Discharge control method, battery management system and power consumption device

Abstract

The present application discloses a discharge control method, a battery management system and an electrical device, and relates to the field of battery technology. The present application discloses a discharge control method, wherein a pre-undervoltage threshold is determined based on a preset undervoltage threshold, as well as a voltage rise and a voltage drop during actual use of a battery pack. Compared with directly using a preset undervoltage threshold for power control, the pre-undervoltage threshold can be determined in real time based on the use of the battery pack, thereby solving the problem that the current determination of the pre-undervoltage threshold cannot guarantee accuracy due to reliance on experience and that actual vehicle calibration testing is complicated. Furthermore, the allowable discharge current and / or allowable discharge power of the battery pack is controlled based on the pre-undervoltage threshold, thereby effectively avoiding undervoltage faults caused by mismatch between the pre-undervoltage threshold and the current use of the battery pack, and effectively preventing the battery from triggering an undervoltage fault.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a discharge control method, a battery management system and an electrical device. Background Art

[0002] The State of Power (SOP) estimation in the Battery Management System (BMS) should ensure that there will be no undervoltage fault during the battery discharge process. Therefore, at the end of discharge, the battery management system needs to compare the minimum cell voltage of the battery pack with the pre-undervoltage threshold to determine whether it is necessary to limit the allowable discharge power and / or allowable discharge current.

[0003] Among them, the determination of the pre-undervoltage threshold is very important. If the pre-undervoltage threshold is set too low, the battery cannot be protected, and an undervoltage fault may be triggered, causing the electric vehicle to lose power; if the pre-undervoltage threshold is set too high, the actual discharge capacity of the battery cannot be brought into play, affecting the power of the entire electric vehicle.

[0004] At present, the determination of the pre-undervoltage threshold in the discharge control method mainly relies on experience-based formulation and actual vehicle calibration testing. The former cannot guarantee accuracy and has a complicated verification process. The latter takes a long time to conduct actual vehicle calibration testing and has high requirements on ambient temperature, etc. In addition, the calibration results cannot cover complex working conditions, which can easily lead to undervoltage faults during battery discharge. Summary of the invention

[0005] The main purpose of the present application is to provide a discharge control method, a battery management system and an electrical device, which can determine the pre-undervoltage threshold in real time through the use of the battery pack, thereby solving the problem that the current pre-undervoltage threshold determination relies on experience and cannot guarantee accuracy, and the actual vehicle calibration test is complicated, thereby effectively preventing the battery from triggering an undervoltage fault.

[0006] To achieve the above objectives, the present application proposes a discharge control method, the method comprising:

[0007] Obtain the minimum module temperature and maximum module temperature of the battery pack, and the remaining power of the battery pack, wherein the minimum module temperature is the lowest temperature of all modules in the battery pack, and the maximum module temperature is the highest temperature of all modules in the battery pack; determine the allowable discharge current, ohmic impedance and polarization impedance of the battery pack according to the minimum module temperature, the maximum module temperature, and the remaining power of the battery pack; determine the voltage rise and voltage drop according to the ohmic impedance and / or the polarization impedance, and the allowable discharge current, wherein the voltage rise is caused by the current of the battery pack dropping to a preset limp current, and the voltage drop is caused by the ohmic impedance and / or the polarization impedance during the discharge of the battery pack; determine a pre-undervoltage threshold according to a preset undervoltage threshold, the voltage rise and the voltage drop; and control the allowable discharge current and / or allowable discharge power of the battery pack according to the pre-undervoltage threshold.

[0008] In one embodiment, the voltage rise and voltage drop are determined according to the ohmic impedance and / or the polarization impedance, and the allowable discharge current, including: calculating the voltage rise according to the allowable discharge current and the ohmic impedance; calculating the first voltage drop caused by the ohmic impedance and the polarization impedance during the discharge of the battery pack according to the allowable discharge current, the ohmic impedance and the polarization impedance. In this embodiment, the pre-undervoltage threshold can be determined according to the voltage rise, the first voltage drop and the preset undervoltage threshold. In this way, power control using the pre-undervoltage threshold can prevent the battery from having an undervoltage problem in advance.

[0009] In one embodiment, the voltage rise and voltage drop are determined according to the ohmic impedance and / or the polarization impedance, and the allowable discharge current, including: calculating the voltage rise according to the allowable discharge current and the ohmic impedance; and calculating the second voltage drop caused by the polarization impedance during the discharge of the battery pack according to the allowable discharge current and the polarization impedance. In this embodiment, the pre-undervoltage threshold can be determined according to the voltage rise, the second voltage drop, and the preset undervoltage threshold. In this way, power control using the pre-undervoltage threshold can prevent the battery from having an undervoltage problem in advance.

[0010] In one embodiment, controlling the allowable discharge current and / or allowable discharge power of the battery pack according to the pre-under-voltage threshold includes: determining whether the minimum cell voltage in the battery pack is less than the pre-under-voltage threshold, wherein the pre-under-voltage threshold is determined based on the allowable discharge current, the ohmic impedance and the polarization impedance; if the minimum cell voltage is less than the pre-under-voltage threshold, controlling the allowable discharge current and / or allowable discharge power of the battery pack according to a preset control strategy.

[0011] In one embodiment, controlling the allowable discharge current and / or allowable discharge power of the battery pack according to the pre-under-voltage threshold includes: determining whether the estimated minimum single cell voltage of the battery pack after a first preset time period is less than the pre-under-voltage threshold, the minimum single cell voltage of the battery pack after the first preset time period includes the voltage drop caused by the ohmic impedance, and the pre-under-voltage threshold is determined based on the allowable discharge current and the polarization impedance; if the minimum single cell voltage of the battery pack after the first preset time period is less than the pre-under-voltage threshold, controlling the allowable discharge current and / or allowable discharge power of the battery pack according to a preset control strategy.

