Calibration method of state of charge and battery system for providing calibration method

Abstract

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. The battery system of the present invention comprises: a storage unit for storing mapping data in which a state of charge estimated on the basis of an integrated value of a cell current and a first open circuit voltage estimated by a predetermined model that simulates a cell voltage corresponding to the cell current are mapped to each other at each predetermined cycle; and a control unit that estimates a relationship map between a plurality of states 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, if the number of times of storing the mapping data satisfies a predetermined reference number of times, determines whether the number of times of storing the mapping data satisfies a predetermined reference number of times. If yes, calculating a plurality of relation graphs by reflecting a plurality of preset error values in a first relation graph, calculating a plurality of sum values of distances between each of the plurality of relation graphs and the plurality of pieces of mapping data, an error value corresponding to a minimum value among the plurality of sum values is determined as a final error value between the first open circuit voltage and the second open circuit voltage, and whether to calibrate an initial value of a state of charge (SOC) is determined by determining whether the final error value belongs to a predetermined reference range.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is based on and claims the benefit of priority from Korean Patent Application No. 10-2023-0079004 filed in the Korean Intellectual Property Office on June 20, 2023, the disclosure of which is incorporated herein by reference in its entirety.

[0003] The present disclosure relates to a method for calibrating an initial value of a state of charge (SOC) and a battery system for providing the same. Background Art

[0004] The state of charge (SOC) of a battery may indicate the relative amount of energy stored in the battery. For example, the SOC may be expressed as a percentage (%) obtained by dividing the current capacity of the battery by the total capacity of the battery.

[0005] SOC is a key element for managing systems that operate using battery power. Therefore, accurate measurement of SOC can serve as an indicator of the core competitiveness of battery manufacturers.

[0006] There are various methods for estimating the SOC of a battery, including a voltage-SOC estimation method (e.g., an open circuit voltage method) and a current integration method (e.g., a coulomb counting method). The voltage-SOC estimation method can estimate the SOC by measuring the open circuit voltage (OCV) of the battery and comparing the measured OCV with a SOC-OCV relationship graph. The current integration method, also known as the coulomb counting method, can estimate the SOC by adding or subtracting a current integration value to or from an initial SOC value during a charge or discharge cycle.

[0007] The voltage SOC estimation method is a simple method of estimating the SOC by measuring only the voltage of the battery, but its disadvantage is that it is difficult to estimate the SOC in real time because the current charging or discharging in the battery remains in the battery even after it is cut off (turned on), which requires a pause time for accurate estimation.

[0008] In addition, in the case of lithium iron phosphate (Li-FePO 4 ) batteries, the OCV tends to remain at a plateau. That is, it is difficult to accurately estimate the OCV of batteries made of lithium iron phosphate (Li-FePO 4 That is, for various reasons, the SOC of batteries made of, for example, lithium iron phosphate (Li-FePO 4 ) may be estimated only by the current integration method, and not by the voltage SOC estimation method.

[0009] The current integration method is a common method that can estimate SOC in real time, but the disadvantage is that an accurate initial value may not be obtained at the beginning of the estimation, or the measurement error of the current sensor that measures the battery current and the error that occurs during the analog-to-digital conversion (ADC) may be continuously accumulated during the estimation. For example, since the SOC estimation in the current integration method depends on the initial SOC value, when the initial value is inaccurate, the SOC estimation may have errors, and in addition, as the battery operating time increases, the accuracy of the SOC estimation may decrease when the errors accumulate.

[0010] To solve the above problem, the operator can, for example, send a full charge control signal to the battery management system (BMS) within an estimated time interval (e.g., about two weeks) where the error has been accumulated. Then, the battery management system (BMS) charges the battery, and when the SOC of the battery reaches a fully charged state (100%), the initial value of the SOC is reset to 100% to calibrate the SOC. That is, the SOC estimation method using the current integration method requires a cumbersome process of fully charging the battery at periodic intervals in order to calibrate the initial SOC value. Summary of the invention

[0011] Technical issues

[0012] The present disclosure seeks to provide an SOC calibration method for calibrating an initial SOC value of a battery based on accumulated data even if the battery is not fully charged, and a battery system for providing the method.

[0013] Technical Solution

[0014] According to an embodiment of the present disclosure, a battery system is provided, the battery system being used to estimate the state of charge (SOC) of the battery cell by integrating the cell current flowing in the battery cell, the battery system comprising: a memory storing mapping data in each predetermined storage cycle, the mapping data mapping the SOC of the battery cell estimated based on the integrated value of the cell current and a first open circuit voltage estimated by a predetermined model simulating a cell voltage corresponding to the cell current; and a controller, the controller performing the following process, the process comprising: when the number of times the mapping data is stored reaches a predetermined reference number of times, When a calibration cycle is reached, a first relationship diagram is estimated based on a predetermined SOC open circuit voltage lookup table, wherein the first relationship diagram is a relationship diagram between a plurality of SOCs and a plurality of open circuit voltages stored in the memory; a plurality of relationship diagrams are calculated by reflecting a plurality of preset error values ​​in the first relationship diagram; a sum value of distances between each of the plurality of relationship diagrams and the mapping data is calculated; an error value corresponding to a minimum value among the plurality of sum values ​​is determined as a final error value between the first open circuit voltage and the second open circuit voltage; and whether the final error value falls within a predetermined reference range is determined to determine whether to calibrate the initial SOC value.

