A method and system for charge equalization of a battery pack

Abstract

The application provides a charge equalization method and system for a battery pack. The method comprises: applying a wideband sweep signal to a single cell and collecting impedance responses of the cell at different frequencies to obtain an AC impedance spectrum of the cell when the battery pack is in a charging intermittent period or a static stage; extracting an aging quantitative parameter representing a current aging state of the cell from a preset frequency interval of the AC impedance spectrum; correcting a pre-stored harmonic-impedance distribution of the cell on-line based on the extracted aging quantitative parameter and a pre-stored aging correction model to generate a real-time harmonic-impedance mapping relationship matching the current aging state of the cell; and adjusting a harmonic of a charging energy signal applied to the battery pack according to the real-time harmonic-impedance mapping relationship to realize charge equalization among the cells. The application dynamically corrects the harmonic-impedance mapping relationship by on-line extraction of the cell aging parameter, realizes charge equalization of the battery pack throughout the whole life cycle, and solves the problem of mismatch between the pre-stored distribution and the aging state.

Description

Technical Field

[0001] This invention relates to the field of battery management systems, and more specifically to a charge balancing method and system for battery packs. Background Technology

[0002] Rechargeable electrochemical battery packs are the core power source for various new energy devices and portable electronic devices. They are typically composed of dozens to hundreds of cells connected in series, parallel, or a combination of series and parallel to meet the device's voltage and capacity requirements. The battery pack's performance, cycle life, and operational safety depend not only on the electrochemical characteristics of the individual cells but also on the consistency of the charge state among the cells within the pack. In actual use, due to objective factors such as cell manufacturing process tolerances, differences in operating temperature, uneven distribution of charging and discharging current, different cell self-discharge rates, and differences in aging after long-term cycling, the charge state of the cells within the battery pack is prone to imbalance.

[0003] Battery cell charge imbalance can trigger a series of chain reactions: during charging, cells with a high state of charge tend to reach the cutoff voltage prematurely, forcing the battery pack to terminate charging, while cells with a low state of charge cannot be fully charged, resulting in a significant reduction in the usable capacity of the battery pack; during discharging, cells with a low state of charge are prone to premature over-discharge, which not only accelerates the failure of the active materials inside the cell but may also lead to safety accidents such as lithium plating and thermal runaway. To solve the problem of battery pack cell charge imbalance, in recent years, battery pack charge balancing technology based on cell harmonic-impedance characteristics has become a research hotspot. For example, by utilizing the characteristic that the impedance of a cell changes with the harmonic frequency of the charging signal, the harmonic-impedance distribution of the cells is pre-stored, the harmonic frequency of the corresponding cell's minimum impedance value is identified, and by adjusting the harmonics of the charging energy signal, cells with a low state of charge preferentially absorb charging energy, thereby achieving charge balance between cells.

[0004] However, in practical engineering applications, the aforementioned equalization technology based on harmonic-impedance characteristics has a core flaw: it is difficult to adapt to the aging state of the battery cell throughout its entire life cycle. Specifically, this is manifested in the following ways:

[0005] 1) There will be a mismatch between the pre-stored harmonic impedance distribution and the actual state of the battery cell. Specifically, during long-term charge and discharge cycles, the battery cell will experience aging phenomena such as increased ohmic impedance, thickening of the solid electrolyte interphase (SEI) film, and failure of active materials. Its harmonic impedance characteristics will drift significantly. However, the pre-stored harmonic impedance distribution before leaving the factory is a fixed value and cannot be dynamically adjusted with the aging state of the battery cell. This results in a serious mismatch between the harmonic frequency of the charging signal and the actual minimum impedance frequency of the battery cell, and the equalization accuracy will continue to deteriorate with the increase of the number of cycles.

[0006] 2) Differential aging of series and parallel cells can exacerbate the failure of equalization. Specifically, the operating environment (temperature, current) of each cell in a series and parallel battery pack is naturally different, resulting in inconsistent aging rates and significant differences in impedance drift between different cells. A uniform pre-stored harmonic-impedance distribution cannot achieve personalized adaptation at the individual cell level, further amplifying the charge imbalance between cells.

[0007] 3) Harmonic mismatch can lead to secondary safety and aging issues. Specifically, when the harmonic frequency is mismatched with the actual minimum impedance frequency of the cell, additional impedance is introduced inside the cell, causing the cell to heat up more during charging. This heating, in turn, accelerates cell aging, easily creating a vicious cycle of "aging-mismatch-more severe aging." At the same time, the additional impedance reduces the energy absorption efficiency of the cell, easily leading to undercharging of some cells and overcharging of others, significantly increasing the safety risk of thermal runaway in the battery pack.

