Traction network and method for electric or hybrid vehicle

Abstract

The invention relates to a traction network (1) for an electric or hybrid vehicle, comprising a high-voltage battery (2), at least one inverter (3, 4), at least one intermediate circuit capacitor (C1, C2), and a traction line (HV +, HV-), the traction line (HV +, HV-) being designed as a one-piece cable, the traction line (HV +, HV-) being stranded in at least one section (A1), the traction line (HV +, HV-) being not stranded in at least one section (A2), the traction line (HV +, HV-) being connected to the high-voltage battery (2). The invention also relates to a method for determining a section (A1) having a strand.

Description

TECHNICAL FIELD

[0001] The invention relates to a traction network for an electric or hybrid vehicle and to a method for determining parameters of such a traction network. BACKGROUND

[0002] Traction networks for electric or hybrid vehicles have a high-voltage battery, at least one inverter, at least one intermediate circuit capacitor and a traction line, which is usually designed as a one-piece cable. Thus, the traction cable is a single piece of wire with an insulation layer.

[0003] Usually, undesired oscillating circuits are formed in the traction network, which generate undesired reactive currents, which then produce high magnetic field strengths along the traction line. Such undesired oscillating circuits are produced, for example, by the intermediate circuit capacitor and the line inductance of the traction line. These magnetic fields produce eddy currents in the adjacent vehicle body and exert forces on the vehicle body, which leads to vibrations of the vehicle body and, in turn, to interference noises in the kilohertz range. This problem becomes even more severe in unshielded traction lines, since they eliminate the ohmic attenuation of the shield, so that the quality of the parasitic oscillating circuits is higher and, thus, the interference resonances are more pronounced.

[0004] From DE 10 200 8 051 495 A1 a traction line for an electric or hybrid vehicle is known. The problems that arise due to high magnetic field strengths are also solved there, mainly with regard to the interference of other components, such as adjacent low-voltage cables. There, the basic possibility of twisting the traction cable to reduce the magnetic field is discussed. However, this approach is rejected, since the traction line is difficult to twist due to its thickness and a small twisting distance (lay length) cannot be achieved during the twisting.

[0005] In order to solve this problem, DE 10 200 8 051 495 A1 proposes to divide the cable into a large number of thin wires and then to twist the thin wires of HV+ and HV- in pairs, which twisted pairs are tied and untied again at their ends. However, this is very complex in terms of reinforcement technology, since each thin wire has to be insulated. Another problem of the twisting is the increase of the total length of the cable, which leads to weight and cost problems. Another problem is that the twisting reduces the inductance, which shifts the resonance frequency to higher frequencies. If the resonance frequency moves in the range of the clock frequency of the pulse inverter, power losses can occur. SUMMARY

[0006] The technical problem addressed by the invention is to create a traction network for an electric or hybrid vehicle, in which the interference noise is reduced.

[0007] The solution to the technical problem is derived from a traction network having the features of claim 1. Further advantageous embodiments of the invention result from the dependent claims.

[0008] The traction net for an electric or hybrid vehicle comprises at least one high voltage battery, at least one inverter, at least one intermediate circuit capacitor and traction lines, each traction line being designed as a one-piece cable, i.e. in particular not consisting of a multitude of thin single wires. Two traction lines are twisted in at least one section, while the traction lines are not twisted in at least one section. The basic idea is to twist the traction lines only in certain areas where due to the design large eddy currents are induced in the vehicle body, thereby reducing the magnetic field strength generated and thus the noise. Since the twisting does not occur over the entire length, the change in the resonance frequency is not critical. The additional weight is also reduced compared to a complete twisting. It is also possible to provide a plurality of sections in which both traction lines are twisted. The length of the sections with twisting is preferably less than 75% of the total length and more preferably less than / equal to 50% of the total length.

[0009] In one embodiment, the traction lines are designed as unshielded traction lines.

[0010] In another embodiment, elements are arranged at the end of the sections and are designed to prevent untwisting. For example, the ends can be fixed with a wrapping tape or a cable tie and elements must also be provided which prevent rotation within the section.

[0011] In an alternative embodiment, the ends of the sections are fixed to a member which is rigidly mounted as such.

