Patent ID: 12199317

DETAILED DESCRIPTION

In the following description of the embodiments of the invention, identical or similar elements are denoted using identical reference signs, in which case a repeated description of these elements is dispensed with in individual cases. The figures only schematically illustrate the subject matter of the invention.

FIG.1shows a schematic illustration of a first embodiment of a battery system10proposed according to the invention.

In this case, the battery system10comprises a battery pack5that has a negative pole21, a positive pole22and a plurality of battery cells2connected in series with one another, each having a cell voltage UZ, and a pack voltage divider25.

The battery system10furthermore comprises a coupling network that has a first negative terminal11and a first positive terminal12, and a coupling voltage divider15. In this case, the first positive terminal12is able to be connected to the positive pole22by way of a positive main switch SH+ and the first negative terminal11is able to be connected to the negative pole21by way of a negative main switch SH−. The main switches SH+, SH− are designed for example in the form of electromechanical relays or contactors.

The pack voltage divider25in this case has a positive pack measurement resistor RP+ and a positive sub-pack measurement resistor RSP+ that are connected in series with one another between the positive pole22and a first reference point50and are able to be disconnected from the positive pole22or the first reference point50by way of a positive pack measurement switch SP+. The pack voltage divider25furthermore has a negative pack measurement resistor RP− and a negative sub-pack measurement resistor RSP− that are connected in series with one another between the negative pole21and the first reference point50and are able to be disconnected from the negative pole21or the first reference point50by way of a negative pack measurement switch SP−. The first reference point50in this case constitutes a floating reference potential for a voltage measurement.

The battery system10furthermore has an insulation voltage divider27. The insulation voltage divider27in this case comprises a positive insulation measurement resistor RIso+ and a positive sub-insulation measurement resistor RSIso+ that are connected in series with one another between the positive pole22and a second reference point60and are able to be disconnected from the positive pole22or the second reference point60by way of a positive insulation measurement switch SIso+. The insulation voltage divider27also comprises a negative insulation measurement resistor RIso− and a negative sub-insulation measurement resistor RSIso− that are connected in series with one another between the negative pole21and the second reference point60and are able to be disconnected from the negative pole21or the second reference point60by way of a negative insulation measurement switch SIso−. The second reference point60in this case constitutes a ground potential for a voltage measurement.

The respective measurement switches SP+, SP−, SIso+, SIso− are designed for example in the form of MOSFETs or relays.

A positive pack measured voltage UP+ dropped across the positive sub-pack measurement resistor RSP+ is measured by a high-voltage measurement channel. Likewise, a negative pack measured voltage UP− dropped across the negative sub-pack measurement resistor RSP− is measured by a high-voltage measurement channel. A pack voltage UP is calculated from the positive and the negative pack measured voltage UP+, UP−.

A positive insulation measured voltage UIso+ dropped across the positive sub-insulation measurement resistor RSIso+ is measured by a low-voltage measurement channel. Likewise, a negative insulation measured voltage UIso− dropped across the negative sub-insulation measurement resistor RSIso− is measured by a low-voltage measurement channel. An insulation voltage UIso is calculated from the positive and the negative insulation measured voltage USio+, UIso−.

The coupling network also has an intermediate circuit capacitor CL that is connected between the first positive terminal12and the first negative terminal11.

The coupling voltage divider15in this case has a positive coupling measurement resistor RK+ and a positive sub-coupling measurement resistor RSK+ that are connected in series with one another between the first positive terminal12and the first reference point50. The coupling voltage divider15furthermore has a negative coupling measurement resistor RK− and a negative sub-coupling measurement resistor RSK− that are connected in series with one another between the first negative terminal11and the first reference point50.

A positive coupling measured voltage UK+ dropped across the positive sub-coupling measurement resistor RSK+ is measured by a high-voltage measurement channel. Likewise, a negative coupling measured voltage UK− dropped across the negative sub-coupling measurement resistor RSK− is measured by a high-voltage measurement channel. A coupling voltage UK is calculated from the positive and the negative coupling measured voltage UK+, UK−.

