DE102022210963A1 - Method for determining a secondary current in a rotor of an electrical machine - Google Patents

Abstract

Method for determining a secondary current in a rotor of an electrical machine (2), in particular a separately excited synchronous machine, of an electrical arrangement (1), which electrical arrangement (1) has a primary side (4) and a secondary side (5), wherein an inverter (7) is arranged on the primary side (4) and the rotor of the electrical machine (2) is arranged on the secondary side (5), wherein the primary side (4) and the secondary side (5) are coupled to one another by means of a transmission device (6), in particular a transformer, wherein a primary current is detected on the primary side (4) and a secondary current, in particular a rotor current, is determined on the secondary side (5) based on the detected primary current.

Description

The invention relates to a method for determining a secondary current in a rotor of an electrical machine, in particular a separately excited synchronous machine, of an electrical arrangement, which electrical arrangement has a primary side and a secondary side, wherein an inverter is arranged on the primary side and the rotor of the electrical machine is arranged on the secondary side, wherein the primary side and the secondary side are coupled to one another by means of a transmission device, in particular a transformer.

Methods for determining secondary currents in rotors of electrical machines, in particular in separately excited synchronous machines, are generally known from the prior art. The use of separately excited synchronous machines is advantageous, for example, in terms of cost advantages or the reduced use of heavy rare earths. In contrast, there is the requirement for active current supply to the rotor of the electrical machine, which is carried out, for example, by carbon brushes and slip rings. Alternatively, contactless current transmission via a transformer or a transmitter is possible. With contactless current transmission, however, the determination of the secondary current in the rotor can only be carried out to a limited extent, since the rotor rotates at a comparatively high speed and is surrounded by a coolant, for example, and can run in oil.

In order to be able to determine the secondary current in the rotor, a comparatively complex model of the electrical machine is used, which requires a comparatively high computing power or storage capacity.

The invention is based on the object of specifying an improved method for determining the secondary current in the rotor of the electrical machine, which is in particular less complex.

The object is achieved by a method having the features of claim 1. Advantageous embodiments are the subject of the subclaims.

As described at the beginning, the invention relates to a method for determining a secondary current in a rotor of an electrical machine, in particular in a rotor of a separately excited synchronous machine. The separately excited synchronous machine can be part of an electrical arrangement that has a primary side and a secondary side. In principle, the terms primary side and secondary side can be chosen arbitrarily, and individual components of the electrical arrangement can be divided and assigned arbitrarily. The rotor is arranged on the secondary side of the electrical machine, or the rotor is assigned to the secondary side. The primary side has an inverter through which currents can be generated that are to be fed to the rotor. A transmission device, in particular a transformer, is arranged between the primary side and the secondary side, or the primary side is coupled to the secondary side via the transmission device. The coupling via the transmission device allows the currents generated by the inverter to be fed to the secondary side without contact.

The secondary side and the primary side can each have several other components. The secondary side in particular also has a rectifier, by means of which the alternating currents generated by the inverter can be rectified. In other words, the inverter generates alternating currents, which can then be transmitted contactlessly to the secondary side via the transmission device, with direct current being generated on the secondary side via the rectifier from the transmitted alternating current, which can then be fed to the rotor as a secondary current.

The invention is based on the finding that a primary current is detected on the primary side and a secondary current, in particular a rotor current, is determined on the secondary side based on the detected primary current. The invention therefore proposes, instead of a complex model of the electrical machine that is based on a large number of operating parameters or instead of carrying out a direct current measurement of the secondary current on the secondary side, to instead detect the primary current on the primary side and use this as the basis for determining the secondary current on the secondary side.

Advantageously, the primary current can be measured much more easily on the primary side, since the primary side ultimately describes the stationary or a stationary part of the electrical arrangement, so that a current measurement in a comparatively fast rotating system, which may also be surrounded by a coolant or lubricant, in particular oil, can be omitted. Instead, the primary current can be detected with a suitable sensor, for example a current sensor, and the secondary current can be determined based on the detected primary current. In particular, it can be exploited that the primary current is converted into the secondary current via the transmission device, so that a secondary current is provided depending on the primary current called up at a current operating point or the secondary current is always generated depending on the currently called up primary current. The secondary current on the secondary side is therefore not recorded directly, but "determined indirectly", namely by recording, for example based on a direct measurement, the primary current.

