Reliability evaluation method for high-power converter

Abstract

The invention relates to the technical field of state monitoring of power electronic devices, in particular to a reliability evaluation method for a high-power converter, which comprises the following steps of: acquiring saturation voltage drop, turn-off delay time and load current of an IGBT (Insulated Gate Bipolar Translator) module in the high-power converter at a target moment; respectively obtaining a power loss correction factor and a thermal resistance adjustment factor at the current moment; and optimizing power loss and thermal resistance parameters in the Foster model at the target moment by using the power loss correction factor and the thermal resistance adjustment factor at the target moment, correspondingly obtaining a junction temperature estimation value of the IGBT module at the target moment, and evaluating the reliability of the high-power converter at the target moment according to the junction temperature estimation value. The Foster model can better adapt to thermal characteristic changes of the IGBT module under different working conditions and aging states, and the overall accuracy and reliability of junction temperature estimation are improved.

Description

Technical Field

[0001] The invention relates to the technical field of power electronic device state monitoring, and in particular to a reliability evaluation method for a high-power converter. Background Art

[0002] In power electronics applications such as electric vehicles, photovoltaic power generation, and industrial inverters, the reliability of IGBT modules (Insulated Gate Bipolar Transistor) in high-power converters is crucial. The junction temperature of the IGBT module is a key factor affecting its reliability. Excessive junction temperature will lead to accelerated aging or even failure of the IGBT module. Accurate and real-time evaluation of the junction temperature of the IGBT module is of great significance for ensuring the safe and reliable operation of the power electronics system.

[0003] The existing junction temperature evaluation methods of IGBT modules mainly include direct measurement method, temperature sensitive electrical parameter method (TSEP) and thermal model method. Among them, although the direct measurement method (such as infrared thermal imager) is accurate, it is not suitable for online monitoring; the TSEP method uses the relationship between certain electrical parameters of the IGBT module (such as Vce(on), tdoff) and the junction temperature to indirectly estimate the junction temperature, which has the potential for online monitoring, but the TSEP method is easily affected by device aging, individual differences and multi-factor coupling; the thermal model method (such as Foster model and Cauer model) calculates the junction temperature by establishing a thermal resistance network model of the IGBT module, but the traditional thermal model usually uses fixed model parameters that cannot reflect the impact of aging and temperature changes of the IGBT module on the thermal parameters, and the accuracy of the power loss calculation in the model needs to be improved.

[0004] Specifically, for the existing IGBT module junction temperature evaluation method based on the thermal resistance network model (Foster model), the thermal resistance ( ) and heat capacity ( ) parameters are usually obtained through experimental calibration in an offline state and are regarded as constants. In the actual operation of the IGBT module, these thermal parameters will change significantly due to device aging (such as bonding wire degradation, solder layer fatigue, etc.) and continuous changes in junction temperature. The solidification of model parameters will cause the Foster model to be unable to accurately reflect the actual thermal characteristics of the IGBT module, affecting the accuracy of junction temperature estimation. Secondly, the calculation of power loss in the traditional Foster model is also relatively rough, and is only obtained through the loss curve provided by the IGBT data manual or through simplified switching loss and conduction loss calculation formulas. It fails to fully consider the complex loss characteristics of the IGBT module under different operating conditions (such as different load currents, switching frequencies, bus voltages, etc.), thereby reducing the accuracy of junction temperature estimation.

[0005] Therefore, how to accurately correct the power loss calculation in the Foster model and dynamically adjust the thermal resistance parameters of the Foster model to improve the accuracy of junction temperature evaluation of IGBT modules using the Foster model has become an urgent problem to be solved. Summary of the invention

[0006] In view of this, an embodiment of the present invention provides a reliability assessment method for a high-power converter to solve the problem of how to accurately correct the power loss calculation in the Foster model, and dynamically adjust the thermal resistance parameters of the Foster model to improve the accuracy of junction temperature assessment of the IGBT module using the Foster model.

[0007] An embodiment of the present invention provides a reliability assessment method for a high-power converter, the method comprising the following steps: Collecting the saturation voltage drop, shutdown delay time and load current of the IGBT module in the high-power converter at the target time, and obtaining the reference saturation voltage drop and reference shutdown delay time of the IGBT module under specific working conditions; Obtaining the power loss correction factor at the current moment according to the deviation between the saturation voltage drop at the target moment and the reference saturation voltage drop, and the modulation characteristics of the load current at the target moment; Obtaining a thermal resistance adjustment factor at the target moment according to changes in the saturation voltage drop and the shutdown delay time at the target moment relative to the reference saturation voltage drop and the reference shutdown delay time, and the power loss correction factor; The power loss correction factor and thermal resistance adjustment factor at the target moment are used to optimize the power loss and thermal resistance parameters in the Foster model at the target moment, and the estimated junction temperature of the IGBT module at the target moment is obtained accordingly. The reliability of the high-power converter at the target moment is evaluated based on the estimated junction temperature.

