Battery active equalization method and system based on buck-boost equalization

Abstract

The present application relates to the technical field of battery management, in particular to a battery active equalization method and system based on BUCK-BOOST equalization, comprising: selecting an equalization target according to an equalization strategy combined with voltage information, an associated target associated with the equalization target, and determining an equalization direction, controlling the equalization switch of the associated target to be connected, and adopting a specific equalization mode for voltage equalization; In view of the problem that the battery equalization method in the prior art adjusts the charging and discharging of each single battery, the efficiency is low, the voltage discrimination process of the adjacent target of the equalization target is introduced, thereby establishing the voltage gradient distribution relationship in the series loop, and then determining the energy flow direction that can be used for equalization as the equalization direction. When the potential above the equalization target is higher, the BUCK mode is used to step down the voltage on the downside to make the overall potential difference tend to be consistent; When the potential below the equalization target is higher, the Boost mode is used to step up the voltage on the upside to make the overall potential difference tend to be consistent, thereby improving the overall equalization efficiency.

Description

Technical Field

[0001] This invention relates to the field of battery management technology, specifically to a battery active balancing method and system based on BUCK-BOOST balancing. Background Technology

[0002] Lithium iron phosphate (LFP) battery cells are often connected in series or parallel to form battery modules, battery clusters, or battery systems. Due to differences in manufacturing processes and usage environments, the internal resistance and capacity of individual battery cells change during use, and these differences gradually increase with usage time. These differences limit the charge and discharge performance of the battery pack due to the significant variations in individual cell sizes, negatively impacting the battery pack's lifespan, performance, and safety. Battery balancing technology, as a key technology for improving battery pack inconsistency, achieves consistent battery pack management by redistributing energy from individual cells, which is crucial for improving the overall performance of energy storage systems and ensuring the efficient and safe operation of battery packs.

[0003] For example, patent application CN200710125562.9 discloses a method for equalizing and controlling a battery pack and a battery pack charging method. The method includes the following steps: a battery management chip or microcontroller determines whether the voltage of all individual batteries is within a set voltage range. If so, when a battery's voltage is greater than the equalization voltage value, and the voltage difference between that battery and the battery with the lowest voltage is greater than the upper equalization voltage difference value, the charging current is detected by a current sensing resistor. Based on the charging current, a corresponding equalization current is set for energy equalization. When the voltage of the battery being equalized is less than the equalization voltage value, or the voltage difference between the battery being equalized and the battery with the lowest voltage is less than the lower equalization voltage difference value, the battery stops discharging. Centralized control via a chip or microcontroller offers high reliability and allows for flexible setting of various control parameters, making it widely applicable.

[0004] For example, patent application CN200910092039.X discloses a dynamic balancing device for automotive power batteries, belonging to the field of electric vehicle or hybrid vehicle power battery technology. It includes a DC-DC converter and a multi-channel electromechanical switch; the DC-DC converter is connected to the output terminals of the battery pack and the common terminal of the multi-channel electromechanical switch on both sides. The multi-channel electromechanical switch includes a stepper motor, armature, coil, contacts, etc. Based on the measured battery voltage, the multi-channel electromechanical switch connects the highest-voltage individual cell to the bidirectional DC-DC converter to charge the battery pack; similarly, it connects the lowest-voltage individual cell to the bidirectional DC-DC converter, using the battery pack to charge the lowest-voltage individual cell. This device achieves dynamic balancing of the power battery, reduces circuit design complexity, and decreases size; it is a low-cost dynamic balancing device for automotive power batteries.

[0005] However, in actual implementation, the inventors found that this type of technical solution usually involves charging and discharging specific battery cells during vehicle charging to make their voltage approach that of other cells, which requires a long equalization time. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, a battery active balancing method based on BUCK-BOOST balancing is provided; furthermore, a system for implementing this method is also provided.

[0007] The specific technical solution is as follows: A battery active balancing method based on BUCK-BOOST balancing, applicable to balancing circuits, wherein the balancing circuit includes balancing switches set for each battery cell; multiple battery cells are connected in series to form a battery pack, the balancing switch at the beginning of the battery pack serves as the upper balancing switch, and the balancing switch at the end of the battery pack serves as the lower balancing switch; the battery active balancing method includes: step S1: collecting the individual battery cell voltage and calculating the average voltage within the pack; step S2: generating an intra-pack voltage difference based on the individual battery cell voltage in each battery pack, and generating an inter-pack voltage difference based on the intra-pack average voltage, and then determining at least one balancing strategy based on the intra-pack voltage difference and the inter-pack voltage difference; the balancing strategy includes intra-pack balancing, inter-pack balancing, and inter-pack balancing followed by pack balancing. Internal balancing composition; Step S3: Select a balancing target and associated targets based on the balancing strategy and voltage information, and determine the balancing direction; Step S4: Control the balancing switch of the associated targets to be turned on according to the balancing direction and perform voltage balancing on the balancing targets using a specific balancing mode; The balancing target is the battery cell and / or the battery pack; The associated targets are the battery cells or the battery pack located before and after the balancing target; The balancing direction is either balancing towards the front stage of the balancing target or balancing towards the rear stage of the balancing target; The balancing mode is Boost mode discharge when the balancing direction is towards the front stage of the balancing target, and Buck mode discharge when the balancing direction is towards the rear stage of the balancing target.

[0008] On the other hand, step S2 includes: step S21: comparing the voltages of multiple individual cells within each battery pack to obtain the highest and lowest individual cell voltages within the pack, and comparing the average voltages within all packs to obtain the highest and lowest battery pack voltages; step S22: subtracting the highest and lowest individual cell voltages within the pack to obtain the intra-pack voltage difference, and subtracting the highest and lowest battery pack voltages to obtain the inter-pack voltage difference; step S23: determining the intra-pack voltage difference discrimination result based on the intra-pack voltage difference and a preset intra-pack voltage difference threshold, and determining the inter-pack voltage difference discrimination result based on the inter-pack voltage difference and a preset inter-pack voltage difference threshold; step S24: matching the intra-pack voltage difference discrimination result and the inter-pack voltage difference discrimination result to obtain the actual balancing strategy.

