METHOD FOR CHECKING A MODEL TEMPERATURE OF AN ELECTRICAL MACHINE ASCERTAINED BY MEANS OF A TEMPERATURE MODEL, AND MOTOR VEHICLE

Abstract

A method for checking a model temperature of an electrical machine ascertained by a temperature model. At least one manipulated variable relating to the electrical machine is specified by a regulation of the electrical machine as a function of a setpoint variable. A model value of the manipulated variable is ascertained as a function of the manipulated variable and the model temperature from a machine model comprising at least one temperature-dependent parameter. A difference between the actual manipulated variable of the regulation and the model value of the manipulated variable and/or a difference between a variable derived from the actual manipulated variable of the regulation and a corresponding further variable derived from the model value of the manipulated variable is ascertained. The difference is compared to a limiting value and, if the limiting value is exceeded, a deviation of the model temperature from an actual temperature of the electrical machine is detected.

Claims

1. A method for checking a model temperature of an electrical machine ascertained by a temperature model, comprising: at least one manipulated variable relating to the electrical machine is specified by a regulation of the electrical machine as a function of a setpoint variable, wherein a model value of the manipulated variable is ascertained as a function of the manipulated variable and the model temperature from a machine model comprising at least one temperature-dependent parameter, wherein a difference between the actual manipulated variable of the regulation and the model value of the manipulated variable and/or a difference between a variable derived from the actual manipulated variable of the regulation and a corresponding further variable derived from the model value of the manipulated variable is ascertained, wherein the difference is compared to a limiting value and, if the limiting value is exceeded, a deviation of the model temperature from an actual temperature of the electrical machine is detected.

2. The method as claimed in claim 1, wherein a setpoint current is used as the setpoint variable and/or in that a control voltage is used as the manipulated variable.

3. The method as claimed in claim 1, wherein a manipulated variable is used which acts on a winding of the electrical machine, in particular a stator winding or a rotor winding of the electrical machine.

4. The method as claimed in claim 3, wherein a phase voltage of the winding is used as a variable derived from the actual manipulated variable of the regulation and/or as a corresponding further variable derived from the model value of the manipulated variable.

5. The method as claimed in claim 1, wherein the regulation takes place by means of a field-oriented regulation and/or in that at least one variable corresponding to the manipulated variable of the field-oriented regulation is ascertained by means of the machine model.

6. The method as claimed in claim 1, wherein a model of a thermal network, which comprises the electrical machine and at least one cooling device, is used as the temperature model.

7. The method as claimed in claim 1, a winding resistance and/or a temperature-dependent magnetic flux is used as the temperature-dependent parameter of the machine model.

8. The method as claimed in claim 1, wherein the difference is only ascertained if the manipulated variable and/or the model value of the manipulated variable exceed a limiting value.

9. The method as claimed in claim 1, wherein the manipulated variable of the regulation, the model value of the manipulated variable from the machine model, and the difference are continuously ascertained during the operation of the electrical machine at different times, wherein an item of error information which describes a deviation of the model temperature from an actual temperature of the electrical machine is generated when a predefined number of ascertained differences each exceed the limiting value within a predefined time interval.

10. The method as claimed in claim 1, wherein a permanently excited synchronous machine, a separately excited synchronous machine, or an asynchronous machine is used as the electrical machine.

11. A motor vehicle comprising: at least one electrical machine, a control unit, and a regulation, by which a manipulated variable relating to the electrical machine is ascertainable as a function of a setpoint variable, wherein the control unit is configured to carry out a method as claimed in claim 1.

12. The motor vehicle as claimed in claim 11, wherein the electrical machine is a traction electric motor of the motor vehicle and/or in that the electrical machine is coupled to a cooling device, in particular a coolant circuit, of the motor vehicle.

13. The method as claimed in claim 2, wherein a manipulated variable is used which acts on a winding of the electrical machine, in particular a stator winding or a rotor winding of the electrical machine.

