A method for calculating the equalization capability of a battery pack autonomous equalization system

Abstract

A method for calculating the balancing capability of an autonomous balancing system for a battery bank is proposed. Based on the numerical relationship between the discharge current and battery voltage of the autonomous balancing system, as well as the numerical relationship between battery voltage and discharge amount, a calculation formula is derived for the relationship between the autonomous balancing start time and the battery voltage before and after balancing suspension. A method for calculating the balancing capability of the autonomous balancing system when the battery bank is in a ground open-circuit suspension state is established. Taking the on-orbit charging and discharging state of the on-orbit battery bank and the on-state of the autonomous balancing system, the on-orbit state of the battery bank is divided into three stages. A method for calculating the discharge amount of the parallel block composed of each battery cell in each stage is established. The voltage and maximum voltage difference value after one cycle in orbit are calculated. Through continuous iterative calculation, the changes of voltage value and maximum voltage difference value with the on-orbit cycle are determined, thereby evaluating the balancing capability of the autonomous balancing system.

Description

Technical Field

[0001] This invention relates to a method for calculating the balancing capability of an autonomous balancing system for a battery pack, belonging to the field of satellite battery pack configuration technology design. Background Technology

[0002] Battery packs consist of multiple cells connected in series and parallel. During long-term charge-discharge cycles in orbit, differences in the charge retention capacity and capacity decay rate among the individual cells cause voltage differences between the cells (parallel blocks) to diverge, thus affecting the on-orbit power supply performance of the battery pack. Therefore, most satellites are equipped with equalization modules to perform on-orbit equalization of the battery packs. However, traditional equalization modules are large in size and weight and require satellite telemetry and remote control resources. As a result, some satellite battery packs are beginning to be equipped with autonomous equalization systems to replace traditional equalization modules.

[0003] The general principle of an autonomous balancing system is as follows: when the voltage of a single battery cell falls below a certain threshold, the system does not activate; however, when the battery voltage exceeds this threshold, the system independently discharges current to each cell. The higher the voltage of a single cell, the greater the discharge current; therefore, cells with higher voltages discharge more electricity, thus achieving voltage balancing across the battery pack. The discharge current of the autonomous balancing system depends on the voltage of the individual battery cells. As the discharge current accumulates over time, the discharge amount gradually increases, causing the individual battery cell voltage to gradually decrease. In other words, the battery voltage and the discharge current of the autonomous balancing system influence each other and both change with the balancing time. The relationship between the battery voltage, balancing current, and time is complex, making it difficult to accurately calculate the balancing time of the autonomous balancing system and the voltage difference between the individual battery cells after balancing (i.e., the balancing capability). Furthermore, for battery packs on in-orbit satellites, the voltage of each individual battery cell is simultaneously affected by the satellite's on-orbit operating conditions, making the calculation of the balancing capability of the autonomous balancing system for in-orbit battery packs even more challenging.

[0004] The inability to accurately calculate the balancing capability of the battery pack's autonomous balancing system poses a challenge to its design. Improper configuration can result in weak on-orbit balancing capabilities, or even complete failure to achieve balancing, or over-design of the system leading to resource waste. Therefore, finding a method for calculating the balancing capability of the autonomous balancing system is crucial, providing a theoretical basis for battery pack design and on-orbit fault analysis. Summary of the Invention

[0005] The technical problem solved by this invention is: addressing the lack of accurate design and evaluation methods for autonomous balancing systems in the existing technology, this invention proposes a method for calculating the balancing capability of an autonomous balancing system for a battery pack.

[0006] The present invention solves the above-mentioned technical problem through the following technical solution:

[0007] A method for calculating the balancing capability of a battery pack autonomous balancing system includes:

[0008] Calculate the self-discharge current based on the charge retention rate and capacity of the individual battery cells;

[0009] Determine the relationship between the voltage and discharge capacity of a single battery cell;

[0010] Determine the quantitative relationship between the equalization start time of the battery pack autonomous equalization system and the initial cell voltage before equalization and the cell voltage after equalization with the battery open-circuit idle.

[0011] Based on the obtained quantitative relationship, the calculation formula for the relationship between battery voltage and equalization start time is determined, and the calculation formula for the relationship between battery voltage and equalization start time when the battery is left open until the voltage is lower than the threshold voltage for the autonomous equalization system to start is derived.

[0012] Calculate the voltage value of the parallel block formed by the individual cells in the battery pack at the end of the on-orbit constant voltage charging phase;

[0013] Calculate the discharge amount of the battery at the end of the on-orbit constant voltage charging phase;

[0014] Calculate the time value of the parallel block formed by the individual cells in the battery pack during the constant current charging period of one cycle in orbit.

[0015] Calculate the discharge value of the parallel block formed by the individual cells in the battery pack during the constant current charging period of one cycle in orbit.

[0016] Calculate the time value of the parallel block formed by the individual cells in the battery pack during the constant current discharge segment of one cycle in orbit.

