Health early warning method based on charging internal resistance of battery pack

Abstract

The invention discloses a health early warning method based on the charging internal resistance of a battery pack, and belongs to the technical field of batteries, the charging process of the battery pack comprises a constant current charging stage, and the health early warning method comprises the following steps: selecting a characteristic state-of-charge set; establishing a charge state-open circuit voltage corresponding relation table; a complete constant-current charging process is executed in a room temperature environment before the battery pack serves, and the charging internal resistance corresponding to each characteristic charge state is calculated and recorded to serve as the reference internal resistance; online monitoring and internal resistance calculation after service; and health state judgment and early warning: comparing the charging internal resistance calculated after service with the corresponding reference internal resistance, and giving out health early warning when the charging internal resistances calculated in recent n times of continuous m characteristic charge states all exceed the reference internal resistance by more than k times. The problem that in the prior art, the health state of the battery needs to be evaluated by means of special instruments and equipment or a special test process is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a health early warning method based on charging internal resistance of a battery pack. BACKGROUND

[0002] At present, battery technology has been widely used in various fields such as transportation, industry, consumer electronics, energy storage, etc. In actual application, in order to meet the demand of equipment for energy, power and voltage output, a plurality of battery units are usually connected in series to form a battery pack for use. The health state of the battery pack directly determines the running safety, stability and service life of the equipment. However, during the long-term service of the battery, complex physical and chemical changes will occur inside, such as degradation of electrode material structure, decomposition of electrolyte, thickening of SEI film, etc. These changes will inevitably lead to performance degradation of the battery, and the increase of charging internal resistance is one of the important manifestations of performance degradation. Taking the field of electric vehicles as an example, safety accidents such as fire and explosion often occur during charging. In-depth analysis of the causes of the accident shows that most of them are closely related to the poor health state of the battery pack and the abnormal increase of the charging internal resistance. When the charging internal resistance is too large, a large amount of Joule heat will be generated during charging, and serious heat generation will easily occur at a certain stage of charging. If the heat cannot be dissipated in time, it will further intensify the internal side reactions of the battery, eventually leading to thermal runaway and causing irreparable loss.

[0003] In order to avoid the above safety risks, people have developed various technologies to evaluate the health state of the battery pack, and try to give an early warning when the health state of the battery is poor. However, in the current known technical solutions, it is usually necessary to use special instruments and equipment or special test procedures to evaluate the health state of the battery, which has high equipment cost, complex operation and affects the daily use of the battery pack.

[0004] Therefore, the present application provides a new solution to solve the above problems. SUMMARY

[0005] The purpose of the present application is to provide a health early warning method based on charging internal resistance of a battery pack, which solves the problem that the health state of the battery needs to be evaluated by using special instruments and equipment or special test procedures in the prior art.

[0006] The above technical purpose of the present application is achieved by the following technical scheme.

[0007] A health early warning method based on charging internal resistance of a battery pack, the charging process of the battery pack including a constant current charging phase, the method comprising the following steps: selecting a set of characteristic state of charge; establishing a correspondence table of state of charge-open circuit voltage: before the battery pack leaves the factory, the open circuit voltage corresponding to all characteristic states of charge at room temperature is obtained by testing, and a correspondence table of state of charge-open circuit voltage is established; acquiring reference internal resistance: before the battery pack is put into service, a complete constant current charging process is performed at room temperature, and the charging internal resistance corresponding to each of the characteristic states of charge is calculated and recorded as the reference internal resistance; online monitoring and internal resistance calculation after service: after the battery pack is put into service, the charging internal resistance corresponding to the characteristic state of charge that can be obtained at the moment is calculated during the charging process at room temperature; health state judgment and early warning: the charging internal resistance calculated after service is compared with the corresponding reference internal resistance, and when the charging internal resistance calculated for the last n times of each of the m characteristic states of charge exceeds k times of the reference internal resistance, a health warning is issued.

[0008] Further preferably, during the selection of the set of characteristic states of charge, the set is a series of states of charge from SOC min to SOC max with an interval of ΔSOC. wherein SOC min and SOC max are the minimum and maximum allowable states of charge of the battery pack, and ΔSOC is the interval value of the state of charge.

[0009] Further preferably, the SOC min is 0-30%, and the SOC max is 70-100%.

[0010] Further preferably, during the acquisition of the reference internal resistance, before the battery pack is put into service, it is adjusted to SOC min , a specific constant current charging is performed at room temperature until a stop condition is reached, and the charging internal resistance corresponding to all characteristic states of charge in the charging process is calculated and recorded as the reference internal resistance.

