Method for checking a motor model temperature determined by means of a temperature model and motor vehicle

Abstract

The invention relates to a method for checking a model temperature of an electric machine (2) determined by means of a temperature model, wherein at least one control variable of the electric machine (2) is predetermined by a controller of the electric machine (2) as a function of a target variable; wherein a model value of the control variable is determined from the target variable and the model temperature by means of a machine model which comprises at least one temperature-dependent parameter; wherein a difference between the actual control variable of the controller and the model value of the control variable and / or a difference between a variable derived from the actual control variable of the controller and a further variable derived correspondingly from the model value of the control variable is determined; wherein the difference is compared with a limit value, and a deviation of the model temperature from the actual temperature of the electric machine (2) is detected in the event of an excess of the limit value.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for checking a motor model temperature determined by means of a temperature model, wherein at least one regulating variable of a motor is predetermined by a regulator of the motor in accordance with a target variable. The present application furthermore relates to a motor vehicle. BACKGROUND

[0002] In the case of a motor, the temperature in the interior of the motor, for example the temperature of the powered stator winding of the motor, can be determined by means of a temperature sensor. However, the use of such a temperature sensor increases the expenditure and costs in the manufacture of the motor. Furthermore, a high degree of reliability of the temperature determination can be required, for example in the case of a motor used as a traction motor in a motor vehicle, so that the failure rate of the applied temperature sensor should also be taken into account. There is therefore an interest in a method with which the temperature of a motor can be determined without the use of a temperature sensor. For this purpose, different solutions are known from the prior art.

[0003] In document US 9614472 B2, a system for determining the temperature in the interior of a motor is described. Therein, the temperature of the winding of the motor is determined by measuring its temperature-dependent resistance.

[0004] In document EP 1180671 A1, a brushless AC electric generator is described, which comprises a temperature measuring unit for determining the temperature of the field winding. The temperature of the field winding is determined by the temperature measuring unit from the winding voltage and the current fed into the winding.

[0005] From document DE 10 2014 200 337 A1, a method for powering a stator winding of an electrically motor-operable AC field motor is known. Herein, a bias current is applied to the phase current fed into the stator winding, wherein the bias current is adjusted by means of a vector-based method such that the bias current does not generate a torque in the motor. The direct current resulting therefrom, which is superimposed on the phase current, is then used to determine the temperature of the stator winding by means of the resistance of the stator winding.

[0006] Also document US 8084984 B2 relates to a system for measuring and controlling the temperature of a stator winding in an AC motor, wherein the temperature detection is determined by means of a direct current by the resistance of the winding.

[0007] Document DE 20 2016 101 853 U1 describes an electronic circuit for detecting the current winding temperature of a phase winding / strang winding. Therein, one or more two-pole elements having a temperature-dependent impedance are connected in parallel to two winding connection terminals of a phase winding of a motor. By detecting the current response in the motor feed line related to the temperature-dependent impedance, the temperature of the phase winding is determined.

[0008] In the document DE 10 2010 038 560 A1 a temperature estimation for a stator winding of an electric machine is described. Therein an angular velocity of the electric machine is determined as well as a total power loss for each phase of the electric machine. Subsequently the temperature of the stator winding is estimated by a combined thermal impedance for the phase and a stator winding power loss component on the total power loss. The combined thermal impedance has here a first thermal impedance between the stator winding and the stator core as well as a second thermal impedance between the electronic core and the electric machine coolant.

[0009] In the document US 7340968 B2 the temperature of a rotating magnet in an electric machine is determined by measuring a temperature dependent electric machine force.

[0010] Also in the document DE 3 736 303 T2 a temperature measurement of a brushless direct current electric machine by means of an integration of an electric machine force in a currentless winding is realized.

[0011] From the document DE 10 2014 016 452 B4 a method for determining a stator winding temperature of an electric machine is known. Therein a magnetic flux in the electric machine is determined in a no-load of the electric machine. In a case of an activated short circuit of the electric machine the temperature of the stator winding is determined from the magnetic flux and a flowing short circuit current. The temperature is subsequently used as a starting temperature for a temperature model of the electric machine, wherein by means of the temperature model a temperature of the electric machine at different operating points can be calculated.

