Method for operating an energy converter, control unit and energy converter

Abstract

The invention relates to a method for determining the remaining normal availability of a semiconductor module (24), which is thermally coupled to a cooling device (20), wherein a predetermined electrical load (34) is applied to the semiconductor module (24) in the case of cooling predetermined by the cooling device (20), the temperature (36) of a semiconductor element (28) of the semiconductor module (24) is detected at least for the predetermined electrical load (34) of the semiconductor module (24), the detected temperature (36) is compared with a reference temperature (40) in a first comparison, wherein the reference temperature (40) corresponds to the predetermined electrical load (34) in the case of the predetermined cooling, and at least based on the first comparison, prediction data (44) for the remaining normal availability of the semiconductor module (24) up to the end of the availability are derived.

Description

Technical Field

[0001] The invention relates to a method for determining the remaining normal availability of a semiconductor module, which is thermally coupled to a cooling device. The invention also relates to a method for operating an energy converter connected to an electric machine, which energy converter electrically couples the electric machine to an intermediate DC circuit, for the purpose of electrical coupling, at least one semiconductor module thermally coupled to the cooling device cooperates with at least one energy storage device electrically coupled to the semiconductor module, and the semiconductor module is operated for the electrical coupling of the intermediate DC circuit to the electric machine in a predeterminable switching operation. The invention also relates to a control unit for controlling at least one semiconductor module thermally coupled to the cooling device. Finally, the invention also relates to an energy converter for connecting to an electric machine, the energy converter having at least one semiconductor module, at least one cooling device thermally coupled to at least one semiconductor module, at least one energy storage device electrically coupled to at least one semiconductor module, connection contacts for connecting the electric machine, intermediate circuit connections for connecting the energy converter to the intermediate DC circuit, and a control unit electrically coupled to at least one semiconductor module, the control unit being used to control at least one semiconductor module in a predeterminable switching operation to electrically couple the intermediate DC circuit to the electric machine. Background Art

[0002] Such methods, control units and energy converters are generally known in the prior art, so that no particular reference is required. The prior art relates in particular to the use of semiconductor modules, which are used in various ways in the prior art to convert electrical energy in very different ways. The conversion of electrical energy is usually carried out with the aid of an energy converter, which can be designed, for example, as an inverter.

[0003] An inverter is a form of energy converter that couples an intermediate DC circuit with an AC network in an electrical energy-technical manner so that electrical energy can be exchanged between the intermediate DC circuit and the AC network. For this purpose, it is usually provided that the energy converter has at least one switching element that cooperates with an electrical energy store. The at least one switching element is usually formed by a semiconductor module that can include one or more semiconductor switching elements.

[0004] On the AC voltage side, the AC network can be formed, for example, by an electric machine, in particular a multiphase electric machine. By controlling at least one switching element by means of a control unit in switching operation, the desired switching function of the inverter or energy converter can be realized, thereby realizing the desired drive function with the electric machine.

[0005] For this purpose, the switching elements are usually operated with a predetermined clock rate which is significantly higher than the frequency of at least one phase AC voltage of the AC power network. The desired energy-technical coupling can thus be generated by means of specific control methods, such as pulse width modulation (PWM) or similar methods. For this purpose, the control unit provides specific switching signals for at least one switching element or each of a plurality of switching elements, so that the at least one switching element or the plurality of switching elements can be operated in the desired manner during switching operation.

[0006] It has been shown that semiconductor modules, in particular depending on the type of power module, are subject to aging, which also depends on temperature excursions of the semiconductor elements, which can be caused, for example, by changing electrical loads. After a certain number of temperature cycles associated with load changes, the end of the availability for the normal availability of the semiconductor module is reached, and the end of the availability can lead to a failure of the semiconductor module. This can also be caused by the separation of different structural and connecting layers and the thermal connection of the semiconductor elements to the cooling device, which is thus deteriorated. The failure of a semiconductor module, in particular the failure of an energy converter having at least one semiconductor module, has been shown to be disruptive and can even lead to dangerous situations in some cases. It is therefore desirable to provide information about the remaining normal availability of the semiconductor module, so that on the one hand maintenance can be carried out in good time before a failure of the semiconductor module, and on the other hand maintenance is only necessary when the end of the availability can be foreseen.

[0007] To this end, the temperature of the semiconductor element has hitherto usually been determined via a thermal model. In this case, the temperature detected by means of a temperature sensor is output at the cooling device, and an approximate value is calculated for the actual temperature of the semiconductor element. The corresponding temperature excursion of the semiconductor element can be estimated or calculated based on the semiconductor element temperature calculated in this way. The number of temperature cycles until the semiconductor module fails can be determined for at least one semiconductor module by empirical studies using load change experiments. The load change intensity is determined for a preset relatively large temperature excursion (for example, greater than 70 K).