[0009] On the other hand, when the balancing strategy is intra-group balancing, step S3 includes: step A31: for the battery pack to be balanced, subtract the intra-group voltage difference threshold and the individual cell voltage to determine the individual cell deviation; step A32: select the battery cell with the largest individual cell deviation as the balancing target, and obtain the battery cell adjacent to the balancing target as the first target to be identified; step A33: compare the individual cell voltages of the first target to be identified, and take the smaller target as the actual target, and generate the corresponding balancing direction.

[0010] On the other hand, when the balancing strategy is inter-group balancing, step S3 includes: step B31: subtracting the inter-group voltage difference threshold and the intra-group average voltage to determine the battery pack deviation of each battery pack; step B32: selecting the battery pack with the largest battery pack deviation as the balancing target, and obtaining the battery pack adjacent to the balancing target as the second target to be identified; step B33: comparing the intra-group average voltage of the second target to be identified, and taking the smaller second target to be identified as the actual target, and generating the corresponding balancing direction.

[0011] On the other hand, when the balancing strategy is to balance between groups first and then within groups, steps S3 and S4 are first executed according to the process of balancing between groups, and then the process is reversed to before step S3, and steps S3 and S4 are executed according to the process of balancing within groups.

[0012] On the other hand, when the balancing strategy is intra-group balancing, step S4 includes: step A41: selecting the balancing switch between the balancing target and the associated target according to the balancing direction and turning it on; step A42: determining the discharge direction based on the balancing direction, then executing the corresponding balancing mode, and collecting the intra-group balancing voltage difference between the balancing target and the associated target in real time; step A43: comparing the intra-group balancing voltage difference with a preset intra-group balancing stop threshold to determine whether balancing is completed; if yes, stopping the current balancing process; if no, returning to step A42.

[0013] On the other hand, when the balancing strategy is inter-group balancing, step S4 includes: step B41: selecting the uppermost and lowermost balancing switches among the associated targets and turning them on; step B42: determining the discharge direction based on the balancing direction, then executing the corresponding balancing mode, and collecting the inter-group balancing voltage difference between the balancing target and the associated target in real time; step B43: comparing the inter-group balancing voltage difference with a preset inter-group balancing stop threshold to determine whether balancing has been completed; if yes, stopping the current balancing process; if no, returning to step B42.

[0014] On the other hand, it also includes an active balancing process, which includes: Step C1: Calculate the corresponding state of charge difference based on the state of charge values ​​of the battery pack and the individual battery cells, and proceed to step C2 when the state of charge difference reaches the state of charge balancing threshold; Step C2: Select the corresponding balancing strategy and perform balancing.

[0015] An active battery balancing system is provided for implementing the above-described active battery balancing method. The active battery balancing system includes: a data acquisition circuit, which is connected to each individual battery cell and acquires the voltage of each cell; a balancing switch, which is connected to the positive terminal of each individual battery cell and then to a subsequent switching circuit; and a processing module, which is connected to the data acquisition circuit, the balancing switch, and the switching circuit. The processing module acquires the individual battery cell voltage and controls the balancing switch and the switching circuit to perform balancing.

[0016] On the other hand, the acquisition circuit is implemented using an RC circuit.

[0017] The above technical solution has the following advantages or beneficial effects: Addressing the low efficiency of existing battery balancing methods that adjust charge and discharge of individual cells one by one, a voltage discrimination process for adjacent targets of the balancing target is introduced. This establishes the voltage gradient distribution relationship in the series circuit, thereby determining the energy flow direction that can be used for balancing. When the potential above the balancing target is high, a BUCK mode is used to reduce the voltage downwards to make the overall potential difference more uniform; when the potential below the balancing target is high, a Boost mode is used to increase the voltage upwards to make the overall potential difference more uniform, thus improving the overall balancing efficiency. Attached Figure Description

[0018] Embodiments of the invention will be described more fully with reference to the accompanying drawings. However, the drawings are for illustration and explanation only and do not constitute a limitation on the scope of the invention.

[0019] Figure 1 This is an overall schematic diagram of an embodiment of the present invention; Figure 2This is a schematic diagram of step S2 in an embodiment of the present invention; Figure 3 This is a schematic diagram of step A31 in an embodiment of the present invention; Figure 4 This is a schematic diagram of step A41 in an embodiment of the present invention; Figure 5 This is a schematic diagram of the equalization switch in an embodiment of the present invention; Figure 6 This is a schematic diagram of step B31 in an embodiment of the present invention; Figure 7 This is a schematic diagram of step B41 in an embodiment of the present invention; Figure 8 This is a schematic diagram of step C1 in an embodiment of the present invention; Figure 9 This is a schematic diagram of the system in an embodiment of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0022] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0023] This invention includes: a battery active balancing method based on BUCK-BOOST balancing, applicable to balancing circuits, the balancing circuit including balancing switches set for each battery cell; multiple battery cells connected in series to form a battery pack, the balancing switch located at the beginning of the battery pack serving as the upper balancing switch, and the balancing switch located at the end of the battery pack serving as the lower balancing switch; as shown... Figure 1As shown, the active battery balancing method includes: Step S1: Collecting the voltage of individual battery cells and calculating the average voltage within the battery pack; Step S2: Generating intra-pack voltage difference based on the individual battery cell voltage and inter-pack voltage difference based on the average voltage within the battery pack, and then determining at least one balancing strategy based on the intra-pack voltage difference and inter-pack voltage difference; The balancing strategy consists of intra-pack balancing, inter-pack balancing, and balancing between packs first and then intra-pack balancing; Step S3: Selecting the balancing target and associated targets based on the balancing strategy and voltage information, and determining the balancing direction; Step S4: Controlling the balancing switch of the associated targets according to the balancing direction and performing voltage balancing on the balancing targets using a specific balancing mode; The balancing target is a battery cell and / or battery pack; The associated targets are battery cells or battery packs located before and after the balancing target; The balancing direction is balancing towards the front stage of the balancing target or balancing towards the rear stage of the balancing target; The balancing mode is Boost mode discharge when the balancing direction is towards the front stage of the balancing target, and Buck mode discharge when the balancing direction is towards the rear stage of the balancing target.