[0012] Besides the determination of a temperature of an electric machine by measuring a temperature dependent quantity in the electric machine a temperature determination by means of a temperature model of the electric machine is also possible. With the temperature model a model temperature of the electric machine can be determined accordingly during an operation of the electric machine. In order to obtain a model temperature which corresponds as exactly as possible to an actual temperature of the electric machine it is highly important that the model assumptions for the temperature model are correct. Therein it is striven that a check of the model assumptions or of a model temperature determined based on the model assumptions is possible as cost-effectively as possible and in particular without the application of temperature sensors. SUMMARY

[0013] The invention is based on the object to propose an improved method for checking a model temperature of an electric machine determined by means of a temperature model, which method is in particular realizable cost-effectively.

[0014] To solve this object, according to the application, in a method of the type mentioned at the outset, a model value of the manipulated variable is determined from a motor model comprising at least one temperature-dependent parameter, as a function of the manipulated variable and of the model temperature; wherein a difference between the actual manipulated variable of the regulator and the model value of the manipulated variable and / or a difference between a variable derived from the actual manipulated variable of the regulator and a further variable derived correspondingly from the model value of the manipulated variable is determined; wherein the difference is compared with a limit value, and a deviation of the model temperature from the actual temperature of the motor is detected in the event of the limit value being exceeded.

[0015] The regulator of the motor generates a manipulated variable as a function of a predetermined target variable, which manipulated variable acts on the motor in order to set the manipulated variable as a function of the predetermined target variable. By means of the regulator it is advantageously possible here to compensate for disturbances acting on the motor without an actual measurement of the respective disturbance variable. As a result, temperature-dependent effects which enter into the manipulated variable determined by the regulator are also taken into account in the regulator of the motor. The manipulated variable determined by the regulator is therefore at least partially dependent on the temperature of the motor or on the temperature of components of the motor acted on by the manipulated variable.

[0016] In addition to the actual manipulated variable generated by the regulator, according to the application a model value of the manipulated variable is also determined using a motor model comprising at least one temperature-dependent parameter. As the temperature for the motor model, the model temperature determined by means of a temperature model is applied here which is to be checked. If the model temperature input in the motor model by means of the at least one temperature-dependent parameter corresponds to the actual temperature of the motor, the model value of the manipulated variable determined by means of the motor model here corresponds to the value of the actual manipulated variable.

[0017] This means that, in the event of a deviation of the model temperature from the actual temperature of the motor, a deviation of the model value of the manipulated variable from the actual manipulated variable occurs. This deviation is determined in that a difference is formed from the actual manipulated variable of the regulator and the model value of the manipulated variable, wherein the difference is compared with a limit value. In the event of the limit value being exceeded, a deviation of the model temperature from the actual temperature of the motor can be detected accordingly.

[0018] It is possible in addition or alternatively for a further variable to be determined from the actual manipulated variable and from the model value of the manipulated variable respectively, wherein a difference between the further variable derived from the actual manipulated variable and the further variable derived from the model value of the manipulated variable is also compared with a limit value accordingly. A deviation of the model temperature from the actual temperature can also be detected in the event of this limit value being exceeded accordingly.

[0019] The limits for comparison with the difference between the actual control variable and the model value of the control variable can here be equal to or different from the limits for comparison with the difference of the respective further variable. The limits can here each be zero or greater, wherein in particular the respective difference is compared with the associated limit. The application of limits greater than zero can advantageously compensate for further, interfering variables acting on the control path and / or influencing factors not modelled in the motor model in the checking of the model temperature.

[0020] The motor model in particular describes the relationship of the control variable to the target variable taking into account at least one temperature-dependent parameter of the motor and can for this purpose comprise at least one arithmetic rule. If for the determination or calculation of the model value of the control variable from the target variable is required, further, temperature-independent parameters can also be included in the motor model. The type of the parameters and / or the at least one arithmetic rule describing the relationship of the control variable to the target variable can here depend on the type or configuration of the motor and the applied control variable and the applied target variable.

