WO2025056597A1 - Electric circuit, method for determining a malfunction of a contactor, computer program, computer-readable storage medium, battery control device, battery, and motor vehicle - Google Patents

Abstract

The invention relates to an electric circuit (1) and to a method for determining a malfunction of a contactor (2a) in a high-voltage branch (3). A measurement voltage source (6) supplies a measurement voltage (U _M ) to the high-voltage branch (3) in a measurement voltage supply branch (5) which is electrically connected in parallel to the contactor (2a) and generates a voltage drop (U ₁ ) across the contactor (2a) in the high-voltage branch (3). The measurement voltage source (6) is connected and disconnected by the battery control device (9) in parallel to an activation or deactivation of the contactor (2a) in order to measure the respective voltage drop across the contactor (2) upon activating and deactivating the measurement voltage source (6) in order to determine the respective switch state of the contactor (2a) prior to and/or after the activation or deactivation of the contactor (2a). If the voltage drop (U ₁ ) is the same upon activating and deactivating the maximum voltage source (6), the contactor (2a) is in a closed switching state, whereas if there is a difference between the measured voltage drop (U ₁ ), the contactor (2a) is in an open switching state.

Description

Electrical circuit and method for determining a fault condition of a contactor, a computer program, a computer-readable storage medium, a battery control device, a battery and a motor vehicle

Technical field

The present invention relates to an electrical circuit and a method for determining a fault condition of a contactor, a computer program, a computer-readable storage medium, a battery control device, a battery and a motor vehicle.

State of the art

A battery, particularly in a motor vehicle, is electrically separated from a high-voltage circuit by means of a contactor. The high-voltage circuit connects the battery to an electrical load in the motor vehicle, such as an electric motor. When the contactor is electrically connected and disconnected in the high-voltage circuit, wear can occur due to switching operations, for example due to an arc during electrical separation. This can cause the contactor to become welded to a contact, causing the contactor contacts to stick together and the contactor to no longer open. Alternatively, the contactor can jam and no longer close. This can result in a contactor fault condition, which poses a danger in the high-voltage circuit if the contactor does not have the switching state it should have due to sticking or jamming. Therefore, the switching state of the contactor must be checked to determine whether or not there is a defect in the contactor, in particular sticking or jamming of the contactor.

For example, CN 203241517 U discloses a detection system for the contact closure state of a motor vehicle relay. CN 108287536 A discloses a device and method for detecting sintering of a negative contactor. CN 107688146 A discloses a method for detecting a contactor state. CN 104142466 A discloses a system and method for detecting the closed state of motor vehicle relay contacts. DE 10 2011 004 516 A1 discloses a circuit and a Method for diagnosing switching contacts in a battery-powered road vehicle is known.

Description of the invention

Based on the known prior art, it is an object of the present invention to provide an improved electrical circuit for determining a fault condition of a contactor, a corresponding method for determining a fault condition of a contactor as well as a computer program, a computer-readable storage medium, a battery control unit, a battery and a motor vehicle.

The object is achieved by an electrical circuit for determining a fault condition of a contactor having the features of claim 1. Advantageous further developments emerge from the subclaims, the description, and the figures.

Accordingly, an electrical circuit for determining a fault condition of a contactor is proposed, comprising the contactor, which is electrically arranged in a high-voltage branch and configured to electrically close or open the high-voltage branch, and comprising a measuring voltage feed branch for feeding a measuring voltage into the high-voltage branch, wherein the measuring voltage feed branch comprises a measuring voltage source and an electrical resistor and is electrically connected in parallel with the contactor in the high-voltage branch. The electrical circuit is characterized in that it comprises a measuring device configured to measure a voltage drop across the contactor in the high-voltage branch.

The fault condition can be the presence of a defect or the absence of a defect. For example, the defect can be that the contactor does not assume the switching state according to a signal to open or close the contactor. The defect can therefore be that the contactor sticks or blocks at a contact. On the other hand, there can be no defect if the contactor assumes the switching state according to the signal to open or close the contactor. There can therefore be no defect if the contactor does not stick or block at a contact. The contactor can be designed as a relay. The contactor can be electrically connected to the high-voltage branch, so that the contactor is designed to electrically close or open the high-voltage branch. In addition, the high-voltage branch can be designed to be electrically connected to a terminal of a battery and/or to a high-voltage circuit. particularly in a motor vehicle. The high-voltage branch can thus be an electrical line between a high-voltage source and an electrical load, with the contactor electrically connecting or disconnecting them. The high-voltage source can be a battery, particularly a traction battery of a motor vehicle.

The measuring voltage supply branch can be electrically connected to the high-voltage branch such that, when the contactor is closed, a measuring current generated by the measuring voltage source flows through the contactor. Optionally, the resistor can be configured to limit the measuring current. Switching the measuring voltage source on and off can generate a measuring current that flows through the resistor and the contactor and changes depending on the switching state of the contactor and/or the measuring voltage source.

The measuring voltage source can be configured as a DC voltage source, which can provide a measuring voltage that can be lower than the terminal voltage of the battery. For example, the measuring voltage source can be configured as an electrical capacitor that can be charged by the terminal voltage of the battery.

Alternatively, the measuring voltage source can be configured as an alternating voltage source, which can provide an alternating voltage whose peak value can be lower than the terminal voltage of the battery. For this purpose, the measuring device can be configured to measure an alternating voltage.

Additionally or alternatively, the measurement voltage source can be designed as a charge pump. This allows the measurement voltage to be adjusted to different "loads" of the measurement path, eliminating the need for separate voltage regulation of the measurement voltage.

