Method for improving discharge energy 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 discharge energy of a multi-branch parallel battery system, which comprises the following steps: step 1, when the whole automobile is started, a battery management system respectively calculates the maximum allowable power of each branch according to the current state information of the multi-branch battery system; 2, the minimum value of the maximum instantaneous discharge power, calculated in the step 1, of each branch is obtained and multiplied by the parallel connection number of the current multi-branch PACK system, the maximum allowable power of the current system is obtained, and the maximum instantaneous discharge power capacity of each branch is the maximum allowable power of the branch; 3, in the actual whole vehicle operation process, the whole vehicle conducts battery power control according to the maximum allowable power calculated by the battery management system, and system power adjustment is conducted according to the maximum allowable power of the branches. According to the invention, the number of related parameters required by the control strategy is reduced, the computational logic is simple, the algorithm robustness is high, the stability is good, and the control precision is high.

Description

Technical Field

[0001] The invention belongs to the technical field of new energy vehicles, and in particular relates to a method for improving the discharge energy of a multi-branch parallel battery system. Background Art

[0002] In recent years, electric commercial vehicles have developed rapidly due to their advantages of low freight, low maintenance costs, and ease of use. Compared with traditional electric passenger vehicles, electric commercial vehicles have a long operating time, and the vehicle still needs to maintain excellent acceleration performance and transportation efficiency when fully loaded or heavily loaded. Therefore, electric commercial vehicles need to be equipped with a larger energy source - a larger power battery system.

[0003] In order to meet the use needs of commercial heavy-duty electric vehicles, current commercial heavy-duty electric vehicles usually connect multiple single-branch battery systems in parallel to form a large energy system PACK system of 300 to 800Kwh. However, multi-branch parallel battery systems have problems such as large differences in internal resistance and OCV voltage between branches. Therefore, during the use of the entire vehicle, there will be uneven current distribution between each branch. For multi-branch battery systems, whether charging or discharging, uneven current problems will exist. At the same time, due to the large energy and overall system volume of the multi-branch battery system, the poor thermal management control effect inside the multi-branch battery system will lead to a large temperature difference inside the battery. The large temperature difference will aggravate the resistance difference between the branches of the multi-branch battery system.

[0004] The instantaneous power available to the battery energy system is calculated based on the current temperature and SOC state of the battery system. If the instantaneous available power of the battery system exceeds the available power of the battery energy system, it will cause the battery voltage to drop sharply, the vehicle to break down due to undervoltage, and the battery life to be poor. If the instantaneous power of the battery system is lower than the available power of the battery energy system, it will cause problems such as poor acceleration performance of the vehicle. Under the premise of avoiding undervoltage and breaking down of the whole vehicle, ensuring the excellent acceleration performance of electric commercial vehicles, and calculating the maximum available instantaneous power according to the current state of the battery system has become one of the research topics in the battery control industry. Therefore, how to ensure that when a multi-branch battery system is discharged and used, the discharge capacity current of each branch meets the maximum discharge capacity of the branch system, and to ensure that the maximum allowable use of the PACK system is increased as much as possible without the problem of undervoltage and breaking down of the whole vehicle, and to ensure the excellent acceleration performance of the whole vehicle has become one of the current research directions in the industry.

[0005] In the prior art, the internal resistance of the battery at different SOCs and temperatures is calculated, and then the internal resistance is stored in the software control, and then the power is adjusted and controlled according to the difference in internal resistance. However, in actual applications, it will be affected by factors such as battery temperature distribution and battery aging, resulting in a large difference between the internal resistance of the battery and the actual internal resistance of the battery during actual control; this further leads to a long convergence time, poor stability, and poor control accuracy of the control method. Moreover, this type of method requires testing the internal resistance value, resulting in a large amount of testing, many calculation parameters, and complex calculation logic. In actual use, the testing cost is high and the maintenance cost is high. Summary of the invention

[0006] The purpose of the present invention is to provide a method for improving the discharge energy of a multi-branch parallel battery system, which is used to solve the technical problems in the prior art that the control method has a long convergence time, poor stability, poor control accuracy, large test volume, and many calculation parameters due to factors such as battery temperature distribution and battery aging.

