Battery passive equalization method

Abstract

The invention discloses a battery passive equalization method, which comprises the following steps of: electrifying a battery system, and reading historical equalization storage data; the state of the battery system is judged, and when the state of the battery system is a static state or a charging end state, an equalization threshold value is obtained; determining battery cells needing to be equalized based on the equalization threshold value, calculating the time required for equalization of the corresponding battery cells, clearing the battery cell equalization accumulation time, and calculating the battery cell equalization accumulation time; on the basis of meeting the system equalization condition and the battery cell equalization condition, judging whether the battery cell needs to be equalized or not; and the battery system is powered off, the equalization data are stored, and the equalization data are used as historical equalization storage data during next equalization. According to the invention, full-time-domain equalization is realized within the equalization time according to the system and battery cell conditions, and the equalization time and opportunity are effectively increased. And meanwhile, passive equalization can be preferentially carried out on the battery cells with relatively high electric quantity, the inconsistency of the battery cells is reduced, and the equalization efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of battery management technology, specifically relating to a passive battery balancing method. Background Technology

[0002] Due to the differences in cell manufacturing, use, and storage, individual cells exhibit varying states. These inconsistent cells are connected in series and parallel to form a battery pack (PACK). The overall capability of the PACK is limited by individual cells; a single deteriorating cell will restrict the overall PACK capability. To reduce the impact of cell inconsistency on the overall PACK capability, a balancing function is introduced. By discharging or charging the cells, the state error between cells is kept within an acceptable range.

[0003] Currently, most mass-produced BMSs use discharge (passive balancing) as their balancing method. When a cell meets the balancing activation conditions, it discharges through the balancing resistor corresponding to the cell to consume electricity, reduce the difference in charge between cells, improve the consistency of the battery system, enable the battery system to perform at its maximum capacity, and improve the battery system's lifespan.

[0004] However, in related technologies, for large-capacity PACK systems, the current balancing current is small and the balancing time is short, resulting in low balancing efficiency. At the same time, the existing judgment conditions for whether balancing is needed are mostly based on a fixed threshold type, which limits many scenarios and also has an impact. Summary of the Invention

[0005] The purpose of this invention is to propose a passive battery balancing method to solve the problems in the prior art.

[0006] Therefore, the present invention provides a battery passive balancing method, comprising: The battery system is powered on and reads historical equalization storage data, which includes cell equalization status data. Determine the state of the battery system, and when the battery system is in a static state or at the end of charging, obtain the equalization threshold. The cells that need to be balanced are determined based on the equalization threshold, the equalization time required for the corresponding cells is calculated, the cumulative equalization time of the cells is cleared and the cumulative equalization time of the cells is calculated. Based on satisfying the system balancing conditions and the cell balancing conditions, it is determined whether the cell needs to be balanced. If it needs to be balanced, the battery system sends a balancing start command, and the corresponding cell begins balancing; otherwise, balancing is not started. The battery system is powered off and the equalization data is stored. This equalization data is used as historical equalization storage data for the next equalization.

[0007] As a further description of the above technical solution, the historical equalization storage data includes system sleep time, cumulative cell equalization time, and cell equalization flag bit, wherein the cell equalization flag bit is used to indicate whether the cell needs equalization.

[0008] As a further description of the above technical solution, determining that the battery system is in a static state includes: System hibernation time ≥30min or When the battery system is powered on, the absolute value of the current of the battery system is ≤5A and the duration is ≥30min.

[0009] As a further description of the above technical solution, determining the state of the battery system, when the battery system is in a static state, involves obtaining the balancing threshold by calculating the dynamic balancing threshold using the following formula: Vcell thrd =(1-a)*Vcell avg +a*VCell min; Among them, VCell min Minimum cell voltage; Vcell avg Average cell voltage; Vcell thrd The dynamic equilibrium threshold; 'a' represents the weighting ratio of the minimum cell voltage, where 'a' ranges from 0 to 1. Fixed equalization thresholds include thresholds for enabling equalization and thresholds for disabling equalization.

