Method for checking the electrical conductivity of a coolant in a battery, battery with residual current measuring device and motor vehicle with such a battery

Abstract

The present invention describes a method for measuring fault currents in a battery (100) to monitor the electrical conductivity of coolant and to detect insulation faults. Measuring the fault current between high-voltage and low-voltage potentials improves the safety of the battery (100) and prevents it from being activated in the event of impermissible conductivity. In addition to the method, the invention comprises a battery with a suitable measuring device (108) and a motor vehicle with such a battery (100).

Description

SCOPE OF APPLICATION AND STATE OF THE ART

[0001] The present invention relates to a method for checking the electrical conductivity of coolants in immersion-cooled batteries. It further relates to a battery with a corresponding measuring device and to a motor vehicle that has such a battery.

[0002] An immersion-cooled battery is a battery in which the battery cells are directly immersed in a dielectric fluid to enable particularly efficient heat dissipation. This cooling method is used especially in high-performance batteries in electric vehicles, stationary energy storage systems, and even in aviation.

[0003] The dielectric fluid absorbs heat directly from the surface of the battery cells, enabling efficient temperature equalization between the cells. This prevents local overheating of individual battery cells, thus extending battery life. The heated coolant can be cooled, for example, via an external heat exchanger before being returned to the battery.

[0004] Naturally, the coolant used must not exceed a certain electrical conductivity. This must therefore be monitored.

[0005] Known systems for monitoring the electrical conductivity of coolants in traction batteries measure the conductivity directly in the coolant. These systems use sensors that determine the electrical conductivity of the coolant and trigger actions such as warnings or filter activation when critical values ​​are exceeded. For example, DE 102019130799 A1 describes a system that performs a direct measurement of the conductivity and, based on this measurement, either deionizes the fluid or issues warnings.

[0006] However, one problem with this direct measurement method is that it only measures at specific points within the cooling circuit and does not allow for a comprehensive system analysis. Furthermore, it can be prone to errors if contaminants are unevenly distributed or concentrated in specific areas of the battery.

[0007] German patent DE 102022104201 A1 describes a temperature control system for traction batteries that includes sensors for determining the conductivity of the heat transfer medium. It explains that one sensor can be located in the lower part of the battery housing and another in the upper part to increase measurement accuracy. The conductivity measurement is used to determine whether the heat transfer medium is contaminated, which could affect the system's functionality. Furthermore, it describes that the system can diagnose the conductivity of the medium to monitor its quality and ensure it remains within permissible limits. It also mentions that the system can trigger a warning function if the medium's conductivity is borderline or harmful, thus preventing damage and ensuring safety.

[0008] This measurement method also only measures at specific points within the cooling circuit and does not allow for a comprehensive system analysis.

[0009] DE 102019202403 A1 describes a battery system whose cells are enclosed in an electrically insulating housing containing a cooling fluid. It describes a measuring circuit that is part of an insulation monitoring sensor circuit and measures the insulation resistance of the cooling fluid to monitor its conductivity and ensure that it remains within permissible limits. If the conductivity of the cooling fluid exceeds a limit or becomes harmful, the battery system is to be switched to a protected state or a warning message is to be issued to ensure safety and prevent activation of the battery system.

[0010] However, the insulation resistance is typically measured between the casing and the battery, which means that only a limited area is monitored.

[0011] German patent DE 102019215688 A1 describes a system for monitoring the quality of the coolant in a battery for electric or hybrid vehicles, specifically aimed at preventing short circuits. A water sensor is used to measure the water content in the coolant in order to monitor the fluid's electrical conductivity and ensure that it remains within safe limits. A control device is provided that issues control commands, such as warning messages or system shutdown, if a defined water content is exceeded, in order to prevent damage. The system is intended for use after a coolant change or during maintenance work to check the fluid's quality.

[0012] The described measurement method therefore focuses exclusively on monitoring the water content in the coolant using a water sensor, which means it only allows indirect conclusions to be drawn about the electrical conductivity of the coolant. TASK AND SOLUTION

[0013] Against the above background, the invention aims to provide a reliable method for checking the electrical insulation in a battery, capable of detecting not only the conductivity of the coolant but also potential insulation faults throughout the entire battery. Furthermore, the invention provides a battery and a motor vehicle that utilize this method.

