Method for setting relationship between on-state voltage drop of power device and junction temperature under large current switching state

Abstract

The application provides a method for setting the relationship between the on-state voltage drop and the junction temperature of a power device under a large current switching state. The device is operated under a switching state, a large current flowing through the device is a square wave current with a fixed amplitude and a fixed duty cycle, and the operating junction temperature and the reference point temperature are set by controlling the operating conditions of a control circuit and the temperature of a heat sink. After the device operates to a thermal steady state, the on-state voltage drop and the reference point temperature are measured, then the large current is cut off and a constant small current is injected into the device to measure the junction temperature. The equivalent temperature of the packaging material is represented by the reference point temperature, and a linear relationship among the on-state voltage drop, the reference point temperature and the junction temperature under a large current is fitted. The application can flexibly control the self-heating and external heating conditions of the device during setting, and the influence of the temperature of the packaging material on the on-state voltage drop is considered, thereby improving the accuracy of predicting the junction temperature by the on-state voltage drop under a large current.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, in particular, to a method for setting the relationship between the on-state voltage drop and the junction temperature of a power device under a large current switching state. BACKGROUND

[0002] As a core component in power electronic systems, power devices are one of the main factors causing the failure of power electronic systems, and the aging failure of power devices is usually caused by the long-term fluctuation of the junction temperature of the device. Therefore, accurately predicting the junction temperature of the power device under working conditions is of great significance to the evaluation of the reliability of the power electronic system. Among them, using the on-state voltage drop under large current as a temperature-sensitive parameter to predict the junction temperature is widely used because of its low invasiveness and fast response.

[0003] In order to predict the junction temperature of the power device using the on-state voltage drop under large current, the relationship between the on-state voltage drop and the junction temperature under large current must be set. The existing setting method is usually carried out in a temperature chamber, and a pulse current is passed through the device to measure the on-state voltage drop at different temperatures. In such a setting method, the junction temperature of the device is controlled by the heating of the temperature chamber, and the internal temperature of the device is uniformly distributed and equal to the temperature of the temperature chamber. However, in actual working conditions, the power device operates in a switching state, and the increase of the junction temperature is caused by the self-heating of the device loss, and the internal temperature distribution is uneven. Such differences will cause the temperature of the encapsulation material (such as bonding wire, connection terminal) inside the device to be different from that during the setting, and the resulting voltage drop will also be different, resulting in errors in the measurement of the junction temperature. SUMMARY

[0004] In view of the defects in the prior art, the purpose of the present application is to provide a method for setting the relationship between the on-state voltage drop and the junction temperature of a power device under a large current switching state.

[0005] According to one aspect of the present application, a method for setting the relationship between the on-state voltage drop and the junction temperature of a power device under a large current switching state is provided, comprising:

[0006] Obtaining the relationship between the on-state voltage drop and the junction temperature under a constant small current;

[0007] Controlling the switching state of the measured device through the drive signal, so that the current flowing through the measured device is a square wave current with fixed amplitude and fixed duty cycle, and the maximum value of the square wave current is a set large current value and the minimum value is zero;

[0008] Under the switching state, the self-heating condition of the measured device is set by controlling the operating condition of the circuit, and the external heating condition of the measured device is set by controlling the temperature of the heat sink; after the measured device operates under the self-heating condition and the external heating condition to reach a thermal steady state, the current, the on-state voltage drop under a large current, and the reference point temperature of the measured device are measured;

[0009] The measured device is turned off by the driving signal, and immediately turned on by the driving signal after the current flowing through the measured device is reduced to zero, and a constant small current is injected to measure the junction temperature of the measured device;

[0010] The circuit operating conditions and the heat sink temperature are changed to make the measured device work in different thermal steady states, and a plurality of sets of on-state voltage drop, reference point temperature and junction temperature data of the measured device under the set large current are measured;

[0011] The relationship between the on-state voltage drop, reference point temperature and junction temperature of the measured device under the set large current is fitted by using a linear equation.