[0007] The method for improving the discharge energy of a multi-branch parallel battery system comprises the following steps.

[0008] Step 1: When the vehicle is started, the battery management system calculates the maximum allowable power of each branch according to the current status information of the multi-branch battery system.

[0009] Step 2: Take the minimum value of the maximum instantaneous discharge power of each branch calculated in step 1, and multiply it by the number of parallel connections of the current multi-branch PACK system to obtain the maximum allowable power of the current system. The maximum instantaneous discharge power capacity of each branch is the maximum allowable power of the branch.

[0010] Step 3: During actual vehicle operation, the vehicle controls the battery power according to the maximum allowable power calculated by the battery management system, and adjusts the system power according to the maximum allowable power of the branch.

[0011] Preferably, step 3 comprises.

[0012] 3.1 First, subtract the actual power of the corresponding branch from the maximum allowable power of each branch to get the difference. According to the positive or negative value of the difference, determine whether the actual power of a branch is greater than the maximum allowable power of the branch, so as to determine the increase or decrease direction of power regulation.

[0013] 3.2 Take the minimum value from the difference and multiply it by the number of branches in the system to obtain the power regulation initial threshold of the system power, and adjust the maximum allowable power of the system based on the power regulation initial threshold.

[0014] 3.3 Within the range of the calculated initial threshold value of power regulation, a closed-loop regulation algorithm is used to adjust the actual power of the system according to the previously determined increase or decrease direction.

[0015] Preferably, in step 3.1, when the actual power of each branch is not greater than the maximum allowable power corresponding to each branch, all differences are positive, and the actual power of each branch needs to be increased; when the actual power of at least one branch exceeds the maximum allowable power corresponding to the branch, there is a negative difference, and the actual power of each branch needs to be reduced.

[0016] Preferably, the process of adjusting the actual power of the system includes: first determining the direction of increase or decrease of the adjustment, then recording the initial threshold of the power adjustment as Value_Initial, dividing the value Value_Initial that needs to be increased or decreased by a coefficient A less than 1, to obtain an initial value Value_InitialA greater than Value_Initail, and then calculating the adjustment power required from the actual power to the maximum allowable power in real time, the specific calculation formula is: Power_Sys = A*(Value_InitialA+Power_Diff)+P*Power_Diff,

[0017] Among them, Power_Diff is the required adjustment power. During the adjustment process, this value can be positive or negative according to the real-time calculation result. When it needs to be increased, the required adjustment power is a positive number, and when it needs to be decreased, the required adjustment power is a negative number. P is a coefficient greater than 0 and less than 1. Power_Sys represents the adjusted system power and is the final output of this method.

[0018] Preferably, the state information includes maximum temperature, minimum temperature, maximum SOC and minimum SOC.

[0019] Preferably, step 1 comprises.

[0020] 1.1 Calculate the maximum allowable discharge current capacity of each branch, combine the maximum SOC and minimum SOC of each branch with the maximum temperature and minimum temperature of each branch in pairs, query the corresponding results in the discharge capacity current table based on the combination results and take the minimum value to obtain the maximum discharge current capacity of the corresponding branch.

[0021] 1.2 The maximum discharge current capability is multiplied by the current PACK voltage of the branch to obtain the corresponding maximum instantaneous discharge power capability.

[0022] The present invention has the following advantages: the existing technology regulates and controls power according to the difference in internal resistance values, which will be affected by factors such as battery temperature distribution and battery aging. The internal resistance value obtained based on the test is large in test volume, with many calculation parameters and complex calculation logic. The present invention greatly reduces the number of related parameters required by the control strategy through innovations in the calculation of the maximum allowable power of each branch of a multi-branch battery system and the power regulation method. The calculation logic is simple, the algorithm is highly robust, the stability is good, and the control accuracy is high. At the same time, the adjustment strategy does not rely on the battery cell test parameters, the actual control accuracy is high, the control algorithm converges quickly, and the maintenance cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention is a flow chart of a method for improving the discharge energy of a multi-branch parallel battery system. DETAILED DESCRIPTION

[0024] The specific implementation modes of the present invention are further explained in detail below by describing the embodiments with reference to the accompanying drawings, 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.

