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, which relate to the field of battery technology. When determining the predicted voltage of the smallest battery cell at a future moment, the voltage drop caused by the accumulated polarization of the battery pack during use is taken into account, so that the predicted voltage is closer to the polarization state of the battery pack at a future moment. Therefore, the discharge control method in the embodiment of the present application can predict in advance whether the battery pack will have an undervoltage risk at a future moment based on the predicted voltage, thereby controlling the allowable discharge current and / or allowable discharge power of the battery pack in advance, thereby preventing battery undervoltage and improving the safety performance of the battery pack.

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 popularity of electric vehicles makes the stability of power batteries during discharge particularly important, especially to avoid undervoltage failures. When the vehicle accelerates or decelerates suddenly, the battery is prone to polarization, causing the battery voltage to drop rapidly, and may even trigger undervoltage conditions.

[0003] In order to effectively solve the problem of undervoltage of power batteries, the current method is that the battery management system monitors the voltage of the smallest battery cell in real time. The battery management system limits the allowable discharge power and / or allowable discharge current according to the voltage of the smallest battery cell to ensure that the battery operates within a safe voltage range, thereby preventing battery undervoltage and ensuring the safe driving of electric vehicles.

[0004] However, the method of limiting the allowable discharge power and / or allowable discharge current according to the voltage of the smallest battery cell cannot predict the undervoltage risk at a future time in advance, and the undervoltage prevention effect is not good. Summary of the invention

[0005] The main purpose of this application is to provide a discharge control method, a battery management system and an electrical device, aiming to provide a discharge control method with higher accuracy, which can predict the undervoltage risk at a future moment in advance according to the predicted voltage and prevent the battery undervoltage problem in advance.

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

[0007] Obtain the remaining power, temperature and actual voltage of the smallest battery cell at the current sampling moment, and obtain the actual current and allowable discharge current of the battery pack at the current sampling moment, wherein the smallest battery cell is the battery cell with the least remaining power among the multiple battery cells of the battery pack; predict the voltage drop of the battery pack due to cumulative activating at a future moment according to the remaining power and temperature of the smallest battery cell at the current sampling moment, the actual current and allowable discharge current of the battery pack at the current sampling moment, and at least one of the actual voltages of the smallest battery cell at the current sampling moment and N sampling moments before the current sampling moment; determine the predicted voltage of the smallest battery cell at the future moment according to the actual voltage and the voltage drop at the current sampling moment; and control the allowable discharge current and / or allowable discharge power of the battery pack according to the predicted voltage.

[0008] In one embodiment, the voltage drop of the battery pack due to accumulated polarization includes: a first voltage drop of the battery pack due to ohmic polarization, and a second voltage drop of the battery pack due to concentration polarization and electrochemical polarization; the predicting of the voltage drop of the battery pack due to accumulated polarization at a future time according to at least one of the remaining power and temperature of the smallest battery cell at the current sampling moment, the actual current and the allowable discharge current of the battery pack at the current sampling moment, and the actual voltage of the smallest battery cell at the current sampling moment and N sampling moments before the current sampling moment includes: predicting the first voltage drop of the battery pack due to ohmic polarization at a future time according to the remaining power and temperature of the smallest battery cell at the current sampling moment, the actual current and the allowable discharge current of the battery pack at the current sampling moment; predicting the second voltage drop of the battery pack due to concentration polarization and electrochemical polarization at a future time according to the actual voltage of the smallest battery cell at the current sampling moment and N sampling moments before the current sampling moment.

[0009] In this embodiment, different calculation methods are used to calculate the voltage drop caused by polarization of different properties, which further improves the accuracy of predicting the voltage drop caused by the cumulative polarization.

[0010] In one embodiment, predicting the first voltage drop of the battery pack due to ohmic polarization at a future time according to the remaining power and temperature of the smallest battery cell at the current sampling time, as well as the actual current and the allowable discharge current of the battery pack, includes: determining the ohmic impedance of the battery pack at the current sampling time according to the remaining power and temperature of the smallest battery cell at the current sampling time; predicting the first voltage drop of the battery pack due to ohmic polarization at a future time according to the actual current of the battery pack at the current sampling time, the allowable discharge current and the ohmic impedance.

[0011] In this embodiment, the battery pack current is preset to rise from the actual current at the current sampling moment to the allowable discharge current at a future moment, so as to predict the first voltage drop caused by ohmic polarization after the current rises at a future moment, thereby improving the accuracy of predicting the first voltage drop at a future moment.

[0012] In one embodiment, predicting the second voltage drop of the battery pack due to concentration polarization and electrochemical polarization at a future time based on the actual voltage of the minimum battery cell at the current sampling moment and N sampling moments before the current sampling moment includes: determining the weighted average historical voltage drop of N sampling periods before the current sampling moment based on the actual voltage of the minimum battery cell at the current sampling moment and N sampling moments before the current sampling moment; predicting the second voltage drop of the battery pack due to concentration polarization and electrochemical polarization at a future time based on the weighted average historical voltage drop of N sampling periods before the current sampling moment.

[0013] In this embodiment, the historical pressure drop can be understood as the pressure drop caused by concentration polarization and electrochemical polarization. In this way, by calculating the weighted average historical pressure drop of N sampling cycles before the current sampling moment, the second pressure drop of the battery pack caused by concentration polarization and electrochemical polarization at the future moment is predicted, thereby improving the accuracy of predicting the second pressure drop at the future moment.

