CN110865307A - A kind of battery module residual energy detection method - Google Patents

Abstract

The invention relates to a method for detecting residual energy of a battery module, comprising: S1. Obtaining performance data of different single cells, and connecting single cells with consistent performance data to form a battery module; S2. According to the performance data of the single cells And the connection relationship of each single cell in the battery module, respectively obtain the detection current, charge cut-off voltage and discharge cut-off voltage of the battery module, wherein, the detection current is I ₃ current; S3, adopt the detection current to carry out the battery module. Discharge with constant current to the discharge cut-off voltage of the battery module, then stop discharging, and let the battery module stand for 1 hour; S4. Use the detection current to charge the battery module with constant current to the charge cut-off voltage of the battery module, and record the constant current The current charging time; S5, according to the detection current and the constant current charging time, the capacity of the battery module is obtained, which is the residual energy detection value of the battery module. Compared with the prior art, the present invention shortens the residual energy detection time on the basis of ensuring the accuracy.

Description

A kind of battery module residual energy detection method

technical field

The invention relates to the technical field of storage batteries, in particular to a method for detecting residual energy of a battery module.

Background technique

In recent years, there has been a significant increase in the number of pure electric vehicles, which are considered to be the best alternative to conventional vehicles for dealing with global warming and environmental pollution. Lithium-ion batteries have become one of the main power sources for electric vehicles due to their high efficiency, high specific energy and long service life. However, the growing demand and production of lithium-ion batteries will raise issues of battery recycling and disposal in the coming years.

Usually, the average service life of a power battery is 5-8 years, and its performance decays with the increase of charging times. When the battery capacity decays to less than 80% of the rated capacity, the power battery is no longer suitable for electric vehicles. However, after testing, maintenance, and reorganization, the retired batteries can still be further utilized in many fields such as energy storage, distributed photovoltaic power generation, household electricity, and low-speed electric vehicles. Before using these retired batteries in a cascade, in order to ensure the safe use and optimal performance of the retired batteries, it is necessary to perform residual energy detection (SOH diagnosis) on the retired battery modules.

According to the standard "Recycling and Utilization of Remaining Energy of Vehicle Power Batteries" (GB/T34015-2017) issued by the China National Standards Committee, after the battery cells or battery modules are retired, the capacity should be calibrated 3-5 times with I ₅ current. The experiment can only be ended when the capacity range of 3 times is less than 3% of the rated capacity. Among them, constant current charging and constant voltage charging need to be performed respectively during capacity calibration, and the static time after each calibration is not more than 1 hour. The residual energy detection process of the core or battery module in the greenhouse needs to occupy a testing instrument for 36 to 60 hours. How to quickly detect the residual energy of the retired battery capacity has become one of the key problems faced by the battery modules in the cascade utilization.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a rapid battery module residual energy detection method in order to overcome the above-mentioned defects of the prior art.

The object of the present invention can be achieved through the following technical solutions: a method for detecting residual energy of a battery module, comprising the following steps:

S1. Obtain performance data of different single cells, and connect cells with consistent performance data to form a battery module;

S2, according to the performance data of the single cell and the connection relationship of each single cell in the battery module, respectively calculate and obtain the detection current, charge cut-off voltage and discharge cut-off voltage of the battery module, wherein the detection current is ₁ current;

S3. Use the detection current to discharge the battery module with constant current to the discharge cut-off voltage of the battery module, then stop discharging, and let the battery module stand for 1 hour;

S4. Use the detection current to charge the battery module with constant current to the charging cut-off voltage of the battery module, and record the constant current charging time;

S5. Calculate the capacity of the battery module according to the detection current and the constant current charging time, which is the residual energy detection value of the battery module.

Further, the performance data in the step S1 includes the rated capacity, charge cut-off voltage and discharge cut-off voltage of the single battery.

Further, the step S2 specifically includes the following steps:

S21, according to the rated capacity of the single cell and the connection relationship of each single cell in the battery module, calculate the _I3 current;

S22 , according to the charge cut-off voltage and discharge cut-off voltage of the single cell, and in combination with the connection relationship of each single cell in the battery module, calculate the charge cut-off voltage and the discharge cut-off voltage of the battery module.