[0015] According to another embodiment of the present disclosure, a battery system is provided, which is used to estimate the state of charge of a battery cell by integrating a cell current flowing in a battery cell, and the battery system includes: a memory, which stores mapping data in each predetermined storage cycle, and the mapping data maps the state of charge (SOC) estimated based on the integrated value of the cell current and a first open circuit voltage estimated by simulating a predetermined model of a cell voltage corresponding to the cell current; and a controller, which performs the following process, which includes: when the number of times the mapping data is stored reaches a predetermined reference number so that a calibration cycle arrives, estimating a plurality of second open circuit voltages corresponding to a plurality of SOCs stored in the memory based on a predetermined SOC open circuit voltage lookup table; calculating a final error value corresponding to the degree of difference 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 matching between the plurality of first open circuit voltages stored in the memory and the plurality of second open circuit voltages; and determining whether the final error value falls within a predetermined reference range to determine whether to calibrate the initial SOC value.

[0016] According to another embodiment of the present disclosure, a method for calibrating the state of charge includes the following steps: when a predetermined storage cycle arrives, estimating the state of charge (SOC) and a first open circuit voltage of the battery cell based on an integral value of a cell current flowing in the battery cell and a predetermined model for simulating a cell voltage corresponding to the cell current, respectively; storing mapping data mapping the SOC and the first open circuit voltage in a memory; when the number of times the mapping data is stored reaches a predetermined reference number so that a calibration cycle arrives, estimating a plurality of second open circuit voltages corresponding to a plurality of SOCs stored in the memory based on a predetermined SOC open circuit voltage lookup table; calculating a final error value corresponding to the degree of difference 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 matching between the plurality of first open circuit voltages stored in the memory and the plurality of second open circuit voltages; determining whether the final error value falls within a predetermined reference range; and when it is determined that the final error value exceeds the predetermined reference range, calibrating the initial SOC value.

[0017] Beneficial Effects

[0018] The present disclosure can calibrate the error of the SOC estimated by the current integration method by using a simple method even if the battery is not fully charged (100%). BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a block diagram illustrating a battery system according to an embodiment of the present disclosure.

[0020] Figure 2 It is shown that the storage Figure 1 Conceptual diagram of multiple estimation modules and mapping tables in a storage unit.

[0021] Figures 3 to 7 is a graph illustrating a method of estimating a first open circuit voltage according to an embodiment.

[0022] Figure 8 is a view showing an example of indicating whether a first open circuit voltage and a second open circuit voltage match according to an embodiment.

[0023] Fig. 9 is a view showing another example of indicating whether a first open circuit voltage and a second open circuit voltage match according to an embodiment.

[0024] Fig.10 is a flow chart illustrating a method of calibrating a state of charge (SOC) according to an embodiment. DETAILED DESCRIPTION

[0025] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The same or similar reference numerals will be used to represent the same or similar components, and their repeated description will be omitted. The terms "module" and / or "unit" may be added separately at the end of the component name or used together to facilitate the description of the present disclosure, and the terms themselves do not have different meanings or functions. When describing the embodiments of the present disclosure, if it is determined that the detailed description of the related known technology will obscure the key points of the embodiment, the detailed description may be omitted. In addition, the accompanying drawings are intended only to facilitate the understanding of the embodiments described herein, without limiting the technical ideas of the present disclosure, and should be interpreted as including all modifications, equivalents and substitutions included in the technical points and scope of the present disclosure.

[0026] Terms with ordinal numbers such as first, second, etc. may be used to describe various components but should not be construed as limiting the components. These terms are only used to distinguish one component from other components.

[0027] When two components are “coupled” or “connected” to each other, the description should be understood to indicate not only that the two components are directly coupled or connected to each other, but also that another component may exist between the two components. Meanwhile, when two components are “directly coupled” or “directly connected” to each other, the description should be understood to indicate that another component does not exist between the two components.

[0028] In the following description of this document, terms such as “including” and “having” are intended to specify the features, numbers, steps, operations, components, parts and combinations thereof described herein, but should not be interpreted as excluding the existence or possible addition of one or more other features, numbers, steps, operations, components, parts and combinations thereof.

