A method and system for estimating junction temperature of an inverter

Abstract

The application provides a junction temperature estimation method and system of an inverter, the inverter is provided with an NTC thermistor on one side; the method comprises the following steps: based on a first-order Foster thermal network model, the temperature increase value of each power unit is calculated according to the transient loss of each power unit in the inverter, the thermal resistance and the heat capacity of the thermal network model of the inverter; the temperature increase value of each power unit is summed with the temperature value of the thermistor respectively, as the junction temperature estimation value of each power unit. The model order of the application is lower, is more beneficial to realize digitization, responds faster, can observe the junction temperature in real time online, and realizes high-precision estimation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of motor controllers, and particularly relates to a junction temperature estimation method and system of an inverter. BACKGROUND

[0002] During the operation of an electric vehicle, the motor controller is frequently started and stopped, the speed is increased and decreased, and the torque is increased and decreased. The power devices in the motor controller generate power loss, which further causes the junction temperature of the power module to fluctuate. Under long-term thermal stress of large power and temperature fluctuations, the bond wires on the chip fall off and break, and the solder layer cavities and cracks, which seriously shortens the service life of the power module. Real-time acquisition of the junction temperature of the power unit is crucial for system reliability evaluation, vehicle thermal management, and life prediction.

[0003] It is not easy to obtain the junction temperature from the structural characteristics and packaging characteristics of the power module chip. There are many methods for estimating the junction temperature, which are mainly divided into thermal sensitive electrical parameter estimation method, physical contact estimation method, infrared imaging method, and thermal network model estimation method according to the estimation accuracy, implementation degree, and whether it is suitable for engineering.

[0004] The physical contact measurement method directly obtains temperature information through a temperature sensor. Since there is a certain distance between the chip and the NTC thermistor, the NTC thermistor cannot accurately measure the temperature at the chip, and the junction temperature change reflected by the NTC thermistor has a certain delay.

[0005] The infrared imaging method usually uses an infrared imager and can analyze the transient state of the junction temperature. However, this method must disassemble the upper cover of the packaged module, which is not practical in actual engineering applications. Generally, the infrared imager is used to verify the accuracy of the junction temperature estimation model.

[0006] The thermal sensitive electrical parameter estimation method estimates the junction temperature by taking the on-state voltage as the thermal sensitive electrical parameter to form an electrical parameter database. When a certain electrical parameter value is measured, the corresponding junction temperature is obtained through the database. This method has high accuracy, but generally requires additional measurement circuit to obtain the thermal sensitive electrical parameter value, which is not suitable for online junction temperature estimation in engineering.

[0007] The thermal network model estimation method analogizes the characteristics of heat conduction to Ohm's law in electrical engineering, analogizes thermal resistance to electrical resistance, analogizes thermal capacity to electrical capacity, and analogizes power loss to current. Thermal resistance and thermal capacity are combined to form a thermal model, which is similar to an RC low-pass circuit. Generally, a Cauer thermal network model or a Forster thermal network model is used to simulate the thermal impedance of a power module. The Cauer model is related to the actual physical material of each layer of the device, and the calculation is difficult and the modeling is complex. The Foster model has no actual meaning in terms of the actual physical structure, and can be obtained according to the expected thermal resistance parameter resolution fitting according to the power loss input and the measured point thermal response. However, most thermal network models only consider a single thermal path and do not consider the thermal coupling between chips. In addition, the junction temperature estimation schemes proposed in many documents are based on the average loss of the device and cannot reflect the transient loss of the electric vehicle in normal operation.

[0008] In view of the above methods, according to the destructiveness of the power module, the estimation accuracy, whether to increase additional circuit, physical contact measurement, infrared imaging method and thermal sensitive electrical parameter estimation method are not suitable for the junction temperature estimation of the power module of the electric vehicle. In addition, the thermal network model needs to consider the specific topology structure of the power module and the heat dissipation for improvement. SUMMARY

[0009] The purpose of the present application is to solve the problems existing in the background art, and to provide a junction temperature estimation method and system for an inverter, which has a lower model order, is more conducive to digitalization, has a faster response, can observe the junction temperature in real time online, and can achieve high-precision estimation.

