Inter-unit communication method in battery management system and communication system in BMS

Abstract

The invention belongs to the field of battery management, and particularly relates to an inter-unit communication method in a battery management system and a communication system in a BMS. In the hardware layer, a distributed communication module is arranged at each battery cell unit; the communication modules at the battery cell units are in communication connection by adopting a daisy chain architecture to form a CMU, and a chain head unit in the CMU is in communication connection with the BMU; when the BMU issues a data acquisition instruction, a message containing an effective address segment, a command segment, a data segment, an effective load segment and a verification segment is sent to the CMU; the object receiving the message firstly judges whether to execute an instruction and forward an original message or an updated message according to the information of the effective address field; and according to the information of the effective load segment, selecting to forward the message to a unit in a next chain or to return. And the BMU extracts data segment information according to the returned message to complete a data acquisition task. The problem that a BMS system of an existing battery pack cannot realize wire harness simplification and communication efficiency improvement at the same time is solved.

Description

Technical Field

[0001] This invention belongs to the field of battery management, specifically relating to a method for inter-cell communication within a battery management system, a communication system within a BMS, and a battery pack. Background Technology

[0002] As a core component of new energy vehicles and energy storage systems, the safety and reliability of power batteries have received widespread attention. The Battery Management System (BMS), acting as the "intelligent brain" of the battery pack, undertakes critical tasks such as real-time monitoring of battery parameters including voltage, temperature, capacity, and internal resistance, ensuring the safe operation of the battery pack and extending its service life.

[0003] The BMS architecture consists of an analog front-end (AFE), a master control unit (BMU), a state of battery health (SOH), and a slave control unit (CMU). The AFE collects battery voltage, temperature, and current readings; the BMU monitors battery pack parameters and balances charge levels; the SOH assesses battery health; and the CMU monitors individual battery cells and transmits data to the BMU. The BMS system architecture employs a multi-layered design, including a data acquisition layer, a communication layer, and a control execution layer, with the communication layer being particularly critical. Currently, mainstream BMS communication architectures primarily utilize the CAN bus technology.

[0004] The CAN bus is based on the ISO 11898 standard and uses twisted-pair cables for differential voltage transmission, allowing communication without a central control. However, as battery pack integration increases (such as the 96-cell battery module in the Tesla Model 3), its disadvantages in pin resource consumption and wiring complexity become apparent. In addition, CAN communication has limitations such as channel errors leading to congestion, asynchronous differential signal consistency issues, unpredictable node states, and high implementation costs.

[0005] The daisy-chain architecture is a communication architecture different from the CAN bus. It eliminates the need for separate wiring between communication units; instead, it connects different objects that need to communicate sequentially and interacts through an internal communication protocol. Compared to the CAN bus solution, the daisy-chain architecture has simpler wiring, reduces bus occupancy, and achieves higher communication density. However, the chain-like communication characteristic also introduces rate limitations; when the number of connected units exceeds 64, the communication latency increases to over 2.5ms. Introducing a traditional daisy-chain architecture into power batteries requires traversing all cells to collect data, even if only monitoring data from a few cells in a localized area of ​​the battery pack is needed. Therefore, the existing daisy-chain architecture is unsuitable for power battery packs containing hundreds or thousands of cells. Summary of the Invention

[0006] To address the issue that existing battery pack BMS systems cannot simultaneously achieve both wiring harness simplification and communication efficiency, this invention provides a method for inter-cell communication within a battery management system, a communication system within a BMS, and a battery pack.

[0007] The technical solution provided by this invention is as follows: A cell-to-cell communication method within a battery management system is provided for bidirectional communication between the main control unit (BMU) and the analog front-ends (AFEs) at each cell unit. This cell-to-cell communication method includes: Distributed communication modules are installed at each cell unit; each cell unit's communication module is electrically connected to its respective AFE. The communication modules at each cell unit are connected in a daisy-chain architecture to form a slave control unit (CMU), and the head unit in the CMU is connected to the BMU.

[0008] When the BMU issues a data acquisition command, it sends a message to the CMU containing a valid address segment, a command segment, a data segment, a payload segment, and a check segment.

