DE102019133252A1 - Method for operating a battery system, battery system and cell interconnection for a battery system - Google Patents

Abstract

The invention relates to a method for operating a battery system (10), the battery system (10) having a communication network (12) and a cell interconnection with a large number of electrically conductive interconnected, switchable battery cells (14). By means of the communication network (12), switching requests (26) are transmitted from a central control device (18) of the battery system (10) to the individual battery cells (14). A known maximum transmission latency occurs here. The central control device (18), taking into account the known maximum transmission latency, defines a switching point in time (ts) for a respective switching request (26), which determines a future point in time for executing the respective switching request (26), and transmits this to a respective battery cell (14) . A cell processor (30) of the respective battery cell (14) recognizes the occurrence of the switching time (ts) by monitoring a battery cell clock (20) of the respective battery cell (14) and executes the respective switching request (26) when the switching time (ts) occurs. As a result, fluctuations between total transmission latencies between individual battery cells are abstracted, so that the battery cells switch time-synchronously with a certain precision.

Description

The invention relates to a method for operating a battery system, the battery system comprising at least one communication network and a cell interconnection with a plurality of electrically conductive interconnected, switchable battery cells that are connected to the communication network as communication participants. The invention also relates to such a battery system and to a cell interconnection for such a battery system.

A cell interconnection within the meaning of the present invention is designed in particular to provide electrical voltages in a range of more than 60 volts, in particular in a range of several 100 volts (corresponding to a so-called high-voltage battery). Such electrical voltages can be provided in that a multiplicity of individual battery cells are electrically connected to one another in the cell interconnection. As a rule, some of the battery cells are each connected to form what are known as battery modules. A cell interconnection within the meaning of the present invention can also be designed to provide a voltage range of less than 60 volts and, for example, comprise at least two battery cells. In connection with the present invention, the individual battery cells are preferably designed as switchable battery cells or so-called smart cells, each of which can be individually connected and disconnected from the circuit in an electrically conductive manner by appropriately activating switching elements. There are three possible switch positions in particular: switched on, bridged and switched off (circuit is interrupted).

In order to be able to coordinate the use (i.e. adding and / or disconnecting) of respective individual battery cells and / or individual battery modules within the battery system, a central control device (for example a battery management system or BMS) can be provided which is connected to the individual battery cells and / or or the battery modules can communicate in order to issue switching commands. A communication network, for example a controller area network (CAN according to FIG ISO 11898 ), in particular a CAN with a flexible data rate (so-called CAN FD according to ISO 11898-1: 2015 ), into which the battery cells and / or the battery modules and the central control device can be integrated as communication participants. The communication network can also be wireless or as a wireless network, for example radio-based.

Status information on the individual battery cells and / or the individual battery modules can be received in the central control device. State information can describe, for example, a state of health (SoH) or a current state of charge (SoC) of a respective battery cell. Depending on the received status information, which can be detected by sensors of the individual battery cells, for example, the central control device can then coordinate the use, that is, the switching on and off, of the respective battery modules and / or individual battery cells within the battery.

In this context, describes the WO 2008/055505 A1 a battery management system for controlling the charging and discharging processes of a large number of batteries. Each of the batteries has a plurality of control circuits which monitor and control the charging of the individual batteries. These units are controlled by a central microcontroller, which can bypass a battery during a charging process if it is fully charged, and can stop a battery from discharging during a discharge process if it is completely discharged. Disadvantageously, the central microcontroller can only react to current battery states. It is not possible to plan the use and future control of the batteries.

The US 2017/0353042 A1 describes a battery system with a so-called smart battery and a bus system (communication bus) for distributing or assigning a respective available electrical energy to individual parts of the smart battery. Each battery in the Smart Battery can be individually controlled and integrated into the charging and discharging processes. In addition, clocks are provided for the batteries, which can be synchronized with one another and with a higher-level clock. In this way, sensor data of the batteries can be provided with time stamps and stored together. From this, retrospective statistics can be created on the respective sensor data. So sensor data can be provided with time stamps in order to create a history. A future application planning of the individual batteries can also not be provided here in a disadvantageous manner.

The invention is based on the object of coordinating future use of individual battery cells and / or battery cell modules in a battery system of the type described at the outset.

The object is achieved by the subjects of the independent claims. Beneficial Further developments of the invention are described by the dependent claims, the following description and the figures.

