A sodium-ion battery soc estimation method and system for a direct-current screen

Abstract

The present application relates to the technical field of sodium-ion battery health management, in particular to a sodium-ion battery SOC estimation method and system for a DC screen. First, the ohmic impedance and polarization impedance of each battery are obtained, and the reference ohmic impedance and reference polarization impedance are extracted. Further, the capacity loss index is obtained according to the difference between the ohmic impedance of each battery and the reference ohmic impedance, combined with the difference between the polarization impedance and the reference polarization impedance. Further, the historical minimum polarization reference of the battery pack is maintained, and the correction loss value is obtained according to the difference between the current reference polarization impedance and the historical minimum polarization reference, combined with the capacity loss index. Further, the correction loss value is converted into a single battery charge loss amount. Finally, based on the single battery charge loss amount, the system effective SOC of the battery pack is determined according to the series short board effect of the battery pack, and reliable basis is provided for operation and maintenance personnel.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery health management technology, specifically to a method and system for estimating the state of charge (SOC) of sodium-ion batteries for DC power supplies. Background Technology

[0002] As a critical backup energy source, the reliability of DC power systems (DC power supplies) depends on the immediate output capability of battery banks. With the application of sodium-ion batteries, monitoring the state of charge (SOC) under long-term float charging conditions presents challenges.

[0003] First, due to the voltage clamping of the float charge and the weak float charge current, traditional open-circuit voltage methods and ampere-hour integration methods are difficult to apply. Second, existing operation and maintenance monitoring mainly relies on short-term shallow discharge inspections, but the voltage response collected within this window is a mixture of multiple factors: changes in contact impedance caused by loose terminals, impedance drift caused by ambient temperature fluctuations, and increased internal resistance caused by battery aging, all of which are superimposed on the voltage signal.

[0004] Due to the lack of individual temperature sensors and full lifecycle calibration data, existing technologies struggle to extract subtle features caused solely by SOC depletion from mixed signals. This often results in false fault reports due to increased contact impedance or the true shortcomings being masked by low ambient temperatures. Summary of the Invention

[0005] To address the technical problem of accurately identifying the true capacity loss of sodium-ion batteries under limited floating charge and shallow discharge conditions in DC power supply systems, the present invention aims to provide a method and system for estimating the state of charge (SOC) of sodium-ion batteries in DC power supply systems. The specific technical solution adopted is as follows: A method for estimating the state of charge (SOC) of a sodium-ion battery for a DC power supply, the method comprising: When the battery pack is in automatic inspection mode, the voltage and current of each individual battery cell are acquired; Based on the transient voltage change at the beginning of discharge and combined with the real-time current, the ohmic impedance of each cell is obtained; the load voltage of each cell after a preset discharge period is obtained, and the polarization impedance of each cell is obtained by combining the ohmic impedance, the real-time current, and the float charge holding voltage; based on the distribution of the ohmic impedance and polarization impedance of the cells in the battery pack, the reference ohmic impedance and reference polarization impedance are extracted. Based on the difference between the ohmic impedance of each battery cell and the reference ohmic impedance, and combined with the difference between the polarization impedance and the reference polarization impedance, a capacity loss index is obtained; the historical minimum polarization reference of the battery pack is maintained, and a corrected loss value is obtained based on the difference between the current reference polarization impedance and the historical minimum polarization reference, and combined with the capacity loss index. Based on a preset impedance loss-capacity loss mapping model, the corrected loss value is converted into the single-cell charge loss; based on the series short-board effect of the battery pack, the effective SOC of the battery pack is determined based on the single-cell charge loss.

[0006] Furthermore, the method for obtaining the polarization impedance includes: For each cell, the net electrochemical voltage is obtained by combining the ohmic impedance, the real-time current, and the load voltage; the polarization impedance is obtained based on the degree of decrease of the net electrochemical voltage relative to the float holding voltage under a unit real-time current.

[0007] Furthermore, the method for obtaining the capacity loss index includes: The ohmic ratio is obtained based on the difference between the ohmic impedance of each cell and the reference ohmic impedance; the connection status of the individual cells is determined based on the ohmic ratio. For each battery cell identified as having a connection problem, exit the analysis process and mark the SOC status as invalid; For each battery cell determined to be connected normally, the polarization ratio is obtained based on the difference between the polarization impedance and the reference polarization impedance; the capacity deficit index is obtained by combining the polarization ratio and the ohmic ratio.

