Method and device for monitoring state of health of contactor

Abstract

To monitor a state of a health of at least one contactor in a battery pack.SOLUTION: There is provided a method, in which at least one switchable first contactor (1) is arranged between an interface (7) in a first interface line (5) and at least one battery cell (4), and at least one switchable second contactor (2) is arranged between an interface (7) in a second interface line (6) and at least one battery cell (4), wherein the method includes a step of measuring a first differential voltage between both ends of the opened first contactor (1) and / or measuring a second differential voltage between both ends of the opened second contactor (2), and a step of monitoring a state of the health of the first contactor (1) based on the measured first differential voltage and / or determining a state of the health of the second contactor (2) based on the measured second differential voltage.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for monitoring the state of health of at least one contactor in a battery pack, and further relates to a battery control system for use in and for a battery pack. [Background technology]

[0002] Vehicles powered by electric motors utilize a battery system to deliver energy to the drive system. Such battery systems often consist of multiple battery packs, which in turn consist of multiple battery modules, each housing multiple battery cells.

[0003] To ensure the operational safety of the battery pack, it should be of intrinsically safe design and is therefore intended to be able to be switched into an external disconnect state by means of integrated contactors. The contactors integrated within the battery pack therefore assume a primary function and it is therefore necessary to monitor their function.

[0004] A method for the diagnosis of wear-related contactor aging is known from DE102012215190A1. The insulation resistance, i.e. the electrical resistance of an open contactor, decreases over the service life of the contactor. Measurement of the insulation resistance of the contactor with respect to voltage and current therefore makes it possible to draw conclusions about the state of health of the contactor. As soon as the insulation resistance falls below a limit value, measures are carried out according to the disclosure of DE102012215190A1.

[0005] DE102012209138A1 discloses a method for determining the state of health of a fuse, according to which the current flowing in the fuse is measured and recorded in order to enable a continuous determination of the state of health of the fuse.

[0006] DE102014200265A1 discloses a battery system with a high-voltage battery and a protection circuit, the functional state of which is monitored. In particular, for this purpose a protection circuit upstream of the circuit is assigned to a contactor. This circuit comprises two parallel-connected circuit branches, in each of which a fuse and a current sensor are arranged. Evaluation of the respective current values ​​flowing in the protection circuit allows a diagnosis of the functional state of the protection circuit.

[0007] DE102015006206A1 discloses a high-voltage system with a switching contactor. In particular, the risk of contactor sticking, i.e. of a switchable contactor such that the switchable contactor is no longer switchable, is identified. As an approach to a solution for the prevention of the problematic effects of contactor sticking, it is proposed to connect the switching contactor in series with another switching element. In this way, redundancy of the high-voltage system is achieved, thereby reducing the dependency on a single switching contactor. Summary of the Invention [Problem to be solved by the invention]

[0008] Based on known prior art, it is an object of the present invention to provide an improved method for monitoring the state of health of at least one contactor in a battery pack, together with a battery control system and the battery pack. [Means for solving the problem]

[0009] This object is achieved by a method having the features of claim 1, a battery control system having the features of claim 10 and a battery pack having the features of claim 11. Advantageous further developments proceed from the dependent claims, the description and the figures.

[0010] Accordingly, a method is proposed for monitoring the condition of at least one contactor in a battery pack.

[0011] A contactor may be an electromechanical isolation element in an electrical circuit, for example a relay.

[0012] The state of health may refer to the condition of a contactor that is evidence of its properties. In particular, it can be understood as the insulating capacity of the corresponding contactor, i.e. the contactor's ability to electrically insulate, for example a battery pack, from the rest of the battery system. One parameter that indicates the insulating capacity is the insulation resistance of the contactor. The insulation resistance can be understood as the resistance constituted across an open contactor.

[0013] The corresponding value of insulation resistance may depend essentially on the air gap between the contactor contacts within the contactor's interrupter chamber. An intact, unused contactor may exhibit an insulation resistance of the order of several gigaohms.

[0014] However, over its useful life, the insulation resistance may decrease, which may be described as the aging of the contactor. This decrease in the insulation resistance of the contactor may be caused, for example, by contamination, wear, and / or arc erosion on the contactor contacts (which may result in a corresponding decrease in the insulation resistance). Other factors that may cause a decrease in the insulation resistance of the contactor include contaminants, dust, and particles present in the contactor housing, which are conductive to the formation of bridges or conductive paths between the contactor contacts. Furthermore, a decrease in the insulation resistance may also be caused by purely mechanical factors, such as, for example, limited mobility of the contactor contacts relative to each other (which results in the contactor contacts in an open state not being spaced far enough apart from each other to be similarly conductive to the formation of bridges or conductive paths).