[0012] In another embodiment, the traction net has at least one second inverter with at least one second intermediate circuit capacitor. This makes it possible, for example, to implement all-wheel drive. However, this leads to the current on the traction lines becoming greater and, due to the larger capacitance, the resonance frequency is shifted to higher frequencies.

[0013] In another embodiment, the high voltage battery is connected to at least one further auxiliary unit, wherein the supply line to the at least one further auxiliary unit is twisted in at least one section and not twisted in at least one section.

[0014] The sections in which the traction lines should be twisted can be determined, for example, by acoustic tests. Preferably, critical sections are predetermined.

[0015] To this end, a method for determining the twisted sections of the traction net described previously is proposed, the method comprising the following steps:

[0016] - creating a traction net model by taking into account the vehicle body data,

[0017] - implementing a field simulation procedure by applying and varying the current on the traction lines,

[0018] - calculating the vehicle body current,

[0019] - determining areas of high current density in the vehicle body,

[0020] - repeating the method steps for the sectionally stranded traction line in the areas of high current density, wherein the length of the sections and the lay of the stranding are varied, and

[0021] - determining the length of the sections and the lay with at least one local minimum of the current density.

[0022] The sections determined in this way can then be produced using the determined lays. BRIEF DESCRIPTION OF DRAWINGS

[0023] The application is explained in more detail below using preferred exemplary embodiments. The drawings show:

[0024] Figure 1 Schematic block diagram of a traction network with two inverters,

[0025] Figure 2 Schematic diagram of a partially stranded traction cable,

[0026] Figure 3 Schematic diagram of the current gain versus frequency for unshielded and shielded traction lines,

[0027] Figure 4 Schematic diagram of the current amplification for unstranded, partially stranded and fully stranded unshielded traction lines

[0028] Figure 5 Schematic flow diagram for determining the stranding sections. DETAILED DESCRIPTION

[0029] Figure 1 A traction network 1 for an electric vehicle is shown very schematically. The traction network 1 has a high-voltage battery 2 and two inverters 3, 4, which are preferably designed as pulse inverters. An intermediate circuit capacitor Cl is arranged on the DC voltage side of the inverter 3, and a further intermediate circuit capacitor C2 is arranged on the DC voltage side of the inverter 4. Electric machines 5, 6 are arranged on the AC voltage side of the inverters 3, 4. The high-voltage battery 2 is connected to the inverters 3, 4 via the traction lines HV+, HV-. A supply line 7 is also shown, via which the high-voltage battery 2 is connected to a further auxiliary unit 8 (for example an air-conditioning compressor, a heater,...).

[0030] The two intermediate circuit capacitors Cl, C2 and the traction lines HV+, HV- with their inductances L form an oscillating circuit, the resonant frequency f res approximately applies:

[0031]

[0032] In the case of an unshielded traction network 1, the line inductance L increases compared to a shielded vehicle electrical system. This means the resonance is more pronounced. Furthermore, the unshielded cable has lower losses (ohmic component, R) compared to a shielded cable. This increases the quality Q of the oscillating circuit and increases the resonance gain.

[0033]

[0034] If the clock frequency of at least one of inverters 3 and 4 is now selected so that it is within the range of the resonant frequency, then a very high reactive current of tens or hundreds of A will be exhibited.

[0035] These currents generate a high magnetic field along the traction wire, leading to losses (current heat, conduction) and load or heating of intermediate circuit capacitors C1 and C2. Furthermore, voltage fluctuations in the onboard electrical system can negatively impact the function of the HV components and potentially reduce the torque delivered by the drive.

[0036] To better understand, when the stimulus (I) PWR If the current is constant at 1 A, the system behavior can be interpreted as the current gain a. i . Figure 3 Examples of shielded and unshielded systems are shown, with a line length of 3 m and capacitances of C1 = 600 µF and C2 = 400 µF.

[0037] Current gain a i Displayed as a function of frequency, where solid lines represent unshielded traction wires and dashed lines represent shielded traction wires.