[0008] To address the aforementioned technical shortcomings, there is an urgent need to develop a method and system that can dynamically correct harmonic-impedance distribution as the battery cell ages and achieve high-precision charge balancing throughout the battery pack's entire lifecycle. Summary of the Invention

[0009] Based on the technical problems described above, this invention provides a charge balancing method and system for battery packs. By extracting the aging quantification parameters of the battery cells online and dynamically correcting the harmonic-impedance mapping relationship, combined with a differentiated balancing strategy based on aging stages and a periodic calibration update mechanism, high-precision charge balancing is achieved throughout the entire life cycle of the battery pack. At the same time, it delays cell aging, reduces heat generation and the risk of overcharging and over-discharging. Moreover, this invention only requires adding a software algorithm module to the existing hardware architecture without adding any new core hardware, resulting in low modification costs, strong compatibility, and easy large-scale application.

[0010] Specifically, according to one aspect of the present invention, a charge balancing method for a battery pack is provided, the battery pack comprising a plurality of electrochemical cells connected in series and / or in parallel, the method comprising the following steps:

[0011] S1. When the battery pack is in the charging interval or resting stage, a wideband sweep frequency signal is applied to a single cell through an impedance measurement circuit, and the impedance response of the cell at different frequencies is collected to obtain the AC impedance spectrum of the cell.

[0012] S2, extract at least one aging quantization parameter characterizing the current aging state of the cell from the preset frequency range of the AC impedance spectrum;

[0013] S3. Based on the extracted aging quantification parameters and the pre-stored aging correction model, the pre-stored cell harmonic-impedance distribution is corrected online to generate a real-time harmonic-impedance mapping relationship that matches the current aging state of the cell.

[0014] S4. Based on the real-time harmonic-impedance mapping relationship, adjust the harmonics of the charging energy signal applied to the battery pack to achieve charge balance between cells.

[0015] According to certain preferred embodiments of the present invention, the aging quantization parameters include the high-frequency ohmic impedance increment ΔR0 extracted from the real part of the high-frequency impedance of the AC impedance spectrum, and / or the SEI film impedance increment ΔR extracted from the real part of the mid-frequency impedance of the AC impedance spectrum. SEI .

[0016] According to certain preferred embodiments of the present invention, the high-frequency band is a frequency range of 1 kHz to 10 kHz, and the mid-frequency band is a frequency range of 1 Hz to less than 1 kHz.

[0017] According to certain preferred embodiments of the present invention, the pre-stored aging correction model is pre-established in the following manner:

[0018] Full life cycle aging test was conducted on the same type of battery cells, and impedance spectrum data of the battery cells were collected at different aging stages;

[0019] A full life cycle aging calibration database is constructed based on the collected impedance spectrum data. The calibration database stores the aging quantification parameters of cells at different aging stages and the corresponding measured minimum impedance frequency.

[0020] Based on the calibration database, an aging correction model is established with the aging quantification parameters as input and the minimum impedance frequency correction coefficient as output.

[0021] According to certain preferred embodiments of the present invention, the aging correction model is a linear correction model, a polynomial correction model, or a neural network correction model obtained by fitting the calibration database.

[0022] According to certain preferred embodiments of the present invention, the method further includes classifying the battery cell into multiple different aging levels based on the proportion of the high-frequency ohmic impedance increment ΔR0 relative to the initial factory value, and matching differentiated charge balance control strategies to the battery cells of different aging levels.

[0023] According to certain preferred embodiments of the present invention, classifying the battery cells into multiple different aging grades includes classifying the battery cells as follows:

[0024] Healthy battery cells have a high-frequency impedance increment ΔR0 that is less than 5% of the initial factory value.

[0025] For mildly aged battery cells, the increase in ohmic impedance ΔR0 in the high-frequency band is greater than or equal to 5% of the initial factory value and less than 20% of the initial factory value.

[0026] For severely aged battery cells, the increase in ohmic impedance ΔR0 in the high-frequency band is greater than or equal to 20% of the initial value at the factory.

[0027] According to certain preferred embodiments of the present invention, the differentiated charge balance control strategy for matching cells with different aging levels includes:

[0028] For healthy battery cells, the harmonics of the charging energy signal are controlled to match its minimum impedance frequency based on the real-time harmonic-impedance mapping relationship.