[0017] Calculate the discharge amount of the parallel block formed by the individual cells in the battery pack during the constant current discharge period of one cycle in orbit.

[0018] Calculate the time value of the discharge current disconnection segment of the on-orbit one-cycle autonomous balancing system for each individual battery cell in the parallel block formed by the parallel block in the orbital one-cycle autonomous balancing system based on the calculated time value and discharge amount value.

[0019] Calculate the discharge current disconnection value of the parallel block formed by each individual battery cell in the on-orbit one-cycle autonomous balancing system.

[0020] Based on the calculated discharge value, the self-discharge current value of the parallel block formed by each individual battery cell, and the orbital cycle time, calculate the total discharge value of the parallel block formed by each individual battery cell in the battery pack during one orbital cycle.

[0021] Based on the calculated total discharge value for one on-orbit cycle, calculate the voltage value before the start of constant voltage charging in the next on-orbit cycle.

[0022] Calculate the maximum voltage difference of the parallel block formed by the individual cells of the battery pack after one on-orbit cycle;

[0023] Based on the obtained voltage difference and the voltage value before the start of constant voltage charging in the next on-orbit cycle, recalculate the voltage value and other parameters before the start of the constant voltage charging segment of the parallel block formed by each individual battery in the next orbit cycle, and calculate the maximum voltage difference of the parallel block formed by each individual battery after the battery pack has passed the next orbit cycle.

[0024] The maximum voltage difference and voltage value of the parallel block formed by each individual cell of the battery pack after several orbital cycles are calculated iteratively to obtain the balancing capability information parameters of the battery pack's autonomous balancing system.

[0025] The specific method for calculating the self-discharge current is as follows:

[0026]

[0027] In the formula, U j U is the threshold voltage for the autonomous balancing system to start the balancing discharge current. cell Let be the voltage of a single battery cell, and n be the number of equalization chips configured in each autonomous equalization system.

[0028] The relationship between the voltage of a single battery cell and its discharge capacity is expressed as follows:

[0029]

[0030] In the formula, A UQ This represents the slope of the battery voltage-capacity curve. For lithium-ion batteries, this value can be approximated as a constant within a relatively small battery voltage range.

[0031] The specific expression for the self-discharge current of a single battery cell is as follows:

[0032]

[0033] In the formula, I z C is the self-discharge current of the cell; C is the cell capacity; H is the 28-day charge retention rate of the cell.

[0034] The quantitative relationship between the equalization start-up time and the initial cell voltage before equalization, and the cell voltage after equalization with the battery open-circuit idle, is as follows:

[0035]

[0036] In the formula, the balanced startup time is t. j Before equalization, the individual cell voltage is U0; after equalization, the individual cell voltage is U. B .

[0037] The threshold voltage is preset based on the design value of the autonomous balancing system. When the voltage of a single battery cell is always greater than the threshold voltage, the discharge current of the autonomous balancing module will always exist.

[0038]

[0039] When the voltage of a single battery cell is never greater than the threshold voltage, the discharge current of the self-balancing module is non-existent.

[0040]

[0041] The on-orbit operation of the individual cells and parallel blocks formed by the individual cells in the battery pack, as well as the autonomous balancing system, includes the constant voltage charging stage and U cell >U j Constant current charging segment and U cell >U j , constant current discharge section and U cell >U j Equalization system discharge current disconnection section U cell j ;

[0042] The method for calculating the voltage value of the parallel block formed by the individual cells in the battery pack at the end of the on-orbit constant voltage charging section is as follows:

[0043]

[0044] In the formula, U 1 mcv U represents the voltage after the first cycle of constant voltage charging of the m-th (1≤m≤s) unit or parallel block is completed; 0 m This represents the initial voltage at which the m-th individual unit or parallel block begins constant-voltage charging;

[0045] I mz This represents the self-discharge current of the m-th cell or parallel block, expressed as the capacity C of the individual cell. m and 28-day charge retention rate H m Calculated result; t cv A represents the duration of the constant voltage charging phase during one cycle of the battery pack in orbit. UQ The slope of the voltage-capacity curve of the parallel battery block is represented by , and n represents the total number of equalization chips configured in a parallel block.​

[0046] The calculation method for the discharge amount at the end of the on-orbit constant voltage charging phase of the battery is as follows:

[0047]

[0048] In the formula, the discharge quantity is Q. 1 mcv At the current moment U 0 m >U j .

[0049] The calculation method for the time value of the parallel block formed by the individual battery cells during the constant current charging period of one cycle in orbit is as follows:

[0050]

[0051] In the formula, the time value is t. 1 mc At the current moment U m >U j .

[0052] The calculation method for the discharge capacity of the parallel block formed by the individual battery cells during the constant current charging phase of one cycle in orbit is as follows:

[0053]

[0054] In the formula, the discharge quantity is Q. 1 mcb At the current moment U m >U j .