The measuring device can be configured to measure a voltage drop across the contactor, in particular a change in the voltage drop and/or the measuring current across the contactor. For example, the measuring device can have measuring points in the high-voltage branch that are electrically connected to the terminals of the contactor, with one of the measuring points optionally being electrically connected to a terminal connection of the battery, in particular via the high-voltage branch. This provides the advantage that the measuring voltage does not need to be readjusted due to changing measuring conditions, such as contactor aging or a change in the vehicle load, which can cause different loads on the circuit between the measuring voltage source and the contactor via the measuring voltage supply branch. The measuring voltage can therefore be variable to determine the fault condition.

Furthermore, the electrical resistance in the measurement voltage supply branch can be designed variably, as it only serves to limit the current. For example, the resistor can be high-ohmic or designed as a pre-charging resistor. This can reduce component costs.

The electrical circuit may include a battery control unit configured to determine the fault condition of the contactor by comparing the measured voltage drop when the measuring voltage source is switched on and off. The battery control unit may include the measuring device for this purpose.

In a closed circuit between the measuring voltage source and the contactor, the voltage drop can be essentially or almost zero when the contactor is closed, because the contactor itself has a comparatively low electrical resistance. In contrast, the voltage drop across the contactor when the contactor is open can essentially be the measuring voltage, in particular a sum or difference between the measuring voltage and the terminal voltage.

Therefore, when the contactor is in a closed switching state, the voltage drop across the contactor can be essentially or almost zero. The measured voltage drop across the contactor can therefore be essentially the same when the contactor is in a closed switching state, whether the measuring voltage source is switched on or off. The battery control unit can be configured to determine that the contactor is in a closed switching state if the measured voltage drop is the same when the measuring voltage source is switched on or off. Conversely, the battery control unit can be configured to determine that the contactor is in an open switching state if the measured voltage drop is different when the measuring voltage source is switched on or off. The battery control unit can therefore be configured to output an error message based on whether or not an error condition, e.g. a defect in the contactor, exists. The battery control unit can be configured to switch the measuring voltage source on and off and optionally switch the contactor on or off in parallel and/or to measure the voltage drop across the contactor with the measuring voltage source switched on and off using the measuring device in parallel with the contactor being switched on and/or off. "Parallel" can mean before and/or after the contactor is switched on or off.

In a first embodiment, the battery control unit can, for example, be configured to switch the measuring voltage source on and off and measure the respective voltage drop across the contactor. Thus, the battery control unit can determine whether the contactor is in an open or closed switching state. This offers the advantage that even varying environmental conditions do not affect the reliability of the measurement, because the error determination is based solely on a before-and-after comparison of the measured voltage drops.

In a second embodiment, the battery control unit can, for example, be configured to switch the measuring voltage source on and off after switching the contactor on or off in order to determine whether the contactor is in an open or closed switching state. Additionally, the battery control unit can be configured to switch the measuring voltage source on and off before switching the contactor on or off in order to determine whether the contactor is in an open or closed switching state.

This has the advantage that a plausibility check of the contactor's switching state can be carried out before and after a contactor switching operation, thus reducing the probability of a false alarm about the presence of a defect.

The battery control unit can be configured to determine a defect in the contactor, in particular sticking of the contactor to a contact, if the measured voltage drop is the same when the measuring voltage source is switched on and off and optionally in parallel with the output of an opening signal to the contactor, and/or to determine proper functioning of the contactor, in particular opening of the contactor, if the measured voltage drop is different when the measuring voltage source is switched on and off and optionally in parallel with the output of the opening signal to the contactor.

For example, the battery control unit can be set up to, after the opening

Signal to the contactor to switch the measuring voltage source on and off and to The voltage drop across the contactor is measured using the measuring device. If the measured voltage drop is the same when the measuring voltage source is switched on and off, the battery control unit can be configured to determine that the contactor is closed and, optionally, that the contactor is defective, in particular that the contactor is stuck. If, on the other hand, the measured voltage drop is different when the measuring voltage source is switched on and off, the battery control unit can be configured to determine that the contactor is open and, optionally, that the contactor is not defective.

This has the advantage that even varying environmental conditions do not affect the reliability of the measurement and the likelihood of a false alarm is reduced. Instead of switching the measurement voltage source on and off, the measurement voltage source can be switched on and off.

Additionally or alternatively, the battery control unit can be configured to switch the measuring voltage source on and off before and after the opening signal is output to the contactor in order to determine the switching state of the contactor before and after the opening signal is output. For example, if the measured voltage drop differs when the measuring voltage source is switched on and off before the opening signal is output, the battery control unit can be configured to determine that the contactor is already open, in particular blocked, and optionally that there is a contactor defect. Additionally or alternatively, if the measured voltage drop is the same when the measuring voltage source is switched on and off before the opening signal is output, the battery control unit can be configured to determine that the contactor is in a closed switching state and optionally that there is no defect. Additionally or alternatively, the battery control unit can be configured to determine, if the measured voltage drop is the same when the measuring voltage source is switched on and off, that the contactor is in a closed switching state and, additionally, that a defect, in particular a contactor sticking, is present. Additionally or alternatively, the battery control unit can be configured to determine, if the measured voltage drop is different when the measuring voltage source is switched on and off, that the contactor is in an open switching state and, optionally, that no defect is present. Thus, for example, the battery control unit can be configured to determine that there is no defect in the contactor if the contactor is in a closed switching state before the opening signal is output and is in an open switching state after the opening signal is output to the contactor.

This has the advantage of reducing the probability of a false alarm.

The battery control unit can be configured to determine the proper functioning of the contactor, in particular a closing of the contactor, if the measured voltage drop is the same when the measuring voltage source is switched on and off and optionally in parallel with the output of a closing signal to the contactor and/or to determine the defect of the contactor, in particular a blocking of the contactor, if the measured voltage drop is different when the measuring voltage source is switched on and off and optionally in parallel with the output of the closing signal to the contactor.