[0029] For mildly aged battery cells, the adjustment range of harmonic frequencies is narrowed, and the iteration frequency of impedance measurement and harmonic adjustment is increased.

[0030] For severely aged battery cells, a low-amplitude reverse harmonic discharge pulse is superimposed on the harmonic adjustment based on the real-time harmonic-impedance mapping relationship.

[0031] According to certain preferred embodiments of the present invention, the amplitude of the reverse harmonic discharge pulse is 5% to 10% of the rated charging current of the cell, and its frequency matches the real-time minimum impedance frequency of the heavily aged cell.

[0032] According to certain preferred embodiments of the invention, the differentiated charge balance control strategy for heavily aged cells further includes limiting their maximum charging current.

[0033] According to certain preferred embodiments of the present invention, the method further includes a periodic calibration and update step: after each preset number of charge-discharge cycles, a complete wideband frequency sweep is performed on all cells in the battery pack to update the aging quantization parameters of each cell and the parameters of the aging correction model.

[0034] According to certain preferred embodiments of the present invention, the preset number of cycles is 100 charge-discharge cycles.

[0035] Using the method of this invention, the aging quantification parameters (ΔR0, ΔR) of the battery cell are extracted online. SEIThis invention combines an aging correction model to dynamically correct harmonic-impedance distribution, generating a real-time harmonic-impedance mapping relationship that matches the current aging state of the cell. This effectively solves the defect in existing technologies where the pre-stored fixed distribution is mismatched with the cell's aging state, ensuring that the charge balance accuracy of the battery pack remains stable throughout its entire life cycle. Furthermore, this invention performs aging quantification parameter extraction and harmonic-impedance distribution correction for individual cells, achieving personalized balance control at the single-cell level. This adapts to the differentiated aging rates and impedance drift levels of cells within a series-parallel battery pack, avoiding balance errors caused by uniform control and significantly improving the balance consistency of multi-cell battery packs. In addition, it classifies cells into three levels based on their aging degree and matches them with differentiated balance strategies. Healthy cells prioritize charging speed, lightly aged cells enhance balance accuracy, and heavily aged cells are superimposed with reverse pulse discharge and current limiting. This not only meets the usage needs of cells in different aging states but also avoids the overcharging risk of heavily aged cells, while reducing heat generation introduced by additional impedance, breaking the vicious cycle of "aging-mismatch-more severe aging."

[0036] According to another aspect of the present invention, a charge balancing system for a battery pack is provided, comprising a charging signal shaping circuit, an impedance measurement circuit, and a controller in communication with the battery pack, wherein,

[0037] The impedance measurement circuit includes an aging feature extraction unit, which is configured to apply a wideband sweep frequency signal to a single cell and collect the impedance response of the cell at different frequencies when the battery pack is in a charging intermittent period or a resting stage, so as to obtain the AC impedance spectrum of the cell and extract at least one aging quantization parameter characterizing the current aging state of the cell from a preset frequency range of the AC impedance spectrum.

[0038] The controller is used to control the charging signal shaping circuit to adjust the harmonics of the charging energy signal based on the harmonic-impedance mapping relationship of the battery cell, so as to achieve charge balance between the battery cells. The controller includes an online harmonic distribution self-correction module, which is used to correct the pre-stored harmonic-impedance distribution of the battery cell online based on the aging quantization parameters and the pre-stored aging correction model, and generate a real-time harmonic-impedance mapping relationship that matches the current aging state of the battery cell.

[0039] According to certain preferred embodiments of the present invention, the controller further includes an aging grading differentiation control module, used to divide the battery cell into multiple different aging levels according to the aging quantification parameters, and to match differentiated charge balance control strategies for battery cells of different aging levels.

[0040] According to certain preferred embodiments of the present invention, the controller further includes a periodic calibration update module, which triggers the impedance measurement circuit to perform a complete wideband frequency sweep on all cells in the battery pack after each preset number of charge-discharge cycles, so as to update the aging quantization parameters of each cell and the parameters of the aging correction model.

[0041] According to certain preferred embodiments of the present invention, the aging feature extraction unit comprises:

[0042] A wideband sweep frequency signal generation subunit is used to generate a sweep frequency signal within a predetermined frequency range;

[0043] Impedance spectrum acquisition subunit is used to acquire the voltage and current response signals of the battery cell at different frequencies;

[0044] The aging parameter calculation subunit is used to calculate the AC impedance spectrum of the battery cell based on the collected impedance response, and extract quantitative parameters characterizing the aging state of the battery cell from a preset frequency range.

