CN111458650B - Method for estimating peak power of lithium ion power battery system - Google Patents

Abstract

The invention relates to a method for estimating the peak power of a lithium ion power battery system, (1) carrying out peak power test on single batteries forming the battery system at different temperatures and SOC; (2) Calculating the peak power of the single battery through the charging ohmic internal resistance, the discharging ohmic internal resistance and the voltage of the single battery; (3) Estimating the peak power P of the battery system under different temperatures and SOC by combining the peak power of the single battery according to the electric quantity required by the power battery system and the serial number and parallel number of the battery system; (4) The result of the peak power estimation of the battery system is corrected. The invention can solve the problems of repeated random experiments, long period, large workload and high requirements on test equipment in the process of directly measuring the peak power of the conventional battery system, and has good universality for different types of lithium ion batteries.

Description

A method for estimating peak power of lithium-ion power battery system

technical field

The invention belongs to the technical field of lithium-ion power batteries, and in particular relates to a method for estimating the peak power of a lithium-ion power battery system.

Background technique

With the increasing energy and environmental problems, new energy vehicles have become the key direction of future development in various countries. Due to the advantages of high energy density and low cost, lithium-ion batteries are widely used in electric vehicles. The battery power state SOP (State Of Power) is the limit power that the battery can input and output in different states, which indicates the battery's ability to withstand charging and discharging power. Peak power is one of the important performance indicators of electric vehicles. The vehicle should be accelerated and climbed according to the SOP strategy formulated by the BMS during driving to achieve reasonable use of the battery, avoid overcharging or overdischarging the battery, and prolong the service life of the battery. However, through The test to measure the peak power of the battery system has the problems of long cycle, heavy workload, and high requirements for test equipment. Therefore, it is of great significance to estimate the peak power of the battery system through a reasonable method.

Contents of the invention

The purpose of the present invention is to provide a method for estimating the peak power of a lithium-ion power battery system to solve the problem of repeated random experiments in the process of directly measuring the peak power of the existing battery system, and there are long periods, heavy workload, and high requirements for test equipment. question.

To achieve the above object, the present invention adopts the following technical solutions:

A method for estimating peak power of a lithium-ion power battery system, comprising the following steps:

(1) Perform peak power tests on the single batteries that make up the battery system at different temperatures and SOCs. The peak power test temperatures include: 55°C, 45°C, 25°C, 10°C, 0°C, -10°C, - Single peak power at 20°C, test SOC range: 10% to 90%.

(2) Calculate the peak power of the single battery through the charging ohmic internal resistance and discharging ohmic internal resistance and voltage of the single battery;

(3) Estimate the peak power P of the battery system at different temperatures and SOCs according to the power required by the power battery system and the number of series and parallels of the battery system, combined with the peak power of the single battery;

(4) Correct the result of the peak power estimation of the battery system.

In step (1), the single battery is subjected to a peak power test, and the specific steps are as follows:

(11) After fully charging the single battery with 1C constant current and constant voltage at the set temperature, put it aside for a period of time at the ambient temperature to be tested;

(12) Stop discharging after discharging with a constant current of 1C until the cut-off voltage, and record the discharge capacity at this temperature;

(13) After fully charging the single battery with 1C constant current and constant voltage at the set temperature, put it aside for a period of time at the ambient temperature to be tested, and adjust the SOC of the single battery to 90% by 1C constant current discharge;

(14) Put the single battery on hold for 1 hour, record the open circuit voltage V ₁ , discharge it with a 5Q constant current for t seconds, record the discharge voltage V _t1 at the tth second, leave it for 40 seconds, record the open circuit voltage V ₃ , and then use a 3.75Q constant current Current charging V _S , record charging voltage V _t2 ;

(15) Discharge with a constant current of 1C, adjust the SOC to 80%, repeat step (14), and use 10% as the difference to test the peak power test of 70%-20% under different SOC in turn, and stop the test when the SOC is 10%;

(16) Calculate the peak power value P of the single battery under different temperatures and SOC.

The peak power test temperature of the monomer in step (1) includes: 55°C, 45°C, 25°C, 10°C, 0°C, -10°C, -20°C, the peak power of the monomer, and the test SOC range is: 10% to 90 %.

