Life assessment device and power conversion device

Abstract

A service life diagnostic device (1) comprises a Vce amplifier (12), a Vee amplifier (13), and a service life diagnostic unit (21). The Vce amplifier (12) measures a voltage (Vce) between a collector main terminal (6) connected to a collector electrode of a semiconductor element (5) mounted to a semiconductor device (2) and an emitter main terminal (8) connected to an emitter electrode of the semiconductor element (5). The Vee amplifier (13) measures a voltage Vee between the emitter main terminal (8) and an emitter reference terminal (9) connected to the emitter electrode. The service life diagnostic unit (21) diagnoses the service life of the semiconductor device (2) using the value of a correlation between the change over time of the voltage Vce and the change over time of the voltage Vee.

Description

[Technical field]

[0001] The present disclosure relates to a lifetime assessment device for a semiconductor device and a power conversion device. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2010-81796 (Patent Document 1) discloses a technique for diagnosing deterioration of a joint between an electrode of a semiconductor element in a semiconductor module used in a semiconductor device and a terminal of the semiconductor module. This technique measures the voltage between multiple terminals of the semiconductor module, estimates the degree of deterioration of the joint from the result of comparing the change over time of the measured voltage with a predetermined diagnostic standard, and predicts the remaining life of the semiconductor device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-81796 A Summary of the Invention [Problem to be solved by the invention]

[0004] In general, even if multiple semiconductor modules have the same specifications, there are individual differences in the characteristics of the multiple semiconductor modules. Therefore, in the technology disclosed in Patent Document 1, if the change over time in voltage according to the characteristics of a certain semiconductor module is used as a diagnostic criterion, there is a possibility that the remaining life of a semiconductor device using another semiconductor module will be erroneously diagnosed. In other words, the technology disclosed in Patent Document 1 does not eliminate the individual differences in the characteristics of the semiconductor modules, so the accuracy of diagnosing the remaining life is low.

[0005] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide a lifetime assessment device and a power conversion device that are capable of accurately assessing the remaining lifetime of a semiconductor device. [Means for solving the problem]

[0006] A lifetime assessment device according to an aspect of the present disclosure assesses the lifetime of a semiconductor device. The lifetime assessment device includes a first voltage meter, a second voltage meter, and a diagnostic unit. The first voltage meter measures a first voltage between a first terminal connected to a first electrode of a semiconductor element mounted on the semiconductor device and a second terminal connected to a second electrode of the semiconductor element. The second voltage meter measures a second voltage between the second terminal and a third terminal connected to the second electrode. The diagnostic unit diagnoses the lifetime of the semiconductor device using a correlation value between a change over time of the first voltage and a change over time of the second voltage. Effect of the Invention

[0007] According to the present disclosure, a correlation value between a change over time of a first voltage and a change over time of a second voltage is used for lifetime diagnosis. The change over time of the first voltage and the change over time of the second voltage vary for each individual semiconductor module including a semiconductor element, a first terminal, a second terminal, and a third terminal. However, the variation in the change over time of the correlation value for each individual semiconductor module is small. Therefore, a highly accurate lifetime diagnosis can be performed while eliminating the influence of individual differences in the semiconductor module. [Brief description of the drawings]

[0008] [Figure 1] 1 is a block diagram showing an example of a configuration of a life assessment device according to a first embodiment of the present disclosure. [Diagram 2] 1 is a schematic cross-sectional view showing an example of an internal structure of a semiconductor module. [Diagram 3] 11 is a diagram showing the relationship between the degree of deterioration (life consumption rate) of a semiconductor module 30A and the changes over time of voltages Vce and Vee. FIG. [Figure 4] 13 is a diagram showing the relationship between the degree of deterioration (life consumption rate) of a semiconductor module 30B and changes over time in voltages Vce and Vee. FIG. [Diagram 5] 11 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in a semiconductor module 30A. [Figure 6]13 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in a semiconductor module 30B. FIG. [Figure 7] 11 is a diagram showing the effect of slight fluctuations in the values ​​of voltages Vce and Vee. [Figure 8] FIG. 13 is a diagram showing a change over time in the correlation value “Vee magnification / Vce magnification” calculated in a second example of life assessment. [Figure 9] 13 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in a semiconductor module 30A when the voltage at the time when the life consumption rate is 30% is used as a reference value. FIG. [Figure 10] 13 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in a semiconductor module 30B when the voltage at the time when the life consumption rate is 30% is used as a reference value. FIG. [Figure 11] 13 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in a semiconductor module 30A when the voltage at the time when the life consumption rate is 40% is used as a reference value. FIG. [Figure 12] 13 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in a semiconductor module 30B when the voltage at the time when the life consumption rate is 40% is used as a reference value. FIG. [Figure 13] 13 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in a semiconductor module 30A when the voltage at the time when the life consumption rate is 50% is used as a reference value. FIG. [Figure 14] 13 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in a semiconductor module 30B when the voltage at the time when the life consumption rate is 50% is used as a reference value. FIG. [Figure 15] 13 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in a semiconductor module 30A when the voltage at the time when the life consumption rate is 60% is used as a reference value. FIG. [Figure 16] 13 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in a semiconductor module 30B when the voltage at the time when the life consumption rate is 60% is used as a reference value. FIG. [Figure 17] FIG. 11 is a block diagram showing an example of a configuration of a life assessment device according to a third embodiment of the present disclosure. [Figure 18] FIG. 11 is a block diagram showing a configuration of a power conversion system to which a power conversion device according to a fourth embodiment of the present disclosure is applied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated in principle. The size relationship of each component in the following drawings may differ from the actual one.

[0010] Embodiment 1 (Overall configuration of lifespan diagnosis device) 1 is a block diagram showing an example of a configuration of a lifetime assessment device according to a first embodiment of the present disclosure. The lifetime assessment device 1 is connected to a semiconductor device 2 and assesses the lifetime of the semiconductor device 2. Specifically, the lifetime assessment device 1 assesses the lifetime of the semiconductor device 2 by diagnosing a deterioration state of an electrical joint in a semiconductor module 30 inside the semiconductor device 2.

