Calculation Method for Cumulative Damage Degree of IGBT Power Module in Electric Vehicles

Abstract

A method for calculating the cumulative damage degree of an IGBT power module in an electric vehicle, which relates to a method for digital calculation specifically applicable to a specific application, is a method for calculating the cumulative damage degree of an IGBT power module in an electric vehicle based on an improved Manson model. The steps are as follows: Obtain the basic parameters and driving conditions of the electric vehicle, the parameters of the permanent magnet synchronous motor, and the parameters of the IGBT power module; Obtain the junction temperature-time curve data of the IGBT power module, preprocess the junction temperature-time curve data, and establish a time series of peak and valley values of the junction temperature; Based on the rain flow counting method, process the time series of peak and valley values of the junction temperature to establish a junction temperature load spectrum; The LESIT model can be used to calculate the cyclic life of the IGBT power module under constant amplitude load; Establish an improved Manson model to calculate the cumulative damage degree of the IGBT power module under random variable amplitude load. The present invention does not require parameters determined by the physical characteristics of devices (such as IGBT power modules) obtained by fitting a large amount of experimental data. The mathematical formula only contains the load cyclic life, which is more easily implemented in actual engineering; The influence of the load size is added to the calculation process, and the interaction between adjacent loads is considered, making up for the deficiency in the accuracy of the calculation result of the total damage degree of the IGBT power module in the existing method, which cannot more conform to the cumulative process of fatigue damage in the actual working condition.

Description

Technical Field

[0001] The technical solution of the present invention relates to the field specifically applicable to electric vehicles, and more particularly to a method for calculating the cumulative damage degree of an IGBT power module of an electric vehicle. Background Art

[0002] With the growth of the global population and the continuous expansion of energy demand, the economic model solely relying on the development of fossil energy is becoming increasingly unsustainable. The development and efficient utilization of clean energy have become the theme of the current social development. As an efficient way to develop and utilize clean energy, the accelerated development of new energy power generation, smart grid, and electric vehicles is of great significance. Photovoltaic power generation, high-voltage power transmission, and electric vehicles in this field are particularly popular. Electric vehicles include battery electric vehicles, hybrid electric vehicles, and fuel cell vehicles. Battery electric vehicles have many advantages such as low pollution, low noise, low energy consumption, high efficiency, easy maintenance, and wide application range. Therefore, in order to improve energy utilization efficiency, achieve a green lifestyle, and implement the global sustainable development strategy, electric vehicles are being vigorously developed.

[0003] An electric vehicle drives the wheels forward through the energy of a storage battery by means of a motor drive system. As one of the core components in the drive system of a battery electric vehicle, the reliability and operating life of an inverter greatly affect the normal operation of the entire vehicle of the battery electric vehicle. With the development of battery electric vehicle technology and the increasing market demand, power semiconductor devices, especially IGBT power modules, have gradually been widely used in the inverters of battery electric vehicles. Accurately obtaining the damage degree of the IGBT module of a battery electric vehicle is beneficial to the reasonable design and daily maintenance of the electric vehicle, and is also an important factor in improving the durability of the entire vehicle. The junction temperature of the IGBT module directly affects the normal operation of the module. The increase or fluctuation of the junction temperature will cause irreversible permanent fatigue damage to the IGBT power module. With the gradual accumulation of fatigue damage, the IGBT power module develops in the direction of failure. Therefore, accurately calculating the damage degree of the IGBT power module is of great help for the reasonable design of the equipment and the timing arrangement for planning to replace the IGBT module.

[0004] Currently, the methods for calculating the damage degree of IGBT power modules under complex working conditions at home and abroad can be summarized as the following steps: First, obtain the junction temperature-time curve data of the IGBT power module under a given mission cycle curve. Then, use the rainflow counting method to process the junction temperature-time curve to obtain the junction temperature load spectrum. Finally, according to the linear fatigue cumulative damage theory, calculate the fatigue cumulative damage degree under the given mission cycle. The linear fatigue cumulative damage theory simplifies the fatigue mechanism of the IGBT power module to a large extent. It is considered that the fatigue damage under different temperature load levels is carried out independently, and the damage under all load levels can be linearly accumulated. When the fatigue damage accumulates to a certain value, the IGBT power module fails. The damage degree calculation method applying the linear fatigue cumulative damage theory is convenient to calculate and easy to implement in actual engineering.