In the step (2), the calculation of the peak-to-peak power P of the single battery is based on the data of the 60S single peak power test of the step (1), combined with the following formula:

Among them: R ₁ is the charging ohmic internal resistance, R ₂ is the discharging ohmic internal resistance, V ₁ and V ₃ are the open circuit voltages, V _min and V _max are the upper and lower limit voltages of the single battery charge and discharge respectively, and V _t1 are the discharge voltages after 60 seconds of discharge. The test data obtained the voltages of 10s, 20s, 30s, 40s, 50s, and 60s, and V _t2 is the voltage of 10s, 20s, 30s, 40s, 50s, and 60s obtained from the charging 60S test data respectively.

In described step (4), amend by following formula:

P'=P(T,t,soc)*M*N*λ

Among them: T is the ambient temperature of the battery, t is the charging and discharging time, soc is the state of charge of the battery, M is the number of battery system strings, N is the number of parallel battery systems, λ is a correction factor, the value is 0.7, and P is a single cell Battery peak power.

It can be seen from the above technical solution that the method for estimating the peak power of the lithium-ion power battery system according to the present invention can solve the problem of repeated random experiments in the process of directly measuring the peak power of the existing battery system, and there is a long cycle, a large workload, and a heavy load on the test equipment. For demanding problems, this method can quickly estimate the peak power of the battery system, and it has good universality for different types of lithium-ion batteries.

Description of drawings

Fig. 1 is a flow chart of the method of the present invention.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing:

As shown in Figure 1, the method for estimating the peak power of the lithium-ion power battery system in this embodiment is as follows:

A battery system with normal single cells with a rated capacity of 20Ah (electricity=40AH*358.4V=14.336Kwh) is used as the estimated target to estimate the peak power of the system referring to steps a) to steps d).

Step 1: Test the peak power of the single batteries that make up the battery system at different temperatures and SOCs. The specific test steps are as follows:

S1: Charge the single battery at 25°C with a constant current of 1C (20A) to 3.65V and convert to a constant voltage. After fully charging at a cut-off current of 1A, put it aside at the ambient temperature to be tested, and discharge with a constant current of 1C (20A) to cut off the voltage Stop discharging after 2.0V, record the discharge capacity Q at this temperature;

S2: Charge the single battery at 25°C with a constant current of 1C20A to 3.65V to a constant voltage. After being fully charged at a current of 0.05C (1A), leave it at the ambient temperature to be tested for 20 hours, and adjust the discharge at a constant current of 1C (20A). The SOC of the single battery is 90%;

S3: The single battery is put on hold for 1h; record the open circuit voltage V1, discharge with a 5*Q constant current for 60s, record the discharge voltage Vt1 (where t records a voltage every 10S), put it aside for 40s, record the open circuit voltage V3, and then use 3.75* Q current constant current charging for 60s, record the charging voltage Vt2 (where t records a voltage every 10S);

S4: Discharge at a constant current of 1C (20A), adjust the SOC to 80%, repeat step S3, and test the pulse charge and discharge performance under different SOCs by analogy, until the SOC10% ends.

S5: Finally calculate the peak power value P of the single battery at different temperatures and SOC

Step 2: Calculating the peak-to-peak power P of the single battery is based on the data of the 60S test in step 1, combined with the following formula:

Charging ohmic internal resistance R ₁ =(V _t2 -V ₃ )/3.75Q (1)

Discharge ohmic internal resistance R ₂ =(V ₁ -V _t1 )/5Q (2)

P _put =(V ₁ -V _min )*V _min /R ₂ (3)

P _charge = (V _max -V ₃ )*V _max /R ₁ (4)

Among them: V1 and V3 are the open circuit voltage; Vmin and _Vmax are the upper and lower limit voltages of the single battery charging and discharging, respectively, 2.0 to 3.65V; voltage. V _t2 is the voltage of 10s, 20s, 30s, 40s, 50s, 60s obtained for charging 60s test data.

As shown in Table 1 below, calculate the peak power of a 20Ah single battery at 25°C, SOC 10%-90%, and 10s (Vmin=2.0V, Vmax=3.65V)

According to the 60s pulse test data, the voltages Vt1 and Vt2 of 20s, 30s, 40s, 50s, 60s are respectively obtained, and so on, it can be calculated that the 20Ah single battery is at 25℃, SOC10%～90%, 20s, 30s, 40s, 50s, Peak power under 60s.