The battery system10also comprises a positive main fuse42and, for the diagnosis thereof, a first positive auxiliary voltage divider44. In this case, the positive main fuse42is connected between the positive main switch SH+ and the first positive terminal12. In this case, the first positive auxiliary voltage divider44comprises a positive main fuse measurement resistor RHS+ and a positive sub-main fuse measurement resistor RSHS+ that are connected in series with one another between a first connection of the positive main fuse42, which is connected to the positive main switch SH+, and the first reference point50.

A first positive auxiliary measured voltage US1+ dropped across the positive sub-main fuse measurement resistor RSHS+ is measured by a high-voltage measurement channel.

The coupling network furthermore has a second positive terminal14for connecting the battery system10to a charger, such as for example a vehicle charger. In this case, a positive charging fuse46is connected to a second positive auxiliary voltage divider48between the second positive terminal14and the first positive terminal12. The second positive auxiliary voltage divider48in this case comprises a positive charging fuse measurement resistor RLS+ and a positive sub-charging fuse measurement resistor RSLS+ that are connected in series with one another between the second positive terminal14and the first reference point50.

A second positive auxiliary measured voltage US2+ dropped across the positive sub-charging fuse measurement resistor RSLS+ is measured by a high-voltage measurement channel.

The battery system10furthermore comprises a fast-charging network. The fast-charging network in this case has a negative fast-charging connection31and a positive fast-charging connection32. The positive fast-charging connection32is in this case able to be connected to the first positive terminal12by way of a positive charging switch SL+ and the negative fast-charging connection31is able to be connected to the first negative terminal11by way of a negative charging switch SL−. The battery system10furthermore comprises a charging voltage divider35. The charging voltage divider35in this case comprises a positive charging measurement resistor RL+ and a positive sub-charging measurement resistor RSL+ that are connected in series with one another between the positive fast-charging connection32and the first reference point50, and a negative charging measurement resistor RL− and a negative sub-charging measurement resistor RSL− that are connected in series between the negative fast-charging connection31and the first reference point50. The charging switches SL+, SL− are designed for example in the form of electromechanical relays or contactors.

A positive charging measured voltage UL+ dropped across the positive sub-charging measurement resistor RSL+ is measured by a high-voltage measurement channel. Likewise, a negative charging measured voltage dropped across the negative sub-charging measurement resistor RSL− is measured by a high-voltage measurement channel. A charging voltage UL is calculated from the positive and the negative charging measured voltage UL+, UL−.

The positive pack measurement resistor RP+ in the present case has a value of 5 MΩ. The positive sub-pack measurement resistor RSP+ in the present case has a value of 50 kΩ. The negative pack measurement resistor RP− in the present case has a value of 5 MΩ. The negative sub-pack measurement resistor RSP− in the present case has a value of 50 kΩ. A resistance ratio of the pack voltage divider25corresponds approximately to a ratio of the positive pack measurement resistor RP+ to the negative pack measurement resistor RP−. In the present case, the resistance ratio of the pack voltage divider25is thus:
RP+/RP−=5/5=1

The positive insulation measurement resistor RIso+ in the present case has a value of 1 MΩ. The positive sub-insulation measurement resistor RSIso+ in the present case has a value of 10 kΩ. The negative insulation measurement resistor RSIso− in the present case has a value of 1 MΩ. The negative sub-insulation measurement resistor RSIso− in the present case has a value of 10 kΩ. A resistance ratio of the insulation voltage divider27corresponds approximately to a ratio of the positive insulation measurement resistor RIso+ to the negative insulation measurement resistor RIso−. In the present case, the resistance ratio of the insulation voltage divider27is thus:
RIso+/RIso−=1/1=1

The positive coupling measurement resistor RK+ in the present case has a value of 3 MΩ. The positive sub-coupling measurement resistor RSK+ in the present case has a value of 30 kΩ. The negative coupling measurement resistor RK− in the present case has a value of 7 MΩ. The negative sub-coupling measurement resistor RSK− in the present case has a value of 70 kΩ. A resistance ratio of the coupling voltage divider15corresponds approximately to a ratio of the positive coupling measurement resistor RK+ to the negative coupling measurement resistor RK−. In the present case, the resistance ratio of the coupling voltage divider15is thus:
RK+/RK−=3/7≈0.429

