A method for calculating the junction temperature of IGBT modules considering heat sink

Abstract

The present invention relates to an IGBT junction temperature estimation method, specifically a method for calculating the junction temperature of an IGBT module taking into account a heat sink. From an engineering application perspective, the present invention uses finite element simulation results to determine the coupling of the FWD / IGBT chip in the thermal grease layer under different operating conditions for high-power converter IGBT modules with significantly varying operating conditions, and then obtains its mathematical expression. By comprehensively considering the computational resource overhead and accuracy issues of junction temperature estimation, a thermal network mathematical model is proposed that accounts for the loss coupling of the IGBT chip and FWD chip under different operating conditions. This mathematical model has a simple structure and a small amount of computation, and can achieve more accurate real-time response to dynamic changes in IGBT junction temperature in engineering applications.

Description

Technical Field

[0001] The present invention relates to an IGBT junction temperature estimation method, in particular to an IGBT module junction temperature calculation method considering a heat sink. Background Art

[0002] Insulated-gate bipolar transistor (IGBT) modules, the most commonly used power devices in power electronics systems, are currently widely used in high-speed railways, energy vehicles, and aerospace industry control. Due to the complexity of operating conditions and the cumulative effects of long-term electrothermal stress, IGBT modules are prone to failure. Research has found that among various failure factors, approximately 55% of module failures are induced by temperature. Therefore, accurately estimating the IGBT junction temperature is crucial for system reliability assessment, health management, and cycle life prediction.

[0003] An IGBT module typically contains multiple IGBT chips and multiple FWD chips. The layout of the IGBT and FWD chips, as well as the structure of the heat sink, results in varying temperatures across the IGBT and FWD chips. This uneven temperature distribution results in varying thermal stresses on each IGBT and FWD chip. IGBT and FWD chips with higher temperatures experience greater thermal stress and are often damaged first. This damage increases the electrical stress on other chips, accelerating IGBT module failure. Therefore, monitoring the maximum junction temperature of the IGBT and FWD chips within an IGBT module is crucial.

[0004] During the heat transfer process from the IGBT and FWD chips to the heat sink via the IGBT module, in addition to vertical heat transfer, lateral heat diffusion also occurs, which inevitably causes the losses generated by the IGBT and FWD chips to couple within the heat transfer path. Optical non-contact measurement methods use measuring instruments such as infrared thermal imagers to observe the IGBT junction temperature. However, the use of infrared measuring instruments is costly and requires the IGBT package module to be shelled and silicone removed, which is destructive and cannot meet real-time measurement requirements. Thermosensitive electrical parameter estimation methods use real-time measurement of thermosensitive electrical parameters to reversely estimate the IGBT junction temperature. These methods include the low-current saturation voltage drop method, the drive voltage drop difference ratio method, and the switching transient induced voltage method. For thermosensitive electrical parameters, the collected electrical signals are weak and susceptible to electromagnetic interference, requiring additional auxiliary test equipment and high costs. The finite element model estimation method is used to build a three-dimensional model of the IGBT module and heat sink, and the finite element simulation method is used to obtain the junction temperature. The finite element simulation method takes a long time to build the three-dimensional model of the IGBT module and cooling system with complex structures. For long-term power consumption loads, it consumes a lot of computing time and cost, and the simulation efficiency is not high. Summary of the Invention

[0005] The present invention aims to improve the efficiency and accuracy of IGBT module junction temperature calculation and solves the following problems from the perspective of practical engineering application: (1) constructing an improved IGBT module thermal network model considering thermal coupling; (2) revealing the coupling law between IGBT chip loss and FWD chip loss under different working conditions; (3) providing an IGBT module + thermal grease + heat sink structure, extracting thermal network model parameters through finite element simulation, and realizing the dynamic response calculation of the maximum junction temperature of IGBT chip and FWD chip in the IGBT module.

