Method for improving charging remaining time precision of multi-branch parallel battery system

Abstract

The invention belongs to the technical field of new energy automobiles, and discloses a method for improving the charging remaining time precision of a multi-branch parallel battery system. The method comprises the following steps of: 1, respectively testing a multi-branch battery system, establishing a charging window table of battery charging capability under different temperatures and different SOCs, and obtaining an OCV value of each branch battery system under different SOCs and different temperatures; and step 2, testing the internal resistance values of the single-branch battery system under different SOCs and different temperatures. And step 3, calculating the charging remaining time of the single-branch battery system based on the charging window table. And 4, according to the charging remaining time calculated in the step 3 as the single-branch charging remaining time, calculating and coupling the charging remaining time of the single-branch battery system so as to calculate the charging remaining time of the multi-branch battery system. According to the invention, for a multi-branch battery system, the problem of inaccurate calculation of the remaining charging time caused by non-uniform current is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy vehicles, and particularly relates to a method for improving the accuracy of the remaining charging time of a multi-branch parallel battery system. Background Art

[0002] In order to meet the usage requirements of commercial heavy-duty electric trucks, current commercial heavy-duty electric trucks usually combine multiple single-branch battery systems in parallel to form a large-energy system PACK system with a capacity of 300 - 800 Kwh. However, there are problems such as large differences in internal resistance and OCV voltage between branches in a multi-branch parallel battery system. Therefore, during the use of the whole vehicle, there will be an uneven distribution of the current magnitude between each branch. Although it is expected that the actual current distribution of each branch battery system is averaged, due to the resistance differences between each branch, for a multi-branch battery system, whether it is charging or discharging, the problem of uneven current distribution will exist.

[0003] When a new energy electric vehicle is charging, the charging pile will display how long it will take to fully charge during this charging process. This value is called the remaining charging time in the industry of the Battery Management System (BMS). The BMS calculates an accurate remaining charging time value based on conditions such as the current state, SOC state, and temperature state of the battery pack, and then sends this value to the charging pile in real time. The charging pile displays the specific value on the screen of the charging pile according to this sent digital signal. An accurate remaining charging time can better help the driver reasonably arrange work and daily routines. Especially for the electric heavy-duty truck industry, drivers need accurate remaining charging time information to maximize the use of the whole vehicle operation time and thus earn higher operation profits.

[0004] At different temperatures and different SOC states, the maximum charge rate of the battery is different. The charge rate of the battery is represented by C, and 1C represents the rate at which the battery is fully charged in 1 hour. As the SOC gradually increases, the maximum charge rate of the battery gradually decreases. As the battery temperature increases, the maximum charge rate of the battery gradually increases. Since there is a safe battery usage range, when the battery temperature rises beyond a certain temperature threshold, it may cause potential safety hazards to the battery. Therefore, when the battery temperature rises to this temperature, charging is also prohibited.

[0005] When the whole vehicle plugs in the charging gun and enters the charging state, the remaining charging time will be displayed. Therefore, for the calculation of the remaining charging time, when the BMS detects the moment when the whole vehicle plugs in the charging gun, it needs to calculate an accurate value. Since the charging ability of the battery is different at different temperatures and different SOC states. Therefore, for the calculation of the remaining charging time, it is necessary to estimate the charging path of this charging process.

[0006] In a multi-branch battery system, due to the problem of uneven current distribution, during the actual charging process, there will be a difference between the actual charging current of each branch and the expected charging current value, resulting in a large deviation in the calculation of the remaining charging time. Therefore, in view of the problem of uneven current distribution in the multi-branch battery system, which leads to inaccurate calculation of the remaining charging time, the present invention patent has invented a method to improve the accuracy of the remaining charging time of a multi-branch parallel battery system. Summary of the Invention

[0007] The object of the present invention is to provide a method for improving the accuracy of the remaining charging time of a multi-branch parallel battery system, which is used to solve the technical problem that in the existing multi-branch battery system, due to the uneven current distribution phenomenon, the calculation of the remaining charging time is inaccurate.

[0008] The method for improving the accuracy of the remaining charging time of a multi-branch parallel battery system includes the following steps.

