Voltage converter for a motor vehicle

Abstract

The disclosure relates to a voltage converter (100) for a motor vehicle, wherein the voltage converter (100) is connectable to a high-voltage network (HVN), in particular a high-voltage battery (HVB), of the motor vehicle, and to a low-voltage network (LVN), in particular a low-voltage battery (LVB), of the motor vehicle, wherein the voltage converter (100) is configured to convert a high-voltage direct current (HV) applied to the high-voltage network (HVN) into a low-voltage direct current (LV) output at the low-voltage network (LVN), and / or to convert a low-voltage direct current (LV) applied to the low-voltage network (LVN) into a high-voltage direct current (HV) output at the high-voltage network (HVN), comprising: - a low-voltage switching device (110) for controlling and / or monitoring the voltage converter (100),and- a low-voltage interface (120) for feeding the low-voltage direct current (LV) from the voltage transformer (100) into the low-voltage network (LVN) and / or for feeding the low-voltage direct current (LV) from the low-voltage network (LVN) into the voltage transformer (100), wherein the low-voltage interface (120) comprises:- a low-voltage interface positive terminal (121), and- a low-voltage interface negative terminal (122), wherein the low-voltage interface positive terminal (121) is connectable to the low-voltage network (LVN) via a first high-ampere line (HAL), and / or wherein the low-voltage interface negative terminal (122) is connectable to the low-voltage network (LVN) via a second high-ampere line (HAL').

Description

The disclosure relates to a voltage converter for a motor vehicle. Voltage converters are well known in the automotive industry and are installed in vehicles, especially electric vehicles, between high-voltage networks, particularly high-voltage batteries (e.g., 800V or 400V batteries), and low-voltage networks, particularly low-voltage electrical systems (such as 12V electrical systems) or low-voltage batteries (e.g., 12V batteries). German patent application DE 10 2022 106 978 A1 discloses a converter device for a vehicle's electrical system. German patent application DE 10 2021 200 414 A1 relates to a vehicle's electrical system. German patent application US 2015 / 0291041 A1 discloses a power supply device for a vehicle. Voltage converters are known that are designed to convert a high-voltage direct current (DC) voltage applied to a high-voltage network into a low-voltage DC voltage output from a low-voltage network. Such voltage converters are also called High Voltage to Low Voltage Direct Current to Direct Current Converters (abbreviated "HVLVDCDC" or "HLD"). These voltage converters can alternatively or additionally convert a low-voltage DC voltage applied to a low-voltage network into a high-voltage DC voltage output from a high-voltage network. If both functions are performed simultaneously, it is called a bidirectional HLD. The voltage converter includes a low-voltage switching device (often referred to as the "LV part" or "internal LV switching part(s)" or "LV part"). The low-voltage switching device is designed to control and / or monitor the voltage converter and can, for example, establish communication with other components in the low-voltage network and / or the vehicle's high-voltage network. Furthermore, the voltage converter includes a low-voltage interface for feeding the low-voltage DC voltage from the voltage converter into the low-voltage network and / or for feeding the low-voltage DC voltage from the low-voltage network into the voltage converter, wherein the low-voltage interface includes a low-voltage interface positive terminal and a low-voltage interface negative terminal. The low-voltage switching device has typically been supplied with low-voltage DC voltage and grounded via the vehicle's low-voltage electrical system. The vehicle's low-voltage electrical system comprises a first low-ampere line (e.g., "terminal 30" of the 12 V electrical system) and a second low-ampere line (e.g., "terminal 31" of the electrical system), wherein a positive terminal of the low-voltage battery can be connected to the first low-ampere line, and a negative terminal of the low-voltage battery can be connected to the second low-ampere line. The low-voltage electrical system is designed, for example, to supply and / or control a low-voltage DC load via the first and second low-ampere lines. The first and / or the second low-ampere line preferably have a conductor cross-section of no more than 35 mm², preferably 25 mm².This is advantageous because only small electrical currents flow through these lines, typically a maximum of 30 amperes. Such low electrical currents are advantageous and therefore desirable for supplying and / or controlling the low-voltage network, especially low-voltage loads within the network (e.g., in CAN bus systems). The low-ampere lines are designed accordingly, for example, in terms of conductor length and cross-section. Supplying power and grounding the low-voltage switching device of the voltage converter via the vehicle's low-voltage network is disadvantageous and ineffective. Firstly, the voltage converter itself generates low-voltage DC voltage suitable for powering the low-voltage switching device. Secondly, supplying power and grounding the low-voltage switching device via the vehicle's low-voltage network represents a significant additional expense in terms of providing further components (such as connectors, cables, etc.). Previously, current was typically exchanged between the vehicle's low-voltage battery and the low-voltage interface of the voltage converter via the low-ampere lines of the low-voltage network, for example, to charge the low-voltage battery or to pre-charge the high-voltage network. This is disadvantageous because the low-ampere lines are designed to carry small currents, which can slow down or impair the charging of the low-voltage battery or the pre-charging of the high-voltage network. Furthermore, if high (charging) currents are reached, the low-ampere lines of the low-voltage network can be overloaded (e.g., thermally). The object of the present invention was, among other things: - to eliminate the need to connect the low-ampere lines of the low-voltage network (e.g., terminals 30 and 31 of the 12V electrical system) and the associated additional effort; - to utilize the existing voltage potentials in such a way as to achieve as many advantages as possible from a strategic and financial point of view; - to process possible potential differences between the components of the voltage