[0012] In addition, to achieve the above-mentioned purpose, the present application also proposes a battery management system, which includes: a sampling circuit, used to obtain the minimum module temperature and the maximum module temperature of the battery pack, and the remaining power of the battery pack, the minimum module temperature is the lowest temperature of all modules in the battery pack, and the maximum module temperature is the highest temperature of all modules in the battery pack; a controller, used to determine the allowable discharge current, ohmic impedance and polarization impedance of the battery pack according to the minimum module temperature, the maximum module temperature, and the remaining power of the battery pack; and also used to determine the voltage rise and voltage drop according to the ohmic impedance and / or the polarization impedance, and the allowable discharge current, wherein the voltage rise is caused by the current of the battery pack dropping to a preset limp current, and the voltage drop is caused by the ohmic impedance and / or the polarization impedance during the discharge of the battery pack; a pre-undervoltage threshold is determined according to the preset undervoltage threshold, the voltage rise and the voltage drop, and the allowable discharge current and / or the allowable discharge power of the battery pack is controlled according to the pre-undervoltage threshold.

[0013] In addition, to achieve the above objectives, the present application also proposes an electrical device, which includes a battery management system as described in the above embodiments.

[0014] One or more technical solutions proposed in this application have at least the following technical effects:

[0015] A discharge control method is proposed in an embodiment of the present application, which determines a pre-undervoltage threshold value according to changes in an allowable discharge current, ohmic impedance and / or polarization impedance during the use of the battery pack. Specifically, the pre-undervoltage threshold value is determined based on a preset undervoltage threshold value, as well as a voltage rise and a voltage drop during actual use of the battery pack. Compared with directly using a preset undervoltage threshold value for power control, the pre-undervoltage threshold value can be determined in real time according to the use of the battery pack, which solves the problem that the current determination of the pre-undervoltage threshold value cannot guarantee accuracy due to reliance on experience and the actual vehicle calibration test is complicated. In addition, controlling the allowable discharge current and / or allowable discharge power of the battery pack according to the pre-undervoltage threshold value can effectively avoid undervoltage faults caused by mismatches between the pre-undervoltage threshold value and the current use of the battery pack, and effectively prevent the battery from triggering an undervoltage fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0018] Figure 1 A schematic diagram of a flow chart provided for the first embodiment of the discharge control method of the present application;

[0019] Figure 2 A schematic diagram of a flow chart provided for the second embodiment of the discharge control method of the present application;

[0020] Figure 3 A schematic diagram of a flow chart provided for the third embodiment of the discharge control method of the present application;

[0021] Figure 4 A flow chart of the fourth embodiment of the discharge control method of the present application;

[0022] Figure 5 A vehicle voltage curve diagram for power control using the pre-undervoltage threshold value formulated in the embodiment of the present application and for power control using the pre-undervoltage threshold value formulated directly based on experience;

[0023] Figure 6 A schematic diagram of the module structure of a battery management system according to an embodiment of the present application.

[0024] The purpose, features and advantages of this application will be further described in conjunction with the embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0025] It should be understood that the specific embodiments described herein are only used to explain the technical solutions of the present application and are not used to limit the present application.

[0026] In order to facilitate understanding of the technical solutions of the embodiments of the present application, some terms involved in the embodiments of the present application are briefly explained below.

[0027] 1. Battery Cell

[0028] A battery cell is the most basic unit of a battery. It is the smallest independent energy storage unit in a battery system. It consists of a positive electrode, a negative electrode, an electrolyte, and a separator, and can store and release electrical energy through chemical reactions. A battery cell has a minimum capacity and voltage, and usually requires multiple battery cells to be connected in series or in parallel to form a battery module.

[0029] 2. Battery module

[0030] A battery module is usually composed of multiple battery cells connected in series and parallel. In some examples, the battery module also includes components such as a battery management system (BMS), a thermal management system (TMS), a connector, and a housing. A battery module can provide a higher voltage and capacity than a battery cell and is usually used in electric vehicles, energy storage systems, etc. It is worth noting that a battery module may include at least one battery cell.

[0031] 3. Battery Pack

[0032] A battery pack is composed of multiple battery modules connected in series and parallel. In some cases, the battery pack also includes necessary electrical connections, battery management systems, thermal management systems, and other protection components. The battery pack can provide higher voltage and capacity and is the final assembly form of battery systems such as electric vehicles and energy storage systems.

[0033] 4. Minimum single cell voltage

[0034] The minimum cell voltage of a battery pack refers to the voltage value of the battery cell with the lowest voltage among all the battery cells in a battery pack. In a lithium-ion battery pack, each single cell usually has its rated voltage, and the performance and health of the entire battery pack largely depends on the voltage balance of these single cells.

[0035] 5. Minimum module temperature and maximum module temperature

[0036] The battery pack includes multiple modules. The minimum module temperature refers to the lowest temperature of all modules in the battery pack during operation, and the maximum module temperature refers to the highest temperature of all modules in the battery pack during operation.

[0037] 6. Remaining power

[0038] The remaining power (State Of Charge, SOC for short) is the ratio of the available power in the battery to the nominal capacity. For each battery cell in the battery pack, there is a corresponding SOC indicating the state of charge of the battery cell; for the entire battery pack, there is also a corresponding total SOC indicating the state of charge of the battery pack.

[0039] 7. Battery impedance

[0040] Battery impedance consists of two main parts: ohmic impedance and polarization impedance.

[0041] Ohmic impedance is also called Direct Current Resistance (DCR), which is the inherent resistance inside the battery. It is mainly composed of the battery's electrode materials, electrolytes, diaphragms, and internal connections. Ohmic impedance causes the battery to generate heat during discharge and is a source of battery energy loss. Ohmic impedance is a static impedance that does not change over time and has little to do with the battery's operating state (such as SOC, temperature, etc.).

[0042] Polarization impedance refers to the additional impedance caused by electrochemical reactions during the charge and discharge process of the battery. This impedance is related to the electrode surface reaction, electrolyte ion transport, and state changes of the electrode material. Polarization impedance is a dynamic impedance that changes with the working state of the battery (such as current size, SOC, temperature, etc.) and time. In the early stage of battery discharge, the polarization impedance is large, but as the discharge progresses, the polarization impedance will gradually decrease.

