Electric machine with electrical conductor

Abstract

Vehicle with an N-phase inverter (1) and with an N-phase electric machine (3), wherein each phase of the inverter is assigned to a specific phase of the electric machine and is electrically connected to it via a phase conductor, wherein - an electrically conductive conductor system (5) is assigned to the phase conductors, - the conductor system (5) is arranged in an electrically insulated manner from the phase conductors, - the conductor system (5) is arranged essentially parallel to the phase conductors, - the conductor system (5) is essentially designed as an electrical flat conductor, and - the flat conductor is designed with N segments.

Description

[0001] The invention relates to a vehicle with an N-phase inverter and with an N-phase electric machine, wherein each phase of the inverter is assigned to a specific phase of the electric machine and is electrically connected to it via a phase conductor.

[0002] DE 103 12 254 A1 relates to a traction motor in electrically or diesel-electrically powered vehicles, wherein the traction motor mounted in a housing is earthed via an earthing capacitor.

[0003] JP 2006-080215 A discloses a power electronics system for vehicles in which a high-frequency potential change is not transmitted to the vehicle. Current, converted from direct current to alternating current by an inverter, is supplied to a motor via three shielded wires. The inverter and motor are housed separately in metal enclosures. The enclosures are grounded to the vehicle via ground wires.

[0004] DE 11 2009 002 491 T5 shows a vehicle motor drive system comprising: a motor mounted on an unsprung vehicle body and generating drive power for rotating a wheel when supplied with electric power; an inverter mounted on a sprung vehicle body, converting a direct electric current into an alternating electric current and then supplying the electric power to the motor; and a shielded wire as a power cable from the motor to the inverter.

[0005] DE 34 20 250 A1 discloses a device with which several stackable electrical devices, preferably with the same external dimensions, can be connected to a common power source. For this purpose, each of the devices is equipped with its own electrical cable, which has the plug part of a connector at one end and the socket part of a connector at the other end. When stacking the devices, the plug part and socket part of each device inevitably interlock, creating a continuous electrical cable.

[0006] Automotive drive technology increasingly uses electric motors that are supplied with electrical power by power electronic units known as inverters, converters, or drive electronics. In this process, more and more electrical and electronic components are being concentrated in a small installation space in a vehicle.

[0007] Due to the high clock frequencies of the inverter, which are in the very low frequency range, i.e. up to 100 kHz, high-frequency interference occurs. This interference is caused by harmonics of the sinusoidal fundamental wave of the phase currents and by the edge steepness of the switching signals through the inverter. In the frequency spectrum, this interference is in the range > 1 MHz. This interference spreads as voltage or current fluctuations via the phase conductors in the form of parasitic capacitances, i.e. capacitive coupling, and stray inductances, i.e. inductive coupling, sometimes throughout the entire vehicle and can interfere with other vehicle components such as a radio receiver. According to the state of the art, the electrical machine and the inverter can be earthed via a grounding wire as a measure against the interference signals, see for example EP 2514078 A1.

[0008] It is an object of the invention to describe an improved vehicle with an N-phase inverter and with an N-phase electric machine.

[0009] This object is achieved by a vehicle according to claim 1. Advantageous embodiments and further developments of the invention emerge from the dependent claims.

[0010] According to the invention, an electrically conductive conductor system is assigned to the phase conductors, the conductor system is arranged electrically insulated from the phase conductors and the conductor system is arranged substantially parallel to the phase conductors.

[0011] This means that the conductor system is essentially laid together with the phase conductors. The effect is that the impedance for interference currents in the vehicle is minimal and the voltage drop of the interference voltage is minimized. The minimized impedance results from the fact that interference currents, for physical reasons—referring to the basic principle that current spreads from higher potential to lower potential—have the property of closing an electrical interference circuit from the interference source to a sink. Here, the inverter acts as both a source and a sink.

[0012] According to a preferred embodiment of the invention, the conductor system has a first electrical connection and a second electrical connection, the first electrical connection is implemented within a housing of the inverter and the second electrical connection is implemented within a housing of the electrical machine.

[0013] In this design, the conductor system extends into the interior of the component housings. This has the particular advantage of delivering the interference current via a path with the lowest possible impedance and shortest possible spatial distance. The lower the impedance of the interference current circuit, the lower the interference voltage drop in the vehicle.

[0014] According to a further variant of the invention, the electrical inverter has a phase output for each phase, the first electrical connection is galvanically isolated from all phase outputs and the first electrical connection is connected to a first ground connection point within the housing of the inverter.

[0015] The electrical connection of the conductor system is therefore formed within the housing of the inverter, but isolated from the phase outputs and phase taps within the inverter.

[0016] According to a further embodiment of the invention, the electrical machine has a phase input for each phase, the second electrical connection is galvanically isolated from all phase inputs and the second electrical connection is connected to a second ground connection point within the housing of the inverter.

