Insulation monitor and method of operation thereof

Abstract

The invention relates to an insulation monitor (1) for a motor vehicle high-voltage on-board power system (2), wherein the on-board power system (2) comprises an HV battery (3) and is electrically isolated from a vehicle ground (PA), wherein a Y-capacitance (C Y_P ,C Y_N ) is provided between the positive potential (H+) and the vehicle ground (PA) and between the negative potential (H-) and the vehicle ground (PA), respectively, wherein the insulation monitor (1) has a current source (4) or a voltage source, wherein the insulation monitor (1) further comprises a voltmeter (5) for measuring at least one of the potentials (H+, H-), wherein the insulation monitor (1) is configured to load a negative current (I) by means of the current source (4) if the potential (H+) measured by the voltmeter (5) is above a predetermined upper limit value, and to load a positive current (I) by means of the current source (4) if the potential (H+) measured by the voltmeter (5) is below a predetermined lower limit value, the positive current being limited to a maximum permissible contact current in the event of an insulation fault and the size of the insulation resistance (R iso_P ,R iso_N ) being inferred from the voltage measured by the voltmeter (5) and from the recharging current (I) fed in.

Description

Technical Field

[0001] This invention relates to an insulation monitor for a high-voltage on-board electrical network in a motor vehicle and a method for operating such an insulation monitor. Background Technology

[0002] DE 10 2019 202 892 A1 discloses an on-board electrical grid device for a motor vehicle, wherein the on-board electrical grid device has a high-voltage storage device for providing a first high-voltage potential and a second high-voltage potential different from the first high-voltage potential, thereby enabling the pickup of a total voltage between the first and second high-voltage potentials. Furthermore, the on-board electrical grid device has a first insulation resistance between the first high-voltage potential and a predetermined electrical ground, and a second insulation resistance between the second high-voltage potential and the predetermined electrical ground, as well as an insulation monitoring device designed to monitor the first and second insulation resistances. The HV (high-voltage) on-board electrical grid of a vehicle with an electric drive system generally consists of at least an HV battery with a battery contactor and HV power-consuming devices such as pulse inverters. Generally, the high-voltage on-board electrical grid is implemented as an IT (i.e., Isole Terre) system and is therefore completely electrically isolated from the vehicle ground. However, parasitic resistance in cables, HV power-consuming devices, batteries, etc., creates a high-impedance connection between the positive or negative high-voltage potential and the vehicle ground, i.e., the so-called insulation resistance or the aforementioned corresponding first and second insulation resistances. As long as this resistance is of a high ohmic value, i.e., in the megaohm range, there is no danger. For safety reasons, insulation resistance is continuously monitored using an insulation monitoring device, also known as an insulation monitor. If it falls below a specified threshold, a warning is generated, and depending on the operating condition, the high-voltage vehicle electrical network is disconnected from the battery via a battery contactor, creating a safer state. In addition to insulation resistance, capacitance exists in each HV vehicle electrical network, particularly the so-called ground capacitance, located between the HV terminal and vehicle ground. These capacitances arise from parasitic effects, such as those caused by cable shielding, and are sometimes intentionally incorporated to improve EMC (electromagnetic compatibility) characteristics. According to the formula E=½ CU... 2The capacitor C stores electrical energy E under a applied voltage U. If a person subsequently touches both the high-voltage contact and the vehicle ground simultaneously, the capacitor discharges or recharges through the person, potentially posing a hazard if the current is too high. To maintain a low potential hazard, limits are set in the capacitor for the maximum permissible stored electrical energy, or more precisely, the effective electrical energy, according to different standards. This directly results in a limitation on the maximum permissible total capacitance based on the total HV voltage. Furthermore, for safety reasons, a worst-case scenario must be assumed, starting with the maximum asymmetric HV on-board electrical grid that exists when the HV pole-to-ground voltage is approximately equal to the total HV voltage. This is particularly likely to occur during the vehicle's service life due to fouling resistance or leakage current. Because of the aforementioned limitation on the maximum permissible total capacitance, there is no potential hazard in the case of an asymmetric on-board electrical grid, i.e., when the voltages between the positive high-voltage potential and ground differ as do the voltages between the negative high-voltage potential and ground. Besides the limitation on the maximum permissible total capacitance, another potential issue in this case, namely the asymmetrical vehicle-to-grid configuration, is that when the vehicle is connected to a charging station (e.g., via a DC charging interface), the positive or negative voltage potentials relative to ground of the charging station and the vehicle may differ. This could lead to an undesirable and uncertain compensation process when the charging station is activated, which in the worst case could hinder charging. Summary of the Invention

[0003] The objective of this invention is to provide an improved insulation monitor for a high-voltage on-board electrical network in a motor vehicle and an improved method of operating such an insulation monitor.

