A lithium primary battery soc estimation method based on current and temperature state information

Abstract

A lithium primary battery SOC estimation method based on current and temperature state information: selecting the same type of lithium primary battery, discharging to the cut-off voltage under different temperature environments according to the set power or current, recording the cumulative discharge capacity of the battery during the discharging process; according to the test results, establishing an array list with the environmental temperature as the independent variable and the battery capacity as the dependent variable, selecting the rated capacity of the battery, and establishing a mathematical model; collecting the current environmental temperature of the lithium primary battery in real time, calculating the discharge capacity of the battery at the current temperature; collecting the discharge current of the lithium primary battery in real time, and calculating the discharged capacity of the lithium primary battery. The present application realizes the real-time estimation and real-time correction of the online SOC of the lithium primary battery, improves the safety and reliability of the battery use, not only can prevent the over-discharge of the lithium primary battery, but also can provide reliable and accurate battery remaining capacity information for the whole machine product, and provides a reliable basis for the use strategy making and real-time adjustment of the whole machine product.

Description

TECHNICAL FIELD

[0001] The application relates to a lithium primary battery SOC estimation method. BACKGROUND

[0002] Lithium primary batteries have become a research hotspot of current primary power sources due to their excellent storage performance and high specific energy characteristics. At present, the battery system has been increasingly applied to fields such as outdoor equipment, emergency rescue and unmanned aerial vehicles. The lithium primary battery can not only replace the original battery system of a product to improve the overall performance of the product, but also directly promote the development process of the product which cannot be further developed and produced due to the limitation of the power supply system. With the deepening of engineering application, the BMS technology of the lithium primary battery becomes more and more important, and becomes the key to improving the safety, reliability and environmental adaptability of the lithium primary battery. Among them, SOC estimation is the core technology of the BMS to ensure that the lithium primary battery can be used to the full under the premise of safety and reliability, and plays a crucial role in improving the efficiency, reliability of task completion, safety and controllability of discharge, battery thermal management and the like of the lithium primary battery. At present, the research on SOC is mainly carried out for lithium secondary batteries. However, the power output capability of the lithium primary battery is poorer than that of the lithium secondary battery, and the voltage of the lithium primary battery is very sensitive to the changes of temperature, current and load power and the like. Especially in the discharge process, the voltage noise of the battery is particularly obvious, so that the research results obtained according to the lithium secondary battery are difficult to be directly applied to the lithium primary battery. Now, whether high-precision SOC estimation can be realized has become one of the important factors affecting whether the lithium primary battery can be large-scale engineering application, and needs to be solved urgently.

[0003] In the current engineering application, the SOC estimation of the lithium primary battery is mainly realized by using the open-circuit voltage method or the ampere-hour integral method. The above two methods have obvious deficiencies in engineering application. The open-circuit voltage method needs the battery to be static for a period of time, and the open-circuit voltage is stable, and then the method can be used. Otherwise, the SOC estimation deviation may be too large due to the inaccuracy of the open-circuit voltage, and the method cannot realize online SOC estimation. The ampere-hour integral method is based on the battery discharge current, but the integral itself is more suitable for the statistics of the used capacity. Therefore, when estimating the remaining capacity, a large deviation is easy to occur due to the difference in the available capacity of the lithium primary battery at different use temperatures.

[0004] Therefore, for a certain lithium primary battery system, how to effectively predict the battery state of charge according to the available observation state information of the battery to ensure the safety of the battery in use and provide accurate reference basis for the adjustment of the product use strategy, and then improve the product reliability has important significance. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art and provide a lithium primary battery SOC estimation method based on current and temperature state information, which can improve the reliability and intelligent degree of lithium primary battery products.

[0006] The technical solution adopted by the present application is: a lithium primary battery SOC estimation method based on current and temperature state information, comprising the following steps:

[0007] 1) Select lithium primary batteries of the same type, discharge them to the cut-off voltage at a set power or current in different temperature environments, and record the cumulative discharge capacity of the batteries during the discharge process;

[0008] 2) Establish an array list with the ambient temperature as the independent variable and the battery capacity C as the dependent variable according to the test results, select the battery capacity at normal temperature T N = 25℃ as the rated capacity C N , and establish a mathematical model with the ambient temperature as the independent variable and the battery capacity C as the dependent variable, which is as follows:

[0009] C i = (At x 2 +Bt x +D)×C N (1)

[0010] Wherein, T i is the current ambient temperature; C i is the lithium primary battery capacity at T i ; C N is the rated capacity of the lithium primary battery; t x is an intermediate variable, t x = 1-T i / T N ; A, B, and D are fitting calculation coefficients, which are obtained through the array list and formula (1).

[0011] 3) Real-time acquisition of the current ambient temperature T i of the lithium primary battery, calculation of the discharge capacity C i of the battery at the current temperature T i according to formula (1);

[0012] 4) Real-time acquisition of the discharge current I i of the lithium primary battery, and calculation of the discharged capacity C d of the lithium primary battery during the current working process using formula (2);

[0013] C d =∑(I i *t i ) (2)

[0014] Wherein: t i is the time interval from the last current sampling to the current current sampling;

[0015] 5) According to formula (3), the current battery SOC value is estimated in real time,

[0016] SOC i = 1-C d / C i -SOC R (3)

[0017] Wherein: SOC i is the current SOC estimation value; SOC R is the historical cumulative SOC estimation value, if it is the first discharge, SOC R = 0;

[0018] 6) Replace SOC i with SOC R in real time during the discharge process.

