A method for calibrating the charge state and a battery system providing the method.
The battery system addresses inaccuracies in SOC estimation by integrating cell current and open-circuit voltage mapping, enabling precise calibration without full charging, thus improving SOC estimation accuracy.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- LG ENERGY SOLUTION LTD
- Filing Date
- 2024-04-24
- Publication Date
- 2026-07-29
AI Technical Summary
Existing methods for estimating the state of charge (SOC) of lithium iron phosphate (Li-FePO4) batteries face challenges such as difficulty in real-time estimation with the voltage-state method and inaccuracies in the current integration method due to initial value errors and measurement errors, requiring cumbersome full charge calibration processes.
A battery system that estimates SOC by integrating cell current and uses a storage unit to map estimated SOC and open-circuit voltage, calculating error values to determine if initial SOC calibration is needed without requiring a full charge state, utilizing a control unit to adjust the SOC based on error analysis.
Enables accurate SOC calibration without full charging, reducing errors and maintaining accuracy over time by using integrated current and open-circuit voltage mapping and error analysis.
Smart Images
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Abstract
Description
Technical Field
[0001] Cross - reference to Related Applications This application claims the benefit of priority based on Korean Patent Application No. 10 - 2023 - 0079004 filed on June 20, 2023, and all the contents disclosed in the Korean patent application document are incorporated herein by reference.
[0002] The present invention relates to a method for calibrating an initial value of a state of charge (SOC) and a battery system providing the method.
Background Art
[0003] The state of charge (SOC) of a battery can indicate the relative amount of energy stored in the battery. For example, the state of charge (SOC) can be expressed as a percentage (%) by dividing the current capacity of the battery by the total capacity of the battery.
[0004] The state of charge (SOC) is a very important factor in managing a system operated by the power of a battery. Therefore, accurately measuring the state of charge (SOC) can be used as an indicator showing the core competitiveness of battery manufacturers.
[0005] There are various methods for estimating the state of charge (SOC) of a battery, such as an open - circuit voltage method and a coulomb counting method. The open - circuit voltage method may be a method of measuring the open - circuit voltage (OCV) of a battery and estimating the state of charge (SOC) by comparing the measured open - circuit voltage (OCV) with a SOC - OCV relationship graph. The coulomb counting method, also known as the current integration method, is a method of estimating the state of charge (SOC) by adding or subtracting (in the case of discharge) the value obtained by integrating the current during the charge or discharge cycle to the initial value of the state of charge (SOC).
[0006] The voltage-charge state estimation method is a simple method that estimates the battery state by simply measuring the battery voltage. However, it has the disadvantage that real-time estimation is difficult because current remains inside the battery even after the charging and discharging current is interrupted (opened), and a rest period is required for accurate estimation.
[0007] In addition, batteries made of lithium iron phosphate (Li-FePO4) have the characteristic that their open-circuit voltage (OCV) remains in a plateau state. In other words, batteries made of lithium iron phosphate (Li-FePO4) present a problem in that it is difficult to accurately estimate the state of charge (SOC) from the open-circuit voltage (OCV). That is, for example, batteries made of lithium iron phosphate (Li-FePO4) can only have their SOC estimated using the current integration method, not the voltage-state of charge estimation method, due to a variety of reasons.
[0008] On the other hand, while the current integration method allows for real-time estimation and is widely used, it has disadvantages such as the inability to accurately know the initial value in the initial estimation stage, measurement errors from the current sensor that measures battery current, and errors that occur during the analog-to-digital conversion (ADC) process, which accumulate continuously during estimation. For example, the current integration method relies on the initial value of the state of charge (SOC) to estimate it, so if the initial value is not accurate, errors may occur in the estimation of the state of charge (SOC). Furthermore, as the battery operating time increases, errors accumulate, and the accuracy of the state of charge (SOC) decreases.
[0009] One way to solve this problem is for the administrator to transmit a full charge control signal to the Battery Management System (BMS) at intervals when an accumulation of errors is expected (e.g., every two weeks). The BMS then charges the battery, and when the battery's state of charge (SOC) reaches a full charge (100%), it resets the initial value of the SOC to 100% and calibrates the SOC. In other words, this method of estimating the state of charge (SOC) using current integration requires the cumbersome process of periodically charging the battery to a full charge state in order to calibrate the initial value of the SOC. [Overview of the project] [Problems that the invention aims to solve]
[0010] The present invention provides a method for calibrating the charge state of a battery, which calibrates the initial value of the charge state (SOC) based on accumulated data, even without charging the battery to a fully charged state, and a battery system that provides this method. [Means for solving the problem]
[0011] A battery system according to one feature of the present invention is a battery system that estimates the State of Charge (SOC) of a battery cell by integrating the cell current flowing through the battery cell, and includes a storage unit that stores mapping data, which maps the estimated State of Charge based on the integrated value of the cell current and a first open-circuit voltage estimated by a predetermined model that replicates the cell voltage corresponding to the cell current, at predetermined storage cycles; and a control unit that, when the number of times the mapping data has been stored has reached a predetermined reference number and a calibration cycle has arrived, estimates a first relationship graph, which is a relationship graph between a plurality of State of Charge (SOC) and a plurality of open-circuit voltages stored in the storage unit, based on a predetermined State of Charge-Open-Circuit Voltage Lookup Table, calculates a plurality of relationship graphs by reflecting a plurality of error values set in advance in the first relationship graph, calculates the sum of the distances between each of the plurality of relationship graphs and the plurality of mapping data, determines the error value corresponding to the minimum of the plurality of sums as the final error value between the first open-circuit voltage and the second open-circuit voltage corresponding to the State of Charge, and determines whether or not to calibrate the initial value of the State of Charge (SOC) by determining whether or not the final error value belongs to a predetermined reference range.