[0014] This problem is solved by a method as described in claim 1. Furthermore, the battery according to claim 3 and the motor vehicle according to claim 5 are encompassed by the invention. Preferred embodiments of the invention are defined in dependent claims 2 and 4.

[0015] The method according to the invention is a method for checking the electrical conductivity of a coolant in a battery, and it comprises the following steps: a. Performing a fault current measurement between a high-voltage potential (HV+ / -) and a low-voltage potential (LV-) in the battery; b. Issuing a warning and / or preventing battery activation if the result of the fault current measurement is outside a predefined limit.

[0016] The procedure is preferably carried out after a service or replacement of the coolant, before the battery is activated.

[0017] According to the invention, preferably, battery activation is only possible if the measured conductivity remains within permissible limits. Activation can be carried out, in particular, by a battery management system (BMS) associated with or encompassed by the battery.

[0018] Preferably, the electrical conductivity of the coolant is determined within the framework of the method based on the result of the fault current measurement. Under these conditions, the predefined limit value can be a predefined electrical conductivity, and the result of the fault current measurement can be a determined electrical conductivity.

[0019] The measurement approach according to the invention ensures that not only does the coolant itself possess sufficiently high insulating properties, but also that no undesirable leakage currents occur in the entire system. This is particularly advantageous for modular battery systems in which several separate modules are interconnected.

[0020] This results in the following advantages: - Increased safety: The residual current measurement can detect insulation faults before the battery is activated, thus preventing dangerous leakage currents. - System-wide monitoring: Unlike direct conductivity measurement, fault current measurement can monitor the entire battery system, including the connection between individual modules. - Better adaptation to modular systems: The approach is scalable and can be applied to battery systems with multiple separate modules. - Reduction of false alarms: The measurement only issues a warning when critical leakage currents actually occur, and not just due to locally increased conductivity in the coolant.

[0021] In the context of the present invention, a high-voltage potential (HV+ / -) is understood to be an electrical voltage of 60 volts direct current or more.

[0022] In the context of the present invention, a low-voltage potential (LV-) is understood to be an electrical voltage that lies below the high-voltage limit. The low-voltage potential includes, for example, ground or reference potentials of a 12V, 24V, or 48V system. These can serve as a reference for fault current measurement relative to the high-voltage potentials (HV+ and HV-).

[0023] In the context of the present invention, a fault current measurement is defined as the detection of an unwanted electric current that occurs in the immersion-cooled battery due to an insulation fault or an unwanted connection between an active conductor of the battery with the high-voltage potential (HV+ / -) and an active conductor of the battery with the low-voltage potential (LV-) and that is made possible by an electrical conductivity of the coolant.

[0024] The fault current measurement is preferably carried out in several steps to ensure that no impermissible leakage currents are present in the battery before it is activated.

[0025] For measurement, the battery is in a deactivated state, i.e., it is electrically disconnected from external loads or inverters. If maintenance or a coolant change has been performed, it is preferably ensured that the battery is completely filled and vented before the measurement. The fault current measurement is preferably initiated by the aforementioned BMS. Preferably, a measuring device or an electronic circuit is connected between HV+ and LV- and / or between HV- and LV- as the measuring device. For example, a high-precision differential current sensor or a measuring bridge can be used to determine whether an unexpected current flow occurs between the high-voltage potential and the low-voltage potential. If no significant fault current is detected, the battery is considered electrically safe, and battery activation is enabled. If a critical fault current occurs, this means either: a) Excessively high conductivity of the coolant, which may indicate, for example, impurities or a faulty exchange process. b) A general insulation fault in the battery, e.g. due to damaged cell modules or faulty electrical connections.

[0026] In such a case, as mentioned above, the BMS can issue a warning message and / or prevent the battery from being activated to avoid damage or safety risks.

[0027] If a fault current occurs, the following measures can be taken depending on the cause: - Check and, if necessary, replace the coolant if it shows increased conductivity. - Diagnosis of the electrical insulation of the battery through additional tests or insulation measurements. - Battery activation will be blocked until the fault has been resolved.