The secondary current can thus be determined based on the detected or measured primary current. To do this, the primary current can be detected and a jump point in the primary current identified. In other words, the jump point of the primary current can be detected and the secondary current determined based on the jump point. As described, the current profile of the primary current is directly related to the secondary current that is set in the rotor of the electrical machine. The jump point of the primary current can therefore be used to determine the secondary current set in the operating state. The jump point arises in particular due to the comparatively large inductance formed by the windings on the rotor of the electrical machine and the rectifier on the secondary side. Since the DC current on the secondary side can change little or almost not at all due to the inductance, the transformer creates a jump point in the primary current (i.e. on the primary side), which allows the secondary current to be determined.

As described, the jump point of the primary current is recorded and the secondary current is determined based on the jump point. The secondary current can be determined in particular based on a high point and a low point, in particular a corrected low point, of the jump point. When selecting the high point and/or in particular the low point, boundary conditions that, for example, affect the susceptibility to errors in determining the respective high point or low point or generally the measurability can be taken into account. In principle, other points, i.e. substitute values, can also be used to determine the respective high point or low point or to record the respective high point or low point of the jump point and a correction can then be made to the actual high point or low point. This allows, for example, the current value to be measured or recorded at a substitute value and to determine the respective high point or low point by subsequently correcting the current value at the substitute value to the actual low point if the measurability or the susceptibility to errors when determining the current value at the substitute value allows an improvement in the determination of the actual high point or low point, for example if a direct determination of the actual high point or low point is more complex or more susceptible to errors.

As described at the beginning, the secondary current is basically based on the currently called up primary current. It can be taken into account that the jump point corresponds to twice the actual secondary current. The secondary current can be determined based on half the value of the jump point, in particular between the high point and the low point. When the direction of current flow in the rotor is reversed, i.e. the direction of flow of the secondary current is reversed, a change from the positive flow direction to the negative flow direction (or vice versa) occurs, so that the amount of the primary current at the jump point or the amount of the jump point between the high point and the low point basically corresponds to twice the actually flowing secondary current. Thus, when determining the secondary current based on the jump point of the primary current, it can be taken into account that the jump point is basically generated by the change in the direction of current flow and thus the secondary current is determined based on half the value of the jump point, i.e. half the "height" of the jump point.

A further development of the method described here can provide that the secondary current is determined from the primary current based on the transmission ratio of the transmission device. As described above, the primary current is transmitted to the secondary side via the transmission device, so that the transmission ratio of the transmission device can be taken into account in order to improve the determination of the secondary current based on the primary current. In other words, the transmission ratio of the transmission device can be taken into account when determining the secondary current in order to determine the secondary current based on the primary current transmitted from the primary side to the secondary side.

bestimmt wird. Hierbei bezeichnet I_S den Sekundärstrom, ü das Übersetzungsverhältnis der Übertragungseinrichtung, also das Wicklungsverhältnis zwischen Primärseite und Sekundärseite, I_P1 den Stromwert der Primärseite am Hochpunkt der Sprungstelle und I_P2,corr den Stromwert der Primärseite am Tiefpunkt der Sprungstelle bzw. den auf den Tiefpunkt der Sprungstelle korrigierten Stromwert, falls dieser an einem Ersatzwert erfasst wurde. Wie beschrieben, kann der Sekundärstrom basierend auf der Sprungstelle, also der Differenz der Stromwerte zwischen einem Hochpunkt und einem Tiefpunkt an der Sprungstelle bestimmt werden. Anstelle den Stromwert an dem Tiefpunkt direkt zu messen bzw. zu erfassen kann auch ein Stromwert an einem Ersatzwert bestimmt werden, der beispielsweise besser messbar ist, und anschließend kann der Stromwert auf den tatsächlichen Tiefpunkt korrigiert werden. Demnach kann der Sekundärstrom basierend auf dem korrigierten Tiefpunkt $I_{P\mathrm{2,}corr}=I_{P2}+\frac{V_{dc}\ast \mathrm{\Delta }t}{L}$

