Electric drive system power device solder layer health state monitoring method and system and vehicle

Abstract

The invention relates to the technical field of electric drive systems, in particular to an electric drive system power device solder layer health state monitoring method and system and a vehicle, and the method comprises the following steps: determining a to-be-monitored power device chip according to the position of an NTC thermistor on an electric drive system; enabling a rotor of the driving motor to stay at a preset position before the vehicle is parked; when the vehicle is in a parking state, applying a preset current to the to-be-monitored power device chip, and collecting temperature fluctuation data of the NTC thermistor; according to the collected temperature fluctuation data, the thermal resistance of a solder layer of the corresponding power device is searched through a preset first data table; comparing the obtained thermal resistance with preset thermal resistance, and judging the health state of the solder layer of the power device; the first data table is a corresponding relation table of different cooling water temperatures, thermal resistances of different power device solder layers and temperature fluctuation data of the NTC thermistor. The aging state of the solder layer of the power device can be monitored on line.

Description

Technical Field

[0001] The present invention relates to the technical field of automotive electric drive systems, and particularly relates to a method and system for monitoring the health state of a solder layer of a power device in an electric drive system, and a vehicle. Background Art

[0002] With the rapid development of new energy vehicles, power devices, as the core components for realizing AC-DC conversion in electric drive systems, play a crucial role in the normal operation of electric drive systems in terms of their long-term reliability. The health state of power devices is closely related to their usage environment, operating conditions, and operating time. Due to the differences in the usage conditions of vehicle owners, there are significant differences in the remaining life of power devices in new energy vehicle electric drive systems. Under long-term harsh operating conditions, the aging and failure of power devices, especially the aging of the solder layer, may trigger faults in the vehicle's power system, and may further lead to safety accidents, causing property and safety losses.

[0003] The aging of power devices is mainly manifested in two parts: the aging of the solder layer and the failure of metal bond wires. Among them, the aging of the solder layer often precedes the failure of the bond wires and is one of the main inducements for the failure of the bond wires. Therefore, online monitoring of the aging state of the solder layer of power devices is of crucial significance for ensuring the long-term reliable operation of electric drive systems.

[0004] However, most of the existing methods for monitoring the aging of the solder layer of power devices do not fully consider the particularities of new energy vehicle electric drive systems, such as the limitations of circuit topologies, mechanical structures, etc. on the monitoring methods. Some methods require additional data acquisition and processing equipment and place multiple temperature sensor modules at the bottom of the power device, which is not conducive to integration into the electric drive system and increases the cost. Other methods rely on complex thermal network models or require calculating the losses and junction temperatures of IGBT devices, which also increases the complexity and cost of implementation. There are also methods that propose using characteristic quantities such as the inflection point of the shell temperature rise threshold to monitor aging, but still require installing temperature sensors on the outer shell of the IGBT device and do not fully consider the influence of changes in thermal losses on the temperature rise curve. In addition, there are methods that attempt to evaluate the aging of IGBT devices through ultrasonic scanning, but require using relatively large ultrasonic sensors and related equipment and cannot achieve online measurement.

[0005] In summary, the existing methods for monitoring the aging of the solder layer of power devices have many deficiencies, such as requiring additional equipment, being complex to implement, having a high cost, or being unable to achieve online measurement.

[0006] Therefore, it is necessary to develop a new method, system, and vehicle for monitoring the health state of the solder layer of power devices in an electric drive system. Summary of the Invention

[0007] The object of the present invention is to provide a method, a system and a vehicle for monitoring the health state of the solder layer of a power device in an electric drive system, which can realize on-line monitoring of the aging state of the solder layer of the power device without adding additional devices.

[0008] In a first aspect, a method for monitoring the health state of the solder layer of a power device according to the present invention includes the following steps:

[0009] Determine the power device chip to be monitored according to the position of the NTC thermistor on the electric drive system;

[0010] Before the vehicle stops, make the rotor of the drive motor stay at a preset position;

[0011] When the vehicle is in a stopped state, apply a preset current to the power device chip to be monitored and collect the temperature fluctuation data of the NTC thermistor;

[0012] Find the thermal resistance of the corresponding power device solder layer according to the collected temperature fluctuation data through a preset first data table;

[0013] Compare the obtained thermal resistance with the preset thermal resistance to judge the health state of the power device solder layer;

[0014] The first data table is a corresponding relationship table of the thermal resistance of different cooling water temperatures, different power device solder layers and the temperature fluctuation data of the NTC thermistor.

[0015] Optionally, select the power device chip closest to the NTC thermistor as the power device chip to be monitored, so as to avoid the problem that the measurement effect is not obvious due to too large thermal time constant.

