阅读说明：本技术 用于确定功率电子装置的温度的方法、设备、功率电子装置 (Method and device for determining temperature of power electronic device and power electronic device ) 是由 M·希布 于 2020-03-18 设计创作，主要内容包括：本发明涉及一种用于确定功率电子装置(1)的温度的方法,所述功率电子装置具有至少一个换向电路(2)和通过换向电路(2)通电/可通电的负载(3),其中换向电路(2)包括第一半导体开关装置(4)和第二二极管(9),所述第一半导体开关装置具有第一半导体开关(5)和可选的第一二极管(6),其中第二二极管(9)和负载(3)彼此并联地与第一半导体开关(5)连接,其中随第一半导体开关(5)导通之后监控至少在第二二极管(9)中引起反向电流期间流过第二二极管(9)的电流的电流分布,并且其中根据电流分布确定第二二极管(9)的势垒层的温度。提出：根据电流分布求出流过换向电路(2)的电路电流的电流值一方和通过反向电流引起的电流极值{Imax)另一方之间的差,并且第二二极管(9)的势垒层的温度根据该差确定。(The invention relates to a method for determining the temperature of a power electronic device (1) having at least one commutation circuit (2) and a load (3) that is/can be energized by means of the commutation circuit (2), wherein the commutation circuit (2) comprises a first semiconductor switching device (4) and a second diode (9), the first semiconductor switch arrangement has a first semiconductor switch (5) and optionally a first diode (6), wherein the second diode (9) and the load (3) are connected in parallel with each other to the first semiconductor switch (5), wherein the current distribution of the current flowing through the second diode (9) at least during the reverse current induced in the second diode (9) is monitored after the first semiconductor switch (5) has been switched on, and wherein the temperature of the barrier layer of the second diode (9) is determined from the current profile. It proposes: a difference between one of current values of a circuit current flowing through the commutation circuit (2) and the other of current limit values { Imax) caused by a reverse current is obtained from the current distribution, and the temperature of the barrier layer of the second diode (9) is determined based on the difference.)

1. A method for determining a temperature of a power electronic device (1) having at least one commutation circuit (2) and a load (3) which is energized by the commutation circuit (2), wherein the commutation circuit (2) comprises a first semiconductor switching device (4) having a first semiconductor switch (5) and optionally a first diode (6), and a second diode (9), wherein the second diode (9) and the load (3) are connected in parallel with each other with the first semiconductor switch (5), wherein a current distribution of a current flowing through the second diode (9) during at least a reverse current is induced in the second diode (9) is monitored after the first semiconductor switch (5) is turned on, and wherein a temperature of a barrier layer of the second diode (9) is determined from the current distribution,

the difference between one of the current values of the circuit current flowing through the commutation circuit (2) and the other of the current limit values (Imax) caused by the reverse current is determined from the current distribution, and the temperature of the barrier layer of the second diode (9) is determined from the difference.

2. The method according to claim 1, characterized in that the temperature of the barrier layer of the second diode (9) is found from a correction value corresponding to a current value of a load current flowing through the load (3).

3. Method according to any of the preceding claims, characterized in that the current through the second diode (9) is measured to monitor the current distribution.

4. Method according to any of the preceding claims, characterized in that a voltage distribution of the parasitic inductances (16) is detected and the current distribution is found from the detected voltage distribution.

5. Method according to any of the claims, characterized in that the current profile before the occurrence of a reverse current induced in the second diode (9) is monitored, wherein the current value of the circuit current flowing through the commutation circuit (2) is derived from the current profile before the occurrence of the reverse current.

6. Method according to any of the preceding claims, characterized in that a current distribution after the occurrence of a reverse current induced in the second diode (9) is monitored, wherein from the current distribution a plateau current value occurring after the occurrence of the reverse current is found, wherein the maximum amount (I) of the reverse current (I) is the maximum amount_rr,max) Is determined from the difference and the plateau current, wherein the temperature of the barrier layer of the second diode (9) is determined from the maximum amount (I) of the reverse current_rr,max) And (4) determining.

7. Method according to any of the preceding claims, characterized in that the temperature of the barrier layer of the second diode (9) is determined from the intermediate loop voltage applied at the power electronics (1).

8. Method according to any of the preceding claims, characterized in that the temperature of the barrier layer of the second diode (9) is determined according to the duration of conduction of the first semiconductor switch (5).