[0009] Upon receiving a message, any head or middle unit in the CMU first performs verification and parsing; then it compares its own address with the valid address range. (1) If the comparison is successful, the instruction is executed, and the corresponding data segment content is added according to the execution result before updating the message. Then check whether the payload has reached the preset value. If yes, the message is forwarded to the next unit in the chain; otherwise, the message is sent back.

[0010] (2) If the comparison fails, the received original message will be forwarded directly to the next unit in the chain.

[0011] BMU extracts data segment information based on the returned messages to complete the data acquisition task.

[0012] As a further improvement of the present invention, in the message transmitted by the daisy-chain bus, the payload segment has a fixed length and its contents include valid bits, value bits and flag bits.

[0013] The valid bit indicates the number of objects whose instructions should be executed in the current acquisition command. The numeric bit indicates the number of objects whose instructions have been executed during the transmission of the current acquisition command. The flag bit indicates whether the effective load has reached a preset value; a value of 1 indicates that the effective load has been reached, and a value of 0 indicates that the effective load has not been reached.

[0014] As a further improvement of the present invention, the method for any chain head unit or chain middle unit to check whether the effective load has reached a preset value is as follows: After executing the instructions and updating the data segment content, the value of the numeric segment is incremented by one; then it is determined whether the value of the numeric segment is equal to the value of the valid segment. If they are equal, it means that the effective load has reached the preset value, and the flag bit is set to 1; otherwise, it means that the effective load has not reached the preset value, and the flag bit is kept at 0.

[0015] As a further improvement of the present invention, the content of the valid address field in the message includes the address information of the communication modules of all the acquisition objects corresponding to the data acquisition command; the information length of the valid address field is related to the preset number of acquisition objects.

[0016] As a further improvement of the present invention, the data segment in the message sent by the BMU is blank; the maximum length of the data segment in any message is related to the number of data acquisition objects and the instruction type of the current data acquisition task.

[0017] As a further improvement of the present invention, each communication module of CMU includes a verification unit, which uses the CRC-8 verification method to verify the data according to the content of the verification segment.

[0018] All head units and middle units can use the same check code. Alternatively, the head units and each middle unit can use different check codes; in this case, the verification unit pre-calculates and stores the CRC result table corresponding to all possible check codes, and completes the verification by looking up the table.

[0019] As a further improvement of the present invention, after receiving a message, the chain head unit or each chain unit in the CMU first extracts the checksum of the check segment, then uses the checksum to perform calculations to obtain the CRC result, and finally completes the verification based on the CRC result: (1) If the verification is successful, then the message content is parsed; (2) If the verification fails, the communication error flag is triggered and the communication error flag is sent back.

[0020] As a further improvement of the present invention, after receiving the returned communication error flag, the BMU reissues the data acquisition command.

[0021] As a further improvement of the present invention, in the CMU, the signals transmitted between the various communication units adopt Manchester encoding; so as to complete the transmission of clock and data simultaneously through a single signal line.

[0022] The present invention also includes a BMS intra-communication system, which includes: an analog front end, a slave control unit, a master control unit, and a health assessment unit.

[0023] The system comprises several modules: a simulation front-end corresponding to each individual cell in the battery pack, used to monitor the battery voltage, temperature, and current of each cell; a slave control unit including a communication module at each cell, electrically connected to its respective simulation front-end; and a daisy-chain architecture for communication between the communication modules at each cell. One communication module is designated as the head unit, communicating with the master control unit; the remaining modules are sequentially connected units in the chain. The slave control unit transmits monitoring data from each cell to the master control unit. The master control unit monitors battery pack parameters and balances charge levels based on the data uploaded by the slave control units. A health assessment unit evaluates the health of the battery pack based on the monitoring data collected by the master control unit from each cell.

[0024] In the BMS communication system provided by this invention, the slave control unit and the master control unit use the inter-unit communication method in the battery management system described above to conduct bidirectional communication in order to realize the issuance of data acquisition commands and the uploading of monitoring data.

[0025] The invention also includes a battery pack that employs the BMS communication system as described above.