[0045] The charge balancing system of the battery pack of the present invention only requires the integration of an aging feature extraction unit in the impedance measurement circuit and the development of software function modules in the controller on the basis of the existing harmonic-impedance characteristic-based balancing system. No new core power devices or other hardware are required, resulting in low modification costs. It can be directly adapted to various existing lithium-ion, sodium-ion and other electrochemical battery packs, as well as various application scenarios such as electric vehicles, energy storage systems, and portable electronic devices. It has strong compatibility and is easy to scale up production and apply. Attached Figure Description

[0046] The accompanying drawings are provided in this specification to more clearly explain the technical solutions of the present invention; however, the art is not limited thereto. The flowcharts shown in the drawings are merely illustrative and do not necessarily include all contents and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be decomposed, combined, or partially merged, so the actual execution order may change according to the actual situation.

[0047] Figure 1 This is a schematic flowchart of a charge balancing method for a battery pack according to one embodiment of the present invention;

[0048] Figure 2 This is a flowchart illustrating an aging-stage differentiated charge balance control strategy according to one embodiment of the present invention.

[0049] Figure 3 This is a block diagram of the charge balancing system of a battery pack according to one embodiment of the present invention.

[0050] Explanation of reference numerals in the attached figures:

[0051] S1-S4. Flowchart of the battery pack charge balancing method; 20. Flowchart of the aging-stage differentiated charge balancing control strategy; 30. Battery pack charge balancing system; 301. Power supply; 302. Charging signal shaping circuit; 303. Battery pack; 304. Impedance measurement circuit; 305. Aging feature extraction unit; 305a. Wideband sweep frequency signal generation subunit; 305b. Impedance spectrum acquisition subunit; 305c. Aging parameter calculation subunit; 306. Controller; 306a. Harmonic distribution online self-correction module; 306b. Aging-stage differentiated control module; 306c. Periodic calibration update module. Detailed Implementation

[0052] 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, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0053] Example 1

[0054] like Figure 1 As shown, the charge balancing method for the battery pack of the present invention includes the following main steps:

[0055] S1. When the battery pack is in the charging interval or resting stage, a wideband sweep frequency signal is applied to a single cell through an impedance measurement circuit, and the impedance response of the cell at different frequencies is collected to obtain the AC impedance spectrum of the cell.

[0056] S2, extract at least one aging quantization parameter characterizing the current aging state of the cell from the preset frequency range of the AC impedance spectrum;

[0057] S3. Based on the extracted aging quantification parameters and the pre-stored aging correction model, the pre-stored cell harmonic-impedance distribution is corrected online to generate a real-time harmonic-impedance mapping relationship that matches the current aging state of the cell.

[0058] S4. Based on the real-time harmonic-impedance mapping relationship, adjust the harmonics of the charging energy signal applied to the battery pack to achieve charge balance between cells.

[0059] For example, it can be applied to a battery pack consisting of 16 lithium iron phosphate cells connected in series, with a cell rated capacity of 50Ah, a rated voltage of 3.2V, a battery pack nominal voltage of 51.2V, and a single cell initial ohmic impedance R at the factory. 0initial =8mΩ, initial SEI film impedance R SEI-initial=15mΩ, initial minimum impedance frequency f min-initial =1kHz.

[0060] First, during the pre-calibration stage before the battery leaves the factory, a full life cycle aging test is conducted on cells of the same model to collect impedance spectrum data of the cells at different aging stages. The specific steps are as follows:

[0061] 1) Full life cycle aging test and data acquisition. Test conditions were: 25℃ ambient temperature, charge-discharge cycle at 1C rate, with a full-band AC impedance spectrum test performed on the cell every 50 cycles, sweeping from 10kHz to 0.01Hz. The ohmic impedance R0 and SEI film impedance R of the cell were recorded at different cycle numbers. SEI and the corresponding minimum impedance frequency f min Calculate the impedance increment ΔR0 relative to the factory initial value based on the measured value: ΔR0 = (R0 - R 0initial ) / R 0initial、 ΔR SEI =(R SEI -R SEI-initial ) / R SEI-initial， A full lifecycle aging calibration database was constructed, which contains the correspondence between "aging quantification parameters - measured minimum impedance frequency", as shown in Table 1 below.