[0016] Optionally, the first data table is obtained by calibration, specifically:

[0017] Select the power device chip closest to the NTC thermistor as the heat source;

[0018] Obtain the thermal response time from the heat source to the NTC thermistor;

[0019] Before the vehicle stops, make the rotor of the drive motor stay at a preset position;

[0020] When the vehicle is in a stopped state, apply a preset current to the heat source, and set the power loss frequency and heat loss frequency of the heat source according to the thermal response time, adjust the cooling water temperature and the thermal resistance of the power device solder layer for multiple tests, and collect the temperature fluctuation data of the NTC thermistor during the test process, and establish a first data table based on the temperature fluctuation data, the cooling water temperature and the thermal resistance of the power device solder layer;

[0021] Among them, the temperature fluctuation data includes at least one of the maximum temperature fluctuation, the minimum temperature fluctuation, and the temperature fluctuation phase shift angle. By selecting the power device chip closest to the NTC thermistor as the heat source, it can ensure that the thermistor can accurately and quickly sense the temperature change of the heat source, thereby improving the accuracy and sensitivity of temperature monitoring. Obtain the thermal response time from the heat source to the NTC thermistor, which reflects the speed at which the temperature change of the heat source is transmitted to the thermistor. In subsequent tests, this time parameter can be used to more accurately control the power loss and heat loss of the heat source, and to more precisely collect temperature fluctuation data. Before the vehicle stops, make the rotor of the drive motor stay at a preset position, reducing potential interference caused by different positions of the motor rotor. Apply a preset current to the heat source, and set the power loss frequency and heat loss frequency of the heat source according to the thermal response time. This step allows adjusting the power and heat loss of the heat source according to different test requirements, so as to obtain more comprehensive test data. Adjust the cooling water temperature and the thermal resistance of the solder layer of the power device for multiple tests. This step takes into account the influence of different cooling conditions and solder layer states on temperature fluctuations, making the established first data table more universal and applicable. Collect the temperature fluctuation data of the NTC thermistor during the test, including at least one of the maximum temperature fluctuation, the minimum temperature fluctuation, and the temperature fluctuation phase shift angle. These data provide rich information for subsequent data analysis and modeling. Based on the collected temperature fluctuation data, the cooling water temperature, and the thermal resistance of the solder layer of the power device, establish a first data table, which provides a reliable reference basis for subsequent monitoring of the aging state of the solder layer of the power device.

[0022] Optionally, obtaining the thermal response time from the heat source to the NTC thermistor is specifically as follows:

[0023] Apply a preset current to the heat source;

[0024] Collect the temperatures of the NTC thermistor and the heat source;

[0025] Based on the temperatures of the NTC thermistor and the heat source, obtain the thermal response time;

[0026] Or:

[0027] Build a finite element model of the power device;

[0028] In the finite element model of the power device, apply a preset current at the power device chip serving as the heat source;

[0029] Record the temperatures of the NTC thermistor and the heat source during the simulation to obtain the thermal response time;

[0030] Among them, the thermal response time is the time required for the temperature of the NTC thermistor to reach stability after the temperature of the heat source starts to change. The present invention provides two methods, namely experiments and simulations, to obtain the thermal response time from the heat source to the NTC thermistor, providing strong technical support for the online monitoring of the aging state of the solder layer of power devices.

[0031] In a second aspect, a method for monitoring the health state of the solder layer of a power device according to the present invention includes the following steps:

[0032] Determine the power device chip to be monitored according to the position of the NTC thermistor on the electric drive system;

[0033] During vehicle operation, collect the power loss frequency of the power device chip to be monitored and the phase shift of the temperature waveform of the NTC thermistor;

[0034] According to the collected power loss frequency and temperature waveform phase shift, look up the thermal resistance of the corresponding power device solder layer through a preset second data table;

[0035] Compare the obtained thermal resistance with the preset thermal resistance to judge the health state of the solder layer;

[0036] Among them, the second data table is the corresponding relationship between the thermal resistance of different power loss frequencies and different power device solder layers and the phase shift of the temperature waveform of the NTC thermistor.

[0037] Optionally, select the power device chip closest to the NTC thermistor as the power device chip to be monitored, so as to avoid the problem of unclear measurement results due to too large a thermal time constant.

[0038] Optionally, the second data table is obtained through calibration, specifically:

[0039] Select the power device chip closest to the NTC thermistor as the heat source;

[0040] Obtain the thermal response time from the heat source to the NTC thermistor, and set the power loss frequency of the heat source according to the thermal response time;

[0041] During vehicle operation, adjust the power loss frequency of the heat source and the thermal resistance of the power device solder layer for multiple tests, and collect the temperature waveform data of the NTC thermistor during the test process;

[0042] Extract the phase shift information from the collected temperature waveform data to obtain the temperature waveform phase shift;

[0043] A second data table is obtained based on the temperature waveform phase shift, the power loss frequency of the heat source, and the thermal resistance of the solder layer of the power device. By considering the thermal response time, the power loss frequency, and the dynamic changes during vehicle operation, the second data table established by the present invention more accurately reflects the actual aging state of the solder layer of the power device. Since the test is carried out during vehicle operation, the established second data table is more adaptable to the actual working environment, and can improve the practicability and reliability of the monitoring system. Based on the second data table, real-time online monitoring of the aging state of the solder layer of the power device can be achieved.

