METHOD AND DEVICE FOR DETERMINING A ROTOR TEMPERATURE VALUE FOR AN ELECTRIC MOTOR

Abstract

Disclosed is a method for determining a rotor temperature value T.sub.Rot for an electric machine, such as an electric motor. In one example, the method includes calculating a support value P.sub.cu2_Trot using a rotor temperature value T.sub.rot that is determined with a temperature model and a motor current value I.sub.sdq. An auxiliary value P.sub.cu2_Ref can be determined using a motor torque T.sub.rq and a motor slip value ω.sub.slip. The support value P.sub.cu2_Trot can be linked with the auxiliary value P.sub.cu2_Ref in order to obtain a corrected rotor temperature value Delta.sub.Trot. Furthermore, the temperature model can be modified using the corrected rotor temperature value Delta.sub.Trot in order to obtain a corrected temperature model. Finally, the rotor temperature value T.sub.Rot can be determined using the corrected temperature model.

Claims

1. A method (300) for determining a rotor temperature value (T.sub.rot) for an electric machine (105), wherein the method (300) comprises: calculating (305) a support value (P.sub.cu2_Trot) using a rotor temperature value (T.sub.rot) determined with a temperature model (120), and a motor current value (I.sub.sdq); determining (310) an auxiliary value (P.sub.cu2_Ref) using a motor torque (T.sub.rq) and a motor slip value (ω.sub.slip); linking (315) of the support value (P.sub.cu2_Trot) with the auxiliary value (P.sub.cu2_Ref) in order to obtain a corrected temperature value (Delta.sub.Trot); modifying (320) the temperature model (120), using the corrected temperature value (Delta.sub.Trot) in order to obtain a corrected temperature model (120); and determining (325) the rotor temperature value (T.sub.rot) using the corrected temperature model (120).

2. The method according to claim 1, wherein in the linking step (315) the support value (P.sub.cu2_Trot) is subtracted from the auxiliary value (P.sub.cu2_Ref) in order to obtain an error value (e).

3. The method according to claim 2, wherein in the linking step the corrected rotor temperature value (Delta.sub.Trot) is determined using a regulator (K), which uses the error value (e) as the input parameter.

4. The method according to claim 1, wherein in the determination step (310) the torque is calculated using a scaling factor (p.sub.z) and/or a magnetic flux value (ψ) and a current (I), in particular by means of the formula
T.sub.rq= 3/2(p.sub.z).Math.(ψ.sub.sαI.sub.sβ−ψ.sub.sβI.sub.sα), wherein ψ.sub.sα represents a magnetic flux magnitude in the stator in the direction α, I.sub.sβ represents a current in the stator in the direction β, and wherein ψ.sub.sβ represents a magnetic flux magnitude in the stator in the direction β, and I.sub.sα represents a current in the stator in the direction α.

5. The method according to claim 1, wherein in the calculation step (305) the support value (P.sub.cu2_Trot) is calculated using a rotor resistance (R.sub.r) and a first rotor current value (I.sub.rd) and a second rotor current value (I.sub.rq), in particular using the formula P.sub.cu2_Trot= 3/2.Math.R.sup.r.Math.(I.sub.rd.sup.2+I.sub.rq.sup.2).

6. The method according to claim 5, wherein in the calculation step (305) the rotor resistance is calculated using a basic electrical resistance value in the rotor (R.sub.r20) and an adaptation factor, wherein the adaptation factor is calculated using a scaling value (α.sub.r) and the rotor temperature value (T.sub.rot), and wherein the rotor resistance is calculated using the formula R.sub.r=R.sub.r20.Math.(1+α.sub.r(T.sub.rot−20)).

7. The method according to claim 5, wherein in the calculation step (305) the support value (P.sub.cu2_Trot) is calculated using a main inductance (L.sub.m) and a rotor inductance (L.sub.r), wherein a ratio of the main inductance to the rotor inductance is calculated as a function of characteristic curves (400) and/or currents (I.sub.sd) and (I.sub.sq) in the stator.

