A method for predicting junction temperature based on turn-off loss of SiC MOSFETs

Abstract

This invention discloses a method for predicting junction temperature based on turn-off loss of SiC MOSFETs, belonging to the fields of power electronics and electrical engineering. The method combines a turn-off loss model with a junction temperature prediction model based on turn-off loss, and includes the following steps: First, a SiC MOSFET turn-off loss model considering parasitic parameters is established; second, a junction temperature prediction model based on SiC MOSFET turn-off loss is established offline; third, the turn-off loss is calculated online according to the loss model; and finally, the loss data is substituted into the junction temperature prediction model to obtain the predicted junction temperature value. This invention can predict the turn-off loss and junction temperature of SiC MOSFETs under different operating conditions, and has advantages such as strong real-time performance, ease of implementation, and high model accuracy; it provides an efficient and accurate solution for the thermal evaluation and junction temperature prediction of silicon carbide power devices.

Description

Technical Field

[0001] This invention relates to the fields of power electronics and electrical engineering, and in particular to a method for predicting the junction temperature of a SiC MOSFET. Background Technology

[0002] In power electronic systems, approximately 31% of failures are caused by power device malfunctions, and about 60% of these power device failures are temperature-related. Although SiC materials possess superior thermal properties, the limitations of traditional packaging heat dissipation and the high thermal conductivity of SiC forces SiC MOSFETs to withstand greater thermal stress during operation. Excessive thermal stress can lead to the detachment of internal bond wires and the cracking of the solder layer within the SiC MOSFET, ultimately causing the entire module to fail. Junction temperature is a key characteristic of the thermal performance of SiC MOSFETs, and its prediction is a prerequisite for SiC MOSFET thermal management, condition monitoring, and lifetime prediction. Therefore, researching accurate methods for estimating SiC MOSFET junction temperature is crucial, and accurate prediction and extraction of junction temperature is a key technical challenge that needs to be overcome in the application of SiC MOSFET devices.

[0003] Junction temperature measurement methods can be broadly categorized into four main types: physical contact methods, optical methods, thermal network methods, and temperature-sensitive electrical parameter methods. While physical contact and optical methods are simple to implement, they both require damaging or altering the packaging structure to create a measurement channel, making them highly invasive. Furthermore, in terms of response speed, physical contact methods are limited by the presence of thermal capacitance in the contact layer, optical methods require corresponding optical processing, and thermal network methods require complex model calculations, all of which are subject to significant limitations. In contrast, the temperature-sensitive electrical parameter method utilizes the device itself as a temperature sensor, establishing a relationship between internal electrical parameters and the chip junction temperature. This method obtains the junction temperature by measuring the electrical parameters, without altering the module packaging structure and boasts a fast response time. It offers advantages such as simple principle, rapid response, online measurement, and non-destructive device packaging, making it considered the most promising junction temperature measurement method.

[0004] Using temperature-sensitive electrical parameters to predict the junction temperature of SiC MOSFETs has several drawbacks, including the small values ​​of some electrical parameters, low temperature sensitivity, and susceptibility to parasitic circuit parameters, leading to errors in junction temperature estimation. Therefore, selecting appropriate temperature-sensitive electrical parameters for accurate junction temperature detection is crucial for SiC MOSFETs.

[0005] This patent addresses the problems of current junction temperature prediction methods based on turn-off losses, such as the difficulty in achieving online detection and low model accuracy. It establishes a SiC MOSFET turn-off loss model that considers nonlinear parasitic parameters and proposes a junction temperature prediction method based on SiC MOSFET turn-off losses. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes a method that combines a turn-off loss model with a junction temperature prediction model based on turn-off loss, effectively solving the problems of difficulty in achieving online detection and low model accuracy in current junction temperature prediction methods based on turn-off loss.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for predicting junction temperature based on turn-off loss of SiC MOSFETs includes the following steps:

[0009] Step S1: Establish an equivalent circuit model of SiC MOSFET considering parasitic parameters. By analyzing and modeling the turn-off transient process, obtain the state equations for each stage of the turn-off process, and then establish a turn-off loss model of SiC MOSFET considering parasitic parameters.

