Method and device for ascertaining a y capacitor of a vehicle energy supply system

Abstract

The invention describes a device for ascertaining capacitor information relating to at least one Y capacitor of an energy supply system of a motor vehicle. The device is designed to change the switching state of the measuring switching element of an asymmetrical insulation monitoring unit of the motor vehicle such that an electrical charge transfer process is effected between a first Y capacitor and a second Y capacitor of the energy supply system of the motor vehicle. The device is also configured to capture measurement data relating to the temporal profile of the voltage at the second Y capacitor during the charge transfer process, and to determine the capacitor information on the basis of the temporal profile using a proportionality coefficient, wherein the proportionality coefficient depends on whether the second Y capacitor is charged or discharged during the charge transfer process.

Description

[0001] Method and device for determining a Y-capacitance of a

[0002] Vehicle power supply system

[0003] The invention relates to a method and a corresponding device for determining an estimated value of the Y-capacitance, in particular the capacitance of one or more Y-capacitors, of the electrical energy supply system of a motor vehicle.

[0004] An electrically powered vehicle comprises an electric drive motor that is operated with electrical energy from an electrical energy storage device. The alternating voltage for operating the drive motor is generated using an inverter on the basis of 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, that are operated using the high-voltage direct voltage. The electrical energy storage device and, if applicable,The inverter and the DC-DC converter can be part of an electrical power supply system that supplies the motor vehicle's electric drive unit. To meet electromagnetic compatibility (EMC) requirements, the power supply system typically has Y capacitors between the individual poles or potentials of the power supply system and the vehicle ground. Furthermore, the power supply system typically has parasitic components that contribute to the Y capacitances between the individual poles or potentials of the power supply system and the vehicle ground.

[0005] This document addresses the technical task of detecting a possible impairment of a Y-capacitance, in particular a Y-capacitor, of the electrical power supply system of a motor vehicle in an efficient, precise and reliable manner.

[0006] 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.

[0007] According to one aspect, a device for determining

[0008] Capacitance information relating to a Y-capacitance, in particular relating to the capacitance of at least one Y-capacitor, of the energy supply system of a motor vehicle is described. The energy supply system can have an electrical (in particular an electrochemical) energy store which is designed to provide electrical energy at a specific direct voltage. The direct voltage can have a value of 300V or more, in particular 400V or more. The electrical energy can be provided, for example, for operating an electric drive motor of the motor vehicle. The electrical energy store typically has a first pole (e.g. a positive pole) and a second pole (e.g. a negative pole), between which the direct voltage is applied and via which the electrical energy is provided.

[0009] The energy supply system can further comprise a first and a second potential line 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 configured to generate a multiphase alternating voltage for the electric (drive) machine of the motor vehicle.

[0010] The energy supply system comprises a first Y-capacitance, in particular a first Y-capacitor, which can be arranged between the first potential line and a reference potential, in particular the vehicle ground, as well as a second Y-capacitance, in particular a second Y-capacitor, which can be arranged between the second potential line and the reference potential. The Y-capacitances, in particular the Y-capacitors, can be used to meet EMC requirements.

[0011] Furthermore, the energy supply system comprises an asymmetric insulation monitoring unit which can be configured to monitor a first insulation resistance between the first potential line and the reference potential and / or a second insulation resistance between the second potential line and the reference potential.

[0012] The asymmetric insulation monitoring unit can comprise a first resistor series circuit and a second resistor series circuit, wherein the first resistor series circuit can be arranged between the first potential line and the reference potential, and wherein the second resistor series circuit can be arranged between the second potential line and the reference potential. The first resistor series circuit and the second resistor series circuit can each comprise two resistors connected in series. Furthermore, the first resistor series circuit and the second resistor series circuit can have the same resistance values.