[0011] The semiconductor module 30 includes a semiconductor element 5. The semiconductor element 5 is, for example, an IGBT (Insulated-Gate Bipolar Transistor), a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), or other semiconductor element. The semiconductor element 5, which is an IGBT, will be described below. The semiconductor element 5 has a collector electrode, an emitter electrode, and a gate electrode. The semiconductor module 30 has a collector main terminal 6, a gate terminal 7, an emitter main terminal 8, and an emitter reference terminal 9 as terminals connected to the electrodes of the semiconductor element 5. The collector main terminal 6 is connected to the collector electrode of the semiconductor element 5 via a collector side main circuit connection part 10 such as a metal wire, a metal ribbon, or a metal plate. The emitter main terminal 8 is connected to the emitter electrode of the semiconductor element 5 via an emitter side main circuit connection part 11 such as a metal wire, a metal ribbon, or a metal plate. The gate terminal 7 is connected to the gate terminal of the semiconductor element 5. The emitter reference terminal 9 is connected to the emitter electrode of the semiconductor element 5.

[0012] The semiconductor element 5 is driven to be in either an on state in which a large current flows from the collector main terminal 6 to the emitter main terminal 8, or an off state in which no current flows from the collector main terminal 6 to the emitter main terminal 8. The on and off states are switched depending on whether a positive or negative voltage is applied between the gate terminal 7 and the emitter reference terminal 9. Note that no large current flows between the gate terminal 7 and the emitter reference terminal 9.

[0013] In the semiconductor element 5, a large current flows intermittently from the collector main terminal 6 to the emitter main terminal 8. As a result, deterioration is likely to occur in the collector side main circuit connection part 10 and the emitter side main circuit connection part 11. On the other hand, since no large current flows through the gate terminal 7 or the emitter reference terminal 9, deterioration is unlikely to occur in these connections. Therefore, the life spans of the collector side main circuit connection part 10 and the emitter side main circuit connection part 11 are selected as the diagnosis targets.

[0014] 1, the lifetime diagnosis device 1 includes a diagnosis processing unit 3 and a display unit 4. The diagnosis processing unit 3 diagnoses the deterioration state of the collector side main circuit connection unit 10 and the emitter side main circuit connection unit 11, thereby diagnosing the lifetime of the semiconductor device 2. The diagnosis processing unit 3 displays the diagnosis result on the display unit 4. The display unit 4 is, for example, a liquid crystal display. The display unit 4 may be located outside the lifetime diagnosis device 1.

[0015] The diagnostic processing unit 3 is configured by software executed on a calculation device such as a microcomputer or a CPU (Central Processing Unit), and hardware such as circuit devices that realize various functions.

[0016] The diagnosis processing unit 3 includes a Vce amplifier 12, a Vee amplifier 13, reference value storage units 14, 15, aging change extraction units 16, 17, a correlation value calculation unit 18, a storage unit 19, a aging change calculation unit 20, and a lifetime diagnosis unit .

[0017] The Vce amplifier 12 measures the voltage between the collector main terminal 6 and the emitter main terminal 8, and amplifies the measurement result to a voltage Vce suitable for post-processing. The Vce amplifier 12 outputs the voltage Vce to the time-dependent change extraction unit 16.

[0018] The Vee amplifier 13 measures the voltage between the emitter reference terminal 9 and the emitter main terminal 8, and amplifies the measurement result to a voltage Vee suitable for post-processing. The Vee amplifier 13 outputs the voltage Vee to a time-dependent change extraction unit 17.

[0019] The reference value storage unit 14 stores a first reference value, which is the value of the voltage Vce measured before starting to use the semiconductor device 2 (i.e., in an unused state). The first reference value is measured when the semiconductor module 30 is in an on-state.

[0020] The reference value storage unit 15 stores a second reference value, which is the value of the voltage Vee measured before starting to use the semiconductor device 2 (i.e., in an unused state). The second reference value is measured when the semiconductor module 30 is in an on-state.

[0021] The first and second reference values ​​are preferably representative values ​​repeatedly measured in an environment suitable for measuring the voltages Vce and Vee.

[0022] The time-varying extraction unit 16 compares the voltage Vce output from the Vce amplifier 12 with a first reference value stored in the reference value storage unit 14 to extract the time-varying voltage Vce according to the time elapsed since the first reference value was measured. Specifically, the time-varying extraction unit 16 calculates a value indicating the time-varying voltage Vce (hereinafter referred to as "time-varying amount ΔVce"). The time-varying amount ΔVce is, for example, the difference between the value of the voltage Vce output from the Vce amplifier 12 and the first reference value, the magnification of the value of the voltage Vce output from the Vce amplifier 12 with respect to the first reference value, or a value obtained by subtracting a first constant from the magnification. The first constant is, for example, 1.

[0023] The time-varying extraction unit 17 compares the voltage Vee output from the Vee amplifier 13 with the second reference value stored in the reference value storage unit 15 to extract the time-varying voltage Vee according to the time elapsed since the second reference value was measured. Specifically, the time-varying extraction unit 17 calculates a value indicating the time-varying voltage Vee (hereinafter referred to as "time-varying amount ΔVee"). The time-varying amount ΔVee is, for example, the difference between the value of the voltage Vee output from the Vee amplifier 13 and the second reference value, the magnification of the value of the voltage Vee output from the Vee amplifier 13 with respect to the second reference value, or a value obtained by subtracting a second constant from the magnification. The second constant is, for example, 1.

[0024] The correlation value calculation unit 18 calculates a correlation value between the change over time of the voltage Vce and the change over time of the voltage Vee. Specifically, the correlation value calculation unit 18 calculates a correlation value between the amount of change over time ΔVce calculated by the change over time extraction unit 16 and the amount of change over time ΔVee calculated by the change over time extraction unit 17. The correlation value is, for example, the difference between the amount of change over time ΔVce and the amount of change over time ΔVee, or the ratio of the amount of change over time ΔVee divided by the amount of change over time ΔVce. The correlation value calculation unit 18 stores the calculated correlation value in the memory unit 19.

[0025] The storage unit 19 stores the correlation value calculated by the correlation value calculation unit 18 in association with the time information.

[0026] The time-varying calculation unit 20 calculates a time-varying amount ΔCor indicating a time-varying amount of the correlation value by using the correlation value calculated by the correlation value calculation unit 18 and the past correlation value stored in the storage unit 19. The time-varying amount ΔCor is, for example, the absolute value of the correlation value calculated by the correlation value calculation unit 18, or the difference between the correlation value calculated by the correlation value calculation unit 18 and the past correlation value stored in the storage unit 19. The past correlation value is, for example, the most recent correlation value among the correlation values ​​stored in the storage unit 19, or the correlation value at a time preceding the present time by a predetermined period among the correlation values ​​stored in the storage unit 19. Alternatively, the time-varying amount ΔCor may be a value obtained by dividing the difference between the correlation value calculated by the correlation value calculation unit 18 and the past correlation value stored in the storage unit 19 by the elapsed time (i.e., a first-order differential coefficient with respect to time). The elapsed time is the time from the time indicated by the time information corresponding to the past correlation value to the present time. The amount of change over time ΔCor may be a value obtained by dividing the difference between the correlation value calculated by the correlation value calculation unit 18 and the past correlation value stored in the memory unit 19 by the elapsed time, and then further dividing the result by the elapsed time (i.e., the second-order differential coefficient with respect to time).

