On-board electrical system and method for a motor vehicle

Abstract

The invention relates to an on-board electrical system (1) of a motor vehicle, comprising at least one HV battery (2) for supplying a positive potential (H+) and a negative potential (H-) and at least one HV consumer (3, 4), and having an insulation resistance (R) to a vehicle earth (PA) that is electrically separated from the on-board electrical system (1). iso_P , R iso_N ), and a Y capacitance (C Y_P , C Y_N ) is provided, and a voltage center tap (6) between a positive potential (H+) and a negative potential (H-) within the vehicle electrical system (1) or within a component of the vehicle electrical system (1) is provided with an ohmic coupling resistor (R K ) to the vehicle earth (PA).

Description

[Technical Field]

[0001] The invention relates to an on-board electrical system for a motor vehicle according to the preamble of claim 1. [Background technology]

[0002] Patent Document 1 discloses an on-board electrical system for a motor vehicle, which comprises a high-voltage energy storage device for providing a first high-voltage potential and a second high-voltage potential different from the first high-voltage potential, such that a total voltage can be tapped between the first and second high-voltage potentials. The on-board electrical system further comprises a first insulation resistance between the first high-voltage potential and a predetermined electrical ground, a second insulation resistance between the second high-voltage potential and the predetermined electrical ground, and an insulation monitoring device designed to monitor the first and second insulation resistances. The high-voltage (HV) on-board electrical system of a vehicle with an electric drive typically comprises at least an HV battery with a battery contactor and HV consumers (such as a pulse inverter). Generally, the high-voltage on-board electrical system is implemented as an IT (Isole Terre) network and is therefore completely electrically isolated from the vehicle ground. However, parasitic resistances in cables, HV consumers, batteries, etc. create a high-impedance connection between the positive or negative high-voltage potential and the vehicle earth, known as the insulation resistance, or the first and second insulation resistances mentioned above. As long as this resistance is high, i.e., in the megaohm range, there is no danger. For safety reasons, this insulation resistance is permanently monitored by an insulation monitoring device (also called an insulation monitor). If it falls below a defined threshold, an alarm is triggered and, depending on the operating state, the HV onboard electrical system is disconnected from the battery by a battery contactor, thereby establishing a safe condition. In addition to this insulation resistance, all HV onboard electrical systems have capacitances, particularly so-called earth capacitances, located between the HV connection and the vehicle earth. These capacitances arise due to parasitic effects, for example, due to cable shielding, and can even be intentionally added to improve EMC (electromagnetic compatibility) behavior. E = 1 / 2 × C × U2 According to the formula, these capacitors with capacitance C store energy E when a voltage U is applied. If a person then simultaneously touches the high-voltage contacts and the vehicle earth, these capacitors can be discharged or charged through the human body. In principle, this could lead to danger if these currents are too high. Therefore, to minimize potential danger, various standards impose limits on the maximum allowable energy, or more precisely, the effective energy, that can be stored in the capacitors. This directly translates into a limit on the maximum allowable total capacitance depending on the total HV voltage. Furthermore, for safety reasons, it is necessary to assume the worst case scenario and assume a maximally asymmetrical HV onboard electrical system, which exists when the voltage of the HV pole measured with respect to earth corresponds almost to the full HV voltage. This can occur, in particular, due to dirt resistance or leakage currents over the service life. The aforementioned limit on the maximum allowable total capacitance ensures that no potential danger exists even in an asymmetrical onboard electrical system, i.e., when the voltage between the positive high-voltage potential and earth and the voltage between the negative high-voltage potential and earth are different. Besides the drawback of the limitation of the maximum allowable total capacitance, in this case, i.e. with an asymmetric on-board electrical system, it may also happen that when the vehicle is connected to a charging station, for example via a DC charging interface, the charging station and the vehicle have different positive or negative voltage potentials relative to earth. This may lead to undesirable and undefined equalization processes when the charging station is switched on, and in the worst case, may prevent charging. [Patent Document 1] DE102019202892A1 Summary of the Invention [Problem to be solved by the invention]

[0003] The present invention is based on the problem of providing an improved on-board electrical system for motor vehicles, in particular electrically driven motor vehicles. [Means for solving the problem]

[0004] This problem is solved according to the invention by an on-board electrical system for a motor vehicle according to claim 1.

[0005] Advantageous embodiments of the invention are the subject of the dependent claims.