[0005] In the process of calculating the fatigue cumulative damage, the linear fatigue cumulative damage theory does not consider the mutual influence between different loads and lacks the consideration of other fatigue mechanisms. The damage degree obtained by this method is less than the actual damage degree, and the accuracy of the fatigue cumulative damage degree of the IGBT power module is not good. If we want to improve the accuracy of the damage degree calculation under the variable amplitude load mission cycle, we need to consider using the non-linear fatigue cumulative damage theory, taking into account the interaction between adjacent temperature loads and incorporating relevant factors into the damage degree calculation model. The research on calculating the fatigue cumulative damage degree of IGBT power modules by this non-linear fatigue cumulative damage method is not sufficient. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for calculating the cumulative damage degree of the IGBT power module of an electric vehicle, which calculates the actual damage degree of the IGBT power module under random variable amplitude loads, and the calculation result takes into account the mutual influence between adjacent loads; the mathematical formula of this method only contains the cycle life of the load cycle and does not require a large amount of experimental data fitting to obtain the parameters determined by the physical characteristics of the device (such as: IGBT power module), making it easier to implement operation and calculation in actual engineering; compared with the existing method, this method no longer considers that the fatigue damage under various load levels is carried out independently, and the damage degree caused by each load cycle will be affected by the fatigue damage that has occurred in history. A series of load cycles are interlocked and interact with each other, and the damage degrees caused are not independent; the total damage degree of the IGBT power module obtained by the improved Manson model for multiple stages is greater than the total damage degree obtained by separately calculating and then accumulating multiple stages. The calculation result of the improved Manson model is more in line with the cumulative process of fatigue damage in actual working conditions, making up for the deficiency that the solution result of the total cumulative damage degree of the existing method is quite different from the actual situation.

[0007] The technical solution adopted by the present invention to solve this technical problem is: an electric IGBT power module cumulative damage degree calculation method, which is an IGBT power module cumulative damage degree calculation method based on an improved Manson model, and its steps are as follows:

[0008] Step 1: Obtain the parameters of the pure electric vehicle and the IGBT power module;

[0009] Obtain the basic parameters and driving conditions of the pure electric vehicle, the parameters of the permanent magnet synchronous motor, and the IGBT power module, so as to prepare for obtaining the junction temperature-time curve of the IGBT power module in one working cycle;

[0010] Step 2: Obtain the junction temperature-time curve data of the IGBT power module, and process the data to obtain the junction temperature peak-valley value time series;

[0011] At present, the original data required by the mainstream damage degree calculation methods for IGBT power modules applied to complex working conditions at home and abroad is the junction temperature-time curve of the IGBT module within the task cycle. Preprocess the junction temperature-time curve to obtain the junction temperature peak-valley value time series;

[0012] Step 3: Based on the rain flow counting method for processing the junction temperature peak-valley value time series, obtain the junction temperature load spectrum;

[0013] Extract the initial junction temperature, the final junction temperature, and all junction temperature extreme points arranged in chronological order from the junction temperature peak-valley value time series obtained in Step 2, and use the rain flow counting method to process the junction temperature peak-valley value time series to obtain the junction temperature load spectrum;

[0014] When using the rain flow counting method to obtain the junction temperature load spectrum of the IGBT power module, place the junction temperature peak-valley value time series vertically, record the abscissa as strain, corresponding to the junction temperature in this article, and the ordinate as time;

[0015] Step 4: Calculate its cycle life using the IGBT power module life model;