[0044] Optionally, obtaining the thermal response time from the heat source to the NTC thermistor specifically includes:

[0045] Applying a preset current to the heat source;

[0046] Collecting the temperatures of the NTC thermistor and the heat source;

[0047] Based on the temperatures of the NTC thermistor and the heat source, obtaining the thermal response time;

[0048] Or:

[0049] Building a finite element model of the power device;

[0050] In the finite element model of the power device, applying a preset current at the power device chip serving as the heat source;

[0051] Recording the temperatures of the NTC thermistor and the heat source during the simulation process to obtain the thermal response time;

[0052] Wherein, the thermal response time is the time required for the temperature of the NTC thermistor to reach stability starting from the change in the temperature of the heat source. The present invention provides two methods, namely experiment and simulation, to obtain the thermal response time from the heat source to the NTC thermistor, providing strong technical support for the online monitoring of the aging state of the solder layer of the power device.

[0053] In a third aspect, a health state monitoring system for a solder layer of a power device according to the present invention includes a memory and a controller. A computer-readable program is stored in the memory, and when the computer-readable program is called by the controller, it can execute the steps of the method for monitoring the health state of the solder layer of the power device as described in the present invention.

[0054] In a fourth aspect, a vehicle according to the present invention employs the health state monitoring system for a solder layer of a power device as described in the present invention.

[0055] Advantages of the present invention:

[0056] The present invention proposes a method for monitoring the health status of the solder layer of power devices in the electric drive system of electric vehicles. The method fully considers the working conditions of power devices in the actual operating environment of electric vehicles, and is designed based on the principle that aging of the solder layer will lead to an increase in thermal resistance, thereby lengthening the thermal response time constant. In specific implementation, when the vehicle is in a parked state, current is applied to the power device chip, and the NTC thermistor of the power device is used to collect the temperature fluctuations and response time changes caused thereby. When the vehicle is in a working state, the power loss frequency of the power device chip to be monitored and the temperature waveform phase shift of the NTC thermistor are collected.

[0057] Since the aging state of the solder layer will affect the thermal response characteristics, the current aging state of the solder layer can be evaluated by monitoring the thermal response of the NTC thermistor and comparing it with the known data of the power device under different aging states. This method does not require any additional components to be added to the electric drive system of the electric vehicle. Real-time monitoring of the aging state of the solder layer of the power device can be achieved by simply programming the on and off of the power device and collecting the temperature fluctuation data of the NTC thermistor. In addition, this method is not only applicable to newly produced electric drive systems, but can also be applied to power devices that have been loaded into the electric drive system of electric vehicles through software version updates to achieve continuous monitoring of the solder layer state. The implementation cost of the present invention is low and it is easy to apply in large-scale mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a schematic diagram of the structure of the power device chip and the NTC thermistor inside the power device in the embodiment of the present application;

[0059] Figure 2 is a schematic diagram of a second-order thermal network model in an embodiment of the present application;

[0060] Figure 3 It is a fourth-order Cauer thermal network model of a power device in the embodiment of the present application;

[0061] Figure 4 is a thermal response temperature curve obtained by a fourth-order Cauer thermal network model of a power device under a change in thermal resistance in an embodiment of the present application;

[0062] Figure 5 is a flow chart of the method for monitoring the health status of the solder layer of a power device described in Example 1 of the present application;

[0063] Figure 6 It is a schematic diagram of the actual physical structure of the heat source and the NTC thermistor described in the embodiment of the present application;

[0064] Figure 7It is a schematic diagram of the preset position of the rotor described in Embodiment 1 of the present application;

[0065] Figure 8 It is a schematic circuit diagram of the preset current described in Embodiment 1 of the present application;

[0066] Figure 9 It is a schematic circuit diagram of the stage where the preset current is freewheeling through a diode described in Embodiment 1 of the present application;

[0067] Figure 10 It is one of the current waveforms generated in Embodiment 1 of the present application;

[0068] Figure 11 It is another current waveform generated in Embodiment 1 of the present application;

[0069] Figure 12 It is a schematic diagram of the increased loss and unchanged phase shift of temperature fluctuation in Embodiment 2 of the present application;

[0070] Figure 13 It is a schematic diagram of the increased water temperature, deteriorated heat dissipation conditions, and unchanged phase shift of temperature fluctuation in Embodiment 2 of the present application;

[0071] Figure 14 It is a flowchart of the method for monitoring the health status of the solder layer of the power device described in Embodiment 2 of the present application;

[0072] Figure 15 It is a flowchart of the system for monitoring the health status of the solder layer of the power device described in the embodiments of the present application;

[0073] In the figure: 1 - NTC thermistor, 2 - power device chip, 3 - memory, 4 - controller. Detailed implementation manners

[0074] The following will describe the implementation manners of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for explaining the present invention, rather than for limiting the protection scope of the present invention.

[0075] Before describing the embodiments of the present invention, first describe the reason why the aging of the solder layer of the power device causes the change in the thermal response speed from the power device chip 2 to the NTC thermistor 1:

[0076] Such as Figure 1As shown, it is the structure of the power device chip 2 and the NTC thermistor 1 inside the power device. For the heat conduction path from the power device chip 2 to the NTC thermistor 1, a second-order Cauer thermal network model can be used for analysis. As Figure 2 shown, when the power device chip 2 generates heat, a differential equation regarding the temperature of the NTC thermistor 1 is established according to Kirchhoff's law:

[0077]

[0078] where: R 1 is the thermal resistance from the power device chip to the NTC thermistor, C 1 is the heat capacity from the power device chip to the NTC thermistor, R 2 is the thermal resistance from the NTC thermistor to the heat sink, C 2 is the heat capacity from the NTC thermistor to the heat sink, T 1 is the temperature of the NTC thermistor, T 2 is the ambient temperature, P 0 is the power loss. represents the rate of change of (T 1 -T 2 ) with respect to time t, that is, the speed of temperature change. then represents the rate of change of the rate of change of (T 1 -T 2 ) with respect to time t, that is, the rate of temperature change in the form of acceleration.

