Method for storing a cell monitoring circuit error and lithium-ion battery

Abstract

Method for storing an error of a cell monitoring circuit for monitoring at least one electrochemical cell of a lithium-ion accumulator, wherein, according to the method, when the lithium-ion accumulator transitions into a sleep state, a sleep command is sent from a control device to the cell monitoring circuit (S4), - wherein the sending of the sleep command from the control device to the cell monitoring circuit is linked to a confirmation request to the cell monitoring circuit, and - in the event of non-receipt of a confirmation from the cell monitoring circuit (S5), the control device resends the sleep command and / or the confirmation request after a time interval (S4), - wherein after a predefined number of sleep commands and / or confirmation requests for which no confirmation was received (S7),- wherein error information relating to the cell monitoring circuit is stored in an error memory of the control device and in an error memory of a vehicle control unit (S15), wherein the error information is stored redundantly in the error memory of the control device and in the error memory of a vehicle control unit (S15).,

Description

Prior ArtThe present invention relates to a method for storing a fault of a lithium-ion battery in a fault memory. The invention further relates to a lithium-ion rechargeable battery.In electrically driven vehicles, a rechargeable battery is typically used as energy source. Lithium-ion batteries are frequently used, since these have the greatest energy density available up to now with the lowest weight. However, these accumulators are very sensitive to overcharge as well as deep discharge. When overcharge exceeds a certain voltage value per cell, typically 4.25 V, the cell becomes unstable and a self-boosting heating process (thermal runaway) can be initiated. Also, discharge below a certain threshold promotes unfavourable chemical processes in the cell, leading to its irreversible deterioration. For this reason, there is an accumulator management system which, by means of a control device of the accumulator and by means of cell monitoring circuits on individual cells of the accumulator, frequently on all cells, monitors the cell voltages and can be involved in triggering countermeasures. For example, over- and under-charging is prevented by opening a main switching device, which can comprise, for example, one or more charging or main load contactors. This is referred to as deep discharge protection. During operation of an electrically driven vehicle, a situation may occur in which the installed rechargeable battery is exhausted due to the driving operation, for example as a result of longer diversions, increased energy consumption, malfunction of a controlled charging station or the like. This depletion of the accumulator is manifested in that a lower voltage threshold of one or more cells is reached, which can be detected by means of the cell monitoring circuits connected to the cells and whereupon the deep-discharge protection is activated. The disadvantage of this is that even if the deep discharge protection device reaches, i.e. the main switching device is open to all external loads, the power supply to the cell monitoring circuits is still maintained under certain conditions, for example in the event of an accident involving mechanical damage to the battery control electronics, electromigration-related short circuits. Software Failures in Battery Management System or the like. The cell monitoring circuits do not belong to the external loads, but remain connected to the respective electrochemical cells, even if, for example, a main contactor is open. Typically, the cell monitoring circuits are put in their sleep mode not by the deep discharge protection but by a sleep command, which may fail. In this situation, the cell monitoring circuitry continues to consume power from the accumulator. In particular, if this takes place over a longer time, there is an acute risk of deep discharge, especially since the accumulator can already be in a state of maximum permissible discharge after a longer driving operation.The same can also take place if the lithium-ion accumulator is placed in a sleep mode after the electric motor is switched off. In this case, end consumers in the low-voltage range drive down their current requirement and the control device sends a sleep command to the cell monitoring circuits, in particular if it establishes this. When a cell monitoring circuit is erroneously not placed in the sleep mode, a deep discharge threatens as described above.It is possible to connect the sleep command to a confirmation request to a cell monitoring circuit and receive a confirmation of the sleep mode from the cell monitoring circuit, for example, via a CAN bus. If this fails, the sleep command can be retransmitted and repeated for all cell monitoring circuits that have not responded until all cell monitoring circuits have responded. In one development, the aforementioned method is carried out while a main switching device of the lithium-ion accumulator, with which electrical current flow from and to the lithium-ion accumulator can be interrupted, is open. When opening the main switching device, a signal is preferably sent to the user about this event, in particular when the main switching device has been opened because a low state of charge of the lithium-ion battery is present, which is preferably communicated to the user. In a development of the method, the number of sleep commands and / or confirmation requests to the cell monitoring circuit is stored, in particular in the control device which sends the sleep command and / or a confirmation request to the cell monitoring circuits. Optionally, a cell monitoring circuit from which no confirmation has been received at the control device after a predefined number of sleep commands and / or confirmation requests can be forcibly disconnected from its cell to be monitored in such a way that it is no longer discharged by the cell monitoring circuit, in particular by means of electrical connections and interruption devices provided for this purpose.A disadvantage of the method described above is that it cannot be understood in the vehicle whether cell monitoring circuits are defective and / or cells are cut off positively. Because forcibly switched-off cells are typically taken from a cell packet, this further has the disadvantage that it