For example, the battery control unit can be configured to switch the measuring voltage source on and off after outputting the closing signal to the contactor and to measure the voltage drop across the contactor using the measuring device. If the measured voltage drops are the same, the battery control unit can be configured to determine that the contactor is closed and, optionally, that there is no contactor defect. If, however, the measured voltage drop is different when the measuring voltage source is switched on and off, the battery control unit can be configured to determine that the contactor is open and, optionally, that there is a contactor defect, in particular, that the contactor is blocked.

This has the advantage that even varying environmental conditions do not affect the reliability of the measurement and the likelihood of a false alarm is reduced. Instead of switching the measurement voltage source on and off, the measurement voltage source can be switched on and off.

Additionally or alternatively, the battery control unit can be configured to switch the measuring voltage source on and off before and after the closing signal is output to the contactor in order to determine the switching state of the contactor before and after the closing signal is output. For example, the battery control unit can be configured to a difference in the measured voltage drop when the measuring voltage source is switched on and off before the closing signal is output, to determine that the contactor is open and optionally that there is no defect in the contactor. Additionally or alternatively, the battery control unit can be set up to determine, if the measured voltage drop is the same when the measuring voltage source is switched on and off before the closing signal is output, that the contactor is in a closed switching state and optionally that there is a defect in the contactor, in particular sticking of the contactor. Additionally or alternatively, the battery control unit can be set up to determine, if the measured voltage drop is the same when the measuring voltage source is switched on and off after the closing signal is output, that the contactor is in a closed switching state and optionally that there is no defect. Additionally or alternatively, the battery control unit can be configured to determine, in the event of a difference in the measured voltage drop when the measuring voltage source is switched on and off, after the closing signal has been output, that the contactor is in an open switching state and that, optionally, there is a defect, in particular a blocking of the contactor.

Thus, for example, the battery control unit can be configured to determine that there is no defect in the contactor if the contactor is in an open switching state before the closing signal is output and is in a closed switching state after the closing signal is output.

This has the advantage that the probability of a false alarm can be reduced through an additional plausibility check.

The measurement voltage supply branch can comprise a diode, which can optionally be configured to electrically block the measurement voltage supply branch in a direction toward a terminal connection of a battery and/or a reference point. The diode can be configured to block an electrical current from the high-voltage circuit emanating from the electrical load. Conversely, the diode can be configured to conduct a measurement current emanating from the measurement voltage source. This has the advantage of reducing interference and thus reducing the likelihood of a false alarm. The above-mentioned object is further achieved by a method for determining a fault condition of a contactor having the features of claim 7. Advantageous developments of the method emerge from the subclaims as well as the present description and the figures.

Accordingly, a method is proposed for determining a fault condition of a contactor that is electrically arranged in a high-voltage branch and is designed to electrically close or open the high-voltage branch, wherein a measuring voltage is fed into the high-voltage branch by means of a measuring voltage source in a measuring voltage feed branch, which comprises the measuring voltage source and an electrical resistor and is electrically connected in parallel to the contactor in the high-voltage branch. The method is characterized in that a voltage drop across the contactor in the high-voltage branch is measured by means of a measuring device. The measuring voltage can be a direct voltage or an alternating voltage, wherein the measuring device is designed to measure the respective type of voltage, for example a direct voltage or an alternating voltage. The measuring points of the measuring device in the high-voltage branch can each be electrically connected to the contactor, wherein optionally one of the measuring points of the measuring device can be connected to a terminal connection of the battery, in particular a negative or positive terminal connection of the battery.

For example, the measuring voltage source can be configured to generate an alternating voltage, and the measuring device can be configured to measure the alternating voltage from the measuring voltage source, in particular an effective value of the alternating voltage. This allows the measuring voltage to be better distinguished from the terminal voltage of the battery in the high-voltage branch.

This offers the advantage that by measuring the voltage drop across the contactor, only the same or different voltage drop needs to be determined when the measuring voltage source is switched on and off to verify the contactor's switching state. Furthermore, the measuring voltage does not need to be readjusted due to changing measuring conditions, such as contactor aging or a change in the vehicle load, which can place different loads on the measuring circuits. The measuring voltage can therefore be varied to determine the fault condition, thus reducing the likelihood of a false alarm. Furthermore, the resistor in the measurement voltage supply branch can be designed variably, as it only serves to limit the current. For example, the resistor can be high-ohmic or designed as a pre-charging resistor. This can reduce component costs.

The fault state of the contactor can be determined by comparing the measured voltage drop when the measuring voltage source is switched on and off. For example, the voltage drop across the contactor in the high-voltage branch can be measured using the measuring device when the measuring voltage source is switched on and off, or vice versa. The voltage drops when the measuring voltage source is switched on and off can be compared and checked for similarity or difference. Alternatively, a difference between the voltage drops can be calculated and a check can be made to determine whether the difference is essentially zero or not. Based on the similarity and/or difference between the voltage drops when the measuring voltage source is switched on and off, the switching state and, optionally, the fault state of the contactor can be determined depending on a switching command. This has the advantage that the method for determining the fault state is independent of environmental conditions, such as contactor aging or feedback from the electrical load, thus reducing the probability of a false alarm being generated.

Additionally or alternatively, the measured voltage or a sum or difference of the measured voltage and the terminal voltage can be applied to the open contactor as a measured voltage drop. In contrast, with the closed contactor, the measured voltage drop can be essentially zero.

This offers the advantage that the determination of the fault condition is less dependent on ambient and measurement conditions, because only a comparison of two measured values is required to determine the fault condition. This eliminates the need to adjust the voltage sources to avoid false alarms.