[0028] The battery according to the invention is preferably suitable for carrying out the method according to the invention. It comprises the following components: a. A plurality of electrochemical cells connected to form an energy storage unit; b. A conductor that carries a high-voltage potential (HV+ / -) during operation and a conductor that carries a low-voltage potential (LV-) during operation; c. A residual current measuring device for measuring residual currents between the high-voltage potential (HV+ / -) and the low-voltage potential (LV-); d. A battery management system (BMS) that initiates the fault current measurement.

[0029] Preferably, the battery is a lithium-ion or sodium-ion battery.

[0030] As explained above, the battery is an immersion-cooled battery and therefore contains a coolant. The coolant must have the following properties: - Highly electrically insulating (low conductivity) - Good thermal conductivity - Chemical stability over long periods - Non-corrosive to battery cells and housing materials - Low viscosity for good circulation

[0031] Particularly suitable are, for example, synthetic hydrocarbons (e.g. mineral oils), silicone oils (e.g. polydimethylsiloxane) and fluorinated liquids (fluorocarbons, fluoroolefins).

[0032] As already mentioned in the description of the method according to the invention, the residual current measuring device can, for example, be a differential current sensor or a measuring bridge. Reference is made to the above explanations in this regard.

[0033] In preferred embodiments, the battery comprises a. A control unit that enables activation or deactivation of the battery based on the measurement of the residual current.

[0034] Any motor vehicle comprising the described battery is encompassed by the present invention. DESCRIPTION OF THE DRAWING

[0035] Further advantages and aspects of the invention will become apparent from the following description of the drawing.

[0036] The drawing shows Fig. 1 A schematic representation to illustrate the method and battery according to the invention.

[0037] The in Fig. The battery shown comprises three battery modules 102, 103, and 104, as well as a BMS 107. Each battery module 102, 103, and 104 comprises a plurality of interconnected electrochemical cells. The battery is immersion-cooled and includes a container 101 containing a coolant. The coolant flows to the battery modules 102, 103, and 104 via line 105 and returns via line 106. The battery includes one conductor carrying a high-voltage potential HV+ during operation, another conductor carrying a high-voltage potential HV- during operation, and a third conductor carrying a low-voltage potential LV- during operation. Fig.(1, labeled HV+, HV-, and LV-). A measuring device 108 can be arranged between these conductors, which, after servicing or replacement of the coolant, enables a residual current measurement to be performed between a high-voltage potential HV+ / - and a low-voltage potential LV- in the battery. Based on the result of the residual current measurement, the electrical conductivity of the coolant can be determined. If this is outside a predefined limit value, a warning is issued and activation of the battery is prevented.

[0038] The fault current measurement is preferably carried out in the following steps: 1. Measurement between HV and LV potentials: After maintenance or replacement of the coolant, a fault current measurement is carried out between the high-voltage potentials (HV+ / -) and the low-voltage potentials (LV-). 2. Conductivity check via fault currents: The battery management system (BMS) 108 evaluates the measurement results and determines whether the conductivity of the coolant is within permissible limits. 3. Diagnosis and warning: If excessive conductivity or an insulation fault is detected, the system issues a warning and prevents battery activation. 4. Battery activation: If the measurement is within the permissible limits, battery activation is enabled.

Claims

[1] Method for measuring the fault current in an immersion-cooled battery (100), comprising the steps: a. Performing a fault current measurement between a high-voltage potential (HV+ / -) and a low-voltage potential (LV-) in the battery; b. Issuing a warning and / or preventing battery activation if the result of the fault current measurement is outside a predefined limit. [2] Method according to claim 1, characterized by the following additional feature: a. Based on the result of the fault current measurement, the electrical conductivity of the coolant is determined. [3] Battery (100), comprising: a. A plurality of electrochemical cells connected to form an energy storage unit; b. A conductor that carries a high-voltage potential (HV+ / -) during operation and a conductor that carries a low-voltage potential (LV-) during operation; c. A residual current measuring device (108) for measuring residual current between the high-voltage potential (HV+ / -) and the low-voltage potential (LV-); d. A battery management system (107) that initiates the fault current measurement. [4] Battery according to claim 1, characterized by the following additional feature: a. It includes a control unit that enables activation or deactivation of the battery based on the fault current measurement. [5] Motor vehicle comprising a battery (100) according to one of claims 3 or 4.

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