Method for checking an insulation state of a battery or battery system

Abstract

A method for checking an insulation state of a battery or battery system comprising at least two batteries, comprising the following steps: measuring a voltage between a connection element of the battery and a ground over a predefined time; evaluating the measured voltage and determining whether a change in the measured voltage is present at time point that corresponds to a predefined temporal threshold value; and outputting a safety signal characterizing the insulation state on the basis of the established result.

Claims

1. A method for checking an insulation state of at least one of: a battery and a battery system comprising at least two batteries, comprising the following steps: measuring a voltage between a connection element of the battery and a ground over a predefined time; evaluating the measured voltage and determining whether a change in the measured voltage is present at a time point that corresponds to a predefined temporal threshold value; and outputting a safety signal characterizing the insulation state on the basis of the determined result.

2. The method as claimed in claim 1, wherein that at least two connection elements are provided and the method is carried out for each connection element of the battery.

3. The method as claimed in claim 2, wherein the temporal threshold value is defined by a parasitic capacitance of at least one of: the battery and the battery system and a resistance of at least one of: the battery and the battery system.

4. The method as claimed in claim 3, wherein the parasitic capacitance is defined in a battery-specific manner.

5. The method as claimed in claim 4, wherein the parasitic capacitance is at least one of: measured and/or computed for at least one of: the battery and or the battery system.

6. The method as claimed in claim 5, wherein the resistance is between 50 kOhm and 250 kOhm.

7. The method as claimed in claim 6, wherein the resistance is at least one of: a predefined starting resistance and a nominal resistance.

8. The method as claimed in claim 7, wherein the voltage change is determined for at least one of: the last two to five measurement points, and when this has at least one predefined minimum magnitude.

9. The method as claimed in claim 8, wherein the safety signal is furthermore output on the basis of an absolute voltage value measured at the time point.

10. The method as claimed in claim 9, wherein in the event of a voltage change determined at the time point, the safety signal comprises at least one of: an actuation signal for a high-voltage switching device and, in the absence of a voltage change, a further insulation check.

11. A checking module for checking an insulation state of at least one of: a battery and a battery system, wherein the checking module is configured to: measure a voltage between a connection element of the battery and a ground over a predefined time; evaluate the measured voltage and determine whether a change in the measured voltage is present at a time point that corresponds to a predefined temporal threshold value; and output a safety signal characterizing the insulation state on the basis of the determined result.

12. A battery system comprising at least two batteries and a checking module at least one of: communicatively and electrically conductively coupled thereto, wherein the checking module is configured to: measure a voltage between a connection element of the battery and a ground over a predefined time; evaluate the measured voltage and determine whether a change in the measured voltage is present at a time point that corresponds to a predefined temporal threshold value; and output a safety signal characterizing the insulation state on the basis of the determined result.

13. The battery system as claimed in claim 12 comprising a high-voltage switching device that is configured to connect each battery on the basis of a safety signal output by the checking module.

14. The method as claimed in claim 1, wherein the at least two batteries comprise at least one of: a high-voltage battery and a high-voltage battery system for use as at least one of: a traction battery of an electric vehicle and in static storage applications

15. The method as claimed in claim 5, wherein the parasitic capacitance is increased by a predefined safety factor for determining the temporal threshold value.

16. The method as claimed in claim 6, wherein the resistance is between 75 kOhm and 175 kOhm.

17. The method as claimed in claim 8, wherein the voltage change is determined for the last two to three measurement points.

18. The checking module of claim 11, wherein the battery is a traction battery of an electric vehicle.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0046] Preferred further embodiments of the invention will be explained in more detail through the following description of the Figures, in which:

[0047] FIGS. 1A and 1B show a schematic depiction of insulation faults in a battery system having two batteries with respect to a chassis in an electric vehicle;

[0048] FIG. 2 shows an exemplary voltage measurement curve in the normal state without insulation faults in a conventional method; and

[0049] FIGS. 3A and 3B show a schematic illustration of an exemplary voltage measurement curve without and with insulation faults, respectively.

DETAILED DESCRIPTION

[0050] Preferred exemplary embodiments are described below with reference to the Figures. In this case, identical, similar or functionally identical elements in the various Figures are provided with identical reference signs and a repeated description of these elements is in some cases omitted in order to avoid redundancies.

[0051] FIG. 1A schematically shows a battery system 1 having two batteries 10, wherein the batteries 10 are electrically conductively connected in series with one another via corresponding connection lines 12 or connection elements. Further connection lines are also provided to electrically conductively connect the battery system or the respective batteries 10 to a load, for example via a disconnector and/or a high-voltage switching device (not shown). Each battery 10 furthermore comprises a positive pole 14 and a negative pole 16, which are able to be electrically coupled by way of the corresponding connection lines.