[0014] In one embodiment, the method of determining the weighted average historical voltage drop of N sampling periods before the current sampling moment based on the actual voltage of the minimum battery cell at the current sampling moment and the N sampling moments before the current sampling moment includes: determining the changing trend of the voltage drop rate of the minimum battery cell within the N sampling periods based on the actual voltage of the minimum battery cell at the current sampling moment and the N sampling moments before the current sampling moment; and determining the weighted average historical voltage drop of the N sampling periods before the current sampling moment based on the changing trend of the voltage drop rate of the minimum battery cell within the N sampling periods and the calculation method of the weighted average historical voltage drop corresponding to the changing trend.

[0015] In this embodiment, the changing trend of the voltage drop rate of the smallest battery cell within N sampling cycles is used to distinguish the current charging and discharging scenarios of the battery pack, and the weighted average historical voltage drop corresponding to the changing trend is calculated to determine the weighted average historical voltage drop corresponding to different charging and discharging scenarios, so that the prediction result is more accurate.

[0016] In addition, to achieve the above-mentioned purpose, the present application also proposes a battery management system, which includes: a sampling circuit, which is used to obtain the remaining power, temperature and actual voltage of the smallest battery cell at the current sampling moment, and obtain the actual current and allowable discharge current of the battery pack at the current sampling moment, wherein the smallest battery cell is the battery cell with the least remaining power among multiple battery cells in the battery pack; a controller, which is used to predict the voltage drop of the battery pack caused by cumulative energization at a future moment based on the remaining power and temperature of the smallest battery cell at the current sampling moment, the actual current and allowable discharge current of the battery pack at the current sampling moment, and at least one of the actual voltages of the smallest battery cell at the current sampling moment and N sampling moments before the current sampling moment; determine the predicted voltage of the smallest battery cell at the future moment based on the actual voltage and the voltage drop at the current sampling moment; and control the allowable discharge current and / or allowable discharge power of the battery pack based on the predicted voltage.

[0017] In addition, to achieve the above objectives, the present application also proposes an electrical device, which includes the battery management system in the above embodiment.

[0018] One or more technical solutions proposed in this application have at least the following technical effects:

[0019] In the embodiment of the present application, the voltage drop of the battery pack due to cumulative polarization at the future moment is predicted based on the remaining power and temperature of the smallest battery cell at the current sampling moment, the actual current and the allowable discharge current of the battery pack, and at least one of the actual voltages of the smallest battery cell at the current sampling moment and the N sampling moments before the current sampling moment. The predicted voltage of the smallest battery cell at the future moment is determined by combining the voltage drop due to cumulative polarization at the future moment and the actual voltage of the smallest battery cell at the current sampling moment. Since the battery pack has cumulative polarization during use, and cumulative polarization is the main factor causing the battery voltage drop, in the present embodiment, when determining the predicted voltage of the smallest battery cell at the future moment, the voltage drop caused by cumulative polarization during use of the battery pack is taken into account, so that the predicted voltage is closer to the polarization state of the battery pack at the future moment. Therefore, the discharge control method in the embodiment of the present application can predict in advance whether the battery pack has an undervoltage risk at the future moment according to the predicted voltage, thereby controlling the allowable discharge current and / or allowable discharge power of the battery pack in advance, thereby preventing battery undervoltage and improving the safety performance of the battery pack. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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.

[0021] 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.

[0022] Figure 1 A schematic diagram of a flow chart provided for the first embodiment of the discharge control method of the present application;

[0023] Figure 2 A schematic diagram of a flow chart provided for the second embodiment of the discharge control method of the present application;

[0024] Figure 3 A schematic diagram of a flow chart provided for the third embodiment of the discharge control method of the present application;

[0025] Figure 4 A flow chart of the fourth embodiment of the discharge control method of the present application;

[0026] Figure 5 A flow chart of the fifth embodiment of the discharge control method of the present application;

[0027] Figure 6 This is the first voltage change trend diagram of the battery pack in N sampling cycles of this application;

[0028] Figure 7 This is the second voltage variation trend diagram of the battery pack in N sampling cycles of this application;

[0029] Figure 8 This is the third voltage variation trend diagram of the battery pack in N sampling cycles of this application;

[0030] Fig. 9 This is the fourth voltage variation trend diagram of the battery pack in N sampling cycles of this application;

[0031] Fig.10 This is a schematic diagram of the module structure of the battery management system according to an embodiment of the present application.

[0032] 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

[0033] 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.

[0034] 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.

[0035] 1. Battery Cell

[0036] 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.

[0037] 2. Battery module

[0038] 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.

[0039] 3. Battery Pack

[0040] 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.

[0041] 4. Remaining power

[0042] The remaining capacity (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.

[0043] 5. Cumulative Activation

[0044] Accumulated positive polarization refers to the phenomenon that charge accumulates inside the battery due to the electrochemical reaction of the electrode material, electrolyte and solid electrolyte interface film on the electrode surface during the battery charging and discharging process. This charge accumulation will cause the internal voltage to drop, thereby causing the terminal voltage of the battery to drop. The voltage drop caused by accumulated positive polarization is a comprehensive concept, which includes the voltage drop caused by various reasons during the battery charging and discharging process. These reasons can be divided into several main types:

[0045] (1) Ohmic polarization

[0046] The voltage drop caused by the internal resistance of the battery (including the contact resistance of the electrode material, electrolyte, separator and electrode-electrolyte interface). This voltage drop is instantaneous, and once the current stops, the ohmic polarization disappears.

[0047] (2) Concentration polarization

[0048] Voltage drop due to uneven ion concentration inside the battery. During the charge and discharge process, the difference in lithium ion concentration between the surface and the interior of the electrode causes an imbalance in the charge on the electrode surface.

[0049] (3) Electrochemical polarization

[0050] The voltage drop is caused by the fact that the electrochemical reaction speed cannot keep up with the current change. This involves the charge transfer reaction on the electrode surface and the deposition of substances on the electrode surface.

