temperature points of the IGBT module are measured by infrared thermography, and the short-circuit current amplitude corresponding to each temperature point is measured and recorded, thereby establishing a curve or lookup table showing the correspondence between short-circuit current and junction temperature. This calibration process is usually performed when the module is in thermal equilibrium and not connected to an inductor box to ensure the accuracy of the calibration results.

[0025] During power cycling testing, when it is necessary to determine the actual junction temperature of the IGBT module, the normal PWM drive is briefly paused at a preset sampling time. Instead, a very short-circuit test pulse is applied to the IGBT under test, and the instantaneous value of the short-circuit current is acquired at that moment. Based on the pre-calibrated short-circuit current-junction temperature correspondence, an initial junction temperature is calculated by looking up a table or interpolation. This initial junction temperature reflects the temperature state exhibited by the IGBT based on its electrical characteristics at the current moment. However, since the short-circuit current-junction temperature characteristic is usually obtained under standard test conditions, while the overall ambient temperature of the module may change during actual testing, directly using the initial junction temperature as the actual junction temperature may result in deviation.

[0026] Therefore, this embodiment introduces a calibration mechanism based on NTC temperature sensors. While applying a short-circuit test pulse, the current reference point temperature is acquired by NTC temperature sensors installed in each arm of the IGBT module. Since the reference point temperature reflects the steady-state temperature of the substrate inside the IGBT module, it can be used as an indication of the ambient temperature or reference temperature. The currently measured reference point temperature is compared with the reference temperature used during short-circuit current calibration, for example, a fixed case temperature of 25°C during calibration, to calculate the temperature deviation. Based on the physical characteristics of the IGBT, there is a quantifiable compensation relationship between junction temperature changes and short-circuit current changes. For example, the initial junction temperature can be corrected using a preset temperature compensation coefficient k: Actual junction temperature = Initial junction temperature + k × Temperature deviation.

[0027] Finally, the actual junction temperature obtained through the above correction is the actual junction temperature of the IGBT module at the current moment. It should be noted that, since the amplitude of the short-circuit current is mainly affected by the carrier characteristics of the hottest region inside the IGBT module, the actual junction temperature obtained by this method reflects the maximum junction temperature in the active region of the IGBT module.

[0028] S12: Adjust the duty cycle of the PWM modulation signal based on the current deviation between the actual output current and the reference current value of the IGBT module; After obtaining the reference current value, the actual output current is further acquired in real time and compared with the reference current value to calculate the current deviation. This current deviation serves as the input to the inner current loop. After processing by the current controller, it outputs an adjustment value used to adjust the duty cycle of the PWM (Pulse Width Modulation) signal. The response speed of the inner current loop is much faster than that of the outer temperature loop, enabling it to quickly eliminate current deviation and ensure that the actual output current accurately follows the reference current value. Based on this, by introducing current closed-loop control, the system possesses rapid response capabilities, overcoming interference factors including but not limited to DC bus voltage fluctuations and line impedance changes, ensuring the accuracy and stability of the actual output current. This provides constant and controllable power loss for the IGBT module, ensuring accurate junction temperature control.

[0029] S13: Based on the PWM modulation signal, control each IGBT in the IGBT module so that the IGBT module applies the DC voltage on the DC bus to the inductor box after voltage transformation, so that the actual junction temperature of the IGBT module is used as the target junction temperature for testing. The adjusted PWM modulation signal is applied to the gates of each IGBT in the IGBT module, controlling their high-frequency turn-on and turn-off. Under the control of the PWM modulation signal, the IGBT module converts the DC voltage on the DC bus into an AC square wave voltage, which is applied to the inductor box. Since the inductor box is an inductive load, a continuous and variable current is generated under the action of the AC square wave voltage, causing the IGBT and anti-parallel diode to conduct alternately and generate power loss. This power loss causes the IGBT junction temperature to rise. Through the above dual closed-loop regulation, the actual junction temperature of the IGBT module is always kept close to the target test junction temperature. Based on this, by connecting the IGBT module to an inductor box with a purely inductive load, the current path and heating mechanism under actual operating conditions such as motor drive are realistically simulated. Each IGBT in the IGBT module can alternately conduct and output in the form of sinusoidal current or DC according to the actual operating conditions and perform a long-term switching process, so that both IGBT and diode participate in heating, reproducing the thermal coupling effect in actual operation, and providing a realistic stress environment for power cycle testing. Based on this, the control algorithm ensures that a large current sufficient to raise the junction temperature of the IGBT in the IGBT module flows through it. Compared with providing a large current through a programmable current source to raise the junction temperature of the IGBT, the method in this application requires lower costs. Furthermore, the control of programmable current sources in traditional technologies is usually achieved through computer control systems. The communication protocol and data processing processes are subject to delays, especially in high-frequency and highly dynamic testing scenarios. The system response speed cannot meet the real-time control requirements, resulting in a mismatch between the test waveform and the actual operating waveform, which affects the authenticity of the test. In contrast, this application uses PWM modulation signals to directly control each IGBT in the IGBT module, which can ensure the real-time performance and accuracy of IGBT control, ensure the validity and accuracy of test results, and allow multiple IGBTs in the IGBT module to be tested simultaneously, thus improving testing efficiency.

