METHOD FOR DETERMINING THE ERROR VOLTAGE OF A CURRENT CONVERTER AND THREE-PHASE MACHINE HAVING ERROR VOLTAGE COMPENSATION

Abstract

The invention relates to a method for determining an error voltage of a current converter to which a load, in particular in the form of a three-phase machine such as an asynchronous machine, is connected, is determined and if necessary compensated, wherein an output voltage on the current converter is increased stage-by-stage or step-by-step and which is measured here as a current adjusting a step response. The invention further relates to a three-phase machine, for example in the form of an asynchronous machine having power electronics comprising a current converter and in the form of a compensation device for compensating the error voltage of the current converter. The invention further relates to a method for operating and/or controlling such a three-phase machine, in which the error voltage of the current converter is determined and compensated. According to the invention, the error voltage is determined from the current measured as a step response and from a resistance of the load, wherein said resistance is determined from a target voltage jump and from a simultaneously measured actual current jump in a relatively high current range of at least 30% of at least 50% of the rated current of the end stage of the current converter.

Claims

1-16. (canceled)

17. A method of determining an error voltage of a current converter to which a load is connected, comprising: applying a voltage at the output side to the current converter, wherein the applying comprises increasing the voltage stagewise or stepwise; measuring the current adopted as the step response in the applying of the voltage, determining the error voltage from the current measured as the step response and from a resistance of the load; and determining the resistance from a desired voltage jump from a measured actual current jump in a current range of at least 33% or of at least 50% of a nominal current of the current converter.

18. The method of claim 17, wherein the determination of the resistance of the load is carried out independently of the error voltage of the current converter.

19. The method of claim 17, further comprising selecting the desired voltage jump for determining the resistance such that the step response adapted in the form of the final value of the current is measured in a current range of 75% to 125% or 90% to 105% of the nominal current of an end stage of the current converter.

20. The method of claim 17, further comprising determining the resistance in accordance with the relationship: $R_1=\frac{\Delta U_{d,\mathrm{des}}}{\Delta I_{d,\mathrm{act}}}$ where R.sub.1 is the resistance of the load, ΔU.sub.d,des is a predetermined desired voltage jump, and ΔI.sub.d,act is the actual current jump measured at said desired voltage jump.

21. The method of claim 17, further comprising determining the error voltage in accordance with the relationship:
u.sub.F=U.sub.d,des−R.sub.1I.sub.d,max where u.sub.F is the error voltage, U.sub.d,des is an end value of the desired voltage jump, R.sub.1 is the resistance of the load, and I.sub.d,max is an end value of the current measured as the step response.

22. The method of claim 17, further comprising determining an error voltage characteristic curve that indicates the error voltage in dependence on the current.

23. The method of claim 22, wherein the determining of the error voltage characteristic curve further comprises determining from a plurality of measurement points of the error voltage, wherein the determining from a plurality of measurement points comprises a linear interpolation between such measurement points.

24. The method of claim 17, further comprising determining the error voltage in operation of the load, with the resistance of the load and the actual current used for this purpose being determined in operation of the load.

25. The method of claim 24, further comprising operating the load in a stationary state in the determination of the error voltage, wherein the stationary state comprises being at a standstill.

26. The method of claim 17, wherein a three-phase machine is connected to the current converter as the load, and wherein the three-phase machine comprises an asynchronous machine.

27. The method of claim 17, wherein the current converter comprises a frequency converter.

28. A method of operating and/or controlling a three-phase machine, comprising: determining and optionally compensating an error voltage of a current converter to which the three-phase machine is connected, determining the error voltage of the current converter, wherein the determining of the error voltage comprises the method of claim 17.

29. The method of claim 28, further comprising determining a current dependent correction value for the control of the current converter, wherein the correction value compensates the error voltage, with reference to an error voltage characteristic curve that is determined for the current converter and that indicates the error voltage of the current converter in dependence on the current.

30. The method of claim 28, selecting an end stage of the current converter to match the three-phase machine such that a nominal current of the three-phase machine corresponds to the nominal current of the end stage of the current converter.

31. A three-phase machine, wherein the three-phase machine is an asynchronous machine, the three-phase machine comprising: power electronics comprising a current converter comprising a frequency converter, and a control device to control the current converter for controlling the operation of the three-phase machine; wherein the control device comprises a determination device for determining an error voltage of the current converter; and wherein the determination device has a desired voltage module for setting a desired voltage increased jumpwise at an output side at the current converter and a current detection device for detecting an actual current adopted as the step response; wherein the determination device is configured to determine the error voltage in operation of the three-phase machine from the actual current measured as the step response and from a resistance of the three-phase machine and to determine the resistance from a desired voltage jump and an actual current jump determined in a current range of at least 30% or of at least 50% of the nominal current of the end stage.