[0027] The life diagnosis unit 21 diagnoses the life of the semiconductor device 2 based on the amount of change over time ΔCor calculated by the change over time calculation unit 20. Specifically, the life diagnosis unit 21 diagnoses the life of the collector side main circuit connection unit 10 and the emitter side main circuit connection unit 11 based on the amount of change over time ΔCor. The life diagnosis unit 21 displays information showing the diagnosis result (hereinafter referred to as "life information") on the display unit 4. This allows a user of the semiconductor device 2 to perform maintenance of the semiconductor device 2 at an appropriate time by checking the life information.

[0028] (Internal structure of a semiconductor module) Fig. 2 is a schematic cross-sectional view showing an example of the internal structure of a semiconductor module. As shown in Fig. 2, a semiconductor module 30 includes a semiconductor element 5. The semiconductor element 5 is generally obtained by performing electrode processing on a flat semiconductor. In the example shown in Fig. 2, the semiconductor element 5 has a collector electrode 5a formed on the lower surface of the semiconductor and an emitter electrode 5b formed on the upper surface of the semiconductor.

[0029] The collector electrode 5a is connected to a metal plate 22. The metal plate 22 is connected to the collector main terminal 6 via a collector side main circuit connection part 10. In the example of FIG. 2, a bonding wire is used as the collector side main circuit connection part 10. The bonding wire is made of aluminum, copper, or other alloys. The bonding wire is joined to a terminal or an electrode by applying ultrasonic waves to crush it.

[0030] The emitter electrode 5b is connected to the emitter main terminal 8 via an emitter side main circuit connection portion 11. In the example of Fig. 2, a bonding wire is used as the emitter side main circuit connection portion 11. Furthermore, the emitter electrode 5b is connected to the emitter reference terminal 9 via a connection portion 23. A bonding wire is used as the connection portion 23.

[0031] 2, a large current flows through a current path 24 that flows from the collector main terminal 6 to the emitter main terminal 8. On the other hand, no large current flows through a connection portion 23 that connects the emitter reference terminal 9 and the emitter electrode 5b.

[0032] By alternately switching between the on state and the off state in the semiconductor module 30, a state in which a large current flows through the path 24 and a state in which no current flows through the path 24 are repeated. As a result, the amount of heat generated by the semiconductor element 5 fluctuates greatly, and the temperature of the semiconductor element 5 rises and falls. As a result, due to the difference in the thermal expansion coefficient between the metal connected to the semiconductor element 5 and the semiconductor element 5, strain is repeatedly applied between the semiconductor element 5 and the metal, making the joint between the semiconductor element 5 and the metal more susceptible to deterioration.

[0033] In the example shown in FIG. 2, the collector electrode 5a is connected to the collector-side main circuit connection part 10 via the metal plate 22. The contact area between the collector electrode 5a and the metal plate 22 is much larger than the contact area between the emitter electrode 5b and the emitter-side main circuit connection part 11. Therefore, the joint between the semiconductor element 5 and the metal plate 22 is less susceptible to distortion due to heat. Note that the collector-side main circuit connection part 10 and the metal plate 22 are both made of metal. Therefore, although the contact area between the collector-side main circuit connection part 10 and the metal plate 22 is small, the joint between the collector-side main circuit connection part 10 and the metal plate 22 is less susceptible to distortion due to heat.

[0034] On the other hand, the emitter side main circuit connection part 11 is directly connected to the emitter electrode 5b, and the contact area between the emitter side main circuit connection part 11 and the emitter electrode 5b is small. Therefore, the joint between the semiconductor element 5 and the emitter side main circuit connection part 11 is easily affected by distortion due to heat. Similarly, the connection part 23 is directly connected to the emitter electrode 5b, and the contact area between the connection part 23 and the emitter electrode 5b is small. Therefore, the joint between the semiconductor element 5 and the connection part 23 is also easily affected by distortion due to heat. However, the current flowing through the emitter side main circuit connection part 11 is larger than the current flowing through the connection part 23, and therefore the joint between the semiconductor element 5 and the emitter side main circuit connection part 11 is directly exposed to the heat generated by the semiconductor element 5 and therefore deteriorates the fastest.

[0035] (Changes in voltages Vce and Vee over time) Next, an example of the change over time of the voltages Vce and Vee due to the deterioration of the junctions will be described. The voltage Vce is the voltage between the collector main terminal 6 and the emitter main terminal 8 on the path 24 shown in Fig. 2. The voltage Vee is the voltage between the emitter reference terminal 9 and the emitter main terminal 8. The emitter reference terminal 9 does not exist on the path 24. In this way, the voltages Vce and Vee are voltages on different paths. Therefore, the changes over time of the voltages Vce and Vee due to the deterioration of the junctions may be different from each other.

[0036] FIG. 3 is a diagram showing the relationship between the degree of deterioration (life consumption rate) of the semiconductor module 30A and the change over time of the voltages Vce and Vee. In FIG. 3, the "magnification to the reference value" is shown as the change over time ΔVce and ΔVee. That is, the magnification of the value of the voltage Vce output from the Vce amplifier 12 to the first reference value (hereinafter referred to as the "Vce magnification") and the magnification of the value of the voltage Vee output from the Vee amplifier 13 to the second reference value (hereinafter referred to as the "Vee magnification") are graphed. In FIG. 3, the vertical axis shows the magnification to the reference value (Vce magnification, Vee magnification). The horizontal axis shows the ratio (hereinafter referred to as the "life consumption rate") obtained by dividing the elapsed time from the start of use by the entire life period until the semiconductor module becomes unusable.

[0037] As shown in Fig. 3, the Vce magnification and the Vee magnification increase with the passage of time (i.e., as the life consumption rate increases). At the start of use of the semiconductor module 30A (i.e., when the life consumption rate is 0%), the voltages Vce and Vee are equal to the first and second reference values, respectively. Therefore, both the Vce magnification and the Vee magnification are 1.