[0006] The present invention is implemented by adopting the following technical solutions: a method for calculating the junction temperature of an IGBT module considering the heat sink, building a thermal network model of the maximum junction temperature of the IGBT chip and the FWD chip, and according to the thermal network model, the junction temperature T j_igbt The calculation formula is as follows:

[0007] T j_igbt =ΔT jc_igbt +ΔT grease_igbt +ΔT plate_igbt +T a ,

[0008] Among them, T j_igbt : Maximum junction temperature of IGBT chip; ΔT jc_igbt : The temperature rise from the junction to the case of the IGBT chip with the highest junction temperature; ΔT grease_igbt : The temperature rise of the thermal grease layer corresponding to the IGBT chip with the highest junction temperature; ΔT plate_igbt : The temperature rise of the heat sink corresponding to the IGBT chip with the highest junction temperature; T a : Radiator cooling medium inlet temperature;

[0009] FWD chip junction temperature T j_fwd The calculation formula is as follows:

[0010] T j_fwd =ΔT jc_fwd +ΔT grease_fwd +ΔT plate_fwd +T a ,

[0011] Where: T j_fwd : Maximum junction temperature of the FWD chip, ΔT jc_fwd : Maximum junction temperature FWD chip junction to case temperature rise, ΔT grease_fwd : The temperature rise of the thermal grease layer corresponding to the FWD chip with the highest junction temperature, ΔT plate_fwd : The FWD chip with the highest junction temperature corresponds to the radiator temperature rise.

[0012] The above-mentioned method for calculating the junction temperature of the IGBT module considering the heat sink is as follows:

[0013]

[0014]

[0015]

[0016] Among them, R igbt 、C igbt : Thermal resistance and thermal capacitance calculated based on the temperature difference between the maximum junction temperature of the IGBT chip and its corresponding vertical case temperature;

[0017] R grease_igbt 、C grease_igbt : Thermal resistance and thermal capacitance calculated based on the vertical temperature difference of the thermal grease layer corresponding to the maximum junction temperature of the IGBT chip;

[0018] R plate_igbt 、C plate_igbt : Thermal resistance and heat capacity calculated based on the temperature difference between the heat sink surface temperature at the point with the maximum junction temperature of the IGBT chip and the inlet temperature of the cold zone medium;

[0019] P igbt : IGBT chip power loss;

[0020] P fwd : FWD chip power loss;

[0021] P′ fwd : Thermal grease layer, FWD chip loss coupled to the partial loss of the IGBT chip heat transfer path;

[0022] k fwd : The coefficient of the loss generated on the FWD coupled to the IGBT heat transfer path by the thermal grease layer.

[0023] The above-mentioned method for calculating the junction temperature of the IGBT module considering the heat sink is as follows:

[0024]

[0025]

[0026]

[0027] R fwd 、C fwd : Thermal resistance and thermal capacitance calculated based on the temperature difference between the maximum junction temperature of the FWD chip and its corresponding vertical case temperature;

[0028] R grease_fwd 、C grease_fwd : Thermal resistance and thermal capacitance calculated based on the vertical temperature difference of the thermal grease layer corresponding to the maximum junction temperature of the FWD chip;

[0029] R plate_fwd、C plate_fwd : Thermal resistance and heat capacity calculated based on the temperature difference between the heat sink surface temperature at the maximum junction temperature of the FWD chip and the inlet temperature of the cold zone medium;

[0030] P′ igbt : Thermal grease layer, IGBT chip loss coupled to the heat transfer path of the FWD chip;

[0031] k igbt : The coefficient of the loss generated on the IGBT in the heat transfer path coupled from the thermal grease layer to the FWD.

[0032] The above-mentioned method for calculating the junction temperature of the IGBT module considering the heat sink performs steady-state simulation according to different loss settings and extracts the thermal resistance R of the thermal grease layer. grease_igbt and R grease_fwd and coupling coefficient k igbt and k fwd .

[0033] The above-mentioned method for calculating the junction temperature of the IGBT module considering the heat sink is to give the rated loss input, perform transient simulation, extract the temperature at different points, and calculate the parameter R according to the dynamic calculation formula of the thermal network model. igbt and C igbt 、R fwd and C fwd 、C grease_igbt 、C grease_fwd 、R plate_igbt and C plate_igbt 、R plate_fwd and C plate_fwd Identification.

[0034] The above-mentioned method for calculating the junction temperature of an IGBT module taking into account a heat sink considers a three-layer structure in the thermal network model, namely, the IGBT module, thermal grease, and heat sink. In the IGBT module, there is no coupling of losses generated between the IGBT chip and the FWD chip. In the thermal grease layer, the losses generated between the IGBT chip and the FWD chip are partially coupled. The losses generated between the IGBT chip and the FWD chip are fully coupled after being transferred to the heat sink.

[0035] The above-mentioned method for calculating the junction temperature of an IGBT module taking the heat sink into consideration calculates coupling-related parameters through steady-state simulation data using Icepak or Fluent finite element simulation software.

