Method for operating an electric machine

Abstract

The present invention relates to a method for operating an electric machine (1), wherein a value (2) of a maximum first torque (4) that the electric machine (1) can provide in a future interval (3) is calculated by the method, and by limiting the torque provided in the interval (3) to said value (2), overheating due to power losses (6) of at least one of the at least one semiconductor (5) required for the transmission of electrical power is prevented, or a risk of overheating and a derating effect are predicted and prevented, or both. [Selected Figure] Figure 1

Description

[Technical field]

[0001] The invention relates to a method for operating an electric machine, which is used in particular in a motor vehicle, preferably for driving a motor vehicle. [Background technology]

[0002] Electric machines supplied with electrical energy from an inverter are often used in motor vehicles, e.g. as traction drives. Due to electrical losses in the inverter and due to electrical and mechanical losses in the electric machine, these components heat up during operation of the electric machine. In case of a sudden increase in temperature, the heated components need to be protected from thermal damage. This protection is achieved by reducing the power transmitted to the electric machine (derating) and by a corresponding reduction in the resulting power losses.

[0003] To reduce the effects of thermal derating on the vehicle's operating strategy, it would be desirable to predict the possible power reduction over time. However, the power loss depends on many factors and parameters (engine parameters, saturation characteristics, semiconductor characteristics, temperature, torque, rotational speed, intermediate circuit voltage, regulation strategy, aging, etc.). Therefore, it is difficult or impossible to calculate the thermally possible maximum power as a function of torque and rotational speed, which cannot be measured analytically.

[0004] It is therefore an object of the present invention to at least partially solve the problems existing in the prior art, in particular by providing a method which makes it possible to predict in advance any power reductions which may be required in due course. Summary of the Invention [Means for solving the problem]

[0005] These objects are achieved by a method according to the features of claim 1. Further advantageous embodiments of the method and of the invention are specified in the further claims. It should be noted that the features specified individually in the claims can be combined with one another in any technically feasible manner to define further embodiments of the invention. The features specified in the claims are also described more precisely and in more detail in the present specification, where further preferred embodiments of the invention are presented.

[0006] Here, a method of operating an electric machine contributes, in which a value of a maximum first torque that said electric machine can provide in a future (i.e. future) interval is calculated. Overheating of at least one of said at least one semiconductor necessary for the transmission of electric power due to power losses (or a risk of overheating and / or a derating effect is predicted and prevented) is prevented by limiting the torque provided in said interval to said value, said power losses occurring during the operation of the electric machine to generate said torque. The method comprises the steps of: a) determining a number of electrical parameters of the operation of the electric machine at a current time (i.e., now) (e.g., rotational speed, voltage of the electric machine); b) calculating a maximum second torque of the electric machine that can be generated with these electrical parameters; c) calculating the possible power loss in the at least one semiconductor when a maximum possible second torque is applied; d) calculating a first temperature determinable from the power loss present during the interval, the first temperature being determined of the semiconductor junction layer of the at least one semiconductor if the determined first temperature is higher than the maximum allowed second temperature; e) repeatedly carrying out steps b) to d) so that the value of the maximum second torque that can be generated by step b) becomes smaller and smaller, this repetition being carried out until the first temperature calculated by step d) corresponds at most to the maximum allowable second temperature of the semiconductor junction layer; and then f) operating the electric machine during said interval with a torque having at most the value determined by the method, or, if the electric machine operates with a higher torque, shortening this interval and operating the electric machine with said higher torque (only) during the shortened interval. At least

[0007] In particular, knowledge of the properties of the semiconductors used can be used to calculate the temperature at a particular operating point (consisting for example of torque, rotational speed and voltage) of the electric machine. Thus, if necessary, a control loop is suggested in which the torque is solely calculated by the control loop in one or several iteration steps. This torque is the maximum that can be used to operate the electric machine (so that the components do not overheat unacceptably) in an interval (after the execution of the method) (just at start-up).

[0008] The control loop in particular follows steps a) to e) and at least steps c) to e). Parameters (e.g. rotational speed and voltage) can be used as input variables for the control loop. A second torque possible with these parameters can be determined, for example in a control unit, and used as input variable for the control loop.