[0030] S14: Determine the actual junction temperature data and actual output current data during the control process of each IGBT in the IGBT module, and output the IGBT module test results based on the actual junction temperature data and actual output current data.

[0031] Throughout the testing process, actual junction temperature and output current data for each IGBT were continuously collected and recorded. This data includes, but is not limited to, junction temperature variation curves over time, current waveforms, and power losses. After the test, the recorded data was processed and analyzed, outputting test results including, but not limited to, junction temperature fluctuation amplitude, cycle count, and failure time. Based on this, it is possible not only to determine the bonding phases, solder, and terminal conditions within the IGBT module, thereby confirming whether the IGBT module meets the preset lifespan requirements, but also to determine its performance degradation patterns, providing objective basis for device selection, thermal design optimization, and reliability assessment.

[0032] It should be noted that this application can not only complete the power cycle test of each IGBT in the IGBT module in one go, but also takes into account that the lower bridge arm in the IGBT module will bear a larger back electromotive force, and further screens each IGBT in the lower bridge arm. That is, based on the test results, it can be determined whether each IGBT in the lower bridge arm can withstand the back electromotive force under actual working conditions.

[0033] In summary, the dual closed-loop control enables accurate simulation of the IGBT module junction temperature, and the connection between the IGBT module and the inductor box reproduces the thermal stress of the IGBT module under actual operating conditions, thereby more accurately determining the power cycle test results of the IGBT module under actual operating conditions.

[0034] Based on the above embodiments: As a preferred embodiment, before determining the actual junction temperature data and actual output current data during the control process of each IGBT in the IGBT module, the method further includes: Set the preset test duration; The test starts when the control of the IGBTs in the IGBT module begins. If the duration of the test on the IGBT module reaches the preset test duration, the test is terminated, and the process proceeds to determine the actual junction temperature data and actual output current data during the control of each IGBT in the IGBT module.

[0035] In this embodiment, firstly, a preset test duration is set according to the testing requirements. This preset test duration can be determined in advance based on the IGBT module specifications, application scenarios, or reliability verification standards, for example, set to 1000 hours, 2000 hours, or longer. Setting the preset test duration provides a clear termination benchmark for the testing process, ensuring that IGBT modules from different batches or models are comparable under the same test duration, facilitating consistency assessment and lifespan comparison.

[0036] Secondly, the start time of the test is defined as the beginning of control over the IGBT in the IGBT module. Specifically, when the first PWM modulation signal is output to drive the IGBT to conduct, causing the IGBT to begin generating power loss and resulting in a rise in junction temperature, the timer starts accumulating the test time. Based on this, the pre-charging phase and standby phase after the IGBT module is powered on, i.e., the time period during which no power loss occurs, are excluded. This ensures that the timing only covers the process during which the IGBT actually experiences thermal stress, thus making the statistics of the test duration more accurate.

[0037] During the test, the cumulative test time is continuously monitored and compared with the preset test duration. If the cumulative test time has not yet reached the preset test duration, the test continues, and the power cycle process of steps S11 to S13 is repeated; if the cumulative test time reaches the preset test duration, the system automatically terminates the power cycle test and proceeds to step S14, which determines and records the actual junction temperature data and actual output current data during the test, and finally outputs the test results.