[0011] Further preferably, the stop condition of the specific constant current charging stage is that the terminal voltage of the battery pack reaches or exceeds a set constant current charging voltage threshold.

[0012] Further preferably, during the establishment of the correspondence table of state of charge-open circuit voltage, the battery pack is adjusted to different characteristic states of charge at room temperature respectively, and the open circuit voltage values are recorded to form the correspondence table of state of charge-open circuit voltage.

[0013] It is further preferred that, in the online monitoring after service and the internal resistance calculation process, the battery pack after service, for each charging in a room temperature environment, the charging internal resistance corresponding to all characteristic states of charge in the state of charge range is calculated and recorded in the specific constant current charging stage.

[0014] It is further preferred that, in the online monitoring after service and the internal resistance calculation process, the battery pack after service, for each charging in a room temperature environment, the charging internal resistance corresponding to all characteristic states of charge in the state of charge range is calculated and recorded in the specific constant current charging stage. Step 1, according to the state of charge data in the specific constant current charging stage, all characteristic states of charge contained in the change range are found; Step 2, for each characteristic state of charge, the battery pack temperature and the terminal voltage data when the battery pack is charged to the characteristic state of charge in a specific constant current manner are found; Step 3, for each characteristic state of charge, the open-circuit voltage data corresponding to the characteristic state of charge are found from the relationship table; Step 4, for each characteristic state of charge, the difference between the corresponding terminal voltage and the open-circuit voltage is divided by the charging current, and the corresponding charging internal resistance is obtained.

[0015] It is further preferred that the room temperature is 15-25 DEG C.

[0016] It is further preferred that the value range of the parameter m is 2-10, the value range of n is 2-20, and the value range of k is 2-20.

[0017] In summary, the present application has the following beneficial effects: (1) The health early warning method of the present application is realized by using the data passively collected in the battery pack charging process, without the need for certain specific charging and discharging operations on the battery pack, without the limitation of the number of times of charging the battery pack and the state of charge change range of each charging, and only the existing sensor and other hardware and software facilities of the battery management system are needed in the collection process, without the need for adding specific instruments, without affecting the user, so that the overall cost is low, simple and easy to operate, and suitable for a wide range of applications.

[0018] (2) The present application closely surrounds the specific constant current charging stage of the battery pack charging process, and the charging internal resistance corresponding to all characteristic states of charge is obtained based on the analysis of the terminal voltage, state of charge and temperature data in this stage, the open-circuit voltage value required in the internal resistance calculation process considers the factors of state of charge and battery pack temperature, and only the internal resistance corresponding to a few characteristic states of charge is involved, so that the precision is high and the calculation amount is small.

[0019] (3) The application performs a specific constant current charging in the whole range on the battery before the battery pack serves, and obtains the baseline resistance data, and calculates and records the charging resistance after each charging after the battery serves, and according to the statistical principle, only when the charging resistances obtained by the m adjacent characteristic state of charge are k times of the baseline resistance, the battery pack resistance is considered to be too large, and a health warning needs to be sent. This method can eliminate accidental factors, improve the reliability of the warning judgment, effectively avoid false reports, and is more scientific and reasonable.

[0020] The resistance calculation of the application is based on the specific constant current charging stage of the battery charging process, which can provide a good calculation and comparison basis. In addition, the application is different from the prior art, and has the outstanding advantages of no interference, simple and easy to use, scientific and reasonable, high reliability, and is suitable for battery packs that are often in room temperature environment and have a specific constant current charging stage. The problem of needing to use special instruments or special test procedures to evaluate the battery health status in the prior art is solved. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a flow chart of the health warning method in a preferred embodiment of the application; Figure 2 is a flow chart of the charging resistance calculation in a preferred embodiment of the application. DETAILED DESCRIPTION

[0022] The application will be further described below with reference to the drawings.

[0023] The application provides a health warning method based on the charging resistance of a battery pack. The core of the method is to use the data of the constant current charging stage of the battery pack in the room temperature environment, calculate the resistance of the specific characteristic state of charge (SOC) point, and compare it with the baseline resistance of the battery pack in the healthy state, so as to realize the online and non-interference monitoring and warning of the health state.

[0024] The battery pack is composed of lithium ion battery monomers, and the battery pack charging process includes a constant current charging stage. The specific constant current charging refers to constant current charging according to a certain fixed current to the corresponding stop condition. The stop condition is that the terminal voltage of the battery pack reaches or exceeds the set constant current charging voltage threshold.