[0008] However, during normal operation of the semiconductor module, generally only small temperature excursions occur, for example in the range of approximately 10 K to approximately 35 K. Larger temperature excursions occur only occasionally.

[0009] The above-mentioned thermal model for determining the remaining availability is disadvantageous because the current power loss is taken into account as a calculation quantity, which is obtained via a small number of storage points. In addition, the model does not take into account that the thermal resistance between the semiconductor element and the cooling surface can change with the progressive use of the semiconductor module, especially become larger. By measuring the load change capability in a temperature deviation greater than 70K combined with batch differences of semiconductor modules, with the limited accuracy of determining the current loss and the change of the thermal resistance depending on the conventional availability, these points lead to a very imprecise conclusion of the availability end point or the remaining availability. Therefore, maintenance is usually carried out explicitly before the availability end point even if there is actually enough distance to the availability end point. This is highly costly and expensive.

[0010] EP 3 054 306 A1 also discloses a method and a device and a circuit arrangement for determining the aging of a power semiconductor module. JP 2011-196703 A also discloses a power cycle life estimation for a power semiconductor module. EP 3 203 250 A1 also discloses a method and a device for estimating the damage level or expected life of a power semiconductor module. Finally, US 2009 / 0046406 A1 discloses a semiconductor device. Summary of the invention

[0011] The basic object of the present invention is to accurately determine the end point of availability or the remaining normal availability of a semiconductor module.

[0012] Regarding this method, according to a first aspect, it is proposed that, in the case of cooling preset by a cooling device, a semiconductor module is loaded with a preset electrical load, the temperature of the semiconductor elements of the semiconductor module is detected at least for the preset electrical load of the semiconductor module, the detected temperature is compared with a reference temperature in a first comparison, wherein the reference temperature corresponds to the preset electrical load in the case of the preset cooling, and predictive data for the remaining normal availability of the semiconductor module until the end of the availability are derived at least based on the first comparison.

[0013] Regarding this method, according to a second aspect, it is proposed that, under preset cooling by a cooling device, a semiconductor module is loaded with a preset electrical load, a thermal resistance between the semiconductor elements of the semiconductor module and the cooling device is obtained, the obtained thermal resistance is compared with a reference thermal resistance in a second comparison, and predictive data for the remaining normal availability of the semiconductor module until the end of the availability are obtained at least based on the second comparison.

[0014] With regard to this method for operating an energy converter, it is proposed in particular that according to the invention the remaining normal availability of at least one semiconductor module is determined.

[0015] With regard to such a control unit, according to a first aspect, it is particularly proposed that the control unit is designed to, in the case of cooling preset by a cooling device, load the semiconductor module with a preset electrical load, detect the temperature of the semiconductor elements of the semiconductor module at least for the preset electrical load of the semiconductor module, compare the detected temperature with a reference temperature in a first comparison, wherein the reference temperature corresponds to the preset electrical load in the case of the preset cooling, and derive prediction data for the remaining normal availability of the semiconductor module until the end of the availability at least based on the first comparison.

[0016] With regard to such a control unit, according to a second aspect, it is particularly proposed that the control unit is designed to, under preset cooling by a cooling device, load the semiconductor module with a preset electrical load, obtain a thermal resistance between the semiconductor elements of the semiconductor module and the cooling device, compare the obtained thermal resistance with a reference thermal resistance in a second comparison, and determine predictive data for the remaining normal availability of the semiconductor module until the end of the availability at least based on the second comparison.

[0017] In particular, it is proposed with regard to such an energy converter that a control unit is designed according to the invention.

[0018] The invention is based on the idea that, according to the first aspect, almost direct or direct detection of the temperature of the semiconductor element, or according to the second aspect, determination of the thermal resistance, prediction data can be derived more accurately than before. In this case, specific properties of the semiconductor module or the semiconductor elements of the semiconductor module can be taken into account in order to detect the actual temperature of the semiconductor element. Thus, for example, temperature detection can be implemented in an IGBT as follows, namely by detecting the threshold voltage of the IGBT with the aid of a voltage sensor. The threshold voltage generally depends on the temperature of the semiconductor element or the temperature of the semiconductor chip of the IGBT. In addition, it can of course be proposed that the semiconductor element, for example, includes an integrated PN junction, which can be used as a temperature sensor. In this context, reference is also made to the European Power Electronics and Applications Conference (EPE 2016, ECCE Europe, Karlsruhe, Germany, September 2016) The publication by M et al. “Application issues of an online temperature estimation method in a high-power 4.5kV IGBT module based on the gate-emitter threshold voltage”.