[0008] Furthermore, when the ohm ratio is greater than a preset connection abnormality threshold, the corresponding single battery cell is determined to be connected abnormally; when the ohm ratio is less than or equal to the preset connection abnormality threshold, the corresponding single battery cell is determined to be connected normally.

[0009] Furthermore, the method for maintaining the historical minimum polarization benchmark includes: When the historical minimum polarization reference in the storage is empty, the current reference polarization impedance is compared with the preset upper limit of the new battery polarization impedance standard to obtain the historical minimum polarization reference. When a valid historical minimum polarization reference exists in the memory, the current reference polarization impedance is compared with the historical minimum polarization reference for updating.

[0010] Furthermore, the method for obtaining the historical minimum polarization reference by comparing the current reference polarization impedance with the preset upper limit of the new battery polarization impedance standard includes: If the current reference polarization impedance is not greater than the upper limit of the preset new battery polarization impedance standard, then the reference polarization impedance is used as the historical minimum polarization reference; if the current reference polarization impedance is greater than the upper limit of the preset new battery polarization impedance standard, then the current reference polarization impedance is reduced by a preset aging retrospective factor to obtain the historical minimum polarization reference.

[0011] Furthermore, the method for obtaining the effective SOC of the system includes: The individual charge loss is converted into the true holding capacity rate, and the minimum of the true holding capacity rate is taken as the effective SOC of the system.

[0012] Furthermore, after obtaining the effective SOC of the system, it also includes: Based on the nominal rated capacity of the battery pack and the effective state of charge (SOC) of the system, combined with the preset load current, the remaining backup time is obtained.

[0013] Furthermore, the median of the ohmic impedance and the polarization impedance of the cells in the current battery pack are extracted respectively, and used as the reference ohmic impedance and the reference polarization impedance.

[0014] The present invention also proposes a sodium-ion battery SOC estimation system for DC power supplies, the system comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement any of the steps of the sodium-ion battery SOC estimation method for DC power supplies described above.

[0015] The present invention has the following beneficial effects: This invention first obtains the ohmic impedance and polarization impedance of each battery cell, isolates and quantifies the physical connection state from the mixed signal, and independently extracts the characteristic components representing the battery's chemical state. Then, it extracts the reference ohmic impedance and reference polarization impedance, converting the absolute impedance measurements into relative values ​​relative to the group reference. Furthermore, based on the difference between the ohmic impedance of each battery cell and the reference ohmic impedance, combined with the difference between the polarization impedance and the reference polarization impedance, a capacity loss index is obtained. Through dual differentiation processing, the synchronous impedance increment caused by aging common-mode factors is effectively offset, while retaining and highlighting the specific deviation characteristics of polarization impedance caused by SOC loss. Furthermore, it maintains the historical minimum polarization reference of the battery pack, and based on the difference between the current reference polarization impedance and the historical minimum polarization reference, combined with the capacity loss index, obtains a corrected loss value, improving the detection sensitivity and accuracy of weak capacity bottleneck signals in aging battery packs. The corrected loss value is further converted into individual cell charge loss. Finally, based on the series bottleneck effect of the battery pack, the effective SOC of the battery pack is determined based on the individual cell charge loss. This invention solves the industry problem of flat voltage platform and easily interfered shallow discharge signal under float charging conditions by separating ohmic / polarization impedance in the time domain, using statistical differential to suppress temperature drift and aging interference, and introducing historical benchmark adaptive compensation to accurately decouple and estimate sodium-ion battery SOC. Attached Figure Description

[0016] To more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A flowchart illustrating a method for estimating the state of charge (SOC) of a sodium-ion battery for a DC power supply, provided in one embodiment of the present invention. Figure 2 A flowchart illustrating a method for obtaining a capacity deficit index, provided as an embodiment of the present invention. Detailed Implementation

[0018] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of a sodium-ion battery SOC estimation method and system for DC power supplies based on the present invention. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0020] The following description, in conjunction with the accompanying drawings, details a specific scheme for a sodium-ion battery SOC estimation method and system for DC power supplies provided by this invention.

[0021] Please see Figure 1 The document illustrates a flowchart of a method for estimating the state of charge (SOC) of a sodium-ion battery for a DC power supply, provided by an embodiment of the present invention. The method specifically includes: Step S1: When the battery pack is in automatic inspection mode, acquire the voltage and current of each individual battery cell.