The measuring voltage source can be switched on and off and optionally the contactor can be switched on or off in parallel and/or the voltage drop across the contactor can be measured with the measuring voltage source switched on and off using the measuring device in parallel with the contactor being switched on and/or off. In a first embodiment, for example, the measuring voltage source can be switched on and off, and the respective voltage drop across the contactor can be measured using the measuring device. This allows the battery control unit to determine whether the contactor is in an open or closed switching state. This offers the advantage that even varying environmental conditions do not affect the reliability of the measurement, because the error determination is based solely on a before-and-after comparison of the measured voltage drops.

In a second embodiment, for example, the measuring voltage source can be switched on and off after the contactor is switched on or off to determine whether the contactor is in an open or closed switching state. This provides the advantage that a plausibility check of the contactor's switching state can be performed before and after a contactor switching operation, thus reducing the likelihood of a false alarm regarding the presence of a defect.

If the measured voltage drop is the same when the measuring voltage source is switched on and off and optionally in parallel with the output of an opening signal to the contactor, the presence of a defect in the contactor, in particular sticking of the contactor to a contact, can be determined and/or if the measured voltage drop is different when the measuring voltage source is switched on and off and optionally in parallel with the output of the opening signal to the contactor, proper function of the contactor can be determined, in particular opening of the contactor.

For example, after the opening signal is sent to the contactor, the measuring voltage source can be switched on and off, and the voltage drop across the contactor can be measured using the measuring device. If the measured voltage drops are the same, it can be determined that the contactor is closed and, optionally, that a contactor defect exists, in particular, that the contactor is sticking. If, on the other hand, the measured voltage drop is different when the measuring voltage source is switched on and off, it can be determined that the contactor is open and, optionally, that there is no contactor defect.

This has the advantage that even varying environmental conditions do not affect the reliability of the measurement and the likelihood of a false alarm is reduced. Instead of switching the measurement voltage source on and off, the measurement voltage source can be switched on and off. Additionally or alternatively, the measuring voltage source can be switched on and off before and after the opening signal is output to the contactor in order to determine the switching state of the contactor before and after the closing signal is output. For example, if the measured voltage drop differs when the measuring voltage source is switched on and off before the opening signal is output, it can be determined that the contactor is open and optionally that there is a defect in the contactor, in particular that the contactor is blocked. Additionally or alternatively, if the measured voltage drop is the same when the measuring voltage source is switched on and off before the opening signal is output, it can be determined that the contactor is in a closed switching state and optionally that there is no defect in the contactor. Additionally or alternatively, if the measured voltage drop is the same when the measuring voltage source is switched on and off after the closing signal is output, it can be determined that the contactor is in a closed switching state and optionally that there is a defect, in particular that the contactor is sticking. Additionally or alternatively, if there is a difference in the measured voltage drop when the measuring voltage source is switched on and off, after the opening signal has been output, it can be determined that the contactor is in an open switching state and, optionally, that there is no defect in the contactor.

Thus, for example, it can be determined that there is no defect in the contactor if the contactor is in an open switching state before the open signal is output to the contactor and is in a closed switching state after the open signal is output.

This has the advantage that the probability of a false alarm can be reduced by an additional plausibility check.

If the measured voltage drop is the same when the measuring voltage source is switched on and off, and optionally in parallel with the output of a closing signal to the contactor, the proper functioning of the contactor, in particular, the contactor closing, can be determined. If the measured voltage drop is different when the measuring voltage source is switched on and off, and optionally in parallel with the output of the closing signal to the contactor, the contactor defect can be determined, in particular, the contactor blocking. "Parallel" can mean before and/or after the output of the closing signal. For example, after the closing signal is sent to the contactor, the measuring voltage source can be switched on and off, and the voltage drop across the contactor can be measured using the measuring device. If the measured voltage drops are the same, it can be determined that the contactor is closed and, optionally, that there is no contactor defect. If, however, the measured voltage drop is different when the measuring voltage source is switched on and off, it can be determined that the contactor is open and, optionally, that there is a contactor defect, in particular, that the contactor is blocked.

This has the advantage that even varying environmental conditions do not affect the reliability of the measurement and the likelihood of a false alarm is reduced. Instead of switching the measurement voltage source on and off, the measurement voltage source can be switched on and off.

Additionally or alternatively, the measuring voltage source can be switched on and off before and after the closing signal is output to the contactor in order to determine the switching state of the contactor before and after the closing signal is output. For example, if the measured voltage drop differs when the measuring voltage source is switched on and off before the closing signal is output, it can be determined that the contactor is open and, optionally, that there is no defect in the contactor. Additionally or alternatively, if the measured voltage drop is the same when the measuring voltage source is switched on and off before the closing signal is output, it can be determined that the contactor is in a closed switching state and, optionally, that there is a defect in the contactor, in particular that the contactor is sticking. Additionally or alternatively, if the measured voltage drop is the same when the measuring voltage source is switched on and off after the closing signal is output, it can be determined that the contactor is in a closed switching state and, optionally, that there is no defect.

Additionally or alternatively, if there is a difference in the measured voltage drop when the measuring voltage source is switched on and off, after the closing signal has been output, it can be determined that the contactor is in an open switching state and that optionally there is a defect, in particular a blocking of the contactor.

Thus, for example, it can be determined that there is no defect in the contactor if the contactor is in an open state before the close signal is issued to the contactor. switching state and after the close signal is output in a closed

switching state.

This has the advantage that the probability of a false alarm can be reduced through an additional plausibility check.

