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

Abstract

The invention provides a method for setting a relationship between conduction voltage drop and junction temperature of a power device in a large-current on-off state, and the method enables a tested device to work in the on-off state, and the large current flowing through the device is a square wave current with a fixed amplitude and a fixed duty ratio. The operation junction temperature and the reference point temperature are set by controlling the operation condition of the circuit and the temperature of the radiator; after the device runs to a thermal steady state, measuring the conduction voltage drop and the reference point temperature of the device, then cutting off a large current, and injecting a constant small current into the measured device to measure the junction temperature of the measured device; the equivalent temperature of the packaging material is represented by the reference point temperature, and a linear relation among the conduction voltage drop, the reference point temperature and the junction temperature under the large current is fitted. According to the invention, the self-heating and external heating conditions of the whole timer can be flexibly controlled, and the influence of the temperature of the packaging material on the conduction voltage drop is considered, so that the accuracy of predicting the junction temperature by using the conduction voltage drop under large current is improved.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a method for adjusting the relationship between the on-state voltage drop and the junction temperature of a power device in a high-current switching state. Background Art

[0002] As the core components of power electronic systems, power devices are one of the most important factors causing power electronic system failures. The aging failure of power devices is usually caused by the long-term junction temperature fluctuations of the devices. Therefore, accurately predicting the junction temperature of power devices under working conditions is of great significance to the reliability assessment of power electronic systems. Among them, using the on-state voltage drop under high current as a temperature-sensitive parameter to predict junction temperature is widely used because of its advantages such as low invasiveness and fast response.

[0003] In order to predict the junction temperature of power devices using the on-state voltage drop under high current, the relationship between the on-state voltage drop and the junction temperature under high current must be adjusted first. The existing adjustment 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 an adjustment method, the junction temperature of the device is controlled by heating the temperature chamber, and the temperature inside the device is evenly distributed and equal to the temperature of the temperature chamber. In actual working conditions, the power device operates in a switching state, and the increase in junction temperature is caused by the loss of the device and self-heating, and the internal temperature distribution is uneven. Such a difference will cause the temperature of the packaging material (such as bonding wires and connection terminals) inside the device to be different from that during adjustment under actual working conditions, and the voltage drop generated is also different, which will lead to errors in junction temperature measurement. Summary of the invention

[0004] In view of the defects in the prior art, an object of the present invention is to provide a method for adjusting the relationship between the on-state voltage drop and the junction temperature of a power device under a high current switching state.

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

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

[0007] Controlling the switch state of the device under test by a driving signal so that the current flowing through the device under test is a square wave current with a fixed amplitude and a fixed duty cycle, wherein the maximum value of the square wave current is a set large current value and the minimum value is zero;

[0008] In the switch state, the self-heating condition of the device under test is set by controlling the circuit operation condition, and the external heat condition of the device under test is set by controlling the heat sink temperature; when the device under test reaches a thermal steady state under the self-heating condition and the external heat condition, the current, the on-state voltage drop under a large current, and the reference point temperature of the device under test are measured;

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

[0010] Changing the circuit operating conditions and the heat sink temperature to make the device under test work in different thermal steady states, and measuring multiple groups of high current conduction voltage drop, reference point temperature and junction temperature data of the device under test under the set high current;

[0011] A linear equation is used to fit the relationship between the on-state voltage drop, the reference point temperature and the junction temperature of the device under test at the set high current.

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

[0013] Preferably, the step of obtaining the relationship between the on-state voltage drop and the junction temperature under a constant low current includes:

[0014] Placing the device under test in a temperature box or on a heating plate;

[0015] A constant small current is passed through and the temperature of the temperature box or the heating plate is changed, and the conduction voltage drop under the small current corresponding to different temperatures is recorded;

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

[0017] Preferably, under the condition of keeping the set large current unchanged, the loss of the device under test can be changed by changing the circuit operating conditions, thereby changing the self-heating conditions of the device under test;

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

[0019] Preferably, the reference point temperature includes the shell temperature of the device under test, the heat sink temperature, and the temperature of a thermal resistor integrated in a power module.

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

[0021] Preferably, the use of a linear equation to fit the relationship between the on-state voltage drop, the reference point temperature and the junction temperature of the device under test at the set high current includes:

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

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

[0024] Among them, V ce k is the on-state voltage drop of the device under test under high current, j Junction temperature T j Temperature coefficient, k i is the packaging material temperature T i The temperature coefficient, c is T i and T j The on-state voltage drop value when both are 0;

[0025] Replace the package material temperature T in the above relationship with the junction temperature and reference point temperature. i , then 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] Among them, k j ’ The junction temperature after temperature replacement is T j Temperature coefficient, k r is the reference point temperature T r The temperature coefficient of

[0028] Preferably, the packaging material temperature T of the relationship is replaced by the junction temperature and the reference point temperature. i ,include:

[0029] When the device under test reaches thermal stability, the temperature of its packaging material 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 packaging material temperature, T j is the junction temperature of the device under test, T r is the reference point temperature, α is the relationship coefficient between the three temperatures;

[0032] Substitute the linear combination into the relationship and get k after sorting. j ', k r Value, k j '=k j +α·k i , k r =k i -α·k i .

