Battery pack equalization method, controller and battery pack charging system

Abstract

Provided in the present application are a battery pack equalization method, a controller and a battery pack charging system. The battery pack equalization method is applied to a battery pack charging process, and a battery pack comprises a plurality of battery cells. The method comprises: acquiring voltage values of a plurality of battery cells (S101); when the voltage values of the plurality of battery cells are all within a preset voltage range and satisfy an equalization condition, selecting a reference battery cell from among the plurality of battery cells, and using the battery cells among the plurality of battery cells other than the reference battery cell as battery cells to be equalized (S103); calculating a voltage difference between each battery cell to be equalized and the reference battery cell (S105); and on the basis of the calculated voltage difference, equalizing the corresponding battery cell to be equalized (S107).

Description

Battery pack balancing method, controller and battery pack charging system

[0001] This application claims priority to Chinese Patent Application No. 202511407151.3, filed with the Chinese Patent Office on September 28, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of energy storage equipment technology, specifically to a battery pack balancing method, controller, and battery pack charging system. Background Technology

[0003] As energy storage systems continue to expand in scale, battery packs are often composed of a large number of cells electrically connected in series and parallel to meet higher voltage and energy specifications. However, due to factors such as manufacturing variations, differences in capacity and internal resistance distribution, inconsistent polarization characteristics, uneven temperature distribution, and different aging processes, even under the same operating conditions, cells will still exhibit subtle differences in charge acceptance and voltage response. Considering measurement and system factors such as sampling accuracy, synchronization, and differences in connection impedance, these subtle differences accumulate and amplify after multiple cycles, eventually evolving into significant capacity deviations. The direct consequence is that during charging, high-capacity cells trigger overvoltage protection earlier, limiting the overall charging progress and thus reducing the usable capacity of the battery pack.

[0004] To mitigate the impact of these inconsistencies on system performance, the industry commonly employs cell balancing strategies. Common approaches fall into two main categories: passive balancing typically uses parallel resistors and switches to discharge higher-voltage cells during charging or resting phases to reduce voltage differences; active balancing improves balancing efficiency by transferring energy between cells or between cells and the bus. In engineering implementation, this is usually combined with a power management system to monitor individual cell charge levels and trigger balancing based on preset thresholds and strategies, aiming to improve consistency and maximize available capacity at the end of charging and discharging.

[0005] However, in practical applications, existing balancing strategies still have shortcomings, especially at the charging end. The difference in charge between cells is easily misjudged under the influence of temperature disturbances, polarization effects and measurement noise, leading to a mismatch in balancing strength, resulting in over-balancing or under-balancing, which in turn affects charging efficiency, available capacity and lifespan consistency. Summary of the Invention

[0006] In a first aspect, embodiments of this application provide a battery pack balancing method applied during the charging process of a battery pack, the battery pack comprising multiple battery cells, the method comprising: acquiring the voltage values ​​of the multiple battery cells; in response to the voltage values ​​of the multiple battery cells all being within a preset voltage range and satisfying balancing conditions, selecting a reference battery cell from the multiple battery cells, the battery cells other than the reference battery cell being selected as cells to be balanced; calculating the voltage difference between each cell to be balanced and the reference battery cell; and balancing the corresponding cells to be balanced according to the voltage difference corresponding to the cells to be balanced.

[0007] Secondly, embodiments of this application also provide a controller, including a memory and a processor, wherein the memory is configured to store computer programs or instructions; when the computer programs or instructions are executed by the processor, the balancing method of the above-described embodiments is implemented.

[0008] Thirdly, embodiments of this application also provide a battery pack charging system, including a controller and a battery pack, wherein the controller is configured to perform the equalization method of the above embodiments.

[0009] This application's balancing scheme uses voltage as the basis for balancing the charge levels of battery cells. It is particularly suitable for balancing adjustments before a cell is fully charged. In the high-slope region of the later charging stage, where voltage surges relative to charge levels, measuring the charge levels allows for more precise characterization of subtle differences in charge levels between cells, providing higher-precision and more reliable data support for the balancing operation. Furthermore, after selecting a reference cell, this application calculates the voltage difference between each cell to be balanced and the reference cell, and performs independent balancing operations on each cell accordingly. This allows for individual adjustments for each cell, avoiding over-balancing or under-balancing caused by fixed balancing rules and parameters.