[0015] At least the aforementioned factors play a role in considering the insulation resistance of a contactor and are considered here in their entirety because, in the first instance, the only factor of importance for the operation of a contactor in a battery system is whether or not the contactor is able to perform the specified isolation of the battery cells from the load.

[0016] This decrease in insulation resistance is sometimes referred to as contactor aging, and as mentioned above, aging can be due to mechanical, chemical, and electrical reasons. Depending on the frequency of switching operations to interrupt the current and the magnitude and direction of each current switched, contactor aging will proceed more quickly or more slowly.

[0017] Below a certain insulation resistance, for example 300 kilohms, safe isolation of the battery pack from the rest of the battery system and the essential safe shutdown can no longer be achieved reliably under all load conditions, especially at high currents, because unintended further conduction of the current flux that is intended to be interrupted would occur, for example due to the occurrence of arcs between the switching contacts.

[0018] The battery pack comprises at least one battery cell for electrochemical storage of electrical energy, as well as a first interface wire and a second interface wire for delivery of electrical energy to the interface.

[0019] The interface may be configured, for example, in the form of a high-voltage socket-outlet, so that the battery pack can be electrically connected to the battery system by a single plug-in connection. In the vehicle, the connection of the battery pack to the battery system may be performed, for example, via a "vehicle interface box" (VIB), in which further battery packs are interconnected to form a logically constructed vehicle battery, for example for the formation of a high-voltage system for the operation of the vehicle driven by an electric motor.

[0020] A battery pack may include multiple battery modules, each of which may house individual electrochemical battery cells, which are responsible for the actual storage of electrical energy.

[0021] In the first interface line, at least one switchable first contactor is arranged between the interface and the at least one battery cell, and in the second interface line, at least one switchable second contactor is arranged between the interface and the at least one battery cell. This arrangement of the first and second contactors between the interface and the battery cell allows safe isolation of the battery cell from the interface, thereby improving safety standards and controllability.

[0022] The method according to the invention comprises the steps of: measuring a first differential voltage across the open first contactor, the first differential voltage being a voltage present in the battery pack, the voltage present in the battery pack being measured, inter alia, at least across the open first contactor;

[0023] Alternatively or additionally, a second differential voltage is measured across the open second contactor. Like the first differential voltage, the second differential voltage may also be a voltage present in the battery pack, the voltage present in the battery pack being measured at least across, among other things, the open second contactor.

[0024] The method according to the invention further comprises a step for monitoring a state of health of the first contactor based on the measured first differential voltage, since the first differential voltage is measured at least in part across the open first contactor, thereby making it possible to monitor the state of health of the first contactor as the first differential voltage changes in response to aging of the contactor and thus further in response to variations in insulation resistance associated with aging of the contactor.

[0025] However, it should be noted that in the proposed method, the internal resistance of the contactor is not explicitly determined. In particular, no current measurements are performed in addition to the voltage measurements, and therefore without a current measurement the internal resistance cannot be calculated from the differential voltage. The method relies exclusively on the measurement of the differential voltage.

[0026] The process step for "monitoring" generates an output variable based on the "first differential voltage" as an input variable, which conveys information about the state of the health of the first contactor to another system component, such as another control device, a display unit, a user, etc. In its simplest form, this may be solely information about whether the measured differential voltage exceeds a specified value or remains below a specified value.

[0027] Alternatively or additionally, the state of health of the second contactor is monitored based on the measured second differential voltage. This allows monitoring of the state of health of the second contactor, since like the first contactor, the second differential voltage is measured at least partially via the open second contactor. The effect of the method on one contactor is therefore applicable to the other contactor as well. In other words, the method therefore allows monitoring of the ageing process in at least one contactor, solely based on the measurement of at least one differential voltage.

[0028] Thus, according to the proposed method, the voltage drop across an open contactor is measured, in this way both the electrical and the mechanical functioning of the contactor is monitored.

[0029] The proposed method makes it possible to draw conclusions regarding the state of health of the first contactor and / or the second contactor taking into account a simple voltage measurement.

[0030] Conversely, resistance measurements requiring the determination of a current flux that varies significantly between the two operating states "open contactor" and "closed contactor" are correspondingly ignored, with the result that the method can be performed without additional current measurements.

[0031] On the one hand, the precision of the proposed method allows a high degree of operational safety, since the state of the contactor's health and thus the existence of safe operating conditions can be reliably monitored, and on the other hand, the method allows for precise adjustment of maintenance cycles, since contactors can be utilized up to EOL (end of life) and do not have to be decommissioned upon completion of a predefined number of switching cycles.

[0032] Advantageously, the method may comprise at least one of the following further steps: monitoring a state of health of the first contactor based on a comparison of the measured first differential voltage with a first voltage threshold and / or determining a state of health of the second contactor based on a comparison of the measured second differential voltage with a second voltage threshold.