is no longer known to an accumulator management system which capacity and which capacity the accumulator has. Undetected defective cell monitoring circuitry may also result in deep discharge of their monitored cells.Document EP 2 574 948 A2 discloses monitoring for electrical storage. A monitoring unit monitors the state of a battery serving as an electric storage. The monitoring prevents the electrical storage device from becoming an abnormal state.The document DE 10 2004 052 905 A1 discloses an energy management system in a motor vehicle comprising a battery which powers a control unit, a battery monitor device coupled to the battery for determining a state of charge of the battery, and a quiescent current manager which, depending on the state of charge of the battery, sends an instruction to the control unit for actuating a load connected to the control unit.Disclosure of the InventionAccording to the invention, a method for storing a fault of a cell monitoring circuit of a lithium-ion accumulator in a fault memory is proposed. The cell monitoring circuit monitors an electrochemical cell of the lithium-ion battery. When the lithium-ion battery enters a sleep state, a control device sends a sleep command to at least one, preferably all, cell monitoring circuits. In one variant, the sleep command is sent only to the cell monitoring circuitry for which there is no entry in the fault memory. The transmission of the sleep command is associated with an acknowledgement request, which may be transmitted, for example, individually or implemented in the cell monitoring circuit in response to a sleep command or the like. If such an acknowledgement is not received by a cell monitoring circuit, this means in most cases that it has not gone into the sleep state. The control device can then send a sleep command again, in particular to the cell monitoring circuits which have not sent an acknowledgment to the sleep command sent previously. According to the invention, after a predefined number of sleep commands and / or confirmation requests for which no confirmation has been received, error information is stored in the error memory belonging to the control device of the accumulator and the error information is stored in an error memory which is part of a vehicle control device. Particularly preferably, the fault information is stored in both fault memories mentioned in order to provide more security by redundancy, for example against short circuits or overloading of the battery system, wherein a specific defective cell monitoring circuit is preferably identifiable on the basis of the fault information. Fault information may mean, for example, that a cell monitoring circuit is defective or has not been automatically put into the sleep state. The method sequence described above is carried out in particular when an electric motor or a vehicle in which an electric motor is installed is switched off. Such a switching off of the vehicle or electric motor can also be carried out automatically. The sleep state can be activated by the control device if end consumers in the vehicle, such as control modules or the like, supplied by the lithium-ion accumulator after the vehicle or the electric motor has been switched off reduce their current requirement in the low-voltage range, in particular to a minimum. In particular, the control device can detect the drop in the load, whereupon it sends the sleep command. It is also conceivable to send the sleep command if the power output of the battery falls below a predefined threshold. The threshold is defined by the power consumption of the vehicle components when the vehicle is at a standstill. The sleep command and / or the confirmation may be sent via a CAN bus, for example. Between the decision whether there is no confirmation of the sleep command and the retransmission of a sleep command, a time interval is allowed to wait which can be varied. In particular, it can be varied in that the time interval becomes shorter with the number of sleep commands transmitted. The proposed method makes it possible to detect faults already before a deep discharge occurs. In addition, the probability is higher that a fault is corrected before deep discharge occurs.When all the cell monitoring circuits have been placed in the sleep mode and / or have been forcibly disconnected after they have not been placed in the sleep mode, the controller preferably sets itself to a sleep state. At the same time, a counter counts the number of sleep commands transmitted, and the count value is stored. This can take place, for example, by means of software, in that the value is stored in a variable, or by means of hardware, for example by means of counter flip-flops. If this count value exceeds a predefined value, for example the values 3 or 4, then the cell monitoring circuits which have not yet been put into the sleep mode are forcibly switched off, for example by hardware using a relay or switch, by interrupting the measurement and supply lines between the relevant cell monitoring circuits and their associated cells or associated modules which comprise the respectively associated cell.In this way, irreversible damage to the cell is more likely to be avoided. Then, no service lives arise due to necessary repairs, for example the replacement of cells.The dependent claims show preferred developments of the invention.In another embodiment of the method, the forced deactivation of cells that are forced deactivated as a result of the failure of the cell monitoring circuits to switch to the sleep mode is reversed again when an electric vehicle comprising the accumulator or an electric motor as a load is started or when battery functionalities are checked. In this case, the supply lines of the forcibly switched-off cell monitoring circuits are again switched to continuous and still further, preferably all remaining, electronic monitoring components are switched from the sleep mode into an activity mode. Such a check can be carried out in particular in the case of prolonged service lives.In a further embodiment of the method, the forced deactivation of cell monitoring circuits involves the transmission of information about the forced deactivation to a receiver which is not the current user of the lithium-ion battery or of the vehicle in which it is installed, namely in particular an external receiver such as, for example, a workshop, an emergency service, the manufacturer of the battery and / or a vehicle manufacturer. Preferably, the message is transmitted via mobile radio. In particular, information is sent from the fault memory, in particular which cell monitoring circuits are affected and which type is the fault stored. With the aid of this information, a defective cell monitoring circuit can be replaced or repaired more easily.Brief Description of the DrawingsHereinafter, the embodiments of the invention will be described in detail with reference to the accompanying drawings. In the drawing, the following is: FIG. 1 shows a schematic illustration of a method sequence of an embodiment of the method according to the invention.Embodiment of the InventionFIG. 