Method and device for identifying an impaired component of an on-board electrical system of a vehicle

Abstract

The invention relates to a device for identifying an impairment of a component of an on-board electrical system of a motor vehicle, the on-board electrical system comprising multiple different components which each contribute to a total Y capacitance of the on-board electrical system. The device is designed to determine an estimated value of the total Y capacitance of the on-board electrical system. The device is also designed to identify, on the basis of the determined estimated value and on the basis of a capacitance model of the on-board electrical system, a component of the on-board electrical system that has an impairment, the capacitance model indicating how the total Y capacitance of the on-board electrical system is composed of multiple individual Y capacitances of the corresponding multiple components.

Description

[0001] Method and device for determining an impaired

[0002] Component of a vehicle electrical system

[0003] The invention relates to a method and a corresponding device for determining and / or detecting a defective component of the electrical system of a motor vehicle.

[0004] An electrically powered vehicle comprises an electric drive motor that is powered by electrical energy from an electrical energy storage device. The alternating voltage for operating the drive motor is generated using an inverter based on the high-voltage direct voltage provided by the energy storage device. Furthermore, when using a current-excited drive motor, the excitation voltage for the rotor of the drive motor can be generated from the direct voltage of the energy storage device using a DC-DC converter. In addition, an electrically powered vehicle usually has one or more other electrical consumers, such as an air conditioning system, each of which is powered by the high-voltage direct voltage.

[0005] The electrical energy storage unit, the inverter, one or more high-voltage consumers, and / or the DC-DC converter are part of the on-board electrical system that supplies the motor vehicle's electric drive unit. To meet electromagnetic compatibility (EMC) requirements, the on-board electrical system typically has Y capacitors between the individual poles or potentials of the on-board electrical system and the vehicle ground. Furthermore, the various components of the on-board electrical system typically have parasitic capacitances that contribute to the total Y capacitances between the individual poles or potentials of the on-board electrical system and the vehicle ground.

[0006] This document addresses the technical task of detecting a fault in a component of the electrical (high-voltage) system of a motor vehicle in an efficient, precise and reliable manner.

[0007] The problem is solved by each of the independent claims. Advantageous embodiments are described, among other things, in the dependent claims. It should be noted that additional features of a patent claim dependent on an independent patent claim can form a separate invention, independent of the combination of all features of the independent patent claim, without the features of the independent patent claim or only in combination with a subset of the features of the independent patent claim, which invention can be made the subject of an independent claim, a divisional application, or a subsequent application. This applies equally to technical teachings described in the description, which can form an invention independent of the features of the independent patent claims.

[0008] According to one aspect, a device for detecting a deterioration of a component of an electrical system of a motor vehicle is described. An example of a deterioration of a component is damage to the component or a disconnection of the component from the electrical system. The electrical system can have an electrical (in particular an electrochemical) energy storage device that is designed to provide electrical energy with a specific electrical system voltage (i.e., a direct voltage). The electrical system voltage is typically in the high-voltage range at 60V or more, in particular at 300V or more. The electrical energy can be provided for operating the electric drive motor of the motor vehicle. The electrical energy storage device typically has a first pole (e.g., a positive pole) and a second pole (e.g.,a negative pole) between which the vehicle electrical system voltage is applied and via which the electrical energy is provided.

[0009] The vehicle electrical system can further comprise a first and a second potential line, which are (galvanically) coupled to the first and second poles of the electrical energy storage device, respectively. The electrical energy from the electrical energy storage device can be supplied via the potential lines to an inverter, which is designed to generate a multiphase alternating voltage for the electric (drive) machine of the motor vehicle.

[0010] The vehicle electrical system typically includes a first Y capacitor, which can be arranged between the first potential line and a reference potential, in particular the vehicle ground, and a second Y capacitor, which can be arranged between the second potential line and the reference potential. The Y capacitors can be used to meet EMC requirements.

[0011] The electrical system comprises a plurality of different components, each of which contributes to the total Y capacitance of the electrical system. The total Y capacitance can include the capacitance of the first or second Y capacitor. Furthermore, the total Y capacitance can include a plurality of individual Y capacitances of the corresponding plurality of components of the electrical system. This document generally refers to a Y capacitance, which refers to the Y capacitance between a potential line (e.g., the positive or negative line) and the reference potential (e.g., the vehicle ground).