bestimmt werden. Dabei bezeichnet der Parameter I_P2 den Stromwert am Hochpunkt, I_P2,corr den Stromwert am tatsächlichen Tiefpunkt bzw. am korrigierten Tiefpunkt, V_dc die Zwischenkreisspannung, d den duty-cycle bzw. die Abtastrate, f_sw die Schaltfrequenz und L₁ die primärseitige (Selbst-) Induktivität des Übertragers bzw. der Übertragungseinrichtung.Furthermore, the method may provide that the secondary current I _S is based on $I_S=\frac{1}{2}\ddot{\text{u}}\left(I_{P1}-I_{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="DE102022210963A1\_0008.png"\; state="\{\{state\}\}">P</figure-callout>}\mathrm{2,}cOrr}\right)$

is determined. Here, I _S is the secondary current, ü is the transmission ratio of the transmission device, i.e. the winding ratio between the primary side and the secondary side, I _P1 is the current value of the primary side at the high point of the jump point and I _P2,corr is the current value of the primary side at the low point of the jump point or the current value corrected to the low point of the jump point if this was recorded at a substitute value. As described, the Secondary current can be determined based on the jump point, i.e. the difference in the current values between a high point and a low point at the jump point. Instead of directly measuring or recording the current value at the low point, a current value can also be determined at a substitute value that is, for example, easier to measure, and then the current value can be corrected to the actual low point. Accordingly, the secondary current can be determined based on the corrected low point. $I_{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="DE102022210963A1\_0008.png"\; state="\{\{state\}\}">P</figure-callout>}\mathrm{2,}cOrr}=I_{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="DE102022210963A1\_0008.png"\; state="\{\{state\}\}">P</figure-callout>}2}+\frac{V_{dc}\ast \mathrm{\Delta }t}{L}$

The parameter I _P2 denotes the current value at the high point, I _P2,corr the current value at the actual low point or the corrected low point, V _dc the intermediate circuit voltage, d the duty cycle or the sampling rate, f _sw the switching frequency and L ₁ the primary-side (self-) inductance of the transformer or the transmission device.

The method can also be further developed in such a way that a stator induction of a stator current on the rotor is determined. Advantageously, in the method described, the effect of the stator current flowing in the stator on the secondary current can also be determined. This allows improved control of the electrical machine during operation, since the effects of the stator induction on the rotor can also be determined.

In addition to the method, the invention relates to a detection device for determining a secondary current in a rotor of an electrical machine, in particular a separately excited synchronous machine, of an electrical arrangement, which electrical arrangement has a primary side and a secondary side, wherein an inverter is arranged on the primary side and the rotor of the electrical machine is arranged on the secondary side, wherein the primary side and the secondary side are coupled to one another by means of a transmission device, in particular a transformer, wherein the detection device is designed to detect a primary current on the primary side and to determine a secondary current, in particular a rotor current, on the secondary side based on the detected primary current.

The invention also relates to a motor vehicle, comprising an electrical arrangement with a primary side and a secondary side, wherein an inverter is arranged on the primary side and the rotor of an electrical machine is arranged on the secondary side, wherein the primary side and the secondary side are coupled to one another by means of a transmission device, in particular a transformer, and comprising a detection device as described above. The method described above can thus be used for determining the secondary current in the electrical machine of the electrical arrangement of the motor vehicle.

In principle, all advantages, details and features described in relation to the method are fully transferable to the detection device and the motor vehicle and vice versa.

• 1 einen schematischen Ausschnitt einer elektrischen Anordnung; und
• 2 ein schematisches Stromdiagramm eines Primärstroms.