converter and the other vehicle components in such a way that no disadvantages result; - to find a concept regarding grounding, supply, and separation that meets the requirements with minimal effort, power consumption, space requirements, and weight. At the very least, the purpose of the invention is to create an alternative to the state of the art. The invention solves the problem(s) according to claim 1. Preferred embodiments are the subject of the dependent claims. According to the present disclosure, the low-voltage interface positive terminal can be connected to the low-voltage network, in particular to a low-voltage battery positive terminal of the low-voltage battery, via a first high-ampere line, and / or the low-voltage interface negative terminal can be connected to the low-voltage network, in particular to a low-voltage battery negative terminal of the low-voltage battery, via a second high-ampere line. The low-ampere lines of the low-voltage network are not designed or suitable for the higher currents required to charge the low-voltage battery or pre-charge the high-voltage network via the voltage converter (up to 240 A) (see above). Using the high-ampere lines is advantageous. In particular, the first high-ampere line and / or the second high-ampere line can have a conductor cross-section of at least 40 mm², preferably 50 mm². This allows higher charging currents of up to 240 A to be realized for charging the low-voltage battery and / or for pre-charging the high-voltage network. Compared to the prior art, the low-voltage circuitry of the voltage converter can include a ground wire, which is conductively connected to the negative terminal of the low-voltage interface of the voltage converter. Microcontrollers, power supply and logic circuits, as well as the gate driver side of the low-voltage circuitry, reference the negative terminal of the low-voltage interface. The low-voltage circuitry does not need to be grounded via the low-voltage network. No additional effort is required for providing further components (e.g., connectors, cables, etc.). Furthermore, the low-voltage circuit device can include a power supply line, which is conductively connected to the positive terminal of the low-voltage interface. Microcontrollers, power supply and logic circuits, as well as the gate driver side of the low-voltage circuit device, are powered by the positive terminal of the low-voltage interface. The low-voltage circuit device does not need to be powered via the low-voltage network (LVN). No additional effort is required for providing further components (e.g., connectors, cables, etc.). The negative terminal of the low-voltage interface, in particular the second high-amperage line, can be connected to a conductive chassis of the vehicle for grounding the low-voltage switching device and / or the low-voltage interface. This advantageously eliminates the need for additional components (such as cables, connectors, etc.). The voltage converter may include a separation barrier and / or an overcurrent protection device. The separation barrier and / or the overcurrent protection device may preferably be arranged between the low-voltage switching device and the low-voltage interface. The separation barrier may provide a minimum resistance, in particular of at least 300 ohms, thus limiting the current flow between the low-voltage switching device of the voltage converter and the vehicle's low-voltage network. The overcurrent protection device may be configured to interrupt the current flow between the low-voltage switching device of the voltage converter and the vehicle's low-voltage network when a maximum current is exceeded. Consequently, unwanted currents between the low-voltage switching device and other low-voltage components, particularly the low-voltage network, can be minimized or avoided.Such unwanted currents result in particular from potential differences between the voltages present at the low-voltage interface of the voltage converter and at the low-voltage network of the vehicle. The voltage converter can include a housing in which the low-voltage interface negative terminal is insulated from the housing, thus preventing current flow from the low-voltage interface negative terminal through the housing. This can be advantageous, for example, to avoid unwanted currents through high-voltage components of the voltage converter and / or the vehicle, particularly through the high-voltage shields of high-voltage cables. Undesired return current paths from the low-voltage interface or from the low-voltage switching device through the housing to high-voltage components of the vehicle, or vice versa, can be effectively avoided. For example, screw connections between the circuit board and the housing are not connected to the ground wire of the low-voltage interface. Reference symbol list 100Voltage ConverterHV Component / HLD / High Voltageto Low Voltage Direct Current to DirectCurrent Converter / HVLVDCDC 110 Low-voltage switching device LV part / (Internal) LV switching part(s) / LV part 111 Power supply line 112 Ground wire LV ground / Ground of the LV circuit components 120 Low-voltage interface (12V) power interface 121 Low-voltage interface positive terminal B+ bolt 122 Low-voltage interface negative terminal B-bolt 130 Separation barrier 140 Overcurrent protection device 150 cases HV High-voltage direct current HVN High-voltage network HV-DC network / HV-DC electrical system HVBHigh-voltage batteryHV battery / HV Battery / HV-Bat LV Low Voltage Direct Current LVN Low-voltage network LV-on-board power supply / 12V network / 12-V on-board power supply LVB Low-voltage battery LV battery / 12-V battery LVBP Low-voltage battery positive terminal Positive terminal of the 12V battery LVBM Low-voltage battery negative terminal Negative terminal of the 12V battery LVV Low-voltage consumer LV load 1 / LV load 2 / External LV circuit section(s) LAL First low ampere line Terminal 30 / T30 LAL'Second low ampere line Terminal 31 / T31 HAL First High Ampere Line HAL' Second high amperage line / vehicle chassis The above list of reference numerals contains the reference numerals used in the first column, the generic terms used for each of these reference numerals in the second column, and the example terms (not an exhaustive list) that can be used for each of these generic terms in the third column. Any embodiments of this disclosure relating to the example terms are applicable by analogy to any embodiments encompassed by the generic terms. Any embodiments of this disclosure relating to the generic terms are applicable by analogy to any embodiments