[0029] Figure 1 is a block diagram showing a battery system according to an embodiment. Figure 2 It is shown that the storage Figure 1 Conceptual diagram of multiple estimation modules and mapping tables in a storage unit. Figure 3 is a view showing an example of a graph corresponding to cell voltages of battery cells during operation of a vehicle system equipped with the battery system according to an embodiment. Figure 4 is a view showing an example of a graph corresponding to a cell current of a battery cell during operation of a system of a car equipped with a battery system according to an embodiment.

[0030] Reference Figure 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 .

[0031] The battery 10 may include a plurality of battery cells (Cell1 to Celln) connected in series or in parallel. In an embodiment, each battery cell may be a rechargeable secondary cell. A predetermined number of battery cells may be connected in series to form a battery module, a predetermined number of battery modules may be connected in series to form a battery pack, and a predetermined number of battery packs may be connected in parallel to form a battery bank, so that the required power can be provided to an external device. Figure 1 The battery 10 having a plurality of battery cells (Cell1 to Celln) connected in series is shown, but the present disclosure is not limited thereto. The battery 10 may be configured in units of a battery module, a battery pack, or a battery bank.

[0032] Each of the plurality of battery cells (Cell1 to Celln) is electrically connected to the BMS 40 through a wire. The BMS 40 may collect and analyze various information about the battery cells, including information about the plurality of battery cells (Cell1 to Celln), to control, for example, charging, discharging, and protection operations of the battery cells, and may control the operation of the relay 30.

[0033] exist Figure 1 In the embodiment, the battery 10 is connected between two output terminals (OUT1 and OUT2) of the battery system 1. The relay 30 is connected between the positive electrode (anode) of the battery system 1 and the first output terminal (OUT1), and the current sensor 20 is connected between the cathode (negative electrode) of the battery system 1 and the second output terminal (OUT2). Figure 1 The components and connection relationships between the components shown are merely examples, and the present disclosure is not limited thereto.For example, the BMS 40 may be manufactured as a modular chip that may be wirelessly connected to each of a plurality of battery cells (Cell1 to Celln).

[0034] The current sensor 20 is connected in series on a current path between the battery 10 and an external device. The current sensor 20 can measure a battery current, ie, a charging current and a discharging current, flowing through the battery 10 and transmit the measurement result to the BMS 40.

[0035] The relay 30 is a switch for controlling the electrical connection between the battery system 1 and an external device. When the relay 30 is turned on, the battery system 1 is electrically connected to the external device, thereby performing charging or discharging. When the relay 30 is turned off, the battery system 1 is electrically disconnected from the external device. At this time, the external device can be a charger in a charging cycle in which the external device supplies power to the battery to charge the battery 10, or a load in a discharging cycle in which the battery 10 discharges the power to the external device.

[0036] The BMS 40 may include a monitoring unit 41 , a storage unit 43 , and a control unit 45 .

[0037] The monitoring unit 41 is electrically connected to the positive electrode (anode) and the negative electrode (cathode) of each of the plurality of battery cells (Cell1 to Celln), and measures the cell voltage, that is, the voltage across each of the plurality of battery cells (Cell1 to Celln). Figure 3 It may be an example of a graph showing the cell voltage measured by the monitoring unit 41 in a time period from 0 seconds to about 12200 seconds. Figure 3 It may be a graph representing the average voltage of a plurality of battery cells. At each predetermined storage cycle (e.g., every 0.1% of ΔSOC), the monitoring unit 41 may transmit the cell voltage corresponding to the storage duration DT (e.g., 60 seconds) to the control unit 45. The storage duration DT may correspond to the time period between adjacent storage cycles.

[0038] The monitoring unit 41 may measure the cell voltage of each of the plurality of battery cells (Cell1 to Celln) using various well-known methods, and calculate the cell current based on the measured cell voltage. For example, the cell current may be calculated using the average voltage of the above-mentioned cell and the resistance of all the cells. In addition, the monitoring unit 41 may measure the cell current of each of the plurality of battery cells (Cell1 to Celln) using a current sensor (not shown) provided in each battery cell. For example, Figure 4 It may be a graph representing the cell current calculated or measured by the monitoring unit 41 during a period of 0 seconds to about 12200 seconds. The monitoring unit 41 may transmit the cell current corresponding to the storage duration DT to the control unit 45 at each storage cycle.

[0039] The storage unit 43 may store an 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 an SOC calibration module 43-12. At this time, the first open circuit voltage OCV_1 and the second open circuit voltage OCV_2 may each correspond to the open circuit voltage OCV. Figures 5 to 9 Detailed Description Figure 2 Multiple estimation modules and mapping tables shown in .

[0040] The control unit 45 may calibrate the initial SOC value of the battery 10 using the plurality of estimation modules 43-2, 43-4, 43-8, 43-10, 43-12 and the mapping table 43-6 stored in the storage unit 43. Figures 5 to 10 How the control unit 45 calibrates the initial SOC value is described in detail.