[0055] The calculation method for the time value of the parallel block formed by the individual cells during the constant current discharge period of one cycle in orbit is as follows:

[0056]

[0057] In the formula, I d This represents the constant current discharge current of the battery pack in orbit, at the current moment U. m >U j .

[0058] The calculation method for the discharge capacity of the parallel block formed by the individual cells during the constant current discharge period of one cycle in orbit is as follows:

[0059]

[0060] In the formula, the discharge quantity is Q. 1 mdb At the current moment U m >U j .

[0061] The calculation method for the time value of the discharge current disconnection segment of the on-orbit one-cycle autonomous balancing system formed by the parallel blocks of individual batteries is as follows:

[0062]

[0063] In the formula, T represents the on-orbit cycle time of the battery pack, and U represents the current time. m j .

[0064] The calculation method for the discharge current disconnection segment of the on-orbit one-cycle autonomous balancing system formed by the parallel blocks of individual cells is as follows:

[0065]

[0066] In the formula, the discharge quantity is Q. 1 mz At the current moment U m j .

[0067] The total discharge amount includes:

[0068] The constant-voltage charging voltage of the battery pack is equal to the product of the autonomous balancing system's start-up threshold voltage and the number of batteries connected in series, and the total discharge value of the parallel block formed by the corresponding individual batteries when the voltage of the parallel block is greater than the autonomous balancing system's start-up threshold voltage during the constant-voltage charging stage is:

[0069]

[0070] The total discharge value of the parallel block of the battery pack, formed by the individual cells, when the voltage of the block remains below the start-up threshold voltage of the autonomous balancing system throughout the current orbital cycle:

[0071]

[0072] The total discharge capacity of the parallel block formed by the corresponding individual cells when the constant voltage charging voltage of the battery pack is greater than the product of the autonomous balancing system start-up threshold voltage and the number of series-connected batteries, and the voltage of the parallel block formed by the constant voltage charging stage is greater than the autonomous balancing system start-up threshold voltage:

[0073]

[0074] Voltage value U before the start of constant voltage charging in the next on-orbit cycle 1 m The calculation method is as follows:

[0075]

[0076] In the formula, s is the number of individual cells or parallel blocks connected in series in the battery pack.

[0077] ​​The maximum voltage difference ΔU of the parallel block formed by the individual cells 1 The calculation method is as follows:

[0078]

[0079] By recalculating the voltage value U of the parallel block formed by each individual cell in the next orbital cycle before the start of the constant voltage charging phase, the voltage value U of the parallel block formed by each individual cell is recalculated. 2 1. U 2 2…U 2 m …U 2 s Obtain the maximum voltage difference ΔU of the parallel block formed by each individual cell in the current orbital cycle. 2 The value is then used to iteratively calculate subsequent orbital periods, determining the parallel block voltage U formed by each individual cell after x orbital periods in orbit. x m Numerical value and maximum pressure difference ΔU x The balancing capability of the battery pack's autonomous balancing system is assessed based on changes in conditions.

[0080] The advantages of this invention compared to the prior art are:

[0081] This invention provides a method for calculating the balancing capability of an autonomous balancing system for a battery pack. It accurately calculates the balancing time and the voltage difference between individual battery cells after balancing. Through iterative calculation, it calculates the changes in voltage values ​​of individual cells and parallel blocks within the battery pack, as well as the maximum voltage difference, with the on-orbit cycle period. This allows for the evaluation of the balancing capability of the autonomous balancing system and the prediction of voltage difference changes between individual battery cells in the on-orbit battery pack. This provides a theoretical basis for the design of battery packs with autonomous balancing systems and for on-orbit fault analysis, solving the problem of the lack of accurate design and evaluation methods for autonomous balancing systems in current technologies. Attached Figure Description

[0082] Figure 1 Flowchart of the method for calculating the balancing capability of the battery pack autonomous balancing system provided for the invention; Detailed Implementation

[0083] A method for calculating the balancing capability of an autonomous balancing system for battery packs is disclosed. This method can accurately calculate the balancing time and the voltage difference between individual battery cells after balancing. Furthermore, it predicts the voltage difference changes between individual battery cells in the on-orbit battery pack through calculation, providing a theoretical basis for battery pack design with an autonomous balancing system and on-orbit fault analysis. The specific steps are as follows:

[0084] Calculate the self-discharge current based on the charge retention rate and capacity of the individual battery cells;

[0085] Determine the relationship between the voltage and discharge capacity of a single battery cell;

[0086] Determine the quantitative relationship between the equalization start time of the battery pack autonomous equalization system and the initial cell voltage before equalization and the cell voltage after equalization with the battery open-circuit idle.

[0087] Based on the obtained quantitative relationship, the calculation formula for the relationship between battery voltage and equalization start time is determined, and the calculation formula for the relationship between battery voltage and equalization start time when the battery is left open until the voltage is lower than the threshold voltage for the autonomous equalization system to start is derived.

