DE102017203656A1 - Method and device for controlling an electric drive and electric drive - Google Patents

Abstract

The invention relates to a method for controlling an electric drive (2), which comprises an electrical machine (22) and an inverter (21), comprising the steps of: determining (S1) temperature information relating to the electrical machine (22) and the inverter ( 21); and setting (S2) an operating point of the electric machine (22) and a switching frequency (f _PWM ) of the inverter (21) using the determined temperature information and taking into account a torque command (M _target ) as well as predetermined thermal load information relating to the electric drive (2 ).

Description

The present invention relates to a method for controlling an electric drive, a device for controlling an electric drive and an electric drive.

State of the art

Electric drives include temperature sensitive components which can be damaged or destroyed by high thermal stress. Therefore, it is necessary to recognize at an early stage that certain components could enter a thermal boundary area in order to initiate appropriate countermeasures in good time. Possible here is a derating of the electric drive, d. H. a reduction in the maximum permissible torque or the maximum permissible currents of the electric drive.

This is from the publication DE 10 2014 220 208 A1 a corresponding control device for an electric machine, wherein the operating point of the electric machine is adjusted based on a torque command and based on detected temperatures of a stator and a rotor of the electric machine.

Disclosure of the invention

The invention provides a method for controlling an electric drive with the features of claim 1, a device for controlling an electric drive with the features of claim 8 and an electric drive with the features of claim 10 ready.

According to a first aspect, the invention accordingly relates to a method for controlling an electric drive, wherein the electric drive comprises an electric machine and an inverter. Temperature information relating to the electrical machine and to the inverter is determined. An operating point of the electric machine and a switching frequency of the inverter are set using the determined temperature information and taking into account a torque specification as well as predetermined thermal capacity information relating to the electric drive.

According to a second aspect, the invention accordingly relates to a device for controlling an electric drive, wherein the electric drive comprises an electric machine and an inverter. The device comprises a temperature determination device, which is designed to determine temperature information relating to the electrical machine and with respect to the inverter. Furthermore, the device comprises an adjusting device, which is designed to set an operating point of the electric machine and a switching frequency of the inverter using the determined temperature information and taking into account a torque specification and taking into account predetermined thermal capacity information with respect to the electric drive.

According to a third aspect, the invention therefore relates to an electric drive with an inverter, an electrical machine and a device for controlling the inverter and the electric machine.

Preferred embodiments are the subject of the respective subclaims.

Advantages of the invention

The invention enables a holistic view of both the electrical machine and the inverter. This makes it possible to optimize both the operating point and the switching frequency, ie to come as close as possible to certain specifications or target values. At the same time it is ensured that the maximum thermal load capacity of the electric drive, ie both the electrical machine and the inverter, is not exceeded. By both the operating point of the electric machine and the switching frequency of the inverter are available as degrees of freedom, there are more opportunities to perform a corresponding power regulation or derating the electric machine. For example, even if the electrical machine has already reached its thermal limits by adapting the operating point, derating can be further delayed since, due to variation of the Switching frequency of the inverter further heating of the electrical machine at the expense of heating of the inverter can be prevented. In this case, derating must only take place if the inverter or components of the inverter also hit the thermal load limit. The invention therefore makes it possible to optimally utilize the thermal capacities of the electric drive. In particular, the invention provides a thermal management method which better exploits the thermal capacities of the components in overload conditions. As a result, ultimately more continuous output can be achieved. Preferably, further information can be determined, such as how long the currently requested torque, ie the torque specification can still be met. In addition to a higher continuous power and improved recuperation is possible.

The invention is also advantageous in the context of electric drive design processes, as thermal management may allow for a smaller design of the machine, thereby reducing costs.

According to a preferred development of the method, the temperature information comprises a temperature of a rotor of the electrical machine and / or a temperature of a stator of the electrical machine and / or a temperature of diodes of the inverter and / or a temperature of transistors of the inverter. All temperature-critical components of both the electrical machine and the inverter are thus taken into account in determining the operating point of the electrical machine and the switching frequency of the inverter.