[0021] The model temperature to be checked is determined by means of a temperature model, which in particular calculates the temperature of the motor from at least one arithmetic rule on the basis of operating parameters of the motor. In particular, operating parameters having a significant influence on the temperature of the motor can be taken into account. This can be, for example, the stator current, the current in the field winding, the torque of the motor and / or the rotational speed of the motor. The operating duration of the motor or the power achieved in the motor during the operating duration can also be taken into account.

[0022] The temperature model can in particular also take into account or calculate the cooling power of a cooling device connected to the motor and / or determine the heat flow from the motor into the cooling system. Operating parameters of the cooling device, such as the cooling water temperature and / or the delivered coolant quantity, can also be taken into account, for example. In this way, the temperature of the motor can be determined as a model temperature from the past operating points of the motor and from the operating points of the cooling system.

[0023] The method according to the application has the advantage that the accuracy of the model temperature can be checked without the need for further sensors for determining the temperature. The existing sensors for the control are sufficient for determining the control variable. In the case of a motor operated by means of an inverter and a battery, this can be, for example, the voltage of the DC voltage intermediate circuit and / or the phase current flowing into the motor, which can be used in the current control, for example. Furthermore, parameters determined and / or saved in another way can advantageously be applied for the motor model, so that sensors do not have to be applied for determining the model value of the control variable.

[0024] By means of the method it is advantageously possible to check the temperature model or to check the model temperature determined by means of the temperature model without having to apply further sensors, for example in the cooling system coupled to the electric machine, in order to identify an incorrect model temperature. The use of further temperature sensors and / or pressure sensors in the cooling system for checking the cooling system function has the disadvantage that these sensors at least partially reduce the initial cost advantage achieved by the elimination of temperature sensors in the electric machine and moreover reintroduce sensors which are prone to faults into the overall system.

[0025] By means of the method according to the application it is possible to check the model temperature determined by means of the temperature model, i.e. to check the conformity of the determined model temperature with the actual temperature of the electric machine. In the determination of the deviation of the model temperature from the actual temperature, for example a fault message can be generated by the control device configured for carrying out the method, the fault message indicating the deviation, in particular indicating a too high actual temperature of the electric machine. The fault message can be made known to the user of the electric machine and / or transmitted to a further control device also in the motor vehicle comprising the electric machine.

[0026] According to the application it can be provided that a target current is applied as target variable and / or that a regulating voltage is applied as regulating variable. By means of the regulator it is thus possible to generate at least one regulating voltage in accordance with the predetermined target current, the regulating voltage acting on the electric machine. By means of the regulating voltage a current is generated in the electric machine which corresponds to the predetermined target variable.

[0027] In a preferred design of the application it can be provided that a regulating variable is applied which acts on the winding of the electric machine, in particular on the stator winding or the rotor winding of the electric machine. The winding of the electric machine can be a single-phase winding or a multi-phase winding. The regulating variable can here in particular be a single-phase regulating voltage or a multi-phase regulating voltage which is applied to the winding or to the individual phases of the winding. As the temperature of the electric machine it is preferably possible to determine the temperature of the winding, in particular of the stator winding and / or of the rotor winding.

[0028] According to the application it can be provided that the phase voltage / strangspannung of the winding is used as a variable derived from the actual regulating variable of the regulator and / or as a further variable derived from the model value of the regulating variable, respectively. Depending on the type or embodiment of the regulator, it is possible to derive the phase voltage from the regulating variable generated by the regulator as a further variable. It is in particular possible to apply a regulating voltage as regulating variable which acts on the multi-phase winding of the electric machine and which drops / resides on the individual phases of the winding there, respectively, as phase voltage.

[0029] In a preferred design of the application it can be provided that the regulator is implemented by means of a field-oriented controller and / or at least one variable corresponding to an adjustment variable of the field-oriented controller is determined by means of a motor model. It is possible, for example, that the regulator determines the voltage U D and U Q as an adjustment variable by means of the field-oriented controller as a function of the target current, which acts on the multiphase winding of the motor. From the adjustment variable U D and U Q a phase voltage in the multiphase winding can be determined, so that the phase voltage can be used as a further variable derived from the adjustment variable.