The above-mentioned object is further achieved by a computer program or a computer-readable storage medium on which the computer program is stored. The computer program comprises instructions which, when executed by a control unit, in particular a battery control unit, cause the control unit to carry out the said method. The computer-readable storage medium can be a punched card, a (floppy disk) storage medium, a hard disk, a CD, a DVD, a USB (Universal Serial Bus) storage device, a RAM (Random Access Memory), a ROM (Read Only Memory), and/or an EPROM (Erasable Programmable Read Only Memory). Preferably, the computer-readable storage medium can be a RAM or a ROM, with particular use being made of a flash memory. The computer-readable storage medium can also be a data communications network that enables the downloading of program code, such as the Internet, or other systems. The computer program can, for example, be an application for embedded systems.

The above-mentioned object is further achieved by a battery control unit or a battery management system comprising the computer-readable storage medium. The battery control unit can comprise at least one processor and/or at least one memory, wherein program instructions can be stored in the memory, which can cause the at least one processor to execute the said method. The battery control unit or the battery management system can have a data processing device or at least one processor device configured to carry out an embodiment of the method according to the invention. The processor device can for this purpose have at least one microprocessor and/or at least one microcontroller and/or at least one FPGA (Field Programmable Gate Array) and/or at least one DSP (Digital Signal Processor). Furthermore, the processor device can have program code configured to carry out the embodiment of the method according to the invention when executed by the processor device. The program code can be stored in a data memory or processor device. The battery control unit or the battery management system can be designed to use the measuring device to To measure the voltage drop across the contactor in the high-voltage branch. For this purpose, the battery control unit or the battery management system can include the measuring device or be communicatively connected to the measuring device via a signal line.

The above-mentioned object is further achieved by a battery or a battery system comprising the computer-readable storage medium or the battery control unit. The battery or battery system can comprise multiple battery packs that are spatially distributed in the motor vehicle but can be connected to a charging device and/or an electrical consumer via a common connection.

The above-mentioned object is further achieved by a motor vehicle comprising the computer-readable storage medium or the battery control unit or the battery or the battery system. The motor vehicle can preferably be configured as a motor vehicle, in particular as a passenger car or truck, or as a passenger bus or motorcycle. The motor vehicle can be electrically powered (EV) or, in particular, a hybrid electric vehicle (HEV, PHEV), wherein the components provided for this purpose in the motor vehicle can each be an electrical consumer of the battery system.

The invention also includes implementations that comprise a combination of the features of several of the described embodiments.

Short description of the characters

Preferred further embodiments of the invention are explained in more detail by the following description of the figures. In the figures:

Figure 1 shows a schematic representation of the electrical circuit in a battery of a motor vehicle; and

Figure 2 shows a schematic representation of the procedure for determining the fault condition of the contactor.

Detailed description of preferred embodiments

Preferred embodiments are described below with reference to the figures. Identical, similar or equivalent elements are identified in the different figures with identical reference symbols, and a repeated description of these elements is partly omitted in order to avoid redundancies.

Figure 1 schematically shows a motor vehicle 13 on the left-hand side, in which a high-voltage circuit 4 comprising a battery 16 in a battery system 19 and an electrical load 12 are electrically connected. The electrical load 12 can be an electrical consumer of the motor vehicle 13, such as an electric motor. The high-voltage circuit 4 is shown enlarged on the right-hand side, with the electrical load 12 in the high-voltage circuit 4 being connected to the battery system 19 via the battery output 22 comprising a positive and a negative battery connection HV+, HV-. The respective battery connection HV+, HV- is electrically connected via the contactor 2 to a corresponding terminal connection 15 of the battery 16 via the high-voltage branch 3. The battery system 19 comprises the battery 16, which comprises at least one battery cell, and the electrical circuit 1. In addition, the battery system 19 comprises a precharging circuit 20, 21 comprising a precharging resistor 20 and a precharging contactor 21, which can optionally be structurally identical to the contactors 2a, 2b. Furthermore, the battery system 19 comprises the battery output 22 with the negative and positive battery terminals HV+, HV-, via which the electrical load 12 is electrically connected to the battery system 19. For safe operation of the battery system 19, the battery cells 16 must be electrically separated beyond doubt from the battery output 22 by means of the contactors 2a, 2b. The contactors 2a, 2b can each be designed as a relay and are arranged in a high-voltage branch 3 of the high-voltage circuit 4. The high-voltage branch 3 can, for example, electrically connect the terminal connection 15 to the corresponding battery connection HV+, HV-, whereby the contactor 2a, 2b can electrically disconnect the respective high-voltage branch 3. At high voltages emanating from the battery cells 16 in the motor vehicle 13, welding of the contactors 2a, 2b can occur due to arcs occurring within the contactors 2a, 2b, which can lead to sticking of the contacts of the contactor 2a, 2b, so that in case of doubt the respective contactor 2a, 2b does not disconnect the electrical connection in the high-voltage branch 3. This represents a hazard. Therefore, this hazard should be detected and avoided by means of the electrical circuit 1.

For this purpose, the electrical circuit 1 can be used, by means of which a fault condition or the functionality of the contactor 2a at the negative battery terminal HV- can be checked. Additionally or alternatively, the electrical circuit 1 can be electrically arranged at the positive battery terminal HV+. The electrical circuit 1 comprises a high-voltage branch 3, in which the contactor 2a to be tested is arranged. The high-voltage branch 3 is designed to be electrically connected to the high-voltage circuit 4 and, in particular, to electrically connect the battery connection HV+, HV- to the corresponding terminal connection 15 of the battery 16. The battery system 19 comprises the high-voltage branch 3, wherein the high-voltage circuit 4 connects the battery system 19 to the electrical load 12. The high-voltage branch 3 can be electrically arranged in a branch of the high-voltage circuit 4, in particular between the battery 16 and the battery output 22 and/or the load 12. The battery system 19 can comprise the branch. The electrical circuit 1 further comprises a measuring voltage feed branch 5, which comprises at least one measuring voltage source 6 and an electrical resistor 7 and is electrically connected in parallel to the contactor 2a in the high-voltage branch 3. The measuring voltage source 6 in the measuring voltage supply branch 5 is configured to feed a measuring voltage U _M into the high-voltage branch 3, with the electrical resistor 7 merely having a current-limiting function. For example, the resistor 7 can be designed as a precharging resistor 20.