[0006] The present invention provides an on-board electrical system for a motor vehicle, which includes at least one HV battery for supplying a positive potential and a negative potential and at least one HV consumer device, and an insulation monitor for monitoring an insulation resistance with respect to a vehicle earth electrically isolated from the on-board electrical system, with a Y capacitance provided between the positive potential and the vehicle earth and between the negative potential and the vehicle earth. According to the present invention, a voltage center tap between the positive potential and the negative potential in the on-board electrical system or in a component of the on-board electrical system is connected to the vehicle earth by an ohmic coupling resistor. The insulation monitor may be configured, for example, as a resistive insulation monitor.

[0007] The solution according to the invention results in very small deviations of the potential distribution from a symmetrical distribution. Therefore, the amount of energy / charge stored in the Y capacitance is always very close to the achievable minimum. This allows for a larger Y capacitance in the vehicle electrical system while still meeting legal regulations regarding stored energy / charge. This means that more advantageous and / or better EMC filtering is possible for the components of the high-voltage vehicle electrical system.

[0008] According to the invention, the voltage center tap is located between two resistors connected as a voltage divider or is formed by a capacitive voltage divider.

[0009] In accordance with the present invention, the coupling resistor is configured as a series connection of a fixed resistor and a variable resistor.

[0010] In one embodiment, the resistors of the voltage divider are configured as series connected HV consumers or as the internal resistance of at least two series connected HV batteries.

[0011] In one embodiment, the resistance of the voltage divider is significantly smaller than the coupling resistance and the measured resistance of the isolation monitor configured as a resistive isolation monitor.

[0012] In one embodiment, the measurement resistance and the coupling resistance are in the range of greater than 100 kilohms.

[0013] In one embodiment, the following list is provided via coupling resistors: -Series connection of HV voltage supplies for control boards, - Series connection of half-bridges and / or H-bridges, -Multi-level half-bridge, -Series connection of inverters, -Multilevel inverter, a heater circuit comprising a series connection of two or more heater elements; - Taps at the connection points of battery modules connected in series, At least one of these is connected to the vehicle ground.

[0014] In alternative embodiments, the coupling resistors may also be formed from fixed and / or variable resistors.

[0015] The on-board electrical system may be part of a motor vehicle, particularly an electrically powered motor vehicle.

[0016] When the coupling resistor is configured as a series connection of a fixed resistor and a variable resistor, the variable resistor can be set high when the vehicle is not connected to a DC charging station, and can be set low when the vehicle is connected to a DC charging station.

[0017] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic diagram of an on-board electrical system of a motor vehicle; [Figure 2] 1 is a schematic diagram of an embodiment of an on-board electrical system of a motor vehicle. [Figure 3] 2 is a schematic diagram of a further embodiment of an on-board electrical system of a motor vehicle; [Figure 4] 2 is a schematic diagram of a further embodiment of an on-board electrical system of a motor vehicle; [Figure 5] 2 is a schematic diagram of a further embodiment of an on-board electrical system of a motor vehicle; [Figure 6] 2 is a schematic diagram of a further embodiment of an on-board electrical system of a motor vehicle; [Figure 7] 2 is a schematic diagram of a further embodiment of an on-board electrical system of a motor vehicle; [Figure 8] FIG. 1 is a schematic diagram of a simulation setup for an embodiment of an on-board electrical system of a motor vehicle. [Figure 9] FIG. 10 is a schematic diagram showing the simulation results of a simulation without a coupling resistor. [Figure 10] FIG. 10 is a schematic diagram showing a simulation result of a simulation with a coupling resistor. DETAILED DESCRIPTION OF THE INVENTION

[0019] In all the drawings, the same reference numerals are used to designate corresponding parts.

[0020] FIG. 1 is a schematic diagram of an on-board electrical system 1 of a motor vehicle, for example an electrically powered motor vehicle.

[0021] The vehicle electrical system 1 is, for example, an HV (high voltage) vehicle electrical system and typically includes at least one HV battery 2 and HV consumers 3, 4. Essentially, the vehicle electrical system 1 is electrically isolated from the vehicle earth PA. Due to parasitic effects, an insulation resistance R is formed between the positive potential H+ and the vehicle earth PA, and between the negative potential H- and the vehicle earth PA. iso_P , R iso_N For safety reasons, the insulation resistance R iso_P , R iso_N Furthermore, there is provided an insulation monitor 5 that monitors the Y capacitance C between the positive potential H+ and the vehicle earth PA, and between the negative potential H- and the vehicle earth PA. Y_P , C Y_N is provided.