[0013] The asymmetric insulation monitoring unit comprises one (possibly exactly one) measuring switching element (e.g., a MOSFET or an IGBT). The measuring switching element can be designed to directly couple an intermediate point within the first resistor series circuit (in particular, the intermediate point between the two resistors of the first resistor series circuit) to the second potential line (when the measuring switching element is closed) or to decouple it from it (when the measuring switching element is open), depending on the switching state of the measuring switching element. The measuring switching element can, for example, be designed to directly couple the intermediate point within the first resistor series circuit, past the second resistor series circuit, to the second potential line (by closing the measuring switching element).

[0014] The asymmetric insulation monitoring unit can have a measuring unit for measuring the voltage across a resistor in the second resistor series circuit. The measuring unit can, in particular, be arranged parallel to the resistor in the second resistor series circuit, which is directly connected to the second potential line.

[0015] The device is configured to change the switching state of the measuring switching element of the asymmetric insulation monitoring unit of the motor vehicle, so that a transfer process of electrical charge between the first Y-capacitance, in particular the first Y-capacitor, and the second Y-capacitance, in particular the second Y-capacitor, of the energy supply system of the motor vehicle is effected.

[0016] The device can in particular be configured to cause the measuring switching element to be closed, so that the intermediate point within the first resistor series circuit is directly coupled to the second potential line in order to effect a charge transfer process in which electrical charge is transferred from the second Y-capacitance, in particular from the second Y-capacitor, to the first Y-capacitance, in particular to the first Y-capacitor. Alternatively or additionally, the device can be configured to cause the measuring switching element to be opened, so that the intermediate point within the first resistor series circuit is decoupled from the second potential line in order to effect a charge transfer process in which electrical charge is transferred from the first Y-capacitance, in particular from the first Y-capacitor, to the second Y-capacitance, in particular to the second Y-capacitor.

[0017] If necessary, a transfer process of electrical charge can be effected alternately from the second Y-capacitance, in particular from the second Y-capacitance, to the first Y-capacitance, in particular to the first Y-capacitor (by closing the measuring switching element), and then back from the first Y-capacitance, in particular from the first Y-capacitor, to the second Y-capacitance, in particular to the second Y-capacitor (by opening the measuring switching element). The device is further configured to acquire measurement data relating to the temporal variation of the voltage at the second Y-capacitance, in particular at the second Y-capacitor, during the transfer process. The measurement data can comprise a temporal sequence of measured values ​​of the voltage at the second Y-capacitance, in particular at the second Y-capacitor, (or a voltage proportional thereto) during the transfer process.The device can be configured to record the measurement data relating to the time profile of the voltage at the second Y-capacitance, in particular at the second Y-capacitor, during the charging process using the measuring unit of the insulation monitoring unit.

[0018] Furthermore, the device is configured to determine the capacitance information based on the time profile and using a proportionality coefficient, in particular using a proportionality factor. The proportionality coefficient can depend on whether the second Y-capacitance, in particular the second Y-capacitor, is charged or discharged during the recharging process. In particular, it can be determined whether the measurement data were acquired for a recharging process in which the second Y-capacitance, in particular the second Y-capacitor, was discharged. A first proportionality coefficient can then be used to determine the capacitance information.On the other hand, if it is detected that measurement data were acquired for a recharging process in which the second Y-capacitance, in particular the second Y-capacitor, was charged, a second proportionality coefficient may be used which differs from the first proportionality coefficient.

[0019] The proportionality coefficients (for a charging or discharging process of the second Y-capacitance, in particular the second Y-capacitor) can be determined experimentally in advance and, if necessary, stored in a memory unit of the motor vehicle. The capacity information can include an estimated value of the one or more Y-capacitances (in particular an estimated value of the average capacity or the total capacity) and / or an estimated value of the capacity of the one or more Y-capacitors of the energy supply system.

[0020] By using an asymmetric insulation monitoring unit in combination with different proportionality coefficients for a charging or discharging process of the second Y-capacitance, in particular the second Y-capacitor, the capacitance information relating to the one or more Y-capacitances of the energy supply system can be determined in a particularly efficient and precise manner.