[0010] As a further description of the above technical solution, the cells that need to be balanced based on the balancing threshold include: If V Cell -Vcell thrd If V ≥ xmV, then equilibrium is required; Cell -Vcell thrd If ≤ymV, then balancing is not required; Where x is the threshold for enabling equalization and y is the threshold for disabling equalization.

[0011] As a further description of the above technical solution, the calculation of the equalization time required for the corresponding battery cell includes: Based on the OCV curve and the current voltage of the cell that needs to be balanced, determine the current SOC of the cell; Cell equalization time required = (SOC - SOC) w -SOC p *Cap*60 / Curr; SOC w =(1-a)SOCavg +aSOC min; SOC avg SOC min These represent the average and minimum true SOC on the same branch, in percentage terms. SOC p The accuracy of the system's SOC calculation is expressed in % (%). Cap indicates the cell capacity under current battery health conditions, measured in Ah. Curr represents the equalizing current, measured in amperes (A). The equalization time required for the battery cell, in minutes.

[0012] As a further description of the above technical solution, determining that the battery system is in the charging end state includes: The maximum cell voltage is greater than or equal to the preset voltage threshold and the current is less than a multiple of the preset battery rated capacity.

[0013] As a further description of the above technical solution, the state of the battery system is determined, and when the battery system state is the end of charging, an equalization threshold is obtained. The equalization threshold includes a SOC-on equalization threshold and a SOC-off equalization threshold.

[0014] As a further description of the above technical solution, determining whether the battery cell needs balancing includes: If SOC-SOCw-SOCp≥SOCstr, then equilibrium is required; if SOC-SOCw-SOCp≤SOCstp, then equilibrium is not required. Wherein, SOC refers to the SOC of each battery cell. w =(1-a)SOC avg +aSOC min ; SOC str SOC stp These are the threshold values ​​for enabling and disabling SOC equalization, respectively, and are fixed values.

[0015] As a further description of the above technical solution, the calculation of the equalization time required for the corresponding battery cell includes: Cell equalization time required = (SOC - SOC) w -SOC p *Cap*60 / Curr; SOC avg SOC min These represent the average and minimum true SOC on the same branch, in percentage terms. SOC p The accuracy of the system's SOC calculation is expressed in % (%). Cap indicates the cell capacity under current battery health conditions, measured in Ah. Curr represents the equalizing current, measured in amperes (A). The equalization time required for the battery cell, in minutes.

[0016] As a further description of the above technical solution, the system equilibrium conditions include at least: No sampling or equalization type faults; No over-temperature or over-current faults; No total voltage undervoltage / overvoltage fault; No high-voltage interlock fault No insulation fault; No communication failure on the motherboard.

[0017] As a further description of the above technical solution, the cell balancing conditions include at least: The cell voltages are all collected and effective; No battery cell voltage too low fault; SOC is within the preset range; Remaining cell balancing time ≥ kmin Wherein, the remaining time for cell balancing = the time required for cell balancing - the cumulative balancing time * the balancing duty cycle, and K is the preset threshold for the remaining time.

[0018] Beneficial effects: This invention provides a passive battery balancing method. Through a full-time-domain balancing strategy, different balancing variables can be selected based on operating conditions, and the required balancing time for each cell can be calculated. Within the balancing time, full-time-domain balancing is achieved based on system and cell conditions, effectively increasing balancing time and timing. Simultaneously, through a dynamic balancing threshold calculation method, passive balancing of cells with higher charge levels can be prioritized, reducing cell inconsistency and improving balancing efficiency. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A flowchart of the battery passive balancing method provided by the present invention.

[0021] Figure 2 A flowchart illustrating the battery passive balancing method provided by this invention. Detailed Implementation

[0022] The invention will be more readily understood by referring to the following detailed description of preferred embodiments and included examples. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In case of conflict, the definitions in this specification shall prevail.