[0012] The plurality of components may include

[0013] • the electrical, in particular electrochemical, energy storage device, which is designed to store and provide electrical energy for the on-board network;

[0014] • the electrical machine designed to drive the motor vehicle;

[0015] • the inverter, which is designed to generate phase currents for the operation of the electrical machine based on the vehicle electrical system voltage; and / or

[0016] • one or more electrical consumers that are designed to be operated directly with electrical energy from the vehicle's electrical system (the vehicle's electrical system voltage can be applied directly to the one or more electrical consumers).

[0017] The individual components can each be operated based on the vehicle electrical system voltage present between the first potential line and the second potential line. Furthermore, the individual components can each have a housing that is (electrically conductively) coupled to the reference potential via an equipotential bonding conductor. Alternatively or additionally, the housing of a component can be coupled to the reference potential via the shield of a line leading to or away from the component. A first end of the line can be arranged on the component, and the shield of the line can be (electrically conductively) connected at the first end to the housing of the component. The opposite second end of the line can be arranged on another component of the vehicle electrical system, and the shield of the line can be (electrically conductively) connected at the second end to the housing of the other component.The connection of the housing of a component to the reference potential can thus be achieved indirectly via the shield of a cable (and via the housing of another component).

[0018] The device can be configured to detect as an impairment that the housing of a component is separated from the reference potential (and thus there is no electrically conductive connection between the housing and the reference potential, neither via the equipotential bonding conductor nor via the shield of an electrical line of the vehicle electrical system).

[0019] The device is configured to determine an estimated value of the total Y capacitance of the vehicle electrical system. For this purpose, the temporal variation of the voltage across a measuring resistor of the insulation monitoring unit can be determined using a (symmetrical or asymmetrical) insulation monitoring unit (where the temporal variation is determined, for example, as part of the insulation resistance monitoring). The estimated value of the total Y capacitance can then be determined efficiently and precisely based on the temporal variation of the voltage.

[0020] The device is further configured to identify, on the basis of the determined estimated value and on the basis of a capacitance model of the vehicle electrical system, a component of the vehicle electrical system (i.e., one of the plurality of components of the vehicle electrical system) that exhibits an impairment. The impairment of the component may comprise an impairment, in particular an interruption, of the equipotential bonding conductor with which the housing of the component is electrically connected to the reference potential of the vehicle electrical system. Alternatively or additionally, the impairment of the component may comprise an impairment of a function of the component (in particular a function that affects the individual Y capacitance of the component). The capacitance model may specify and / or model and / or depend on how the total Y capacitance of the vehicle electrical system is composed of the plurality of individual Y capacitances of the corresponding plurality of components.The capacity model can be determined in advance, e.g., experimentally and / or learned. The capacity model can, for example, include experimentally determined characteristic data and / or characteristic maps.

[0021] The device may further be configured to effect at least one measure with respect to the identified component. Examples of measures include:

[0022] • the issuing of a notice, in particular via a user interface of the motor vehicle;

[0023] • the entry of an error in the error memory of the motor vehicle; and / or

[0024] • interfering with the operation of the motor vehicle.

[0025] A device is thus described which uses the analysis of the total Y capacitance of the vehicle electrical system to efficiently and reliably identify a deteriorated component, in particular a component with a deteriorated equipotential bonding conductor.

[0026] The capacity model can specify a target value for the total Y capacity (which should be present if no component is impaired). The device can be configured to compare the determined estimated value with the target value. Based on the comparison, it can then be reliably determined whether, and if so, that at least one of the plurality of components is impaired.

[0027] The device can be configured to determine a deviation (in particular the difference) of the determined estimated value from the target value of the total Y capacity of the vehicle electrical system. The component of the plurality of components exhibiting an impairment can then be identified in a particularly precise manner based on the deviation and the capacity model.

[0028] The device can, in particular, be configured to compare the determined deviation with the plurality of individual Y capacitances of the corresponding plurality of components. The component with the impairment can then be reliably identified based on the comparison. In particular, the component can be identified that has an individual Y capacitance corresponding to (in particular equivalent to) the determined deviation.

[0029] According to another aspect, an electrical system for a motor vehicle is described. The electrical system comprises a plurality of different components, each of which contributes to the total Y-capacitance of the electrical system. Furthermore, the electrical system comprises the device described in this document.

[0030] According to a further aspect, a (road) motor vehicle (in particular a passenger car or a truck or a bus or a motorcycle) is described which comprises the device described in this document and / or the on-board network described in this document.

