Battery and battery system comprising a battery

Abstract

Battery system (10) comprising at least one battery module (12) with a plurality of battery cells (14) connected in series or parallel, and comprising a plurality of current conductors (16), wherein the current conductors (16) are each connected to at least one battery cell (14), and comprising at least one current sensor (11) for determining the current flowing through the battery module (12), characterized in that at least one current conductor (16) comprises at least one inductance-increasing means (19) for selectively increasing the total inductance of the battery system (10) such that the at least one inductance-increasing means (19) is adapted to a measuring frequency of the current sensor (11), wherein the rate of increase of a short-circuit current flowing through the at least one battery module (12) is limited such that at least two measuring points of the current sensor (11) fall within the duration of the current increase to the short-circuit current.wherein the battery system (10) has a total inductance in the range of greater than or equal to 10 mH, and the measurement frequency defines measurements at a time interval of greater than or equal to 1 ms to less than or equal to 100 ms.

Description

[0001] The present invention relates to a battery with improved safety. The present invention further relates to a battery system comprising such a battery. State of the art

[0002] Various energy storage devices, such as lithium-based energy storage systems or lithium-ion batteries, have become indispensable in modern life. Applications include not only fully electric vehicles and hybrid vehicles, but also power tools, consumer electronics, computers, mobile phones, and other devices.

[0003] In electrically powered vehicles, for example, lithium-based batteries are often used as electrical energy storage devices (EES) because they offer a particularly high energy density at a low weight compared to nickel- or lead-based energy storage devices. Typically, electrical energy storage devices are implemented as individual cells connected in series or as cells connected in parallel. The individual cells are usually grouped into modules, so the overall battery is constructed as a series connection of modules.

[0004] To reduce the risk posed by energy storage devices or batteries, disconnect devices are often provided which can interrupt an electrical conductor, for example in the event of a short circuit.

[0005] Document DE 10 2011 121 604 A1, for example, discloses a method for protecting an electrical or electronic system, in particular a high-voltage battery system in an electric or hybrid vehicle, from electrical overcurrent and / or short circuit. This method includes at least a measuring device for measuring an operating current, a circuit breaker for interrupting the current, and a control unit for tripping the circuit breaker. An unusually high current increase is used as an indicator of an impending short circuit. Furthermore, the method may include adjusting a setpoint for current interruption to the inductance of the system.

[0006] Document WO 2005 / 115805 A1 also discloses an electronic battery protection switch that is connected between the battery and the vehicle's electrical system in motor vehicles. This switch provides a purely electronic overcurrent and short-circuit protection mechanism, which is intended to enable significantly faster disconnection. It is further described that, at the time the load circuit is disconnected, a small current flows due to the finite rate of current rise caused by the inductance of the load circuit.

[0007] Document EP 0 590 167 A1 further discloses a line switch for high-frequency applications with low currents up to 16 A, which operates with a semiconductor element whose internal resistance is low at a specific control voltage at a control electrode and a working voltage at working electrodes located in the forward direction in a conductor, and whose internal resistance increases abruptly with increasing voltage at the working electrodes. It is provided that a small inductance of a maximum of 100 nH is connected in the load current.

[0008] Document DE 10 2009 007 969 A1 describes a short-circuit protection device for limiting short-circuit currents in high-energy DC networks, in particular battery systems in submarine DC networks. Such a device comprises, to limit the short-circuit current, an ohmic resistor and a switch connected in parallel to the resistor to bypass the resistor when there is no short circuit.

[0009] Further designs of battery systems with short-circuit switches and sensors are described, for example, in DE 10 2014 214 984 A1, EP 2 811 548 A1 and DE 10 2011 121 604 A1. Disclosure of the invention

[0010] The present invention relates to a battery system comprising at least one battery module with a plurality of battery cells connected in series or parallel, and comprising a plurality of current conductors, wherein the current conductors are each connected to at least one battery cell, and comprising at least one current sensor for determining the current flowing through the battery module, wherein at least one current conductor comprises at least one inductance-increasing means for selectively increasing the total inductance of the battery system such that the at least one inductance-increasing means is adapted to a measuring frequency of the current sensor, wherein the rate of current rise of a short-circuit current flowing through the at least one battery module is limited such that at least two measuring points of the current sensor fall within the duration of the current rise to the short-circuit current, wherein the battery system has a total inductancewhich lies within a range of greater than or equal to 10 mH, and that the measurement frequency defines measurements at a time interval of greater than or equal to 1 ms to less than or equal to 100 ms.

