An active balancing control method for power batteries

Abstract

This invention discloses an active balancing control method for power batteries. Based on the first average SOC of individual battery cells during charging and discharging, unsuitable battery cells are identified and eliminated. Based on the second average SOC of the remaining cells after elimination, a method is used to determine whether to select a target for balancing. If selected, a balancing control band is determined based on the second average SOC. The battery cells to be balanced are then identified according to the balancing control band and grouped and paired. Finally, an active balancing circuit is used to balance all paired battery cells. This invention eliminates unsuitable battery cells before balancing, resulting in better overall battery balancing. Determining the balancing control band based on the average SOC of individual battery cells and selecting the target for balancing through the balancing control band is more accurate. Grouping and pairing the battery cells to be balanced through the balancing control band, and then using a specific active balancing circuit to balance the paired battery cells, results in higher reliability.

Description

Technical Field

[0001] This invention belongs to the field of power battery technology, specifically relating to an active balancing control method for power batteries. Background Technology

[0002] The operating voltage of the drive motor in an electric vehicle reaches several hundred volts, while the voltage of a single battery cell is only 2-4V. Therefore, the battery system in an electric vehicle requires hundreds of cells connected in series and parallel. Due to tolerances in process control, there are differences between battery cells after they come off the production line. At the same time, after the battery is installed in the vehicle, it undergoes frequent high-power charging and discharging, and the uneven temperature distribution caused by the cooling system further exacerbates the inconsistency between battery cells, thus affecting the overall performance of the battery. Therefore, the balancing of the battery is very important.

[0003] Based on energy control methods, energy equilibrium is divided into active equilibrium and passive equilibrium. Active equilibrium, also known as energy transfer equilibrium, refers to controlling the flow of energy from high-energy cells to low-energy cells. Passive equilibrium, also known as energy dissipation equilibrium, refers to dissipating the energy of high-energy cells. From an energy utilization perspective, active equilibrium is more efficient than passive equilibrium.

[0004] Currently, the existing active balancing solution involves adding an active balancing circuit to the power battery system. The active balancing circuit includes a capacitor or inductor or DC-DC converter connected to each power battery cell and a switch. It collects the voltage of each cell or calculates the state of charge (SOC) of each cell, calculates the average voltage or average SOC, and thereby filters out high-energy and low-energy cells. Energy is then transferred from high-energy cells to low-energy cells through active voltage balancing.

[0005] Existing active balancing technology can achieve energy transfer and balance of the power battery by adding an active balancing circuit, but it has the following disadvantages:

[0006] 1) Active balancing involves connecting capacitors or inductors or DC-DC converters to each power battery cell with switches, resulting in complex circuitry and high hardware costs.

[0007] 2) Selecting the balancing target solely based on average voltage or average SOC results in inaccurate structural selection;

[0008] 3) Energy transfer is limited to between two adjacent cells. If energy transfer between non-adjacent cells is required, multiple switching operations are necessary, which can easily lead to energy loss and low balancing efficiency. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the aforementioned background technology and provide a low-cost, highly reliable, and highly efficient active balancing control method for power batteries.

[0010] The technical solution adopted in this invention is: an active balancing control method for power batteries.

[0011] Based on the first average SOC of the battery cells during charging and discharging of the power battery, battery cells that are not suitable for equalization are identified and eliminated.

[0012] Based on the second average SOC of the remaining battery cells after exclusion, determine whether to select a target to be balanced; if selected, determine the balance control band based on the second average SOC.

[0013] The battery cells to be balanced are determined based on the equalization control band, and then grouped and paired.

[0014] The power battery is balanced by controlling the active balancing circuit to balance all paired battery cells.

[0015] Furthermore, the process of identifying battery cells unsuitable for balancing is as follows:

[0016] During charging, if the first average SOC is greater than the first set value, all battery cells are sorted and numbered in order of voltage from low to high. Starting from the battery cell with the highest voltage, M battery cells are selected, and the first difference between the individual SOC of each of the M battery cells and the first average SOC is calculated. The battery cells with the first difference less than the second set value are identified, and the corresponding battery cell number is recorded as the first number group.

[0017] During discharge, if the first average SOC is less than the third set value, all battery cells are sorted and numbered in order of voltage from low to high. Starting from the battery cell with the lowest voltage, M battery cells are selected, and the second difference between the individual SOC of each of the M battery cells and the first average SOC is calculated. The battery cells whose second difference is less than the second set value are identified, and their corresponding battery cell numbers are recorded as the second number group.