encompassed by the example terms. Any embodiments relating to the generic terms and / or the example terms can be combined arbitrarily. Character description The revelation is illustrated by way of example in the following figures. These show: - In Diagram 1a to c: A circuit diagram of the voltage transformer according to the revelation - In Diagram 2: A circuit diagram of the voltage transformer according to the revelation HV and LV in vehicles High-voltage (HV) components in electric vehicles almost always also contain low-voltage (LV) circuitry. The LV section typically controls and monitors the HV section and establishes communication with other LV components in the vehicle. Diagrams 1a to c show an example and simplified section of a vehicle's electrical system. Two low-voltage (LV) and three high-voltage (HV) components are shown. LV system To supply the low-voltage (LV) portion of such components, 12 V and ground are typically connected (e.g., vehicle terminals 30 and 31). However, instead of a constant positive supply, switched branches can also be used (e.g., terminal 30T, terminal 15, terminal 30c, etc.). This explanation also applies to other LV voltages below 60 V, such as 24 V or 48 V systems (the corresponding supply terminals have different numbers). For the sake of simplicity, the following discussion will only refer to the 12 V system and terminals 30 and 31. The negative terminal of a 12V battery is usually connected to the vehicle chassis. However, this revelation also applies to vehicles where the negative terminal of the LV battery is not connected to the chassis. The housing of LV components can be, but does not have to be, connected to the vehicle body. Vehicle components are usually interconnected via low-voltage (LV) lines, e.g., via analog measuring lines, digital signal lines, or via communication bus lines (e.g., CAN bus). HV system High-voltage (HV) components can be connected to other HV components in the vehicle via HV cables: - These HV cables are usually shielded. - For EMC reasons, the shield is usually connected to the housings of the HV components on both sides. Conductive housings of high-voltage components must be connected to the vehicle chassis. The connecting cable for this so-called equipotential bonding is subject to special requirements (e.g., limiting the ohmic resistance). HLD for LV supply in vehicles without combustion engines Vehicles powered by fossil fuels typically have a generator (alternator) that converts the mechanical energy of the drive shafts, which comes from an internal combustion engine or is generated through recuperation, into electrical energy and uses it to charge a 12V battery or supply the 12V electrical system. In vehicles that obtain the necessary energy for propulsion from a battery (hereinafter referred to as HV battery), the former alternator is usually replaced by an HLD (High Voltage to Low Voltage Direct Current to Direct Current Converter, HVLVDCDC). In forward operation (buck mode), the HLD supplies the 12V electrical system or charges the 12V battery with energy from the HV-DC electrical system. This energy originates from the HV battery or is generated through recuperation in the HV electric motors and fed back into the system by the HV inverters. The positive and negative terminals of the HLD's 12V power interface are referred to as B+ and B- terminals: - The B+ terminal is connected to the positive terminal of the 12V battery via a wire. - The B- terminal is connected to the negative terminal of the 12V battery via a wire. The vehicle chassis can also be used as a conductor, either partially or completely, instead of a wire. - Considerable currents, e.g., 200 A, flow through B+ and B-. Some HLDs are also able to temporarily transfer energy in reverse from LV to HV, called reverse operation (boost mode), e.g. to precharge the HV-DC network before it is connected to the HV battery, or to test the health of the LV battery. Diagram 1a to c shows an HV component on the right-hand side, which contains an HLD. Energy is transferred from the HV to the LV side using a transformer. If terminals 30 and 31 are used in the HV component containing the HLD, parallel paths exist to the connections via B+ and B-. Care must then be taken to ensure that the high currents do not unintentionally flow through terminals 30 and 31 in certain cases, as these typically have a small conductor cross-section. Diagrams 1a to c show terminals 30 and 31. They are not connected to the component containing the HLD in the diagram. Also not shown are additional components required between the LV battery and terminal 30, such as distribution boxes, switches, and fuses. Parallel single-wire connections, used to avoid cable harness branches, are also not shown. Separation of the HLD negative pole The negative terminal of the 12V output of the HLD can be connected to the housing of the component containing the HLD, or it can be isolated from its housing. This revelation can be applied in both cases. The motivation for such separation is to ensure that return current enters the high-voltage terminal (HLD) only or predominantly via the negative terminal, and not, or only minimally, via the housing. This avoids unwanted return current paths that could flow through the ground shields of high-voltage (HV) cables and overload them (see "HV System" above): If the vehicle body is used for the B current path, the separated B terminal can be bolted to it via a ground strap. This connection bridges the insulation between the B terminal and the housing, as the housing is also connected to the chassis via suspension and equipotential bonding. However, unwanted currents through the housing are still dampened if the path between the mounting point and the low-voltage (LV) battery has a lower resistance than the path back to the housing and via the HV shields.