1 schematically shows the flow of a first embodiment of a method for storing a fault of a cell monitoring circuit of a lithium-ion battery. The cell monitoring circuit, not shown, is connected to a cell of the accumulator by means of power supply and / or measurement connections in order to monitor its state, in particular its cell voltage. Status information of the cell can be sent from the cell monitoring circuit via one or more signal connections to a control device of the accumulator, in particular via a CAN bus. The controller monitors the state of the accumulator via the cell monitoring circuits. The controller may send a sleep command to the cell monitoring circuits to put them in a sleep mode in which power consumption thereof is reduced or suppressed. This sleep mode can prevent the supply current for the cell monitoring circuits from reducing the charge in the cells they monitor. Such a situation may be critical, for example, when an electrically operable vehicle is installed with the accumulator having consumed its energy up to a critical threshold. In particular, the parking of the vehicle may also be critical if the parking time is sufficient for the supply current for a cell monitoring circuit to bring the state of charge of a cell below a deep discharge threshold. The method is triggered by switching off an electric motor supplied by the lithium-ion accumulator, for example because a vehicle in which the electric motor and the accumulator are installed is to be shut down. The beginning of the method according to the second embodiment is step S 13, in which the electric motor is switched off. In a subsequent step S 14, further consumers supplied from the lithium-ion accumulator are shut down. These are, for example, end consumers which are supplied with voltages in the low-voltage range. The power consumption of these consumers is reduced by the shutdown. The power consumption can be reduced even further by opening a main switching device which connects the accumulator to its consumers. During a service life, the accumulator is thus less highly discharged. Then, the process proceeds to step S4, in which the controller (BCU) sends a sleep command to each of the cell monitoring circuits. This is triggered in particular by the fact that the power consumption of power consumers dropping when the battery is shut down is detected in the periphery of the accumulator, in particular when these are placed in a sleep mode.However, when external loads are disconnected from the battery, the power supply to the cell monitoring circuits from the battery or sense lines between cell monitoring circuits and their monitored cell is not interrupted. Current may thus continue to flow from the accumulator through cell monitoring circuitry and discharge the accumulator. In order to prevent further power consumption of the cell monitoring circuits, the control device sends a sleep command to the cell monitoring circuits in a step S 4 in order to put them into the sleep mode. In a step S5, the controller awaits an acknowledgement signal from each cell monitoring circuit to which a sleep command has been sent. If this criterion is fulfilled, the control device switches itself into the sleep mode in a step S 6 and the method is ended. In this way, the power consumption is further reduced.If an acknowledgment signal is not received from each cell monitoring circuit, the method proceeds via a feedback from step S 5 back to step S 4. In the feedback, a further step S7 is interposed, in which information on a number of sleep commands that the controller has sent to cell monitoring circuits is accessed. Alternatively or additionally, the number of feedback passes may also be stored, particularly for individual cell monitoring circuits. In step S 7, it is checked how often the sleep command has already been transmitted. If the sleep command has been transmitted less than X times, the method moves from step S 7 to step S 4 after a waiting time Δt, in which a new sleep command is transmitted. By the transition to step S 4, the loop of method steps S 4, S 5 and S 7 is closed. The waiting time Δt can be decreased with each retransmission of a sleep command. Each transmission and / or retransmission is stored, in particular in a variable or in a counter, which in particular operates with flip-flops. However, if it is determined in step S 7 that the sleep command has already been transmitted X times, the method proceeds to step S 8, in which forced shut-off of cell monitoring circuits that are not yet in the sleep mode is effected. These are the cell monitoring circuits from which an acknowledgment signal is expected but was not received despite an X-fold sleep command. The forced disconnection can be effected via an interruption device with which a power supply between the accumulator and a cell monitoring circuit can be interrupted. The interrupt device can be controlled from the control device, preferably independently of other processes. Preferably, signal lines are provided for this control which are independent of the normal communication between the control device and the cell monitoring circuits. In a step S 10, an external receiver, for example an emergency service, the battery manufacturer, a workshop or a vehicle manufacturer of a vehicle into which the battery is installed, is informed of the state of the battery. In a further step S15 following the forced shut-down, information about defective cell monitoring circuits is stored in a fault memory. This fault memory is preferably a fault memory of the control device or of a vehicle control device. In order to ensure that this information is not lost, for example as a result of short circuits or overloading of the battery system, it is proposed to store the information redundantly in both of the said memories.

