Undervoltage protection method of vehicle battery pack, battery management system and vehicle controller

Abstract

The invention belongs to the technical field of battery under-voltage protection, and particularly relates to an under-voltage protection method for a vehicle battery pack, a battery management system and a vehicle controller, and the method comprises the steps: obtaining the whole pack voltage of the battery pack and the monomer voltage of each internal battery cell in the high-speed driving process of a vehicle in a batch production stage; carrying out undervoltage grading diagnosis according to the voltage of the whole pack and the single voltages of all the battery cells, so as to determine a target discharge limit strategy according to the undervoltage grade after determining that the battery pack has an undervoltage fault; and executing the target discharge limit strategy to realize under-voltage protection of the battery pack. According to the method, the battery pack can be well protected in the vehicle development stage, the situation that under-voltage damage of the battery pack is caused by immature data is avoided, monitoring can be carried out according to the single sampling voltage and the whole pack voltage in the driving process, the under-voltage severe degree is distinguished, corresponding power level limiting response is made, the battery pack can be protected, and the service life of the battery pack is prolonged. And the driving feeling and the driving safety can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery undervoltage protection, and specifically relates to an undervoltage protection method for a vehicle battery pack, a battery management system, and a vehicle controller. Background Art

[0002] With the rapid development of new energy vehicles and the substantial increase in the number of vehicles in use, battery safety issues are frequent, so the BMS (Battery Manager System) battery management system has received more and more attention from the industry. Among them, battery cell undervoltage, overvoltage, overtemperature and other conditions may cause irreversible damage to the battery pack. Therefore, it is necessary to design, optimize and improve strategies to prevent battery cell overdischarge and undervoltage and corresponding treatment measures to prevent battery pack damage as much as possible. Summary of the invention

[0003] In view of the shortcomings of the prior art mentioned above, the purpose of the present invention is to provide a battery undervoltage protection strategy based on BMS control, which can cover most vehicle usage scenarios and take corresponding protection measures through diagnosis before and after the battery cell is undervoltage, so as to protect the battery safety as much as possible.

[0004] To achieve the above-mentioned object and other related objects, the present invention provides an undervoltage protection method for a vehicle battery pack, comprising: obtaining the whole pack voltage of the battery pack and the single cell voltage of each internal battery cell during high-speed driving of the vehicle in the mass production stage; performing undervoltage classification diagnosis based on the whole pack voltage and the single cell voltages of all battery cells, so as to determine a target discharge limit strategy based on the undervoltage level after confirming that the battery pack has an undervoltage fault; and executing the target discharge limit strategy to achieve undervoltage protection for the battery pack.

[0005] According to a specific embodiment of the present invention, the step of performing undervoltage grading diagnosis based on the whole pack voltage and the single cell voltages of all battery cells to determine the target discharge limit strategy based on its undervoltage level after confirming that the battery pack has an undervoltage fault includes: verifying the validity of the single cell voltages of all battery cells; when the single cell voltages of all battery cells are valid, performing a first undervoltage grading diagnosis based on the single cell voltages of all battery cells to confirm whether the battery pack has an undervoltage fault and its corresponding first undervoltage level, and determining the target discharge limit strategy based on the first undervoltage level after the battery pack has an undervoltage fault.

[0006] According to a specific embodiment of the present invention, the step of performing a first undervoltage classification diagnosis based on the single cell voltages of all battery cells to confirm whether an undervoltage fault occurs in the battery pack and its corresponding first undervoltage level includes: identifying the smallest single cell voltage from all battery cells, and comparing it with the threshold ranges of different first undervoltage levels, respectively, to confirm whether an undervoltage fault occurs in the battery pack and its corresponding first undervoltage level; wherein the threshold ranges of different first undervoltage levels are related to the current temperature of the battery cell.

[0007] According to a specific embodiment of the present invention, the step of performing undervoltage grading diagnosis based on the whole pack voltage and the single cell voltages of all battery cells to determine the target discharge limit strategy based on the undervoltage level after confirming that the battery pack has an undervoltage fault also includes: when the single cell voltages of one or more battery cells are invalid, performing a second undervoltage grading diagnosis based on the whole pack voltage to confirm whether the battery pack has an undervoltage fault and its corresponding second undervoltage level, and determining the target discharge limit strategy based on the second undervoltage level after the battery pack has an undervoltage fault.

[0008] According to a specific embodiment of the present invention, the step of performing a second under-voltage classification diagnosis based on the whole pack voltage to confirm whether an under-voltage fault occurs in the battery pack and its corresponding second under-voltage level includes: comparing the whole pack voltage with a threshold range of different second under-voltage levels to confirm whether an under-voltage fault occurs in the battery pack and its corresponding second under-voltage level; wherein the threshold range of different second under-voltage levels is related to the current temperature of the battery pack.