[0031] According to a further aspect, a method for detecting an impairment of a component of an electrical system of a motor vehicle is described, wherein the electrical system comprises a plurality of different components, each of which contributes to a Y total capacity of the electrical system.

[0032] The method comprises determining an estimated value of the total Y capacity of the vehicle electrical system. Furthermore, the method comprises identifying, based on the determined estimated value and a capacity model of the vehicle electrical system, a component of the vehicle electrical system that exhibits an impairment. The capacity model can specify and / or depend on how the total Y capacity of the vehicle electrical system is composed of a plurality of individual Y capacities of the corresponding plurality of components.

[0033] It should be noted that the aspects described in connection with the device, in particular the claims described in connection with the device, are also to be applied to the method as corresponding method features.

[0034] According to another aspect, a software (SW) program is described. The SW program can be configured to be executed on a processor (e.g., on a vehicle control unit) and thereby to carry out the method described in this document.

[0035] According to a further aspect, a storage medium is described. The storage medium can comprise a software program configured to be executed on a processor and thereby to carry out the method described in this document.

[0036] It should be noted that the methods, devices, and systems described in this document can be used alone or in combination with other methods, devices, and systems described in this document. Furthermore, any aspects of the methods, devices, and systems described in this document can be combined in a variety of ways. In particular, the features of the claims can be combined in a variety of ways. Furthermore, features listed in parentheses are to be understood as optional features. The invention is described in more detail below using exemplary embodiments.

[0037] Figure 1a shows exemplary components of a vehicle with an electric drive motor;

[0038] Figure 1b shows an exemplary insulation monitoring unit;

[0039] Figure 2 shows an exemplary voltage curve when discharging the second Y capacitor;

[0040] Figure 3 shows an exemplary capacity model for an on-board network; and

[0041] Figure 4 is a flowchart of an exemplary method for detecting a degraded component of an on-board electrical system.

[0042] As stated at the outset, this document is concerned with efficiently and reliably detecting a possible impairment of a component of an electrical system of a motor vehicle. In this context, Fig. 1a shows exemplary components of a vehicle 140 having an electric machine 103 for driving the vehicle 140. The electric machine 103 is coupled to one or more wheels 141 of the vehicle 140 in order to drive the one or more wheels 141 and thus the vehicle 140. The electric machine 103 is operated with electrical energy from an electrical, in particular an electrochemical, energy storage device 130. The energy storage device 130 can be designed to provide a direct current with a specific direct voltage.

[0043] The vehicle 140 has an inverter 100 configured to generate phase voltages and / or phase currents for the different phases of the electric machine 103 based on the DC voltage from the energy storage device 130. The inverter 100 can be operated by a (control) device 101 of the vehicle 100.

[0044] The inverter 100 can, as shown by way of example in Fig. 1b, be electrically connected to the electrical energy storage device 130 via potential lines 151, 152. A first potential line 151 can lead to a first pole and a second potential line 152 can lead to a second pole of the electrical energy storage device 130. The first potential line 151 can be at a first potential (e.g., at a positive potential, such as high voltage+ or HV+) and the second potential line 152 can be at a second potential (e.g., at a negative potential, such as HV-). The potential lines 151, 152 connected to the electrical energy storage device 130 can each be decoupled from the inverter 100 by a line switching element 159 (e.g., by a MOSFET).

[0045] Fig. 1b shows, in addition to the inverter 100, a DC-DC converter 110 which is configured to generate the excitation voltage for the rotor of the electric machine 103 on the basis of the DC voltage provided by the electrical energy storage device 130, ie on the basis of the vehicle electrical system voltage.

[0046] For safe operation of the motor vehicle 100, the individual potential lines 151, 152 should each have relatively high insulation resistances Riso+ and Riso-, respectively, relative to the vehicle ground 153 (generally relative to a reference potential). The insulation resistances Riso+ and Riso- could be reduced due to a defect in the electrical energy storage device 130 and / or due to a defect in one of the potential lines 151, 152 and / or due to a defect in the inverter 100. The vehicle 100 can have an insulation monitoring unit 150 to monitor the insulation resistances. The insulation monitoring unit 150 can be configured to specifically determine the first insulation resistance Riso+ between the first potential line 151 and ground (generally the reference potential) 153 and the second insulation resistance Riso- between the second potential line 152 and ground 153.For this purpose, a measuring voltage (e.g., corresponding to the potential difference between the respective potential and ground) can be applied between the respective potential line 151, 152 and ground 153, and the resulting measuring current can be recorded. The respective insulation resistance can then be determined from the ratio between the measuring voltage and the measuring current.