[0019] The present invention also utilizes the following recognition, that is, in particular with respect to the first aspect, when the electrical load is preset and the cooling is preset by the cooling device, the increase in the detected temperature or the increase in the detected temperature deviation can be used for aging and thus for the remaining conventional availability of the semiconductor module. From this recognition, it is also possible to empirically derive a reference temperature that is considered for implementing the first comparison. This can be achieved, for example, by laboratory experiments, in particular using statistical methods and / or similar methods. Therefore, predictive data can be determined for the remaining conventional availability of the semiconductor module until the end of the availability based on the comparison. For this purpose, predictive data can be derived, for example, based on the difference between the detected temperature and the reference temperature. Therefore, the detected temperature is considered for deriving predictive data according to the first aspect.

[0020] For the second aspect, the following recognition is used, that is, the thermal resistance between the semiconductor element and the cooling device can be taken into account in order to obtain prediction data. Here, the following recognition is used, that the thermal resistance can also depend on the aging of the semiconductor module, because the thermal resistance itself can increase with the extension of the aging of the semiconductor module. For this reason, the thermal resistance can be used to obtain prediction data within the scope of the second comparison. For this reason, a reference thermal resistance provided for the second comparison is determined. The reference thermal resistance can also be determined by laboratory experiments, especially using statistical methods and / or similar methods. Therefore, when the thermal resistance between the semiconductor element and the cooling device is obtained, the prediction data can also be obtained by the second comparison.

[0021] In order to be able to increase the accuracy or to better take into account specific applications of the semiconductor module, both aspects can of course therefore also be used in combination with one another.

[0022] In the scope of the present disclosure, semiconductor modules are particularly used for the mechanical construction of semiconductor switching elements, wherein the semiconductor element is thermally coupled to a cooling surface, and the cooling surface can be coupled to a cooling device on its side so as to be able to discharge the heat generated during the normal operation of the switching element, and the semiconductor element can be composed of, for example, a semiconductor chip or the like. For this purpose, the semiconductor element is usually fixedly connected to the cooling surface by means of a mechanical connection method and / or a mechanical connection mechanism, so that the transition thermal resistance that is as favorable as possible can be achieved. Therefore, the semiconductor module can have at least one semiconductor element. However, according to requirements, the semiconductor module can also have other semiconductor elements, and the other semiconductor elements can have separate cooling surfaces or at least a part is connected to a separate cooling surface together. The semiconductor module usually includes a housing, which provides a cooling surface. At the same time, the housing can be used to achieve, for example, sealing to the external atmosphere, so that the semiconductor element or multiple semiconductor elements can be protected from external mechanical and atmospheric influences.

[0023] The energy converter can include at least one single semiconductor module as a switching element. However, multiple semiconductor modules can also be provided as required in order to achieve the desired energy conversion function. In order to realize the energy converter, the energy converter usually also includes an electrical energy storage or at least electrically coupled to this type, for example one or more capacitors, one or more electrical coils and / or the like. Of course, a combined circuit can also be provided thereby. The energy conversion function of the energy converter is realized by means of a semiconductor module in cooperation with at least one energy storage.

[0024] At least one semiconductor module forming at least one switching element of the energy converter has at least one control interface to realize the desired switching function, at which a switching signal provided by a control unit can be loaded to realize the desired switching function of the semiconductor module. The switching signal can be a binary switching signal, which can occupy at least two state values ​​so as to provide the desired switching function of the semiconductor module. The switching signal can be formed, for example, by a pulse sequence for loading the control interface. This is mainly advantageous in semiconductor modules including thyristors and GTOs. In addition, a rectangular signal switching signal can be set in a transistor, wherein the corresponding switching state of the switching element or semiconductor module can correspond to one of the potentials of the rectangular signal. Such a signal is suitable for transistors, in particular for bipolar transistors, field effect transistors or the like.

[0025] In the context of the present disclosure, the switching element is generally designed as a semiconductor switching element, preferably a controllable electronic switching element, such as a controllable electronic semiconductor switch, for example a transistor operated in switching operation, a thyristor in a combined circuit, a gate turn-off thyristor (GTO), an insulated gate bipolar transistor (IGBT) preferably in combination with a reverse diode or the like. However, the switching element can also be formed essentially by a field effect transistor, in particular a metal oxide semiconductor field effect transistor (MOSFET).