- This ground cable should not be confused with the equipotential bonding, which connects the housing and chassis and must meet specific requirements. - In the worst case, the B ground cable could be interrupted. The negative output of the HLD would then draw current from the housing via the isolation, which (in terms of conventional current direction) would enter either through the HV cable shields or via the equipotential bonding. The current through the HV cable shields must be limited to an acceptable level by resistive isolation, e.g., 10 A. - In this context, "insulation between B and housing" does not necessarily mean insulation in the sense of insulation coordination as protection against electric shock. In most cases, resistive isolation (resistive decoupling, minimum contact resistance) is sufficient. - Diagrams 1a to c show the intended return current path (thick line) in Fig. 1a, and in Figs. 1b and 1c...1c Two examples of unwanted backflow paths (thick line in each case) in B- separated from the housing. If the B-bolt is not to be separated from the housing but connected to it, then there must be no parallel current paths, i.e., there must be no shielded HV connections to other HV components, or currents via these paths must be suppressed by other means. Protection of the HLD against static and dynamic reverse polarity It could happen that when replacing the 12V battery in the vehicle, a permanent polarity reversal occurs, or that the 12V system is reversed for a certain period of time (e.g., several minutes) when jump-starting from an external source. Since HLDs often contain semiconductor switches on the output side that can only interrupt the current in one direction, the HLD represents a short circuit in these cases. Even during operation, brief (< 5 ms) polarity reversals can occur, for example, if the HLD goes into emergency shutdown during forward operation with high current flow, due to the inductance of the B+ B- loop:- Since HLDs often contain electrolytic capacitors on the output side, which must not be reversed, this can lead to damage to components. To prevent such damage, there are various solutions: One possibility is, for example, to use one (or several parallel) switches connected in series to the B+ terminal inside, referred to below as RPP (Reverse Polarity Protection) switches. These allow current flow via B+ from the outside to the inside at all times, but from the inside to the outside only when the HLD (High Voltage Device) is switched on, and as long as B+ has a higher voltage potential than B-. Control of the HLD Since the number of microprocessors should be kept low due to software overhead, the HLD often shares its controlling microprocessor with other subcomponents. Frequently, the HLD's control is handled by a central microcontroller in the LV circuitry, but control from the HV side would also be possible. Diagrams 1a to c show an impedance in the component containing the HLD, representing internal LV loads. One of these could be a system base chip that generates additional voltages such as 5 V, 3.3 V, or 1.1 V from the 12 V supply and uses them to power a microprocessor. The microprocessor itself is not shown in Diagrams 1a to c. Diagram 2 shows a highly simplified example of an HV component with an HLD, specifically an HV box: - It contains an HLD, an onboard charger (OBC), and a junction box (JB). - The HV component has different voltage domains: the LV domain and various HV domains (HV-DC domain, HV-AC-Grid domain). - A microprocessor MCU1 located in the LV domain handles overall control and the control of the HLD. - A second microprocessor MCU2, located in the HV-AC-Grid domain and referenced to N, controls the OBC. - Both microprocessors are connected to each other via an isolated CAN bus. - MCU1 communicates with the vehicle via a non-isolated CAN bus and a digital interface T30c. - Terminals T30 and T31 are often also connected (but not in this disclosure). Effort required for connecting terminals 30 and 31 All HV components (including HV components that include an HLD) require a power supply for their LV circuitry and therefore usually also a connection to terminals 30 and 31, including: - the cable harnesses required for this and - the fuse required to protect the line. This represents a considerable amount of effort and expense. Use and separation of available voltage potentials In components containing an HLD, its output potentials B+ and B- are also available for internal use. However, these can differ from terminals 30 and 31 due to the following reasons: - High DC currents – e.g., between B+ and the positive terminal of the 12V battery – cause a (usually small) voltage drop across the resistive conductor of the corresponding cable for the duration of the current flow. - At terminal 30, for example, only small or medium supply currents typically flow, so such a voltage drop does not occur there, or only minimally. - High current gradients, combined with the conductor inductances of the corresponding current paths (e.g., loop B+ / cable / 12V battery / chassis / B-), lead to short-term (sometimes significant) voltage spikes or undervoltages (e.g., between B+ and B-), up to and including reverse polarity. High current gradients are caused, for example, when switching high-current consumers on and off, during contact interruptions at the B+ or B- terminals, or during an emergency shutdown of the high-voltage disconnect device (HLD) during high current flow.- In the loop between terminal 30, the load, and terminal 31, only small or medium supply currents typically flow, so the voltage fluctuations that occur there are smaller and occur at different times. - This results in voltage differences both between B+ and terminal 30, and between B- and terminal 31. - Both effects are more pronounced the further the low-voltage battery is from the high-voltage terminal (HLD). Depending on the location in the vehicle, this can involve cable lengths of several meters. These potential differences can cause problems if different circuit components use different power rails and ground references. Additional voltage potentials that must be considered are supplied via existing LV interfaces to other devices. If B- is separated from the housing and therefore its voltage can also differ, the number of voltage potentials increases even further. At the same time, the number of microprocessors should be kept low due to the software overhead. Since one and the same microprocessor cannot easily handle circuit sections with different voltage references, a decision must be made regarding which potentials are used and how, in order to minimize costs (e.g., for isolated couplers or differentially measuring operational amplifiers) and the disruptive influence of the potential differences. The task was to: - eliminate the connection of terminals 30 and 31 and the associated additional costs for components containing an HLD; - utilize the existing positive and negative potentials in such a way as to achieve as many advantages as possible from a strategic and financial perspective; - process possible potential differences in such a way that no disadvantages arise; - find a concept regarding mass, supply and separation that meets the requirements with minimal effort, power consumption, space requirement and weight. Diagrams 1a to c and 2 each show a constellation in which