[0025] like Figure 1 As shown, the present invention provides a method for improving the discharge energy of a multi-branch parallel battery system, comprising the following steps.

[0026] Step 1: When the vehicle is started, the battery management system (BMS) calculates the maximum allowable power of each branch according to the current state information of the multi-branch battery system. The state information includes the maximum temperature, minimum temperature, maximum SOC and minimum SOC. The specific calculation method of this step is as follows.

[0027] 1.1 Calculate the maximum allowable discharge current capacity of each branch, combine the maximum SOC and minimum SOC of each branch with the maximum temperature and minimum temperature of each branch in pairs, query the corresponding results in the discharge capacity current table based on the combination results and take the minimum value to obtain the maximum discharge current capacity of the corresponding branch.

[0028] 1.2 The maximum discharge current capability is multiplied by the current PACK voltage of the branch to obtain the corresponding maximum instantaneous discharge power capability.

[0029] For example: Assuming that the maximum SOC of branch 1 calculated by branch 1 is 13%, the minimum SOC is 12%, the maximum temperature is 25°C, and the minimum temperature is 20°C, then based on the four combination results of (maximum SOC 13%, maximum temperature 25°C), (maximum SOC 13%, minimum temperature 20°C), (minimum SOC 13%, maximum temperature 25°C), (minimum SOC 12%, minimum temperature 20°C), check the discharge capacity current table respectively, take the minimum value according to the obtained discharge current result, and get the maximum discharge current capacity of the current branch 1. Then multiply it by the current PACK voltage of the current branch 1 to get the current maximum instantaneous discharge power capacity of branch 1.

[0030] Step 2: Take the minimum value of the maximum instantaneous discharge power of each branch calculated in step 1, and multiply it by the number of parallel connections of the current multi-branch PACK system (i.e. the number of branches in the battery system) to obtain the maximum allowable power of the current system. The maximum instantaneous discharge power capacity of each branch is the maximum allowable power of the branch.

[0031] Assuming that the current system is a parallel battery system with 3 branches, the calculated maximum allowable power of branch 1 is 100Kw, the maximum allowable power of branch 2 is 150Kw, and the maximum allowable power of branch 3 is 150Kw. The maximum allowable power of the current system is Min{100Kw, 120Kw, 150Kw}*3=300Kw.

[0032] Step 3: During actual vehicle operation, the vehicle controls battery power based on the maximum allowable power calculated by the battery management system.

[0033] Due to the problem of uneven current in multi-branch battery systems, the actual power of each branch of the battery system does not meet the maximum output power expected by the current branch. Therefore, it is necessary to adjust the system power according to the maximum allowable power of the branch, as follows.

[0034] 3.1 First, subtract the actual power of the corresponding branch from the maximum allowable power of each branch to get the difference. According to the positive or negative value of the difference, determine whether the actual power of a branch is greater than the maximum allowable power of the branch, so as to determine the increase or decrease direction of power regulation.

[0035] When the actual power of each branch is not greater than the corresponding maximum allowable power of each branch, all differences are positive, which means that each branch has not exerted the maximum capacity of the battery pack system, resulting in poor power performance of the entire vehicle. Therefore, for this working condition, the actual power of each branch needs to be increased.

[0036] When the actual power of at least one branch exceeds the maximum allowable power corresponding to the branch, the difference is negative, and the more it exceeds, the smaller the negative difference is. This means that the actual power of some branches exceeds the maximum allowable power of the corresponding branches, which will cause undervoltage in the battery system cells and cause the entire vehicle to break down. Therefore, for this working condition, the actual power of each branch needs to be reduced.

[0037] The following is an example to illustrate this step.