[0026] For the purpose of energy conversion, at least one semiconductor module is usually operated in switching operation. For semiconductor switches using transistors, switching operation means that in the switched-on switching state, a very low resistance is provided between the interfaces of the transistor forming the switching path, so that a large current can be achieved at a small residual voltage. In contrast, in the switched-off switching state, the switching path of the transistor is high-resistance, that is, the switching path provides a high resistance, so that at a high voltage provided at the switching path, there is essentially no or only a very low, especially negligible, current. This is different from the linear operation in transistors, which is usually not used in such energy converters.

[0027] The control unit provides the function for generating the switching signal. Other functions, in particular functions related to the energy converter, such as monitoring functions, safety functions and / or the like can also be implemented by the control unit. For this purpose, the control unit can include hardware circuits and / or program-controlled computing units or the like. The control unit can of course be designed for separate components. However, the control unit can also be at least partially included in the drive device including the energy converter or in the upper-level controller of the energy converter.

[0028] The motor can be a DC motor or an AC motor. As an AC motor, the motor can be a single-phase or multi-phase AC motor. The motor can be, for example, a synchronous motor, an asynchronous motor or the like. When the motor is a synchronous motor, the synchronous motor can be designed, for example, as a permanent magnet motor. However, the synchronous motor can also be designed as a separately excited motor or the like. Of course, combinations of these can also be considered, in order to be able to realize, for example, specific drive functions that may influence the magnetic flux.

[0029] The clock frequency corresponds substantially to the frequency with which a switching signal for at least one semiconductor module is provided by the control unit. Provision can be made here for the pulses for controlling the individual switching elements to be synchronized with the clock frequency in order to provide switch-on and switch-off periods for the switching elements.

[0030] At least one semiconductor module is usually designed as a power semiconductor module, which is sometimes also referred to as a power module, so that the desired cooling is achieved by the cooling device during normal operation. Due to the electrical load of the semiconductor module during normal operation, heat is generated in the semiconductor module, which is discharged by means of the cooling device to avoid overheating of the semiconductor module. Heat also occurs in the semiconductor module during normal operation because current is conducted and thus through-losses occur. Heat is also generated because switching losses occur during the changeover between the switched-on switching state and the switched-off switching state.

[0031] For this purpose, the prediction data can be used to provide corresponding instructions for informing the user. The user can be informed by means of the instructions which estimated service life or remaining normal availability for the semiconductor module is still available. The instructions can also be used to plan maintenance so that the semiconductor module can be used as extensively as possible until the end of the availability and corresponding maintenance can be carried out in good time before a semiconductor module fails. As a result, the costs for maintenance and operation of semiconductor modules and devices (e.g., energy converters or the like) using semiconductor modules can be reduced.

[0032] Preferably, the prediction data are formed, for example, by electrical signals. The prediction data can, for example, include digital data. However, the prediction data can also basically include analog data. The prediction data can be determined or derived by a processing unit of the control unit. For this purpose, the processing unit can, for example, include an electric circuit, a program-controlled computing device, a combination of these or the like. The processing unit can be designed as a separate component of the control unit. However, the control unit can also be included in a superior control unit, which, for example, controls a device including a semiconductor module.

[0033] In order to obtain the prediction data, the comparison result is provided for the control unit and is particularly used for at least the first comparison and / or the second comparison of the processing unit. For this purpose, the contrast signal is used by the processing unit when implementing the corresponding comparison to obtain the prediction data. The prediction data can be obtained in addition to the use of statistical methods. For this purpose, the average value, variance and / or the like can be obtained. For this purpose, other reference data can also be used, for example, can be stored in a storage unit of the control unit, especially the processing unit. In addition, of course, the reference data can also be provided by an external storage device at least partially via a communication connection between the storage device and the control unit or the processing unit. Thus, there is a feasible solution, that is, to centrally provide reference data so that the reference data can be maintained or updated in a simple manner. In addition, the reference data can therefore also be provided for a plurality of different control units or processing units. The reference data can be determined, for example, using one or more reference semiconductor modules. This can be determined, for example, in laboratory studies. Different feasible solutions for obtaining the prediction data can of course also be combined with each other.

[0034] The description corresponding to the prediction data can be, for example, an electrical, optical, hydraulic, pneumatic or tactile signal. The description can also be a combination of one or more of the above signals. The description can be determined by the prediction data, by supplying the prediction data to a processing unit, such as a signaling device or the like, the signaling device is therefore determined according to the corresponding description, so that a display that can be understood by the user of the relevant information can be provided according to the corresponding description. The corresponding description can be provided for the remaining normal availability in particular as a predicted amount and / or predicted duration of the temperature change of the semiconductor element. For example, a reference thermal resistance can be determined at the beginning of the normal availability of the semiconductor module. If the resulting thermal resistance reaches a value that exceeds the reference thermal resistance, for example, by about 20%, this can lead to a direct upcoming end of availability. The prediction data are derived accordingly.