[0088] Calculate the voltage value of the parallel block formed by the individual cells in the battery pack at the end of the on-orbit constant voltage charging phase;

[0089] Calculate the discharge amount of the battery at the end of the on-orbit constant voltage charging phase;

[0090] Calculate the time value of the parallel block formed by the individual cells in the battery pack during the constant current charging period of one cycle in orbit.

[0091] Calculate the discharge value of the parallel block formed by the individual cells in the battery pack during the constant current charging period of one cycle in orbit.

[0092] Calculate the time value of the parallel block formed by the individual cells in the battery pack during the constant current discharge segment of one cycle in orbit.

[0093] Calculate the discharge amount of the parallel block formed by the individual cells in the battery pack during the constant current discharge period of one cycle in orbit.

[0094] Calculate the time value of the discharge current disconnection segment of the on-orbit one-cycle autonomous balancing system for each individual battery cell in the parallel block formed by the parallel block in the orbital one-cycle autonomous balancing system based on the calculated time value and discharge amount value.

[0095] Calculate the discharge current disconnection value of the parallel block formed by each individual battery cell in the on-orbit one-cycle autonomous balancing system.

[0096] Based on the calculated discharge value, the self-discharge current value of the parallel block formed by each individual battery cell, and the orbital cycle time, calculate the total discharge value of the parallel block formed by each individual battery cell in the battery pack during one orbital cycle.

[0097] Based on the calculated total discharge value for one on-orbit cycle, calculate the voltage value before the start of constant voltage charging in the next on-orbit cycle.

[0098] Calculate the maximum voltage difference of the parallel block formed by the individual cells of the battery pack after one on-orbit cycle;

[0099] Based on the obtained voltage difference and the voltage value before the start of constant voltage charging in the next on-orbit cycle, recalculate the voltage value and other parameters before the start of the constant voltage charging segment of the parallel block formed by each individual battery in the next orbit cycle, and calculate the maximum voltage difference of the parallel block formed by each individual battery after the battery pack has passed the next orbit cycle.

[0100] The maximum voltage difference and voltage value of the parallel block formed by each individual cell of the battery pack after several orbital cycles are calculated iteratively to obtain the balancing capability information parameters of the battery pack's autonomous balancing system.

[0101] The following description, in conjunction with the accompanying drawings and preferred embodiments, provides further details:

[0102] In the current embodiment, such as Figure 1 As shown, taking the autonomous balancing module configured with the C41815RH battery balancing chip as an example, the battery pack balancing capability calculation method proposed in this invention will be further described in detail with reference to the accompanying drawings and specific embodiments.

[0103] It is known that the self-balancing module configured with a C41815RH battery balancing chip has a balancing discharge current I. b With the voltage U of the battery cell cell It satisfies equation (1).

[0104]

[0105] In the formula U j U represents the threshold voltage for the autonomous balancing system to start balancing discharge current. cell denoted as the individual battery cell voltage, and n represents the number of equalization chips configured in each autonomous equalization system.

[0106] This invention is achieved through the following calculation methods and steps:

[0107] Step 1: Calculate the self-discharge current of a single battery cell according to equation (2).

[0108]

[0109] In the formula, C is the cell capacity; H is the cell charge retention rate over 28 days.

[0110] Step 2 expresses the relationship between the individual battery cell voltage and the discharge capacity of the autonomous balancing system through a mathematical formula. For lithium-ion batteries, formula (3) is satisfied.

[0111]

[0112] In the formula, A UQ This represents the slope of the battery voltage-capacity curve. For lithium-ion batteries, this value can be approximated as a constant within a relatively small battery voltage range.

[0113] Step 3 can obtain the equalization time t according to Equation (4). j The quantitative relationship with the single-cell voltage U0 before equalization and the single-cell voltage U after equalization and shelving. B

[0114]

[0115] Step 4 calculates the quantitative relationship between the battery voltage and the equalization time according to Equation (5) and Equation (6). Among them, Equation (5) is applicable to the process where the single-cell voltage of the battery is always greater than the threshold voltage, that is, the discharge current of the self-equalization module always exists; while Equation (6) is applicable to the situation where the voltage of the battery is lower than the threshold voltage of the equalization chip after shelving, and the self-equalization module no longer generates a discharge current.

[0116]

[0117]

[0118] Above, Equation (4), Equation (5) and Equation (6) are applicable to the calculation of the equalization ability of the self-equalization system of the battery pack in the ground open-circuit shelving state (that is, no charging and discharging). Among them, Equation (4) can be used to calculate the time required for the battery voltage to be discharged from U0 (U j <U0≤4.2V) to the single-cell voltage U B (U j <U B ≤4.2V) through the current discharge of the self-equalization system; Equation (5) and Equation (6) can be used to calculate the battery voltage after the initial voltage U0 (U j <U0≤4.2V) passes through the time t. Equation (4), Equation (5) and Equation (6) are also the basic calculations for the on-orbit equalization ability calculation of the battery pack self-equalization system.