[0012] Preferably, the measured device is a power semiconductor device, including controllable power semiconductor devices and power diodes, and the package of the power semiconductor device adopts one or more of module-based, crimping, and discrete packaging technologies; and the material of the power semiconductor device adopts one or more of silicon, silicon carbide, and gallium nitride.

[0013] Preferably, the on-state voltage drop and junction temperature relationship under the constant small current includes:

[0014] The measured device is placed in a temperature chamber or on a hot plate;

[0015] A constant small current is passed, and the temperature of the temperature chamber or the hot plate is changed, and the on-state voltage drop under the small current corresponding to different temperatures is recorded;

[0016] The linear relationship between the on-state voltage drop under the small current and the junction temperature is fitted, which is used for junction temperature measurement in the setting process.

[0017] Preferably, under the condition of keeping the set large current unchanged, the loss of the measured device can be changed by changing the circuit operating conditions, so as to change the self-heating conditions of the measured device.

[0018] The circuit operating conditions include one or more of bus voltage, switching frequency, duty cycle, and driving resistance.

[0019] Preferably, the reference point temperature includes the case temperature, heat sink temperature, and integrated thermal resistance temperature of the power module of the measured device.

[0020] Preferably, the heat sink has heating and cooling functions, and the reference point temperature changes with the temperature change of the heat sink; the reference point temperature can be set to a constant value.

[0021] Preferably, the relationship between the on-state voltage drop, reference point temperature and junction temperature of the measured device under the set large current is fitted by using a linear equation, including:

[0022] Considering the influence of the temperature distribution inside the device, a relationship is obtained:

[0023] V ce = k j ·T j + k i ·T i + c (1)

[0024] wherein V ce is the on-state voltage drop of the device under test at a large current, k j is the temperature coefficient of the junction temperature T j , k i is the temperature coefficient of the package material temperature T i , and c is the on-state voltage drop value when both T i and T j are 0;

[0025] Replacing the package material temperature T i in the relationship with the junction temperature and the reference point temperature, the on-state voltage drop of the device under test after reaching thermal steady state is expressed as a linear function of the junction temperature and the reference point temperature, specifically:

[0026] V ce = k j ·T j + k r ·T r + c (2)

[0027] wherein k j ’ is the temperature coefficient of the junction temperature T j after temperature replacement, and k r is the temperature coefficient of the reference point temperature T r .

[0028] Preferably, the replacement of the package material temperature T i in the relationship with the junction temperature and the reference point temperature includes:

[0029] When the device under test reaches thermal steady state, its package material temperature is expressed as a linear combination of the junction temperature and the reference point temperature:

[0030] T i = α·T j + (1-α)·T r (3)

[0031] T i is the package material temperature, T j is the junction temperature of the device under test, T r is the reference point temperature, and α is the relationship coefficient among the three temperatures.

[0032] Substitute the linear combination into the relationship, and after arrangement, obtain k j ’、k r Take values, k j ’=k j +α·k i , k r =k i -α·k i .

[0033] Preferably, for different large current and driving voltage values, the relationship between the on-state voltage drop under the large current, the reference point temperature and the junction temperature is also different.

[0034] Preferably, when the setting result is used for the junction temperature prediction, the selection of the reference point should be ensured to be the same as that used when setting the relationship between the on-state voltage drop and the junction temperature of the power device under the large current switch state, and the junction temperature is calculated by measuring the on-state voltage drop under the large current of the measured device and the reference point temperature.