[0022] In one embodiment of the present invention, the system establishes real-time monitoring of the battery pack, synchronously acquiring the total loop current of the battery pack and the voltage (terminal voltage) of each individual battery cell at a sampling frequency of not less than 10Hz. Before the DC power supply controller starts the automatic inspection program, the system is in a steady-state float charging monitoring mode. At this time, the current flowing through the battery pack is only a microampere-level sustaining current, which can be approximately regarded as a zero-current state.

[0023] The system iterates through each individual cell in the battery pack (treating each individual cell as a battery cell or a single battery), reads and latches the first cell. The steady-state terminal voltage of a single cell before the start of automatic inspection is marked as the float charge holding voltage. Among them, subscript This represents the physical location index number of a single battery cell, with a value range of [value range missing]. to , The total number of cells connected in series in the battery pack (e.g.) ).

[0024] When the system detects that the loop current jumps from the float charge state to the constant current discharge value set by the automatic inspection, the system marks the step trigger moment of the current detection process. This indicates the start time of discharge, and the constant current discharge value is recorded as the inspection current. .

[0025] To ensure a sufficient signal-to-noise ratio, the inspection current is required. The strength is not less than the current value corresponding to a 0.05C rate, for example, 100Ah corresponds to not less than 5A, where C is the rated capacity of the battery pack.

[0026] If the actual inspection current is lower than this lower limit, the system will prompt that the signal-to-noise ratio is insufficient and suspend the estimation process. The automatic inspection mode is triggered and executed autonomously by the DC power supply control system (for example, by briefly reducing the output voltage of the charger to make the battery pack enter a constant current discharge state). This control mechanism is existing technology and will not be described in detail here.

[0027] It should be noted that the analysis process for each automatic inspection is the same. Here, we will only describe the current (latest) automatic inspection and will not repeat the explanation.

[0028] Step S2: Based on the transient voltage change at the beginning of the discharge phase and combined with the real-time current, obtain the ohmic impedance of each cell; obtain the load voltage of each cell after a preset discharge period, and combine the ohmic impedance, real-time current, and float charge holding voltage to obtain the polarization impedance of each cell; based on the distribution of ohmic impedance and polarization impedance of the cells in the battery pack, extract the reference ohmic impedance and reference polarization impedance.

[0029] Since ohmic impedance (including tabs, bus connections, and electrolyte resistance) exhibits purely resistive characteristics, it responds extremely quickly to changes in current. In sodium-ion batteries, the instantaneous voltage drop at the moment of current step loading (millisecond level) is mainly caused by the battery's internal ohmic resistance and external physical connection impedance. Therefore, based on the transient voltage change at the beginning of discharge and combined with the real-time current, the ohmic impedance of each battery is obtained, and the physical connection state is first separated and quantified from the mixed signal.

[0030] After the battery pack has been continuously discharged for a period of time, the battery voltage enters a relatively steady state. At this time, in addition to the ohmic voltage drop, the voltage mainly reflects the voltage drop caused by electrochemical polarization (concentration polarization and electrochemical polarization). Therefore, by obtaining the load voltage of each cell after a preset discharge period, and combining it with the ohmic impedance, real-time current and float charge holding voltage, and subtracting the voltage drop caused by physical factors, the net voltage drop generated purely by the electrochemical process is obtained. Thus, the polarization impedance of each cell is obtained, accurately capturing the weak impedance characteristics caused by single cell self-discharge (SOC loss), and independently extracting the characteristic components characterizing the chemical state of the battery.

[0031] Within the same battery pack, all cells are typically in nearly identical macroscopic environments (especially temperature fields). Therefore, changes in ambient temperature have a synchronous, common-mode effect on the absolute impedance of each cell. Furthermore, during normal aging of the battery pack, the aging trends of most cells also exhibit statistical consistency. Therefore, based on the distribution of ohmic and polarization impedances within the battery pack, reference ohmic and polarization impedances are extracted. This transforms absolute impedance measurements into relative values ​​with respect to the group reference, thus offsetting the multiplicative effects of ambient temperature fluctuations and overall battery pack aging on the absolute impedance value.