[0011] A battery as described above allows for improved short-circuit detection or short-circuit current limiting in a simple and cost-effective manner, thereby improving safety during the operation of such a battery, especially in an electrically powered vehicle.

[0012] The term "battery" can be understood, in a manner understandable to those skilled in the art, to mean either a primary battery or, more preferably, a secondary battery, i.e., a rechargeable accumulator, which can preferably be operated with direct current. For example, the battery can be a lithium battery, such as a lithium-ion battery. In particular, a battery as described above can be a traction battery of an electrically powered vehicle.

[0013] The battery described above comprises at least one battery module with a plurality of battery cells connected in series or parallel. The battery cells can, for example, be lithium-ion cells, which are generally known to those skilled in the art. The number and configuration of the battery cells can be adapted to the desired application. For example, in the case of an electrically powered vehicle, the battery cells as a whole, distributed across several battery modules of the battery system, can deliver a nominal voltage of 200 V or greater, for example 400 V or higher, and a nominal maximum current of up to 100 A or greater than or equal to 100 A, for example 120 A or greater, approximately 240 A or higher.

[0014] Furthermore, a plurality of current conductors are provided, each connected to at least one battery cell. The current conductors allow the battery cells to be connected in series or parallel within battery modules, for example, in a manner known per se, or they can connect a plurality of battery modules, such as two battery modules. The current conductors can also connect the battery cells or modules to an external connection. For example, the current conductors can be high-current connectors, i.e., connecting conductors capable of withstanding the aforementioned currents. Thus, the current conductors are specifically designed to withstand currents of at least 100 A, i.e., to remain stable when carrying a current of 100 A. This implies, in a manner understandable to those skilled in the art, that in certain embodiments, carrying currents higher than 100 A may also be possible.

[0015] The battery also includes at least one current sensor for determining the current flowing through the battery module, whereby the current sensor can operate at a defined measurement frequency. The measurement frequency specifies the time interval at which individual measurements can be taken.

[0016] The measured values ​​of such a current sensor, such as a shunt sensor or a Hall sensor, can be evaluated at discrete time points, which, as described above, can be defined by the measurement frequency. If necessary, to reduce the processing power of a control unit, the data can be averaged and / or filtered by software and further processed at a lower repetition rate. The measuring range of these current sensors can, for example, be designed for the specified system current, meaning it can only extend slightly beyond the maximum operating current, such as up to 50% above it.

[0017] At least one conductor can include an inductance-enhancing element. In the context of the present invention, this can particularly mean that the overall inductance of the battery module or battery system increases with the inclusion of this element compared to a battery module without it. An electrical conductor of the same length as the conductor equipped with the inductance-enhancing element and which is straight can serve as a comparison.

[0018] The conductor with the inductance-enhancing element is preferably a conductor that is directly connected to at least one battery cell, for example, and can preferably be located directly inside a battery. For example, the conductor can be a high-current connector. Such a component can thus be individually adapted to the desired application. Furthermore, this allows for particularly simple implementation and retrofitting.

[0019] By using one or more inductance-enhancing devices, the total inductance L of the battery module can be significantly increased compared to conventional battery modules. This increase in inductance allows for a longer time constant t = L / R, where R is the internal resistance of the battery. This delays the battery's step response to a short circuit, enabling the battery management system to reliably detect an overcurrent and, if necessary, activate a disconnect device, as explained in detail below.

[0020] The at least one inductance-increasing means is selected such that it is adapted to a measurement frequency of the current sensor, so that the rate of increase of a short-circuit current flowing through the battery module is limited such that at least two measurement points of the current sensor, and in particular at least five measurement points, fall within the duration of the current rise to the short-circuit current. Such an adaptation or selection of the inductance-increasing means or means offers significant advantages over prior art solutions.

[0021] For example, in electrically powered vehicles, a battery or battery system as described above may be equipped with one or more devices to limit short-circuit currents or to disconnect an electrical conductor in the event of a short circuit. For this purpose, fuses may be provided in the electrical conductors. This prevents the risk of fire or damage to cells. The fuses may be made of tapered conductors, such as copper conductors, which may have several constrictions arranged in series or parallel. In the event of a short circuit, these constrictions can melt and thus interrupt the conductor.