[0009] According to a specific embodiment of the present invention, the step of performing undervoltage grading diagnosis according to the whole pack voltage and the single cell voltages of all battery cells to determine the target discharge limit strategy according to the undervoltage level after confirming that the battery pack has an undervoltage fault includes: verifying the validity of the single cell voltages of all battery cells and the validity of the whole pack voltage; when the single cell voltages of all battery cells are valid and the whole pack voltage is valid, performing a first undervoltage grading diagnosis according to the single cell voltages of all battery cells to confirm whether the battery pack has an undervoltage fault and its corresponding first undervoltage level, and determining a first discharge limit strategy according to the first undervoltage level after the battery pack has an undervoltage fault; and performing a second undervoltage grading diagnosis according to the whole pack voltage to confirm whether the battery pack has an undervoltage fault and its corresponding second undervoltage level, and determining a second discharge limit strategy according to the second undervoltage level after the battery pack has an undervoltage fault; selecting the one with a higher priority from the first discharge limit strategy and the second discharge limit strategy as the target discharge limit strategy.

[0010] According to a specific embodiment of the present invention, it also includes: obtaining the single cell voltage of each battery cell in the battery pack during the testing process of the vehicle in the development stage; performing undervoltage diagnosis based on the single cell voltages of all battery cells to control the battery pack to lower the high voltage after confirming that the battery pack has an undervoltage fault; wherein, the vehicle is identified as being in the development stage or the mass production stage through the interface status.

[0011] According to a specific embodiment of the present invention, the step of performing undervoltage diagnosis based on the single cell voltages of all battery cells includes: verifying the validity of the single cell voltages of all battery cells; when the single cell voltages of all battery cells are valid, identifying the smallest one from the single cell voltages of all battery cells, and comparing it with a preset threshold to confirm whether an undervoltage fault occurs in the battery pack; wherein the threshold is higher than the threshold range set for the undervoltage graded diagnosis.

[0012] A method for undervoltage protection of a vehicle battery pack comprises: obtaining the whole pack current, the remaining power, and the single cell voltage of each internal battery cell of the battery pack during parking or low-speed driving of the vehicle in the batch production stage; diagnosing a small current over-discharge fault according to the single cell voltages of all battery cells, the remaining power of the battery pack, and the whole pack current; when a small current over-discharge fault occurs in the battery pack, limiting the battery pack from continuing to discharge and prohibiting it from having high voltage.

[0013] According to a specific embodiment of the present invention, the step of performing a small current over-discharge fault diagnosis based on the single cell voltages of all battery cells, the remaining power of the battery pack and the current of the entire pack includes: verifying the validity of the single cell voltages of all battery cells: if the single cell voltages of all battery cells are valid, performing a small current over-discharge fault diagnosis based on the minimum single cell voltage, the remaining power of the battery pack and the current of the entire pack; wherein, when the minimum single cell voltage is less than a preset threshold value, the current of the entire battery pack is within a preset small current range, and the remaining power of the battery pack is less than the preset power, it is determined that a small current over-discharge fault has occurred in the battery pack.

[0014] According to a specific embodiment of the present invention, after limiting the battery pack from continuing to discharge and prohibiting it from applying high voltage, it also includes: identifying the plug-in status of the vehicle; when the vehicle is plugged in for charging, allowing the battery pack to apply high voltage; and monitoring the abnormal discharge behavior of the battery pack during charging to control the battery pack to reduce high voltage when charging fails and continues to discharge.

[0015] According to a specific embodiment of the present invention, the step of monitoring the abnormal discharge behavior of the battery pack during charging to control the high voltage of the battery pack when charging fails and continues to discharge includes: calculating the ampere-hour integral of the battery pack discharge current to determine whether the battery pack fails to charge and continues to discharge.

[0016] A battery management system, characterized in that it includes a processor, the processor is coupled to a memory, the memory stores program instructions, and when the program instructions stored in the memory are executed by the processor, the above-mentioned method is implemented.

[0017] A vehicle controller comprises the battery management system mentioned above.

[0018] The present invention provides a vehicle battery pack undervoltage protection method, which can monitor the single cell sampling voltage and the whole pack voltage during vehicle driving, thereby distinguishing the severity of undervoltage and making a corresponding power limit level response, so as not to lose power immediately, thereby protecting the battery pack and improving driving experience and driving safety. In addition, the battery pack can be well protected during the vehicle development stage to prevent the battery pack from being damaged by undervoltage due to immature data, thus saving compensation for damaged battery packs.