[0024] Specifically, addressing the low efficiency of existing battery balancing methods that adjust charge and discharge of individual cells one by one, a voltage discrimination process for adjacent targets of the balancing target is introduced. This establishes the voltage gradient distribution relationship in the series circuit, thereby determining the energy flow direction that can be used for balancing. When the potential above the balancing target is high, a BUCK mode is used to reduce the voltage of all battery cells or battery packs on the lower side to make the overall potential difference closer to uniform. When the potential below the balancing target is high, a Boost mode is used to increase the voltage of all battery cells or battery packs on the upper side to make the overall potential difference closer to uniform, thus improving the overall balancing efficiency.

[0025] Specifically, the aforementioned active battery balancing method is primarily configured as a software implementation within a battery management system for controlling power battery packs, battery storage systems, and other equivalent equipment. In this system, at least a single battery pack is a loop formed by several battery cells connected in series, and there may be other external connections, such as parallel connections to a bus. Within the battery pack, an upper and lower relationship can be determined based on the potential direction. In the series loop, for any battery cell or battery pack, the one located at its high potential end is considered the upper side, and the one located at its low potential end is considered the lower side.

[0026] The battery pack here is an equivalent virtual concept, referring to a combination of a specific number of battery cells as a battery pack. Its purpose is to balance the entire battery pack to eliminate anomalies in the potential difference gradient when large voltage deviations occur. In actual products, this battery pack may or may not overlap with the battery module.

[0027] For each battery cell, an equalization switch is set up, which is connected to the subsequent switching circuit to establish a conduction loop for discharge. The equalization process is completed by discharging the higher voltage battery cell to the upper or lower side to eliminate the potential difference gradient.

[0028] In actual operation, the system makes judgments based on two dimensions: individual battery cells and battery packs.

[0029] The individual cell determination process addresses situations where the voltage of a single cell within a battery pack is significantly higher than that of other cells, triggering an intra-pack balancing process. The battery pack determination process addresses situations where the average voltage of the battery pack is significantly higher than that of other battery packs, triggering an inter-pack balancing process.

[0030] Since the battery pack releases more energy during the balancing process, when both individual battery cells and the battery pack need to be balanced, the energy of the battery pack that needs to be balanced is released first, and then the individual battery cells within the pack are further adjusted.

[0031] During the adjustment process, the main method used is to achieve efficient potential energy release by superimposing series voltages.

[0032] Taking intra-group balancing as an example, after determining the balancing target, the battery cell requiring balancing is used as the dividing point. Adjacent battery cells are extracted as associated targets. By comparing the voltages of these associated targets, the upper side is divided into a high-voltage zone or a low-voltage zone, and the lower side into a low-voltage zone or a high-voltage zone. Then, the high-voltage zone on one side discharges to the low-voltage zone via the balancing target as a whole. This is a discharge process from a high-voltage source to a low-voltage load; the voltage difference is the sum of the voltages of multiple batteries, not a small voltage difference of a single battery. The larger the voltage difference, the larger the balancing current and the faster the balancing speed, under the same loop resistance.

[0033] The equilibrium direction can be determined based on the different voltage distributions. When the upper side is a high-voltage region and the lower side is a low-voltage region, it indicates that the upper potential is high, and energy is suitable for flowing from top to bottom. In this case, the BUCK mode is used for voltage reduction discharge, and energy flows from the higher voltage side battery cell to the lower voltage side battery cell.

[0034] When the upper side is a low-voltage area and the lower side is a high-voltage area, it means that the lower potential is high and the energy is suitable to flow from bottom to top. The BOOST mode is used for boost charging, and the energy flows from the lower voltage side battery pack to the higher voltage side battery pack.

[0035] In both of the above cases, if battery cells with large voltage deviations identified during previous screening are inserted into the battery pack, the following situations may occur: Assuming that the upper side is determined to be a high-voltage area and the lower side to be a low-voltage area based on comparisons of related targets, the balancing direction is downward, and the balancing mode is BUCK mode, there are two possible voltage situations for the battery cells pointed to by the balancing target: If the battery cell targeted by the balancing target is the highest voltage cell, it is loaded in the series circuit of BUCK mode. Energy will flow from the high-voltage area above it and the battery cell itself to the low-voltage area below. Discharging the "purely low-voltage side" using the "high-voltage side including the balancing target" reduces the average voltage of the high-voltage side, solving the "bulge" problem. Increasing the average voltage of the low-voltage side solves the "sink" problem.

[0036] If the battery cell targeted by the balancing target is the lowest voltage cell, it is loaded in the series circuit of BUCK mode, and energy flows from the high-voltage area above it to the battery cell and the low-voltage area below it. Discharging the low-voltage side, which includes the balancing target, with the "pure high-voltage side" rapidly raises the overall voltage of the low-voltage side.