[0021] The device can be configured to determine a time constant of the voltage variation across the second Y-capacitance, in particular across the second Y-capacitor, based on the measurement data. The capacitance information can then be determined particularly precisely based on the time constant and using the proportionality coefficient.

[0022] The device may be configured to determine the capacity information based on the following formula, where TLade / Entiade is the time constant, where KlLade / £ntZadeder c ~~c

[0023] is the proportionality coefficient, and where y+ 2 y~ is a value, in particular the mean value, of the first Y-capacitance and the second Y-capacitance, in particular of the capacitances of the first Y-capacitor and the second Y-capacitor. In this way, the capacitance information can be determined in a particularly precise manner. The device can be configured to determine a resistance value of at least one insulation resistance (in particular of the first and / or the second insulation resistance) of the energy supply system using the asymmetrical insulation monitoring unit, in particular using the recorded measurement data. The capacitance information can then also be determined in a particularly precise manner on the basis of the determined resistance value of the insulation resistance. In particular, the proportionality coefficient (specific for the charging or discharging process) can be determined.The discharge process of the second Y capacitor can be determined based on the measured insulation resistance value and then used to determine the capacitance information. This can further increase the accuracy of the capacitance information.

[0024] The device can in particular be designed to calculate a resistance coefficient K based on the following formula w to determine

[0025] This is

[0026] • Riso+ is the resistance value of the first insulation resistor (which is arranged in particular in parallel with the first Y-capacitance);

[0027] • Riso- the resistance value of the second insulation resistor (which is arranged in particular in parallel with the second Y-capacitance);

[0028] • Rmess is the value of the measuring resistor used to acquire the measurement data (where the measuring resistor can correspond to the series connection of the resistors Rc and Rd mentioned in this document and / or can be expressed by the series connection of the resistors Rc and Rd; in particular, the measuring resistor R mess the resistance of the second resistor series circuit); and / or

[0029] • 11 an operator that determines the effective resistance value of the parallel circuit from the resistance specified before and after the operator. The resistance coefficient K w is typically independent of whether the second Y-capacitance is charged or discharged during the transfer process.

[0030] The device can be configured to calculate the proportionality coefficient (and thus the capacitance information) on the basis of the resistance coefficient K wIn particular, the proportionality coefficient can be determined as where K La a e / Unload e i n (experimentally determined) basic proportionality coefficient, which depends on whether the second Y-capacitance is charged or discharged during the transfer process. The basic proportionality coefficient can be determined in advance (experimentally) and stored in a memory unit (since the basic proportionality coefficient is typically constant and remains unchanged during operation of the power supply system). On the other hand, the resistance coefficient K w during operation of the power supply system (at any given time). This can further increase the accuracy of the capacity information.

[0031] The proportionality coefficient described in this document, in particular the basic proportionality coefficient, allows the asymmetry of the asymmetric insulation monitoring unit used to be taken into account in an efficient and precise manner when determining the capacitance information.

[0032] The device can be configured to determine a first final voltage at the second Y-capacitance after completion of a charge transfer process in which the second Y-capacitance is discharged. The first final voltage can be determined on the basis of the measurement data relating to the time profile of the voltage at the second Y-capacitance during a charge transfer process in which electrical charge is transferred from the second Y-capacitance to the first Y-capacitance. Furthermore, the device can be configured to determine a second final voltage at the second Y-capacitance after completion of a charge transfer process in which the second Y-capacitance is charged. The second final voltage can be determined on the basis of the measurement data relating to the time profile of the voltage at the second Y-capacitance during a charge transfer process in which electrical charge is transferred from the first Y-capacitance to the second Y-capacitance.

[0033] The capacitance information, in particular the proportionality coefficient, can be determined in a particularly efficient and precise manner based on the first end voltage and the second end voltage. The first and second end voltages can be used instead of the resistance values ​​of the first and second insulation resistors to determine the capacitance information, in particular the proportionality coefficient, in a particularly efficient and precise manner. In particular, the above-mentioned resistance coefficient K w determined based on the first and second final voltage.