[0038] As the deterioration of the junction progresses over time, the electrical resistance of the junction increases. Therefore, the voltages Vce and Vee increase, and the Vce and Vee magnifications also increase. However, since the voltages Vce and Vee are voltages on different paths, the behavior of the Vce and Vee magnifications with respect to the progression of deterioration of the junction is not the same. In the example shown in FIG. 3, the Vee magnification is always greater than the Vce magnification. For example, at the time when the life consumption rate is 80% (i.e., when 80% of the total life period has elapsed), the Vee magnification is 1.5, while the Vce magnification is 1.015. In other words, the value of the voltage Vee has increased by 50% from the second reference value, while the value of the voltage Vce has increased by only 1.5% from the first reference value. At the time when the life consumption rate is 100%, the Vee magnification is 4, while the Vce magnification is 1.5.

[0039] In predicting the lifespan of a semiconductor module, it is important to accurately predict how much longer the semiconductor module can be used while it is in use, i.e., the remaining lifespan. For example, if the user of the semiconductor module can be notified of "20% remaining lifespan" as lifespan diagnosis information when the remaining lifespan of the semiconductor module is 20%, the user of the semiconductor module can make arrangements in advance to replace the semiconductor module, enabling planned maintenance. If the accuracy of this prediction is low, the semiconductor module may reach the end of its lifespan and become unusable before the user can perform the replacement work, resulting in a problem in which the semiconductor device cannot be used.

[0040] Conventionally, remaining life information is notified based on changes in the Vce magnification and the Vee magnification as shown in Fig. 3. For example, when the Vee magnification reaches 1.5, remaining life information indicating that the remaining life is 20% is notified.

[0041] However, such a conventional method has low accuracy in predicting the life span because there are individual differences in the characteristics of the semiconductor modules 30, and even in semiconductor modules 30 with the same specifications, the changes in the amounts of change over time ΔVce and ΔVee relative to the life span consumption rate may differ due to the individual differences between the semiconductor modules 30.

[0042] Fig. 4 is a diagram showing the relationship between the degree of deterioration (life consumption rate) of the semiconductor module 30B and the change over time in the voltages Vce and Vee. The semiconductor module 30B is a separate module with the same specifications as the semiconductor module 30A. As in Fig. 3, Fig. 4 shows a graph with the vertical axis representing the magnification (Vce magnification, Vee magnification) relative to the reference value and the horizontal axis representing the life consumption rate.

[0043] 4, in the semiconductor module 30B, the Vce and Vee magnifications also increase with the passage of time (i.e., as the lifetime consumption rate increases). However, the changes in the Vce and Vee magnifications in the semiconductor module 30B are different from the changes in the Vce and Vee magnifications in the semiconductor module 30A. Specifically, the point at which the Vee magnification becomes 1.5 is the point at which the lifetime consumption rate of the semiconductor module 30A becomes 80%, whereas the point at which the lifetime consumption rate of the semiconductor module 30B becomes 90%. In the semiconductor module 30B, the Vee magnification is 1.3 at the point at which the lifetime consumption rate becomes 80%.

[0044] 3, when a life assessment method is adopted that notifies remaining life information indicating that the remaining life is 20% when the Vee magnification reaches 1.5, the following problem occurs. That is, when the life assessment method is applied to the semiconductor module 30B, remaining life information indicating that the remaining life is 20% is notified when the life consumption rate is 90%. In this way, remaining life information indicating a remaining life that is different from the actual remaining life is notified, and the accuracy of the life assessment is low.

[0045] In consideration of such problems, the life assessment device 1 according to the first embodiment performs more accurate life assessment using a correlation value between the change over time of the voltage Vce and the change over time of the voltage Vee. The reason why the accuracy of the life assessment is improved by using the correlation value will be described below.

[0046] (Improvement of accuracy of life diagnosis) The parameters indicating the characteristics of the semiconductor module 30 include various parameters other than the voltages Vce and Vee. In general, the values ​​of these parameters vary from one semiconductor module 30 to another even if the semiconductor module 30 has the same specifications. This can be caused by variations in the quality of the components, variations in processing conditions during the manufacturing process, and the like. Although the values ​​of the parameters indicating the characteristics vary from one semiconductor module to another, the correlation between the values ​​of these parameters is maintained for the same semiconductor module. This is because the factors that determine the magnitude of the values ​​of these parameters depend on the product specifications, that is, the design. For example, if the amount of change over time ΔVce increases under certain manufacturing conditions, the amount of change over time ΔVee also increases. For this reason, the correlation between the amounts of change over time ΔVce and ΔVee is the same for products with the same specifications, even if the individual semiconductor modules are different. In other words, the correlation between the amounts of change over time ΔVce and ΔVee is constant for multiple semiconductor modules 30 with the same specifications.

[0047] For example, as shown in FIG. 3, in the semiconductor module 30A, of the changes over time ΔVce and ΔVee with respect to the life consumption rate, the change over time ΔVee increases early and the rate of increase gradually increases toward the end of the life. On the other hand, the change over time ΔVce does not increase easily from the early to the middle period and maintains a value significantly lower than the change over time ΔVee. The rate of increase of the change over time ΔVce suddenly increases toward the end of the life. This relationship is also seen in the changes over time ΔVce and ΔVee in the semiconductor module 30B shown in FIG. 4. The values ​​of the changes over time ΔVce and ΔVee in the semiconductor module 30B are smaller than the changes over time ΔVce and ΔVee in the semiconductor module 30A. Therefore, the values ​​of the changes over time ΔVce and ΔVee in the semiconductor module 30B cannot be simply compared to the values ​​of the changes over time ΔVce and ΔVee in the semiconductor module 30A. However, the correlation between the amounts of change over time ΔVce and ΔVee in the semiconductor module 30B is the same as the correlation between the amounts of change over time ΔVce and ΔVee in the semiconductor module 30A. That is, the shape of the graph shown in Fig. 4 is a shape obtained by reducing the graph shown in Fig. 3 along the vertical axis.

[0048] The present disclosure utilizes the fact that the correlation between characteristics of multiple semiconductor modules 30 of the same specifications is constant to diagnose the lifespan of the semiconductor module 30. Specifically, in the first embodiment, the correlation between the amounts of change over time ΔVce and ΔVee is utilized. This enables highly accurate lifespan diagnosis that eliminates individual variations.