[0051] The "accumulation" in cumulative polarization refers to the gradual accumulation of these polarization phenomena during repeated charge and discharge of the battery, resulting in a gradual decline in battery performance. When referring to the voltage drop caused by cumulative polarization, it usually includes the voltage drop caused by ohmic impedance, as well as the voltage drop caused by concentration polarization and electrochemical polarization. The cumulative effect of these voltage drops will affect the overall performance of the battery, including reduced capacity, reduced efficiency, and shortened life.

[0052] 6. Allowable discharge current

[0053] 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.

[0054] 7. Allowable discharge power

[0055] 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.

[0056] 8. Undervoltage

[0057] "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.

[0058] Brownouts may cause the following problems:

[0059] (1) Battery performance degradation: Long-term undervoltage operation will damage battery performance and reduce the 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 operating under undervoltage may pose safety risks, such as internal short circuits or leakage.

[0060] 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.

[0061] 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.

[0062] The popularity of electric vehicles makes the stability of power batteries during discharge particularly important, especially to avoid undervoltage failures. When the vehicle accelerates or decelerates suddenly, the battery is prone to polarization, causing the battery voltage to drop rapidly, and may even trigger undervoltage conditions.

[0063] In order to ensure the driving safety of the vehicle, it is necessary to monitor various properties of the power battery. One of the useful properties is the battery terminal voltage. The battery terminal voltage can be used to define the allowable charging cut-off voltage and discharging cut-off voltage to provide information for determining the use boundary of the power battery and preventing the battery from over-discharging.

[0064] The current method is that the battery management system monitors the voltage of the smallest battery cell in real time. The battery management system limits the allowable discharge power and / or allowable discharge current based on the voltage of the smallest battery cell to ensure that the battery operates within a safe voltage range, thereby preventing battery undervoltage and ensuring safe driving of electric vehicles.

[0065] However, the method of limiting the allowable discharge power and / or allowable discharge current according to the voltage of the smallest battery cell cannot predict the undervoltage risk at a future time in advance, and the undervoltage prevention effect is not good.

[0066] To this end, a discharge control method is proposed in an embodiment of the present application, the method comprising: first, obtaining the remaining power, temperature and actual voltage of the smallest battery cell at the current sampling moment, and obtaining the actual current and allowable discharge current of the battery pack at the current sampling moment, the smallest battery cell being the battery cell with the least remaining power among multiple battery cells in the battery pack; secondly, predicting the voltage drop of the battery pack due to cumulative positivity at a future moment based on the remaining power and temperature of the smallest battery cell at the current sampling moment, the actual current and allowable discharge current of the battery pack, and at least one of the actual voltages of the smallest battery cell at the current sampling moment and N sampling moments before the current sampling moment; finally, determining the predicted voltage of the smallest battery cell at a future moment based on the actual voltage and voltage drop at the current sampling moment.

[0067] Since the battery pack has accumulated polarization during use, and accumulated polarization is the main factor causing battery voltage drop, in this embodiment, when determining the predicted voltage of the smallest battery cell at a future moment, the voltage drop caused by the accumulated polarization of the battery pack during use is taken into account, so that the predicted voltage is closer to the polarization state of the battery pack at a future moment. Therefore, the discharge control method in the embodiment of the present application can predict in advance whether the battery pack will have an undervoltage risk at a future moment based on the predicted voltage, thereby controlling the allowable discharge current and / or allowable discharge power of the battery pack in advance, thereby preventing battery undervoltage and improving the safety performance of the battery pack.

[0068] It should be noted that the execution subject 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 electric car, electric bicycle, etc. that includes a battery management system.

[0069] The present embodiment and the following embodiments are described below by taking a battery management system as an example.

[0070] 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.

[0071] In this embodiment, the discharge control method includes steps S10 to S40:

[0072] Step S10, obtaining the remaining power, temperature and actual voltage of the smallest battery cell at the current sampling moment, and obtaining the actual current and allowable discharge current of the battery pack at the current sampling moment.

[0073] The battery management system can set a fixed sampling period to obtain relevant data of the battery pack, and perform sampling every other sampling period. For example, the sampling period can be set to 100 milliseconds, and sampling can be performed every 100 milliseconds. Alternatively, the battery management system can also set a fixed sampling time, for example, 0 milliseconds, 50 milliseconds, 80 milliseconds, etc., to obtain relevant data of the battery pack according to the fixed sampling time.

[0074] For each sampling moment, the battery management system obtains the remaining power SOC, temperature T and actual voltage Vmin of the smallest battery cell at the current sampling moment; and obtains the actual current I and allowable discharge current Ip of the entire battery pack at the current sampling moment. Among them, the smallest battery cell is the battery cell with the least remaining power among the multiple battery cells in the battery pack.

[0075] Among them, the battery management system is pre-set with an allowable discharge current meter, which includes the allowable discharge current of the battery pack corresponding to the smallest battery cell in the battery pack at different temperatures and different remaining power. According to the remaining power and temperature of the smallest battery cell at the current sampling moment, the allowable discharge current Ip corresponding to the smallest battery cell at the current sampling moment can be obtained by querying the allowable discharge current meter through a linear difference lookup table.

[0076] Step S20, predicting the voltage drop of the battery pack due to cumulative activation at a future time based on the remaining power and temperature of the smallest battery cell at the current sampling time, the actual current and allowable discharge current of the battery pack, and the actual voltage of the smallest battery cell at the current sampling time and N sampling times before the current sampling time.