[0033] The first and second voltage thresholds may be preset or may be dynamically adjusted over the life of the circuit. The first and second voltage thresholds may assume the same or different values ​​relative to each other. Due to the corresponding comparison with the voltage thresholds, the method may be performed in a robust manner without high computational effort.

[0034] According to the method, advantageously, at least one differential voltage can be measured taking into account at least one reference potential, and preferably at least one cross voltage is measured via each open contactor. The reference potential is a voltage present in the battery pack and different from the differential voltage. The reference potential can vary according to the state of charge and state of health of the battery pack or battery cells.

[0035] The crossover voltage may be, for example, the voltage drop across a contactor, e.g., an open contactor, and another component in the circuit.

[0036] The crossover voltage can furthermore be a measured variable, recorded at any event by the battery control system. The measured crossover voltage can therefore be taken into account, firstly, with regard to contactor aging and secondly, for the monitoring of other characteristic variables in the battery pack. This improves the efficiency of the processes carried out in the battery pack and the responsiveness of the battery pack.

[0037] According to this method, advantageously, differential voltages for the first and second contactors may be measured with respect to an interface node facing the interface and with respect to a battery cell node facing the battery cell, respectively, the first differential voltage being a first crossover voltage existing between the interface node of the first contactor and the battery cell node of the second contactor, and / or the second differential voltage being a second crossover voltage existing between the interface node of the second contactor and the battery cell node of the first contactor, such that each crossover voltage may be present at a mutually electrically separate point in the battery pack circuit.

[0038] The first and second contactors may interrupt the respective electric wires. An interface node may be understood as a node in a circuit arranged between the interface and the respective contactor. Correspondingly, a battery cell node may be understood as a node in a circuit arranged between the respective contactor and at least one battery cell. The respective node may correspond to a closed contact or a connection terminal of a contactor. Alternatively, the node may be provided at any point between the contactor and the interface or at least one battery cell.

[0039] Advantageously, the method may include at least one of the following steps: generating an alarm signal if the first crossover voltage achieves or exceeds an alarm voltage threshold and / or generating an alarm signal if the second crossover voltage achieves or exceeds a second alarm voltage threshold. The alarm signal may be transmitted by the battery control device to another control device, a display unit or a user to indicate a marginal state of health of the first or second contactor. The alarm signal is generated before any switching of the respective contactor is inhibited, thus allowing replacement of the contactor without forced shutdown of the battery pack. Maximum operational safety is thus combined with optimal utilization.

[0040] Advantageously, the method may comprise at least one of the following steps: inhibiting switching of the first contactor if the first crossover voltage exceeds a first voltage threshold and / or inhibiting switching of the second contactor if the second crossover voltage exceeds a second voltage threshold and / or inhibiting switching of the first and second contactors if the first crossover voltage exceeds the first voltage threshold or the second crossover voltage exceeds the second voltage threshold.

[0041] Both the alarm voltage threshold and the voltage threshold can be established in volts and are freely selectable. On the one hand, manufacturer data regarding contactor aging and on the other hand the requisite safety margins can be taken into account. As soon as the switching of a contactor is inhibited, the contactor is no longer closed, despite a corresponding command, in order to ensure disconnection from at least one battery cell and the interface. If identical components are used for the first and second contactor, it is advantageous to specify identical values ​​for the first and second voltage threshold.

[0042] The warning voltage threshold may constitute a percentage of the voltage threshold. For example, an alarm may be triggered if the respective considered crossover voltage is 80% of the voltage threshold. The warning voltage threshold is therefore 80% of the voltage threshold. The margin between the warning voltage threshold and the voltage threshold may take into account regular user behavior, e.g. in a vehicle application, allowing the vehicle user to schedule an appointment with the vehicle user's service workshop, until which the vehicle continues to operate regularly without safety stops during normal use. In other words, the warning voltage value is set such that the vehicle can operate safely throughout the entire regular driving period and the service intervals can also be observed.

[0043] Advantageously, the method may include at least one of the steps of determining a first reference potential between the battery cell node of the first contactor and the battery cell node of the second contactor and / or determining a second reference potential between the interface node of the first contactor and the interface node of the second contactor, the first voltage threshold being preferably determined according to the first reference potential and the second voltage threshold being preferably determined according to the second reference potential. Each reference potential is appropriate for the conditions of the battery pack, e.g. the state of charge of the battery pack, taking into account. The establishment of a relationship between the reference potentials and the voltage thresholds allows for dynamic adjustment of the voltage thresholds. This increases the flexibility and adaptability of the method.

