Measuring arrangement for insulation monitoring in an on-board network and on-board network with a measuring arrangement

Abstract

Measuring arrangement (1) for insulation monitoring in an on-board network with a first and a second high-voltage network line (2, 3), the measuring arrangement comprising: - a low-voltage network (51) with an evaluation circuit (19) and a potential connection (4), - a first voltage divider (6) which is electrically connected between the first high-voltage power line (2) and the second high-voltage power line (3) and has a first voltage divider tap (52) at which a first voltage signal (S1) can be tapped, - a second voltage divider (13) which is electrically connected between the first or the second high-voltage mains line (2, 3) on the one hand and the potential connection (4) on the other hand and has a second voltage divider tap (53) at which a second voltage signal (S2) can be tapped, wherein the evaluation circuit (19) is electrically connected on the signal input side to the first and second voltage divider taps (52, 53) and is designed to evaluate the first and / or second voltage signal (S1, S2) or signals derived therefrom and to determine an insulation state in the vehicle electrical system based on the evaluation result, wherein the measuring arrangement (1) has a third voltage divider (16) which is electrically connected between the first or the second high-voltage mains line (2, 3) on the one hand and the potential connection (4) on the other hand and has a third voltage divider tap (68) which is electrically connected to the evaluation circuit (19) and at which a third voltage signal (S3) can be tapped; wherein the evaluation circuit (19) is further designed to evaluate the third voltage signal (S3) or a signal derived therefrom and to determine the insulation state based on the evaluation result.

Description

[0001] The application relates to a measuring arrangement for insulation monitoring in an on-board electrical system, in particular of a motor vehicle, and an on-board electrical system, in particular of a motor vehicle, with a measuring arrangement.

[0002] The electrical system architecture of a motor vehicle or an electric vehicle powered by an energy source uses voltage that poses a hazard if touched. This is generally the case with voltages greater than 50V. An HV energy source (HV is the abbreviation for high voltage) is usually made up of several battery cells connected in series and parallel. The HV energy source provides a powerful voltage that poses a high risk of injury to those touching it if touched. Accordingly, continuous monitoring of the insulation status of such an electrical system, especially in a motor vehicle, is very important.

[0003] The publication DE 10 2019 218 502 A1 describes a test circuit for testing the insulation between an electrical circuit and a vehicle body. The test circuit has a first input that is in contact with the first pole, a second input that is in contact with the second pole, and a third input that is in contact with the vehicle body. A first measuring path with at least one first measuring resistor and a first voltage tap for a first voltage runs between the first input and the second input, and a second measuring path with a second voltage tap for a second voltage runs between the second input and the third input. A first changeover switch can establish a connection between the first voltage tap and the third input when closed.When the first changeover switch is open and closed, a value for the first and / or second voltage is recorded, and the electrical resistance of the first and second insulation resistances is determined from the recorded values of the first voltage and / or the second voltage. After the first changeover switch is opened and closed, the time profile of the first voltage and / or the second voltage is recorded, and the values of the first and / or the second voltage are determined as a function of the time profiles of the first and / or the second voltage.

[0004] The document DE 10 2017 119 992 A1 describes a monitoring device for monitoring an electrical energy source, wherein the monitoring device has a respective measuring circuit for each pole of the energy source, which is designed to connect the pole to a reference potential via a voltage divider, and wherein an evaluation device is designed to detect a respective voltage value at the respective voltage divider and to determine a source voltage indication for a source voltage of the energy source on the basis of the detected voltage values.In at least one of the measuring circuits, its total electrical resistance depends on a switching state of a respective switching element and the evaluation device is designed to set at least two different switching configurations of the measuring circuits by switching the respective switching element and to determine total resistance information on insulation resistances of the energy source based on the voltage values recorded in the switching configurations.

[0005] Document EP 2 309 636 B1 describes a leakage current detector of a construction machine, comprising a motor drive circuit for driving a motor by a battery via an inverter; a signal output device for applying a voltage signal adapted to detect a leakage current between the motor drive circuit and a body of the construction machine; a signal detection device for detecting the voltage signal applied by the signal output device; and an engine operation detection device for detecting whether or not the engine is in an operating state.The detector further comprises determining means for determining an occurrence or non-occurrence of the leakage current, the determining means determining the occurrence or non-occurrence of the leakage current based on the signal detected by the signal detecting means, under the condition that the non-operational state of the motor is detected by the motor operation detecting means.

[0006] It is therefore desirable to provide a means by which the insulation state of such an on-board network, especially of a motor vehicle, can be easily monitored.

[0007] According to the invention, a measuring arrangement for insulation monitoring in an on-board electrical system, in particular of a motor vehicle, and an on-board electrical system, in particular of a motor vehicle, with a measuring arrangement are provided. Advantageous developments are the subject of the dependent claims.

[0008] According to a first aspect of the invention, a measuring arrangement for insulation monitoring in an on-board electrical system, in particular of a motor vehicle, is provided, wherein the on-board electrical system has a first and a second high-voltage network line as a supply and discharge line of a high-voltage current.

[0009] The measuring arrangement comprises a low-voltage network and a first and a second voltage divider. The low-voltage network, in turn, has an evaluation circuit and a potential connection, which is in particular a ground connection. The first voltage divider is electrically connected between the first high-voltage network line and the second high-voltage network line and has a first voltage divider tap from which a first voltage signal can be tapped. The second voltage divider is electrically connected between the first or the second high-voltage network line on the one hand and the potential connection on the other hand and has a second voltage divider tap from which a second voltage signal can be tapped. The evaluation circuit is electrically or signal-wise connected to the first and second voltage divider taps on the signal input side.The evaluation circuit is designed to evaluate the first and / or the second voltage signal or signals derived therefrom and to determine an insulation state or an insulation fault in the vehicle electrical system based on the evaluation result.

[0010] The measuring arrangement further comprises a third voltage divider which is electrically connected between the first or second high-voltage power line on the one hand and the potential connection on the other. The third voltage divider has a third voltage divider tap which is electrically connected to the evaluation circuit and from which a third voltage signal can be tapped. If the second voltage divider is electrically connected between the first high-voltage power line and the potential connection, the third voltage divider is electrically connected between the second high-voltage power line and the potential connection. However, if the second voltage divider is electrically connected between the second high-voltage power line and the potential connection, the third voltage divider is electrically connected between the first high-voltage power line and the potential connection.The evaluation circuit is further designed to evaluate the third voltage signal or a signal derived therefrom and to determine the insulation state of the vehicle electrical system based on the evaluation result.

[0011] Advantageously, voltage signals can be provided by means of the first and second voltage dividers at the first and second voltage divider taps, with which the voltage conditions in the vehicle electrical system are monitored. For example, the evaluation circuit can generate information about an insulation fault depending on the first and / or second voltage signal. An insulation fault can occur, for example, between the first or second high-voltage power line on the one hand and the low-voltage network on the other. The information about an insulation fault can be the information that an insulation fault has been detected or the information that no insulation fault has been detected. Alternatively, the information about an insulation fault can be a value of an insulation resistance or a range specification of a value of an insulation resistance.