The invention is based on the knowledge that communication between a battery management system or a central control device of a battery system and respective further communication participants, in particular individual battery cells, by means of a communication network of the type described above is always subject to a transmission latency. In other words, the invention is based on the knowledge that fluctuating delays (so-called jitter) can occur on a respective communication path between the central control device and an individual battery cell, which can negatively affect the coordination of switching processes of several battery cells.

The invention therefore provides a method for operating a battery system. The battery system has at least one communication network and a cell interconnection with a multiplicity of switchable battery cells interconnected in an electrically conductive manner. The battery system can therefore have one or more communication networks. A respective switchable battery cell or smart cell is designed to be connected to or separated from a circuit of the cell interconnection in an individually electrically conductive manner by activating respective switching elements. A (central) system clock of the battery system specifies an absolute system time for the battery system. The respective battery cell clocks synchronized with the system clock specify the respective cell times for the battery cells. In connection with the present invention, the term “clock” is understood to mean a device for recording or logging a time that is familiar to a person skilled in the art. In particular, this also includes a counter or timer, in particular a nanosecond timer. A device known as the Capture Compare Unit is also included in the term “clock” in the present case.

The battery system also has a central control device. In the event that several communication networks are present, these can preferably be logically connected to one another by the central control device or a central battery management system (battery management system as gateway). The central control device, for example a central microcontroller, transmits at least one switching request by means of the at least one communication network to at least one respective battery cell of the plurality of battery cells. The at least one switching request describes a respectively required switching state of the at least one respective battery cell. A required switching state can be, for example, that the at least one respective battery cell is connected in an electrically conductive manner to a circuit of the cell interconnection or is separated or bridged from it.

When the at least one switching request is transmitted, there is a known maximum transmission latency. In other words, there is a maximum transmission latency or an overall transmission latency that can occur in particular in the worst-case scenario (worst-case scenario). The transmission latency or a latency period includes in particular: (i) a processing time of the respective switching request in the central control device, (ii) a processing time of the respective switching request in a transceiver of the central control device, (iii) waiting times for bus arbitration , (iv) a transmission duration of the respective switching request as a function of a number of bits of the respective switching request or message, (v) a signal transit time of an electrical signal transmitting the respective switching request, (vi) a processing time on the battery cell side in a transceiver of the respective battery cell and (vii) a further processing time in the respective battery cell. With the exception of point (v) of the above list, a respective jitter or fluctuation can occur with all of the mentioned components of the latency period or with all of the above-mentioned individual delays. This fluctuation can turn out differently for each battery cell in the circuit. At point (v) signal transit time, there is generally no jitter, since the length of an electrical connection within the communication network generally does not change. The processing time in the transceiver device of the at least one respective battery cell can occur, for example, when the at least one switching request is received and / or during a decoding of the respective switching request.

After receiving and decoding the at least one switching request, a cell processor of the at least one respective battery cell executes the switching request. The switching request is carried out in that the cell processor controls a switching element of the at least one respective battery cell, whereby the respectively required switching state is established or set. The switching element can be, for example, a semiconductor component, for example a field effect transistor (FET).

According to the invention, taking into account the known maximum transmission latency, the central control device defines a switching time for the at least one switching request and transmits this to the transceiver by means of the at least one communication network. The switching time can be transmitted together with the transmission of the respective switching request or in a separate message. The switching time determines a future system time of the system time of the battery system for executing the at least one switching request. The switching time or the switching point in time therefore represents an absolute system time at which the switching request or the switching command is to be implemented by the respective battery cell. In other words, the absolute system time is preferably selected or established by the central control device in such a way that a difference between the switching time and a current system time is greater than the above-mentioned maximum transmission latency in the worst-case scenario. In this way it can be avoided that the switching time is already in the past when a respective message has been decoded in a battery cell.

According to the invention, the cell processor recognizes the occurrence of the switching time by monitoring the battery cell clock of the at least one respective battery cell, which is synchronized with the system time, and executes the at least one switching request when the switching time occurs. In other words, the required switching state is only actually established by the respective smart cell or by the cell processor of the respective smart cell when the occurrence of the switching time has been recognized by the cell processor. The cell processor can monitor the battery cell clock as part of a cyclical query (so-called polling). As described below, monitoring can also be based on interrupts.