[0043] 8. Allowable discharge current

[0044] The allowable discharge current refers to the maximum discharge current that the battery pack can safely withstand. Exceeding this current value may have an adverse effect on the performance and life of the battery pack. The allowable discharge current is usually determined by the battery manufacturer based on the design and test results of the battery and provided in the battery's technical specification.

[0045] 9. Allowable discharge power

[0046] The allowable discharge power refers to the maximum discharge power allowed by the battery under specific conditions. This power value is determined by the battery manufacturer based on the battery design and performance test. The allowable discharge power is crucial to the safe use and performance of the battery.

[0047] 10. DC internal resistance

[0048] Direct Current Resistance (DCR) is a parameter that measures the internal resistance of a battery or capacitor during discharge. Specifically, DCR is the degree of resistance to current flow inside the battery under constant current discharge conditions. It is usually calculated by measuring the voltage drop and discharge current of the battery during discharge. DCR reflects the resistance of the internal impedance of the battery to current flow during discharge and is an important indicator for evaluating battery performance.

[0049] 11. Constant current discharge DC internal resistance meter

[0050] The constant current discharge DC internal resistance meter is used to record the changes in the DC internal resistance of the battery during constant current discharge. It usually includes the DCR values ​​at different temperatures and different SOCs. The constant current discharge DC internal resistance meter can be a 60-second discharge DC internal resistance meter, which is used to record the changes in the DC internal resistance of the battery pack at different temperatures and different SOCs during the 60-second constant current discharge process.

[0051] Through this table, we can understand the internal resistance characteristics of the battery under longer discharge conditions.

[0052] 12. Rapid discharge DC internal resistance meter

[0053] The fast discharge DC internal resistance meter is used to record the DC internal resistance of the battery when it is discharged quickly in a very short time. It usually includes the DCR values ​​at different temperatures and different SOCs. It reflects the internal resistance characteristics of the battery under high-speed discharge or pulse discharge conditions. The fast discharge DC internal resistance meter can be a 0.1 second discharge DC internal resistance meter, which is used to record the changes in the DC internal resistance of the battery pack at different temperatures and different SOCs during the fast discharge process in a very short time (0.1 second).

[0054] Through this table, we can understand the internal resistance characteristics of the battery when it is discharged in a very short time.

[0055] 13. Limp Mode

[0056] Limp Home Mode is a protection function of the vehicle's electronic control unit. When the vehicle's electronic control system detects a fault, the limp home mode will be activated to ensure that the vehicle can still drive safely to the nearest maintenance point at the lowest performance level.

[0057] In this mode, the vehicle's acceleration, top speed and power output are generally limited, but are sufficient to allow the driver to move the vehicle to a safe location.

[0058] 14. Limp Current

[0059] Limp current refers to the amount of current that the electronic control unit of the vehicle allows to pass in limp mode in order to maintain the vehicle's most basic driving ability. This current value is usually lower than the current in normal working conditions.

[0060] The limp current is set to ensure the basic driving function of the vehicle while avoiding further damage caused by the fault and minimizing the impact on vehicle performance.

[0061] 15. Undervoltage

[0062] "Undervoltage" means that the voltage of a battery cell or battery module in a battery pack drops to a specific threshold value below its normal operating voltage during the discharge process. For lithium-ion batteries, each battery cell has a minimum operating voltage limit. If the voltage of a battery cell drops below this limit during the discharge process, it is considered to have occurred.

[0063] Undervoltage may cause the following problems: (1) Degraded battery performance: Long-term undervoltage operation will damage battery performance and reduce battery cycle life. (2) Battery damage: Severe undervoltage may cause irreversible changes in the internal chemical properties of the battery, causing battery damage or even failure. (3) Safety risks: Lithium batteries may have safety risks when operating under voltage, such as internal short circuit or leakage.

[0064] In the battery management system, the pre-undervoltage threshold is a pre-set protection voltage value, which is usually higher than the minimum operating voltage limit of the battery cell. When the voltage of the battery cell drops to the pre-undervoltage threshold, the battery management system will take measures to limit the discharge current or power to prevent the battery cell voltage from further dropping to the undervoltage state. The setting of the pre-undervoltage threshold needs to comprehensively consider factors such as the battery type, specification, usage conditions, safety requirements, and performance targets.

[0065] In order to better understand the technical solution of the present application, a detailed description will be given below in conjunction with the accompanying drawings and specific implementation methods.

[0066] The State of Power (SOP) estimation in the Battery Management System (BMS) should ensure that there will be no undervoltage fault during the battery discharge process. Therefore, at the end of discharge, the battery management system needs to compare the minimum cell voltage with the pre-undervoltage threshold to determine whether it is necessary to limit the allowable discharge power and / or the allowable discharge current.

[0067] Among them, the determination of the pre-undervoltage threshold is very important. If the pre-undervoltage threshold is set too low, the battery cannot be protected, and an undervoltage fault may be triggered, causing the electric vehicle to lose power; if the pre-undervoltage threshold is set too high, the actual discharge capacity of the battery cannot be brought into play, affecting the power of the entire electric vehicle.

[0068] At present, the determination of the pre-undervoltage threshold in the discharge control method mainly relies on experience-based formulation and actual vehicle calibration testing. The former cannot guarantee accuracy and has a complicated verification process. The latter takes a long time to conduct actual vehicle calibration testing and has high requirements on ambient temperature, etc. In addition, the calibration results cannot cover complex working conditions, which can easily lead to undervoltage faults during battery discharge.

[0069] In view of this, a discharge control method is proposed in an embodiment of the present application. First, the minimum module temperature and the maximum module temperature of the battery pack, as well as the remaining power of the battery pack, are obtained; then, the allowable discharge current, ohmic impedance and polarization impedance of the battery pack are determined according to the minimum module temperature, the maximum module temperature, and the remaining power of the battery pack, and the voltage rise and voltage drop are determined according to the ohmic impedance and / or polarization impedance, as well as the allowable discharge current, wherein the voltage rise is caused by the current of the battery pack dropping to a preset limp current, and the voltage drop is caused by the ohmic impedance and / or polarization impedance during the discharge of the battery pack;

[0070] According to the undervoltage threshold, voltage rise and voltage drop, the pre-undervoltage threshold is determined; finally, the allowable discharge current and / or allowable discharge power of the battery pack is controlled according to the pre-undervoltage threshold.