[0012] Advantageously, the second and third voltage signals are provided with high impedance using the second and third voltage dividers between the first and second high-voltage power lines, respectively, on the one hand, and the potential connection, on the other. The total voltage between the two high-voltage power lines can be measured by the second and third voltage dividers. This enables a double and therefore redundant measurement of the total voltage using the first, second, and third voltage dividers. Due to the redundancy, a drift in one of the voltage dividers can be detected. Thus, in one example, one of two high-voltage measurements can be replaced by high-impedance voltage measurements of each of the two poles of the high-voltage network against the low-voltage ground.

[0013] According to one embodiment of the measuring arrangement, the first voltage divider has a first total resistance value. The first total resistance value is, for example, greater than 50 kiloohms or, alternatively, greater than 200 kiloohms. Alternatively, the first total resistance value is in a range between 50 kiloohms and 2 megaohms or between 200 kiloohms and 1 megaohm. A total voltage is present between the first and second high-voltage power lines. The first voltage divider advantageously allows for rapid measurement of the total voltage. This is useful for controlling a power output stage.

[0014] According to one embodiment of the measuring arrangement, the second voltage divider has a second total resistance value. The second total resistance value is greater than 5 megaohms, alternatively greater than 10 megaohms. Alternatively, the second total resistance value is in a range between 5 megaohms and 100 megaohms or between 10 megaohms and 50 megaohms. The second voltage divider is advantageously implemented with high resistance.

[0015] According to one embodiment of the measuring arrangement, the first voltage divider has a first resistance value between the first voltage divider tap and the first high-voltage power line and a second resistance value between the first voltage divider tap and the second high-voltage power line. The first resistance value is at least ten times the second resistance value.

[0016] According to one embodiment of the measuring arrangement, the second voltage divider has a third resistance value between the second voltage divider tap on the one hand and the first or second high-voltage mains line on the other hand, and a fourth resistance value between the second voltage divider tap and the potential connection.

[0017] According to one embodiment of the measuring arrangement, the third voltage divider has a third total resistance value. The third total resistance value is greater than 5 megaohms, alternatively greater than 10 megaohms. Alternatively, the second total resistance value is in a range between 5 megaohms and 100 megaohms or between 10 megaohms and 50 megaohms. The third voltage divider is advantageously implemented with high resistance.

[0018] In one example, the second total resistance value and the third total resistance value are equal or approximately equal. Advantageously, the second and third voltage dividers create symmetry between the voltages of the first and second high-voltage power lines and a ground potential at the potential terminal.

[0019] According to one embodiment of the measuring arrangement, the second voltage divider comprises a first number N of resistors that are electrically connected in series with one another and are electrically connected between the first or second high-voltage power line and the second voltage divider tap. The second voltage divider further comprises a second number M of resistors that are electrically connected in series with one another and are electrically connected between the second voltage divider tap and the potential connection. The first number N is, for example, 1, 2, 3 or 4 or greater than 1 or greater than 2 or greater than 3. The second number M is, for example, 1, 2, 3 or 4 or greater than 1 or greater than 2 or greater than 3. If, in one example, the first number N is equal to 1, the only resistor of the first number N of resistors is electrically connected between the first or second high-voltage power line and the second voltage divider tap.If in an example the second number M is equal to 1, the only resistor of the second number M of resistors is electrically connected between the second voltage divider tap and the potential terminal.

[0020] According to a further development of the measuring arrangement, the second voltage divider comprises a controllable bypass switch. The bypass switch bypasses at least one resistor of the first number N of resistors, wherein the first number N is greater than 1. Alternatively, the bypass switch bypasses at least one resistor of the second number M of resistors, wherein the second number M is greater than 1. In this case, the evaluation circuit is designed as a control and evaluation circuit and is electrically or signal-wise connected to a control terminal of the bypass switch on the control signal output side and is designed to output a control signal to the control terminal of the bypass switch.

[0021] According to a further development of the measuring arrangement, the evaluation circuit is designed, in a first measuring phase, to output the control signal with a first value that places the bypass switch in a conductive state, and to process a first (measured) value of the second voltage signal and a first (measured) value of the first and / or third voltage signal. Furthermore, the evaluation circuit is designed, in a second measuring phase, to output the control signal with a second value that places the bypass switch in a non-conductive state, and to process a second (measured) value of the second voltage signal and a second (measured) value of the first and / or third voltage signal. Furthermore, the evaluation circuit is designed to provide information about an insulation fault depending on the first and second (measured) values of the second voltage signal and on the first and second (measured) values of the first and / or third voltage signal.The (measured) values of the second voltage signal and the (measured) values of the first and / or third voltage signals are determined, for example, when the vehicle is stationary or not in operation, or when it is moving or in operation. Information about the insulation fault can thus be generated using the (measured) values of the second and third voltage signals, or using the (measured) values of the second and first voltage signals, or using the (measured) values of the second, first, and third voltage signals. This advantageously also allows for the detection of a distributed insulation resistance violation.

[0022] According to one embodiment of the measuring arrangement, the evaluation circuit is designed to provide the information about the insulation fault as a value of an insulation resistance or as a range indication of a value of an insulation resistance.

[0023] According to a further development of the measuring arrangement, a voltage drop across the at least one resistor that can be bridged by the bypass switch is less than 100 volts, alternatively less than 70 volts, or alternatively less than 50 volts. The at least one resistor is selected such that the voltage drop across it can reach a maximum of the value specified above. The voltage drops when the bypass switch is non-conductive. Thus, the bypass switch can be implemented with a low-voltage switch and thus with minimal effort.

[0024] According to one embodiment of the measuring arrangement, the evaluation circuit comprises an analog / digital converter whose signal input is electrically connected to the second voltage divider tap. The connection is free of a data coupler, such as an optocoupler or an inductive coupler.

[0025] According to one embodiment of the measuring arrangement, the third resistance value and / or the fourth resistance value can be adjusted by a control signal from the evaluation circuit that controls the bypass switch. Advantageously, the number of data couplers in the measuring arrangement is kept low.

[0026] According to one embodiment of the measuring arrangement, the ratio of the third resistance value to the fourth resistance value has a minimum value RMIN and a maximum value RMAX. The maximum value is greater than the minimum value according to the following equation: RMIN⋅1.05 <RMAX<RMIN⋅1.5, alternatively RMIN⋅1.1 <RMAX<RMIN⋅1.4 oder alternatively RMIN⋅1.2 <RMAX<RMIN 1.3.

[0027] The control signal determines whether the minimum value or the maximum value is set.