[0035] Compared with the prior art, the embodiment of the present application has at least one of the following beneficial effects:

[0036] The method for setting the relationship between the on-state voltage drop and the junction temperature of the power device under the large current switch state in the embodiment of the present application can flexibly control the self-heating and external heating conditions of the device during setting, and the influence of the internal temperature distribution of the device on the on-state voltage drop is considered, thereby improving the accuracy of the junction temperature prediction using the on-state voltage drop under the large current. BRIEF DESCRIPTION OF DRAWINGS

[0037] Other characteristics, objects and advantages of the present application will become more apparent from the following detailed description of non-restrictive embodiments, with reference to the accompanying drawings:

[0038] Figure 1 The flow chart of the method for setting the relationship between the on-state voltage drop and the junction temperature of the power device under the large current switch state provided by an embodiment of the present application;

[0039] Figure 2 The principle diagram of the setting circuit in a preferred embodiment of the present application;

[0040] Figure 3 The waveform diagram when a group of on-state voltage drops under the large current, reference point temperatures and junction temperatures are measured in a preferred embodiment of the present application;

[0041] Figure 4 The equivalent circuit model of the power device in a preferred embodiment of the present application;

[0042] Figure 5 The equivalent thermal circuit model for indicating the temperature of the packaging material of the power device in a preferred embodiment of the present application. DETAILED DESCRIPTION

[0043] The application will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the application. These are all within the scope of protection of the application.

[0044] In various embodiments of the application, two professional terms are involved: large current and small current. The large current is the working current that can cause the device to produce a significant temperature rise, and for devices of different capacities, it is usually several tens or hundreds of amperes; the small current is the measurement current that does not cause the device to produce a significant temperature rise, and for devices of different capacities, it is usually several tens or hundreds of milliamperes.

[0045] In an embodiment of the application, a method for setting the relationship between the on-state voltage drop and the junction temperature of a power device under a large current switching state is provided, as shown in FIG. 1, the main process of which is as follows: Figure 1

[0046] S100, obtaining the relationship between the on-state voltage drop and the junction temperature under a constant small current;

[0047] S200, controlling the switching state of the measured device through the driving signal, so that the current flowing through the measured device is a square wave current with a fixed amplitude and a fixed duty cycle, the maximum value of the square wave current is a set large current value, and the minimum value is zero;

[0048] S300, under the switching state, setting the self-heating condition of the measured device by controlling the operating condition of the circuit, and setting the external heating condition of the measured device by controlling the temperature of the heat sink; after the measured device operates under the self-heating condition and the external heating condition to reach a thermal steady state, the current, the on-state voltage drop under the large current, and the reference point temperature of the measured device are measured;

[0049] S400, latching the measured device through the driving signal, and immediately turning on the measured device through the driving signal and injecting a constant small current to measure the junction temperature of the measured device after the current flowing through the measured device is reduced to zero;

[0050] S500, determining whether to change the operating condition, if yes, returning to S300 to change the circuit operating condition and the heat sink temperature, so that the measured device works in different thermal steady states, and a plurality of sets of on-state voltage drop under the large current, reference point temperature, and junction temperature data of the measured device under the set large current are measured; if not, entering S600.

[0051] S600, using a linear equation to fit the relationship between the on-state voltage drop, the reference point temperature, and the junction temperature of the measured device under the set large current.

[0052] ​In the above embodiment, the measured device works in a large current switching state, the working condition is flexible and controllable, and multiple sets of experimental data of the device under different working conditions can be obtained. Considering the uneven internal temperature distribution, the temperature of the packaging material is combined with the junction temperature and the reference point temperature to correct the relationship between the on-voltage drop and the junction temperature, so that the prediction effect is more accurate.

[0053] In a preferred embodiment of the present application, S100 is implemented to obtain the relationship between the on-voltage drop under a constant small current and the junction temperature. Specifically, the measured device is usually placed in a temperature box or on a heating plate, a constant small current is passed, and the temperature of the temperature box or the heating plate is changed, the on-voltage drop under the small current corresponding to different temperatures is recorded, and a linear relationship between the on-voltage drop under the small current and the junction temperature is fitted, which is used for junction temperature measurement in subsequent setting process.

[0054] It should be noted that in other embodiments, this step can be performed after other steps are completed, and only needs to be prepared when the constant small current is injected to measure the junction temperature of the measured device.