[0019] In addition, the present invention takes into account the situation of small current over-discharge and also takes into account working conditions such as plug-in charging failure, covering most vehicle usage scenarios and playing a protective role before the battery cell is under-voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of the overall flow of a specific embodiment of an undervoltage protection method for a vehicle battery pack provided by the present invention; Figure 2 A schematic flow chart of a specific embodiment of an undervoltage protection method for a vehicle battery pack provided by the present invention; Figure 3 A schematic flow chart of another specific embodiment of an undervoltage protection method for a vehicle battery pack provided by the present invention; Figure 4 A schematic flow chart of another specific embodiment of an undervoltage protection method for a vehicle battery pack provided by the present invention; Figure 5 This is a structural block diagram of a specific embodiment of a battery management system provided by the present invention. DETAILED DESCRIPTION

[0021] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. Embodiments of the present application are provided in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0023] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0024] In the following description, numerous details are discussed to provide a more thorough explanation of the embodiments of the present invention. However, it is obvious to those skilled in the art that the embodiments of the present invention can be implemented without these specific details. In other embodiments, well-known structures and devices are shown in the form of block diagrams rather than in detail to avoid making the embodiments of the present invention difficult to understand.

[0025] Example 1 See also Figure 1 As shown, the present application mainly provides a method for undervoltage protection of a vehicle battery pack, which is mainly divided into three parts. First, an undervoltage diagnosis strategy is added to the BMS development stage of the vehicle. When the battery pack is about to be damaged, the relay on the high-voltage circuit can be disconnected to protect the safety of the battery pack by lowering the high voltage. This function can be turned off in the vehicle mass production stage, so as to reduce the frequency of fault reporting and avoid affecting the vehicle experience. Second, the undervoltage diagnosis and protection response are divided into multiple levels according to the undervoltage level of the vehicle battery pack. Different levels correspond to different power levels of output restrictions, which can protect the battery without completely losing power of the vehicle, thereby ensuring driving safety. Third, a diagnostic strategy for small current over-discharge is added, and conditions such as SOC, current, voltage, vehicle speed and whether the gun is successfully inserted can be considered to perform over-discharge protection in an all-round way, which plays a protective role before the battery pack is actually undervoltage. Based on the above, the software protection strategy of BMS can be improved from all scenarios to achieve undervoltage protection of the vehicle battery pack.

[0026] First, for the vehicle development stage, the software program in the BMS can be made to recognize this stage through logic design, and then turn on the corresponding undervoltage protection function. In actual applications, the development of BMS needs to continuously test its related performance both at the software level and the hardware level, and correspondingly needs to establish a connection through its software interface or hardware interface. When the vehicle is actually put into production, these test interfaces will be closed accordingly to avoid affecting the normal operation of the BMS or the core technology being cracked by other manufacturers.

[0027] Therefore, relevant software programs for identifying the interface status can be written in the BMS in advance, so that the BMS can correctly identify the current status, thereby enabling the undervoltage protection function of the battery pack during the development stage to avoid irreversible damage to the battery pack during the test process.

[0028] In addition, this function is only enabled during the development phase. When the BMS recognizes that the interface status has changed, or cannot recognize the corresponding interface status, that is, the vehicle has begun production (batch production phase), this function will be disabled accordingly to avoid redundancy with other undervoltage protection strategies. Moreover, this can also play an error-proofing function. Even if the data setting of this function is incorrect, it will not affect the undervoltage protection strategy in the batch production phase.

[0029] Specific steps are as follows Figure 2 As shown, including: Step S100, obtaining the single cell voltage of each battery cell in the battery pack during the vehicle testing process in the development stage.

[0030] Step S120 , performing undervoltage diagnosis based on the single cell voltages of all the battery cells, so as to control the battery pack to lower the high voltage after confirming that the battery pack has an undervoltage fault.

[0031] It can be seen that for undervoltage fault identification in the vehicle development stage, by collecting the single cell voltage of each battery cell in the battery pack in real time, when the minimum value of the single cell voltage Umin (the smallest of all single cell voltages) is less than or equal to the preset threshold value Uprotect (slightly higher or basically equal to the initial threshold value of undervoltage risk provided by the battery cell manufacturer), and after a delay time (for example, 2s), it still maintains the above state, it means that the battery pack has an undervoltage fault. In this case, the BMS will first report the undervoltage fault and send a high-voltage request message, so that the actuator will cut off the relay on the high-voltage circuit to reduce the high voltage and prevent the battery pack from continuing to discharge. It can be understood here that the response is to directly reduce the high voltage instead of just limiting the power, which can protect the battery in a timely manner to a large extent.

[0032] Furthermore, the above-mentioned undervoltage fault identification can also simultaneously monitor other factors such as the current parameters and SOC parameters of the battery pack, thereby improving the reliability of undervoltage diagnosis. Without making too many restrictions on this, the modifications and improvements made to the embodiments of the present invention by those skilled in the art without departing from the spirit of the present invention still fall within the scope of the invention application patent of the present invention.