[0079] According to the solution method of the second-order non-homogeneous linear differential equation with constant coefficients, the response calculation formula for the temperature of the NTC thermistor 1 relative to the ambient temperature is obtained as:

[0080]

[0081] According to formula (2), the following conclusion can be drawn: The increase in thermal resistance will lead to a slowdown in the thermal response speed of the NTC thermistor 1. When an alternating loss is applied to the power device chip 2, the heat transfer process will also slow down accordingly. Therefore, by applying an alternating loss to the power device chip 2 and observing the thermal response of the NTC thermistor 1, the aging degree of the power device solder layer can be inferred reversely.

[0082] To verify this inference, in the embodiment of the present application, a fourth-order Cauer thermal network model is constructed to simulate the thermal behavior of the power device, especially the thermal response when an alternating loss is applied at the chip, as Figure 3 shown. Through the fourth-order Cauer thermal network model, the temperature fluctuation situation of the power device under the condition of increasing thermal resistance can be simulated, and the specific results are as Figure 4 shown.

[0083] Figure 4 shows the temperature fluctuation characteristics of the power device under different thermal resistance conditions, including the maximum value, minimum value of the temperature fluctuation, and the difference in phase shift ( Figure 4 The change of the minimum value of the temperature fluctuation is shown at A1 in

[0084] Example 1

[0085] As Figure 5 shown, a method for monitoring the health state of the solder layer of a power device includes the following steps:

[0086] Determine the power device chip 2 to be monitored according to the position of the NTC thermistor 1 on the electric drive system.

[0087] Before the vehicle stops, make the rotor of the drive motor stay at a preset position.

[0088] When the vehicle is in a parked state, apply a preset current (i.e., apply an alternating loss) to the power device chip 2 to be monitored, and collect the temperature fluctuation data of the NTC thermistor 1.

[0089] According to the collected temperature fluctuation data, look up the thermal resistance of the corresponding power device solder layer through a preset first data table. Among them, the first data table is a correspondence table of the thermal resistance of different cooling water temperatures, different power device solder layers, and the temperature fluctuation data of the NTC thermistor 1.

[0090] Compare the obtained thermal resistance with the preset thermal resistance to judge the health state of the power device solder layer.

[0091] In a possible embodiment, as Figure 6 shown, the power device chip 2 closest to the NTC thermistor 1 (as the upper bridge arm or the lower bridge arm in the half-bridge module) is used as the heat source for heat loss excitation to avoid the problem that the measurement effect is not obvious due to too large a thermal time constant.

[0092] In a possible embodiment, the first data table is obtained through calibration. The specific calibration method is as follows:

[0093] Select the power device chip 2 closest to the NTC thermistor 1 as the heat source.

[0094] Obtain the thermal response time from the heat source to the NTC thermistor 1.

[0095] Before the vehicle stops, make the rotor of the drive motor stay at a preset position.

[0096] When the vehicle is in a parked state, apply a preset current to the heat source, set the power loss frequency and heat loss frequency of the heat source according to the heat response time, adjust the cooling water temperature and the thermal resistance of the solder layer of the power device, conduct multiple tests, and collect the temperature fluctuation data of the NTC thermistor 1 during the test process. Establish a first data table based on the temperature fluctuation data, the cooling water temperature, and the thermal resistance of the solder layer of the power device. The temperature fluctuation data includes the maximum temperature fluctuation, the minimum temperature fluctuation, and the temperature fluctuation phase shift angle.

[0097] In a possible embodiment, obtain the heat response time from the heat source to the NTC thermistor 1 and use it as a reference for setting the subsequent power loss period. It is required that the power loss period should be less than the heat response time from the heat source to the NTC thermistor 1 to ensure that the temperature fluctuation of the NTC thermistor 1 does not reach a steady state. There are the following two ways to obtain the heat response time from the heat source to the NTC thermistor 1:

[0098] The first way: Apply a preset current to the heat source to ensure that the temperature of the heat source power device chip 2 rises. Then use a temperature acquisition device to collect the temperatures of the NTC thermistor 1 and the heat source. Based on the temperatures of the NTC thermistor 1 and the heat source, obtain the heat response time. Among them, the heat response time is the time required for the temperature of the NTC thermistor 1 to reach stability starting from the change in the temperature of the heat source.

[0099] The second way: Build a finite element model of the power device; in the finite element model of the power device, apply a preset current at the power device chip 2 serving as the heat source to ensure that the temperature of the heat source power device chip 2 rises. Record the temperatures of the NTC thermistor 1 and the heat source during the simulation process through software to obtain the heat response time. Among them, the heat response time is the time required for the temperature of the NTC thermistor 1 to reach stability starting from the change in the temperature of the heat source.