[0030] Correspondingly, by means of the motor model it is likewise possible to determine the phase voltage that can be expected for a given model temperature using the target current to be checked. This can be achieved, for example, in such a way that by means of the motor model a model value for U D and U Q is likewise determined, from which a model value of the phase voltage is derived as a corresponding variable. As described above, it is then possible to form the difference between the phase voltage determined by means of the model and the phase voltage determined by the actual current variable of the regulator and to compare it with a limit value.

[0031] According to the application, as a temperature model a thermal network model can be applied, which thermal network comprises the motor and at least one cooling device. This advantageously enables the function of the cooling device to be checked by checking the model temperature of the temperature model. In the temperature model it is assumed that the function of the cooling device is correct, wherein the cooling power of the cooling device has a decisive effect on the temperature of the motor. In the case of a model temperature that at least substantially corresponds to the actual temperature, the difference determined by means of the method according to the application remains below the limit value, so that it can be concluded that the function of the cooling device is correct. In the temperature model, which is configured as a thermal network, in particular the heat generation in the motor and the heat flowing into and out of the motor, in particular the heat flowing into the cooling system, can be calculated and taken into account for determining the model temperature. As described above, operating parameters of the motor and / or the cooling system can also be taken into account and used for determining the model temperature.

[0032] The deviation of the actual temperature of the electric machine from the model temperature of the electric machine determined under the assumption of a correct functioning of the cooling device can be an indication that no cooling power or only a reduced cooling power is generated by the cooling device. By determining the correctness of the determined model temperature of the electric machine, it can also be concluded that the cooling device is functioning correctly. This advantageously enables a check of the condition of the entire cooling device. Advantageously, in this way it is possible to detect fault conditions in the cooling device, such as an undiagnosable failure of the coolant pump and / or a blockage of the coolant inlet in the cooling device and / or the electric machine, since in such cases it is possible to start from an increase in the actual temperature relative to the model temperature.

[0033] It can be provided in accordance with the application that the winding resistance and / or the temperature-dependent magnetic flux are applied as temperature-dependent parameters of the electric machine model. The number and type of temperature-dependent parameters applied in the electric machine model can depend on the type and model of the electric machine, the type of the control variable applied or the determination of the model value of the control variable, and / or on the various temperature-dependent effects of the electric machine.

[0034] It can be provided in a preferred design of the application that the difference is determined only when the control variable and / or the model value of the control variable exceeds a limit value. This enables the difference to be determined not in operating states of the electric machine in which the control variable only has a very small amplitude, if it is not possible and / or not plausible to base the small control variable or the small model value of the control variable on a limit value to be compared with the difference. In this case, in particular, separate limit values can be applied for the control variable and the model value of the control variable. Furthermore, the limit value associated with the control variable or the model value of the control variable can be different from the limit value with which the difference of the control variable and the model value of the control variable and / or a further variable derived from these variables, respectively, is compared.

[0035] It can be provided in a preferred design of the application that, during operation of the electric machine, the control variable of the controller, the model value of the control variable from the electric machine model, and the difference are determined continuously at different times, wherein a fault message is generated if a predetermined number of the determined differences each exceeds a limit value within a predetermined time interval, the fault message describing a deviation of the model temperature of the electric machine from the actual temperature.

[0036] The fault message can then be output by the control device implementing the method according to the application to a user of the electric machine and / or to a further control device. The fault message can then be applied and / or taken into account in the operation of the electric machine or in the operation of a motor vehicle comprising the electric machine. For example, a warning can be output on the basis of the fault message, and / or the target variable can be reduced in order to prevent the electric machine from heating up further.

[0037] It can be provided in accordance with the application that as electric machine a permanent-magnet synchronous electric machine, a separately excited synchronous electric machine or an asynchronous electric machine is applied. The method can be implemented here in different types of electric machines, wherein the respective applied electric machine model can be matched to the applied electric machine type accordingly.

[0038] It can be provided in accordance with the application that the motor vehicle comprises at least an electric machine, a control device and a regulator, by means of which a regulation variable relating to the electric machine can be determined as a function of a target variable, wherein the control device is designed to implement the method as described above.