[0077] During the use of the battery pack, the internal charge of the battery accumulates due to the electrochemical reaction, that is, the battery has cumulative polarization. Due to the polarization phenomenon, the battery voltage will drop. Therefore, in this embodiment, when determining the predicted voltage of the smallest battery cell at a future moment, the voltage drop caused by the cumulative polarization of the battery pack during use must be taken into account. Based on this, in this step, the voltage drop of the battery pack caused by the cumulative polarization at a future moment is predicted based on the remaining power and temperature of the smallest battery cell at the current sampling moment, the actual current and allowable discharge current of the battery pack, and the actual voltage of the smallest battery cell at the current sampling moment and N sampling moments before the current sampling moment.

[0078] Step S30, determining the predicted voltage of the minimum battery cell at a future time according to the actual voltage and voltage drop at the current sampling time.

[0079] Step S40: controlling the allowable discharge current and / or allowable discharge power of the battery pack according to the predicted voltage.

[0080] Specifically speaking, for the above steps S30 and S40, the voltage Vp of the minimum battery cell at the future moment can be calculated by the following formula (1):

[0081] Vp=Vmin-∆V(1)

[0082] Among them, Vmin is the actual voltage of the smallest battery cell at the current sampling moment, and ∆V is the voltage drop caused by cumulative activation at a future moment.

[0083] In this embodiment, when determining the predicted voltage of the minimum battery cell at a future time, the voltage drop caused by the cumulative polarization of the battery pack during use is taken into account, so that the predicted voltage is closer to the polarization state of the battery pack at the future time. Therefore, the discharge control method in the embodiment of the present application can predict in advance whether the battery pack will have an undervoltage risk at a future time based on the predicted voltage, thereby controlling the allowable discharge current and / or allowable discharge power of the battery pack in advance, thereby preventing battery undervoltage.

[0084] The following describes how to predict the voltage drop of a battery pack due to cumulative activation at a future time.

[0085] The accumulated polarization of the battery includes: ohmic polarization, concentration polarization and electrochemical polarization. These three polarization phenomena of the battery will cause the battery voltage to decrease. Therefore, in this embodiment, when predicting the voltage drop of the battery pack due to accumulated polarization at a future time, it is necessary to predict the voltage drop caused by these three polarization relationships. Figure 2 , Figure 2 This is a flow chart of the second embodiment of the discharge control method of the present application. Step S20 in the first embodiment includes step S201 and step S202.

[0086] Step S201 , predicting the first voltage drop of the battery pack due to ohmic polarization at a future time according to the remaining power and temperature of the smallest battery cell at the current sampling time, the actual current of the battery pack and the allowable discharge current.

[0087] Since the voltage drop caused by ohmic polarization is related to the change in current, in this embodiment, the first voltage drop caused by ohmic polarization in the battery pack at a future moment is predicted based on the actual current of the battery pack, the allowable discharge current, the remaining power of the minimum battery cell, and the temperature at the current sampling moment.

[0088] Step S202 , predicting a second voltage drop of the battery pack caused by concentration polarization and electrochemical polarization at a future time according to the actual voltage of the smallest battery cell at the current sampling time and N sampling times before the current sampling time.

[0089] Since ohmic polarization is instantaneous, once the current stops changing, ohmic polarization will disappear. When the battery pack is in the stable discharge stage, the current change is small, so the ohmic polarization caused by the change in current size can be ignored. Concentration polarization and electrochemical polarization gradually accumulate during the repeated discharge of the battery. Therefore, in this embodiment, the historical data of the actual voltage of the smallest battery cell, that is, the actual voltage of the smallest battery cell at the current sampling moment and the N sampling moments before the current sampling moment, can be used to predict the second voltage drop caused by concentration polarization and electrochemical polarization of the battery pack at future moments, so that the predicted second voltage drop is more in line with the state of concentration polarization and electrochemical polarization of the battery at future moments, and the predicted second voltage drop is more accurate.

[0090] In this implementation, since ohmic polarization is instantaneous, while concentration polarization and electrochemical polarization are gradually accumulated, the first voltage drop of the battery pack due to ohmic polarization at the future moment is predicted based on the remaining power and temperature of the smallest battery cell at the current sampling moment, the actual current of the battery pack, and the allowable discharge current; the second voltage drop of the battery pack due to concentration polarization and electrochemical polarization at the future moment is predicted based on the actual voltage of the smallest battery cell at the current sampling moment and the N sampling moments before the current sampling moment. The sum of the first voltage drop and the second voltage drop is the voltage drop caused by cumulative polarization at the future moment. In other words, different calculation methods are used to calculate the voltage drop caused by polarization of different properties, which further improves the accuracy of predicting the voltage drop caused by cumulative polarization.

[0091] The following describes how to predict the first voltage drop of the battery pack due to ohmic polarization at a future moment.

[0092] In one possible implementation, referring to Figure 3 , Figure 3 This is a flow chart of the third embodiment of the discharge control method of the present application. Step S201 in the second embodiment includes step S2011 and step S2012.

[0093] Step S2011: Determine the ohmic impedance of the battery pack according to the remaining power and temperature of the smallest battery cell at the current sampling moment.

[0094] The battery management system is pre-set with a battery ohm impedance meter, which includes the ohm impedance of the smallest battery cell actually measured at different temperatures and different remaining capacities. According to the remaining capacity and temperature of the smallest battery cell at the current sampling moment, the battery ohm impedance meter can be queried by linear interpolation to obtain the ohm impedance R0 of the smallest battery cell at the current sampling moment.

[0095] Step S2012: predicting the first voltage drop of the battery pack due to ohmic polarization at a future time according to the actual current, allowable discharge current and ohmic impedance of the battery pack at the current sampling time.