[0017] The electrical connection of the conductor system is therefore formed within the housing of the electrical machine, but isolated from the phase outputs and phase taps within the inverter.

[0018] Furthermore, it is advantageous if the first ground connection point is electrically connected to the housing of the inverter and the second ground connection point is electrically connected to the housing of the electrical machine.

[0019] This means that the two ground connection points within the respective housings establish an electrical connection to the respective housings.

[0020] In this way, a parasitic, capacitively coupled interference current, which is transmitted, for example, to the housing of the electrical machine, is discharged in a directed manner via the conductor system.

[0021] According to the invention, the conductor system is essentially designed as an electrical flat conductor, wherein the flat conductor is formed as N-members.

[0022] A multi-segment conductor has weight advantages over a single-segment flat conductor. A single-segment conductor, in particular, cleverly exploits the proximity effect, which causes a high-frequency interference current to flow at the shortest possible distance to the respective phase conductor through which the interference current propagates. This results in a current distribution within the flat conductor that essentially exhibits N current paths on the flat conductor, with each of the current paths being assigned to one of the N phase conductors. These current paths run parallel on the flat conductor at the shortest possible distance from the phase conductors.

[0023] The distance between the phase conductors and the conductor system is particularly important. Due to the proximity effect, the current flows back along the return conductor at the smallest possible distance to the respective phase conductors. This further minimizes the area spanned by the circuit consisting of the forward and return conductors, thus reducing the impedance. This, in turn, has a positive effect on the electrical emission behavior of the entire cable arrangement consisting of phase conductors and the conductor system, as it minimizes the interference voltage drop.

[0024] The invention is based on the following considerations: In mechanically connected combinations of an inverter (IV) and an electric machine (EM), the two components are often decoupled for acoustic and mechanical reasons. This decoupling results in galvanic isolation between the inverter and the machine. Currently, the state-of-the-art bridges the transitions resulting from this decoupling by flexible galvanic connections, particularly stranded wires, on the outer surfaces of the components.

[0025] The external connections transmit interference to the component housing, resulting in unwanted electromagnetic radiation. Furthermore, the stranded wires, due to their design and the required cable lengths, represent an increased impedance, which in turn leads to increased electromagnetic radiation from the components.

[0026] Electromagnetic radiation can affect both radio reception in a vehicle and other electronic components. Furthermore, external stranded wires are increasingly exposed to influences such as corrosion and aging, which further degrade their electrical properties over time and exacerbate negative electromagnetic radiation, which can interfere with other components.

[0027] In addition, metal strands, e.g. made of copper, represent a significant cost and weight factor.

[0028] High-frequency current or voltage disturbances emanating from the inverter unit and referred to here as I Stör or U Stör are superimposed on the useful signal of the electrical machine and spread to the machine via the phase lines or busbars arranged between the inverter and the EM.

[0029] For physical reasons - here we refer to the basic principle that current spreads from a higher potential to a lower potential - the disturbances have the property of closing an electrical circuit from the source (here the IV) to the sink (here also the IV).

[0030] However, due to a mechanical decoupling of EM and IV, a return path is galvanically interrupted. This galvanically high-impedance transition represents a potential source for the interference current I Stör Compared to a transition with a stranded wire according to the state of the art, this represents a higher impedance. This is due to the fact that the electrical interference circuit without a stranded wire has a longer current path, e.g., over body or housing parts. The longer current path also results in a further increase in the interference voltage U Stör compared to the situation with attached stranded wire.

[0031] An alternative approach is to cleverly optimize the length of the current path of the electrical interference circuit. To do this, a flat conductor common to all phases or assigned to each individual phase of the interference suppression device is insulated from the phase conductor and arranged parallel to it. This conductor or these conductors are referred to as a conductor system. The conductor system connects the electrical ground of the interference suppression device with the ground of the interference suppression device in its sealed area. The sealed area is an area within an interference suppression device housing that is suitably protected against moisture ingress, e.g., by a plastic enclosure.

[0032] This design is particularly advantageous. As an alternative to routing the interference current via a stranded wire from the housing exterior to the housing exterior, the interference current is routed from the EM within its housing back to the IV, i.e., along an optimized, short path parallel to the phase conductor. This leads to a reduction in the impedance of the interference current circuit by shortening the interference current return path to almost the maximum possible. This is made possible by routing the conductor system as close as possible to the phase conductors.

[0033] This measure results in a significant reduction in electromagnetic radiation. Compared to a single-strand connection, the problems of corrosion and aging of the electrical connection between the EM and IV are significantly reduced, while simultaneously reducing weight and cost.

[0034] A preferred embodiment of the invention is described below with reference to the accompanying drawings. Further details, preferred embodiments, and developments of the invention will become apparent from these.