[0037] Similarly, assuming that the lower side is determined to be a high-voltage area and the upper side to be a low-voltage area based on the comparison of associated targets, the balancing direction is upward, and the balancing mode is BOOST mode, there are two possible voltage situations for the battery cells pointed to by the balancing target: If the battery cell targeted by the balancing target is the highest voltage cell, it is loaded in the series circuit of BOOST mode. Energy will flow from the high-voltage region below it and the battery cell itself to the low-voltage region above it. The "high-voltage side, including the balancing target," discharges onto the "purely low-voltage side." Lowering the average voltage of the high-voltage side solves the "bulge" problem. Raising the average voltage of the low-voltage side solves the "sink" problem.

[0038] If the battery cell targeted by the balancing target is the lowest voltage cell, it is loaded in the series circuit of BOOST mode, and energy flows from the high-voltage area below it to the battery cell and the low-voltage area above it. Discharging the low-voltage side, which includes the balancing target, with the "pure high-voltage side" rapidly raises the overall voltage of the low-voltage side.

[0039] When the situation becomes inter-group equilibrium, the above situation is the same, except that the object of comparison becomes the average voltage between groups, and during the discharge process, the discharge channel is established upward or downward with the battery pack as the smallest unit.

[0040] The above design allows us to identify the most anomalous potential energy during the equilibrium process, determine the direction of the potential energy gradient, and decide which direction the energy flows most smoothly. It selects the most efficient energy transfer path, maximizing efficiency and exhibiting characteristics of fast convergence and strong robustness.

[0041] Specifically, by prioritizing "group offsets" rather than "isolated points," ineffective equalization time is reduced. If only the highest and lowest individual cells are identified and equalized between them, and the highest point is an isolated point, energy is only transferred between the highest and lowest points, resulting in very small energy transfers each time. However, by calculating the offset value and judging the voltage of adjacent, related targets above and below, the system ensures that the high-voltage side charges the entire low-voltage side, instead of just the lowest one. This increases the rate of voltage drop by approximately 3 to 4 times.

[0042] Meanwhile, traditional SOC-based equalization requires precise knowledge of battery capacity, internal resistance, and OCV-SOC curves. These parameters change as the battery ages, leading to SOC estimation errors of 5-10%, resulting in mis-equalization. Relying solely on directly measured voltage and average voltage means the strategy's effectiveness remains largely unchanged after battery aging.

[0043] Furthermore, during the inter-group equalization process, individual cell voltage measurements may have noise and error of ±1~5mV. Directly comparing the voltages of two individual cells may lead to misjudgment. Using average voltages (Va, Vb, group average) disperses the measurement error, improving the signal-to-noise ratio by √N times (N is the number of cells participating in the averaging). The measurement error of a single cell is σ=5mV, with a misjudgment probability of approximately 5%. After averaging three cells, the average error σ / √3≈2.88mV, reducing the misjudgment probability to below 3%. When calculating the average of five cells, the impact of faults caused by single cell failures or transient interference is reduced to 20%, preventing the system from entering an incorrect equalization mode due to an abnormal measurement of a single cell.

[0044] In one embodiment, such as Figure 2 As shown, step S2 includes: Step S21: Comparing the voltages of multiple individual cells within each battery pack to obtain the highest and lowest individual cell voltages within the pack, and comparing the average voltages within all packs to obtain the highest and lowest battery pack voltages; Step S22: Subtracting the highest and lowest individual cell voltages within the pack to obtain the intra-pack voltage difference, and subtracting the highest and lowest battery pack voltages to obtain the inter-pack voltage difference; Step S23: Determining the intra-pack voltage difference by comparing it with a preset intra-pack voltage difference threshold to obtain an intra-pack voltage difference determination result, and determining the inter-pack voltage difference by comparing it with a preset inter-pack voltage difference threshold to obtain an inter-pack voltage difference determination result; Step S24: Matching the intra-pack voltage difference determination results and the inter-pack voltage difference determination results to obtain the actual balancing strategy.

[0045] Specifically, in order to achieve a better balancing effect, in this embodiment, the voltage of each individual battery cell is first collected by a separate acquisition circuit established within the battery pack. Then, based on the pre-configured battery number and battery grouping information, the voltage of each individual battery cell is mapped to the corresponding battery group, and the average voltage within the group is calculated by taking the average value.

[0046] Then, two processes are carried out: within-group comparison and between-group comparison.

[0047] Specifically, the intra-group comparison includes: for each battery pack, the individual cell voltages of multiple cells are measured. First, they are sorted by value to obtain the highest and lowest individual cell voltages within the group. Then, the highest and lowest individual cell voltages are subtracted directly to obtain the intra-group voltage difference. The intra-group voltage difference is then compared with a pre-calibrated intra-group voltage difference threshold to determine whether the voltage difference deviation within the battery pack exceeds normal operating conditions and requires equalization, thus forming the intra-group voltage difference judgment result.

[0048] Inter-group comparison includes: for each battery pack, the intra-group average voltage is measured, and the packs are first sorted by value to obtain the highest and lowest battery pack voltages. Then, the highest and lowest battery pack voltages are subtracted directly to obtain the inter-group voltage difference. The inter-group voltage difference is then compared with a pre-calibrated inter-group voltage difference threshold to determine whether the voltage difference deviation between multiple battery packs exceeds normal operating conditions and requires equalization, thus forming an inter-group voltage difference discrimination result.

[0049] Since there are three processing strategies in the actual equilibration process, it is also necessary to match the intra-group pressure difference judgment results and inter-group pressure difference judgment results to obtain the actual equilibration strategy, including performing only intra-group equilibration, performing only inter-group equilibration, and performing inter-group equilibration first and then intra-group equilibration. This is determined based on the triggering conditions of the intra-group pressure difference judgment results and inter-group pressure difference judgment results that are judged as "yes".