[0010] This application, under the premise of meeting the preset voltage range and balancing conditions, uses the relative voltage difference of the reference cell to perform balancing, which is equivalent to using a more precise voltage index for alignment in the high-slope sensitive area at the end of charging. Compared with related technologies, the technical solution of this application can reduce the deviation caused by inaccurate reference data, improve the consistency and balancing efficiency at the end of full charge, thereby improving the full charge effect and releasing usable capacity. Attached Figure Description

[0011] Figure 1 is one of the flowcharts of the battery pack balancing method provided in the embodiments of this application;

[0012] Figure 2 is a second schematic flowchart of the battery pack balancing method provided in the embodiments of this application;

[0013] Figure 3 is a third schematic flowchart of the battery pack balancing method provided in the embodiments of this application;

[0014] Figure 4 shows the voltage-capacity curve of a lithium iron phosphate battery cell. Detailed Implementation

[0015] Please refer to Figure 1. This application provides a battery pack balancing method, controller, and battery pack charging system to avoid the situation in related technologies where multiple cells in a battery pack charge at different speeds, which would cause a single cell to trigger protection after being fully charged, preventing the other cells from being fully charged.

[0016] In a first aspect, this application provides a battery pack balancing method applied during the battery pack charging process. The battery pack includes multiple battery cells, and the method includes the following steps:

[0017] S101, Obtain the voltage values ​​of multiple battery cells;

[0018] S103. When the voltage values ​​of multiple cells are all within the preset voltage range and meet the balancing conditions, a reference cell is selected from the multiple cells, and the cells other than the reference cell are used as cells to be balanced.

[0019] S105. Calculate the voltage difference between each cell to be balanced and the reference cell;

[0020] S107. Equalize the corresponding cells to be balanced according to the voltage difference between the cells to be balanced.

[0021] To ensure stable charging voltage and energy input, most rechargeable batteries have a relatively long voltage plateau in the middle charge region of their charging curve, which means that the slope of the voltage-charge curve is close to 0. Typically, the plateau period includes at least 5%-95% of the charge. At the beginning and end of charging, the voltage enters a high-slope region, especially when the battery is close to full charge, where the voltage is extremely sensitive to small changes in charge.

[0022] The characteristics of a battery cell's charging curve mean that voltage amplifies subtle differences in charge levels between cells, particularly during the near-empty and fully charged phases. This application's balancing scheme uses voltage as a basis for balancing cell charge levels, making it particularly suitable for adjustments before full charge. In the high-slope region of the later charging phase, the voltage value surges relative to the charge level. Measuring the charge level allows for more precise characterization of subtle differences in charge levels between cells, providing more accurate and reliable data support for the balancing operation. Furthermore, after selecting a reference cell, this application calculates the voltage difference between each cell to be balanced and the reference cell, and performs independent balancing operations on each cell accordingly. This allows for individual adjustments for each cell, avoiding over-balancing or under-balancing caused by fixed balancing rules and parameters.

[0023] Related technologies often use power level detection or a loose power threshold to trigger equalization, which is prone to over-equalization or under-equalization due to estimation errors and measurement noise. This application, under the premise of meeting the preset voltage range and equalization conditions, uses the relative voltage difference of a reference cell to perform equalization, which is equivalent to using a more precise voltage index for alignment in the high-slope sensitive area at the end of charging. Compared with related technologies, the technical solution of this application can reduce the deviation caused by inaccurate reference data, improve the consistency and equalization efficiency at the end of full charging, thereby improving the full charging effect and releasing usable capacity.

[0024] The preset voltage range is a voltage interval that characterizes a preset linear relationship between the cell's voltage and charge values, where the slope is greater than a preset slope. The charge value is used to characterize the cell's state of charge.

[0025] This embodiment triggers and executes equalization within a voltage range where the slope between voltage and charge values ​​approaches a preset linear relationship greater than a preset slope. This approach balances accuracy and calculability: on the one hand, a larger slope means that the same voltage difference will be amplified into a more easily distinguishable voltage difference, which can more sensitively characterize the subtle differences in the degree of charge between the cell to be equalized and the reference cell; on the other hand, limiting the preset voltage range to a near-linear segment allows the voltage-charge mapping relationship to be mapped once using an approximately constant slope. This facilitates the stable and rapid conversion of voltage difference into charge difference for further application in equalization operations, reducing model complexity and real-time computational burden, while also minimizing the impact of noise and estimation errors on equalization decisions.