[0035] The processing unit or the signaling device can be included in the control unit. However, the control unit can also be designed as a separate processing unit or a separate signaling device, a signaling device that is in communication connection with the control unit. Of course, a combination of these can also be provided. The processing unit or the signaling device processes the prediction data so that the desired corresponding description or display of the information can be achieved. This can depend on the signaling device and in particular on which medium the signaling device uses for the description of the information. Thus, the signaling device can be designed, for example, for optical, acoustic and / or tactile output of the information, wherein the prediction data is processed in a suitable manner so that the desired output of the information can be achieved. It can be proposed here that, for example, when the signaling device provides different output possibilities, the output type of the information can be set by the user. For this purpose, the corresponding input mechanism can be designed so that it can be set by the user.

[0036] The control unit can be designed as a separate component which can include its own housing. However, the control unit is preferably a component of a superordinate controller of a device which uses semiconductor modules, for example energy converters or the like.

[0037] In order to obtain the prediction data, the semiconductor module is loaded with a preset electrical load under the condition of preset cooling by the cooling device. The corresponding preset operating state can be achieved by the preset electrical load, so that the corresponding power loss of the semiconductor module can be determined. The power loss can correspond to the thermal power, which can be discharged by the cooling device to ensure the normal operation of the semiconductor module. For this purpose, it can be provided that the preset electrical load includes a preset switching mode with a preset voltage load and / or current load. As a result, it is possible to achieve defined framework conditions for detecting the temperature or thermal resistance so that the respective corresponding comparison can be carried out normally.

[0038] Routine availability includes in particular the routine use of semiconductor modules for implementing electronic control functions, for example as switching elements in energy converters, in energy distribution devices and / or the like. Routine availability here refers to the fact that the semiconductor module is operated in a routine operating range (safe operating range, SOA) during routine operation of the device comprising the semiconductor module. Usually, this specification refers to the manufacturer's specification. Preferably, the end of the availability for the routine availability of the semiconductor module is characterized accordingly as follows, i.e. the desired or required function of the semiconductor module can no longer be reliably provided under operating conditions according to the SOA, for example because the semiconductor module is no longer available due to a fault in the semiconductor element or similar reasons.

[0039] It is preferably proposed that, once the preset electrical load is obtained in the case of the preset cooling, the electrical load and the cooling of the semiconductor module are detected during normal operation and a comparison is performed. It is thus possible to also obtain prediction data during normal operation of the semiconductor module. In this case, a further development is based on the idea that the preset load and the preset cooling can be repeatedly implemented at a specific time point in normal operation, which time point can also be set. In this case, in order to obtain the prediction data, separate test signals do not need to be set for normal load and normal cooling. In this development, normal operation can also continue without interruption.

[0040] According to one refinement, it is proposed that cooling is preset by means of a cooling device and an electrical load outside of normal operation. This makes it possible to obtain prediction data at a preset time. This can be done, for example, before the implementation of normal operation or also during interruptions or breaks in operation. This design is particularly suitable when the preset electrical load and / or the preset electrical cooling is not or only rarely achieved during normal operation of the semiconductor module.

[0041] It is also proposed to store the temperature detected and / or the resulting thermal resistance for a preset load under a preset cooling condition. It is thus possible to record the aging of the semiconductor module and at the same time to more accurately derive the reference temperature or the reference thermal resistance by means of supplementary parameters, so that the derivation of the prediction data can be further improved. In addition, it is possible to insert a cooling device and strengthen the cooling function, so that the temperature increase of the semiconductor element can be reduced due to the aging effect. This can expand the conventional application of the semiconductor module. In this case, it is preferred to adapt the reference temperature and / or the reference thermal resistance accordingly.

[0042] Preferably, the forecast data are derived before the end of the availability of the normal availability of the semiconductor module is reached. The forecasted still available availability of the semiconductor module can thus be displayed by means of the forecast data with the aid of corresponding instructions. Preferably, the user can thus be continuously informed of the remaining normal availability so that specific application scenarios requiring reliable functioning of the semiconductor module can be planned accordingly if necessary. The forecast data thus derived can be used not only for the end of the availability.

[0043] It is also proposed that the end of the availability is displayed when the difference between the detected temperature and the reference temperature and / or the difference between the thermal resistance obtained and the reference thermal resistance is greater than a preset reference value. It can be achieved that possible dangerous failures of the semiconductor module can be eliminated in advance by maintenance. For example, the semiconductor module can be replaced for this purpose. This can be an advantage, especially in safety-related uses of semiconductor modules. The reference value can be determined empirically, for example, by laboratory experiments or the like. In addition, the reference value can also be determined taking into account statistical evaluation methods.