[0038] Then you can consider measuring or calculating the inverter current (I0). PWR To estimate the reactive current in the system, as shown below:

[0039]

[0040] Figure 2 The diagram now schematically illustrates how the traction wires HV+ and HV- are twisted together in section A1, and how they are untwisted in another section A2. Element 9 is positioned at the end of section A1 to prevent the traction wires HV+ and HV- from untwisting. Twisting reduces the inductance L, causing the resonant frequency to shift to a higher frequency, such as... Figure 4 As shown. The unshielded, unstretched traction wires HV+ and HV- have the highest current gain a. i The solid lines show the resonant behavior of the partially stranded traction wires HV+ and HV- (e.g., Figure 2 (As shown). The fully stranded traction lines HV+ and HV- have the lowest current gain a. iHowever, it has the highest resonant frequency. Therefore, in addition to its weight advantage, the partially stranded traction wires HV+ and HV- also have an advantage in terms of resonant frequency.

[0041] Figure 5 A possible flowchart for determining segment A1 is shown. In the first step S1, a model of the traction cable 1 is built considering vehicle body data. Material properties of the vehicle body panels and weld joints are preferably considered. Such vehicle body data is typically provided in NASTRAN format. For example, the planned wiring of the traction cable is taken from a harness list (KBL data). In the second step S2, a field simulation is then performed, thereby specifying the current (and determining the resulting current density in the vehicle body in a locally analytical manner). In the third step S3, regions with high current density in the vehicle body are identified from the simulation data, i.e., regions with current densities greater than a threshold. In the fourth step S4, the length of segment A1 of the traction cable strand is then varied. Furthermore, the strand pitch is also varied, and the simulation in step S2 and the determination in step S3 are repeated, with the corresponding results temporarily stored (step S5). An evaluation is then performed in step S6, where the length of segment A1 and the strand pitch with at least one local minimum current density in the body are selected, because effects such as resonant frequency or weight should be taken into account. Therefore, the global minimum current density is not necessarily the optimal overall solution. In step S7, the selected data is then put into production.

[0042] List of reference numerals

[0043] 1 Traction net

[0044] 2. High-voltage battery

[0045] 3 Inverter

[0046] 4 Inverter

[0047] 5 motors

[0048] 6 motors

[0049] 7 Power supply lines

[0050] 8 Auxiliary Units

[0051] 9 components

[0052] HV+ traction line

[0053] HV-traction line

[0054] Section A1

[0055] Section A2

[0056] C1 intermediate circuit capacitor

[0057] C2 intermediate circuit capacitor

Claims

1. Traction network (1) for an electric or hybrid vehicle, comprising a high-voltage battery (2), at least one inverter (3, 4), at least one intermediate circuit capacitor (CI, C2) and a traction line (HV+, HV-), wherein, The traction line (HV+, HV-) is designed as a one-piece cable, characterized in that the traction line (HV+, HV-) is stranded in at least one section (A1), wherein the traction line (HV+, HV-) is not stranded in at least one section (A2).

2. The traction net according to claim 1, characterized in that The traction line (HV+, HV-) is designed as an unshielded traction line.

3. Traction net according to claim 1 or 2, characterized in that An element (9) is arranged at the end of the section (A1), which is designed to prevent unstranding.

4. Traction net according to claim 1 or 2, characterized in that The end of the section (A1) is fixed to a component.

5. Traction net according to any of the preceding claims, characterized in that The traction network (1) has at least one second inverter (4) with at least one second intermediate circuit capacitor (C2).

6. Traction net according to any of the preceding claims, characterized in that The high-voltage battery (2) is connected to at least one further auxiliary unit (8), wherein the supply line (7) to the at least one further auxiliary unit (8) is stranded in at least one section (A1) and not stranded in at least one section (A2).

7. A method for determining a section (A1) with stranding of a traction network (1) according to claim 1, comprising the following steps: - establishing a model of the traction network taking into account the body data (S1), - carrying out a field simulation procedure by applying a current on the traction line (S2), - calculating the body current, - determining areas of high current density in the body (S3), - repeating the method steps for a sectionally stranded traction line in the areas of high current density, wherein the length of the section and the lay of the stranding are varied (S4), - determining the length of the section (A1) and the lay at which the current density has at least one local minimum (S6).

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