[0034] The capacitance information, in particular the proportionality coefficient, is preferably determined using a predefined model for the insulation monitoring unit, wherein the model can depend on one or more resistors (in particular on the resistor series circuits) of the insulation monitoring unit.

[0035] The device can be configured to determine, based on the capacitance information, that the first Y capacitance, in particular the first Y capacitor, and / or the second Y capacitance, in particular the second Y capacitor, exhibit an impairment. For this purpose, the capacitance information can be compared with one or more threshold values. In response to a detected impairment, an indication can be output to a user of the motor vehicle. This can ensure particularly safe and reliable operation of the motor vehicle and / or the energy supply system. The device can be configured to determine the capacitance information repeatedly, in particular periodically (in each case based on currently acquired measurement data). Current capacitance information can be determined at a sequence of consecutive points in time.Furthermore, based on the current capacity information, it is possible to check whether there is any impairment of one or more Y-capacitances, in particular of one or more Y-capacitors. If an impairment is present, a notification can be issued to the user of the motor vehicle. By repeatedly determining capacity information, a change in one or more Y-capacitances, in particular the capacity of one or more Y-capacitors, can be detected particularly reliably and quickly.

[0036] The device can be configured to determine first capacitance information based on the measurement data for a charge transfer process in which the second Y-capacitance, in particular the second Y-capacitor, is discharged (and using the first proportionality coefficient). Furthermore, second capacitance information can be determined based on the measurement data for a (possibly directly subsequent) charge transfer process in which the second Y-capacitance, in particular the second Y-capacitor, is charged (and using the second proportionality coefficient). The capacitance information relating to the one or more Y-capacitances, in particular relating to the capacitance of the one or more Y-capacitors, can then be determined in a particularly precise manner based on the first capacitance information and the second capacitance information (in particular based on the sum and / or the mean value of the first capacitance information and the second capacitance information).

[0037] According to a further aspect, an electrical energy supply system for a motor vehicle is described. The energy supply system comprises an electrical energy storage device (for storing electrical energy) and a first and a second potential line, which are coupled to the first and second poles (e.g., to the positive pole and the negative pole, respectively) of the electrical energy storage device. Electrical energy from the electrical energy storage device can be provided via the potential lines for operating an electrical (drive) machine of the motor vehicle. The nominal voltage at the electrical energy storage device and / or between the two potential lines can be 300V or more, in particular 400V or more.

[0038] The energy supply system further comprises (e.g. for EMC purposes) a first Y-capacitance, in particular a first Y-capacitor, which is arranged between the first potential line and a reference potential, in particular the vehicle ground, and a second Y-capacitance, in particular a second Y-capacitor, which is arranged between the second potential line and the reference potential.

[0039] Furthermore, the power supply system comprises an asymmetric insulation monitoring unit configured to monitor the first insulation resistance between the first potential line and the reference potential and / or the second insulation resistance between the second potential line and the reference potential. The asymmetric insulation monitoring unit advantageously preferably has only a single measuring switching element (e.g., a MOSFET or IGBT) in order to be able to perform the measurements for monitoring the two insulation resistances.

[0040] The energy supply system further comprises the device described in this document, which is configured to determine capacitance information relating to the first Y capacitance and / or the second Y capacitance, in particular relating to the capacitance of the first Y capacitor and / or the second Y capacitor. The capacitance information may comprise an estimated value of the first Y capacitance and / or the second Y capacitance and / or an estimated value of the capacitance of the first Y capacitor and / or the second Y capacitor (in particular the mean value and / or the total value of the capacitances of the first Y capacitor and the second Y capacitor).

[0041] 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 energy supply system described in this document.