According to a preferred development of the method, the thermal load information comprises a maximum temperature of the rotor and / or a maximum temperature of the stator and / or a maximum temperature of the diodes of the inverter and / or a maximum temperature of the transistors of the inverter. Preferably, the operating point of the electrical machine and the switching frequency of the inverter are set such that the temperatures of the respective components do not exceed the maximum temperatures.

According to a preferred development of the method, setting the operating point of the electrical machine comprises calculating a d-axis component of a current vector of the electrical machine and a q-axis component of the current vector of the electrical machine. The calculated current vector is preferably adjusted by a subordinate field-oriented control.

According to a preferred embodiment of the method, the adjustment of the operating point of the electrical machine and the switching frequency of the inverter by optimizing a quality function, which depends on the operating point of the electric machine, the switching frequency of the inverter and the torque input.

According to a preferred development of the method, temperature profiles of components of the electric drive as a function of the operating point of the electrical machine and the switching frequency of the inverter are determined on the basis of a model taking into account the determined temperature information. Preferably, the optimization is further carried out under the secondary condition that the temperature profiles are within predetermined value ranges. The temperature profiles include in particular information regarding expected temperature changes, d. H. a predicted temperature development of components of the electric drive. The temperature profiles may extend over a time interval up to a given future time. According to the invention, this ensures that the temperatures of the components do not rise too high and thus do not overheat the components of the electric drive.

According to a preferred embodiment of the method, a weighting of a deviation of an actual torque of the electric machine from the torque input in the quality functional is adjustable. This makes it possible to switch between different operating modes of the electric drive. For example, in a sport mode, the weighting may be performed such that the actual torque is as close as possible to the torque command, ie that a term of the quality function, which includes the deviation of the actual torque from the torque command, is weighted as strongly as possible. As a result, the operating point and the switching frequency are set such that the actual torque is as close as possible to the torque specification. In particular, a derating of the electric drive is delayed as long as possible. Conversely, in an Eco mode, the deviation of the actual torque from the torque command can be weighted less, so that the derating is done earlier. The torque is thereby throttled earlier, whereby the power consumption of the electric drive decreases.

According to a preferred embodiment of the device, the temperature detecting device is adapted to measure a temperature of a rotor of the electric machine and / or a temperature of a stator of the electric machine and / or a temperature of diodes of the inverter and / or a temperature of transistors of the inverter. Alternatively, estimation methods for temperature determination can also be used.

list of figures

• 1 ein schematisches Blockschaltbild einer Vorrichtung zur Regelung eines elektrischen Antriebs gemäß einer Ausführungsform der Erfindung;
• 2 einen beispielhaften Verlauf von Temperaturen von Komponenten einer elektrischen Maschine;
• 3 einen beispielhaften Verlauf von Temperaturen von Komponenten eines Wechselrichters;
• 4 einen beispielhaften Verlauf einer Schaltfrequenz des Wechselrichters;
• 5 einen beispielhaften Verlauf von Strömen einer elektrischen Maschine;
• 6 einen beispielhaften Verlauf eines Drehmoments des elektrischen Antriebs;
• 7 einen beispielhaften Verlauf einer Leistung des elektrischen Antriebs;
• 8 ein schematisches Blockschaltbild eines elektrischen Antriebs gemäß einer Ausführungsform der Erfindung; und
• 9 ein Flussdiagramm eines Verfahrens zur Regelung eines elektrischen Antriebs.

Show it:

• 1 a schematic block diagram of an apparatus for controlling an electric drive according to an embodiment of the invention;
• 2 an exemplary course of temperatures of components of an electric machine;
• 3 an exemplary course of temperatures of components of an inverter;
• 4 an exemplary course of a switching frequency of the inverter;
• 5 an exemplary course of currents of an electrical machine;
• 6 an exemplary course of a torque of the electric drive;
• 7 an exemplary course of a power of the electric drive;
• 8th a schematic block diagram of an electric drive according to an embodiment of the invention; and
• 9 a flowchart of a method for controlling an electric drive.