[0025] As shown in Figure 1 , 2 The health warning method includes the following steps: S1, selecting a characteristic state of charge set The characteristic state of charge set is from SOC min , and increases according to the interval of ΔSOC until SOCmax A series of state of charge. Among them, SOC min and SOC max are the minimum and maximum allowable state of charge of the battery pack, and ΔSOC is the state of charge interval value.

[0026] Specifically, within the allowable operating range of the battery pack (for example, from SOC min = 10% to SOC max = 95%), a series of characteristic state of charge points are selected at fixed intervals ΔSOC (for example, 5%), forming the set {10%, 15%, 20%, …, 95%}. These discrete points will be used as reference anchor points for subsequent internal resistance calculation and health judgment, avoiding the huge computational load caused by continuous calculation in the full range.

[0027] Preferably, the minimum allowable state of charge SOC min of the battery pack ranges from 0 to 30%, and the maximum allowable state of charge SOC max ranges from 70 to 100%.

[0028] S2, establishing a state of charge-open circuit voltage correspondence table Before the battery pack is shipped, the open circuit voltage corresponding to each characteristic state of charge at room temperature is obtained by testing.

[0029] Specifically, the battery pack is adjusted to each characteristic state of charge determined in step S1 at room temperature, respectively, and the corresponding open circuit voltage value at each state of charge is recorded, thereby forming a state of charge-open circuit voltage correspondence table.

[0030] S3, obtaining reference internal resistance Before the battery pack is put into service, a complete constant current charging process is performed at room temperature, and the charging internal resistance corresponding to each characteristic state of charge is calculated and recorded as the reference internal resistance.

[0031] Specifically, before the battery pack is put into service, the battery pack is discharged to the minimum allowable state of charge SOC min , and then charged at a specific constant current until its stop condition is reached in a room temperature environment. Then, the charging internal resistance corresponding to all characteristic states of charge within the state of charge range of this charging process is calculated and recorded as the respective reference internal resistance.

[0032] S4, online monitoring and internal resistance calculation after service After the battery pack is put into service, the charging internal resistance corresponding to the characteristic state of charge that can be obtained at the current is calculated during the charging process at room temperature, that is, for each charging at room temperature, the charging internal resistance corresponding to all characteristic states of charge within the state of charge range is calculated and recorded at the specific constant current charging stage.

[0033] S5, health state judgment and early warning The charging internal resistance calculated in step S4 after service is compared with the corresponding reference internal resistance in step S3. If there are m characteristic states of charge immediately adjacent, and the charging internal resistance of each of the m characteristic states of charge recorded in the last n times is k times or more than the reference internal resistance, it is considered that the internal resistance of the battery pack is too large, and a health warning is issued, wherein m, n and k are all preset positive integers.

[0034] Preferably, the value range of parameter m is 2-10, the value range of n is 2-20, and the value range of k is 2-20.

[0035] Preferably, in steps S4 and S5, the charging internal resistance is calculated by the following method: During the charging process of the battery pack, the temperature, terminal voltage, state of charge data and ambient temperature of the battery pack at a certain constant current charging stage are recorded. If it is judged that the ambient temperature is room temperature, the charging internal resistance corresponding to all characteristic states of charge at the certain constant current charging stage is calculated according to the following steps: Step 1, according to the state of charge data at the certain constant current charging stage, find all the characteristic states of charge contained in its change range; Step 2, for each characteristic state of charge, find the battery pack temperature and terminal voltage data when the battery pack is charged to the characteristic state of charge in a certain constant current manner; Step 3, for each characteristic state of charge, find the open circuit voltage data corresponding to the characteristic state of charge from the relationship table; Step 4, for each characteristic state of charge, let the difference between the corresponding terminal voltage and open circuit voltage be divided by the charging current, and the corresponding charging internal resistance is obtained.

[0036] Preferably, the room temperature in the above steps S1-S5 is 15-25℃, and the temperature of the environment where the battery pack is located is collected in real time by placing the battery pack in the temperature measuring point of the external environment.

[0037] Preferably, all data collection, analysis and health warning of the battery pack are based on its battery management system (BMS). The battery management system can issue a health warning to the user of the battery pack through the network, reminding the user to hand over the battery pack to professional personnel for detailed inspection and maintenance.