The positive charging measurement resistor RL+ in the present case has a value of 7 MΩ. The positive sub-charging measurement resistor RSL+ in the present case has a value of 70 kΩ. The negative charging measurement resistor RL− in the present case has a value of 3 MΩ. The negative sub-charging measurement resistor RSL− in the present case has a value of 30 kΩ. A resistance ratio of the charging voltage divider35corresponds approximately to a ratio of the positive charging measurement resistor RL+ to the negative charging measurement resistor RL−. In the present case, the resistance ratio of the charging voltage divider35is thus:
RL+/RL−=7/3≈2.333

The battery system10furthermore comprises a control device70that has a microcontroller72having a low-voltage A/D converter73for converting analog measured data from the low-voltage measurement channels into digital data. The measurement points of the insulation voltage dividers27are in this case electrically connected to the low-voltage A/D converter73or the low-voltage measurement channels of the low-voltage A/D converter73.

The control device70furthermore comprises a high-voltage A/D converter74for converting analog measured data from the high-voltage measurement channels into digital data. The measurement points of the pack voltage divider25, of the coupling voltage divider15, of the charging voltage divider35, of the first positive auxiliary voltage divider44and of the second positive auxiliary voltage divider48are in this case electrically connected to the high-voltage A/D converter74or the high-voltage measurement channels of the high-voltage A/D converter74. The first reference point50is also electrically connected to the high-voltage A/D converter74. The high-voltage A/D converter74is in this case connected to the microcontroller72via a galvanically isolated communication bus76.

The pack voltage divider25, the insulation voltage divider27, the coupling voltage divider15, the charging voltage divider35, the first positive auxiliary voltage divider44and the second positive auxiliary voltage divider48may also in this case be installed in the control device70.

Provision is furthermore made, for the positive main switch SH+, for a precharging circuit40that is connected in parallel with the positive main switch SH+ and has a precharging resistor RVL and a precharging switch SVL connected in series with the precharging resistor RVL.

The following table illustrates the calculation of the pack voltage UP of the battery pack5, of the voltages USH+, USH1−, USL+, USL− dropped across the respective switch SH+, SH−, SL+, SL−, of the voltages UHS+, ULS+ dropped across the respective positive fuses42,46, of the coupling voltage UK and of the charging voltage UL from the abovementioned measured voltages UP+, UP−, UK+, UK−, UL+, UL−, US1+, US2+. By way of example, the pack voltage UP is calculated by subtracting the negative pack measured voltage UP− (subtrahend) from the positive pack measured voltage UP+(minuend), that is to say the pack voltage UP is given by the formula UP=UP+−UP−.

SubtrahendUP+UP−US1+UK+UK−UL+UL−US2+MinuendUP+—UPUSH+—————UP−————USH−———US1+———UHS+————UK+————UKUSL+—USL+UK−——————USL−—UL+——————UL—UL−————————US2+————————

FIG.2shows a schematic illustration of a second embodiment of the battery system10proposed according to the invention. In this case, the second embodiment of the battery system10proposed according to the invention is illustrated in highly simplified form.

The battery system10in this case comprises two battery packs5, specifically a first battery pack51and a second battery pack52. The two battery packs51,52are each designed in a manner identical to the battery pack5inFIG.1, and each comprises a negative pole21, a positive pole22, and a plurality of battery cells2connected in series with one another. The battery system10in this case comprises two pack voltage dividers25(cf.FIG.1) that are each assigned to a battery pack51,52. The two battery packs51,52are in this case connected in series with one another between the positive pole22of the first battery pack51and the negative pole21of the second battery pack52by way of a pack switch SPP. A first positive main switch SH1+ and a first negative main switch SH1− are provided for the first battery pack51. A second positive main switch SH2+ and a second negative main switch SH2− are provided for the second battery pack52. A respective precharging circuit40is provided for the two positive main switches SH1+, SH2. The precharging circuit40for the first positive main switch SH1+ is connected in parallel with the first positive main switch SH1+ and in this case comprises a first precharging resistor RVL1and a first precharging switch SVL1connected in series with the first precharging resistor RVL1. The precharging circuit40for the second positive main switch SH2+ is connected in parallel with the second positive main switch SH2+ and in this case comprises a second precharging resistor RVL2and a second precharging switch SVL2connected in series with the second precharging resistor RVL2.