[0044] According to an improved solution, a load signal for setting the maximum load of the semiconductor module is outputted according to the difference between the detected temperature and the reference temperature and / or the difference between the obtained thermal resistance and the reference thermal resistance. Thus, the load reduction can be achieved, for example, by the control unit, so that the availability of the device including the semiconductor module can be expanded. Therefore, the availability end can be delayed. In addition, it can be achieved that the fault state can be maintained until maintenance can be carried out, such as to replace the semiconductor module. Thus, the reliability can be improved together.

[0045] As a supplement to the semiconductor module in the energy converter for electrically coupling the motor to the intermediate DC circuit, it can be proposed that the motor is controlled according to vector control and the current that specifically forms the field is set to a preset electrical load for the motor. It can be achieved that a large thermal load of the semiconductor element can be reached in a short time. Therefore, the detected temperature and / or the resulting thermal resistance can be used to derive prediction data, as described above. In this case, the prediction data can therefore be derived in an existing device or application without additional intervention in this regard. It is particularly advantageous that, due to the current that forms the field, the motor does not need to generate a torque, so that no undesirable influence is generated by the motor.

[0046] Preferably, the field-forming current is set outside the normal operation of the electric machine. This allows the condition that the predetermined electrical load and the predetermined cooling can be set almost freely, since the operation of the electric machine does not need to be taken into account. The application of the method according to the invention can be improved in this way. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Further features, advantages and effects are obtained from the following embodiments according to the drawings. The same reference numerals in the drawings represent the same features and functions. The drawings show:

[0048] Figure 1 A circuit diagram of a drive device having an asynchronous motor connected to an inverter is shown;

[0049] Figure 2 A schematic cross-sectional view of an IGBT module arranged on a heat sink is shown in a schematic cross section; and

[0050] Figure 3 Shows the Figure 2 A diagram showing a preset electrical load of the IGBT module and the corresponding temperature; and

[0051] Figure 4 A flow chart showing the process of the method according to the present invention is shown. DETAILED DESCRIPTION

[0052] Figure 1The circuit diagram of a drive device 10 is shown with an inverter 14 as an energy converter, which comprises three connecting contacts 46 for connecting a three-phase asynchronous machine 12. The asynchronous machine 12 comprises phases U, V, W. The inverter 14 further comprises connecting contacts 48, via which the inverter is connected to an intermediate DC circuit 16 having an intermediate circuit capacitor 18. The connecting contacts 48 form the intermediate circuit connection.

[0053] The inverter 14 has IGBT modules 24 or switching elements as semiconductor modules, which are switched in pairs in a series circuit in a known manner, the central terminals 50 of which are connected to the corresponding connecting contacts 46 .

[0054] The inverter 14 further comprises a control unit 22 which provides switching signals to an IGBT module 24 , so that the IGBT module is operated in a switching mode. As a result, the asynchronous machine 12 can be coupled to the intermediate DC circuit 16 in a predeterminable manner.

[0055] The control unit 22 is further connected to a display unit 30 , and the operating parameters and real-time operating data of the drive device 10 , in particular the inverter 14 , can be displayed via the display unit.

[0056] Figure 2 The schematic mechanical structure of the IGBT module 24 is shown as follows. Figure 1 As used in the inverter 14. Figure 2 A cross-sectional view is shown. It can be seen that the IGBT module 24 has a housing 52 which includes a mounting plate 26. The mounting plate 26 is arranged on a connection face 54 connected to a heat sink 20 which provides heat dissipation. The heat sink 20 provides the intended cooling.

[0057] In order to achieve the best possible heat dissipation for the IGBT module 24, the mounting plate 26 and the connection surface 54 are designed to be matched to each other. This achieves a particularly favorable or low transition thermal resistance. Therefore, the mounting plate 26 provides a cooling surface.

[0058] The semiconductor element 28 is fixed to the mounting plate 26 on the inner side of the housing above the layer structure (not shown). The layer structure serves as a thermal and mechanical connection between the semiconductor element 28 and the mounting plate 26.

[0059] The semiconductor element 28 provides the actual IGBT. A preset transition thermal resistance is provided with respect to the semiconductor element 28 and the mounting board 26 .

[0060] It can also be seen that the semiconductor element 28 has a contact surface 32 opposite the mounting plate 26, which is connected by means of known adhesive bonding to corresponding connecting contacts of the IGBT module 24, not shown. A mechanical connection and a corresponding electrical connection can be achieved in this way.