[0023] like Figure 1-2 As shown, a passive battery balancing method includes: The battery system is powered on and reads historical equalization storage data, which includes cell equalization status data. In one embodiment, the cell equalization status data includes at least the system sleep time, the cumulative equalization time of the cells, the time required for cell equalization, and the cell equalization flag. By reading the system sleep time, the current state of the battery system can be determined, providing a timing basis for subsequent decisions. That is, by comparing the time interval between this power-on and the last power-off (i.e., the sleep time), the system can accurately determine whether the vehicle is parked for a short time (such as waiting at a red light) or left idle for a long time (such as parked overnight), so as to facilitate subsequent determination of whether the battery system is in a static state.

[0024] Reading the cumulative balancing time and the time required for cell balancing can be used to achieve breakpoint continuation of the balancing task and protection against over-balancing. When the battery system was last powered off, it saves the balancing time of each cell. After power-on, by reading this data and comparing it with the calculated total time required, the remaining balancing time can be obtained. This effectively ensures that the balancing task will not be interrupted or reset due to vehicle power failure, making full use of every possible balancing opportunity, accumulating a longer effective balancing time, and greatly improving balancing efficiency.

[0025] By reading the cell balancing flag, which identifies which cells were deemed necessary for balancing before the last power-down, the system can quickly resume balancing operations without immediately recalculating the state of all cells upon power-up. This reduces the initial computational load on the CPU and accelerates system response. This ensures the balancing system can quickly get to work, prioritizing energy dissipation for the cells with the highest imbalance, achieving the priority balancing effect sought by the dynamic threshold strategy, and thus rapidly converging system inconsistencies.

[0026] The state of the battery system is determined. When the battery system is in a static state or at the end of charging, the equalization threshold is obtained. By actively identifying the best time window for efficient and accurate equalization, such as when the battery system is in a static state or at the end of charging, the dynamic equalization threshold can be calculated to perform equalization when the conditions are met. This can solve the problem of low equalization efficiency caused by the fixed time period in traditional equalization strategies.

[0027] Specifically, it can intelligently identify the state of the battery system, i.e., the timing, and select a suitable window for balancing. Traditional strategies have a single and fixed balancing timing, while this application creatively distinguishes between two operating conditions: static and end-of-charge. Under these two conditions, the battery system has no load or very low current, and the cell voltage tends to be stable. The measured values ​​can most accurately reflect the inherent state of the cell (OCV), thus providing high-precision input data for balancing. This fundamentally avoids misjudgments caused by fluctuations in operating conditions and lays the foundation for efficient balancing.

[0028] In calculating the dynamic balancing threshold, the traditional fixed voltage threshold method is abandoned. By selecting different dynamic threshold calculation methods under different conditions, the precise and prioritized allocation of balancing resources can be achieved, ensuring that balancing energy is used where it is most needed, thereby improving balancing efficiency. Based on the equalization threshold, the cells requiring equalization are identified, the equalization time for each cell is calculated, and the accumulated equalization time for each cell is reset to zero. First, the cells to be equalized are determined. Each time the optimal equalization window is entered, the old historical accumulated time is reset to zero, meaning the system re-plans the equalization task based on the latest and most accurate cell status. The theoretically required time is calculated by combining parameters such as cell capacity and equalization current, setting personalized and quantified equalization targets for each cell. This avoids interference from historical data, prevents accumulated errors, and makes subsequent breakpoint resume management more accurate and efficient, effectively preventing over-equalization.

[0029] Based on meeting the system balancing conditions and cell balancing conditions, it is determined whether the cell needs balancing. If balancing is required, the battery system sends a balancing start command, and the corresponding cell begins balancing. Otherwise, balancing is not started. Specifically, it is determined whether the current remaining balancing time is within the allowable range. When the current remaining balancing time is within the allowable range, balancing can be performed. When it is not, balancing is not performed to prevent over-balancing.

[0030] When the battery system is powered off, it stores equalization data. This equalization data serves as historical equalization storage data for the next equalization, including the cumulative equalization time of the cells, the time required for equalization, and the cell equalization flag. This enables the continuity and accumulation of the equalization strategy, effectively solving the problems of short time and low efficiency in traditional equalization strategies, and achieving equalization across the entire time domain.

[0031] In one embodiment, the following conditions are used to determine whether the battery system is in a static state: System hibernation time ≥30min or When the battery system is powered on, the absolute value of the current of the battery system is ≤5A and the duration is ≥30min.