[0028] According to one embodiment of the measuring arrangement, the minimum value of the third resistance value is at least ten times the maximum value of the fourth resistance value.

[0029] According to one embodiment of the measuring arrangement, the second voltage divider comprises the first number N of resistors and the second number M of resistors. The measuring arrangement further comprises at least one current source arranged in series with the first number N of resistors of the second voltage divider and / or with the second number M of resistors of the second voltage divider. The first number N of resistors is electrically connected to the second number M of resistors via the second voltage divider tap. In one example, the current source injects a measuring current that causes a potential shift between the first and second high-voltage power lines and the low-voltage power grid. The evaluation circuit evaluates the second voltage signal and generates information about an insulation fault therefrom.

[0030] According to one embodiment of the measuring arrangement, the low-voltage network comprises a battery which is electrically connected to the evaluation circuit for supplying the evaluation circuit and to the potential connection.

[0031] According to one embodiment, the measuring arrangement comprises a data coupler that couples the first voltage divider tap to a signal input of the evaluation circuit. The data coupler comprises, for example, an optocoupler or an inductive or capacitive coupler.

[0032] According to a second aspect of the invention, an on-board network, in particular of a motor vehicle, is provided.

[0033] The vehicle electrical system comprises a first and a second high-voltage power line, a previously described measuring arrangement, and a power output stage, in particular an inverter or a DC-DC converter, with at least one first semiconductor switch and at least one second semiconductor switch. The at least one first semiconductor switch is electrically connected between the first high-voltage power line and a first phase connection of the power output stage. Similarly, the at least one second semiconductor switch is electrically connected between the second high-voltage power line and the first phase connection.

[0034] For example, the evaluation circuit of the measuring arrangement of the vehicle electrical system is further configured to de-conduct the at least one first and at least one second semiconductor switch and to provide information about an insulation fault depending on a (measured) value of the second voltage signal and a (measured) value of the third voltage signal. The (measured) value of the second voltage signal and the (measured) value of the third voltage signal are determined, for example, when the vehicle is stationary or not in operation.

[0035] For example, the vehicle electrical system further comprises a resistor that is electrically connected between the first phase connection and the potential connection, in particular the ground connection. In this case, the evaluation circuit is further designed to provide information about an insulation fault depending on at least two (measured) values of the second voltage signal and at least two (measured) values of the third voltage signal. The at least two (measured) values of both the second and the third voltage signal are determined with different settings of the power output stage. The (measured) values of the second voltage signal and the (measured) values of the third voltage signal are determined, for example, when the vehicle is stationary or not in operation.

[0036] For example, the evaluation circuit is further designed - to switch the at least one first and the at least one second semiconductor switch of the power output stage to non-conductive mode and to record or process a first (measured) value of the second voltage signal and a first (measured) value of the third voltage signal, and / or - to switch the at least one first semiconductor switch of the power output stage to conducting and to switch the at least one second semiconductor switch of the power output stage to non-conducting and to record or process a second (measured) value of the second voltage signal and a second (measured) value of the third voltage signal, and / or - to switch the at least one first semiconductor switch of the power output stage to non-conductive mode and to switch the at least one second semiconductor switch of the power output stage to conductive mode and to record or process a third (measured) value of the second voltage signal and a third (measured) value of the third voltage signal.

[0037] The evaluation circuit is designed, for example, to switch the first and second semiconductor switches of the power output stage to non-conductive mode and to process a first (measured) value of the second voltage signal and a first (measured) value of the third voltage signal. Alternatively or additionally, the evaluation circuit is designed to switch the first semiconductor switch of the power output stage to conductive mode and the second semiconductor switch of the power output stage to non-conductive mode and to process a second (measured) value of the second voltage signal and a second (measured) value of the third voltage signal. Alternatively or additionally, the evaluation circuit is designed to switch the first semiconductor switch of the power output stage to non-conductive mode and the second semiconductor switch of the power output stage to conductive mode and to process a third (measured) value of the second voltage signal and a third (measured) value of the third voltage signal.Thus, the resistor connected to the first phase connection is subjected to a different voltage. The resistor causes an intentional insulation fault. The resistor has a predetermined resistance value or resistance range.

[0038] For example, the evaluation circuit can evaluate the first, second, and third (measured) values of the two voltage signals (and thus set the power output stage to three different settings), or evaluate the first and second (measured) values of the two voltage signals, or evaluate the first and third (measured) values of the two voltage signals, or evaluate the second and third (measured) values of the two voltage signals (and thus set the power output stage to two of the three different settings). The two voltage signals comprise the second and third voltage signals. The evaluation circuit is designed to provide information about an insulation fault depending on two or three (measured) values of the second voltage signal and two or three (measured) values of the third voltage signal.

[0039] According to one embodiment of the vehicle electrical system, the evaluation circuit is designed to provide the information about an insulation fault as a value of an insulation resistance or as a range indication of a value of an insulation resistance.

[0040] According to a further development of the vehicle electrical system, the power output stage has a second phase connection, a third semiconductor switch which is electrically connected between the first high-voltage power line and the second phase connection, and a fourth semiconductor switch which is electrically connected between the second high-voltage power line and the second phase connection.

[0041] According to a further development of the on-board network, the power output stage additionally comprises at least a third phase connection, a fifth semiconductor switch which is electrically connected between the first high-voltage power line and the third phase connection, and a sixth semiconductor switch which is electrically connected between the second high-voltage power line and the third phase connection.

[0042] According to one embodiment of the vehicle electrical system, the measuring arrangement further comprises a first filter capacitor, which is electrically connected between the first high-voltage power line and the potential connection, in particular the ground connection, and a second filter capacitor, which is electrically connected between the second high-voltage power line and the potential connection, in particular the ground connection. The first and second filter capacitors can also be referred to as first and second interference suppression capacitors or Y capacitors.

[0043] According to one embodiment of the vehicle electrical system, the measuring arrangement further comprises a first filter resistor, which is electrically connected between the first high-voltage power line and the potential connection, in particular the ground connection, and a second filter resistor, which is electrically connected between the second high-voltage power line and the potential connection, in particular the ground connection. The first and second filter resistors can also be referred to as first and second discharge resistors or as first and second Y-resistors. The first and second filter capacitors and the first and second filter resistors form a low-pass filter. In one example, the second and third voltage dividers are implemented as discharge resistors for the first and second filter capacitors.

[0044] According to one embodiment of the vehicle electrical system, it further comprises a buffer capacitor electrically connected between the first high-voltage power line and the second high-voltage power line. The vehicle electrical system further comprises a discharge circuit comprising a series circuit with a discharge resistor and a discharge switch. The series circuit is electrically connected between the first high-voltage power line and the second high-voltage power line. The buffer capacitor and the first voltage divider have low-pass properties.