[0049] (First example of lifespan diagnosis) A first life diagnosis example by the diagnosis processing unit 3 will be described with reference to Figs. 5 and 6. Fig. 5 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in the semiconductor module 30A. Fig. 6 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in the semiconductor module 30B. Figs. 5 and 6 show an example in which a value obtained by subtracting a first constant "1" from the magnification of the voltage Vce to a first reference value (hereinafter referred to as "Vce rise rate") is extracted as the amount of change over time ΔVce. Similarly, Figs. 5 and 6 show an example in which a value obtained by subtracting a second constant "1" from the magnification of the voltage Vee to a second reference value (hereinafter referred to as "Vee rise rate") is extracted as the amount of change over time ΔVee. Figs. 5 and 6 show graphs in which the horizontal axis represents the life consumption rate, the left vertical axis represents the Vce rise rate and the Vee rise rate, and the right vertical axis represents the correlation value. The correlation value is the ratio of the rate of increase of Vee divided by the rate of increase of Vce.

[0050] The correlation value, which indicates the correlation between the time-dependent changes ΔVce and ΔVee, is different from the Vce rise rate and Vee rise rate in that it does not increase monotonically, but instead rises once and then starts to decline, forming a mountain-shaped curve with a peak. The reason for this is that, as mentioned above, the voltage Vee increases early on and continues to rise relatively monotonically, whereas the voltage Vce does not increase much in the early stage and then suddenly rises at the end. Due to this difference, the correlation value rises in the early stage, strongly reflecting the rise in the voltage Vee, but as it approaches the end, the voltage Vce starts to increase suddenly, so the rise in the correlation value is suppressed and the correlation value becomes maximum. After that, at the end, the rate of rise of the voltage Vce increases suddenly, so the correlation value starts to decrease. For this reason, the correlation value forms a mountain-shaped curve with a peak.

[0051] As shown in Figures 5 and 6, the shape of the graph showing the change over time of the correlation value in the semiconductor module 30A is consistent with the shape of the graph showing the change over time of the correlation value in the semiconductor module 30B. Specifically, as shown in Figure 5, in the case of the semiconductor module 30A, the point at which the correlation value becomes maximum, i.e., the point at which the first-order differential coefficient of the correlation value becomes 0, is the point at which the life consumption rate is 80%. As shown in Figure 6, in the case of the semiconductor module 30B, the point at which the correlation value becomes maximum, i.e., the point at which the first-order differential coefficient of the correlation value becomes 0, is also the point at which the life consumption rate is 80%. Thus, the point at which the correlation value becomes maximum is the point at which the life consumption rate is 80% in both the semiconductor modules 30A and 30B.

[0052] Therefore, the aging calculation unit 20 calculates the first-order differential coefficient of the correlation value as the aging amount ΔCor indicating the aging of the correlation value. The life assessment unit 21 can determine that the remaining life is 20% when the first-order differential coefficient of the correlation value is 0. This makes it possible to eliminate individual variations and perform a highly accurate life assessment.

[0053] Alternatively, the time-varying calculation unit 20 may further calculate a second-order differential coefficient of the correlation value as the time-varying change amount ΔCor indicating the time-varying change of the correlation value. The life assessment unit 21 may perform the life assessment using not only the first-order differential coefficient of the correlation value but also the second-order differential coefficient. For example, the time when the second-order differential coefficient of the correlation value becomes 0 corresponds to an inflection point of the correlation value curve, and is the time when the rate of increase of the correlation value changes from increasing to decreasing. As shown in Figs. 5 and 6, in both the semiconductor modules 30A and 30B, the time when the second-order differential coefficient of the correlation value becomes 0 is the time when the life consumption rate becomes 70%. Therefore, the life assessment unit 21 can determine that the remaining life is 30% in response to the second-order differential coefficient of the correlation value becoming 0. This enables a highly accurate life assessment that eliminates individual variations.

[0054] Furthermore, the aging calculation unit 20 may calculate the ratio between the peak value, which is the correlation value when the first derivative coefficient becomes 0, and the correlation value thereafter, as the aging amount ΔCor indicating the aging of the correlation value. By checking this ratio, the life assessment unit 21 may diagnose that the life consumption rate is 96% and the remaining life is 4% in response to the correlation value dropping to half of the peak value. This enables the life assessment unit 21 to display an end warning on the display unit 4.

[0055] (Second example of lifespan diagnosis) In the first life assessment example, since the Vce increase rate (the value obtained by subtracting the first constant "1" from the magnification of the voltage Vce with respect to the first reference value) is extracted as the amount of change over time ΔVce, the amount of change over time ΔVce is close to 0 in the initial stage. Similarly, since the Vee increase rate (the value obtained by subtracting the second constant "1" from the magnification of the voltage Vee with respect to the second reference value) is extracted as the amount of change over time ΔVee, the amount of change over time ΔVee is close to 0 in the initial stage. Therefore, when the ratio of the amount of change over time ΔVee divided by the amount of change over time ΔVce is calculated as the correlation value, the correlation value may fluctuate greatly. This is because the correlation value is calculated by dividing a small value close to 0 by a small value close to 0. As a result, a small fluctuation in the measured values ​​of the voltages Vce and Vee may cause a large fluctuation in the correlation value. Therefore, the correlation value is likely to be inaccurate in the initial stage.

[0056] Fig. 7 is a diagram showing the effect of slight fluctuations in the voltages Vce and Vee. When there are fluctuations in the voltages Vce and Vee due to issues with the accuracy of voltage measurement, the correlation value, which is the ratio of the amount of change over time ΔVee (rate of increase in Vee) divided by the amount of change over time ΔVce (rate of increase in Vce), fluctuates greatly in the early stages, as shown in Fig. 7. Such large fluctuations in the correlation value may affect the diagnosis of the life span.

[0057] Therefore, the time-change extraction unit 16 extracts the value obtained by subtracting the first constant "0" from the Vce magnification (i.e., the Vce magnification itself) as the amount of change over time ΔVce. Similarly, the time-change extraction unit 17 extracts the value obtained by subtracting the second constant "0" from the Vee magnification (i.e., the Vee magnification itself) as the amount of change over time ΔVee. Then, the correlation value calculation unit 18 calculates the ratio of the Vee magnification divided by the Vce magnification (Vee magnification / Vce magnification) as the correlation value indicating the correlation between the change over time in the voltage Vce and the change over time in the voltage Vee.

[0058] FIG. 8 is a diagram showing the change over time of the correlation value "Vee magnification / Vce magnification" calculated in the second life assessment example. As shown in FIG. 8, since the Vce magnification and the Vee magnification are extracted as the amounts of change over time ΔVce and ΔVee, respectively, the amounts of change over time ΔVce and ΔVee are stable without being affected by slight fluctuations in the measured values ​​of the voltages Vce and Vee. In other words, in the early stage, the correlation value "Vee magnification / Vce magnification" increases gradually with the increase in the life consumption rate. This makes it possible to monitor minute deterioration of the joint in the early stage.