[0010] Step S2: Perform an offline calibration procedure to obtain the mapping relationship between the selected SiC MOSFET turn-off loss and the known junction temperature offline, and establish a junction temperature prediction model based on the SiC MOSFET turn-off loss.

[0011] Step S3: Perform numerical solution. Input the initial values ​​of each state variable into the calculation tool, and then complete the solution within the solution cycle to obtain the values ​​of each state variable. Update the parameters in the state equation based on these calculated values. Repeat this process until the relevant boundary conditions are met, and then proceed to the next state equation. The data from each calculation is saved, and the turn-off loss can be obtained through numerical calculation.

[0012] Step S4: Simulate different operating conditions of the power device by adjusting the initial values ​​of the state variables in step S3, substitute the SiC MOSFET turn-off loss calculation results into the junction temperature prediction model based on SiC MOSFET turn-off loss established in step S2, and calculate the junction temperature value according to the mapping relationship between turn-off loss, junction temperature and operating conditions.

[0013] Furthermore, in step S1, an equivalent circuit model of SiC MOSFET considering parasitic parameters is established, and the state equations for each stage of the turn-off transient process are obtained by analyzing and modeling the turn-off process: state equation group A1 for the turn-off delay stage, state equation group A2 for the voltage rise stage, state equation group A3 for the current fall stage, and state equation group A4 for the turn-off oscillation stage.

[0014] The state equation set A1 for the turn-off delay stage is as follows:

[0015]

[0016] The state equations A2 for the voltage rise phase are as follows:

[0017]

[0018] The state equations A3 for the current-decreasing phase are as follows:

[0019]

[0020] The state equations A4 for the turn-off oscillation phase are as follows:

[0021]

[0022] Among them, v GS This refers to the gate-source voltage of the SiC MOSFET, v. DS i is the drain-source voltage. D V is the drain current. DRV To drive positive pressure, V DC As an ideal voltage source equivalent to the DC bus, V TH For the threshold voltage, g fs For transconductance; I L As an ideal current source equivalent to the load inductance, C J The equivalent junction capacitance of SiC SBD; C ISS C OSS C RSS These are the input capacitance, output capacitance, and transfer capacitance of the SiC MOSFET, respectively; R G L is the gate drive resistor of the SiC MOSFET. G L D L S These are the gate, drain, and source parasitic inductances of a SiC MOSFET, respectively; L loop For stray inductance, R loop For stray resistance;

[0023] Based on the state equations A1 for the turn-off delay stage, A2 for the voltage rise stage, A3 for the current fall stage, and A4 for the turn-off oscillation stage, a SiC MOSFET turn-off loss model considering parasitic parameters is established:

[0024]

[0025] Among them, E off To reduce the shutdown loss, R G C is the gate drive resistor of the SiC MOSFET. GD For gate-drain parasitic capacitance, I L V is the inductor current. DC V is the bus voltage. DS(ON) For the on-state voltage drop, VDRV To drive positive pressure, V TH For the threshold voltage, C ISS g is the input capacitance of the SiC MOSFET. fs For transconductance, L S This refers to the parasitic inductance of the SiC MOSFET source. Further, the process of establishing the junction temperature prediction model based on the turn-off loss of the SiC MOSFET in step S2 is as follows:

[0026] Step S21: By building a dual-pulse test platform, set the junction temperature T of the SiC MOSFET. j And operating conditions: bus voltage V DC Inductor current I L ;

[0027] Step S22: Test the turn-off loss of the SiC MOSFET under different junction temperatures and operating conditions, and plot the turn-off loss versus junction temperature T. j A diagram showing the relationship between operating conditions;

[0028] Step S23: Adjust turn-off losses and junction temperature T j The relationship between the turn-off loss and the junction temperature T is decoupled and fitted to obtain the relationship between the turn-off loss and the junction temperature T. j The mapping relationship between the operating conditions and the junction temperature is the junction temperature prediction model based on the turn-off loss of SiC MOSFETs:

[0029] T j =αE off +βI L +δ

[0030] Where α, β, and δ are constant values ​​obtained from the fitting, and E off To shut down losses, I L This represents the inductor current value.