[0026] The technical solution provided by this invention has the following beneficial effects: This invention overcomes the biases of those skilled in the art by innovatively applying a daisy-chain architecture to inter-cell communication in a Battery Management System (BMS), significantly reducing the number of wiring harnesses, lowering system costs and wiring complexity, supporting multi-node expansion, and making it suitable for highly integrated battery packs. Based on this, and using an improved protocol layer, the BMS can promptly send back messages when performing non-global data acquisition tasks, thereby greatly improving system data throughput and reducing transmission latency.

[0027] This invention also integrates a CRC-8 check mechanism into the communication system, improving data integrity and security, preventing noise interference, and increasing protocol efficiency to more than 1.5 times that of traditional solutions. This allows the new communication system to be compatible with low-power designs, meet automotive-grade requirements, improve SOC estimation accuracy, and extend the lifespan of the power battery. Attached Figure Description

[0028] Figure 1 This is a communication architecture diagram of the master and slave devices using a daisy-chain bus in Embodiment 1 of the present invention.

[0029] Figure 2 This is a flowchart of the inter-cell communication method within the battery management system provided in Embodiment 1 of the present invention.

[0030] Figure 3 This is a schematic diagram of the BMS intra-communication system provided in Embodiment 2 of the present invention.

[0031] Figure 4 This is a signal diagram of the encoding end using Manchester encoding in the simulation experiment.

[0032] Figure 5 This is a signal diagram of the decoding end using Manchester encoding in the simulation experiment.

[0033] Figure 6 This is a signal diagram illustrating the data transmission process using a custom protocol in a simulation experiment. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0035] Example 1 Communication architectures and protocols in battery management systems (BMS) cannot simultaneously reduce the number of wiring harnesses while ensuring communication efficiency and reducing communication latency. This embodiment provides a method for inter-cell communication within a BMS, enabling bidirectional communication between the main control unit (BMU) and the analog front-ends (AFEs) at each cell unit, thereby facilitating the issuance of data acquisition commands and the uploading of monitoring data.

[0036] Based on the traditional CAN bus, the improvement of the inter-cell communication method within the battery management system provided in this embodiment includes two aspects: hardware layer and protocol layer; specifically, it includes the following: (1) The traditional four-wire SPI communication protocol has problems of numerous wire harnesses and severe interference when facing a large number of lithium battery cell units. In order to simplify the wire harness, this embodiment uses a daisy chain bus to connect the main control unit and each cell unit.

[0037] (2) When the various communication modules on the daisy-chain bus interact, this embodiment uses Manchester encoding for all types of transmitted messages to further simplify the wiring harness within the system and improve the anti-interference capability of the data. Each communication module can use Manchester encoding to transmit data and clock simultaneously, merging SCK+MOSI into a single signal line.

[0038] (3) Based on the daisy chain architecture, this experiment redesigns a custom communication protocol. The protocol is based on the slave device and can combine the address information and payload information in each message to trigger data forwarding and data return, thereby improving the efficiency of instruction and data transmission under non-global monitoring tasks in BMS.

[0039] (4) This embodiment can also integrate a CRC-8 verification mechanism in each communication module to ensure the integrity of data transmitted between different objects and prevent noise and malicious tampering.

[0040] In detail, at the hardware layer, such as Figure 1 As shown, the scheme in this embodiment sets up distributed communication modules at each battery cell unit; the communication module at each battery cell unit is electrically connected to its respective AFE; in practical applications, the two can be connected through signal acquisition lines, low-voltage harnesses, or FPC sampling harnesses. The communication modules at each battery cell unit are connected in a daisy-chain architecture to form a slave control unit (CMU). In the slave control unit, one communication module is designated as the chain head unit, which is connected to the master control unit; the remaining communication modules are connected sequentially as chain middle units.

[0041] At the protocol layer, the signals transmitted between communication units use Manchester encoding to simultaneously transmit clock and data via a single signal line. Meanwhile, this embodiment further defines a completely new message format, such as... Figure 2 As shown, the messages transmitted between the various communication objects connected on a daisy chain include a valid address segment, a command segment, a data segment, a payload segment, and a check segment.