[0071] In the embodiment of the present application, the pre-under-voltage threshold is determined according to the changes in the allowable discharge current, ohmic impedance and / or polarization impedance during the use of the battery pack. Specifically, the pre-under-voltage threshold is determined based on a preset under-voltage threshold, as well as the voltage rise and voltage drop during the actual use of the battery pack. Compared with directly using the preset under-voltage threshold for power control, the pre-under-voltage threshold can be determined in real time according to the use of the battery pack, which solves the problem that the current determination of the pre-under-voltage threshold cannot guarantee accuracy due to reliance on experience and the complexity of actual vehicle calibration testing. In addition, the allowable discharge current and / or allowable discharge power of the battery pack is controlled according to the pre-under-voltage threshold, which can effectively avoid under-voltage faults caused by the mismatch between the pre-under-voltage threshold and the current use of the battery pack, and effectively prevent the battery from triggering an under-voltage fault.

[0072] It should be noted that the executor of this embodiment can be a device that has data collection function, data processing function and program running function, such as: a battery management system, or an electrical device including a battery management system, such as: an electric car, an electric bicycle, etc.

[0073] The present embodiment and the following embodiments are described below by taking a battery management system as an example.

[0074] Based on the above content, the present application embodiment provides a discharge control method, referring to Figure 1 , Figure 1 This is a flow chart of the first embodiment of the discharge control method of the present application.

[0075] In this embodiment, the discharge control method includes steps S10 to S50:

[0076] Step S10: Obtain the minimum module temperature and the maximum module temperature of the battery pack, and the remaining power of the battery pack.

[0077] The minimum module temperature is the lowest temperature of all modules in the battery pack, and the maximum module temperature is the highest temperature of all modules in the battery pack. The battery management system uses temperature sensors to obtain the minimum module temperature T1 and the maximum module temperature T2 of the battery pack.

[0078] The battery management system can calculate or estimate the remaining power of the battery cell with the lowest voltage in the battery pack, and use the remaining power of the battery cell with the lowest voltage as the remaining power of the entire battery pack, or directly calculate or estimate the remaining power of the entire battery pack.

[0079] It is worth noting that the methods by which the battery management system calculates or estimates the remaining power of the battery cell with the lowest voltage or the entire battery pack include: current calculation method, open circuit voltage method, coulomb counting method and model prediction method, etc., which are not introduced in detail in this embodiment.

[0080] It should be noted that in this embodiment, the data of the battery pack is required to be obtained for each battery pack, that is, the data of the battery pack is obtained in real time, so as to obtain the real-time pre-undervoltage threshold.

[0081] Step S20, determining the allowable discharge current, ohmic impedance, and polarization impedance of the battery pack according to the minimum module temperature, the maximum module temperature, and the remaining power of the battery pack.

[0082] Since the allowable discharge current, ohmic impedance and polarization impedance of the battery pack will change during use, it is necessary to determine the allowable discharge current, ohmic impedance and polarization impedance of the battery pack in real time. In this embodiment, the allowable discharge current, ohmic impedance and polarization impedance of the battery pack are determined based on the minimum module temperature, maximum module temperature, remaining capacity of the battery pack, and the allowable discharge current table corresponding to different preset temperatures and different remaining capacities, the constant current discharge DC internal resistance table and the fast discharge DC internal resistance table corresponding to different preset temperatures and different remaining capacities.

[0083] The constant current discharge DC internal resistance meter can be a 60-second discharge DC internal resistance meter, and the fast discharge DC internal resistance meter can be a 0.1-second discharge DC internal resistance meter. The allowable discharge current meter corresponding to different preset temperatures and different residual capacities, and the 60-second discharge DC internal resistance meter and the 0.1-second discharge DC internal resistance meter corresponding to different preset temperatures and different residual capacities can be obtained by actually measuring the battery pack in advance.

[0084] Step S30, determining the voltage rise and voltage drop according to the ohmic impedance and / or polarization impedance, and the allowable discharge current.

[0085] In this embodiment, the voltage rise is caused by the current of the battery pack decreasing to a preset limp current, and the voltage drop is caused by the ohmic impedance and / or polarization impedance during the discharge process of the battery pack.

[0086] Because the allowable discharge current, ohmic impedance and polarization impedance of the battery pack will change during use, if the pre-undervoltage threshold is not adjusted accordingly, an undervoltage fault may be triggered. In this embodiment, the voltage rise and voltage drop during actual use of the battery pack can be determined in real time, and the pre-undervoltage threshold can be adjusted accordingly, thereby effectively preventing the battery from triggering an undervoltage fault.

[0087] Step S40, determining a pre-undervoltage threshold according to a preset undervoltage threshold, voltage rise and voltage drop.

[0088] In the embodiment of the present application, the pre-under-voltage threshold is determined according to the changes in the allowable discharge current, ohmic impedance and / or polarization impedance during the use of the battery pack. Specifically, the pre-under-voltage threshold is determined based on a preset under-voltage threshold, as well as the voltage rise and voltage drop during the actual use of the battery pack. Compared with directly using the preset under-voltage threshold for power control, the pre-under-voltage threshold can be determined in real time according to the use of the battery pack, which solves the problem that the current determination of the pre-under-voltage threshold relies on experience and cannot guarantee accuracy, and the actual vehicle calibration test is complicated.

[0089] Step S50: controlling the allowable discharge current and / or allowable discharge power of the battery pack according to the pre-undervoltage threshold.

[0090] In the embodiment of the present application, the allowable discharge current and / or allowable discharge power of the battery pack is controlled according to the pre-undervoltage threshold, thereby effectively avoiding undervoltage faults caused by the mismatch between the pre-undervoltage threshold and the current usage of the battery pack, and effectively preventing the battery from triggering undervoltage faults.