[0096] In this embodiment, the actual current of the battery pack is a current with positive and negative signs. A positive actual current indicates that the battery pack is discharging, and a negative actual current indicates that the battery pack is being recharged. Battery pack recharging refers to the process of recovering energy through an energy recovery mechanism and storing it back in the battery during the use of the battery pack. Battery pack recharging is not the same as battery pack charging. Battery pack charging requires an external power supply, while battery pack recharging does not require an external power supply.

[0097] Regardless of whether the battery pack is discharging or recharging, the first voltage drop ∆V1 caused by ohmic polarization R0 at the future moment can be calculated by the following formula (2):

[0098] ∆V1=(Ip-I)*R0(2)

[0099] Wherein, Ip is the allowable discharge current of the battery pack at the current sampling moment, I is the actual current of the battery pack at the current sampling moment, and R0 is the ohmic impedance of the battery pack at the current sampling moment. In the case of controlled discharge, I is less than or equal to Ip.

[0100] In this embodiment, the battery pack current is preset to rise from the actual current I at the current sampling moment to the allowable discharge current Ip at a future moment, so as to predict the first voltage drop caused by ohmic polarization after the current rises at a future moment, thereby improving the accuracy of predicting the first voltage drop at a future moment.

[0101] The following describes how to determine the second voltage drop caused by concentration polarization and electrochemical polarization at a future moment.

[0102] In a possible implementation, the second voltage drop of the battery pack caused by concentration polarization and electrochemical polarization at a future time can be predicted by calculating the weighted average historical voltage drop of N sampling periods before the current sampling time. Figure 4 , Figure 4 This is a flow chart of the fourth embodiment of the discharge control method of the present application. Step S202 in the second embodiment includes step S2021 and step S2022.

[0103] Step S2021: Determine the weighted average historical voltage drop of N sampling periods before the current sampling moment according to the actual voltage of the minimum battery cell at the current sampling moment and N sampling moments before the current sampling moment.

[0104] In this embodiment, the actual voltage of the minimum battery cell at the current sampling moment and the actual voltage of the minimum battery cell at N sampling moments before the current sampling moment, a total of the actual voltage of the minimum battery cell at N+1 sampling moments. Taking two adjacent sampling moments as a sampling cycle, the voltage drop of the minimum battery cell in N sampling cycles is calculated based on the actual voltage of the minimum battery cell at these N+1 sampling moments. The weighted average historical voltage drop of N sampling cycles can be calculated based on the voltage drop of the minimum battery cell in N sampling cycles. The weighted average historical voltage drop is used to characterize the voltage magnitude that the voltage of the minimum battery cell may drop within one sampling cycle.

[0105] Step S2022: predicting the second voltage drop of the battery pack due to concentration polarization and electrochemical polarization at a future time according to the weighted average historical voltage drop of N sampling periods before the current sampling time.

[0106] The "future moment" is assumed to be the moment after a preset time from the current sampling moment. Assuming the preset time is ∆t1, the weighted average historical pressure drop of N sampling periods before the current sampling moment is dV. Then the second pressure drop caused by concentration polarization and electrochemical polarization at the future moment can be the weighted average historical pressure drop of dV multiplied by the preset time ∆t1, that is, V2=dV×∆t1.

[0107] In this embodiment, the historical pressure drop can be understood as the pressure drop caused by concentration polarization and electrochemical polarization. In this way, by calculating the weighted average historical pressure drop of N sampling cycles before the current sampling moment, the second pressure drop of the battery pack caused by concentration polarization and electrochemical polarization at the future moment is predicted, thereby improving the accuracy of predicting the second pressure drop at the future moment.

[0108] In the high current discharge scenario, the battery polarization is serious and the voltage drop rate is fast, while in the low current discharge scenario, the battery polarization is light and the voltage drop rate is slow. Therefore, in order to accurately predict the second voltage drop caused by concentration polarization and electrochemical polarization of the battery pack in the future, it is necessary to consider the current charging and discharging scenario of the battery pack and determine the calculation method of the corresponding second voltage drop based on the current charging and discharging scenario of the battery pack.

[0109] In this embodiment, the change trend of the voltage drop rate of the smallest battery cell within N sampling cycles is used to distinguish the current charging and discharging scenarios of the battery pack, and the weighted average historical voltage drop corresponding to the change trend is calculated to determine the weighted average historical voltage drop corresponding to different charging and discharging scenarios, so that the prediction result is more accurate. Figure 5 , Figure 5 This is a flow chart of the fifth embodiment of the discharge control method of the present application. Step S2021 in the fourth embodiment includes step S2021-1 to step S2021-2.

[0110] Step S2021 - 1 : Determine the change trend of the voltage drop rate of the smallest battery cell within N sampling periods according to the actual voltage of the smallest battery cell at the current sampling moment and N sampling moments before the current sampling moment.

[0111] In one implementation, the voltage drop in each of the N sampling cycles before the current sampling moment can be calculated based on the actual voltage of the minimum battery cell at the current sampling moment and the N sampling moments before the previous sampling moment. Assuming that the current sampling moment is t10, the actual voltage of the corresponding minimum battery cell is Vmin_10, and the moments before the sampling moment are t9, t8, t7, and t6, the actual voltage of the minimum battery cell corresponding to the moment t9 is Vmin_9, and the voltage drop corresponding to the sampling period from t9 to t10 is Vmin_10-Vmin_9.

[0112] The voltage drop in each sampling cycle is divided by the duration of each sampling cycle to obtain the voltage drop rate within the sampling cycle. In this way, the voltage drop rate of the minimum battery cell within N sampling cycles and the changing trend of the voltage drop rate of the minimum battery cell within N sampling cycles can be calculated based on the voltage drop in each sampling cycle in the N sampling cycles before the current sampling moment.