[0033] It should be added that the validity of the collected single cell voltage needs to be verified, that is, the data collected by the relevant collection device needs to be checked to avoid data abnormalities caused by failure of the collection device, which in turn affects the accuracy of the battery pack undervoltage diagnosis. Of course, it is not limited to the validity verification of the single cell voltage. If other parameters, such as current parameters, SOC parameters, etc. are also relied on for comprehensive diagnosis, verification is also required, and only when all data are valid can the battery pack be diagnosed for undervoltage diagnosis. For example, when the collected single cell voltages of all cells are valid, the minimum value can be used to diagnose whether the battery pack has an undervoltage fault. Otherwise, a direct alarm response will be issued to remind the developer.

[0034] Secondly, for the vehicle mass production stage, the undervoltage protection function configured by the BMS can also be enabled by identifying the interface status, but it is not limited to this method, and there is no restriction on how to enable the undervoltage protection function. It can be understood here that the undervoltage protection function configured in the mass production stage is different from the undervoltage protection function configured in the above development stage. Considering that the vehicle cannot directly apply high voltage to the battery pack during driving, different levels of undervoltage faults can be divided to limit the output power of the battery pack, thereby further protecting the safety of the vehicle battery pack while ensuring the safety of the driver and the vehicle. For example, a high-level undervoltage fault will limit a higher output power, while a low-level undervoltage fault will limit a lower output power, which will not affect the driving of the vehicle and can also maintain the safety of the battery.

[0035] Specific steps are as follows Figure 3 As shown, including: Step S210, obtaining the whole battery pack voltage and the single cell voltage of each internal battery cell during high-speed driving of the vehicle in the mass production stage.

[0036] Step S220, performing undervoltage classification diagnosis based on the whole pack voltage and the single cell voltages of all the cells, so as to determine a target discharge limit strategy according to the undervoltage level after confirming that the battery pack has an undervoltage fault.

[0037] Step S230, executing the target discharge limit strategy to implement undervoltage protection for the battery pack.

[0038] It should be noted that in this embodiment, four levels of undervoltage faults are divided, and by collecting the single cell voltage of each battery cell in the battery pack in real time, it is possible to diagnose whether the battery pack has an undervoltage fault and its corresponding undervoltage level.

[0039] In the case of the least severe undervoltage, an additional level of undervoltage fault diagnosis is added. That is, when the minimum value Umin of the cell voltage is less than or equal to the preset threshold Uwarn, and this state persists after a delay time (e.g., 5 s), it indicates that an undervoltage fault has occurred in the battery pack. In this case, the BMS will first report the undervoltage fault. Moreover, since the undervoltage situation is relatively mild, a message can be sent to reduce the discharge power to 80% of the maximum power, and a response to limit the output power to 80% of the maximum power is executed.

[0040] For a more severe undervoltage situation, a second level of undervoltage fault diagnosis is added. That is, when the minimum value Umin of the cell voltage is less than or equal to the preset threshold Ualarm (Ualarm < Uwarn), and this state persists after a 5 s delay time, it indicates that the undervoltage situation in the battery pack has worsened. Similarly, the BMS first reports the undervoltage fault, and then sends a message to reduce the discharge power to 50% of the maximum power to execute a more stringent response of limiting the output power to 50% of the maximum power.

[0041] If the undervoltage continues to deteriorate, a third level of undervoltage fault diagnosis is added. That is, when the minimum value Umin of the cell voltage is less than or equal to the preset threshold Uerror (Uerror < Ualarm < Uwarn), and this state persists after a 5 s delay time, it indicates that the undervoltage in the battery pack continues to deteriorate. The BMS continues to first report the undervoltage fault, and then sends a message to reduce the discharge power to 20% of the maximum power to further limit the discharge power of the battery pack.

[0042] If the undervoltage still does not improve, a fourth level of undervoltage fault diagnosis is added. That is, when the minimum value Umin of the cell voltage is less than or equal to the preset threshold Uerrftal (Uerrftal < Uerror < Ualarm < Uwarn), and this state persists after a 2 s delay time, the BMS reports the undervoltage fault and then sends a message to reduce the discharge power to 0, no longer allowing the battery pack to discharge. It is also possible to implement stepping down the high voltage at a lower vehicle speed through the VCU (Vehicle Control Unit) and cut off the relay on the high voltage circuit to fundamentally protect the battery pack.