[0009] The second torque determined or calculated (if necessary subsequently) during steps b) to e) is not in particular physically generated by the electric machine before reaching step f), but is merely used to calculate the value determined in step f).As an alternative to this, it is possible that the second torque reduced by the differential torque is physically generated by the electric machine (and then further reduced by subsequent iterative steps).

[0010] Thus, in particular steps a) to f) are performed one after the other in the order given, and, if desired, at least partly in parallel in time, where steps c) to e) are performed repeatedly in the order given, in particular once steps a) and b) have been performed, and then (if desired, as a conclusion) step f) is performed after steps a) to e) of the method.

[0011] In particular, the method itself is executed continuously during operation of the electric machine or during operation of the vehicle, the method being executed in particular only when overheating of the electric machine or of a component can be expected.

[0012] The electrical parameters in step a) include in particular (at least or exclusively) the current rotational speed of the electric machine and the current voltage available for operating the electric machine.

[0013] To carry out step c), the control loop includes at least one calculation model. The parameters (e.g. rotational speed and voltage) and the calculated second torque are used as inputs. The power losses for these inputs are generated as results by the calculation model.

[0014] The computational model takes into account, inter alia, the characteristics of the electric machine and each of its components (i.e. what is needed to supply and transmit electrical energy to the electric machine, i.e. engine parameters, saturation characteristics, semiconductor characteristics, temperature, aging, etc.) and the control strategies for the electric machine and each of its components.

[0015] In step d) the cooling capacity available for cooling the at least one semiconductor may be taken into account.

[0016] The control loop includes, inter alia, a temperature model for determining the first temperature, for which, inter alia, the power loss calculated in step c) as well as the coolant mass flow rate and the coolant temperature can be used as inputs.

[0017] In step e), in particular, a difference between the calculated first temperature and a maximum permissible second temperature is formed, with reference to which a differential torque deltaT is determined by the controller, which differential torque deltaT is determined in step b) in a subsequent iteration by subtracting the (calculated) maximum second torque T of the previous iteration. n (n=1, 2, 3, ...) and the maximum second torque T n+1 can be calculated.

[0018] Preferably, the controller is an I controller (integral controller) or a PI controller (proportional integral controller).

[0019] In a preferred embodiment, the electric machine is operated with a polyphase (preferably three-phase) alternating current of an inverter with a (known) switching frequency. The electrical parameters determined in step a) may at least comprise, as a present voltage, the intermediate circuit voltage of the inverter. In step b1), which follows step b), at least the following further electrical parameters are determined: - Line current of each phase of polyphase AC current - Line voltage of each phase of polyphase AC current Power factor or cosφ or both

[0020] In electrical engineering, the power factor (also known as the effective power factor) is, among other things, the ratio of the amplitude of the real power P to the apparent power S. cosφ is the phase shift angle between the fundamental oscillations of the current and the voltage. In particular, cosφ can provide a more accurate value than the power factor, although this may require more computational power.

[0021] A control loop, in particular a control loop suitable for carrying out the method according to the preferred embodiment, comprises at least one calculation model with a first part model and a second part model for carrying out step c), where the first part model uses as inputs the electrical parameters (e.g. rotational speed and intermediate circuit voltage) and the calculated maximum second torque.

[0022] The first partial model takes into account, inter alia, the characteristics of the electric machine and each of its components (i.e. what is needed to supply and transfer electrical energy to the electric machine, i.e. engine parameters, saturation characteristics, semiconductor characteristics, temperature, aging, etc.) and the control strategies for the electric machine and each of its components.

[0023] As a result of the first partial model, the line current of each phase of the AC current, the line voltage of each phase of the AC current, and the power factor or cos φ are obtained.

[0024] The second partial model uses as inputs, in particular the results of the first partial model and the parameters of the intermediate circuit voltage and the switching frequency, on the basis of which the power losses calculated according to step c) are determined in the second partial model.

[0025] In step c), in particular the characteristics (engine parameters, saturation characteristics, semiconductor characteristics, temperature, aging, etc.) and the control strategies for the electric machine and each component (necessary to supply and transmit electrical energy to the electric machine) are taken into account.

