A reliability evaluation method for a high-power converter

Abstract

The present invention relates to the technical field of power electronic device state monitoring, and particularly to a reliability evaluation method for a high-power converter. The method collects the saturation voltage drop, turn-off delay time, and load current of the IGBT module in the high-power converter at the target moment, and respectively obtains the power loss correction factor and thermal resistance adjustment factor at the current moment; uses the power loss correction factor and thermal resistance adjustment factor at the target moment to optimize the power loss and thermal resistance parameters in the Foster model at the target moment, and correspondingly obtains the estimated junction temperature value of the IGBT module at the target moment, and evaluates the reliability of the high-power converter at the target moment according to the estimated junction temperature value, so that the Foster model can better adapt to the thermal characteristic changes of the IGBT module under different working conditions and aging states, and improve the overall accuracy and reliability of the junction temperature estimation.

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 using the Foster model to evaluate the junction temperature of IGBT modules has become an urgent problem to be solved. Summary of the Invention

[0006] In view of this, embodiments of the present invention provide a method for evaluating the reliability of 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 using the Foster model to evaluate the junction temperature of IGBT modules.

[0007] Embodiments of the present invention provide a method for evaluating the reliability of a high-power converter, the method comprising the following steps:

[0008] Collect the saturation voltage drop, turn-off delay time, and load current of the IGBT module in the high-power converter at the target moment, and obtain the reference saturation voltage drop and reference turn-off delay time of the IGBT module under specific working conditions;

[0009] 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, obtain the power loss correction factor at the current moment;

[0010] According to the changes in the saturation voltage drop and turn-off delay time at the target moment relative to the reference saturation voltage drop and the reference turn-off delay time, and the power loss correction factor, obtain the thermal resistance adjustment factor at the target moment;

[0011] Use the power loss correction factor and thermal resistance adjustment factor at the target moment to optimize the power loss and thermal resistance parameters in the Foster model at the target moment, and correspondingly obtain the estimated value of the junction temperature of the IGBT module at the target moment, and evaluate the reliability of the high-power converter at the target moment according to the estimated value of the junction temperature.

[0012] Preferably, the step of 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:

[0013] Take the load current at the target moment as the independent variable in a preset load current modulation function to obtain the corresponding load current modulation value, where the load current modulation function is used to characterize the modulation effect of the load current on the saturation voltage drop, and the greater the load current, the greater the modulation effect on the saturation voltage drop;

[0014] Calculate the difference between the saturation voltage drop at the target time and the reference saturation voltage drop, and record the ratio between the difference and the reference saturation voltage drop as the saturation voltage drop difference value at the target time;

[0015] Use the gradient descent algorithm to obtain the influence coefficient of the saturation voltage drop at the target time on the power loss, obtain the product of the influence coefficient, the saturation voltage drop difference value, and the load current modulation value, and take the sum of the constant 1 and the product as the power loss correction factor at the current time.

[0016] Preferably, obtaining the thermal resistance adjustment factor at the target time according to the change of the saturation voltage drop and the turn-off delay time at the target time relative to the reference saturation voltage drop and the reference turn-off delay time, and the power loss correction factor includes:

[0017] Calculate the difference between the saturation voltage drop at the target time and the reference saturation voltage drop, and record the ratio between the difference and the reference saturation voltage drop as the saturation voltage drop difference value at the target time;

[0018] Calculate the difference between the turn-off delay time at the target time and the reference turn-off delay time, and record the ratio between the difference and the reference turn-off delay time as the turn-off delay time difference value at the target time;

[0019] According to the saturation voltage drop difference value and the turn-off delay time difference value, respectively obtain the first weight of the saturation voltage drop change on the thermal resistance adjustment and the second weight of the turn-off delay time change on the thermal resistance adjustment;

[0020] According to the saturation voltage drop difference value, turn-off delay time difference value, the first weight, the second weight, and the power loss correction factor at the target time, obtain the thermal resistance adjustment factor at the target time.