[0010] The technical scheme adopted by the present application is: a junction temperature estimation method for an inverter, the inverter is provided with an NTC thermistor on one side; the method comprises the following steps:

[0011] Based on a first-order Foster thermal network model, the temperature increase value of each power unit is calculated according to the transient loss, thermal resistance and thermal capacity of each power unit in the inverter;

[0012] The temperature increase value of each power unit and the temperature value of the thermistor are summed up as the junction temperature estimation value of each power unit.

[0013] In the above technical scheme, a low-pass filter is used to simulate a first-order Foster thermal network model; the input of the low-pass filter is used to simulate the transient loss of the power unit, and the output of the low-pass filter is used to simulate the temperature increase value of the power unit; the filter coefficient is used to represent the switching period of the inverter, and the transient loss, thermal resistance and thermal capacity of the power unit.

[0014] In the technical solution, the process of obtaining the transient loss of the power unit comprises: obtaining the conduction current of each power unit at different time points through the three-phase current and the duty ratio of the inverter in normal operation; and obtaining the transient loss of each power unit at different time points according to the conduction current of each power unit at different time points.

[0015] In the technical solution, the process of obtaining the conduction current of each power unit at different time points comprises: fitting the actual phase current of the inverter changing with time according to the three-phase current of the inverter at the previous two time points and the current time point; and obtaining the conduction current of the power unit at the current time point based on the actual phase current of the inverter at the current time point and the duty ratio.

[0016] In the technical solution, the actual phase current of the inverter changing with time is fitted according to the following formula: s

[0017]

[0018] In the formula, IsLLst represents the three-phase current at the time point two time points ago, IsLst represents the three-phase current at the time point one time point ago, Is represents the three-phase current at the current time point, and t represents the time point.

[0019] In the technical solution, the transient loss of the power unit comprises the conduction loss of the switching device and the diode, and the switching loss of the switching device and the reverse recovery loss of the diode.

[0020] In the technical solution, the process of obtaining the transient loss of any power unit comprises: substituting the conduction current of the power unit at the current time point, the DC bus voltage of the inverter and the junction temperature of the power unit at the previous time point into a transient loss calculation model to obtain the transient loss of the power unit at the current time point; and the transient loss calculation model is used to represent the mathematical relationship between the transient loss of the power unit and the conduction current, the junction temperature of the power unit and the DC bus voltage of the inverter.

[0021] In the technical solution, the expression of the transient loss calculation model is:

[0022] P Loss,SiC+diode = P cond,SiC + P cond,Diode + P sw,SiC + P Reserve,Diode .

[0023]

[0024]

[0025] In the formula, P Loss,SiC+diode represents the transient loss of the power unit; P cond,SiC represents the conduction loss of the switching device in the power unit; P​cond,Diode represents the conduction loss of the diode in the power unit; P sw,SiC represents the switching loss of the switching device in the power unit; P Reserve,Diode represents the reverse recovery loss of the diode in the power unit; T j represents the junction temperature of the power unit, i d represents the conduction current of the switching device in the power unit; I f represents the conduction current of the diode in the power unit; U dc represents the DC bus voltage of the inverter; D(t) represents the duty cycle of the inverter; T s represents the switching period of the inverter; f1(), f2(), f3(), and f4() represent the first function, the second function, the third function, and the fourth function, respectively.

[0026] In the technical solution, the expression of the filter coefficient Fac_filter is:

[0027]

[0028] wherein T s represents the switching period of the inverter, R represents the thermal resistance of the power unit, and C represents the thermal resistance heat capacity of the power unit.

[0029] In the technical solution, the junction temperature estimation value T j (t) of the power unit at the current time t is calculated by using the following formula:

[0030] T j (t) = Fac_filter·P Loss,SiC+diode (t) + (1-Fac_filter)T j (t-1) + T NTC

[0031] wherein T NTC represents the current time thermal resistance temperature value.