[0026] The electric traction drives used today are, in particular, permanent magnet synchronous machines with reluctance. This means that the desired torque cannot be uniquely assigned to the currents, and that the phase relationship of the currents also influences the torque. The freedom in choosing the current amplitude and the phase relationship of the currents can be used in various ways, for example to increase the efficiency of the electric machine or to maintain a desired control reserve.

[0027] The choice of current amplitude and current phase relationship has a direct impact especially on losses in the converter (inverter) and in the electric machine and should therefore also be taken into account when determining / estimating temperatures.

[0028] Here, the characteristics of the engine parameters, the saturation characteristics, the semiconductor characteristics, the temperature, the aging should be taken into account, especially in this order. The engine parameters of the electric machine, including saturation, are essential, for example, when determining the current, the voltage, cosφ, the desired torque (depending on the control strategy described above). The semiconductor characteristics are necessary for the temperature model. In the simplest case, the semiconductor characteristics can be assumed to be linearly dependent on the phase current and the DC voltage. The semiconductor characteristics can be stored with any desired accuracy and complexity, for example, as an analytical function of the current and the voltage, but no longer a linearly dependent function of the current and the voltage, taking into account the semiconductor temperature, taking into account the aging, taking into account the variations between the individual components, or as a combination of several of the above.

[0029] Furthermore, the modulation scheme as well as the control strategy is important for electrical losses, for example with respect to the difference between continuous and discontinuous schemes. The type of modulation may be considered in the thermal model and may also influence the selection of the current amplitude and current phase relationship.

[0030] The interval may in particular have a length of at most 10 seconds, preferably at most 7 seconds.

[0031] The interval may in particular have a length of at least 0.5 seconds, preferably at least 2 seconds.

[0032] In particular, the length of the interval is determined depending on the operating point of the electric machine or depending on the operating mode of the vehicle, etc. In particular, the length of the interval may vary during operation of the electric machine, and the interval may be shortened (during or immediately after the method) depending on the actually applied torque, in particular if the actually applied torque exceeds the value determined by the method.

[0033] The electric machine is in particular a first drive unit of the motor vehicle. If, in this interval, the torque required to drive the motor vehicle exceeds the value of the torque determined by the method according to step f), at least one second drive unit of the motor vehicle (e.g. a combustion engine or the like) can be switched on to increase the torque supplied.

[0034] The interval can also be determined in particular taking into account the switchable use of further drive units.

[0035] Furthermore, an electric drive arrangement is proposed, which comprises at least an electric machine, an energy source (e.g. a battery or an inverter arranged between the electric machine and the battery) and at least one semiconductor, capable of supplying electric energy of an energy source via said semiconductor to operate the electric machine. The electric drive arrangement may comprise a control unit, which is suitably designed or configured to perform the aforementioned method. The control unit is thus capable of performing the method or the control unit is capable of performing the method during operation of the motor vehicle.

[0036] In particular, the control unit may utilize a control loop or the control loop may be integrated into the control unit.

[0037] The torque is simply calculated by the control loop in one or more iterative steps, as required, so that this torque is the maximum available for operating the electric machine (so that components do not overheat unacceptably) in and during the interval (after execution of the method) (suitably shortened, right at start-up).

[0038] The control loop in particular follows steps a) to e) (in particular also step b1)) of the method and follows at least steps c) to e). Parameters (e.g. rotational speed and voltage, if necessary also switching frequency, coolant mass flow rate, coolant temperature) can be used as input variables for the control loop. A second torque possible with these parameters can be determined e.g. in a control unit and used as input variable for the control loop.

[0039] It is further proposed a vehicle as follows: The vehicle comprises at least an electric drive mechanism and can be driven (at least) by an electric machine of the electric drive mechanism.

[0040] The statements made about the method apply equally to the drive mechanism and to the vehicle and vice versa.

[0041] The method may also be carried out by a computer or by a processor in a (vehicle) control unit.

[0042] Therefore, a system for processing data is further proposed, comprising a processor adapted and configured to carry out the method or to carry out part of the steps of the proposed method.

[0043] A computer-readable storage medium can be provided having instructions which, when executed by a computer / processor, cause the computer / processor to perform the method or to perform at least some of the steps of the proposed method.