[0043] Among them, the values of the above thresholds Uerrftal, Uerror, Ualarm, and Uwarn are all related to the current temperature of the battery cell. For example, in this embodiment, the smallest one among the cell voltages is selected for judgment, and accordingly, the temperature of the battery cell corresponding to the minimum value of the cell voltage can be detected, so as to select the thresholds Uerrftal, Uerror, Ualarm, and Uwarn within the corresponding temperature range. In this regard, for each of Uerrftal, Uerror, Ualarm, and Uwarn, the values in different temperature ranges can be preset in advance and stored in the database for direct calling, so as to ensure the reliability of the undervoltage fault diagnosis.

[0044] It can be seen that the minimum value of the single cell voltage is used to determine whether the battery pack has an undervoltage fault and the corresponding undervoltage level, so as to execute the corresponding discharge limit strategy to protect the safety of the battery pack.

[0045] Similarly, before performing undervoltage diagnosis based on the minimum cell voltage, the validity of the cell voltage also needs to be verified, that is, when the cell voltages of all cells are valid, the minimum cell voltage is compared with the preset threshold range.

[0046] Furthermore, in order to avoid the situation where the single cell voltage of the battery cell is invalid and thus the undervoltage diagnosis cannot be performed, a redundant setting is also made to collect the entire battery pack voltage in real time to diagnose whether the battery pack has an undervoltage fault and its corresponding undervoltage level.

[0047] Specifically, multiple fault levels can also be pre-divided, and corresponding fault diagnosis can be set accordingly. When the collected whole pack voltage BattPrs_u is less than or equal to the threshold Upack set for different fault levels, and this state is maintained after a delay of 5s, it indicates that the battery pack has an undervoltage fault. The BMS first reports the undervoltage fault, and then sends the discharge power down to a preset value, for example, down to 0, and sends a slow high voltage through the VCU, that is, after the VCU receives this fault signal, it will slowly reduce the power to 0 within 60s, and finally lower the high voltage to protect the battery pack and give the driver enough time to park. The specific hierarchical diagnosis will not be described in detail. It is basically consistent with the above-mentioned feature of using the single cell voltage of the battery cell for undervoltage hierarchical diagnosis. The whole pack voltage of the battery pack is compared with different preset thresholds to determine the undervoltage fault level, so as to respond to the corresponding discharge limit strategy. Among them, the value of the preset threshold for different fault levels is also related to the current temperature of the battery pack. For any undervoltage fault level, it is necessary to determine the value of the current undervoltage fault level preset threshold according to the current temperature of the battery pack to adapt to the temperature change of the battery pack.

[0048] Based on the above, when the single cell voltage of the battery cell is valid, that is, all single cell voltages are verified to be valid, the single cell voltage of the battery cell can be used to perform undervoltage classification diagnosis. When the single cell voltage of the battery cell is invalid, that is, one or more single cell voltages are invalid, then the entire pack voltage of the battery pack can be used to perform undervoltage classification diagnosis, thereby realizing dual protection function.

[0049] Therefore, the validity of the entire battery pack voltage also needs to be verified. If both the single cell voltage of the battery cell and the entire battery pack voltage are valid, then the first undervoltage classification diagnosis can be performed based on the single cell voltage of the battery cell, and it can be confirmed whether the battery pack has an undervoltage fault and its corresponding first undervoltage level, so as to determine the corresponding first discharge limit strategy based on the first undervoltage level. Moreover, the second undervoltage classification diagnosis can be performed based on the entire battery pack voltage, and it can be confirmed whether the battery pack has an undervoltage fault and its corresponding second undervoltage level, so as to determine the corresponding second discharge limit strategy based on the second undervoltage level.

[0050] It can be understood here that the first undervoltage classification diagnosis and the second undervoltage classification diagnosis may be consistent or inconsistent, that is, the fault levels divided may be the same or different, and the discharge limit strategies may be the same or different. Accordingly, the results of the undervoltage classification diagnosis of the battery pack using the single cell voltage and the whole pack voltage of the battery pack may be different, and the discharge limit strategies that need to be responded to may also conflict.

[0051] In this regard, when it is necessary to respond to the first discharge limit strategy and the second discharge limit strategy at the same time, it is necessary to confirm the target discharge limit strategy. Specifically, the one with a higher priority is selected from the first discharge limit strategy and the second discharge limit strategy for response. For example, at this time, the first discharge limit strategy needs to limit the discharge power of the battery pack to 30%, and the second discharge limit strategy needs to limit the discharge power of the battery pack to 40%. Correspondingly, the former is used as the target discharge limit strategy and the response is executed.

[0052] In addition, when any of the collected battery pack voltage and cell voltage is invalid, the valid voltage can be used for undervoltage classification diagnosis. When both voltages are invalid, a timely alarm response is issued to remind the user.