[0004] According to the present invention, this task is accomplished by an insulation monitor for a high-voltage on-board electrical network of a motor vehicle and a method for operating the insulation monitor for the high-voltage on-board electrical network of a motor vehicle.

[0005] According to the present invention, an insulation monitor for a high-voltage on-board electrical network of a motor vehicle is provided, wherein the on-board electrical network includes an HV battery and is electrically isolated from the vehicle ground, wherein insulation resistance exists between the positive potential of the HV battery and the vehicle ground and between the negative potential of the HV battery and the vehicle ground due to parasitic effects, wherein Y capacitors are respectively provided between the positive potential and the vehicle ground and between the negative potential and the vehicle ground, wherein the insulation monitor has a current source or voltage source for recharging the Y capacitors, wherein the current source is connected between the vehicle ground and one of the said potentials, and wherein the insulation monitor further includes a voltmeter for measuring at least one of the said potentials.

[0006] According to the invention, the current source or voltage source is further configured to balance the potential, wherein the insulation monitor is configured to apply a negative current by means of the current source when the potential measured by the voltmeter is higher than a predetermined upper limit value, and to apply a positive current by means of the current source when the potential measured by the voltmeter is lower than a predetermined lower limit value, the current being limited to the maximum permissible contact current under insulation fault conditions, and the insulation resistance is inferred based on the voltage measured by the voltmeter and based on the fed recharging current.

[0007] When using the insulation monitor of this invention, the difference between the HV potential distribution and a symmetrical HV potential distribution is very small. Therefore, the energy content / charge stored in the Y capacitor is always very close to the achievable minimum. This allows for a larger Y capacitor within the HV system while still meeting legal requirements regarding stored energy / charge. Consequently, more advantageous / better EMC filtering can be achieved in HV components. Attached Figure Description

[0008] The invention will be explained in detail below with reference to the figures, wherein:

[0009] Figure 1 A schematic diagram of an insulation monitor for use in a motor vehicle's onboard electrical system is shown.

[0010] Figure 2 A schematic graph is shown to illustrate the changes in current and potential of the relay output, which are loaded by a current source, over time. Detailed Implementation

[0011] Corresponding components are labeled with the same reference numerals in all drawings.

[0012] Figure 1 A schematic diagram is shown of an insulation monitor 1 for an onboard electrical network 2, particularly for motor vehicles, especially those with electric drive systems.

[0013] The vehicle electrical network 2 is, for example, an HV (high-voltage) vehicle electrical network and generally includes at least one HV battery 3 and HV power-consuming devices not shown herein. The internal resistance R of the HV battery 3 is also shown in the figure. i_batt Generally, the vehicle electrical network 2 is electrically isolated from the vehicle ground PA. Due to parasitic effects, there are insulation resistances R between the positive potential H+ and the vehicle ground PA, and between the negative potential H- and the vehicle ground PA, respectively. iso_P R iso_N For safety reasons, an insulation monitor 1 is installed, which monitors the insulation resistance R. iso_P R iso_N In addition, Y capacitors C are respectively installed between the positive potential H+ and the vehicle ground PA, and between the negative potential H- and the vehicle ground PA. Y_P C Y_N Although it is not explicitly shown in the diagram that it belongs to C. Y_PC Y_N The line resistance is a factor, but it inevitably appears in real circuits, just like the internal resistance R of the HV battery 3. i_batt It wasn't added on purpose.

[0014] The high-voltage battery 3 can have, for example, a rated voltage of 800 volts.