[0032] Preferably, in one embodiment of the present invention, the voltage sampling value at the sampling time before the battery pack discharges is selected. Voltage sampling value at the start of discharge Calculate the absolute value of the difference between each battery at these two moments, as... This approximates the transient voltage drop amplitude captured in a hardware system with a limited sampling frequency (e.g., below 1 kHz), representing the transient voltage change.

[0033] Calculate the first according to Ohm's law. Ohmic impedance of a single cell ,Will As molecules, As the denominator, the ratio of the fraction is used as... The ohmic impedance vector is obtained. Vector quantification measures the smoothness of the physical conductive circuit of each individual battery cell under the current operating conditions.

[0034] Preferably, in one embodiment of the present invention, the length of the preset discharge period is 60 seconds, corresponding to... At 60 seconds after the start, the terminal voltage of each battery is collected. This is the loaded (discharging) state, so it is called the loaded voltage, which represents the continuous discharge voltage.

[0035] For each cell, the ohmic impedance and real-time current are first combined to obtain the ohmic voltage drop component, and then the net electrochemical voltage is obtained by combining it with the load voltage, thus obtaining the effective chemical potential after eliminating the influence of physical connection. Then, the polarization impedance is obtained based on the degree of decrease in net electrochemical voltage relative to float holding voltage under unit real-time current.

[0036] As an example, consider the ohmic impedance. and The product of the load voltage and the ohmic voltage drop component is used as the net electrochemical voltage.

[0037] Will As the denominator, the difference between the float charge holding voltage and the net electrochemical voltage is used as the numerator, and the fractional ratio is used as the polarization impedance of the corresponding single cell.

[0038] Furthermore, considering that the vast majority of individual cells in a battery pack are in a healthy and consistent state during normal operation, while faults (such as capacity loss or poor connection) usually manifest as outliers in a few cells, the median, as a robust statistic, can effectively ignore the influence of these few outliers, thereby extracting the benchmark that best represents the current overall health level of the battery pack. Therefore, the median of the ohmic impedance and polarization impedance of the cells in the current battery pack are extracted as the benchmark ohmic impedance and benchmark polarization impedance, and the median is used to represent the distribution characteristics of the data.

[0039] It should be noted that the analysis process is the same for each battery; only one example is described here, and will not be repeated. In this example, the monitoring current is used. Constant current discharge is performed, using the default method. The calculation is performed using real-time current; in other embodiments of the invention, the implementer may use real-time collected current for the calculation.

[0040] Step S3: Based on the difference between the ohmic impedance of each cell and the reference ohmic impedance, and combined with the difference between the polarization impedance and the reference polarization impedance, obtain the capacity loss index; maintain the historical minimum polarization reference of the battery pack, and based on the difference between the current reference polarization impedance and the historical minimum polarization reference, and combined with the capacity loss index, obtain the corrected loss value.

[0041] During long-term float charging aging, ohmic impedance (characterizing physical connectivity and ionic conductivity) and polarization impedance (characterizing electrochemical reaction kinetics) typically exhibit a statistically positive correlation, meaning that overall aging leads to an increase in both impedance baselines. However, when a single cell experiences capacity loss (decreased state of charge), it primarily triggers a specific increase in polarization impedance, while having a relatively smaller impact on ohmic impedance. This difference in response patterns provides a theoretical basis for separating aging background noise from capacity loss signals.

[0042] Therefore, based on the difference between the ohmic impedance of each cell and the reference ohmic impedance, combined with the difference between the polarization impedance and the reference polarization impedance, the capacity loss index is obtained. Through dual differentiation processing, the impedance synchronous increment caused by aging common-mode factors is effectively offset, and the polarization impedance specific deviation characteristics caused by SOC loss are preserved and highlighted.

[0043] As battery packs age, overall aging causes the baseline polarization impedance of all cells to rise continuously. This rise in the overall baseline "compresses" the dynamic range of the absolute value of the capacity deficit index between cells, making the capacity difference signal that was very obvious in the early stages of operation become weak and difficult to distinguish in the later stages, resulting in a decrease in detection sensitivity.

[0044] To construct a health status reference system across time dimensions and maintain the historical minimum polarization benchmark of the battery pack, the difference between the current benchmark polarization impedance and the historical minimum polarization benchmark is compared with the gap between the current aging state and the historical optimal state. Combined with the capacity loss index, the characteristic signal compressed due to the baseline rise can be dynamically amplified to obtain the corrected loss value, thereby improving the detection sensitivity and accuracy of weak capacity short-term signals in aging battery packs.