The battery system10comprises a coupling network that has a first negative terminal11and a first positive terminal12, and a coupling voltage divider15(cf.FIG.1). The first negative terminal11is in this case able to be connected to the negative pole21of the first battery pack51by way of the first negative main switch SH1− and is able to be connected to the negative pole21of the second battery pack52by way of the second negative main switch SH2−. The first positive terminal12is in this case able to be connected to the positive pole22of the first battery pack51by way of the first positive main switch SH1+ and is able to be connected to the positive pole22of the second battery pack52by way of the second positive main switch SH2+. The coupling network furthermore comprises a second positive terminal14for connecting the battery system10to a charger, such as for example a vehicle charger. The second positive terminal14is in this case connected to the first positive terminal12via a positive charging fuse46.

The battery system10furthermore comprises a fast-charging network that has a negative fast-charging connection31and a positive fast-charging connection32, and a charging voltage divider35(cf.FIG.1). The negative fast-charging connection31is able to be connected to the negative pole21of the first battery pack51by way of a negative charging switch SL−. The positive fast-charging connection32is able to be connected to the positive pole22of the second battery pack52by way of a positive charging switch SH+.

To simplify the illustration inFIG.2, the two pack voltage dividers25, the coupling voltage divider15and the charging voltage divider35are not illustrated. For the positive charging fuse46, provision is made for a second positive auxiliary voltage divider48(cf.FIG.1), this likewise not being illustrated inFIG.2.

The method proposed according to the invention may be expanded or adapted for the second embodiment of the battery system10proposed according to the invention inFIG.2.

FIG.2schematically shows that a first positive pack measured voltage UP1+, a first negative pack measured voltage UP1−, a second positive pack measured voltage UP2+, a second negative pack measured voltage UP2−, a positive coupling measured voltage UK+, a negative coupling measured voltage UK−, a positive charging measured voltage UL+, a negative charging measured voltage UL- and a second positive auxiliary measured voltage US2+ are measured.

The following table illustrates the calculation of the pack voltages UP1, UP2of the respective battery packs51,52, of the overall pack voltage UPS, of the voltages USH1+, USH2+, USH1−, USH2−, USL+, USL−, USPP dropped across the respective switches SH1+, SH2+, SH1−, SH2−, SL+, SL−, SPP, of the voltage ULS+ dropped across the positive charging fuse46, of the coupling voltage UK and of the charging voltage UL from the abovementioned measured voltages UP1+, UP1−, UP2+, UP2−, UK+, UK−, UL+, UL−, US2+. By way of example, the first pack voltage UP1is calculated by subtracting the first negative pack measured voltage UP1− (subtrahend) from the first positive pack measured voltage UP 1+(minuend), that is to say the first pack voltage UP1is given by the formula UP1=UP1+−UP1−.

SubtrahendUP1+UP1−UP2+UP2−UK+UK−UL+UL−US2+MinuendUP1+—UP1—USPPUSH+————UP1−—————USH1−—USL−—UP2+—UPS—UP2USH2+—USL+——UP2−—————USH2−———UK+—————UK——ULS+UK−—————————UL+———————UL—UK−—————————US2+—————————

FIG.3shows a schematic illustration of temporal profiles of the measured voltages of the battery system10illustrated inFIG.1, and temporal profiles of control signals for controlling the pack measurement switches SP+, SP−, the main switches SH+, SH− and the precharging switch SVL.

FIG.3illustrates a two-dimensional coordinate system100. The two-dimensional coordinate system100in this case comprises a first axis140, on which time is plotted, and a second axis150, perpendicular to the first axis140, on which voltage is plotted.