[0044] Advantageously, the method may comprise the following steps: determining the state of health of the first and / or second contactor before any switching process for closing the respective contactor, based on measuring the differential voltage for monitoring the state of health before each switching operation of the respective contactor, a corresponding determination of the state of health is possible without increased effort, which allows reliable monitoring of the state of health at any time, further increasing safety.

[0045] Advantageously, the method may also perform a step for continuous measurement of the first and / or second differential voltages. It should be understood that by continuous measurement, at each processor time interval in the control device, the corresponding differential voltage is measured. Thus, fluctuations, including sudden fluctuations, of the state of health of the respective contactor are directly detected. This has a positive impact on the dynamics of the monitoring.

[0046] The proposed battery control system for use in a battery pack is suitable for carrying out the method according to the invention.

[0047] For this purpose, corresponding signal lines are provided and corresponding functions are structurally implemented. The battery control system can be an electronic module, comprising a processor in which various input signals are converted into output signals. The potential input signals are statements regarding the state of health of the contactors, and the respective differential voltages comprise potential output signals.

[0048] The proposed battery pack for supplying electrical energy to an electronic drive unit comprises the following components: at least one battery cell, a first interface line and a second interface line for delivery of electrical energy to the interface, at least one switchable first contactor arranged in the first interface line and at least one switchable second contactor arranged in the second interface line. The battery pack further comprises the aforementioned battery control system. The corresponding components of the battery pack have already been mentioned together with the aforementioned method. The corresponding features disclosed with reference to the method are also applicable to the battery pack.

[0049] The above objective is also achieved by a non-volatile computer readable storage medium having stored thereon machine executable instructions for the execution of the above method.

[0050] Further preferred embodiments of the present invention will now be described in more detail with reference to the following figure description. [Brief description of the drawings]

[0051] [Figure 1] FIG. 2 is a schematic diagram of a circuit having a first contactor and a second contactor. [Diagram 2] FIG. 2 is a simplified schematic diagram for representing a first crossover voltage and a second crossover voltage. [Diagram 3] FIG. 2 is another schematic diagram of a circuit having a first contactor and a second contactor. [Figure 4] FIG. 2 is an equivalent circuit diagram of a circuit having a first contactor and a second contactor. [Diagram 5] FIG. 11 is a first diagram of simulated crossover voltages plotted against the insulation resistance of the first contactor. [Figure 6] FIG. 13 is a second diagram of simulated crossover voltages plotted against the insulation resistance of the second contactor. [Figure 7] FIG. 13 is a third diagram of a set of simulated crossover voltages plotted against insulation resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] Preferred exemplary embodiments are described below with reference to the figures. Identical, similar, or similarly functioning elements in various figures are identified with the same reference numerals, and in places, any repeated description of such elements is omitted to avoid redundancy.

[0053] 1 shows a schematic representation of a battery pack 3 comprising at least one diagrammatically illustrated battery cell 4 for electrochemical storage of electrical energy. A battery pack 3 of this type may for example be provided in a vehicle for the delivery of traction energy.

[0054] A plurality of battery cells 4 provided in a battery pack 3 may be constructed in the form of a battery module, and a plurality of battery modules may also be provided in a battery pack. A plurality of battery packs 3 may be interconnected in a battery system, which may ultimately be provided for the delivery of driving energy. The battery system may be, for example, a "high voltage system" operating at a rated voltage of 400V or 800V.

[0055] The battery pack 3 comprises a first interface line 5 and a second interface line 6. The first interface line 5 and the second interface line 6 deliver electrical energy to an interface 7. The interface 7 may for example be provided in the form of a high-voltage socket outlet allowing a simple electrical plug-in connection to the battery system. In other words, the battery pack 3 may be connected at the interface 7 to the rest of the battery system, and regardless of the internal structure of the battery pack 3, in particular whether one or several battery modules are arranged in the battery pack 3 or whether the battery cells 4 in the battery pack 3 are constructed in a different way, electrical energy is transferred exclusively from the battery pack 3 to the rest of the battery system via a single plug-in connection. Correspondingly, in principle, the battery system considers the battery pack 3 as a single battery.

[0056] An interface 7 for the connection of the battery pack 3 can also be arranged on a vehicle interface box (VIB) so that in this way the battery pack 3 can be utilized, for example, for the configuration of a high-voltage system (not shown), for example for the propulsion of a drive unit of the vehicle.

[0057] In the battery pack 3 according to Fig. 1 a circuit is represented with a first contactor 1 and a second contactor 2. The first contactor 1 is arranged in a first interface line 5 and the second contactor 2 is arranged in a second interface line 6. The function of the first contactor 1 and the second contactor 2 is the isolation of the battery cell 4 from the interface 7, so that with the contactors 1, 2 open the interface 7 is not connected to the battery cell 4 and therefore there is no voltage. Correspondingly, the function of the contactors 1, 2 is the connection and disconnection of the battery pack 3. By means of the contactors 1, 2 a safe shutdown of the battery pack 3 can also be performed if the battery pack 3 or the entire battery system exhibits an unstable or marginal state.