[0026] It should be emphasized that high-slope regions exist at both ends of the voltage-charge curve of the battery cell. Although this application primarily addresses the balancing problem when the battery cell is fully charged, i.e., it targets the range where the charge value is close to 100%, those skilled in the art can also use the technical solution disclosed in this application to balance the low charge range without any inventive effort. While in most cases, balancing the low charge range can be achieved by directly discharging all the battery cells, there are situations where precise control to a specific low charge value is required. In such cases, a preset voltage range can be mapped to the low charge range, and the preset balancing condition can be set to discharge a battery cell to a specific preset charge. Therefore, this should not be used to limit the scope of protection of this application.

[0027] For the balancing condition when the battery cell is fully charged, the energy value corresponding to the voltage value within the preset voltage range is not less than the balancing threshold. The balancing threshold is the energy value that represents when the battery cell is approaching a fully charged state.

[0028] It should be understood that "fully charged" as referred to in this application can be understood as the current charge level of the battery pack or cell being close to or reaching the theoretical maximum charge level. Correspondingly, a fully charged state should be understood as the cell having reached its maximum achievable charge level. Perhaps due to cell aging or other reasons, the current charge level is still some distance from the theoretical maximum charge level, but it is impossible to further increase the current charge level through charging.

[0029] The voltage at the battery cell terminal fluctuates greatly due to factors such as temperature, internal resistance, and instantaneous current. Different brands and models of battery cells have different calibrated voltages and real-time voltage curves during charging. Limiting the equilibrium range by voltage has poor universality. In this embodiment, the charge value is used as the trigger condition, transforming the difficult-to-stabilize voltage value criterion into a more controllable charge value criterion, which facilitates unified management and control.

[0030] In addition, when most cells have reached the equalization threshold and met the equalization conditions (e.g., at least one cell is fully charged), but individual cells have not yet reached the equalization threshold, the system can determine that the deviation is abnormal, such as the corresponding cell's capacity decay, abnormal internal resistance, or connection problem, thereby triggering a fault alarm and maintenance recommendations.

[0031] According to one embodiment of this application, the equalization threshold is within the power error range of [99%, 99.8%]. For example, when the power value of the battery cell is greater than 99.5%, it is determined that the battery cell is close to being fully charged. The range of voltage values ​​corresponding to the power values ​​above this is the preset voltage range.

[0032] This embodiment provides reference values. The equalization threshold is within the [99%, 99.8%] charge error range, ensuring that equalization is triggered only when the cell is nearly fully charged. The high-slope segment of the voltage-charge curve is used to improve the discrimination accuracy. At the same time, setting the threshold within a narrow high charge value window facilitates consistent calibration under mass production and different operating conditions, while also taking into account slight capacity differences between different cells, thus improving the stability and compatibility of equalization triggering.

[0033] In conjunction with the first aspect and referring to FIG2, according to one embodiment of this application, balancing the corresponding cells to be balanced based on the voltage difference between the cells to be balanced includes:

[0034] S201. Calculate the equalization time required for the battery cell to be equalized based on the voltage difference corresponding to the battery cell to be equalized.

[0035] S203. Perform a balancing operation on each cell to be balanced for the required balancing time.

[0036] In existing equalization schemes, mapping relationships and even modulation functions have been generally established for passive resistance discharge, active transfer, and charging under different operating conditions. That is, there are mature conversion parameters and calibrations for converting the difference in charge capacity to the equalization time. Within the voltage range where the slope between the voltage value and the charge capacity value approaches a preset linear relationship greater than a preset slope, the slope between the charge capacity value and the voltage value can be approximated as a fixed value. That is, the more sensitive and stable voltage difference obtained in the high-slope range near full charge in this embodiment can be quickly converted into the charge capacity difference, and then the existing time formula and control table can be directly applied to achieve timed equalization of each cell to be equalized. This not only meets the technical effect to be achieved in this application and improves the accuracy of the triggering criterion, but also seamlessly integrates with existing software calibration, facilitating rapid implementation and engineering deployment, and reducing the cost of recalibration and control strategy modification.

[0037] In conjunction with the first aspect and referring to FIG3, according to one embodiment of this application, calculating the equalization time required for the battery cell to be equalized based on the voltage difference corresponding to the battery cell to be equalized includes:

[0038] S301. Multiply the equalization time within the preset voltage range by the proportional coefficient of the corresponding voltage difference and the voltage difference corresponding to the cell to be equalized to obtain the first equalization time. Take the smaller of the first equalization time and the preset second equalization time as the equalization time required for the cell to be equalized.