[0022] Fluctuations in the vehicle electrical system 1, caused in particular by an insulation monitor 5, which may be configured as a resistance insulation monitor, may be detected in the vehicle electrical system 1 or in a component of the vehicle electrical system 1, for example, by two consumer resistances R connected as a voltage divider in FIG. VP and R VN This can be mitigated by using a voltage centre tap 6 in the HV consumers 3, 4, indicated by a fixed resistor R F and variable resistor R V A coupling resistor R K In the illustrated embodiment, a coupling resistor R K is the fixed resistance R F and variable resistor R V The circuit is configured as a series connection of:

[0023] In another embodiment, the voltage center tap 6 may be formed by a capacitive voltage divider.

[0024] Coupling resistance R KBy coupling the voltage center tap 6 to the vehicle earth PA by K If the value of does not change during the measurement of the insulation monitor 5, the insulation resistance R iso_P , R iso_N The insulation monitor 5 does not affect its function in the calculation of the insulation value. Y_P , C Y_N This reduces the amount of energy stored in the charging station. This is advantageous for improved filtering of active, especially cyclical, HV components and for vehicles with higher DC system voltages (e.g., 800 V). Furthermore, when coupling HV systems with different insulation designs, it is also possible to avoid overloading the insulation of weakly designed HV systems; for example, when charging an 800 V vehicle, the insulation of a 500 V charging station is protected by the electrically coupled charging system.

[0025] In the insulation monitor 5, the coupling resistor R K This allows the charging process to occur more quickly, significantly reducing the recognition time.

[0026] Fixed resistance R F and variable resistor R V The use of series connection allows the HV system to have a lower Y capacitance C Y_P , C Y_N If the vehicle is equipped with a Y capacitance C, a higher isolation can be tolerated, for example when the vehicle is not connected to a DC charging station. Y_P , C Y_N If is higher, e.g. when the vehicle is connected to a DC charging station, the coupling resistance R K is the variable resistor R V and the potential shift is made smaller by the insulation monitor 5.

[0027] As an example of a possible use of the ohmic coupling of the voltage center tap 6 to the vehicle earth PA, -Series connection of HV voltage supplies for control boards, - Series connection of half-bridges and H-bridges, -Multi-level half-bridge, -Series connection of inverters, -Multilevel inverter, a heater circuit comprising a series connection of two or more heater elements; - Taps at the connection points of battery modules connected in series, Examples include:

[0028] Preferably, the impedance of the series connection of the HV consumers 3, 4 or the HV source is determined by a coupling resistor R K and is significantly smaller than the measurement resistance of the insulation monitor 5. Measurement resistance R mess_p , R mess_n and coupling resistance R K Since the impedance can be in the hundreds of kiloohms or even megaohms, a series connection of HV consumers 3, 4 or HV sources does not require high power consumption, as they present a very small impedance. To this extent, auxiliary voltage supplies are also suitable for this use. In the case of HV sources, the source impedance and / or internal resistance must be taken into account, which is usually in the megaohm range and therefore also meets this requirement.

[0029] The following diagram shows a fixed resistor R F and variable resistor R V Instead of a series connection of K However, in all cases, only the fixed resistor R F and variable resistor R V A series connection of

[0030] 2 is a schematic diagram of an embodiment of an on-board electrical system 1 of a motor vehicle, for example an electrically powered motor vehicle. The embodiment according to FIG. 2 largely corresponds to the embodiment according to FIG. 1. However, the voltage center tap 6 has two capacitances C x_P , C x_N The voltage is formed by a capacitive voltage divider consisting of:

[0031] Furthermore, the vehicle electrical system 1 is connected to a three-phase AC voltage connection 7 via a rectifier 8 with power factor correction (three-level PFC, for example a Wien rectifier).

[0032] 3 is a schematic diagram of an embodiment of an on-board electrical system 1 of a motor vehicle, for example an electrically powered motor vehicle. The embodiment according to FIG. 3 largely corresponds to the embodiment according to FIG. 1. However, the voltage center tap 6 has two capacitances C x_P , C x_N The voltage is formed by a capacitive voltage divider consisting of:

[0033] Furthermore, the in-vehicle electrical system 1 is connected to the in-vehicle three-level DC boost converter 11 via a Y capacitance C y_P1 , C y_N1 , insulation resistance R iso_P1 , R iso_N1 and connected to a DC charging station 9 shown with an output capacitance C, and two capacitances C x_P , C x_N The capacitive voltage divider consisting of i is arranged in the three-level DC boost converter 11. Furthermore, the vehicle earth PA is connected to the earth PA' of the charging station 9 via an earth cable 12.

