METHOD FOR MONITORING A COIL TEMPERATURE

Abstract

In a method for monitoring a winding temperature of a winding of an electric machine powered by a converter, a heating power applied to the winding of the electric machine is determined and evaluated using a thermal model. A relative increase in a resistance of the winding, when the winding heats up, is determined from the heating power in comparison with a standard reference value for 20° C. winding temperature. The winding temperature is calculated from the relative increase in the resistance, and a warning signal and/or a switch-off signal is generated when a critical winding temperature value is exceeded.

Claims

1.-10. (canceled)

11. A method for monitoring a winding temperature of a winding of an electric machine powered by a converter, said method comprising: determining a heating power applied to the winding of the electric machine; evaluating the heating power using a thermal model; determining from the heating power a relative increase in a resistance of the winding, when the winding heats up, in comparison with a standard reference value for 20° C. winding temperature; calculating the winding temperature from the relative increase in the resistance; and generating a warning signal and/or a switch-off signal when a critical winding temperature value is exceeded.

12. The method of claim 11, wherein the winding is a copper winding or individual UVW motor strands.

13. The method of claim 11, wherein the winding temperature is a copper temperature.

14. The method of claim 11, wherein the heating power applied to the winding is determined on a converter side,

15. The method of claim 11, further comprising: measuring the heating power applied to the winding for a period of time; and determining from the heating power an average heating power.

16. The method of claim 11, wherein the heating power applied to the winding is determined during ongoing converter operation.

17. The method of claim 15, further comprising comparing the average heating power with a defined and/or previously determined heating power.

18. The method of claim 17, wherein the average heating power is compared with the defined and/or previously determined heating power at a known winding temperature.

19. The method of claim 15, further comprising determining a change in a winding resistance by a relative change in the determined heating power in relation to the heating power of a cold winding.

20. The method of claim 19, wherein the change in the winding resistance is determined at a reference temperature of the winding T_cu=20° C.

21. The method of claim 12, further comprising monitoring each of the strands individually.

22. The method of claim 12, further comprising determining a phase heating power of each of the strands based on a commutation angle.

23. Apparatus for monitoring a winding temperature of a winding of an electric machine powered by a converter, said apparatus configured to: determine a heating power applied to the winding of the electric machine, evaluate the heating power using a thermal model; determine from the heating power a relative increase in a resistance of the winding, when the winding heats up, in comparison with a standard reference value for 20° C. winding temperature; calculate the winding temperature from the relative increase in the resistance; and generate a warning signal and/or a switch-off signal when a critical winding temperature value is exceeded.

24. A drive, comprising: a dynamoelectric machine including a winding; a converter powering the dynamoelectric machine; and an apparatus for monitoring a winding temperature of the winding of the dynamoelectric machine, said apparatus configured to: determine a heating power applied to the winding of the electric machine, evaluate the heating power using a thermal model; determine from the heating power a relative increase in a resistance of the winding, when the winding heats up, in comparison with a standard reference value for 20° C. winding temperature; calculate the winding temperature from the relative increase in the resistance; and generate a warning signal and/or a switch-off signal when a critical winding temperature value is exceeded.

Description

[0066] The invention is described and explained in more detail hereinafter with reference to the exemplary embodiments shown in the figures, in which:

[0067] FIG. 1 shows a possible sequence of the method according to the invention,

[0068] FIG. 2 shows a drive,

[0069] FIG. 3 shows a comparison of two courses of the winding temperature,

[0070] FIG. 4 FIG. 5 and FIG. 6 show courses from an exemplary load cycle.

[0071] FIG. 1 shows a possible sequence of the method according to the invention.

[0072] The method for monitoring a winding temperature of a winding of an electric machine, the electric machine being fed by a converter, comprises the following method steps:

[0073] In a method step S1, a heating power applied to the winding is determined.

[0074] In a method step S2, the heating power is evaluated by means of a thermal model.

[0075] In a method step S3, a warning signal and/or a switch-off signal is generated when a critical winding temperature value associated with the heating power is exceeded.

[0076] As already explained, the heating power of the winding is determined. Advantageously, this is achieved in that the heating power is calculated from currents or voltages measured in the converter.

[0077] Two exemplary cases are:

[0078] If the complete output power of the converter is preferably used entirely for heating the ohmic winding resistance (at a standstill, n=0, the mechanical output power of the motor is Pmech=0; the current motor rotational speed is advantageously known to the converter continuously, i.e. preferably at any instant), the heating power is determined by the converter or within the converter by means of measurement of Ux and Ix in the 3-phase system.

[0079] In this case, it is possible to speak of a measured heating power.