[0038] Example 1: The current maximum permissible power of the system is 300Kw, and the actual power used by the vehicle is also 300Kw, but the actual power distribution of each branch is: branch 1 is 80Kw, branch 2 is 120Kw, and branch 3 is 100Kw. The corresponding maximum permissible power of branch 1 is 100Kw, the maximum permissible power of branch 2 is 150Kw, and the maximum permissible power of branch 3 is 150Kw. Therefore, it can be calculated that the actual power of branch 1 has a margin of 20Kw from its maximum permissible power, the actual power of branch 2 has a margin of 30Kw from its maximum permissible power, and the actual power of branch 3 has a margin of 50Kw from its maximum permissible power. The actual power of branch 1, branch 2, and branch 3 did not reach the maximum permissible power of the corresponding branch, and the maximum capacity of the battery pack system was not brought into play, resulting in poor power performance of the vehicle.

[0039] Example 2: The maximum allowable power of the current maximum system is 300Kw, and the actual power used by the vehicle is also 300Kw, but the actual power distribution of each branch is: branch 1 is 120Kw, branch 2 is 80Kw, and branch 3 is 100Kw. The corresponding maximum allowable power of branch 1 is 100Kw, the maximum allowable power of branch 2 is 150Kw, and the maximum allowable power of branch 3 is 150Kw. Therefore, it can be calculated that the actual discharge power of branch 1 exceeds its maximum allowable power by 20Kw, the actual discharge power of branch 2 has a margin of 70Kw from its maximum allowable power, and the actual discharge power of branch 3 has a margin of 50Kw from its maximum allowable power. The actual power of branch 1 exceeds the maximum allowable power of branch 1, which may cause undervoltage of the battery system monomer and cause the vehicle to break down.

[0040] 3.2 Take the minimum value from the difference and multiply it by the number of branches in the system to obtain the power regulation initial threshold of the system power, and adjust the maximum allowable power of the system based on the power regulation initial threshold.

[0041] Based on Examples 1 and 2 in the previous step 3.1, the calculation content of this step includes:

[0042] Example 1: According to the data in step 3.1, the data of the initial threshold value of power regulation is: Min{100-80, 150-120, 150-100}*3=60Kw. The result is positive, that is, the actual power of the current system needs to be increased by 60Kw. The current maximum allowable power of the system is 360Kw. The maximum allowable power of the system is adjusted to avoid the maximum allowable power from limiting the adjustment of the actual power, so that the system can give full play to the performance of the battery pack system.

[0043] Example 2: According to the data in step 3.1, the data of the initial threshold value of power regulation is: Min{80-100, 150-120, 150-100}*3=-60Kw. The result is negative, that is, the actual power of the current system needs to be reduced by 60Kw. The current maximum allowable power of the system is 240Kw. The maximum allowable power of the system is adjusted to continuously limit the actual power of the entire system after adjustment to avoid the problem that the actual power of a branch exceeds its maximum allowable power.

[0044] 3.3 Within the range of the calculated initial threshold value of power regulation, a closed-loop regulation algorithm is used to adjust the actual power of the system according to the previously determined increase or decrease direction.

[0045] With the actual operation of the vehicle, the difference between the maximum allowable power and the actual power of each branch is also changing in real time. Based on the initial adjustment power threshold of the system, the closed-loop algorithm is adjusted so that the actual power of each branch reaches or is closest to the maximum allowable power of the branch without exceeding the maximum allowable power of the branch, thus achieving maximum utilization of the battery pack system performance.

[0046] The process of adjusting the actual power of the system includes: first determining the direction of increase or decrease of the adjustment, then recording the initial threshold of power adjustment as Value_Initial, dividing the value Value_Initial that needs to be adjusted up or down by a coefficient A less than 1, and obtaining an initial value Value_InitialA greater than Value_Initail, and then calculating the adjustment power required from the actual power to the maximum allowable power in real time. The specific calculation formula is: Power_Sys = A*(Value_InitialA+Power_Diff)+P*Power_Diff,

[0047] Among them, Power_Diff is the required adjustment power, and this value can be positive or negative according to the real-time calculation result during the adjustment process. When it needs to be adjusted up, the required adjustment power is positive, and when it needs to be adjusted down, the required adjustment power is negative; P is a coefficient greater than 0 and less than 1; Power_Sys represents the adjusted system power, which is the final output of this method.