Further, the step S21 specifically includes the following steps:

S211. Calculate the rated capacity of the battery module according to the rated capacity of the single battery and the connection relationship of each single battery in the battery module;

S212. Calculate the _I3 current according to the rated capacity of the battery module.

Further, the rated capacity of the battery module in the step S211 is specifically:

Among them, H is the rated capacity of the battery module, s _c is the rated capacity of the series part of the single cells in the battery module, _pc is the rated capacity of the parallel part of the single cells in the battery module, and n is the parallel connection of the single cells. The number, h is the rated capacity of the single battery;

And when there are no single cells connected in series in the battery module, s _c =0; when there are single cells connected in series in the battery module, s _c =h.

Further, the _I3 current in the step S212 is specifically:

Further, the discharge cut-off voltage of the battery module in the step S22 is specifically:

Among them, F is the discharge cut-off voltage of the battery module, s _d is the discharge cut-off voltage of the series part of the single cells in the battery module, p _d is the discharge cut-off voltage of the parallel part of the single cells in the battery module, and m is the series connection. The number of single cells, f is the discharge cut-off voltage of the single cell;

And when there are no single cells in parallel in the battery module, p _d =0; when there are single cells in parallel in the battery module, p _d =f.

Further, the charging cut-off voltage of the battery module in the step S22 is specifically:

Among them, R is the charging cut-off voltage of the battery module, s _e is the charging cut-off voltage of the series part of the single cells in the battery module, p _e is the charging cut-off voltage of the parallel part of the single cells in the battery module, and m is the series connection. The number of single cells, r is the charging cut-off voltage of the single cell;

And when there are no single cells connected in parallel in the battery module, p _e =0; when there are single cells in parallel in the battery module, p _e =r.

Further, the capacity of the battery module in the step S5 is:

C _w =t*I ₃

Among them, C _w is the capacity of the battery module, and t is the constant current charging time.

Compared with the prior art, the present invention uses _I3 current as the detection current to charge and discharge the battery module with constant current, which increases the charge and discharge rate during the residual energy detection, and can greatly reduce the residual energy detection time. It is only necessary to perform constant current charging on the battery module, which saves the process of constant voltage charging and further reduces the residual energy detection time. While maintaining the residual energy detection accuracy, solving the problem of long time-consuming residual energy detection is beneficial to the subsequent echelon utilization of retired batteries.

Description of drawings

Fig. 1 is the method flow schematic diagram of the present invention;

2a is a comparison diagram of the constant current charging capacity of the battery module under different residual energy detection methods in the embodiment;

2b is a comparison diagram of the constant voltage charging capacity of the battery module under different residual energy detection methods in the embodiment;

3a is a comparison diagram of the actual charging capacity of the battery module under different residual energy detection methods in the embodiment;

3b is a comparison diagram of the actual charging time of the battery module under different residual energy detection methods in the embodiment;

FIG. 4 is a comparison diagram of test errors of different residual energy detection methods in the embodiment.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in Figure 1, a method for detecting residual energy of a battery module includes the following steps:

S1. Obtain performance data of different single cells, and connect cells with consistent performance data to form a battery module;

S2, according to the performance data of the single cell and the connection relationship of each single cell in the battery module, respectively calculate and obtain the detection current, charge cut-off voltage and discharge cut-off voltage of the battery module, wherein the detection current is ₁ current;

S3. Use the detection current to discharge the battery module with constant current to the discharge cut-off voltage of the battery module, then stop discharging, and let the battery module stand for 1 hour;

S4. Use the detection current to charge the battery module with constant current to the charging cut-off voltage of the battery module, and record the constant current charging time;

S5. Calculate the capacity of the battery module according to the detection current and the constant current charging time, which is the residual energy detection value of the battery module.