[0058] In the depicted exemplary embodiment, the first contactor 1 is arranged between an interface node 8 facing the interface 7 and a battery cell node 10 facing the battery cell 4. The first contactor 1 can thus break or establish an electrical connection between the interface node 8 and the battery cell node 10.

[0059] Similarly, a second contactor 2 is arranged between an interface node 9 facing the interface 7 and a battery cell node 11 facing the battery cell 4. The second contactor 2 can thus break or establish an electrical connection between the interface node 9 and the battery cell node 10.

[0060] Figure 1 represents both the first contactor 1 and the second contactor 2 in an open position. In this position, each contactor 1, 2 delivers a respective insulation resistance.

[0061] It should be noted that the representation according to Fig. 1 is intended to illustrate the operation of the method according to this exemplary embodiment, and therefore neither the number of contactors, nor the number of battery cells, nor the number of interface lines is of a limiting nature.

[0062] Typically, the insulation resistance of the contactors 1, 2 exceeds 300 megohms. However, during the various switching cycles, the contactors wear out, for example as a result of contact wear, arc erosion or fusion at the contacts, if during switching, residual currents flow and arcs are generated accordingly. As a result of this wear, the insulation resistance of the contactors may decrease, so that, upon achievement of a predefined insulation resistance, the contactors can no longer be utilized, since the insulation of the battery cells 4 from the interface 7 can no longer be guaranteed. This insulation resistance may be, for example, 300 kilohms. Achieving this insulation resistance means that the respective contactor has reached the end of its life and needs to be replaced.

[0063] In ideal operation, the contactor switches only to the interrupted state, so that contactor aging is essentially caused exclusively by mechanical wear. This aging can be monitored by measuring the switching cycles. However, in case of unforeseen operating conditions or non-optimal configurations of the control, switching can be performed even when the current is flowing. Depending on the frequency of switching operations for interrupting the current and the direction of the respective current that is switched, the contactor aging will proceed more quickly or more slowly.

[0064] It is therefore necessary to monitor contactor aging more accurately in order to prevent the continued use of contactors that are no longer safe in the battery pack 3. Conversely, it is intended to prevent premature replacement of contactors in order to preserve resources.

[0065] According to the exemplary embodiment depicted here, a first differential voltage Udif,1 across the open first contactor 1 and / or a second differential voltage Udif,2 across the open second contactor 2 is measured accordingly. By referring to the first measured differential voltage Udif,1 or the measured second differential voltage Udif,2 it is possible to determine the state of health of the first contactor 1 or the second contactor 2, or at least to establish whether the respective contactor can still be operated safely.

[0066] In the first instance, a differential voltage can be understood as the measured voltage that exists between two points.

[0067] FIG. 2 shows certain differential voltages. Thus, as the first differential voltage Udif,1, the first crossover voltage Ukreuz,1 is measured. As the second differential voltage Udif,2, the second crossover voltage Ukreuz,2 is measured. The first crossover voltage Ukreuz,1 exists between the interface node 8 of the first contactor 1 and the battery cell node 11 of the second contactor 2. The second crossover voltage Ukreuz,2 exists between the battery cell node 10 of the first contactor 1 and the interface node 9 of the second contactor 2. Thus, the crossover voltages Ukreuz,1,2 make it possible to draw conclusions regarding the voltage drop on the first contactor 1 or the second contactor 2 in relation to a fixed reference value, in each case with reference to a fixed reference value, i.e. with reference to the battery node 11 and the interface node 9 of the second contactor 2, respectively. Typically, the second interface line 6 is at earth potential, so in this case the respective reference potential is ground.

[0068] In addition to the crossover voltages Ukreuz,1,2, in the circuit according to Fig. 2, a first reference voltage Uref,1 and a second reference voltage Uref,2 are also measured. The first reference voltage Uref,1 is present between the battery cell node 10 of the first contactor 1 and the battery cell node 11 of the second contactor 2 and therefore corresponds to the voltage of the battery cell 4.

[0069] The second reference voltage Uref,2 exists between the interface node 8 of the first contactor 1 and the interface node 9 of the second contactor 2 and therefore corresponds to the voltage applied to the interface 7. By reference to the first reference voltage Uref,1, the first crossover voltage Ukreuz,1 can be normalized. By reference to the second reference voltage Uref,2, the second crossover voltage Ukreuz,2 can be normalized.

[0070] 3 shows another representation of the circuitry of a battery pack 3. This battery pack also comprises an interface 7, allowing for example connection to a high voltage system.