[0119] According to the on-orbit opening states of each single cell of the battery pack and its self-equalization system, it is divided into three stages: constant-voltage charging stage (and U cell >U j ), constant-current charging stage and constant-current discharging stage (and U cell >U j ), equalization system discharge current disconnection stage (U cell <U j ). The battery pack consists of several single cells. Every p single cells form a parallel block, and the voltages of all single cells within the parallel block are the same. The battery pack has a total of s parallel blocks (or single cells when p = 1) connected in series.

[0120] The constant-voltage charging stage, constant-current charging stage, constant-current discharging stage and U cell &U j ​The size relationship is not necessarily related; they are two independent conditions. This patent divides the on-orbit process into two stages, U cell ≥U j Time and U cell j The calculation methods and formulas differ for the two phases: balanced startup and no startup. However, for the balanced startup phase (U... cell >U j The calculation methods and formulas for the battery in the constant voltage charging stage, constant current charging stage, and constant current discharging stage are also different, hence this classification.

[0121] Step 5: Calculate the on-orbit constant voltage charging section (and U) of each individual cell (parallel block) of the battery pack according to equation (7). 0 m >U j The voltage value after the end.

[0122]

[0123] In the formula:

[0124] U 1 mcv This represents the voltage after the first cycle of constant voltage charging of the m-th (1≤m≤s) unit (parallel block) is completed;

[0125] U 0 m This represents the initial voltage at which the m-th individual unit (parallel block) begins constant voltage charging;

[0126] I mz This represents the self-discharge current of the m-th cell (parallel block), which is determined by the capacity C of the cell. m and 28-day charge retention rate H m The result obtained by substituting into equation (2);

[0127] The m in the subscript represents the corresponding parameter of the mth cell or parallel block in the battery pack; if the subscript contains a number (such as 1, 2...) or s (number of series connections in the battery pack), it represents the corresponding parameter of the 1st, 2nd...sth (corresponding serial number) cell or parallel block in the battery pack.

[0128] t cv This indicates the duration of the constant voltage charging phase during one cycle of the battery pack in orbit.

[0129] It should be noted that in the calculation of the on-orbit balancing capability of the battery pack, A in the formula... UQ The slope of the voltage-capacity curve of the parallel battery block represents the slope of the parallel block voltage curve, and n represents the total number of equalization chips configured in a parallel block. This explanation also applies to subsequent calculations.

[0130] ​Step 6: Calculate the on-orbit constant voltage charging section (and U) of each individual cell (parallel block) of the battery pack according to equation (8). 0 m >U j Discharge quantity Q after the end of the process 1 mcv value.

[0131]

[0132] Step 7: Calculate the on-orbit one-cycle constant current charging period (and U) of each individual cell (parallel block) of the battery pack according to equation (9). m >U j ) time t 1 mc value.

[0133]

[0134] In the formula, I c This indicates the on-orbit constant current charging current of the battery pack.

[0135] Step 8: Calculate the on-orbit one-cycle constant current charging period (and U) of each individual cell (parallel block) of the battery pack according to equation (10). m >U j The discharge quantity Q 1 mcb value.

[0136]

[0137] Step 9: Calculate the on-orbit one-cycle constant current discharge segment (and U) of each cell (parallel block) of the battery pack according to equation (11). m >U j ) time t 1 md value.

[0138]

[0139] In the formula, I d This indicates the constant current discharge current of the battery pack in orbit.

[0140] Step 10: Calculate the on-orbit one-cycle constant current discharge segment (and U) of each cell (parallel block) of the battery pack according to equation (12). m >U j The discharge quantity Q 1 mdb value.

[0141]

[0142] Step 11: Calculate the discharge current disconnection segment (U) of each cell (parallel block) of the battery pack during one cycle of autonomous balancing system operation in orbit according to equation (13).m j ) time t 1 mz value.

[0143]

[0144] In the formula, T represents the on-orbit cycle time of the battery pack.

[0145] Step 12: Calculate the discharge current disconnection segment (U) of each cell (parallel block) of the battery pack during one cycle of autonomous balancing system operation in orbit according to equation (14). m j The discharge quantity Q 1 mz value.

[0146]

[0147] Step 13: Calculate the total discharge capacity Q of each cell (parallel block) of the battery pack in one orbital cycle according to equations (15), (16), and (17). 1 m总 value.

[0148]

[0149]

[0150]

[0151] in:

[0152] Equation (15) is only applicable when the constant voltage charging voltage of the battery pack is equal to the start-up threshold voltage of the autonomous balancing system × the number of batteries in series, and the voltage of the corresponding single cell (parallel block) is greater than the start-up threshold voltage of the autonomous balancing system at this stage;

[0153] Equation (16) only applies to the case where the voltage of the corresponding cell (parallel block) of the battery pack is always less than the start-up threshold voltage of the autonomous balancing system during this track cycle;

[0154] Equation (17) is only applicable when the constant voltage charging voltage of the battery pack is greater than the start-up threshold voltage of the autonomous balancing system × the number of battery packs connected in series, and the voltage of the corresponding single cell (parallel block) is greater than the start-up threshold voltage of the autonomous balancing system at this stage.