[0032] In the technical solution, the construction process of the transient loss calculation model includes: performing a double-pulse experiment on each bridge arm of the inverter in sequence; measuring the turn-on loss, turn-off loss, and reverse recovery loss of the power unit on the test bridge arm under different conduction currents, bus voltages, and temperatures, respectively; and then fitting to obtain the coefficients of the third function and the fourth function in the transient loss calculation model of the power unit on the bridge arm; and fitting the first function and the second function through a conduction characteristic curve diagram provided by a power unit manufacturer.

[0033] In the technical solution, the thermal resistance and the thermal capacity of the thermal network model of the inverter are obtained through thermal testing or a chip data manual.

[0034] In the technical solution, the process of obtaining the thermal resistance and the thermal capacity of the thermal network model of the inverter through thermal testing comprises: obtaining a transient thermal impedance curve of the inverter through thermal testing; and calculating the thermal resistance and the thermal capacity of the thermal network model of the inverter based on a first-order Foster thermal network model.

[0035] In the technical solution, the process of obtaining the thermal resistance and the thermal capacity of the thermal network model of the inverter through thermal testing comprises: obtaining a transient thermal impedance curve of the inverter through thermal testing; and calculating the thermal resistance and the thermal capacity of the thermal network model of the inverter based on a first-order Foster thermal network model.

[0036] The application also provides a junction temperature estimation method of an inverter.

[0037] The application has the advantages that the application can realize real-time observation of the junction temperatures of the power units in the inverter, ensure that the switching devices always work in the safe working area, and provide certain guidance for thermal management and derating of the motor controller and life analysis of the devices. Without adding any measuring devices, the application calculates the losses of the upper and lower bridge arms through a software method, does not need to distinguish various working conditions such as blockage and no load, respectively obtains the transient losses of the six power units, combines the Foster thermal network model, takes the NTC thermistor as a reference point, has a lower model order, is more conducive to digitalization, and has a small time constant corresponding to the NTC thermistor and a faster response. The junction temperature is observed in real time and online, and high-precision estimation is realized.

[0038] Further, the application simulates a first-order Foster thermal network model by using a low-pass filter to obtain the temperature rise of the power unit, effectively improves the calculation efficiency, saves the calculation cost, and ensures the calculation precision.

[0039] Further, in a PWM cycle, the three-phase current samples are a constant value, but the actual phase current changes. The application fits a continuous current IS(t) by using the three latest currents, so that the actual phase current used for subsequent calculation is more accurate and can better reflect the current working state of the inverter.

[0040] Further, the application fully considers the power losses of the switching devices and the diodes to ensure the calculation precision of the junction temperature.

[0041] Further, the application substitutes the conduction current of the power unit at the current time, the DC bus voltage of the inverter, and the junction temperature of the power unit at the previous time into the transient loss calculation model to obtain the transient loss of the power unit at the current time, fully considers the junction temperature change process, and effectively ensures the calculation precision of the subsequent junction temperature.

[0042] Further, the transient loss calculation model fully considers the working state of the inverter in different time periods in a switching cycle, and effectively improves the calculation accuracy of the transient loss.

[0043] Further, the filter coefficient calculation method fully considers the influence of the inverter itself and the switching cycle on the subsequent temperature rise, and effectively ensures the accuracy of the junction temperature estimation.

[0044] Further, the junction temperature estimation method of the power unit adopts a first-order model while considering the development process of the junction temperature change, thereby saving the calculation cost while ensuring the calculation accuracy.

[0045] Further, the transient loss calculation model is constructed by the results of the double pulse experiment, so as to ensure that the model parameters can fully reflect the actual properties of the inverter and ensure the accuracy of the subsequent junction temperature estimation.

[0046] Further, the thermal resistance and the thermal capacity of the thermal network model of the inverter are tested by the thermal test, so as to fully reflect the actual properties of the inverter and ensure the accuracy of the subsequent junction temperature estimation.

[0047] Further, the infrared detector is used to verify the results of the junction temperature estimation, thereby further improving the estimation accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 The figure is a method flowchart of the present application.