[0018] Battery cells with the same number in the first and second numbering groups are not suitable for balancing.

[0019] Furthermore, for the remaining battery cells after elimination, if the second average SOC at the end of the charging phase is greater than the fourth set value, or the second average SOC at the end of the discharging phase is less than the fifth set value, then the target to be balanced is determined; otherwise, the active balancing ends.

[0020] Furthermore, the range of the equalization control band is:

[0021] (SOC AGM -λ SOC *S SOC SOC AGM +λ SOC *S SOC ),

[0022] Among them, SOC AGM For the second average SOC, λ SOC S is the range factor. SOC This represents the SOC variance of the remaining battery cells after exclusion.

[0023] Furthermore, the range factor is determined using the following formula.

[0024] λ SOC =ΔSOC IRG / ΔSOC RRG

[0025] Wherein, ΔSOC RRG ΔSOC is the range between the maximum and minimum SOC of a single power battery cell. IRG This is the range between the maximum SOC of a single power battery cell and the initial SOC of the power battery when it leaves the factory.

[0026] Furthermore, the SOC of the remaining battery cells after elimination is compared with the equalization control band. Battery cells whose SOC is not within the range of the equalization control band are the battery cells to be equalized.

[0027] Furthermore, the process of grouping and pairing is as follows: the battery cells to be balanced are sorted in order of SOC from low to high, and the battery cells to be balanced are divided into two groups according to the equalization control band. The first group consists of battery cells with SOC lower than the lower limit of the equalization control band, and the second group consists of battery cells with SOC higher than the upper limit of the equalization control band. The battery cells in the first group and the second group are paired according to the rule of lowest SOC battery cell, second lowest SOC battery cell, ... highest SOC battery cell.

[0028] Furthermore, the active balancing circuit includes a capacitor, a first switch group, and a second switch group. Several switches in the first and second switch groups are connected in parallel. The number of switches in the first and second switch groups is the same as the number of battery cells in the power battery. One end of several switches in the first switch group is connected to one end of the capacitor, and the other end is connected to the positive terminal of several battery cells in the power battery. One end of several switches in the second switch group is connected to the other end of the capacitor, and the other end is connected to the negative terminal of several battery cells in the power battery.

[0029] Furthermore, the balancing process is as follows: for each paired battery cell, the low-SOC battery cell is connected to the active balancing circuit to charge the low-SOC battery cell; the high-SOC battery cell is connected to the active balancing circuit to discharge the high-SOC battery cell.

[0030] Furthermore, the discharge amount during discharge and the charging amount during charging are both 1 / 2*(SOC). H -SIC L )*C B SOC H For high SOC battery cells, SOC L For low-SOC battery cells, C B This refers to the rated capacity of a single battery cell.

[0031] The beneficial effects of this invention are:

[0032] This invention eliminates unsuitable battery cells before balancing, resulting in better balancing of the final power battery; it determines the balancing control band based on the average SOC of the battery cells, and selects the target battery cells to be balanced based on the balancing control band, making the determined target battery cells more accurate; it groups and pairs the target battery cells to be balanced through the balancing control band, and a specific active balancing circuit balances the paired battery cells, resulting in higher reliability. Attached Figure Description

[0033] Figure 1 This is a flowchart of the present invention.

[0034] Figure 2 This is a schematic diagram of the active equalization circuit of the present invention. Detailed Implementation

[0035] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0036] like Figure 1 As shown, this invention provides an active balancing control method for power batteries.

[0037] Based on the first average SOC of the battery cells during charging and discharging of the power battery, battery cells that are not suitable for equalization are identified and eliminated.

[0038] Based on the second average SOC of the remaining battery cells after exclusion, determine whether to select a target to be balanced; if selected, determine the balance control band based on the second average SOC.

[0039] The battery cells to be balanced are determined based on the equalization control band, and then grouped and paired.

[0040] The power battery is balanced by controlling the active balancing circuit to balance all paired battery cells.

[0041] In the above scheme, the process of identifying battery cells that are unsuitable for balancing is as follows:

[0042] During charging, the first average SOC of all battery cells is detected and judged in real time. If the first average SOC is detected to be greater than the first set value, all battery cells are sorted and numbered in order of voltage from low to high. Starting from the battery cell with the highest voltage, M battery cells are selected, and the first difference between the individual SOC of the M battery cells and the first average SOC is calculated. All battery cells whose first difference is less than the second set value are identified, and the corresponding battery cell numbers are recorded as the first number group.