[0053] It can be seen that the protection coverage can be improved by distinguishing undervoltage conditions to limit the power output response, and by limiting the faults according to the severe undervoltage conditions of the single cell or the undervoltage conditions of the whole pack. Even if there is a problem with the single cell voltage sampling, undervoltage protection can be performed by sampling the voltage of the whole pack. Or if there is a problem with the sampling of the whole pack voltage, undervoltage protection can be performed by sampling the single cell voltage, thereby improving the reliability of battery pack undervoltage diagnosis.

[0054] It should also be added that the voltage threshold set for diagnosing undervoltage faults using the individual cell voltage of the battery cell during the development stage needs to be higher than the voltage threshold set during the mass production stage, that is, Uerrftal < Uerror < Ualarm < Uwarn < Uprotect. It can be understood that since the capabilities of the BMS need to be continuously adjusted and tested during the development stage, in order to avoid damage to the battery pack during this process, the upper limit of the threshold is raised to fully protect the safety of the battery pack. During the mass production stage, the BMS state has tended to be stable, and relatively dangerous situations are basically unlikely to occur again, and the corresponding threshold can be set according to the actual capabilities of the battery pack.

[0055] The above undervoltage diagnosis is specifically applied when the vehicle is traveling at high speed. When the vehicle is parked or traveling at low speed, the following method can be used to尽可能 avoid the occurrence of undervoltage faults in the battery pack.

[0056] The specific steps are as Figure 4 shown, including: Step S310, obtain the overall current, remaining power, and individual cell voltages of each cell inside the battery pack of the vehicle during parking or low-speed driving in the mass production stage.

[0057] Step S320, perform small current over-discharge fault diagnosis based on the individual cell voltages of all cells, as well as the remaining power and overall current of the battery pack.

[0058] Step S330, when a small current over-discharge fault occurs in the battery pack, limit the battery pack from continuing to discharge and prohibit it from going high voltage.

[0059] Identify the abnormal discharge behavior of the battery pack through small current over-discharge fault diagnosis, so as to stop it in time to avoid the occurrence of undervoltage faults in the battery pack. Specifically, by real-time collecting the individual cell voltages of each cell inside the battery pack and the overall current of the battery pack (incoming current), when the minimum value Umin of the individual cell voltage < Ulowsoc (generally set Ulowsoc > Uwarn), and the overall current i is in the small current range of [-2A, 2A], and this state remains after 3 minutes, the BMS reports a fault. It should be noted here that it is also necessary to first verify the validity of the individual cell voltages of the battery cells, and identify the minimum value Umin from the individual cell voltages of all cells after confirming their effectiveness.

[0060] Furthermore, this fault diagnosis can also take into account the SOC condition of the battery pack. When SOC < 3% and the above conditions are met, the BMS will report a fault again. Finally, the BMS can send a message that the feedback power and discharge power drop to 0, and execute a response, thereby avoiding the situation where the battery pack is in a high-voltage state, the power is low, and the battery pack continues to discharge at a small current, so as to protect the battery pack before the undervoltage situation actually occurs. It can also be understood that if the vehicle is driving at a low speed, the discharge power of the battery pack can be controlled to slowly drop to 0. If the vehicle is in a parking state, the battery pack can be directly controlled to lower the high voltage.

[0061] In addition, for this fault, high voltage is generally prohibited to avoid continued discharge after high voltage is applied. But at the same time, when this fault occurs, the user will plug in the gun to charge and replenish energy with high voltage. Taking this situation into consideration, the function of high voltage on the battery pack can be allowed under the condition of plugging in the gun, and the fault is cleared when Umin>Ulowsoc. Here, in order to avoid failure of charging with the gun plugged in and the battery pack continues to discharge under high voltage, the discharge current of the battery pack can be integrated in ampere hours to monitor the abnormal discharge behavior of the battery pack, and when the integral value reaches a certain threshold such as 150As, a fault is reported, and the corresponding BMS sends a message that the feedback power and discharge power drop to 0, limits the output power of the battery pack to 0, requests to disconnect the relay on the high voltage circuit to lower the high voltage, and prohibits the high voltage again. Alternatively, when the BMS receives relevant messages about battery pack charging failure reported by other functional modules, it can also directly control the battery pack to lower the high voltage, thereby protecting the situation where the small current over-discharge fault is cleared by the plug-in charging scenario, but the charging failure causes continued discharge and continues to damage the battery pack.

[0062] It should be noted that the step division of the above methods is only for clear description. When implemented, they can be combined into one step or some steps can be split and decomposed into multiple steps. As long as they contain the same logical relationship, they are all within the scope of protection of this application; adding insignificant modifications to the algorithm or process or introducing insignificant designs without changing the core design of the algorithm and process are all within the scope of protection of this application.

[0063] Example 2 See also Figure 5 As shown, an embodiment of the present application further provides a battery management system, including a memory 2, a processor 1, and a program stored in the memory and executable on the processor, wherein the processor implements the steps of any of the above methods when executing the program.