[0062]

[0063] (2) Pre-stored harmonic-impedance distribution. Apply a wideband sweep signal from 0.01Hz to 10kHz to a brand new battery cell of the same model, collect the AC impedance modulus of the battery cell at each harmonic frequency, and perform nonlinear curve fitting on the frequency-impedance data by Gaussian fitting + polynomial fitting. Extract the frequency-impedance data of 7 key frequency points (0.01Hz, 1Hz, 100Hz, 1kHz, 5kHz, and 10kHz) to form a simplified table. The fitted curve model and the key frequency point data table together serve as the pre-stored harmonic-impedance distribution of the battery cell at the factory and are pre-stored in the storage unit of the controller.

[0064] (3) Establish an aging correction model. Based on the full life cycle aging calibration database, an aging correction model is established using bivariate polynomial fitting. The model expression is:

[0065] Where K is the minimum impedance frequency f min The correction factor, f min-real = K·f min-initial f min-initialThe initial minimum impedance frequency is pre-stored at the factory. a0 to a5 are model coefficients obtained through least squares fitting, calibrated after testing to a0=1.02, a1=0.08, a2=0.05, a3=0.02, a4=0.01, and a5=0.015. The full lifecycle aging calibration database, aging correction model, and factory-pre-stored harmonic-impedance distribution are pre-stored in the controller's storage unit.

[0066] Secondly, during the online operation phase, real-time charge balance control is implemented.

[0067] During battery pack charging, the following operations are performed during the pulse intervals (50-millisecond interval windows every 10 seconds) of the constant current charging phase:

[0068] (1) Acquisition of AC impedance spectrum. The aging feature extraction unit sequentially applies a wideband sweep signal from 10kHz to 0.01Hz to the 16 cells, acquires the impedance response of each cell at different frequencies, and calculates the AC impedance spectrum of the cells.

[0069] (2) Extracting aging quantization parameters. Extract the current ohmic impedance R0 from the real part of the impedance spectrum in the high-frequency band from 1kHz to 10kHz, and calculate the increment ΔR0 relative to the initial factory value; extract the current SEI film impedance R from the real part of the impedance spectrum in the mid-frequency band from 1Hz to 1kHz. SEI Calculate the increment ΔR relative to the initial factory value. SEI Repeat the above process to extract the aging characteristic parameters of all 16 battery cells in sequence, and transmit the parameters to the controller's online harmonic distribution self-correction module in real time.

[0070] (3) Online correction of harmonic-impedance distribution. The online self-correction module for harmonic distribution will extract the ΔR0 and ΔR of each cell in real time. SEI Input the pre-stored aging correction model respectively, and calculate the current f of each cell. min The correction factor K is used to calculate the actual minimum impedance frequency f of each cell. min-real Based on the corrected f min-real The system performs online correction of the pre-stored harmonic-impedance distribution, generates a real-time harmonic-impedance mapping relationship that matches the current aging state of each cell, and completes the personalized correction of 16 cells.

[0071] (4) Achieve charging harmonic signal adjustment and charge balancing. Based on the real-time harmonic-impedance mapping relationship, the controller identifies cells with low charge state as target cells and controls the charging signal shaping circuit to generate a signal matching the target cell. min-realThe charging energy signal is precisely matched with the minimum impedance frequency of the target cell. Because the harmonic frequency of the charging signal is precisely matched with the minimum impedance frequency of the target cell, the target cell can absorb charging energy with the lowest impedance, achieving rapid charge replenishment while avoiding heat generation and energy loss due to impedance mismatch. For other cells, because the harmonic frequency of the charging signal does not perfectly match their current minimum impedance frequency, they absorb relatively less energy, thus achieving charge balance between cells.

[0072] Example 2

[0073] This embodiment is based on the same hardware system as Embodiment 1, but introduces differentiated aging control in the control strategy, such as... Figure 2 As shown.

[0074] Step 1: Classify the aging level of the battery cells.

[0075] After extracting the ohmic impedance increment ΔR0 of each cell, the aging grading differentiation control module divides the cells into three aging levels based on the proportion of ΔR0 relative to the initial factory value:

[0076] Healthy battery cell: ΔR0 < 5% of the initial value. In this embodiment, the ΔR0 of this type of battery cell is 1%~4%. The internal electrochemical characteristics of the battery cell are stable and the harmonic-impedance characteristics have a small drift amplitude.