8. The method according to claim 5, wherein in the calculation step (305) the second rotor current (I.sub.rq) is calculated using the main inductance (L.sub.m) and the rotor inductance (L.sub.r) and a current in the stator (I.sub.sq), using the formula I.sub.rq=−(L.sub.m/L.sub.r).Math.I.sub.sq.

9. The method according to claim 5, wherein in the calculation step (305) the first rotor current (I.sub.rd) is calculated using the rotor inductance (L.sub.r) and a magnetic flux (ψ.sub.rd) in the rotor and the main inductance (L.sub.m) and a current (I.sub.sd) in the stator, using the formula I.sub.rd=(1/L.sub.r).Math.(ψ.sub.rd−L.sub.mI.sub.sd).

10. The method according to claim 1, wherein in the determination step (310) the auxiliary value (P.sub.cu2_Ref) is determined by multiplying the motor torque (T.sub.rq) by the motor slip ω.sub.slip.

11. A device configured to carry out and/or control the steps (305, 310, 315, 320, 325) of the method (300) according to claim 1.

12. (canceled)

13. (canceled)

14. The device according to claim 11, comprising computer-executable code that, when executed by the device, performs the method (300) according to claim 1.

15. A non-transitory computer-readable medium comprising program instructions that are executable by a processor to determine a rotor temperature value (T.sub.rot) of an electric machine (105), the program instructions comprising: calculating (305) a support value (P.sub.cu2_Trot) using a rotor temperature value (T.sub.rot) determined with a temperature model (120), and a motor current value (I.sub.sdq); determining (310) an auxiliary value (P.sub.cu2_Ref) using a motor torque (T.sub.rq) and a motor slip value (ω.sub.slip); linking (315) the support value (P.sub.cu2_Trot) with the auxiliary value (P.sub.cu2_Ref) in order to obtain a corrected temperature value (Delta.sub.Trot); modifying (320) the temperature model (120), using the corrected temperature value (Delta.sub.Trot) in order to obtain a corrected temperature model (120); and determining (325) the rotor temperature value (T.sub.rot) using the corrected temperature model (120).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] An example of the invention is explained in greater detail with reference to the attached drawings, which show:

[0022] FIG. 1: A schematic representation of a vehicle with an electric machine, for which a variant described herein, of an example embodiment of a method for determining a rotor temperature value, can be used;

[0023] FIG. 2: A schematic representation of an example embodiment of a device for controlling a method for determining a rotor temperature for an electric machine;

[0024] FIG. 3: A flow chart of an example embodiment of a method for determining a rotor temperature for an electric machine;

[0025] FIG. 4: A schematic representation of an example embodiment of a saturation behavior in the main inductance L.sub.m and rotor inductance L.sub.r of the electric machine, with the help of characteristic curves;

[0026] FIG. 5: A schematic representation of a measured rotor temperature and an estimated rotor temperature;

[0027] FIG. 6: A schematic representation of a measured rotor temperature and an estimated rotor temperature;

[0028] FIG. 7: A schematic representation of a measured rotor temperature and an estimated rotor temperature; and

[0029] FIG. 8: A schematic representation of a measured rotor temperature and an estimated rotor temperature.

DETAILED DESCRIPTION

[0030] In the following description of preferred example embodiments of the present invention, the elements shown in the various figures which function in similar ways are denoted by the same or similar indexes, so there is no need for repeated descriptions of the said elements.

[0031] FIG. 1 shows a schematic representation of a vehicle 100 with an electric machine 105, according to an embodiment. Only as an example, the vehicle 100 is a truck with overall weight 12 tonnes, which has as its drive motor an electric machine, in this case for example an asynchronous motor. In this example embodiment, the asynchronous motor comprises a rotor 110 and a stator 115, whose temperatures can be calculated by means of a temperature model 120 of a device 125. This calculated temperature can then, for example, be used for further control tasks of the electric machine 105, such as in order to avoid overheating of the electric machine 105 during operation, which however, is not the central focus of the approach presented here and will not therefore be discussed further at this time. In this example embodiment, the solution of individual differential equations of the temperature model 120 has the general form T(t)=ΔP.sub.v.Math.R.sub.w (1−e.sup.(t/RwCw))+T0. In this, solely as an example, T0 represents the initial value of the temperature to be estimated.