In all figures, the same or functionally identical elements and devices are provided with the same reference numerals. The numbering of method steps is for the sake of clarity and generally should not imply a particular chronological order. In particular, several method steps can be carried out simultaneously. Various embodiments can be combined as desired, if appropriate.

Description of the embodiments

1 shows a schematic block diagram of a device 1 for controlling an electric drive 2 according to an embodiment of the invention. The electric drive to be controlled 2 includes an inverter 21 , which is coupled to a DC voltage source and converts the provided DC voltage into AC voltage and an electrical machine 22 of the electric drive 2 provides. The electric drive 2 may be part of a drive for a vehicle, for example.

The device 1 further comprises a temperature detecting means 11 , which is adapted to temperature information relating to the electrical machine 22 and the inverter 21 to investigate. For example, the temperature detecting device 11 comprise at least one temperature sensor, which is adapted to a temperature of the inverter 21 and / or the electric machine 22 to eat. In particular, the temperature determination device 11 be adapted to respective current temperatures of components of the inverter 21 and the electric machine 22 to measure. So can the inverter 21 Diodes and transistors include and the electric machine 22 may include a rotor and a stator. The temperature information includes a temperature of the rotor of the electric machine 22 , a temperature of the stator of the electric machine, a temperature of diodes of the inverter 21 and a temperature of transistors of the inverter 21 , The transistors of the inverter 21 For example, they are designed as IGBTs.

Further, the temperature detecting means 11 also be adapted to temperature information with respect to the electrical machine 22 and the inverter 21 using an empirical or physical model. The temperature detecting device 11 can take into account existing driving cycles, road profiles and / or navigation data to estimate the current temperatures.

Preferably, the temperature detecting means 11 additionally designed, taking into account the determined temperature information, temperature profiles of the components of the electric drive 2 to investigate. The temperature curves can in this case from an operating point of the electric machine 22 and a switching frequency f _{PWM of} the inverter 21 depend. The working point of the electric machine 22 is preferably by a d-axis component i _{d of} a current vector of the electric machine 22 and by a q-axis component i _{q of} the current vector of the electrical machine 22 certainly. The temperature detecting device 11 can thus provide a prediction model, by means of which the temperature determination device, for example, an expected stator temperature T _stator (k + 1) at a future time in dependence on a stator temperature T _stator (k) at the present time, a cooling temperature T _cool , an operating point i _d , i _{q of} the electric machine 22 and a switching frequency f _{PWM of} the inverter 21 calculated according to the following formula: $${\text{T}}_{\text{stator}}\left(\text{k}+1\right)={\text{f}}_1\left({\text{T}}_{\text{stator}}\left(\text{k}\right){\text{, T}}_{\text{cool}}{\text{, i}}_{\text{d}}{\text{, i}}_{\text{q}}{\text{, f}}_{\text{PWM}}\right)\text{,}$$

$${\text{T}}_{\text{diode}}\left(\text{k}+1\right)={\text{f}}_3\left({\text{T}}_{\text{diode}}\left(\text{k}\right){\text{, T}}_{\text{cool}}{\text{, i}}_{\text{d}}{\text{, i}}_{\text{q}}{\text{, f}}_{\text{PWM}}\right)\text{,}$$

$${\text{T}}_{\text{IGBT}}\left(\text{k}+1\right)={\text{f}}_4\left({\text{T}}_{\text{IGBT}}\left(\text{k}\right){\text{, T}}_{\text{cool}}{\text{, i}}_{\text{d}}{\text{, i}}_{\text{q}}{\text{, f}}_{\text{PWM}}\right)\text{.}$$