[0113] In another implementation, the actual voltage of the minimum battery cell at the current sampling moment and N sampling moments before the previous sampling moment can be displayed in a coordinate system with the horizontal axis as time and the vertical axis as voltage. The change curve of the actual voltage of the minimum battery cell can be obtained by fitting and other methods, and the change trend of the voltage drop rate of the minimum battery cell can be determined based on the change curve of the actual voltage of the minimum battery cell.

[0114] Step S2021-2: Determine the weighted average historical voltage drop of N sampling periods before the current sampling moment according to the change trend of the voltage drop rate of the smallest battery cell within N sampling periods and the calculation method of the weighted average historical voltage drop corresponding to the change trend.

[0115] In the high-current discharge scenario, the battery polarization is serious and the voltage drop rate is fast, while in the low-current discharge scenario, the battery polarization is light and the voltage drop rate is slow. The discharge scenario of the battery pack in N sampling cycles can be determined by the changing trend of the voltage drop rate of the smallest battery cell in N sampling cycles. For example, if the voltage drop rate in the first few sampling cycles is greater than the voltage drop rate in the last few sampling cycles, it indicates that the battery pack is discharged with a large current first and then with a small current; conversely, if the voltage drop rate in the first few sampling cycles is less than the voltage drop rate in the last few sampling cycles, it indicates that the battery pack is discharged with a small current first and then with a large current.

[0116] The battery pack discharge scenarios may include: (1) continuous high current discharge; (2) continuous low current discharge; (3) high current discharge first and then low current discharge; (4) low current discharge first and then high current discharge; (5) high current discharge first and then high current discharge after the battery is recharged; (6) low current discharge first and then low current discharge after the battery is recharged; (7) high current discharge first and then low current discharge after the battery is recharged; (8) low current discharge first and then high current discharge after the battery is recharged.

[0117] Since battery polarization is more serious in high-current discharge scenarios, if the battery is discharged with a high current first and then with a low current, the voltage drop generated during the high-current discharge stage must be considered when determining the weighted average historical voltage drop corresponding to the discharge scenario. If the battery is discharged with a low current first and then with a high current, the voltage drop generated during the low-current discharge stage can be ignored when determining the weighted average historical voltage drop corresponding to the discharge scenario, and the weighted average historical voltage drop corresponding to the discharge scenario can be calculated directly based on the voltage drop generated during the high-current discharge stage.

[0118] Based on the above considerations, the changing trends of the voltage drop rates corresponding to the above 8 battery pack discharge scenarios can be divided into two categories:

[0119] (1) If the change trend is: within N sampling cycles, the voltage drop rate of the smallest battery cell within p1 consecutive sampling cycles is greater than the voltage drop rate of the smallest battery cell within q1 consecutive sampling cycles, where the sum of p1 and q1 is less than or equal to N, and the p1 consecutive sampling cycles are before the q1 consecutive sampling cycles.

[0120] That is to say, the battery pack discharges with a large current in the first p1 sampling cycles and discharges with a small current in the last q1 sampling cycles. If the sum of p1 and q1 is less than N, the battery may be recharged. Since the battery polarization is serious in the high current discharge scenario and is less severe in the low current discharge scenario, the weight value a of the voltage drop corresponding to the first p1 sampling cycles can be set larger, and the weight value b of the voltage drop corresponding to the last q1 sampling cycle can be set smaller, that is, a is greater than or equal to b.

[0121] Then the weighted average historical voltage drop dV of N sampling periods can be expressed by the following formula (3):

[0122] dV=dV1*a+dV2*b(3)

[0123] Among them, dV1 is the first average historical pressure drop within p1 consecutive sampling periods, dV2 is the second average historical pressure drop within q1 consecutive sampling periods, a is the weight value of the first average historical pressure drop, b is the weight value of the second average historical pressure drop, the sum of a and b is 1, and a is greater than or equal to b.

[0124] Specific as Figure 6 As shown, the voltage drop rate of the smallest battery cell in p2 consecutive sampling cycles is greater than the voltage drop rate of the smallest battery cell in q2 consecutive sampling cycles, and p2+q2=N, that is, the battery is in a low current discharge scenario after a high current discharge. Since the cumulative positive change in the high current discharge stage is greater than the cumulative positive change in the low current discharge stage, the weight value a of the first average historical voltage drop dV1 in p1 consecutive sampling cycles is greater than or equal to the weight value b of the second average historical voltage drop in q1 consecutive sampling cycles, and the sum of a and b is 1. Then the weighted average historical voltage drop dV of N sampling cycles = dV1*a+dV2*b.

[0125] Reference Figure 7 , the voltage drop rate of the smallest battery cell in p2 consecutive sampling cycles is greater than the voltage drop rate of the smallest battery cell in q2 consecutive sampling cycles, and p2+q2<N, that is, the battery is in a scenario of high-current discharge followed by recharging and then low-current discharge. Since the cumulative positive change in the high-current discharge stage is greater than the cumulative positive change in the low-current discharge stage, the weight value a of the first average historical voltage drop dV1 in p1 consecutive sampling cycles is greater than or equal to the weight value b of the second average historical voltage drop in q1 consecutive sampling cycles, and the sum of a and b is 1. Then the weighted average historical voltage drop dV of N sampling cycles = dV1*a+dV2*b.

[0126] (2) If the change trend is: within N sampling cycles, the voltage drop rate of the smallest battery cell within p2 consecutive sampling cycles is less than or equal to the voltage drop rate of the smallest battery cell within q2 consecutive sampling cycles, where the sum of p2 and q2 is less than or equal to N, and the p2 consecutive sampling cycles are before the q2 consecutive sampling cycles.