[0061] In order to now determine the remaining normal availability of the IGBT module 24, the cooling by the heat sink 20 and the electrical load of the IGBT module 24 are monitored. Figure 3 ) of the preset electrical load, the semiconductor module 24 is simultaneously connected according to the curve 36 ( Figure 3 ) detects the corresponding temperature of the semiconductor element 28. A reference temperature according to the curve 40 has already been determined for an electrical load predefined according to the curve 34.

[0062] In the comparison carried out by the control unit 22, the temperature detected according to the curve 36 is compared with the temperature obtained according to the curve 40. The prediction data ( Figure 4 ), the prediction data is processed by the display unit 30 so that the display unit 30 illustrates the remaining availability and the remaining usage period.

[0063] In the present case, the temperature is determined for the IGBT module 24 by measuring the threshold voltage of the IGBT module 24. This voltage is known from the temperature of the corresponding semiconductor chip, so that the actual temperature of the semiconductor element 28 can be determined from the determined value of this voltage. In the present case, the prediction data 44 ( Figure 4 ) thus depends on the difference between the detected temperature according to curve 36 and the reference temperature according to curve 40. The reference temperature can be derived using models, statistical evaluation methods and laboratory experiments.

[0064] Depend on Figure 3 It can also be seen how the detected temperature behaves itself when cooling by the cooling device, here the radiator 20, is disrupted because, for example, an air filter or the like is provided. This is shown by the curve 38. It can be seen that the rate of increase in this case is less than that represented by the curve 36. The control unit 22 can thus recognize whether the cooling by the radiator 20 is still sufficient or even impaired. The control unit 22 can therefore distinguish this situation from the prediction data 44 which can correspond to aging.

[0065] Figure 3A schematic diagram is shown in which the abscissa of time is arranged in seconds. The ordinate on the left is the temperature and is arranged in degrees Celsius, and the ordinate on the right is the power and is arranged in watts. Curve 34 shows the preset electrical load of the corresponding IGBT module 24. It can be seen that the preset electrical load currently includes two rectangular pulses, wherein the first rectangular pulse in time is a continuous rectangular pulse with a power of about 300 watts, which is relatively short in time. After a short power interruption, the second rectangular pulse follows, which lasts for about 160 seconds and provides a power of more than 500 W. The preset electrical load causes the temperature of the semiconductor element 28 of the IGBT module 24 according to curve 36.

[0066] For a corresponding reference temperature of such a load of the IGBT module 24, the curve 40 indicates that the IGBT module is in good condition. It can be seen that the distance between the curve 36 and the curve 40 increases with increasing aging. A preset maximum distance between the curve 36 and the curve 40 is reached or exceeded, which is determined as the end point of availability. The distance or the difference between the curve 36 and the curve 40 can therefore be used to determine or predict the remaining normal availability. For this purpose, the control unit 22 includes a processing unit, not described in further detail, which determines the remaining normal availability using statistical methods and provides a corresponding output as a signal of the display unit 30. The processing unit evaluates the provided signal and provides a corresponding information output to the user.

[0067] Figure 4 A schematic flow chart of the process of the method according to the invention is shown. The method starts in step 56. In a corresponding step, a preset electrical load is detected. After that, in a step, the temperature of the IGBT module is detected simultaneously. Then, the detected temperature is compared with a reference temperature 40 in a comparison step 42. Subsequently, in a subsequent step, prediction data are derived based on the comparison. The method ends in step 58.

[0068] The present invention can more reliably warn the plant operator of the drive device 10 that a power semiconductor failure may be imminent. Therefore, corresponding maintenance can be planned in time to avoid major damage and long failure time of the inverter 14. As a result, the failure of the IGBT module can be identified in time, and major further damage to the drive device 10, especially to the inverter 14, can be avoided to a large extent.

[0069] The current embodiments are only for explaining the present invention and should not limit the present invention.

Claims

1. A method for operating an energy converter connected to an electric machine, the energy converter electrically coupling the electric machine to an intermediate DC circuit (16), for the purpose of the electrical coupling, at least one semiconductor module thermally coupled to a cooling device and at least one energy storage device electrically coupled to the semiconductor module cooperate, and the semiconductor module is operated to electrically couple the intermediate DC circuit (16) to the electric machine in a predeterminable switching operation, wherein A remaining conventional availability of at least one of the semiconductor modules is determined by: - in normal operation, the semiconductor module is subjected to a predetermined electrical load with a predetermined cooling by the cooling device, wherein the predetermined electrical load comprises a predetermined switching pattern with a predetermined voltage load and / or current load, - detecting the temperature of the semiconductor element (28) of the semiconductor module at least for a predetermined electrical load of the semiconductor module, - in a first comparison, the detected temperature is compared with a reference temperature, wherein, in the case of the predefined cooling, the reference temperature is assigned to the predefined electrical load, and - based on at least the first comparison, predictive data for the remaining conventional availability of the semiconductor module up to the end of the availability are derived, In this case, the electrical load and the cooling of the semiconductor modules are detected during normal operation and a comparison is carried out as soon as a preset electrical load is obtained under preset cooling, wherein the electric machine is controlled according to vector control and a field-specific current is set for the electric machine to a preset electrical load.