[0019] The lithium primary battery described in step 1) is one or more of lithium-metal oxide batteries, lithium-carbon fluoride batteries, and lithium-iron disulfide batteries.

[0020] Step 1) includes: selecting a set number of the same type of lithium primary batteries that have passed inspection, and numbering the lithium primary batteries, discharging the lithium primary batteries at a set power or current at an interval of 5℃ per grade in a set temperature range, discharging to the cut-off voltage, recording the cumulative discharge capacity of the lithium primary batteries, and the sample of lithium primary batteries in each grade is not less than 2, and the average value of the cumulative discharge capacity of the lithium primary battery sample in the grade is taken as the lithium primary battery capacity at the ambient temperature.

[0021] The SOC R described in step 5) is the historical cumulative SOC estimation value, which is read from the Flash chip of the lithium primary battery BMS.

[0022] The lithium primary battery SOC estimation method based on current and temperature state information provided by the application, for the lithium primary battery system, realizes real-time estimation and real-time correction of the lithium primary battery online SOC through the combination of test data and real-time state information, improves the safety and reliability of the battery, not only can prevent the lithium primary battery from over-discharging, but also can provide reliable and accurate battery remaining capacity information for the whole machine product, provides a reliable basis for the whole machine product use strategy making and real-time adjustment, and improves the reliability and intelligent degree of the lithium primary battery product. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a flowchart of the lithium primary battery SOC estimation method based on current and temperature state information provided by the application.

[0024] Figure 2 is a block diagram of the battery management system used in the present application. DETAILED DESCRIPTION

[0025] A lithium primary battery SOC estimation method based on current and temperature state information will be described in detail below in combination with embodiments and drawings.

[0026] As shown in the drawings, the lithium primary battery SOC estimation method based on current and temperature state information comprises the following steps: Figure 1

[0027] 1) Selecting lithium primary batteries of the same type, discharging them to the cut-off voltage at a set power or current in different temperature environments, and recording the cumulative discharge capacity (Ah) of the batteries during the discharging process; comprising:

[0028] Selecting a set number of qualified lithium primary batteries of the same type, numbering the lithium primary batteries, discharging them at a set power or current in every 5℃ interval within a set temperature range, discharging them to the cut-off voltage, recording the cumulative discharge capacity of the lithium primary batteries, and taking the average value of the cumulative discharge capacity of the lithium primary battery samples in each interval as the lithium primary battery capacity at the ambient temperature.

[0029] The lithium primary battery is one or more of lithium-metal oxide batteries, lithium-carbon fluoride batteries, and lithium-iron disulfide batteries.

[0030] 2) Establishing an array list with the ambient temperature as the independent variable and the battery capacity C as the dependent variable according to the test results, and the array list is as follows:

[0031] Temperature / °C Battery capacity / Ah 25 10.00 20 9.93 15 9.74 …… ……

[0032] Selecting the battery capacity at room temperature T N = 25℃ as the rated capacity C N , establishing a mathematical model with the ambient temperature as the independent variable and the battery capacity C as the dependent variable, and the mathematical model is as follows:

[0033] C i = (At x 2 +Bt x +D)×C N (1)

[0034] Wherein, C i is the lithium primary battery capacity at T i ; C N is the rated capacity of the lithium primary battery; t x is an intermediate variable, t​x =1-T i / T N T i The current ambient temperature is denoted as A; A, B, and D are the fitting calculation coefficients, which are obtained through the array list and formula (1).

[0035] 3) Real-time acquisition of the current ambient temperature T of the lithium primary battery i The current temperature is calculated as T according to formula (1). i The discharge capacity C of the battery i ;

[0036] 4) Real-time acquisition of lithium primary battery discharge current I i The discharged capacity C of the lithium primary battery during its current operation is calculated using formula (2). d ;

[0037] C d =∑(I i *t i (2)

[0038] Where: t i This is the time interval between the last current sampling and the current current sampling.

[0039] 5) Estimate the current battery SOC value in real time according to formula (3).

[0040] SOC i =1-C d / C i -SOC R (3)

[0041] Among them: SOC i This is the current estimated SOC value; SOC R The historical cumulative SOC estimate is read from the Flash chip of the lithium primary battery BMS. If it is the first discharge, the SOC is... R =0;

[0042] 6) During the discharge process, the SOC is maintained in real time. i Replace SOC R .

[0043] The lithium primary battery BMS described in this invention uses an existing BMS, such as... Figure 2As shown, the system includes: an MCU module; and connected to the MCU module are: a current acquisition module for acquiring the current of the lithium primary battery, a temperature acquisition module for acquiring the temperature of the lithium primary battery, a data recording module for storing lithium primary battery information, and a communication module for data interaction with external devices. The current acquisition module can be implemented using a Hall effect device or a voltage divider sampling resistor; the temperature acquisition module can use different types of temperature sensors depending on the form of the lithium primary battery cell, such as a thin-film NTC temperature resistor for soft-pack battery cells; the data recording module uses a Flash chip; and the communication module can use a CAN module. The MCU module is software developed using the method of this invention.