[0127] That is to say, the battery pack discharges with a small current in the first p2 sampling cycles and discharges with a large current in the last q2 sampling cycles. If the sum of p1 and q1 is less than N, the battery may be recharged. Since the battery polarization is serious in the high current discharge scenario and is relatively mild in the low current discharge scenario, the voltage drop caused in the first p2 sampling cycles can be ignored, and the weight value of the voltage drop corresponding to the last q2 sampling cycles can be set to 1.

[0128] Then the weighted average historical voltage drop dV of N sampling periods can be expressed by the following formula (4):

[0129] dV = dV3 (4)

[0130] Wherein, dV3 is the third average historical voltage drop within q2 consecutive sampling periods.

[0131] See also Figure 8, the voltage drop rate of the smallest battery cell in p2 consecutive sampling cycles is equal to the voltage drop rate of the smallest battery cell in q2 consecutive sampling cycles, that is, the battery is in a continuous high current or continuous low current discharge scenario, and the cumulative positive change can be considered continuous. At this time, the weighted average historical voltage drop dV = the third average historical voltage drop in q2 consecutive sampling cycles. Among them, Figure 8 The dotted line in is used to indicate the boundary between p2 sampling periods and q2 sampling periods.

[0132] See also Fig. 9 , the voltage drop rate of the smallest battery cell in p2 consecutive sampling cycles is less than the voltage drop rate of the smallest battery cell in q2 consecutive sampling cycles, that is, the battery is in a scenario of small current discharge and then large current discharge. At this time, the weighted average historical voltage drop dV = the third average historical voltage drop in q2 consecutive sampling cycles.

[0133] In one implementation, the allowable discharge current and / or allowable discharge power of the battery pack is controlled according to the predicted voltage, including: when the predicted voltage is less than a pre-undervoltage threshold, the allowable discharge current and / or allowable discharge power of the battery pack is controlled according to a preset control strategy.

[0134] The battery management system can determine the predicted voltage of the smallest battery cell at a future moment, and compare the predicted voltage with the pre-undervoltage threshold. If the predicted voltage is less than the pre-undervoltage threshold, it indicates that the battery pack may be undervoltage at a future moment. At this time, the battery management system can control the allowable discharge current and / or allowable discharge power of the battery pack according to a preset control strategy, for example, reducing the allowable discharge current and / or reducing the allowable discharge power. When the battery management system prevents the battery pack from undervoltage, it can adjust the allowable discharge power or the allowable discharge current separately, or adjust both at the same time, depending on the specific application scenario and battery characteristics.

[0135] It is worth noting that in step S10 of the above embodiment, if the allowable discharge current and / or allowable discharge power of the battery pack is adjusted according to the predicted voltage, that is, the actual allowable discharge current of the battery pack is different from the allowable discharge current obtained by looking up the table according to the remaining power and temperature of the battery pack, then the predicted voltage at the next sampling moment is calculated based on the adjusted allowable discharge current.

[0136] In this embodiment, the battery management system compares the predicted voltage with the pre-undervoltage threshold, and can predict in advance whether the battery pack will have an undervoltage risk in the future, thereby preventing battery undervoltage in advance and improving the safety performance of the battery pack.

[0137] This application also provides a battery management system, please refer to Fig.10 , the battery management system includes:

[0138] The sampling circuit 10 is used to obtain the remaining power, temperature and actual voltage of the smallest battery cell at the current sampling moment, and to obtain the actual current and allowable discharge current of the battery pack at the current sampling moment. The smallest battery cell is the battery cell with the least remaining power among the multiple battery cells in the battery pack.

[0139] The controller 20 predicts the voltage drop of the battery pack due to cumulative activating at a future moment based on the remaining power and temperature of the smallest battery cell at the current sampling moment, the actual current and the allowable discharge current of the battery pack, and the actual voltage of the smallest battery cell at the current sampling moment and at N sampling moments before the current sampling moment; and determines the predicted voltage of the smallest battery cell at the future moment based on the actual voltage and voltage drop at the current sampling moment, and controls the allowable discharge current and / or allowable discharge power of the battery pack based on the predicted voltage.

[0140] The battery management system provided in the embodiment of the present application adopts the discharge control method in the above embodiment to improve the accuracy of the voltage prediction result.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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 included in the protection scope of the present application. Therefore, the protection scope of the present application.

Claims

1. A discharge control method, characterized in that: The method comprises: Obtaining the remaining power, temperature and actual voltage of the smallest battery cell at the current sampling moment, and obtaining the actual current and allowable discharge current of the battery pack at the current sampling moment, wherein the smallest battery cell is the battery cell with the least remaining power among the multiple battery cells of the battery pack; Predicting the voltage drop of the battery pack due to cumulative activation at a future time according to the remaining power and temperature of the smallest battery cell at the current sampling time, the actual current and the allowable discharge current of the battery pack at the current sampling time, and the actual voltage of the smallest battery cell at the current sampling time and N sampling times before the current sampling time; Determining the predicted voltage of the minimum battery cell at the future time according to the actual voltage and the voltage drop at the current sampling time; The allowable discharge current and / or allowable discharge power of the battery pack is controlled according to the predicted voltage.