[0059] However, the correlation value "Vee magnification / Vce magnification" is not suitable for detecting a sudden rise in the voltage Vce near the end. Therefore, the time-varying change extracting units 16 and 17 extract the Vce magnification and the Vee magnification as the amounts of change over time ΔVce and ΔVee, respectively, until the timing at which the stable Vce rise rate and Vee rise rate can be extracted (hereinafter referred to as "switching timing"). After the switching timing, the time-varying change extracting units 16 and 17 extract the Vce rise rate and the Vee rise rate as the amounts of change over time ΔVce and ΔVee, respectively. The correlation value calculating unit 18 calculates the correlation value "Vee magnification / Vce magnification" as a correlation value indicating the correlation between the change over time of the voltage Vce and the change over time of the voltage Vee until the switching timing, and calculates the correlation value "Vee rise rate / Vce rise rate" after the switching timing. This allows the life assessment unit 21 to assess the life in the early stage using the change over time in the correlation value "Vee magnification / Vce magnification" and to assess the life in the final stage using the change over time in the correlation value "Vee rise rate / Vce rise rate." As a result, it is possible to accurately monitor both the early stage and final stage deterioration.

[0060] The constant subtracted from the magnification is not limited to 0 or 1, and may change from a value close to 0 to a value close to 1 from the initial stage to the final stage. This makes it possible to calculate a correlation value that is more appropriate for predicting the life span of the semiconductor module 30 in accordance with its use.

[0061] (advantage) As described above, the life assessment device 1 according to the first embodiment includes the Vce amplifier 12, the Vee amplifier 13, and the life assessment unit 21. The Vce amplifier 12 operates as a voltage meter that measures the voltage Vce between the collector main terminal 6 connected to the collector electrode of the semiconductor element 5 mounted on the semiconductor device 2, and the emitter main terminal 8 connected to the emitter electrode of the semiconductor element 5. The Vee amplifier 13 operates as a voltage meter that measures the voltage Vee between the emitter main terminal 8 and the emitter reference terminal 9 connected to the emitter electrode. The life assessment unit 21 assesses the life of the semiconductor device 2 using a correlation value between the change over time of the voltage Vce and the change over time of the voltage Vee.

[0062] According to the above configuration, the correlation value of the change over time of the voltages Vce and Vee is used for the life diagnosis. Although the change over time of the voltages Vce and Vee varies for each individual semiconductor module 30, the variation in the change over time of the correlation value for each individual semiconductor module 30 is small. Therefore, it is possible to perform a highly accurate life diagnosis that eliminates the influence of individual differences in the semiconductor modules 30.

[0063] The amount of change in voltage Vce over time ΔVce is indicated, for example, by a value obtained by subtracting a first constant from the magnification of the value of voltage Vce relative to a first reference value (Vce magnification or Vce rise rate). The amount of change in voltage Vee over time ΔVee is indicated, for example, by a value obtained by subtracting a second constant from the magnification of the value of voltage Vee relative to a second reference value (Vee magnification or Vee rise rate). The correlation value is, for example, the ratio of the amount of change in voltage Vce over time to the amount of change in voltage Vee over time ΔVee (Vee magnification / Vce magnification or Vee rise rate / Vce rise rate).

[0064] By using Vee magnification / Vce magnification or Vee rise rate / Vce rise rate as the correlation value, the curve showing the change over time of the correlation value becomes mountain-shaped with a peak at a specific life consumption rate. Therefore, the life assessment unit 21 can detect that a specific life consumption rate has been reached in response to the correlation value becoming a maximum, and can output life information showing the remaining life. By checking the life information, the user of the semiconductor device 2 can carry out maintenance at an appropriate time.

[0065] The first constant and the second constant are, for example, 1. This makes it possible to increase the difference between the amount of change over time ΔVce and the amount of change over time ΔVee in the terminal stage, thereby improving the accuracy of the life assessment in the terminal stage.

[0066] The first constant and the second constant are, for example, 0. In this way, in the early stage of use of the semiconductor device 2, the correlation value becomes a stable value and gradually increases with an increase in the life consumption rate. This makes it possible to monitor minute deterioration of the joints in the semiconductor device 2 in the early stage.

[0067] The first reference value is the value of the voltage Vce measured before starting to use the semiconductor device 2. The second reference value is the value of the voltage Vee measured before starting to use the semiconductor device 2.

[0068] Before using the semiconductor device 2, it is possible to repeatedly measure the voltages Vce and Vee in an environment suitable for measuring the voltages Vce and Vee, and the voltages Vce and Vee can be measured with high accuracy. This increases the reliability of the correlation value calculated for the subsequent lifetime diagnosis, and improves the accuracy of the lifetime diagnosis.

[0069] Embodiment 2 In the first embodiment, the values ​​of the voltages Vce and Vee measured before the start of use of the semiconductor device 2 (i.e., in an unused state) are used as the first and second reference values, respectively. However, in this case, it is not possible to perform a life diagnosis on the semiconductor device 2 whose voltages Vce and Vee have not been measured before the start of use.

[0070] Therefore, in order to perform a lifetime diagnosis of the semiconductor device 2 in which the voltages Vce and Vee have not been measured before use begins, the reference value memory units 14 and 15 of embodiment 2 store the values ​​of the voltages Vce and Vee measured after use of the semiconductor device 2 begins as first and second reference values, respectively.

[0071] Fig. 9 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in semiconductor module 30A when the voltage at the time when the life consumption rate is 30% is used as the reference value. Fig. 10 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in semiconductor module 30B when the voltage at the time when the life consumption rate is 30% is used as the reference value. Figs. 9 and 10, like Figs. 5 and 6, show graphs with the life consumption rate on the horizontal axis, the amounts of change over time ΔVce and ΔVee (Vce increase rate, Vee increase rate) on the left vertical axis, and the correlation value "Vee magnification / Vce magnification" on the right vertical axis.

[0072] 9 and 10, the values ​​of the amounts of change over time ΔVce and ΔVee at the same life consumption rate are different between the semiconductor module 30A and the semiconductor module 30B. In other words, the life consumption rate cannot be estimated, and the remaining life cannot be predicted, from only the values ​​of the amounts of change over time ΔVce and ΔVee.