[0050] In one embodiment, when the equilibrium strategy is within-group equilibrium, such as Figure 3 As shown, step S3 includes: Step A31: For the battery pack to be balanced, subtract the voltage difference threshold within the pack and the voltage of each individual cell to determine the deviation of the individual cell; Step A32: Select the individual cell with the largest deviation as the balancing target, and obtain the individual cells adjacent to the balancing target as the first target to be identified; Step A33: Compare the individual cell voltages of the first target to be identified, and take the smaller first target to be identified as the actual target, and generate the corresponding balancing direction.

[0051] Specifically, for battery packs that require intra-pack balancing, the current cell voltage of each individual cell in the pack is first subtracted from the intra-pack voltage difference threshold, and the difference is used to determine the deviation of the individual cells.

[0052] It should be noted that in actual comparisons, inter-group equalization may have already been performed before intra-group equalization, therefore it is necessary to remeasure the individual cell voltages. The intra-group voltage difference threshold can be the polarization voltage calculated and calibrated under specific operating conditions, or the current intra-group average voltage can be directly selected as a reference.

[0053] Subsequently, the battery cell with the largest difference, i.e., the individual cell with the largest deviation, is taken as the balancing target. This balancing target could be the one with the highest voltage or the lowest voltage within the battery pack. At this point, the battery cells adjacent to the balancing target are further obtained as the first target to be judged and associated.

[0054] The voltage of individual cells of the first target to be identified is compared to determine whether the area above or below the target is a high-voltage or low-voltage region. A voltage distribution slope is then established to determine the energy flow direction as the corresponding balancing direction. Furthermore, in subsequent balancing processes, adjacent balancing switches or balancing switches of the target to which the balancing direction points are used as nodes for establishing pathways; therefore, the smaller of the first target to be identified is used as the actual target.

[0055] In one embodiment, when the equilibrium strategy is within-group equilibrium, such as Figure 4 As shown, step S4 includes: Step A41: Selecting the equalization switch between the equalization target and the associated target to conduct according to the equalization direction and the voltage comparison between the equalization target and the associated target; Step A42: Determining the discharge direction based on the equalization direction, then executing the corresponding equalization mode, and collecting the intra-group equalization voltage difference between the equalization target and the associated target in real time; Step A43: Comparing the intra-group equalization voltage difference with the preset intra-group equalization stop threshold to determine whether equalization is completed; if yes, stopping the current equalization process; if no, returning to step A42.

[0056] Specifically, after determining the actual balancing target, associated target, and balancing direction, the balancing switch between the balancing target and associated target is first selected and turned on according to the balancing direction, and the discharge direction is determined based on the balancing direction, and then the corresponding balancing mode is executed.

[0057] In reality, there are four scenarios: If the deviation between the average voltage within the group and the highest single cell voltage within the group is greater than the deviation between the average voltage within the group and the lowest single cell voltage within the group, and the upper voltage is greater than the lower voltage, the active balancing mode is set to BUCK mode. The main control circuit controls the balancing switch corresponding to the associated target on the lower side to be turned on, and the battery balancing target and the battery above the balancing target discharge the battery below the balancing target.

[0058] If the deviation between the average voltage within the group and the highest single cell voltage within the group is greater than the deviation between the average voltage within the group and the lowest single cell voltage within the group, and the upper voltage is less than the lower voltage, the main control circuit controls the active balancing mode to be enabled in BOOST mode. The main control circuit controls the balancing target's balancing switch to be turned on, and the battery balancing target and the battery located below the balancing target discharge the battery located above the balancing target.

[0059] The deviation between the average voltage within the group and the highest single cell voltage within the group is less than the deviation between the average voltage within the group and the lowest single cell voltage within the group, and the upper voltage is greater than the lower voltage, the active balancing mode is set to the BUCK mode, the main control circuit controls the balancing switch of the balancing target to be turned on, and the battery located above the balancing target discharges to the balancing target and the battery located below the balancing target.

[0060] The deviation between the average voltage within the group and the highest single cell voltage within the group is less than the deviation between the average voltage within the group and the lowest single cell voltage within the group, and the upper voltage is less than the lower voltage, the main control circuit controls the active balancing mode to be enabled in BOOST mode, the main control circuit controls the balancing switch corresponding to the associated target on the lower side to be turned on, and the battery located below the balancing target discharges to the balancing target and the battery located above the balancing target.

[0061] If the deviation between the average voltage within a group and the voltage of the highest-voltage individual cell in the group is greater than the deviation between the average voltage within a group and the voltage of the lowest-voltage individual cell in the group, the highest-voltage individual cell in the group is selected as the balancing target. The main control circuit controls the active balancing circuit to switch back and forth between BUCK mode and BOOST mode by judging the average voltage of batteries above the balancing target and the average voltage of batteries below the balancing target. The balancing target continuously discharges other batteries until the voltage difference with other batteries is less than the threshold preset by the main control circuit, and then the group balancing operation stops.

[0062] If the deviation between the average voltage within the group and the voltage of the highest-voltage individual cell in the group is less than the deviation between the average voltage within the group and the voltage of the lowest-voltage individual cell in the group, then the lowest-voltage individual cell in the group is selected as the balancing target. The main control circuit controls the active balancing circuit to switch back and forth between BUCK mode and BOOST mode by judging the average voltage of batteries above the balancing target and the average voltage of batteries below the balancing target. Other batteries continuously discharge to the balancing target until the voltage difference with other batteries is less than the threshold preset by the main control circuit, and then the group balancing operation stops.

[0063] Let's take two adjacent battery cells as an example. When the voltage of a single cell BAT1 is higher than the voltage of BAT2, and the preset equalization threshold is reached, the main control circuit controls the cell switch S1 to conduct, and generates a PWM drive with a certain frequency and duty cycle to turn on the polarity switch. At this time, the inductor stores or releases energy according to the different polarities of the polarity switch. For example... Figure 5 As shown, the entire equilibrium process is divided into the following three stages.