[0042] According to a further aspect, a method for determining capacitance information relating to at least one Y capacitance, in particular relating to the capacitance of at least one Y capacitor, of a power supply system of a motor vehicle is described. The method comprises changing the switching state of a measuring switching element of an asymmetric insulation monitoring unit of the motor vehicle, such that a transfer process of electrical charge is effected between a first Y capacitance, in particular between a first Y capacitor, and a second Y capacitance, in particular a second Y capacitor, of the power supply system of the motor vehicle (in which the second Y capacitance, in particular the second Y capacitor, is charged or discharged).

[0043] The method further comprises acquiring measurement data relating to the temporal variation of the voltage at the second Y-capacitance, in particular at the second Y-capacitor, during the charging process, and determining the capacitance information based on the temporal variation using a proportionality coefficient. The proportionality coefficient can depend on whether the second Y-capacitance, in particular the second Y-capacitor, is being charged or discharged during the charging process.In particular, a first proportionality coefficient can be used to determine the capacitance information when the second Y-capacitance, in particular the second Y-capacitor, is discharged during the charging process, and a (different) second proportionality coefficient can be used to determine the capacitance information when the second Y-capacitance, in particular the second Y-capacitor, is charged during the charging process.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] Figure 1a shows exemplary components of a vehicle with an electric drive motor;

[0049] Figure 1b shows an exemplary asymmetric insulation monitoring unit;

[0050] Figure 2a shows an exemplary voltage curve when discharging the second Y capacitor;

[0051] Figure 2b shows an example of a voltage curve when charging the second Y capacitor; and

[0052] Figure 3 is a flowchart of an exemplary method for determining capacitance information relating to the capacitance of at least one Y capacitor of an electrical energy supply system of a motor vehicle.

[0053] As stated at the outset, this document is concerned with efficiently and reliably detecting a possible impairment of a Y capacitor of an electrical power supply 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.

[0054] 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.

[0055] 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).

[0056] 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.

[0057] 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.

[0058] Fig. 1b shows an 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-.

[0059] 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).

[0060] The measurement 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. 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 resistor series circuits is coupled to ground 153 (generally to the reference potential).

[0061] Using the measuring unit 156, measuring currents can be determined for the two measuring situations or switching states “measuring switching element 155 closed” and “measuring switching element 155 open”, which can be used to determine the values ​​of the insulation resistances Riso+ and Riso-.

[0062] The energy storage device 130 and the potential lines 151, 152 are part of a power supply 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 power supply 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. The (voltage) measured values ​​recorded during insulation resistance monitoring can be used efficiently to determine the condition of the Y capacitors C y +, C y . to monitor, especially to detect early impairment of a Y capacitor C y +, C y . to recognize.

[0063] It should be noted that the aspects described in this document for one or more Y-capacitors are generally applicable to one or more Y-capacitances. A Y-capacitance can include the capacitance of a Y-capacitor and, if applicable, one or more other parasitic components.

[0064] For this purpose, as shown by way of example in Figures 2a and 2b, the time course 221, 241 of the voltage 200 at the second Y-capacitor C 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.

[0065] The subsequent opening of the measuring switching element 155 (at time 231) leads to a charging of the second Y capacitor C y . and a rising voltage curve 241, wherein the voltage 200 increases from the second voltage 202 to the first voltage 201. The charge for charging the second Y capacitor C y . is supplied by the first Y capacitor C y + provided.

[0066] The falling voltage curve 221 can be represented by a first reference curve 222 (e.g. an exponential curve or a hyperbola) with a first time constant T Discharge can be approximated, and the rising voltage curve 241 can be represented by a second reference curve 242 (e.g. an exponential curve or a hyperbola) with a second time constant La de can be approximated. From the time constants, an estimate of the capacitance of the Y capacitors C can be calculated using the following formula y+, C y . can be determined:

[0067] The proportionality factor ^Charge / Discharge when using an asymmetric insulation monitoring unit 150 depends on whether a discharge or a charging of the second Y-capacitor C y . The proportionality factors ^charge / discharge can be determined experimentally in advance (and stored on a memory unit). The device 101 of the vehicle 100 can be configured to obtain capacitance information regarding the capacitance of the Y capacitors C during operation of the vehicle 100 using the method described in this document. y +, C y . In particular, a c ~~c