[0009] Step 1: Test the multi-branch battery system separately, establish a charging window table of the battery charging ability at different temperatures and different SOCs, and obtain the OCV values of each branch battery system at different SOCs and different temperatures.

[0010] Step 2: Test the internal resistance values of a single-branch battery system at different SOCs and different temperatures.

[0011] Step 3: Calculate the remaining charging time of the single-branch battery system based on the charging window table.

[0012] Step 4: Use the remaining charging time calculated in Step 3 as the remaining charging time of the single-branch, and couple the calculation of the remaining charging time of the single-branch battery system to calculate the remaining charging time of the multi-branch battery system.

[0013] Preferably, the specific testing method of Step 1 is as follows.

[0014] 1.1. Adjust the branch battery system at different SOCs, after standing for a certain time, detect and record the corresponding static voltage value.

[0015] 1.2. Calculate the corresponding static OCV voltage values at different temperatures and different SOCs according to Step 1.1, record the corresponding charging rates in the charging window table, and store the corresponding values in the relevant calculation and storage hardware for software to call when in use.

[0016] Preferably, the specific testing method of Step 2 is as follows.

[0017] 2.1. Adjust the branch battery system at different SOCs, after standing for a certain time, apply a certain rate of current value, charge for a certain time, and calculate the internal resistance value during the current period. The calculation formula is as follows:

[0018]

[0019] where U 充电后电压 is the voltage after charging for a certain time, U 静置电压 is the rest voltage after the branch battery system is rested for a certain time before charging, I 电流 is the current during charging, R 10S is the internal resistance value during charging.

[0020] 2.2. Calculate the internal resistance values corresponding to different temperatures and different SOCs for a certain charging time in the charging window table according to step 2.1 respectively. The relevant values are stored in the relevant calculation storage hardware and are called by the software when in use.

[0021] Preferably, step 3 specifically includes.

[0022] 3.1. When the BMS detects the vehicle plug-in gun signal, start the charging remaining time calculation operation logic, and first determine the charging target SOC value.

[0023] 3.2. Calculate the difference between the charging target SOC and the current maximum SOC according to the SOC of the current branch battery system.

[0024] 3.3. Divide the difference calculation result in step 3.2 based on the set unit time to obtain several unit intervals of SOC.

[0025] 3.4. Calculate the charging time based on the unit interval of SOC and the corresponding data in the charging window table.

[0026] 3.5. Iteratively calculate step 3.4 until the SOC is iteratively calculated to the charging target. Then the total remaining charging time is equal to the sum of the remaining charging times calculated for each unit interval of SOC.

[0027] Preferably, in step 3.4, the calculation formula for the charging time of the unit interval of SOC is: T i～i+1 = SOC t0 / I T(i～i+1) ; where T i～i+1 represents the charging time required from the current SOC to the next SOC after a unit interval, SOC t0 is the unit interval of SOC, and I T(i～i+1) is the charging current looked up in the table during the corresponding charging process, that is, the battery charging rate corresponding in the charging window table.

[0028] And the calculation formula for updating the looked-up temperature is: Tem i+1 = T i～i+1 × Tem Ri + Temi ; where Tem i represents the temperature corresponding to the current SOC of the branch battery system, and Tem Ri represents the heating rate corresponding to the current SOC value and temperature, and T i～i+1 represents the charging time required for the next segment of SOC after the current SOC reaches a unit interval, and Tem i+1 represents the temperature corresponding to the next segment of SOC of the branch battery system after charging a unit interval.

[0029] Preferably, step 4 specifically includes.

[0030] 4.1. Establish a 0th-order equivalent circuit model corresponding to the current multi-branch PACK system.

[0031] 4.2. When the vehicle plug-in gun signal is detected, the charging remaining time calculation logic is started for each branch respectively, and the dynamic terminal voltages of the batteries in each branch during charging are equal.

[0032] 4.3. Calculate the charging remaining time of each branch respectively according to step 3.

[0033] 4.4. Iteratively calculate the charging remaining time of each branch according to step 4.3 until the SOC of any branch is iteratively calculated to the charging target, and the total charging remaining time is equal to the charging remaining time of the branch that first reaches the charging target.