[0080] If the motor supplies a mechanical output power for the time interval under consideration (Pmech≠0 because n≠0), the heating power of the winding is advantageously determined or calculated from the supplied output power of the converter by subtracting the mechanical power (Pmech) supplied by the motor.

[0081] The heating power of the winding is preferably calculated according to the formula: P_cu=P_output−P_mech, for which purpose the converter advantageously has all the required variables, namely P_mech=M_motor*n and the motor torque M_motor=Iq*k_T.

[0082] In this case, Iq denotes the torque-forming current which is generated and applied to the motor by the converter (i.e., in this case, in addition to the rotational speed n, the current I.sub.q is also a variable known to the converter), k_T is the torque constant of the motor, which is preferably read in for each motor with its so-called converter parameter list.

[0083] With reference to the formulae mentioned, the heating power P_cable, which is produced on the lines between the converter and the motor, can be drawn off in order to obtain the pure heating power in the motor winding. For this purpose, corresponding data are advantageously known via lines which can be read into the converter as parameters for the drive configuration (see also reference characters 101 in FIG. 2).

[0084] In most cases, a proportion of the cable heating power is much smaller in comparison to the heating power in the winding and if line data is not known, this proportion can be disregarded. Nevertheless, the proposed method can be used only with reduced accuracy.

[0085] FIG. 2 shows a drive 4. The drive 4 has an electric machine 2 and a converter 1. The converter comprises an apparatus for carrying out the method described above.

[0086] The apparatus can have hardware, for example measurement technology for detecting operating variables. The apparatus can also have a calculation model.

[0087] The converter 1 is connected to a network 100, comprising L1, L2, L3 and PE.

[0088] A detection of operating variables, in particular operating variables at the current time such as currents, voltages, torque and rotational speed, is represented by a block 103. The operating variables are processed in a thermal model 104. A block 105 is used for an initialization procedure in which a reference measurement is advantageously carried out.

[0089] A determination of the winding temperature, in particular strand-related, takes place in a block 106.

[0090] A thermal motor protection 102 preferably generates the warning or switch-off signal.

[0091] Converter 1 and machine 2 are connected via a line 101. The figure shows the currents i.sub.U (t), i.sub.V (t) and i.sub.W (t). Advantageously, these are operating currents during ongoing operation. Furthermore, the figure shows the line resistances R.sub.L,U, R.sub.L,V and R.sub.L,W.

[0092] In addition, line data are taken into account in the model 104. This is represented by block 107 and by block 108.

[0093] Block 107 advantageously provides information about an ambient temperature T.sub.0.

[0094] Block 108 advantageously provides information, in particular at ambient temperature, about line data such as the line resistance, a line cross-section and a line length.

[0095] In the figure, the machine 2 comprises three strands U, V and W.

[0096] Machine data is also taken into account in model 104. This is represented by block 109.

[0097] Block 109 advantageously provides information about winding resistances R.sub.U, R.sub.V and R.sub.W, winding cross-sections, weight and currents.

[0098] FIG. 3 shows a comparison between a course 20 of the winding temperature determined by means of the method with a course 21 determined by means of an e-function.

[0099] The course 21 shows a simulation of the winding temperature T.sub.Cu(t) over time t within only one time constant t of the e-function. This represents a thermal motor model with only one thermal capacity, a so-called one-mass model. The course 21 shows a marked deviation from the determined real-time course 20 during a heating process.

[0100] The figure also shows a tangent 10 for τ.sub.meas and a tangent 11 for τ.sub.e, The tangents show the marked deviation between the initial gradients of the two courses.

[0101] Thus, it is clear that in the case of methods resulting in the course 21, large safety margins are required, leading to poor motor utilization.

[0102] The method according to the invention, which is based on a real-time measurement of the winding temperature by means of a measurement of the heating power, preferably during ongoing converter operation, enables very good motor utilization.

[0103] In FIG. 4, FIG. 5 and FIG. 6, courses from an exemplary load cycle of the motor operation are shown. The figures show a current course, measured heating power (for three strands and a sum value) and the resulting course of the winding temperature (for three strands).

[0104] FIG. 4 shows an exemplary course 200 of a current I.sub.ms of the strands U, V, W as a function of time t. FIG. 5 shows an exemplary course 202 of the heating power P.sub.Cu of the strands U, V, W as a function of time t. FIG. 5 also shows a course 201 of a total heating power P.sub.Cu. FIG. 6 shows exemplary courses 203 (strand U), 204 (strand V) and 205 (strand W) of the winding temperature T.sub.Cu as a function of time t. In addition, a course of a cooling water temperature 206 is shown.