[0077] Mildly aged cells: 5% ≤ ΔR0 < 20% of the initial value. In this embodiment, the ΔR0 of this type of cell is 6%~18%. The cell shows a slight increase in ohmic impedance, a small amount of thickening of the SEI film, and a slight drift in harmonic-impedance characteristics.

[0078] Severely aged cells: ΔR0 ≥ 20% of the initial value. In this embodiment, the ΔR0 of this type of cell is 22%~25%. The ohmic impedance of the cell increases significantly, the SEI film thickens significantly, the harmonic-impedance characteristics drift a large amplitude, and there is a risk of accelerated aging due to overcharging.

[0079] In this embodiment, the 16 cells of the battery pack were tested and determined to be: 10 healthy cells, 4 slightly aged cells, and 2 heavily aged cells.

[0080] Step 2: Implement differentiated charge balance control strategies for cells of different aging levels.

[0081] Differentiated charge balance control strategies are adopted for different types of battery cells:

[0082] (1) Healthy cell control strategy

[0083] For 10 healthy battery cells, the same basic equalization control strategy as in Example 1 is adopted to prioritize the charging speed and energy efficiency of the battery pack. Based on real-time harmonic-impedance mapping, the controller identifies healthy cells with low state of charge as target cells and controls the charging signal shaping circuit to generate a signal matching the target cell. min-real The charging energy signal is prioritized to ensure the charging speed of the battery pack. The iteration cycle for impedance measurement and harmonic adjustment is 10 seconds, and the harmonic frequency adjustment range is 0.01Hz~10kHz.

[0084] (2) Mildly Aging Cell Control Strategy

[0085] For four slightly aged battery cells, the harmonic frequency adjustment range was narrowed from the initial 0.01Hz~10kHz to 100Hz~5kHz to focus on the key frequency bands of cell response characteristic changes. Simultaneously, the iteration frequency of impedance measurement and harmonic adjustment was increased, shortening the iteration cycle to 5 seconds. By increasing the control frequency and narrowing the adjustment range, the charge balance accuracy control of the slightly aged cells was enhanced, avoiding balance errors caused by impedance fluctuations due to aging.

[0086] (3) Severely Aging Cell Control Strategy

[0087] For two heavily aged battery cells, a low-amplitude reverse harmonic discharge pulse is superimposed on harmonic adjustment based on the real-time harmonic-impedance mapping relationship. The amplitude of the reverse pulse is set to 8% of the cell's rated charging current, and its frequency is matched to the cell's real-time minimum impedance frequency f. min-real When the state of charge of a severely aged battery cell is too high, this reverse pulse can achieve precise discharge balancing, transferring excess charge to other cells or feeding it back through the charging circuit. Simultaneously, the controller outputs a current-limiting command to the charging circuit, limiting the maximum charging current of the cell to 40% of the rated charging current, preventing accelerated aging due to overcharging and reducing the risk of thermal runaway.

[0088] Step 3: Implement coordinated equalization control of multi-level cells.

[0089] When a battery pack contains cells of three types—healthy, slightly aged, and heavily aged—the controller prioritizes the protection of heavily aged cells, prioritizes charging healthy cells, and precisely balances the charging signal for slightly aged cells. This is achieved by performing multi-harmonic frequency composite shaping on the charging energy signal: the charging signal shaping circuit generates a signal containing data from healthy cells and slightly aged cells. min-real The composite harmonic frequency signal is simultaneously superimposed with a reverse discharge pulse and current limiting for severely aged cells, achieving synchronous charge balance of the three types of cells. This ensures the overall charge state consistency of the battery pack and enables personalized health management for cells in different aging states, breaking the vicious cycle of "aging-harmonic mismatch-more severe aging".

[0090] Through the aforementioned differentiated control strategy, this invention achieves charge balance while also taking into account the health management of cells in different aging states, effectively slowing down the aging process of the cells.

[0091] Example 3

[0092] like Figure 3 As shown, the charge balancing system of the battery pack of the present invention includes a charging signal shaping circuit, an impedance measurement circuit, and a controller that are communicatively connected to the battery pack. The battery pack is composed of multiple electrochemical cells connected in series and / or in parallel, and the positive and negative electrodes of each cell are connected to the impedance measurement circuit through cell taps.