[0032] Simple thermal networks have inherent correction properties by virtue of thermal compensation processes whose result is that any brief temperature falsifications diminish. The duration of such compensation processes is in the range of the thermal time constant T.sub.w=R.sub.w.Math.C.sub.w. Thus, such compensation processes are fairly slow. A simulated driving cycle with a 12-tonne truck on a hilly stretch shows that the rotor temperature limit is reached within a few minutes after a cold start. Specific operating boundary conditions, such as variations of the ambient and the coolant temperature, varying loads and driving profiles, or frequent terminal status changes in the vehicle, demand rapid correction preferably within a few seconds in order to be able to ensure component protection and availability.

[0033] FIG. 2 shows a schematic representation of an example embodiment of a device 125 for controlling a method for determining a rotor temperature value for an electric machine as described in the preceding FIG. 1. The device 125 represented in this case corresponds or is similar to the device described in the preceding FIG. 1. In this example embodiment, the device 125 is designed to control a method as described in the next FIG. 3. For that purpose, the device 125 comprises a temperature model 120, which in the context of use in an asynchronous motor can also be called an ASM temperature model. By means of the temperature model 120, using known values such as the coolant temperature T.sub.cooling, the stator temperature T.sub.stat and the power loss Pv of the electric machine, a rotor temperature T.sub.rot can be calculated. For the precise calculation of a rotor temperature value T.sub.rot in the event of a change of operating boundary conditions such as ambient temperature, coolant temperature, varying loads and driving profiles, or frequent terminal status changes, or to correct the calculated temperature value within a few seconds, in this example embodiment the device 125 comprises a rotor temperature correction module 200. The rotor temperature correction module 200 comprises a calculation unit 202 for calculating a support value P.sub.cu2 using the rotor temperature T.sub.rot and a motor current value I.sub.sdq. In addition, the rotor temperature correction module 200 comprises a determination unit 204 for determining an auxiliary value P.sub.cu2_ref using a motor torque T.sub.rq and a motor slip value ψ.sub.slip. Both the support value P.sub.cu2 and the auxiliary value P.sub.cu2_ref indicate a calculated rotor copper loss or a heat loss performance of the rotor, wherein the auxiliary value P.sub.cu2_ref represents a reference value whose reference calculations are based on the electric machine. The two values P.sub.cu2 and P.sub.cu2_ref can be linked with one another in a linking unit 205 of the rotor temperature correction module 200, so that, only as an example, the support value P.sub.cu2 can be subtracted from the auxiliary value P.sub.cu2_ref. In this example embodiment, an error value e can be determined from the difference between the two values. This error value e can be attributed to a falsification of the estimated temperature T.sub.rot and can be corrected with the help of a simple proportional regulator. Owing to the integrating behavior of the route, for example no PI regulator is needed in this case. In this example embodiment, the regulator K can be connected “promptly” directly after a terminal status change and after an adjustable time can be set more slowly or switched off. The rotor temperature correction module 200 also comprises a modification unit 210, which is designed, using the emitted temperature correction value Delta.sub.Trot, to modify or correct the temperature model 120.

[0034] By means of a determination unit 215, using the corrected temperature model 120, in turn the rotor temperature value T.sub.rot can be determined by the device 125.