[0045] According to one embodiment of the on-board electrical system, the first to the sixth semiconductor switch are implemented as a transistor from the following group, wherein the group comprises an insulated-gate bipolar transistor (IGBT), a metal-insulator-semiconductor field-effect transistor (MISFET), a metal-oxide-semiconductor field-effect transistor (MOSFET), a high-electron-mobility transistor (HEMT), and a junction-FET (JFET).

[0046] According to one embodiment of the vehicle electrical system, the first to the sixth semiconductor switch are each realized as a transistor with a substrate material that is silicon (abbreviated Si), silicon carbide (abbreviated SiC), gallium nitride (abbreviated GaN), aluminum gallium nitride (abbreviated AlGaN), aluminum indium nitride (abbreviated AlInN) or indium gallium arsenide (abbreviated InGaAs).

[0047] According to one embodiment of the vehicle electrical system, the first to the sixth semiconductor switches are implemented identically. The first to the sixth semiconductor switches are implemented, for example, as discrete transistors. The first to the sixth semiconductor switches are implemented as power transistors.

[0048] According to one embodiment of the vehicle electrical system, the first to sixth semiconductor switches are implemented as n-channel transistors. The first to sixth semiconductor switches are realized as normally-off transistors.

[0049] According to one embodiment of the on-board electrical system, the measuring arrangement comprises an additional voltage divider that is electrically connected between the first high-voltage power line and the second high-voltage power line and has an additional voltage divider tap that is electrically connected to the evaluation circuit. The electrical connection between the additional voltage divider tap and a signal input of an analog / digital converter of the evaluation circuit is realized, for example, via a data coupler of the measuring arrangement. The data coupler is designed, for example, as an optocoupler or an inductive or capacitive coupler. The additional voltage divider has a first resistance value between the additional voltage divider tap and the first high-voltage power line and a second resistance value between the additional voltage divider tap and the second high-voltage power line.For example, the first resistance value of the additional voltage divider is at least ten times the second resistance value of the additional voltage divider. The first resistance value of the additional voltage divider is, for example, greater than the first resistance value of the first voltage divider. The second resistance value of the additional voltage divider is, for example, greater than the second resistance value of the first voltage divider.

[0050] Thus, the additional voltage divider has a higher resistance than the first voltage divider. The total voltage can be measured by the additional voltage divider. This allows for a dual measurement (and thus redundant measurement) of the total voltage using the first and additional voltage dividers. Due to the redundancy, drift in the first and additional voltage dividers can be detected.

[0051] According to a further aspect of the invention, an electric vehicle or an electrically driven vehicle is provided, which comprises: the previously described on-board electrical system with the measuring arrangement, an electric motor which is electrically connected to the first phase connection or to the phase connections, a battery arrangement with a first and a second battery connection, a first circuit breaker which is electrically connected between the first high-voltage power line and the first battery connection, and a second circuit breaker which is electrically connected between the second high-voltage power line and the second battery connection.

[0052] According to one embodiment of the electric vehicle, the first and second circuit breakers are implemented as contactors, circuit breakers or power transistors.

[0053] The measurement setup described here is particularly suitable for electric vehicles. The features described in connection with the measurement setup can therefore also be applied to electric vehicles, and vice versa.

[0054] In one example, the measuring setup is designed for HV voltage measurement and balancing the HV network with vehicle ground. The measuring setup is implemented to discharge the filter capacitors. The measuring setup performs an insulation resistance measurement. The measuring setup includes a drive converter for electromobility.

[0055] Further embodiments and developments of the measuring arrangement or the electric vehicle result from the following in connection with the Fig. 1 and Fig. 2. Identical, similar, or similarly functioning circuit components and components are provided with the same reference numerals in the figures. Fig. 1 shows an embodiment of a measuring arrangement. Fig. 2 shows another embodiment of a measuring arrangement.

[0056] Fig. Figure 1 shows an exemplary embodiment of an on-board electrical system of an electric vehicle with a measuring arrangement 1 having an inverter 18 as a power output stage. The measuring arrangement 1 comprises a first and a second high-voltage power line 2, 3, which are electrically connected to a battery arrangement 50. A low-voltage network 51 of the measuring arrangement 1 has an evaluation circuit 19 and a potential connection or ground connection 4.

[0057] The measuring arrangement 1 further comprises a first voltage divider 6 and a second voltage divider 13. The measuring arrangement 1 or the inverter 18 comprises a first to a third phase connection 54 to 56 for electrically connecting an electric motor 20 or its winding phases. The inverter 18 electrically connects the first and second high-voltage power lines 2, 3 to the first, second, and third phase connections 54 to 56. The evaluation circuit 19 is electrically connected to the inverter 18 on the output side.

[0058] The first voltage divider 6 is electrically connected to the first high-voltage power line 2 and to the second high-voltage power line 3. The first voltage divider 6 has a first voltage divider tap 52, which is coupled to the evaluation circuit 19. The measuring arrangement 1 includes a data coupler 75, which couples the first voltage divider tap 52 to an input of the evaluation circuit 19. The first voltage divider 6 has a first resistance value between the first voltage divider tap 52 and the first high-voltage power line 2 and a second resistance value between the first voltage divider tap 52 and the second high-voltage power line 3. The first resistance value is at least ten times the second resistance value. The first voltage divider 6 comprises a first number K of resistors 61 to 65, which are arranged in series between the first high-voltage power line 2 and the first voltage divider tap 52.The first voltage divider 6 comprises a second number L of resistors 66 arranged in series between the first voltage divider tap 52 and the second high-voltage power line 3. In . Fig. In the example shown in Figure 1, the first number K is 5 and the second number L is 1.

[0059] The second voltage divider 13 is electrically connected to the second high-voltage power line 3 and the potential connection 4. The second voltage divider 13 is electrically connected to the second high-voltage power line 3 and to the potential connection 4. The second voltage divider 13 has a second voltage divider tap 53, which is electrically connected to the evaluation circuit 19 via a line not shown. The second voltage divider 13 has a first resistance value between the second voltage divider tap 53 and the second high-voltage power line 3 and a second resistance value between the second voltage divider tap 53 and the potential connection 4. The value of the first resistance value is at least ten times the maximum value of the second resistance value.

[0060] In one example, the second voltage divider 13 comprises a first and a second resistor 41, 46 and a current source 60 arranged in series with the second resistor 46. The first resistor 41 has, for example, the first resistance value and the second resistor 46 has, for example, the second resistance value.