[0055] In a preferred embodiment of the present application, the measured device is a power semiconductor device, including controllable power semiconductor devices and power diodes, and the packaging of the power semiconductor device adopts one or more of the module-based, crimping, and discrete packaging technologies; and the material of the power semiconductor device adopts one or more of silicon, silicon carbide, and gallium nitride.

[0056] In a preferred embodiment of the present application, step S200 is implemented, which is specifically implemented by the circuit schematic diagram as shown in Figure 2 As shown in Figure 2 It can be seen that the four power devices are connected in an H-bridge structure with an inductive load. Each power device can be used as a measured device. The H-bridge circuit is operated in a switching state, and the duty cycles of the two phases are set to constant values. At this time, the circuit current is approximately a constant direct current. The difference between the duty cycles of the two phases is controlled to control the current size of the load inductance. At this time, the current flowing through the measured device is a square wave current with fixed amplitude and fixed duty cycle, and the maximum value of the square wave current is the set large current value and the minimum value is zero.

[0057] In a preferred embodiment of the present application, under the condition of keeping the set large current unchanged, the loss of the measured device can be changed by changing the circuit operating conditions, so as to change the self-heating condition of the measured device. In some specific embodiments, the circuit operating conditions of step S300 are one or more of bus voltage, switching frequency, duty cycle, and driving resistance. The reference point temperature includes the shell temperature of the measured device, the heat sink temperature, and the temperature of the integrated thermal resistance in the power module.

[0058] By changing the bus voltage, switching frequency, duty cycle, drive resistance and other circuit operating conditions, the measured device can be operated under different self-heating conditions. By heating or cooling the controllable temperature radiator, the measured device can be operated under different external heating conditions. By measuring the on-voltage drop and small current injection circuit, the on-voltage drop of the measured device under switching state and small current injection state can be measured.

[0059] In some embodiments, as shown in Figure 3 , it is a set of on-voltage drop, reference point temperature and junction temperature data waveform diagram under large current.

[0060] First, set the circuit operating conditions and radiator temperature, so that the measured device operates in switching state and reaches thermal steady state. Measure the on-voltage drop of the measured device under large current switching state and the reference point temperature under thermal steady state. Then, lock all device drive signals to quickly reduce the load current to zero, and reapply the drive signal to the measured device and inject a small current to measure the junction temperature. After changing the circuit operating conditions and radiator temperature to make the measured device operate in large current switching state again, repeat the measurement process, that is, obtain multiple sets of on-voltage drop, reference point temperature and junction temperature data, which are used to fit the relationship between the three by using linear equation. Figure 3

[0061] Based on the above embodiments, multiple sets of on-voltage drop, reference point temperature and junction temperature data are obtained. In a preferred embodiment of the present application, S600 is implemented to fit the relationship between the on-voltage drop, reference point temperature and junction temperature of the measured device under the set large current by using linear equation. Specifically, as shown in Figure 4 , it is a circuit model equivalent to a power device. The on-voltage drop of the measured device is the sum of the voltage drop of the chip and the voltage drop of the packaging material. The voltage drop of the chip is a linear function of the junction temperature, and the voltage drop of the packaging material is a linear function of the packaging material temperature. Therefore, the on-voltage drop of the measured device is a linear function of the junction temperature and the packaging material temperature, and the formula is:

[0062] V ce = k j ·T j + k i ·T i + c (1)

[0063] Where V ce is the on-voltage drop of the measured device under large current, k j is the temperature coefficient of the junction temperature T j , k i is the temperature coefficient of the packaging material temperature T i , and c is the on-voltage drop value when T i and T j are both 0. ​

[0064] Further, as shown in Figure 5 is an equivalent thermal circuit for representing the temperature of the power device packaging material, the packaging material temperature can be represented as a point in the thermal circuit from the junction to the reference point, when the device under test works in the switching state and reaches thermal steady state, the packaging material temperature can be represented according to the equivalent thermal circuit as:

[0065] T i = α·T j + (1-α)·T r (3)

[0066] Wherein, T i is the packaging material temperature, T j is the junction temperature of the device under test, T r is the reference point temperature, and α is the relationship coefficient between the three temperatures, the specific value is R ir / (R ji +R ir ). Wherein R ir is the equivalent thermal resistance of the packaging material to the reference point, R ji is the equivalent thermal resistance from the junction to the packaging material, and the value of the equivalent thermal resistance is related to the structure of the device itself and the selection of the reference point. Through the formula, the influence of the packaging material temperature which is difficult to measure on the on-state voltage drop is characterized by the parameters which are easy to measure.