[0016] The currently most commonly used IGBT power module life model is the LESIT model. Using the LESIT model, the cycle life of the IGBT power module under constant amplitude load can be calculated. This model believes that the fatigue damage of the IGBT module is mainly determined by the mean value of the junction temperature and its fluctuation amplitude. One junction temperature fluctuation cycle (load cycle) corresponds to a pair of junction temperature fluctuation amplitudes and the mean value of the junction temperature cycle. The LESIT model can calculate the total number of cycles until failure when the IGBT module continuously operates with this junction temperature fluctuation cycle. The analytical expression of this model is as follows:

[0017]

[0018] Among them, Nf is the cyclic life of the IGBT module, i.e., the total number of cycles until failure under a constant amplitude temperature load; A is a positive constant related to the operating characteristics, physical state, etc. of the device; ΔT j is the amplitude of the junction temperature fluctuation; T m is the mean value of the junction temperature period; α is a parameter to be fitted, obtained by fitting the module life data; Q is the activation energy related to the material; R is the Boltzmann constant; take A = 640, α = -5, R = 8.314 J·mol -1 ·K -1 , Q = 7.8×10 4 J·mol -1 ;

[0019] Step Five, improve the Manson model to calculate the cumulative damage degree of the IGBT power module under random variable amplitude loads;

[0020] To more comprehensively reflect the physical process of fatigue accumulation, the method for calculating the cumulative damage degree D of the IGBT power module under random variable amplitude loads using the improved Manson model is as follows:

[0021] (5.1) In the case of random variable amplitude loads, each load cycle is associated with the previous load cycle, and the solution formula for calculating the cumulative damage degree D of the IGBT power module using the improved Manson model is:

[0022]

[0023] Among them, order of magnitude;

[0024] (5.2) According to the calculation formula of the cumulative damage degree D of the IGBT power module, the fatigue damage degree caused by a single load cycle and the cumulative fatigue damage degree caused by multiple load cycles can be obtained respectively as:

[0025]

[0026]

[0027] Among them, order of magnitude;

[0028] The above method for calculating the cumulative damage degree of the IGBT power module of an electric vehicle, wherein the junction temperature - time curve is the junction temperature - time curve of the IGBT power module obtained from various parameters and driving conditions of the electric vehicle within one working cycle. During the acceleration and uphill stages of a pure electric vehicle, the IGBT junction temperature rises significantly. During the constant - speed driving stage, the IGBT junction temperature returns to a lower level, and during the deceleration stage, the junction temperature further decreases;

[0029] In the above-mentioned method for calculating the cumulative damage degree of the IGBT power module of an electric vehicle, the basic parameters and driving conditions of the electric vehicle, the permanent magnet synchronous motor (PMSM) and the parameters of the IGBT power module are obtained and input into the computer by a known method, and the computer, display and MATLAB computer software are all commercially available;

[0030] The above-mentioned method for calculating the cumulative damage degree of the IGBT power module of an electric vehicle, the idea of ​​obtaining the junction temperature-time curve, the LESIT model, and the rain flow counting method are existing technologies and are well known to technicians in this technical field.

[0031] The beneficial effects of the present invention are as follows: compared with the prior art, the present invention has the following characteristics:

[0032] (1) The method of the present invention can calculate the fatigue cumulative damage degree of the IGBT power module with high accuracy. The improved Manson model is used to obtain better damage calculation results than other fatigue cumulative damage theories, which is more conducive to the reasonable design of pure electric vehicles, the arrangement of the time for replacing the IGBT module and the formulation of the vehicle maintenance plan, which is not available in the existing methods;

[0033] (2) The calculation of fatigue cumulative damage degree of IGBT power module based on the method of the present invention incorporates the influence of load size, amplifies the fatigue damage caused by load cycles with shorter cycle life, and reduces the fatigue damage caused by load cycles with longer cycle life. In other words, the improved Manson model takes into account the interaction between adjacent loads, which is more consistent with the accumulation process of fatigue damage in actual working conditions than other models. This feature provides a very valuable reference method for calculating fatigue cumulative damage degree of IGBT power module in systems with extremely high reliability requirements.