The invention has the advantage that fluctuations in the transmission latency between the individual battery cells can be abstracted or rendered harmless. As a result, switching that is synchronous in time or at the same time can advantageously be achieved with greater precision than is known. In addition, a maximum known transmission latency on a respective communication path within the communication network can be abstracted or rendered harmless. In other words, the implementation or execution of a respective switching request can take place independently of the transmission latency mentioned and / or independently of a fluctuation in the transmission latency. For this purpose it can be provided, for example, that a respective cell processor has a memory in which incoming switching requests can be stored and a respective incoming switching request can be withheld until the switching time assigned to it occurs. In this way, a respective transmission time can advantageously be decoupled in time from a respective desired switching time. Use of a respective battery cell can therefore be planned for a future point in time. By using suitable clocks, the use can be planned and carried out in particular with a high resolution in the microsecond or sub-microsecond range.

The invention also includes embodiments which result in additional advantages.

One embodiment provides that the central control device defines a respective switching point in time as a common switching point in time for a predetermined subgroup of battery cells. In other words, a common switching point in time applies to all battery cells of the predetermined subgroup. The predetermined subgroup can be compiled or selected dynamically during operation and can comprise two, three, four, five or generally any number of battery cells of the cell interconnection. The predetermined subgroup can also include all battery cells of the cell interconnection. The cell processors of the battery cells of the respectively dynamically selected predetermined subgroup thus execute respective switching requests synchronously when the common switching point in time occurs. The respective switching requirements can differ or be identical. The respective switching requests and / or the common switching time can be summarized in a message or transmitted in separate messages. By defining the switching time described here as a common switching time for several battery cells, there is the advantage that respective switching requests can be implemented simultaneously on several battery cells, regardless of the transmission latency, or at least with a higher temporal precision than with the known ones. In this way, for example, undesired loading of an individual battery cell can advantageously be avoided.

The above-described effect of the simultaneous execution of respective switching requests when the common switching time occurs for several battery cells is based on an advantageous development, according to which the battery cells of the predetermined subgroup are electrically connected to one another to form a parallel connection. The parallel connection is resolved or bridged by the Cell processors of the battery cells execute respective switching requests synchronously when the common switching time occurs. In other words, the parallel-connected battery cells of the parallel connection are simultaneously disconnected, connected or bridged by a circuit of the cell connection, in that the cell processors of the battery cells execute respective switching requests synchronously when the common switching time occurs. Any delays in the transmission of the switching requests and / or other effects that affect the transmission latency no longer have any influence on the execution time of a respective switching request. In the case of the parallel connection described, it becomes particularly clear how undesired loading of individual battery cells can be avoided. If, for example, a parallel circuit consisting of several electrically interconnected battery cells is to be bridged, then in order to avoid unwanted loading or unwanted overloading or even a short circuit of individual battery cells it is necessary that the battery cells are actually all bridged at (essentially) the same point in time. In other words, synchronous switching at the time of switching can prevent certain switch combinations from causing damage, such as mutual short-circuiting of battery cells connected in parallel. This is ensured by the embodiment described here, since the corresponding switching request is carried out synchronously in all battery cells when the common switching point in time occurs. In contrast to the known simultaneous disconnection of several battery cells by controlling a common main contactor, there is the advantage of increased flexibility, since the battery cells of the parallel connection can otherwise be controlled individually, i.e. individually introduced into the cell interconnection and individually separated from the cell interconnection.

Another embodiment provides that a respective cell processor has a memory, the cell processor storing incoming switching requests in the memory and holding back a respective incoming switching request until the switching time assigned to it occurs. In this way, a respective transmission time can advantageously be decoupled in time from a respective desired switching time.

For example, if the central control device has a current transmission capacity, the central control device can transmit respective switching requests to the transmission / reception devices of the battery cells concerned, even if the assigned switching times are far, in particular longer than 100 microseconds, in the future. In this way, the central control device can flexibly allocate the capacities available to it.

As described above, the absolute switching time is preferably always selected by the central control device in such a way that a fluctuation in the transmission latency can be intercepted. However, if for whatever reason the respective switching request is only evaluated by a battery cell after the switching time (after decoding), it can preferably be provided that the respective battery cell (or its cell processor) executes the switching request as quickly as possible or immediately .