32. The three-phase machine of claim 31, wherein the determination device is configured to determine the resistance of the three-phase machine independently of the error voltage; and/or to use a desired voltage jump and an actual current jump in a current range of 75% to 125% or 90% to 105% of the nominal current of an end stage of the current converter to determine the resistance; and/or to determine the resistance in accordance with the relationship: $R_1=\frac{\Delta U_{d,\mathrm{des}}}{\Delta I_{d,\mathrm{act}}},$ wherein R.sub.1 is the resistance, ΔU.sub.d,des is the predetermined desired voltage jump, and ΔI.sub.d,act is the actual current jump determined in this process; and/or to determine the error voltage in accordance with the relationship u.sub.F=U.sub.d,des−R.sub.1I.sub.d,max, where u.sub.F is the error voltage, U.sub.d,des is the end value of the desired voltage jump, R.sub.1 is the resistance, and I.sub.d,max is the end value of the current determined in the desired voltage increased jumpwise.

Description

[0032] The invention will be explained in more detail in the following with respect to an embodiment and to associated drawings. There are shown in the drawings:

[0033] FIG. 1: a diagram-like representation of a jump-wise increasing desired voltage curve u.sub.d,des over time and a step response adopted in this process in the form of an actual current i.sub.d,act over time for the parameter identification of a three-phase machine such as an asynchronous motor;

[0034] FIG. 2: an error voltage characteristic curve u.sub.F(i.sub.d) of the current dependent error voltage of a frequency converter to which said three-phase machine is connected determined from the desired voltage extent and from the detected actual current response in accordance with FIG. 1;

[0035] FIG. 3: a schematic representation of a voltage jump and the actual current response resulting therefrom in a low current range and of a desired voltage jump and the actual current adopted as a response in a high current range close to the nominal current of the three-phase machine to illustrate the influence of the error voltage compensation on the voltage jumps, with the true actual voltage extent also being entered in addition to the desired voltage extent in the two desired voltage diagrams to illustrate the different amounts of deformation in dependence on the current level; and

[0036] FIG. 4: a schematic representation of an asynchronous machine that is connected to a frequency converter.

[0037] As FIG. 4 shows, a three-phase machine 1, for example in the form of an asynchronous motor, can be connected to a frequency converter FU that, for example, converts a sinusoidal voltage 2 applied at the input side into a step-like output voltage u.sub.d with which said asynchronous motor is operated. It is, however, understood that the voltage 2 at the input side just like the converted voltage u.sub.d at the output side can have different properties and the frequency converter FU can implement different conversion properties.

[0038] The operation of the frequency converter FU can be variably controlled via a control device 3 that can have an input device 4 to operate and control the three-phase machine 1 in the desired manner.

[0039] To be able to determine the error voltage u.sub.F occurring at the frequency converter FU and to be able to compensate it in operation of the three-phase machine 1, said control device 3 can have a determination device 5 that can, for example, be implemented in the form of a software module in the control device 3 to operate the three-phase machine 1 or the frequency converter FU in a determination mode for determining the error voltage and to be able to set specific voltage values at the frequency converter.

[0040] Said determination device 5 can in particular comprise a desired voltage module 6 that applies a desired voltage u.sub.d,des to the frequency converter FU that increases stagewise at the output side such as is shown in FIG. 1. The desired voltage u.sub.d,des can, for example, be raised by a respective unchanging desired voltage jump in steps specified timewise, for example such that the desired voltage u.sub.d,des is increased by 0.4 V every three seconds, cf. FIG. 1, with this only to be understood by way of example.

[0041] The determination device 5 can furthermore comprise a current measurement device 7 by means of which the step response adopted with respect to the voltage jumps in the form of the actual current i.sub.d,act can be measured at the three-phase machine 1, for example. As FIG. 1 shows, the actual current extent i.sub.d,act resulting over time can be determined in amperes by means of the current measurement device 7 and the current jumps ΔI.sub.d,act respectively adopted can be determined.