[0031] Furthermore, in step S3, based on the state equations for each stage of the shutdown process, the initial values ​​of each state variable are input into the calculation tool, and the time step is set:

[0032] Step S31: First, calculate sub-period 1, solve the state equation system A1 for the turn-off delay stage, and after a single time step, determine whether the boundary condition v is satisfied. GS <V p , where v GS V is the gate-source voltage. p The Miller plateau voltage is defined as the duration of this stage as t1-t0. If the boundary condition is met, the drain-source voltage, gate-source voltage, drain current, and duration parameters calculated for this time period are stored, and sub-cycle 2 is calculated. If the condition is not met, a single time step is run again.

[0033] Step S32: After satisfying the boundary conditions of sub-period 1, begin calculating sub-period 2, solve the state equation system A2 for the voltage rise stage, and define the duration of this stage as t2-t1, while satisfying the boundary condition v D <-V F Then store the solution data for this stage and begin calculating sub-cycle 3;

[0034] Step S33: After satisfying the boundary conditions for sub-period 2, begin calculating sub-period 3, solving the state equation system A3 for the current decrease stage. Define the duration of this stage as t3-t2, and satisfy the boundary condition v. GS <V TH Then store the solution data for this stage and begin calculating sub-cycle 4;

[0035] Step S34: After satisfying the boundary conditions of sub-period 3, start calculating sub-period 4, solve the state equation set A4 for the turn-off oscillation stage, define the duration of sub-period 4 as t4-t3, and store the solution data for this stage after running a single time step.

[0036] Step S35: The data from each calculation is saved, and the turn-off loss can be obtained through numerical calculation. The formula for calculating the turn-off loss using the integral method is:

[0037]

[0038] Furthermore, step S4 simulates different operating conditions of the power device by adjusting the initial value of the state variable in step S3, and obtains the data and turn-off loss of each stage through calculation tools.

[0039] Substitute the SiC MOSFET turn-off loss calculation result into the junction temperature prediction model based on SiC MOSFET turn-off loss established in step S2, and calculate the junction temperature value according to the mapping relationship between turn-off loss, junction temperature and operating conditions.

[0040] Furthermore, the state variables mentioned in step S3 include drain-source voltage, drain current, and duration.

[0041] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0042] (1) This invention proposes a method that combines a turn-off loss model with a junction temperature prediction model based on turn-off loss, and achieves accurate prediction of the junction temperature of SiC MOSFET through numerical calculation. An equivalent circuit model of SiC MOSFET considering parasitic parameters is established. When analyzing the turn-off process and establishing the state equations for each stage, the influence of nonlinear parasitic parameters is fully considered to closely approximate the actual circuit and improve the accuracy of the model's prediction.

[0043] (2) To address the current difficulty in online detection of turn-off losses of SiC MOSFETs, this method does not require complex drain-source voltage and drain current detection and extraction steps. By substituting the circuit operating conditions into the calculation tool, the turn-off losses can be accurately and quickly calculated. Attached Figure Description

[0044] Figure 1 This is a framework diagram of a junction temperature prediction method based on SiC MOSFET turn-off loss in this invention.

[0045] Figure 2 This is the equivalent circuit diagram of a SiC MOSFET double-pulse circuit considering nonlinear parasitic parameters in this invention;

[0046] Figure 3 This is a flowchart of the junction temperature prediction model based on SiC MOSFET turn-off loss in this invention.