[0034] 4 is a schematic diagram of an embodiment of an on-board electrical system 1 of a motor vehicle, for example an electrically powered motor vehicle. The embodiment according to FIG. 4 largely corresponds to the embodiment according to FIG. 1. However, the voltage center tap 6 has two capacitances C x_P , C x_N The voltage is formed by a capacitive voltage divider consisting of:

[0035] Furthermore, the in-vehicle electrical system 1 is connected to a series connection of H-bridges 13 and 14 of an LV-DCDC converter or an isolated DCDC converter of an in-vehicle charger, for example.

[0036] FIG. 5 is a schematic diagram of an embodiment of an on-board electrical system 1 of a motor vehicle, for example an electrically powered motor vehicle.

[0037] The vehicle electrical system 1 comprises two HV batteries 2.1, 2.2 or battery strings connected in series and one HV consumer 3. The vehicle electrical system 1 is electrically isolated from the vehicle earth PA. Due to parasitic effects, an insulation resistance R is formed between the positive potential H+ and the vehicle earth PA, and between the negative potential H- and the vehicle earth PA. iso_P , R iso_N For safety reasons, the insulation resistance R iso_P , R iso_N An insulation monitor 5 is provided to monitor the

[0038] Furthermore, there are Y capacitances C between the positive potential H+ and the vehicle earth PA, and between the negative potential H- and the vehicle earth PA. Y_P , C Y_N The HV consumer 3 is connected between a positive potential H+ and a negative potential H-.

[0039] Fluctuations in the vehicle electrical system 1 caused by the insulation monitor 5, which may in particular be configured as a resistive insulation monitor, can be mitigated by using a voltage center tap 6 in the vehicle electrical system 1 or in a component of the vehicle electrical system 1, for example in the HV batteries 2.1, 2.2, which are connected in series in FIG. 5 and whose internal resistances thus form a voltage divider. This voltage center tap 6 then has a fixed resistance R F and / or variable resistor R V A coupling resistor R K The vehicle ground PA is connected via

[0040] 6 is a schematic diagram of an embodiment of an on-board electrical system 1 of a motor vehicle, for example an electrically powered motor vehicle. The embodiment according to FIG. 6 largely corresponds to the embodiment according to FIG. 1. However, the voltage center tap 6 has two capacitances C x_P , C x_N The voltage is formed by a capacitive voltage divider consisting of:

[0041] Furthermore, the vehicle electrical system 1 is connected to a three-level inverter 15 of an electric machine 16. This three-level inverter 15 may be configured, for example, as a three-level NPC inverter, a T-type inverter or a flying inverter.

[0042] 7 is a schematic diagram of an embodiment of an on-board electrical system 1 of a motor vehicle, for example an electrically powered motor vehicle. The embodiment according to FIG. 7 largely corresponds to the embodiment according to FIG. 1. However, the voltage center tap 6 has two capacitances C x_P , C x_N The voltage is formed by a capacitive voltage divider consisting of:

[0043] Furthermore, the vehicle electrical system 1 is connected to a series connection of two electric machines 16 and two B&B-bridge inverters 17 .

[0044] 8 is a schematic diagram of a simulation setup for an embodiment of an on-board electrical system 1 of a motor vehicle, for example an electrically driven motor vehicle. The embodiment according to FIG. 8 largely corresponds to the embodiment according to FIG. 1. Furthermore, two measuring resistors R of an insulation monitor 5 are connected between the positive potential H+ and the vehicle earth PA, as well as between the negative potential H− and the vehicle earth PA. mess_p , R mess_n are arranged to be switchable by the respective switches S1 and S2. Furthermore, the Y capacitance C Y_P , C Y_N and a cable resistance R L are shown, which are inevitably present in real components, so that even very low resistance values, e.g., 0.01 ohms, must be taken into account in the simulation.

[0045] The following simulation parameters were used: R iso_p =10 8 Ohms R iso_n =10 8 Ohms R mess_p =R mess_n =2 * 10 6 Ohms Frequency f=1 / 20Hz Voltage U=800V R VP =U * U / 1000 R VN =U * U / 1000

[0046] Figure 9 shows the coupling resistance R K Switching position U of switches S1 and S2 when simulated without S1 , U S2 , potentials H+, H- and calculated insulation resistance R iso_P , R iso_N over time t.

[0047] Due to the high level of isolation of the HV on-board electrical system 1, the insulation monitor 5, especially the resistive insulation monitor, causes a clear shift in the potentials H+, H-. Y_P , C Y_N receives a voltage that is approximately equivalent to that of the HV battery 2. Therefore, the amount of energy is very high. The charging time is quite slow due to the high impedance resistor, and in this example, charging has not yet finished within the cycle time of the insulation monitor 5.