[0032] If either of the above two conditions is met, the battery system is considered to be in a static state.

[0033] In one embodiment, once the battery system is determined to be in a static state, the dynamic equilibrium threshold can be obtained through a weighted calculation based on the average voltage and the minimum voltage, as follows: Vcell thrd =(1-a)*Vcell avg +a*VCell min; Among them, VCell min Minimum cell voltage; Vcell avg Average cell voltage; Vcell thrd The dynamic equilibrium threshold; 'a' represents the weighting ratio of the minimum cell voltage, where 'a' ranges from 0 to 1. Fixed equalization thresholds include thresholds for enabling equalization and thresholds for disabling equalization.

[0034] This dynamic balancing threshold reflects the degree of inconsistency in the entire battery pack. By adjusting the weighting ratio 'a', the degree of balancing can be flexibly controlled. For example, at the end of charging, a larger value for 'a' can fully utilize the balancing capability, balancing more cells at this time. At the end of discharging, a smaller value for 'a' can avoid undervoltage caused by over-balancing, balancing cells with higher voltage. When the system imbalance is high, appropriately reducing the value of 'a' can reduce the number of cells balancing simultaneously, prioritizing the balancing of cells with higher imbalance.

[0035] In one embodiment, after calculating the dynamic balancing threshold, the balanced cells are determined, specifically: If V Cell -Vcell thrd If V ≥ xmV, then equilibrium is required; Cell -Vcell thrd If ≤ymV, then balancing is not required; Where x is the threshold for enabling equalization and y is the threshold for disabling equalization, both in mV.

[0036] In one embodiment, based on the relationship between the cell voltage and the OCV curve, the current SOC of the cell is obtained, and the required equalization time of the cell is calculated. Specifically: Cell equalization time required = (SOC - SOC) w -SOC p *Cap*60 / Curr; SOC w =(1-a)SOC avg +aSOC min; SOC avg SOC min These represent the average and minimum true SOC on the same branch, in percentage terms. SOC p The accuracy of the system's SOC calculation is expressed in % (%). Cap indicates the cell capacity under current battery health conditions, measured in Ah. Curr represents the equalizing current, measured in amperes (A). The equalization time required for the battery cell, in minutes.

[0037] At the same time, the cumulative cell balancing time is reset to zero. Based on the cell balancing status fed back from the board, the duty cycle is considered, and the cumulative cell balancing time is added back.

[0038] In one embodiment, determining that the battery system is in the charging terminal state includes: The maximum cell voltage is greater than or equal to a preset voltage threshold, and the current is less than a multiple of the preset battery rated capacity. For example, the maximum cell voltage is greater than or equal to bmV; and the lookup current in the charging table (map) is less than or equal to dC. Here, b and d are fixed thresholds, which vary depending on the cell material system. C is the charge / discharge rate, i.e., a multiple of the battery rated capacity (Ah), for example, 1C = rated capacity (A).

[0039] In one embodiment, the state of the battery system is determined. When the battery system state is at the end of charging, an balancing threshold is obtained. The balancing threshold includes a SOC-on balancing threshold and a SOC-off balancing threshold. Specifically, at the end of charging, SOC is used as the balancing variable, and the following determination is made: If SOC-SOCw-SOCp≥SOCstr, then equilibrium is required; if SOC-SOCw-SOCp≤SOCstp, then equilibrium is not required. Wherein, SOC refers to the SOC of each battery cell. w =(1-a)SOC avg +aSOC min ; Then calculate the equalization time required for the corresponding battery cell using the following formula: Cell equalization time required = (SOC - SOC) w -SOC p *Cap*60 / Curr; SOC avg SOC min These represent the average and minimum true SOC on the same branch, in percentage terms. SOC p The accuracy of the system's SOC calculation is expressed in % (%). Cap indicates the cell capacity under current battery health conditions, measured in Ah. Curr represents the equalizing current, measured in amperes (A). The equalization time required for the battery cell, in minutes.

