METHOD FOR DETERMINING AN INTERMEDIATE CIRCUIT VOLTAGE

Abstract

A method for determining an intermediate circuit voltage U.sub.DC,Ideal in an electrical system, which includes a battery, a DC-DC converter, a DC-AC converter, and an electrical machine. The battery is connected to the DC-DC converter, the DC-DC converter is connected to the DC-AC converter, and the DC-AC converter is connected to the electrical machine. An intermediate circuit of the electrical system is formed by the DC-DC converter and the DC-AC converter. A line-to-line voltage .Math..sub.LL, which is applied to a conductor of the electrical machine, is determined, wherein a maximum degree of modulation m.sub.max of the line-to-line voltage .Math..sub.LL is determined. The intermediate circuit voltage U.sub.DC,Ideal is determined according to the equation

[00001]$U_{DC,\mathrm{Ideal}}=\frac{{\hat{U}}_{LL}}{m_{\max }}$

Claims

1. A method for determining an intermediate circuit voltage U.sub.DC,Ideal in an electrical system, which includes a battery, a DC-DC converter, a DC-AC converter, and an electrical machine, the method comprising: the battery is connected to the DC-DC converter, the DC-DC converter is connected to the DC-AC converter, and the DC-AC converter is connected to the electrical machine, wherein an intermediate circuit of the electrical system is formed by the DC-DC converter and the DC-AC converter, wherein a line-to-line voltage .Math..sub.LL, which is applied to a conductor of the electrical machine, is determined, wherein a maximum degree of modulation m.sub.max of the line-to-line voltage .Math..sub.LL is determined, wherein the intermediate circuit voltage U.sub.DC,Ideal is determined according to the equation $U_{DC,\mathrm{Ideal}}=\frac{{\hat{U}}_{LL}}{m_{\max }}$

2. The method as claimed in claim 1, wherein the line-to-line voltage .Math..sub.LL describes a peak value of a voltage between the conductor and ground.

3. The method as claimed in claim 1, wherein the line-to-line voltage .Math..sub.LL is measured within the DC-AC converter.

4. The method as claimed in claim 1, wherein the line-to-line voltage .Math..sub.LL is determined indirectly and is transmitted to the DC-DC converter via a bus system.

5. The method as claimed in claim 1, wherein the maximum degree of modulation m.sub.max is varied.

6. The method as claimed in claim 1, wherein the intermediate circuit voltage U.sub.DC,Ideal is delimited by a minimum value and a maximum value, taking into consideration a limitation block.

7. The method as claimed in claim 1, which is carried out for an electrical system of a vehicle, wherein the electrical machine is used to drive the vehicle.

8. The method as claimed in claim 1, wherein the intermediate circuit voltage U.sub.DC,Ideal is determined via a software function.

9. A determination system for determining an intermediate circuit voltage U.sub.DC, Ideal in an electrical system, comprising: a battery, a DC-DC converter, a DC-AC converter, and an electrical machine, wherein the battery is connected to the DC-DC converter, the DC-DC converter is connected to the DC-AC converter, and the DC-AC converter is connected to the electrical machine, wherein an intermediate circuit of the electrical system is formed by the DC-DC converter and the DC-AC converter, wherein the determination system has a determination unit and a computing unit, wherein the determination unit is designed to determine a line-to-line voltage .Math..sub.LL, which is applied to a conductor of the electrical machine, wherein the computing unit is designed to determine the intermediate circuit voltage .Math..sub.LL taking into consideration a maximum degree of modulation m.sub.max of the intermediate circuit voltage U.sub.DC,Ideal according to the equation $U_{DC,\mathrm{Ideal}}=\frac{{\hat{U}}_{LL}}{m_{\max }}$

10. The method as claimed in claim 2, wherein the line-to-line voltage .Math..sub.LL is measured within the DC-AC converter.

11. The method as claimed in claim 2, wherein the line-to-line voltage .Math..sub.LL is determined indirectly and is transmitted to the DC-DC converter via a bus system.