[0043] During discharge, the first average SOC of all battery cells is detected and judged in real time. If the first average SOC is less than the third set value, all battery cells are sorted and numbered in order of voltage from low to high. Starting from the battery cell with the lowest voltage, M battery cells are selected, and the second difference between the individual SOC of each of the M battery cells and the first average SOC is calculated. The battery cells whose second difference is less than the second set value are identified, and their corresponding battery cell numbers are recorded as the second number group. The value of M is 5%*N. If 5%*N is not an integer, it is rounded down and then 1 is added. N is the number of battery cells in the power battery.

[0044] Battery cells with the same number in the first and second numbering groups are not suitable for balancing.

[0045] In the above scheme, for the remaining battery cells after excluding those unsuitable for equalization, if the second average SOC at the end of the charging phase (where the voltage changes of different battery cells are inconsistent during charging, and the highest voltage among all battery cells at the end of charging is greater than the charging end reference voltage of the corresponding battery system, such as 3.6V for LFP battery system and 4V for ternary battery system) is greater than the fourth set value, or if the second average SOC at the end of the discharging phase (where the lowest voltage among all battery cells is less than the discharging end reference voltage of the corresponding battery system, such as 2.7V for LFP battery system and 3.6V for ternary battery system) is less than the fifth set value, then the target to be equalized is determined; otherwise, active equalization ends.

[0046] In the above scheme, the range of the equalization control band is:

[0047] (SOC AGM -λ SOC *S SOC SOC AGM +λ SOC *S SOC ),

[0048] Among them, SOCAGM For the second average SOC, λ SOC S is the range factor. SOC This represents the SOC variance of the remaining battery cells after exclusion.

[0049] The range factor λ is determined using the formula. SOC =ΔSOC IRG / ΔSOC RRG

[0050] Wherein, ΔSOC RRG ΔSOC is the range between the SOC of the battery cell with the highest SOC and the SOC of the battery cell with the lowest SOC among all battery cells in the power battery. IRG This represents the maximum SOC of a single battery cell and the initial SOC of the power battery when it leaves the factory.

[0051] In the above scheme, the SOC of the remaining battery cells after exclusion is compared with the equalization control band. Battery cells whose SOC is outside the range of the equalization control band are the battery cells to be equalized. The battery cells to be equalized include a high SOC portion and a low SOC portion. If the number of cells in the two portions is the same, the equalization control band remains unchanged; if the number of cells in the two portions is different, such as the number of battery cells in the high SOC portion being more than the number of battery cells in the low SOC portion, the lower limit of the equalization control band is adjusted (increased) to make the number of cells in the two portions the same; if the number of battery cells in the high SOC portion is less than the number of battery cells in the low SOC portion, the upper limit of the equalization control band is adjusted (decreased) to make the number of cells in the two portions the same.

[0052] In the above scheme, the process of grouping and pairing is as follows: the battery cells to be balanced are sorted in order of SOC from low to high, and the battery cells to be balanced are divided into two groups according to the equalization control band. The first group consists of cells with an SOC lower than the lower limit of the equalization control band (i.e., SOC). AGM -λ SOC *S SOC The battery cells are arranged in ascending order of State of Charge (SOC) as A1, A2, ..., An. The second group consists of cells with an SOC higher than the upper limit of the equalization control band (i.e., SOC). AGM +λ SOC *S SOC The battery cells are arranged in order of SOC from low to high as B1, B2, ... Bn; the battery cells in the first group and the second group are paired according to the rule of the lowest SOC battery cell (A1, B1), the second lowest SOC battery cell (A2, B2), ... the highest SOC battery cell (An, Bn).

[0053] In the above scheme, such as Figure 2As shown, the active balancing circuit includes a capacitor, a first switch group, and a second switch group. The number of switches in the first and second switch groups is the same as the number of battery cells in the power battery, which is N. One end of each of the N switches in the first switch group is connected to one end of the capacitor, and the other end of each of the N switches in the first switch group is connected to the positive terminal of each of the N battery cells in the power battery. One end of each of the N switches in the second switch group is connected to the other end of the capacitor, and the other end of each of the N switches in the second switch group is connected to the negative terminal of each of the N battery cells in the power battery. The capacitance value is determined by the formula C = Q / U, where Q is the coulomb amount of charge that the capacitor can store, in As, and Q is 5% * CB * 3600, where CB is the rated capacity of the power battery cell, and U is set to 4V. If the rated capacity of the power battery cell is 100Ah, then the capacitance C = 5% * 100 * 3600 / 4 = 4500F.