[0040] Then, the accumulated cell balancing time is reset to zero. Based on the cell balancing status fed back from the board, and considering the balancing duty cycle, the accumulated balancing time of each cell is added up. Specifically, after recalculating the dynamic threshold and the balancing time required based on the latest and most accurate cell state (voltage / SOC), the old historical accumulated time is reset to zero. This operation avoids interference from potentially inaccurate timing data accumulated under past unbalanced operating conditions on the new balancing task, providing a clean timing starting point for this balancing process based on precise decision-making.

[0041] Meanwhile, this invention directly collects the actual state feedback from the board (such as whether it is truly conducting and discharging) and accumulates it over time, realizing accurate measurement of the equalization process. This ensures that the "cumulative time" mastered by the system is infinitely close to the actual energy consumption time of the battery cell, eliminating errors caused by communication delays, actuator failures, etc., and greatly improving the reliability and accuracy of equalization management.

[0042] Furthermore, to avoid overheating due to continuous heating of the balancing resistor, the balancing operation of the slave board typically adopts PWM mode, i.e., intermittent operation (e.g., 100ms operation, 900ms pause, duty cycle of 10%). In this invention, when accumulating time, it does not simply accumulate the physical time, but multiplies the physical time by the duty cycle to convert it into effective balancing time. For example, at a 10% duty cycle, if actual discharge lasts for 1 hour, the accumulated time only increases by 6 minutes. This conversion ensures that the calculated remaining balancing time strictly corresponds to the actual energy required, achieving precise control.

[0043] In another embodiment, the system determines whether a cell needs balancing by judging whether the allowed balancing time minus the cumulative balancing time is greater than or equal to x hours. x is a threshold value that can be set according to specific needs. The allowed balancing time minus the cumulative balancing time is the calculated remaining available balancing time. If this remaining time is much less than a threshold (x hours), it means that the current ignition cycle may end soon (e.g., the user is about to park and turn off the engine), and the remaining time is insufficient to significantly improve the cell's condition. In this case, the system can intelligently choose not to activate balancing. This avoids the energy loss, computational resource consumption, and unnecessary thermal load caused by frequently starting and stopping the balancing circuit, thereby concentrating system resources on effective balancing tasks that have sufficient time to execute. This optimizes balancing efficiency from a system scheduling perspective.

[0044] In one embodiment, the system balance condition and the cell balance condition are determined based on BMS parameters: If all of the following conditions are met, the system is considered to be in equilibrium: Faults related to non-sampling (current / voltage) and equalization; No over-temperature or over-current faults; No total voltage undervoltage / overvoltage fault; No high-voltage interlock fault No insulation fault; No communication failure on the motherboard.

[0045] If all of the following conditions are met, the cell balance condition is considered satisfied: The cell voltages are all collected and effective; No battery cell voltage too low fault; SOC is within the normal range; The remaining time for cell balancing is ≥ kmin. The remaining time for cell balancing is = the time required for cell balancing - the cumulative balancing time * the balancing duty cycle, where k is a preset threshold for the remaining time.

[0046] If the system and cell conditions for balancing are met, and the third and fourth steps determine whether cell balancing is required, a balancing enable command is sent to the slave board if balancing is needed; otherwise, a balancing disable command is sent. During the balancing process, the system and cell conditions are assessed in real time. If the conditions are not met, a balancing disable command is sent.

[0047] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of battery passive equalization, the method comprising: The method comprises the following steps: The battery system is powered on, and historical balancing storage data is read, wherein the historical balancing storage data comprises cell balancing state data; A state to which the battery system belongs is determined, and a balancing threshold is obtained when the state of the battery system is a static state or a state at the end of charging; Based on the balancing threshold, a cell that needs to be balanced is determined, the time required for balancing of the corresponding cell is calculated, and the cell balancing cumulative time is cleared and calculated; Based on the system balancing condition and the cell balancing condition, it is determined whether the cell needs to be balanced, and if so, the battery system sends a balancing start instruction, and the corresponding cell starts balancing, otherwise, balancing is not started; The battery system is powered off, and balancing data is stored, which is used as historical balancing storage data for the next balancing.