[0071] In addition to the first contactor 1 and the second contactor 2, an auxiliary contactor 12 is provided in the circuit. An auxiliary resistor 13 is connected in the circuit upstream of the auxiliary contactor 12. The auxiliary contactor 12 and the auxiliary resistor 13 are connected to the interface node 8 of the first contactor 1 and to the battery pack node 10 of the first contactor 1. The function of the auxiliary contactor 12 and the auxiliary resistor 13 upon connection of the battery pack 3 to the battery system is to allow precharging of the capacitances present in the battery system via the auxiliary resistor 13, so that there is no sudden flow of excessively high currents, which would result in high loading of the battery cells 4 upon connection of the battery pack 3 to the battery system and high loading and wear of the contactors upon closing of the contactors 1, 2. Such protection circuits of this type are known in principle.

[0072] The basic operating mode of voltage-based monitoring of the state of health of the first contactor 1 or the second contactor 2 remains unaffected by the auxiliary contactor 12 and the auxiliary resistor 13 .

[0073] The different arrows in Fig. 3 represent the different measurement voltages. The first crossover voltage Ukreuz,1, the second crossover voltage Ukreuz,2, the first reference voltage Uref,1 and the second reference voltage Uref,2 are known from Fig. 2.

[0074] Furthermore, in the circuit according to Fig. 3, various auxiliary voltages are measured. A first auxiliary voltage Uhilf,1 is present between the interface node 9 of the second contactor 2 and ground. A second auxiliary voltage Uhilf,2 is applied between a point upstream of the battery resistor 15 and the battery cell node 11 of the second contactor 2. A third auxiliary voltage Uhilf,3 is applied between a point upstream of the battery resistor 15 and another ground. A fourth auxiliary voltage Uhilf,4 is applied between the battery cell node 11 of the second contactor 2 and another ground.

[0075] Various auxiliary voltages are used to provide the battery control system with a detailed picture of the voltage conditions in the circuit according to Figure 3. Battery resistor 15 is shown only diagrammatically for representation of the resistance within battery pack 3. For illustrative purposes only, Figure 3 shows DC current source 14 as a battery cell.

[0076] Another circuit is shown in Figure 4. The circuit according to Figure 4 represents an equivalent circuit diagram of the battery pack 3, including the measurement assembly.

[0077] The internal resistance of the first contactor 1, together with the internal resistance of the second auxiliary contactor 12 and the protection resistor 13, can be assigned to a first common internal resistance 16. The second contactor 2 can be assigned to a second internal resistance 17. The DC current source 14 or the at least one battery cell 4 can be assigned to a replacement battery 18. Various resistors 19 are shown in the circuit, the function of which will not be described in detail here, but merely to represent the conditions within the battery cells.

[0078] A measuring shunt 20 is used to determine the voltage drop due to the first crossover voltage Ukreuz,1. A measuring shunt 21 is used to determine the voltage drop due to the second crossover voltage Ukreuz,2. Another measuring shunt 22 is used to determine the voltage drop due to the first reference voltage Uref,1. Another measuring shunt 23 is used to determine the voltage drop due to the second reference voltage Uref,2. It is thus possible to determine the respective crossover voltages by reference to the voltage drops on the measuring shunts 20, 21. This allows an efficient monitoring or determination of the ageing process in the respective contactor 1, 2 or of the internal resistances 16, 17 assigned to the contactor 1, 2.

[0079] Figure 5 shows an exemplary simulated voltage characteristic of the crossover voltage plotted against the insulation resistance, i.e. against the electrical resistance of the respective open contactor. With respect to Figure 5, the upper characteristic corresponds to the voltage characteristic of the first crossover voltage Ukreuz,1, and the lower characteristic corresponds to the voltage characteristic of the second crossover voltage Ukreuz,2. This is merely exemplary, and the reverse assignment may equally well be applied.

[0080] In the example according to Fig. 5, the first contactor 1 undergoes considerable aging and its internal resistance decreases. In the simulation, it is simultaneously assumed that the second contactor 2 maintains its (high) internal resistance and therefore does not undergo visible aging. This can be deduced from the first crossover voltage Ukreuz,1, i.e. the upper characteristic. Thus, the crossover voltage Ukreuz,1 increases as the insulation resistance of the first contactor 1 decreases. In other words, the first contactor 1 can no longer completely insulate the first interface 5 from the voltage generated by the battery cell 4 and therefore in this case a voltage transfer occurs across the open contactor 1. This is detected by the measurement of the first crossover voltage Ukreuz,1.