The invention is explained below using an embodiment with reference to the figures. The figures are schematic representations and show:

• 1 a schematic section of an electrical arrangement; and
• 2 a schematic current diagram of a primary current.

1 shows a schematic section of an electrical arrangement 1, for example an electrical arrangement 1 of a motor vehicle. The motor vehicle is not shown in detail, but can have the electrical arrangement 1 described. The electrical arrangement 1 has an electrical machine 2, which is also only shown in detail. For example, a rotor winding 3 of the rotor of the electrical machine 2 is shown schematically. The electrical machine 2 is, for example, a separately excited synchronous machine. Basically, the electrical arrangement 1 has a primary side 4 and a secondary side 5, which are schematically separated from one another, for example by a transmission device 6, for example a transformer.

The primary side 4 is assigned an inverter 7, which is designed to generate a primary current that can be transmitted as alternating current to the secondary side 5 via the transmission device 6. The secondary side 5 is assigned a rectifier 8 next to the rotor winding 3 or next to the rotor or generally to the electrical machine, which generates the secondary current from the transmitted alternating current, which can be fed to the rotor, for example the rotor winding 3. The components of the primary side 4 and the secondary side 5 shown in the dashed boxes are simultaneously separated into a stationary part of the electrical arrangement 1 and a rotating part of the electrical arrangement 1 by the transmission device 6, which, as described, is designed for contactless current transmission between the primary side 4 and the secondary side 5. It is therefore difficult to directly detect or measure the secondary current, since it is generated in the rotating part of the electrical arrangement 1. Since the rotor of the electrical machine is usually equipped with several 10,000 revolutions/min and possibly also runs in a coolant, such as oil, a direct measurement is comparatively complex to realize.

The method described here therefore proposes not to measure the secondary current directly, but to determine it, namely based on the primary current that flows on the primary side 4 of the electrical arrangement 1. Since the primary side 4 is stationary, it is much easier to detect the primary current than it would be to detect the secondary current on the secondary side 5. To this end, the method described takes advantage of the fact that the current profile of the primary current on the primary side 4 basically describes the course of the secondary current on the secondary side 5, or that there is a direct dependency between the primary current and the secondary current. In this case, the primary current is measured or detected and a jump point 9 (see 2 ) is identified, from which the secondary current can be determined. For detecting the primary current, the electrical arrangement 1 can have a detection device, for example with at least one current sensor and a control or computing device, or can be coupled to such a device.

In particular, a high point 10 and a low point 11 of the jump point 9 can be determined or the corresponding current values of the primary current at the high point 10 and the low point 11 can be recorded. If a direct determination of the current value at the low point 11 is not possible, a substitute value 12 can be used, at which the current value is determined and then converted into a corrected current value at the low point 11. The same applies to the high point 10. This means that if a direct determination of the current value at the high point 10 is not possible, a substitute value 13 can be used, at which the current value is determined and then converted into a corrected current value at the high point 10. The values in 2 However, the positions of the replacement values 12 and 13 shown are not to be understood as concrete positions, but only as examples because the replacement value 13, for example, also lies between its 2 shown position and the high point 10. The same applies to the replacement point 12.

bestimmt werden, wobei ü das Übersetzungsverhältnis der Übertragungseinrichtung 6, also beispielsweise das Wicklungsverhältnis $\frac{N_P}{N_S}$

der Übertragungseinrichtung 6, I_P1 den Stromwert des Primärstroms am Hochpunkt und I_P2,corr den Stromwert des Primärstroms am Tiefpunkt 11 bzw. am korrigierten Tiefpunkt 11 beschreibt.In principle, the secondary current I _S can be calculated based on $I_S=\frac{1}{2}\ddot{\text{u}}\left(I_{P1}-I_{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="DE102022210963A1\_0008.png"\; state="\{\{state\}\}">P</figure-callout>}\mathrm{2,}cOrr}\right)$

where ü is the transmission ratio of the transmission device 6, for example the winding ratio $\frac{N_P}{N_S}$

the transmission device 6, I _P1 describes the current value of the primary current at the high point and I _P2,corr describes the current value of the primary current at the low point 11 or at the corrected low point 11.