terminals 30 and 31 are no longer connected to the component containing the HLD. The problem was solved, for example, by the following three concepts, which can solve the problem separately and in any combination: Ground Concept: Compared to the known prior art, the low-voltage switching device (110) of the voltage converter (100) can include a ground line (112), wherein the ground line (112) is conductively connected to the low-voltage interface negative terminal (122) of the low-voltage interface (120) of the voltage converter (100) for grounding the low-voltage switching device (110). Microcontrollers, power supply and logic circuits, as well as the control side of gate drivers located in the low-voltage switching device (110) reference the low-voltage interface negative terminal (122) of the low-voltage interface (120). The low-voltage switching device (110) does not need to be grounded via the low-voltage network (LVN). No additional effort is required for providing further components (e.g., connectors, cables, etc.). The ground of the LV circuit components within the component containing the HLD is not connected to the vehicle terminal 31, but to the ground of the B-bolt of the HLD. Terminal 31 is not connected to the device. The hatched area in Diagram 2 shows the circuit parts that reference B. Incoming 12V digital signals are evaluated relative to B-, outgoing signals use the B- reference for the "low" level. Within the LV circuit sections, other potentials can be used as ground, e.g., PowerGround, especially if an EMC filter such as a common-mode choke is located between the B output and the HLD for EMC reasons (this may be necessary because a B output not connected to the chassis emits more conducted interference; see Diagram 2). The output of gate drivers and the source terminal of low-side MOSFETs located in the LV power section (Diagram 2, "LV Power Part") then reference, for example, this PowerGround (in this case, the gate drivers have a separation or isolation between the drive side, which references B, and the output side). Microcontrollers, power supply and logic circuits, as well as the control side of gate drivers located in the LV domain, each reference B potential. Diagrams 1a to c also show the connection of the internal LV mass with B-. Supply concept Furthermore, the low-voltage switching device (110) can include a power supply line (111), wherein the power supply line (111) is conductively connected to the low-voltage interface positive terminal (121) for the power supply of the low-voltage switching device (110). Microcontrollers, power supply and logic circuits, as well as the control side of gate drivers located in the low-voltage switching device (110) are supplied with voltage via the low-voltage interface positive terminal (121) of the low-voltage interface (120). The low-voltage switching device (110) does not need to be supplied with voltage via the low-voltage network (LVN). No additional effort is required for providing further components (e.g., connectors, cables, etc.). The low-voltage circuit components (including microcontroller, etc.) are not powered by the vehicle's terminal 30, but by the B+ terminal of the high-voltage terminal block. Terminal 30 is not connected (and therefore not measured or monitored). This takes advantage of the fact that the HLD itself is the component that supplies the LV electrical system and the LV battery by drawing energy from the HV-DC network and transferring it to the LV electrical system. Since B+ and B- are connected to the LV battery, a power supply is provided even when the HLD is inactive: - To power up the component containing the HLD and to power up the HLD itself, energy is drawn from the outside via B+ and B-. - As soon as the forward operation (buck mode) of the HLD is active, energy is supplied to the outside via B+ and B-. For incoming 12V digital signals, an input measurement range is used that includes sufficient margin to accurately detect the signal, even if its voltage is elevated due to potential differences. Outgoing 12V digital signals use the B+ reference to generate a "high" level. The voltage difference between B+ and B- can fluctuate significantly, more so than that between terminals 30 and 31 (due to the high currents and current gradients, as follows):- Therefore, B+, B-, and the connected LV circuit components are protected against overvoltage (including voltage transients according to ISO 7637-2), undervoltage, and short-term reverse polarity by using, for example, reverse polarity protection diodes, buffer capacitors / filters, and / or by using components that tolerate limited short-term reverse polarity (e.g., special electrolytic capacitors that are also approved for short-term, minor reverse polarity).- RPP switches, as another possible protective measure against (here: short-term) reverse polarity, help to limit the magnitude of the negative voltage between B+ and B- in the internal circuit components, but increase the magnitude of the negative voltage (e.g.,down to -30 V) in the circuit sections located between the RPP switch and the B+ terminal, or even further out. This high value results from an increase in the B- potential due to a high current gradient and the inductance of the B+-B loop. Fluctuations in the tapped supply voltage are further reduced by selecting a point in the output range of the HLD where the output voltage is particularly constant, e.g., at the positive terminal of smoothing capacitors. After the tap, the supply voltage is further smoothed by using an input filter. The measures described here are not shown in the diagrams. The high-voltage terminal (HLD) is capable of generating high currents. In the event of a short circuit in the connected low-voltage supply, these currents would flow into the short circuit and release large amounts of energy, potentially leading to a thermal event. Simultaneously, the voltage drop across B+ and B- could result in an impermissible undervoltage. Therefore, overcurrent protection is implemented near the tap for the internal supply, for example, in the form of a fuse, or—in the case of branched supply paths—in the form of multiple fuses adapted to the respective substructures. The overcurrent protection is designed to interrupt the current flow, for example, when a certain I²t threshold is exceeded.