[0061] The measuring arrangement 1 comprises an additional voltage divider 9, which is electrically connected to the first high-voltage power line 2 and the second high-voltage power line 3. The additional voltage divider 9 is electrically connected to the first high-voltage power line 2 and to the second high-voltage power line 3. The additional voltage divider 9 has an additional voltage divider tap 69, which is coupled to the evaluation circuit 19. An additional data coupler 76 couples the additional voltage divider tap 69 to the evaluation circuit 19. The additional voltage divider 9 has a first resistance value between the additional voltage divider tap 69 and the first high-voltage power line 2 and a second resistance value between the additional voltage divider tap 69 and the second high-voltage power line 3.The first resistance value of the additional voltage divider 9 is at least ten times the second resistance value of the additional voltage divider 6. The additional voltage divider 9 comprises a first number K' of resistors 61' to 65' arranged in series between the first high-voltage power line 2 and the additional voltage divider tap 69. The additional voltage divider 9 comprises a second number L' of resistors 66' arranged in series between the additional voltage divider tap 69 and the second high-voltage power line 3. In . Fig. In the example shown in Figure 1, the first number K' is 5 and the second number L' is 1.

[0062] A first voltage signal S1 is present at the first voltage divider tap 52. The data coupler 75 outputs a signal S1' derived from the first voltage signal S1. A second voltage signal S2 is present at the second voltage divider tap 52. An additional voltage signal S4 is present at the additional voltage divider tap 69. The additional data coupler 76 outputs a signal S4' derived from the additional voltage signal S4. The evaluation circuit 19 outputs a signal SIS containing information about an insulation fault.

[0063] The first resistance value of the additional voltage divider 9 is greater than the first resistance value of the first voltage divider 6. The second resistance value of the additional voltage divider 9 is greater than the second resistance value of the first voltage divider 6. The first voltage divider 6 therefore has a shorter settling time than the additional voltage divider 9. The first voltage divider 6 has a higher accuracy than the additional voltage divider 9. The advantage of the higher resistance values of the additional voltage divider 9 is the lower losses that occur at the additional voltage divider 9. Losses can, for example, lead to a circuit board heating up and also have a negative effect on the power consumption of the vehicle. In one example, the measuring arrangement 1 or parts thereof are applied to the circuit board.

[0064] The measuring arrangement 1 comprises a first filter capacitor 10, which is electrically connected to the first high-voltage power line 2 and to the potential connection 4, and a second filter capacitor 11, which is electrically connected to the second high-voltage power line 3 and to the potential connection 4. The measuring arrangement 1 optionally comprises a first filter resistor 71, which is electrically connected to the first high-voltage power line 2 and to the potential connection 4, and optionally a second filter resistor 72, which is electrically connected to the second high-voltage power line 3 and to the potential connection 4. The first filter resistor 71 is electrically connected to the first high-voltage power line 2 and to the potential connection 4. The second filter resistor 72 is electrically connected to the second high-voltage power line 3 and to the potential connection 4.

[0065] The measuring arrangement 1 comprises a buffer capacitor 7, which is electrically connected to the first high-voltage power line 2 and to the second high-voltage power line 3. The measuring arrangement 1 further comprises a discharge circuit 8. The discharge circuit 8 includes a series circuit with a discharge resistor 73 and a discharge switch 74. The series circuit is electrically connected to the first high-voltage power line 2 and to the second high-voltage power line 3.

[0066] The inverter 18 comprises first to sixth current paths 81-86. The first current path 81 comprises a first semiconductor switch 91. The first high-voltage power line 2 is electrically connected to the first phase terminal 54 via the first current path 81. The second current path 82 comprises a second semiconductor switch 92. The first phase terminal 54 is electrically connected to the second high-voltage power line 3 via the second current path 82. The third current path 83 comprises a third semiconductor switch 93. The first high-voltage power line 2 is electrically connected to the second phase terminal 55 via the third current path 83. The fourth current path 84 comprises a fourth semiconductor switch 94. The second phase terminal 55 is electrically connected to the second high-voltage power line 3 via the fourth current path 84. The fifth current path 85 comprises a fifth semiconductor switch 95.The first high-voltage power line 2 is electrically connected to the third phase terminal 56 via the fifth current path 85. The sixth current path 86 includes a sixth semiconductor switch 96. The third phase terminal 56 is electrically connected to the second high-voltage power line 3 via the sixth current path 86.

[0067] The first to sixth semiconductor switches 91 to 96 are implemented as insulated-gate bipolar transistors (IGBTs). The IGBTs are n-channel IGBTs. The IGBTs are normally off.

[0068] The low-voltage network 51 includes a battery 70, which is electrically connected to the evaluation circuit 19 and to the potential connection 4. The battery 70 supplies the evaluation circuit 19.

[0069] An on-board electrical system 90 of an electric vehicle comprises the measuring arrangement 1 and the electric motor 20, which is electrically connected to the first, second, and third phase connections 54 to 56. The measuring arrangement 1 comprises the high-voltage network 5 and the low-voltage network 51. The on-board electrical system 90 further comprises the battery arrangement 50 with a first and a second battery connection. A first circuit breaker 17 of the measuring arrangement 1 electrically connects the first high-voltage network line 2 to the first battery connection. A second circuit breaker 77 of the measuring arrangement 1 electrically connects the second high-voltage network line 3 to the second battery connection.

[0070] A first voltage V1 is applied to the first high-voltage power line 2. A second voltage V2 is applied to the second high-voltage power line 3. The total voltage is thus VGE=V1-V2. The potential connection 4 has the ground potential GND. The first and second voltages V1, V2 are symmetrical to the ground potential GND. The following applies: V1−GND=GND−V2 or |V1−GND|=|V2−GND|

[0071] In Fig. 1 shows electrical components of a typical on-board electrical system architecture of the on-board electrical system 90, whose drive is supplied from an energy source whose voltage poses a hazard if touched. The battery arrangement 50 represents the HV energy source, which is usually made up of several battery cells 57 connected in series and parallel. The HV energy source provides a powerful voltage, which poses a high risk of injury to those touching it if touched. The HV energy source and all consumers connected to the HV energy source, as well as the cables required for the electrical connection, are referred to as the high-voltage network 5, abbreviated to HV network or HV on-board network.

[0072] Battery 70 represents a low-voltage source, abbreviated to LV energy source. For example, battery 70 is implemented as a 12V battery. Contact with the 12V voltage generally does not pose a danger to the person touching it. The LV energy source and all consumers connected to the LV energy source as well as the cables required for electrical connection are referred to below as low-voltage network 51, abbreviated to LV network. The LV network 51 has no special protection against direct contact. Uninsulated metallic parts of the vehicle body are generally used as ground connections for the LV network 51. Direct contact with ground-carrying parts of the LV network 51 is intended as a normal condition. The HV network 5, on the other hand, is protected against direct contact and is safely insulated from the LV network 51.If the HV network 5 is touched at two points with different potentials, there is a risk of electric shock. If an electrical connection is established between the two networks by touching the HV network 5 at one point and part of the LV network 51, there is initially no risk of electric shock for the person touching it, as the circuit cannot be closed. However, if the insulation between the HV network 5 and LV network 51 is damaged, there is a subsequent risk from touching the HV network 5 at a single point. Damage to the insulation can occur due to improper handling or due to aging of the material.