In order to verify the validity of the method proposed by the present invention, the battery modules used in this embodiment are from 4 retired lithium iron phosphate power module battery modules (15P4S, 15 parallel 4 strings) on the Chery S18B electric vehicle. The capacity is 40Ah, and it consists of 4 15P1S battery cells connected in series. The rated voltage of the 15P1S battery cells is 3.2V. According to the 5% SOH difference, the retired battery modules are divided into four capacity grades from the 70-90% SOH range, as shown in Figure 1. Among them, 70-75%, 75-80%, 80-85% and 85 -90% of the SOH calibration adopts the Protocol 2 protocol. The Protocol 2 protocol refers to the Shanghai standard "Technical Specifications for Performance Testing of Energy Storage Batteries for Smart Grids". Each section selects a retired battery module as the test object, and a total of four are selected. Retired battery modules for comparison of remaining capacity tests of various protocols. Table 1 shows the basic performance and battery name markings of these four battery modules before the experiment.

Table 1

serial number Capacity (Ah C₃) Internal resistance (mΩ) SOH(%) SOH interval (%) #1 35.36 18.0 88.40 85-90 #2 33.21 19.5 83.03 80-85 #3 30.05 21.0 75.13 75-80 #4 28.66 20.0 71.65 70-75

1I ₁ (1C rate, 40A), 1I ₃ (1/3C rate, 13.3A), 1I ₅ (1/5C rate, 8A) and 1I ₁₀ (1/10C rate, 4A) for four retired batteries respectively The module performs charge and discharge detection, and marks the four detected currents as Protocol 1, Protocol 2, Protocol 3, and Protocol 4, respectively. Protocol 1 refers to the national standard "Electrical Performance Requirements and Experimental Methods of Power Batteries for Electric Vehicles", Protocol 2 refers to Shanghai Standard "Technical Specifications for Performance Testing of Energy Storage Batteries for Smart Grids", and Protocol 3 refers to "Recycling and Utilization of Power Batteries for Vehicles" Yu Neng Detection", Protocol 4 is a low-rate capacity test method.

Taking the 1I ₃ current of Protocol 2 as an example, the retired battery module adopts 1I ₃ (1/3C rate, 13.3A) constant current discharge, and the constant current discharge cut-off condition is to discharge to cut-off voltage (4×2.7V=10.8V) , let stand for 1 hour; then use 1I ₃ constant current charging, the constant current charging cut-off condition is to charge to the cut-off voltage (4×3.65V=14.6V), and then constant voltage charging, the constant voltage charging cut-off condition is that the charging current decreases Stop charging the battery to 0.1*I ₃ (1.2A) or the single-cell voltage is greater than the single-cell cut-off voltage (3.75V), and let it stand for 1 hour; then use 1I ₃ to discharge, and the constant current discharge cut-off condition is to discharge to cut-off voltage ( 4×2.7V=10.8V), end after completing the steps. Finally, the battery capacity (in Ah) was calculated with the current value of 1I ₃ (A) and the charging time data. At the same time, the 1I ₃ (A) current was used as the research object, and the charging and discharging cut-off conditions of the battery module were changed to explore the relationship between the capacity value detected by the residual energy of the retired battery module and the charging and discharging cut-off conditions.

Protocol 5 adopts the residual energy detection method proposed by the present invention. The discharge cut-off condition is the total voltage of the battery module (2.7×n)V, and the charge cut-off condition is (3.65×n)V, and does not include the single core in the module. Voltage monitoring and constant voltage charging test protocol, the discharge cut-off condition of Protocol 6 is the battery module voltage (2.7×n)V, and after the constant current charging reaches the cut-off condition (3.65×n)V, the constant voltage charging is continued until the charging The current is reduced to 0.1*I ₃ , and the charging process does not include the excessive constant voltage test protocol of single-cell voltage monitoring. In this embodiment, n=4. Table 2 shows the test current and cut-off conditions of the capacity test protocol (Protocol) of 6 different schemes.