[0054] In the above scheme, the balancing process is as follows: For each paired battery cell group, first connect the low-SOC battery cell to the active balancing circuit to charge the low-SOC battery cell; after charging is completed, disconnect the low-SOC battery cell, and then connect the high-SOC battery cell to the active balancing circuit to discharge the high-SOC battery cell. The discharge amount during discharge and the charging amount during charging are both 1 / 2 * (SOC). H -SIC L )*C B SOC H For high SOC battery cells, SOC L For low-SOC battery cells, C B This refers to the rated capacity of a single battery cell.

[0055] Example

[0056] First, select the power battery cells that are unsuitable for equalization. These cells have limited storage capacity and exhibit rapid voltage increases during charging and rapid voltage decreases during discharging. The selection method is as follows: during charging, when the first average SOC (SOC) is reached... AGN When the SOC is greater than 80%, all individual cell voltages are sorted from smallest to largest. Starting from the highest voltage, (5%*N) voltage samples are extracted (if 5%*N is not an integer, it is rounded up to the nearest integer and then incremented by 1). If the difference between the SOC (SOCi) of these individual cells and the average SOC (SOCAGN) is less than 5%, the corresponding cell number is recorded. During discharge, when the average SOC (SOCAGN) is less than 20%, all individual cell voltages are sorted from smallest to largest. Starting from the lowest voltage, (5%*N) voltage samples are extracted (if 5%*N is not an integer, it is rounded up to the nearest integer and then incremented by 1). If the difference between the SOC (SOCi) of these individual cells and the first average SOC (SOCAGN) is less than 5%, the corresponding cell number is recorded. AGNIf the difference is less than 5%, the corresponding cell number is recorded; if the two cell numbers are the same, the corresponding cell is not suitable for balancing. Power battery cells that are not suitable for balancing should be replaced in time and will not participate in subsequent balancing control.

[0057] Secondly, the target to be balanced is determined: this stage consists of two steps, namely, the timing conditions for selecting the target and the setting of the balance control band. Based on the external characteristics of the power battery's charging and discharging, the consistency of individual battery cells varies greatly at the end of charging and discharging. The end of charging corresponds to the second average SOC of the power battery (SOC...). AGM The second average SOC (SOC) in this invention is higher. AGM When the discharge end is greater than 80%, the second average SOC of the power battery corresponds to the discharge end. AGM The second average SOC (SOC) is low in this invention. AGM Since the SOC is less than 20%, the timing condition for selecting the equilibrium target is the average SOC of the power battery. AGM The SOC is greater than 80% or less than 20%. After the timing conditions for selecting the equilibrium target are met, the range ΔSOC between the maximum and minimum SOC of the power battery cell is calculated. RRG The difference between the initial range ΔSOC and the initial range of the power battery when it leaves the factory. IRG Through formula λ SOC =ΔSOC IRG / ΔSOC RRG Calculate the SOC range factor of the power battery cells at that time, and the power battery equalization control band is (SOC) AGM -λ SOC *S SOC SOC AGM +λ SOC *S SOC The power battery cells whose SOC is outside the range of this equalization control zone are the targets to be equalized, where S SOC This represents the variance of the state of charge (SOC) of all power battery cells at that time.

[0058] Finally, an active balancing strategy is formulated: the SOC of the target battery cells is sorted from smallest to largest, and the SOC of the target battery cells is divided into two groups according to the balancing control zone, namely, those with an SOC less than or equal to the target battery cells. AGM -λ SOC *S SOC Low SOC and greater than or equal to SOC AGM +λ SOC *S SOC The system is divided into two groups with high SOC (State of Charge). Within each group, the cells with the lowest SOC are paired, followed by the cells with the next lowest SOC, and then the cells with the highest SOC, and so on, to complete the active balancing of the battery cell pairing groups. Each paired high SOC (State of Charge) cell is then paired with the cells with the highest SOC.H ) and low SOC (SOC L ) Calculate the average, i.e., 1 / 2 * (SOC) H +SOC L Assuming the high-SOC battery cell is numbered j and the low-SOC battery cell is numbered k, then the first switch group connects the positive and negative terminals of cell j#. Cell j# charges the capacitor by 1 / 2 * (SOC) H -SOC L )*C B After charging is complete, the N-channel switch connects the positive and negative terminals of cell k#, and the capacitor discharges cell k# with a discharge amount of 1 / 2 * (SOC). H -SOC L )*C B After discharge, the next pairing is performed for equalization, and so on, until all battery cell pairs in the power battery are equalized. Once the equalization of the battery cell pairs is completed, the current active equalization cycle is finished, and the process of selecting unsuitable cells for equalization begins again to enter the next cycle.