Additionally, the measurement voltage supply branch comprises a diode 11, which blocks the measurement voltage supply branch 5 in a direction toward a terminal connection 15 of the battery or battery cells 16. This prevents a backflow or feedback of electrical current from the load 12 into the measurement voltage supply branch 5 in order to avoid an influence of the electrical load 12 on a voltage measurement by means of the measuring device 8.

The electrical circuit 1 further comprises the measuring device 8, which is configured to measure the measuring voltage U _M at the contactor 2a in the high-voltage branch 3. In this case, by comparing the measuring voltage measured by the measuring device 8 by a battery control unit 9 in parallel with the switching on or off of the contactor 2a, the fault state of the contactor 2a can be determined by the battery control unit 9. The electrical circuit 1 can further comprise the battery control unit 9, which is configured to switch the measuring voltage source 6 on and off. In addition, the battery control unit 9 is configured to switch the contactor 2a, 2b and optionally the pre-charging contactor 21 on and off. For example, the battery control unit 9 can be configured to switch the measuring voltage source 6 on and off by means of the switch 14. The switch 14 can be different from the contactor 2a because the measuring voltage U _M can be smaller than the terminal voltage U _B of the battery 16. For this purpose, the Battery control unit 9 is communicatively connected to switch 14, contactor 2a, and measuring device 8 via signal line 17. Signal line 17 can be, for example, an electrical or optical signal line.

For example, the measuring voltage source 6 can be designed as a DC voltage source, wherein the measuring voltage U _M generated by it can be smaller than the terminal voltage U _B of the battery 16. For example, the measuring voltage U _M can be a DC voltage in the range from 0 to 10 V. The measuring device 8 can be designed to measure a DC voltage.

Alternatively, the measuring voltage source 6 can be designed as an alternating current source, wherein the measuring voltage U _M generated by it is different from the terminal voltage U _B of the battery 16, wherein, in addition, a peak value of the alternating voltage can be smaller than a voltage value of the terminal voltage U _B. For this purpose, the measuring device 8 can be designed to measure an alternating voltage, in particular an effective value of the alternating voltage. As a result, the measuring voltage U _M can be measured independently of the terminal voltage U _B of the battery 16.

Additionally or alternatively, the measuring voltage source 6 can be designed as a charge pump, wherein the measuring device 8 is configured to measure the measuring voltage U _M generated by the charge pump.

The measuring device 8 is designed to measure the measuring voltage U _M and, optionally, additionally, the terminal voltage U _B of the battery 16 at the contactor 2a at the measuring points 18 in the high-voltage branch 3. The high-voltage branch 3 can be electrically connected to a positive or negative terminal connection 15 of the battery 16 because the fault state of the contactor 2a is determined from a change in the measuring voltage U _M when the measuring voltage source 6 is switched on and off by the battery control unit 9 in parallel with the contactor 2a being switched on and off. Thus, no absolute values of the measuring voltage U _M are necessary as comparison values. At least one measuring point 18 can be electrically connected to the terminal connection 15 of the battery 16.

For this purpose, the battery control unit 9 is designed to switch the measuring voltage source 6 on and off before and/or after the respective opening signal or closing signal is output to the contactor 2a and to supply the measured voltage to the measuring points 18 on the contactor 2a measured voltage drop U-^ with the measuring voltage source 6 switched on and off. When the contactor 2a is closed, the voltage drop U ₁ is the same when the measuring voltage source 6 is switched on and off because the closed contactor 2a has a negligibly small electrical resistance between the measuring points 18, so that the voltage drop U ₁ measured by means of the measuring device 8 when the measuring voltage source 6 is switched on and off is essentially 0 V. In contrast, when the contactor 2a is open, the measured voltage drop U ₁ is the measuring voltage U _M when the measuring voltage source 6 is switched on and, for example, 0 V when the measuring voltage source 6 is switched off. Alternatively, when the contactor 2a is open, the measured voltage drop U ₁ is the sum or the difference between the terminal voltage U _B and the measuring voltage U _M when the measuring voltage source 6 is switched on, and only the terminal voltage U _B when the measuring voltage source 6 is switched off. Therefore, both voltage drops _U1 measured at contactor 2a are the same or different depending on the open or closed switching state of contactor 2a, so that a comparison of absolute voltage values with threshold values is not necessary. By comparing the measured voltage drops, battery control unit 9 can determine whether the contactor is actually closed or not. This makes the method independent of operational voltage tolerances and the positioning of electrical circuit 1 at a positive or negative terminal connection 15 of battery 16.

For example, the battery control unit 9 is configured to determine a defect in the contactor 2a, in particular sticking of the contactor 2a at a contact, if the measured voltage drop _U1 is the same when the measuring voltage source 6 is switched on and off, and optionally after an opening signal has been output to the contactor 2a. Additionally or alternatively, the battery control unit 9 is configured to determine proper functioning of the contactor 2a, in particular opening of the contactor 2a, if the measured voltage drop _U1 is different when the measuring voltage source 6 is switched on and off, and additionally after the opening signal has been output to the contactor 2a.

Additionally or alternatively, the battery control unit 9 is configured to switch the measuring voltage source 6 on and off before and after the opening signal is output to the contactor 2a and to determine whether the contactor 2a is in a closed or open switching state before and after the opening signal is output. The battery control unit 9 is configured to determine that there is no defect in the contactor 2a if the contactor 2a before the opening signal is issued, it is in a closed switching state and after the opening signal is issued, contactor 2a is in an open switching state.