[0064] The memory includes at least one type of readable storage medium, which includes flash memory, mobile hard disk, multimedia card, card-type memory (such as SD or DX memory, etc.), magnetic memory, disk, optical disk, etc. The memory may be a mobile hard disk in some embodiments, and may also be an external storage device in other embodiments, such as a plug-in mobile hard disk, a smart memory card (Smart Media Card, SMC), a secure digital (Secure Digital, SD) card, a flash card, etc. The memory may be used not only to store application software and various data installed in the battery management system, but also to temporarily store data that has been output or is to be output.

[0065] In some embodiments, the processor may be composed of an integrated circuit, for example, a single packaged integrated circuit, or a plurality of integrated circuits with the same or different functions, including one or more central processing units (CPUs), microprocessors, digital processing chips, graphics processors, and a combination of various control chips. The processor is a control core (Control Unit), which uses various interfaces and lines to connect various components of the entire battery management system, and executes various functions and processes data of the battery management system by running or executing programs or modules stored in the memory, and calling data stored in the memory.

[0066] The processor executes the operating system of the battery management system and various installed application programs. The processor executes the application programs to implement the steps in the above method embodiment.

[0067] Exemplarily, the program may be divided into one or more modules, which are stored in the memory and executed by the processor to complete the present invention. The one or more modules may be a series of program instruction segments capable of completing specific functions, which are used to describe the execution process of the program in the battery management system.

[0068] Example 3 An embodiment of the present application also provides a vehicle controller, comprising the battery management system described above.

[0069] In summary, the present invention provides a vehicle battery pack undervoltage protection method, which can protect the battery pack well during the vehicle development stage to prevent immature data from causing undervoltage damage to the battery pack, thereby saving compensation for damaged battery packs. At the same time, when the battery cell is actually undervoltage during driving, it can be monitored not only based on the single cell sampling voltage but also based on the collected whole pack voltage, and the severity of the undervoltage can be distinguished, and a corresponding power limit level response can be made, so that power will not be lost immediately, which can protect the battery pack and improve driving experience and driving safety.

[0070] In addition, the present invention takes into account the situation of small current over-discharge and also takes into account working conditions such as plug-in charging failure, covering most vehicle usage scenarios and playing a protective role before the battery cell is under-voltage.

[0071] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

[0072] In the description of this specification, the description with reference to the terms "some embodiments", "other embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic description of the above terms does not necessarily refer to the same embodiment or example.

Claims

1. A vehicle battery pack undervoltage protection method, characterized in that: include: Obtain the battery pack voltage and the single cell voltage of each battery cell during high-speed driving of mass-produced vehicles; Performing undervoltage classification diagnosis according to the whole pack voltage and the single cell voltages of all the cells, so as to determine a target discharge limit strategy according to the undervoltage level after confirming that the battery pack has an undervoltage fault; The target discharge limit strategy is executed to achieve undervoltage protection for the battery pack.

2. The undervoltage protection method for a vehicle battery pack according to claim 1, characterized in that: The steps of performing undervoltage classification diagnosis according to the whole pack voltage and the single cell voltages of all the cells to determine the target discharge limit strategy according to the undervoltage level after confirming that the battery pack has an undervoltage fault include: Verify the validity of the single cell voltage of all batteries; When the single cell voltages of all battery cells are valid, the first undervoltage classification diagnosis is performed based on the single cell voltages of all battery cells to confirm whether an undervoltage fault occurs in the battery pack and its corresponding first undervoltage level, and after an undervoltage fault occurs in the battery pack, the target discharge limit strategy is determined based on its first undervoltage level.

3. The undervoltage protection method for a vehicle battery pack according to claim 2, characterized in that: The steps of performing a first undervoltage classification diagnosis according to the single cell voltages of all the battery cells to confirm whether an undervoltage fault occurs in the battery pack and its corresponding first undervoltage level include: Identify the smallest single cell voltage from all the battery cells, and compare it with the threshold ranges of different first undervoltage levels to confirm whether an undervoltage fault occurs in the battery pack and its corresponding first undervoltage level; The threshold ranges of different first undervoltage levels are related to the current temperature of the battery cell.

4. The undervoltage protection method for a vehicle battery pack according to claim 2, characterized in that: The step of performing undervoltage classification diagnosis according to the whole pack voltage and the single cell voltages of all the cells to determine the target discharge limit strategy according to the undervoltage level after confirming that the battery pack has an undervoltage fault also includes: When the single cell voltage of one or more battery cells is invalid, a second undervoltage classification diagnosis is performed based on the voltage of the entire pack to confirm whether an undervoltage fault occurs in the battery pack and its corresponding second undervoltage level, and after an undervoltage fault occurs in the battery pack, the target discharge limit strategy is determined based on its second undervoltage level.