[0042] The desired voltage module 6 is here advantageously configured such that the desired voltage is increased so much in the parameter identification mode until a measured current I.sub.d,max measured as a response results in the range of the nominal current of the three-phase machine 1. If, for example, the nominal current I.sub.N of the three-phase machine 1 amounts to 25 amperes, the voltage u.sub.d,des can be increased for so long until a current in the range of approximately 25 A is adopted.

[0043] The excitation with said voltage jumps can here advantageously take place in a stationary state. The three-phase machine 1 can, for example, be excited while at a standstill.

[0044] Said determination device 5 can here determine the error voltage u.sub.F using the relationship

u.sub.F=U.sub.d,des−R.sub.1I.sub.d,max

where u.sub.F is the error voltage, u.sub.d,des is respectively the end value of the desired voltage jump R1 and the stator resistance of the three-phase machine 1 and i.sub.d,max is the end value of the step response in the form of the adopted current.

[0045] To determine said stator resistance R.sub.1 of the three-phase machine 1, said determination device 5 uses the relationship

[00002]$R_1=\frac{\Delta U_{d,\mathrm{des}}}{\Delta I_{d,\mathrm{act}}},$

where R.sub.1 is said stator resistance, ΔU.sub.d,des is a desired voltage jump, and ΔI.sub.d,act, is the step response adopted in this process in the form of the adopted current change, as is shown by way of example in FIG. 1.

[0046] In this process, the determination device 5, however, does not use any desired voltage jump and the current change adopted there in a low current range, but rather a voltage jump ΔU.sub.d,des of the desired voltage and the step response adopted there in the form of the current changes ΔI.sub.d,act in a sufficiently high current range that is advantageously close to the nominal current of the end stage of the current converter and/or of the three-phase machine 1. Said desired voltage jump ΔU.sub.d,des and the current change ΔI.sub.d,act adopted in this process can in particular be in a current range of 75%-100% or 90%-100% of the nominal current I.sub.F of the end stage and/or of the nominal current I.sub.N of the three-phase machine 1.

[0047] If namely said measurement takes place with a sufficiently high current, the stator resistance R.sub.1 can be approximately exactly calculated without taking account of the error voltage. This measurement can ideally be performed in the range of the nominal current of the end stage since the characteristic curve u.sub.F(i.sub.d) extends approximately horizontally in the range of the nominal current, whereby the error voltage is canceled or its influence is negligible. The characteristic curve (u.sub.F)i.sub.d) that flattens more and more toward the nominal current can be seen from FIG. 2.

[0048] The current dependent deformation of the voltage jump can in particular be seen from FIG. 3. If, for example, with the low current I.sub.d,max=125.9 mA, the desired voltage jump specified for this of ΔU.sub.d,des=1.5 V is looked at, FIG. 3, left hand side there, shows that the voltage jump after the error voltage compensation has taken place is deformed by a relatively large amount so that the real voltage jump ΔU.sub.d,act only amounts to approximately ΔU.sub.d,act=119.6 mV.

[0049] If, however, such a desired voltage jump of ΔU.sub.d,des=1.5 V (from, for example, 16.5 V to 18 V) at a relatively high current of I.sub.d,max=11.3 A, the actual voltage jump is deformed by a much smaller amount, cf. FIG. 3, right hand side there. The real jump level ΔU.sub.d,act amount to approximately 1.3 V here.

[0050] If the desired voltage jump in a current range disposed even closer to the nominal current of the end stage is looked at, in particular in the range of approximately I.sub.N=25 A, the actual real jump level of the voltage jump ΔU.sub.d,act even more exactly approximates the specified desired value ΔU.sub.d,des=1.5 V since the characteristic curve of the error voltage U.sub.F(i.sub.d) extends approximately horizontally in the range of the nominal current I.sub.N=25 A (no longer shown in FIG. 2 since the characteristic curve u.sub.F(i.sub.d) is there only shown up to a current of approximately 12.5 A).

[0051] If the stator resistance R.sub.1 is determined from the values acquired at said high current I.sub.d,max32 11.3 A, the stator resistance R.sub.1 can be calculated as follows using the above-specified relationship:

[00003]$R_1=\frac{1.5V}{11.2732A-9.8689A}=1.07\Omega$

[0052] The characteristic curve extent of the current dependent error voltage U.sub.F(i.sub.d) can then be determined from the determined stator resistance R.sub.1 using said relationship

U.sub.F=U.sub.d,des−R.sub.1I.sub.d,max

for example in that linear interpolation is performed between the 13 measurement points shown there.