[0091] The following describes how to determine the allowable discharge current, ohmic impedance and polarization impedance of a battery pack in combination with feasible implementation methods:

[0092] In one possible implementation, refer to Figure 2 , the above step S20 includes the following steps S201 to S203:

[0093] Step S201 , determining the allowable discharge current of the battery pack according to the minimum module temperature, the maximum module temperature, the remaining power of the battery pack, and a preset allowable discharge current table.

[0094] The preset allowable discharge current table includes values ​​of allowable discharge current at different temperatures and different residual capacities.

[0095] In one implementation, the allowable discharge current of the battery pack is determined based on the minimum module temperature, the maximum module temperature, the remaining power of the battery pack, and a preset allowable discharge current table, including: determining a first current value based on the minimum module temperature, the remaining power of the battery pack, and a preset allowable discharge current table; determining a second current value based on the maximum module temperature, the remaining power of the battery pack, and a preset allowable discharge current table; determining the allowable discharge current of the battery pack based on the first current value and the second current value.

[0096] In this implementation, when the minimum module temperature and the remaining power of the battery pack are known, a first current value can be obtained in a preset allowable discharge current table by means of a linear interpolation table lookup, and the first current value is the allowable discharge current value corresponding to the battery pack at the minimum module temperature; when the maximum module temperature and the remaining power of the battery pack are known, a second current value can be obtained in a preset allowable discharge current table by means of a linear interpolation table lookup, and the second current value is the allowable discharge current value corresponding to the battery pack at the maximum module temperature. The smaller value of the first current value and the second current value can be taken as the allowable discharge current Imax of the battery pack.

[0097] In another implementation, the average temperature is calculated based on the minimum module temperature and the maximum module temperature of the battery pack, and the allowable discharge current Imax of the battery pack is obtained in a preset allowable discharge current table by linear interpolation based on the average temperature and the remaining power of the battery pack.

[0098] Step S202, determining the ohmic impedance of the battery pack according to the minimum module temperature, the maximum module temperature, the remaining power of the battery pack, and a preset fast discharge DC impedance table.

[0099] The preset fast discharge DC impedance meter is used to record the DC internal resistance of the battery during fast discharge in a very short time, while the ohmic impedance is instantaneous and the polarization impedance is continuous. Therefore, in this embodiment, the DC impedance in the fast discharge DC impedance meter can be regarded as the ohmic impedance.

[0100] The calculation cycle of the power control strategy in the embodiment of the present application is 100ms. Therefore, the fast discharge DC impedance table can be a 0.1 second discharge DC impedance table, and the 0.1 second discharge DC impedance table includes the 0.1 second discharge DC impedance value of the battery pack at different temperatures and different remaining powers.

[0101] In one implementation, when the minimum module temperature and the remaining power of the battery pack are known, a first impedance value can be obtained in a preset fast discharge DC impedance table by means of a linear interpolation table lookup, and the first impedance value is the fast discharge DC impedance corresponding to the battery pack at the minimum module temperature; when the maximum module temperature and the remaining power of the battery pack are known, a second impedance value can be obtained in a preset fast discharge DC impedance table by means of a linear interpolation table lookup, and the second impedance value is the fast discharge DC impedance corresponding to the battery pack at the maximum module temperature. The larger value of the first impedance value and the second impedance value can be taken as the ohmic impedance R0 of the battery pack.

[0102] In another implementation, the average temperature is calculated based on the minimum module temperature and the maximum module temperature of the battery pack, and the ohmic impedance R0 of the battery pack is obtained in the preset fast discharge DC impedance table by linear interpolation based on the average temperature and the remaining power of the battery pack.

[0103] Step S203, determining the polarization impedance of the battery pack according to the minimum module temperature, the maximum module temperature, the remaining power of the battery pack, a preset fast discharge DC impedance table, and a preset constant current discharge DC impedance table.

[0104] The preset fast discharge DC impedance meter is used to record the DC internal resistance of the battery during fast discharge in a very short time, and the preset constant current discharge DC impedance meter is used to record the DC internal resistance of the battery during constant current discharge. Ohmic impedance is instantaneous, and polarization impedance is continuous. Therefore, in this embodiment, the DC impedance in the fast discharge DC impedance meter can be regarded as ohmic impedance, and the DC impedance in the constant current discharge DC impedance meter can be regarded as the sum of ohmic impedance and polarization impedance.

[0105] In the embodiment of the present application, the calculation cycle of the power control strategy is 100ms, so the preset fast discharge DC impedance table can be a 0.1 second discharge DC impedance table, and the constant current discharge DC impedance table can be a 60 second discharge DC impedance table. The 60 second discharge DC impedance table includes the 60 second discharge DC impedance of the battery pack at different temperatures and different remaining powers.

[0106] Exemplarily, the polarization impedance of the battery pack is determined according to the minimum module temperature, the maximum module temperature, the remaining power of the battery pack, a preset fast discharge DC impedance table, and a preset constant current discharge DC impedance table, including: determining a first impedance value according to the minimum module temperature, the remaining power of the battery pack, and the preset fast discharge DC impedance table; determining a second impedance value according to the maximum module temperature, the remaining power of the battery pack, and the preset fast discharge DC impedance table; determining a third impedance value according to the minimum module temperature, the remaining power of the battery pack, and the preset constant current discharge DC impedance; determining a fourth impedance value according to the maximum module temperature, the remaining power of the battery pack, and the preset constant current discharge DC impedance; determining the polarization impedance of the battery pack according to the first impedance value, the second impedance value, the third impedance value, and the fourth impedance value.

[0107] Since the DC impedance in the fast discharge DC impedance table can be regarded as the ohmic impedance in this embodiment, and the DC internal resistance in the constant current discharge DC impedance table can be regarded as the sum of the ohmic impedance and the polarization impedance. Therefore, in this embodiment, the larger value of the first impedance value and the second impedance value can be taken as the ohmic impedance R0 of the battery pack, and the larger value of the third impedance value and the fourth impedance value can be taken as the sum of the ohmic impedance R0 and the polarization impedance Rp of the battery pack. In this way, the larger value of the third impedance value and the fourth impedance value minus the larger value of the first impedance value and the second impedance value can be used to obtain the current polarization impedance Rp of the battery pack.