[0064] During the BAT1 discharge phase: the voltage of cell BAT1 is higher than that of cell BAT2, cell switch SW1 is turned on, polarity switch QA is turned on, and QB is turned off. Cell BAT1, cell switch SW1, inductor L, and polarity switch QA form a discharge circuit, and cell BAT1 discharges. During this period, inductor L continues to store energy. After time T1, the switch is turned off, and the inductor current reaches its peak value Ip.

[0065] BAT2 charging stage: Cell switch SW1 is turned on, polarity switch QA is turned off, and QB is turned on. Cell BAT2, cell switch SW1, inductor L, and polarity switch QB form a charging circuit. During this period, inductor L releases energy to charge cell BAT2. After time T2, the inductor current continuously decreases to IL.

[0066] Balancing phase: Cell switch SW1 is open, polarity switches QA and QB are open, and there is no current in the circuit. After multiple charge-discharge cycles, excess charge in cell BAT1 is transferred to cell BAT2 through inductor, completing the balancing of the batteries in the group.

[0067] In the actual control process, the control endpoint is determined based on the voltage comparison, including the intra-group equalization voltage difference between the equalization target and the associated target, and the intra-group equalization stop threshold is compared with the intra-group equalization voltage difference to determine whether equalization has been completed.

[0068] In one embodiment, when the equilibrium strategy is between-group equilibrium, such as Figure 6 As shown, step S3 includes: Step B31: Subtracting the inter-group voltage difference threshold and the intra-group average voltage to determine the battery group deviation of each battery group; Step B32: Selecting the battery group with the largest battery group deviation as the balancing target, and obtaining the battery group adjacent to the balancing target as the second target to be identified; Step B33: Comparing the intra-group average voltage of the second target to be identified, and taking the smaller second target to be identified as the actual target, and generating the corresponding balancing direction.

[0069] Specifically, for battery packs requiring inter-pack balancing, the average voltage within each pack is first subtracted from the inter-pack voltage difference threshold, and the difference is used to determine the deviation of a single cell. This inter-pack voltage difference threshold can be selected as the average of the average voltages within all packs.

[0070] Subsequently, the battery pack with the largest difference, i.e., the largest deviation of individual cells, is taken as the balancing target. This balancing target may be the battery pack with the largest average voltage within the group or the battery pack with the smallest average voltage within the group. At this point, the battery packs adjacent to the balancing target are further obtained as the second target to be judged and associated.

[0071] The average voltage within the group of the second target to be identified is compared to determine whether the area above or below the balancing target is a high-voltage or low-voltage zone. A voltage distribution slope is then established to determine the energy flow direction as the corresponding balancing direction. Furthermore, in the subsequent balancing process, adjacent balancing switches or balancing switches of the balancing target pointing to the balancing direction are used as nodes for path establishment; therefore, the smaller second target to be identified is taken as the actual balancing target.

[0072] In one embodiment, when the equilibrium strategy is between-group equilibrium, such as Figure 7 As shown, step S4 includes: Step B41: Select the uppermost and lowermost equalization switches of the selected equalization target or associated target to conduct according to the voltage comparison between the equalization target and the associated target; Step B42: Determine the discharge direction based on the equalization direction, then execute the corresponding equalization mode, and collect the inter-group equalization voltage difference between the equalization target and the associated target in real time; Step B43: Compare the inter-group equalization voltage difference with the preset inter-group equalization stop threshold to determine whether equalization is completed; if yes, stop the current equalization process; if no, return to step B42.

[0073] Specifically, after determining the equilibrium objective, a comparison is made between the equilibrium objective and the related objectives to generate four scenarios: The target group's average voltage is higher than the average voltage of all groups, and the upper voltage is greater than the lower voltage. The active balancing mode is set to enable the inter-group BUCK mode. The main control circuit controls the target group's switch S1 to turn on and controls the lower group's switch S4 to turn on, so that the target group's battery discharges to the lower group's battery.

[0074] The target group's average voltage is higher than the average voltage of all groups, and the upper voltage is lower than the lower voltage. The main control circuit controls the active balancing mode to enable the inter-group BOOST mode. The main control circuit controls the target group's switch S4 to be turned on and controls the upper group's switch S1 to be turned on, so that the target group's battery discharges to the upper battery group's battery.

[0075] The target group's average voltage is lower than the average voltage of all groups, and the upper voltage is greater than the lower voltage. The active balancing mode is set to enable the inter-group BUCK mode. The main control circuit controls the target group's switch S4 to turn on and controls the upper group's switch S1 to turn on, allowing the upper battery group's battery to discharge to the target battery group's battery.

[0076] The average voltage of the target group is lower than the average voltage of all groups, and the upper voltage is less than the lower voltage. The main control circuit controls the active balancing mode to enable the inter-group BOOST mode. The main control circuit controls the switch S1 of the target group to be turned on and controls the switch S4 of the lower group of the target group to be turned on, so that the battery of the upper battery group of the target group discharges to the battery of the target battery group.

[0077] The target group's average voltage is higher than the average voltage of all groups. The main control circuit determines the average voltage of the batteries above and below the average voltage of the batteries below, and controls the active balancing circuit to switch back and forth between BUCK mode and BOOST mode. In both working modes, the target group continuously discharges the batteries in the upper or lower group until the voltage difference between the batteries in the group is less than the inter-group balancing threshold preset by the main control circuit, and then stops the inter-group balancing operation.

[0078] If the average voltage of the target group is lower than the average voltage of all groups, the main control circuit determines the average voltage of the batteries above and below the average voltage of the batteries below the target group, and controls the active balancing circuit to switch back and forth between BUCK mode and BOOST mode. In both working modes, the upper or lower group of the target group continuously discharges the target group's batteries until the voltage difference between the batteries in the groups is less than the inter-group balancing threshold preset by the main control circuit, and then the inter-group balancing work stops.