[0093] The charging signal shaping circuit is electrically connected to the positive and negative terminals of the battery pack. It is used to receive control commands from the controller, shape the input DC power signal, generate a charging energy signal containing the target harmonic components, and transmit it to the battery pack.

[0094] The impedance measurement circuit includes an aging feature extraction unit, which further includes:

[0095] A wideband sweep frequency signal generation subunit is used to generate a sweep frequency signal within a predetermined frequency range;

[0096] Impedance spectrum acquisition subunit is used to acquire the voltage and current response signals of the battery cell at different frequencies;

[0097] The aging parameter calculation subunit is used to calculate the AC impedance spectrum of the battery cell based on the collected impedance response, and extract quantitative parameters characterizing the aging state of the battery cell from a preset frequency range.

[0098] The controller employs an automotive-grade microcontroller unit (MCU), including an online harmonic distribution self-correction module, an aging-stage differentiated control module, and a periodic calibration update module. The controller is communicatively connected to both the charging signal shaping circuit and the impedance measurement circuit. It receives aging quantization parameters uploaded by the impedance measurement circuit, executes online correction and differentiated control algorithms, and sends control commands to the charging signal shaping circuit.

[0099] The harmonic distribution online self-correction module is used to correct the pre-stored cell harmonic-impedance distribution online based on the aging quantization parameters and the pre-stored aging correction model, generating a real-time harmonic-impedance mapping relationship that matches the current aging state of the cell; the aging graded differential control module is used to divide the cell into multiple different aging levels according to the aging quantization parameters, and match differentiated charge balance control strategies for cells of different aging levels; the periodic calibration update module is used to trigger the impedance measurement circuit to perform a complete wideband frequency sweep on all cells in the battery pack after each preset number of charge-discharge cycles, so as to update the aging quantization parameters of each cell and the parameters of the aging correction model.

[0100] Under the system architecture of this invention, by integrating an aging feature extraction unit into the impedance measurement circuit and embedding an online harmonic distribution self-correction module in the controller, the system achieves real-time sensing and dynamic response to the aging state of the battery cell. This fundamentally solves the problem of mismatch between the pre-stored harmonic distribution and the actual impedance frequency caused by cell aging, thereby enabling the continuous maintenance of high-precision charge balance throughout the entire battery life cycle.

[0101] It should be noted that the logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be specifically implemented in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus or device (such as a computer system, a system including a processor or other system that can fetch and execute instructions from an instruction execution system, apparatus or device).

[0102] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0103] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0104] It should also be further understood that the term "and / or" as used in this specification refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0105] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A charge balancing method for a battery pack, the battery pack comprising multiple electrochemical cells connected in series and / or parallel, characterized in that, The method includes the following steps: S1. When the battery pack is in the charging interval or resting stage, a wideband sweep frequency signal is applied to a single cell through an impedance measurement circuit, and the impedance response of the cell at different frequencies is collected to obtain the AC impedance spectrum of the cell. S2, extract at least one aging quantization parameter characterizing the current aging state of the cell from the preset frequency range of the AC impedance spectrum; S3. Based on the extracted aging quantification parameters and the pre-stored aging correction model, the pre-stored cell harmonic-impedance distribution is corrected online to generate a real-time harmonic-impedance mapping relationship that matches the current aging state of the cell. S4. Based on the real-time harmonic-impedance mapping relationship, adjust the harmonics of the charging energy signal applied to the battery pack to achieve charge balance between cells. The pre-stored aging correction model is pre-established in the following manner: Full life cycle aging test was conducted on the same type of battery cells, and impedance spectrum data of the battery cells were collected at different aging stages; A full life cycle aging calibration database is constructed based on the collected impedance spectrum data. The calibration database stores the aging quantification parameters of cells at different aging stages and the corresponding measured minimum impedance frequency values. Based on the calibration database, an aging correction model is established using the aging quantization parameters as input and the minimum impedance frequency correction coefficient as output. The expression of the aging correction model is as follows: K = a0 + a1·ΔR0 + a2·ΔR SEI + a3·ΔR 2 0 + a4·ΔR 2 SEI + a5·ΔR0·ΔR SEI Where K is the correction coefficient for the minimum impedance frequency, a0-a5 are the model coefficients obtained by least squares fitting, ΔR0 is the high-frequency ohmic impedance increment extracted from the real part of the high-frequency impedance of the AC impedance spectrum, and ΔR SEI The impedance increment of the SEI film is extracted from the real part of the mid-frequency impedance of the AC impedance spectrum.