Claims

Method for storing a fault of a cell monitoring circuit for monitoring at least one electrochemical cell of a lithium-ion battery, wherein, according to the method, upon a transition of the lithium-ion battery into a sleep state, a sleep command is sent (S4) from a control device to the cell monitoring circuit, - wherein the sending of the sleep command of the control device to the cell monitoring circuit is connected to an acknowledgement request to the cell monitoring circuit, and - in the case of a non-receipt of an acknowledgement of the cell monitoring circuit (S5), the control device sends the sleep command and / or the acknowledgement request again (S4) after a time interval, - wherein, after a predefined number of sleep commands and / or acknowledgement requests for which no acknowledgement was received (S7), wherein fault information regarding the cell monitoring circuit is stored in a fault memory of the controller and in a fault memory of a vehicle controller (S15), wherein the fault information is redundantly stored in the fault memory of the controller and in the fault memory of a vehicle controller (S15).Method according to claim 1, wherein after the predefined number of sleep commands and / or confirmation requests for which no confirmation has been received (S5), a forced disconnection of the cell monitoring circuit from its cell is effected (S8), in particular after three or four times no reception of the confirmation of the cell monitoring circuit (S5, S7), and fault information about the forced disconnection of the cell monitoring circuit is stored in the fault memory (S15).The method of claim 2, wherein forced disabling of forced disable cell monitoring circuitry is suspended upon starting an electric vehicle or motor or upon checking battery functionalities.Method according to one of the preceding claims, in which a receiver receives (S10) a forced disconnection signal which is not the user of the lithium-ion battery, in particular a workshop, an emergency service, the manufacturer of the battery and / or a vehicle manufacturer.The method according to any one of the preceding claims, wherein the controller enters a sleep mode (S6) after receiving (S5) the acknowledgement from the cell monitoring circuit.Lithium-ion accumulator having a control device, a cell and a cell monitoring circuit connected to the cell, wherein a method according to one of the preceding claims can be carried out with the lithium-ion accumulator.

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