Table 2

Table 3 shows the actual charge capacity (C _ch ) and actual discharge capacity (C _dis ) of 4 battery modules with different battery modules under 6 different test protocols. From Table 3, it can be seen that the charge capacity and discharge capacity of the battery are very close, so for the S18 EV battery module, the charging capacity can be used instead of the discharging capacity to analyze the actual capacity of the battery module.

table 3

Figure 2a shows the charging capacity value C _cc of four battery modules under constant current charging under six different test protocols. Compared with the first type of protocol, the capacities of the four modules #1, #2, #3, and #4 show a trend of slightly increasing at first and then decreasing slightly. Among them, Protocol 2, Protocol 3, Protocol 4, Protocol 5, Protocol 6 The C _cc values under these five protocols are very close, and the measured values of Protocol 1 are quite different from other protocols. Using Protocol 4 as a comparison, the maximum error between Protocol 1 and Protocol 4 is 2.51Ah (7.422%SOH), which is 9 hours less than the detection time of Protocol 4; the maximum error between Protocol 5 and Protocol 4 is 0.22Ah (0.651%SOH) , and the detection time is 7 hours less than Protocol 4. Therefore, the constant current section of Protocol 5, as a method for detecting the remaining energy of the battery, is superior to other protocols for the constant current section detection scheme in terms of time and accuracy.

Figure 2b shows the charging capacity value C _cv of constant voltage charging under 6 different test protocols. It can be seen from Figure 2b that the C _cv value shows a gradual downward trend with the decrease of the test current, and no longer decreases when the C _cv value drops to 0. However, as the capacity of the battery module decreases, the internal cell consistency deteriorates. The constant voltage charging process reaches the upper limit of the cell voltage of 3.75V in advance, which makes the constant voltage charging process end earlier, which is the main reason for the decrease in the C _cv value. Comparing Protocol 4 and Protocol 5, the maximum difference in C _cv value does not exceed 0.36Ah (1.08% SOH), so the analysis of C _cv value also shows that the constant current section of Protocol 5 can be used for residual energy detection.

Figure 3a shows the measured charging capacity values of battery modules (#1, #2, #3, #4) under 6 different capacity test protocols (Protocol 1, Protocol 2, Protocol 3, Protocol 4, Protocol 5, Protocol 6) ( C _ch , which is the sum of the C _cc value and C _cv ). Among them, the C _ch of Protocol 5 is equal to the value of C _cc . According to Figure 3a, the C _ch values of #1 and #2 modules have a slight downward trend under the first 5 protocols, until they increase in protocol 6, and the C _ch values of #3 and #4 modules are higher in the six protocols. It is a slight upward trend, and the difference in the remaining capacity of the retired battery and the consistency of the battery is the main reason for this difference.

Figure 3b shows the required charging capacity of battery modules (#1, #2, #3, #4) under 6 different capacity test protocols (Protocol 1, Protocol 2, Protocol 3, Protocol 4, Protocol 5, Protocol 6). time. Among them, Protocol 5 is the constant current period. As can be seen from Figure 3b, the single detection time of Protocol 5 is 15 hours shorter than that of Protocol 4, and 3 hours shorter than that of Protocol 2 and Protocol 6.

Figure 4 is a comparison of the measured charging capacity of the battery using Protocol 4 protocol under 5 different capacity test protocols (Protocol 1, Protocol 2, Protocol 3, Protocol 5, Protocol 6)). The modules (#1, #2, #3, #4) The error of the measured charging capacity value, it can be found that the protocol Protocol 1, Protocol 2, and Protocol 6 have relatively large errors, which are above 3%, and the protocols Protocol 3 and Protocol 5 are within 2% error.

To sum up, when the residual energy detection method proposed by the present invention is applied in this embodiment, Protocol 5 first discharges the retired battery module with I ₃ (1/3C rate, 13.3A) constant current to the discharge cut-off voltage (4× 2.7V=10.8V), let stand for 1 hour; then charge with I ₃ constant current to the charging cut-off voltage (4×3.65V=14.6V); finally, according to I ₃ (A) constant current charging current value and charging time data , and calculate the battery capacity (in Ah), which is the residual energy detection value of the battery module. The measurement error of this method is within 2%, and the measurement time is reduced by 3-15 hours compared with other methods. From the perspective of commercialization of retired battery modules, a large number of retired battery modules are retired from the market. It is very necessary to shorten the residual energy detection time. It is necessary to ensure a certain measurement accuracy while shortening the time. The flow segment is the most suitable in terms of time efficiency and accuracy. Therefore, the method proposed in the present invention can be used to detect the residual energy of the retired battery module, and the purpose of reducing the residual energy detection time can be achieved on the basis of ensuring the detection accuracy.