[0036] The above-mentioned method for calculating the junction temperature of an IGBT module taking the heat sink into consideration calculates the thermal resistance and thermal capacitance parameters through transient simulation data using Icepak or Fluent finite element simulation software.

[0037] From an engineering application perspective, this paper examines the coupling between the FWD / IGBT chip and the thermal grease layer under varying operating conditions in high-power converter IGBT modules, using finite element simulation results. This analysis then provides a mathematical representation of the coupling. By comprehensively considering the computational overhead and accuracy of junction temperature estimation, a thermal network mathematical model is developed that accounts for the loss coupling between the IGBT and FWD chips under varying operating conditions. This model, with its simple structure and minimal computational effort, enables more accurate, real-time response to dynamic changes in IGBT junction temperature in engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is the thermal network model of IGBT module.

[0039] Figure 2 Enter the curve for dynamic loss.

[0040] Figure 3 Junction temperature curve calculated for the thermal network model. DETAILED DESCRIPTION

[0041] 1. The present invention proposes Figure 1 The thermal network model for calculating the maximum junction temperature of the IGBT and FWD chips in the structure shown. This thermal network considers a three-layer structure: the IGBT module, thermal grease, and heat sink. In the IGBT module, there is no coupling between the losses generated by the IGBT and FWD chips. In the thermal grease layer, the losses generated by the IGBT and FWD chips are partially coupled. After the losses are transferred to the heat sink, they are fully coupled.

[0042] Figure 1 In , the loss input is defined as follows:

[0043] P igbt : IGBT chip power loss

[0044] P fwd : FWD chip power loss

[0045] P′ fwd :The thermal grease layer, FWD chip loss coupled to the IGBT chip heat transfer path loss

[0046] P″ fwd : The heat sink FWD chip loss is coupled to the IGBT chip, and there is P fwd =P′ fwd +P″ fwd

[0047] P′ igbt :The thermal grease layer, IGBT chip loss coupled to the FWD chip heat transfer path loss

[0048] P″ igbt : The heat sink IGBT chip loss is coupled to the FWD chip, and there is P igbt =P′ igbt +P″ igbt Figure 1 In the figure, the thermal resistance and thermal capacitance parameters are defined as follows:

[0049] R igbt 、C igbt : Thermal resistance and heat capacity calculated based on the temperature difference between the maximum junction temperature of the IGBT chip and its corresponding vertical case temperature;

[0050] R grease_igbt 、C grease_igbt : Thermal resistance and heat capacity calculated based on the vertical temperature difference of the thermal grease layer corresponding to the maximum junction temperature of the IGBT chip;

[0051] R plate_igbt 、C plate_igbt : Thermal resistance and heat capacity calculated based on the temperature difference between the heat sink surface temperature at the point with the maximum junction temperature of the IGBT chip and the inlet temperature of the cold zone medium;

[0052] R fwd 、C fwd : Thermal resistance and heat capacity calculated by the temperature difference between the maximum junction temperature of the FWD chip and its corresponding vertical case temperature;

[0053] R grease_fwd 、C grease_fwd : Thermal resistance and heat capacity calculated based on the vertical temperature difference of the thermal grease layer corresponding to the maximum junction temperature of the FWD chip;

[0054] R plate_fwd 、C plate_fwd : Thermal resistance and heat capacity calculated based on the temperature difference between the heat sink surface temperature at the maximum junction temperature of the FWD chip and the inlet temperature of the cold zone medium.

[0055] According to the above thermal network model, the IGBT module chip junction temperature T j The calculation is determined by the following relationship.

[0056] y=f(△T jc ,△T grease ,△T plate ,T a ) (1)

[0057] For the IGBT chip junction temperature T j_igbt The specific formula is as follows:

[0058] T j_igbt =ΔT jc_igbt +ΔT grease_igbt +ΔT plate_igbt +Ta (2)

[0059] in:

[0060] T j_igbt : Maximum junction temperature of IGBT chip

[0061] ΔT jc_igbt : Maximum junction temperature IGBT chip junction to case temperature rise

[0062] ΔT grease_igbt : The temperature rise of the thermal grease layer corresponding to the IGBT chip with the highest junction temperature

[0063] ΔT plate_igbt : The temperature rise of the radiator corresponding to the highest junction temperature of the IGBT chip

[0064] T a : Radiator cooling medium inlet temperature

[0065]

[0066]

[0067]