[0039] It can be provided in accordance with the application that the electric machine is a drive electric machine of the motor vehicle; and / or the electric machine is coupled to a cooling device, in particular to a coolant circuit, of the motor vehicle.

[0040] All advantages and design solutions described above in connection with the method according to the application apply analogously to the motor vehicle according to the application. Correspondingly, the advantages and design solutions described in connection with the motor vehicle according to the application apply to the method according to the application. BRIEF DESCRIPTION OF DRAWINGS

[0041] Further advantages and details of the application result from the embodiments described hereinafter and from the attached drawings. Therein:

[0042] Figure 1 a schematic diagram of a motor vehicle according to the application is shown;

[0043] Figure 2 a first block diagram for representing a first embodiment of the method according to the application is shown; and

[0044] Figure 3 a second block diagram for representing a second embodiment of the method according to the application is shown. DETAILED DESCRIPTION

[0045] An embodiment of a motor vehicle 1 is shown in Figure 1 The motor vehicle 1 comprises an electric machine 2 as drive electric machine. The motor vehicle 1 furthermore comprises an electrical energy accumulator 3, which is connected to the electric machine 2 by means of a power electronics device 4. By means of the power electronics device 4, a direct current obtained from the energy accumulator 3 can be converted into an alternating current for powering the electric machine 2. The energy accumulator 3 can be embodied, for example, as a traction battery of the motor vehicle 1.

[0046] By means of the power electronics 4 an alternating current for supplying the electric machine 2, for example the stator winding, can be generated. Due to the stator current generated in the electric machine 2 by means of the power electronics 4 the electric machine 2 heats up during operation. The electric machine 2 is therefore coupled to a cooling device 5 of the motor vehicle 1, wherein the heat generated in the electric machine 2 can be discharged by means of the cooling device 5. The cooling device 5 is shown here merely schematically and can in particular cool further components of the motor vehicle 1, for example the energy store 3 and / or the power electronics 4, in addition to the electric machine 2.

[0047] The motor vehicle 1 furthermore comprises a regulating device 6 which is set up for regulating the electric machine 2. The regulating device 6 here generates a regulating variable relating to the electric machine 2 in dependence on a predetermined target variable. For example the regulating device 6 can generate a regulating voltage as a regulating variable in dependence on a target current. The regulating voltage can for example be a three-phase alternating voltage, so that the three-phase stator winding of the electric machine 2 can be supplied. The target current can for example be determined by a motor control device (not shown) of the motor vehicle 2 and transmitted to the regulating device 6.

[0048] The motor vehicle 1 furthermore comprises a control device 7 which determines a model temperature of the electric machine 2 by means of a temperature model of the electric machine 2 saved in the control device 7. As a temperature model here a model of a thermal network can be applied, wherein the thermal network comprises the electric machine 2 and the cooling device 5.

[0049] By means of the temperature model it is achieved that the temperature of the electric machine 2 is modelled in dependence on different operating parameters of the motor vehicle 1, in particular operating parameters of the electric machine 2, the energy store 3 and / or the power electronics 4. The temperature of the electric machine 2 can for example be the winding temperature of the stator winding of the electric machine 2, to which the electric machine is subjected to a regulating voltage by means of the power electronics 4 in dependence on the predefinition of the regulating device 6.

[0050] In order to determine the model temperature the temperature model can take into account operating parameters of the cooling system 5 in addition to operating parameters of the electric machine 2, such as the stator current, the current in the field winding, the torque of the electric machine and / or the rotational speed of the electric machine. Furthermore the operating duration of the electric machine 2 or the corresponding power achieved during the operating duration in the electric machine 2 can also be taken into account, since these parameters have a significant influence on the heat generation in the electric machine 2 and in turn also on the electric machine temperature. By means of the description of the thermal network comprising at least the electric machine 2 and the cooling device 5 the heat generation in the electric machine and the heat flowing to or from the electric machine 2, in particular into the cooling system 5, can be calculated and used for determining the model temperature.

[0051] Furthermore, the temperature model can comprise one or more calculation rules, which can be stored, for example, in the control device 7. The operating parameters required for the calculation of the model temperature of the electric machine 2, the cooling device 5 and / or of further components, such as the energy store 3 or the power electronics 4, can be transmitted here by the respective components and / or the control devices connected thereto to the control device 7. In order to check the correctness of the model temperature determined by means of the temperature model, the control device 7 is further provided to carry out a method for checking the model temperature of the electric machine 2 determined by means of the temperature model.