[0044] The following are specific examples:

[0045] 1. A lithium-metal oxide battery (capacity of 10Ah at 25℃) was subjected to a 1C rate discharge test in the temperature range of -40℃ to 25℃ using the method of the present invention. The data list based on the test results is shown in Table 1.

[0046] Temperature / °C Capacity / Ah 25 10.00 20 9.91 15 9.78 10 9.61 5 9.26 0 9.15 -5 9.01 -10 8.82 -15 8.74 -20 8.56 -25 8.31 -30 8.04 -35 7.88 -40 7.52

[0047] After the test is completed, the data is processed according to formula (1) to obtain the following specific parameters:

[0048] C i =(-0.0084x 2 -0.0708x+1.0016)×10Ah

[0049] Among them, C i The battery capacity at the current ambient temperature, -40℃≤T i ≤25℃;

[0050] 2. SOC estimation logic strategy based on battery current and temperature state information, such as... Figure 1 As shown, the specific process is as follows:

[0051] (1) Read historical data records from the BMS and obtain the historical cumulative value SOC. R ;

[0052] (2) Real-time acquisition of battery ambient temperature information T via BMS i The current temperature is calculated as T according to formula (1). i The discharge capacity C of the battery i Where, A = -0.0084, B = -0.0708, D = 1.0016, C0 = 10Ah.

[0053] (3) Real-time acquisition of battery current I via BMSi Calculate the time interval t between two adjacent current samples. i For example, if the BMS sampling frequency is 2Hz, then t i =0.5s. Calculate the discharged capacity C of the battery during its current operation based on formula (2). d ;

[0054] (4) Based on the aforementioned calculation results, estimate the current battery SOC value in real time according to formula (3). i ;

[0055] (5) The real-time estimated SOC i The data is promptly stored in the BMS flash chip and the original SOC value is replaced. R SOC R =SOC i ;

[0056] (6) The remaining battery capacity (SOC) is determined through the BMS data interaction function. N Uploaded to the entire system in real time.

[0057] Although preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art, under the guidance of the present invention, can make many other modifications without departing from the spirit and scope of the claims. These modifications all fall within the scope of protection of the present invention.

Claims

1. A lithium primary battery SOC estimation method based on current and temperature state information, characterized by, It comprises the following steps: 1) selecting the same type of lithium primary battery, discharging to the cut-off voltage under different temperature environments at a set power or current, and recording the cumulative discharge capacity of the battery during the discharging process; 2) According to the test results, a list of arrays is established with the ambient temperature as the independent variable and the battery capacity C as the dependent variable, and the normal temperature T N = 25℃ is selected as the battery capacity N , a mathematical model is established with the ambient temperature as the independent variable and the battery capacity C as the dependent variable, and the mathematical model is as follows: C i = (At x 2 +Bt x +D) x C N (1) where T i is the current ambient temperature; C i is the lithium primary battery capacity at T i ; C N is the lithium primary battery rated capacity; t x is an intermediate variable, t x = 1 - T i / T N ; A, B, D are fitting calculation coefficients, obtained through the array list and equation (1); 3) Real-time acquisition of the current ambient temperature T of the lithium primary battery i , according to formula (1) to calculate the discharge capacity C of the battery when the current temperature is T i . i ; 4) real-time acquisition of the discharge current I of the lithium primary cell i ; and calculating the discharged capacity C of the lithium primary cell during the current working process by using formula (2) d ; C d =∑(I i *t i ) (2) wherein: t i is the time interval from the last current sample to the current sample; 5) estimating the current battery SOC value in real time according to formula (3), SOC i = 1 - C d / C i -SOC R (3) Where: SOC i is the current SOC estimate; SOC R is the historical cumulative SOC estimate, and SOC R = 0 if it is the first discharge. 6) real-time SOC during discharging i replacement SOC R .

2. The lithium primary battery SOC estimation method based on current and temperature state information according to claim 1, characterized by, The lithium primary battery in step 1) is one or more than one of a lithium-metal oxide battery, a lithium-carbon fluoride battery, and a lithium-iron disulfide battery. 3.The lithium primary battery SOC estimation method based on current and temperature state information according to claim 1, characterized in that, Step 1) comprises: selecting a set number of the same type of lithium primary batteries that have passed the inspection, numbering the lithium primary batteries, discharging at a set power or current at the same rate every 5℃ interval in a set temperature range, discharging to the cut-off voltage, recording the cumulative discharge capacity of the lithium primary battery, and taking the average value of the cumulative discharge capacity of the lithium primary battery sample in each interval as the capacity of the lithium primary battery under the ambient temperature. 4.The lithium primary battery SOC estimation method based on current and temperature state information according to claim 1, characterized in that, SOC described in step 5) R is read from the Flash chip of the lithium primary battery BMS.

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