14. The method as claimed in claim 2, wherein the regulation takes place by means of a field oriented regulation and/or in that at least one variable corresponding to the manipulated variable of the field-oriented regulation is ascertained by means of the machine model.

15. The method as claimed in claim 3, wherein the regulation takes place by means of a field-oriented regulation and/or in that at least one variable corresponding to the manipulated variable of the field-oriented regulation is ascertained by means of the machine model.

16. The method as claimed in claim 4, wherein the regulation takes place by means of a field-oriented regulation and/or in that at least one variable corresponding to the manipulated variable of the field-oriented regulation is ascertained by means of the machine model.

17. The method as claimed in claim 2, wherein a model of a thermal network, which comprises the electrical machine and at least one cooling device, is used as the temperature model.

18. The method as claimed in claim 3, wherein a model of a thermal network, which comprises the electrical machine and at least one cooling device, is used as the temperature model.

19. The method as claimed in claim 4, wherein a model of a thermal network, which comprises the electrical machine and at least one cooling device, is used as the temperature model.

20. The method as claimed in claim 5, wherein a model of a thermal network, which comprises the electrical machine and at least one cooling device, is used as the temperature model.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0041] Further advantages and details of the present invention result from the exemplary embodiments described below and on the basis of the drawings. In the figures:

[0042] FIG. 1 shows a schematic illustration of a motor vehicle according to the invention,

[0043] FIG. 2 shows a first block diagram to illustrate a first exemplary embodiment of a method according to the invention, and

[0044] FIG. 3 shows a second block diagram to illustrate a second exemplary embodiment of a method according to the invention.

DETAILED DESCRIPTION

[0045] FIG. 1 shows an exemplary embodiment of a motor vehicle 1. The motor vehicle 1 comprises an electric machine 2 as a traction electric motor. The motor vehicle 1 furthermore comprises an electrical energy storage device 3, which is connected to the electrical machine 2 via power electronics 4. The power electronics 4 can convert a direct current taken from the energy storage device 3 into an alternating current for energizing the electrical machine 2. The energy storage device 3 can be designed as a traction battery of the motor vehicle 1, for example.

[0046] The power electronics 4 can generate an alternating current for energizing, for example, a stator winding of the electrical machine 2. Due to the stator current generated by the power electronics 4 in the electrical machine 2, the electrical machine 2 can heat up during operation. The electrical machine 2 is therefore coupled to a cooling device 5 of the motor vehicle 1, wherein the heat generated in the electrical machine 2 can be dissipated via the cooling device 5. The cooling device 5 is only shown schematically in the present case and, in addition to the electrical machine 2, can also in particular cool further components of the motor vehicle 1, for example the energy storage device 3 and/or the power electronics 4.

[0047] The motor vehicle 1 furthermore comprises a regulating unit 6, which is configured to regulate the electrical machine 2. The regulating unit 6 generates a manipulated variable relating to the electrical machine 2 as a function of a predefined setpoint variable. For example, the regulating unit 6 can generate a control voltage as a manipulated variable as a function of a setpoint current. The control voltage can be, for example, a three-phase AC voltage, so that a three-phase stator winding of the electrical machine 2 can be energized. The setpoint current can be ascertained, for example, by a motor control device (not shown) of the motor vehicle 2 and transmitted to the regulating unit 6.

[0048] The motor vehicle 1 furthermore comprises a control unit 7 which determines a model temperature of the electrical machine 2 by means of a temperature model of the electrical machine 2 stored in the control unit 7. A model of a thermal network, which comprises the electrical machine 2 and the cooling device 5, can be used as the temperature model.

[0049] The temperature model makes it possible to model a temperature of the electrical machine 2 as a function of various operating parameters of the motor vehicle 1, in particular operating parameters of the electrical machine 2, the energy storage device 3, and/or the power electronics 4. The temperature of the electrical machine 2 can be, for example, a winding temperature of the stator winding of the electrical machine 2 to which a control voltage is applied by the power electronics 4 as specified by the regulating unit 6.