[0038] As a preferred embodiment, before determining the actual junction temperature data and actual output current data during the control process of each IGBT in the IGBT module, the method further includes: Before the preset test duration is reached, determine whether there are any faulty IGBTs in the IGBT module that have short-circuit or open-circuit faults. If present, it indicates that the IGBT module has a failure anomaly.

[0039] In this embodiment, before the test duration reaches the preset test duration, the system monitors in real time whether there are any short-circuit or open-circuit faults in the IGBT module. A short-circuit fault refers to the formation of a low-resistance path between the collector and emitter of the IGBT due to breakdown or solder melting, which manifests as overcurrent flowing even when the IGBT is off. An open-circuit fault refers to the interruption of the current path due to bonding wire detachment, chip burnout, or other reasons, which manifests as no current flowing or an abnormally reduced current when the IGBT is on. In this embodiment, a fault detection circuit integrated into the test system collects the collector-emitter voltage Vce and the current flowing through each IGBT in real time and identifies the fault based on preset fault criteria. Specifically, when an abnormal decrease in Vce is detected during IGBT off-peak hours or an abnormal increase in current is detected during IGBT on-peak hours, a short-circuit fault is identified; when an abnormal increase in Vce is detected during IGBT on-peak hours or an abnormal decrease or even zero current is detected during IGBT on-peak hours, an open-circuit fault is identified.

[0040] Secondly, if an IGBT with a short circuit or open circuit is detected, the IGBT module is determined to have failed. Therefore, regardless of whether the cumulative test time has reached the preset test duration, as long as any IGBT is detected to have a short circuit or open circuit, the system determines that the IGBT module has failed and terminates the current test. At this point, the system no longer continues to execute the power cycle process from steps S11 to S13, but directly proceeds to step S14, recording the actual junction temperature data and actual output current data at the time of failure, and outputting the failure time, failure type (short circuit or open circuit), and failure location as the test results.

[0041] As a preferred embodiment, before determining the reference current value based on the junction temperature deviation between the target test junction temperature and the actual junction temperature of the IGBT module, the method further includes: Static parameter tests are performed on each IGBT in the IGBT module to obtain the initial static parameters of each IGBT. The initial static parameters include the collector-emitter initial saturation voltage drop and the gate initial threshold voltage.

[0042] In this embodiment, static parameter testing is performed on each IGBT in the IGBT module before starting the power cycle test. Static parameter testing refers to the process of measuring the fundamental electrical characteristics of the IGBT when it is in the off state or a low-current conducting state. These characteristics reflect the physical structure and material state of the IGBT itself and are independent of operating conditions. Static parameter testing is usually performed at room temperature, but it can also be performed separately at different case temperatures as needed to obtain characteristic curves of parameter changes with temperature. In this embodiment, the static parameter test is performed on each IGBT in the IGBT module to ensure that the initial state of each device under test is completely recorded.

[0043] Secondly, the initial static parameters of each IGBT are obtained through static parameter testing. These initial static parameters include at least the collector-emitter initial saturation voltage drop Vce(sat)_0 and the gate initial threshold voltage Vge(th)_0. The collector-emitter saturation voltage drop refers to the voltage drop between the collector and emitter when the IGBT is fully turned on under specified gate voltage and collector current, reflecting the on-resistance of the connection path between the chip and external terminals. The gate threshold voltage is the minimum gate voltage required for the IGBT to turn on, reflecting the characteristics of the gate oxide layer.

[0044] As a preferred embodiment, after determining whether there is a faulty IGBT with a short circuit or open circuit in the IGBT module before the preset test duration is reached, the method further includes: If not, after the preset test duration is reached, static parameter tests are performed on each IGBT in the IGBT module to obtain the current static parameters of each IGBT. The current static parameters include the current collector-emitter saturation voltage drop and the current gate threshold voltage. The first rate of change of the collector-emitter saturation voltage drop of each IGBT is determined based on the current collector-emitter saturation voltage drop and the initial collector-emitter saturation voltage drop of each IGBT. The second rate of change of the gate threshold voltage of each IGBT is determined based on the current gate threshold voltage and the initial gate threshold voltage of each IGBT. IGBTs with a first rate of change greater than a first threshold and / or a second rate of change greater than a second threshold are identified as failed IGBTs.