Step 3: Calculate the number of strings (M) and parallels (N) of the battery system according to the power demanded by the power battery system. For the battery system (power=40AH*358.4V=14.336Kwh), the number of strings M=358.4/3.2 =112, and the number N=40Ah/20Ah=2, considering the impact of battery consistency and battery life, correct the peak power under ideal conditions, P'=P(T,t,soc)*M*N *λ, where the correction factor λ=0.7.

According to Table 1, calculate the peak power of a 20Ah single battery at 25°C, SOC 10%-90%, and 10s to estimate the peak power of the battery system. The results are shown in Table 2:

By analogy, the peak power of the battery system at different temperatures, SOC 10% to 90%, 10s, 20s, 30s, 40s, 50s, and 60s can be calculated.

The above-mentioned embodiments are only descriptions of preferred implementations of the present invention, and are not intended to limit the scope of the present invention. Variations and improvements should fall within the scope of protection defined by the claims of the present invention.

Claims (4)

1. A method for peak power estimation of lithium-ion power battery system, is characterized in that, comprises the following steps: (1) Perform peak power tests on the single cells that make up the battery system at different temperatures and SOCs; (2) Calculate the peak power of the single battery through the charging ohmic internal resistance and discharging ohmic internal resistance and voltage of the single battery; (3) Estimate the peak power P of the battery system at different temperatures and SOCs according to the power required by the power battery system and the number of series and parallels of the battery system, combined with the peak power of the single battery; (4) Correct the result of the peak power estimation of the battery system; In step (1), the single battery is subjected to a peak power test, and the specific steps are as follows: (11) After fully charging the single battery with 1C constant current and constant voltage at the set temperature, put it aside for a period of time at the ambient temperature to be tested; (12) Stop discharging after discharging with a constant current of 1C until the cut-off voltage, and record the discharge capacity at this temperature; (13) After fully charging the single battery with 1C constant current and constant voltage at the set temperature, put it aside for a period of time at the ambient temperature to be tested, and adjust the SOC of the single battery to 90% by 1C constant current discharge; (14) Put the single battery on hold for 1 hour, record the open circuit voltage V ₁ , discharge it with a 5Q constant current for t seconds, record the discharge voltage V _t1 at the tth second, leave it for 40 seconds, record the open circuit voltage V ₃ , and then use a 3.75Q constant current Current charging V _S , record charging voltage V _t2 ; (15) Discharge with a constant current of 1C, adjust the SOC to 80%, repeat step (14), and use 10% as the difference to test the peak power test of 70%-20% under different SOC in turn, and stop the test when the SOC is 10%; (16) Calculate the peak power value P of the single battery under different temperatures and SOC. 2. The method for estimating the peak power of a lithium-ion power battery system according to claim 1, wherein in step (1), the peak power test temperature includes: 55°C, 45°C, 25°C, 10°C, 0°C, -10°C, -20°C monomer peak power, test SOC range: 10% ~ 90%. 3. A method for estimating peak power of a lithium-ion power battery system as claimed in claim 1, characterized in that: in said step (2), calculating the peak power P of a single battery is based on the peak power of a single battery in step (1) Test the data of 60S, combined with the following formula:

Among them: R ₁ is the charging ohmic internal resistance, R ₂ is the discharging ohmic internal resistance, V ₁ and V ₃ are the open circuit voltages, V _min and V _max are the upper and lower limit voltages of the single battery charge and discharge respectively, and V _t1 are the discharge voltages after 60 seconds of discharge. The test data obtained the voltages of 10s, 20s, 30s, 40s, 50s, and 60s, and V _t2 is the voltage of 10s, 20s, 30s, 40s, 50s, and 60s obtained from the charging 60S test data respectively. 4. The method for estimating the peak power of the lithium-ion power battery system according to claim 1, characterized in that: in the step (4), the correction is carried out by the following formula: P'=P(T,t,soc)*M*N*λ Among them: T is the ambient temperature of the battery, t is the charging and discharging time, soc is the state of charge of the battery, M is the number of battery system strings, N is the number of parallel battery systems, λ is a correction factor, the value is 0.7, and P is a single cell Battery peak power.

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