[0015] Insulation monitor 1 includes a current source 4, for example an electrically isolated current source, for supplying current to the Y capacitor C. Y_P、 C Y_N Recharging and symmetry of the potentials H+ and H-. Current source 4 is connected for this purpose between vehicle ground PA and one of the potentials H+ or H- (in this case, potential H+). Insulation monitor 1 also includes a voltmeter 5 for measuring one of the potentials H+ or H- (in this case, potential H+). Furthermore, insulation monitor 1 includes a control device that controls or adjusts the recharging current I to be applied by current source 4 based on the value of potential H+ measured by voltmeter 5. This control device is represented in the figure by relay 6, an adder 7, two multipliers 8 and 9, and three constant values ​​10, 11, and 12, but can also be formed in any other suitable manner. Insulation monitor 1 or its control device is configured to apply a current I, for example -40µA, by current source 4 when the potential H+ measured by voltmeter 5 is higher than, for example, 440V, and when the potential H+ measured by voltmeter 5 is lower than, for example, 360V, by current source 4 applying a current I, for example +40µA. The insulation monitor 1 is configured such that it can carry a current I not exceeding the maximum current intensity, which is specifically within the range of + / -10mA. However, in exceptional cases, this configuration of the insulation monitor 1 can also carry even higher current intensities.

[0016] Figure 2 A schematic graph is shown to illustrate the output A of relay 6, the current I loaded by current source 4, the measured potential H+, and the potential H- as a function of time t.

[0017] After measuring the voltage with voltmeter 5 to start the vehicle electrical network 2 in order to determine the HV potential distribution, a symmetrical distribution of potentials H+ and H- about the vehicle ground PA is first established by applying current I with current source 4. A constant current I applied by current source 4 is determined (maintaining the symmetrical potential distribution at this time) for subsequent calculation of insulation resistance R. iso_P R iso_NBased on the symmetrical distribution of potentials H+ and H-, a smaller positive and / or negative value is applied to potentials H+ and H- with respect to the symmetrical distribution by feeding another accumulated current I from current source 4. The current I applied by current source 4 is limited to the maximum permissible contact current under insulation fault conditions. Based on the measured voltage between the positive potential H+ and vehicle ground PA or between the negative potential H- and vehicle ground PA, and based on the fed-in recharge current I, the insulation value, i.e., the insulation resistance R, can be deduced. iso_P R iso_N The magnitude of the potential distribution varies with respect to a predetermined voltage offset relative to a symmetrical potential distribution. Therefore, the insulation monitor is configured to change the potential (H+, H-) distribution with a predetermined voltage offset relative to a symmetrical distribution, wherein this voltage offset can be, for example, a high voltage in the double digits, particularly reaching a range of + / -50V. However, in exceptional cases, the insulation monitor 1 may be configured to apply even higher voltage offsets.

[0018] In an alternative implementation, the insulation monitor 1 may have a voltage source (such as an electrically isolated voltage source) instead of the current source 4 and determine the insulation resistance R by applying a voltage. iso_P R iso_N Size.

[0019] Figure 2 Simulation results are shown for the following case, namely, insulation resistance R iso_P It is 30 megohms and the insulation resistance R iso_N It is 10 megohms. From the extremely asymmetric distribution of potentials H+ and H- (i.e., Y capacitance C) Y_P C Y_N Starting with a high energy content in the circuit, insulation monitor 1 actively establishes a symmetrical potential distribution of H+ and H-. It can be seen that the negative current I required to reduce the positive potential H+ lasts for a longer period than the positive current I used to reduce the negative potential H-, which is caused by the asymmetrical resistance distribution. However, insulation monitor 1 can still determine the insulation resistance R based on determined parameters such as recharge time and the potential distribution of H+ and H-. iso_P R iso_N The value of . It now has information about the different duty cycles of the recharge current I instead of information about the asymmetric steady state.