9. Method according to one of the preceding claims, characterized in that the temperature of the barrier layer of the second diode (9) is determined by means of a family of characteristics and/or a look-up table.

10. Method according to any of the preceding claims, characterized in that the current distribution and/or the voltage distribution is measured on a side of the second diode (9) facing away from the first semiconductor switching device (4) or on a side of the first semiconductor switching device (4) facing away from the second diode (9).

11. Method according to one of the preceding claims, characterized in that, for configuring the power electronic device (1) as a half bridge (2), the power electronic device (1) has a second semiconductor switch arrangement (7) with a second semiconductor switch (8) and the second diode (9), wherein a current distribution during a reverse current induced in the first diode (6) is monitored after the second semiconductor switch (8) is turned on, and wherein the temperature of the barrier layer of the first diode (6) is determined from the current distribution during the reverse current induced in the first diode (6).

12. Method according to any of the preceding claims, characterized in that the monitoring of the current profile is initiated in dependence on the point in time of the switching off of the second semiconductor switch (8).

13. Method according to any of the preceding claims, characterized in that the reverse current is integrated and the temperature of the barrier layer of the second diode (9) is determined from the integration.

14. An apparatus (20) for determining the temperature of a power electronic device (1), wherein the power electronic device (1) has at least one commutation circuit (2) and a load (3) that is energized by the commutation circuit (2), wherein the commutation circuit (2) comprises a first semiconductor switching device (4) having a first semiconductor switch (5) and optionally a first diode (6), and a second diode (9), wherein the second diode (9) and the load (3) are connected in parallel with each other with the first semiconductor switch (5), characterized in that the apparatus (20) is specifically designed as a control apparatus for: performing the method of any one of claims 1 to 13 in normal use.

15. A power electronic device (1) having at least one commutation circuit (2) and a load (3) that is energized by the commutation circuit (2), wherein the commutation circuit (2) comprises a first semiconductor switching device (4) having a first semiconductor switch (5) and optionally a first diode (6), and a second diode (9), wherein the second diode (9) and the load (3) are connected in parallel with each other to the first semiconductor switch (5), characterized in that an arrangement (20) according to claim 14 is provided.

Technical Field

The invention relates to a method for determining the temperature of a power electronic device having at least one commutation circuit and a load which is/can be energized by means of the commutation circuit, wherein the commutation circuit comprises a first semiconductor switch device having a first semiconductor switch and optionally a first diode, and a second diode, wherein the second diode and the load are connected in parallel with the first semiconductor switch, wherein a current profile of a current flowing through the second diode during at least a reverse current in the second diode is monitored after the first semiconductor switch is switched on, and wherein the temperature of a barrier layer of the second diode is determined from the current profile.

The invention also relates to a device for carrying out the method mentioned at the outset.

The invention also relates to a power electronic device having such a device.

Background

During operation of the power electronics, the power semiconductors of the power electronics, for example power semiconductor switches or diodes, are subjected to a large load. In order to protect the power semiconductors from thermal overload, the temperature of the power semiconductors or of the power electronics is generally determined and the power electronics are operated as a function of the determined temperature.

To determine that the temperature is known: an NTC temperature sensor is integrated into the power electronics. It is also known that: the temperature-dependent electrical semiconductor properties of the power semiconductors of the power electronics are determined and the temperature of the power semiconductors is determined from the determined temperature-dependent electrical semiconductor properties. For example, the forward voltage of a power semiconductor is such a temperature-dependent electrical semiconductor characteristic.

A method for determining the Temperature of a Power electronic device of the type set forth at the outset is known from the publication "Online High-Power p-i-n Diode Junction Temperature Extraction With Reverse Recovery surface Storage Charge" IEEE traces, On Power Electronics, pages 2558 and 2567, 4 months 2017 (Luo et al). The power electronics comprise a commutation circuit and a load which is/can be energized by the commutation circuit. The commutation circuit has a first semiconductor switching device comprising a first semiconductor switch and a first diode and a second diode. The second diode and the load are connected in parallel with each other to the first semiconductor switch. The presence of the first diode is optional for constituting the commutation circuit. The first semiconductor switch and the second diode form a commutation circuit by: that is, the current flowing through the second diode in the forward direction is commutated to the first semiconductor switch as the first semiconductor switch is turned on. This means that: the current through the second diode decreases and the current through the first semiconductor switch increases simultaneously, wherein the load current through the load remains constant. According to Luo et al, the current distribution of the current flowing through the second diode is monitored during the reverse current induced in the second diode after the first semiconductor switch is turned on. A reverse current is understood to mean a current which flows through the diode in the opposite direction to the forward direction of the diode, for example the second diode. The reverse current is generated as follows: with the current flowing in the forward direction of the diode, the remaining carriers exist in the space charge region of the diode, and these carriers are removed from the space charge region. To monitor the current profile, the voltage of the parasitic inductance of the commutation circuit is measured during the occurrence of the reverse current, which voltage corresponds to the current profile, Luo et al, wherein the temperature of the barrier layer of the second diode is then determined from the magnitude of the voltage profile of the voltage of the parasitic inductance.