[0059] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Contents not described in detail in this specification belong to prior art known to those skilled in the art.

Claims

1. A method for active balancing control of a power battery, characterized in that: Based on the first average SOC of the battery cells during charging and discharging of the power battery, battery cells that are not suitable for equalization are identified and eliminated. Based on the second average SOC of the remaining battery cells after exclusion, determine whether to select a target to be balanced; if selected, determine the balance control band based on the second average SOC. The battery cells to be balanced are determined based on the equalization control band, and then grouped and paired. The power battery is balanced by controlling the active balancing circuit to balance all paired battery cells. The process of identifying battery cells that are unsuitable for balancing is as follows: During charging, if the first average SOC is greater than the first set value, all battery cells are sorted and numbered in order of voltage from low to high. Starting from the battery cell with the highest voltage, M battery cells are selected, and the first difference between the individual SOC of each of the M battery cells and the first average SOC is calculated. The battery cells with the first difference less than the second set value are identified, and the corresponding battery cell number is recorded as the first number group. During discharge, if the first average SOC is less than the third set value, all battery cells are sorted and numbered in order of voltage from low to high. Starting from the battery cell with the lowest voltage, M battery cells are selected, and the second difference between the individual SOC of each of the M battery cells and the first average SOC is calculated. The battery cells whose second difference is less than the second set value are identified, and their corresponding battery cell numbers are recorded as the second number group. Battery cells with the same number in the first and second numbering groups are battery cells that are not suitable for balancing. For the remaining battery cells after elimination, if the second average SOC at the end of the charging phase is greater than the fourth set value, or the second average SOC at the end of the discharging phase is less than the fifth set value, then the target to be balanced is determined; otherwise, the active balancing ends. The SOC of the remaining battery cells after elimination is compared with the equalization control band. Battery cells whose SOC is not within the range of the equalization control band are the battery cells to be equalized. The process of grouping and pairing is as follows: the battery cells to be balanced are sorted in order of SOC from low to high, and the battery cells to be balanced are divided into two groups according to the equalization control band. The first group consists of battery cells with SOC below the lower limit of the equalization control band, and the second group consists of battery cells with SOC above the upper limit of the equalization control band. The battery cells in the first group and the second group are paired according to the rule of lowest SOC battery cells, second lowest SOC battery cells, ... highest SOC battery cells.

2. The active balancing control method for power batteries according to claim 1, characterized in that: The range of the equalization control band is (SOC) AGM -λ SOC ×S SOC SOC AGM +λ SOC ×S SOC ), Among them, SOC AGM For the second average SOC, λ SOC S is the range factor. SOC This represents the SOC variance of the remaining battery cells after exclusion.

3. The active balancing control method for power batteries according to claim 2, characterized in that: The range factor is determined using the following formula. l SOC =ΔSOC IRG / ΔSOC RRG , Wherein, ΔSOC RRG ΔSOC is the range between the highest and lowest SOC of a single battery cell. IRG This is the range between the maximum SOC of a single battery cell and the initial SOC of the power battery when it leaves the factory.

4. The active balancing control method for power batteries according to claim 1, characterized in that: The active balancing circuit includes a capacitor, a first switch group, and a second switch group. Several switches in the first and second switch groups are connected in parallel. The number of switches in the first and second switch groups is the same as the number of battery cells in the power battery. One end of several switches in the first switch group is connected to one end of the capacitor, and the other end is connected to the positive terminal of several battery cells in the power battery. One end of several switches in the second switch group is connected to the other end of the capacitor, and the other end is connected to the negative terminal of several battery cells in the power battery.

5. The active balancing control method for power batteries according to claim 1, characterized in that: The balancing process is as follows: for each paired battery cell, first connect the low SOC battery cell to the active balancing circuit to charge the low SOC battery cell; then connect the high SOC battery cell to the active balancing circuit to discharge the high SOC battery cell.

6. The active balancing control method for power batteries according to claim 5, characterized in that: The charging amount during charging and the discharging amount during discharging are both 1 / 2 × (SOC) H -SIC L )×C B SOC H For high SOC battery cells, SOC L For low-SOC battery cells, C B This refers to the rated capacity of a single battery cell.

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