2. The method according to claim 1, characterized in that A thermal resistance between the semiconductor element (28) and the cooling device is determined and the determined thermal resistance is compared with a reference thermal resistance in a second comparison, wherein the prediction data are additionally determined based on the second comparison.

3. The method according to claim 2, characterized in that The temperatures detected and / or the resulting thermal resistances for the predefined loads are stored when the cooling is predefined.

4. The method according to claim 3, characterized in that: The aging of the semiconductor module is recorded by the storage, so that the cooling function is enhanced due to aging effects.

5. The method according to claim 1, characterized in that The forecast data are derived before an availability end point for conventional availability of the semiconductor module is reached.

6. The method according to claim 1, characterized in that When the difference between the detected temperature and the reference temperature is greater than a preset reference value, the availability end point is displayed.

7. The method according to claim 1, characterized in that A load signal for setting a maximum load of the semiconductor module is outputted according to a difference between the detected temperature and the reference temperature.

8. The method according to claim 1, characterized in that The current which forms the field is provided outside normal operation of the electrical machine.

9. A method for operating an energy converter connected to an electric machine, the energy converter electrically coupling the electric machine to an intermediate DC circuit (16), for the purpose of the electrical coupling, at least one semiconductor module thermally coupled to a cooling device and at least one energy storage device electrically coupled to the semiconductor module cooperate, and the semiconductor module is operated to electrically couple the intermediate DC circuit (16) to the electric machine in a predeterminable switching operation, wherein: A remaining conventional availability of at least one of the semiconductor modules is determined by: - in normal operation, the semiconductor module is subjected to a predetermined electrical load with a predetermined cooling by the cooling device, wherein the predetermined electrical load comprises a predetermined switching pattern with a predetermined voltage load and / or current load, - determining a thermal resistance between the semiconductor element (28) of the semiconductor module and the cooling device, - comparing the thermal resistance obtained with a reference thermal resistance in a second comparison, and - at least as a function of the second comparison, predictive data for the remaining conventional availability of the semiconductor module up to the end of the availability are derived, In this case, the electrical load and the cooling of the semiconductor modules are detected during normal operation and a comparison is carried out as soon as a preset electrical load is obtained under preset cooling, wherein the electric machine is controlled according to vector control and a field-specific current is set for the electric machine to a preset electrical load.

10. The method according to claim 9, characterized in that The resulting thermal resistance is stored.

11. The method according to claim 10, characterized in that The aging of the semiconductor module is recorded by the storage, so that the cooling function is enhanced due to aging effects.

12. The method according to claim 9, characterized in that The forecast data are derived before an availability end point for conventional availability of the semiconductor module is reached.

13. The method according to claim 9, characterized in that When the difference between the obtained thermal resistance and the reference thermal resistance is greater than a preset reference value, the availability end point is displayed.

14. The method according to claim 9, characterized in that A load signal for setting a maximum load of the semiconductor module is outputted according to a difference between the obtained thermal resistance and the reference thermal resistance.

15. The method according to claim 9, characterized in that The current which forms the field is provided outside normal operation of the electrical machine.

16. A control unit (22) for controlling at least one semiconductor module, the semiconductor module being thermally coupled to a cooling device, wherein: The control unit (22) is designed to carry out the method according to any one of claims 1 to 15.

17. An energy converter for connecting to an electric machine, the energy converter comprising: - at least one semiconductor module, - at least one cooling device thermally coupled to at least one of said semiconductor modules, at least one energy store electrically coupled to at least one of the semiconductor modules, - connection contacts (46) for connecting the electric motor, - an intermediate circuit connection for connecting the energy converter to an intermediate DC circuit (16), and a control unit (22) electrically coupled to at least one of the semiconductor modules, the control unit (22) being used to control at least one of the semiconductor modules in a predeterminable switching mode in order to electrically couple the intermediate DC circuit (16) and the electric machine to one another, It is characterized in that The control unit (22) is a control unit (22) according to claim 16.

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