[0068] For the FWD chip junction temperature T j_fwd The specific formula is as follows:

[0069] T j_fwd =ΔT jc_fwd +ΔT grease_fwd +ΔT plate_fwd +T a (6)

[0070] in:

[0071] T j_fwd : Maximum junction temperature of FWD chip

[0072] ΔT jc_fwd : Maximum junction temperature FWD chip junction to case temperature rise

[0073] ΔT grease_fwd : The temperature rise of the thermal grease layer corresponding to the FWD chip with the highest junction temperature

[0074] ΔT plate_fwd : The FWD chip with the highest junction temperature corresponds to the radiator temperature rise

[0075] T a : Radiator cooling medium inlet temperature

[0076]

[0077]

[0078]

[0079] 2. Obtain the coupling law of the thermal grease layer under different working conditions.

[0080] A detailed finite element model of the multilayer structure of the IGBT module, including a heat sink, was established. In engineering applications, IGBT and FWD chip losses are typically caused by two factors: large fluctuations in load current and changes in the modulation scheme. Large changes in load current typically cause increases or decreases in IGBT and FWD chip losses, while changes in the modulation scheme can cause changes in the loss distribution ratio between the IGBT and FWD chips. Therefore, the loss changes caused by changes in operating conditions such as load and modulation scheme are organized into the following finite element simulation loss prediction method:

[0081] IGBT loss given P igbt_g : Rated P igbt_e , 0.8P igbt_e , 0.6P igbt_e , 0.4P igbt_e , 0.2P igbt_e

[0082] FWD loss given by P fwd_g :0.05P igbt_g , 0.1P igbt_g , 0.2P igbt_g , 0.4P igbt_g , 0.6P igbt_g , 0.8P igbt_g 、P igbt_g .

[0083] Among them, P igbt_e For the rated loss of IGBT, for each IGBT given loss, different proportions of FWD loss are selected to simulate the changes in the value and proportion of the IGBT and FWD losses under all operating conditions.

[0084] For the above-mentioned losses of various IGBT and FWD combinations, steady-state simulation calculations are performed using finite element simulation software such as Icepak or Fluent to obtain the temperature difference ΔT corresponding to the thermal grease layer in the vertical direction at the maximum junction temperature of the IGBT chip and the FWD chip. grease_igbt and △T grease_fwd .

[0085] P igbt 、P fwd Loss and △T grease_igbt and △T grease_fwdAs is known, equations (10) and (11) are used as the calculation formulas for the steady-state junction temperature considering coupling, and the least squares method is used to identify the coupling coefficients k of the IGBT and FWD chips in the thermal grease layer respectively. igbt and k fwd and thermal resistance R grease_igbt and R grease_fwd .

[0086]

[0087]

[0088] 3. Thermal Network Model Parameter Acquisition

[0089] The second step completes the calculation of the steady-state thermal resistance of the thermal grease coupling layer. This step explains the extraction of other parameters.

[0090] Establish a detailed finite element model of the multilayer structure of the IGBT module with a heat sink structure, set the IGBT chip and FWD chip losses to rated values, perform transient simulation calculations using finite element simulation software such as Icepak or Fluent, and obtain the temperature difference ΔT corresponding to the thermal grease layer in the vertical direction at the maximum junction temperature of the IGBT chip and FWD chip. jc_igbt and △T jc_fwd , △T grease_igbt and △T grease_fwd , △T plate_igbt and △T plate_fwd Time series, use equations (3), (7), (4), (8), (5), and (9) to identify parameters and obtain R igbt and C igbt 、R fwd and C fwd 、C grease_igbt 、C grease_fwd 、R plate_igbt and C plate_igbt 、R plate_fwd and C plate_fwd .

[0091] Example 1

[0092] (1) Build an IGBT module + thermal grease + water-cooled baseplate model in ANSYS;

[0093] (2) Perform steady-state simulation according to different loss settings to extract the thermal resistance and coupling coefficient of the thermal grease layer;

[0094] (3) Given the rated loss input, perform transient simulation, extract the temperature at different points, and perform parameter identification according to the dynamic calculation formula of the thermal network model;

[0095] (4) Build Figure 1The thermal network model shown in Figure 1 sets the parameters obtained in steps (2) and (3) and gives the loss as Figure 2 As shown, the junction temperature of IGBT and FWD is calculated as Figure 3 shown.