[0022] However, such constrictions weaken the conductor's structure, which can cause the narrow sections to break under vibration, leading to altered fuse characteristics and an unauthorized or unintended interruption of the circuit. Even during operation with specified peak currents, the constrictions can heat up at these points, causing the fuse to age, which can also lead to changes in the safety characteristics and unauthorized circuit interruptions.

[0023] Furthermore, fuses have a specific characteristic: if the current flowing is only slightly above the value specified for the fuse to trip, it can take several seconds, up to 100 seconds or more, for the current to be interrupted. At very high currents, however, the fuse can trip in less than 1 millisecond. Therefore, fuses, at least one of which can be included in a battery as described above, can significantly increase safety, but still offer room for improvement.

[0024] It can therefore be advantageous that a fuse can be omitted in the aforementioned battery system. This allows the battery system to be designed to be particularly cost-effective and can also increase its long-term stability.

[0025] Furthermore, in a battery system as described above, such as in vehicles, one or more irreversible or reversible disconnect devices, such as contactors, may be provided. These devices disconnect the battery from the vehicle's electrical system or traction network when the battery is not in use, for example, when the vehicle is not in use. This disconnection, for example, via a two-pole connection, limits the area of ​​the vehicle under voltage (e.g., >60 V) to the battery's interior. These disconnect devices also protect the battery from, for example, deep discharge or overcharging. For this purpose, the disconnect devices can not only carry and disconnect the specific operating current but can also disconnect significantly higher currents, such as up to 400%, at least several times. Furthermore, the disconnect device can be used to disconnect a conductor in the event of a short circuit.The disconnect devices are typically controlled by the control unit, such as the battery management system. The control unit can be supplied with current values ​​by the detection device for detecting current flowing through the battery module and, if a current exceeding a threshold is present, activate the disconnect device to interrupt a short circuit.

[0026] Due to the low internal resistance of lithium-ion batteries, for example, very high short-circuit currents are possible, which can exceed both the measuring range of the current sensors used and the isolation capability of the isolation device, at least in current peaks.

[0027] Since the current typically rises very rapidly during a short circuit, for example due to a faulty control signal or short circuit of an IGBT, or due to contact between two live parts, the current sensor reading can conventionally jump from the current reading to the limit of its range between each sampling step. The time between sampling steps can be greater than 0.5 ms, for example, 1 ms or more. In this state, it is difficult for the control unit to determine whether the current is still within a range that can be interrupted by the disconnect device. In this case, it is therefore necessary to rely on the function of the fuse. After the external short circuit has been cleared, the system can only be restarted by replacing the fuse.

[0028] Since high short-circuit currents can damage the cells despite the fuse tripping, and because the current is interrupted very quickly by the fuse in such cases, the current sensor's measuring range limit may not be detected. This is because the short-circuit current and the interruption can occur between two sampling steps, or the measuring range limit may only be reached for one sampling step. In the latter case, because in the vehicle environment, errors can occur due to interference, fluctuations in the electrical system, etc., a single detection of the measuring range limit often does not result in an error entry in the fault memory. Therefore, it is often questionable whether the affected cells, and thus the battery pack, can continue to be operated after the fuse has blown.

[0029] This problem does not occur when using the battery described above. Because the at least one inductance-increasing means is adapted to a measurement frequency of the current sensor, such that the rate of increase of a short-circuit current flowing through the battery module is limited to the point that at least two measurement points of the current sensor fall within the time it takes for the current to rise to the short-circuit current, it is possible to determine at least two, preferably at least five, measured values ​​for the current flowing through the battery module before the current reaches the magnitude of a short-circuit current. This ensures that a short-circuit current is determined safely and reliably, and the multiple measurement results also rule out a measurement error or a faulty closure of a circuit breaker.This allows for a safe determination of whether and to what extent a battery can still be operated after a circuit breaker has been closed.

[0030] Because the physically possible rate of current rise is significantly limited by the inductance increase of at least one conductor, the control unit can activate the battery's own disconnect devices in time before the current-limited short-circuit current exceeds the range that the disconnect device can still isolate. This allows the battery to continue operating despite an externally occurring short circuit, as the fuse does not trip due to the disconnect device's isolation of the short-circuit current. However, it should be noted that the fuse may be aged and should be replaced soon. Furthermore, if it is possible to design the detection and disconnection system with sufficient reliability, the fuse can be omitted entirely.