[0073] In contrast, the curve of the correlation value "Vee rise rate / Vce rise rate" shows the same shape for the semiconductor module 30A and the semiconductor module 30B. Specifically, the curve of the correlation value "Vee rise rate / Vce rise rate" is mountain-shaped with a peak near a life consumption rate of 76%. Therefore, the life diagnosis unit 21 can diagnose the life of the semiconductor module 30 with higher accuracy based on the correlation value curve, regardless of individual differences of the semiconductor module 30.

[0074] When a voltage at a time point other than when the life consumption rate is 30% is used as the reference value, the curve showing the change in correlation value over time will have a different shape from the curves shown in Figures 9 and 10. However, the curve showing the change in correlation value over time will have the same shape regardless of individual differences in semiconductor modules 30.

[0075] FIG. 11 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in the semiconductor module 30A when the voltage at the time of the life consumption rate of 40% is used as the reference value. FIG. 12 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in the semiconductor module 30B when the voltage at the time of the life consumption rate of 40% is used as the reference value. FIG. 13 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in the semiconductor module 30A when the voltage at the time of the life consumption rate of 50% is used as the reference value. FIG. 14 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in the semiconductor module 30B when the voltage at the time of the life consumption rate of 50% is used as the reference value. FIG. 15 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in the semiconductor module 30A when the voltage at the time of the life consumption rate of 60% is used as the reference value. Fig. 16 is a diagram showing the correlation between the amounts of change over time ΔVce and ΔVee in the semiconductor module 30B when the voltage at the time when the life consumption rate is 60% is used as the reference value. Similar to Figs. 9 and 10, Figs. 11 to 16 show graphs in which the horizontal axis represents the life consumption rate, the left vertical axis represents the amounts of change over time ΔVce and ΔVee (Vce increase rate, Vee increase rate), and the right vertical axis represents the correlation value "Vee magnification / Vce magnification."

[0076] As shown in Figures 11 to 16, the curves showing the change over time of the correlation value "Vee rise rate / Vce rise rate" show the same shape if the consumed life rate at the time of measuring the voltage set as the reference value is the same. That is, the correlation value curve shown in Figure 11 has the same shape as the correlation value curve shown in Figure 12. The correlation value curve shown in Figure 13 has the same shape as the correlation value curve shown in Figure 14. The correlation value curve shown in Figure 15 has the same shape as the correlation value curve shown in Figure 16.

[0077] When the values ​​of the voltages Vce and Vee measured after the start of use of the semiconductor device 2 are used as the first and second reference values, respectively, the lifetime consumption rate at the time of measurement is usually unknown. However, as shown in FIG. 9 to FIG. 16, the shape of the correlation value curve depends on the lifetime consumption rate at the time of measurement of the voltages Vce and Vee used as the first and second reference values. Therefore, the lifetime assessment unit 21 pre-stores a plurality of correlation value curves having different lifetime consumption rates at the time of measurement of the voltages Vce and Vee used as the first and second reference values. The lifetime assessment unit 21 compares the curve indicating the time change of the correlation value output from the aging calculation unit 20 with the plurality of pre-stored curves. The lifetime assessment unit 21 may select the curve that is most similar to the curve indicating the time change of the correlation value output from the aging calculation unit 20 from the plurality of pre-stored curves, and diagnose the lifetime of the semiconductor module 30 based on the selected curve. For example, as shown in Figures 15 and 16, when the correlation value has been consistently decreasing since the start of measurement, the life assessment unit 21 can estimate that the life consumption rate at the start of measurement is more than 60%. Also, when the selected curve is the curve shown in Figures 11 and 12, the life assessment unit 21 can estimate that the life consumption rate is about 73% in response to the change in the correlation value from increasing to decreasing.

[0078] In this way, in the second embodiment, even if the first and second reference values ​​are set after the use of the semiconductor device 2 has started, the lifetime diagnosis of the semiconductor device 2 is possible.

[0079] Embodiment 3 Fig. 17 is a block diagram showing an example of the configuration of a lifetime assessment device according to embodiment 3 of the present disclosure. Life span assessment device 1A according to embodiment 3 differs from lifetime assessment device 1 shown in Fig. 1 in that it includes diagnostic processing unit 3A instead of diagnostic processing unit 3. Diagnostic processing unit 3A differs from diagnostic processing unit 3 in that it includes a Vce amplifier 12A instead of Vce amplifier 12.

[0080] The Vce amplifier 12A measures the voltage between the collector main terminal 6 and the emitter reference terminal 9, and amplifies the measurement result to a voltage Vce suitable for post-processing. The Vce amplifier 12A outputs the voltage Vce to the time-dependent change extraction unit 16.

[0081] In the third embodiment, as in the first embodiment, the lifetime of the semiconductor device 2 can be diagnosed based on a correlation value indicating the correlation between the change over time of the voltage Vce and the change over time of the voltage Vee. In the third embodiment, the voltage Vce is less susceptible to the influence of the emitter-side main circuit connection portion 11. Therefore, compared to the first embodiment, the difference between the amount of change over time ΔVce and the amount of change over time ΔVee may be enlarged. Therefore, depending on the configuration of the semiconductor module 30, the configuration of the first embodiment or the configuration of the third embodiment may be adopted. This allows the lifetime of the semiconductor device 2 to be diagnosed more appropriately depending on the configuration of the semiconductor module 30.

[0082] Embodiment 4 In the fourth embodiment, a semiconductor device to be diagnosed by the lifespan assessment device according to the above-mentioned first, second, and third embodiments is applied to a power conversion device. Although the present disclosure is not limited to a specific power conversion device, the following describes the fourth embodiment in the case where the present disclosure is applied to a three-phase inverter.

[0083] FIG. 18 is a block diagram illustrating a configuration of a power conversion system to which a power conversion device according to a fourth embodiment of the present disclosure is applied. As illustrated in FIG.

[0084] The power conversion system shown in Fig. 18 is composed of a power source 100, a power conversion device 200, and a load 300. The power source 100 is a DC power source and supplies DC power to the power conversion device 200. The power source 100 can be composed of various things, for example, a DC system, a solar cell, or a storage battery, or it may be composed of a rectifier circuit connected to an AC system or an AC / DC converter. The power source 100 may also be composed of a DC / DC converter that converts DC power output from a DC system into a predetermined power.

[0085] The power conversion device 200 is a three-phase inverter connected between the power source 100 and the load 300, converts DC power supplied from the power source 100 into AC power, and supplies the AC power to the load 300. As shown in Fig. 18, the power conversion device 200 includes a main conversion circuit 201 that converts DC power into AC power and outputs it, and a control circuit 203 that outputs a control signal for controlling the main conversion circuit 201 to the main conversion circuit 201. Furthermore, the power conversion device 200 includes the above-mentioned life assessment device 1 (or life assessment device 1A).