Further, the temperature detecting means 11 Based on the prediction model in an analogous manner, a temperature T _{rotor of} a rotor of the electric machine 22 , a temperature T _diode of diodes of the inverter 21 or a temperature T _IGBT of transistors of the inverter 21 at a future time depending on a respective corresponding temperature at the present time, a cooling temperature T _cool , from the operating point i _d , i _{q of} the electric machine 22 and the switching frequency f _{PWM of} the inverter 21 determine, ie according to the following formulas: $${\text{T}}_{\text{rotor}}\left(\text{k}+1\right)={\text{f}}_2\left({\text{T}}_{\text{rotor}}\left(\text{k}\right){\text{, T}}_{\text{cool}}{\text{, i}}_{\text{d}}{\text{, i}}_{\text{q}}{\text{, f}}_{\text{PWM}}\right)\text{.}$$

$${\text{T}}_{\text{diode}}\left(\text{k}+1\right)={\text{f}}_3\left({\text{T}}_{\text{diode}}\left(\text{k}\right){\text{, T}}_{\text{cool}}{\text{, i}}_{\text{d}}{\text{, i}}_{\text{q}}{\text{, f}}_{\text{PWM}}\right)\text{.}$$

$${\text{T}}_{\text{IGBT}}\left(\text{k}+1\right)={\text{f}}_4\left({\text{T}}_{\text{IGBT}}\left(\text{k}\right){\text{, T}}_{\text{cool}}{\text{, i}}_{\text{d}}{\text{, i}}_{\text{q}}{\text{, f}}_{\text{PWM}}\right)\text{,}$$

In the formulas 1 to 4 f ₁ , f ₂ , f ₃ , f ₄ denote respective model-dependent functions. These functions can be determined on the basis of a physical model, but can also be determined on the basis of characteristics of the electric drive. While the temperature information is thus on current temperatures of the components of the electric drive 2 The temperature profiles also relate to future temperatures of the components of the electric drive 2 ,

The device 1 further comprises an adjustment device 12 , which is adapted to the operating point i _d , i _{q of} the electric machine 22 and the switching frequency f _{PWM of} the inverter 21 adjust. The adjustment device 12 determines for this purpose a quality function J, which of the operating point i _d , i _{q of} the electric machine 22 , the switching frequency f _{PWM of} the inverter 21 , an operating point specification i _{d, destination} , i _{q, destination} , a switching frequency specification f _{PWM, target} and a torque _input M _target depends. The quality functional J can be given by the following formula: $$\text{J}={\text{k}}_1{\left({\text{i}}_{\text{d}}-{\text{i}}_{\text{d}}{\text{.}}_{\text{aim}}\right)}^2+{\text{k}}_2{\left({\text{i}}_{\text{q}}-{\text{i}}_{\text{q}\text{,aim}}\right)}^2+{\text{k}}_3{\left(\text{M}-{\text{M}}_{\text{aim}}\right)}^2\mathrm{+}{\text{k}}_4{\left({\text{f}}_{\text{PWM}}\mathrm{-}{\text{f}}_{\text{PWM}\text{,aim}}\right)}^2\text{,}$$

The operating point specification i _{d, target} , i _{q, target} corresponds to a predetermined target value for the operating point i _d , i _q , the switching frequency specification f _{PWM, target} corresponds to a predetermined target value for the switching frequency f _PWM and the torque specification M _target corresponds to a predetermined target value for the Torque M. Typical criteria for determining i _{d, target} and i _{q, target} are the maximum efficiency or the maximum torque per ampere. In reality, however, the target values can not always be achieved without certain components of the electric drive 2 reach their thermal capacity limits. By the weighting factors k ₁ to k _{4, however} , the respective contributions to the quality function J can be weighted accordingly. By setting the weighting factors k ₁ to k ₄ , the different target values can be changed. For example, in a sport mode, the weighting factor k _{3 of} the torque M may be increased, and in an eco mode, the weighting factor k _{3 of} the torque M may be decreased. By changing the weighting k ₃ , a deviation of the actual torque M from the torque _input M _target or from the target value for the torque is thus adjustable.