[0052] In the exemplary embodiment, two insulation faults are present, as illustrated by the corresponding lightning symbol. In this example, the insulation or galvanic isolation of the positive pole 14 of the respective battery 10 with respect to the chassis 18 (or other ground) is not complete, meaning that the respective poles 14 are electrically conductively connected to the chassis 18. Even on its own, such an insulation fault with an individual battery 10 with respect to the chassis 18 should be considered problematic and should be avoided.

[0053] In the case of providing a battery system 1 in which the batteries 10 are intended to be connected to one another, there is however the additional risk of a short circuit being generated between the batteries 10 via the chassis 18, which may then lead to a high current flow and thus a risk to the batteries 10 and to the user. By way of example, when a conductive connection is established between the positive pole of one battery and the negative pole of the other battery due to the insulation faults with the batteries 10 and the respective other poles are then closed by the high-voltage switching device, an uncontrolled high current flow may occur. Such insulation faults should accordingly be avoided and are detected in accordance with the suggested method.

[0054] FIG. 1B illustrates a parallel circuit between the batteries 10. In this example, there is an insulation fault at the positive pole 14 of one battery 10 and an insulation fault at the negative pole 16 of the other battery, as indicated by the corresponding lightning symbol.

[0055] FIG. 2 illustrates an exemplary voltage measurement curve of a conventional insulation measurement in the normal state without insulation faults, wherein a high voltage U is applied with a small current between a connection line and the ground of the vehicle. The voltage U (in volts) is then measured over a predefined time t (in seconds). The measuring method constitutes a standard method, wherein, in this specific example, a parasitic capacitance of 1 ?F per connection line and a resistance of 5000 kOhm in the case of a voltage of the battery system of around 403 V is assumed.

[0056] The voltage measurement is carried out for each connection line over a predefined time of 7 seconds, wherein first the positive pole 14 and then the negative pole 16 are measured, in each case with R0 (on the left) and successively with nominal resistance (on the right). As illustrated with the rectangular marking, at the end of the respective measurement, voltage saturation 20 occurs, wherein no further voltage change (that is relevant or within a predefined tolerance range) is measured at this time point. Based on these measurements and the achieved voltage saturation, according to this method, a resistance that characterizes the insulation state of the battery is calculated. It may be seen that such a method may require up to 30 seconds. Depending on the required accuracy, the resistance and the parasitic capacitance, the measurement may also last even longer.

[0057] FIGS. 3A and 3B schematically illustrate the technical advantage of the checking method according to the invention. Based on a predefined parasitic capacitance, which is preferably measured and/or calculated or computed for the respective type of battery, and a predefined resistance, which is characteristic of at least one insulation fault, with a known voltage of the battery, a temporal threshold value 22 at which voltage saturation should occur in the event of the occurrence of a corresponding insulation fault is determined.

[0058] FIG. 3A illustrates a normal case in which no insulation fault is present. In this case, a voltage change 24 dU/dt is determined at the time point that corresponds to the temporal threshold value 22. From this it is determined that voltage saturation has not yet occurred at this time point and hence a (critical) insulation fault may be ruled out. In this case, it is possible to output a safety signal that indicates a fault-free state and it is possible, for example, to output an actuation signal for a high-voltage switching device in order to close the latter and provide an electrically conductive connection between the battery or the battery system and a load, such as an electric motor.

[0059] In FIG. 3B, however, an insulation fault or a small parasitic capacitance is present. The voltage saturation therefore occurs quicklyspecifically before the temporal threshold value 22 has been reached and exceeded. In other words, no voltage change is established at the time point of the temporal threshold value 22 and a safety signal that indicates an insulation fault being present and/or that initiates a further alternative check of the insulation state is accordingly output. In other words, voltage saturation 20 has already occurred at the temporal threshold value 22.

[0060] In this manner a fast check of the insulation state is enabled that considerably reduces the waiting time for the user compared to resistance-based checking methods.

[0061] Where applicable, all individual features set forth in the exemplary embodiments may be combined with one another and/or exchanged without departing from the scope of the invention.

LIST OF REFERENCE SIGNS

[0062] 1 Battery system [0063] 10 Battery [0064] 12 Connection line or connection element [0065] 14 Positive pole [0066] 16 Negative pole [0067] 18 Chassis or ground [0068] 20 Voltage saturation [0069] 22 Temporal threshold value [0070] 24 Voltage change [0071] U Voltage (V) [0072] t Time (s)