12. The method as claimed in claim 2, wherein the maximum degree of modulation m.sub.max is varied.

13. The method as claimed in claim 3, wherein the maximum degree of modulation m.sub.max is varied.

14. The method as claimed in claim 4, wherein the maximum degree of modulation m.sub.max is varied.

15. The method as claimed in claim 2, wherein the intermediate circuit voltage U.sub.DC,Ideal is delimited by a minimum value and a maximum value, taking into consideration a limitation block.

16. The method as claimed in claim 3, wherein the intermediate circuit voltage U.sub.DC,Ideal is delimited by a minimum value and a maximum value, taking into consideration a limitation block.

17. The method as claimed in claim 4, wherein the intermediate circuit voltage U.sub.DC,Ideal is delimited by a minimum value and a maximum value, taking into consideration a limitation block.

18. The method as claimed in claim 5, wherein the intermediate circuit voltage U.sub.DC,Ideal is delimited by a minimum value and a maximum value, taking into consideration a limitation block.

19. The method as claimed in claim 2, which is carried out for an electrical system of a vehicle, wherein the electrical machine is used to drive the vehicle.

20. The method as claimed in claim 3, which is carried out for an electrical system of a vehicle, wherein the electrical machine is used to drive the vehicle.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0035] The invention is illustrated schematically in the drawings in the context of embodiments, and will be described schematically and in detail with reference to the drawings.

[0036] FIG. 1 shows a schematic illustration of an electrical system and an embodiment of the determination system according to the invention, using which an embodiment of the method according to the invention is carried out for the electrical system.

[0037] FIG. 2 shows a schematic illustration of a diagram which is used in the embodiment of the method according to the invention.

[0038] The figures will be described coherently and comprehensively. The same components are assigned the same reference numerals.

DETAILED DESCRIPTION

[0039] The electrical system shown schematically in FIG. 1 comprises a battery 2, a direct current-direct current converter or DC-DC converter 4, a direct current-alternating current converter or DC-AC converter 6, and an electrical machine 8. The battery 2 and the DC-DC converter 4 are connected to one another via two lines 10a, 10b. In addition, the DC-DC converter 4 and the DC-AC converter 6, here their DC outputs, are connected to one another via two lines 12a, 12b. Furthermore, the electrical machine 8 has three conductors 14a, 14b, 14c or phases, wherein one conductor 14a, 14b, 14c or one line is connected in each case to the DC-AC converter 6, here to its AC output. The electrical system shown has a high-voltage or HV system topology. The electrical system is also designed as part of a high-voltage traction network for a vehicle, for example a motor vehicle.

[0040] FIG. 1 also shows a schematic illustration of an embodiment of the determination system according to the invention, which here comprises a determination unit 50 and a computing unit 52, wherein this embodiment of the determination system is designed to carry out the embodiment of the method according to the invention for determining an intermediate circuit voltage 31 U.sub.DC,Ideal, as it is indicated in the diagram of FIG. 2. In a further embodiment, a limited ideal intermediate circuit voltage 40 U.sub.DC,Ideal,lim is also determined.

[0041] It is provided here that a line-to-line voltage 22 .Math..sub.LL between two conductors 14a, 14b, 14c of the electrical machine 8 is determined using the determination unit 50, wherein the line-to-line voltage 22 .Math..sub.LL is indicated in the diagram from FIG. 2. In the method, an algorithm, as is shown on the basis of the diagram from FIG. 2, is taken into consideration with software assistance by the computing unit 52. This diagram is divided into a first block 54 and a second block 56.

[0042] In the method, the line-to-line voltage 22 .Math..sub.LL is divided at a division 30 by the maximum degree of modulation 26 m.sub.max, wherein an ideal intermediate circuit voltage 31 U.sub.DC,Ideal is determined.