[0045] If no short-circuit or open-circuit anomalies are detected during the entire test, the test continues until the preset test duration is reached. When the cumulative test time reaches the preset test duration, the power cycling process is terminated, and static parameter tests are immediately performed on each IGBT in the IGBT module. The static parameter tests performed at this time use the same test conditions and methods as the initial calibration before the test to ensure the comparability of the two test results. Through this test, the current static parameters of each IGBT are obtained. The current static parameters include at least the current collector-emitter saturation voltage drop Vce(sat)_n and the current gate threshold voltage Vge(th)_n.

[0046] Secondly, the parameter change rate is calculated based on the comparison between the current static parameters and the initial static parameters of each IGBT. Specifically, for each IGBT, the first change rate ΔVce is calculated according to the formula (Vce(sat)_n - Vce(sat)_0) / Vce(sat)_0, based on its current collector-emitter saturation voltage drop Vce(sat)_n and initial collector-emitter saturation voltage drop Vce(sat)_0. Simultaneously, the second change rate ΔVge is calculated according to the formula (Vge(th)_n - Vge(th)_0) / Vge(th)_0, based on its current gate threshold voltage Vge(th)_n and initial gate threshold voltage Vge(th)_0. These two change rates quantify the degree of degradation of two key parameters of the IGBT during power cycling testing. ΔVce mainly reflects the health status of the connection path between the chip and external terminals, such as the bonding wires, while ΔVge mainly reflects the characteristic changes of the gate oxide layer.

[0047] Finally, failure is determined based on the calculated rate of change. For each IGBT, it is determined whether its first rate of change ΔVce is greater than a preset first threshold, and / or whether its second rate of change ΔVge is greater than a preset second threshold. If either condition is met, i.e., ΔVce exceeds the first threshold or ΔVge exceeds the second threshold, the IGBT is determined to be a failed IGBT. The first and second thresholds can be preset according to industry standards or empirical values, for example, the first threshold can be set to 5% and the second threshold to 10%.

[0048] As a preferred embodiment, before determining the reference current value based on the junction temperature deviation between the target test junction temperature and the actual junction temperature of the IGBT module, the method further includes: The dynamic parameters of each IGBT in the IGBT module are tested using a dual-pulse test circuit to obtain the initial turn-on loss and initial turn-off loss of each IGBT.

[0049] Before starting the power cycle test, both static and dynamic parameter tests are required. Specifically, a dual-pulse test circuit is used to perform dynamic parameter tests on each IGBT in the IGBT module. The dual-pulse test is specifically designed to measure the performance parameters of the IGBT during the switching process. Its basic principle is to apply two consecutive pulse signals to the gate of the IGBT: the first pulse raises the current to a preset target value, and the turn-off process is measured when the pulse is turned off; after a short interval, the second pulse is applied, and the turn-on process is measured when the pulse is turned on. This test method allows for the individual observation of the IGBT's turn-on and turn-off transient processes under precisely controlled voltage, current, and temperature conditions, avoiding interference from heat accumulation and waveform distortion during continuous switching. In this embodiment, the dynamic parameter test targets each IGBT in the IGBT module, ensuring that the initial state of the switching characteristics of each device under test is completely recorded.

[0050] Secondly, through dynamic parameter testing, the initial turn-on loss Eon_0 and initial turn-off loss Eoff_0 of each IGBT were obtained. Turn-on loss Eon refers to the energy loss caused by the overlap of voltage and current during the IGBT's transition from the off state to the on state; turn-off loss Eoff refers to the energy loss caused by the IGBT's transition from the on state to the off state. These two parameters are core indicators for evaluating IGBT switching performance and are also important bases for assessing the thermal stress of the device under actual operating conditions. During the testing process, the waveforms of the IGBT's collector-emitter voltage Vce and collector current Ic were simultaneously acquired using high-precision voltage and current probes. Integral calculations were performed for the turn-on and turn-off phases respectively to obtain the specific values ​​of Eon and Eoff. Since switching losses change with device aging, these two initial values ​​constitute the benchmark for subsequent comparisons.

[0051] Compared with static parameter testing, dynamic parameter testing can more directly reflect the performance of IGBTs under actual switching conditions, providing more comprehensive data support for the reliability assessment and life prediction of IGBT modules.