Disclosure of Invention

The method according to the invention with the features of claim 1 has the advantage that: the temperature of the barrier layer of the second diode is reliably determined. To this end, according to the invention: a difference between one of current values of a circuit current flowing through the commutation circuit and the other of current limit values caused by a reverse current is obtained from the current distribution, and the temperature of the barrier layer of the second diode is determined based on the difference. The current limit caused by the reverse current is understood here to mean the maximum or minimum of the current distribution during the reverse current through the second diode. Typically, the current limit value exhibits a minimum value, since the reverse current is a current opposite to the forward direction of the second diode. Of course, the current limit value may be expressed as a maximum value according to a processing method when the current limit value or the current distribution is obtained. This is based on: the current limit or difference of the reverse current is correlated with the temperature of the barrier layer of the second diode, so that the temperature of the barrier layer of the second diode can be determined from the current limit or difference. Thus, the current extrema or difference of the reverse current is a temperature dependent electrical semiconductor characteristic. The current value of the circuit current is understood to be the current value of the current flowing through at least one element of the commutation circuit. The current value of the circuit current is preferably determined from the current distribution. Preferably, for this purpose, the current distribution before or after the occurrence of the reverse current induced in the second diode is taken into account.

According to a preferred embodiment, the temperature of the barrier layer of the second diode is determined from a correction value corresponding to the current value of the load current flowing through the load. This is based on: before the first semiconductor switch is turned on, a current flows through the second diode, the current value of the current corresponding to the current value of the load current flowing through the load. Further based on: the current value of the current flowing through the second diode or the current value of the load current before the first semiconductor switch is turned on affects the current limit value of the reverse current. By taking into account the current value of the load current flowing through the load in the form of a correction value, the accuracy in determining the temperature of the barrier layer of the second diode is thus improved.

Preferably, the current flowing through the second diode is measured to monitor the current distribution. The following advantages are obtained therefrom: the current distribution is provided directly. Thereby simplifying the evaluation or determination of the temperature of the barrier layer of the second diode. Preferably, the current distribution through the second diode is measured directly and without potential. The current distribution is measured, for example, by means of hall sensors, rogowski sensors, etc. Alternatively or in addition thereto, the current distribution is preferably measured directly and in conjunction with an electrical potential. For this purpose, the voltage applied to the resistor or the voltage distribution of said voltage is measured and the current distribution is calculated from the voltage distribution by means of ohm's law. Since only the correction factor has to be multiplied to determine the current distribution, this is also based on: the current distribution is directly measured, wherein the calibration factor is related to the resistance value of the resistor.

According to a preferred embodiment, it is provided that: the voltage distribution of the parasitic inductance is detected, and the current distribution is found from the detected voltage distribution. The following advantages are obtained therefrom: the method can be implemented technically simply. This is based on: the voltage profile corresponds to the slope of the current profile. Therefore, the current distribution can be obtained by integrating the voltage distribution of the parasitic inductance. For this purpose, the following equation (1.1) is preferably used, where Δ V_SSCorresponding to the voltage value, L, of the parasitic inductance_parAn inductance corresponding to the parasitic inductance, and I_DThe current values corresponding to the current distribution.

In this case, the current limit then usually exhibits a maximum value.

Preferably, the current profile of the current caused in the second diode before the occurrence of the reverse current is monitored, wherein the current value of the circuit current flowing through the commutation circuit is determined from the current profile before the occurrence of the reverse current. The current value of the current path is preferably determined as the plateau current value occurring before the occurrence of a reverse current or before the current commutates from the second diode to the first semiconductor switch. The following advantages are obtained therefrom: the temperature of the barrier layer of the second diode can be determined directly from the determined difference. Alternatively, the current value during the commutation of the current from the second diode to the first semiconductor switch is determined as the current value of the circuit current.