[0108] In the embodiment of the present application, the battery management system may include two power control strategies, one is a power control strategy based on the actual minimum cell voltage of the battery pack, which can perform power control according to the real-time voltage value to avoid battery undervoltage in real time. The other is a power control strategy based on predicted voltage, which can perform power control according to the predicted voltage to prevent battery undervoltage in advance. Since the predicted voltage in the power control strategy based on predicted voltage includes the voltage drop caused by ohmic impedance, when determining the pre-undervoltage threshold, there is no need to consider the voltage drop problem caused by ohmic impedance, and only the voltage drop problem caused by polarization impedance needs to be considered.

[0109] The following describes how to determine the pre-undervoltage threshold according to the allowable discharge current, ohmic impedance and / or polarization impedance in the power control strategy based on the actual minimum cell voltage in combination with feasible implementation methods:

[0110] In one possible implementation, refer to Figure 3 , the above step S30 includes the following steps S3011 and S3012:

[0111] Step S3011, calculating the voltage rise according to the allowable discharge current and the ohmic impedance.

[0112] When the battery pack current drops from the allowable discharge current Imax to the preset limp current Ibx, the voltage will rise briefly due to various factors such as battery internal resistance, polarization effect, internal chemical reaction, BMS adjustment, and battery cell inconsistency.

[0113] Since ohmic polarization is proportional to the current, ohmic polarization gradually decreases during the current reduction process. If the current decreases by ΔI, the voltage rise caused by the decrease in ohmic polarization is ΔV=ΔI*R0. Based on this, if the current drops to the preset limp current, the voltage rise caused by the decrease in ohmic polarization is V1=(Imax-Ibx)*R0.

[0114] Step S3012: Calculate a first voltage drop caused by the ohmic impedance and the polarization impedance during the discharge of the battery pack according to the allowable discharge current, the ohmic impedance and the polarization impedance.

[0115] After obtaining the allowable discharge current Imax, the ohmic impedance R0 and the polarization impedance Rp of the battery pack, the first voltage drop V2 = Imax*(R0 + Rp) generated by the ohmic impedance R0 and the polarization impedance Rp can be obtained.

[0116] Based on the above possible implementation methods, see Figure 3 In the embodiment of the present application, step S40 includes the following steps:

[0117] Step S401, determining a first pre-undervoltage threshold according to a preset undervoltage threshold, a voltage rise and a first voltage drop.

[0118] In a possible implementation, the first pre-undervoltage threshold Vp1 is calculated by the following formula (1):

[0119] Vp1=Vq-V1+V2(1)

[0120] Wherein, Vq is a preset undervoltage threshold, V1 is a voltage rise, and V2 is a first voltage drop.

[0121] In the embodiment of the present application, the actual minimum cell voltage is compared with the pre-undervoltage threshold to perform power control. Since the vehicle including the battery pack is not in limp mode, the actual minimum cell voltage of the battery pack does not include the voltage rise caused by the current dropping to the preset limp current, and the first voltage drop caused by the ohmic impedance and polarization impedance. Therefore, in the embodiment of the present application, the voltage rise and the first voltage drop are superimposed on the preset undervoltage threshold in advance to obtain the first pre-undervoltage threshold. Using the first pre-undervoltage threshold for power control can prevent the battery from having an undervoltage problem in advance.

[0122] Realistically, the preset undervoltage threshold may be an undervoltage level 1 voltage threshold of the battery pack, and the undervoltage level 1 voltage threshold of the battery pack may be obtained by querying parameter information of the battery pack.

[0123] Based on the above possible implementation methods, see Figure 3 , step S50 in the embodiment of the present application includes the following steps S5011~S5012.

[0124] Step S5011: Determine whether the minimum cell voltage in the battery pack is less than the first pre-undervoltage threshold. If the determination is yes, proceed to step S5012; if the determination is no, return to step S10.

[0125] Step S5012: Control the allowable discharge current and / or allowable discharge power of the battery pack according to a preset control strategy.

[0126] In the embodiment of the present application, the battery management system adopts a power control strategy based on the minimum cell voltage, and compares the actual minimum cell voltage Vmin of the battery pack with the first undervoltage threshold Vp1 to perform power control. Since the voltage rise and the first voltage drop are superimposed in advance in the first pre-undervoltage threshold, the use of the first pre-undervoltage threshold for power control can prevent the battery from having an undervoltage problem in advance. In the case where it is determined that the actual minimum cell voltage Vmin of the battery pack is less than the first pre-undervoltage threshold Vp1, it is determined that the battery pack may have an undervoltage. At this time, controlling the allowable discharge current and / or allowable discharge power of the battery pack according to the preset control strategy can effectively prevent the battery from triggering an undervoltage fault. For example, the preset control strategy is such as reducing the allowable discharge current and / or allowable discharge power of the battery pack. In the case where it is determined that the actual minimum cell voltage Vmin of the battery pack is not less than the first pre-undervoltage threshold Vp1, return to execute step S10 to re-determine the pre-undervoltage threshold and make a comparison.

[0127] The following describes how to determine the pre-undervoltage threshold according to the allowable discharge current, ohmic impedance and polarization impedance in the power control strategy based on the predicted voltage in combination with feasible implementation methods:

[0128] In one possible implementation, refer to Figure 4 , the above step S30 includes the following steps S3021 and S3022:

[0129] Step S3021, calculating the voltage rise according to the allowable discharge current and the ohmic impedance.

[0130] Step S3021 is the same as step S3011 in the above embodiment and will not be described again in this embodiment to avoid repetition.

[0131] Step S3022: Calculate the second voltage drop caused by the polarization impedance according to the allowable discharge current and the polarization impedance.