5. The undervoltage protection method for a vehicle battery pack according to claim 4, characterized in that: The step of performing a second undervoltage classification diagnosis according to the whole pack voltage to confirm whether an undervoltage fault occurs in the battery pack and its corresponding second undervoltage level includes: Comparing the whole pack voltage with the threshold ranges of different second undervoltage levels to confirm whether an undervoltage fault occurs in the battery pack and its corresponding second undervoltage level; Among them, the threshold ranges of different second under-voltage levels are related to the current temperature of the battery pack.

6. The undervoltage protection method for a vehicle battery pack according to claim 1, characterized in that: The steps of performing undervoltage classification diagnosis according to the whole pack voltage and the single cell voltages of all the cells to determine the target discharge limit strategy according to the undervoltage level after confirming that the battery pack has an undervoltage fault include: Verify the validity of the single cell voltage of all cells and the validity of the entire pack voltage; When the single cell voltages of all cells are valid and the whole pack voltage is valid, Performing a first undervoltage classification diagnosis according to the single cell voltages of all the battery cells to confirm whether an undervoltage fault occurs in the battery pack and its corresponding first undervoltage level, and determining a first discharge limit strategy according to the first undervoltage level after an undervoltage fault occurs in the battery pack; and Performing a second undervoltage classification diagnosis according to the whole pack voltage to confirm whether an undervoltage fault occurs in the battery pack and its corresponding second undervoltage level, and determining a second discharge limit strategy according to the second undervoltage level after the undervoltage fault occurs in the battery pack; Selecting a higher priority one from the first discharge limit strategy and the second discharge limit strategy as a target discharge limit strategy.

7. The undervoltage protection method for a vehicle battery pack according to claim 1, characterized in that: Also includes: Obtain the single cell voltage of each battery cell in the battery pack during the vehicle testing process in the development stage; Perform undervoltage diagnosis based on the single cell voltage of all cells to control the battery pack to lower the high voltage after confirming that the battery pack has an undervoltage fault; Among them, the vehicle is in the development stage or the mass production stage through the interface status.

8. The undervoltage protection method for a vehicle battery pack according to claim 7, characterized in that: The steps for undervoltage diagnosis based on the single cell voltage of all cells include: Verify the validity of the single cell voltage of all batteries; When the single cell voltages of all cells are valid, identify the smallest single cell voltage from all cells and compare it with the preset threshold to confirm whether the battery pack has an undervoltage fault; The threshold is higher than the threshold range set for undervoltage classification diagnosis.

9. A vehicle battery pack undervoltage protection method, characterized in that: include: Obtain the battery pack current, remaining power, and single cell voltage of each battery cell during parking or low-speed driving of the vehicle in the mass production stage; Perform low current over-discharge fault diagnosis based on the single cell voltage of all cells, the remaining power of the battery pack, and the current of the entire pack; When a small current over-discharge fault occurs in the battery pack, the battery pack is restricted from further discharge and high voltage is prohibited.

10. The undervoltage protection method for a vehicle battery pack according to claim 9, characterized in that: The steps for diagnosing a low current over-discharge fault based on the single cell voltage of all cells, the remaining capacity of the battery pack, and the current of the entire pack include: Verify the validity of the single cell voltage of all cells: If the single cell voltages of all battery cells are valid, a small current over-discharge fault diagnosis is performed based on the minimum single cell voltage, the remaining power of the battery pack and the current of the entire pack; among them, when the minimum single cell voltage is less than a preset threshold, the entire pack current of the battery pack is within a preset small current range, and the remaining power of the battery pack is less than the preset power, it is determined that a small current over-discharge fault has occurred in the battery pack.

11. The undervoltage protection method for a vehicle battery pack according to claim 9, characterized in that: After limiting the battery pack from continuing to discharge and prohibiting high voltage on it, it also includes: Identify the vehicle's gun-insertion status; When the vehicle is plugged in for charging, the battery pack is allowed to be charged with high voltage; The abnormal discharge behavior of the battery pack is monitored during charging to control the high voltage of the battery pack when charging fails and discharge continues.

12. The undervoltage protection method for a vehicle battery pack according to claim 11, characterized in that: The steps of monitoring abnormal discharge behavior of the battery pack during charging to control the high voltage of the battery pack when charging fails and continues to discharge include: Calculate the ampere-hour integral of the battery pack discharge current to determine whether the battery pack has failed to charge and continues to discharge.

13. A battery management system, characterized in that: The method comprises a processor, wherein the processor is coupled to a memory, wherein the memory stores program instructions, and when the program instructions stored in the memory are executed by the processor, the method according to any one of claims 1 to 12 is implemented.

14. A vehicle controller, characterized in that: Includes the battery management system as described in claim 13.

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