FIG.3shows a temporal profile102of the floating reference potential of the first reference point50, a temporal profile104of the positive pack measured voltage UP+, a temporal profile106of the negative pack measured voltage UP−, a temporal profile108of the positive coupling measured voltage UK+, a temporal profile110of the negative coupling measured voltage UK− and a temporal profile112of the first positive auxiliary measured voltage US1+.

Likewise shown are a temporal profile130of a control signal for controlling the positive pack measurement switch SP+, a temporal profile132of a control signal for controlling the negative pack measurement switch SP−, a temporal profile134of a control signal for controlling the negative main switch SH−, a temporal profile136of a control signal for controlling the precharging switch SVL and a temporal profile138of a control signal for controlling the positive main switch SH+.

Following an initialization phase114of the high-voltage A/D converter74, a connection check is performed on the high-voltage measurement channels while the main switches SH+, SH− and insulation measurement switches SIso+, SIso− are open. In this case, a first measurement120, a second measurement122, a third measurement124and a fourth measurement126are performed. A set of voltages, specifically a positive pack measured voltage UP+, a negative pack measured voltage UP−, a positive coupling measured voltage UK+, a negative coupling measured voltage UK−, a positive charging measured voltage UL+, a negative charging measured voltage UL−, a first positive auxiliary measured voltage US1+ and a second positive auxiliary measured voltage US2+, is measured in each of the measurements120,122,124,126. In this case, evaluating the voltages UP+, UP−, UK+, UK−, UL+, UL−, US1+, US2+ measured in the respective measurements120,122,124,126makes it possible to check whether the high-voltage measurement channels are connected to the appropriate measurement points. Each measured voltage UP+, UP−, UK+, UK−, UL+, UL−, US1+, US2+ in each of the measurements120,122,124,126is in this case sampled multiple times, preferably 3 to 5 times, and an average of the acquired values is formed. This average of the corresponding measured voltage UP+, UP−, UK+, UK−, UL+, UL−, US1+, US2+ is stored and referred to as measured value of the respective voltages UP+, UP−, UK+, UK−, UL+, UL−, US1+, US2+.

The first measurement120is first performed before closure of the positive and the negative pack measurement switch SP+, SP−. The level of the floating reference potential of the first reference point50is initially undefined. This may be caused for example by an even distribution of the insulation resistances of the battery cells2. The same also applies to the coupling measured voltages UK+, UK−, the magnitude of which depends on the distribution of the insulation resistances of the battery pack5and the external components connected to the coupling network. The residual voltage of the intermediate circuit capacitor CL leads to a difference between the positive coupling measured voltage UK+ and the negative coupling measured voltage UK−. The coupling voltage UK may also be calculated when the measurement of the positive and negative pack measured voltage UP+, UP− has not yet finished, specifically SP+ and/or SP− are open.

Following the first measurement120, an offset drift check may be performed for the high-voltage A/D converter74.

The positive pack measurement switch SP+ is then closed. On account of the pack voltage divider25, the floating reference potential of the first reference point50is brought to a positive pack potential, in this case UP/2. The second measurement122is performed after a waiting time Δt for settling behavior of the potentials following closure of the positive pack measurement switch SP+. Since the floating reference potential is brought to the positive pack potential, a low measured value of the positive pack measured voltage UP+ is acquired. On account of the open main switches SH+, SH−, the coupling voltage UK and the charging voltage UL are decoupled in the first and the second measurement120,122. A respective change is acquired for the coupling measured voltages UK+, UK−, the charging measured voltages UL+, UL- and the first and the second positive auxiliary measured voltage US1+, US2+. In this case, this change corresponds approximately to a negative change in the floating reference potential.

The positive pack measurement switch SP+ is then opened and the negative pack measurement switch SP− is closed. The third measurement124is performed after a waiting time Δt

for settling behavior of the potentials following the closure of the negative pack measurement switch SP−. When the negative pack measurement switch SP− is closed, the floating reference potential is brought to the negative pack potential, here −UP/2. A respective perceptible change is acquired for the coupling measured voltages UK+, UK−, the charging measured voltages UL+, UL− and the first and the second positive auxiliary measured voltage US1+, US2+ between the second measurement122and the third measurement124. In this case, this change likewise corresponds approximately to a negative change in the floating reference potential.