[0052] To this end, the control device 7 determines a model value of the adjustment variable on the basis of the adjustment variable of the regulator implemented by means of the adjustment device 6 and the model temperature determined by means of the temperature model, in the case of the use of an electric machine model comprising at least one temperature-dependent parameter. The current target variable applied by the adjustment device 6 can also be transmitted to the control device 7 by the adjustment device 6 or the electric machine control device of the motor vehicle 2. Furthermore, each adjustment variable generated in accordance with the target variable is transmitted to the control device 7 by the adjustment device 6. It is possible for the adjustment device 6 and the control device 7 to be implemented in a common control device.

[0053] Furthermore, the control device 7 is provided to determine a difference between the actual adjustment variable of the regulator and the model value of the adjustment variable, wherein the difference is compared to a limit value. In the case of an excess of the limit value, a deviation of the model temperature from the actual temperature of the electric machine 2 is detected by the control device 7.

[0054] In addition or alternatively thereto, the control device 7 can be provided to determine a further variable derived from the actual adjustment variable and from the model value of the adjustment variable, respectively, wherein the difference of the further variable derived from the actual adjustment variable of the regulator and the further variable derived from the model value of the adjustment variable, respectively, is compared to a limit value, wherein a deviation of the model temperature from the actual temperature of the electric machine is detected in the case of an excess of the limit value.

[0055] The control device 7 makes use here of the effect that the temperature, for example the winding temperature, of the electric machine 2 is included in the determination of the adjustment variable by means of the regulator. By comparing the model value of the adjustment variable generated by the model temperature to be checked with the actual adjustment variable, it can be determined whether the model temperature coincides at least substantially with the actual temperature or whether a deviation exceeding the limit value exists between the model value of the adjustment variable and the actual adjustment variable.

[0056] In this way, the model temperature can be checked without measuring the temperature in the electric machine 2. Advantageously, by checking the model temperature, the functional mode of the cooling device 5 can also be checked, since in the event of insufficient cooling of the electric machine 2 by the cooling device 5, for example due to a failure of the coolant pump and / or a blockage of the coolant channels in the cooling device 5 and / or in the electric machine 2, a heating of the electric machine 2 occurs which exceeds the temperature determined by the temperature model on the basis of a correct functional mode of the cooling device 5.

[0057] In Figure 2 an embodiment of the method for checking the model temperature of the electric machine 2 carried out by the control device 7 is shown. In this embodiment, the electric machine 2 is implemented as a permanent-magnet synchronous machine.

[0058] The three-phase stator winding of the permanent-magnet synchronous machine is supplied with current-regulated electrical current by the regulating device 6, wherein the current regulation is implemented as field-oriented control. The three-phase winding voltage for the stator winding of the electric machine 2 is determined by the regulating device 6 on the basis of a predetermined target current. This three-phase winding voltage is described in the field-oriented control range by the voltages U D and U Q .

[0059] In Figure 2 a block diagram 8 of the method carried out by the control device 7 is shown, in which the actual regulating variables U D,t and U Q,t represent the input of a section 9, in which the actual phase voltages U S,t are determined from the regulating variables U D,t and U Q,t in accordance with the following equations:

[0060]

[0061] In addition, in a section 10 of the section 9 shown, a limit value comparison with the limit value U th，1 is carried out in order to avoid a determination of the phase voltages U s，t in the event of very small voltages. This limit value comparison can also be carried out at another location in the section 9, for example after the square root extraction of the regulating variables U D，t and U Q，t and / or before the squaring, wherein the absolute value of the limit value U th，1 can be adapted accordingly.