[0100] In a possible embodiment, in order to ensure that the rotor of the drive motor of the vehicle (generally referring to an electric vehicle) can accurately stay at a preset position before parking, specific measures are taken during the aging test of the solder layer of the power device. Specifically as follows:

[0101] When heating the power device chip 2 by applying a current, it can be ensured that this process does not trigger any torque that can drive the motor rotor to rotate. The preset position of the rotor is as Figure 7As shown, the determination of the preset position is based on a principle: that is, by energizing any two phases of the drive motor to generate a synthetic magnetic field, and the polarity of this magnetic field will directly determine the preset position where the rotor should stay. In short, the preset position of the rotor is accurately set and controlled according to the polarity of the synthetic magnetic field after energization. Since there is a large reduction ratio from the drive motor to the wheels of the electric vehicle, and the health status detection program of the power device solder layer can be automatically activated when the rotor approaches this preset position, passengers will not feel that the rotor pre-positioning program has been activated.

[0102] In a possible embodiment, in order to heat the heat source, a current is applied through the circuit as shown in Figure 8 and Figure 9 . Assuming that Figure 8 and Figure 9 in the circuit shown, S 3 is the power device chip 2 serving as the heat source. First, turn on S 3 and S 6 to apply a voltage to two phases of the drive motor (see Figure 8 ), and the magnitude of the generated current is:

[0103]

[0104] where i(t) is the current to be applied at the t-th moment, U dc is the voltage, R is the total resistance of the circuit, and L is the total inductance of two phases of the drive motor. Calculate the required current according to formula (3) to ensure that the generated current does not exceed the maximum allowable current of the electric drive system. Then turn off S 6 for freewheeling, see Figure 8 , and consume the current in the inductor. By adjusting the on and off times of S 3 and S 6 , the application of different power loss frequencies can be achieved. The current waveform generated in this way is as shown in Figure 10 . Or in the freewheeling stage, turn off S 3 , and turn on S 1 or S 5 , and the generated current waveform is as shown in Figure 11 .

[0105] In a possible embodiment, during the calibration process, through adjusting the cooling water temperature and the thermal resistance of the power device solder layer, multiple tests are carried out, and the temperature fluctuation data of the NTC thermistor 1 during the test are collected under the set power loss frequency, set heat loss frequency, different cooling water temperatures, and the thermal resistance of the power device solder layer (different aging degrees of the power device solder layer correspond to different thermal resistances), and a first data table is established based on the temperature fluctuation data, the cooling water temperature, and the thermal resistance of the power device solder layer.

[0106] In a possible embodiment, the thermal resistance of the solder layer of the power device is found according to the collected temperature fluctuation data through a preset first data table, which specifically includes:

[0107] The first method: The collected temperature fluctuation data includes the maximum temperature fluctuation value. According to the cooling water temperature and the maximum temperature fluctuation value, the thermal resistance of the solder layer of the power device is obtained by looking up the first data table, and then the aging degree of the solder layer of the power device is evaluated. In this method, the first data table is at least a correspondence table of different cooling water temperatures, the thermal resistance of different power device solder layers, and the maximum temperature fluctuation value of the NTC thermistor 1.

[0108] The second method: The collected temperature fluctuation data includes the minimum temperature fluctuation value. According to the cooling water temperature and the minimum temperature fluctuation value, the thermal resistance of the solder layer of the power device is obtained by looking up the first data table, and then the aging degree of the solder layer of the power device is evaluated. In this method, the first data table is at least a correspondence table of different cooling water temperatures, the thermal resistance of different power device solder layers, and the minimum temperature fluctuation value of the NTC thermistor 1.

[0109] The third method: The collected temperature fluctuation data includes the temperature fluctuation phase shift angle. According to the cooling water temperature and the temperature fluctuation phase shift angle, the thermal resistance of the solder layer of the power device is obtained by looking up the first data table, and then the aging degree of the solder layer of the power device is evaluated. In this method, the first data table is at least a correspondence table of different cooling water temperatures, the thermal resistance of different power device solder layers, and the temperature fluctuation phase shift angle of the NTC thermistor 1.

[0110] Before running the health status monitoring program, it should be ensured that the vehicle has been completely cooled. After the vehicle has been completely cooled, the cooling water temperature is equal to the ambient temperature, which can be obtained through the vehicle's built-in temperature sensor. And within a short time (1s - 2s) of collecting the temperature fluctuation, the cooling water cannot be heated, so it can be ensured that the heat dissipation conditions remain unchanged during this period. Only the temperature fluctuations at different cooling water temperatures need to be collected as a data set, without considering the change of the cooling water temperature over time.

[0111] In a possible embodiment, the thermal resistance obtained by looking up the table is compared with the preset thermal resistance to judge the health status of the solder layer of the power device, specifically:

[0112] If the increase in the thermal resistance obtained by looking up the table relative to the preset thermal resistance (i.e., the initial thermal resistance) is between 0% and less than 5% (i.e., 0% ≤ increase < 5%), it means that the solder layer of the power device is healthy.