[0155] The calculation formulas for each individual cell differ under three different conditions, as shown in the following three formulas for calculating Qm_total_1. For the same battery pack, different cells may meet different calculation conditions, hence the different calculation formulas.

[0156] ​​Step 14: Calculate the voltage value U of each cell (parallel block) of the battery pack after one on-orbit cycle and before the start of the next constant voltage charging cycle according to equation (18). 1 m value.

[0157]

[0158] Step 15: Calculate the maximum voltage difference ΔU between each cell (parallel block) of the battery pack after one on-orbit cycle and before the start of the next constant voltage charging cycle, according to equation (19). 1 value.

[0159]

[0160] Step 16 is the voltage U of each individual unit (parallel block) calculated by equation (18) in step 14. 1 1. U 1 2…U 1 m …U 1 s The values, other parameters of each individual cell (parallel block), parameters of the battery pack balancing system, and on-track parameters of the battery pack are substituted into equations (7) to (18) according to steps 6 to 14 to calculate the voltage U of each individual cell (parallel block) on the next track. 2 1. U 2 2…U 2 m …U 2 s The numerical value can then be substituted into equation (19) in step 15 to calculate the maximum voltage difference ΔU between each cell (parallel block) of the next-track battery pack. 2 value.

[0161] Step 17 can be repeated iteratively to calculate the voltage U of each individual cell (parallel block) of the battery pack after several orbital cycles. x m Numerical value and maximum pressure difference ΔU x The balancing capability of the battery pack's autonomous balancing system can be evaluated by observing the maximum differential pressure values ​​of each individual cell (parallel block) in the battery pack as they change over the on-orbit cycle. The superscript numbers (e.g., 1, 2…) in the physical quantities represent the corresponding parameters of the battery pack or individual cells (parallel blocks) during the 1st, 2nd…th on-orbit cycles.

[0162] After verifying the on-orbit cycle test of the battery pack with the autonomous balancing system, the test results of the maximum pressure difference of each cell (parallel block) of the battery pack changing with the number of cycles were compared with the calculation results of the balancing capability algorithm of the autonomous balancing system of the battery pack in this invention. The two trends are completely consistent and the absolute values ​​are also very close, proving that the calculation method of this invention is reasonable and feasible.

[0163] Based on the calculation results and experimental verification results of the balancing capability algorithm of the battery pack autonomous balancing system according to this invention, the following pattern is obtained: Given the charge retention capability (or difference value) of each cell (parallel block) in the battery pack, and provided that the corresponding autonomous balancing system has not completely failed (meaning the corresponding autonomous balancing system has completely lost its balancing current discharge function), the maximum voltage difference of each cell (parallel block) in the battery pack will gradually decrease with each cycle (under the conditions described above, it may gradually increase in some cases) to a certain steady-state value. After reaching the steady-state maximum voltage difference of the battery pack, the maximum voltage difference of each cell (parallel block) no longer changes with the increase of the cycle number. Therefore, the steady-state value of the maximum voltage difference of each cell (parallel block) in the battery pack obtained by the balancing capability algorithm of the battery pack autonomous balancing system according to this invention is used as the definition of the balancing capability of the battery pack autonomous balancing system. Obviously, the smaller the steady-state voltage difference value, the stronger the balancing capability of the autonomous balancing system; conversely, the larger the value, the weaker the capability. Therefore, the method for calculating the balancing capability of the battery pack autonomous balancing system of the present invention can provide a theoretical basis for the design of battery packs equipped with autonomous balancing systems.

[0164] Based on the calculation results of the balancing capability algorithm of the battery pack autonomous balancing system according to this invention, the following conclusions can also be drawn: If, during the on-orbit or ground charge-discharge cycle test of a battery pack equipped with an autonomous balancing system, the maximum voltage difference between each cell (parallel block) of the battery pack gradually increases with each cycle, and this value cannot converge to a certain steady-state value, there is only one reason for this phenomenon: the autonomous balancing system corresponding to at least one cell (parallel block) of the battery pack has failed and completely lost its function of discharging the balancing current to the corresponding cell (parallel block); and the cell (parallel block) corresponding to the failure of the autonomous balancing system can be identified by the change in voltage of each cell (parallel block) of the battery pack with each cycle. Therefore, the balancing capability calculation method of the battery pack autonomous balancing system of this invention can provide a theoretical basis for the analysis of certain on-orbit faults of battery packs equipped with autonomous balancing systems.