[0043] In the embodiment of the method presented here, the first block 54 represents an equation

[00004]$U_{DC,\mathrm{Ideal}}=\frac{{\hat{U}}_{LL}}{m_{\max }},$

[0044] which is used by the computing unit 52 and describes a dependency of the intermediate circuit voltage 31 U.sub.DC,Ideal on the line-to-line voltage 22 .Math..sub.LL.

[0045] In a further embodiment of the method, a second block 56 is also taken into consideration by the computing unit 52, using which a limitation of the ideal intermediate circuit voltage 31 U.sub.DC,Ideal determined on the basis of the equation is carried out, wherein this second block 56 can also be referred to as a limitation block. A minimum value 32 U.sub.DC,min for the intermediate circuit voltage 31 U.sub.DC,Ideal and a maximum value 34 U.sub.DC,max for the intermediate circuit voltage 31 U.sub.DC,Ideal are defined and/or predetermined via this second block 56. The ideal intermediate circuit voltage 31 U.sub.DC,Ideal is compared in a first comparison 36 to the minimum value 32 U.sub.DC,min. In addition, the ideal intermediate circuit voltage 31 U.sub.DC,Ideal determined using the equation is also compared in a second comparison 38 to the maximum value 34 U.sub.DC,max for the intermediate circuit voltage 31 U.sub.DC,Ideal.

[0046] If the first comparison 36 shows that the ideal intermediate circuit voltage 31 U.sub.DC,Ideal is to be lower than the minimum value 32 U.sub.DC,min provided for this purpose, a limited ideal intermediate circuit voltage 40 U.sub.DC,Ideal, lim determined as part of the limitation is set to the minimum value 32 U.sub.DC,min. If, on the other hand, the second comparison 38 shows that the ideal intermediate circuit voltage 31 U.sub.DC,Ideal calculated using the equation is to be greater than the maximum value 34 U.sub.DC, max provided for this purpose, the limited ideal intermediate circuit voltage 40 U.sub.DC,Ideal,lim to be determined is set to the maximum value 34 U.sub.DC,max. If the ideal intermediate circuit voltage 31 U.sub.DC,Ideal determined via the equation is to be minimally as low as the minimum value 32 U.sub.DC,min or maximally as high as the maximum value 34 U.sub.DC,max, the limited ideal intermediate circuit voltage 40 U.sub.DC,Ideal, lim also corresponds to the ideal intermediate circuit voltage 31 U.sub.DC,Ideal.

[0047] Such a limitation is carried out to protect components of the DC-AC converter 6 and to ensure that the DC-AC converter 6 functions properly. The line-to-line voltage 22 .Math..sub.LL is set by the DC-AC converter 6, wherein the line-to-line voltage 22 .Math..sub.LL is also independent of a limited ideal intermediate circuit voltage 40 U.sub.DC,Ideal,lim, which is adapted accordingly. If the electrical machine 8 is designed in one embodiment as a permanent-magnet synchronous machine (PSM), it is conceivable that it can influence the line-to-line voltage 22 .Math..sub.LL in towed operation of the vehicle.

[0048] Without the use of the DC-DC converter 4, a voltage of the battery and thus the input voltage of the DC-AC converter 6 also change between the limits, i.e., between the minimum value 32 U.sub.DC,min and the maximum value 34 U.sub.DC,max. A voltage at the input of the DC-AC converter 6 can be influenced using the DC-DC converter 4.

LIST OF REFERENCE SIGNS

[0049] 2 battery

[0050] 4 DC-DC converter

[0051] 6 DC-AC converter

[0052] 8 electrical machine

[0053] 10a, 10b line

[0054] 12a, 12b line

[0055] 14a, 14b, 14c conductor

[0056] 22 line-to-line voltage

[0057] 26 degree of modulation

[0058] 30 division

[0059] 31 ideal intermediate circuit voltage

[0060] 32 minimum value

[0061] 34 maximum value

[0062] 36 comparison

[0063] 38 comparison

[0064] 40 limited ideal intermediate circuit voltage

[0065] 50 determination unit

[0066] 52 computing unit

[0067] 54 block

[0068] 56 block