[0012] A battery system according to another feature of the present invention is a battery system that estimates the State of Charge (SOC) of a battery cell by integrating the cell current flowing through the battery cell, and includes a storage unit that stores mapping data in which the estimated charge state based on the integral value of the cell current and a first open-circuit voltage estimated by a predetermined model that replicates the cell voltage corresponding to the cell current are mapped at predetermined storage cycles, and a control unit that, when the number of times the mapping data has been stored has reached a predetermined reference number and a calibration cycle has arrived, estimates a plurality of second open-circuit voltages corresponding to a plurality of charge states (SOCs) stored in the storage unit based on a predetermined charge state-open-circuit voltage lookup table, calculates a final error value corresponding to the degree of mismatch between the plurality of first open-circuit voltages and the plurality of second open-circuit voltages based on a predetermined cost function that quantifies the degree of agreement between the plurality of first open-circuit voltages and the plurality of second open-circuit voltages, determines whether the final error value falls within a predetermined reference range, and determines whether or not to calibrate the initial value of the charge state (SOC).
[0013] A method for calibrating the state of charge according to yet another feature of the present invention includes the steps of: estimating the state of charge and a first open-circuit voltage of a battery cell based on the integral value of the cell current flowing through the battery cell and a predetermined model that replicates the cell voltage corresponding to the cell current, respectively, when a predetermined storage cycle has arrived; storing mapping data on which the state of charge and the first open-circuit voltage are mapped in a storage unit; estimating a plurality of second open-circuit voltages corresponding to a plurality of state of charge (SOC) stored in the storage unit based on a predetermined state of charge-open-circuit voltage lookup table when the number of times the mapping data has been stored has reached a predetermined reference number and the calibration cycle has arrived; calculating a final error value corresponding to the degree of mismatch between the plurality of first open-circuit voltages and the plurality of second open-circuit voltages based on a predetermined cost function that quantifies the degree of agreement between the plurality of first open-circuit voltages and the plurality of second open-circuit voltages, and determining whether the final error value falls within a predetermined reference range; and, if, as a result of the determination, the final error value exceeds the predetermined reference range, calibrating the initial value of the state of charge (SOC). [Effects of the Invention]
[0014] An embodiment of the present invention allows for the calibration of errors in the State of Charge (SOC) by the current integration method using a simple method, even without charging the battery to a fully charged state (100%). [Brief explanation of the drawing]
[0015] [Figure 1] This is a block diagram illustrating a battery system according to one embodiment. [Figure 2] This is a conceptual diagram that provides a detailed explanation of the multiple estimation modules and mapping tables stored in the storage unit shown in Figure 1. [Figure 3] This graph illustrates a method for estimating the first open-circuit voltage using one embodiment. [Figure 4] This graph illustrates a method for estimating the first open-circuit voltage using one embodiment. [Figure 5]This graph illustrates a method for estimating the first open-circuit voltage using one embodiment. [Figure 6] This graph illustrates a method for estimating the first open-circuit voltage using one embodiment. [Figure 7] This graph illustrates a method for estimating the first open-circuit voltage using one embodiment. [Figure 8] This is an illustrative diagram illustrating whether or not the first open-circuit voltage and the second open-circuit voltage coincide, based on one embodiment. [Figure 9] This is another illustrative diagram illustrating whether or not the first open-circuit voltage and the second open-circuit voltage coincide, based on one embodiment. [Figure 10] This flowchart illustrates a method for calibrating the charging state using other examples. [Modes for carrying out the invention]
[0016] The embodiments disclosed herein will be described in detail below with reference to the attached drawings, but identical or similar components will be numbered with the same or similar drawing numbers, and redundant descriptions thereof will be omitted. The suffixes “module” and / or “part” used for components in the following description are added or mixed for the sole purpose of facilitating the creation of the specification and do not have any distinguishing meaning or role in themselves. Furthermore, in describing the embodiments disclosed herein, if it is determined that a specific description of related known technology may obscure the gist of the embodiments disclosed herein, such detailed description will be omitted. In addition, the attached drawings are merely for the purpose of facilitating the understanding of the embodiments disclosed herein, and it should be understood that the attached drawings do not limit the technical ideas disclosed herein and include all modifications, equivalents or substitutes that fall within the concept and technical scope of the present invention.
[0017] Terms including ordinal numbers, such as "first," "second," etc., can be used to describe a variety of components, but the components are not limited by such terms. These terms are used solely for the purpose of distinguishing one component from another.
[0018] When a component is referred to as being "connected" or "attached" to another component, it should be understood that it may be directly connected or attached to the other component, or there may be other components in between. In contrast, when a component is referred to as being "directly connected" or "directly attached" to another component, it should be understood that there are no other components in between.
[0019] In this application, terms such as "comprising" or "having" are intended to specify the presence of the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and it should be understood that the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof is not precluded in advance.
[0020] FIG. 1 is a block diagram illustrating a battery system according to an embodiment, FIG. 2 is a conceptual diagram illustrating in detail a plurality of estimation modules and mapping tables stored in the storage unit of FIG. 1, FIG. 3 is an example of a graph corresponding to the cell voltage of a battery cell while an automotive system equipped with a battery system according to an embodiment is operating, and FIG. 4 is an example of a graph corresponding to the cell current of a battery cell while an automotive system equipped with a battery system according to an embodiment is operating.
[0021] Referring to FIG. 1, the battery system 1 includes a battery 10, a current sensor 20, a relay 30, and a battery management system (hereinafter referred to as "BMS") 40.