[0041] Figure 5 is with Figure 3 An enlarged view of a first cell voltage (eg, a voltage measured within 60 seconds) corresponding to a predetermined storage duration DT is shown in FIG. Figure 6 is with Figure 4 An enlarged view of the cell current corresponding to a predetermined storage duration DT (eg, the current measured within 60 seconds) is shown in FIG. Figure 7 is a graph showing a first cell voltage and a second cell voltage according to an embodiment. Figure 8 is a view showing an example of indicating whether a first open circuit voltage and a second open circuit voltage match according to an embodiment. Fig. 9 is a view showing another example of indicating whether a first open-circuit voltage and a second open-circuit voltage match using the concept of a cost function according to an embodiment.

[0042] In the following description, the cell voltage measured by the monitoring unit 41 will be referred to as the first cell voltage. The second cell voltage to be described later refers to the cell voltage calculated by the equivalent circuit model (ECM) based on the cell current measured by the monitoring unit 41. For example, Figure 3 and Figure 5 Each graph and Figure 7 The first graph A may correspond to a graph of a first battery cell voltage. Figure 7 The second graph B may correspond to a graph of the second battery cell voltage.

[0043] The SOC estimation module 43-2 may include an algorithm for estimating the SOC corresponding to a predetermined storage cycle by adding an integrated value of the cell current within a predetermined period of time to an initial SOC value of the battery cell. For example, the SOC estimation module 43-2 may include an algorithm of a coulomb counting method, which is a well-known current integration method.

[0044] Reference Figure 4 and Figure 6 For example, when the Nth storage cycle T2 arrives, the control unit 45 may use the SOC estimation module 43-2 to integrate the cell current within the storage duration DT, and add the integrated value of the cell current to the initial SOC value, thereby estimating the SOC corresponding to the arrival time of the Nth storage cycle T2. At this time, the storage duration DT may correspond to the time period between two adjacent storage cycles T1 and T2. The initial SOC value added to the integrated value of the cell current may be the SOC corresponding to the N-1th storage cycle T1.

[0045] The first open circuit voltage estimation module 43-4 may estimate the first open circuit voltage OCV_1 corresponding to the arrival time of the predetermined storage period T based on the curve of the cell current corresponding to the storage duration DT. According to an embodiment, the control unit 45 may estimate the first open circuit voltage OCV_1 corresponding to the arrival time of the second storage period T2 based on the curve of the cell current corresponding to the storage duration DT (= T2-T1).

[0046] For example, first, the first open circuit voltage estimation module 43-4 may include an equivalent circuit model (ECM) for simulating a cell voltage corresponding to a cell current by using an equivalent circuit of a battery cell. For example, the ECM may be a model containing three parameters for simulating a cell voltage of a battery cell. These three parameters may include an internal resistance R, an open circuit voltage OCV, and a time constant "τ" (tau) in an equivalent circuit of a capacitor. The internal resistance R, the open circuit voltage OCV, and the time constant "τ" of the capacitor may be variables derived by a fitting algorithm to be described later. For example, when a cell current is input to the ECM, the ECM may calculate an IR drop (ohmic drop) to calculate a second cell voltage. However, not limited to this type of ECM, the control unit 45 may use various types of well-known ECMs to generate a cell voltage corresponding to a cell current. In addition, the cell current and the second cell voltage may be, for example, a cell current curve and a second cell voltage curve corresponding to a storage duration DT.

[0047] According to the implementation mode, reference Figure 6 and Figure 7 , the control unit 45 can generate Figure 7 in Figure 6 The second cell voltage curve B (dashed line) corresponds to the cell current curve. Figure 5 The first cell voltage curve shown may correspond to Figure 7 The first cell voltage curve A (solid line).

[0048] Next, refer to Figure 7 , the first open circuit voltage estimation module 43-4 may include a fitting algorithm for fitting the first cell voltage curve A and the second cell voltage curve B to each other to estimate the first open circuit voltage OCV_1. By using the fitting algorithm, the control unit 45 may fit the second cell voltage curve B to be close to the first cell voltage curve A, thereby deriving three parameters of the ECM, namely, including the internal resistance R, the open circuit voltage OCV and the time constant "τ". That is, the control unit 45 may extract the open circuit voltage OCV as one of the three parameters by utilizing the fitting algorithm. According to an embodiment, the open circuit voltage OCV extracted by the fitting algorithm may be the first open circuit voltage OCV_1.

[0049] The mapping table 43-6 may store mapping data in which the SOC and the first open circuit voltage OCV_1 estimated at each predetermined storage cycle are mapped. The following Table 1 is an example of the mapping table. For example, referring to Figure 5 and Figure 6 When the Nth storage cycle T2 arrives, the control unit 45 may estimate the SOC by using the SOC estimation module 43-2 through the current integration method, and at the same time, calculate the first open circuit voltage OCV_1 by using the first open circuit voltage estimation module 43-4. The control unit 45 may map and store the SOC and the first open circuit voltage OCV_1 corresponding to the arrival time of the Nth storage cycle T2 in the mapping table 43-6.