[0034] (3) Compared with the existing methods, the fatigue cumulative damage calculation based on the method of the present invention eliminates the parameters determined by the physical characteristics of the device (such as IGBT power module) that require a large amount of experimental data fitting. The mathematical formula only contains the load cycle life, which is easier to implement in actual engineering;

[0035] (4) The improved Manson model in the method of the present invention is divided into three stages to calculate the fatigue cumulative damage degree and then accumulate the total damage degree result. The results calculated by this method are all greater than the total damage degree calculated in each stage. Unlike other linear models that directly linearly accumulate the damage degrees generated by multiple task cycles, the improved Manson model takes into account the influence of the task cycles completed in the past, and the damage degree generated by each task cycle does not exist in isolation;

[0036] (5) The method for calculating the cumulative damage degree of the IGBT power module of an electric vehicle in the present invention is not limited to the calculation of the cumulative damage degree of the IGBT power module of an electric vehicle, and can also be extended to the calculation of the cumulative damage degree of other products. Description of the Drawings

[0037] The present invention will be further described below in conjunction with the drawings and embodiments.

[0038] Figure 1 It is a schematic flow chart of the method of the present invention.

[0039] Figure 2 It is a diagram showing the speed and slope change of the pure electric vehicle in Embodiment 1.

[0040] Figure 3 It is a junction temperature-time curve diagram of the IGBT module in Embodiment 1.

[0041] Figure 4 It is a statistical result diagram of the junction temperature load spectrum of the IGBT module in Embodiment 1.

[0042] Figure 5 It is a diagram showing the total damage degree result of the improved Manson model for calculating the fatigue cumulative damage theory in Embodiment 1.

[0043] Figure 6 It is a diagram showing the total damage degree result of the Miner model for calculating the fatigue cumulative damage theory in Embodiment 1. Detailed Embodiment

[0044] Figure 1 It shows that the process of the method for calculating the cumulative damage degree of the IGBT power module of an electric vehicle in the present invention is: start → obtain the basic parameters and driving conditions of the electric vehicle, the parameters of the permanent magnet synchronous motor and the IGBT power module, and input all the data into the computer → obtain the junction temperature-time curve data of the IGBT power module → preprocess the junction temperature-time curve data to establish a time series of the peak and valley values of the junction temperature → based on the rain flow counting method, process the time series of the peak and valley values of the junction temperature to obtain the junction temperature load spectrum → use the LESIT model to calculate the cyclic life of the IGBT power module under constant amplitude load → improve the Manson model to calculate the cumulative damage degree of the IGBT power module under random variable amplitude load → display and output the result of the cumulative damage degree of the IGBT power module on the computer display screen, and end.

[0045] Embodiment 1

[0046] Calculation of the cumulative damage degree of the IGBT power module of a pure electric vehicle.

[0047] Step 1: Obtain the basic parameters and driving conditions of the pure electric vehicle, the parameters of the permanent magnet synchronous motor and the IGBT power module;

[0048] In this example, the basic parameters of the pure electric vehicle are shown in Table 1.

[0049] Table 1. Basic Parameters of Pure Electric Vehicle

[0050]

[0051] With the improvement of the performance and the reduction of the cost of permanent magnet materials, permanent magnet synchronous motors are gradually becoming one of the mainstream motors in electric vehicle drive systems due to their advantages such as high efficiency, high power factor, and high power density. In this example, the simulation parameters of the permanent magnet synchronous motor used in the pure electric vehicle are shown in Table 2.

[0052] Table 2. Parameters of Permanent Magnet Synchronous Motor (PMSM)

[0053]

[0054] The IGBT power module used in the inverter of the pure electric vehicle adopts the DF300R07PE4_B6 module of Infineon Technologies AG. This module is mainly applied to high-frequency switching, chopping, motor drive, UPS systems, etc. By consulting its technical information manual, its parameters are shown in Table 3.

[0055] Table 3. Parameters of DF300R07PE4_B6 Module

[0056]

[0057]

[0058] The battery pack voltage of the IGBT power module used in the inverter is set to 320V, and the IGBT switching frequency is set to 10 kHz.