The positive pack measurement switch SP+ is then closed and the fourth measurement126is performed after a waiting time Δt for settling behavior of the potentials following closure of the positive pack measurement switch SP+.

The pack voltage UP, the main switch voltages USH+, USH− and the charging switch voltages USL+, USL− are able to be calculated by way of the measured values, acquired in the respective measurements120,122,124,126, of the respective measured voltages UP+, UP−, UK+, UK−, UL+, UL−, US1+, US2+.

For a battery system10according toFIG.2, the two positive pack measurement switches SP+(cf.FIG.1) and the two negative pack measurement switches SP− (cf.FIG.1) may be connected together in order to achieve a large potential shift of the floating reference potential for the connection check.

If the positive main fuse42has burned through or is defective, it will be expected that the first positive auxiliary measured voltage US1+ will have values of zero until the precharging switch SVL or the positive main switch SH+ is closed. It is therefore necessary to delay a check for the first positive auxiliary measured voltage US1+ at open load until precharging is requested and a voltage rise is identified at the coupling network either with a positive coupling measured voltage UK+ or with a coupling voltage UK that is calculated from the positive and the negative coupling measured voltage UK+, UK−.

In this case, that is to say if all four measurements120,122,124,126for the first positive auxiliary measured voltage US1+ indicate values of zero, the positive main switch voltage USH+ should be calculated from the positive pack measured voltage UP+ and the positive coupling measured voltage UK+, even before precharging is requested, in order to allow a main switch and/or precharging switch diagnosis even if the electrical connection for measuring the first positive auxiliary measured voltage US1+ is interrupted.

If, after activation of the precharging, a voltage rise above a threshold value is established for the first positive auxiliary measured voltage US1+, the positive main switch voltage USH+ should go back to being calculated from the positive pack measured voltage UP+ and the first positive auxiliary measured voltage US1+.

The positive and the negative main switch voltage USH+, USH− also change on account of the shift in the floating reference potential, as long as the corresponding main switch SH+, SH− is open.

If it is established that the high-voltage measurement channel for measuring the positive coupling measured voltage UK+ is not connected to the appropriate measurement point and an identical measured value other than zero is acquired both for the first positive auxiliary measured voltage US1+ and for the second positive auxiliary measured voltage US2+, meaning that none of the positive fuses42,46are defective, the coupling voltage UK should be calculated from the first positive auxiliary measured voltage US1+ and the negative coupling measured voltage UL−.

FIG.4shows a schematic illustration of a method sequence200of a method proposed according to the invention for diagnosing the battery system10illustrated inFIG.1.

In a method step201, the microcontroller72is started up. In this case, the high-voltage A/D converter74is started so as to read measured values. Following the initialization phase114(cf.FIG.3) of the high-voltage A/D converter74, in a method step202, a connection check is performed on the high-voltage measurement channels while the main switches SH+, SH− and insulation measurement switches SIso+, SIso− are open. In this case, four measurements120,122,124,126are performed in succession. By evaluating the voltages UP+, UP−, US1+, UK+, UK−, UL+, UL−, US2+ measured in the respective measurements, it is checked whether a high-voltage measurement channel is connected to the measurement point assigned thereto. A switching state diagnosis is likewise performed for the main switches SH+, SH−. In this case, the main switch voltages USH+, USH− dropped across the respective main switches SH+, SH− are calculated and evaluated.

In a method step203, an insulation check is performed. In this case, an insulation voltage UIso is calculated. An insulation resistance of the battery pack5is likewise calculated. After the insulation resistance of the battery pack5has been calculated, the insulation check is ended. This insulation check is also referred to as fast insulation check.

In a method step204, it is checked whether a switch-on signal for the battery system10is present, by way of which switch-on signal the battery system10is switched on. Method step204is repeated until the switch-on signal for the battery system10is present.

If the switch-on signal for the battery system10is present, in a method step205, the negative main switch SH− is first closed. A contactor-open diagnosis is then performed for the negative main switch SH−. In this case, it is checked whether the negative main switch SH− is actually closed.