[0052] As a preferred embodiment, after determining whether there is a faulty IGBT with a short circuit or open circuit in the IGBT module before the preset test duration is reached, the method further includes: If not, after the preset test duration is reached, the dynamic parameters of each IGBT in the IGBT module are tested through the dual-pulse test circuit to obtain the current turn-on loss and current turn-off loss of each IGBT. The change in turn-on loss is determined based on the difference between the current turn-on loss and the initial turn-on loss and the first ratio of the initial turn-on loss; The change in turn-off loss is determined based on the difference between the current turn-off loss and the initial turn-off loss and a second ratio of the initial turn-off loss. IGBTs that exhibit changes in turn-on losses exceeding the third threshold and / or changes in turn-off losses exceeding the fourth threshold are classified as failed IGBTs.

[0053] If no short-circuit or open-circuit anomalies are detected in any IGBT during the entire test, the test continues until the preset test duration is reached. When the cumulative test time reaches the preset test duration, the system automatically terminates the power cycling process and immediately performs dynamic parameter testing on each IGBT in the IGBT module. The dynamic parameter test performed at this time uses the same test conditions and methods as the initial calibration before the test, that is, it is measured using a dual-pulse test circuit under the same bus voltage, gate resistance, load current, and case temperature conditions to ensure the comparability of the two test results. Through this test, the current turn-on loss Eon_n and the current turn-off loss Eoff_n of each IGBT are obtained.

[0054] Secondly, based on the comparison between the current dynamic parameters and the initial dynamic parameters of each IGBT, the change in switching losses is calculated. Specifically, for each IGBT, the change in turn-on loss ΔEon is calculated using the formula ΔEon=(Eon_n-Eon_0) / Eon_0, based on its current turn-on loss Eon_n and initial turn-off loss Eon_0; simultaneously, the change in turn-off loss ΔEoff is calculated using the formula ΔEoff=(Eoff_n-Eoff_0) / Eoff_0, based on its current turn-off loss Eoff_n and initial turn-off loss Eoff_0. These two changes quantify the degree of degradation of the IGBT's turn-on and turn-off characteristics during power cycling tests. Among them, the change in turn-on loss ΔEon mainly reflects the change in the voltage-current overlap region during the IGBT turn-on process, which may be related to the degradation of the gate oxide layer, the aging of the metallization layer on the chip surface, or the degradation of the bonding lines; the change in turn-off loss ΔEoff mainly reflects the changes in tail current and voltage rise rate during the turn-off process, which may be related to the change in carrier lifetime or internal defects of the chip.

[0055] Finally, failure is determined based on the calculated changes. For each IGBT, it is determined whether the change in its turn-on loss ΔEon is greater than a preset third threshold, and / or whether the change in its turn-off loss ΔEoff is greater than a preset fourth threshold. If either condition is met, i.e., ΔEon exceeds the third threshold or ΔEoff exceeds the fourth threshold, the IGBT is determined to be a failed IGBT. For example, the third and fourth thresholds are both set to 10% or 15%. Even if the device has not experienced a short circuit or open circuit, and no static parameters are out of tolerance, it can still be determined to be failed if the switching loss increases significantly. This identifies IGBTs that have not completely failed but whose switching performance has significantly degraded, significantly improving the accuracy and reliability of power cycle testing.

[0056] As a preferred embodiment, adjusting the duty cycle of the PWM modulation signal based on the current deviation between the actual output current of the IGBT module and the reference current value includes: During each switching cycle, the peak value of the three-phase output current of the IGBT module is detected and used as the actual output current. The difference between the actual output current and the reference current value is defined as the current deviation; Perform PI calculations on the current deviation to determine the target control voltage; The duty cycle of the PWM modulation signal is adjusted based on the target control voltage.

[0057] In each switching cycle, the peak value of the three-phase output current of the IGBT module is detected and taken as the actual output current. Since the IGBT module is connected to the inductor box in this test method, the output current waveform is a continuous triangular or sawtooth wave under square wave voltage drive, and its amplitude changes periodically with the switching state. By detecting the current peak value in each switching cycle, the current amplitude information for the current cycle can be accurately obtained. This amplitude directly determines the power loss during IGBT conduction. Compared with instantaneous value control, peak detection can more directly reflect the amplitude characteristics of the current and avoid sampling errors caused by current waveform distortion or transient interference during switching. In specific implementation, the peak hold circuit or ADC can be used to sample the current at its maximum value in each switching cycle to obtain an accurate actual output current value.