[0021] Preferably, obtaining the first weight of the saturation voltage drop change on the thermal resistance adjustment and the second weight of the turn-off delay time change on the thermal resistance adjustment according to the saturation voltage drop difference value and the turn-off delay time difference value includes:

[0022] Calculate the sum of the absolute value of the saturation voltage drop difference value and the absolute value of the turn-off delay time difference value, and take the ratio between the absolute value of the saturation voltage drop difference value and the sum value as the first weight of the saturation voltage drop change on the thermal resistance adjustment; take the ratio between the absolute value of the turn-off delay time difference value and the sum value as the second weight of the turn-off delay time change on the thermal resistance adjustment.

[0023] Preferably, obtaining the thermal resistance adjustment factor at the target moment according to the saturation voltage drop difference value, turn-off delay time difference value, the first weight, the second weight, and the power loss correction factor at the target moment includes:

[0024] Based on the first weight and the second weight, perform a weighted sum of the saturation voltage drop difference value and the turn-off delay time difference value at the target moment to obtain the corresponding weighted sum value, obtain the addition result of the constant 1 and the weighted sum value, and use the product of the addition result and the power loss correction factor as the thermal resistance adjustment factor at the target moment.

[0025] Preferably, using the power loss correction factor and the thermal resistance adjustment factor at the target moment to optimize the power loss and thermal resistance parameters in the Foster model at the target moment, and correspondingly obtaining the junction temperature estimation value of the IGBT module at the target moment includes:

[0026] Among them, represents the junction temperature estimation value of the IGBT module at the target moment t, represents the ambient temperature where the IGBT module is located at the target moment t, m represents the order of the Foster model (i.e., the number of links), represents the thermal resistance adjustment factor at the target moment t, represents the thermal resistance parameter of the j-th link of the Foster model at the target moment t, 1 represents a constant, represents the exponential function with the natural constant as the base, represents the time step, represents the heat capacity parameter of the j-th link of the Foster model at the target moment t, represents the power loss correction factor at the target moment t, represents the power loss at the target moment t, represents the adjusted thermal resistance parameter, represents the corrected power loss.

[0027] Preferably, the load current modulation function is:

[0028]

[0029] Among them, represents the load current modulation value corresponding to the load current at the target moment t, 1 represents a constant, represents the first-order term coefficient corresponding to the target moment t, represents the load current at the target moment t, denotes the quadratic coefficient corresponding to the target time t, where the linear coefficient and the quadratic coefficient are obtained by using the gradient descent algorithm.

[0030] The beneficial effects of the embodiments of the present invention compared with the prior art are as follows:

[0031] By introducing a power loss correction factor obtained based on the saturation voltage drop and the load current, the present invention optimizes the power loss parameters in the Foster model, can dynamically and finely correct the calculation results of the traditional power loss, thereby more accurately evaluating the actual power loss. At the same time, taking the turn-off delay time of the IGBT module as the basis for adjusting the thermal resistance parameter, and introducing the power loss correction factor to obtain the thermal resistance adjustment factor to optimize the thermal resistance parameter in the Foster model, can introduce the dynamic information of the turn-off delay time into the calculation of the thermal resistance parameter, so that when using the Foster model to evaluate the junction temperature of the IGBT module, it can better adapt to the thermal characteristic changes 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. Description of the Drawings

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0033] Figure 1 It is a flowchart of a method for reliability evaluation of a high-power converter provided in Embodiment 1 of the present invention. Detailed Embodiments

[0034] The following will describe in detail the embodiments of the present disclosure. The examples of the embodiments are shown in the drawings. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present disclosure and should not be construed as limiting the present disclosure.

[0035] It should be noted that the terms "first", "second", etc. in the specification of the present disclosure and the above drawings are used to distinguish similar objects and do not necessarily need to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances 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. On the contrary, they are only examples of devices and methods consistent with some aspects of the present disclosure.

[0036] To illustrate the technical solution of the present invention, specific embodiments are used for illustration below.

[0037] See Figure 1 , which is a method flowchart of a reliability evaluation method for a high-power converter provided in Embodiment 1 of the present invention. As Figure 1 shown, the method may include:

[0038] Step S101, collect the saturation voltage drop, turn-off delay time, and load current of the IGBT module in the high-power converter at the target moment, and obtain the reference saturation voltage drop and reference turn-off delay time of the IGBT module under specific working conditions.