[0008] Preferably, obtaining the power loss correction factor at the current moment according to the deviation between the saturation voltage drop at the target moment and the reference saturation voltage drop, and the modulation characteristics of the load current at the target moment, includes: The load current at the target moment is used as an independent variable in a preset load current modulation function to obtain a corresponding load current modulation value, wherein the load current modulation function is used to characterize the modulation effect of the load current on the saturation voltage drop, and the larger the load current, the greater the modulation effect of the saturation voltage drop; Calculating the difference between the saturated pressure drop at the target time and the reference saturated pressure drop, and recording the ratio of the difference to the reference saturated pressure drop as the saturated pressure drop difference value at the target time; The influence coefficient of the saturation voltage drop on the power loss at the target moment is obtained by using a gradient descent algorithm, the product of the influence coefficient, the saturation voltage drop difference value and the load current modulation value is obtained, and the sum of a constant 1 and the product is used as the power loss correction factor at the current moment.

[0009] Preferably, obtaining the thermal resistance adjustment factor at the target moment according to the changes of the saturation voltage drop and the shutdown delay time at the target moment relative to the reference saturation voltage drop and the reference shutdown delay time, and the power loss correction factor, comprises: Calculating the difference between the saturated pressure drop at the target time and the reference saturated pressure drop, and recording the ratio of the difference to the reference saturated pressure drop as the saturated pressure drop difference value at the target time; Calculating the difference between the turn-off delay time at the target moment and the reference turn-off delay time, and recording the ratio between the difference and the reference turn-off delay time as the turn-off delay time difference value at the target moment; According to the saturated voltage drop difference value and the shutdown delay time difference value, respectively obtaining a first weight of the saturated voltage drop change on the thermal resistance adjustment and a second weight of the shutdown delay time change on the thermal resistance adjustment; A thermal resistance adjustment factor at the target moment is obtained according to the saturation voltage drop difference value, the shutdown delay time difference value, the first weight, the second weight, and the power loss correction factor at the target moment.

[0010] Preferably, the obtaining, according to the saturated voltage drop difference value and the shutdown delay time difference value, a first weight of the saturated voltage drop change on the thermal resistance adjustment and a second weight of the shutdown delay time change on the thermal resistance adjustment respectively include: Calculate the sum of the absolute value of the saturation voltage drop difference value and the absolute value of the shutdown delay time difference value, and use the ratio between the absolute value of the saturation voltage drop difference value and the sum as the first weight of the saturation voltage drop change for thermal resistance adjustment; use the ratio between the absolute value of the shutdown delay time difference value and the sum as the second weight of the shutdown delay time change for thermal resistance adjustment.

[0011] Preferably, obtaining the thermal resistance adjustment factor at the target moment according to the saturation voltage drop difference value, the shutdown delay time difference value, the first weight, the second weight, and the power loss correction factor at the target moment includes: Based on the first weight and the second weight, the saturation voltage drop difference value and the shutdown delay time difference value at the target moment are weightedly summed to obtain a corresponding weighted sum value, the addition result of the constant 1 and the weighted sum value is obtained, and the product of the addition result and the power loss correction factor is used as the thermal resistance adjustment factor at the target moment.

[0012] Preferably, the power loss correction factor and thermal resistance adjustment factor at the target moment are used to optimize the power loss and thermal resistance parameters in the Foster model at the target moment, and the estimated junction temperature of the IGBT module at the target moment is obtained accordingly, including:

[0013] in, represents the estimated junction temperature of the IGBT die at the target time t, represents the ambient temperature of the IGBT module at the target time t, m represents the order of the Foster model (that is, the number of links), represents the thermal resistance adjustment factor at the target time t, represents the thermal resistance parameter of the jth link of the Foster model at the target time t, 1 represents a constant, represents an exponential function with a natural constant as base, represents the time step, represents the heat capacity parameter of the jth link of the Foster model at the target time t, represents the power loss correction factor at the target time t, represents the power loss at the target time t, represents the adjusted thermal resistance parameter, Indicates the corrected power loss.

[0014] Preferably, the load current modulation function is:

[0015] in, represents the load current modulation value corresponding to the load current at the target time t, 1 represents a constant, represents the coefficient of the first-order term corresponding to the target time t, represents the load current at the target time t, represents the quadratic term coefficient corresponding to the target time t, wherein the linear term coefficient and the quadratic term coefficient are obtained using a gradient descent algorithm.

[0016] Compared with the prior art, the embodiments of the present invention have the following beneficial effects: The present invention introduces a power loss correction factor obtained based on the saturation voltage drop and the load current to optimize the power loss parameters in the Foster model, and can dynamically and finely correct the calculation results of the traditional power loss, so as to more accurately evaluate the actual power loss. At the same time, the turn-off delay time of the IGBT module is used as the basis for adjusting the thermal resistance parameters, and the power loss correction factor is introduced to obtain the thermal resistance adjustment factor to optimize the thermal resistance parameters in the Foster model. The dynamic information of the turn-off delay time can be introduced into the calculation of the thermal resistance parameters, so that when the Foster model is used to evaluate the junction temperature of the IGBT module, it can better adapt to the changes in the thermal characteristics of the IGBT module under different working conditions and aging states, improve the overall accuracy and reliability of the junction temperature estimation, and thus improve the accuracy of the reliability evaluation of the high-power converter based on the junction temperature estimation value. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0018] Figure 1 It is a method flow chart of a reliability assessment method for a high-power converter provided in Embodiment 1 of the present invention. DETAILED DESCRIPTION

[0019] Embodiments of the present disclosure are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present disclosure, but should not be understood as limiting the present disclosure.