[0058] Secondly, the difference between the actual output current and the reference current value is defined as the current deviation. The reference current value is calculated by the temperature outer loop based on the junction temperature deviation and represents the target current amplitude required at present. The actual output current is the peak current detected during the current switching cycle, reflecting the actual current amplitude applied to the IGBT module. By comparing the two, the current deviation signal is calculated. This deviation signal is the input quantity for current closed-loop control, and its sign and magnitude reflect the degree of deviation between the actual current and the target current, providing a quantitative basis for subsequent adjustments.

[0059] Then, a PI calculation is performed on the current deviation to determine the target control voltage. Finally, the duty cycle of the PWM modulation signal is adjusted based on the target control voltage. In digital control systems, the duty cycle of the PWM signal is typically generated by comparing the modulating wave with the carrier wave. In this step, the target control voltage obtained from the PI calculation is used as the instantaneous value of the modulating wave and compared with a fixed-frequency triangular carrier wave: when the amplitude of the modulating wave is greater than the amplitude of the carrier wave, a high level is output; otherwise, a low level is output. In this way, changes in the target control voltage are directly mapped to changes in the PWM duty cycle, thereby adjusting the amplitude of the square wave voltage applied to the inductor box and achieving precise control of the output current. When the target control voltage increases, the duty cycle increases, and the output current amplitude increases; when the target control voltage decreases, the duty cycle decreases, and the output current amplitude decreases.

[0060] Please refer to Figure 2 , Figure 2 This application provides a schematic diagram of a test system for an IGBT module. The input terminal of the IGBT module is connected to a DC bus, and the output terminal of the IGBT module is connected to an inductor box. The system includes: The first determining unit 21 is used to determine a reference current value based on the junction temperature deviation between the target test junction temperature and the actual junction temperature of the IGBT module. The adjustment unit 22 is used to adjust the duty cycle of the PWM modulation signal based on the current deviation between the actual output current of the IGBT module and the reference current value. Control unit 23 is used to control each IGBT in the IGBT module based on PWM modulation signal, so that the IGBT module applies the DC voltage on the DC bus to the inductor box after voltage transformation, so that the actual junction temperature of the IGBT module is the target test junction temperature. The second determining unit 24 is used to determine the actual junction temperature data and actual output current data during the control process of each IGBT in the IGBT module, and output the IGBT module test results based on the actual junction temperature data and actual output current data.

[0061] For a description of the testing system for the IGBT module provided by this invention, please refer to the above method embodiments; the invention itself will not be described in detail here.

[0062] Please refer to Figure 3 , Figure 3 A schematic diagram of a test apparatus for an IGBT module provided in this application includes: Memory 31 is used to store computer programs; The processor 32 is used to implement the steps of the test method for the IGBT module as described above when executing a computer program.

[0063] For a description of the testing device for the IGBT module provided by this invention, please refer to the above method embodiments; the invention will not be described again here.

[0064] As a preferred embodiment, it also includes an IGBT module, a programmable voltage source, and an inductor box; The output of the programmable voltage source is connected to the DC bus to provide DC bus voltage; The input terminal of the IGBT module is connected to the DC bus, and the output terminal of the IGBT module is connected to the inductor box; the control terminal of the IGBT module is connected to the processor.

[0065] It may also include a host computer, such as a PC, connected to the processor, to provide the processor with the target test junction temperature, as well as the setting of the frequency of the PWM modulation signal and the preset test duration. The processor may be, but is not limited to, a DSP, and the IGBT module and the inductor box are connected in a star configuration to ensure that the inductor box acts as a load to carry the excitation current.

[0066] Based on this, under the vector control of the IGBT module test system, the IGBTs in each bridge arm will be turned on alternately in a sinusoidal manner, realizing the simulation of dynamic heat exchange scenario between multi-phase bridge arms. This simulates the actual working conditions in terminal applications such as new energy vehicle motors, thereby more effectively stimulating and screening potential failure problems in IGBT modules such as bonding wires and solders that may be caused by thermal fatigue.

[0067] like Figure 4 and Figure 5 As shown, Figure 4 This is a schematic diagram of the d-axis equivalent circuit of the motor control system provided in this application. Figure 5 This is a schematic diagram of the q-axis equivalent circuit of the motor control system provided in this application.