[0035] In detail, schematically shows Fig. 1 Inverter and electrical machine with phase conductors and conductor system for interference suppression

[0036] The Fig. Figure 1 schematically shows a section of a high-voltage vehicle electrical system with a three-phase inverter (1) with three phase outputs (u, v, w) of a bridge circuit unit (2) of the inverter with three half-bridges. The phase currents are transmitted to a stator system of an electric machine (3) via three phase lines. The inverter, bridge circuit unit, and electric machine each have a housing (1a, 2a, 3a).

[0037] The phase currents are formed as a sinusoidal signal with respect to their fundamental waveform. Due to non-ideal system functioning and the steepness of the edge when switching the Hall bridges (in the kHz range), the fundamental waveform is superimposed in the frequency spectrum with high-frequency interference signals (in the MHz range).

[0038] At high frequencies, interference current circuits formed by the interference voltage U Stör an interference source (6) and the interference current I Stör predominantly closed by parasitic capacitances. For example, electromagnetic interference can be transmitted to the housing of the electrical machine via a parasitic capacitance (4) on the machine side. This effect is also referred to as common-mode interference.

[0039] According to the state of the art, the housing of the electrical machine (3a) is electrically connected to the housing of the inverter (2a) via an electrical conductor (not in Fig. 1 shown).

[0040] In order to prevent the connected components in the vehicle from being influenced by further couplings, according to the embodiment in Fig. 1, a conductor system (5, dashed line) is arranged between the inverter and the electrical machine. However, this conductor system does not essentially function as a return conductor for the functional phase currents of the neutral conductor system, but rather as a return conductor system for high-frequency interference currents of the electrical machine-inverter arrangement.

[0041] The conductor system is designed as a flat, metallic conductor that runs from within the housing of the bridge circuit unit to the interior of the housing of the electric machine, galvanically isolated from the phase outputs. The conductor system is also integrated into the electric machine, galvanically isolated from the phase inputs.

[0042] The respective electrical connections of the conductor system in the inverter and in the electric machine are conductively connected to ground connection points within these components. This can be the housing (3a) on the electric machine side and the housing of the bridge circuit unit (2a) on the inverter side, which are each contacted from their inner sides. Non-rigid, conductive elements (7a, 7b) are preferably suitable for mechanical decoupling from the respective housings, e.g., with ground straps.

[0043] Additionally, the metallic flat conductor is arranged parallel to the phase conductors with a minimal spacing. The minimum spacing is essentially limited by aspects such as requirements for ease of installation, short-circuit protection due to vibration, and minimum clearances and creepage distances for flashover protection.

[0044] This arrangement of the conductor system effectively returns interference currents to the interference source (6).

[0045] Due to the spatial proximity, the impedance of the conductor loop formed by the interference current circuit, consisting of the phase conductor and the flat conductor of the conductor system, is minimized. This results in a lower impedance compared to, for example, a technical solution with ground straps outside the components, according to which the return line is established via the outer housings of the electrical machine (3a) and inverter (1a) and a stranded wire electrically connecting them (not in Fig. 1). In this sense, the term impedance minimization is to be understood in this document.

[0046] Furthermore, by utilizing the proximity effect, an energetic optimization of the interference current flow and thus a further reduction of the inductance of the conductor loop via the conductor system is achieved compared to a solution, for example, using cables or stranded wires over the outside of the housing of the electrical machine and inverter.

[0047] The advantages of this solution include not only effective interference suppression in the high-frequency range, but also its durability and robustness. This is due to the fact that all electrical connections for interference suppression are located within the enclosure. This increases corrosion resistance.

Claims

[1] Vehicle with an N-phase inverter (1) and with an N-phase electric machine (3), wherein each phase of the inverter is assigned to a specific phase of the electric machine and is electrically connected to it via a phase conductor, wherein - an electrically conductive conductor system (5) is assigned to the phase conductors, - the conductor system (5) is arranged electrically insulated from the phase conductors, - the conductor system (5) is arranged substantially parallel to the phase conductors, - the conductor system (5) is essentially designed as an electrical flat conductor, and - the flat conductor is N-element. [2] Vehicle according to claim 1, characterized by , that - the conductor system (5) has a first electrical connection and a second electrical connection, - the first electrical connection is implemented within a housing (2a) of the inverter (1), and - the second electrical connection is implemented within a housing (3a) of the electrical machine (3). [3] Vehicle according to claim 2, characterized by , that - the electrical inverter (1) has a phase output for each phase, - the first electrical connection is galvanically isolated from all phase outputs, and - the first electrical connection is connected to a first ground connection point within the housing (2a) of the inverter (1). [4] Vehicle according to claim 3, characterized by , that - the electrical machine (3) has a phase input for each phase, - the second electrical connection is galvanically isolated from all phase inputs, and - the second electrical connection is connected to a second ground connection point within the housing (3a) of the electrical machine (3). [5] Vehicle according to claim 4, characterized by , that - the first ground connection point is electrically connected to the housing (2a) of the inverter (1) and - the second ground connection point is electrically connected to the housing (3a) of the electrical machine (3).

Images