[0059] Step 2: Obtain the junction temperature-time curve data of the IGBT power module, and process the data to obtain the time series of the peak and valley values of the junction temperature;

[0060] In this example, the junction temperature cycle of the IGBT power module used in the inverter during the driving of the pure electric vehicle in a working cycle is used as the random variable amplitude load for damage degree calculation. First, the pure electric vehicle accelerates to 10 m / s on a flat road surface, then travels at a constant speed for 10 s, then decelerates to 5 m / s, travels at a constant speed for 10 s on a road surface with a slope of 6°, then accelerates again, accelerates to 20 m / s and travels at a constant speed for 10 s, and finally decelerates to a stop. This working cycle simulates the complex driving conditions of vehicles on the road network. The working cycle lasts for 90 s and the total mileage is 925 m. Figure 2 Shows the driving conditions of an electric vehicle in a working cycle.

[0061] Obtain various parameters and driving conditions of the pure electric vehicle in Step 1, and obtain the junction temperature-time curve of the IGBT power module within one working cycle as shown in Figure 3 . Preprocess the junction temperature-time curve data to obtain the time series of the peak and valley values of the junction temperature.

[0062] Step 3: Based on the rainflow counting method for processing the time series of the peak and valley values of the junction temperature, obtain the junction temperature load spectrum;

[0063] After obtaining the junction temperature-time curve of the IGBT under random variable amplitude load, use the rainflow counting method to process it to obtain the statistical result of the junction temperature load spectrum as shown in Figure 4 . Figure 4 Among them, the cycle life with a numerical value exceeding the coordinate axis range can be regarded as an infinite cycle life. The larger the amplitude of the junction temperature fluctuation, the smaller the cycle life.

[0064] Step 4: Calculate the cycle life of the IGBT power module using the life model;

[0065] The cycle life of the IGBT power module under constant amplitude load can be calculated using the LESIT model. One cycle of junction temperature fluctuation corresponds to a pair of junction temperature fluctuation amplitudes and the mean value of the junction temperature cycle. The LESIT model can calculate the total number of cycles until failure when the IGBT module operates continuously with this junction temperature fluctuation cycle. The analytical expression of this model is as follows:

[0066]

[0067] Among them, N f is the cycle life of the IGBT module, that is, the total number of cycles until failure under constant amplitude temperature load; A is a normal constant related to the operating characteristics, physical state, etc. of the device; ΔT j is the amplitude of the junction temperature fluctuation; T m is the mean value of the junction temperature cycle; α is a parameter to be fitted, obtained by fitting the module life data; Q is the activation energy related to the material; R is the Boltzmann constant; take A = 640, α = -5, R = 8.314 J·mol -1 ·K -1 , Q = 7.8×10 4 J·mol -1 .

[0068] Step 5: Improve the Manson model to calculate the cumulative damage degree of the IGBT power module under random variable amplitude load.

[0069] In the case of random variable amplitude load, taking into account the previous load cycle of each load cycle, the solution formula for calculating the cumulative damage degree D of the IGBT power module using the improved Manson model is:

[0070]

[0071] Among them, order of magnitude;

[0072] In order to verify that the calculation results of the improved Manson model of the present invention are more in line with the actual situation, the present invention compares the results of calculating the fatigue cumulative damage degree by the improved Manson model with the calculation results of the Miner model. Figure 4 The total damage degree of the theory of calculating fatigue cumulative damage by the improved Manson model shown in Figure 5 The total damage degree of the theory of calculating fatigue cumulative damage by the Miner model shown in. The total damage degree of the IGBT module calculated by the Miner model is 2.81×10 -6 , while the calculation result of the improved Manson model is 9.28×10 -6 . Compared with the Miner model, the calculation result of the improved Manson model has increased by 230.3%. The improved Manson model amplifies the fatigue damage caused by the load cycle with a small cycle life and reduces the fatigue damage caused by the load cycle with a large cycle life. If the cycle life of a load cycle is less than the cycle life of the adjacent next load cycle, then this load cycle increases the fatigue damage caused by the adjacent next load cycle. If the cycle life of a load cycle is greater than the cycle life of the adjacent next load cycle, then this load cycle does not affect the fatigue damage caused by the adjacent next load cycle. The improved version of the Manson model associates each load cycle with the adjacent load cycles before and after it, resulting in results that are significantly different from those of the Miner model.