[0039] This calculation method can also be expressed as the following formula: t=min[t0,f*△U]; where t is the equalization time, f is the proportional coefficient between the equalization time and the corresponding voltage difference within the preset voltage range, t0 is the preset second equalization time, and △U is the voltage difference corresponding to the cell to be equalized.

[0040] In this embodiment, a maximum equalization time is preset. When the equalization time directly calculated from the voltage difference corresponding to the cell to be equalized is greater than the maximum equalization time, the maximum equalization time is used as the actual equalization time. Thus, within the preset voltage range, the equalization time is still obtained by linearly mapping the voltage difference corresponding to the cell to be equalized, facilitating calibration and implementation. Simultaneously, the upper limit t0 of the maximum equalization time limits extreme or abnormally large voltage differences, avoiding over-equalization and thermal risks caused by measurement noise or temperature transients, thereby improving robustness and safety.

[0041] In addition, in engineering practice, distributed iteration can be further implemented. After a single equilibrium is completed, ΔU is resampled before the next round is calculated, allowing the equilibrium process to gradually converge. Alternatively, an alarm mechanism can be set up. If f*ΔU > t0, it indicates an unexpected situation and an alarm is issued so that operators can take emergency measures.

[0042] In conjunction with the first aspect, according to one embodiment of this application, the equalization condition is that the power value corresponding to at least one battery cell is not less than the full charge threshold, where the full charge threshold is the power value that characterizes the battery cell as being in a fully charged state.

[0043] As previously analyzed, the cell terminal voltage fluctuates significantly due to factors such as temperature, internal resistance, and instantaneous current. Different brands and models of cells exhibit different rated voltages and real-time voltage curves during charging. Limiting the balancing range based on voltage has poor universality. This embodiment sets the balancing condition to initiate balancing only after at least one cell's charge value is not less than the full charge threshold. Using charge value as the criterion facilitates unified management and control.

[0044] When any cell reaches the full charge threshold, it means that the entire pack has entered the range of being about to be fully charged. At this time, the equalization is triggered so that the total capacity of the battery pack after the equalization is completed is closer to the theoretical capacity of a full charge. This provides a consistent cell state basis for the subsequent transition to the charging cutoff or float charging stage, reducing the errors that may occur during the subsequent charging process.

[0045] According to one embodiment of this application, the full charge threshold is within the power error range of [99.9%, 100%].

[0046] This embodiment provides reference values, calibrating the full charge threshold within a power error range of [99.9%, 100%]. This narrow range is close to the full charge point, ensuring that the full charge determination is sufficiently rigorous, avoiding premature equalization due to early full charge determination, while also taking into account mass production consistency and slight capacity differences between different battery cells. Without significantly increasing the risk of overcharging, it improves the stability and portability of full charge determination and equalization triggering.

[0047] In conjunction with the first aspect, according to one embodiment of this application, the reference cell is the cell corresponding to the smallest voltage value among a plurality of cells, and balancing the corresponding cell to be balanced according to the voltage difference includes: discharging the cell to be balanced according to the voltage difference; or the reference cell is the cell corresponding to the largest voltage value among a plurality of cells, and balancing the corresponding cell to be balanced according to the voltage difference includes: charging the cell to be balanced according to the voltage difference.

[0048] This embodiment discloses an exemplary balancing method, which selects the lowest voltage cell as a reference and discharges the cells to be balanced that have a higher voltage according to their corresponding voltage difference, or selects the highest voltage cell as a reference and supplements the cells to be balanced that have a lower voltage according to their corresponding voltage difference. Those skilled in the art can flexibly switch between these methods depending on the charging and discharging scenario and hardware capabilities.

[0049] In addition, when there is a reference cell with a "constantly low" or "constantly high" value for a long period of time, the system can also determine potential capacity degradation or abnormal internal resistance, triggering alarms and maintenance suggestions, thereby ensuring both consistency and energy efficiency and safety.

[0050] The technical solution of this application is described below with reference to one embodiment.

[0051] Please refer to Figure 4 for the Open Circuit Voltage (OCV) - State of Charge (SOC) curve of the lithium iron phosphate (LFP) cell. In the middle SOC-OCV range, the cell voltage difference is small, making it impossible to determine the accurate balancing time. However, in the high SOC and low SOC ranges, the slope of SOC-OCV is larger. The voltage difference is used to calibrate the charging gap between the cell to be balanced and the reference cell.