Claims

1. A method for calculating the junction temperature of an IGBT module taking into account a heat sink, characterized by: Build a thermal network model of the maximum junction temperature of the IGBT chip and FWD chip. According to the thermal network model, the junction temperature of the IGBT chip T j_igbt The calculation formula is as follows: j_igbt =ΔT jc_igbt +ΔT grease_igbt +ΔT plate_igbt +T a , where T j_igbt : Maximum junction temperature of IGBT chip; ΔT jc_igbt : The temperature rise from the junction to the case of the IGBT chip with the highest junction temperature; ΔT grease_igbt : The temperature rise of the thermal grease layer corresponding to the IGBT chip with the highest junction temperature; ΔT plate_igbt : The temperature rise of the heat sink corresponding to the IGBT chip with the highest junction temperature; T a : Radiator cooling medium inlet temperature; Among them, R igbt 、C igbt : Thermal resistance and thermal capacitance calculated based on the temperature difference between the maximum junction temperature of the IGBT chip and its corresponding vertical case temperature; R grease_igbt 、C grease_igbt : Thermal resistance and thermal capacitance calculated based on the vertical temperature difference of the thermal grease layer corresponding to the maximum junction temperature of the IGBT chip; R plate_igbt 、C plate_igbt : Thermal resistance and heat capacity calculated based on the temperature difference between the heat sink surface temperature at the point with the maximum junction temperature of the IGBT chip and the inlet temperature of the cold zone medium; P igbt : IGBT chip power loss; P fwd : FWD chip power loss; P′ fwd : Thermal grease layer, FWD chip loss coupled to the partial loss of the IGBT chip heat transfer path; k fwd : The coefficient of the loss generated on the FWD coupled to the IGBT heat transfer path by the thermal grease layer; FWD chip junction temperature T j_fwd The calculation formula is as follows: T j_fwd =ΔT jc_fwd +ΔT grease_fwd +ΔT plate_fwd +T a , where: T j_fwd : Maximum junction temperature of the FWD chip, ΔT jc_fwd : Maximum junction temperature FWD chip junction to case temperature rise, ΔT grease_fwd : The temperature rise of the thermal grease layer corresponding to the FWD chip with the highest junction temperature, ΔT plate_fwd : The temperature rise of the heat sink corresponding to the FWD chip with the highest junction temperature; R fwd 、C fwd : Thermal resistance and thermal capacitance calculated based on the temperature difference between the maximum junction temperature of the FWD chip and its corresponding vertical case temperature; R grease_fwd 、C grease_fwd : Thermal resistance and thermal capacitance calculated based on the vertical temperature difference of the thermal grease layer corresponding to the maximum junction temperature of the FWD chip; R plate_fwd 、C plate_fwd : Thermal resistance and heat capacity calculated based on the temperature difference between the heat sink surface temperature at the maximum junction temperature of the FWD chip and the inlet temperature of the cold zone medium; P′ igbt : Thermal grease layer, IGBT chip loss coupled to the heat transfer path of the FWD chip; k igbt : The coefficient of the loss generated on the IGBT coupled to the heat transfer path of the thermal grease layer to the FWD; According to different loss settings, steady-state simulation is performed to extract the thermal resistance R of the thermal grease layer. grease_igbt and R grease_fwd and coupling coefficient k igbt and k fwd Given the rated loss input, perform transient simulation, extract the temperature at different points, and calculate the parameter R according to the dynamic calculation formula of the thermal network model. igbt and C igbt 、R fwd and C fwd 、C grease_igbt 、C grease_fwd 、R plate_igbt and C plate_igbt 、R plate_fwd and C plate_fwd Identification.

2. The method for calculating the junction temperature of an IGBT module considering a heat sink according to claim 1, wherein: This thermal network model considers a three-layer structure: IGBT module, thermal grease, and heat sink. On the IGBT module, there is no coupling of losses between the IGBT chip and the FWD chip. In the thermal grease layer, the losses between the IGBT chip and the FWD chip are partially coupled. The losses between the IGBT chip and the FWD chip are fully coupled after being transferred to the heat sink.

3. The method for calculating the junction temperature of an IGBT module considering a heat sink according to claim 2, wherein: The coupling-related parameters are calculated using steady-state simulation data from Icepak or Fluent finite element simulation software.

4. The method for calculating the junction temperature of an IGBT module considering a heat sink according to claim 2, wherein: Calculate thermal resistance and heat capacity parameters using transient simulation data using Icepak or Fluent finite element simulation software.

Images