[0068] In motor control systems, Figure 4 and Figure 5 The resistance R in the circuit consists of the resistance of the motor body, the resistance in the electrical circuit, and the internal resistance of the power devices. , These are the inductance of the motor body and the inductance in the electrical circuit, namely the q-axis inductance and the d-axis inductance; Let be the component of the rotating electromotive force generated by the q-axis current on the d-axis. Let be the component of the rotating electromotive force generated by the d-axis current on the q-axis. The three are the rotating electromotive forces generated by the permanent magnet, and all three are induced electromotive forces from the rotation of the motor. The electrical angular velocity of the motor rotor. For d-axis current, This refers to the q-axis current, which is the DC component of the three-phase stator current of the motor after Clark and Park transformations in the rotating dq coordinate system. It is a permanent magnet flux linkage.

[0069] In motor control systems, the core idea of ​​using the dq coordinate system for vector control is to transform the three-phase AC quantities of the AC motor into DC quantities in a two-phase rotating coordinate system (dq coordinate system) through coordinate transformation. and This achieves decoupled control of the motor torque and magnetic field. This process involves two key transformations: Clark transformation: transforms a three-phase stationary coordinate system (abc) into a two-phase stationary coordinate system (α-β). Park transformation: Converts a two-phase stationary coordinate system (α-β) into a two-phase rotating coordinate system (dq).

[0070] Figure 4 The diagram shows the d-axis equivalent circuit, which reflects the d-axis voltage. The relationship between electric current and magnetic flux. Figure 5 The diagram shows the q-axis equivalent circuit, which reflects the q-axis voltage. The relationship between electric current and magnetic flux.

[0071] The mathematical model for the electric motor is as follows: ; However, in this test system, since the three-phase windings of the inductor box only have stator coils and no rotor, the induced electromotive force of the motor rotation can be ignored, i.e. , and All are zero. Furthermore, the vector control system outputs direct current, which is zero per unit time. , Since the value of is constant, the differential equation can be ignored, thus the voltage equation in the coordinate system simplifies to the following form: ; Where Rs is the sum of the module's internal resistance and inductance. According to the vector calculation formula, by giving a preset test junction temperature, the current reference value can be determined in combination with the actual junction temperature, and then a large current can be applied to the IGBT module to realize the power cycle test of the IGBT module.

[0072] Of course, the circuit also needs to include a current detection module and a temperature detection module to detect the actual output current and actual junction temperature. The temperature detection module may include, but is not limited to, the NCTs set on each arm of the IGBT module. The temperature detection module acquires the resistance value of the NCTs set on each arm in real time to obtain the reference point temperature T_ntc of each arm; based on the real-time acquired output current and bus voltage of each IGBT, it calculates the real-time power loss P of each IGBT; based on a preset thermal network model, and according to the reference point temperature T_ntc, the real-time power loss P, and the pre-stored thermal impedance parameters, it calculates the actual junction temperature T_j of each IGBT.

[0073] Please refer to Figure 6 , Figure 6 This is a schematic diagram of the structure of a computer-readable storage medium provided in this application. The computer-readable storage medium 41 stores a computer program 42. When the computer program 42 is executed by the processor 32, it implements the steps of the test method for the IGBT module as described above.

[0074] For a description of the computer-readable storage medium provided by the present invention, please refer to the above method embodiments; the present invention will not be described again here.

[0075] It should also be noted that, in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0076] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A testing method for an IGBT module, characterized in that, The input terminal of the IGBT module is connected to the DC bus, and the output terminal of the IGBT module is connected to the inductor box; the method includes: The reference current value is determined based on the junction temperature deviation between the target test junction temperature and the actual junction temperature of the IGBT module. The duty cycle of the PWM modulation signal is adjusted based on the current deviation between the actual output current of the IGBT module and the reference current value. Based on the PWM modulation signal, each IGBT in the IGBT module is controlled so that the IGBT module applies the DC voltage on the DC bus to the inductor box after voltage transformation, so that the actual junction temperature of the IGBT module is the target test junction temperature; The actual junction temperature data and actual output current data of each IGBT in the IGBT module are determined during the control process, and the IGBT module test results are output based on the actual junction temperature data and the actual output current data.