[0165] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

[0166] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for calculating the balancing capability of a battery pack autonomous balancing system, characterized in that... include: Calculate the self-discharge current based on the charge retention rate and capacity of the individual battery cells; Determine the relationship between the voltage and discharge capacity of a single battery cell; Determine the quantitative relationship between the equalization start time of the battery pack autonomous equalization system and the initial cell voltage before equalization and the cell voltage after equalization with the battery open-circuit idle. Based on the obtained quantitative relationship, the calculation formula for the relationship between battery voltage and equalization start-up time is determined, and the calculation formula for the relationship between battery voltage and equalization start-up time when the battery is left open until the voltage is lower than the threshold voltage for the autonomous equalization system to start is derived. Calculate the voltage value of the parallel block formed by the individual cells in the battery pack at the end of the on-orbit constant voltage charging phase; Calculate the discharge amount of the battery at the end of the on-orbit constant voltage charging phase; Calculate the time value of the parallel block formed by the individual cells in the battery pack during the constant current charging period of one cycle in orbit. Calculate the discharge value of the parallel block formed by the individual cells in the battery pack during the constant current charging period of one cycle in orbit. Calculate the time value of the parallel block formed by the individual cells in the battery pack during the constant current discharge segment of one cycle in orbit. Calculate the discharge amount of the parallel block formed by the individual cells in the battery pack during the constant current discharge period of one cycle in orbit. Calculate the time value of the discharge current disconnection segment of the on-orbit one-cycle autonomous balancing system for each individual battery cell in the parallel block formed by the parallel block in the orbital one-cycle autonomous balancing system based on the calculated time value and discharge amount value. Calculate the discharge current disconnection value of the parallel block formed by each individual battery cell in the on-orbit one-cycle autonomous balancing system. Based on the calculated discharge value, the self-discharge current value of the parallel block formed by each individual battery cell, and the orbital cycle time, calculate the total discharge value of the parallel block formed by each individual battery cell in the battery pack during one orbital cycle. Based on the calculated total discharge value for one on-orbit cycle, calculate the voltage value before the start of constant voltage charging in the next on-orbit cycle. Calculate the maximum voltage difference of the parallel block formed by the individual cells of the battery pack after one on-orbit cycle; Based on the obtained voltage difference and the voltage value before the start of constant voltage charging in the next on-orbit cycle, recalculate the voltage value and other parameters before the start of the constant voltage charging segment of the parallel block formed by each individual battery in the next orbit cycle, and calculate the maximum voltage difference of the parallel block formed by each individual battery after the battery pack has passed the next orbit cycle. The maximum voltage difference and voltage value of the parallel block formed by each individual cell of the battery pack after several orbital cycles are calculated iteratively to obtain the balancing capability information parameters of the battery pack's autonomous balancing system.

2. The method for calculating the balancing capability of a battery pack autonomous balancing system according to claim 1, characterized in that: The specific method for calculating the self-discharge current is as follows: In the formula, U j U is the threshold voltage for the autonomous balancing system to start the balancing discharge current. cell Let be the voltage of a single battery cell, and n be the number of equalization chips configured in each autonomous equalization system.

3. The method for calculating the balancing capability of a battery pack autonomous balancing system according to claim 2, characterized in that: The relationship between the voltage of a single battery cell and its discharge capacity is expressed as follows: In the formula, A UQ This represents the slope of the battery voltage-capacity curve. For lithium-ion batteries, this value is considered a constant within the battery voltage range. The specific expression for the self-discharge current of a single battery cell is as follows: In the formula, I z C is the self-discharge current of the cell; C is the cell capacity; H is the 28-day charge retention rate of the cell.

4. The method for calculating the balancing capability of a battery pack autonomous balancing system according to claim 3, characterized in that: The quantitative relationship between the equalization start-up time and the initial cell voltage before equalization, and the cell voltage after equalization with the battery open-circuit idle, is as follows: In the formula, the balanced startup time is t. j Before equalization, the individual cell voltage is U0; after equalization, the individual cell voltage is U. B .

5. The method for calculating the balancing capability of a battery pack autonomous balancing system according to claim 4, characterized in that: The threshold voltage is preset based on the design value of the autonomous balancing system. When the voltage of a single battery cell is always greater than the threshold voltage, the discharge current of the autonomous balancing module will always exist. When the voltage of a single battery cell is never greater than the threshold voltage, the discharge current of the self-balancing module is non-existent.

6. The method for calculating the balancing capability of a battery pack autonomous balancing system according to claim 5, characterized in that: The on-orbit operation of the individual cells and parallel blocks formed by the individual cells in the battery pack, as well as the autonomous balancing system, includes the constant voltage charging stage and U cell >U j Constant current charging segment and U cell >U j , constant current discharge section and U cell >U j Equalization system discharge current disconnection section U cell j ;​ The method for calculating the voltage value of the parallel block formed by the individual cells in the battery pack at the end of the on-orbit constant voltage charging section is as follows: In the formula, U 1 mcv U represents the voltage after the first cycle of constant voltage charging of the m-th individual unit or parallel block is completed, 1≤m≤s; 0 m This represents the initial voltage at which the m-th individual unit or parallel block begins constant-voltage charging; I mz This represents the self-discharge current of the m-th cell or parallel block, expressed as the capacity C of the individual cell. m and 28-day charge retention rate H m Calculated result; t cv A represents the duration of the constant voltage charging phase during one cycle of the battery pack in orbit. UQ The slope of the voltage-capacity curve of the parallel battery block is represented by , and n represents the total number of equalization chips configured in a parallel block.