[0049] Figure 2 The figure is an inverter current flow direction schematic diagram of the specific embodiment.

[0050] Figure 3 The figure is a Foster thermal network model principle diagram. DETAILED DESCRIPTION

[0051] The present application will be further described in detail below in combination with the drawings and specific embodiments, so as to facilitate clear understanding of the present application, but they do not constitute limitation to the present application.

[0052] Embodiment 1

[0053] As shown in the figure, the present application provides a junction temperature estimation method of an inverter, wherein the inverter is provided with an NTC thermistor on one side; the method comprises the following steps: Figure 1 Based on a first-order Foster thermal network model, the temperature increase value of each power unit is calculated according to the transient loss, the thermal resistance and the thermal capacity of each power unit in the inverter.

[0054]

[0055] ​The temperature increase value of each power unit is summed with the thermistor temperature value as a junction temperature estimation value of each power unit.

[0056] Specifically, the inverter in the application acts between a DC power source of an electric vehicle and a three-phase motor, and is used to realize DC / AC conversion between the DC power source and the three-phase motor. The inverter comprises a three-phase bridge arm, which is composed of six power units, and each power unit comprises a switching device and a diode in anti-parallel connection. A thermistor is arranged on one side of the inverter to obtain a junction temperature reference value. In the embodiment, the switching device is a silicon carbide device.

[0057] The principle of the application will be further explained below with reference to specific embodiments.

[0058] As shown in Figure 1 , embodiment 1 is executed on a matlab platform, and specifically comprises the following steps:

[0059] In the first step, three-phase currents of the inverter are collected in real time during normal operation of the inverter.

[0060] According to the three-phase currents of the inverter at the previous two time points and the current time point, an actual phase current of the inverter changing with time is fitted; specifically, the actual phase current of the inverter changing with time I s (t) is fitted by using the following formula:

[0061]

[0062] wherein IsLLst represents the three-phase current at the time point two time points ago, IsLst represents the three-phase current at the time point one time point ago, Is represents the three-phase current at the current time point, and t represents the time point.

[0063] Since the three-phase current is a constant value sampled in one PWM period, but the actual phase current is changing, the three latest time points are used to fit a continuous current I S (t) in the application, so that the actual phase current used for subsequent calculation is more accurate and can better reflect the current working state of the inverter.

[0064] In the switching period of the inverter, the rising edge time is and the falling edge time is Let the direction of the power unit flowing to the three-phase motor be positive. As shown in Figure 2As shown, if the current is positive, the upper bridge arm switching device is turned on or the lower bridge arm diode is freewheeling. It is defined that the switching device performs switching action at t1, the switching device is in the on state in the time period of t1-t2, and the switching device performs turn-off action at t2. The diode is freewheeling in the time periods of 0-t1 and t2-1, the on time of the switching device is duty, and the freewheeling time of the diode is 1-duty. Therefore, a transient loss calculation model is obtained, and the expression is:

[0065] P Loss,SiC+diode cond,SiC +P cond,Diode +P sw,SiC +P Reserve,Diode ;

[0066]

[0067] P Loss,SiC+diode represents the transient loss of the power unit; P cond,SiC represents the on loss of the switching device in the power unit; P cond,Diode represents the on loss of the diode in the power unit; P sw,SiC represents the switching loss of the switching device in the power unit; P Reserve,Diode represents the reverse recovery loss of the diode in the power unit; T j represents the junction temperature of the power unit, i d represents the on current of the switching device in the power unit; I f represents the on current of the diode in the power unit; U dc represents the DC bus voltage of the inverter; D(t) represents the duty ratio of the inverter; T s represents the switching period of the inverter; f1(), f2(), f3(), and f4() respectively represent the first function, the second function, the third function, and the fourth function, and the calculation coefficients in the expressions of the first function, the second function, the third function, and the fourth function are known quantities.

[0068] The first function is used to represent the mathematical relationship between the on resistance r dson of the switching device and the junction temperature of the power unit in which the switching device is located, i.e., r dson =f1(T j ).