2. The testing method for the IGBT module as described in claim 1, characterized in that, Before determining the actual junction temperature data and actual output current data during the control process of each IGBT in the IGBT module, the following steps are also included: Set the preset test duration; The test begins when the control of the IGBTs in the IGBT module is started. If the duration of the test on the IGBT module reaches the preset test duration, the test is terminated, and the process proceeds to the step of determining the actual junction temperature data and actual output current data during the control of each IGBT in the IGBT module.

3. The test method for the IGBT module as described in claim 2, characterized in that, Before determining the actual junction temperature data and actual output current data during the control process of each IGBT in the IGBT module, the following steps are also included: Before the duration reaches the preset test duration, determine whether there is a faulty IGBT in the IGBT module that has a short circuit or open circuit. If present, then the IGBT module is determined to have a failure anomaly.

4. The test method for the IGBT module as described in claim 3, characterized in that, Before determining the reference current value based on the junction temperature deviation between the target test junction temperature and the actual junction temperature of the IGBT module, the following steps are also included: Static parameter tests are performed on each IGBT in the IGBT module to obtain the initial static parameters of each IGBT. The initial static parameters include the collector-emitter initial saturation voltage drop and the gate initial threshold voltage.

5. The test method for the IGBT module as described in claim 4, characterized in that, Before the preset test duration is reached, after determining whether there is a faulty IGBT with a short circuit or open circuit in the IGBT module, the process further includes: If not, after the duration reaches the preset test duration, static parameter tests are performed on each IGBT in the IGBT module to obtain the current static parameters of each IGBT. The current static parameters include the current collector-emitter saturation voltage drop and the current gate threshold voltage. The first rate of change of the collector-emitter saturation voltage drop of each IGBT is determined based on the current collector-emitter saturation voltage drop and the initial collector-emitter saturation voltage drop of each IGBT. The second rate of change of the gate threshold voltage of each IGBT is determined based on the current gate threshold voltage and the initial gate threshold voltage of each IGBT. IGBTs that exhibit the condition that the first rate of change is greater than the first threshold and / or the second rate of change is greater than the second threshold are identified as failed IGBTs.

6. The test method for the IGBT module as described in claim 3, characterized in that, Before determining the reference current value based on the junction temperature deviation between the target test junction temperature and the actual junction temperature of the IGBT module, the following steps are also included: The dynamic parameters of each IGBT in the IGBT module are tested using a dual-pulse test circuit to obtain the initial turn-on loss and initial turn-off loss of each IGBT.

7. The test method for the IGBT module as described in claim 6, characterized in that, Before the preset test duration is reached, after determining whether there is a faulty IGBT with a short circuit or open circuit in the IGBT module, the process further includes: If not, after the duration reaches the preset test duration, the dynamic parameters of each IGBT in the IGBT module are tested through the dual-pulse test circuit to obtain the current turn-on loss and current turn-off loss of each IGBT. The change in activation loss is determined based on the difference between the current activation loss and the initial activation loss and a first ratio of the initial activation loss; The change in turn-off loss is determined based on the difference between the current turn-off loss and the initial turn-off loss and a second ratio of the initial turn-off loss; IGBTs that exhibit a change in turn-on loss exceeding the third threshold and / or a change in turn-off loss exceeding the fourth threshold are classified as failed IGBTs.

8. The test method for the IGBT module as described in any one of claims 1-7, characterized in that, Adjusting the duty cycle of the PWM modulation signal based on the current deviation between the actual output current of the IGBT module and the reference current value includes: During each switching cycle, the peak value of the three-phase output current of the IGBT module is detected and used as the actual output current; The difference between the actual output current and the reference current value is defined as the current deviation; The current deviation is calculated using a PI method to determine the target control voltage; The duty cycle of the PWM modulation signal is adjusted based on the target control voltage.

9. A testing device for an IGBT module, characterized in that, include: Memory, used to store computer programs; A processor, configured to implement the steps of the test method for an IGBT module as described in any one of claims 1-8 when executing a computer program.

10. The testing apparatus for the IGBT module as described in claim 9, characterized in that, It also includes IGBT modules, programmable voltage sources, and inductor boxes; The output terminal of the programmable voltage source is connected to the DC bus to provide DC bus voltage; The input terminal of the IGBT module is connected to the DC bus, and the output terminal of the IGBT module is connected to the inductor box; the control terminal of the IGBT module is connected to the processor.

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