[0045] Preferably, in one embodiment of the present invention, please refer to Figure 2 The flowchart illustrates a method for obtaining a capacity loss index according to an embodiment of the present invention, specifically including: Step S201: Obtain the ohmic ratio based on the difference between the ohmic impedance of each cell and the reference ohmic impedance; determine the connection status of the individual cells based on the ohmic ratio.

[0046] Since ohmic impedance directly quantifies the conductivity of the external physical circuits of a battery (such as terminals and connectors), an ohmic ratio significantly higher than the group benchmark is a clear indicator of physical connection failures (such as loosening or oxidation). Such failures can cause severe distortion in voltage measurements, rendering subsequent voltage-based state of chemical (SOC) estimations meaningless. Therefore, the connection status of individual cells must be determined first.

[0047] As an example, the ohmic impedance of each cell is used as the numerator, the reference ohmic impedance is used as the denominator, and the ratio of the fractions is used as the ohmic ratio of each cell. The preset connection failure threshold is 1.5. When the ohm ratio is greater than the preset connection failure threshold, the corresponding single battery cell is determined to be connected abnormally; when the ohm ratio is less than or equal to the preset connection failure threshold, the corresponding single battery cell is determined to be connected normally.

[0048] Since the ohmic impedance reflects the inherent resistance of the physical conduction path (including metal components and electrolyte), its physical value is always positive, and the reference ohmic impedance, as the statistical value of the group median, cannot be zero under normal physical connection, this ratio calculation is always valid at the physical level. This embodiment mainly focuses on the "loosening / oxidation" fault with abnormally high impedance. For cases with significantly low impedance (such as short circuits), since it will cause the terminal voltage to become abnormally high and be directly captured by the basic BMS voltage protection mechanism, it is not a contact impedance gradual change hidden danger that this algorithm is concerned with. Therefore, no lower limit threshold is determined here. In other embodiments of the present invention, the implementer can adjust the preset connection abnormality threshold himself.

[0049] Step S202: For each battery cell determined to have a connection abnormality, exit the analysis process and mark the SOC status as invalid.

[0050] For each battery cell determined to have a connection abnormality, the parameters that need to be calculated subsequently are marked as empty or pre-defined codes. For example, the capacity loss index is marked as empty, which realizes accurate isolation and diagnosis of fault modes.

[0051] Step S203: For each cell determined to be connected normally, obtain the polarization ratio based on the difference between the polarization impedance and the reference polarization impedance; combine the polarization ratio and the ohmic ratio to obtain the capacity loss index.

[0052] As an example, the polarization ratio is obtained by dividing the polarization impedance of each cell by the reference polarization impedance, and the polarization ratio of each cell is subtracted from the polarization ratio of the reference polarization impedance. The difference between the two ohm ratios is used as the capacity loss index. The lower limit of the capacity loss index is set to 0; for differences less than 0, a value of 0 is assigned directly. The common-mode rejection factor for aging ranges from 0.8 to 0.95. It is used to introduce a safety margin in differential calculations to prevent the capacity loss characteristic from being incorrectly zeroed (i.e., false negative) due to the ohmic impedance increasing slightly faster than the polarization impedance during aging. It can be obtained by statistically analyzing the growth ratio of the two types of impedances in accelerated aging experiments of sodium-ion batteries of the same model. Implementers can adjust it within the recommended range according to the aging characteristics of the specific battery system. It is an existing conventional parameter calibration method and will not be elaborated further.

[0053] Thus, the vector of the capacity deficit index is obtained. The vector is empty for abnormal connections, effectively filtering out the common-mode impedance increment caused by temperature and aging, and retaining the net characteristics that reflect the specific loss of SOC. The corresponding bit of the abnormally connected unit is empty in the vector.

[0054] The differences between the data are expressed as ratios. Through ratio transformation, the multiplicative effect of temperature on the absolute value of impedance is canceled out in the numerator and denominator, and the characteristics are transformed into dimensionless relative values; the subtrahend term This serves as an estimate of the aging background. By subtracting, the aging increment of the common mode is significantly suppressed, and the remaining residual mainly reflects the polarization impedance specific deviation caused by SOC depletion.

[0055] Since polarization impedance characterizes the hindrance of the electrochemical reaction process inside the battery, it is always positive under discharge conditions, and the median, which serves as the group benchmark, is not zero, this division operation is always meaningful.