[0069] The second function is used to represent the data relationship between the on voltage of the diode and the junction temperature of the power unit in which the diode is located and the on current of the diode, i.e., V f =f2(I f ,T j ).

[0070] In the embodiment, one PWM period is taken as a time point,

[0071] ​The third function characterizes the mathematical relationship between the switching losses of the switching devices and the junction temperature of their respective power units, the on-state current of the switching devices, and the DC bus voltage of the inverter within a PWM cycle, i.e., E sw,SiC =f3(T j i d U dc ).

[0072] The fourth function characterizes the mathematical relationship between the reverse recovery loss of the diode within a PWM cycle and the junction temperature of its power unit, the diode's on-state current, and the inverter's DC bus voltage, i.e., E Reserve,Diode =f4(T j ,I f U dc ).

[0073] The second step is based on the actual phase current I of the inverter at the current moment. s Given the duty cycle D(t), the on-state current in the power unit at the current moment is obtained. The on-state current of the switching device and diode is taken as its actual phase current I at the current moment. s The calculation result of (t).

[0074] The fourth step is to acquire the inverter DC bus voltage at the current time t, and use the on-current of the switching devices and diodes at the current time t, as well as the junction temperature at the previous time t-1, as parameter T. j Substituting these values ​​into the transient loss calculation model, the transient loss of each power unit is calculated. The initial junction temperature is assumed to be 0.

[0075] The fifth step involves simulating a first-order Foster thermal network model using a low-pass filter. The input of the low-pass filter is used to simulate the transient losses of the power unit, and the output of the low-pass filter is used to simulate the temperature increase of the power unit. The filter coefficients are used to characterize the switching cycle of the inverter, as well as the transient losses, thermal resistance, and thermal capacity of the power unit.

[0076] The expression for the filter coefficient Fac_filter is:

[0077]

[0078] Where Ts represents the switching cycle of the inverter, R represents the thermal resistance of the power unit, and C represents the thermal resistance and thermal capacity of the power unit. Since the above three parameters are all known, the filter coefficient Fac_filter is also known.

[0079] Therefore, the estimated junction temperature T of the power unit at the current time t, i.e., the current PWM cycle, can be directly calculated using the following formula. j (t):

[0080] Tj (t) = Fac_filter * P Loss,SiC+diode (t) + (1 - Fac_filter) * T j (t-1)

[0081] + T NTC

[0082] Where, T NTC represents the current time of the thermistor temperature value, which can be collected in real time.

[0083] In the sixth step, the junction temperature of the power unit is collected in real time by the infrared detector as the junction temperature reference value of the power unit. The junction temperature reference value of the power unit at the current time is compared with the estimated junction temperature value of the power unit. If the difference between the two is within the error allowable range, the estimated junction temperature value of the power unit is output, otherwise an error is reported.

[0084] In the process of executing the junction temperature estimation method of the inverter, the calculation coefficients of the first function, the second function, the third function and the fourth function in the transient loss calculation model of the inverter need to be determined first to realize the construction of the transient loss calculation model, and the process includes: performing double pulse experiments on each bridge arm of the inverter in turn: measuring the turn-on loss, turn-off loss and reverse recovery loss of the power unit on the test bridge arm under different conduction currents, bus voltages and temperatures respectively, and then fitting to obtain the coefficients of the third function and the fourth function in the transient loss calculation model of the power unit on the bridge arm; fitting the first function and the second function through the conduction characteristic curve diagram given by the power unit manufacturer. Through the double pulse experiment, the power unit transient loss and the junction temperature are the conventional technical means in the art.

[0085] In the process of executing the junction temperature estimation method of the inverter, the thermal resistance and the thermal capacity of the thermal network model of the inverter also need to be determined first. The thermal resistance and the thermal capacity can be obtained through thermal testing or chip data manual.