[0067] Substitute the packaging material temperature in the on-state voltage drop expression (1) of the device under test with the junction temperature and the reference point temperature, then the on-state voltage drop of the device under test after reaching thermal steady state can be represented as a linear function of the junction temperature and the reference point temperature, the formula is:

[0068] V ce = k j ’·T j + k r ·T r + c (2)

[0069] Wherein, k j ’ is the temperature coefficient of the junction temperature T j after temperature replacement, k r is the temperature coefficient of the reference point temperature T r , and the aforementioned parameters satisfy the calculation relationship of k j ’=k j +α·k i and k r =k i -α·k i . The setting method aims to obtain the values of k j ’, k r and c. In actual junction temperature prediction, the on-state voltage drop and the temperature of the reference point need to be measured and combined with the kj ', k r The value of c is calculated with the measured device junction temperature.

[0070] It should be noted that for different large current and driving voltage values, the relationship between the on-state voltage drop under large current, the reference point temperature and the junction temperature is also different. The set large current and driving voltage should be determined according to the requirements in the actual application scenario. In the above, the driving signal is used to control the switching state of the device. By switching the high and low levels of the driving signal, the device under test can be made to work in the on or off state, thereby controlling the current flowing through the device under test. The driving voltage here refers to the specific value of the high level of the driving signal, that is, the size of the driving voltage applied to the device under test when the device is in the on state. The on-state voltage drop, which is related to the high level of the driving voltage, is used in the above embodiment to calculate the junction temperature. Therefore, the size of the driving voltage used in the setting needs to be selected according to the size of the driving voltage in the actual application. When the setting result is used for junction temperature prediction, the driving voltage used should be the same as that used in the setting.

[0071] In addition, when the setting result is used for junction temperature prediction, the reference point selection should also be the same as that in the setting. The on-state voltage drop under large current of the device under test and the reference point temperature are measured to calculate the junction temperature.

[0072] According to the power device on-state voltage drop and junction temperature relationship setting method under the large current switching state in the foregoing embodiment, the correlation between the obtained on-state voltage drop, reference point temperature and junction temperature data exhibits higher accuracy in predicting junction temperature data. The advantage of this method is its low invasiveness, fast response and high accuracy, so it is more easily applied widely.

[0073] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the above specific embodiments, and those skilled in the art can make various modifications or modifications within the scope of the claims, which does not affect the essential content of the present application. The above preferred features can be used in combination in the case of not conflicting with each other.

Claims

1. A method for setting the relationship between the on-state voltage drop of a power device and the junction temperature in a high-current switching state, characterized in that The method comprises the following steps: Obtaining the relationship between the on-state voltage drop and the junction temperature under a constant small current; Controlling the switching state of the device under test through the driving signal to make the current flowing through the device under test a square wave current with a fixed amplitude and a fixed duty cycle, the maximum value of the square wave current being a set large current value and the minimum value being zero; Under the switching state, setting the self-heating condition of the device under test by controlling the circuit operating condition and setting the external heating condition of the device under test by controlling the temperature of the heat sink; After the device under test reaches thermal steady state under the self-heating condition and the external heating condition, measuring the current, the on-state voltage drop under a large current and the reference point temperature of the device under test; Making the device under test be turned off through the driving signal, and then making the device under test be turned on through the driving signal immediately after the current flowing through the device under test is reduced to zero, and injecting a constant small current to measure the junction temperature of the device under test; Changing the circuit operating condition and the temperature of the heat sink to make the device under test work in different thermal steady states, and measuring multiple sets of on-state voltage drop under a large current, reference point temperature and junction temperature data of the device under test under the set large current; Fitting the relationship among the on-state voltage drop, the reference point temperature and the junction temperature of the device under test under the set large current by using a linear equation.