[0047] Figure 4 This is a flowchart of solving the state equations for the shutdown process in this invention;

[0048] Figure 5 This is a diagram illustrating the overall framework of the junction temperature prediction method based on the SiC MOSFET turn-off loss model in this invention.

[0049] Figure 6 This is a simulation result of the turn-off loss varying with junction temperature in this invention using a two-pulse method. Detailed Implementation

[0050] The following detailed description of some key technologies involved in this invention, in conjunction with the accompanying drawings, supports the claims. To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0051] Figure 1 This is a framework diagram of a junction temperature prediction method based on SiC MOSFET turn-off loss, including the following steps:

[0052] Step S1: Establish an equivalent circuit model of SiC MOSFET considering parasitic parameters. By analyzing and modeling the turn-off transient process, obtain the state equations for each stage of the turn-off process, and then establish a turn-off loss model of SiC MOSFET considering parasitic parameters.

[0053] Step S2: Perform an offline calibration procedure to obtain the mapping relationship between the selected SiC MOSFET turn-off loss and the known junction temperature offline, and establish a junction temperature prediction model based on the SiC MOSFET turn-off loss.

[0054] Step S3: Perform numerical solution. Input the initial values ​​of each state variable into the calculation tool, and then complete the solution within the solution cycle to obtain the values ​​of each state variable. Update the parameters in the state equation based on these calculated values. Repeat this process until the relevant boundary conditions are met, and then proceed to the next state equation. The data from each calculation is saved, and the turn-off loss can be obtained through numerical calculation.

[0055] Step S4: Simulate different operating conditions of the power device by adjusting the initial values ​​of the state variables in step S3, substitute the SiC MOSFET turn-off loss calculation results into the junction temperature prediction model based on SiC MOSFET turn-off loss established in step S2, and calculate the junction temperature value according to the mapping relationship between turn-off loss, junction temperature and operating conditions.

[0056] Figure 2 This is the equivalent circuit diagram of a SiC MOSFET double-pulse circuit considering nonlinear parasitic parameters, where V DC It is an ideal voltage source equivalent to the DC bus; I L As an ideal current source equivalent to the load inductance, C L For load inductance and parasitic capacitance; D H For ideal SiCSBD, C J The equivalent junction capacitance of SiC SBD; C GS C GD C DS These are the gate-source capacitance, gate-drain capacitance, and drain-source capacitance of the SiC MOSFET; L D(int) L S(int) These are the drain and source parasitic inductances introduced into the SiC MOSFET package, respectively; R G(int) R is the gate resistance of the SiC MOSFET. G(ext) For external drive resistor; L G For the parasitic inductance of the gate circuit; L D(ext) and R loop These are the equivalent parasitic inductance and stray resistance of the line between the positive terminal of the DC bus and the drain of the SiC MOSFET, respectively; L S(ext) This represents the parasitic inductance of the line between the source and ground of the SiC MOSFET. D For drain current, i G For gate current, i GS i GD and i DS C GS C GD and C DS displacement current, i CH I is the channel current of the SiC MOSFET. L This is the load current.

[0057] Furthermore, in step S1, an equivalent circuit model of SiC MOSFET considering parasitic parameters is established, and the state equations for each stage of the turn-off transient process are obtained by analyzing and modeling the turn-off process: state equation group A1 for the turn-off delay stage, state equation group A2 for the voltage rise stage, state equation group A3 for the current fall stage, and state equation group A4 for the turn-off oscillation stage.

[0058] State equations A1 for the turn-off delay phase:

[0059]

[0060] State equation set A2 for the voltage rise phase:

[0061]

[0062] State equations A3 for the current-decreasing phase:

[0063]

[0064] State equations A4 for the off-oscillation phase:

[0065]

[0066] By analyzing and modeling the turn-off transient process, mathematical expressions and state equations for each stage of the turn-off process are obtained, and a SiC MOSFET turn-off loss model considering parasitic parameters is then established.