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

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

[0035] Compared with the prior art, the embodiments of the present invention have at least one of the following beneficial effects:

[0036] The method for adjusting the relationship between the on-state voltage drop and the junction temperature of a power device under a high current switching state in the embodiment of the present invention can flexibly control the self-heating and external heating conditions of the adjusting device, and considers the influence of the internal temperature distribution of the device on the on-state voltage drop, thereby improving the accuracy of predicting the junction temperature using the on-state voltage drop under high current. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0038] Figure 1 A flow chart of a method for adjusting the relationship between the on-state voltage drop and the junction temperature of a power device under a high current switching state provided by an embodiment of the present invention;

[0039] Figure 2 It is a principle diagram of a setting circuit in a preferred embodiment of the present invention;

[0040] Figure 3 A waveform diagram of a set of on-state voltage drop, reference point temperature and junction temperature data under a large current measured in a preferred embodiment of the present invention;

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

[0042] Figure 5 An equivalent thermal circuit model for representing the temperature of a power device packaging material according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0043] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

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

[0045] In one embodiment of the present invention, a method for adjusting the relationship between the on-state voltage drop and the junction temperature of a power device under a high current switching state is provided, such as Figure 1 As shown, the main process is as follows:

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

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

[0048] S300, in the switch state, the self-heating condition of the device under test is set by controlling the circuit operation condition, and the external heating condition of the device under test is set by controlling the heat sink temperature; when the device under test reaches a thermal steady state under the self-heating condition and the external heating condition, the current of the device under test, the on-state voltage drop under a large current, and the reference point temperature are measured;

[0049] S400, locking the device under test by a driving signal, turning on the device under test by a driving signal immediately after the current flowing through the device under test drops to zero, and injecting a constant small current to measure the junction temperature of the device under test;

[0050] S500, determine whether to change the operating conditions, if so, return to S300, change the circuit operating conditions and the heat sink temperature, so that the device under test works in different thermal steady states, measure multiple sets of high current conduction voltage drop, reference point temperature and junction temperature data of the device under test under the set high current; if not, enter S600.

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

[0052] In the above embodiment, the device under test works in a high current switching state, the working conditions are 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 packaging material temperature is combined with the junction temperature and the reference point temperature, and the relationship between the on-state voltage drop and the junction temperature is corrected to make the prediction effect more accurate.

[0053] In a preferred embodiment of the present invention, S100 is implemented to obtain the relationship between the on-state voltage drop and the junction temperature under a constant small current. Specifically, the device under test 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-state voltage drop under the small current corresponding to different temperatures is recorded, and a linear relationship between the on-state voltage drop and the junction temperature under the small current is fitted for the junction temperature measurement in the subsequent setting process.

[0054] It should be noted that, in other embodiments, this step can be performed after the other steps are completed, and it only needs to be prepared when a constant small current is injected in S400 to measure the junction temperature of the device under test.

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

[0056] In a preferred embodiment of the present invention, step S200 is implemented as follows: Figure 2 The circuit schematic shown is implemented as Figure 2 As shown, four power devices are connected to form an H-bridge structure with an inductive load. Each power device can be used as a device under test. When the H-bridge circuit is operated in a switching state, the duty cycle of the two phases is set to a constant value. At this time, the circuit current is approximately a constant DC current. The current size of the load inductance is controlled by controlling the difference between the two-phase duty cycles. At this time, the current flowing through the device under test is a square wave current with a fixed amplitude and a fixed duty cycle. 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 invention, under the condition of keeping the set large current unchanged, the loss of the device under test can be changed by changing the circuit operating conditions, thereby changing the self-heating conditions of the device under test. In some specific embodiments, the circuit operating conditions of step S300 are one or more of bus voltage, switching frequency, duty cycle, and drive resistance. The reference point temperature includes the shell temperature of the device under test, the heat sink temperature, and the temperature of the thermal resistor integrated in the power module.

[0058] By changing the circuit operating conditions such as bus voltage, switching frequency, duty cycle, drive resistance, etc., the device under test can be operated under different self-heating conditions. By heating or cooling the temperature-controlled heat sink, the device under test can be operated under different external heat conditions. The on-state voltage drop of the device under test in the switching state and in the small current injection state can be measured through the on-state voltage drop measurement and the small current injection circuit.