[0022] The battery 10 may include multiple battery cells Cell1-Celln connected in series and parallel. In one embodiment, the battery cells may be rechargeable secondary batteries. A predetermined number of battery cells can be connected in series to form a battery module, a predetermined number of battery modules can be connected in series to form a battery pack, and a predetermined number of battery packs can be connected in parallel to form a battery bank, thereby supplying the necessary power to an external device. Figure 1 shows a battery 10 in which multiple battery cells Cell1-Celln are connected in series, but the battery 10 may be configured in units of battery modules, battery packs, or battery banks.
[0023] Each of the multiple battery cells, Cell1-Celln, is electrically connected to the BMS40 via wiring. The BMS40 collects and analyzes various information about the battery cells, including information about the multiple battery cells, to control the charging and discharging of the battery cells, protective operations, etc., and to control the operation of the relay 30.
[0024] In Figure 1, the battery 10 is connected between the two output terminals OUT1 and OUT2 of the battery system 1. A relay 30 is connected between the positive electrode (cathode) of the battery system 1 and the first output terminal OUT1, and a current sensor 20 is connected between the negative electrode (anode) of the battery system 1 and the second output terminal OUT2. The configuration and connections between the configurations shown in Figure 1 are examples, and the invention is not limited thereto. For example, the BMS 40 can be fabricated on a modularized chip and wirelessly connected to each of the multiple battery cells Cell1-Celln.
[0025] The current sensor 20 is connected in series to the current path between the battery 10 and the external device. The current sensor 20 can measure the battery current flowing through the battery 10, i.e., the charging current and the discharging current, and transmit the measurement results to the BMS 40.
[0026] The relay 30 acts as a kind of switch that controls the electrical connection between the battery system 1 and the external device. When the relay 30 is turned ON, the battery system 1 and the external device are electrically connected, and charging or discharging takes place. When the relay 30 is turned OFF, the battery system 1 and the external device are electrically isolated. At this time, the external device may be a charger in a charging cycle where power is supplied to charge the battery 10, or a load in a discharge cycle where the battery 10 discharges power to the external device.
[0027] The BMS40 includes a monitoring unit 41, a storage unit 43, and a control unit 45.
[0028] The monitoring unit 41 is electrically connected to the positive electrode (cathode) and negative electrode (anode) of each of the multiple battery cells Cell1-Celln, and can measure the cell voltage, which is the voltage across each of the multiple battery cells Cell1-Celln. For example, Figure 3 may be an example of a graph showing the cell voltage measured by the monitoring unit 41 over a period from 0 seconds to approximately 12,200 seconds. For example, Figure 3 may be a graph showing the average voltage of multiple battery cells. At each predetermined storage cycle (for example, every △0.1% of SOC), the monitoring unit 41 can transmit the cell voltage corresponding to the storage period DT (for example, 60 seconds) to the control unit 45. The storage period DT can correspond to the period between adjacent storage cycles.
[0029] The monitoring unit 41 can measure the cell voltage of each of the multiple battery cells Cell1-Celln using various conventionally known methods and calculate the cell current based on the measured cell voltages. For example, the cell current can be calculated using the average cell voltage and the overall cell resistance as described above. Alternatively, the monitoring unit 41 may measure the cell current of each of the multiple battery cells Cell1-Celln using a current sensor (not shown) mounted on the battery cell. For example, Figure 4 may be a graph showing the cell currents calculated or measured by the monitoring unit 41 over a period from 0 seconds to approximately 12200 seconds. For each storage cycle, the monitoring unit 41 can transmit the cell current corresponding to the storage period DT to the control unit 45.
[0030] The storage unit 43 may store a State of Charge (SOC) estimation module 43-2, a first open-circuit voltage estimation module 43-4, a mapping table 43-6, a second open-circuit voltage estimation module 43-8, a cost estimation module 43-10, and a State of Charge (SOC) calibration module 43-12. In this case, the first open-circuit voltage (OCV_1) and the second open-circuit voltage (OCV_2) can correspond to the open-circuit voltage (OCV). The multiple estimation modules and mapping table shown in Figure 2 will be described in detail below with reference to Figures 5 to 9.
[0031] The control unit 45 can calibrate the initial value of the charge state (SOC) of the battery 10 using a plurality of estimation modules 43-2, 43-4, 43-8, 43-10, a charge state (SOC) calibration module 43-12, and a mapping table 43-6 stored in the storage unit 43. The method by which the control unit 45 calibrates the initial value of the charge state (SOC) will be described in detail below with reference to Figures 5 to 10.
[0032] Figure 5 is an enlarged view of the first cell voltage (e.g., measured voltage for 60 seconds) corresponding to a predetermined storage period DT shown in Figure 3, as an example; Figure 6 is an enlarged view of the cell current (e.g., measured current for 60 seconds) corresponding to a predetermined storage period DT shown in Figure 4; Figure 7 is a graph showing the first and second cell voltages in one embodiment; Figure 8 is an illustrative diagram to explain whether or not the first open-circuit voltage and the second open-circuit voltage coincide in one embodiment; and Figure 9 is another illustrative diagram to explain whether or not the first open-circuit voltage and the second open-circuit voltage coincide using the concept of a cost function in one embodiment.
[0033] Hereafter, the cell voltage measured by the monitoring unit 41 will be described as the first cell voltage. The cell voltage calculated by the ECM (Equivalent Circuit Model) based on the cell current measured by the monitoring unit 41, as described below, will be described as the second cell voltage. For example, the first graph (A) in Figures 3, 5, and 7 can correspond to the graph of the first cell voltage. As another example, the second graph (B) in Figure 7 can correspond to the graph of the second cell voltage.
[0034] The State of Charge (SOC) estimation module 43-2 may include an algorithm that estimates the State of Charge (SOC) corresponding to a predetermined storage cycle by adding the integral value of the cell current over a predetermined period to the initial value of the State of Charge (SOC) of the battery cell. For example, the State of Charge (SOC) estimation module 43-2 may include a conventionally known current integration method (Coulomb Counting Method) algorithm.