$${\text{T}}_{\text{rotor}}\left(\text{k}\right)\le {\text{T}}_{\text{rotor}\text{,max}}\text{, für alle k von 1 bis N}\text{,}$$

$${\text{T}}_{\text{diode}}\left(\text{k}\right)\le {\text{T}}_{\text{diode}\text{,max}}\text{, für alle k von 1 bis N}\text{,}$$

$${\text{T}}_{\text{IGBT}}\left(\text{k}\right)\le {\text{T}}_{\text{IGBT}\text{,max}}\text{, für alle k von 1 bis N}\text{,}$$

$${\text{i}}_{\text{d}}{}^2+{\text{i}}_{\text{q}}{}^2\le {\text{i}}_{\text{max}}{}^2\text{,}$$

$${\text{u}}_{\text{d}}{}^2+{\text{u}}_{\text{q}}{}^2\le {\text{u}}_{\text{max}}{}^2\text{,}$$

$${\text{f}}_{\text{PWM}\text{,min}}\le {\text{f}}_{\text{PWM}}\le {\text{f}}_{\text{PWM}\text{,max}}\text{.}$$

The adjustment device 12 is designed to the working point i _d , i _{q of} the electric machine 22 and the switching frequency f _{PWM of} the inverter 21 by optimizing the quality function J. The adjustment device 12 in this case takes into account that of the temperature detecting device 11 determined temperature information and temperature profiles. The adjustment device 12 can be designed to the quality function J using the operating point i _d , i _{q of} the electric machine 22 and the switching frequency f _{PWM of} the inverter 21 as optimization variables, using the formulas above 1 to 4 first secondary conditions and as second secondary conditions the values for the operating point i _d , i _{q of} the electric machine 22, the values for voltages u _d , u _{q of} the electric machine 22 and for the switching frequency f _{PWM of} the inverter 21 be limited, for example, according to the following formulas: $${\text{T}}_{\text{stator}}\left(\text{k}\right)\le {\text{T}}_{\text{stator}\text{,Max}}\text{, for all k from 1 to N}\text{.}$$

$${\text{T}}_{\text{rotor}}\left(\text{k}\right)\le {\text{T}}_{\text{rotor}\text{,Max}}\text{, for all k from 1 to N}\text{.}$$

$${\text{T}}_{\text{diode}}\left(\text{k}\right)\le {\text{T}}_{\text{diode}\text{,Max}}\text{, for all k from 1 to N}\text{.}$$

$${\text{T}}_{\text{IGBT}}\left(\text{k}\right)\le {\text{T}}_{\text{IGBT}\text{,Max}}\text{, for all k from 1 to N}\text{.}$$

$${\text{i}}_{\text{<figure-callout id="2" label="d" filenames="DE102017203656A1\_0013.png,DE102017203656A1\_0016.png" state="{{state}}">d</figure-callout>}}{}^2+{\text{i}}_{\text{<figure-callout id="2" label="q" filenames="DE102017203656A1\_0013.png,DE102017203656A1\_0016.png" state="{{state}}">q</figure-callout>}}{}^2\le {\text{<figure-callout id="2" label="i Max" filenames="DE102017203656A1\_0013.png,DE102017203656A1\_0016.png" state="{{state}}">i </figure-callout>}}_{\text{Max}}{}^2\text{.}$$

$${\text{<figure-callout id="2" label="u d" filenames="DE102017203656A1\_0013.png,DE102017203656A1\_0016.png" state="{{state}}">u </figure-callout>}}_{\text{d}}{}^2+{\text{<figure-callout id="2" label="u q" filenames="DE102017203656A1\_0013.png,DE102017203656A1\_0016.png" state="{{state}}">u </figure-callout>}}_{\text{q}}{}^2\le {\text{<figure-callout id="2" label="u Max" filenames="DE102017203656A1\_0013.png,DE102017203656A1\_0016.png" state="{{state}}">u </figure-callout>}}_{\text{Max}}{}^2\text{.}$$

$${\text{f}}_{\text{PWM}\text{, min}}\le {\text{f}}_{\text{PWM}}\le {\text{f}}_{\text{PWM}\text{,Max}}\text{,}$$

In this case, T _{stator, max} , T _{rotor, max} , T _{diode, max} , T _{IGBT, max} and imax are predetermined threshold values, which thermal load information of the electric drive 2 represent. The parameters u _max , f _{PWM, min} and f _{PWM, max} are drive-related threshold values. The parameter N denotes the number of time steps.