In the event that the switching time is equal to 0 (ts = 0) and / or if the switching time is in the past at the moment when the switching request for the battery cell was decoded, the battery cell immediately switches to the desired state (becomes the required switching status is established immediately). Is used, for example, if it does not matter whether the battery cells switch at the same time, the main thing is that they switch to the required switching state as quickly as possible.

As described above, the battery cell clocks are synchronized with the system clock. One embodiment provides that the battery cell clocks are synchronized with the system clock of the battery system when a predetermined synchronization point in time occurs and / or according to a predetermined synchronization clock according to a predetermined synchronization protocol. Various synchronization protocols are known which those skilled in the art will identify as suitable. This includes, for example, the so-called TT CAN (Time Triggered CAN ISO 11898-4: 2004). Another example is the AUTOSAR Time Synchronization over CAN (CanTSyn) module. Other variants of the well-known “Time Synchronization over CAN” can also be selected by a specialist as required.

According to an advantageous development, the respective synchronization time and / or the synchronization clock is determined as a function of a respective current deviation between a respective battery cell clock and the system clock. For example, it can be provided that synchronization always takes place when a current deviation reaches a predetermined limit value. In other words, the synchronization clock is preferably selected in such a way that the precision of the battery cell clocks, that is to say their time deviations, are less than a predetermined limit value. The limit value can preferably be selected as a function of real-time requirements of the battery system. The predetermined limit value is preferably in a range between 0 and 50 microseconds, in particular between 20 and 40 microseconds and very particularly preferably 30 microseconds.

In other words, the respective synchronization time and / or the synchronization clock can be designed as a function of a maximum acceptable deviation of a respective battery cell clock from the system clock, the maximum acceptable deviation depending on the real-time requirements of the battery system and / or the cell interconnection.

An advantageous development provides that in a synchronicity monitoring a discrepancy between the battery cell clock of a respective battery cell and the system clock is determined in a predetermined time interval or test interval and a predetermined protective measure is triggered for the respective battery cell if a currently occurring discrepancy a exceeds the maximum permissible deviation. In other words, a protective measure is triggered if a maximum permissible deviation is exceeded within the test interval or a maximum permissible drift of a respective battery cell clock is not observed. The predetermined protective measure can include, for example, deactivation of the battery cell concerned. The protective measure can also consist in outputting a corresponding notice.

A respective cell processor is preferably designed to execute the switching request for “its” battery cell with the lowest possible latency when the respective switching time occurs. For this purpose, an advantageous embodiment provides that the battery cell clock of the battery cell is monitored in the cell processor on an interrupt-based basis. A respective interrupt can preferably be given a high priority. This ensures, on the one hand, that the respective switching request is carried out with the lowest possible latency and, on the other hand, the computing capacity of the respective cell processor can be used efficiently because it does not have to perform cyclical monitoring of the battery cell clock (polling).

A hardware-based approach for monitoring is particularly preferred. For example, a timer can be used which, after a set time has elapsed, can switch a digital I / O (output compare mode of timer) that is connected to the timer. The respective battery cell sets its own timer so that it expires at the time of switching and then switches the switch.

The invention also relates to a battery system with at least one communication network. By means of the at least one communication network, a central control device, a system clock for specifying an absolute system time and several electrically interconnected, switchable battery cells, having respective battery cell clocks synchronized with the system clock and respective transceiver devices, are connected. A respective battery cell has at least one switching element and is designed to receive a switching request for the at least one switching element by means of the transceiver device from the control device by means of the at least one communication network.

According to the invention, the central control device is designed to generate or calculate a switching time for the switching request, taking into account a maximum known transmission latency of the communication network, and to transmit it to the transceiver. The switching time determines a future system time of the system time for executing the at least one switching request.

Furthermore, it is provided according to the invention that the respective battery cell has a cell processor which is designed to recognize the occurrence of the switching time by monitoring the battery cell clock of the respective battery cell and to execute the at least one switching request when the switching time occurs.

The invention also includes further developments of the battery system according to the invention which have features as they have already been described in connection with the further developments of the method according to the invention. For this reason, the corresponding developments of the battery system according to the invention are not described again here.

A preferred embodiment of the battery system provides that a cell branch connecting electrical connections of the battery cell with a galvanic cell and a bypass branch for bridging the respective galvanic cell are arranged in the respective switchable battery cell, the at least one switching element being a first switching element for opening and closing the cell branch or is designed as a second switching element for opening and closing the bypass branch.