[0050] [Table 1]

[0051] N SOC OCV_1 1 78.0 3.322 2 77.9 3.323 3 77.8 3.321 4 77.7 3.324 … … … n-3 18.1 3.238 n-2 18.0 3.231 n-1 17.9 3.219 n 17.8 3.222

[0052] When the predetermined calibration cycle arrives, the second open circuit voltage (OCV_2) estimation module 43-8 may estimate a plurality of second open circuit voltages OCV_2 corresponding to the SOC stored in the storage unit 43 from the previous calibration cycle T_N-1 until the current calibration cycle T_N based on the SOC_OCV graph or the SOC_OCV lookup table.

[0053] When the storage cycle is repeated for a predetermined reference number of times, the calibration cycle may arrive. For example, the calibration cycle may be set to arrive when the SOC and the first open circuit voltage OCV_1 are mapped and stored in the storage unit 43 100 times. However, it is not limited thereto, and the arrival time of the calibration cycle may be set to various times, such as when the storage cycle is repeated 100 times or more or less than 100 times.

[0054] According to one embodiment, the second open circuit voltage (OCV_2) estimation module 43-8 may calculate a first relationship diagram based on a lookup table, which is a relationship diagram between a plurality of SOCs and a plurality of open circuit voltages stored during a calibration cycle. In addition, the second open circuit voltage (OCV_2) estimation module 43-8 may calculate a plurality of relationship diagrams by reflecting a plurality of preset error values ​​in the first relationship diagram. The plurality of error values ​​correspond to a plurality of input values ​​to be discussed later.

[0055] According to another embodiment, the second open circuit voltage (OCV_2) estimation module 43-8 may estimate a plurality of second open circuit voltages corresponding to a plurality of SOCs stored during the calibration cycle based on a lookup table. For example, it may be assumed that the calibration cycle arrives when mapping data in which the SOC and the first open circuit voltage OCV_1 are mapped is stored 100 times. The second open circuit voltage (OCV_2) estimation module 43-8 may estimate 100 second open circuit voltages OCV_2 corresponding to 100 SOCs, respectively, based on the SOC_OCV lookup table.

[0056] The cost estimation module 43 - 10 may include an algorithm for calculating a final error value between the first open circuit voltage OCV_1 and the second open circuit voltage OCV_2 based on data accumulated during a period from the last calibration cycle T_N-1 until the current calibration cycle T_N. Figure 8 and Fig. 9 , how the control unit 45 calculates the error value by utilizing the cost estimation module will be described in detail.

[0057] exist Figure 8 In Table 1, the plurality of points may be mapping data in which the plurality of SOCs and the plurality of first open circuit voltages OCV_1 in Table 1 are mapped. That is, the number of points may correspond to the number of mapping data stored in Table 1.

[0058] The control unit 45 may calculate a plurality of second open circuit voltages OCV_2 corresponding to a plurality of SOCs in the form of an SOC-OCV graph using the second open circuit voltage estimation module 43-8. Figure 8 In the embodiment, the first SOC-OCV graph C+0 may be a graph generated by the control unit 45 .

[0059] [Formula 1]

[0060]

[0061] Formula 1 may be a formula corresponding to a cost function, for deriving a hypothesis function with the minimum error based on the original value. Here, "n" is the total number of storage cycles corresponding to the calibration cycle, "k" is the sequence number corresponding to the predetermined storage cycle, and the input value "ε" may be set within a predetermined 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, assuming that the input values ​​"ε" are -10, -8, -6, -4, -2, 0, 2, 4, 6, 8, and 10.

[0062] According to one embodiment, the control unit 45 may calculate the sum of the straight-line distances between each of the plurality of relationship graphs and the plurality of mapping data. The control unit 45 may determine an error value corresponding to the minimum value among the plurality of sum values ​​as a final error value between the first open circuit voltage and the second open circuit voltage. The final error value may correspond to the degree of difference between the plurality of first open circuit voltages and the plurality of second open circuit voltages. In addition, the final error value may correspond to the degree of difference between the initial SOC value obtained by calculation and the actual initial SOC value. The unit of the error value may be %.

[0063] According to another embodiment, the control unit 45 may 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) through the above formula 1 corresponding to the cost function. The control unit 45 may determine the error value corresponding to the lowest cost among the multiple costs as the final error value.