The adjustment device 12 can be designed to solve this non-linear optimization problem using a known method, for example by means of sequential quadratic programming (SQP). The adjustment device 12 represents the operating point i _d , i _{q of} the electric machine 22 and the switching frequency f _{PWM of} the inverter 21 to those values that solve the optimization problem.

The exact form of the quality function J is only an example. In particular, the dependence on the variables may also differ from the above quadratic relationship.

The setting of the operating point i _d , i _q and the switching frequency f _PWM is based on a in the 2 to 7 illustrated scenarios exemplified.

As in 2 shown, the electric machine heats up 22 initially, so that up to a first time t _1, the temperatures T _{stator of} the stator and the temperature T _{rotor of} the rotor of the electric machine 22 increase, in particular, the temperature T _{rotor of} the rotor approaches a maximum allowable temperature of 100 ° C.

The temperature T _{diode of} the diodes and the temperature T _{IGBT of} the transistors of the inverter 21 remain substantially constant and are less than the maximum allowable temperature of 100 ° C, as in 3 illustrated.

As in 4 shown is the switching frequency f _{PWM of} the inverter 21 essentially constant, as well as the in 5 illustrated d-axis components i _d and q-axis components i _{q of} the current vector of the electric machine 22 ,

As in 6 illustrated, the torque M substantially corresponds to the torque _command M _target for the torque M. The power P of the electric drive 2 is also constant, as in 7 illustrated.

At time t ₁ it is predicted that the temperature T _{rotor of} the rotor will exceed the maximum permissible temperature of 100 ° C after a short time. In solving the optimization problem, this automatically causes the switching frequency f _{PWM of} the inverter 21 increased, as in 4 to see. This reduces the q-axis component i _{q of} the current vector, while the d-axis component i _{d of} the current vector increases. Due to the switching losses occurring and the increasing current vector norm, the temperatures T _diode, T _{IGBT of} the diodes and the transistors increase. In order to prevent overheating of the transistors, therefore, the switching frequency f _{PWM is} again reduced, as in 4 can be seen. The torque M of the electric drive 2 remains constant and equal to the torque _target M _goal . A derating can be done by varying the switching frequency f _{PWM of} the inverter 21 be further delayed. The output power P of the electric drive 2 stays unchanged.

At a second time t ₂ , the torque M must be reduced to prevent overheating of the transistors and the rotor. Thus, a derating occurs and the torque M is different from the torque command M, as in 6 to see. The output power P of the electric drive 2 sinks.

At a third time t ₃ , finally, the torque _input M _{target is} reduced. As a result, the d-axis component i _d and the q-axis component i _{q of} the current vector decrease, while the switching frequency f _{PWM of} the inverter 21 increases. As a result, the torque _{specification} M _goal can be achieved again.

The invention is not limited to the embodiments shown. Thus, for example, the temperatures and temperature profiles as well as operating parameters of other components of the electric drive 2 be taken into account. For example, a DC link capacitor can be taken into account. Further, also elements of the drive train, a battery or a transmission of a vehicle can be taken into account. In addition to an adjustment of the switching frequency of the inverter and control methods of the inverter can be adjusted accordingly, so that critical components of the inverter 21 experience a low power dissipation. Furthermore, the components of the quality function J can be time-dependent, so that aging or load models are taken into account in the quality functional J.

In 8th is a block diagram of an electric drive 2 illustrated according to an embodiment of the invention. The electric drive 2 includes an inverter 21 , which converts DC voltage into AC voltage and an electric machine 22 of the electric drive 2 provides. The electric machine 22 is designed as a three-phase machine, such as a synchronous machine or asynchronous machine. The electric drive 2 further comprises a device 1 , which is adapted to temperature information relating to the electrical machine 22 and regarding the inverter 21 to determine and an operating point i _q , i _{d of} the electric machine 22 and a switching frequency f _{PWM of} the inverter 21 using the determined temperature information and taking into account a torque _input M _goal and of predetermined thermal capacity information with respect to the electric drive 2 to determine and adjust. The device 1 preferably corresponds to one of the embodiments described above.