beträgt.For example, a determination or measurement of the primary current I _P1 takes place between the times t ₀ and t ₁ , since the current profile of the primary current is approximately constant here. A determination of the current value at the low point 11 of the primary current can take place at time t ₂ or, if this is disadvantageous for the measurability of the current value, a measurement of the current value of the primary current can take place at the substitute value 12, for example between the times t ₂ and t ₃ or at time t ₃ and then a conversion or a correction of the current value by Δi can take place, according to the formula Δi=m*Δt, where $m=\frac{V_{DC}}{L_{\sigma }+Lm}$

amounts.

Advantageously, the specific secondary current is determined without a complex calculation model, i.e. in particular without increased computing effort or storage effort and without a complex measuring device, since the dependency between primary current and secondary current is basically exploited, so that a comparatively inexpensive measurement of the primary current is sufficient to determine the secondary current.

Reference symbols

1

electrical arrangement

2

electric machine

3

Rotor winding

4

Primary page

5

Secondary side

6

Transmission device

7

Inverter

8th

Rectifier

9

Jump point

10

High point

11

Low point

12

Replacement value

13

Replacement value

IS

Secondary current

IP

Primary current

Δi

Correction value

t0-t3

time

Claims (10)

Method for determining a secondary current in a rotor of an electrical machine (2), in particular a separately excited synchronous machine, of an electrical arrangement (1), which electrical arrangement (1) has a primary side (4) and a secondary side (5), wherein an inverter (7) is arranged on the primary side (4) and the rotor of the electrical machine (2) is arranged on the secondary side (5), wherein the primary side (4) and the secondary side (5) are coupled to one another by means of a transmission device (6), in particular a transformer, characterized in that a primary current is detected on the primary side (4) and a secondary current, in particular a rotor current, is determined on the secondary side (5) based on the detected primary current. Procedure according to Claim 1 , characterized in that a jump point (9) of the primary current is detected and the secondary current is determined based on the jump point (9). Procedure according to Claim 2 , characterized in that the secondary current is determined based on a high point (10) and a low point (11), in particular a corrected low point (11), of the jump point (9). Procedure according to Claim 2 or 3 , characterized in that the secondary current is determined based on half the value of the jump point (9), in particular between the high point (10) and the low point (11). Method according to one of the preceding claims, characterized in that the secondary current is determined from the primary current based on the transmission ratio of the transmission device (6). Method according to one of the preceding claims, characterized in that the secondary current is based on $I_S=\frac{1}{2}\ddot{\text{u}}\left(I_{P1}-I_{P\mathrm{2,}cOrr}\right)$

I _S is determined. Method according to one of the preceding claims, characterized in that the secondary current is based on the corrected low point (11) $I_{P\mathrm{2,}cOrr}=I_{P2}+\frac{V_{dc}\ast \mathrm{\Delta }t}{L}$

is determined. Method according to one of the preceding claims, characterized in that a stator induction of a stator current on the rotor is determined. Detection device for determining a secondary current in a rotor of an electrical machine (2), in particular a separately excited synchronous machine, of an electrical arrangement (1), which electrical arrangement (1) has a primary side (4) and a secondary side (5), wherein an inverter (7) is arranged on the primary side (4) and the rotor of the electrical machine (2) is arranged on the secondary side (5), wherein the primary side (4) and the secondary side (5) are coupled to one another by means of a transmission device (6), in particular a transformer, characterized in that the detection device is designed to detect a primary current on the primary side (4) and to determine a secondary current, in particular a rotor current, on the secondary side (5) based on the detected primary current. Motor vehicle, comprising an electrical arrangement (1) with a primary side (4) and a secondary side (5), wherein an inverter (7) is arranged on the primary side (4) and the rotor of an electrical machine (2) is arranged on the secondary side (5), wherein the primary side (4) and the secondary side (5) are coupled to one another by means of a transmission device (6), in particular a transformer, and comprising a detection device according to the preceding claim.

Images