[0035] Referring to Figures 4 and 6, for example, when the Nth storage period T2 arrives, the control unit 45 uses the State of Charge (SOC) estimation module 43-2 to integrate the cell current during the storage period DT, and adds the integrated value of the cell current to the initial value of the State of Charge (SOC) to estimate the State of Charge (SOC) corresponding to the arrival of the Nth storage period T2. At this time, the storage period DT can correspond to the period between two adjacent storage periods T1 and T2. Furthermore, the initial value of the State of Charge (SOC) added to the integrated value of the cell current may be the State of Charge (SOC) corresponding to the (N-1)th storage period T1.
[0036] The first open-circuit voltage estimation module 43-4 can estimate the first open-circuit voltage (OCV_1) corresponding to the arrival of a predetermined storage cycle T, based on the cell current profile corresponding to the storage period DT. In this embodiment, the control unit 45 can estimate the first open-circuit voltage (OCV_1) corresponding to the arrival of the second storage cycle T2, based on the cell current profile corresponding to the storage period (DT=T2-T1).
[0037] Specifically, the first open-circuit voltage estimation module 43-4 can include an equivalent circuit model (ECM) that simulates the cell voltage corresponding to the cell current using the equivalent circuit of a battery cell. For example, the ECM may be a model that simulates the cell voltage of a battery cell, consisting of three parameters. In this case, the three parameters may include the internal resistance (R), the open-circuit voltage (OCV), and the capacitor time constant (tau) within the equivalent circuit. The internal resistance (R), the open-circuit voltage (OCV), and the capacitor time constant (tau) may be variables derived by the fitting algorithm described below. For example, by inputting the cell current to the ECM, the IR drop (Ohmic Drop) can be calculated to determine the second cell voltage. However, the control unit 45 is not limited to the ECM described above, and can generate the cell voltage corresponding to the cell current using various conventionally known forms of ECM. Furthermore, although these are described as cell current and second cell voltage, more specifically, they may be cell current profiles and second cell voltage profiles corresponding to the storage period DT.
[0038] As shown in the embodiment, referring to Figures 6 and 7, the control unit 45 can use the first open-circuit voltage estimation module 43-4 to generate the second cell voltage profile (B, dotted line) in Figure 7, which corresponds to the cell current profile in Figure 6. At this time, the first cell voltage profile shown in Figure 5 can correspond to the first cell voltage profile (A, solid line) in Figure 7.
[0039] Next, referring to Figure 7, the first open-circuit voltage estimation module 43-4 may include a fitting algorithm that fits the first cell voltage profile A and the second cell voltage profile B to estimate the first open-circuit voltage (OCV_1). The control unit 45 can use the fitting algorithm to fit the second cell voltage profile B to be close to the first cell voltage profile A and derive the three parameters that constitute the ECM: internal resistance (R), open-circuit voltage (OCV), and time constant (tau). In other words, the control unit 45 can use the fitting algorithm to extract the open-circuit voltage (OCV), which is one of the three parameters. In this embodiment, the open-circuit voltage (OCV) extracted by the fitting algorithm may be the first open-circuit voltage (OCV_1).
[0040] The mapping table 43-6 may store mapping data in which the state of charge (SOC) and the first open-circuit voltage (OCV_1) estimated for each predetermined storage cycle are mapped. Table 1 below is an example of a mapping table. For example, referring to Figures 5 and 6, when the Nth storage cycle T2 arrives, the control unit 45 can estimate the state of charge (SOC) using the current integration method with the state of charge (SOC) estimation module 43-2, and simultaneously calculate the first open-circuit voltage (OCV_1) using the first open-circuit voltage estimation module 43-4. The control unit 45 can map the state of charge (SOC) and the first open-circuit voltage (OCV_1) corresponding to the arrival of the Nth storage cycle T2 and store it in the mapping table 43-6. [Table 1]
[0041] The second open-circuit voltage (OCV_2) estimation module 43-8 can estimate multiple second open-circuit voltages (OCV_2) corresponding to the state of charge (SOC) stored in the storage unit 43 from the previous calibration cycle T_N-1 to the current calibration cycle T_N, based on the SOC_OCV graph or SOC_OCV lookup table, when a predetermined calibration cycle arrives.
[0042] The calibration cycle can occur when the storage cycle reaches a predetermined reference number of times. For example, the calibration cycle can be set to occur when the number of times the state of charge (SOC) and the first open-circuit voltage (OCV_1) have been mapped and stored in the storage unit 43 is 100. However, it is not limited to this, and the calibration cycle can be set in various ways, such as 100 times or more, or less than 100 times.
[0043] In one embodiment, the second open-circuit voltage (OCV_2) estimation module 43-8 can calculate a first relationship graph, which is a relationship graph between multiple charge states (SOCs) and multiple open-circuit voltages stored during the calibration cycle, based on a lookup table. Furthermore, the second open-circuit voltage (OCV_2) estimation module 43-8 can calculate multiple relationship graphs by reflecting multiple preset error values in the first relationship graph. These multiple error values can correspond to multiple input values, as described below.
[0044] In other embodiments, the second open-circuit voltage (OCV_2) estimation module 43-8 can estimate multiple second open-circuit voltages corresponding to multiple states of charge (SOCs) stored during the calibration cycle, based on a lookup table. For example, suppose the calibration cycle arrives when the number of times the mapping data, which maps the states of charge (SOCs) and the first open-circuit voltage (OCV_1), has been stored reaches 100. The second open-circuit voltage (OCV_2) estimation module can estimate 100 second open-circuit voltages (OCV_2) corresponding to each of the 100 states of charge (SOCs), based on the SOC_OCV lookup table.