[0020] It should be noted that the terms "first", "second", etc. in the specification of the present disclosure and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present disclosure described herein can be implemented in an order other than those illustrated or described herein. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present disclosure. Instead, they are merely examples of devices and methods consistent with some aspects of the present disclosure.

[0021] In order to illustrate the technical solution of the present invention, specific embodiments are provided below for illustration.

[0022] See also Figure 1 , is a method flow chart of a reliability assessment method for a high-power converter provided in Embodiment 1 of the present invention, such as Figure 1As shown, the method may include: Step S101, collecting the saturation voltage drop, shutdown delay time and load current of the IGBT module in the high-power converter at the target time, and obtaining the reference saturation voltage drop and reference shutdown delay time of the IGBT module under specific working conditions.

[0023] High-power converters currently have a broad application background and have become one of the core equipment in multiple industries. Taking wind power converters as an example, the cost of the converter accounts for about 15% of the cost of the entire wind turbine set. The reliability of the converter is an important link to ensure the reliable operation of the wind turbine. Therefore, the reliability of high-power converters is very important. Most of the failures of high-power converters are caused by failures of insulated gate bipolar transistors (IGBTs).

[0024] Compared with other power devices, IGBT modules have the characteristics of high input impedance and high on-current, and the withstand voltage is also high, playing a pivotal role in power electronic systems. With the development of power electronic technology, while the power level and switching frequency of IGBT modules are improved, their reliability is increasingly affected by the junction temperature, and the electromagnetic interference generated by themselves also affects other electronic systems. The power loss generated by the IGBT module during operation causes the junction temperature of the device to rise and fluctuate, resulting in uneven temperature distribution of the internal chip. With the changes in load and operating conditions, the temperature of the IGBT chip fluctuates greatly, and the heat emitted by the chip is transmitted from top to bottom to the cooling system. The mismatch of thermal expansion coefficients between each layer of material inside the IGBT module will cause thermal stress and mechanical stress, accelerate the aging process of the module, cause fatigue of the solder layer, cracks in the bonding wires, and even fall off, and ultimately lead to failure of the IGBT module. Therefore, junction temperature is a key parameter for IGBT module status monitoring.

[0025] In the prior art, a thermal resistance network model (Foster model) is usually used to obtain the real-time junction temperature of the IGBT module, wherein the model parameters of the Foster model are composed of thermal resistance R and thermal capacitance C, and the model parameters are fitted by a transient thermal impedance curve and can be obtained through simulation or experimental processes. However, when using the Foster model to obtain the real-time junction temperature of the IGBT module, firstly, considering that the IGBT module will undergo significant changes in these thermal parameters during actual operation due to device aging (such as bonding wire degradation, solder layer fatigue, etc.) and continuous changes in junction temperature, the solidification of the model parameters causes the model to be unable to accurately reflect the actual thermal characteristics of the IGBT module, affecting the accuracy of the junction temperature estimation; secondly, the calculation of the power loss P in the traditional Foster model is usually rough. Specifically, the calculation of the power loss P is based on the loss curve provided in the IGBT data sheet, or is obtained through simplified switching loss and conduction loss calculation formulas. However, these methods fail to fully consider the complex loss characteristics of the IGBT module under different operating conditions (such as different load currents, switching frequencies, bus voltages, etc.), especially the loss information contained in electrical parameters such as saturation voltage drop and turn-off delay time that are easy to measure online. This is because the dynamic changes in saturation voltage drop and turn-off delay time not only reflect the changes in junction temperature, but also reflect the aging state and real-time loss characteristics of the IGBT module. Ignoring this information will lead to certain errors in the calculation of the power loss P, ultimately reducing the accuracy of the junction temperature estimation.

[0026] It should be noted that using the Foster model to obtain the real-time junction temperature of the IGBT module belongs to the prior art and will not be described in detail here.

[0027] Based on the above analysis, in the embodiment of the present invention, the Foster model is improved through the saturation voltage drop, shutdown delay time and load current of the IGBT module to improve the accuracy of obtaining the real-time junction temperature of the IGBT module using the Foster model, thereby ensuring the accuracy of the reliability assessment of the high-power converter.

[0028] Specifically, since the IGBT module is a three-terminal device with a gate G, a collector C, and an emitter E, a high-precision voltage sensor is installed between the collector C and the emitter E of the IGBT module to measure the saturation voltage drop of the IGBT module in real time. , the sampling frequency should be high enough to capture the saturation voltage drop The rapid change of the IGBT module is not limited here and can be set according to the implementation scenario; the IGBT module's driver chip diagnostic function is used to obtain the IGBT module's shutdown delay time. , the sampling frequency should be consistent with the saturation voltage drop Keep it consistent; by installing a current sensor in the circuit where the IGBT module is located, the load current Ice of the IGBT module is measured in real time, and its sampling frequency should be consistent with the saturation voltage drop Be consistent.

[0029] In the embodiment of the present invention, the time corresponding to the real-time evaluation of the junction temperature of the IGBT module is recorded as the target time t, and the saturation voltage drop, turn-off delay time and load current of the IGBT module at the target time are collected by the above-mentioned collection means, and are recorded as .