[0073] The measuring arrangement 1 is implemented as a drive converter. The measuring arrangement 1 has the inverter 18. The inverter 18 is the most powerful consumer in the HV network 5 and also a significant source of EMC interference (EMC is the abbreviation for electromagnetic compatibility). The measuring arrangement 1 contains a first voltage divider 6 for HV voltage measurement. The HV voltage measurement is usually implemented twice for reasons of functional safety. This means that the measuring arrangement 1 contains the first voltage divider 6 and the additional voltage divider 9. An HV intermediate circuit implements a buffer storage in the form of the buffer capacitor 7 with a capacitance of, for example, approximately 1 mF. The active discharge circuit 8 is provided for the rapid discharge of the buffer storage or buffer capacitor 7 below a voltage at which there is no longer any danger from contact.The first and the additional voltage divider 6, 9 cause a passive discharge to completely discharge the buffer storage or buffer capacitor 7.

[0074] An HV EMC filter has Y capacitors 10, 11, for example, in the order of magnitude of approximately 1 µF. Filter resistors 71, 72 are arranged in parallel with the Y capacitors 10, 11. The filter resistors 71, 72 are also used as discharge resistors, which discharge the residual voltage that remains due to asymmetries of the Y capacitors 10, 11 or asymmetries of the HV network 5 compared to the LV network 51 despite the discharge of the buffer memory 7. The inverter 18 is implemented as a power output stage. The inverter 18 is in the form of a bridge constructed with six semiconductor switches and generates a rotating field from a direct voltage or direct current, abbreviated to a B6 bridge. The evaluation circuit 19 controls the inverter 18.

[0075] The following additional components are generally found outside the inverter 18: The second voltage divider 13 is implemented as an insulation monitor. The insulation monitor continuously measures the ohmic resistance between HV network 5 and LV network 51 during operation. If the resistance becomes too low, there is a risk of contact, and the system is shut down - e.g., by the evaluation circuit 19. The insulation monitor causes a potential shift between the two networks, for example, by injecting a harmless measuring current using the current source 60 between HV network 5 and LV network 51, and measures this potential shift at the second voltage divider terminal 53.

[0076] Symmetry resistors 48, 49 keep the HV network 5 symmetrical to the LV network 51. The HV network 5 is symmetrical to the LV network 51 when the voltages between the first high-voltage network line 2 and a potential connection 4 (i.e., between the positive pole of the HV network 5 and LV ground) and between the potential connection 4 and the second high-voltage network line 3 (i.e., between LV ground and the negative pole of the HV network 5) are equal. The first high-voltage network line 2 can be called the positive pole of the HV network 5. The potential connection 4, to which a ground potential GND is applied, can be called low-voltage ground or LV ground. The second high-voltage network line 3 can be called the negative pole of the HV network 5.

[0077] The circuit breakers 17, 77 are implemented as battery contactors, which play a key role in the design of the vehicle electrical system 90. With open battery contactors 17, 77, components mounted on one side of the contactors cannot function on the disconnected side. The electric motor 20 serves as the electrical machine. The evaluation circuit 19 can include a logic unit, such as a microprocessor or microcontroller. The evaluation circuit 19 includes, for example, one or more analog-to-digital converters that electrically connect the second voltage divider tap 53, the data coupler 75, and / or the additional data coupler 76 to the logic unit.

[0078] Parasitic insulation resistances 21a, 21b, 21c between HV network 5 and potential connection 4 are shown as examples at three randomly selected locations in HV network 5. These locations are within battery arrangement 50, on the line between battery arrangement 50 and inverter 18, and within electric motor 20.

[0079] In an alternative embodiment not shown, the second voltage divider 13 is electrically connected to the first high-voltage power line 2 and the potential terminal 4. The second voltage divider 13 is thus not electrically connected to the second high-voltage power line 3.

[0080] Fig. 2 shows an embodiment of an on-board network of an electric vehicle with a measuring arrangement 1 with an inverter 18, which is a development of the in Fig. 1A. The first resistance value of the second voltage divider 13 is adjustable by a control signal CSW. The minimum value of the first resistance value of the second voltage divider 13 is at least ten times the maximum value of the second resistance value of the second voltage divider 13. The second voltage divider 13 comprises a first number N of resistors 41 to 45, which are arranged in series between the first high-voltage power line 2 and the second voltage divider tap 53. The second voltage divider 13 comprises a second number M of resistors 46, which are arranged in series between the second voltage divider tap 53 and the potential terminal 4. In Fig. In the example shown in Figure 2, the first number N is 5 and the second number M is 1.

[0081] The measuring arrangement 1 comprises a bypass switch 47 that electrically connects a first terminal of a resistor 45 to a second terminal of the resistor 45. If the bypass switch 47 is switched on by the control signal CSW, the resistor 45 is bypassed. The resistor 45 is one of the first number N of resistors 41 to 45. Thus, the first resistance value can be switched between two values using the control signal CSW.

[0082] The measuring arrangement 1 comprises a third voltage divider 16, which is electrically connected to the second high-voltage power line 3 and the potential connection 4. The third voltage divider 16 has a further voltage divider tap 68, which is electrically connected to the evaluation circuit 19. The third voltage divider 16 comprises a first number N' of resistors 41' to 45', which are arranged in series between the second high-voltage power line 3 and the third voltage divider tap 68. The third voltage divider 16 comprises a second number M' of resistors 46', which are arranged in series between the third voltage divider tap 68 and the potential connection 4. In Fig. In the example shown in Figure 2, the first number N' is 5 and the second number M' is 1.

[0083] The second and third voltage dividers 13, 16 ensure the symmetry of the first and second voltages V1, V2 to the ground potential GND. The following applies: V1−GND=GND−V2 oder |V1−GND|=|V2−GND|

[0084] In Fig. 2, at least one of the two HV voltage measurements with the first voltage divider 6 and the additional voltage divider 9 is converted to a high-impedance voltage measurement of the two poles 2, 3 of the HV network 5 against LV ground 4 by means of the second voltage divider 3 and / or the third voltage divider 16. Since this type of voltage measurement measures against LV ground 4, unlike the voltage measurement against the negative pole 3 of the HV network 5, the measurement result does not first have to be transmitted from the HV network 5 to the LV network 51 via a data coupler 75, 76. The disadvantage of this type of voltage measurement is the required, very high measuring resistance. The measuring arrangement 1 is designed in such a way that a balance can be set between interference immunity and response speed in such a high-impedance measuring system. The two voltage measurements required for reasons of redundancy are advantageously carried out differently.A quick voltage measurement is performed as in . Fig. 1 by the first voltage divider 6 and a redundant high-impedance voltage measurement related to LV ground by the second voltage divider 9.