[0064] Each cost may correspond to the sum of the straight-line distances between each of the plurality of mapping data and a given SOC-OCV curve graph. Fig. 9 , indicating that the lower the cost, the higher the matching rate between multiple mapping data and the SOC-OCV curve. Fig. 9 In the example, when the input value "ε" is -2, the cost is the lowest. The input value "ε" corresponding to the lowest cost can be determined as the final error value. The unit of the final error value can be %. That is, for example, the final error value in the given example can be estimated to be -2%.

[0065] exist Fig. 9 In the embodiment, the reference range TH_range may be a range of allowable final error values ​​between the first open circuit voltage OCV_1 and the second open circuit voltage OCV_2. For example, when the final error value falls within the reference range TH_range, the control unit 45 may determine that the error between the initial SOC value obtained by calculation and the actual initial SOC value is small. Then, the control unit 45 may fail to calibrate the initial SOC value. In another example, when the final error value exceeds the reference range, the control unit 45 may determine that the error between the initial SOC value obtained by calculation and the actual initial SOC value is large. The cost calibration module 43-12 may include an algorithm for calibrating the initial SOC value by adding the SOC corresponding to the final error value to the initial SOC value.

[0066] Fig.10 is a flowchart illustrating a SOC calibration method according to an embodiment of the present disclosure.

[0067] In the following, reference will be made to Figures 1 to 10A SOC calibration method and a battery system for providing the same are described in detail.

[0068] Reference Fig.10 , when the predetermined storage period arrives, the BMS 40 estimates the SOC and the first open circuit voltage OCV_1 of the battery cell ( S110 , S120 ).

[0069] For example, the BMS 40 may calculate a cell current curve based on the cell current measured during the storage duration DT. The BMS 40 may calculate a first cell voltage curve A based on the cell voltage measured at both ends of the battery cell during the storage duration DT. The BMS 40 may store the cell current curve and the first cell voltage curve A in the storage unit 43.

[0070] The BMS 40 may add the integrated value of the cell current within the storage duration DT to the initial SOC value of the battery cell to estimate the SOC of the battery cell corresponding to the storage time.

[0071] Reference Figure 4 and Figure 6 For example, when the Nth storage cycle T2 arrives, the BMS 40 integrates the size of the cell current corresponding to the storage duration DT. The BMS 40 may add the integrated value of the cell current to the initial SOC value, thereby estimating the SOC corresponding to the arrival time of the Nth storage cycle T2. At this time, the storage duration DT may correspond to the time period between the N-1th storage cycle T1 and the N-1th storage cycle T2. In addition, the initial SOC value added to the integrated value of the cell current may be the SOC corresponding to the N-1th storage cycle T1.

[0072] At the same time, the BMS 40 may estimate the first open circuit voltage OCV_1 of the battery cell corresponding to the storage cycle based on the equivalent circuit of the battery cell and the cell current. According to an embodiment, the BMS 40 may simulate an equivalent circuit model (ECM) of the cell voltage corresponding to the cell current by using the equivalent circuit of the battery cell, and generate a second cell voltage curve B corresponding to the cell current curve within the storage duration DT.

[0073] For example, in Figure 7 The first cell voltage curve A indicated by a solid line in the example shown may be the voltage at both ends of the battery cell measured by the monitoring unit 41. Furthermore, the second cell voltage curve B indicated by a dotted line may be a cell voltage curve corresponding to the cell current curve calculated by the ECM.

[0074] Subsequently, the BMS 40 may fit the first cell voltage curve A and the second cell voltage curve B to each other to estimate the first open circuit voltage OCV_1. For example, the BMS 40 may fit the second cell voltage curve B to the first cell voltage curve A by changing three parameters forming the ECM, namely, the internal resistance R, the open circuit voltage OCV, and the time constant. The BMS 40 may derive the internal resistance R, the open circuit voltage OCV, and the time constant that make the second cell voltage curve B closest to the first cell voltage curve A. According to an embodiment, the open circuit voltage OCV derived when the second cell voltage curve B is closest to the first cell voltage curve A may correspond to the first open circuit voltage OCV_1.

[0075] Next, the BMS 40 maps and stores the SOC and the first open circuit voltage OCV_1 in the storage unit 43 ( S130 ).

[0076] The BMS 40 may include a mapping table. For example, Table 1 described above may be an example of a mapping table. The mapping table may store mapping data for mapping the SOC calculated by the current integration method at intervals of a storage cycle, and a first open circuit voltage OCV_1 calculated based on the equivalent circuit of the battery cell and the cell current at the same time.

[0077] Next, when the number of storage cycle arrivals reaches a predetermined reference number of times so that the calibration cycle arrives, the BMS 40 estimates a plurality of second open circuit voltages corresponding to a plurality of SOCs stored during the calibration cycle based on an SOC open circuit voltage (OCV) lookup table ( S140 , S150 ).