[0067]

[0068] Among them, E off To reduce the shutdown loss, R G C is the gate drive resistor of the SiC MOSFET. GD For gate-drain parasitic capacitance, I L V is the inductor current. DC V is the bus voltage. DS(ON) For the on-state voltage drop, V DRV To drive positive pressure, V TH For the threshold voltage, C ISS g is the input capacitance of the SiC MOSFET. fs For transconductance, L S This is the source parasitic inductance of a SiC MOSFET.

[0069] Furthermore, such as Figure 3 As shown, the process of establishing the junction temperature prediction model based on SiC MOSFET turn-off loss in step S2 is as follows:

[0070] Step S21: By building a dual-pulse test platform, set the junction temperature T of the SiC MOSFET. j and operating conditions;

[0071] Step S22: Test the turn-off loss of the SiC MOSFET under different junction temperatures and operating conditions, and plot the turn-off loss versus junction temperature T. j A diagram showing the relationship between operating conditions;

[0072] Step S23: Adjust turn-off losses and junction temperature T j The relationship between the turn-off loss and the junction temperature T is decoupled and fitted to obtain the relationship between the turn-off loss and the junction temperature T. j The mapping relationship between the operating conditions and the junction temperature is the junction temperature prediction model based on the turn-off loss of SiC MOSFETs:

[0073] T j =αE off +βI L +δ

[0074] Where α, β, and δ are constant values ​​obtained from the fitting, and E off To shut down losses, I L This represents the inductor current value.

[0075] Furthermore, Figure 4 This is a flowchart for solving the state equations of the shutdown process. In step S3, based on the state equations of each stage of the shutdown process, the initial values ​​of each state variable are input into the calculation tool, and the time step is set.

[0076] Step S31: First, calculate sub-period 1, solve the state equation system A1 for the turn-off delay stage, and after a single time step, determine whether the boundary condition v is satisfied. GS <V p , where v GS V is the gate-source voltage. p The Miller plateau voltage is defined as the duration of this stage as t1-t0. If the boundary condition is met, the drain-source voltage, gate-source voltage, drain current, and duration parameters calculated for this time period are stored, and sub-cycle 2 is calculated. If the condition is not met, a single time step is run again.

[0077] Step S32: After satisfying the boundary conditions of sub-period 1, begin calculating sub-period 2, solve the state equation system A2 for the voltage rise stage, and define the duration of this stage as t2-t1, while satisfying the boundary condition v D <-V F Then store the solution data for this stage and begin calculating sub-cycle 3;

[0078] Step S33: After satisfying the boundary conditions for sub-period 2, begin calculating sub-period 3, solving the state equation system A3 for the current decrease stage. Define the duration of this stage as t3-t2, and satisfy the boundary condition v. GS <V TH Then store the solution data for this stage and begin calculating sub-cycle 4;

[0079] Step S34: After satisfying the boundary conditions of sub-period 3, start calculating sub-period 4, solve the state equation set A4 for the turn-off oscillation stage, define the duration of sub-period 4 as t4-t3, and store the solution data for this stage after running a single time step.

[0080] Step S35: The data from each calculation is saved, and the turn-off loss can be obtained through numerical calculation. The formula for calculating the turn-off loss using the integral method is:

[0081]

[0082] Figure 5 This is a general framework diagram of the junction temperature prediction method based on SiC MOSFET turn-off loss. The method obtains the correspondence between the selected SiC MOSFET turn-off loss and the known junction temperature offline, and uses this offline curve as a reference in the next temperature measurement procedure. The initial values ​​of the state variables are adjusted to simulate different operating conditions of the power device, and data and turn-off losses at each stage are obtained using calculation tools. The SiC MOSFET turn-off loss calculation results are substituted into the junction temperature prediction model based on turn-off loss, and the junction temperature value is calculated according to the mapping relationship between turn-off loss, junction temperature, and operating conditions.