[0038] Preferably, the state of charge of the battery pack is obtained by the ampere-hour integration method. Specifically, an ampere-hour integration meter is connected in series in the battery pack, which is used to collect the charging and discharging current value of the battery pack in real time, and the current is integrated with respect to time to obtain the capacity change of the battery pack during the charging and discharging process, on the basis of which the current state of charge of the battery pack is obtained in real time in combination with the initial state of charge calibrated in advance.

[0039] This invention ingeniously utilizes the electrical parameters of the battery pack under the specific operating condition of constant current charging to accurately calculate the internal resistance. By comparing this internal resistance with a health benchmark, it achieves health status assessment and early warning. This invention eliminates the need for specialized test cycles or offline testing of the battery pack, relying entirely on data from its daily charging process for health evaluation. This avoids interference with user habits and eliminates the need for expensive dedicated testing equipment. All calculations can be performed using existing battery management systems (BMS), significantly reducing implementation costs and achieving "online, seamless" monitoring.

[0040] Furthermore, by limiting the calculation of internal resistance to the constant current charging phase, the constant current is ensured, providing a stable premise for internal resistance calculation. At the same time, by introducing the characteristic state-of-charge point and a pre-calibrated open-circuit voltage relationship table, the SOC estimation error and the influence of temperature on the open-circuit voltage are eliminated, so that the calculated internal resistance value can truly and accurately reflect the ohmic impedance change inside the battery, eliminating the interference of instantaneous factors such as polarization impedance.

[0041] In summary, this invention provides a low-cost, easy-to-implement, reliable, and user-intervention-free battery pack health warning solution, effectively solving the problems of high cost, complex operation, and interference with daily use in existing technologies, and has extremely high industrial application value.

[0042] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0043] Example: A health warning method based on the internal resistance of a battery pack during charging. A battery pack for a certain power tool consists of 1 parallel and 15 series lithium iron phosphate batteries. The rated capacity of the battery pack is 10Ah and the rated total voltage is 48V. Its battery management system can collect the battery pack terminal voltage, charging and discharging current and ambient temperature in real time, and give the state of charge (SOC) of the battery pack during operation through the ampere-hour integral method and the initial state of charge.

[0044] In this embodiment, the battery pack's minimum permissible state of charge (SOC) min =0%, highest permissible state of charge (SOC) max =100%, parameter m=3, parameter n=5, parameter k=4, the charging regime is: constant current charging at 5A to 54.75V, then constant voltage charging until the current is less than 0.5A, that is, its specific constant current charging is always constant current charging at 5A until the battery pack terminal voltage exceeds the constant current charging voltage threshold of 54.75V.

[0045] Reference Figure 1 , 2 Before the battery pack leaves the factory, the open-circuit voltage corresponding to each characteristic state of charge at room temperature is obtained by testing, and a relationship table is formed, as shown in Table 1.

[0046] Table 1: Relationship between state-of-charge and open-circuit voltage Before the battery pack is put into service, it is adjusted to a SOC min , a specific constant current charging is performed once at room temperature until its stop condition is reached, and the reference internal resistance corresponding to all characteristic state-of-charges is calculated as shown in Table 2. Since the terminal voltage of the battery pack exceeds 54.75V when charged to about 96% state-of-charge during the constant current charging stage, the maximum state-of-charge in Table 2 is 95%.

[0047] Table 2: Reference internal resistance table Take 70% state-of-charge as an example to introduce the calculation process of the corresponding reference internal resistance. When the constant current charging is to 70% state-of-charge, the terminal voltage of the battery pack is 49.997V, and the open-circuit voltage value corresponding to this state-of-charge is 49.893V as shown in Table 1, and the reference internal resistance corresponding to the charging at 70% state-of-charge is calculated as (49.997-49.893) / 5=20.8mΩ.

[0048] During a specific constant current charging stage of a certain charging process at room temperature after the battery pack has been in service for three years, the constant current charging is from 21% to 43% state-of-charge, and all characteristic state-of-charges in this range are 20%, 25%, 30%, 35% and 40%. According to the statistical data, it is found that there are three characteristic state-of-charges of 30%, 35% and 40% adjacent to each other, and the charging internal resistance of each characteristic state-of-charge recorded in the last five times is more than four times of the reference internal resistance, so it is considered that the internal resistance of the battery pack is too large, and a health warning is immediately sent to the user of the battery pack through the network to remind him to hand over the battery pack to the professional for detailed inspection and maintenance, so as to avoid thermal runaway and fire caused by too large internal resistance during subsequent charging process.