[0042] The message's valid address segment contains the address information of the communication modules of all objects corresponding to the data acquisition command. The length of the valid address segment is related to the preset number of objects; the more objects the acquisition command sends, the longer the valid address segment. Considering that any command needs a clearly defined execution object, the valid address segment must include the address of at least one communication object. The command segment has a variable length and records the type of command currently issued. For example, in a data acquisition command, the command type in the command segment clearly specifies which monitoring indicators need to be collected. The data segment contains the results of the monitoring indicators uploaded by each command execution object. In practical applications, the data segment in BMU-issued messages is blank; however, as the message is transmitted sequentially between different objects in the daisy chain, the data segment content is continuously updated. The maximum length of the data segment in any message is related to the number of objects and the command type in this round of data acquisition. The payload segment has a fixed length and includes a valid bit, a value bit, and a flag bit. The valid bit indicates the number of objects whose commands should be executed in the current acquisition command. The value bit indicates the number of objects whose commands have been executed during the transmission of the current acquisition command. The flag bit indicates whether the payload has reached a preset value; a value of 1 indicates that the payload has been reached, and a value of 0 indicates that the payload has not been reached. The checksum section records the checksum of each message, and it is also of fixed length. Of course, in practical applications, a fixed-value buffer code can also be set between the functional sections of the message to facilitate message parsing.

[0043] Based on this, the process of command execution and data acquisition in this embodiment is as follows: When the BMU issues a data acquisition command, it sends a message to the CMU containing a valid address segment, a command segment, a data segment, a payload segment, and a check segment; the initial content of the command segment is empty.

[0044] The chain head unit receives the message first. After receiving the message, it first performs verification and parsing; then it compares its own address with the valid address range. If the comparison is successful, it executes the instruction and updates the message by adding the corresponding data segment content according to the execution result. If the comparison fails, it directly forwards the received original message to the next chain unit.

[0045] After the message is updated, the chain head unit continues to check whether the payload has reached the preset value. If so, the message is forwarded to the next chain unit; otherwise, the message is sent back.

[0046] If the head unit is not the instruction execution target, or is not the only instruction execution target, it needs to send the message to the next unit in the chain. Upon receiving a message, any unit in the CMU first performs verification and parsing; then it compares its own address with the valid address range, and uses the same strategy as the head unit to generate a decision based on the judgment result, including: (1) If the comparison is successful, the instruction is executed, and the corresponding data segment content is added according to the execution result before updating the message. Then check whether the payload has reached the preset value. If yes, the message is forwarded to the next unit in the chain; otherwise, the message is sent back.

[0047] (2) If the comparison fails, the received original message will be forwarded directly to the next unit in the chain.

[0048] In this embodiment, each communication module of the CMU includes a verification unit, which uses the CRC-8 checksum method to verify the data based on the content of the checksum segment. In practical applications, all head units and middle units can use the same checksum. Alternatively, the head units and each middle unit can use different checksums; in this case, the verification unit pre-calculates and stores a CRC result table corresponding to all possible checksums, and completes the verification by looking up the table.

[0049] In the CMU, after receiving a message, the head unit or any unit in the chain first extracts the checksum of the check segment, then uses the checksum to calculate the CRC result, and finally completes the verification based on the CRC result. (1) If the verification is successful, then the message content is parsed; (2) If the verification fails, the communication error flag is triggered and the communication error flag is sent back.

[0050] In this embodiment, the method for any chain head unit or chain middle unit to check whether the effective load has reached the preset value is as follows: after executing the instruction and updating the data segment content, the value of the numerical segment is incremented by one; then it is determined whether the value of the numerical segment is equal to the value of the effective segment. If they are equal, it means that the effective load has reached the preset value, and the flag bit is set to 1; otherwise, it means that the effective load has not reached the preset value, and the flag bit is kept at 0.

[0051] At any given time, when the BMU receives a returned message, it parses the contents of the data segment contained within and terminates the current round of data acquisition. If a communication error occurs at any node during the execution of the aforementioned data acquisition task and is detected by the verification unit, the BMU will receive a returned communication error flag. In this case, to ensure the normal execution of the data acquisition task, in this embodiment, the BMU can reissue the data acquisition command.

[0052] Based on the strategies described above, although this embodiment uses a daisy-chain bus for communication, when performing non-global data acquisition tasks, it only needs to determine that the data of all acquisition objects has been successfully acquired based on the contents of the valid address segment and the valid payload segment before sending back messages. It is not necessary to traverse all communication objects in the entire daisy chain to ensure data integrity. This significantly improves the communication efficiency of the BMS and increases data throughput.