[0078] When the number of arrivals of the storage cycle reaches a predetermined reference number of times, the calibration cycle may arrive. For example, the calibration cycle may be set to arrive when the mapping data is stored 100 times in the storage unit 43. However, it is not limited thereto, and the arrival time of the calibration cycle may be set to various times, such as when the storage cycle is repeated 100 times or more or less than 100 times.

[0079] According to an embodiment, the BMS 40 may calculate a first relationship diagram based on a lookup table, which is a relationship diagram between a plurality of SOCs and a plurality of open circuit voltages stored during a calibration period. In addition, the BMS 40 may calculate a plurality of relationship diagrams by reflecting a plurality of preset error values ​​in the first relationship diagram. The plurality of error values ​​may correspond to a plurality of input values ​​described below.

[0080] Reference Figure 8, the first SOC-OCV graph C+0 may correspond to a first relationship graph between a plurality of SOCs estimated during the calibration period and a plurality of second open circuit voltages OCV_2 corresponding thereto. For example, the first SOC-OCV graph C+0 may be a graph corresponding to an input value (ε) "0". For possible prediction, the BMS 40 may calculate a plurality of relationship graphs by reflecting a plurality of preset input values ​​in the first relationship graph. The BMS 40 may calculate a second SOC-OCV graph C-10 corresponding to an input value (ε) "-10". The BMS 40 may generate a third SOC-OCV graph C+10 corresponding to an input value (ε) "+10". That is, the BMS 40 may generate a plurality of SOC-OCV graphs, which are respectively a plurality of relationship graphs corresponding to a plurality of input values ​​(ε=-10, -8, -6, -4, -2, 0, 2, 4, 6, 8, 10). For example, referring to Figure 8 , the input values ​​"ε" may each correspond to the size of the SOC of the first relationship diagram parallelized in the left-to-right direction. Figure 8 In the figure, the plurality of black dots may correspond to the plurality of first mapping data.

[0081] According to another embodiment, the BMS 40 may estimate a plurality of second open circuit voltages corresponding to a plurality of SOCs stored during the calibration period based on a lookup table.

[0082] Next, the BMS 40 calculates a final error value corresponding to the degree of difference 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 ).

[0083] According to one embodiment, the BMS 40 may calculate the sum of the straight-line distances between each of the plurality of relationship diagrams and the plurality of mapping data. The BMS 40 may determine an error value corresponding to the minimum value among the plurality of sum values ​​as a final error value between the first open circuit voltage and the second open circuit voltage. The final error value may correspond to the degree of difference between the plurality of first open circuit voltages and the plurality of second open circuit voltages. In addition, the final error value may correspond to the degree of difference between the initial SOC value obtained by calculation and the actual initial SOC value. The unit of the error value may be %.

[0084] According to another embodiment, the BMS 40 may calculate the final error value based on a predetermined cost function that quantifies the degree of matching between the plurality of first open-circuit voltages and the plurality of second open-circuit voltages. For example, the BMS 40 may derive a plurality of costs corresponding to the plurality of input values ​​"ε" (i.e., a plurality of error values) through the above-mentioned formula 1 corresponding to the cost function. The BMS 40 may determine the error value corresponding to the lowest cost among the plurality of costs as the final error value.

[0085] Refer to formula 1 and Figure 8 , the sum of the straight-line distances between the plurality of first mapping data and the predetermined SOC-OCV relationship diagram may correspond to the cost. For example, the BMS 40 calculates a plurality of costs for a plurality of input values ​​(ε=-10, -8, -6, -4, -2, 0, 2, 4, 6, 8, 10), respectively. The input value "ε" corresponding to the minimum cost among the plurality of calculated costs may correspond to the final error value. For example, referring to Fig. 9 , it can be assumed that the cost is lowest when the input value “ε” is -2. Then, the BMS 40 can calculate -2% as the final error value.

[0086] For example, for each of the plurality of input values ​​(ε=-10, -8, -6, -4, -2, 0, 2, 4, 6, 8, 10), the BMS 40 may substitute the plurality of SOC values, the plurality of first open circuit voltage OCV_1 values, and the plurality of second open circuit voltage OCV_2 values ​​into Formula 1 to calculate the plurality of costs. The plurality of costs calculated based on Formula 1 may correspond to Fig. 9 The graph shown.

[0087] Next, when it is determined that the final error value exceeds the reference range (S170, Yes), the BMS 40 calibrates the initial SOC value (S180). In addition, when it is determined that the final error value does not exceed the reference range (S170, No), the BMS 40 does not calibrate the initial SOC value (S190).

[0088] The reference range TH_range may be a range of allowable final error values. Fig. 9 , it can be assumed that the reference range TH_range corresponds to the range of -5 to +5.