Claims (9)

1. a battery module residual energy detection method, is characterized in that, comprises the following steps: S1. Obtain performance data of different single cells, and connect cells with consistent performance data to form a battery module; S2, according to the performance data of the single cell and the connection relationship of each single cell in the battery module, respectively calculate and obtain the detection current, charge cut-off voltage and discharge cut-off voltage of the battery module, wherein the detection current is ₁ current; S3. Use the detection current to discharge the battery module with constant current to the discharge cut-off voltage of the battery module, then stop discharging, and let the battery module stand for 1 hour; S4. Use the detection current to charge the battery module with constant current to the charging cut-off voltage of the battery module, and record the constant current charging time; S5. Calculate the capacity of the battery module according to the detection current and the constant current charging time, which is the residual energy detection value of the battery module. 2 . The method for detecting residual energy of a battery module according to claim 1 , wherein the performance data in the step S1 includes the rated capacity, charge cut-off voltage and discharge cut-off voltage of the single battery. 3 . 3. The method for detecting residual energy of a battery module according to claim 2, wherein the step S2 specifically comprises the following steps: S21, according to the rated capacity of the single cell and the connection relationship of each single cell in the battery module, calculate the _I3 current; S22 , according to the charge cut-off voltage and discharge cut-off voltage of the single cell, and in combination with the connection relationship of each single cell in the battery module, calculate the charge cut-off voltage and the discharge cut-off voltage of the battery module. 4 . The method for detecting residual energy of a battery module according to claim 3 , wherein the step S21 specifically comprises the following steps: 5 . S211. Calculate the rated capacity of the battery module according to the rated capacity of the single battery and the connection relationship of each single battery in the battery module; S212. Calculate the _I3 current according to the rated capacity of the battery module. 5. The method for detecting residual energy of a battery module according to claim 4, wherein the rated capacity of the battery module in the step S211 is specifically:

Among them, H is the rated capacity of the battery module, s _c is the rated capacity of the series part of the single cells in the battery module, _pc is the rated capacity of the parallel part of the single cells in the battery module, and n is the parallel connection of the single cells. The number, h is the rated capacity of the single battery; And when there are no single cells connected in series in the battery module, s _c =0; when there are single cells connected in series in the battery module, s _c =h. 6. The method for detecting residual energy of a battery module according to claim 5, wherein the _I3 current in the step S212 is specifically:

7. The method for detecting residual energy of a battery module according to claim 3, wherein the discharge cut-off voltage of the battery module in the step S22 is specifically:

Among them, F is the discharge cut-off voltage of the battery module, s _d is the discharge cut-off voltage of the series part of the single cells in the battery module, p _d is the discharge cut-off voltage of the parallel part of the single cells in the battery module, and m is the series connection. The number of single cells, f is the discharge cut-off voltage of the single cell; And when there are no single cells in parallel in the battery module, p _d =0; when there are single cells in parallel in the battery module, p _d =f. 8 . The method for detecting residual energy of a battery module according to claim 7 , wherein the charging cut-off voltage of the battery module in the step S22 is specifically:

Among them, R is the charging cut-off voltage of the battery module, s _e is the charging cut-off voltage of the series part of the single cells in the battery module, p _e is the charging cut-off voltage of the parallel part of the single cells in the battery module, and m is the series connection. The number of single cells, r is the charging cut-off voltage of the single cell; And when there are no single cells connected in parallel in the battery module, p _e =0; when there are single cells in parallel in the battery module, p _e =r. 9. The method for detecting residual energy of a battery module according to claim 1, wherein the capacity of the battery module in the step S5 is: C _w =t*I ₃ Among them, C _w is the capacity of the battery module, and t is the constant current charging time.

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