[0034] Preferably, in step 4.1, the calculation formula for the dynamic terminal voltage of the battery in each branch during charging is as follows: U Branj =OCV branj +I branj *R branj , where the subscript j = 1, 2,..., n represents the jth branch, so U brani represents the dynamic terminal voltage of the battery in the corresponding branch j, OCV brani represents the static OCV value of the battery in the corresponding branch j, I brani represents the dynamic current value of the corresponding branch j, and R brani represents the resistance value of the corresponding branch j.

[0035] Preferably, in step 4.2, each branch is connected in parallel, and there is a mathematical formula for the parallel battery system of the branches:

[0036] OCV bran1 +I bran1 *R bran1 =OCV bran2 +I bran2 *R bran2 =...=OCV branj +

[0037] I branj *R branj =... = OCV brann +I brann *R brann ,

[0038] In step 3, the lookup table charging current corresponding to the current SOC and temperature in each branch can be obtained. In step 4.3, based on the lookup table charging current corresponding to each branch and combined with step 4.2, the allocated current values corresponding to the branches are calculated respectively; the static OCV and internal resistance value R of each branch are obtained by looking up the table based on the values stored after calculation in steps 1 and 2, and then the remaining charging time at present is calculated according to the calculated allocated current values of each branch.

[0039] The present invention has the following advantages: Through the corresponding relationship between the battery and the maximum chargeable rate at different temperatures and different SOC states, on the one hand, the calculation of the allocated current value corresponding to the branch is carried out, and on the other hand, the prediction calculation of the actual charging time of each branch battery system is carried out based on the obtained allocated current value. The influence of temperature and different SOC states is considered for each branch in this process, and the separate prediction calculation for different branches is realized, so as to achieve the effect of reasonably calculating the allocated current value and accurately estimating the remaining charging time of the multi-branch parallel battery system based on the same temperature and different SOC states, and significantly improving the accuracy of the remaining charging time of the multi-branch parallel battery system. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a schematic flow chart of a method for improving the accuracy of the remaining charging time of a multi-branch parallel battery system according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0041] The following is a more detailed description of the specific embodiments of the present invention with reference to the accompanying drawings through the description of the embodiments, so as to help those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention.

[0042] As Figure 1 shown, the present invention provides a method for improving the accuracy of the remaining charging time of a multi-branch parallel battery system, including the following steps.

[0043] Step 1: Test the multi-branch battery system separately, establish a charging window table for the battery charging ability at different temperatures and different SOCs, and obtain the OCV values of each branch battery system at different SOCs and different temperatures.

[0044] The specific test method is as follows:

[0045] 1.1. After the regulating branch battery system stands still for a certain period of time (e.g., 4 h) at different SOCs (e.g., 10%, 20%... 80%), detect and record the corresponding static voltage values.

[0046] 1.2. Calculate the corresponding static OCV voltage values at different temperatures and different SOCs according to Step 1.1, and record the corresponding charging rates in the charging window table. The charging rate of the battery is represented by C, and 1C represents the rate at which the battery is fully charged in 1 hour. The corresponding values are stored in the relevant calculation and storage hardware and are called by the software when in use. The charging window table is shown in Table 1.

[0047] Table 1: Charging Window Table of Battery Charging Capability at Different Temperatures and Different SOCs

[0048]

[0049] Step 2. Test the internal resistance values of the single-branch battery system at different SOCs and different temperatures.

[0050] The specific test method is as follows:

[0051] 2.1. After the regulating branch battery system stands still for a certain period of time (e.g., 4 h) at different SOCs (e.g., 10%, 20%... 80%), apply a current value at a certain rate (e.g., 0.33C) and charge for a certain period of time, such as 10 s, then calculate the internal resistance value for the current 10 s. The calculation formula is as follows:

[0052]

[0053] Where U 充电后电压 i.e., the voltage after charging for 10 s, U 静置电压 i.e., the static voltage after the branch battery system stands still for a certain period of time before charging, I 电流 i.e., the current during charging (0.33C in the example), R 10S i.e., the internal resistance value during charging.

[0054] 2.2. Calculate the internal resistance values for charging for 10 s corresponding to different temperatures and different SOCs in the charging window table according to Step 2.1. The relevant values are stored in the relevant calculation and storage hardware and are called by the software when in use.