[0035] FIG. 3 shows a flow chart of an example embodiment of a method 300 for determining a rotor temperature value for an electric machine, as described in the preceding FIG. 1. The method 300 can be controlled or carried out by a device as described in the preceding FIG. 2. Correspondingly, the method 300 comprises a step 305 of calculating a support value using a rotor temperature value determined with a temperature model and a motor current value. Only as an example, in the calculation step 305 the calculation of the support value takes place using a rotor resistance R.sub.r, a first rotor current value Ira, and a second rotor current value I.sub.rq. In this example embodiment the rotor copper losses are calculated as a function of the rotor temperature by the formula P.sub.cu2_Trot= 3/2.Math.R.sub.r(I.sub.rd.sup.2+I.sub.rq.sup.2). Only optionally, the rotor resistance R.sub.r is calculated using a basic electrical resistance value in the rotor R.sub.r20 and an adaptation factor. In this example embodiment the adaptation factor is calculated using a scaling value α.sub.r and the rotor temperature value T.sub.rot using the formula R.sub.r=R.sub.r20(1+α.sub.r(T.sub.rot−20). Thus, for example, the rotor resistance is calculated with the help of the estimated rotor temperature. Furthermore, only as an example, the rotor currents are calculated using the main inductance L.sub.m and the rotor inductance L.sub.r. For this, only as an example, the second rotor current I.sub.rq is calculated using the main inductance L.sub.m and the rotor inductance L.sub.r and a current in the stator I.sub.sq, using the formula I.sub.rq=−(L.sub.m/L.sub.r)I.sub.sq. In this example embodiment the first rotor current I.sub.rd is calculated using the rotor inductance L.sub.r and a magnetic flux magnitude ψ.sub.rd in the rotor and the main inductance L.sub.m and a current I.sub.sd in the stator, by means of the formula I.sub.rd=1/L.sub.r(ψ.sub.rd−L.sub.mI.sub.sd).

[0036] In addition, the method 300 comprises a step 310 of determining an auxiliary value using a motor torque and a motor slip value. In this determining step 310, only as an example the auxiliary value is determined by multiplying the torque by the motor slip angle. In other words, in this example embodiment the rotor copper losses are determined on the basis of the torque and the slip, using the formula P.sub.cu2_Ref=T.sub.rq.Math.ω.sub.slip. Here, for example, the torque is optionally calculated using a scaling factor p.sub.z and a magnetic flux w and a current I. For that purpose, in this example embodiment the formula T.sub.rq= 3/2(p.sub.z).Math.(ψsαI.sub.sβ−ψ.sub.sβI.sub.sα) is used, wherein, only as an example, ψ.sub.sα represents a magnetic flux magnitude in the stator in the direction α and I.sub.sβ represents a current in the stator in the direction β and wherein ψ.sub.sβ represents a magnetic flux magnitude in the stator in the direction β and I.sub.sα represents a current in the stator in the direction α.

[0037] Following the calculation step 305 and the determination step 310, the method 300 comprises a step 315 of linking the support value with the auxiliary value, in order to obtain a rotor temperature correction value. In this example embodiment, only as an example in the linking step 315 the support value is subtracted from the auxiliary value in order to obtain an error value. In other words, with the calculated rotor losses P.sub.cu2_Ref=T.sub.rq.Math.ω.sub.slip and P.sub.cu2_Trot= 3/2.Math.R.sub.r20(1+α.sub.r(T.sub.rot−20).Math.(L.sub.m/L.sub.r).sup.2.Math.I.sub.rq.sup.2 an error e=P.sub.cu2_Ref−P.sub.cu2_Trot is calculated. In this example embodiment, that error is attributed to a falsification of the estimated temperature T.sub.rot and is corrected with the help of a simple proportional regulator.

[0038] There follows a step 320 of varying the temperature model using the corrected temperature value in order to obtain a corrected temperature model, and a step 325 of determining the rotor temperature value using the corrected temperature model.

[0039] In other words, an important aspect for applying the method 300 is to use various calculation methods for rotor copper losses in order to detect errors. A reference calculation based on the voltage model of the electric machine. A second calculation of P.sub.cu2_Trotor based on the estimated rotor temperature T.sub.rot. In a final step, the difference between the two calculations is corrected in the thermal model by means of a regulator K.