[0030] It should be noted that before the IGBT module is operated for the first time, its saturation voltage drop and shutdown delay time under specific operating conditions (such as room temperature and zero load) are recorded as reference saturation voltage drop and shutdown delay time respectively. and reference turn-off delay time , which is used for the subsequent dynamic characteristics analysis of the IGBT module during actual operation.

[0031] Step S102, obtaining the power loss correction factor at the current moment according to the deviation between the saturation voltage drop at the target moment and the reference saturation voltage drop, and the modulation characteristics of the load current at the target moment.

[0032] The accurate calculation of the power loss P in the Foster model is one of the key factors affecting the accuracy of junction temperature estimation. The power loss obtained by traditional methods that rely on the static loss curve or simplified calculation formula provided in the IGBT data sheet usually has large errors. These calculation methods fail to fully consider the rich information contained in the dynamic characteristics, aging effects, and saturation voltage drop of the IGBT module during actual operation, which are easy to measure online.

[0033] Specifically, the static loss curves provided in the IGBT data sheet are usually measured under specific working conditions and cannot accurately reflect the dynamic power loss of the IGBT module in actual operation. In addition, the aging of the IGBT module will cause changes in its switching characteristics and conduction characteristics, affecting the power loss. More importantly, the saturation voltage drop of the IGBT module is an electrical parameter that is easy to measure online. Its dynamic changes are not only related to the junction temperature, but also closely related to factors such as load current and aging degree. It contains information about the real-time working status and loss characteristics of the IGBT module. However, the traditional power loss calculation method fails to utilize the saturation voltage drop, an important source of information, resulting in a deviation between the calculated result and the actual value.

[0034] Therefore, in order to improve the accuracy of the power loss P in the Foster model and to improve the accuracy of the real-time junction temperature estimation, the saturation voltage drop information measured online is used in the embodiment of the present invention to correct the power loss P obtained in the traditional way. Since the deviation of the saturation voltage drop relative to its initial value (or a certain reference value) can comprehensively reflect the current working state of the IGBT module (such as junction temperature, load current), and the degree of deviation of the aging degree of the IGBT module relative to the initial state (or reference state), and this degree of deviation is closely related to the deviation of the actual value of the power loss relative to the calculated value of the traditional method. Therefore, before using the Foster model to estimate the real-time junction temperature at the target time t, first, according to the deviation between the saturation voltage drop at the target time t and the reference saturation voltage drop, and the modulation characteristics of the load current at the target time t, the power loss correction factor at the current time t is obtained, which is used to correct the power loss obtained in the traditional way, so as to improve the evaluation accuracy of the real-time junction temperature at the target time t.

[0035] Specifically, considering that the influence of the saturation voltage drop on the power loss is not constant, but changes with the change of the load current, usually under heavy load conditions, a small change in the saturation voltage drop will lead to a significant change in the power loss. Therefore, the influence of the saturation voltage drop on the power loss is adjusted according to the load current at the target moment. Specifically: the load current at the target moment is used as the independent variable in the preset load current modulation function to obtain the corresponding load current modulation value, wherein the load current modulation function is used to characterize the modulation effect of the load current on the saturation voltage drop. The larger the load current, the greater the modulation effect of the saturation voltage drop. The load current modulation function is:

[0036] in, represents the load current modulation value corresponding to the load current at the target time t, 1 represents a constant, represents the coefficient of the first-order term corresponding to the target time t, represents the load current at the target time t, represents the quadratic term coefficient corresponding to the target time t, wherein the linear term coefficient and the quadratic term coefficient are obtained using a gradient descent algorithm.

[0037] It should be noted that the load current When it is 0, The value of 1 means that no additional adjustment is made to the saturation voltage drop under no-load or light-load conditions; on the contrary, when the load current increases, The larger the value, the more the effect of the saturation voltage drop needs to be "amplified" as the load current increases.

[0038] Among them, by adjusting the order of the first-order term and the coefficient of the second-order term in the load current modulation function, the shape of the curve can be changed, and the adjustment effect of the actual load current on the saturation voltage drop can be better fitted. Therefore, in order to overcome the limitations brought by fixed parameters and improve the accuracy and adaptability of power loss correction, an online adaptive adjustment strategy is used to dynamically estimate and Specifically: use the load current at the target time t Combined with the gradient descent algorithm, we continuously adjust and value, so that it approaches the optimal value, then and The adaptive adjustment formula is:

[0039] in, Represents the linear coefficient at time t-1 (the moment before the target moment), represents the coefficient of the quadratic term at time t-1 (the moment before the target moment), is the learning rate of the linear coefficient, is the learning rate of the quadratic term coefficient, represents the load current at the target time t, represents the reference current (half of the IGBT rated current), Indicates the power loss correction factor at time t-1 (the moment before the target moment).

[0040] When the load current is greater than the reference current, if the Greater than 1, in order to amplify the effect of saturation voltage drop, it is necessary to increase ,because yes and A monotonically increasing function, so we need to increase and When the load current is less than the reference current, if the previous moment Greater than 1, in order to reduce the impact of saturation voltage drop, it is necessary to reduce , so we need to reduce and value; due to is related to Ice squared, so The adjustment range is larger, and .

[0041] Preferably, in the embodiment of the present invention, Set to between, Set to The learning rate is a recommended value based on experience. Since the larger the learning rate, the faster the adjustment speed, which will lead to parameter fluctuations or instability, it is necessary to start with a small learning rate in practical applications.