[0031] This allows a control unit, such as a battery management system, to reliably detect a short circuit in a particularly advantageous way. Specifically, it enables a distinction to be made as to whether a fuse, if present, has interrupted the circuit due to aging or vibration, or due to a short circuit. It is therefore particularly advantageous to use fault memory entries to determine the battery's fate.

[0032] In the battery described above, the control technology or the measurement cycles are not adapted to the given inductance of the battery. Instead, the inductance is adapted to the existing peripherals of the battery system or the respective battery module and to the adjustable measurement cycles. This makes the battery system particularly advantageous for battery modules with low internal resistance, such as lithium batteries, for example, lithium-ion batteries. Implementing the battery described above into existing battery systems is therefore particularly easy. Furthermore, the risk posed by a short circuit can be significantly reduced through appropriate adaptability.

[0033] In one embodiment, the at least one inductance-increasing means can be selected such that the rate of current rise of a short-circuit current flowing through the battery module is limited to such an extent that at least two measuring points of the current sensor fall within the time it takes for the current to rise to the tripping current of a protective device for interrupting the short-circuit current. Particularly in this embodiment, especially safe operation of the battery can be achieved, since not only can a short circuit be reliably detected, but the short-circuit current can also be reliably interrupted in response to its detection. This is because it can be essentially ruled out that the short-circuit current will exceed the interrupting capacity of the protective device or the interrupting device. This can be particularly advantageous for batteries with low internal resistance, such as lithium-ion batteries.

[0034] In a further embodiment, the at least one inductance-increasing means can be selected such that the battery system has a total inductance in the range of greater than or equal to 10 mH, for example greater than or equal to 20 mH, approximately greater than or equal to 25 mH, to less than or equal to 500 mH, in particular less than or equal to 250 mH, and that the measurement frequency determines measurements at time intervals of greater than or equal to 1 ms to less than or equal to 100 ms. Particularly in this embodiment, a significant increase in the total inductance of the battery module makes it possible to use cost-effective measuring devices or control devices with comparatively low measurement frequencies.Because measurement frequencies in the aforementioned range are common in on-board diagnostics systems for motor vehicles, such as battery management systems, and are usually easy and inexpensive to use, the aforementioned parameters make it possible to combine increased inductance with inexpensive and easy-to-use measurement and evaluation systems.

[0035] For example, the inductance, such as the inductance of the overall system, can be determined by impedance spectroscopy or in a manner known per se by means of an LCR bridge or AC bridge.

[0036] Furthermore, by increasing the inductance to a value greater than or equal to 10 mH, particularly greater than or equal to 20 mH, for example greater than or equal to 25 mH, the inductance-increasing device can be used in a particularly simple way in battery systems with high currents, such as in an electric vehicle. By way of example only, and in no way limiting, a total inductance of 20 mH can be advantageous for a battery with a typical internal resistance of 0.1 ohms, a nominal voltage of 400 V, and a nominal maximum current of 240 A, and a current sensor with a measuring range of 330 A for five measurements at intervals of one millisecond.

[0037] In a further embodiment, at least one conductor can be designed or exhibit an inductance-enhancing structure. This means that the conductor deviates from its conventional shape, such as a straight line, a right angle, or an arc, and instead has a structure, particularly a locally confined one, which generates increased inductance. This increase in inductance can refer specifically to a straight conductor of the same length. In this context, the total length of the conductor may be meant, and not necessarily the geometric length, i.e., the length of the component. The inductance can be determined in the manner generally known to those skilled in the art.

[0038] By having at least one conductor incorporate an inductance-enhancing structure, or by having the inductance-enhancing element formed by the inductance-enhancing structure, increased inductance can be achieved through the conductor itself, potentially without the need for additional elements. This allows for a particularly simple, cost-effective, and efficient inductance design. Furthermore, other components of the battery system can be designed in a largely conventional manner, enabling particularly easy integration into existing systems.

[0039] For example, the conductor can be designed as a loop or coil to increase inductance. In particular, a coil or loop can significantly increase inductance, thus limiting current spikes or high short-circuit currents. The number of coil turns or loops can be adapted to the desired application. For instance, the conductor can be designed in a U-shape, the simplest loop shape, or in a meander shape, representing multiple loops.