[0040] FIG. 4 shows a schematic representation of an example embodiment of the saturation behavior in the main inductance L.sub.m and the rotor inductance L.sub.r of the electric machine with the help of characteristic curves 400. The saturation behavior of the main inductance L.sub.m and the rotor inductance L.sub.r, shown here with the help of characteristic curves as a function of I.sub.sd and I.sub.sq, can be taken into account in step 305 of the method described in the preceding FIG. 3. In this example embodiment the support value is calculated using the main inductance L.sub.m and the rotor inductance L.sub.r, wherein solely as an example a ratio of the main inductance to the rotor inductance is calculated as a function of characteristic curves and currents I.sub.sd and I.sub.sq in the stator. In that way the second calculation of the rotor copper losses is simplified to:

P.sub.cu2_Trot= 3/2.Math.R.sub.r20(1+α.sub.r(T.sub.rot−20)).Math.(L.sub.m/L.sub.r).sup.2.Math.I.sub.rq.sup.2.

[0041] FIG. 5 shows a schematic representation of a measured rotor temperature and an estimated rotor temperature. In the representation shown here, no method was used for determining a rotor temperature value, such as described in the earlier FIG. 3. Correspondingly, a first rotor temperature curve 505, which corresponds to the measured rotor temperature, deviates from a second rotor temperature 510, which corresponds to the estimated rotor temperature.

[0042] FIG. 6 shows a schematic representation of a measured rotor temperature and an estimated rotor temperature. In the representation shown here, the method for determining a rotor temperature value was used, such as described in the earlier FIG. 3. Correspondingly, the deviation of the first rotor temperature curve 505 from the second rotor temperature curve 510 is only minimal.

[0043] FIG. 7 shows a schematic representation of a measured rotor temperature and an estimated rotor temperature. In the representation shown in this case, no method was used for determining a rotor temperature value, such as described in the earlier FIG. 3. Correspondingly, the first rotor temperature curve 505 deviates from the second rotor temperature curve 510.

[0044] FIG. 8 shows a schematic representation of a measured rotor temperature and an estimated rotor temperature. In the representation shown here the method for determining a rotor temperature value was used, such as described in the earlier FIG. 3. Correspondingly, the deviation of the first rotor temperature curve 505 from the second rotor temperature curve 510 is only minimal.

[0045] The example embodiments described and illustrated by the figures are chosen only as examples. Different example embodiments can be combined with one another completely or in relation to individual features. Moreover, one example embodiment can be supplemented by features adopted from another example embodiment.

[0046] Furthermore, method steps according to the invention can be repeated and carried out in a sequence other than that described.

[0047] If an example embodiment contains an “and/or” link between a first feature and a second feature, this can be understood to mean that one form the example embodiment comprises both the first feature and the second feature, whereas another form comprises either only the first feature or only the second feature.

INDEXES

[0048] 100 Vehicle [0049] 105 Electric machine [0050] 110 Rotor [0051] 115 Stator [0052] 120 Temperature model [0053] 125 Device [0054] 200 Rotor temperature correction module [0055] 202 Calculation unit [0056] 204 Determination unit [0057] 205 Linking unit [0058] 210 Modification unit [0059] 215 Determination unit [0060] 300 Method [0061] 305 Calculation step [0062] 310 Determination step [0063] 315 Linking step [0064] 320 Modification step [0065] 325 Determination step [0066] 400 Characteristic curves [0067] 505 First rotor temperature curve [0068] 510 Second rotor temperature curve [0069] ASM Asynchronous machine [0070] Delta.sub.Trot Corrected rotor temperature value [0071] e Error value [0072] I.sub.sdq Motor current [0073] I.sub.sd, I.sub.sq Currents in the stator [0074] K Regulator [0075] L.sub.m Main inductance [0076] L.sub.r Rotor inductance [0077] P.sub.cu2_Ref Auxiliary value [0078] P.sub.cu2_Trot Support value [0079] Pv Power loss [0080] T.sub.cooling Coolant temperature [0081] T.sub.stat Stator temperature [0082] T.sub.rot Rotor temperature [0083] T.sub.rq Motor torque [0084] ω.sub.slip Motor slip