After the contactor-open diagnosis has been successfully completed for the negative main switch SH− and the negative main switch SH− has been identified as being closed, in a method step206, the precharging switch SVL is closed. A precharging switch diagnosis may be performed here in order to check the precharging qualification. This determines whether the positive main switch SH+ is able to be closed.

If the precharging qualification is confirmed positively, in a method step207, the positive main switch SH+ is closed. The precharging switch SVL is opened at the same time or thereafter. Following closure of the positive main switch SH+, a contactor-open diagnosis is performed for the positive main switch SH+ in order to check whether the positive main switch SH+ is actually closed.

After the contactor-open diagnosis has been successfully completed for the positive main switch SH+ and the positive main switch SH+ has been identified as being closed, in a method step208, the voltages USH+, USH− dropped across the two main switches SH+, SH− are monitored continuously in order to check whether there is unintended opening of the respective main switches SH+, SH−. In this case, the voltages USL+, USL− dropped across the positive and the negative charging switch SL+, SL− are likewise monitored. A continuous insulation check is likewise performed.

In a method step209, it is checked whether a switch-on signal for the fast-charging network is present, by way of which switch-on signal the fast-charging network is connected to the battery pack5, or whether a switch-off signal for the battery system10is present, by way of which switch-off signal the battery system10is switched off. Method step209is repeated until the switch-on signal for the fast-charging network is present or until the switch-off signal for the battery system10is present.

If the switch-on signal for the fast-charging network is present, in a method step210, the continuous insulation check is first ended. The negative charging switch SL− is then closed. A contactor-open diagnosis is then performed for the negative charging switch SL−. In this case, it is checked whether the negative charging switch SL− is actually closed.

After the contactor-open diagnosis has been successfully completed for the negative charging switch SL− and the negative charging switch SL− has been identified as being closed, in a method step211, the positive charging switch SL+ is closed. A contactor-open diagnosis is then performed for the positive charging switch SL+ in order to check whether the positive charging switch SL+ is actually closed. After the contactor-open diagnosis has been successfully completed for the positive charging switch SL+ and the positive charging switch SL+ has been identified as being closed, the voltages USH+, USH−, USL+, USL− dropped across the respective main switches SH+, SH− and across the respective charging switches SL+, SL− are monitored continuously in order to check whether there is unintended opening of the respective switches SH+, SH−, SL+, SL−. If a precharging circuit40is provided for the positive charging switch SL+, before closure of the positive charging switch SH+, the precharging switch SVL is closed and a precharging switch diagnosis is performed.

In a method step212, it is checked whether a switch-off signal for the fast-charging network is present, by way of which switch-off signal the fast-charging network is disconnected from the battery pack5. Method step212is repeated until the switch-off signal for the fast-charging network is present.

If the switch-off signal for the fast-charging network is present, in a method step213, the positive charging switch SL+ is first opened. A contactor-stuck diagnosis is then performed for the positive charging switch SL+ in order to check whether the positive charging switch SL+ is actually open.

In a method step214, the negative charging switch SL− is then first opened. A contactor-stuck diagnosis is then performed for both charging switches SL+, SL− in order to ensure that both charging switches SL+, SL− are open. The continuous insulation check is then restarted.

In a method step215, it is checked whether a switch-off signal for the battery system10is present. Method step215is repeated until the switch-off signal for the battery system10is present.

If a switch-off signal for the battery system10is present, in a method step216, the continuous insulation check is first ended. The positive main switch SH+ is then opened. A contactor-stuck diagnosis is then performed for the positive main switch SH+ in order to check whether the positive charging switch SH+ is actually open.

In a method step217, the negative main switch SH− is then first opened. A contactor-stuck diagnosis is then performed for both main switches SH+, SH− in order to ensure that both main switches SH+, SH− are open.

If, in method step209, the switch-off signal for the battery system10is present, method steps216,217are performed in succession.

The invention is not limited to the exemplary embodiments described herein and the aspects highlighted therein. Rather, a multiplicity of modifications that are within the scope of the activities of a person skilled in the art are possible within the range set forth by the claims.