2. The charge balancing method for a battery pack according to claim 1, characterized in that, The high-frequency band is the frequency range from 1 kHz to 10 kHz, and the mid-frequency band is the frequency range from 1 Hz to less than 1 kHz.

3. The charge balancing method for a battery pack according to claim 1, characterized in that, The method further includes classifying the battery cell into multiple different aging levels based on the ratio of the high-frequency band ohmic impedance increment ΔR0 to the initial value at the factory, and matching differentiated charge balance control strategies to the battery cells of different aging levels.

4. The charge balancing method for a battery pack according to claim 3, characterized in that, The method of classifying battery cells into multiple different aging grades includes classifying battery cells as follows: Healthy battery cells have a high-frequency impedance increment ΔR0 that is less than 5% of the initial factory value. For mildly aged battery cells, the increase in ohmic impedance ΔR0 in the high-frequency band is greater than or equal to 5% of the initial factory value and less than 20% of the initial factory value. For severely aged battery cells, the increase in ohmic impedance ΔR0 in the high-frequency band is greater than or equal to 20% of the initial value at the factory.

5. The charge balancing method for a battery pack according to claim 4, characterized in that, The differentiated charge balance control strategies for matching cells with different aging levels include: For healthy battery cells, the harmonics of the charging energy signal are controlled to match its minimum impedance frequency based on the real-time harmonic-impedance mapping relationship. For mildly aged battery cells, the adjustment range of harmonic frequencies is narrowed, and the iteration frequency of impedance measurement and harmonic adjustment is increased. For severely aged battery cells, a low-amplitude reverse harmonic discharge pulse is superimposed on the harmonic adjustment based on the real-time harmonic-impedance mapping relationship.

6. A charge balancing system for a battery pack implementing the charge balancing method according to any one of claims 1-5, comprising a charging signal shaping circuit, an impedance measurement circuit, and a controller communicating with the battery pack, characterized in that, The impedance measurement circuit includes an aging feature extraction unit, which is configured to apply a wideband sweep frequency signal to a single cell and collect the impedance response of the cell at different frequencies when the battery pack is in a charging intermittent period or a resting stage, so as to obtain the AC impedance spectrum of the cell and extract at least one aging quantization parameter characterizing the current aging state of the cell from a preset frequency range of the AC impedance spectrum. The controller is used to control the charging signal shaping circuit to adjust the harmonics of the charging energy signal based on the harmonic-impedance mapping relationship of the battery cell, so as to achieve charge balance between the battery cells. The controller includes an online harmonic distribution self-correction module, which is used to correct the pre-stored harmonic-impedance distribution of the battery cell online based on the aging quantization parameters and the pre-stored aging correction model, and generate a real-time harmonic-impedance mapping relationship that matches the current aging state of the battery cell. The pre-stored aging correction model is pre-established in the following manner: Full life cycle aging test was conducted on the same type of battery cells, and impedance spectrum data of the battery cells were collected at different aging stages; A full life cycle aging calibration database is constructed based on the collected impedance spectrum data. The calibration database stores the aging quantification parameters of cells at different aging stages and the corresponding measured minimum impedance frequency values. Based on the calibration database, an aging correction model is established using the aging quantization parameters as input and the minimum impedance frequency correction coefficient as output. The expression of the aging correction model is as follows: K = a0 + a1·ΔR0 + a2·ΔR SEI + a3·ΔR 2 0 + a4·ΔR 2 SEI + a5·ΔR0·ΔR SEI Where K is the correction coefficient for the minimum impedance frequency, a0-a5 are the model coefficients obtained by least squares fitting, ΔR0 is the high-frequency ohmic impedance increment extracted from the real part of the high-frequency impedance of the AC impedance spectrum, and ΔR SEI The impedance increment of the SEI film is extracted from the real part of the mid-frequency impedance of the AC impedance spectrum.

7. The charge balancing system according to claim 6, characterized in that, The controller also includes an aging-level differentiated control module, which is used to divide the battery cell into multiple different aging levels according to the aging quantification parameters, and match differentiated charge balance control strategies for battery cells of different aging levels.

8. The charge balancing system according to claim 6, characterized in that, The controller also includes a periodic calibration update module, which triggers the impedance measurement circuit to perform a complete wideband frequency sweep on all cells in the battery pack after each preset number of charge-discharge cycles, so as to update the aging quantization parameters of each cell and the parameters of the aging correction model.

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