[0049] The above is only a preferred embodiment of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiments. Any technical solution falling within the concept of the present application shall fall within the protection scope of the present application. It should be noted that for ordinary skilled persons in the technical field, some improvements and modifications without departing from the principles of the present application shall also be considered as the protection scope of the present application.

Claims

1. A health warning method based on the internal resistance of a battery pack during charging, wherein the battery pack charging process includes a constant current charging stage, characterized in that: The method includes the following steps: Select a set of characteristic charged states; Establish a table of correspondence between state of charge and open circuit voltage: Before the battery pack leaves the factory, test and obtain the open circuit voltage corresponding to all characteristic states of charge at room temperature, and establish a table of correspondence between state of charge and open circuit voltage; Obtaining the reference internal resistance: Before the battery pack is put into service, a complete constant current charging process is performed at room temperature, and the charging internal resistance corresponding to each characteristic state of charge is calculated and recorded as the reference internal resistance. Post-service online monitoring and internal resistance calculation: After the battery pack has entered service, during the charging process at room temperature, calculate the charging internal resistance corresponding to the currently available characteristic states of charge; Health status assessment and early warning: The charging internal resistance calculated after service is compared with the corresponding reference internal resistance. When the charging internal resistance calculated in the most recent n times for each of the m consecutive characteristic charged states exceeds k times its reference internal resistance, a health warning is issued.

2. The health warning method based on the internal resistance of a battery pack charging according to claim 1, characterized in that: In the process of selecting the characteristic charged state set, the set is derived from the state of charge (SOC). min Initially, the SOC increases incrementally at intervals of ΔSOC until the SOC is reached. max A series of charged states; Among them, SOC min and SOC max These represent the minimum and maximum permissible states of charge (SOC) of the battery pack, respectively, with ΔSOC being the state-of-charge interval.

3. The health warning method based on the internal resistance of a battery pack charging according to claim 2, characterized in that: The SOC min The SOC is 0-30%. max It is 70-100%.

4. The health warning method based on the internal resistance of a battery pack charging according to claim 2, characterized in that: During the process of obtaining the reference internal resistance, the battery pack is adjusted to SOC before service. min A specific constant current charge is performed at room temperature until the stopping condition is reached. The charging internal resistance corresponding to all characteristic charge states within the charge state range during this charging process is calculated and recorded as their respective reference internal resistances.

5. A health warning method based on the internal resistance of a battery pack during charging, as described in claim 4, characterized in that: The specific constant current charging phase is stopped when the battery pack terminal voltage reaches or exceeds the set constant current charging voltage threshold.

6. The health warning method based on the internal resistance of a battery pack charging according to claim 1, characterized in that: In the process of establishing the state-of-charge-open-circuit voltage correspondence table, the battery pack was adjusted to different characteristic states of charge at room temperature, and its open-circuit voltage value was recorded to form the state-of-charge-open-circuit voltage correspondence table.

7. A health warning method based on the internal resistance of a battery pack during charging, as described in claim 1, characterized in that: During the online monitoring and internal resistance calculation process after the battery pack enters service, for each charge at room temperature, the charging internal resistance corresponding to all characteristic states of charge within its charge state range is calculated and recorded during a specific constant current charging stage.

8. A health warning method based on the internal resistance of a battery pack during charging, as described in claim 1, characterized in that: In obtaining the reference internal resistance and during online monitoring and internal resistance calculation after service, the charging internal resistance calculation method is as follows: During the battery pack charging process, record the battery pack temperature, terminal voltage, state of charge data, and ambient temperature at a specific constant current charging stage. If the ambient temperature is determined to be room temperature, then calculate the charging internal resistance corresponding to all characteristic states of charge at the specific constant current charging stage according to the following steps: Step 1: Based on the state-of-charge data of a specific constant current charging stage, find all characteristic states of charge contained within its range of variation; Step 2: For each characteristic state of charge, find the battery pack temperature and terminal voltage data when the battery pack is charged to that characteristic state of charge in a specific constant current manner; Step 3: For each characteristic state of charge, look up the open-circuit voltage data corresponding to that characteristic state of charge from the relation table; Step 4: For each characteristic charged state, divide the difference between its corresponding terminal voltage and open circuit voltage by the charging current to obtain its corresponding charging internal resistance.

9. A health warning method based on the internal resistance of a battery pack charging according to claim 1 or 8, characterized in that: The room temperature is 15-25℃.

10. A health warning method based on the internal resistance of a battery pack during charging, as described in claim 1, characterized in that: The value range of the parameter m is 2-10, the value range of n is 2-20, and the value range of k is 2-20.

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