[0073] In all the above embodiments, the idea of the Manson model and the method of Miner are prior arts and are well-known to those skilled in the art; the basic parameters and driving conditions of the electric vehicle, and the methods for obtaining and inputting the parameters of the permanent magnet synchronous motor and the IGBT power module into the computer are well-known methods, and the computer, monitor and computer software are all obtained through commercial purchase.

Claims

1. A method for calculating the cumulative damage degree of an IGBT power module for an electric vehicle, which is a method for calculating the cumulative damage degree of an IGBT power module based on an improved Manson model, and the steps are as follows: Step 1: Obtain the parameters of the electric vehicle and the IGBT power module; Obtain the basic parameters and driving conditions of the electric vehicle, the permanent magnet synchronous motor, and the parameters of the IGBT power module, so as to prepare for obtaining the junction temperature-time curve of the IGBT power module within one working cycle; Step 2: Obtain the junction temperature-time curve data of the IGBT power module, and process the data to obtain the junction temperature peak-valley value time series; The original data required for the damage degree calculation method is the junction temperature-time curve of the IGBT module within the mission cycle. The junction temperature-time curve is preprocessed to obtain the junction temperature peak-valley value time series; Step 3: Based on the rainflow counting method for processing the junction temperature peak-valley value time series, obtain the junction temperature load spectrum; Extract the initial junction temperature, the final junction temperature, and all junction temperature extreme points arranged in chronological order from the junction temperature peak-valley value time series obtained in Step 2, and use the rainflow counting method to process the junction temperature peak-valley value time series to obtain the junction temperature load spectrum; When using the rainflow counting method to obtain the junction temperature load spectrum of the IGBT power module, place the junction temperature peak-valley value time series vertically, record the abscissa as strain, corresponding to the junction temperature, and the ordinate as time; Step 4: Calculate its cycle life using the IGBT power module life model; The LESIT model can calculate the total number of cycles until failure when the IGBT module continuously operates with this junction temperature fluctuation period; the analytical expression of this model is as follows: Among them, N f is the cyclic life of the IGBT module, i.e., the total number of cycles until failure under a constant amplitude temperature load; A is a normal constant related to the operating characteristics and physical state of the device; ΔT j is the amplitude of the junction temperature fluctuation; T m is the mean value of the junction temperature cycle; α is a parameter to be fitted, obtained by fitting the module life data; Q is the activation energy related to the material; R is the Boltzmann constant; take A = 640, α = -5, R = 8.314 J·mol -1 ·K -1 , Q = 7.8×10 4 J·mol -1 ; Step 5: Improve the Manson model to calculate the cumulative damage degree of the IGBT power module under random variable amplitude loads; In order to more comprehensively reflect the physical process of fatigue accumulation, the method for calculating the cumulative damage degree D of the IGBT power module under random variable amplitude loads using the improved Manson model is: (5.1) In the case of random variable amplitude loads, associate the previous load cycle of each load cycle, and the solution formula for calculating the cumulative damage degree D of the IGBT power module using the improved Manson model is: Among them, k is order of magnitude; (5.2) According to the calculation formula of the cumulative damage degree D of the IGBT power module, the fatigue damage degree caused by one load cycle and the cumulative fatigue damage degree caused by multiple load cycles can be obtained respectively as: Among them, k is order of magnitude of.

2. The method for calculating the cumulative damage degree of the IGBT power module of an electric vehicle according to claim 1, wherein: The electric vehicle mentioned above is a pure electric vehicle, a hybrid electric vehicle, or a fuel cell vehicle.

Images