[0050] To ascertain the model temperature, the temperature model can also take into consideration operating parameters of the cooling system 5 in addition to operating parameters of the electrical machine 2, such as a stator current, a current in an excitation winding, a torque of the electrical machine, and/or a speed of the electrical machine. Furthermore, the operating time of the electrical machine 2 or the power converted in each case in the electrical machine 2 during the operating time can also be taken into consideration, since these have a significant influence on the heat generation in the electrical machine 2 and thus also on its temperature. By describing the thermal network, which comprises at least the electrical machine 2 and the cooling device 5, the heat generation in the electrical machine and the heat flows to and from the electrical machine 2, in particular into the cooling system 5, can be calculated and used to ascertain the model temperature.

[0051] For this purpose, the temperature model can comprise one or more computing rules, which can be stored in the control unit 7, for example. The operating parameters of the electrical machine 2, the cooling system 5, and/or further components such as the energy storage device 3 or the power electronics 4 required to calculate the model temperature can be transmitted to the control unit 7 by the respective components and/or by control devices connected to the components. In order to check the correctness of the model temperature ascertained by means of the temperature model, the control unit 7 is also configured to carry out a method for checking the model temperature of the electrical machine 2 ascertained by means of the temperature model.

[0052] For this purpose, the control device 7 ascertains a model value of the manipulated variable using a machine model comprising at least one temperature-dependent parameter as a function of the setpoint variable of the regulation implemented by the regulating unit 6 and the model temperature ascertained from the temperature model. The respective present setpoint value which is used by the control device 6 can for this purpose be transmitted from the regulating unit 6 or the motor control device of the motor vehicle 2 to the control unit 7. Furthermore, the regulating unit 6 transmits the manipulated variable generated in each case as a function of the setpoint variable to the control unit 7. It is possible for the regulating unit 6 and the control unit 7 to be implemented in a common control device.

[0053] Furthermore, the control unit 7 is configured to ascertain a difference between the actual manipulated variable of the regulation and the model value of the manipulated variable, wherein the difference is compared to a limiting value. When the limiting value is exceeded, the control device 7 detects a deviation of the model temperature from the actual temperature of the electrical machine 2.

[0054] Additionally or alternatively thereto, the control device 7 can be configured to determine a derived, further variable from the actual manipulated variable and the model value of the manipulated variable, wherein a difference between the further variable derived from the actual manipulated variable of the regulation and the corresponding further variable derived from the model value of the manipulated variable is compared to a limiting value, wherein a deviation of the model temperature from an actual temperature of the electrical machine is detected when the limiting value is exceeded.

[0055] The control device 7 uses the effect that, due to the regulation, a temperature of the electrical machine 2, for example a winding temperature, is included in the ascertainment of the manipulated variable. By comparing the model value of the manipulated variable, which results from the model temperature to be checked, to the actual manipulated variable, it can be ascertained whether the model temperature at least substantially corresponds to the actual temperature or whether there is a deviation between the model value of the manipulated variable and the actual manipulated variable exceeding the limiting value.

[0056] In this way, it is possible to check the model temperature without measuring the temperature in the electrical machine 2. The functioning of the cooling device 5 can advantageously also be checked by checking the model temperature, since in the case of inadequate cooling of the electrical machine 2 by the cooling device 5, for example as a result of a failure of a coolant pump and/or clogging of a coolant channel in the cooling device 5 and/or in the electrical machine 2, heating occurs in the electrical machine 2 which exceeds the temperature ascertained from the temperature model based on the correct functioning of the cooling circuit 5.

[0057] FIG. 2 shows an exemplary embodiment of the method carried out by the control unit 7 for checking the model temperature of the electrical machine 2. In this exemplary embodiment, the electrical machine 2 is designed as a permanently excited synchronous machine.