[0047] Fig. 1b shows an exemplary (asymmetric) insulation monitoring unit 150, which advantageously has only a single measuring switching element 155 to measure the two insulation resistances Riso+ and Riso-. Furthermore, the insulation monitoring unit 150 has an activation switching element 154 that can be closed to enable the measurement of the insulation resistances Riso+ and Riso-.

[0048] The insulation monitoring unit 150 has a first series circuit of measuring resistors Ra, Rb, which can be arranged in parallel with the first insulation resistance Riso+ (by closing the activation switching element 154). Furthermore, the insulation monitoring unit 150 has a second series circuit of measuring resistors Rc, Rd, which can be arranged in parallel with the second insulation resistance Riso- (by closing the activation switching element 154). Preferably, the first resistor series circuit and the second resistor series circuit have equal resistance values ​​(i.e., Ra+Rb = Rc+Rd).

[0049] The measuring current can be detected (by a measuring unit 156) based on the voltage across resistor Rd caused by the current through Rd. The measuring switching element 155 is configured to directly couple or decouple the intermediate point between two resistors Ra and Ra of the first resistor series circuit to the second potential line 152.

[0050] The measurement of the insulation resistances Riso+ and Riso- can be started by closing the activation switching element 154, so that the node between the two series resistor circuits is coupled to ground 153 (generally to the reference potential). Using the measuring unit 156, the values ​​for the two measurement situations or

[0051] For the switching states “measuring switching element 155 closed” and “measuring switching element 155 open”, measuring currents are determined which can be used to determine the values ​​of the insulation resistances Riso+ and Riso-.

[0052] The energy storage device 130 and the potential lines 151, 152 are part of the electrical (high-voltage) electrical system of the vehicle 100, which is designed to supply the electric drive motor 103 of the vehicle 100 with electrical energy. To meet EMC requirements, the electrical system typically has Y capacitors, in particular a first Y capacitor C y + between the first potential line 151 and the reference potential 153 and a second Y-capacitor C y . between the second potential line 152 and the reference potential 153.

[0053] The vehicle electrical system may further comprise one or more electrical consumers 170, which are arranged between the potential lines 151, 152 and which typically each have a (parasitic) Y-capacitance, in particular a first Y-capacitance between the first potential line 151 and the reference potential 153, and a second Y-capacitance between the second potential line 152 and the reference potential 153. Furthermore, the inverter 100 also typically has a (parasitic) first and second Y-capacitance.

[0054] In the following, an example of a Y-capacitance is discussed, which can refer to a first Y-capacitance (between the first potential line 151 and the reference potential 153) and / or to a second Y-capacitance (between the second potential line 152 and the reference potential 153).

[0055] The on-board network can therefore have a Y-total capacity, which results from the

[0056] Capacitance of the Y capacitor and the (parasitic) capacitances of one or more components 151, 152, 100, 103, 110, 170 of the vehicle electrical system.

[0057] The (voltage) measured values ​​acquired during insulation resistance monitoring can be used to efficiently and precisely determine an estimated value of the total Y capacitance. For this purpose, as shown in Fig. 2, the time profile 221 of the voltage 200 at the second Y capacitor C can be measured (using the measuring unit 156). y . are recorded and evaluated. The closing of the measuring switching element 155 (at time 211) during the insulation resistance test leads to a (partial) discharge of the second Y capacitor C y . and a falling voltage curve 221, wherein the voltage 200 drops from a first voltage 201 to a second voltage 202. The charge from the second Y capacitor C y. flows into the first Y capacitor C y + and charges it.

[0058] The voltage curve 221 can be approximated by a reference curve 222 (e.g., an exponential curve or a hyperbola) with a time constant. The estimated value of the total Y capacitance can then be determined based on the time constant (taking into account the one or more resistors of the insulation monitoring unit 150 and / or the insulation resistance).