[0045] The cost estimation module 43-10 may include an algorithm to calculate the final error value between the first open-circuit voltage (OCV_1) and the second open-circuit voltage (OCV_2) based on data accumulated during the period from the previous calibration cycle T_N-1 to the current calibration cycle T_N. Figures 8 and 9 illustrate in detail how the control unit 45 calculates the error value via the cost estimation module.
[0046] Referring to Figure 8, each of the multiple points may be mapping data, which is data where multiple charge states (SOC) and multiple first open-circuit voltages (OCV_1) from Table 1 are mapped. In other words, the number of points can correspond to the number of mapping data stored in Table 1.
[0047] The control unit 45 can calculate multiple second open-circuit voltages (OCV_2) corresponding to multiple states of charge (SOC) in the form of an SOC-OCV graph via the second open-circuit voltage estimation module 43-8. For example, in Figure 8, the first SOC-OCV graph (C+0) may be a graph calculated by the control unit 45.
number
[0048] Formula (1) may also correspond to the cost function used to derive the hypothesis function that has the smallest error from the original value. In formula (1), "Cost" is the cost function for the input value (ε). Here, n is the total number of storage cycles corresponding to the calibration cycle, K is the order corresponding to a given storage cycle, and the input value (ε) may be defined within a given range (ε_min≦ε≧ε_max). For example, the minimum input value (ε_min) may be -10 and the maximum input value (ε_max) may be +10. For example, let's assume the input values (ε) are -10, -8, -6, -4, -2, 0, 2, 4, 6, 8, 10.
[0049] In one embodiment, the control unit 45 can calculate the sum of the straight-line distances between each of the multiple relational graphs and the multiple mapping data. The control unit 45 can determine the error value corresponding to the minimum of the multiple sums as the final error value between the first open-circuit voltage and the second open-circuit voltage. The final error value can correspond to the degree of discrepancy between the multiple first open-circuit voltages and the multiple second open-circuit voltages. Furthermore, the final error value can correspond to the degree of discrepancy between the initial value of the charge state derived by calculation and the actual initial value of the charge state. The unit of the error value can correspond to %.
[0050] In another embodiment, the control unit 45 can derive multiple costs corresponding to multiple input values (ε = -10, -8, -6, -4, -2, 0, 2, 4, 6, 8, 10), i.e., multiple error values, using the formula (1) corresponding to the cost function. The control unit 45 can determine the error value corresponding to the lowest cost among the multiple costs as the final error value.
[0051] The cost can correspond to the sum of the straight-line distances between each of the multiple mapping data points and a given SOC-OCV graph. For example, referring to equation (1) and Figure 9, the lower the cost, the higher the agreement rate between the multiple mapping data points and the SOC-OCV graph. In Figure 9, the cost is lowest when the input value (ε) is -2. The input value (ε) corresponding to the lowest cost can correspond to the final error value. In this case, the unit of the final error value may be %. That is, for example, the final error value in the given example can be estimated to be -2%.
[0052] In Figure 9, the reference range TH_range may be a range in which the final error value between the first open-circuit voltage (OCV_1) and the second open-circuit voltage (OCV_2) is acceptable. For example, if the final error value falls within the reference range TH_range, the control unit 45 can determine that the error between the calculated initial value of the state of charge (SOC) and the actual initial value of the state of charge (SOC) is small. In this case, the control unit 45 may not need to calibrate the initial value of the state of charge (SOC). As another example, if the final error value exceeds the reference range, the control unit 45 can determine that the error between the calculated initial value of the state of charge (SOC) and the actual initial value of the state of charge (SOC) is large. The state of charge (SOC) calibration module 43-12 may include an algorithm that calibrates the initial value of the state of charge (SOC) by adding the state of charge (SOC) corresponding to the final error value to the initial value of the state of charge (SOC).
[0053] Figure 10 is a flowchart illustrating a method for calibrating the charging state according to an embodiment of the present invention.
[0054] The following describes in detail a method for calibrating the charge state and a battery system that provides this method, with reference to Figures 1 to 10.
[0055] Referring to Figure 10, when a predetermined storage cycle arrives, the BMS 40 estimates the charge state (SOC) and the first open-circuit voltage (OCV_1) of the battery cell (S110, S120).
[0056] To explain this in more detail, the BMS40 can calculate a cell current profile based on the cell current measured during the storage period DT. The BMS40 can calculate a first cell voltage profile A based on the cell voltage, which is the voltage across the battery cells measured during the storage period DT. The BMS40 can store the cell current profile and the first cell voltage profile in the storage unit 43.
[0057] The BMS40 can estimate the battery cell's state of charge (SOC) corresponding to a storage cycle by adding the integral of the cell current during the storage period DT to the initial value of the battery cell's state of charge (SOC).
[0058] Referring to Figures 4 and 6, for example, when the Nth storage period T2 arrives, the BMS 40 integrates the magnitude of the cell current corresponding to the storage period DT. The BMS 40 can estimate the state of charge (SOC) corresponding to the arrival of the Nth storage period T2 by adding the integrated value of the cell current to the initial value of the state of charge (SOC). In this case, the storage period DT can correspond to the period between the (N-1)th storage period T1 and the Nth storage period T2. Furthermore, the initial value of the state of charge (SOC) added to the integrated value of the cell current may be the state of charge (SOC) corresponding to the Nth storage period T2.
[0059] Meanwhile, in parallel with this, the BMS40 can estimate the first open-circuit voltage (OCV_1) of the battery cell corresponding to the storage period based on the equivalent circuit and cell current of the battery cell. In the embodiment, the BMS40 can generate a second cell voltage profile B corresponding to the cell current profile during the storage period DT using an Equivalent Circuit Model (ECM) that simulates the cell voltage corresponding to the cell current using the equivalent circuit of the battery cell.