[0058] A three-phase stator winding of the permanently excited synchronous machine is energized by the regulating unit 6 within the scope of a current regulation, wherein the current regulation taking place as a field-oriented regulation. The regulating unit 6 ascertains a three-phase winding voltage for the stator winding of the electrical machine 2 as a function of a predetermined setpoint current.

[0059] This is described in the context of the field-oriented regulation by the voltages U.sub.D and U.sub.Q.

[0060] In the block diagram 8 of the method carried out by the control unit 7 shown in FIG. 2, the actual manipulated variables U.sub.D,t and U.sub.Q,t represent the input of section 9 in which an actual phase voltage U.sub.S,t is ascertained from the manipulated variables U.sub.D,t and U.sub.Q,t according to

U.sub.S,t=√{square root over ((U.sub.D,t).sup.2+(U.sub.Q,t).sup.2)}  (1)

[0061] Furthermore, in the illustrated part 10 of section 9, a limiting value comparison to a first limiting value U.sub.th,1 is carried out in order to avoid the ascertainment of the phase voltage U.sub.S,t at very low voltages. This limiting value comparison can also be carried out at another point in section 9, for example after calculating the root and/or before squaring of the manipulated variables U.sub.D,t and U.sub.Q,t, wherein the absolute value of the limiting value U.sub.th,1, can be adjusted accordingly.

[0062] In a further section 11 of the block diagram 8, a machine model of the electrical machine 2 designed as a permanently excited synchronous machine is shown. Input variables of the machine model are represented by the resistance of the stator winding R.sub.s, the longitudinal component of the setpoint current I.sub.soll,D, the transverse component of the setpoint current I.sub.soll,Q, the longitudinal inductance L.sub.D of the electrical machine 2, the transverse inductance L.sub.Q of the electrical machine 2, the electrical circular frequency ω of the stator variables in the electrical machine 2, and the magnetic flux Ψ in the electrical machine. The stator resistance R.sub.S represents a temperature-dependent parameter of the electrical machine 2 or of the stator winding energized via the regulating unit 6. The magnetic flux Ψ, which is generated by the permanent magnets of a rotor of the electrical machine, can also be used as a temperature-dependent parameter.

[0063] Model values U.sub.D,m and U.sub.Q,m of the manipulated variables U.sub.D,t and U.sub.Q,t are calculated from the input variables of the machine model. As shown in block diagram 8, this is done via the formulas

U.sub.D,m=R.sub.S.Math.I.sub.soll,D−ω.Math.L.sub.Q.Math.I.sub.soll,Q  (2)

and

U.sub.Q,m=R.sub.S.Math.I.sub.soll,Q−ω.Math.L.sub.D.Math.I.sub.soll,D+ω.Math.ψ  (3).

[0064] A model value of the phase voltage U.sub.S,m is calculated from each of the modeled manipulated variables U.sub.D,m and U.sub.Q,m as a derived variable. The calculation is carried out analogously to the calculation of the actual phase voltage U.sub.S,t in section 9. Analogous to the limiting value comparison in section 10, a limiting value comparison of the ascertained, derived variable to a second limiting value U.sub.th,2 is also carried out in section 12.

[0065] In block 13, a difference ΔU.sub.s is formed from the actual phase voltage U.sub.S,t and the model value of the phase voltage U.sub.S,m. In section 14, the absolute value of the difference ΔU.sub.s is then compared to a third limiting value U.sub.th,3. If the limiting value U.sub.th,3 is exceeded, corresponding information is relayed to block 15.

[0066] In block 15, the frequency with which the limiting values are exceeded in section 14 is counted for the duration of a predetermined time period. During this time period, the actual phase voltage U.sub.S,t and the modeled phase voltage U.sub.S,m are continuously ascertained, the difference ΔU.sub.s is determined and compared to the limiting value U.sub.th,3. If a predetermined frequency of exceeding the limiting values has been determined within the predetermined time period, error information is generated by the control unit 7 in block 16.