The invention also relates to a cell interconnection for a battery system, having a plurality of switchable battery cells or smart cells that are interconnected in an electrically conductive manner.

The invention also includes further developments of the cell interconnection according to the invention which have features as already described in connection with the further developments of the method according to the invention and / or the battery system according to the invention have been described. For this reason, the corresponding developments of the cell interconnection according to the invention are not described again here.

The invention also includes the combinations of the features of the described embodiments.

• 1 eine schematische Darstellung eines Batteriesystems;
• 2 eine schematische Darstellung einer einzelnen schaltbaren Batteriezelle;
• 3 eine schematische Darstellung eines zeitsynchronen Ausführens jeweiliger Schaltanforderungen durch eine Mehrzahl an Batteriezellen; und
• 4 eine schematische Darstellung eines Verfahrens zum Betreiben eines Batteriesystems.

Exemplary embodiments of the invention are described below. This shows:

• 1 a schematic representation of a battery system;
• 2 a schematic representation of a single switchable battery cell;
• 3rd a schematic representation of a time-synchronous execution of respective switching requests by a plurality of battery cells; and
• 4th a schematic representation of a method for operating a battery system.

The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual features of the invention that are to be considered independently of one another and that each also develop the invention independently of one another. Therefore, the disclosure is intended to include combinations of the features of the embodiments other than those shown. Furthermore, the described embodiments can also be supplemented by further features of the invention that have already been described.

In the figures, the same reference symbols denote functionally identical elements.

1 shows a schematic representation of a battery system 10 . The battery system 10 has a communication network 12th and a cell interconnection, not described in more detail here, with a large number of individual battery cells 14th on. Exemplarily shows 1 nine battery cells 14th ( 14.1 to 14.9 ). The battery cells 14th are by means of electrically conductive connections 16 electrically connected to each other. A central control device 18th of the battery system 10 is by means of the communication network 12th with the individual battery cells 14th connected. Each of the battery cells 14th the in 1 The embodiment shown has a battery cell clock 20th on. A respective battery cell clock 20th is designed to record a respective cell time tz (see also 3rd ) for a respective battery cell 14th provide. The battery cell clocks 20th of the battery system 10 the 1 are with a higher-level system clock 22nd synchronized. The system clock 22nd can be used as part of the battery system 10 or be designed as part of a higher-level facility. The system clock 22nd represents an absolute or superordinate system time t _SYS (see also 3rd ) ready for the battery system. According to a predetermined synchronization protocol, the battery cell clocks 20th with the system clock 22nd be synchronized.

With reference to those related to 1 designated and described components shows 2 a schematic representation of a single battery cell 14th , which by means of the communication network 12th with the central control device 18th connected is. The battery cell 14th has a transceiver 24 which is set up for this purpose, one by the central control device 18th transmitted switching request 26th to recieve. Transmission of sensor data S from the battery cell that is not described in more detail here 14th by means of the sender / receiver unit 24 over the communication network 12th to the central control device 18th can be made possible. Between control device 18th and respective battery cells 14th a two-way communication can take place.

The battery cell 14th has as a switchable battery cell in the in 2 embodiment shown a cell branch 27 with a first switching element 28 and a bypass branch 29 with a second switching element 28 on. By activating the respective switching elements accordingly 28 can be a cell processor 30th a respective one by the respective switching requirement 26th Establish the switching state described. In the in 2 The embodiment shown has the battery cell 14th in addition, a balancing switch 32 as well as a balancing resistor 34 on. Possible switching states that a battery cell 14th can take are, for example, a state A (cf. 3rd ), which is an activated or an electrically conductive state of the battery cell connected to an environment 14th corresponds to. Another possible state B (compare 3rd ) can lead to a bridged state of the battery cell 14th correspond. Another conceivable state C (compare 3rd ) can, for example, a balancing state of the battery cell 14th correspond. A further state (not shown) can correspond to a state in which the first switching element 28 of the cell branch 27 and the second switching element 28 of the bypass branch 29 are open and the battery cell 14th that is, switched to "high resistance". Finally, either jointly or separately from a respective switching request 26th by means of the communication network 12th a respective switching time ts (compare 3rd ) from the control device 18th to the sender / receiver unit 24 the battery cell 14th be transmitted.