[0059] As already explained above, the total Y capacity is composed of a large number of individual capacities of a corresponding number of components of the on-board network. Examples of components are,

[0060] • a Y capacitor C y ;

[0061] • one or more electrical consumers 170;

[0062] • the inverter 100;

[0063] • the electrical machine 103; and / or

[0064] • the energy storage device 130. The individual capacitances of the individual components can be measured in advance to determine a capacity model 300 of the total Y capacity of the vehicle electrical system (see Fig. 3). The capacity model 300 can indicate how the total Y capacity is composed of the plurality of individual Y capacitances 302 of the corresponding plurality of components 301 of the vehicle electrical system.

[0065] An estimated value of the Y total capacity can be measured during operation of the vehicle electrical system (as described in this document). Using the capacity model 300 for the Y total capacity, it can be recognized that the estimated value of the Y total capacity is lower than the intended target value of the Y total capacity. Furthermore, using the capacity model 300, in particular using the plurality of Y individual capacities 302, it can be determined which component 301 of the vehicle electrical system is impaired. In particular, it can be determined which one or more Y individual capacities 302 do not contribute to the Y total capacity. Based on the one or more identified Y individual capacities 302, it is then possible to draw conclusions about the one or more components 301 associated with them.

[0066] As already explained above, a motor vehicle 140 has an insulation monitoring system for monitoring the insulation resistance. The insulation monitoring system measures the insulation resistance between the HV potentials 151, 152 and ground 153. If the measured insulation resistance falls below one or more resistance thresholds, one or more safety measures (such as issuing a warning, restricting availability, and / or completely shutting down the vehicle electrical system) can be initiated.

[0067] The housings of the individual HV components 170, 301 are connected to ground potential 153 via so-called PA (potential equalization) conductors. These can be direct screw connection elements or cables. It is typically only with relatively great effort to verify whether the individual PA conductors are connected correctly and / or whether the specified resistance values ​​of the individual PA conductors are maintained over their service life. Errors in the connection of the individual components 170, 301 can occur, for example, due to a faulty component, a deviation in the factory process, or after maintenance with part replacement.

[0068] The presence of the PA conductors of the individual components 170, 301 can be checked based on the estimated value of the Y total capacitance. Each HV component 170, 601 has an individual Y capacitance between the HV potentials 151, 152 and the ground potential 153, and thus contributes to the Y total capacitance of the HV system (i.e., the on-board electrical system). A loss of the Y total capacitance can be detected based on the determined estimated value of the Y total capacitance. Furthermore, the faulty component 170, 301 can be identified based on the value of the capacitance loss, since each HV component 170, 301 contributes a very specific and known amount (i.e., a specific Y individual capacitance 302) to the Y total capacitance.

[0069] For example, following the production of a vehicle 140, an estimated value of the total Y capacitance of the HV system of the vehicle 140 can be determined. Based on the estimated value, it can be recognized that a certain capacitance threshold is not reached. By comparing this with a characteristic map (i.e., with a capacitance model 300) in which the respective Y capacitance specification, possibly including tolerances, (i.e., the respective individual Y capacitance 302) is stored for each HV component 301, it can be recognized that the estimated value has been reduced by the Y capacitance specification of a specific component 301 (e.g., the electric machine 103). A check of the equipotential bonding conductor and / or the functionality of the identified component 301 can then be initiated. Fig. 4 shows a flowchart of a (possibly computer-implemented) method 400 for detecting an impairment of a component 301 of an electrical system of a motor vehicle 140.The electrical system comprises a plurality of different components 301, each of which contributes to a total Y capacitance of the electrical system. The method 400 can be executed by a device 101 of the motor vehicle 140.

[0070] The method 400 includes determining 401 an estimate of the total Y capacity of the vehicle electrical system (using the method described in this document).

[0071] Furthermore, the method 400 includes identifying 402, based on the determined estimated value and based on a capacity model 300 of the vehicle electrical system, a component 301 of the vehicle electrical system that exhibits an impairment. The capacity model 300 can specify and / or model how the Y total capacity of the vehicle electrical system is composed of the plurality of Y individual capacities 302 of the corresponding plurality of components 301. The capacity model 300 can be in the form of one or more characteristic maps and / or characteristic curves, for example. Alternatively or additionally, the capacity model 300 can be in the form of a model learned via machine learning (e.g., with one or more neural networks).

[0072] Method 400 can be repeated at a sequence of consecutive points in time (e.g., periodically). This allows for permanently reliable monitoring of the vehicle electrical system.