[0132] After obtaining the allowable discharge current Imax, ohmic impedance R0 and polarization impedance Rp of the battery pack, the second voltage drop V3 = Imax*Rp generated by the polarization impedance Rp.

[0133] Based on the above possible implementation methods, see Figure 4 In the embodiment of the present application, step S40 includes the following steps:

[0134] Step S402, determining a second pre-undervoltage threshold according to a preset undervoltage threshold, a voltage rise, and a second voltage drop.

[0135] In a possible implementation, the second pre-undervoltage threshold Vp2 is calculated by the following formula (2):

[0136] Vp2=Vq-V1+V3(2)

[0137] Wherein, Vq is the preset undervoltage threshold, V1 is the voltage rise, and V3 is the second voltage drop.

[0138] In the embodiment of the present application, the predicted voltage is compared with the pre-undervoltage threshold to perform power control. Since the vehicle including the battery pack is not in limp mode, the predicted voltage does not include the voltage rise caused by the current dropping to the preset limp current, and since the predicted voltage includes the voltage drop caused by the ohmic impedance, it does not include the second voltage drop caused by the polarization impedance. Therefore, in the embodiment of the present application, the voltage rise and the second voltage drop are superimposed on the preset undervoltage threshold in advance to obtain the second pre-undervoltage threshold. Using the second pre-undervoltage threshold for power control can prevent the battery from having an undervoltage problem in advance.

[0139] Based on the above possible implementation methods, see Figure 4 , step S50 in the embodiment of the present application includes the following steps S5021~S5022.

[0140] Step S5021: Determine whether the estimated minimum cell voltage of the battery pack after the first preset time is less than the second pre-undervoltage threshold. If the determination is yes, proceed to step S5022; if the determination is no, return to step S10.

[0141] Step S5022: Control the allowable discharge current and / or allowable discharge power of the battery pack according to a preset control strategy.

[0142] In this embodiment, the minimum cell voltage of the battery pack after the first preset time includes the voltage drop caused by the ohmic impedance, which can be obtained by subtracting the voltage drop caused by the ohmic impedance from the actual minimum cell voltage Vmin of the battery pack. Assuming that the battery pack is discharged at the allowable discharge current corresponding to the battery pack after the first preset time, the voltage drop caused by the ohmic impedance after the first preset time is dV=∆I×R0, where ∆I=I t1-I t2 , I t1 It is expressed as the allowable discharge current corresponding to the battery pack, I t2 Represents the actual current of the battery pack, where I t1 Greater than or equal to I t2 In this way, the minimum cell voltage V 预 It can be expressed as V 预 =Vmin-∆I×R0.

[0143] The battery management system in the embodiment of the present application adopts a power control strategy based on the predicted voltage (i.e., the minimum single cell voltage of the battery pack after the first preset time length), and adopts the minimum single cell voltage V after the first preset time length of the battery pack. 预 The power control is performed by comparing with the second pre-undervoltage threshold Vp2. Since the voltage rise and the second voltage drop are superimposed in advance in the second pre-undervoltage threshold, the power control using the second pre-undervoltage threshold can prevent the battery from having an undervoltage problem in advance. 预 When the voltage Vp2 is less than the second pre-undervoltage threshold value Vp2, it is determined that the battery pack may be undervoltage. At this time, the allowable discharge current and / or allowable discharge power of the battery pack is controlled according to a preset control strategy. The preset control strategy is, for example, to reduce the allowable discharge current and / or allowable discharge power of the battery pack. 预 If it is not less than the second pre-under-voltage threshold Vp2, the process returns to step S10 to redetermine the second pre-under-voltage threshold and compare it.

[0144] like Figure 5 As shown, there is a vehicle voltage curve diagram for power control using the pre-undervoltage threshold formulated in the embodiment of the present application and for power control using the pre-undervoltage threshold formulated directly based on experience. It can be seen that the control method for the pre-undervoltage threshold determined based on the method of the embodiment of the present application can effectively prevent the battery from triggering an undervoltage fault.

[0145] This application also provides a battery management system, please refer to Figure 6 , the battery management system includes:

[0146] The sampling circuit 10 is used to obtain the minimum module temperature and the maximum module temperature of the battery pack, as well as the remaining power of the battery pack. The minimum module temperature is the lowest temperature of all modules in the battery pack, and the maximum module temperature is the highest temperature of all modules in the battery pack.

[0147] The controller 20 is used to determine the allowable discharge current, ohmic impedance and polarization impedance of the battery pack according to the minimum module temperature, the maximum module temperature and the remaining power of the battery pack; it is also used to determine the voltage rise and voltage drop according to the ohmic impedance and / or polarization impedance and the allowable discharge current, wherein the voltage rise is caused by the current of the battery pack dropping to a preset limp current, and the voltage drop is caused by the ohmic impedance and / or polarization impedance during the discharge of the battery pack; according to the preset undervoltage threshold, the voltage rise and the voltage drop, a pre-undervoltage threshold is determined, and the allowable discharge current and / or the allowable discharge power of the battery pack is controlled according to the pre-undervoltage threshold.

[0148] The battery management system provided in the present application adopts the discharge control method in the above embodiment, which can solve the problem that the current pre-undervoltage threshold determination relies on experience and cannot guarantee accuracy, and the actual vehicle calibration test is complicated.

[0149] Compared with the prior art, the beneficial effects of the battery management system provided in the present application are the same as the beneficial effects of the discharge control method provided in the above embodiment, and other technical features in the battery management system are the same as the features disclosed in the above embodiment method, which will not be repeated here.

[0150] An embodiment of the present application further provides an electrical device, which includes a battery management system as described in the above embodiment. The electrical device may be an electric car, an electric bicycle, industrial electrical equipment, etc.

[0151] It should be understood that the various parts disclosed in this application can be implemented by hardware, software, firmware or a combination thereof. In the description of the above embodiments, specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0152] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be covered by the protection scope of the present application.