[0039] At present, high-power converters have a broad application background and have become one of the core devices in multiple industries. Taking the wind power converter as an example, the cost of the converter accounts for about 15% of the total cost of the entire wind turbine. 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, and most of the failures of high-power converters are caused by the failures of Insulate Gate Bipolar Transistors (IGBTs).

[0040] Compared with other power devices, the IGBT module has the characteristics of high input impedance and high conduction current, and also has a relatively high breakdown voltage value, playing a crucial role in power electronic systems. With the development of power electronic technology, while improving the power level and switching frequency of the IGBT module, its reliability is more and more affected by the junction temperature, and the electromagnetic interference generated by itself also affects other electronic systems. The power loss generated when the IGBT module works causes the increase and fluctuation of the device junction temperature, resulting in uneven temperature distribution of the internal chip. With the change of load and operating conditions, the temperature of the IGBT chip fluctuates greatly. The heat dissipated by the chip is conducted from top to bottom to the cooling system. The mismatch of the thermal expansion coefficients between each layer of materials inside the IGBT module will lead to the generation of thermal stress and mechanical stress, accelerating the aging process of the module, causing solder layer fatigue, bond wire cracks or even detachment, and ultimately resulting in the failure of the IGBT module. Therefore, the junction temperature is a key parameter for the state monitoring of the IGBT module.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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 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 Keep consistent.

[0045] In the embodiment of the present invention, the moment corresponding to the real-time evaluation of the junction temperature of the IGBT module is denoted as the target moment t. Using the above acquisition means, the saturation voltage drop, turn-off delay time, and load current of the IGBT module at the target moment are respectively collected and denoted as .

[0046] It should be noted that before the IGBT module runs for the first time, its saturation voltage drop and turn-off delay time under specific working conditions (such as room temperature and zero load) are recorded as the reference saturation voltage drop and the reference turn-off delay time respectively, which are used for the dynamic characteristic analysis of the IGBT module during its actual operation.

[0047] Step S102, 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, obtain the power loss correction factor at the current moment.

[0048] 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. However, the power loss obtained by traditional methods relying on the static loss curve provided in the IGBT data sheet or simplified calculation formulas usually has a large error. These calculation methods do not fully consider the dynamic characteristics, aging effect, and rich information contained in easily measurable electrical parameters such as the saturation voltage drop of the IGBT module during its actual operation.

[0049] Specifically, the static loss curve provided in the IGBT data sheet is usually measured under specific working conditions and cannot accurately reflect the dynamic power loss of the IGBT module during actual operation. In addition, the aging of the IGBT module will cause changes in its switching and conduction characteristics, affecting the power loss. More importantly, the saturation voltage drop of the IGBT module is an easily measurable electrical parameter. Its dynamic change is not only related to the junction temperature but also closely related to factors such as load current and aging degree, containing information about the real-time working state and loss characteristics of the IGBT module. However, traditional power loss calculation methods do not utilize this important information source of the saturation voltage drop, resulting in a deviation between the calculation result and the actual value.

[0050] Therefore, in order to improve the accuracy of the power loss P in the Foster model and enhance the precision of real-time junction temperature estimation, in the embodiments of the present invention, the power loss P obtained conventionally is corrected by using the on-line measured saturation voltage drop information. 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 the junction temperature and load current), as well as the degree of deviation of the aging degree of the IGBT module relative to the initial state (or reference state), and there is a close correlation between this degree of deviation and the deviation of the actual value of the power loss relative to the calculated value by the conventional method. Therefore, before estimating the real-time junction temperature at the target time t using the Foster model, 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 conventional manner to improve the evaluation accuracy of the real-time junction temperature at the target time t.