[0044] Descriptions of the method may be transferred to the computer-implemented method and vice versa.

[0045] For the avoidance of doubt, ordinal numbers used herein (such as "first," "second," "third," etc.) are primarily intended to distinguish between several similar objects, values, or steps; i.e., these ordinal numbers do not necessarily define any dependency or ordering of these objects, values, or steps relative to one another. If a dependency or ordering is necessary, this will be set forth herein or will be apparent to those skilled in the art from a review of the embodiments described herein.

[0046] The present invention and technical background will be described in more detail below with reference to the drawings. It should be noted that the present invention is not intended to be limited by the exemplary embodiments shown in the drawings. In particular, unless otherwise specified, it is possible to extract partial features of the technical contents described in the drawings and combine them with other components and knowledge from this specification. [Brief description of the drawings]

[0047] [Figure 1] FIG. 2 shows a diagram of a first embodiment of a control loop. [Diagram 2] FIG. 2 shows a diagram of a second embodiment of a control loop. [Diagram 3] 1 shows a first illustration of the effect of the method. [Figure 4] A second illustration of the effectiveness of the method is shown. [Diagram 5] A third diagram of the effect of the method is shown. [Figure 6] Indicates a car. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] Fig. 1 shows a diagram of a first embodiment of a control loop 29. In step a) the respective electrical parameters 7 of the operation of the electric machine 1 at the current time (i.e. now) are determined or read (in this case the rotation speed 12 and the voltage 13). In step b) the maximum second torque 8 of the electric machine 1 that can be generated with these electrical parameters 7 is calculated, this maximum second torque being first used as an input value. In step c) the possible power loss 6 in the at least one semiconductor 5 when the maximum possible second torque is applied is calculated. This calculation is carried out in a calculation model 30, which uses as input values ​​the respective electrical parameters 7 (i.e. the rotation speed 12 and the voltage 13) and the calculated second torque 8. As a result, the calculation model 30 generates the power loss 6 present as these input values.

[0049] In step d), the determined first temperature 9 of the semiconductor junction layer 10 of the at least one semiconductor 5 is calculated, while the first temperature 9 is determined from the power loss 6 present in the interval 3. In step d), the cooling capacity 14 available for cooling the at least one semiconductor 5 can be taken into account.

[0050] The control loop 29 includes a temperature model 33 for determining the first temperature 9. As inputs for the temperature model 33 the power loss 6 calculated in step c), the coolant mass flow rate and the coolant temperature (here summarised as cooling capacity 14) are used.

[0051] According to step e), steps b) to d) are repeatedly performed so that the value 2 of the maximum second torque 8 that can be generated according to step b) becomes smaller and smaller, and this repetition is performed until the first temperature 9 calculated according to step d) corresponds at most to the maximum allowable second temperature 11 of the semiconductor junction layer 10.

[0052] In step e), a difference 15 between the calculated first temperature 9 and the maximum allowable second temperature 11 is obtained, on the basis of which a differential torque 17 is determined by a controller 16. In a subsequent iteration of steps b), the differential torque 17 is calculated based on the maximum (calculated) second torque 8T that can be generated from the previous iteration. n (n=1, 2, 3, ...) and subtract the maximum second torque 8T that can be generated for the following steps c) to d). n+1 can be calculated.

[0053] If the determined first temperature 9 calculated in step d) corresponds at most to the maximum permissible second temperature 11 of the semiconductor junction layer 10, step f) is executed, which operates the electric machine 1 with a torque having at most the value 2 determined by the method, during an interval 3 (the interval can be shortened accordingly, if necessary, if a higher level controller requires a higher torque).

[0054] The second torque 8 determined or calculated (continuously, if necessary) during steps b) to e) is not physically generated directly by the electric machine 1 before reaching step f), but is merely used to calculate the value 2 determined in step f).

[0055] Thus, steps a) to f) are performed one after the other in the order described and, if desired, at least partly in parallel in time, where steps c) to e) are performed repeatedly in the order described, in particular once steps a) and b) have been performed, and then, if desired, step f) is performed after steps a) to e) of the method as a final step.