[0073] The analysis of the total Y capacitance makes it possible to efficiently and reliably detect a degraded component 301 of an HV electrical system. The present invention is not limited to the embodiments shown. In particular, it should be noted that the description and the figures are intended only to illustrate the principle of the proposed methods, devices, and systems by way of example.

Claims

Claims 1) Device (101) for detecting an impairment of a component (301) of an electrical system of a motor vehicle (140); wherein the electrical system comprises a plurality of different components (301), each of which contributes to a Y total capacity of the electrical system; wherein the device (101) is configured - to determine an estimate of the total Y capacity of the on-board network; - on the basis of the determined estimated value and on the basis of a capacity model (300) of the vehicle electrical system, to identify a component (301) of the vehicle electrical system that exhibits an impairment; wherein the capacity model (300) indicates how the Y total capacity of the vehicle electrical system is composed of a plurality of Y individual capacities (302) of the corresponding plurality of components (301). 2) Device (101) according to claim 1, wherein - the capacity model (300) specifies a target value of the Y total capacity; and - the device (101) is set up, - to compare the estimated value with the target value; and - to determine on the basis of the comparison that at least one of the plurality of components (301) has an impairment. 3) Device (101) according to one of the preceding claims, wherein the device (101) is arranged - to determine a deviation of the estimated value from a target value of the total Y capacity of the on-board network; and - on the basis of the deviation and on the basis of the capacity model (300), the component (301) of the plurality of components (301) identify that has an impairment. 4) Device (101) according to claim 3, wherein the device (101) is arranged - to compare the determined deviation with the plurality of Y individual capacitances (302) of the corresponding plurality of components (301); and - to identify the component (301) with the impairment on the basis of the comparison. 5) Device (101) according to claim 4, wherein the device (101) is configured to identify the component (301) having a Y individual capacitance (302) corresponding to the determined deviation. 6) Device (101) according to one of the preceding claims, wherein the device (101) is arranged - to determine, using an insulation monitoring unit (150), a time profile (221) of a voltage (200) at a measuring resistor of the insulation monitoring unit (150); and - to determine the estimated value of the total Y capacity based on the time course (221) of the voltage (200). 7) Device (101) according to one of the preceding claims, wherein - the device (101) is configured to effect at least one measure with respect to the identified component (301); and - the measure includes in particular, - the output of an indication, in particular via a user interface of the motor vehicle (140); - entering an error in an error memory of the motor vehicle (140); and / or - an interference with the operation of the motor vehicle (140). 8) Device (101) according to one of the preceding claims, wherein the plurality of components (301) comprises - an electrical, in particular an electrochemical, energy storage device (130) which is designed to store and provide electrical energy for the on-board network; - an electric machine (103) arranged to drive the motor vehicle (140); - an inverter (100) which is configured to generate phase currents for the operation of the electric machine (103) on the basis of an on-board network voltage of the on-board network; and / or - one or more electrical consumers (170) which are designed to be operated with electrical energy from the on-board network. 9) Device (101) according to one of the preceding claims, wherein the vehicle electrical system has a vehicle electrical system voltage in the high-voltage range at 60V or more, in particular at 300V or more. 10) Device (101) according to one of the preceding claims, wherein - the vehicle electrical system has a first potential line (151), a second potential line (152) and a reference potential (153); - the individual components (301) are each operated on the basis of the vehicle electrical system voltage present between the first potential line (151) and the second potential line (152); and - the individual components (301) each have a housing which is coupled to the reference potential (153) via a potential equalization conductor. 11) Device (101) according to one of the preceding claims, wherein the impairment of a component (301) comprises - an impairment, in particular an interruption, of a potential equalisation conductor with which a housing of the component (301) is electrically connected to a reference potential (153) of the vehicle electrical system; and / or - an impairment of a function of the component (301). 12) Method (400) for detecting an impairment of a component (301) of an electrical system of a motor vehicle (140); wherein the electrical system comprises a plurality of different components (301), each of which contributes to a Y total capacity of the electrical system; wherein the method (400) comprises, - determining (401) an estimated value of the total Y capacity of the on-board network; and - Identifying (402), on the basis of the determined estimated value and on the basis of a capacity model (300) of the vehicle electrical system, a component (301) of the vehicle electrical system that exhibits an impairment; wherein the capacity model (300) indicates how the Y total capacity of the vehicle electrical system is composed of a plurality of Y individual capacities (302) of the corresponding plurality of components (301).

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