[0048] The present invention is described above by way of example in conjunction with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the inventive concept and technical solution of the present invention, or the inventive concept and technical solution 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 discharge energy of a multi-branch parallel battery system, characterized in that: The following steps are involved: Step 1: When the vehicle is started, the battery management system calculates the maximum allowable power of each branch according to the current status information of the multi-branch battery system; Step 2: Take the minimum value of the maximum instantaneous discharge power of each branch calculated in step 1, and multiply it by the number of parallel connections of the current multi-branch PACK system to obtain the maximum allowable power of the current system. The maximum instantaneous discharge power capacity of each branch is the maximum allowable power of the branch. Step 3: During actual vehicle operation, the vehicle controls the battery power according to the maximum allowable power calculated by the battery management system, and adjusts the system power according to the maximum allowable power of the branch.

2. A method for improving the discharge energy of a multi-branch parallel battery system according to claim 1, characterized in that: The step 3 comprises: 3.1 First, subtract the actual power of the corresponding branch from the maximum allowable power of each branch to get the difference. According to the positive or negative value of the difference, determine whether the actual power of a branch is greater than the maximum allowable power of the branch, so as to determine the increase or decrease direction of power regulation; 3.2 Take the minimum value from the difference and multiply it by the number of branches in the system to obtain the power regulation initial threshold of the system power, and adjust the maximum allowable power of the system based on the power regulation initial threshold; 3.3 Within the range of the calculated initial threshold value of power regulation, a closed-loop regulation algorithm is used to adjust the actual power of the system according to the previously determined increase or decrease direction.

3. A method for improving the discharge energy of a multi-branch parallel battery system according to claim 2, characterized in that: In step 3.1, when the actual power of each branch is not greater than the maximum allowable power corresponding to each branch, all differences are positive, and the actual power of each branch needs to be increased; when the actual power of at least one branch exceeds the maximum allowable power corresponding to the branch, there is a negative difference, and the actual power of each branch needs to be reduced.

4. A method for improving the discharge energy of a multi-branch parallel battery system according to claim 2, characterized in that: The process of adjusting the actual power of the system includes: first determining the direction of increase or decrease of the adjustment, then recording the initial threshold of power adjustment as Value_Initial, dividing the value Value_Initial that needs to be adjusted up or down by a coefficient A less than 1, and obtaining an initial value Value_InitialA greater than Value_Initail, and then calculating the adjustment power required from the actual power to the maximum allowable power in real time. The specific calculation formula is: Power_Sys = A*(Value_InitialA+Power_Diff)+P*Power_Diff, Among them, Power_Diff is the required adjustment power. During the adjustment process, this value can be positive or negative according to the real-time calculation result. When it needs to be increased, the required adjustment power is a positive number, and when it needs to be decreased, the required adjustment power is a negative number. P is a coefficient greater than 0 and less than 1. Power_Sys represents the adjusted system power and is the final output of this method.

5. A method for improving the discharge energy of a multi-branch parallel battery system according to claim 1, characterized in that: The state information includes a maximum temperature, a minimum temperature, a maximum SOC, and a minimum SOC.

6. A method for improving the discharge energy of a multi-branch parallel battery system according to claim 1, characterized in that: The step 1 comprises: 1.1 Calculate the maximum allowable discharge current capacity of each branch, combine the maximum SOC and minimum SOC of each branch with the maximum temperature and minimum temperature of each branch, query the corresponding result in the discharge capacity current table based on the combination result and take the minimum value to obtain the maximum discharge current capacity of the corresponding branch; 1.2 The maximum discharge current capability is multiplied by the current PACK voltage of the branch to obtain the corresponding maximum instantaneous discharge power capability.

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