[0056] Figure 2 shows a diagram of a second embodiment of a control loop 29. See the description of figure 1. This particularly preferred embodiment relates to an electric machine 1 operating with a polyphase (preferably three-phase) alternating current from an inverter 18 with a (known) switching frequency 19. The electrical parameters 7 determined in step a) comprise as present voltage 13 the intermediate circuit voltage of the inverter 18. In a step b1) following step b), at least the following further electrical parameters 7 are determined: - Polyphase AC line current for each phase 20 · Line voltage of each phase of polyphase AC current21 Power factor 22

[0057] A control loop 29 for carrying out the method according to the preferred embodiment comprises a calculation model 30 with a first part model 31 and a second part model 32 for carrying out step c). The first part model 31 uses as inputs the electrical parameters 7 (rotational speed 12 and intermediate circuit voltage as voltage 13) and the calculated second torque 8.

[0058] The first partial model 31 takes into account the characteristics of the electric machine 1 and each component (e.g. engine parameters, saturation characteristics, semiconductor characteristics, temperature, aging, etc.) (required to supply and transmit electrical energy to the electric machine 1, i.e. e.g. inverter 18, semiconductors 5, etc.) and a control strategy for the electric machine 1 and each component.

[0059] As a result of the first partial model 31, the line current 20 of each phase of the AC current, the line voltage 21 of each phase of the AC current, and the power factor 22 are obtained.

[0060] The second partial model 32 uses as input values ​​the results of the first partial model 31 and the parameters of the intermediate circuit voltage as voltage 13 and the switching frequency 19. On the basis of these input values ​​the second partial model 32 determines the power loss 6 calculated according to step c).

[0061] Figures 3-5 show several diagrams illustrating the effect of the method. In each of the upper diagrams, the torque 4, 8 is plotted on the vertical axis. The torque 4, 8 is shown normalized in each case. In each of the lower diagrams, the temperature is plotted on the vertical axis. The temperature is also shown normalized. In both diagrams of each figure, the time 28 is plotted on the horizontal axis.

[0062] FIG. 3 shows curves of torque 4, 8 and temperature when interval 3 has a length of 2 seconds. In the upper diagram, the maximum second torque 8 that can be generated with currently available electrical parameters 7 is shown (first curve 34). Furthermore, second curve 35 shows the torque calculated with (varying) values ​​2, which is available in interval 3 having a length of 2 seconds without overheating semiconductor 5. Third curve 36 shows the actually applied torque, following second curve 35 with a time interval corresponding to the interval (length of 2 seconds). In the lower diagram, fourth curve 37 shows the (current) temperature of semiconductor 5 or semiconductor junction layer 10 resulting from the applied torque (according to third curve 36). Fifth curve 38 shows the temperature of semiconductor junction layer 10 that arises when torque according to second curve 35 is applied and that must be maintained taking into account the length of the interval of 2 seconds. When the current temperature according to the fourth curve 37 reaches a certain third temperature 39, derating starts from a first point in time 40, which necessarily reduces the maximum power that can be supplied to the electric machine and thus the power losses (see first curve 34). The effect of derating is that a parameter or current or torque is limited, so that the maximum second torque 8 that can be generated is continuously reduced from the first point in time 40 onwards (first curve 34).

[0063] The third curve 36 corresponds at a certain point in time to at most the first curve 34. The method establishes a value 2 of the maximum deliverable first torque 4, through which overheating (and thus excessive derating) is avoided. In this way, it is ensured that the calculated first temperature 9 remains below the maximum permissible second temperature 11 of the semiconductor junction layer 10.