[0068] Estimated value for y+ 2 y ~ (or a value proportional to it). Based on the capacitance information, it can be determined whether there is a defect in the Y capacitors C y +, C y. For this purpose, the determined capacitance of the Y capacitors C y +, C y . be compared with a predefined capacitance threshold. If the determined capacitance of the Y capacitors C y +, C y . is smaller than the capacitance threshold, the Y capacitors C y +, C y . can be detected. Furthermore, an indication of the detected impairment of the Y capacitors C y +, C y . be issued.

[0069] The insulation monitoring of a power supply system is thus used to determine the capacitances of the Y capacitors. A passive insulation monitor 150 uses voltage measurements to indirectly determine insulation resistance. Different switching states of the insulation monitor 150 result in charging and discharging curves 221, 241 in the voltage profile. These charging processes occur via the Y capacitors between the HV potentials 151, 152 and the vehicle ground 153. The capacitance of the Y capacitors can be determined from the temporal progression of the charging processes.

[0070] Fig. 3 shows a flowchart of a (possibly computer-implemented) method 300 for determining capacitance information with respect to the capacitance of at least one Y-capacitor C y +, C y. of the energy supply system of a motor vehicle 100. The energy supply system can be designed to provide electrical energy for operating an electric drive motor 103 of the motor vehicle 100. The energy supply system can have a first Y-capacitor C y + between the first potential line 151 (e.g. the plus line) and the reference potential 153 (in particular the vehicle ground), as well as a second Y-capacitor C y . between the second potential line 152 (e.g., the negative line) and the reference potential 153. The method 300 can be carried out by a (control) device 101 of the motor vehicle 100.

[0071] The method 300 comprises changing 301 the switching state of the measuring switching element (e.g. the MOSFET) 155 of the asymmetric insulation monitoring unit 150 (of the power supply system) of the motor vehicle 100, so that a transfer process of electrical charge between the first Y-capacitor C y + and the second Y capacitor C y . of the power supply system of the motor vehicle 100. Depending on the switching state, electrical charge can be transferred from the first Y-capacitor C y + to the second Y capacitor C y . transmitted (e.g. when opening the measuring switching element 155), or from the second Y-capacitor C y . on the first Y-capacitor C y + transmitted (e.g., when the measuring switching element 155 is closed). The change 301 in the switching state of the measuring switching element 155 can be effected as part of the monitoring of one or more insulation resistances of the power supply system.

[0072] The method 300 further comprises the acquisition 302 of measurement data relating to the time course 221, 222 of the voltage 200 at the second Y-capacitor C y . during the charging process. In particular, it is possible to determine the time constant with which the voltage 200 increases or decreases.

[0073] Furthermore, the method 300 comprises determining 303 the capacitance information relating to the capacitance of the one or more Y capacitors based on the time profile 221, 222 using a proportionality coefficient (in particular a proportionality factor). The proportionality coefficient can have been determined experimentally in advance (and stored in a memory unit of the motor vehicle). Furthermore, the proportionality coefficient can depend on whether the second Y capacitor Cy- is being charged or discharged during the recharging process. In particular, a different proportionality coefficient can be used when the second Y capacitor Cy- is being charged than when the second Y capacitor Cy- is being discharged.

[0074] The use of an asymmetric insulation monitor 150 in combination with the use of different proportionality coefficients for the charging and discharging process allows the capacitance of one or more Y capacitors of the motor vehicle's power supply system to be determined in a particularly efficient and precise manner.

[0075] The present invention is not limited to the embodiments shown. In particular, it should be noted that the description and the figures only exemplify the principle of the proposed methods, devices and

[0076] systems are intended to illustrate.