[0060] For example, as illustrated in Figure 7, the first cell voltage profile A, shown as a solid line, may be the voltage across the battery cell measured by the monitoring unit 41. The second cell voltage profile B, shown as a dotted line, may be the cell voltage profile corresponding to the cell current profile calculated via the ECM.
[0061] Next, the BMS40 can estimate the first open-circuit voltage (OCV_1) by fitting the first cell voltage profile A and the second cell voltage profile B. Specifically, the BMS40 can fit the second cell voltage profile B to the first cell voltage profile A by changing the three parameters that constitute the ECM: internal resistance (R), open-circuit voltage (OCV), and time constant. The BMS40 can derive the internal resistance (R), open-circuit voltage (OCV), and time constant that bring the second cell voltage profile B closest to the first cell voltage profile A. In this embodiment, when the second cell voltage profile B is closest to the first cell voltage profile A, the extracted open-circuit voltage (OCV) can correspond to the first open-circuit voltage (OCV_1).
[0062] Next, the BMS40 maps the state of charge (SOC) and the first open-circuit voltage (OCV_1) and stores them in the storage unit 43 (S130).
[0063] The BMS40 may include a mapping table. For example, Table 1 above may be an example of a mapping table. The mapping table may store mapping data in which the state of charge (SOC), calculated by the current integration method for each storage cycle, and the first open-circuit voltage (OCV_1), calculated simultaneously based on the equivalent circuit and cell current of the battery cell, are mapped.
[0064] Next, when the number of storage cycles corresponds to a predetermined reference number and the calibration cycle arrives, the BMS40 estimates multiple second open-circuit voltages corresponding to multiple charge states stored during the calibration cycle based on the state of charge (SOC)-open-circuit voltage (OCV) lookup table (S140, S150).
[0065] The calibration cycle can occur when the storage cycle reaches a predetermined number of times. For example, the calibration cycle can be set to occur when the mapping data has been stored in the storage unit 43 100 times. However, it is not limited to this, and the calibration cycle can be set in various ways, such as 100 times or more, or less than 100 times.
[0066] In one embodiment, the BMS40 can calculate a first relationship graph, which is a relationship graph between multiple charge states (SOCs) and multiple open-circuit voltages stored during the calibration cycle, based on a lookup table. Furthermore, the BMS40 can calculate multiple relationship graphs by reflecting multiple preset error values in the first relationship graph. These multiple error values can correspond to multiple input values, as described below.
[0067] Referring to Figure 8, the first SOC-OCV graph (C+0) can correspond to a first relationship graph between multiple second open-circuit voltages (OCV_2) corresponding to multiple charge states (SOCs) estimated during the calibration cycle. For example, the first SOC-OCV graph (C+0) may correspond to the input value (ε) "0". For predictability, the BMS40 can calculate multiple relationship graphs by reflecting multiple input values pre-set in the first relationship graph. The BMS40 can calculate a second SOC-OCV graph (C-10) corresponding to the input value (ε) "-10". The BMS40 can calculate a third SOC-OCV graph (C+10) corresponding to the input value (ε) "+10". In other words, the BMS40 can calculate multiple SOC-OCV graphs, each corresponding to multiple input values (ε = -10, -8, -6, -4, -2, 0, 2, 4, 6, 8, 10). For example, referring to Figure 8, the input value (ε) can correspond to the magnitude of the SOC used to translate the first relation graph horizontally. In Figure 8, multiple points can correspond to multiple first mapping data points.
[0068] In other embodiments, the BMS40 can estimate multiple second open-circuit voltages corresponding to multiple states of charge (SOCs) stored during the calibration cycle, based on a lookup table.
[0069] Next, the BMS40 calculates a final error value corresponding to the degree of discrepancy between the first open-circuit voltage (OCV_1) and the second open-circuit voltage (OCV_2) (S160), and determines whether the calculated final error value exceeds a predetermined reference range TH_range (S170).
[0070] In this embodiment, the BMS40 can calculate the sum of the straight-line distances between each of the multiple relational graphs and multiple mapping data points. The BMS40 can determine the error value corresponding to the smallest of the multiple sums as the final error value between the first open-circuit voltage and the second open-circuit voltage. The final error value can correspond to the degree of discrepancy between the multiple first open-circuit voltages and the multiple second open-circuit voltages. Furthermore, the final error value can correspond to the degree of discrepancy between the calculated initial charge state and the actual initial charge state. The unit of the error value can correspond to %.
[0071] In the embodiment, the BMS40 can calculate the final error value based on a predetermined cost function that quantifies the degree of agreement between a plurality of first open-circuit voltages and a plurality of second open-circuit voltages. For example, the BMS40 can derive a plurality of costs corresponding to a plurality of input values (ε), i.e., a plurality of error values, using the formula (1) corresponding to the cost function. The BMS40 can determine the error value corresponding to the lowest cost among the plurality of costs as the final error value.
[0072] Referring to formula (1) and Figure 8, the sum of the straight-line distances between multiple first mapping data points and a given SOC-OCV relationship graph can correspond to the cost. For example, BMS40 calculates multiple costs for each of the multiple input values (ε = -10, -8, -6, -4, -2, 0, 2, 4, 6, 8, 10). The input value (ε) corresponding to the minimum cost among the calculated multiple costs can correspond to the final error value. For example, referring to Figure 9, we assume that the cost is lowest when the input value (ε) is -2. Then, BMS40 can calculate the final error value as -2%.
[0073] Specifically, for each of the multiple input values (ε = -10, -8, -6, -4, -2, 0, 2, 4, 6, 8, 10), the BMS40 can calculate multiple costs by substituting the values of multiple states of charge (SOC), multiple first open-circuit voltages (OCV_1), and multiple second open-circuit voltages (OCV_2) into formula (1). In other words, the multiple costs calculated by substituting into formula (1) correspond to the graph shown in Figure 9.