[0051] Specifically, considering that the influence degree of the saturation voltage drop on the power loss is not constant but changes with the load current. Usually, in the case of heavy load, a small change in the saturation voltage drop will cause a significant change in the power loss. Therefore, the influence degree of the saturation voltage drop on the power loss is adjusted according to the load current at the target time. Specifically: taking the load current at the target time as the independent variable in the preset load current modulation function to obtain the corresponding load current modulation value, where the load current modulation function is used to characterize the modulation effect of the load current on the influence of the saturation voltage drop, and the greater the load current, the greater the modulation effect of the influence of the saturation voltage drop. The load current modulation function is:

[0052]

[0053] Wherein, represents the load current modulation value corresponding to the load current at the target time t, 1 represents a constant, represents the first-order term coefficient corresponding to the target time t, represents the load current at the target time t, represents the second-order term coefficient corresponding to the target time t, where the first-order term coefficient and the second-order term coefficient are obtained by using the gradient descent algorithm.

[0054] It should be noted that when the load current is 0, the value of is 1, indicating that no additional adjustment is made to the influence of the saturation voltage drop in the no-load or light-load case; on the contrary, when the load current increases, the greater the value of, indicating that as the load current increases, the influence of the saturation voltage drop needs to be "amplified".

[0055] Among them, by adjusting the degree of the first-order term and the coefficient of the second-order term in the load current modulation function, the curve shape 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 adopted to dynamically estimate and values. Specifically: Using the load current at the target time t and combining with the gradient descent algorithm, continuously adjust and values to make them approach the optimal values. Then and the adaptive adjustment formulas are:

[0056] Among them, represents the coefficient of the first-order term at time t-1 (the previous moment of the target time), represents the coefficient of the second-order term at time t-1 (the previous moment of the target time), is the learning rate of the coefficient of the first-order term, is the learning rate of the coefficient of the second-order term, represents the load current at the target time t, represents the reference current (half of the IGBT rated current), represents the power loss correction factor at time t-1 (the previous moment of the target time).

[0057] When the load current is greater than the reference current, if at the previous moment is greater than 1, in order to amplify the influence of the saturation voltage drop, it is necessary to increase . Since is and a monotonically increasing function, so it is necessary to increase and values; when the load current is less than the reference current, if at the previous moment is greater than 1, in order to reduce the influence of the saturation voltage drop, it is necessary to reduce , so it is necessary to reduce and values; since is related to the square of Ice, so the adjustment range of is larger, and .

[0058] Preferably, in the embodiment of the present invention, is set to be between , is set to be Between them, 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. Therefore, in actual applications, it is necessary to start with a small learning rate.

[0059] Further, after obtaining the modulation degree of the influence of the load current on the saturation voltage drop at the current moment t (the load current modulation value ), further analyze the deviation of the saturation voltage drop at the target moment t from the reference value to characterize the current working state of the IGBT module. Specifically: Calculate the difference between the saturation voltage drop at the target moment and the reference saturation voltage drop, and record the ratio between the difference and the reference saturation voltage drop as the saturation voltage drop difference value at the target moment.

[0060] Preferably, the calculation expression of the saturation voltage drop difference value at the target moment t is:

[0061]

[0062] Wherein, represents the saturation voltage drop difference value at the target moment t, represents the reference saturation voltage drop, represents the saturation voltage drop at the target moment t.

[0063] It should be noted that, represents the deviation of the saturation voltage drop at the target moment from the initial value. The larger this deviation, the farther the current state of the IGBT module deviates from the initial state, and the greater the deviation of the actual power loss from the power loss obtained traditionally; dividing by normalizes the saturation voltage drop deviation to eliminate the influence of dimensions.

[0064] Finally, use the gradient descent algorithm to obtain the influence coefficient of the saturation voltage drop at the target moment on the power loss, obtain the product of the influence coefficient, the saturation voltage drop difference value and the load current modulation value, and take the sum of the constant 1 and the product as the power loss correction factor at the current moment.

[0065] Among them, the calculation expression of the power loss correction factor at the current moment is:

[0066]

[0067] Wherein, represents the power loss correction factor at the current moment t, 1 represents a constant, represents the influence coefficient of the saturation voltage drop at the target moment t on the power loss, represents the saturation voltage drop difference value at the target moment t, represents the load current modulation value corresponding to the load current at the target moment t.