[0085] In addition to the cost advantage due to the unnecessary data coupling between HV network 5 and LV network 51, the high-impedance voltage measurement related to LV ground brings further advantages: The spanned resistance network can Fig. 1, replace the balancing resistors 48, 49 of the HV network 5 with the LV network 51. Likewise, the first, second and third voltage dividers 3, 6, 16 take over the function of the discharge resistors 71, 72 (in Fig. 1) of the Y capacitors 10, 11.

[0086] By a simple modification, the measurement of the insulation resistance can also be carried out using the second voltage divider 13 (similar to Fig. 1) can be performed using the same hardware. The second voltage divider 13 is designed for insulation monitoring. If one were to assume that an insulation fault can only occur locally as an individual fault between the first high-voltage power line 2 and potential connection 4 or between the second high-voltage power line 3 and potential connection 4 (insulation resistance 21b or 21d), the high-impedance voltage measurement would be sufficient to detect the insulation fault even without the bypass switch 47. However, if one assumes that an insulation fault can occur distributed across HV+ and HV- (21b and 21d) or at an intermediate potential (21a), the value of the total insulation fault can be determined with a slight modification. The total insulation fault here refers to the parallel connection of all insulation resistances between HV potentials and ground.

[0087] In one embodiment, the insulation resistance is measured exclusively when the electric vehicle is stationary and therefore when the on-board network 90 is not in operation. Here, the measuring arrangement 1 can be Fig. 2 including the resistor 23, but without the bypass switch 47. The resistor 23 is arranged between one of the three phase connections 54 to 56 and the potential connection 4. Even if all semiconductor switches 91 to 96 of the inverter 18 are open, an asymmetrical insulation fault 21b can be detected by comparing the two measured voltages against LV ground GND at the second voltage divider tap 53 and the third voltage divider tap 68. In the case of an unfavorable location of the insulation fault 21a or in the case of distributed insulation faults, the triggering threshold cannot be determined exactly. For this reason, the resistor 23 is introduced. This can be connected via at least one semiconductor switch from the first, third and fifth semiconductor switches 91, 93, 95 of the inverter 18 to the first high-voltage power line 2 orvia at least one semiconductor switch from the second, fourth, and sixth semiconductor switches 92, 94, 96 of the inverter 18 to the second high-voltage power line 3. The insulation resistance can be precisely determined by the two measuring voltages in at least two of the three possible semiconductor switch positions (first, third, and fifth semiconductor switches 91, 93, 95 conductive, second, fourth, and sixth semiconductor switches 92, 94, 96 conductive, all semiconductor switches 91 to 96 non-conductive).

[0088] While an evaluation using this simple method would be theoretically conceivable in active inverter operation, it is practically impractical due to the high time constant during the charge reversal of the Y capacitors 10, 11 and the high PWM frequency. A further difficulty with this simple embodiment is the leakage current of the inverter 18, which is not negligible in some semiconductor switch types.

[0089] In an alternative embodiment, an on-board electrical system 90 is present in which the insulation resistance is to be measured even with the active inverter 18, or in which the leakage current of the semiconductor switches 91 to 96 is not negligible. Instead of the resistor 23, the bypass switch 47 is arranged in parallel with a resistor of the first or third voltage divider 13, 16. This assumes the function of establishing an asymmetry in the balancing of the HV network 5 with respect to the LV network 51 when switched on. This asymmetry is impaired by a possible existing insulation fault. The insulation resistance can be precisely determined from the two measurement voltages against the potential connection 4 in both semiconductor switch positions.In one embodiment, the voltage divider resistors can be dimensioned such that the bypass switch 47, even when open, only sees a voltage that can be blocked by a conventional low-voltage switch. A further advantage of this implementation of the insulation resistance measurement is the switchable voltage divider of the high-impedance voltage measurement. This voltage divider is implemented by the second voltage divider 13. This allows the drift of the voltage divider to be detected independently of the plausibility check against the second voltage measurement. By comparing the voltage at the second voltage divider tap 53 with the bypass switch 47 closed and open, a drift of the resistors 41 to 46 can be determined independently of the first and third voltage dividers 6, 16 (with the voltage divider taps 68 and 52).

[0090] Alternatively or additionally, the second and third voltage dividers 13, 16 are checked by comparing the difference between the voltage at the second voltage divider tap 53 and the third voltage divider tap 68 with the voltage at the first voltage divider tap 52. This makes it possible to detect drift in one of the three voltage dividers 6, 13, 16 or in the downstream evaluation circuit. The evaluation circuit 19 comprises, for example, one or more analog-to-digital converters (abbreviated to A / D converters) that electrically couple or electrically connect the second voltage divider tap 53, the third voltage divider tap 68, and / or the data coupler 75 to the logic unit 28. An A / D converter 25 thus electrically connects the second voltage divider tap 53 to the logic unit 28. An A / D converter 26 electrically connects the data coupler 75 to the logic unit 28. An A / D converter 27 electrically connects the third voltage divider tap 68 to the logic unit 28.The logic unit 28 outputs the signal SIS containing information about an insulation fault. The logic unit 28 controls the semiconductor switches 91 to 96 via drivers (not shown). The logic unit 28 outputs the control signal CSW to the bypass switch 47. Advantageously, in the measuring arrangement 1 according to . Fig. 2 only a data coupler is required.

[0091] In an alternative embodiment not shown, the second resistance value of the second voltage divider 13 can be adjusted by a control signal CSW.

[0092] In an alternative embodiment not shown, the third voltage divider 16 is electrically connected between the first high-voltage power line 2 and the potential terminal 4.

[0093] In an alternative embodiment not shown, the measuring arrangement 1 has more than three phase connections. For example, the measuring arrangement 1 has five or six phase connections to which the electric motor 20 is electrically connected. With three phase connections 54 to 56, the electric motor 20 is three-phase. With more than three phase connections, the electric motor 20 uses more than three phases.