[0040] In a further embodiment, the inductance-enhancing device can comprise a magnetically highly permeable material. A magnetically highly permeable material can be understood to be, in particular, a material exhibiting a relative magnetic permeability µr in the range of greater than or equal to 200, for example, greater than or equal to 300, down to approximately less than or equal to 10,000. The relative magnetic permeability µr can be determined according to the standard DIN IEC 60404. By incorporating such materials into the inductance-enhancing structure, the inductance can be effectively increased.

[0041] For example, the magnetically highly permeable material can be present in an inductance-enhancing structure. This allows the design of the inductance-enhancing structure, such as a coil or a loop, to be particularly small, which, for example in electrically powered vehicles, can enable implementation even in confined spaces and with low weight.

[0042] For example, ferrite can be used as a highly magnetically permeable material. Ferrites, in particular, can enable a very high increase in inductance, allowing for a particularly compact design. Manganese-zinc ferrites (MnZn), for instance with the composition Mn, can be used as examples, but are not limited to this. a Zn (1-a) Fe2O4, or nickel-zinc ferrites (NiZn), for example in the composition Ni a Zn (1-a) Fe2O4 can be used.

[0043] It can also be provided that the magnetically highly permeable material is arranged inside the coil windings of a current conductor shaped like a coil, or that the highly permeable material is surrounded by the coil windings. This arrangement can, in turn, be very space-saving, so that it can be used even in confined spaces. Furthermore, this can enable a particularly good increase in inductance.

[0044] Alternatively, the magnetically highly permeable material may at least partially, and in particular completely, enclose a current conductor, for example in the area of ​​the inductance-enhancing structure. For instance, the highly permeable material in the area of ​​the inductance-enhancing structure can serve as a sheath for the current conductor. This design, in turn, can also enable a particularly space-saving implementation. Drawings

[0045] Further advantages and advantageous embodiments of the objects according to the invention are illustrated by the drawings and explained in the following description, wherein the described features, individually or in any combination, can constitute an object of the present invention, unless the context clearly indicates otherwise. It should be noted that the drawings are for descriptive purposes only and are not intended to limit the invention in any way. They show Fig. 1 a schematic view of an embodiment of a battery system consisting of modules with two module connectors whose inductance has been increased according to the invention; and Fig. 2 a schematic view of a further embodiment of a battery sub-system consisting of modules with a battery module connector between two modules according to the invention.

[0046] In the Fig. Figure 1 shows an embodiment of a battery system 10. The battery system 10, which can be, for example, a lithium-ion battery system, has at least one battery module 12 with a plurality of series-connected battery cells 14, wherein in the Fig. Figure 1 shows eight battery modules 12. Furthermore, a plurality of conductors 16 are provided to connect the battery modules 12 to one another. The conductors 16 can be designed to carry currents of 100 A. The conductors 16 are described in detail below. Fig. 1 arranged between or connected to two battery cells 14, wherein the battery cells 14 are then arranged at the end of a battery string forming a battery module 12. It is provided that at least one current conductor 16 is provided with an inductance-increasing means 19 such that the at least one inductance-increasing means 19 is adapted to a measuring frequency of a current sensor 11, wherein the rate of current rise of a short-circuit current flowing through the battery module 12 is limited such that at least two measuring points of the current sensor 11 fall within the duration of the current rise to the short-circuit current.

[0047] In the Fig. Figure 1 shows that the inductance-increasing agent 19 is a magnetically highly permeable material 18, such as a ferrite, which encases or surrounds the current conductors 16.

[0048] Furthermore, a current sensor 11 for detecting current flowing through the battery 10 is shown. This sensor can be arranged not only on the positive conductor as shown, but also on the negative conductor of the battery, between the modules 12, or within one of the modules 12. Two protective devices 13 for interrupting the short-circuit current are also shown; one of these may be sufficient. A control unit 15 for activating the protective device 13 is also provided, which may be connected to the current sensor 11. The control unit could, for example, be the battery management system, which can control the current sensor 11, evaluate the data from the current sensor 11, and control the protective device 13 or disconnecting device. Finally, an electrical connection 17, such as a terminal block, for the battery system 10 is shown.

[0049] In the Fig. Figure 2 shows a further embodiment of a battery 10, wherein a current conductor 16, which is connected to two battery cells 14 via a terminal 20, is designed in the form of a coil as an inductance-enhancing structure, i.e., an inductance-enhancing means 19. For further description, reference is made to the description of Fig. 1. Reference, whereby identical or comparable components are provided with the same reference numerals.

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