[0042] Further, after obtaining the modulation degree of the load current on the saturation voltage drop at the current time t (load current modulation value ), further analyzing the deviation of the saturation voltage drop at the target time t relative to the reference value to characterize the current working state of the IGBT module, specifically: calculating the difference between the saturation voltage drop at the target time t and the reference saturation voltage drop, and recording the ratio of the difference to the reference saturation voltage drop as the saturation voltage drop difference value at the target time.

[0043] Preferably, the calculation expression of the saturation pressure drop difference value at the target time t is:

[0044] in, Indicates the saturation pressure drop difference value at the target time t, Indicates the reference saturation voltage drop, Represents the saturation pressure drop at the target time t.

[0045] It should be noted that Indicates the deviation of the saturation voltage drop at the target time relative to the initial value. The larger the deviation, the farther the current state of the IGBT module deviates from the initial state, and the larger the deviation of the actual power loss from the traditional power loss. Divided by The saturation voltage drop deviation is normalized to eliminate the dimension effect.

[0046] Finally, the gradient descent algorithm is used to obtain the influence coefficient of the saturation voltage drop on the power loss at the target moment, the product of the influence coefficient, the saturation voltage drop difference value and the load current modulation value is obtained, and the sum of the constant 1 and the product is used as the power loss correction factor at the current moment.

[0047] Among them, the calculation expression of the power loss correction factor at the current moment is:

[0048] in, Represents the power loss correction factor at the current time t, 1 represents a constant, It represents the influence coefficient of saturation voltage drop on power loss at target time t, Indicates the saturation pressure drop difference value at the target time t, Indicates the load current modulation value corresponding to the load current at the target time t.

[0049] It should be noted that the power loss correction factor takes into account the saturation voltage drop of the IGBT module. The dynamic change information of the load current Ice is introduced to more accurately reflect the power loss of the IGBT module under actual working conditions. Specifically, the power loss correction factor consists of three parts: the reference value (constant term 1), the saturation voltage drop The deviation term and load current modulation term of the IGBT module are as follows: The constant term 1 sets the reference for power loss correction, ensuring that the power loss correction factor is 1 when the IGBT module is in the initial state or reference state, that is, no correction is made to the traditionally obtained power loss; the saturation voltage drop The deviation term is the core of the power loss correction factor. This term reflects the impact of the saturation voltage drop at the target time deviating from the initial value on the power loss. The increase in the saturation voltage drop of the IGBT usually means an increase in junction temperature, an increase in load current or device aging. It is a positive coefficient obtained by data fitting, reflecting the saturation pressure drop The sensitivity of the relative changes to the power loss effect, The larger the value, the higher the saturation voltage drop. The greater the impact on power loss, the When , the term is positive, , the power loss increases, which is related to the saturation voltage drop This is consistent with the physical fact that an increase in voltage leads to increased losses.

[0050] In order to overcome the limitations of fixed parameters and improve the accuracy and adaptability of the power loss correction factor, an online adaptive adjustment strategy is used to dynamically estimate Specifically, the saturation voltage drop at the target time t is used , Turn-off delay time , and combined with the gradient descent algorithm, continuously adjust value, so that it approaches the optimal value, then The adaptive adjustment formula is:

[0051] in, represents the influence coefficient at time t-1 (the moment before the target moment), is the learning rate of saturation voltage drop, is the learning rate of the turn-off delay time, represents the saturation voltage drop at the target time t, represents the turn-off delay time at the target time t, represents the saturation pressure drop at time t-1 (the moment before the target moment), represents the shutdown delay time at time t-1 (the previous moment of the target moment), Indicates the power loss correction factor at time t-1 (the moment before the target moment).

[0052] It should be noted that if or Increase, and the last moment ,illustrate Too small, need to be enlarged get On the contrary, if or Lower, and the previous moment ,illustrate Too big and need to be reduced get .

[0053] Preferably, in the embodiment of the present invention, Set to between, Set to The learning rate is a recommended value based on experience. Since the larger the learning rate, the faster the adjustment speed will cause parameter fluctuations or instability, it is necessary to start with a small learning rate in practical applications.

[0054] At this point, the power loss correction factor at the current time t is obtained .

[0055] Step S103, obtaining a thermal resistance adjustment factor at the target moment according to changes in the saturation voltage drop and the shutdown delay time at the target moment relative to the reference saturation voltage drop and the reference shutdown delay time, and the power loss correction factor.

[0056] The above is based on the introduction of saturation voltage drop Power loss correction factor To improve the calculation accuracy of the power loss P in the Foster model. However, the thermal resistance parameter R in the Foster model is usually regarded as a constant, or is only calibrated in an offline state. This processing method ignores the dynamic changes of the thermal resistance parameter caused by junction temperature changes and device aging during the actual operation of the IGBT module, thereby limiting the further improvement of the junction temperature estimation accuracy.

[0057] Specifically, the change in the junction temperature of the IGBT module will directly affect the thermophysical properties of its internal materials, thereby changing the size of the thermal resistance. In addition, the long-term operation of the IGBT module will lead to aging phenomena such as degradation of the bonding wire and fatigue of the solder layer. These aging phenomena will significantly increase the thermal resistance on the heat conduction path. The traditional Foster model regards the thermal resistance parameter as a constant and cannot reflect these dynamic changes caused by temperature and aging, which will cause the model to deviate from the actual situation.