2. The method of claim 1, wherein, The historical balancing storage data comprises system sleep time, cell balancing cumulative time, and a cell balancing flag bit, wherein the cell balancing flag bit is used to indicate whether the cell needs to be balanced.

3. The method of claim 2, wherein, The state to which the battery system belongs is determined to be static, comprising: The system sleep time is greater than or equal to 30 minutes, or In the powered-on state of the battery system, the absolute value of the current of the battery system is less than or equal to 5A, and the duration is greater than or equal to 30 minutes.

4. The method of claim 1, wherein, When the state of the battery system is a static state, the balancing threshold is obtained, comprising calculating a dynamic balancing threshold by the following formula: Vcell thrd = (1 - a) * Vcell avg + a * VCell min; VCell min is the minimum cell voltage; Vcell avg Vcell is the average cell voltage; Vcell thrd is a dynamic equalization threshold; a is the weight ratio of the minimum cell voltage, wherein a ranges from 0 to 1; The fixed balancing threshold comprises a threshold for starting balancing and a threshold for stopping balancing.

5. The method of claim 1, wherein, Based on the balancing threshold, a cell that needs to be balanced is determined, comprising: If V Cell - Vcell thrd ≥ xmV then balancing is needed; V Cell - Vcell thrd ≤ ymV then balancing is not needed; wherein V Cell is the cell voltage, x is the threshold for opening the equalization, and y is the threshold for closing the equalization.

6. The method of claim 1, wherein, The time required for balancing of the corresponding cell is calculated, comprising: Based on the OCV curve and the current voltage of the cell that needs to be balanced, the current SOC of the cell is determined; Equalization time required for the cell = (SOC - SOC w -SOC p ) * Cap * 60 / Curr; SOC w = (1 - a)SOC avg + aSOC min; SOC avg , SOC min represent the average and minimum true SOC, in %, on the same branch, respectively SOC p Accuracy, unit for system SOC Cap represents the cell capacity under the current battery health, with the unit of Ah; Curr represents the balancing current, with the unit of A; The balancing time required for the cell, with the unit of min.

7. The method of claim 1, wherein, The state to which the battery system belongs is determined to be at the end of charging, comprising: The maximum cell voltage is greater than or equal to a preset voltage threshold, and the current is less than a preset battery rated capacity multiple.

8. The method of claim 1, wherein, When the state of the battery system is a state at the end of charging, the balancing threshold is obtained, comprising a SOC start balancing threshold and a SOC stop balancing threshold.

9. The method of claim 1, wherein, It is determined whether the cell needs to be balanced, comprising: SOC-SOCw-SOCp is greater than or equal to SOCstr, and balancing is needed; SOC-SOCw-SOCp is less than or equal to SOCstp, and balancing is not needed; wherein SOC is the SOC of each cell, SOC w = (1 - a)SOC avg + aSOC min ; SOC str , SOC stp are respectively a SOC open equalization threshold value, a SOC close equalization threshold value, and are fixed values.

10. The method of claim 1, wherein, The time required for balancing of the corresponding cell is calculated, comprising: Equalization time required for the cell = (SOC - SOC w -SOC p ) * Cap * 60 / Curr; SOC avg , SOC min represent the average and minimum true SOC, in %, on the same branch, respectively SOC p Accuracy, unit for system SOC Cap represents the cell capacity under the current battery health, with the unit of Ah; Curr represents the balancing current, with the unit of A; The balancing time required for the cell, with the unit of min.

11. The method of passive equalization of claim 1, wherein, The system balancing condition at least comprises: No sampling class, balancing class fault; No over-temperature and over-current fault; No total voltage under-voltage / over-voltage fault; No high-voltage interlock fault No insulation fault; No communication fault from the board.

12. The method of claim 1, wherein, The cell balancing condition at least comprises: The cell voltage is collected and valid; No cell voltage too low fault; The SOC is within a preset range; The cell balancing remaining time is greater than or equal to kmin Wherein, the cell equalization remaining time = the cell equalization required time - the equalization accumulated time * the equalization duty cycle, k is the remaining time preset threshold.

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