[0068] It should be noted that the power loss correction factor takes into account the dynamic change information of the saturation voltage drop of the IGBT module and introduces the modulation of the load current Ice, so as to more accurately reflect the power loss under the actual working conditions of the IGBT module. Specifically, the power loss correction factor consists of three parts: the reference value (constant term 1), the deviation term of the saturation voltage drop and the load current modulation term. Among them, the constant term 1 sets the reference for power loss correction to ensure 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 conventionally obtained power loss; the deviation term of the saturation voltage drop is the core of the power loss correction factor. This term reflects the impact of the saturation voltage drop at the target moment deviating from the initial value on the power loss. An increase in the saturation voltage drop of the IGBT usually means an increase in the junction temperature, an increase in the load current or device aging; is a positive coefficient obtained by data fitting, reflecting the sensitivity of the relative change of the saturation voltage drop to the power loss. The larger it is, the greater the impact of the saturation voltage drop on the power loss. When , this term is positive, , and the power loss increases, which is consistent with the physical fact that the increase in the saturation voltage drop leads to an increase in loss.

[0069] Among them, in order to overcome the limitations brought by fixed parameters and improve the accuracy and adaptability of the power loss correction factor, an online adaptive adjustment strategy is adopted to dynamically estimate . Specifically, using the saturation voltage drop at the target moment t, the turn-off delay time , and combining with the gradient descent algorithm, continuously adjust the value of to make it approach the optimal value. Then the adaptive adjustment formula of is:

[0070]

[0071] Among them, represents the influence coefficient at time t - 1 (the previous moment of the target moment), is the learning rate of the saturation voltage drop, is the learning rate of the turn-off delay time, represents the saturation voltage drop at the target moment t, represents the turn-off delay time at the target moment t, represents the saturation voltage drop at time t - 1 (the previous moment of 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).

[0072] 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 .

[0073] 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.

[0074] At this point, the power loss correction factor at the current time t is obtained .

[0075] 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.

[0076] 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.

[0077] Specifically, the change in the junction temperature of the IGBT module will directly affect the thermophysical properties of its internal materials, thereby changing the magnitude of the thermal resistance. In addition, the long-term operation of the IGBT module will cause aging phenomena such as bond wire degradation and solder layer fatigue, and these aging phenomena will significantly increase the thermal resistance on the heat conduction path. The traditional Foster model treats the thermal resistance parameters as constants and cannot reflect these dynamic changes caused by temperature and aging, which will lead to a deviation between the model and the actual situation.

[0078] Therefore, to solve the above problems, the embodiments of the present invention dynamically adjust the thermal resistance parameters in the Foster model. Since the turn-off delay time is an important dynamic parameter of the IGBT module and is very sensitive to the change in the junction temperature, it prolongs as the junction temperature increases. In addition, the aging of the IGBT module will also cause to change. 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

[0079] as the basis for adjusting the thermal resistance parameters.

[0079] Considering that there is a close internal relationship between power loss and thermal resistance, power loss is the root cause of the heat generation of the IGBT module, and thermal resistance determines the ease of heat transfer from the junction region to the environment. If the power loss calculation is inaccurate, the junction temperature estimation will deviate, which will further affect the judgment of the thermal resistance. Therefore, in the embodiments of the present invention, when analyzing the thermal resistance adjustment factor, not only the turn-off delay time and the saturation voltage drop are considered for their dynamic changes, but also the power loss correction factor obtained in step S102 needs to be introduced to realize the linkage between power loss correction and thermal resistance adjustment. This linkage mechanism enables the two key links of junction temperature estimation - power loss calculation and thermal resistance parameter adjustment - to coordinate and correct each other, thereby further improving the overall accuracy and reliability of junction temperature estimation.

[0080] In the embodiments of the present invention, by using the changes in the saturation voltage drop and turn-off delay time at the target moment relative to the reference saturation voltage drop and reference turn-off delay time, and the power loss correction factor, the thermal resistance adjustment factor at the target moment is obtained. The specific process is as follows:

[0081] (1) Calculate the difference between the saturation voltage drop at the target moment and the reference saturation voltage drop, and record the ratio of the difference to the reference saturation voltage drop as the saturation voltage drop difference value at the target moment; calculate the difference between the turn-off delay time at the target moment and the reference turn-off delay time, and record the ratio of the difference to the reference turn-off delay time as the turn-off delay time difference value at the target moment.