[0058] Therefore, in order to solve the above problem, the embodiment of the present invention dynamically adjusts the thermal resistance parameters in the Foster model. It is an important dynamic parameter of the IGBT module and is very sensitive to changes in junction temperature. As the junction temperature increases, the aging of the IGBT module will also cause Therefore, The dynamic change of contains information about the junction temperature and aging state of the IGBT module. Therefore, by introducing the turn-off delay time of the IGBT module As the basis for adjusting thermal resistance parameters.

[0059] Considering the close intrinsic relationship between power loss and thermal resistance, power loss is the root cause of heat generation in the IGBT module, and thermal resistance determines the difficulty of heat transfer from the junction area to the environment. If the power loss calculation is inaccurate, the junction temperature estimation will be biased, which will affect the judgment of thermal resistance. Therefore, in the embodiment of the present invention, when analyzing the thermal resistance adjustment factor, not only the shutdown delay time is considered and saturation pressure drop In view of the dynamic changes of the junction temperature, it is also necessary to introduce the power loss correction factor obtained in step S102 to realize the linkage of power loss correction with thermal resistance adjustment. This linkage mechanism enables the two key links of junction temperature estimation - power loss calculation and thermal resistance parameter adjustment - to be coordinated and corrected with each other, thereby further improving the overall accuracy and reliability of junction temperature estimation.

[0060] In the embodiment of the present invention, the thermal resistance adjustment factor at the target time is obtained by using the changes of the saturation voltage drop and the shutdown delay time at the target time relative to the reference saturation voltage drop and the reference shutdown delay time, and the power loss correction factor. The specific process is as follows: (1) Calculating the difference between the saturation voltage drop at the target time and the reference saturation voltage drop, and recording the ratio of the difference to the reference saturation voltage drop as the saturation voltage drop difference value at the target time; calculating the difference between the shutdown delay time at the target time and the reference shutdown delay time, and recording the ratio between the difference and the reference shutdown delay time as the shutdown delay time difference value at the target time.

[0061] In one embodiment, the saturation voltage drop difference value at the target time t is obtained by referring to the calculation expression of the saturation voltage drop difference value at the target time t. The calculation expression of the turn-off delay time difference value at the target time t is:

[0062] in, represents the turn-off delay time difference value at the target time t, Indicates the reference turn-off delay time, It represents the shutdown delay time at the target time t.

[0063] (2) According to the saturated voltage drop difference value and the shutdown delay time difference value, respectively obtain a first weight of the saturated voltage drop change on the thermal resistance adjustment and a second weight of the shutdown delay time change on the thermal resistance adjustment.

[0064] In one embodiment, the sum of the absolute value of the saturation voltage drop difference value and the absolute value of the shutdown delay time difference value is calculated, and the ratio between the absolute value of the saturation voltage drop difference value and the sum is used as the first weight of the saturation voltage drop change for thermal resistance adjustment; the ratio between the absolute value of the shutdown delay time difference value and the sum is used as the second weight of the shutdown delay time change for thermal resistance adjustment.

[0065] Among them, the first weight of the saturation voltage drop change on the thermal resistance adjustment The calculation expression is:

[0066] Second weight of turn-off delay time variation on thermal resistance adjustment The calculation expression is:

[0067] in, Represents the absolute value function, which avoids the influence of negative value of thermal resistance adjustment factor in calculation due to the measurement error of sensor in practical application. represents the turn-off delay time difference value at the target time t, Indicates the saturation pressure drop difference value at the target time t.

[0068] It should be noted that Delay time for shutdown The weight of the change ensures The greater the relative change, the greater the weight, and when the saturation voltage drop When the relative change is large, The weight of will be reduced accordingly to avoid over-adjustment; Saturation pressure drop The weight of the variation ensures that the saturation voltage drop The greater the relative change, the greater the weight, and when When the relative change is large, The weight will be reduced accordingly.

[0069] (3) Obtaining a thermal resistance adjustment factor at the target moment according to the saturation voltage drop difference value, the shutdown delay time difference value, the first weight, the second weight, and the power loss correction factor at the target moment.

[0070] In one embodiment, the thermal resistance adjustment factor at the target time The calculation expression is:

[0071] in, Indicates the thermal resistance adjustment factor at the target time, is the first weight of the saturation voltage drop change on the thermal resistance adjustment, The second weight of the turn-off delay time change on the thermal resistance adjustment is: represents the turn-off delay time difference value at the target time t, Indicates the saturation pressure drop difference value at the target time t, Indicates the power loss correction factor at the target time, 1 indicates a constant.