Claims

1. A discharge control method, characterized in that: The method comprises: Obtaining the minimum module temperature and the maximum module temperature of the battery pack, as well as the remaining power of the battery pack, wherein the minimum module temperature is the lowest temperature of all modules in the battery pack, and the maximum module temperature is the highest temperature of all modules in the battery pack; Determining an allowable discharge current, ohmic impedance, and polarization impedance of the battery pack according to the minimum module temperature, the maximum module temperature, and the remaining power of the battery pack; Determine a voltage rise and a voltage drop according to the ohmic impedance and / or the polarization impedance, and the allowable discharge current, wherein the voltage rise is caused by the current of the battery pack decreasing to a preset limp current, and the voltage drop is caused by the ohmic impedance and / or the polarization impedance during the discharge of the battery pack; Determining a pre-undervoltage threshold according to a preset undervoltage threshold, the voltage rise and the voltage drop; The allowable discharge current and / or allowable discharge power of the battery pack is controlled according to the pre-undervoltage threshold.

2. The method according to claim 1, characterized in that The determining of the voltage rise and voltage drop according to the ohmic impedance and / or the polarization impedance and the allowable discharge current comprises: Calculating the voltage rise according to the allowable discharge current and the ohmic impedance; A first voltage drop caused by the ohmic impedance and the polarization impedance during the discharge of the battery pack is calculated according to the allowable discharge current, the ohmic impedance and the polarization impedance.

3. The method according to claim 1, characterized in that The determining of the voltage rise and voltage drop according to the ohmic impedance and / or the polarization impedance and the allowable discharge current comprises: Calculating the voltage rise according to the allowable discharge current and the ohmic impedance; A second voltage drop caused by the polarization impedance during the discharge of the battery pack is calculated according to the allowable discharge current and the polarization impedance.

4. The method according to any one of claims 1 to 3, characterized in that The determining the allowable discharge current, ohmic impedance and polarization impedance of the battery pack according to the minimum module temperature, the maximum module temperature, and the remaining power of the battery pack includes: Determining an allowable discharge current of the battery pack according to the minimum module temperature, the maximum module temperature, the remaining power of the battery pack, and a preset allowable discharge current table; Determining the ohmic impedance of the battery pack according to the minimum module temperature, the maximum module temperature, the remaining power of the battery pack, and a preset fast discharge DC impedance table; The polarization impedance of the battery pack is determined according to the minimum module temperature, the maximum module temperature, the remaining power of the battery pack, a preset fast discharge DC impedance table, and a preset constant current discharge DC impedance table.

5. The method according to claim 4, characterized in that The determining the allowable discharge current of the battery pack according to the minimum module temperature, the maximum module temperature, the remaining power of the battery pack, and a preset allowable discharge current table includes: Determining a first current value according to the minimum module temperature, the remaining power of the battery pack, and a preset allowable discharge current table; Determining a second current value according to the maximum module temperature, the remaining power of the battery pack, and a preset allowable discharge current table; An allowable discharge current of the battery pack is determined according to the first current value and the second current value.

6. The method according to claim 4, characterized in that The determining of the polarization impedance of the battery pack according to the minimum module temperature, the maximum module temperature, the remaining power of the battery pack, a preset fast discharge DC impedance table, and a preset constant current discharge DC impedance table includes: Determining a first impedance value according to the minimum module temperature, the remaining power of the battery pack, and the preset fast discharge DC impedance table; Determining a second impedance value according to the maximum module temperature, the remaining power of the battery pack, and the preset fast discharge DC impedance table; Determining a third impedance value according to the minimum module temperature, the remaining power of the battery pack, and the preset constant current discharge DC impedance; Determining a fourth impedance value according to the maximum module temperature, the remaining power of the battery pack, and the preset constant current discharge DC impedance; The polarization impedance of the battery pack is determined according to the first impedance value, the second impedance value, the third impedance value, and the fourth impedance value.

7. The method according to claim 1 or 2, characterized in that: The controlling the allowable discharge current and / or allowable discharge power of the battery pack according to the pre-undervoltage threshold comprises: Determining whether the minimum cell voltage in the battery pack is less than the pre-undervoltage threshold, wherein the pre-undervoltage threshold is determined based on the allowable discharge current, the ohmic impedance, and the polarization impedance; If the minimum single cell voltage is less than the pre-undervoltage threshold, the allowable discharge current and / or allowable discharge power of the battery pack is controlled according to a preset control strategy.

8. The method according to claim 1 or 3, characterized in that: The controlling the allowable discharge current and / or allowable discharge power of the battery pack according to the pre-undervoltage threshold comprises: Determining whether the estimated minimum cell voltage of the battery pack after a first preset time period is less than the pre-undervoltage threshold, wherein the minimum cell voltage of the battery pack after the first preset time period includes a voltage drop caused by the ohmic impedance, and the pre-undervoltage threshold is determined jointly according to the allowable discharge current and the polarization impedance; If the minimum single cell voltage of the battery pack after the first preset time period is less than the pre-undervoltage threshold, the allowable discharge current and / or allowable discharge power of the battery pack is controlled according to a preset control strategy.

9. A battery management system, characterized in that: The battery management system comprises: A sampling circuit, used to obtain a minimum module temperature and a maximum module temperature of a battery pack, and a remaining power of the battery pack, wherein the minimum module temperature is the lowest temperature of all modules in the battery pack, and the maximum module temperature is the highest temperature of all modules in the battery pack; A controller, configured to determine an allowable discharge current, an ohmic impedance, and a polarization impedance of the battery pack according to the minimum module temperature, the maximum module temperature, and the remaining power of the battery pack; It is also used to determine a voltage rise and a voltage drop according to the ohmic impedance and / or the polarization impedance, and the allowable discharge current, wherein the voltage rise is caused by the current of the battery pack dropping to a preset limp current, and the voltage drop is caused by the ohmic impedance and / or the polarization impedance during the discharge of the battery pack; a pre-undervoltage threshold is determined according to a preset undervoltage threshold, the voltage rise and the voltage drop, and the allowable discharge current and / or the allowable discharge power of the battery pack is controlled according to the pre-undervoltage threshold.

10. An electrical device, characterized in that: The electrical device comprises the battery management system as claimed in claim 9 above.

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