According to a preferred embodiment, it is provided that: monitoring a current distribution after occurrence of a reverse current induced in the second diode, wherein a plateau current value occurring after occurrence of the reverse current is found from the current distribution, wherein a maximum amount of the reverse current is found from the difference on the one hand and the plateau current value on the other hand, and wherein a temperature of the barrier layer of the second diode is determined from the maximum amount of the reverse current. In this way, the accuracy of the temperature determination of the second diode is increased. Preferably, the plateau current value is subtracted from the difference in order to find the maximum amount of reverse current.

Preferably, the temperature of the barrier layer of the second diode is determined as a function of the intermediate circuit voltage applied at the power electronics. The intermediate circuit voltage is a voltage provided by a current or voltage source connected to the power electronics. This is based on: the intermediate circuit voltage applied to the power electronics also influences the current limit. Thus, by taking the intermediate circuit voltage into account, the accuracy in determining the temperature of the barrier layer of the second diode is improved.

According to a preferred embodiment, it is provided that: the temperature of the barrier layer of the second diode is determined in accordance with the conduction duration of the first semiconductor switch. The conduction duration can be understood here as the duration of time for which the first semiconductor switch needs to transition from the non-conducting or blocking state to the conducting state. This is based on: the duration of the switching-on of the first semiconductor switch influences the current limit value such that a reduction of the duration, i.e. a faster switching-on of the first semiconductor switch, an increase of the current limit value occurring as a maximum value or a reduction of the current limit value occurring as a minimum limit value is caused.

Preferably, the temperature of the barrier layer of the second diode is determined by means of a family of characteristics and/or a look-up table. Both the family of characteristic curves and the look-up table are suitable measures for taking into account the dependence of the current limit values on the current value of the intermediate circuit voltage and/or the load current when determining the temperature of the barrier layer of the second diode.

According to a preferred embodiment, it is provided that: the current distribution and/or the voltage distribution is measured on the side of the second diode facing away from the first semiconductor switching device or on the side of the first semiconductor switching device facing away from the second diode. The current limit value of the reverse current induced in the second diode can be detected on both of the aforementioned sides. Both sides are therefore suitable for measuring current and voltage distributions. The current limit value usually represents a minimum value if the current distribution is measured on the side of the second diode facing away from the first semiconductor switching device. If the current distribution is measured on the side of the first semiconductor switching device facing away from the second diode, the reverse current appears as an overcurrent corresponding to the reverse current, so that the current limit then appears as a maximum.

Preferably, in order to form the power electronics as a half bridge, the power electronics has a second semiconductor switching device having a second semiconductor switch and a second diode, wherein the current profile during the reverse current induced in the first diode is monitored after the second semiconductor switch is switched on, and wherein the temperature of the barrier layer of the first diode is determined as a function of the current profile during the reverse current induced in the first diode. As described above, the current limit value of the second diode can be detected on the side of the first semiconductor switching device facing away from the second diode and on the side of the second diode facing away from the first semiconductor switching device. From this it follows: it is likewise possible to detect current extremes during the occurrence of the reverse current induced in the first diode on both sides. The half-bridge is usually steered such that the load current flowing through the load has a sinusoidal distribution. For this purpose, the half-bridge or the semiconductor switches of the half-bridge are preferably controlled in a pulse-width-modulated manner. In this case, for example, the first semiconductor switch and the second diode are activated in the time period in which the load current has a positive current value, so that both elements or one of both elements conducts the current. During this time period, the temperature of the barrier layer of the second diode can then be determined by this method. The second semiconductor switch and the first diode are then activated during a time period in which the load current has a negative current value, so that the temperature of the barrier layer of the first diode can be determined by the method during said time period. Preferably, the current distribution during the occurrence of the reverse current induced in the second diode and the current distribution during the occurrence of the reverse current induced in the first diode are monitored on the same side or by means of the same measuring device. The following advantages are obtained therefrom: the temperature of the barrier layer of the first diode and the temperature of the barrier layer of the second diode may be determined by means of the same measuring device. In particular, the power electronics are designed as a half bridge without the temperature of the barrier layer of the first diode having to be determined after the second semiconductor switch has been switched on.