[0094] The invention is not limited to the exemplary embodiments by the description of the invention. Rather, the invention encompasses any novel feature and any combination of features, including in particular any combination of features in the claims, even if this feature or combination itself is not explicitly stated in the claims or exemplary embodiments. List of reference symbols 1 measuring arrangement 2 first high-voltage power line 3 second high-voltage power line 4 Potential connection 5 High-voltage network 6 first voltage divider 7 Buffer capacitor 8 Discharge circuit 9 additional voltage divider 10 first filter capacitor 11 second filter capacitor 13 second voltage divider 16 additional voltage dividers 17 first circuit breaker 18 inverters or power amplifiers 19 Evaluation circuit 20 electric motor 21a, 21b, 21c insulation resistance 23 Resistance 25 to 27 analog / digital converters 28 Logic unit 41 to 46 resistance 41' to 46' resistance 47 Bypass switch 48, 49 Balancing resistor 50 Battery arrangement 51 Low-voltage network 52 first voltage divider tap 53 second voltage divider tap 54 to 56 phase connections 57 battery cells 60 power source 61 to 66 resistance 61' to 66' resistance 68 additional voltage divider tap 69 additional voltage divider tap 70 Battery 71, 72 Filter resistance 73 Discharge resistance 74 discharge switch 75, 76 Data coupler 77 second circuit breaker 81 to 86 current path 90 On-board network 91 to 96 switches CSW control signal SIS Signal S1, S2, S3, S4 voltage signal

Claims

[1] Measuring arrangement (1) for insulation monitoring in an on-board network with a first and a second high-voltage network line (2, 3), the measuring arrangement comprising: - a low-voltage network (51) with an evaluation circuit (19) and a potential connection (4), - a first voltage divider (6) which is electrically connected between the first high-voltage power line (2) and the second high-voltage power line (3) and has a first voltage divider tap (52) at which a first voltage signal (S1) can be tapped, - a second voltage divider (13) which is electrically connected between the first or the second high-voltage mains line (2, 3) on the one hand and the potential connection (4) on the other hand and has a second voltage divider tap (53) at which a second voltage signal (S2) can be tapped, wherein the evaluation circuit (19) is electrically connected on the signal input side to the first and second voltage divider taps (52, 53) and is designed to evaluate the first and / or second voltage signal (S1, S2) or signals derived therefrom and to determine an insulation state in the vehicle electrical system based on the evaluation result, wherein the measuring arrangement (1) has a third voltage divider (16) which is electrically connected between the first or the second high-voltage mains line (2, 3) on the one hand and the potential connection (4) on the other hand and has a third voltage divider tap (68) which is electrically connected to the evaluation circuit (19) and at which a third voltage signal (S3) can be tapped; wherein the evaluation circuit (19) is further designed to evaluate the third voltage signal (S3) or a signal derived therefrom and to determine the insulation state based on the evaluation result. [2] Measuring arrangement (1) according to claim 1, wherein the first voltage divider (6) has a first total resistance value which is greater than 50 kiloohms or in a range between 50 kiloohms and 2 megaohms or between 200 kiloohms and 1 megaohm, and the second voltage divider (13) has a second total resistance value which is greater than 5 megaohms or in a range between 5 megaohms and 100 megaohms or between 10 megaohms and 50 megaohms. [3] Measuring arrangement (1) according to claim 1 or 2, wherein the third voltage divider (16) has a third total resistance value which is greater than 5 megohms or lies in a range between 5 megohms and 100 megohms or between 10 megohms and 50 megohms. [4] Measuring arrangement (1) according to one of claims 1 to 3, wherein the second voltage divider (13) comprises: - a first number N of resistors (41 to 45) which are electrically connected in series with one another and are electrically connected between the first or the second high-voltage mains line (2, 3) on the one hand and the second voltage divider tap (53) on the other hand, and - a second number M of resistors (46) which are electrically connected in series with one another and are electrically connected between the second voltage divider tap (53) and the potential terminal (4). [5] Measuring arrangement (1) according to claim 4, wherein the second voltage divider (13) comprises a controllable bypass switch (47) which bypasses at least one resistor of the first number N of resistors (41 to 45), wherein the first number N is greater than 1, or which bypasses at least one resistor of the second number M of resistors (46), wherein the second number M is greater than 1, and wherein the evaluation circuit (19) is electrically connected on the control signal output side to a control terminal of the bypass switch and is designed to output a control signal (CSW) to the control terminal of the bypass switch (47) for switching the bypass switch (47). [6] Measuring arrangement (1) according to claim 5, wherein the evaluation circuit (19) is designed, in a first measuring phase, to output the control signal (CSW) with a first value which puts the bridging switch (47) into a conductive state, and to process a first value of the second voltage signal (S2) and a first value of the first and / or the third voltage signal (S1, S3), wherein the evaluation circuit (19) is further designed to output the control signal (CSW) with a second value in a second measuring phase, which sets the bridging switch (47) into a non-conductive state, and to process a second value of the second voltage signal (S2) and a second value of the first and / or the third voltage signal (S1, S3), and wherein the evaluation circuit (19) is further designed to provide information about an insulation fault as a function of the first and second values of the second voltage signal (S2) and of the first and second values of the first and / or third voltage signals (S1, S3). [7] Measuring arrangement (1) according to claim 6, wherein the evaluation circuit (19) is further designed to provide the information about the insulation fault as a value of an insulation resistance or as a range indication of a value of an insulation resistance. [8] Measuring arrangement (1) according to one of claims 5 to 7, wherein a voltage dropped across the at least one resistor that can be bridged by the bypass switch (47) is less than 100 volts or less than 70 volts or less than 50 volts. [9] Measuring arrangement (1) according to one of the preceding claims, wherein the evaluation circuit (19) comprises an analog / digital converter (25) whose signal input is electrically connected to the second voltage divider tap (53), wherein the electrical connection is free of a data coupler or an optocoupler or an inductive coupler. [10] On-board network (90), comprising: - a first and a second high-voltage power line (2, 3), - a measuring arrangement (1) according to one of the preceding claims, - a power output stage (18) with at least one first semiconductor switch (91) and at least one second semiconductor switch (92), - wherein the at least one first semiconductor switch (91) is electrically connected between the first high-voltage power line (2) and a first phase connection (54) of the power output stage (18), and the at least one second semiconductor switch (92) is electrically connected between the second high-voltage power line (3) and the first phase connection (54). [11] On-board electrical system (90) according to claim 10, wherein the evaluation circuit (19) is designed to switch the at least one first and the at least one second semiconductor switch (91, 92) non-conductive and to provide information about an insulation fault as a function of a value of the second voltage signal (S2) and of a value of the third voltage signal (S3). [12] On-board electrical system (90) according to claim 10 or 11, further comprising a resistor (23) electrically connected between the first phase terminal (54) and the potential terminal (4), wherein the evaluation circuit (19) is further configured to provide information about an insulation fault as a function of at least two values of the second voltage signal (S2) and of at least two values of the third voltage signal (S3). [13] On-board network (90) according to claim 12, wherein the evaluation circuit (19) is further designed - to switch the at least one first and the at least one second semiconductor switch (91, 92) of the power output stage (18) non-conductive and to detect a first value of the second voltage signal (S2) and a first value of the third voltage signal (S3), and / or - to switch the at least one first semiconductor switch (91) of the power output stage (18) to conduct and to switch the at least one second semiconductor switch (92) of the power output stage (18) to non-conducting and to detect a second value of the second voltage signal (S2) and a second value of the third voltage signal (S3), and / or - to switch the at least one first semiconductor switch (91) of the power output stage (18) non-conductive and to switch the at least one second semiconductor switch (92) of the power output stage (18) conductive and to detect a third value of the second voltage signal (S2) and a third value of the third voltage signal (S3).

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