Claims

Claims 1) Device (101) for determining capacity information with respect to at least one Y-capacitance (C y +, C y .) of a power supply system of a motor vehicle (100); wherein the device (101) is arranged - to change a switching state of a measuring switching element (155) of an asymmetric insulation monitoring unit (150) of the motor vehicle (100) so that a transfer process of electrical charge between a first Y-capacitance (C y +) and a second Y-capacitance (C y .) of the energy supply system of the motor vehicle (100); - measurement data relating to a time profile (221, 222) of a voltage (200) at the second Y-capacitance (C y .) during the transfer process; and - to determine the capacity information on the basis of the time profile (221, 222) using a proportionality coefficient; wherein the proportionality coefficient depends on whether, during the recharging process, the second Y-capacity (C y .) is charged or discharged. 2) Device (101) according to claim 1, wherein the device (101) is arranged - on the basis of the measurement data, a time constant of the temporal course (221, 222) of the voltage (200) at the second Y-capacitance (C y .) and - to determine the capacity information based on the time constant and using the proportionality coefficient. 3) Device (101) according to claim 2, wherein the device (101) is arranged to determine the capacity information based on the following formula, where T charge / discharge is the time constant, where Klcharge / discharge c ~~c is the proportionality coefficient, and where y+ 2 y ~ an average value of the first Y-capacitance (C y +) and the second Y-capacitance (C y .) is. 4) Device (101) according to one of the preceding claims, wherein - the energy supply system comprises an electrical energy store (130) and a first and a second potential line (151, 152) which are coupled to a first and a second pole of the electrical energy store (130), respectively; - the first Y-capacitance (C y +) is arranged between the first potential line (151) and a reference potential (153), in particular a vehicle ground; - the second Y-capacitance (C y .) is arranged between the second potential line (152) and the reference potential (153); and - the asymmetric insulation monitoring unit (150) is configured to monitor a first insulation resistance (Riso+) between the first potential line (151) and the reference potential (153) and / or a second insulation resistance (Riso-) between the second potential line (152) and the reference potential (153). 5) Device (101) according to claim 4, wherein - the asymmetric insulation monitoring unit (150) has a first resistor series circuit (Ra, Rb) and a second resistor series circuit (Rc, Rd); - the first resistor series circuit (Ra, Rb) is arranged between the first potential line (151) and the reference potential (153); - the second resistor series circuit (Rc, Rd) is arranged between the second potential line (152) and the reference potential (153); and - the measuring switching element (155) is designed to couple an intermediate point within the first resistor series circuit (Ra, Rb) directly to the second potential line (152) or to decouple it therefrom depending on the switching state. 6) Device (101) according to claim 5, wherein the device (101) is arranged - to cause the measuring switching element (155) to be closed, so that the intermediate point within the first resistor series circuit (Ra, Rb) is directly coupled to the second potential line (152) in order to cause a charge reversal process in which electrical charge is transferred from the second Y-capacitance (C y .) to the first Y-capacitance (C y +) is transshipped; and / or - to cause the measuring switching element (155) to be opened so that the intermediate point within the first resistor series circuit (Ra, Rb) is decoupled from the second potential line (152) in order to cause a charge reversal process in which electrical charge is transferred from the first Y-capacitance (C y +) to the second Y-capacitance (C y .) is reloaded. 7) Device (101) according to one of claims 5 to 6, wherein - the first resistor series circuit (Ra, Rb) and the second resistor series circuit (Rc, Rd) each comprise two resistors connected in series; and / or - the first resistor series circuit (Ra, Rb) and the second resistor series circuit (Rc, Rd) have the same resistance values. 8) Device (101) according to one of claims 5 to 7, wherein - the asymmetric insulation monitoring unit (150) has a measuring unit (156) for measuring a voltage across a resistor (Rd) of the second resistor series circuit (Rc, Rd); and - the device (101) is arranged to record the measurement data relating to the time profile (221, 222) of the voltage (200) at the second Y-capacitance (C y .) during the transfer process using the measuring unit (156). 