[0056] In a preferred embodiment of the invention, the system maintains a variable in non-volatile memory, namely, maintaining the historical minimum polarization reference of the battery pack. This represents the lowest reference polarization impedance experienced by the battery pack during its life cycle, which is the performance baseline when the battery pack is in optimal physical health or when the ambient temperature is most suitable.

[0057] When the system is powered on for the first time or the battery pack is replaced (cold start), the historical minimum polarization reference in the storage is empty. The historical minimum polarization reference is obtained by comparing the current reference polarization impedance with the preset upper limit of the new battery polarization impedance standard. As an example, a pre-set upper limit for the polarization impedance of a new battery is provided. Determined by the battery specifications, for example ; If the current reference polarization impedance is not greater than the upper limit of the preset new battery polarization impedance standard, it means that the battery pack is in a healthy state. Then the reference polarization impedance is used as the historical minimum polarization reference to complete the reference establishment. If the current reference polarization impedance is greater than the preset upper limit of the new battery polarization impedance standard, it indicates that the system may be deployed on an aged battery pack. To prevent high impedance from being misjudged as the optimal reference, a preset aging backtracking factor is used. Reduce the current reference polarization impedance to obtain the historical minimum polarization reference.

[0058] In this example, Divide the reference polarization impedance by The quotient is used as the historical minimum polarization benchmark.

[0059] In other embodiments of the present invention, the implementer can adjust the settings as needed. In terms of value selection, the implementer can also prompt the user to input the factory calibration value when the current reference polarization impedance is greater than the preset upper limit of the new battery polarization impedance standard, so as to use it as the historical minimum polarization reference.

[0060] When a valid historical minimum polarization reference exists in the memory, the current reference polarization impedance is compared with the historical minimum polarization reference, and the minimum value is selected as the new historical minimum polarization reference.

[0061] Furthermore, by calculating the deviation of the current group benchmark (benchmark polarization impedance) from the historical best benchmark, the overall degradation degree of the battery pack can be quantified, and a nonlinear gain coefficient can be generated accordingly to compensate for the capacity loss index. This nonlinear compensation mechanism ensures that the algorithm's ability to distinguish the weakest cells remains consistent, whether in the new battery stage or after severe aging.

[0062] As an example, group decay gain The calculation formulas include: , This indicates the current reference polarization impedance.

[0063] The squared term in the formula is only a preferred embodiment of the nonlinear amplification strategy, using the group decay gain to represent the difference between the current reference polarization impedance and the historical minimum polarization reference. In practical applications, the exponential term can be adjusted according to the specific aging impedance characteristics of the battery (usually taking a value greater than 1.0). To prevent calculation divergence caused by extreme failures, the system... Set a saturation limit (e.g.) ),when If the direct calculation exceeds 5, it is truncated to 5.

[0064] The capacity loss index of each battery is compared with The product of the values ​​is used as a correction for the loss. Through multiplication, the system automatically stretches the dynamic range of the eigenvalues ​​in the aging context, making the eigenvalue differences that were originally compressed due to the increase in the base value significant again.

[0065] Step S4: Based on the preset impedance loss-capacity loss mapping model, the corrected loss value is converted into the single-cell charge loss; based on the series short-board effect of the battery pack, the effective SOC of the battery pack is determined based on the single-cell charge loss.

[0066] The corrected loss value is a pure, dimensionless characteristic signal with consistent sensitivity throughout its entire lifespan, but this abstract signal itself does not directly represent the capacity percentage. Within the float charge range (e.g., 90%-100% SOC), sodium-ion batteries exhibit a definite and measurable nonlinear functional relationship between their internal electrochemical impedance (characterized by the corrected loss value) and the actual charge loss. Therefore, based on a pre-defined impedance loss-capacity loss mapping model, the corrected loss value is converted into the single-cell charge loss. In a series-connected battery pack in a DC power supply, the charger's output voltage is clamped to a fixed value. The usable capacity of the entire battery pack does not depend on the average value, but is limited by the "shortest" cell with the lowest state of charge. When the system discharges, the lowest-charged cell will reach its discharge cutoff voltage first, triggering a system protection shutdown, preventing other cells from releasing their charge.