[0079] In one embodiment, when the balancing strategy is to balance between groups first and then within groups, steps S3 and S4 are executed first according to the inter-group balancing process, and then the process is reversed to before step S3, and steps S3 and S4 are executed according to the intra-group balancing process.

[0080] Specifically, to achieve better balancing efficiency, when the balancing strategy of first between groups and then within groups is triggered, the inter-group balancing is executed first to trigger a large-scale balancing process, and then the process returns to step S3 and the individual cell voltage is remeasured to execute intra-group balancing, thereby improving balancing efficiency through more energy flow.

[0081] In one embodiment, an active balancing process is also included, such as Figure 8 As shown, the active balancing process includes: Step C1: Calculate the corresponding difference in state of charge (SOC) values ​​based on the SOC values ​​of the battery pack and individual battery cells, and proceed to step C2 when the difference in SOC values ​​reaches the SOC balancing threshold; Step C2: Select the corresponding balancing strategy and perform balancing.

[0082] Specifically, to achieve a better balancing process, this embodiment also uses the SOC value as a balancing variable. Specifically, the controller acquires the state of charge (SOC) values ​​of the battery pack and individual battery cells in real time, and calculates the difference in SOC values ​​between individual cells within the battery pack and between battery packs as references. Balancing begins when the difference in SOC values ​​reaches the SOC balancing threshold.

[0083] In this step, the equilibration strategy controls the energy flow process based on the state of charge value.

[0084] When the SOC difference between the battery pack or individual cells reaches the equalization activation threshold, the upper-level main controller sends an equalization activation command and strategy. When the SOC difference between the battery pack or individual cells is less than the deactivation threshold, the upper-level main controller sends an equalization stop command.

[0085] The upper-level main controller calculates the difference between the highest and lowest SOC of individual units within the group in real time. When the absolute value of the SOC difference exceeds the preset SOC activation threshold within the group... At that time, enable group balancing.

[0086]

[0087] In the formula, The highest SOC among the monomers in the group. The lowest SOC among the monomers in the group. Enable the threshold for SOC within the group.

[0088] The upper-level main controller calculates the average SOC of each individual battery in real time, and calculates the difference between the highest and lowest average SOC of the group. When the absolute value of the SOC difference exceeds the preset inter-group SOC threshold, the controller will trigger a new SOC threshold. At that time, inter-group balancing is enabled.

[0089] ; In the formula, The highest average SOC for the group. This represents the SOC value of the nth battery cell in the group. The lowest average SOC of the group, This represents the SOC value of the i-th battery cell in the group. Enable the threshold for inter-group SOC.

[0090] The actual equilibration process follows the previous process of between-group equilibration, within-group equilibration, and then between-group and within-group equilibration.

[0091] A battery active balancing system for implementing the above-described battery active balancing method, such as... Figure 9 As shown, the active battery balancing system includes: a data acquisition circuit 101, which is connected to each individual battery cell 102 and acquires the voltage of each cell; a balancing switch 103, which is connected to the positive terminal of each individual battery cell 102 and then to a subsequent switching circuit 104; and a processing module 105, which is connected to the data acquisition circuit 101, the balancing switch 103, and the switching circuit 104. The processing module 105 acquires the individual battery voltage and controls the balancing switch and the switching circuit to perform balancing. The data acquisition circuit 101 is implemented using an RC circuit.

[0092] Specifically, to achieve the above processing, in this embodiment, a data acquisition circuit 101 and an equalization switch 103 are respectively set for each battery cell to acquire the cell voltage and establish a loop to the switching circuit 104. The switching circuit 104 corresponds to... Figure 5 The inductor and polarity switch are part of the circuit. The processing module 105 is implemented based on the controller.

[0093] In practical implementation, the overall circuit architecture includes a power supply circuit, a main control circuit, a data acquisition circuit, a communication circuit, and an equalization circuit. The power supply circuit converts the input power to 5V via a DC-DC converter, powering the communication circuit, main control circuit, and equalization circuit. The main control circuit contains an MCU, whose functions are: 1) controlling the operation of the data acquisition circuit and collecting the acquisition results; 2) controlling the operation of the equalization circuit; and 3) communicating with external circuits through the communication circuit. The data acquisition circuit collects voltage and temperature information from multiple battery cells; the equalization circuit equalizes the multiple battery cells. The individual cell voltage acquisition circuit, responding to the control commands of the main controller MCU, collects the operating voltage and temperature of each individual cell in the battery pack in real time. An RC circuit is designed between each individual cell and the acquisition circuit, with resistors and capacitors designed to be 1KΩ / 100nF. This RC circuit reduces the impact of voltage fluctuations on sampling accuracy and also addresses the potential damage to the acquisition circuit during hot-swapping of the connector between the cell and the control board. A single acquisition circuit can collect voltage and temperature data from up to 16 individual cells. The data acquisition circuit transmits the voltage and temperature values ​​of the individual battery cells to the main control circuit via communication with the MCU circuit. Specifically, the first and last acquisition circuits each use a bridge chip to convert their ISOSPI interfaces to four-wire SPI interfaces before communicating with the main control circuit. This forms a ring communication circuit, ensuring that data from all battery cells can still be acquired even if a communication failure occurs in one of the intermediate circuits, further improving the reliability of the acquisition circuit. It is important to note that the power supply design of the acquisition circuit is independent of the sampling channel. This design ensures an acquisition error of ≤±3mV for individual cell voltages within a temperature range of -40℃ to 100℃.