2. The method according to claim 1, characterized in that The voltage drop of the battery pack caused by cumulative polarization includes: a first voltage drop of the battery pack caused by ohmic polarization, and a second voltage drop of the battery pack caused by concentration polarization and electrochemical polarization; The method predicts the voltage drop of the battery pack due to cumulative activation at a future time according to the remaining power and temperature of the smallest battery cell at the current sampling time, the actual current and the allowable discharge current of the battery pack at the current sampling time, and the actual voltage of the smallest battery cell at the current sampling time and N sampling times before the current sampling time, including: Predicting a first voltage drop of the battery pack due to ohmic polarization at a future time according to the remaining power and temperature of the smallest battery cell at the current sampling time, and the actual current and allowable discharge current of the battery pack at the current sampling time; According to the actual voltage of the smallest battery cell at the current sampling moment and N sampling moments before the current sampling moment, a second voltage drop of the battery pack caused by concentration polarization and electrochemical polarization at a future moment is predicted.

3. The method according to claim 2, characterized in that The predicting, based on the remaining power and temperature of the smallest battery cell at the current sampling moment, and the actual current and the allowable discharge current of the battery pack at the current sampling moment, the first voltage drop of the battery pack caused by ohmic polarization at a future moment includes: Determining the ohmic impedance of the battery pack at the current sampling moment according to the remaining power and temperature of the smallest battery cell at the current sampling moment; According to the actual current of the battery pack at the current sampling moment, the allowable discharge current and the ohmic impedance, a first voltage drop of the battery pack caused by ohmic polarization at a future moment is predicted.

4. The method according to claim 3, characterized in that The actual current is a current value with a positive or negative sign, and the first voltage drop ∆V1 is calculated by the following formula: ∆V1=(Ip-I)*R0 Among them, Ip is the allowable discharge current of the battery pack at the current sampling moment, I is the actual current of the battery pack at the current sampling moment, and R0 is the ohmic impedance of the battery pack at the current sampling moment.

5. The method according to claim 2, characterized in that The method predicts the second voltage drop of the battery pack caused by concentration polarization and electrochemical polarization at a future time according to the actual voltage of the minimum battery cell at the current sampling time and N sampling times before the current sampling time, including: Determine a weighted average historical voltage drop of N sampling periods before the current sampling moment according to the actual voltage of the minimum battery cell at the current sampling moment and N sampling moments before the current sampling moment; The second voltage drop of the battery pack caused by concentration polarization and electrochemical polarization at a future time is predicted according to the weighted average historical voltage drop of N sampling periods before the current sampling time.

6. The method according to claim 5, characterized in that The step of determining the weighted average historical voltage drop of N sampling periods before the current sampling moment according to the actual voltage of the minimum battery cell at the current sampling moment and N sampling moments before the current sampling moment includes: Determine a change trend of a voltage drop rate of the minimum battery cell within the N sampling periods according to the actual voltage of the minimum battery cell at the current sampling moment and N sampling moments before the current sampling moment; The weighted average historical voltage drop of N sampling periods before the current sampling moment is determined according to the change trend of the voltage drop rate of the minimum battery cell within the N sampling periods and the calculation method of the weighted average historical voltage drop corresponding to the change trend.

7. The method according to claim 6, characterized in that The step of determining the weighted average historical voltage drop of N sampling periods before the current sampling moment according to the change trend of the voltage drop rate of the minimum battery cell within the N sampling periods and the calculation method of the weighted average historical voltage drop corresponding to the change trend comprises: If the change trend is: within the N sampling periods, the voltage drop rate of the minimum battery cell within p1 consecutive sampling periods is greater than the voltage drop rate of the minimum battery cell within q1 consecutive sampling periods, wherein the sum of p1 and q1 is less than or equal to N, and the p1 consecutive sampling periods are before the q1 consecutive sampling periods, then the weighted average historical voltage drop dV of the N sampling periods can be expressed by the following formula: dV=dV1*a+dV2*b Among them, dV1 is the first average historical pressure drop within p1 consecutive sampling periods, dV2 is the second average historical pressure drop within q1 consecutive sampling periods, a is the weight value of the first average historical pressure drop, b is the weight value of the second average historical pressure drop, the sum of a and b is 1, and a is greater than or equal to b.

8. The method according to claim 6, characterized in that The step of determining the weighted average historical voltage drop of N sampling periods before the current sampling moment according to the change trend of the voltage drop rate of the minimum battery cell within the N sampling periods and the calculation method of the weighted average historical voltage drop corresponding to the change trend comprises: If the change trend is: within the N sampling cycles, the voltage drop rate of the minimum battery cell within p2 consecutive sampling cycles is less than or equal to the voltage drop rate of the minimum battery cell within q2 consecutive sampling cycles, wherein the sum of p2 and q2 is less than or equal to N, and the p2 consecutive sampling cycles are before the q2 consecutive sampling cycles, then the weighted average historical voltage drop dV of the N sampling cycles can be expressed by the following formula: dV=dV3 Wherein, dV3 is the third average historical voltage drop within q2 consecutive sampling periods.

9. The method according to claim 1, characterized in that, The controlling the allowable discharge current and / or allowable discharge power of the battery pack according to the predicted voltage includes: When the predicted 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.

10. A battery management system, characterized in that: The battery management system comprises: A sampling circuit, used to obtain the remaining power, temperature and actual voltage of the smallest battery cell at the current sampling moment, and to obtain the actual current and allowable discharge current of the battery pack at the current sampling moment, wherein the smallest battery cell is the battery cell with the least remaining power among the multiple battery cells of the battery pack; The controller is used to predict the voltage drop of the battery pack due to cumulative activating at a future moment according to the remaining power and temperature of the smallest battery cell at the current sampling moment, the actual current and the allowable discharge current of the battery pack at the current sampling moment, and the actual voltage of the smallest battery cell at the current sampling moment and N sampling moments before the current sampling moment; determine the predicted voltage of the smallest battery cell at the future moment according to the actual voltage and the voltage drop at the current sampling moment; and control the allowable discharge current and / or allowable discharge power of the battery pack according to the predicted voltage.

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

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