[0053] It is particularly important to emphasize that, for the same purpose, in the connection sequence of the daisy-chain bus, the cell units with higher risk levels or closer to the center of the battery pack should be placed closer to the head unit on the daisy-chain bus to ensure that data acquisition tasks in certain high-frequency triggered local areas can be executed more quickly.

[0054] Example 2 Based on the solution in Embodiment 1, this embodiment further provides a BMS-internal communication system, such as... Figure 3 As shown, it includes: a simulation front-end, a slave control unit, a master control unit, and a health assessment unit.

[0055] The simulation front-end corresponds to each cell unit in the battery pack and is used to monitor the battery voltage, temperature, and current of each cell unit. The slave control unit includes a communication module located at each cell unit, and each cell unit's communication module is electrically connected to its respective simulation front-end. The communication modules at each cell unit are connected using a daisy-chain architecture. One communication module is designated as the head unit, which communicates with the master control unit; the remaining communication modules are sequentially connected units in the chain. The slave control unit transmits the monitoring data of each cell unit to the master control unit. The master control unit monitors the battery pack parameters and balances the charge based on the data uploaded by the slave control unit. The health assessment unit assesses the health of the battery pack based on the monitoring data collected by the master control unit from each cell unit. Specifically, in the BMS communication system provided in this embodiment, the slave control unit and the master control unit use the inter-cell communication method within the battery management system as described in Embodiment 1 for bidirectional communication to achieve data acquisition command issuance and monitoring data upload.

[0056] Building upon this, this embodiment also provides a battery pack employing the aforementioned BMS-internal communication system. The battery pack utilizing this BMS-internal communication system can overcome the rate limitations of traditional daisy-chain communication, increasing data throughput to meet the demands of fast charging and high-precision SOC estimation. In practical applications, the entire link can support clock frequencies >50MHz, ensuring real-time response. Therefore, this embodiment overcomes the transmission delay problem caused by node expansion when using a daisy-chain communication architecture in a BMS. Furthermore, this embodiment's solution overcomes noise interference and data tampering risks through a verification mechanism, ensuring the integrity and security of communication data. This solution lays the foundation for achieving low-power, highly integrated automotive-grade applications.

[0057] Performance verification To verify the performance of the inter-cell communication method and the BMS communication system provided by this invention, technicians formulated a simulation experiment plan and conducted simulation tests on the relevant schemes. I. Manchester Encoding and Decoding Verification This experiment first performs Manchester coding on the signal used, and the signal obtained at the coding end... Figure 4 As shown, CLK is the system clock, signal_io is the output code, and send_data is the encoded data. The actual data being encoded is 0xC46A0.

[0058] Based on this, the simulation test sent 0x1F as the data source, and the signal obtained by the decoding end was as follows: Figure 5As shown. The decoding scheme uses a pure clock recovery method (i.e., decoding depends on clock recovery, then the recovered clock is synchronized with the data signal and sampled to obtain the transmitted data), where clk_out and signal_io are the decoded clock and data.

[0059] The above data shows that the solution of the present invention can effectively integrate Manchester encoding and decoding logic at the data sending and receiving ends, so as to further achieve harness compactness.

[0060] II. Communication Protocol Verification This experiment further verifies the data transmission and reception functions of the daisy-chain communication scheme based on the SPI protocol. When writing data, the SPI sequentially sends the address, the data to be written, and the CRC checksum (8'h20, 16'h1234, 8'h29). When reading data, it sends the read address and the number of registers to be read (8'h20, 1). The signals obtained during the simulation process are as follows... Figure 6 As shown.

[0061] According to the data in the figure, both the MOSI and MISO lines are correctly pulled high, and the data transmission and reception functions are correct.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for inter-cell communication within a battery management system, characterized in that, It is used for bidirectional communication between the main control unit (BMU) and the analog front-end (AFE) at each cell unit; it includes: Distributed communication modules are set at each cell unit; the communication module at each cell unit is electrically connected to its respective AFE; the communication modules at each cell unit are connected in a daisy chain architecture to form a slave control unit (CMU), and the head unit in the CMU is connected to the BMU. When the BMU issues a data acquisition command, it sends a message to the CMU containing a valid address segment, a command segment, a data segment, a payload segment, and a check segment. Upon receiving a message, any head or middle unit in the CMU first performs verification and parsing; then it compares its own address with the valid address range. (1) If the comparison is successful, execute the instruction and update the message after adding the corresponding data segment content according to the execution result; then check whether the payload has reached the preset value. If yes, forward the message to the next unit in the chain; otherwise, send the message back. (2) If the comparison fails, the received original message is forwarded directly to the next unit in the chain; BMU extracts data segment information based on the returned messages to complete the data acquisition task.