[0067] Therefore, based on the series bottleneck effect of the battery pack, the effective SOC of the battery pack is determined according to the charge loss of individual cells. This conforms to the actual working boundary of the system, ensures the conservatism and safety of the prediction results, and provides a reliable basis for maintenance personnel to accurately replenish power or replace lagging cells.

[0068] Preferably, in one embodiment of the present invention, the preset impedance loss-capacity loss mapping model is: ; in, Let be the corrected loss value for the i-th battery. Let be the charge loss of the i-th cell, expressed as a percentage. If empty, skip the calculation. The calibration factor is 200 in this example, and the unit is percentage. The starting threshold is 0.05 in this example. Used to filter out normal measurement noise and manufacturing tolerances, when When the charge level is below this threshold, the battery is considered to be fully charged, and the loss is 0. The maximum is 100%, and the maximum cutoff value for calculations exceeding this limit is 100%.

[0069] It should be noted that the specific form and parameter calibration of the impedance loss-capacity loss mapping model are usually completed through charge-discharge tests during the type testing phase before battery commissioning. Implementers can adaptively adjust the starting threshold and calibration coefficient A according to the specific battery model and specifications and the on-site noise level. Since fitting a function model based on experimental data is a standard engineering method in this field, it will not be elaborated upon here.

[0070] Converting individual charge loss into true retention rate ,Right now The minimum actual retained capacity rate is taken as the effective SOC of the system, and the corresponding single cell is marked as the shortest cell.

[0071] In another embodiment of the present invention, in order to provide operations and maintenance personnel with an intuitive system availability assessment, after obtaining the effective SOC of the system, the method further includes: Based on the nominal rated capacity of the battery pack Based on the system's effective SOC and the preset load current, the remaining backup time is obtained. .

[0072] As an example, The product of the system's effective SOC and the preset load current is used as the numerator, and the ratio of the fractions is used as the remaining reserve time. .

[0073] The preset load current is set according to the typical load power of the system, which is 10A in this example.

[0074] The final system, along with the system's effective SOC ( ), Short-staffed cells and cells identified as having connection problems are updated to the human-machine interface. If the value falls below a preset alarm threshold (e.g., 90%), the system will trigger an audible and visual alarm.

[0075] An embodiment of the present invention also provides a sodium-ion battery SOC estimation system for a DC power supply screen. The system includes a memory, a processor, and a computer program. The memory is used to store the corresponding computer program, and the processor is used to run the corresponding computer program. When the computer program runs in the processor, it can implement the sodium-ion battery SOC estimation method for a DC power supply screen described in steps S1-S4.

[0076] In summary, to address the technical problem of accurately identifying the true capacity loss of sodium-ion batteries under the limited conditions of floating charge and shallow discharge in DC power supply systems, this invention provides a method and system for estimating the State of Charge (SOC) of sodium-ion batteries for DC power supply systems. This invention first obtains the ohmic impedance and polarization impedance of each battery cell, extracting the reference ohmic impedance and reference polarization impedance. Further, based on the difference between the ohmic impedance of each battery cell and the reference ohmic impedance, combined with the difference between the polarization impedance and the reference polarization impedance, a capacity loss index is obtained. Further, the historical minimum polarization reference of the battery pack is maintained, and based on the difference between the current reference polarization impedance and the historical minimum polarization reference, combined with the capacity loss index, a corrected loss value is obtained. The corrected loss value is then converted into the individual cell charge loss. Finally, based on the series bottleneck effect of the battery pack, the effective SOC of the battery pack is determined based on the individual cell charge loss. This invention, by separating the ohmic / polarization impedance in the time domain, using statistical differential to suppress temperature drift and aging interference, and introducing historical reference adaptive compensation, accurately decouples and estimates the SOC of sodium-ion batteries, solving the industry problem of flat voltage plateaus and easily interfered shallow discharge signals under floating charge conditions.