[0086] The load 300 is a three-phase motor driven by AC power supplied from the power conversion device 200. The load 300 is not limited to a specific use, but is a motor mounted on various electric devices, and is used as, for example, a motor for a hybrid car, an electric car, a railroad car, an elevator, or an air conditioner.

[0087] The power conversion device 200 will be described in detail below. The main conversion circuit 201 includes switching elements and free wheel diodes (not shown), and converts DC power supplied from the power source 100 into AC power by switching the switching elements, and supplies the AC power to the load 300. There are various specific circuit configurations of the main conversion circuit 201, but the main conversion circuit 201 according to this embodiment is a two-level three-phase full bridge circuit, and can be configured with six switching elements and six free wheel diodes connected in reverse parallel to each switching element. The semiconductor device 2 according to any one of the above-mentioned embodiments 1 to 3 is applied to at least one of the switching elements and free wheel diodes of the main conversion circuit 201. Two switching elements of the six switching elements are connected in series to form upper and lower arms, and each upper and lower arm forms each phase (U phase, V phase, W phase) of the full bridge circuit. The output terminals of each upper and lower arm, i.e., the three output terminals of the main conversion circuit 201, are connected to the load 300.

[0088] The main conversion circuit 201 also includes a drive circuit (not shown) for driving each switching element, but the drive circuit may be built in the semiconductor device 2, or the semiconductor device 2 may include a drive circuit separate from the semiconductor device 2. The drive circuit generates drive signals for driving the switching elements of the main conversion circuit 201 and supplies them to the control electrodes of the switching elements of the main conversion circuit 201. Specifically, in accordance with a control signal from a control circuit 203 (described later), the drive circuit outputs to the control electrodes of each switching element a drive signal for turning the switching element on and a drive signal for turning the switching element off. When maintaining a switching element in the on state, the drive signal is a voltage signal (on signal) equal to or higher than the threshold voltage of the switching element, and when maintaining a switching element in the off state, the drive signal is a voltage signal (off signal) equal to or lower than the threshold voltage of the switching element.

[0089] The control circuit 203 controls the switching elements of the main conversion circuit 201 so that a desired power is supplied to the load 300. Specifically, the control circuit 203 calculates the time (on time) for each switching element of the main conversion circuit 201 to be in the on state based on the power to be supplied to the load 300. For example, the main conversion circuit 201 can be controlled by PWM control that modulates the on time of the switching elements according to the voltage to be output. Then, a control command (control signal) is output to a drive circuit provided in the main conversion circuit 201 so that an on signal is output to a switching element that should be in the on state at each time point, and an off signal is output to a switching element that should be in the off state. The drive circuit outputs an on signal or an off signal as a drive signal to the control electrode of each switching element according to this control signal.

[0090] In the power conversion device according to the present embodiment, the semiconductor device 2 according to any one of the first to third embodiments is applied as a switching element and a free wheel diode of the main conversion circuit 201, and a lifetime assessment device 1 is implemented to assess the lifetime of the semiconductor device 2. Therefore, the remaining lifetime of the semiconductor device 2 can be accurately assessed.

[0091] In the fourth embodiment, an example in which the present disclosure is applied to a two-level three-phase inverter has been described, but the present disclosure is not limited thereto and can be applied to various power conversion devices. In the fourth embodiment, a two-level power conversion device is described, but a three-level or multi-level power conversion device may be used, and the present invention may be applied to a single-phase inverter when power is supplied to a single-phase load. In addition, the present invention can be applied to a DC / DC converter or an AC / DC converter when power is supplied to a DC load or the like.

[0092] Furthermore, the power conversion device to which the present disclosure is applied is not limited to the case where the above-mentioned load is an electric motor, but can also be used, for example, as a power supply device for an electric discharge machine, a laser processing machine, an induction heating cooker, or a non-contact power supply system, and can also be used as a power conditioner for a solar power generation system, a power storage system, etc.

[0093] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is defined by the claims, not by the description of the embodiments described above, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0094] 1,1A life diagnosis device, 2 semiconductor device, 3,3A diagnosis processing unit, 4 display unit, 5 semiconductor element, 5a collector electrode, 5b emitter electrode, 6 collector main terminal, 7 gate terminal, 8 emitter main terminal, 9 emitter reference terminal, 10 collector side main circuit connection unit, 11 emitter side main circuit connection unit, 12,12A Vce amplifier, 13 Vee amplifier, 14,15 reference value memory unit, 16,17 time-dependent change extraction unit, 18 correlation value calculation unit, 19 memory unit, 20 time-dependent change calculation unit, 21 life diagnosis unit, 22 metal plate, 23 connection unit, 24 path, 30 semiconductor module, 100 power supply, 200 power conversion device, 201 main conversion circuit, 203 control circuit, 300 load.

Claims

1. A lifetime assessment device for assessing a lifetime of a semiconductor device, comprising: a first voltage meter that measures a first voltage between a first terminal connected to a first electrode of a transistor mounted on the semiconductor device and a second terminal connected to a second electrode of the transistor; a second voltage meter that measures a second voltage between the second terminal and a third terminal connected to the second electrode; a diagnosis unit that diagnoses a lifetime of the semiconductor device by using a correlation value between the change over time of the first voltage and the change over time of the second voltage.

2. the change in the first voltage over time is represented by a first value obtained by subtracting a first constant from a ratio of the value of the first voltage to a first reference value; the change in the second voltage over time is represented by a second value obtained by subtracting a second constant from a ratio of the value of the second voltage to a second reference value; 2. The lifetime assessment device according to claim 1, wherein the correlation value is a ratio between the first value and the second value.

3. 3. The lifetime assessment device according to claim 2, wherein the first constant and the second constant are 1.

4. 3. The lifetime assessment device according to claim 2, wherein the first constant and the second constant are zero.

5. 5. The life assessment device according to claim 2, wherein the first reference value and the second reference value are values ​​of the first voltage and the second voltage, respectively, measured before use of the semiconductor device begins.

6. 5. The life assessment device according to claim 2, wherein the first reference value and the second reference value are values ​​of the first voltage and the second voltage, respectively, measured after the start of use of the semiconductor device.

7. A life assessment device according to any one of claims 1 to 6, a main conversion circuit having a semiconductor device to be diagnosed by the life diagnosis device, converting input power and outputting the power; a drive circuit that outputs a drive signal for driving the semiconductor device to the semiconductor device; a control circuit that outputs a control signal to the drive circuit to control the drive circuit.

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