7. The method for calculating the balancing capability of a battery pack autonomous balancing system according to claim 6, characterized in that: The calculation method for the discharge amount at the end of the on-orbit constant voltage charging phase of the battery is as follows: In the formula, the discharge quantity is Q. 1 mcv At the current moment U 0 m >U j .

8. The method for calculating the balancing capability of a battery pack autonomous balancing system according to claim 7, characterized in that: The calculation method for the time value of the parallel block formed by the individual battery cells during the constant current charging period of one cycle in orbit is as follows: In the formula, the time value is t. 1 mc At the current moment U m >U j .

9. The method for calculating the balancing capability of a battery pack autonomous balancing system according to claim 8, characterized in that: The calculation method for the discharge capacity of the parallel block formed by the individual battery cells during the constant current charging phase of one cycle in orbit is as follows: In the formula, the discharge quantity is Q. 1 mcb At the current moment U m >U j .

10. The method for calculating the balancing capability of a battery pack autonomous balancing system according to claim 9, characterized in that: The calculation method for the time value of the parallel block formed by the individual cells during the constant current discharge period of one cycle in orbit is as follows: In the formula, I d This represents the constant current discharge current of the battery pack in orbit, at the current moment U. m >U j .

11. The method for calculating the balancing capability of a battery pack autonomous balancing system according to claim 10, characterized in that: The calculation method for the discharge capacity of the parallel block formed by the individual cells during the constant current discharge period of one cycle in orbit is as follows: In the formula, the discharge quantity is Q. 1 mdb At the current moment U m >U j .

12. The method for calculating the balancing capability of a battery pack autonomous balancing system according to claim 11, characterized in that: The calculation method for the time value of the discharge current disconnection segment of the on-orbit one-cycle autonomous balancing system formed by the parallel blocks of individual batteries is as follows: In the formula, T represents the on-orbit cycle time of the battery pack, and U represents the current time. m j .​ 13. The method for calculating the balancing capability of a battery pack autonomous balancing system according to claim 12, characterized in that: The calculation method for the discharge current disconnection segment of the on-orbit one-cycle autonomous balancing system formed by the parallel blocks of individual cells is as follows: In the formula, the discharge quantity is Q. 1 mz At the current moment U m j .​ 14. The method for calculating the balancing capability of a battery pack autonomous balancing system according to claim 13, characterized in that: The total discharge amount includes: The constant-voltage charging voltage of the battery pack is equal to the product of the autonomous balancing system's start-up threshold voltage and the number of batteries connected in series, and the total discharge value of the parallel block formed by the corresponding individual batteries when the voltage of the parallel block is greater than the autonomous balancing system's start-up threshold voltage during the constant-voltage charging stage is: The total discharge value of the parallel block of the battery pack, formed by the individual cells, when the voltage of the block remains below the start-up threshold voltage of the autonomous balancing system throughout the current orbital cycle: The total discharge capacity of the parallel block formed by the corresponding individual cells when the constant voltage charging voltage of the battery pack is greater than the product of the autonomous balancing system start-up threshold voltage and the number of series-connected batteries, and the voltage of the parallel block formed by the constant voltage charging stage is greater than the autonomous balancing system start-up threshold voltage:

15. The method for calculating the balancing capability of a battery pack autonomous balancing system according to claim 14, characterized in that: Voltage value U before the start of constant voltage charging in the next on-orbit cycle 1 m The calculation method is as follows: In the formula, s is the number of individual cells or parallel blocks connected in series in the battery pack.

16. The method for calculating the balancing capability of a battery pack autonomous balancing system according to claim 15, characterized in that: The maximum voltage difference ΔU of the parallel block formed by the individual cells 1 The calculation method is as follows:

17. The method for calculating the balancing capability of a battery pack autonomous balancing system according to claim 16, characterized in that: By recalculating the voltage value U of the parallel block formed by each individual cell in the next orbital cycle before the start of the constant voltage charging phase, the voltage value U of the parallel block formed by each individual cell is recalculated. 2 1. U 2 2…U 2 m …U 2 s Obtain the maximum voltage difference ΔU of the parallel block formed by each individual cell in the current orbital cycle. 2 The value is then used to iteratively calculate subsequent orbital periods, determining the parallel block voltage U formed by each individual cell after x orbital periods in orbit. x m Numerical value and maximum pressure difference ΔU x The balancing capability of the battery pack's autonomous balancing system is assessed based on changes in conditions.

Images