[0086] The specific embodiment constructs the Foster thermal network model as shown in Figure 3 , P loss can be regarded as the current in the circuit, T j and T ntc can be regarded as the voltage. R and C are the sizes of the thermal resistance and thermal capacity parameters. Considering the engineering practicability, the model does not consider the thermal coupling between the switching device and the diode. In the process of thermal testing, a constant current is provided to the inverter and the corresponding loss P loss is calculated. Taking the loss P loss of the inverter as the controllable variable, the difference between the junction temperature of the power unit and the thermistor temperature is measured, and then the transient thermal response curve is obtained.

[0087] The transient thermal response curve Zth The expression is:

[0088]

[0089] The thermal resistance and thermal capacity of the thermal network model of the inverter can be fitted through the transient thermal response curve.

[0090] Embodiment 2

[0091] The application also provides an inverter junction temperature estimation system for implementing the inverter junction temperature estimation method.

[0092] Embodiment 3

[0093] The application provides a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to implement the inverter junction temperature estimation method.

[0094] Embodiment 4

[0095] The application provides an electronic device, which comprises a memory and a processor, the memory and the processor are in communication connection with each other, the memory stores computer instructions, and the processor executes the computer instructions to implement the inverter junction temperature estimation method.

[0096] Those skilled in the art should understand that the embodiments of the application can be provided as a method, a system, or a computer program product. Therefore, the application can be in the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the application can be in the form of a computer program product implemented on one or more computer usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer usable program code.

[0097] The application is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to produce a machine, so that the instructions executed by the computer or other programmable data processing devices produce a device that implements the functions specified in the flowcharts and / or block diagrams. Figure 1 The device that implements the functions specified in one or more flows and / or blocks. Figure 1 The device that implements the functions specified in one or more flows and / or blocks.

[0098] These computer program instructions can also be stored in a computer readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instructions which implement the Figure 1 function specified in the flow or flows and / or blocks Figure 1 of the block or blocks.

[0099] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions that are executed on the computer or other programmable apparatus provide steps for implementing the Figure 1 function specified in the flow or flows and / or blocks Figure 1 of the block or blocks.

[0100] The embodiments of the present application described above with reference to the drawings are merely illustrative, and not restrictive, and many modifications can be made by those skilled in the art without departing from the spirit and scope of the present application, and these are also included in the scope of the present application.

[0101] The contents not described in detail in the specification are the prior art known to those skilled in the art.

Claims

1. A method for estimating the junction temperature of an inverter, wherein an NTC thermistor is provided on one side of the inverter; characterized in that: The method includes the following steps: Based on the first-order Foster thermal network model, the temperature increase of each power unit is calculated according to the transient loss, thermal resistance and thermal capacity of each power unit in the inverter. The sum of the temperature increase of each power unit and the thermistor temperature value is used as the estimated junction temperature of each power unit. The process of obtaining the transient loss of any power unit includes: substituting the current conduction current of the power unit, the DC bus voltage of the inverter, and the junction temperature of the power unit at the previous moment into the transient loss calculation model to obtain the transient loss of the power unit at the current moment; the transient loss calculation model is used to characterize the mathematical relationship between the transient loss of the power unit and the conduction current, junction temperature, and DC bus voltage of the inverter. The expression for the transient loss calculation model is as follows: ； ,i d >0； ,i d <0； ,I f >0； ,I f <0; ; ； ； ； in, This represents the transient loss of the power unit; This represents the conduction loss of the switching devices in the power unit; This indicates the conduction loss of the diodes in the power unit; This represents the switching losses of the switching devices in the power unit; T represents the reverse recovery loss of the diode in the power unit. j Indicates the junction temperature of the power unit, i d I represents the on-state current of the switching devices in the power unit. f U represents the on-state current of the diode in the power unit; dc D(t) represents the DC voltage of the inverter; D(t) represents the duty cycle of the inverter; T s This represents the switching cycle of the inverter; f1(), f2(), f3(), and f4() represent the first function, the second function, the third function, and the fourth function, respectively. The first function is used to characterize the mathematical relationship between the on-resistance of the switching device and the junction temperature of the power cell in which it is located; the second function is used to characterize the data relationship between the on-voltage of the diode and the junction temperature of the power cell in which it is located and the on-current of the diode. Taking one PWM cycle as a moment, the third function is used to characterize the mathematical relationship between the switching loss of the switching device and the junction temperature of the power unit, the on-state current of the switching device, and the DC voltage of the inverter within one PWM cycle; the fourth function is used to characterize the mathematical relationship between the reverse recovery loss of the diode and the junction temperature of the power unit, the on-state current of the diode, and the DC voltage of the inverter within one PWM cycle.