[0082] In one embodiment, the saturation voltage drop difference value at the target time t is obtained with reference 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 as follows:

[0083]

[0084] wherein, represents the turn-off delay time difference value at the target time t, represents the reference turn-off delay time, represents the turn-off delay time at the target time t.

[0085] (2) According to the saturation voltage drop difference value and the turn-off delay time difference value, the first weight of the change in saturation voltage drop on the thermal resistance adjustment and the second weight of the change in turn-off delay time on the thermal resistance adjustment are respectively obtained.

[0086] In one embodiment, the sum value between the absolute value of the saturation voltage drop difference value and the absolute value of the turn-off delay time difference value is calculated, and the ratio between the absolute value of the saturation voltage drop difference value and the sum value is used as the first weight of the change in saturation voltage drop on the thermal resistance adjustment; the ratio between the absolute value of the turn-off delay time difference value and the sum value is used as the second weight of the change in turn-off delay time on the thermal resistance adjustment.

[0087] wherein, the first weight of the change in saturation voltage drop on the thermal resistance adjustment

[0088]

[0089] The second weight of the change in turn-off delay time on the thermal resistance adjustment

[0090]

[0091] wherein, represents the absolute value function, which avoids the influence of negative values in the calculation of the thermal resistance adjustment factor due to the measurement error of the sensor in practical applications, represents the turn-off delay time difference value at the target time t, represents the saturation voltage drop difference value at the target time t.

[0092] It should be noted that, is the weight of the change in the turn-off delay time which ensures that the greater the relative change, the greater the weight, and when the saturation voltage drop has a relatively large change, The weight will be correspondingly reduced to avoid over-adjustment; is the saturation voltage drop The varying weight ensures the saturation voltage drop The greater the relative change, the greater the weight, and when the relative change is large, the weight will be correspondingly reduced.

[0093] (3) Obtain the thermal resistance adjustment factor at the target time according to the saturation voltage drop difference value, turn-off delay time difference value, the first weight, the second weight, and the power loss correction factor at the target time.

[0094] In one embodiment, the thermal resistance adjustment factor at the target time The calculation expression is:

[0095]

[0096] Wherein, represents the thermal resistance adjustment factor at the target time, is the first weight of the saturation voltage drop change on the thermal resistance adjustment, is the second weight of the turn-off delay time change on the thermal resistance adjustment, represents the turn-off delay time difference value at the target time t, represents the saturation voltage drop difference value at the target time t, represents the power loss correction factor at the target time, and 1 represents a constant.

[0097] 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 the junction temperature change and aging effect during the actual operation of the IGBT module. Among them, the thermal resistance adjustment factor is obtained through the base value (constant 1), the influence of the change, the influence of the change, and the power loss correction factor The modulation effect is used for multi-source data analysis. The constant 1 sets the benchmark for thermal resistance adjustment to ensure that the thermal resistance parameters are not adjusted when the IGBT module is in the reference state; The influence of the change is reflected by the value, The influence of the change is reflected by the value. When or the value is positive, it indicates that the thermal resistance increases, which is in line with the physical fact that the increase in junction temperature or aging exacerbates the increase in thermal resistance, corresponding to an increase in the thermal resistance adjustment factor; finally, the power loss correction factor has comprehensively reflected the state information of the IGBT module, and the power loss correction factor is utilized Implement further modulation of the thermal resistance adjustment by implementing power loss correction. If , it indicates that the traditional method underestimates the power loss, and the actual junction temperature may be higher. Therefore, it is necessary to further increase the thermal resistance adjustment factor ; if , it indicates that the traditional method overestimates the power loss, and the actual junction temperature may be lower. Therefore, it is necessary to appropriately reduce the thermal resistance adjustment factor .

[0098] Thus, the thermal resistance adjustment factor at the target time t is obtained .