[0083] Simulations were performed on a SiC MOSFET dual-pulse circuit considering nonlinear parasitic parameters. Figure 6 This is a simulation result of the turn-off loss changing with junction temperature using a two-pulse method. The simulation results show that as the junction temperature increases, the turn-off loss of the SiC MOSFET gradually increases, exhibiting good linearity. Selecting turn-off loss as a temperature-sensitive parameter effectively reflects changes in junction temperature. Further analysis of the relationship between turn-off loss and junction temperature T... j The relationship between turn-off loss and junction temperature T under operating conditions was decoupled and fitted to obtain the relationship between turn-off loss and junction temperature T. j The mapping relationship between turn-off loss and operating conditions is the junction temperature prediction model based on SiC MOSFET turn-off loss. This junction temperature prediction model is used as a reference in the next temperature measurement procedure. Then, the data and turn-off loss of each stage are obtained by solving the state equations. The SiC MOSFET turn-off loss calculation results are substituted into the junction temperature prediction model based on turn-off loss, and the junction temperature value is calculated according to the mapping relationship between turn-off loss, junction temperature and operating conditions.

[0084] The above embodiments are merely illustrative of the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solutions based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A method for predicting junction temperature based on turn-off loss of SiC MOSFETs, characterized in that, Includes the following steps: Step S1: Establish an equivalent circuit model of SiC MOSFET considering parasitic parameters. By analyzing and modeling the turn-off transient process, obtain the state equations for each stage of the turn-off process, and then establish a turn-off loss model of SiC MOSFET considering parasitic parameters. Step S2: Perform an offline calibration procedure to obtain the mapping relationship between the selected SiC MOSFET turn-off loss and the known junction temperature offline, and establish a junction temperature prediction model based on the SiC MOSFET turn-off loss. Step S3: Perform numerical solution. Input the initial values ​​of each state variable into the calculation tool, and then complete the solution within the solution cycle to obtain the values ​​of each state variable. Update the parameters in the state equation based on these calculated values. Repeat this process until the relevant boundary conditions are met, and then proceed to the next state equation. The data from each calculation is saved, and the turn-off loss can be obtained through numerical calculation. Step S4: Simulate different operating conditions of power devices by adjusting the initial values ​​of state variables in step S3, substitute the SiCMOSFET turn-off loss calculation results into the junction temperature prediction model based on SiC MOSFET turn-off loss established in step S2, and calculate the junction temperature value according to the mapping relationship between turn-off loss, junction temperature and operating conditions. The process of establishing the junction temperature prediction model based on SiC MOSFET turn-off loss in step S2 is as follows: Step S21: By building a dual-pulse test platform, set the junction temperature Tj of the SiC MOSFET and the operating conditions: bus voltage. Inductor current ; Step S22: Test the turn-off loss of the SiC MOSFET under different junction temperatures and operating conditions, and plot the turn-off loss versus junction temperature. A diagram showing the relationship between operating conditions; Step S23: Adjust turn-off losses and junction temperature. The relationship between the operating conditions and the decoupled fitting was performed to obtain the relationship between turn-off loss and junction temperature. The mapping relationship between the operating conditions and the junction temperature is the junction temperature prediction model based on the turn-off loss of SiC MOSFETs: ， in, , , The constant value obtained by fitting. To shut down losses, This represents the inductor current value.