[0062] In a further section 11 of the block diagram 8, an electric machine model of the electric machine 2, which is implemented as a permanent-magnet synchronous machine, is shown. The input variables of the electric machine model are the resistance R s of the stator winding, the longitudinal component I soll，D of the target current, the transverse component I soll，Q of the target current, the longitudinal inductance L DThe lateral inductance L of motor 2 Q The electrical angular frequency ω and the magnetic flux ψ of the stator parameters in motor 2. Among these, the stator resistance R... s This is a temperature-related parameter of the stator windings of the motor 2 or the motor powered by the regulating device 6. Furthermore, the magnetic flux ψ generated by the permanent magnets of the motor rotor can also be used as a temperature-related parameter.

[0063] The adjustment parameter U is calculated from the input parameters of the motor model. D，t and U Q，t Model value U D，m and U Q，m As shown in block diagram 8, this is achieved through the following formula:

[0064] U D，m =R S ·I soll，D -ω·L Q ·I soll，Q (2) and

[0065] U Q，m =R S ·I soll，Q -ω·L D ·I soll，D +ω·ψ (3).

[0066] The adjustment parameter U is modeled D，m and U Q，m The phase voltage U is calculated using the derived parameters respectively. s，m The model value. This calculation here is similar to the actual phase voltage U in section 9. s，t The calculation is implemented similarly to the limit comparison in section 10, where the determined, derived parameters and the second limit U are also implemented in section 12. th，2 Comparison of limits.

[0067] The actual phase voltage U is formed in box 13. S，t Model value U of phase voltage S，m The difference ΔU s In section 14, the difference ΔU is immediately followed. s The value of the third limit U th，3 In comparison. When the limit U is exceeded. th，3 In this case, forward the corresponding information to box 15.

[0068] In block 15, the number of times the duration of a predetermined time period exceeds a limit is counted in section 14. During this time period, the actual phase voltage U is continuously determined. S，t and the phase voltage U of the model S，m Determine the difference ΔU s And compare it with the limit value Uth，3 A comparison is made. If it is determined within the predetermined period of time that the limit value is exceeded a predetermined number of times, a fault message is generated in block 16 by the control device 7.

[0069] The fault message describes here a deviation of the actual temperature of the electric machine 2 from a model temperature determined by means of a temperature model. For example, in the case of a fault message it is possible for the regulation of the electric machine 2 to be adapted by the regulation device 6. It is also possible for the fault message to be transmitted to a further control device of the motor vehicle 1, which for example outputs a warning to the driver and / or changes further operating parameters of the motor vehicle 1 in order to in particular prevent the electric machine 2 from heating up further and / or to cause a temperature reduction of the electric machine 2.

[0070] In Figure 3 a second embodiment of the method carried out by the control device 7 is shown in a further block diagram 17. In this embodiment, the electric machine 2 is implemented as an asynchronous electric machine. Analogous to the first embodiment, a stator voltage is generated by the regulation device 2 in field-oriented control in accordance with a predetermined target current, the stator voltage being applied to the three-phase stator winding of the asynchronous electric machine. Analogous to the first embodiment, the regulation variables U D，t and U Q，t are determined here in blocks 9 and 10 from the target current I S，t .

[0071] In section 18 of the block diagram 17, an electric machine model is shown which corresponds to the implementation of the electric machine 2 as an asynchronous electric machine. The input variables of the model are here the resistance R s of the stator winding, the longitudinal component I soll，D of the target current, the transverse component I soll，Q of the target current, the electrical frequency ω at which the current circulates in the stator of the electric machine 2, the main magnetic flux ψ H and the leakage inductance of the asynchronous electric machine.

[0072] From these input variables, the model values U D of the regulation variable U D，m and the model values U Q of the regulation variable U Q，m are determined in accordance with the following equations.

[0073] U D，m = R S · I soll，D - ω · L S · I soll，Q (4) and

[0074] U Q，m = R S · I soll，Q - ω · L S · I soll，D + ω · ψH (5).

[0075] As a parameter in the model of the electrical machine which is dependent on the temperature, the temperature-dependent stator winding resistance R s and / or the temperature-dependent magnetic flux ψ H .

[0076] Similar to the embodiment in the first embodiment, the model value U S，m of the phase voltage is determined from the model values of the regulating parameters as a further parameter derived therefrom. S，m The model value U S，t of the phase voltage is determined from the model value U S，m and the actual phase voltage U s . The difference ΔU th,2 is determined similar to the first embodiment. D,m According to the embodiment of the first embodiment, a comparison with the limit value U Q,m is carried out in section 14, and a count of the limit being exceeded and the generation of a fault message are carried out in blocks 15 and 16.