[0059] In some specific embodiments, Figure 3 As shown in FIG. 1 , it is a set of waveform diagrams of the on-state voltage drop, reference point temperature and junction temperature data under large current.

[0060] First, set the circuit operating conditions and heat sink temperature to make the device under test operate in the switching state and reach thermal stability. In the thermal stability, measure the on-state voltage drop of the device under test in the high current switching state and the reference point temperature. Then lock all device drive signals to quickly reduce the load current to zero, reapply the drive signal to the device under test and inject a small current to measure its junction temperature. After changing the circuit operating conditions and heat sink temperature to make the device under test operate in the high current switching state again, repeat the test. Figure 3 Through the measurement process, multiple sets of on-state voltage drop, reference point temperature, and junction temperature data can be obtained, which are used to fit the relationship between the three using a linear equation.

[0061] Based on the above embodiments, multiple sets of on-state voltage drop, reference point temperature, and junction temperature data are obtained. In a preferred embodiment of the present invention, S600 is implemented to use a linear equation to fit the relationship between the on-state voltage drop, reference point temperature, and junction temperature of the device under test at a set high current. Specifically, Figure 4 As shown, it is a circuit model equivalent to a power device. The on-state voltage drop of the device under test 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-state voltage drop of the device under test is a linear function of the junction temperature and the packaging material temperature. The formula is:

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

[0063] Among them, V ce k is the on-state voltage drop of the device under test under high current, j Junction temperature T j Temperature coefficient, k i is the packaging material temperature T i The temperature coefficient, c is T i and T j The on-state voltage drop is 0.

[0064] Further, such as Figure 5 As shown in the figure, it is an equivalent thermal circuit diagram used to represent 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 the thermal steady state, the packaging material temperature can be expressed according to the equivalent thermal circuit as follows:

[0065] T i = α·T j + (1-α)·T r (3)

[0066] Among them, 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, α is the relationship coefficient between the three temperatures, and the specific value is R ir / (R ji +R ir ). Where R ir is the equivalent thermal resistance from the packaging material to the reference point, R ji is the equivalent thermal resistance from junction to packaging material. The value of equivalent thermal resistance is related to the structure of the device itself and the reference point selection. Through this formula, it is possible to use easy-to-measure parameters to characterize the effect of packaging material temperature on the conduction voltage drop, which is difficult to measure.

[0067] If the package material temperature in the on-state voltage drop expression (1) of the device under test is replaced by the junction temperature and the reference point temperature, the on-state voltage drop of the device under test after reaching thermal steady state can be expressed as a linear function of the junction temperature and the reference point temperature, as follows:

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

[0069] Among them, k j ' is the junction temperature after temperature replacement T j Temperature coefficient, k r is the reference point temperature T r The temperature coefficient of k j '=k j +α·k i With k r =k i -α·k i The purpose of this tuning method is to obtain k j ', k r When actually predicting the junction temperature, it is necessary to measure the on-state voltage drop and the temperature of the reference point and combine the kj ', k r The junction temperature of the device under test can be calculated using the value of c.

[0070] It should be noted that for different high current and driving voltage values, the relationship between the on-state voltage drop, the reference point temperature and the junction temperature under high current is also different. The set high current and driving voltage should be determined according to the needs of the actual application scenario. In the above, the driving signal is used to control the switching state of the device. The high and low level switching of the driving signal can make the device under test work in an 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 magnitude of the driving voltage applied to the device when the device under test is in the on state. In the above embodiment, the temperature-sensitive parameter of the on-state voltage drop is used for junction temperature calculation, and the on-state voltage drop is related to the high level of the driving voltage. Therefore, the magnitude of the driving voltage used during setting needs to be selected according to the magnitude of the driving voltage during actual application. When the setting result is used for junction temperature prediction, it should be ensured that the driving voltage used is the same as that during setting.

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

[0072] According to the method for adjusting the relationship between the on-state voltage drop and junction temperature of the power device under the high current switching state in the aforementioned implementation case, the relationship between the on-state voltage drop, reference point temperature and junction temperature data obtained shows a higher accuracy in predicting the junction temperature data. The advantages of this method are its low invasiveness, fast response and high accuracy, so it is easier to obtain widespread application.

[0073] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various modifications or variations within the scope of the claims, which does not affect the essence of the present invention. The above preferred features can be used in any combination without conflicting with each other.