2. The method according to claim 1, wherein the method is characterized by: The device under test is a power semiconductor device, including controllable power semiconductor devices and power diodes, the packaging of the power semiconductor device adopts one or more of the following technologies: module-based packaging, crimping packaging and discrete packaging technology, and the material of the power semiconductor device adopts one or more of the following materials: silicon, silicon carbide and gallium nitride.

3. The method according to claim 1, wherein the method is characterized by: The method of obtaining the relationship between the on-state voltage drop and the junction temperature under a constant small current comprises the following steps: Placing the device under test in a temperature chamber or on a hot plate; Passing a constant small current and changing the temperature of the temperature chamber or the hot plate, and recording the on-state voltage drop under the small current corresponding to different temperatures; Fitting a linear relationship between the on-state voltage drop under the small current and the junction temperature, which is used for junction temperature measurement in the setting process.

4. The method according to claim 1, wherein the method is characterized by: Under the condition that the set large current is unchanged, the loss of the device under test can be changed by changing the circuit operating condition, so as to change the self-heating condition of the device under test. The circuit operating condition includes one or more of the following: bus voltage, switching frequency, duty cycle and driving resistance.

5. The method according to claim 1, wherein the method is characterized by: The reference point temperature includes the case temperature, the heat sink temperature and the temperature of the thermal resistance integrated in the power module of the device under test.

6. The method according to claim 5, wherein the method is characterized by: The heat sink has heating and cooling functions, and the reference point temperature changes with the temperature change of the heat sink; the reference point temperature can be set to a constant value.

7. The method according to claim 1, wherein the method is characterized by: The method of fitting the relationship among the on-state voltage drop, the reference point temperature and the junction temperature of the device under test under the set large current by using a linear equation comprises the following steps: Considering the influence of the internal temperature distribution of the device, the relationship is obtained as follows: V ce = k j · T j + k i · T i + c (1) Wherein, V ce is the on voltage drop of the device under test at a large current, k j is the temperature coefficient of the junction temperature T j , k i is the temperature coefficient of the package material temperature T i , c is the on voltage drop value when T i and T j are both 0. Replacing the package material temperature T of the relationship with the junction temperature and the reference point temperature i The on-state voltage drop of the device under test after reaching thermal steady state is expressed as a linear function of the junction temperature and the reference point temperature, specifically: V ce = k j · T j + k r · T r + c (2) where k j is the temperature coefficient of the junction temperature T j after the temperature replacement, and kr is the temperature coefficient of the reference point temperature Tr.

8. The method according to claim 7, wherein the method is characterized by: the package material temperature T replacing the relationship by the junction temperature and the reference point temperature i comprising: After the device under test reaches thermal steady state, the temperature of the packaging material of the device under test is expressed as a linear combination of the junction temperature and the reference point temperature as follows: T i = a · T j + (1 - a) · T r (3) T i Tencap is the temperature of the encapsulation material j Tj is the junction temperature of the device under test r Tref is the temperature of the reference point, and a is the relationship coefficient between the three temperatures Substitute the linear combination into the relation, and after rearrangement obtain k j ’ = k r + α · k j ’ = k j - α · k i , k r = k i + α · k i .

9. The method according to claim 8, wherein the method is characterized by, For different large current and driving voltage values, the relationship among the on-state voltage drop under a large current, the reference point temperature and the junction temperature is also different.

10. The method according to claim 8, wherein the method is characterized by: When the setting result is used for the junction temperature prediction, the selection of the reference point should be ensured to be the same as the reference point used for setting the relationship between the on-state voltage drop of the power device and the junction temperature under the large current switch state, and the junction temperature is calculated by measuring the on-state voltage drop of the measured device under the large current and the temperature of the reference point.

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