[0081] To monitor this aging process of the first contactor 1, a first voltage threshold Ukrit,1 is defined. This first voltage threshold Ukrit,1 can be deduced, for example, from a simulation of the circuit represented in FIG. 5, and then the first voltage threshold Ukrit,1 is deduced from the (simulated) internal resistance of the contactor 1, which is assumed to be a limit. In one example, the first voltage threshold Ukrit,1 can be established, for example, with a (simulated) internal resistance of 1.4 megaohms. If the crossover voltage Ukreuz,1 then measured in the circuit exceeds the voltage threshold Ukrit,1, it is assumed that the internal resistance of the contactor 1 has fallen below a limit value and therefore the battery pack 3 can no longer be switched.

[0082] In order to define voltage thresholds that are not specified as absolute values ​​but that adapt to the respective charge state of the battery cells, for example a voltage threshold of 90% of the first reference voltage (400 V in this case) can also be defined. As soon as the measured or detected first crossover voltage Ukreuz,1 achieves or exceeds the first voltage threshold Ukrit,1, a limit state of health of the first contactor 1 is reached. In such a case, closing of the respective contactor can therefore be prevented and a corresponding message can be sent to the battery control device.

[0083] In order to prevent the battery pack from suddenly ceasing to function here without warning due to exceeding the voltage threshold, an alarm voltage threshold can further be defined, for which an alarm message is output to the central battery controller. The alarm voltage threshold is preferably dimensioned such that the battery pack can still operate for some time until the voltage threshold is reached and further use of the battery pack is inhibited. The alarm voltage threshold is preferably set such that, for example in the case of the use of the battery pack in a vehicle, the vehicle driver has enough time during the regular operation of the vehicle to arrange a service appointment at the factory, until which the vehicle continues to operate regularly. The alarm voltage threshold can be set accordingly, for example, to 80% of the reference voltage, which is the alarm value, or to the calculated internal resistance of the respective contactor derived from the simulation. Figure 6 shows another simulation of the crossover voltage plotted against the insulation resistance. In figure 6, the characteristics of the first crossover voltage Ukreuz,1 and the second crossover voltage Ukreuz,2 coincide and therefore only one curve can be recognized. It is assumed here that both contactors 1, 2 undergo the same ageing process. Thus, as the insulation resistance decreases, the crossover voltages Ukreuz,1,2 increase. Thus, in the example shown in FIG. 2, when the second voltage threshold Ucrit,2 is reached, the closing of the respective contactors 1,2 is also inhibited. In FIG. 7, another diagram is represented in which various simulations of the crossover voltage are plotted against the insulation resistance. Here, individual areas are highlighted. In the areas identified with "I", i.e. areas with relatively high resistance and relatively low voltage, the contactors can still reliably perform their function. If the insulation resistance decreases further and the voltage increases further, i.e. in area II, severe aging has already been reached. In this area, an alarm is sent to the respective battery controller. If the respective contactors continue to age, i.e. the resistance as well as the voltage continue to increase, see area III, when the respective contactors open, the disconnection of the respective interface lines from the interface is no longer guaranteed, so that closing is prevented in such areas.This area is also called the fault area, in which the closing of the contactor must be prevented for safety reasons. This is efficiently achieved by the proposed method, where measurements of the crossover voltages are sufficient to allow reliable conclusions to be drawn regarding the state of the contactor health.

[0084] The above method may be implemented in a battery control system, and in a preferred arrangement, the individual execution steps are defined in the form of machine executable instructions that may be executed by a processor of the battery control system. The machine executable instructions may preferably be stored on a non-volatile computer readable storage medium, for example in the form of a ROM, EPROM or hard disk memory.

[0085] To the extent applicable, any of the individual features illustrated in the embodiments may be combined and / or interchanged without departing from the scope of the invention. [Explanation of symbols]

[0086] 1 First Contactor 2 Second Contactor 3 Battery Pack 4 Battery Cells 5 First interface line 6 Second Interface Line 7. Interface 8 First Contactor Interface Node 9 Second Contactor Interface Node 10 Battery cell node of first contactor 11 Battery cell node of second contactor 12 Auxiliary contactor 13 Protective resistor 14 DC current source 15 Battery Resistors 16 Internal Resistance 17 Internal Resistance 18 Replacement Battery 19 Resistor 20 Measuring branch 21 Measuring branch 22 Measuring branch 23 Measuring branch Udif,1 First differential voltage Udif,2 Second differential voltage Ukreuz,1 First crossover voltage Ukreuz,2 Second crossover voltage Uref,1 First reference voltage Uref,2 Second reference voltage Ukrit,1 First voltage threshold Ukrit,2 Second voltage threshold Uhilf,1 First auxiliary voltage Uhilf,2 Second auxiliary voltage Uhilf,3 Third auxiliary voltage Uhilf,4 Fourth auxiliary voltage