2. The inter-cell communication method within the battery management system as described in claim 1, characterized in that: The payload segment in the message is of fixed length, and its content includes valid bits, value bits, and flag bits; The valid bit is used to characterize the number of objects that should be executed in the current acquisition command; The numerical bits are used to characterize the number of objects that have completed instruction execution during the current acquisition instruction transmission process; The flag bit is used to indicate whether the effective load has reached a preset value. A value of 1 indicates that the effective load has been reached, and a value of 0 indicates that the effective load has not been reached.

3. The inter-cell communication method within the battery management system as described in claim 2, characterized in that: The method for any head unit or middle unit of the chain to check whether the effective load has reached the preset value is as follows: After executing the instructions and updating the data segment content, the value of the numeric segment is incremented by one; then it is determined whether the value of the numeric segment is equal to the value of the valid segment. If they are equal, it means that the effective load has reached the preset value, and the flag bit is set to 1; otherwise, it means that the effective load has not reached the preset value, and the flag bit is kept at 0.

4. The inter-cell communication method within the battery management system as described in claim 1, characterized in that: The content of the valid address field in the message includes the address information of the communication modules of all the acquisition objects corresponding to the data acquisition command; the information length of the valid address field is related to the preset number of acquisition objects.

5. The inter-cell communication method within the battery management system as described in claim 1, characterized in that: The data segment in the message sent by BMU is blank; the maximum length of the data segment in any message is related to the number of data acquisition objects and the instruction type in this round of data acquisition task.

6. The inter-cell communication method within the battery management system as described in claim 1, characterized in that: Each communication module of the CMU includes a verification unit, which uses the CRC-8 verification method to verify the data based on the content of the verification segment. The head unit and the middle unit of the chain use a single check code; Alternatively, the head unit and each unit in the chain can use different check codes; The verification unit pre-calculates and stores a table of CRC results corresponding to all possible check codes, and completes the verification by looking up the table.

7. The inter-cell communication method within the battery management system as described in claim 6, characterized in that: After receiving a message, the head unit or any unit in the chain in CMU first extracts the checksum of the check segment, then uses the checksum to calculate the CRC result, and finally completes the verification based on the CRC result. If the verification is successful, proceed with message content parsing; If the verification fails, a communication error flag is triggered and the communication error flag is sent back. And / or, after receiving the returned communication error flag, the BMU reissues the data acquisition command.

8. The inter-cell communication method within the battery management system as described in claim 1, characterized in that: In CMU, the signals transmitted between communication units use Manchester encoding to simultaneously transmit clock and data through a single signal line.

9. A BMS-based communication system, characterized in that, It includes: The analog front end corresponds to each cell unit in the battery pack and is used to monitor the battery voltage, temperature and current of each cell unit; The slave control unit includes a communication module located at each battery cell unit, and each communication module at each battery cell unit is electrically connected to its respective analog front end. The communication modules at each battery cell unit are connected in a daisy-chain architecture. One communication module is designated as the chain head unit, and the chain head unit is connected to the master control unit. The remaining communication modules are connected sequentially as chain middle units. The slave control unit is used to transmit the monitoring data of each battery cell unit to the master control unit. The main control unit is used to monitor battery pack parameters and balance the power based on data uploaded by the slave control unit; The health assessment unit is used to assess the health of the battery pack based on the monitoring data of each cell unit collected by the main control unit. The slave control unit and the master control unit communicate bidirectionally using the inter-unit communication method in the battery management system as described in any one of claims 1-8, so as to realize the issuance of data acquisition commands and the uploading of monitoring data.

10. A battery pack, characterized in that: It employs the BMS intra-communication system as described in claim 9.

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