- However, the power supply path must never be interrupted without justification. This applies to the entire usage profile over the component's lifetime, including all peak and inrush currents that occur during normal operation; otherwise, the entire component, and perhaps even the entire vehicle, would be disabled. The overcurrent protection must therefore be designed to be robust. - Since fuses have large tolerances and a significant margin must be maintained between normal and tripping operation, they are not capable of intercepting all fault conditions involving unintended overcurrent. Therefore, further measures are applied to prevent thermal events or limit their impact: - In circuit sections that are permanently connected to the vehicle's constant positive supply (e.g., even while parked), soft-term SMD capacitors are used. Their connections are flexible and reduce the risk of a multilayer capacitor breaking and causing a short circuit. - The housing of the component containing the HLD is robust and constructed from non-flammable material and is capable of shielding an internal thermal event from the external component environment. - Diagrams 1a to c show the connection of the internal 12 V supply to B+, as well as an example of an intermediate fuse. The housings of the individual components are also shown. - Diagram 2 shows the branch from B+ via a fuse, which is used to supply the CAN transceiver, the system base chip, and other subcomponents. Separation concepts: Separation barrier between internal and external LV circuit components The voltage converter (100) may include a separation barrier (130) and / or an overcurrent protection device (140). The separation barrier (130) and / or the overcurrent protection device (140) may be arranged between the low-voltage switching device (110) and the low-voltage interface (120). The separation barrier (130) may provide a minimum resistance, in particular of at least 300 ohms, so that current flow between the low-voltage switching device (110) of the voltage converter (100) and the low-voltage network (LVN) of the vehicle is limited. The overcurrent protection device (140) may be configured to interrupt the current flow between the low-voltage switching device (110) of the voltage converter (100) and the low-voltage network (LVN) of the vehicle when a maximum current is exceeded.Consequently, unwanted currents between the low-voltage switching device (110) and other low-voltage components, in particular the low-voltage network (LVN), can be minimized or avoided. Such unwanted currents result in particular from potential differences between the voltages present at the low-voltage interface (120) of the voltage converter (100) and at the vehicle's low-voltage network (LVN). A separation barrier is implemented between the LV interfaces of the HV component and the internal LV circuitry because the mating components typically use terminal 30 as the positive potential and terminal 31 (or the local chassis potential there) as the negative potential, and these potentials can differ from B+ and B- (as shown). Otherwise, high equalizing currents or unwanted parasitic supply currents could occur via low-impedance signal lines, for example: - due to resistive or inductive potential differences; - due to increased contact resistance at the B+ or B- terminal, e.g., in the event of a break or loose connection of the high-current line (the output current of the HLD could then flow via the signal lines); - if some components are disconnected from the supply by partial shutdowns, while others remain connected. Therefore, for all LV interfaces that are externally (outside the component containing the HLD) galvanically connected directly or indirectly to B+ or B-, to terminal 30 or 31, or to the LV battery: The ohmic resistance within the component between the signal on the one hand, and B+ or B- on the other, must not fall below a minimum value, e.g., 300 ohms. If this cannot be guaranteed for functional or other reasons, an overcurrent protection device is implemented between the two. Signal inputs are generally high-impedance and therefore already meet this requirement; however, signal outputs are checked or implemented accordingly. CAN transceivers are generally 5V-powered, and the 5V supply typically has current limiting.The current through the CAN_H and CAN_L bus lines is usually additionally limited because the CAN transceiver is either high-impedance (receive mode) or current-limited (transmit mode) on the CAN_H / CAN_L side due to its circuitry, and also has overcurrent detection and shutdown mechanisms. A resistor is used in the 12V supply line for CAN transceivers with a wake-up function, and this resistor does not fall below the aforementioned minimum value. This resistor is usually already present because it is recommended by the CAN transceiver manufacturer (e.g., 1 kΩ). The positive and negative signals of an externally routed interlock loop are not affected by this requirement, as they have no external connection to 12V or ground. Diagram 1a to c shows examples of high-impedance measuring amplifiers for two signal inputs. Due to the separation, voltage differences can occur between internal and external circuit components: - All LV connector signals that have an external connection to the LV system are therefore protected against overvoltage (including voltage transients according to ISO 7637-2) by appropriate protective circuitry (filters, varistors, etc.). For signal lines to and from other components, the following must also be ensured: - Analog signals: - Analog signals are transmitted (double-ended, differential) in both directions, i.e., generated and evaluated; otherwise, ground deviations would lead to signal distortion. - The use of common-mode chokes can additionally help to block short-term ground offsets. - Because this increases the number of lines, which should actually be reduced, this concept is not necessarily advantageous when a large number of analog signals have to be transmitted. - Therefore, diagrams 1a to c and 2 only show digital signals at the LV interface of the component containing the HLD. - Digital signals: - Received signals: If the influence of the DC offset caused by resistive line loads on the threshold between "high" and "low" can be neglected, single-ended transmission is sufficient.This is generally the case with 12 V digital signals. Short-term offsets caused by inductive effects are attenuated to an acceptable level by low-pass filtering between the LV connector and the evaluation unit. The time constant of the low-pass filter must be selected so that inductively caused offsets are sufficiently smoothed without delaying the signal edge of the digital signal longer than acceptable. For example, for signals originating from other electronic control units and generated there with reference to terminals 30 / 31, a low-pass filter with