2. The method for estimating the junction temperature of an inverter according to claim 1, characterized in that: A low-pass filter is used to simulate a first-order Foster thermal network model. The input of the low-pass filter is used to simulate the transient losses of the power unit, and the output of the low-pass filter is used to simulate the temperature increase of the power unit. The filter coefficients are used to characterize the switching cycle of the inverter, as well as the transient losses, thermal resistance, and thermal capacity of the power unit.

3. The method for estimating the junction temperature of an inverter according to claim 1, characterized in that: The process of obtaining the transient loss of the power unit includes: obtaining the conduction current of each power unit at different times by using the three-phase current and duty cycle when the inverter is working normally, and calculating the transient loss corresponding to the power unit at different times based on the conduction current of the power unit at different times.

4. The method for estimating the junction temperature of an inverter according to claim 3, characterized in that: The process of obtaining the on-current of the power unit at different times includes: fitting the actual phase current of the inverter as it changes over time based on the three-phase current of the inverter at the previous two times and the current time; and obtaining the on-current of the power unit at the current time based on the actual phase current and duty cycle of the inverter at the current time.

5. The method for estimating the junction temperature of an inverter according to claim 4, characterized in that: The phase current of the inverter as a function of time is obtained by fitting the following formula. : ； in, This represents the three-phase current at the time two moments ago. The three-phase current at the previous moment. t represents the three-phase current at the current moment; t represents the time.

6. The method for estimating the junction temperature of an inverter according to claim 3, characterized in that: The transient losses of a power unit include the conduction losses of switching devices and diodes, as well as the switching losses of switching devices and the reverse recovery losses of diodes.

7. The method for estimating the junction temperature of an inverter according to claim 2, characterized in that: The filter coefficients The expression is: ； Among them, T s R represents the switching cycle of the inverter, C represents the thermal resistance of the power unit, and C represents the thermal resistance and thermal capacity of the power unit.

8. The method for estimating the junction temperature of an inverter according to claim 7, characterized in that: The estimated junction temperature of the power unit at time t is calculated using the following formula. : ； in, This indicates the current temperature value of the thermistor.

9. The method for estimating the junction temperature of an inverter according to claim 1, characterized in that: The process of constructing the transient loss calculation model includes: conducting a double-pulse experiment on each arm of the inverter in sequence: measuring the turn-on loss, turn-off loss, and reverse recovery loss of the power unit on the test arm under different conduction currents, bus voltages, and temperatures, and then fitting the coefficients of the third and fourth functions in the transient loss calculation model of the power unit on that arm; fitting the first and second functions using the conduction characteristic curves provided by the power unit manufacturer.

10. The method for estimating the junction temperature of an inverter according to claim 7, characterized in that: The thermal resistance and thermal capacity of the inverter's thermal network model can be obtained through thermal testing or chip datasheets.

11. The method for estimating the junction temperature of an inverter according to claim 10, characterized in that: The process of obtaining the thermal resistance and thermal capacity of the inverter's thermal network model through thermal testing includes: obtaining the transient thermal impedance curve of the inverter through thermal testing; and calculating the thermal resistance and thermal capacity of the inverter's thermal network model based on the first-order Foster thermal network model.

12. The method for estimating the junction temperature of an inverter according to claim 11, characterized in that: It also includes the following steps: Infrared detectors were used to collect the junction temperature of each power unit to verify the calculated estimated junction temperature of each power unit.

13. A junction temperature estimation system for an inverter, characterized in that: This system is used to implement the junction temperature estimation method for the inverter according to any one of claims 1-12.

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