[0020] List of reference numerals

[0021] 1 Insulation Monitor

[0022] 2. Vehicle-mounted electrical grid, HV vehicle-mounted electrical grid

[0023] 3HV battery

[0024] 4 Current Sources

[0025] 5. Voltmeter

[0026] 6 relays

[0027] 7. Addition steps

[0028] Multiplication steps 8 and 9

[0029] 10, 11, 12 constant values

[0030] C Y_P C Y_N Y capacitor

[0031] H+, H- potential

[0032] I current, recharge current

[0033] A output

[0034] PA vehicle ground

[0035] R i_batt internal resistance

[0036] R iso_P , R iso_N Insulation resistance

[0037] t time

Claims

1. An insulation monitor (1) for a high-voltage on-board electrical network (2) in a motor vehicle, wherein, The vehicle-mounted electrical network (2) includes a high-voltage battery (3) and is electrically isolated from the vehicle ground. Due to parasitic effects, insulation resistance exists between the positive potential (H+) of the high-voltage battery (3) and the vehicle ground, and between the negative potential (H-) of the high-voltage battery (3) and the vehicle ground. Y capacitors are respectively provided between the positive potential (H+) and the vehicle ground, and between the negative potential (H-) and the vehicle ground. The insulation monitor (1) has a current source (4) or voltage source for recharging the Y capacitors. The current source (4) is connected between the vehicle ground and the positive or negative potential. The insulation monitor (1) also includes a voltmeter (5) for measuring at least one of the positive and negative potentials. in, The current source (4) or voltage source is further configured to make the positive potential and the negative potential symmetrical, wherein the insulation monitor (1) is configured to apply a negative current by means of the current source (4) when the positive potential (H+) measured by the voltmeter (5) is higher than a predetermined upper limit value, and to apply a positive current by means of the current source (4) when the positive potential (H+) measured by the voltmeter (5) is lower than a predetermined lower limit value, the positive current being limited to the maximum permissible contact current in the event of an insulation fault, and the magnitude of the insulation resistance is inferred based on the voltage measured by the voltmeter (5) and based on the fed recharge current. Its characteristic is that the insulation monitor (1) is configured to: after measuring the voltage with the aid of the voltmeter (5) to determine the distribution of the positive and negative potentials in order to start the vehicle electrical network (2), first establish the symmetrical distribution of the positive and negative potentials about the vehicle ground by loading current with the current source (4), determine a constant current applied by the current source (4) to maintain the symmetrical distribution of the potentials so as to subsequently calculate the insulation resistance, and achieve a smaller recharging of the positive and negative potentials with smaller positive and / or negative values ​​about the symmetrical distribution by feeding another accumulated current from the current source (4) based on the symmetrical distribution of the positive and negative potentials.

2. The insulation monitor (1) according to claim 1, characterized in that, The high-voltage battery (3) has a rated voltage of 800 volts, wherein the insulation monitor (1) is configured to change the distribution of the positive and negative potentials by a predetermined voltage offset with respect to the symmetrical distribution.

3. The insulation monitor (1) according to claim 2, characterized in that, The specified voltage offset is + / - 50V.

4. The insulation monitor (1) according to any one of claims 1 to 3, characterized in that, The insulation monitor (1) is configured to load a current not exceeding the maximum current intensity.

5. The insulation monitor (1) according to claim 4, characterized in that, The maximum current intensity is + / - 10mA.

6. A method for operating an insulation monitor (1) for a high-voltage on-board electrical network (2) in a motor vehicle, wherein, The vehicle-mounted electrical network (2) includes a high-voltage battery (3) and is electrically isolated from the vehicle ground. Due to parasitic effects, insulation resistance exists between the positive potential (H+) of the high-voltage battery (3) and the vehicle ground, and between the negative potential (H-) of the high-voltage battery (3) and the vehicle ground. Y capacitors are respectively provided between the positive potential (H+) and the vehicle ground, and between the negative potential (H-) and the vehicle ground. The insulation monitor (1) has a current source (4) or voltage source for recharging the Y capacitors. The current source (4) is connected between the vehicle ground and the positive or negative potential. The insulation monitor (1) also includes a voltmeter (5) for measuring at least one of the positive and negative potentials. in, The positive and negative potentials are symmetrical using the current source (4) or the voltage source, wherein the insulation monitor (1) applies a negative current using the current source (4) when the positive potential (H+) measured by the voltmeter (5) is higher than a predetermined upper limit, and applies a positive current using the current source (4) when the positive potential (H+) measured by the voltmeter (5) is lower than a predetermined lower limit. The positive current is limited to the maximum permissible contact current under insulation fault conditions, and the magnitude of the insulation resistance is inferred based on the voltage measured by the voltmeter (5) and the fed-in recharge current. Its characteristic is that, after measuring the voltage with the voltmeter (5) to determine the distribution of the positive and negative potentials in order to start the vehicle electrical network (2), the insulation monitor (1) first establishes the symmetrical distribution of the positive and negative potentials about the vehicle ground by loading current with the current source (4), determines the constant current applied by the current source (4) to maintain the symmetrical distribution of the potentials so as to subsequently calculate the insulation resistance, and achieves a smaller recharging of the positive and negative potentials with smaller positive and / or negative values ​​about the symmetrical distribution by feeding another accumulated current from the current source (4) based on the symmetrical distribution of the positive and negative potentials.

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