According to a preferred embodiment, it is provided that: the monitoring of the current distribution is started depending on the point in time of the switching off of the second semiconductor switch. The point in time at which the second semiconductor switch is switched off, i.e. is not conducting, is predetermined by the commutation circuit or the control device of the power electronics. The point in time at which the second semiconductor switch is switched off is therefore already known and is advantageously suitable as a trigger or start signal for monitoring the current distribution.

Preferably, the reverse current is integrated and the temperature of the barrier layer of the second diode is determined from the integration. Thereby, the susceptibility of the method is reduced. Here, the integral of the distribution of the reverse current corresponds to the reverse recovery charge Q of the second diode_rr. Reverse recovery charge is also a temperature dependent electrical semiconductor property. The integral of the distribution of the reverse current is preferably determined during the entire duration of the occurrence of the reverse current. Alternatively, only a certain time section of the duration is preferably taken into account in the determination of the integral.

The device according to the invention for determining the temperature of a power electronic apparatus having the features of claim 14 is characterized in that the device is designed specifically as a control device for carrying out the method according to the invention in normal use, wherein the power electronic apparatus has at least one commutation circuit and a load which is energized/energizable by the commutation circuit, wherein the commutation circuit comprises a first semiconductor switching device having a first semiconductor switch and optionally a first diode, and a second diode, wherein the second diode and the load are connected in parallel with one another to the first semiconductor switch. The advantages already mentioned are also obtained. Further preferred features and feature combinations result from the preceding description and from the claims.

The power electronic device according to the invention with the features of claim 15 is characterized in that an apparatus according to the invention is provided, wherein the power electronic device has at least one commutation circuit and a load which is energized/energizable by the commutation circuit, wherein the commutation circuit comprises a first semiconductor switching device with a first semiconductor switch and optionally a first diode and a second diode, wherein the second diode and the load are connected in parallel with the first semiconductor switch. The advantages already mentioned are also obtained. Preferably, the power electronics device has a second semiconductor switching device for forming the commutation circuit as a half bridge, wherein the second semiconductor switching device comprises a second semiconductor switch and a second diode. In particular, the first semiconductor switch and/or the second semiconductor switch are designed as IGBTs. The first diode and/or the second diode are then preferably diodes which are formed separately from the semiconductor switch and are connected in anti-parallel to the semiconductor switch. The first semiconductor switch and/or the second semiconductor switch are preferably designed as MOSFETs. The first diode and/or the second diode is then preferably the body diode of a semiconductor switch in the form of a MOSFET. Alternatively, the first and/or second diode is preferably a diode which is formed separately from the semiconductor switch in the form of a MOSFET and is connected in anti-parallel to the semiconductor switch. In this case, the first semiconductor switch and/or the second semiconductor switch are preferably designed as silicon-based MOSFETs.

Drawings

The invention is described in more detail below with reference to the appended drawings, wherein like and corresponding elements are provided with the same reference numerals. Therefore, the method comprises the following steps:

figure 1 shows a circuit diagram of a power electronic device,

fig. 2 shows two graphs, in which the current distribution through the commutation circuit of the power electronics is shown,

fig. 3 shows a graph in which the voltage distribution of the parasitic inductance and the current distribution found from the voltage distribution are shown,

fig. 4 shows a method for determining the temperature of a diode of a power electronic device according to a first embodiment, and

fig. 5 shows a method for determining the temperature of a diode according to a second embodiment.

Detailed Description

Fig. 1 shows a circuit diagram of a power electronics device 1. The power electronics device 1 has a commutation circuit 2 and a load 3. The commutation circuit 2 is currently designed as a half bridge 2. For this purpose, the commutation circuit 2 has a first semiconductor switching device 4 with a first semiconductor switch 5 and a first diode 6. Furthermore, the commutation circuit 2 has a second semiconductor switching device 7 with a second semiconductor switch 8 and a second diode 9. However, the presence of the first semiconductor switch 5, the second semiconductor switch 8, the first diode 6 and the second diode 9 is not required for the construction of the commutation circuit 2. According to another embodiment of the commutation circuit 2, the first semiconductor switch 5 and optionally the second diode 9 are omitted. The commutation circuit 2 is then designed as a single-quadrant controller and has a second semiconductor switch 8, a first diode 6 and optionally a second diode 9. According to a further embodiment of the commutation circuit 2, the second semiconductor switch 8 and optionally the first diode 6 are omitted. The commutation circuit 2 is then also designed as a single-quadrant controller and has a first semiconductor switch 5, a second diode 9 and optionally a first diode 6.