Furthermore, the battery control unit 9 is configured to determine the proper functioning of the contactor 2a, in particular a closing of the contactor 2a, if the measured voltage drop U ₁ is the same when the measuring voltage source 6 is switched on and off and optionally before and/or after the output of a closing signal to the contactor 2a. If the measured voltage drop U ₁ is different when the measuring voltage source 6 is switched on and off and optionally after the output of the closing signal to the contactor 2a, the battery control unit 9 is configured to determine the defect of the contactor 2a, in particular a blocking of the contactor 2a.

Additionally or alternatively, the battery control unit 9 is configured to switch the measuring voltage source 6 on and off before and after the closing signal is output to the contactor 2a and to determine whether the contactor 2a is in a closed or open switching state. For example, the battery control unit 9 is configured to determine that there is no defect in the contactor 2a if the contactor 2a is in an open switching state before the closing signal is output and the contactor 2a is in a closed switching state after the closing signal is output.

For this purpose, the measuring device 8 is designed to measure the first voltage U ₁ at the measuring points 18. In addition, the measuring device 8 can be designed to measure a second voltage U ₂ and a third voltage U ₃ with respect to a contactor 2b in the high-voltage branch opposite the contactor 2a between the terminal connection 15 (at + of the battery 16) and the battery output (HV+), which is additionally electrically connected in parallel with the pre-charging resistor 20 and the pre-charging contactor 21. The battery control unit 9 can be configured to determine a closure of the opposite contactor 2b if the measured second and third voltages U ₂ and U ₃ are identical, and additionally to determine a fault state of the opposite contactor 2b and/or the pre-charging contactor 21 if they are different. Here, if the second voltage U ₂ and the third voltage U ₃ differ, an open switching state of contactor 2b and/or pre-charging contactor 21 can be determined. For example, a defect can be determined as a fault state if contactor 2b and/or pre-charging contactor 21 should be in a closed switching state. Additionally or alternatively, if the difference between the second voltage U ₂ and the third voltage U ₃ is less than a voltage threshold, a closed switching state of the pre-charging contactor 21 can be determined. For this purpose, the contactor 2b can be in an open switching state. For example, a defect in the pre-charging contactor 21 can be determined as the fault state if the pre-charging contactor 21 should be in an open switching state.

Additionally or alternatively, if the second voltage U ₂ and the third voltage U ₃ are equal, a closed switching state of contactor 2b can be determined. For this purpose, the precharging contactor 21 can be in an open switching state. For example, a defect in contactor 2b can be determined as the fault state if contactor 2b is in an open switching state.

As a result, all contactors 2a, 2b and 21 in the high-voltage circuit 4 of the battery system 19 can be monitored and/or tested with only a single electrical circuit 1 and/or measuring device 8.

Alternatively, the battery control unit 9 can be configured to switch the measuring voltage source 6 on and off instead of switching it on and off.

Figure 2 schematically shows a method for checking the fault state of the contactor 2 for a battery control unit 9.

Optionally, in a first step S1, the measuring voltage source 6 is switched on and off, and a voltage drop across the contactor 2a, in particular across the terminals of the contactor 2a, in the high-voltage branch 3 is measured by means of the measuring device 8. If the measured voltage drop _U1 is the same when the measuring voltage source 6 is switched on and off, a closed switching state of the contactor 2a is determined, whereas if the measured voltage drop _U1 is different when the measuring voltage source 6 is switched on and off, an open switching state of the contactor 2a is determined.

In a second step S2, an open signal or a close signal is optionally output to the contactor 2a.

In a third step S3, the measuring voltage source 6 is switched on or off and a voltage drop at the contactor 2a, in particular at the terminals of the contactor 2a, in the high-voltage branch 3 is measured by means of the measuring device 8. If the measured If the voltage drop U-^ is different when the measuring voltage source 6 is switched on and off, a closed switching state of the contactor 2a is determined, while if the measured voltage drop U ₁ is different when the measuring voltage source 6 is switched on and off, an open switching state of the contactor 2a is determined.

In a fourth step S4, the fault state of the contactor 2a is determined, i.e. whether a defect exists or not.

When an open signal is output, the contactor 2a is not defective if the contactor 2a is in an open switching state after the open signal is output. Additionally or alternatively, the contactor 2a is not defective if the contactor 2a is in a closed switching state before the open signal is output. If, additionally or alternatively, the contactor 2a is in a closed switching state after the open signal is output, there is a defect in the contactor 2a, in particular sticking of the contactor 2a. If, additionally or alternatively, the contactor 2a is in an open switching state before the open signal is output, there is a defect in the contactor 2a, in particular blocking of the contactor 2a.

Additionally or alternatively, the contactor 2a does not have a defect when a closing signal is output if the contactor 2a is in a closed switching state after the closing signal is output. Additionally or alternatively, the contactor 2a does not have a defect if the contactor 2a is in an open switching state before the closing signal is output. If additionally or alternatively the contactor 2a is in an open switching state after the closing signal is output, there is a defect in the contactor 2a, in particular a blocking of the contactor 2a. If additionally or alternatively the contactor 2a is in a closed switching state before the closing signal is output, there is a defect in the contactor 2a, in particular a sticking of the contactor 2a.