3rd FIG. 11 now shows with reference to that in connection with FIGS 1 and 2 designated and described components a schematic representation of a time-synchronous execution of respective switching requests 26th by cell processors 30th three battery cells shown here as an example 14th ( 14.1 to 14.3 ).

In the lower area of the 3rd is a time sequence of at the respective battery cells 14th incoming switching requests 26th shown. The switching requirements 26th do not hit all three battery cells at the same time 14th one, but staggered in time. So meets the switching requirement 26th and a respective switching time ts for the battery cell 14.3 at a time t _14.3 a. The switching request 26th and the switching time ts for the battery cell 14.2 arrives at a time t _14.2 . The switching request 26th and the switching time ts for the battery cell 14.1 arrives at a time t _14.1 . The battery cell clocks 20th of the battery cells 14.1 , 14.2 and 14.3 were at a synchronization time t _SYNC with the system clock 22nd synchronized so that the in 3rd The system time t _SYS shown corresponds to a respective cell time t _Z14.1 , t _Z14.2 , t _Z14.3. Also shows 3rd along the system time axis t _SYS the common switching time ts at which the switching requirements 26th should be executed.

The execution of the respective switching requirements 26th is in the upper area of the 3rd shown schematically. Here it is shown how according to the corresponding switching requirement 26th a respective switching state A, B, C of a respective one of the battery cells 14.1 to 14.3 changes at time ts. The condition of the battery cell 14.3 changes from A to C at time ts. The state of the battery cell 14.2 changes from B to A at switching time ts. The switching status of the battery cell 14.1 finally changes at switching time ts from C to B. 3rd naturally shows a non-exclusive and arbitrarily selected change in the respective states, which only serves to illustrate the method described.

4th shows with reference to the in connection with the 1 to 3rd designated and described components a schematic representation of a method for operating a battery system 10 . In one process step S1 transmits a central control device 18th of the battery system 10 a switching request 26th by means of a communication network 12th to a respective battery cell 14th a cell interconnection of the battery system not described in detail here 10 . The switching request 26th describes a required switching state A, B, C of at least one respective battery cell 14th . At this point it should be mentioned that the possible number of switching states or states is 2 ⁿ , where n is the number of switches or switching elements 28 per battery cell 14th is. So with 2 switches (one each in the cell branch 27 and in the bypass branch 29 ), there are 4 possible states. In a further process step S2 receives a transceiver 24 the battery cell 14th the switching request 26th . In one process step S3 runs a cell processor 30th the battery cell 14th the switching request 26th off by having a switching element 28 the battery cell 14th controls, whereby the respectively required switching state A, B or C is established. In a further process step S4 sets the central control device 18th taking into account a known transmission latency of the communication network 12th (or communication stacks) a switching time ts for the switching request 26th firmly. The central control device transmits the specified switching time ts 18th also by means of the communication network 12th the transceiver 24 the battery cell 14th . The switching time ts determines a future system time of the system time t _{SYS of} the battery system 10 to execute the switching request 26th . In one process step S5 recognizes the cell processor 30th the occurrence of the switching time ts and leads to the switching request when it occurs 26th out.

In a specific embodiment, the method can run as follows: 1) The central control device 18th sends the switching time ts to the battery cell 14th , 2 ) the battery cell 14th receives and decodes the switching time ts, 3) the central control device 18th sends the switching request 26th to the battery cell 14th , 4th ) the battery cell 14th receives and decodes the switching request 26th , 5a) If the switching time ts is already in the past or if the switching time ts = 0 was sent, the cell processor switches 30th the switch or the switching element (s) 28 to the desired state, 5b), however, if the switching time ts is in the future, the battery cell waits 14th until switching time ts and then switches the switch.

The case ts = 0 can be used, for example, when the switches 28 do not have to switch synchronously, they switch immediately after decoding the switching request 26th .

In commercial electric vehicles in lithium-ion-based battery systems, sensor data from the battery cells is communicated to a higher-level control unit or a central control device, the Battery Management System (BMS). Often several battery cells are combined to form so-called modules or cell modules or battery modules, which collect the sensor data from the individual cells or battery cells and send them to the BMS. There are also approaches in which the cells communicate directly with the BMS, whereby the number of communication participants increases considerably.