[0055] Step 3. Calculate the remaining charging time of the single-branch battery system based on the charging window table. Here, the branch battery system is regarded as a single-branch system with only this branch, and the calculation is based on the values in the charging window table.

[0056] 3.1. When the BMS detects the signal of the vehicle plugging in the charging gun, it starts the operation logic for calculating the remaining charging time. First, determine the target SOC value for charging. When fully charged, this target SOC value is 100%.

[0057] 3.2. Calculate the difference between the target SOC for charging and the current maximum SOC based on the SOC of the current branch battery system. Assume the current SOC is 20% and the goal is to fully charge, then the difference between the target SOC for charging and the current maximum SOC is 100% SOC - 20% SOC = 80% SOC.

[0058] 3.3. Divide the difference calculation result in step 3.2 based on the set unit time to obtain several unit intervals of SOC. For example, in the previous step, the obtained difference is 80% SOC. Taking 1% SOC as the unit interval, it is equally divided into 80 parts at equal intervals.

[0059] 3.4. Calculate the charging time based on the unit interval of SOC and the corresponding data in the charging window table. The calculation formula for the charging time of the unit interval of SOC is: T i～i+1 = SOC t0 / I T(i～i+1) ; where, T i～i+1 represents the charging time required from the current SOC to the next segment of SOC after one unit interval, SOC t0 is the unit interval of SOC, and I T(i～i+1) is the charging current obtained by looking up the table during the corresponding charging process, that is, the battery charging rate corresponding in the charging window table. For example, the SOC of the current branch battery system is 20% and the temperature is -10°C, then calculate the charging time from 20% S0C to 21% SOC. SOC t0 is the capacity of 1% SOC, and I T(i～i+1) is obtained by querying the charging window table according to the current SOC value and temperature.

[0060] And the calculation formula for updating the temperature looked up in the table is: Tem i+1 = T i～i+1 ×Tem Ri + Tem i ; where, Tem i represents the temperature corresponding to the current SOC of the branch battery system, Tem Ri represents the heating rate corresponding to the current SOC value and temperature, T i～i+1 represents the charging time required from the current SOC to the next segment of SOC after one unit interval, and Tem i+1 represents the temperature corresponding to the next segment of SOC after charging one unit interval of the branch battery system. For example, Tem i represents the temperature of the current branch battery system, -10°C, and Tem RiIndicates the heating rate during the charging of the battery for a unit interval at 20% SOC and -10°C state, T i～i+1 Obtained from the calculation formula of the charging time per unit interval of SOC, and thus Tem is calculated i+1 , the temperature corresponding to the next segment of SOC after the branch battery system is charged for a unit interval.

[0061] 3.5. Iterate step 3.4 until the SOC is iteratively calculated to the charging target of 100% SOC, then the total remaining charging time is equal to the sum of the remaining charging times calculated for each unit interval of SOC.

[0062] Step 4: The remaining charging time calculated in step 3 is the remaining charging time for a single branch. Couple the calculation of the remaining charging time of the single-branch battery system to calculate the remaining charging time of the multi-branch battery system. The specific method is as follows:

[0063] 4.1. Establish a 0th-order equivalent circuit model corresponding to the current multi-branch PACK system. The calculation formula for the dynamic terminal voltage of each branch battery during charging is as follows: U Branj =OCV branj +I branj *R branj , where j in the subscript = 1, 2,..., n, representing the jth branch. Therefore, U brani represents the dynamic terminal voltage of the battery of branch j, OCV brani represents the static OCV value of the battery of branch j, I brani represents the dynamic current value of branch j, and R brani represents the resistance value of branch j. In the example, there is a two-branch battery system, so the two branches need to be calculated separately. The calculation formulas are as follows: U bran1 =OCV bran1 +I bran1 *R bran1 and U Bran2 =OCV bran2 +I bran3 *R bran2 .

[0064] 4.2. When the vehicle plug-in gun signal is detected, the remaining charging time calculation logic is started for each branch separately. Since each branch is connected in parallel, there is a mathematical formula for the parallel battery system of the branches:

[0065] OCV bran1 +I bran1 *R bran1 =OCV bran2 +I bran2 *R bran2 =...=OCV branj +

[0066] I branj *R branj =... = OCV brann +I brann *R brann ,

[0067] That is, the dynamic terminal voltages of the batteries in each branch are equal during charging.