[0074] Next, if the final error value exceeds the reference range (S170, YES), the BMS40 calibrates the initial value of the state of charge (SOC) (S180). If the final error value does not exceed the reference range (S170, NO), the BMS40 does not calibrate the initial value of the state of charge (SOC) (S190).
[0075] The reference range TH_range may also be the range within which the final error value is acceptable. Referring to Figure 9, let's assume that the reference range TH_range corresponds to -5 to +5.
[0076] For example, assuming that the final error value calculated in S160 is +10%, BMS40 can determine in S170 that the final error value of +10% exceeds the reference range TH_range (S170, YES). In this case, BMS40 can calibrate the initial value of the charge state (SOC) in S180 by adding the charge state (SOC) corresponding to the final error value. Specifically, BMS40 can divide the charge state (SOC) corresponding to the final error value into pre-set time intervals and calibrate the initial value of the charge state (SOC) by adding the divided charge state to the initial value of the charge state (SOC) in divided time units.
[0077] For example, suppose the final error value is +10%, the initial state of charge (SOC) is 50%, and the preset time is 10 minutes. The BMS40 divides the SOC corresponding to the final error value of +10% into 10-minute segments, and adds 5% of the divided SOC (0.1 × 50% = 5%) in 1-minute increments to the initial SOC of 50% for 10 minutes, thereby calibrating the initial SOC to 55%.
[0078] Next, the BMS 40 deletes the multiple mapping data stored in the storage unit 43 and resets the storage unit 43 (S190). Then, a new calibration cycle begins. In other words, the entire process may be repeated from step S110 when a storage cycle arrives after a new calibration cycle has started.
[0079] As another example, assuming that the final error value calculated in S160 is -2%, the BMS40 can determine in S170 that the final error value of -2% does not exceed the reference range TH_range (S170, NO). In this case, the BMS40 does not calibrate the initial value of the state of charge (SOC) and resets the storage unit 43 by deleting the multiple mapping data stored in the storage unit 43 (S190). A new calibration cycle then begins. In other words, the entire process may be repeated from step S110 when a storage cycle arrives after a new calibration cycle has started.
[0080] On the other hand, in one embodiment, the BMS40 may perform state of charge (SOC) calibration only under specific conditions. For example, after calculating the final error value in S160, the BMS40 can determine whether specific conditions are met before determining in S170 whether the final error value exceeds the reference range. For example, after calculating the final error value in S160, the BMS40 may determine whether one or more of the following conditions are met: (1) the number of accumulated mapping data is 100 or more, (2) the interval of the accumulated state of charge (△SOC) is in the range of 30% or more, (3) the current state of charge (SOC) is 55% or less, or (4) the open-circuit voltage (OCV) is 30mV or more, and the BMS40 may be designed to perform step S170 only when such conditions are met. In this way, by designing the BMS40 to perform correction only when specific conditions are met, unnecessarily frequent corrections can be prevented, and resources can be used where they are more urgent.
[0081] On the other hand, the determination of whether such specific conditions are met is not limited to being performed only after S160, but can also be performed after any stage of the process, for example, after any of the stages S120 to S150.
[0082] Although embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modified and improved forms by persons with ordinary skill in the art to which the present invention belongs also fall within the scope of the present invention.
Claims
1. A battery system that estimates the charge state of a battery cell by integrating the cell current flowing through the battery cell, A storage unit stores mapping data in which, at predetermined storage cycles, the charging state estimated based on the integral value of the cell current and a first open-circuit voltage estimated by a predetermined model that replicates the cell voltage corresponding to the cell current are mapped; When the number of times the mapping data has been stored reaches a predetermined reference number and the calibration cycle arrives, the control unit estimates a first relationship graph, which is a relationship graph between a plurality of charge states and a plurality of open-circuit voltages stored in the storage unit, based on a predetermined charge state-open-circuit voltage lookup table, calculates a plurality of relationship graphs by reflecting a plurality of error values set in advance in the first relationship graph, calculates the sum of the distances between each of the plurality of relationship graphs and the mapping data, determines the error value corresponding to the smallest of the plurality of sums as the final error value between the first open-circuit voltage and the second open-circuit voltage corresponding to the charge state, and determines whether the final error value falls within a predetermined reference range, and determines whether or not to calibrate the initial value of the charge state. A battery system including a battery system.
2. The control unit, The battery system according to claim 1, wherein when the Nth storage cycle arrives, the cell current measured during the storage period corresponding to the period from the N-1st storage cycle to the Nth storage cycle is integrated to calculate the integral value, and the charge state corresponding to the N-1st storage cycle is calculated by adding the integral value to the charge state corresponding to the Nth storage cycle.
3. The aforementioned storage unit is In accordance with the storage period, which is the period between adjacent storage cycles, the cell current profile calculated based on the cell current and the first cell voltage profile calculated based on the cell voltage, which is the voltage across the battery cell, are stored. The control unit, The battery system according to claim 1, wherein a second cell voltage profile corresponding to the cell current profile is generated by the model which includes as a parameter the open-circuit voltage based on the equivalent circuit of the battery cell.
4. The control unit, The battery system according to claim 3, wherein the magnitude of the open-circuit voltage corresponding to the time when the first cell voltage profile and the second cell voltage profile are fitted to be closest together is calculated as the first open-circuit voltage.
5. The control unit, The battery system according to claim 1, wherein if the final error value exceeds a predetermined reference range, the charge state corresponding to the final error value is added to the initial value of the charge state to calibrate the initial value of the charge state.
6. The control unit, The battery system according to claim 1, wherein if the final error value exceeds a predetermined reference range, the charging state corresponding to the final error value is divided into predetermined time intervals, and the initial value of the charging state is calibrated by adding the divided charging state to the initial value of the charging state in the divided time units.