As an interface between BMS and cells or cell modules, mainly CAN (-FD) is sometimes used, but more and more proprietary wired communication protocols are also used. With this approach, however, only sensor data is communicated from the cells to the BMS. There are currently no cells in the vehicle that could be individually controlled by electronics at cell level. This means that today no actuators on the cell are actively controlled by the BMS via the communication path. This results in the disadvantage that the controlled disconnection and connection of individual battery cells is currently not provided in electric and hybrid vehicles. Cells are jointly separated from the load by a main contactor. If all cells of the battery (or the cell wiring) were to be controlled by separate wired optical or electrical signals, this would lead to a considerable increase in complexity, weight and costs, since each cell would have to be individually connected to the BMS. With separate wired control lines, the BMS must be able to operate all of these, i.e. it must be connected to all cells. This would require an interface with hundreds of lines, and the BMS would also have to have hundreds of I / Os, which would also lead to massive increased costs.

According to the present invention, the battery system comprises interconnected smart cells, which are equipped with one or more switch elements or switching elements (cf. 2 ). The cells are connected to one another and to the BMS by one or more communication systems or communication networks, e.g. a CAN bus (cf. 1 ). The position of the switches or switching elements of each cell is requested individually by the BMS, whereby the switch positions or required switching states of the individual cells can be summarized in one or more messages. In a further signal, the BMS sends the so-called switching time or the switching time ts. This signal is either combined with the switch positions in a message, or is sent in a separate message. The switching time or the switching time represents an absolute system time with a resolution in the microsecond (µs) or sub-µs range at which the switching request (s) should be carried out by all cells.

When the respective message is received, each cell decodes the data assigned to it on the switching request and the switching time. The desired switch position is only actually implemented by the respective smart cell when the desired switching time is the same as the network-synchronous system time.

This has the advantage that by implementing the switching requirements via a communication bus, weight and costs can be saved, since a control line from the BMS to each individual cell is no longer necessary. The cells and the BMS only need to be connected to a common communication bus. Because the smart cells do not switch immediately when the switching request is received, but rather at the switching time ts, jitter and delays on the communication path are abstracted (cf. 3rd ). This makes it much easier to ensure that the switches actually switch synchronously within the real-time requirements. The necessary real-time properties of the communication channel can thus be significantly reduced.

In order to implement a global clock, synchronization protocols such as Time Triggered CAN (TTCAN) are required to synchronize the clocks of the individual bus participants (i.e. the battery cell clocks and the system clock). The basis for real-time, synchronous switching of the smart cells is a global clock at the battery system level. The precision of the clocks, i.e. the maximum difference of the local clock between Smart Cells and between Smart Cells and the BMS, may only reach a certain maximum value, which is dependent on the real-time requirements of the battery system. The synchronization protocol must therefore be able to synchronize precisely with a certain resolution and be able to guarantee maximum drift.

The implementation of the switching request and the switching time is relatively simple, since these simply have to be defined as communication signals in the communication matrix or the communication network. How these signals are represented and into how many messages they are divided is not decisive here. It is only important that both all switching requests and the switching time are received by all Smart Cells before the switching time actually occurs. This can be implemented, for example, by assigning message IDs with high priority on the CAN bus.

The smart cells are preferably able to switch at the switching time with the lowest possible latency, for example by means of timer-based high-priority interrupts.

Overall, the examples show how switching requirements announced by the invention for smart cell energy storage devices based on a high-precision network-wide clock can be provided.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• WO 2008/055505 A1 [0005]
• US 2017/0353042 A1 [0006]

Non-patent literature cited

• ISO 11898 [0003]
• ISO 11898-1: 2015 [0003]

Claims (11)