[0067] The error information describes a deviation of the actual temperature of the electrical machine 2 from the model temperature ascertained by means of the temperature model. For example, if the error information is present, the regulation of the electrical machine 2 can be adapted by the regulating unit 6. It is also possible for the error information to be transmitted to further control units of the motor vehicle 1 which, for example, output a warning to a driver and/or change further operating parameters of the motor vehicle 1, in particular in order to prevent progressive heating of the electrical machine 2 and/or to effectuate a decrease in the temperature of the electrical machine 2.

[0068] In FIG. 3, a second exemplary embodiment of a method carried out by the control device 7 is shown in a further block diagram 17. In this exemplary embodiment, the electrical machine 2 is designed as an asynchronous machine. Analogously to the first exemplary embodiment, the regulating unit 2 generates a stator voltage in a field-oriented regulation as a function of a predefined setpoint current, which is applied to a three-phase stator winding of the asynchronous machine. Analogously to the first exemplary embodiment, the actual phase voltage U.sub.S,t is ascertained in blocks 9 and 10 from the manipulated variables U.sub.D,t and U.sub.Q,t ascertained by the regulating unit 6.

[0069] In a section 18 of the block diagram 17, a machine model corresponding to the design of the electrical machine 2 as an asynchronous machine is shown. The input variables of the model represent the resistance of the stator winding R.sub.S, the longitudinal component of the setpoint current I.sub.soll,D, the transverse component of the setpoint current I.sub.soll,Q, the electrical frequency ω of the circulation of the currents in the stator of the electrical machine 2, the main flux Ψ.sub.H as well as the leakage inductance L.sub.S of the asynchronous machine.

[0070] From these input variables, according to the formulas

U.sub.D,m=R.sub.s.Math.I.sub.soll,D−ω.Math.L.sub.S.Math.I.sub.soll,Q  (4)

and

U.sub.Q,m=R.sub.S.Math.I.sub.soll,Q−ω.Math.L.sub.S.Math.I.sub.soll,D+ω.Math.ψ.sub.H  (5)

[0071] a model value U.sub.D,m of the manipulated variable U.sub.D and a model value U.sub.Q, m of the manipulated variable U.sub.Q are ascertained. The temperature-dependent stator winding R.sub.S and/or the temperature-dependent magnetic flux Ψ.sub.H are used as temperature-dependent parameters in the machine model.

[0072] Analogously to the explanations in the first exemplary embodiment, a model value of the phase voltage U.sub.S,m is ascertained from these model values of the manipulated variables as a derived, further variable. The difference ΔU.sub.s is ascertained from the model value U.sub.S,m of the phase voltage and from the actual phase voltage U.sub.S,t analogously to the first exemplary embodiment. Corresponding to the explanations of the first exemplary embodiment, a limiting value comparison to a second limiting value U.sub.th,2 then takes place in section 14 and, in blocks 15 and 16, the counting of times the limiting value is exceeded and the generation of the error information.

[0073] In addition to the two exemplary embodiments shown, further exemplary embodiments of the method according to the invention are also possible in which corresponding model values U.sub.D,m and U.sub.Q,m are ascertained in accordance with other rules that correspond to the model of the electrical machine 2. The electrical machine can also be designed, for example, as a separately excited synchronous machine. In addition to considering a manipulated variable acting on a stator winding of the electrical machine 2, the method can also be used, for example, when energizing a rotor winding of an electrical machine 2, wherein the voltage drop across the rotor winding is accordingly considered as the control voltage, for which a model value is ascertainable by means of a corresponding model.

[0074] The values for the limiting values U.sub.TH1, U.sub.TH2, and U.sub.TH3 used in each case can also be selected in dependence on the type and/or the design of the electrical machine 2 and can be adapted accordingly to the electrical machine 2 used. The input variables of the machine models dependent on the machine type can, for example, each be determined by measurement and stored in the control unit 7 as parameters or temperature-dependent characteristic curves or parameter fields.