9) Device (101) according to one of the preceding claims, wherein the device (101) is arranged - to determine a resistance value of at least one insulation resistance (Riso+, Riso-) of the power supply system using the asymmetric insulation monitoring unit (150); and - to determine the capacitance information also on the basis of the determined resistance value of the insulation resistance (Riso+, Riso-). 10) Device (101) according to claim 9, wherein - the device (101) is arranged to determine a resistance coefficient K based on the following formula w to determine - R IS o+ is the resistance value of a first insulation resistor, which is connected in particular in parallel with the first Y-capacitance (C y +) is arranged; - Riso- is the resistance value of a second insulation resistance, which is connected in particular in parallel with the second Y-capacitance (C y .) is arranged; - R mess is the value of a measuring resistor for recording the measurement data; - 11 is an operator which determines the effective resistance value of the parallel circuit from the resistance specified before and after the operator; - the resistance coefficient K w regardless of whether the second Y-capacity (C y .) is being charged or discharged; and - the device (101) is arranged to calculate the proportionality coefficient on the basis of the resistance coefficient K w to determine. 11) Device (101) according to one of the preceding claims, wherein the device (101) is arranged - in particular on the basis of the measurement data relating to the time course (221, 222) of the voltage (200) at the second Y-capacitance (C y .) during a recharging process, in which electrical charge is transferred from the second Y-capacitance (C y .) to the first Y-capacitance (C y +), a first final voltage at the second Y-capacitance (C y .) after completion of the transshipment process; - in particular on the basis of the measurement data relating to the time course (221, 222) of the voltage (200) at the second Y-capacitance (C y .) during a recharging process, in which electrical charge is transferred from the first Y-capacitance (C y +) to the second Y-capacitance (Cy .), a second final voltage is applied to the second Y-capacitance (C y .) after completion of the transfer process; and - to also determine the capacity information based on the first end voltage and the second end voltage. 12) Device (101) according to claim 11, wherein - the device (101) is arranged to determine the capacity information based on a predefined model for the insulation monitoring unit (150); and the model depends in particular on one or more resistors (Ra, Rb, Rc, Rd) of the insulation monitoring unit (150). 13) Device (101) according to one of the preceding claims, wherein the device (101) is arranged - to determine on the basis of the capacity information that the first Y capacity (C y +) and / or the second Y-capacitance (C y .) have an impairment; and - in response thereto, to cause an indication to be issued to a user of the motor vehicle (100). 14) Electrical power supply system for a motor vehicle (100), the power supply system comprising - an electrical energy store (130) and a first and a second potential line (151, 152) which are coupled to a first and a second pole of the electrical energy store (130), respectively; - a first Y-capacitance (C y +), which is arranged between the first potential line (151) and a reference potential (153), in particular a vehicle ground; - a second Y-capacitance (C y .) arranged between the second potential line (152) and the reference potential (153); - an asymmetric insulation monitoring unit (150) configured to monitor a first insulation resistance (Riso+) between the first potential line (151) and the reference potential (153) and / or a second insulation resistance (Riso-) between the second potential line (152) and the reference potential (153); and - a device (101) according to one of the preceding claims, which is arranged to provide capacity information relating to the first Y-capacitance (C y +) and / or the second Y-capacitance (C y .) to determine. 15) Method (300) for determining capacity information relating to the capacity of at least one Y-capacitance (C y +, C y .) of an energy supply system of a motor vehicle (100); wherein the method (300) comprises - Changing (301) a switching state of a measuring switching element (155) of an asymmetric insulation monitoring unit (150) of the motor vehicle (100), so that a transfer process of electrical charge between a first Y-capacitance (C y +) and a second Y-capacitance (C y .) of the energy supply system of the motor vehicle (100); - detecting (302) measurement data relating to a time profile (221, 222) of a voltage (200) at the second Y-capacitance (C y .) during the transfer process; and - determining (303) the capacity information on the basis of the time profile (221, 222) using a proportionality coefficient; wherein the proportionality coefficient depends on whether, during the recharging process, the second Y-capacity (C y .) is charged or discharged.

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