a time constant of 500 to 1000 µs is used between the LV connector interface and the evaluation unit. Diagrams 1a to c schematically show a low-pass filter (LP) in each of the two input channels. Transmitted signals: The same applies to generated and output single-ended signals, except that the low-pass filtering must take place in the receiving control unit.For example, with 12 V digital signals that are evaluated in other electronic control units with reference to terminals 30 / 31, a low-pass filter with a time constant of 500 to 1000 µs is used between the interface and the evaluation unit. - CAN signals: The CAN bus operates differentially and is therefore robust against ground offsets. Common-mode chokes should be used and also help to block voltage offsets. No further measures are required. Separation barrier between housing and internal LV circuitry The voltage converter (100) can include a housing (150) wherein the low-voltage interface negative terminal (122) is insulated from the housing (150) so that current flow from the low-voltage interface negative terminal (122) through the housing (150) is prevented. This barrier is advantageous if B- is to be separated from the housing, for example to avoid unwanted currents via HV shields (so). If B- is used as the LV ground, then in this case it must also be separated from the housing:- That is, screw connections between the circuit board and the housing are not connected to the LV ground. The voltage potential of B- can therefore deviate from the chassis. This can also occur—to a small extent or for short periods—even if B- is externally connected to the chassis via a ground strap and the vehicle body, as high currents or current gradients cause voltage drops due to the impedance of this connection. The deviation between B- and the local chassis can lead to problems if other communication partners use this local, deviating ground and pass it on to the component via signal connections. These problems are mitigated by the aforementioned separation between external and internal low-voltage circuitry. Since B- is not connected to the vehicle body, or only via a ground strap of a certain length, it can emit electromagnetic interference, just like B+ or other interfaces. To reduce this to an acceptable level, EMC filters are used, such as...Common-mode chokes between B+ and B-, or Cy capacitors, in this case between B- (or B+) and chassis (not ground). The separation between battery B and the chassis is intended to prevent unwanted current flow between them (as follows): - If a dedicated wire exists between the negative terminal of the low-voltage battery and battery B, the current can only flow through this wire. However, such a wire is quite expensive. - If the chassis is also used as a conductor, battery B is connected to the body via a ground wire. In this case, the resistance of the current path running through the body between the connection point and the low-voltage battery must be lower than the resistance of the current path leading from the connection point via the equipotential bonding, chassis, and high-voltage shields to the low-voltage battery. - The ratio of the two resistances determines, via the current divider rule, how the return current is divided. - Thus, it becomes clear that the internal ohmic separation only needs to have a certain minimum total ohmic resistance, e.g.100 ohms, which makes the unwanted current paths so much higher in resistance compared to the desired current paths that the DC current in the unwanted paths drops to an acceptable level. EMC capacitors, for example, are also permitted between the B-bolt and the housing. The total impedance between the B-bolt and the housing simply needs to be sufficiently high so that AC currents in the unwanted paths do not exceed an acceptable level. If actual isolation between the B-bolt and the housing is required, and this functional isolation is to be implemented like basic isolation, then, taking into account IEC 61140 and IEC 60664, the limit for touch current (IEC 61140, 5.2.7) is used as the limit for the permissible current flow across the barrier. This current is limited to 10 mA DC in the event of a first fault (e.g., B-bolt breakage). At a maximum...A system voltage of 20 V corresponds to a minimum total resistance of 2 kOhm, namely 100 Ohm / V. Diagram 2 schematically illustrates the grounding, separation, and power supply concept: - In the low-voltage (LV) section, the internal and external sections must be distinguished: a separation barrier (dashed line) runs between them. - B- (and of course B+) is also separated from the chassis. - B- is connected to the chassis via a ground strap. - The chassis is also connected to the chassis via the equipotential bonding. - Elements between B- and the chassis, such as EMC capacitors, are not shown. The voltage converter as disclosed is advantageous. The effort required to connect terminal 30 (cable harness, LV connector pin, input protection circuitry, EMC filter, etc.) is eliminated. Since the tap for the internal B+ supply is an internal connection, it is very reliable. If terminal 30 were used for the LV supply, the device would fail if there were an interruption at the LV connector at terminal 30. The vehicle wiring harness is relieved of current at terminal 30, as it does not have to supply the LV part of the component containing the HLD, since this is supplied via B+ and B- or via the HLD. The effort required to connect terminal 31 (cable harness or connecting line to the body including screw point, LV connector pin, etc.) is eliminated. Since terminals 30 and 31 are not connected, there can be no unwanted back currents via these terminals, and any necessary countermeasures are therefore unnecessary. The LV part of the HLD can be directly controlled by MCU1 without having to bridge any barriers, which would cause costs and performance losses. MCU1 can be used jointly for the main control tasks in the voltage converter or in the HV box (see diagram 2) and for controlling the HLD; an additional microprocessor is not required for this. Compensating for voltage differences between external and internal circuit components using low-pass filters and CAN transceivers, as well as limiting equalizing currents through ohmic separation, saves costs and space compared to a solution using isolated couplers or differentially measuring operational amplifiers. The supply of the internal LV circuit dividers via B+ provides a base load for the output of the HLD, which stabilizes the output voltage that the HLD must generate and keep constant, or facilitates its regulation.