7. A battery system that estimates the charge state of a battery cell by integrating the cell current flowing through the battery cell, A storage unit stores mapping data in which, at predetermined storage cycles, a plurality of first open-circuit voltages estimated by a predetermined model that replicates the charge state estimated based on the integral value of the cell current and the cell voltage corresponding to the cell current are mapped; When the number of times the mapping data has been stored reaches a predetermined reference number and the calibration cycle arrives, the control unit estimates a plurality of second open-circuit voltages corresponding to a plurality of charge states stored in the storage unit based on a predetermined charge state-open-circuit voltage lookup table, calculates a final error value corresponding to the degree of mismatch between the plurality of first open-circuit voltages and the plurality of second open-circuit voltages based on a predetermined cost function that quantifies the degree of agreement between the plurality of first open-circuit voltages and the plurality of second open-circuit voltages, determines whether the final error value falls within a predetermined reference range, and determines whether or not to calibrate the initial value of the charge state. A battery system including a battery system.
8. The control unit, The battery system according to claim 7, wherein the final error value is determined to be the error value corresponding to the smallest cost among a plurality of costs derived by the following formula corresponding to the cost function. [Math 2] Cost is the cost, OCV_1 is the first open-circuit voltage, OCV_2 is the second open-circuit voltage, SOC is the charge state, k is the storage cycle count, n is the reference number, and ε is the error value, which is a plurality of integers that belong to a predetermined range set in advance.
9. The control unit, The battery system according to claim 7, wherein when the Nth storage cycle arrives, the cell current measured during the period from the N-1st storage cycle to the Nth storage cycle is integrated to calculate an integral value, and the charge state corresponding to the N-1st storage cycle is calculated by adding the integral value to the charge state corresponding to the Nth storage cycle.
10. The aforementioned storage unit is In accordance with the storage period, which is the period between adjacent storage cycles, the cell current profile calculated based on the cell current and the first cell voltage profile calculated based on the cell voltage, which is the voltage across the battery cell, are stored. The control unit, The battery system according to claim 7, wherein a second cell voltage profile corresponding to the cell current profile is generated by the model which includes as a parameter the open-circuit voltage based on the equivalent circuit of the battery cell.
11. The control unit, The battery system according to claim 10, wherein the magnitude of the open-circuit voltage corresponding to the time when the first cell voltage profile and the second cell voltage profile are fitted to each other in the closest proximity is calculated as the plurality of first open-circuit voltages.
12. The control unit, The battery system according to claim 7, wherein if the final error value exceeds a predetermined reference range, the initial value of the charge state is calibrated by adding the charge state corresponding to the final error value to the initial value of the charge state.
13. The control unit, The battery system according to claim 7, wherein if the final error value exceeds a predetermined reference range, the charging state corresponding to the final error value is divided into predetermined time intervals, and the initial value of the charging state is calibrated by adding the divided charging state to the initial value of the charging state in the divided time units.
14. When a predetermined storage cycle arrives, the process involves estimating multiple charge states and multiple first open-circuit voltages of the battery cell based on a predetermined model that simulates the integral value of the cell current flowing through the battery cell and the cell voltage corresponding to the cell current, respectively. The steps include: storing mapping data, in which the plurality of charge states and the plurality of first open-circuit voltages are mapped, in the storage unit; When the number of times the mapping data has been stored reaches a predetermined reference number and the calibration cycle arrives, the following steps are taken: estimating a plurality of second open-circuit voltages corresponding to a plurality of charge states stored in the storage unit based on a predetermined charge state-open-circuit voltage lookup table; A step of calculating a final error value corresponding to the degree of mismatch between the plurality of first open-circuit voltages and the plurality of second open-circuit voltages, based on a predetermined cost function that quantifies the degree of agreement between the plurality of first open-circuit voltages and the plurality of second open-circuit voltages, The step of determining whether the final error value falls within a predetermined reference range, A method for calibrating a charging state, which includes the step of calibrating the initial value of the charging state if, as a result of the above determination, the final error value exceeds a predetermined reference range.
15. The step of calculating the final error value is: The charging state calibration method according to claim 14, further comprising the step of determining the final error value to be the error value corresponding to the smallest cost among a plurality of costs derived by the following formula corresponding to the cost function. [Math 3] Cost is the cost, OCV_1 is the first open-circuit voltage, OCV_2 is the second open-circuit voltage, SOC is the charge state, k is the storage cycle count, n is the reference number, and ε is the error value, which is a plurality of integers that belong to a predetermined range set in advance.
16. The step of estimating the plurality of charge states and the plurality of first open-circuit voltages is: In a step corresponding to a storage period which is the period between adjacent storage cycles, the cell current profile calculated based on the cell current and the first cell voltage profile calculated based on the cell voltage which is the voltage across the battery cell are stored in the storage unit, The steps include generating a second cell voltage profile corresponding to the cell current profile using the model which includes the open-circuit voltage based on the equivalent circuit of the battery cell as a parameter, A method for calibrating a charge state according to claim 14, comprising the step of calculating the magnitude of the open-circuit voltage corresponding to the time when the first cell voltage profile and the second cell voltage profile are fitted to each other in the closest proximity as the plurality of first open-circuit voltages.
17. The step of calibrating the initial value of the charging state is: A method for calibrating a charging state according to claim 14, further comprising the step of adding the charging state corresponding to the final error value to the initial value of the charging state, and calibrating the initial value of the charging state.
18. The step of calibrating the initial value of the charging state is: A method for calibrating a charging state according to claim 14, further comprising the steps of dividing the charging state corresponding to the final error value into predetermined time intervals, and calibrating the initial value of the charging state by adding the divided charging state to the initial value of the charging state in units of the divided time intervals.