[0094] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A battery active balancing method based on BUCK-BOOST balancing, characterized in that, This is applicable to an equalization circuit, which includes an equalization switch set for each battery cell; multiple battery cells are connected in series to form a battery pack, with the equalization switch at the beginning of the battery pack serving as the upper equalization switch and the equalization switch at the end of the battery pack serving as the lower equalization switch. The active battery balancing method includes: Step S1: Collecting the voltage of each individual battery cell and calculating the average voltage within the battery pack; Step S2: Generating an intra-pack voltage difference based on the individual battery cell voltage in each battery pack, and generating an inter-pack voltage difference based on the average voltage within the pack, and then determining at least one balancing strategy based on the intra-pack voltage difference and the inter-pack voltage difference; the balancing strategy consists of intra-pack balancing, inter-pack balancing, and inter-pack balancing followed by intra-pack balancing; Step S3: Selecting a balancing target and associated targets related to the balancing target based on the balancing strategy and voltage information, and determining the balancing direction; Step S4: Determining the balancing direction based on the balancing strategy... The equalization switch controlling the associated target is activated, and a specific equalization mode is used to perform voltage equalization on the equalization target; the equalization target is the battery cell and / or the battery pack; the associated target is the battery cell or the battery pack located before and after the equalization target; the equalization direction is equalization towards the front stage of the equalization target or equalization towards the back stage of the equalization target; the equalization mode is Boost mode discharge when the equalization direction is equalization towards the front stage of the equalization target, and Buck mode discharge when the equalization direction is equalization towards the back stage of the equalization target.

2. The battery active balancing method according to claim 1, characterized in that, Step S2 includes: Step S21: Comparing the voltages of multiple individual cells within each battery pack to obtain the highest and lowest individual cell voltages within the pack, and comparing the average voltages within all packs to obtain the highest and lowest battery pack voltages; Step S22: Subtracting the highest and lowest individual cell voltages within the pack to obtain the intra-pack voltage difference, and subtracting the highest and lowest battery pack voltages to obtain the inter-pack voltage difference; Step S23: Determining the intra-pack voltage difference by comparing the intra-pack voltage difference with a preset intra-pack voltage difference threshold to obtain an intra-pack voltage difference determination result, and determining the inter-pack voltage difference by comparing the inter-pack voltage difference with a preset inter-pack voltage difference threshold to obtain an inter-pack voltage difference determination result; Step S24: Matching the intra-pack voltage difference determination result and the inter-pack voltage difference determination result to obtain the actual balancing strategy.

3. The battery active balancing method according to claim 2, characterized in that, When the balancing strategy is intra-group balancing, step S3 includes: Step A31: For the battery pack to be balanced, subtract the intra-group voltage difference threshold and the individual cell voltage to determine the individual cell deviation; Step A32: Select the battery cell with the largest individual cell deviation as the balancing target, and obtain the battery cell adjacent to the balancing target as the first target to be identified; Step A33: Compare the individual cell voltages of the first target to be identified, and take the smaller first target to be identified as the actual target, and generate the corresponding balancing direction.

4. The battery active balancing method according to claim 2, characterized in that, When the balancing strategy is inter-group balancing, step S3 includes: step B31: subtracting the inter-group voltage difference threshold and the intra-group average voltage to determine the battery pack deviation of each battery pack; step B32: selecting the battery pack with the largest deviation as the balancing target, and obtaining the battery pack adjacent to the balancing target as the second target to be identified; step B33: comparing the intra-group average voltage of the second target to be identified, and taking the smaller second target as the actual target, and generating the corresponding balancing direction.

5. The battery active balancing method according to claim 1, characterized in that, When the balancing strategy is to balance between groups first and then within groups, steps S3 and S4 are executed first according to the inter-group balancing process, and then the process is reversed to before step S3, and steps S3 and S4 are executed according to the intra-group balancing process.

6. The active battery balancing method according to claim 1, characterized in that, When the balancing strategy is intra-group balancing, step S4 includes: Step A41: Selecting the corresponding balancing switch to conduct according to the balancing direction and the voltage comparison between the balancing target and the associated target; Step A42: Determining the discharge direction based on the balancing direction, then executing the corresponding balancing mode, and collecting the intra-group balancing voltage difference between the balancing target and the associated target in real time; Step A43: Comparing the intra-group balancing voltage difference with a preset intra-group balancing stop threshold to determine whether balancing is completed; if yes, stopping the current balancing process; if no, returning to step A42.

7. The active battery balancing method according to claim 1, characterized in that, When the balancing strategy is inter-group balancing, step S4 includes: Step B41: Selecting the uppermost and lowermost balancing switches of the balancing target or the associated target to conduct according to the voltage comparison between the balancing target and the associated target; Step B42: Determining the discharge direction based on the balancing direction, then executing the corresponding balancing mode, and collecting the inter-group balancing voltage difference between the balancing target and the associated target in real time; Step B43: Comparing the inter-group balancing voltage difference with a preset inter-group balancing stop threshold to determine whether balancing is completed; if yes, stopping the current balancing process; if no, returning to step B42.

8. The active battery balancing method according to claim 1, characterized in that, It also includes an active balancing process, which includes: Step C1: Calculate the corresponding state of charge difference based on the state of charge values ​​of the battery pack and the individual battery cells, and proceed to step C2 when the state of charge difference reaches the state of charge balancing threshold; Step C2: Select the corresponding balancing strategy and perform balancing.

9. A battery active balancing system, characterized in that, For implementing the active battery balancing method as described in any one of claims 1-8, the active battery balancing system comprises: a data acquisition circuit, which is connected to each individual battery cell and acquires the voltage of each cell; a balancing switch, which is connected to the positive terminal of each individual battery cell and connected to a subsequent switching circuit; and a processing module, which is connected to the data acquisition circuit, the balancing switch, and the switching circuit; the processing module acquires the voltage of each individual battery cell and controls the balancing switch and the switching circuit to perform balancing.

10. The battery active balancing system according to claim 9, characterized in that, The acquisition circuit is implemented using an RC circuit.

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