[0068] Taking an example, the mathematical formula is for a two-branch parallel battery system: OCV bran1 +I bran1 *R bran1 = OCV bran2 +I bran2 *R bran2 .

[0069] 4.3. Calculate the remaining charging time of each branch according to Step 3 respectively.

[0070] Since in Step 3, in the formulas for calculating the remaining charging time of Branch 1 and Branch 2, the lookup table charging current corresponding to the current SOC and temperature can be obtained. Based on the lookup table charging currents corresponding to each branch, combined with Step 4.2, the allocated current values corresponding to each branch are calculated respectively. And the static OCV and internal resistance value R of each branch required for the calculation are obtained by looking up the values stored after the calculations in Steps 1 and 2. Then, according to the calculated allocated current values of each branch, the current remaining charging time is calculated. The specific calculation formula is the same as in Step 3.4, except that the applied values are different, T i～i+1 = SOC t0 / I T(i～i+1) where the I T(i～i+1) adopts the calculated allocated current value.

[0071] Taking an example, the current SOC of Branch 1 is 20% SOC and the temperature is -10°C, and the current SOC of Branch 2 is 25% SOC and the temperature is -5°C. Then, combined with Steps 3.2, 3.3, and 3.4, calculate the remaining charging time of the two branches respectively.

[0072] Among them, the OCV bran1 and R bran1 are obtained by looking up the static OCV and R values stored in Steps 1 and 2 according to the current SOC and temperature of Branch 1. The OCV bran2 and R bran2 are obtained by looking up the static OCV and R values stored in Steps 1 and 2 according to the current SOC and temperature of Branch 2.

[0073] 4.4. Iteratively calculate the remaining charging time of each branch according to step 4.3 until the SOC of any branch is iteratively calculated to the charging target. When it is fully charged, i.e., 100% SOC, the total remaining charging time is equal to the remaining charging time of the branch that first reaches the charging target. In the example, if either branch 1 or branch 2 is charged to 100% SOC to achieve full charge, the remaining charging time of that branch is equal to the total remaining charging time.

[0074] The present invention has been described exemplarily in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited by the above-mentioned manner. As long as various non-substantive improvements are made by adopting the inventive concept and technical solution of the present invention, or the inventive concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for improving the accuracy of the remaining charging time of a multi-branch parallel battery system, characterized in that: It includes the following steps: Step 1: Test the multi-branch battery system separately, establish a charging window table for the battery charging capacity at different temperatures and different SOCs, and obtain the OCV values of each branch battery system at different SOCs and different temperatures; Step 2: Test the internal resistance values of the single-branch battery system at different SOCs and different temperatures; Step 3: Calculate the remaining charging time of the single-branch battery system based on the charging window table; Step 4: Use the remaining charging time calculated in Step 3 as the remaining charging time of the single branch, and couple the calculation of the remaining charging time of the single-branch battery system to calculate the remaining charging time of the multi-branch battery system.

2. A method for improving the accuracy of the remaining charging time of a multi-branch parallel battery system according to claim 1, characterized in that: The specific test method of Step 1 is as follows: 1.

1. Adjust the branch battery system at different SOCs, after standing for a certain time, detect and record the corresponding static voltage value; 1.

2. Calculate the corresponding static OCV voltage values at different temperatures and different SOCs according to Step 1.1, record the corresponding charging rates in the charging window table, and store the corresponding values in the relevant calculation and storage hardware for software call when in use.

3. A method for improving the accuracy of the remaining charging time of a multi-branch parallel battery system according to claim 1, characterized in that: The specific test method of Step 2 is as follows: 2.

1. Adjust the branch battery system at different SOCs, after standing for a certain time, apply a certain rate of current value, charge for a certain time, and calculate the internal resistance value during the current time period. The calculation formula is as follows: where U 充电后电压 i.e., the voltage after charging for a certain time, U 静置电压 i.e., the static voltage after the branch battery system has been static for a certain time before charging, I 电流 i.e., the current during charging, R 10S i.e., the internal resistance value during charging; 2.