[0072] It should be noted that the thermal resistance adjustment factor is used to dynamically adjust the thermal resistance parameters in the Foster model to more accurately reflect the thermal resistance changes caused by junction temperature changes and aging effects in the actual operation of the IGBT module. The thermal resistance adjustment factor is calculated by the base value (constant 1), The impact of changes, Effects of changes and power loss correction factors The constant 1 sets the reference for thermal resistance adjustment, ensuring that the thermal resistance parameters are not adjusted when the IGBT module is in the reference state. The impact of changes The value reflects The impact of changes The value of or When the value is positive, it means that the thermal resistance increases, which is consistent with the physical fact that the increase in junction temperature or aging leads to an increase in thermal resistance, and the corresponding thermal resistance adjustment factor becomes larger; finally, to the power loss correction factor The status information of the IGBT module has been comprehensively reflected, and the power loss correction factor is used To achieve further modulation of thermal resistance adjustment by power loss correction, if , indicating that the traditional method underestimates the power loss, and the actual junction temperature may be higher, so it is necessary to further increase the thermal resistance adjustment factor ;if This indicates that the traditional method overestimates the power loss and the actual junction temperature may be lower, so the thermal resistance adjustment factor needs to be appropriately reduced. .

[0073] At this point, the thermal resistance adjustment factor at the target time t is obtained. .

[0074] Step S104, using the power loss correction factor and thermal resistance adjustment factor at the target moment, optimize the power loss and thermal resistance parameters in the Foster model at the target moment, and obtain the estimated junction temperature of the IGBT module at the target moment, and evaluate the reliability of the high-power converter at the target moment based on the estimated junction temperature.

[0075] The power loss correction factor and thermal resistance adjustment factor at the target moment are obtained through step S102 and step S103, which are respectively used to correct the power loss and the model parameter thermal resistance R in the traditional Foster model. That is, when the real-time junction temperature of the IGBT module at the target moment is obtained by using the Foster model, the corrected power loss and the adjusted thermal resistance parameters are used. Therefore, in the embodiment of the present invention, the power loss correction factor and the thermal resistance adjustment factor at the target moment are substituted into the traditional Foster model, and the power loss and thermal resistance parameters in the Foster model are optimized to obtain an improved Foster model. The improved Foster model formula is as follows:

[0076] in, represents the estimated junction temperature of the IGBT module at the target time t, represents the ambient temperature of the IGBT module at the target time t, m represents the order of the Foster model (that is, the number of links), represents the thermal resistance adjustment factor at the target time t, represents the thermal resistance parameter of the jth link of the Foster model at the target time t, 1 represents a constant, represents an exponential function with a natural constant as base, represents the time step, represents the heat capacity parameter of the jth link of the Foster model at the target time t, represents the power loss correction factor at the target time t, represents the power loss at the target time t, represents the adjusted thermal resistance parameter, Indicates the corrected power loss.

[0077] It should be noted that the ambient temperature of the IGBT module is measured by installing an ambient temperature sensor close to the IGBT module; the adjusted thermal resistance parameter It can more accurately reflect the actual thermal resistance characteristics of the IGBT module at the target time, and the corrected power loss Can better reflect the actual power loss of the IGBT module at the target time; time step It refers to the time interval between the previous moment and the current moment.

[0078] Therefore, by using the improved Foster model and the power loss correction factor and thermal resistance adjustment factor at the target time, the estimated junction temperature of the IGBT module at the target time t can be obtained. Similarly, the estimated junction temperature of the IGBT module at any time can also be obtained. Furthermore, after obtaining the estimated junction temperature of the IGBT module at the target time t, the overall reliability of the high-power converter can be evaluated in combination with the failure model and reliability evaluation method of the IGBT module, and the operation and maintenance of the high-power converter can be guided based on the evaluation results. The details are as follows: First, the Arrhenius model is used to calculate the instantaneous failure rate of the IGBT module. :

[0079] in, is the baseline failure rate, is the activation energy, is the Boltzmann constant, is the estimated junction temperature of the IGBT module at the target time t, represents an exponential function with a natural constant as base, and Obtained by referring to the data sheet of the IGBT module.

[0080] Then, by calculating the instantaneous failure rate Perform numerical integration to obtain the cumulative failure rate of the IGBT module :

[0081] In addition, use Model to estimate the remaining life of IGBT modules: ,in, is the number of failure cycles (lifetime) of the IGBT module, A is the material constant, is the junction temperature fluctuation amplitude, b is The indices, A and b, are obtained from the data sheet of the IGBT module. By rain flow counting method extracted from the time series.

[0082] For the overall reliability of large power converters containing multiple IGBT modules It can be expressed as:

[0083]

[0084] in, It is The reliability of an IGBT module is measured, and M is the number of IGBT modules in the high-power converter.

[0085] Based on the instantaneous failure rate, cumulative failure rate, remaining life and other indicators calculated above, the reliability level of IGBT modules and high-power converters is monitored in real time, and when necessary, an early warning is issued, a protection mechanism is triggered, maintenance decisions are guided, or converter control strategies are optimized, thereby improving the availability and safety of the converter. It should be noted that the calculation of the instantaneous failure rate, cumulative failure rate, remaining life and overall reliability belongs to the prior art and will not be described in detail here.

[0086] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention.