Claims

1. A method for monitoring the state of health of at least one contactor (1, 2) in a battery pack (3), comprising: said battery pack (3) comprising at least one battery cell (4) for electrochemical storage of electrical energy, and a first interface line (5) and a second interface line (6) for delivery of electrical energy to an interface (7); At least one switchable first contactor (1) is arranged in the first interface line (5) between the interface (7) and the at least one battery cell (4), and at least one switchable second contactor (2) is arranged in the second interface line (6) between the interface (7) and the at least one battery cell (4), measuring a first differential voltage (Udif,1) across the open first contactor (1) and / or measuring a second differential voltage (Udif,2) across the open second contactor (2); monitoring a state of health of the first contactor (1) based on the measured first differential voltage (Udif,1) and / or determining a state of health of the second contactor (2) based on the measured second differential voltage (Udif,2); The method includes the steps of:

2. monitoring a state of health of the first contactor (1) based on a comparison of the measured first differential voltage (Udif,1) with a first voltage threshold (Ukrit,1); and / or determining a state of health of the second contactor (2) based on a comparison of the measured second differential voltage (Udif,2) with a second voltage threshold (Ukrit,2); 2. The method according to claim 1 .

3. It is preferred that the at least one differential voltage (Udif, 1, 2) is measured with respect to at least one reference potential (9, 11) and that at least one crossover voltage (Ukreuz, 1, 2) is measured via each of the open contactors (1, 2) relative to the reference potential (9, 11).

3. The method according to claim 1 or 2.

4. the first contactor (1) is arranged between a first interface node (8) facing the interface (7) and a first battery cell node (10) facing the battery cell (4) and / or the second contactor (2) is arranged between a second interface node (9) facing the interface (7) and a second battery cell node (11) facing the battery cell (4), The first differential voltage (Udif,1) is a first crossover voltage (Ukreuz,1) existing between the first interface node (8) of the first contactor (1) and the second battery cell node (11) of the second contactor (2), and / or the second differential voltage (Udif,2) is a second crossover voltage (Ukreuz,2) existing between the second interface node (9) of the second contactor (2) and the first battery cell node (10) of the first contactor (1).

4. The method according to claim 1, wherein the first and second electrodes are connected to a first electrode.

5. inhibiting the switching of the first contactor (1) if the first crossover voltage (Ukreuz,1) or the first differential voltage (Udif,1) exceeds a first voltage threshold (Ukrit,1); and / or The second crossover voltage (Ukreuz,2) or the second differential voltage (Udif,2) is Inhibiting the switching of the second contactor (2) when a second voltage threshold (Ukrit, 2) is exceeded.

5. The method according to claim 1, wherein the first and second electrodes are arranged in a first direction.

6. generating an alarm signal if the first crossover voltage (Ukreuz,1) or the first differential voltage (Udiff,1) exceeds a first alarm voltage threshold and / or generating an alarm signal if the second crossover voltage (Ukreuz,2) or the second differential voltage (Udiff,2) exceeds a second alarm voltage threshold.

6. The method according to claim 1, wherein the first and second electrodes are arranged in a first direction.

7. determining a first reference voltage (Uref,1) between a first battery cell node (10) of the first contactor (1) and a second battery cell node (11) of the second contactor (2); and / or determining a second reference voltage (Uref,2) between a first interface node (8) of the first contactor (1) and a second interface node (9) of the second contactor (2), the first voltage threshold (Ukrit,1) being preferably determined according to the first reference voltage (Uref,1) and the second voltage threshold (Ukrit,2) being preferably determined according to the second reference voltage (Uref,2); 7. The method according to claim 1, wherein the first and second electrodes are arranged in a first direction.

8. monitoring the health status of the first contactor (1) and / or the second contactor (2) before any switching process for closing the respective contactor (1, 2); 8. The method according to claim 1 , wherein the first and second electrodes are arranged in a first direction.

9. Continuous measurement of the first differential voltage (Udif,1) and / or the second differential voltage (Udif,2) 9. The method according to claim 1, wherein the first and second electrodes are arranged in a first direction.

10. A battery control system for use in a battery pack, the battery control system being adapted and arranged to carry out a method according to any one of claims 1 to 9.

11. A battery pack (3) for the delivery of electrical energy for an electric drive unit, comprising: At least one battery cell (4); a first interface line (6) and a second interface line (7) for delivery of electrical energy to the interface (7); at least one switchable first contactor (1) arranged between an interface node (8) in the first interface line (6) and a battery cell node (10); at least one switchable second contactor (2) arranged between an interface node (9) in the second interface line and a battery cell node (11); having The battery control system according to claim 10 . A battery pack (3).

12. A non-volatile computer readable storage medium having stored thereon machine executable instructions for the execution of the method of any one of claims 1 to 9.

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