The second diode 9 and the load 3 are connected in parallel with each other to the first semiconductor switch 5. The first diode 6 and the load 3 are connected in parallel with each other to a second semiconductor switch 8. The power electronics 1 also has a voltage source 10, which comprises a positive pole 11 and a negative pole 12. The positive pole 11 is now connected to the first semiconductor switching device 4. The negative pole 12 is connected to the second semiconductor switching device 7.

The power electronics 1 also have a control circuit 13. The control circuit is configured to: the first semiconductor switch 5 and the second semiconductor switch 8 are operated. For this purpose, the control circuit 13 is connected to the gate of the first semiconductor switch 5 by means of a first resistor 14 and to the gate of the second semiconductor switch 8 by means of a second resistor 15. The control circuit 13 is configured to: the semiconductor switches 5 and 8 are controlled in a pulse width modulated manner such that the load current flowing through the load 3 has a sinusoidal distribution. In this case, when the sinusoidal load current has a positive current value, the current flows on the one hand through the load 3 and on the other hand through the first semiconductor switch 5 and/or the second diode 9. If the sinusoidal load current has a negative current value, the current flows on the one hand through the load 3 and on the other hand through the second semiconductor switch 8 and/or the first diode 6.

Furthermore, the commutation circuit 2 or the power electronics 1 has a parasitic inductance 16, which is located on the side of the second diode 9 facing away from the first semiconductor switching device 4.

In the following, different current distributions of the circuit current flowing through the commutation circuit 2 are explained with reference to fig. 2. The first diagram shown on the left in fig. 2 shows the current distribution I_D. Current distribution I_DThe current flowing through the second diode 9 in the forward direction is described. Here, it is based on: the sinusoidal load current has a positive current value. The current therefore flows on the one hand through the load 3 and on the other hand through the first semiconductor switch 5 and/or the second diode 9. For example, the current distribution I can be measured at the location marked by the arrow 17 in FIG. 1_D. At a first point in time t₁Previously, the first semiconductor switch 5 was not conductive. The current value of the current flowing through the second diode 9 is at a first point in time t₁Which previously substantially corresponds to the current value of the load current flowing through the load 3. From said point of time t₁The first semiconductor switch 5 is at least partially conductive. From this point in time, the current flowing through the second diode 9 commutates to the first semiconductor switch 5. This means that: at a point in time t₁And a second point in time t₂Meanwhile, the current value of the current flowing through the second diode 9 decreases. At the same time, the current value of the current flowing through the first semiconductor switch 5 increases. At a second point in time t₂The current value of the current flowing through the second diode 9 is 0. Over time t₂Thereafter, the remaining carriers existing in the space charge region of the second diode 9 are removed from the space charge region. Thus, at the time point t₂And a point in time t₄In the second diode 9, a reverse current, i.e. a current flowing through the second diode 9 in the opposite direction to the forward direction of the second diode 9, is induced. At a point in time t₃The reverse current having a current limit value I_maxIn this case, the minimum value. The current extreme value I_maxOr current limit I_maxIs related to the temperature of the barrier layer of the second diode 9. It is therefore a temperature-dependent electrical semiconductor property. Over time t₄After that, the reverse current is ended. The current value of the current flowing through the second diode 9 is then substantially 0. Current limit value Imax and time point t₄The difference between the plateau current values occurring thereafter is the maximum amount of reverse current I_rr,max. Current distribution I_BAlso representing the current distribution through the second diode 9. However, the current distribution I_BAnd current distribution I_DCompared with the reversal, so that in this case the current limit value I_maxAppearing as a maximum. Current distribution I_DAnd current distribution I_BIt may also be measured at the location marked by arrow 18 in fig. 1.

The second diagram shown on the right in FIG. 2 shows the current distribution I_C. The current distribution I_CRepresenting the current that can be measured at the location marked by arrow 19 in figure 1. Thus, the current distribution I_CIs the current flowing in the forward direction through the first semiconductor switch 5. Time t₁、t₂、t₃And t₄In each case corresponding to the time points shown in the first diagram. At a point in time t₁Previously, the first semiconductor switch 5 was not conductive, so that the current distribution I was_CThe current value of (2) is 0. As can be seen from the second diagram, at a point in time t₂And t₄A reverse current flowing through the second diode 9 in a direction opposite to the forward direction in the current distribution I_CIs shown as an overcurrent, wherein the maximum amount of overcurrent, I_rr,maxCorresponding to the maximum amount of reverse current I_rr,max. Over time t₄Then, current distribution I_CSubstantially corresponds to the current value of the load current flowing through the load 3.