2. The method for predicting junction temperature based on SiC MOSFET turn-off loss according to claim 1, characterized in that, In step S1, an equivalent circuit model of SiC MOSFET considering parasitic parameters is established, and the state equations of each stage of the turn-off process are obtained by analyzing and modeling the turn-off transient process: state equation group A1 for the turn-off delay stage, state equation group A2 for the voltage rise stage, state equation group A3 for the current fall stage, and state equation group A4 for the turn-off oscillation stage. The state equation set A1 for the turn-off delay stage is as follows: ， The state equations A2 for the voltage rise phase are as follows: ， The state equations A3 for the current-decreasing phase are as follows: ， The state equations A4 for the turn-off oscillation phase are as follows: ， in, This refers to the gate-source voltage of the SiC MOSFET. This is the drain-source voltage. Drain current, To drive positive pressure, It is an ideal voltage source equivalent to the DC bus. Threshold voltage, For transconductance; It is an ideal current source equivalent to the load inductance. The equivalent junction capacitance of SiC SBD; , , These are the input capacitance, output capacitance, and transfer capacitance of the SiC MOSFET, respectively. This is the gate drive resistor of the SiC MOSFET. , , These are the parasitic inductances of the gate, drain, and source of the SiC MOSFET, respectively. For stray inductance, For stray resistance, This indicates taking the derivative with respect to time. This indicates taking the second derivative with respect to time; Using the state equations A1 for the turn-off delay stage, A2 for the voltage rise stage, A3 for the current fall stage, and A4 for the turn-off oscillation stage, a SiCMOSFET turn-off loss model considering parasitic parameters can be established using the integration method. ， in, To shut down losses, This is the gate drive resistor of the SiC MOSFET. This is the gate-drain parasitic capacitance. For inductor current, Bus voltage For conduction voltage drop, To drive positive pressure, Threshold voltage, This is the input capacitance of the SiC MOSFET. For transconductance, This is the source parasitic inductance of a SiC MOSFET.

3. The method for predicting junction temperature based on SiC MOSFET turn-off loss according to claim 1, characterized in that, In step S3, based on the state equations for each stage of the shutdown process, the initial values ​​of each state variable are input into the calculation tool, and the time step is set. Step S31: First, calculate sub-period 1, solve the state equation system A1 for the turn-off delay stage, and determine whether the boundary conditions are met after a single time step. ,in Gate-source voltage, Let Miller plateau voltage be the voltage at which this phase is defined as the duration of this phase. If the boundary condition is met, the drain-source voltage, gate-source voltage, drain current, and duration parameters calculated for that time period are stored, and sub-cycle 2 is calculated. If the condition is not met, a single time step is run again. Step S32: After satisfying the boundary conditions of sub-period 1, begin calculating sub-period 2, solve the state equation set A2 for the voltage rise phase, and define the duration of this phase as... Under the condition of satisfying the boundary conditions Then store the solution data for this stage and begin calculating sub-cycle 3; Step S33: After satisfying the boundary conditions for sub-period 2, begin calculating sub-period 3, solve the state equation set A3 for the current decrease phase, and define the duration of this phase as... Under the condition of satisfying the boundary conditions Then store the solution data for this stage and begin calculating sub-cycle 4; Step S34: After satisfying the boundary conditions for sub-period 3, begin calculating sub-period 4, solve the state equation set A4 for the turn-off oscillation stage, and define the duration of sub-period 4 as... The solution data for that stage is stored after each single time step. Step S35: The data from each calculation is saved, and the turn-off loss can be obtained through numerical calculation. The formula for calculating the turn-off loss using the integral method is: ， in, Let be the drain-source voltage at time t. Let be the drain current at time t. This represents the integral over time.

4. The method for predicting junction temperature based on SiC MOSFET turn-off loss according to claim 1, characterized in that, Step S4 simulates different operating conditions of the power device by adjusting the initial value of the state variable in step S3, and obtains the data and turn-off loss of each stage through calculation tools. Substitute the SiC MOSFET turn-off loss calculation result into the junction temperature prediction model based on SiC MOSFET turn-off loss established in step S2, and calculate the junction temperature value according to the mapping relationship between turn-off loss, junction temperature and operating conditions.

5. The method for predicting junction temperature based on SiC MOSFET turn-off loss according to claim 1, characterized in that, The state variables mentioned in step S3 include drain-source voltage, gate-source voltage, drain current, and duration.

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