2. Calculate the internal resistance values corresponding to different temperatures and different SOCs for a certain charging time in the charging window table according to Step 2.1, and store the relevant values in the relevant calculation and storage hardware for software call when in use.

4. A method for improving the accuracy of the remaining charging time of a multi-branch parallel battery system according to claim 1, characterized in that: Step 3 specifically includes: 3.

1. When the BMS detects the vehicle plug-in gun signal, start the operation logic for calculating the remaining charging time. First, determine the charging target SOC value; 3.

2. Calculate the difference between the charging target SOC and the current maximum SOC according to the SOC of the current branch battery system; 3.

3. Divide the difference calculation result in Step 3.2 based on the set unit time to obtain several unit intervals of SOC; 3.

4. Calculate the charging time based on the unit interval of SOC and the corresponding data in the charging window table; 3.

5. Iteratively calculate Step 3.4 until the SOC is iteratively calculated to the charging target. Then the total remaining charging time is equal to the sum of the remaining charging times calculated for each unit interval of SOC.

5. A method for improving the accuracy of the remaining charging time of a multi-branch parallel battery system according to claim 4, characterized in that: In step 3.4, the calculation formula for the charging time of the unit interval of the SOC is: T i～i+1 = SOC t0 / I T(i～i+1) ; where, T i～i+1 represents the charging time required from the current SOC to the next SOC after a unit interval, SOC t0 is the unit interval of the SOC, and I T(i～i+1) is the charging current obtained by looking up the table during the corresponding charging process, that is, the battery charging rate corresponding in the charging window table; The calculation formula for updating the look-up table temperature is: Tem i+1 = T i～i+1 × Tem Ri + Tem i ; where Tem i represents the temperature corresponding to the current SOC of the branch battery system, Tem Ri represents the heating rate corresponding to the current SOC value and temperature, T i～i+1 represents the charging time required for the next segment of SOC after the current SOC reaches a unit interval, Tem i+1 represents the temperature corresponding to the next segment of SOC of the branch battery system after charging a unit interval.

6. A method for improving the accuracy of the remaining charging time of a multi-branch parallel battery system according to claim 1, characterized in that: Step 4 specifically includes: 4.

1. Establish a 0th-order equivalent circuit model corresponding to the current multi-branch PACK system; 4.

2. When the vehicle plug-in gun signal is detected, start the calculation logic for the remaining charging time for each branch separately. The dynamic terminal voltages of each branch battery during charging are equal; 4.

3. Calculate the remaining charging time of each branch according to Step 3; 4.

4. Iteratively calculate the remaining charging time of each branch according to Step 4.3 until the SOC of any branch is iteratively calculated to the charging target. Then the total remaining charging time is equal to the remaining charging time of the branch that first reaches the charging target.

7. A method for improving the accuracy of the remaining charging time of a multi-branch parallel battery system according to claim 6, characterized in that: In the said step 4.1, the calculation formula for the dynamic terminal voltage of each branch battery during charging is as follows: U Branh = OCV branj + I branj * R branj , where the subscript j = 1, 2, …, n represents the j-th branch, so U brani represents the dynamic terminal voltage of the battery of the corresponding branch j, OCV brani represents the static OCV value of the battery of the corresponding branch j, I brani represents the dynamic current value of the corresponding branch j, and R brani represents the resistance value of the corresponding branch j.

8. A method for improving the accuracy of the remaining charging time of a multi-branch parallel battery system according to claim 7, characterized in that: In Step 4.2, when each branch is connected in parallel, there is a mathematical formula for the branch parallel battery system: OCV bran1 +I bran1 *R bran1 =OCV bran2 +I bran2 *R bran2 =…=OCV branj + I branj *R branj =... = OCV brann +I brann *R brann , In step 3, the look-up table charging current corresponding to the current SOC and temperature in each branch can be obtained. In step 4.3, based on the look-up table charging current corresponding to each branch and combined with step 4.2, the distribution current value corresponding to each branch is calculated respectively; the static OCV and internal resistance value R of each branch are obtained by looking up the table based on the values stored after calculation in steps 1 and 2, and then the remaining charging time is calculated according to the calculated distribution current value of each branch.

Images