Claims

Voltage converter (100) for a motor vehicle, wherein the voltage converter (100) is connectable to a high-voltage network (HVN) of the motor vehicle and to a low-voltage network (LVN) of the motor vehicle, wherein the voltage converter (100) is configured to convert a high-voltage direct current (HV) applied to the high-voltage network (HVN) into a low-voltage direct current (LV) output at the low-voltage network (LVN), and / or to convert a low-voltage direct current (LV) applied to the low-voltage network (LVN) into a high-voltage direct current (HV) output at the high-voltage network (HVN), comprising: - a low-voltage switching device (110) for controlling and / or monitoring the voltage converter (100), and - a low-voltage interface (120) for feeding the low-voltage direct current (LV) from the voltage converter (100) into the low-voltage network (LVN) and / or for feeding the low-voltage direct current (LV) from the low-voltage network (LVN) into the voltage transformer (100),wherein the low-voltage interface (120) comprises: - a low-voltage interface positive terminal (121), and - a low-voltage interface negative terminal (122) wherein the low-voltage interface positive terminal (121) is connectable to the low-voltage network (LVN) via a first high-ampere line (HAL), and / or wherein the low-voltage interface negative terminal (122) is connectable to the low-voltage network (LVN) via a second high-ampere line (HAL'). Voltage converter (100) according to claim 1, wherein the low-voltage switching device (110) comprises a ground line (112) which is conductively connected to the low-voltage interface negative terminal (122) for grounding the low-voltage switching device (110). Voltage converter (100) according to claim 1 or 2, wherein the low-voltage switching device (110) comprises a voltage supply line (111) which is conductively connected to the low-voltage interface positive terminal (121) for the purpose of supplying voltage to the low-voltage switching device (110). Voltage converter (100) according to one of the preceding claims, wherein the low-voltage interface negative terminal (122), in particular the second high-ampere line (HAL'), is connected to a conductive chassis of the vehicle for grounding the low-voltage switching device (110) and / or the low-voltage interface (120). Voltage converter (100) according to one of the preceding claims, wherein the first high ampere line (HAL) and / or the second high ampere line (HAL') has a conductor cross-section of at least 40 mm2, preferably 50 mm2. Voltage converter (100) according to one of the preceding claims, wherein the low-voltage network (LVN) of the vehicle comprises a first low-ampere line (LAL) and a second low-ampere line (LAL'), wherein the low-voltage battery positive terminal (LVBP) is connectable to the first low-ampere line (LAL), and wherein the low-voltage battery negative terminal (LVBM) is connectable to the second low-ampere line (LAL'), wherein the low-voltage network (LVN) is configured to supply and / or control a low-voltage DC load (LVV) via the first low-ampere line (LAL) and the second low-ampere line (LAL'), wherein the first low-ampere line (LAL) and / or the second low-ampere line (LAL') preferably has a conductor cross-section of a maximum of 35 mm², preferably 25 mm². Voltage converter (100) according to one of the preceding claims, wherein the voltage converter (100) comprises a separation barrier (130) and / or an overcurrent protection device (140), wherein the separation barrier (130) and / or the overcurrent protection device (140) is preferably arranged between the low-voltage switching device (110) and the low-voltage interface (120), wherein the separation barrier (130) provides a minimum resistance, in particular of at least 300 ohms, so that a current flow between the low-voltage switching device (110) of the voltage converter (100) and the low-voltage network (LVN) of the vehicle is limited, and wherein the overcurrent protection device (140) is configured to interrupt the current flow between the low-voltage switching device (110) of the voltage converter (100) and the low-voltage network (LVN) of the vehicle when a maximum current is exceeded. Voltage converter (100) according to one of the preceding claims, wherein the voltage converter (100) comprises a housing (150), wherein the low-voltage interface negative terminal (122) is insulated from the housing (150) so that a current flow from the low-voltage interface negative terminal (122) via the housing (150) is prevented.

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