A method for operating a battery system (10), the battery system (10) having at least one communication network (12) and a cell interconnection with a plurality of electrically conductively interconnected, switchable battery cells (14), a system clock (22) having an absolute system time (t _SYS ) specifies for the battery system (10) and battery cell clocks (20) synchronized with the system clock (22) specify respective cell times (tz) for the battery cells (14), wherein a. a central control device (18) of the battery system (10) transmits at least one switching request (26) by means of the at least one communication network (12) to at least one respective battery cell (14) of the plurality of battery cells (14), with a known maximum transmission latency resulting here , wherein the at least one switching request (26) describes a respectively required switching state (A, B, C) of the at least one respective battery cell (14); b. a transceiver (24) of the at least one respective battery cell (14) which receives at least one switching request (26), and c. a cell processor (30) of at least one respective battery cell (14) executes the switching request (26) by activating a switching element (28) of the at least one respective battery cell (14), whereby the respectively required switching state (A, B, C) is established becomes; characterized in that d. the central control device (18), taking into account the maximum known transmission latency, defines a switching time (ts) for the at least one switching request (26) and transmits it to the transceiver (24) by means of the at least one communication network (12), the switching time (ts) determines a future system time of the system time (t _SYS ) of the battery system (10) for executing the at least one switching request (26), e. the cell processor (30) recognizes the occurrence of the switching time (ts) by monitoring the battery cell clock (20) of the at least one respective battery cell (14) and executes the at least one switching request (26) when the switching time (ts) occurs. Procedure according to Claim 1 , wherein the central control device (18) defines a respective switching time (ts) as a common switching time (ts) for a predetermined subgroup of battery cells (14), the cell processors (30) of the battery cells (14) of the predetermined subgroup having respective switching requirements (26 ) execute synchronously when the common switching time (ts) occurs. Procedure according to Claim 2 , the battery cells (14) of the predetermined subgroup being electrically connected to one another to form a parallel connection, the parallel connection being resolved by the cell processors (30) of the battery cells (14) executing respective switching requests (26) synchronously when the common switching time (ts) occurs . Method according to one of the preceding claims, wherein a respective cell processor (30) has a memory, the cell processor (30) storing incoming switching requests (26) in the memory and a respective incoming switching request (26) up to the occurrence of the switching time (ts) assigned to it ) withholds. Method according to one of the preceding claims, wherein the battery _{cell clocks} (20) are synchronized with the system clock (22) of the battery system (10) when a predetermined synchronization time (t SYNC) occurs and / or according to a predetermined synchronization clock according to a predetermined synchronization protocol. Procedure according to Claim 5 , the respective synchronization time point (t _SYNC ) and / or the synchronization clock being determined as a function of a respective current discrepancy between a respective battery cell clock (20) and the system clock (22). Procedure according to Claim 6 , whereby a deviation of the battery cell clock (20) of the respective battery cell (14) from the system clock (22) resulting in a predetermined time interval is determined in a synchronicity monitoring, and a predetermined protective measure is triggered for the respective battery cell (14) if a the currently resulting deviation exceeds a maximum permissible deviation. Method according to one of the preceding claims, wherein the monitoring of the battery cell clock (20) of the at least one respective battery cell (14) in the cell processor (30) is interrupt-based and / or hardware-based. Battery system (10) with at least one communication network (12), wherein by means of the at least one communication network (12) a central control device (18), a system clock (22) for specifying an absolute system time (t _SYS ) and several electrically interconnected, switchable Battery cells (14) having respective battery cell clocks (20) synchronized with the system clock (22) and respective transceiver devices (24) are connected, each battery cell (14) having at least one switching element (28) and being designed to do so by means of the transceiver device (24) from the central control device (18) by means of the at least a communication network (12) to receive a switching request (26) for the at least one switching element (28), characterized in that the central control device (18) is designed to set a switching time, taking into account a known maximum transmission latency of the at least one communication network (12) (ts) for the switching request (26) to be calculated and transmitted to the transceiver (24), the switching time (ts) determining a future system time of the system time (t _SYS ) for executing the at least one switching request (26), wherein the respective battery cell (14) has a cell processor (30) which is designed to detect the occurrence of the switching time (ts) by monitoring the battery cell clock (20) of the respective battery cell (14) and, when the switching time (ts) occurs, the execute at least one switching request (26). Battery system (10) Claim 9 , wherein in the respective switchable battery cell (14) in each case a cell branch (27) connecting electrical connections of the battery cell (14) with a galvanic cell and in each case a bypass branch (29) for bridging the respective galvanic cell is arranged, the at least one switching element ( 28) is designed as a first switching element (28) for opening and closing the cell branch (27) or as a second switching element (28) for opening and closing the bypass branch (29). Cell interconnection for a battery system (10) according to one of the Claims 9 or 10 , having a plurality of switchable battery cells (14) that are electrically interconnected to one another.

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