[0113] If the increase in the thermal resistance obtained by looking up the table relative to the preset thermal resistance is between 5% and less than 10% (i.e., 5% ≤ increase <

[0114] If the increase in the thermal resistance obtained from the look-up table relative to the preset thermal resistance is between 10% and less than 15% (i.e., 10% ≤ increase < 15%), it indicates that the solder layer of the power device is in a moderately aged state.

[0115] If the increase in the thermal resistance obtained from the look-up table relative to the preset thermal resistance is between 10% and less than 15% (i.e., 10% ≤ increase < 15%), it indicates that the solder layer of the power device is in a moderately aged state.

[0116] If the increase in the thermal resistance obtained from the look-up table relative to the preset thermal resistance is between 15% and less than 20% (i.e., 15% ≤ increase < 20%), it indicates that the solder layer of the power device is in a severely aged state.

[0117] If the increase in the thermal resistance obtained from the look-up table relative to the preset thermal resistance reaches or exceeds 20% (i.e., increase ≥ 20%), it indicates that the solder layer of the power device reaches the failure standard.

[0118] As Figure 15 shown, in the embodiment of the present application, a health status monitoring system for the solder layer of a power device includes a memory 3 and a controller 4. A computer-readable program is stored in the memory 3, and when the computer-readable program is called by the controller 4, it can execute the steps of the method for monitoring the health status of the solder layer of the power device as described in the embodiment of the present application.

[0119] In the embodiment of the present application, a vehicle adopts the health status monitoring system for the solder layer of the power device as described in the embodiment of the present application.

[0120] Embodiment 1 mainly relies on monitoring the state of the solder layer of the power device under the conditions of determined losses and the temperature of the cooling water. Although this method is effective, its limitation is that it requires the vehicle to be in a parked state so as to be able to control and maintain these conditions. However, in actual applications, electric vehicles often travel under constantly changing working conditions, and the power loss and the temperature of the cooling water will also fluctuate accordingly. Therefore, the method of Embodiment 1 cannot monitor the aging degree of the solder layer of the power device in real time during the normal use of the vehicle.

[0121] Embodiment 2

[0122] To solve the problem existing in Embodiment 1, that is, the state of the solder layer of the power device cannot be monitored in real time during the normal use of the vehicle, another method for monitoring the health status of the solder layer of the power device is proposed in Embodiment 2 of the present application. This method can obtain the aging degree of the solder layer of the power device in the electric drive system in real time during the use of the electric vehicle.

[0123] To deeply explore the influence of the changes in power loss and the temperature of the cooling water on the temperature measurement of the power device, a comparative analysis was carried out on the temperature fluctuation phase shift curve measured by the NTC thermistor 1 (this analysis is based on the Cauer thermal network model). The Cauer thermal network model can accurately describe the heat conduction process inside the power device.

[0124] like Figure 12 As shown in the figure, the temperature response waveform of NTC thermistor 1 is shown when the power loss of the input power device increases and the power loss frequency remains unchanged. It can be seen from the waveform that as the power loss increases, the phase shift curve of the temperature waveform of NTC thermistor 1 does not change (from Figure 12 This is because when the power loss changes but the power loss frequency remains unchanged, it only affects the magnitude of the temperature waveform, but does not cause a phase shift in the temperature waveform of the NTC thermistor 1.

[0125] like Figure 13 As shown in the figure, it shows the thermal resistance from the power device base to the heat sink ( Figure 3 The temperature response waveform of NTC thermistor 1 when the R3 in the figure increases. Similarly, it can be seen from the waveform that as the thermal resistance increases, the phase shift curve of the temperature waveform of NTC thermistor 1 does not change (from Figure 13 This is because the change in thermal resistance from the power device base plate to the heat sink (the change in thermal resistance caused by the change in cooling water temperature causing the change in heat dissipation conditions) does not directly affect the change in thermal response speed from the power device chip 2 to the NTC thermistor 1, and therefore does not cause a phase shift in temperature fluctuations.

[0126] Based on the above analysis, it can be concluded that during normal use of electric vehicles, although the power loss and cooling water temperature will change, these changes will not affect the effectiveness of the temperature fluctuation phase shift of the NTC thermistor 1 as an indicator for evaluating the degree of aging of the solder layer.

[0127] like Figure 14 As shown, a method for monitoring the health status of a solder layer of a power device comprises the following steps:

[0128] The power device chip 2 to be monitored is determined according to the position of the NTC thermistor 1 on the electric drive system.

[0129] During the operation of the vehicle, the power loss frequency of the power device chip 2 to be monitored and the temperature waveform phase shift of the NTC thermistor 1 are collected.

[0130] According to the collected power loss frequency and temperature waveform phase shift, the thermal resistance of the corresponding power device solder layer is searched through the preset second data table. The second data table is the corresponding relationship between different power loss frequencies, thermal resistance of different power device solder layers and temperature waveform phase shift of NTC thermistor 1.

[0131] The obtained thermal resistance is compared with the preset thermal resistance to determine the health status of the solder layer.