[0099] Step S104: Use the power loss correction factor and the thermal resistance adjustment factor at the target time to optimize the power loss and thermal resistance parameters in the Foster model at the target time, and correspondingly obtain the estimated junction temperature of the IGBT module at the target time. Evaluate the reliability of the high-power converter at the target time according to the estimated junction temperature value.

[0100] Through steps S102 and S103, the power loss correction factor and the thermal resistance adjustment factor at the target time are obtained, which are respectively used to correct the power loss in the traditional Foster model and the model parameter thermal resistance R. That is, when using the Foster model to obtain the real-time junction temperature of the IGBT module at the target time, 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 time are substituted into the traditional Foster model to optimize the power loss and thermal resistance parameters in the Foster model, and an improved Foster model is obtained. The formula of the improved Foster model is as follows:

[0101] Wherein, represents the estimated junction temperature value 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 (i.e., the number of links), represents the thermal resistance adjustment factor at the target time t, represents the thermal resistance parameter of the j-th link of the Foster model at the target time t, 1 represents a constant, represents the exponential function with the natural constant as the base, represents the time step, represents the heat capacity parameter of the j-th 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, represents the corrected power loss.

[0102] It should be noted that the ambient temperature of the IGBT module is measured by an ambient temperature sensor installed close to the IGBT module; the adjusted thermal resistance parameter can more accurately reflect the actual thermal resistance characteristics of the IGBT module at the target time, and the corrected power loss can more reflect the actual power loss of the IGBT module at the target time; the time step refers to the time interval between the previous time and the current time.

[0103] Therefore, by using the improved Foster model, the power loss correction factor, and the 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. Further, 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 by combining 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. Specifically as follows:

[0104] First, use the Arrhenius model to calculate the instantaneous failure rate of the IGBT module :

[0105]

[0106] Among them, is the base 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 the exponential function with the natural constant as the base, and are obtained by referring to the data sheet of the IGBT module.

[0107] Then, by numerically integrating the instantaneous failure rate the cumulative failure rate of the IGBT module is obtained :

[0108]

[0109] In addition, use the model to estimate the remaining life of the IGBT module: , where, is the failure cycle number (life) of the IGBT module, A is the material constant, is the amplitude of the junction temperature fluctuation, and b is the exponent. A and b are obtained from the data sheet of the IGBT module, and are extracted from the time series of by the rain flow counting method.

[0110] For the overall reliability of a high-power converter containing multiple IGBT modules it can be expressed as:

[0111]

[0112]

[0113] where, is the reliability of the th IGBT module, and M is the number of IGBT modules in the high-power converter.

[0114] Based on the above calculated indicators such as the instantaneous failure rate, cumulative failure rate, and remaining life, the reliability levels of the IGBT module and the high-power converter are monitored in real time, and warnings are issued, protection mechanisms are triggered, maintenance decisions are guided, or the converter control strategy is optimized when necessary, so as to improve the availability and safety of the converter. It should be noted that the calculations of the instantaneous failure rate, cumulative failure rate, remaining life, and overall reliability all belong to the prior art and will not be elaborated here in detail.

[0115] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all 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; 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; the difference between the saturation voltage drop at the target moment and the reference saturation voltage drop is calculated, and the ratio between the difference and the reference saturation voltage drop is recorded as the saturation voltage drop difference value at the target moment; the influence coefficient of the saturation voltage drop at the target moment on the power loss 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 the constant 1 and the product is used as the power loss correction factor at the target moment; Calculate the difference between the shutdown delay time at the target moment and the reference shutdown delay time, and record the ratio of the difference to the reference shutdown delay time as the shutdown delay time difference value at the target moment; 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 according to the saturated voltage drop difference value and the shutdown delay time difference value; perform weighted summation on the saturated voltage drop difference value and the shutdown delay time difference value at the target moment based on the first weight and the second weight to obtain a corresponding weighted summation value, obtain a summation result of a constant 1 and the weighted summation value, and use the product of the summation result and the power loss correction factor as the thermal resistance adjustment factor at the target moment; 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, 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.

3. The reliability evaluation method of 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, 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.

4. The reliability evaluation method of a high-power converter according to claim 1, 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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