Claims

1. A reliability assessment method for a high power converter, characterized in that: The reliability assessment method of a high-power converter comprises: Collecting the saturation voltage drop, shutdown delay time and load current of the IGBT module in the high-power converter at the target time, and obtaining the reference saturation voltage drop and reference shutdown delay time of the IGBT module under specific working conditions; Obtaining the power loss correction factor at the current moment according to the deviation between the saturation voltage drop at the target moment and the reference saturation voltage drop, and the modulation characteristics of the load current at the target moment; Obtaining a thermal resistance adjustment factor at the target moment according to changes in the saturation voltage drop and the shutdown delay time at the target moment relative to the reference saturation voltage drop and the reference shutdown delay time, and the power loss correction factor; The power loss correction factor and thermal resistance adjustment factor at the target moment are used to optimize the power loss and thermal resistance parameters in the Foster model at the target moment, and the estimated junction temperature of the IGBT module at the target moment is obtained accordingly. The reliability of the high-power converter at the target moment is evaluated based on the estimated junction temperature.

2. A reliability assessment method for a high-power converter according to claim 1, characterized in that: The obtaining the power loss correction factor at the current moment according to the deviation between the saturation voltage drop at the target moment and the reference saturation voltage drop and the modulation characteristic of the load current at the target moment includes: The load current at the target moment is used as an independent variable in a preset load current modulation function to obtain a corresponding load current modulation value, wherein the load current modulation function is used to characterize the modulation effect of the load current on the saturation voltage drop, and the larger the load current, the greater the modulation effect of the saturation voltage drop; Calculating the difference between the saturated pressure drop at the target time and the reference saturated pressure drop, and recording the ratio of the difference to the reference saturated pressure drop as the saturated pressure drop difference value at the target time; The influence coefficient of the saturation voltage drop on the power loss at the target moment is obtained by using a gradient descent algorithm, the product of the influence coefficient, the saturation voltage drop difference value and the load current modulation value is obtained, and the sum of a constant 1 and the product is used as the power loss correction factor at the current moment.

3. The reliability evaluation method of a high-power converter according to claim 1, characterized in that: The step of obtaining the thermal resistance adjustment factor at the target moment according to the changes of the saturation voltage drop and the shutdown delay time at the target moment relative to the reference saturation voltage drop and the reference shutdown delay time, and the power loss correction factor, comprises: Calculating the difference between the saturated pressure drop at the target time and the reference saturated pressure drop, and recording the ratio of the difference to the reference saturated pressure drop as the saturated pressure drop difference value at the target time; Calculating the difference between the turn-off delay time at the target moment and the reference turn-off delay time, and recording the ratio between the difference and the reference turn-off delay time as the turn-off delay time difference value at the target moment; According to the saturated voltage drop difference value and the shutdown delay time difference value, respectively obtaining a first weight of the saturated voltage drop change on the thermal resistance adjustment and a second weight of the shutdown delay time change on the thermal resistance adjustment; A thermal resistance adjustment factor at the target moment is obtained according to the saturation voltage drop difference value, the shutdown delay time difference value, the first weight, the second weight, and the power loss correction factor at the target moment.

4. A reliability assessment method for a high-power converter according to claim 3, characterized in that: The obtaining, according to the saturated voltage drop difference value and the shutdown delay time difference value, a first weight of the saturated voltage drop change on the thermal resistance adjustment and a second weight of the shutdown delay time change on the thermal resistance adjustment respectively include: Calculate the sum of the absolute value of the saturation voltage drop difference value and the absolute value of the shutdown delay time difference value, and use the ratio between the absolute value of the saturation voltage drop difference value and the sum as the first weight of the saturation voltage drop change for thermal resistance adjustment; use the ratio between the absolute value of the shutdown delay time difference value and the sum as the second weight of the shutdown delay time change for thermal resistance adjustment.

5. The reliability evaluation method of a high-power converter according to claim 3, characterized in that: The step of obtaining the thermal resistance adjustment factor at the target moment according to the saturation voltage drop difference value, the shutdown delay time difference value, the first weight, the second weight, and the power loss correction factor at the target moment includes: Based on the first weight and the second weight, the saturation voltage drop difference value and the shutdown delay time difference value at the target moment are weightedly summed to obtain a corresponding weighted sum value, the addition result of the constant 1 and the weighted sum value is obtained, and the product of the addition result and the power loss correction factor is used as the thermal resistance adjustment factor at the target moment.

6. A reliability assessment method for a high-power converter according to claim 1, characterized in that: The power loss correction factor and thermal resistance adjustment factor at the target time are used to optimize the power loss and thermal resistance parameters in the Foster model at the target time, and the estimated junction temperature of the IGBT module at the target time is obtained accordingly, including: ； in, represents the estimated junction temperature of the IGBT module at the target time t, represents the ambient temperature of the IGBT module at the target time t, m represents the order of the Foster model (that is, the number of links), represents the thermal resistance adjustment factor at the target time t, represents the thermal resistance parameter of the jth link of the Foster model at the target time t, 1 represents a constant, represents an exponential function with a natural constant as base, represents the time step, represents the heat capacity parameter of the jth link of the Foster model at the target time t, represents the power loss correction factor at the target time t, represents the power loss at the target time t, represents the adjusted thermal resistance parameter, Indicates the corrected power loss.

7. A reliability assessment method for a high-power converter according to claim 2, characterized in that: The load current modulation function is: ； in, represents the load current modulation value corresponding to the load current at the target time t, 1 represents a constant, represents the coefficient of the first-order term corresponding to the target time t, represents the load current at the target time t, represents the quadratic term coefficient corresponding to the target time t, wherein the linear term coefficient and the quadratic term coefficient are obtained using a gradient descent algorithm.

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