[0064] FIG. 4 shows the curves of torque 4, 8 and temperature when the interval 3 has a length of 2 seconds. In the upper diagram, the maximum second torque 8 that can be generated with the currently available electrical parameters 7 is shown (first curve 34). Furthermore, the second curve 35 shows the torque calculated with the (varying) values ​​2, which is available in the interval 3 having a length of 2 seconds without overheating the semiconductor 5 (and without the sudden onset of derating). The third curve 36 shows the actually applied torque, which has now been increased up to the maximum second torque 8 that can be generated. In the lower diagram, the fourth curve 37 shows the (current) temperature of the semiconductor 5 or of the semiconductor junction layer 10 resulting from the applied torque (according to the third curve 36). The fifth curve 38 shows the temperature of the semiconductor junction layer 10 that arises when the torque according to the second curve 35 is applied and that must be maintained taking into account the interval having a length of 2 seconds. When the current temperature according to the fourth curve 37 reaches a certain third temperature 39, derating starts from a first point in time 40, which necessarily reduces the maximum power that can be supplied to the electric machine and thus the power losses (see first curve 34). The effect of derating is that the electrical parameter 7 or current or torque is limited, so that the maximum second torque 8 that can be generated is continuously reduced from the first point in time 40 (first curve 34). As a result of the rapid increase in temperature shown in the fourth curve 37, it can be seen that the first point in time 40 (start of derating) occurs significantly earlier than in the case of the ones shown in figures 3 and 5.

[0065] The third curve 36 corresponds at a certain point in time to at most the first curve 34. The method establishes a value 2 of the maximum first torque 4 that can be provided, through which overheating (or the temperature that would occur when the current torque is applied according to the third curve 36) is avoided. In this way it is ensured that the calculated first temperature 9 remains below the maximum permissible second temperature 11 of the semiconductor junction layer 10.

[0066] FIG. 5 shows the curves of torque 4, 8 and temperature when the interval 3 has a length of 2 seconds. In the upper diagram, the maximum second torque 8 that can be generated with the currently available electrical parameters 7 is shown (first curve 34). Furthermore, the second curve 35 shows the torque calculated with the (varying) values ​​2, which is available in the interval 3 having a length of 2 seconds without overheating the semiconductor 5. The third curve 36 shows the actually applied torque, which here follows directly on from the second curve 35. In the lower diagram, the fourth curve 37 shows the (current) temperature of the semiconductor 5 or of the semiconductor junction layer 10 resulting from the applied torque (according to the third curve 36). The fifth curve 38 shows the temperature of the semiconductor junction layer 10 that must be maintained taking into account the interval of 2 seconds length that occurs when the torque according to the second curve 35 is applied. When the current temperature according to the fourth curve 37 reaches a certain third temperature 39, derating starts from a first time point 40, which necessarily reduces the maximum power that can be supplied to the electric machine and thus the power losses. The effect of derating is that the electrical parameter 7 or current or torque is limited, so that the maximum second torque 8 that can be generated is continuously reduced from the first time point 40 (first curve 34). It can be seen that here the derating starts later in time than in the case shown in FIG. 3.

[0067] The third curve 36 corresponds at a certain point in time to at most the first curve 34. The method establishes a value 2 of the maximum first torque 4 that can be provided, through which overheating (or the temperature that would occur when the current torque is applied according to the third curve 36) is avoided. In this way it is ensured that the calculated first temperature 9 remains below the maximum permissible second temperature 11 of the semiconductor junction layer 10.

[0068] Fig. 6 shows a motor vehicle 23. The motor vehicle 23 comprises an electric drive 25, which comprises the electric machine 1, an energy source 26 (e.g. a battery), an inverter 18 arranged between the electric machine 1 and the battery, and a semiconductor 5. The electric energy of the energy source 26, which is necessary to operate the electric machine 1, can be supplied via the semiconductor 5. The electric drive 25 comprises a control unit 27, which is suitably designed or configured to carry out the method described above. The motor vehicle 23 further comprises a further drive unit 24 (e.g. a combustion engine or similar), which can be switched on to increase or replace the torque provided by the electric machine 1. [Explanation of symbols]

[0069] 1 machine 2 Values 3 Interval [sec] 4 First torque [Newton meters] 5. Semiconductors 6 Power loss [Watts] 7 Parameters 8 Secondary torque [Newton meters] 9 First Temperature [Kelvin] 10 Semiconductor junction layer 11 Second Temperature [Kelvin] 12 Rotational speed [rpm] 13 Voltage [Volts] 14 Cooling capacity [Watts] 15 Difference [Kelvin] 16 Controller 17 Torque difference [Newton meters] 18 Inverter 19 Switching frequency [Hertz] 20 Line current [amperes] 21 Line voltage [volts] 22 Power factor 23. Automobiles 24 Drive unit 25 Drive mechanism 26 Energy Sources 27 Control Unit 28 hours 29 Control Loop 30 Computational Model 31 First Part Model 32 Second Part Model 33 Temperature Model 34 1st curve 35 Second curve 36 Third curve 37 4th curve 38 5th curve 39 Third temperature 40 First Time