[0077] It should be noted that the order of the above embodiments of the present invention is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. The processes depicted in the accompanying drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0078] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

Claims

1. A method for estimating the state of charge (SOC) of a sodium-ion battery for a DC power supply, characterized in that, The method includes: When the battery pack is in automatic inspection mode, the voltage and current of each individual battery cell are acquired; Based on the transient voltage change at the beginning of discharge and combined with the real-time current, the ohmic impedance of each cell is obtained; the load voltage of each cell after a preset discharge period is obtained, and the polarization impedance of each cell is obtained by combining the ohmic impedance, the real-time current, and the float charge holding voltage; based on the distribution of the ohmic impedance and polarization impedance of the cells in the battery pack, the reference ohmic impedance and reference polarization impedance are extracted. Based on the difference between the ohmic impedance of each battery cell and the reference ohmic impedance, and combined with the difference between the polarization impedance and the reference polarization impedance, a capacity loss index is obtained; the historical minimum polarization reference of the battery pack is maintained, and a corrected loss value is obtained based on the difference between the current reference polarization impedance and the historical minimum polarization reference, and combined with the capacity loss index. Based on a preset impedance loss-capacity loss mapping model, the corrected loss value is converted into the single-cell charge loss; based on the series short-board effect of the battery pack, the effective SOC of the battery pack is determined based on the single-cell charge loss.

2. The method for estimating the state of charge (SOC) of a sodium-ion battery for a DC power supply according to claim 1, characterized in that, The method for obtaining the polarization impedance includes: For each cell, the net electrochemical voltage is obtained by combining the ohmic impedance, the real-time current, and the load voltage; the polarization impedance is obtained based on the degree of decrease of the net electrochemical voltage relative to the float holding voltage under a unit real-time current.

3. The method for estimating the state of charge (SOC) of a sodium-ion battery for a DC power supply according to claim 1, characterized in that, The methods for obtaining the capacity loss index include: The ohmic ratio is obtained based on the difference between the ohmic impedance of each cell and the reference ohmic impedance; the connection status of the individual cells is determined based on the ohmic ratio. For each battery cell identified as having a connection problem, exit the analysis process and mark the SOC status as invalid; For each battery cell determined to be connected normally, the polarization ratio is obtained based on the difference between the polarization impedance and the reference polarization impedance; the capacity deficit index is obtained by combining the polarization ratio and the ohmic ratio.

4. The method for estimating the state of charge (SOC) of a sodium-ion battery for a DC power supply according to claim 3, characterized in that, When the ohm ratio is greater than a preset connection abnormality threshold, the corresponding single battery cell is determined to be connected abnormally; when the ohm ratio is less than or equal to the preset connection abnormality threshold, the corresponding single battery cell is determined to be connected normally.

5. The method for estimating the state of charge (SOC) of a sodium-ion battery for a DC power supply according to claim 1, characterized in that, The method for maintaining the historical minimum polarization benchmark includes: When the historical minimum polarization reference in the storage is empty, the current reference polarization impedance is compared with the preset upper limit of the new battery polarization impedance standard to obtain the historical minimum polarization reference. When a valid historical minimum polarization reference exists in the memory, the current reference polarization impedance is compared with the historical minimum polarization reference for updating.

6. The method for estimating the state of charge (SOC) of a sodium-ion battery for a DC power supply according to claim 5, characterized in that, The method for obtaining the historical minimum polarization reference by comparing the current reference polarization impedance with the preset upper limit of the new battery polarization impedance standard includes: If the current reference polarization impedance is not greater than the upper limit of the preset new battery polarization impedance standard, then the reference polarization impedance is used as the historical minimum polarization reference; if the current reference polarization impedance is greater than the upper limit of the preset new battery polarization impedance standard, then the current reference polarization impedance is reduced by a preset aging retrospective factor to obtain the historical minimum polarization reference.

7. The method for estimating the state of charge (SOC) of a sodium-ion battery for a DC power supply according to claim 1, characterized in that, The method for obtaining the effective SOC of the system includes: The individual charge loss is converted into the true holding capacity rate, and the minimum of the true holding capacity rate is taken as the effective SOC of the system.

8. The method for estimating the state of charge (SOC) of a sodium-ion battery for a DC power supply according to claim 1, characterized in that, After obtaining the system's valid SOC, the following is also included: Based on the nominal rated capacity of the battery pack and the effective state of charge (SOC) of the system, combined with the preset load current, the remaining backup time is obtained.

9. The method for estimating the state of charge (SOC) of a sodium-ion battery for a DC power supply according to claim 1, characterized in that, The median of the ohmic impedance and the polarization impedance of the cells in the current battery pack are extracted respectively, and used as the reference ohmic impedance and the reference polarization impedance.

10. A sodium-ion battery SOC estimation system for a DC power supply, the system comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the sodium-ion battery SOC estimation method for DC screens as described in any one of claims 1 to 9.

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