[0132] In a possible embodiment,Figure 6 As shown, based on the actual physical structure of the power device chip 2 and the NTC thermistor 1 inside the power device for the electric drive system, the power device chip 2 closest to the NTC thermistor 1 (acting as the upper or lower bridge arm in the half-bridge module) is used as the heat source for heat loss excitation, avoiding the problem that the measurement effect is not obvious due to the too large thermal time constant. Subsequently, only based on the control strategy of the power device, the power loss frequency of the power device chip 2 closest to the NTC thermistor 1 can be deduced.

[0133] In a possible embodiment, the second data table is obtained through calibration. The specific calibration method is as follows:

[0134] Select the power device chip 2 closest to the NTC thermistor 1 as the heat source. Obtain the thermal response time from the heat source to the NTC thermistor 1, and set the power loss frequency of the heat source according to the thermal response time. During vehicle operation, conduct multiple tests by adjusting the power loss frequency of the heat source and the thermal resistance of the power device solder layer, and collect the temperature waveform data of the NTC thermistor 1 during the test process. Extract the phase shift information from the collected temperature waveform data to obtain the temperature waveform phase shift. Based on the temperature waveform phase shift, the power loss frequency of the heat source, and the thermal resistance of the power device solder layer, obtain the second data table.

[0135] In a possible embodiment, obtain the thermal response time from the heat source to the NTC thermistor 1 and use it as a reference for subsequent setting of the power loss period. It is required that the power loss period should be less than the thermal response time from the heat source to the NTC thermistor 1 to ensure that the temperature fluctuation of the NTC thermistor 1 does not reach a steady state. There are the following two ways to obtain the thermal response time from the heat source to the NTC thermistor 1:

[0136] The first way: Apply a preset current to the heat source to ensure that the power device chip 2 of the heat source generates a temperature rise. Then use a temperature acquisition device to collect the temperatures of the NTC thermistor 1 and the heat source; based on the temperatures of the NTC thermistor 1 and the heat source, obtain the thermal response time. Among them, the thermal response time is the time required for the temperature of the NTC thermistor 1 to reach stability starting from the change in the temperature of the heat source.

[0137] The second way: Build a finite element model of the power device; in the finite element model of the power device, apply a preset current at the power device chip 2 acting as the heat source to ensure that the power device chip 2 of the heat source generates a temperature rise. Record the temperatures of the NTC thermistor 1 and the heat source during the simulation process through software to obtain the thermal response time. Among them, the thermal response time is the time required for the temperature of the NTC thermistor 1 to reach stability starting from the change in the temperature of the heat source.

[0138] In a possible embodiment, the input quantities of the second data table are the power loss frequency and the phase shift angle of the temperature waveform of the NTC thermistor 1, and the output quantity of the second data table is the thermal resistance of the solder layer of the power device.

[0139] In a possible embodiment, when the vehicle is in a high-speed operating condition, it is ensured that the power loss period is less than the thermal response time of the power device, and the aging degree acquisition program of the solder layer of the power device is run. The power loss frequency of the heat source and the phase shift angle of the temperature waveform of the NTC thermistor 1 are collected, and the thermal resistance of the solder layer of the power device is obtained by looking up the second data table.

[0140] In a possible embodiment, the thermal resistance obtained by looking up the table is compared with the preset thermal resistance to judge the health state of the solder layer of the power device. Specifically:

[0141] If the increase amount of the thermal resistance obtained by looking up the table relative to the preset thermal resistance (i.e., the initial thermal resistance) is between 0% and less than 5% (i.e., 0% ≤ increase amount < 5%), it means that the solder layer of the power device is healthy.

[0142] If the increase amount of the thermal resistance obtained by looking up the table relative to the preset thermal resistance is between 5% and less than 10% (i.e., 5% ≤ increase amount < 10%), it means that the solder layer of the power device is in a mild aging state.

[0143] If the increase amount of the thermal resistance obtained by looking up the table relative to the preset thermal resistance is between 10% and less than 15% (i.e., 10% ≤ increase amount < 15%), it means that the solder layer of the power device is in a moderate aging state.

[0144] If the increase amount of the thermal resistance obtained by looking up the table relative to the preset thermal resistance is between 15% and less than 20% (i.e., 15% ≤ increase amount < 20%), it means that the solder layer of the power device is in a severe aging state.

[0145] If the increase amount of the thermal resistance obtained by looking up the table relative to the preset thermal resistance reaches or exceeds 20% (i.e., increase amount ≥ 20%), it means that the solder layer of the power device reaches the failure standard.

[0146] As Figure 15 shown, in the embodiment of the present application, a health state monitoring system for the solder layer of a power device includes a memory 3 and a controller 4. A computer-readable program is stored in the memory 3, and when the computer-readable program is called by the controller 4, it can execute the steps of the health state monitoring method for the solder layer of the power device as described in the embodiment of the present application.

[0147] In the embodiment of the present application, a vehicle adopts the health state monitoring system for the solder layer of the power device as described in the embodiment of the present application.