Claims

1. A method of operating an electric machine (1), comprising the steps of: a value (2) of a maximum first torque (4) that the electric machine (1) can provide in a future interval (3) is calculated by the method; The method further comprising: a) determining a number of electrical parameters (7) of the operation of said electric machine (1) at a current time; b) calculating a maximum second torque (8) of said electric machine (1) that can be generated with these electrical parameters (7); c) calculating the possible power loss (6) in at least one semiconductor (5) when said maximum possible second torque (8) is applied; d) calculating a first temperature (9) determinable from the power loss (6) present during the interval (3), said determined first temperature (9) of a semiconductor junction layer (10) of said at least one semiconductor (5); e) repeatedly carrying out steps b) to d) so that the value (2) of the maximum second torque (8) that can be generated by step b) becomes smaller and smaller, this repetition being carried out until the first temperature (9) calculated by step d) corresponds at most to the maximum allowable second temperature (11) of the semiconductor junction layer (10); and then f) operating the electric machine (1) during said interval (3) with said calculated maximum first torque (4), the value (2) of said maximum first torque (4) being at most the value (2) of said maximum second torque (8) determined by said method between steps b) and e); or shortening the interval (3) when the electric machine (1) operates at a torque higher than the calculated maximum first torque (4), and operating the electric machine (1) at a torque higher than the maximum first torque (4) during the shortened interval (3); At least In step e), a difference (15) between the calculated first temperature (9) and the maximum permissible second temperature (11) is formed, A differential torque (17) is determined by a controller (16) with reference to said difference (15), The differential torque is subtracted in step b) of the subsequent iteration from the maximum second torque (8) of the previous iteration to calculate the maximum second torque (8) of the immediately subsequent steps c) to d). A method comprising:

2. 2. The method of claim 1 , The electrical parameters (7) in step a) are the current rotational speed (12) of the electric machine (1); the current voltage (13) available to operate said electric machine (1); Includes A method comprising:

3. The method according to any one of claims 1 and 2, In step d) the cooling capacity (14) available for cooling said at least one semiconductor (5) is taken into account. A method comprising:

4. The method according to any one of claims 1 to 3, The electric machine (1) is operated with a polyphase alternating current from an inverter (18) having a switching frequency (19), The electrical parameters (7) determined in step a) include at least the intermediate circuit voltage of the inverter (18) as a present voltage (13), Step b) is followed by a step b1) in which at least the following further electrical parameters (7) are determined, said further electrical parameters (7) being used in calculating said power losses (6) according to step c): - Line current of each phase of the polyphase AC current (20) - Line voltage of each phase of the multi-phase AC current (21) Power factor (22) A method comprising:

5. The method according to claim 1, further comprising: The interval (3) has a length of at most 10 seconds. A method comprising:

6. The method according to claim 1, further comprising: The interval (3) has a length of at least 0.5 seconds. A method comprising:

7. The method according to claim 1, further comprising: said electric machine (1) being a first drive unit of a motor vehicle (23); If, during said interval (3), the torque required to drive said vehicle (23) exceeds said value (2) of said torque determined by said method according to step f), At least one second drive unit (24) of the vehicle (23) is switched on to increase the torque provided. A method comprising:

8. An electric drive mechanism (25), An electric machine (1); An energy source (26); at least one semiconductor (5) capable of supplying electrical energy from an energy source (26) via said semiconductor (5) to operate said electric machine (1); At least The electric drive mechanism (25) comprises a control unit (27) configured to carry out the method according to any one of claims 1 to 7. An electric drive mechanism (25).

9. A motor vehicle (23), At least one electric drive mechanism (25) according to claim 8, The vehicle (23) can be driven by the electric machine (1) of the drive mechanism (25). A motor vehicle (23).

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