Claims

1. A method for adjusting the relationship between the on-state voltage drop and junction temperature of a power device under a high current switching state, characterized in that: include: Obtain the relationship between the on-state voltage drop and junction temperature under a constant low current; Controlling the switch state of the device under test by a driving signal so that the current flowing through the device under test is a square wave current with a fixed amplitude and a fixed duty cycle, wherein the maximum value of the square wave current is a set large current value and the minimum value is zero; In the switch state, the self-heating condition of the device under test is set by controlling the circuit operation condition, and the external heat condition of the device under test is set by controlling the heat sink temperature; When the device under test reaches a 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; The device under test is locked by a driving signal, and the device under test is turned on by a driving signal immediately after the current flowing through the device under test drops to zero, and a constant small current is injected to measure the junction temperature of the device under test; Changing the circuit operating conditions and the heat sink temperature to make the device under test work in different thermal steady states, and measuring multiple groups of high current conduction voltage drop, reference point temperature and junction temperature data of the device under test under the set high current; A linear equation is used to fit the relationship between the on-state voltage drop, the reference point temperature and the junction temperature of the device under test at the set high current.

2. The method for setting the relationship between the on-state voltage drop and the junction temperature of a power device under a high current switching state according to claim 1, characterized in that: The device under test is a power semiconductor device, including a controllable power semiconductor device and a power diode. The packaging of the power semiconductor device adopts one or more of module-based, crimping-based, and discrete packaging technologies; the material of the power semiconductor device adopts one or more of silicon-based, silicon carbide-based, and gallium nitride-based.

3. The method for setting the relationship between the on-state voltage drop and junction temperature of a power device under a high current switching state according to claim 1, characterized in that: The step of obtaining the relationship between the on-state voltage drop and the junction temperature under a constant low current comprises: Placing the device under test in a temperature box or on a heating plate; A constant small current is passed through and the temperature of the temperature box or the heating plate is changed, and the conduction voltage drop under the small current corresponding to different temperatures is recorded; The linear relationship between the on-state voltage drop and the junction temperature under small current is fitted and used for junction temperature measurement during the setting process.

4. The method for adjusting the relationship between the on-state voltage drop and the junction temperature of a power device under a high current switching state according to claim 1, characterized in that: Under the condition of keeping the set large current unchanged, the loss of the device under test can be changed by changing the circuit operating conditions, thereby changing the self-heating conditions of the device under test; The circuit operating conditions include one or more of bus voltage, switching frequency, duty cycle, and drive resistance.

5. The method for setting the relationship between the on-state voltage drop and the junction temperature of a power device under a high current switching state according to claim 1, characterized in that: The reference point temperature includes the shell temperature of the device under test, the heat sink temperature, and the temperature of the thermal resistor integrated in the power module.

6. The method for setting the relationship between the on-state voltage drop and the junction temperature of a power device under a high current switching state according to claim 5, characterized in that: The radiator has heating and cooling functions, and the reference point temperature changes as the temperature of the radiator changes; the reference point temperature can be set to a constant value.

7. The method for setting the relationship between the on-state voltage drop and the junction temperature of a power device under a high current switching state according to claim 1, characterized in that: The method of fitting the relationship between the on-state voltage drop, the reference point temperature and the junction temperature of the device under test at the set high current using a linear equation includes: Considering the influence of the temperature distribution inside the device, the relationship is obtained: V ce =k j ·T j +k i ·T i +c (1) Among them, V ce k is the on-state voltage drop of the device under test under high current, j is the junction temperature T j Temperature coefficient, k i is the packaging material temperature T i The temperature coefficient, c is T i and T j The on-state voltage drop value when both are 0; Replace the package material temperature T in the above relationship with the junction temperature and reference point temperature. i , then 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) Among them, k j ' is the junction temperature after temperature replacement T j kr is the temperature coefficient of the reference point temperature Tr.

8. The method for setting the relationship between the on-state voltage drop and the junction temperature of a power device under a high current switching state according to claim 7, characterized in that: The packaging material temperature T of the relationship is replaced by the junction temperature and the reference point temperature. i ,include: When the device under test reaches thermal stability, the temperature of its packaging material is expressed as a linear combination of the junction temperature and the reference point temperature: T i =α·T j +(1-a)·T r (3) 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, α is the relationship coefficient between the three temperatures; Substitute the linear combination into the relationship and get k after sorting. j ', k r Value, k j '=k j +α·k i , k r =k i -α·k i .

9. The method for setting the relationship between the on-state voltage drop and the junction temperature of a power device under a high current switching state according to claim 8, characterized in that: For different high current and driving voltage values, the relationship between the on-state voltage drop, the reference point temperature and the junction temperature under the high current is also different.

10. The method for setting the relationship between the on-state voltage drop and the junction temperature of a power device under a high current switching state according to claim 8, characterized in that: When the setting result is used for junction temperature prediction, it should be ensured that the reference point is selected to be the same as the reference point used when setting the relationship between the on-state voltage drop and junction temperature of the power device under high current switching state. The junction temperature is calculated by measuring the on-state voltage drop and reference point temperature of the device under high current.

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