[0052] In this embodiment, the preset voltage range is 3.35V-3.6V. Within this voltage range, the slope of the voltage value and the charge value, dOCV / dSOC, is approximately constant. The correspondence between the charge difference and the equalization time can be determined by those skilled in the art based on experience. In this case, the 250mV voltage difference between 3.35V and 3.6V corresponds to a charge difference of 0.5%. Equalizing a 0.1% SOC difference requires 15 minutes, meaning each 1mV corresponds to 0.3 minutes of equalization time, f = 0.3min / mV. The maximum equalization time is set to the equalization time corresponding to the largest voltage difference within the preset voltage range, i.e., the maximum equalization time t0 = 0.3min / mV * 250mV = 75min.

[0053] For example, the reference cell voltage is 3.5V, the cell to be balanced has a voltage of 3.52V, and the balancing time t = min[t0, f*△U] = min[75min, 0.3min / mV*(3520mV-3500mV)].

[0054] Secondly, this application also provides a controller, including a memory and a processor, wherein the memory is configured to store computer programs or instructions; when the computer programs or instructions are executed by the processor, the balancing method of the above embodiments is implemented.

[0055] Thirdly, this application also provides a battery pack charging system, including a controller and a battery pack, wherein the controller is configured to perform the balancing method of the above embodiments.

[0056] Since both the second and third aspects can achieve the equilibrium method described in the first aspect, they also possess the technical effects of the first aspect. The beneficial effects of the second and third aspects can be referred to the first aspect or any possible implementation of the first aspect, and will not be elaborated here. Based on the implementation methods provided by the above-mentioned multiple aspects, this application can also be further combined to provide more implementation methods.

Claims

1. A battery pack balancing method, applied during the charging process of a battery pack, the battery pack comprising multiple battery cells, the method comprising: Obtain the voltage values ​​of the plurality of battery cells; In response to the fact that the voltage values ​​of the plurality of battery cells are all within a preset voltage range and meet the balancing condition, a reference battery cell is selected from the plurality of battery cells, and the battery cells other than the reference battery cell are used as the battery cells to be balanced. Calculate the voltage difference between each of the cells to be balanced and the reference cell; The corresponding cells to be balanced are balanced according to the voltage difference between them.

2. The balancing method according to claim 1, wherein, The preset voltage range is a voltage interval that represents a preset linear relationship between the voltage value and the charge value of the battery cell, where the slope is greater than a preset slope.

3. The balancing method according to claim 2, wherein, The step of balancing the corresponding battery cells based on the voltage difference between the cells to be balanced includes: The equalization time required for the battery cell to be equalized is calculated based on the voltage difference corresponding to the battery cell to be equalized. The balancing operation is performed on each of the cells to be balanced for the required balancing time.

4. The balancing method according to claim 3, wherein, The step of calculating the equalization time required for the battery cell to be equalized based on the voltage difference corresponding to the battery cell to be equalized includes: The first equalization time is obtained by multiplying the equalization time within the preset voltage range by the proportional coefficient of the corresponding voltage difference and the voltage difference corresponding to the cell to be equalized. The smaller of the first equalization time and the preset second equalization time is taken as the equalization time required for the cell to be equalized.

5. The balancing method according to claim 2, wherein, The energy value corresponding to the voltage value within the preset voltage range is not less than the equalization threshold, which represents the energy level when the battery cell is close to a fully charged state.

6. The balancing method according to claim 5, wherein, The equalization threshold is within the power error range of [99%, 99.8%].

7. The equilibration method according to any one of claims 1-6, wherein, The reference cell is the cell corresponding to the smallest voltage value among the plurality of cells, and the step of balancing the corresponding cells to be balanced according to the voltage difference includes: discharging the cells to be balanced according to the voltage difference; or The reference cell is the cell corresponding to the largest voltage value among the plurality of cells, and the step of balancing the corresponding cell to be balanced according to the voltage difference includes: charging the cell to be balanced according to the voltage difference.

8. The equilibration method according to any one of claims 1-6, wherein, The equalization condition is that the power value corresponding to at least one of the battery cells is not less than the full charge threshold, where the full charge threshold is the power value that indicates the battery cell is already in a fully charged state.

9. The balancing method according to claim 8, wherein, The full charge threshold is within the power error range of [99.9%, 100%].

10. A controller comprising a memory and a processor, the memory being configured to store a computer program or instructions; when the computer program or instructions are executed by the processor, implementing the balancing method of any one of claims 1-9.

11. A battery pack charging system, comprising a controller and a battery pack, the controller being configured to perform the equalization method according to any one of claims 1-9.

Images