[0148] The above embodiments are preferred embodiments of the present invention. However, the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for monitoring the health status of a solder layer of a power device, characterized in that: The following steps are involved: Determining a power device chip (2) to be monitored according to a position of an NTC thermistor (1) on the electric drive system; The rotor of the drive motor is stopped at a preset position before the vehicle stops; When the vehicle is in a parked state, a preset current is applied to the power device chip (2) to be monitored, and temperature fluctuation data of the NTC thermistor (1) is collected; According to the collected temperature fluctuation data, the thermal resistance of the solder layer of the corresponding power device is searched through a preset first data table; Compare the obtained thermal resistance with the preset thermal resistance to determine the health status of the solder layer of the power device; The first data table is a table of corresponding relationships between different cooling water temperatures, thermal resistances of solder layers of different power devices and temperature fluctuation data of the NTC thermistor (1).

2. The method for monitoring the health status of solder layer of a power device according to claim 1, characterized in that: A power device chip (2) that is closest to the NTC thermistor (1) is selected as the power device chip (2) to be monitored.

3. The method for monitoring the health status of solder layer of a power device according to claim 1, characterized in that: The first data table is obtained by calibration, specifically: Select the power device chip (2) closest to the NTC thermistor (1) as the heat source; Obtaining a thermal response time from the heat source to the NTC thermistor (1); The rotor of the drive motor is stopped at a preset position before the vehicle stops; When the vehicle is in a parked state, a preset current is applied to the heat source, and the power loss frequency and the heat loss frequency of the heat source are set according to the thermal response time, the cooling water temperature and the thermal resistance of the solder layer of the power device are adjusted to perform multiple tests, and the temperature fluctuation data of the NTC thermistor (1) during the test are collected, and a first data table is established based on the temperature fluctuation data, the cooling water temperature and the thermal resistance of the solder layer of the power device; The temperature fluctuation data includes at least one of a maximum value of temperature fluctuation, a minimum value of temperature fluctuation and a phase shift angle of temperature fluctuation.

4. The method for monitoring the health status of solder layer of a power device according to claim 3, characterized in that: The thermal response time from the heat source to the NTC thermistor (1) is obtained, specifically: applying a preset current to the heat source; Collect the temperatures of the NTC thermistor (1) and the heat source; Based on the temperature of the NTC thermistor (1) and the heat source, the thermal response time is obtained; or: Build finite element models of power devices; In a finite element model of a power device, a preset current is applied to a power device chip (2) serving as a heat source; During the simulation, the temperatures of the NTC thermistor (1) and the heat source are recorded to obtain the thermal response time. The thermal response time is the time required from the start of the change in the temperature of the heat source to the time when the temperature of the NTC thermistor (1) reaches stability.

5. A method for monitoring the health status of a solder layer of a power device, characterized in that: The following steps are involved: Determining a power device chip (2) to be monitored according to a position of an NTC thermistor (1) on the electric drive system; During vehicle operation, the power loss frequency of the power device chip (2) to be monitored and the temperature waveform phase shift of the NTC thermistor (1) are collected; According to the collected power loss frequency and temperature waveform phase shift, the thermal resistance of the corresponding power device solder layer is searched through a preset second data table; The obtained thermal resistance is compared with the preset thermal resistance to determine the health status of the solder layer; The second data table is a correspondence between different power loss frequencies, thermal resistances of solder layers of different power devices and the temperature waveform phase shift of the NTC thermistor (1).

6. The method for monitoring the health status of solder layer of a power device according to claim 5, characterized in that: A power device chip (2) that is closest to the NTC thermistor (1) is selected as the power device chip (2) to be monitored.

7. The method for monitoring the health status of solder layer of a power device according to claim 5, characterized in that: The second data table is obtained by calibration, specifically: Select the power device chip (2) closest to the NTC thermistor (1) as the heat source; Obtaining a thermal response time from the heat source to the NTC thermistor (1), and setting a power loss frequency of the heat source according to the thermal response time; During vehicle operation, multiple tests are performed by adjusting the power loss frequency of the heat source and the thermal resistance of the solder layer of the power device, and temperature waveform data of the NTC thermistor (1) is collected during the test; Extract phase shift information from the collected temperature waveform data to obtain the temperature waveform phase shift; A second data table is obtained based on the temperature waveform phase shift, the power loss frequency of the heat source, and the thermal resistance of the solder layer of the power device.

8. The method for monitoring the health status of solder layer of a power device according to claim 7, characterized in that: The thermal response time from the heat source to the NTC thermistor (1) is obtained, specifically: applying a preset current to the heat source; Collect the temperatures of the NTC thermistor (1) and the heat source; Based on the temperature of the NTC thermistor (1) and the heat source, the thermal response time is obtained; or: Build finite element models of power devices; In a finite element model of a power device, a preset current is applied to a power device chip (2) serving as a heat source; During the simulation, the temperatures of the NTC thermistor (1) and the heat source are recorded to obtain the thermal response time. The thermal response time is the time required from the start of the change in the temperature of the heat source to the time when the temperature of the NTC thermistor (1) reaches stability.

9. A power device solder layer health status monitoring system, characterized in that: It comprises a memory (3) and a controller (4), wherein the memory (3) stores a computer-readable program, and when the computer-readable program is called by the controller (4), it can execute the steps of the method for monitoring the health status of the solder layer of a power device as claimed in any one of claims 1 to 8.

10. A vehicle, characterized in that: A power device solder layer health status monitoring system as described in claim 9 is used.

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