Where applicable, all individual features shown in the embodiments may be combined and/or exchanged without departing from the scope of the invention. List of reference symbols

I Electrical circuit 2a, 2b contactor

3 high-voltage branch

4 High-voltage circuit

5 Measuring voltage supply branch

6 Measuring voltage source

7 Resistance

8 Measuring device

9 Battery control unit

10 Reference point

I I Diode

12 Electrical load

13 Motor vehicle

14 switches

15 terminal connection

16 Battery

17 Signal line

18 measuring points

19 Battery system

20 Precharge resistor

21 Pre-charging contactor

22 Battery output

HV+ positive battery terminal

HV negative battery terminal

Ui voltage drop

U ₂ second voltage u ₃ third voltage y _M measuring voltage

UB terminal voltage

51 first step

52 second step

53 third step

54 fourth step

Claims

Claims 1 . Electrical circuit (1) for determining a fault state of a contactor (2a), comprising the contactor (2a), which is electrically arranged in a high-voltage branch (3) and is designed to electrically close or open the high-voltage branch (3), comprising a measuring voltage feed branch (5) for feeding a measuring voltage (t _M ) into the high-voltage branch (3), wherein the measuring voltage feed branch (5) comprises a measuring voltage source (6) and an electrical resistor (7) and is electrically connected in parallel to the contactor (2a) in the high-voltage branch (3), characterized in that a measuring device (8) is provided which is designed to measure a voltage drop (Ui) across the contactor (2a) in the high-voltage branch (3). 2. Electrical circuit (1) according to claim 1, characterized in that a battery control unit (9) is provided which is designed to determine the fault state of the contactor (2a) by means of a comparison of the measured voltage drop (U when the measuring voltage source (6) is switched on and off. 3. Electrical circuit (1) according to claim 2, characterized in that the battery control unit (9) is designed to switch the measuring voltage source (6) on and off and optionally to switch the contactor (2a) on or off in parallel and/or to measure the voltage drop (U across the contactor (2a) with the measuring voltage source (6) switched on and off by means of the measuring device (8) in parallel with the contactor (2a) being switched on and/or off. 4. Electrical circuit (1) according to claim 2 or 3, characterized in that the battery control unit (9) is designed to determine a defect of the contactor (2a), in particular a sticking of the contactor (2) at a contact, if the measured voltage drop (U with the measuring voltage source (6) switched on and off is equal and optionally parallel to the output of an opening signal to the contactor (2a), and/or to determine a defect of the contactor (2a), in particular a sticking of the contactor (2) at a contact, if the measured voltage drop (U with the measuring voltage source (6) switched on and off is different and optionally parallel to the output of the opening signal. Signal to the contactor (2a) to determine proper functioning of the contactor (2a), in particular opening of the contactor (2a). 5. Electrical circuit (1) according to one of claims 2 to 4, characterized in that the battery control unit (9) is configured to determine the proper functioning of the contactor (2a), in particular a closing of the contactor (2a), if the measured voltage drop (U with the measuring voltage source (6) switched on and off is the same and optionally in parallel with the output of a closing signal to the contactor (2a), and/or to determine the defect of the contactor (2a), in particular a blocking of the contactor (2a), if the measured voltage drop (U with the measuring voltage source (6) switched on and off is different and optionally in parallel with the output of the closing signal to the contactor (2a). 6. Electrical circuit (1) according to one of the preceding claims, characterized in that the measuring voltage feed branch (5) comprises a diode (11) which is optionally designed to electrically block the measuring voltage feed branch (5) in a direction towards a terminal connection (15) of a battery (16) and/or a reference point (10). 7. Method for determining a fault state of a contactor (2) which is electrically arranged in a high-voltage branch (3) and is designed to electrically close or open the high-voltage branch (3), wherein a measuring voltage (t M ₎ is fed into the high-voltage branch (3) by means of a measuring voltage source (6) in a measuring voltage feed branch (5), which comprises the measuring voltage source (6) and an electrical resistor (7) and is electrically connected in parallel to the contactor (2a) in the high-voltage branch (3), characterized in that a voltage drop across the contactor (2a) in the high-voltage branch (3) is measured by means of a measuring device (8). 8. Method according to claim 7, characterized in that the fault condition of the contactor (2a) is determined by means of a comparison of the measured voltage drop (U) when the measuring voltage source (6) is switched on and off. 9. Method according to claim 7 or 8, characterized in that the measuring voltage source (6) is switched on and off and optionally the contactor (2a) is switched on or off in parallel and/or the voltage drop (U across the contactor (2a) is measured with the measuring voltage source (6) switched on and off by means of the measuring device (8) in parallel with the switching on and/or off of the contactor (2a). 10. The method according to claim 8 or 9, characterized in that if the measured voltage drop (U with the measuring voltage source (6) switched on and off is the same and optionally in parallel with the output of an opening signal to the contactor (2a), the presence of a defect in the contactor (2a), in particular sticking of the contactor (2a) to a contact, is determined and/or if the measured voltage drop (U with the measuring voltage source (6) switched on and off is different and optionally in parallel with the output of the opening signal to the contactor (2a), proper functioning of the contactor (2a) is determined, in particular opening of the contactor (2a). 11 . Method according to one of claims 8 to 10, characterized in that if the measured voltage drop (U with the measuring voltage source (6) switched on and off is equal and optionally in parallel with the output of a closing signal to the contactor (2a), the correct functioning of the contactor (2a), in particular a closing of the contactor (2a), is determined and/or if the measured voltage drop (U with the measuring voltage source (6) switched on and off is different and optionally in parallel with the output of the closing signal to the contactor (2a), the defect of the contactor (2a) is determined, in particular a blocking of the contactor (2a). 12. A computer program or a computer-readable storage medium on which the computer program is stored, wherein the computer program comprises instructions which, when the program is executed by a control unit, in particular a battery control unit (9), cause the control unit to carry out the method according to one of claims 7 to 11. 13. Battery control unit (9) or a battery management system comprising the computer-readable storage medium according to claim 12. 14. Battery (16) or a battery system comprising the computer-readable storage medium according to claim 12 or the battery control device (9) according to claim 13. 15. Motor vehicle (13) comprising the computer-readable storage medium according to claim 12 or the battery control unit (9) according to claim 13 or the battery (16) or the battery system according to claim 14.