[0077] In addition to the two embodiments shown, further embodiments of the method according to the application are possible, in which the corresponding model values U TH1 and U TH2 are determined according to other rules corresponding to the type of the electrical machine 2. For example, the electrical machine 2 can also be designed as a separately excited synchronous machine. In addition to taking into account the regulating parameters acting on the stator winding of the electrical machine 2, the method can also be used, for example, for supplying the rotor winding of the electrical machine 2, in which as a regulating voltage the voltage falling on the rotor winding is taken into account accordingly, for which model values can be determined by means of the corresponding model.

[0078] The values of the limit values U TH3 , U TH2 and U TH1 may likewise be selected in accordance with the type and / or design of the electrical machine 2, corresponding to the electrical machine 2 used. The input parameters of the model of the electrical machine in relation to the type of machine can be determined, for example, by measurement, and saved as parameters or temperature-dependent characteristic curves or parameter fields in the control device 7.

Claims

1. Method for checking a model temperature of an electric machine (2) determined by means of a temperature model, wherein determining at least one actual regulating variable relating to the electric machine (2) from a target variable by means of a regulator of the electric machine (2); determining a regulating variable model value from the target variable and a model temperature by means of an electric machine model which comprises at least one temperature-dependent parameter; determining a difference between the actual regulating variable of the regulator and the regulating variable model value and / or a difference between a variable derived from the actual regulating variable of the regulator and a further variable which is derived correspondingly from the regulating variable model value; comparing the difference with a limit value and determining whether a deviation between the model temperature and the actual temperature of the electric machine (2) exists, wherein a deviation between the model temperature and the actual temperature is detected in the event that the difference exceeds the limit value.

2. The method of claim 1, wherein, As the target variable, a target current is applied, and / or as the regulating variable, a regulating voltage is applied.

3. The method according to claim 1 or 2, characterized in that, As the regulating variable, a regulating variable is applied which acts on a winding of the electric machine, the winding being a stator winding or a rotor winding of the electric machine (2).

4. The method of claim 3, wherein, As the variable derived from the actual regulating variable of the regulator and / or as the further variable which is derived correspondingly from the regulating variable model value, a phase voltage of the winding is applied.

5. The method according to claim 1 or 2, characterized in that, The regulator is implemented by means of a field-oriented controller, and / or at least one variable corresponding to the regulating variable of the field-oriented controller is determined by means of the electric machine model.

6. The method according to claim 1 or 2, characterized in that, As the temperature model, a model of a thermal network is applied, the thermal network comprising the electric machine (2) and at least one cooling device (5).

7. The method according to claim 1 or 2, characterized in that, As the temperature-dependent parameter of the electric machine model, a winding resistance and / or a temperature-dependent magnetic flux is applied.

8. The method of claim 1 or 2, wherein, The difference is determined only when the actual regulating variable and / or the regulating variable model value exceeds the limit value.

9. The method of claim 1 or 2, wherein, The actual regulating variable of the regulator, the regulating variable model value from the electric machine model, and the difference are determined continuously, during operation of the electric machine (2), at different times, wherein a fault message is generated if a predetermined number of the determined differences each exceed the limit value within a predetermined time interval, the fault message describing a deviation between the model temperature and the actual temperature of the electric machine (2).

10. The method of claim 1 or 2, wherein, As the electric machine (2), a permanent-magnet synchronous electric machine, a separately excited synchronous electric machine, or an asynchronous electric machine is applied.

11. Motor vehicle comprising at least one electric machine (2), a control device (7) and a regulator by means of which at least one actual regulating variable relating to the electric machine (2) can be determined from a target variable, wherein the control device (7) is used to implement a method according to one of claims 1 to 10.

12. Motor vehicle according to claim 11, characterized in that The electric machine (2) is a drive electric machine of the motor vehicle (1); and / or the electric machine (2) is coupled to a cooling device (5) of the motor vehicle (1), the cooling device being a coolant circuit.

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