In 9 is a flowchart of a method for controlling an electric drive 2 illustrated. The electric drive 2 includes, as described above, an electric machine 22 and an inverter 21 ,

In a first method step S1, temperature information relating to the electrical machine is obtained 22 and regarding the inverter 21 determined. The temperature information can be based on sensor data and / or on the basis of physical models or characteristics of the electric drive 2 be determined.

In a method step S2, an operating point i _d , i _{q of} the electric machine 22 and a switching frequency f _{PWM of} the inverter 21 set using the determined temperature information and taking into account a torque _input M _target and of predetermined thermal capacity information with respect to the electric drive. Preferably, as described above, a corresponding quality function J is optimized, which from the operating point i _d , i _{q of} the electric machine 22 , the switching frequency f _{PWM of} the inverter 21 and the torque _default M _goal depends.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102014220208 A1 [0003]

Claims (10)

A method of controlling an electric drive (2) comprising an electric machine (22) and an inverter (21), comprising the steps of: determining (S1) temperature information regarding the electric machine (22) and the inverter (21); and adjusting (S2) of a working point of the electrical machine (22) and a switching frequency (f _PWM) of the inverter (21) _(destination M) using the temperature information determined under consideration of a torque setting and of predetermined thermal capacity information relating to the electric drive (2 ). Method according to Claim 1 wherein the temperature information is a temperature (T _r ) of a rotor of the electrical machine (22) and / or a temperature (T _s ) of a stator of the electric machine (22) and / or a temperature (T _d ) of diodes of the inverter (21 ) and / or a temperature (T _IGBT ) of transistors of the inverter (21). Method according to Claim 2 , wherein the thermal load information is a maximum temperature (T _{rotor, max} ) of the rotor and / or a maximum temperature of the stator (T _{stator, max} ) and / or a maximum temperature (T _{diode, max} ) of the diodes of the inverter (21) and or a maximum temperature (T _{IGBT, max} ) of the transistors of the inverter (21). The method of any one of the preceding claims, wherein adjusting the operating point of the electric machine (22) comprises calculating a d-axis component (i _d ) of a current vector of the electric machine (22) and a q-axis component (i _q ) of the electric machine's current vector (22). Method according to one of the preceding claims, wherein adjusting the operating point of the electric machine (22) and the switching frequency (f _PWM) of the inverter (21) by optimizing a quality function (J), which from the operating point of the electric machine (22), the switching frequency (f _PWM ) of the inverter (21) and the torque command (M _target ) depends. Method according to Claim 5 , wherein based on a model taking into account the determined temperature information temperature profiles of components of the electric drive (2) depending on the operating point of the electric machine (22) and the switching frequency (f _PWM ) of the inverter (21) are determined, and wherein the optimization under the secondary condition is carried out that the temperature curves are within predetermined value ranges. Method according to one of Claims 5 or 6 wherein a weighting of a deviation of an actual torque of the electric machine (22) from the torque command (M _target ) in the quality functional is adjustable. Device (1) for controlling an electric drive (2), wherein the electric drive (2) comprises an electric machine (22) and an inverter (21), comprising: temperature detecting means (11) adapted to provide temperature information relating to electrical machine (22) and the inverter (21) to determine; and an adjusting device (12) which is adapted to a working point of the electric machine (22) and a switching frequency (f _PWM ) of the inverter (21) using the determined temperature information and taking into account a torque command (M _target ) and predetermined thermal To set resilience information with respect to the electric drive (2). Device (1) according to Claim 8 wherein the temperature detecting means (11) is adapted to a temperature (T _r ) of a rotor of the electric machine (22) and / or a temperature (T _s ) of a stator of the electric machine (22) and / or a temperature (T _d ) of diodes of the inverter (21) and / or a temperature (T _IGBT ) of transistors of the inverter (21) to measure or estimate. Electric drive (2), comprising an inverter (21), an electric machine (22) and a device (1) for controlling the inverter (21) and the electric machine (22) according to one of Claims 8 or 9 ,

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