[0048] Figure 10 shows the 6 Coupling resistance R in ohms K The switching position U of switches S1 and S2 when simulated S1 , U S2 , potentials H+, H- and calculated insulation resistance R iso_P , Riso_N over time t.

[0049] In this simulation, the coupling resistor R K It is clear that the fluctuation of the potentials H+ and H- is significantly less than that of the system without the Y capacitance C. The maximum potential of H+ and H- is 531V, and the minimum potential of H+ and H- is 269V. Y_P , C Y_N The amount of energy in the insulation resistance R iso_P , R iso_N Small coupling resistance R K This allows charging to be performed much faster, and therefore the insulation monitor 5 can detect insulation failure in a shorter time. [Explanation of symbols]

[0050] 1. Vehicle electrical system 2 HV battery 2.1, 2.2 HV battery 3 HV consumer equipment 4 HV consumer equipment 5 Insulation monitor 6 Voltage Center Tap 7 Three-phase AC voltage connection 8 rectifier 9 DC charging station 11 Three-level DC boost converter 12 Earth cable 13 H-bridge 14 H-bridge 15 Three-level inverter 16 Electrical Machinery 17 B&Bridge Inverter C output capacitance C x_P , C x_N capacitance C Y_P , C Y_N Y capacitance C y_P1 , C y_N1 Y capacitance H+, H- potential PA vehicle ground PA' Earth R F fixed resistance R iso_P , R iso_N Insulation resistance R K Coupling Resistor R L Cable Resistance R mess_p , R mess_n Measuring Resistance R V variable resistor R VP ,R VN consumer resistance R iso_P1 , R iso_N1 Insulation resistance S1, S2 switches t time U S1 , U S2 Switching Position

Claims

1. An on-board electrical system (1) of a motor vehicle comprises a high-voltage battery (2) with at least one battery contactor for supplying a positive potential (H+) and a negative potential (H-), and at least one high-voltage consuming device (3, 4), and an insulation monitor (5) is provided for monitoring an insulation resistance (R iso_P) between the positive potential (H+) and a vehicle earth (PA) and an insulation resistance (R iso_N) between the negative potential (H-) and the vehicle earth (PA), and a Y capacitance (C Ｙ＿Ｐ , C Ｙ＿Ｎ In the vehicle electrical system (1), The voltage center tap (6) between the positive potential (H+) and the negative potential (H-) in the vehicle electrical system (1) or in a component of the vehicle electrical system (1) is located between two resistors connected as a voltage divider or is formed by a capacitive voltage divider, and does not include an ohmic coupling resistor (R Ｋ ) to the vehicle earth (PA), the resistance of the voltage divider is configured as the series connection of the high-voltage consumers (3, 4) represented by two consumer resistances (R VP , R VN ) or as the internal resistance of at least two series connection of high-voltage batteries (2.1, 2.2), and the capacitive voltage divider is made up of two capacitances (C x_P , C x_N ), The coupling resistance (R Ｋ ) is a fixed resistor (R Ｆ ) and variable resistor (R Ｖ 1. An in-vehicle electrical system (1) configured as a series connection of:

2. The resistors of the voltage divider are connected to the coupling resistor (R Ｋ ) and the measured resistance (R ｍｅｓｓ＿ｐ , R ｍｅｓｓ＿ｎ 2. The vehicle electrical system (1) according to claim 1, characterized in that it is smaller than the

3. The measured resistance (R ｍｅｓｓ＿ｐ , R ｍｅｓｓ＿ｎ ) and the coupling resistor (R Ｋ 3. The vehicle electrical system (1) according to claim 2, characterized in that the resistance of the resistor R1 is in the range of greater than 100 kilohms.

4. The coupling resistance (R Ｋ ) via the following list, - series connection of high voltage supply for control boards, - series connection of half-bridges and / or H-bridges, - multi-level half-bridges, - Series connection of inverters, - multilevel inverters, a heater circuit comprising a series connection of two or more heater elements; - Taps at the connection points of series battery module connections, 4. The vehicle electrical system (1) according to claim 1, wherein at least one of the power supplies is connected to the vehicle earth (PA).

5. A vehicle equipped with an on-board electrical system (1) according to any one of claims 1 to 3.

6. 6. The method for operating a vehicle according to claim 5, wherein the coupling resistor (R Ｋ ) is the fixed resistor (R Ｆ ) and the variable resistor (R Ｖ ) connected in series, and when the vehicle is not connected to a DC charging station, the variable resistor (R Ｖ ) is set high, and when the vehicle is connected to a DC charging station, the variable resistor (R Ｖ ) is set low.

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