Fig. 3 shows a voltage distribution Δ V of the voltage applied at the parasitic inductance 16. At this point in time t₁、t₂、t₃And t₄Also corresponding to the points in time shown in the first diagram of fig. 2. At time t₁And t₃In between, the voltage applied at the parasitic inductance 16 has a positive voltage value. At a point in time t₃And t₄Meanwhile, the voltage applied at the parasitic inductance 16 has a negative voltage value. Over time t₄After that, the voltage value is substantially 0. The current distribution I can be determined from the voltage distribution Δ V, the current distribution and the current distribution I_B、I_DAnd I_CAnd (7) corresponding. For this purpose, the voltage distribution Δ V is integrated. The determined current profile I then corresponds to the measurable current profile I_C。

Next, a first embodiment of a method for determining the temperature of the barrier layer of the second diode 9 is explained with reference to fig. 4. The method is carried out at a point in time at which the load current through the load 3, which has a sinusoidal distribution, has a positive current value. Similarly, when the load current passing through the load 3 has a negative current value, a method for determining the temperature of the barrier layer of the first diode 6 may be performed.

In step S1, monitoring of the current distribution through the second diode 9 is started upon detection of a trigger or start signal. Currently, the turning off, i.e. non-conduction, of the second semiconductor switch 8 is detected as a trigger. In step S2, the current applied at one of the sites marked by the arrows 17, 18 or 19 or the voltage applied at the parasitic inductance 16 is selectively measured to monitor the current distribution. As an alternative to the voltage of the parasitic inductance 16, the voltage of the parasitic inductance present on the side of the first semiconductor switching device 7 facing away from the second semiconductor switching device 7 is measured. If the voltage is measured in step S2, a current distribution is found from the voltage distribution of the voltage in step S3. For this purpose, the voltage distribution is integrated. Thereafter, refer to step S4. If the current is measured in step S2, refer directly to step S4.

In step S4, the current limit value I occurring between times t2 and t4, i.e. during the occurrence of the reverse current, is determined from the current distribution_maxAnd the other of the current values of the circuit currents flowing through the commutation circuit 2. The current value of the circuit current is preferably a current value determined from the current distribution. Preferably, the selection is at timePoint t₂Before, i.e. before the occurrence of the reverse current, particularly preferably at the time t₁The current value of the current distribution before, i.e. at the point in time when the first semiconductor switch 5 is non-conductive, is taken as the current value of the circuit current. In step S5, an intermediate circuit voltage, that is, a voltage applied between the positive electrode 11 and the negative electrode 12 is determined or supplied. In step S6, the current value of the load current flowing through the load 3 is obtained or supplied. The load current flowing through the load 3 is preferably determined from the current distribution. Alternatively, the load current is determined by a separate current measuring device assigned to the load 3. In step S7, the temperature of the barrier layer of the second diode 9 is determined from the determined difference, the intermediate circuit voltage, and the load current flowing through the load 3.

Fig. 5 shows a further embodiment of a method for determining the temperature of the barrier layer of the second diode 9. The embodiment shown in fig. 5 differs from the embodiment shown in fig. 4 in particular in that: after the counter current is determined from the current distribution, i.e. at the time t₄The plateau current value that occurs thereafter. In step S8, the maximum amount I of reverse current is then determined from the difference and the plateau current_rr,max. In step S7, the maximum amount I of reverse current is then used_rr,maxThe intermediate circuit voltage and the current value of the load current determine the temperature of the barrier layer of the second diode 9. The second embodiment shown in fig. 5 has an improved accuracy compared to the embodiment shown in fig. 4.

Referring to fig. 1, a power electronics device 1 has an apparatus 20. The device 20, which is only schematically shown, is configured for: a method for determining the temperature of the barrier layer of the second diode 9 is performed. For this purpose, the device 20 is connected in communication with a measuring apparatus, which supplies the device 20 with the current value of the load current flowing through the load 3, the intermediate circuit voltage and the measured voltage value or the measured current value.