[0089] For example, when the final error value calculated in S160 is +10%, the BMS 40 may determine in S170 that the final error value of +10% exceeds the reference range (TH_range) (S170, Yes). In this case, in S180, the BMS 40 may calibrate the initial SOC value by adding the SOC corresponding to the final error value to the initial SOC value. For example, the BMS 40 may divide the SOC corresponding to the final error value according to a preset time, and add the divided SOC to the initial SOC value in units of the divided time to calibrate the initial SOC value.

[0090] For example, it can be assumed that the final error value is +10%, the initial SOC value is 50%, and the preset time is 10 minutes. The BMS 40 can divide the SOC corresponding to the final error value +10% by 10 minutes, and add the divided SOC 5% (0.1×50%=5%) to the initial SOC value 50% in units of 1 minute (e.g., 0.5% / min) within 10 minutes, so that the (SOC) initial value can be calibrated to 55%.

[0091] Next, the BMS 40 deletes the plurality of mapping data stored in the storage unit 43 to reset the storage unit 43 (S190). Then, a new calibration cycle starts. That is, after the new calibration cycle starts, when the storage cycle arrives, the entire process may be repeated from S110.

[0092] In another example, assuming that the final error value calculated in S160 is -2%, the BMS 40 may determine in S170 that the final error value -2% does not exceed the reference range TH_range (S170, No). In this case, the BMS 40 resets the storage unit 43 by deleting the plurality of mapping data stored in the storage unit 43 without calibrating the initial SOC value (S190). Then, a new calibration cycle begins. That is, after the new calibration cycle begins, when the storage cycle arrives, the entire process may be repeated from S110.

[0093] Meanwhile, according to an embodiment, the BMS 40 may calibrate the SOC only under a specific condition based on the error value of the estimated SOC. For example, after calculating the final error value in S160, the BMS 40 may determine whether a specific condition is met before determining in S170 whether the final error value calculated in S160 exceeds a reference range. For example, after calculating the final error value in S160, the BMS 40 may determine whether one or more of the following conditions are met: (1) whether the number of accumulated data pairs is more than 100 pairs; (2) whether the interval of the accumulated SOC (ΔSOC) is within a range of more than 30%; (3) whether the current SOC is less than 55%, or (4) whether the open circuit voltage OCV is more than 30mV. Then, the BMS 40 can perform S170 only when one or more of the above conditions are met. In this way, the BMS 40 is configured to calibrate only when a specific condition is met, so that unnecessary frequent calibration can be avoided and resources can be used for more urgent purposes.

[0094] The determination of whether a specific condition is satisfied may not be performed only after S160 but may be performed in any step of the process, for example, after any one of steps S120 to S150 .

[0095] Although the embodiments of the present disclosure have been described in detail, the protection scope of the present disclosure is not limited to the embodiments. A person skilled in the art in the field of the present disclosure may make various modifications and improvements, and the various modifications and improvements are also included in the protection scope of the present disclosure.

Claims

1. A battery system, the battery system being used to estimate the state of charge (SOC) of the battery cell by integrating the battery cell current flowing in the battery cell, the battery system comprising: a memory configured to store mapping data, in each predetermined storage period, the mapping data mapping the SOC estimated based on the integrated value of the cell current and a first open circuit voltage estimated by a predetermined model simulating a cell voltage corresponding to the cell current; as well as A controller is configured to perform the following process, the process comprising: When the number of times the mapping data is stored reaches a predetermined reference number of times so that a calibration period arrives, estimating a first relationship diagram based on a predetermined SOC open circuit voltage lookup table, the first relationship diagram being a relationship diagram between a plurality of SOCs and a plurality of open circuit voltages stored in the memory; calculating a plurality of relationship graphs by reflecting a plurality of preset error values ​​in the first relationship graph; Calculating a sum of distances between each of the plurality of relationship graphs and the mapping data; determining an error value corresponding to a minimum value among a plurality of sum values ​​as a final error value between the first open circuit voltage and the second open circuit voltage; and It is determined whether the final error value falls within a predetermined reference range to determine whether to calibrate the initial SOC value.

2. The battery system according to claim 1, wherein: When the Nth storage cycle arrives, the controller calculates the integral value by integrating the cell current measured during the storage duration from the N-1th storage cycle to the Nth storage cycle, and adds the integral value to the SOC corresponding to the N-1th storage cycle, thereby calculating the SOC corresponding to the Nth storage cycle.

3. The battery system according to claim 1, wherein: The memory stores a cell current curve calculated based on the cell current and a first cell voltage curve calculated based on a cell voltage for a storage duration, the cell voltage being a voltage at both ends of the battery cell, the storage duration being a time period between adjacent storage cycles, and The controller generates a second cell voltage curve corresponding to the cell current curve through a model including an open circuit voltage as a parameter based on an equivalent circuit of the battery cell.

4. The battery system according to claim 3, wherein: The controller calculates the magnitude of the open circuit voltage as the first open circuit voltage when the first cell voltage curve and the second cell voltage curve are fitted to be closest to each other.

5. The battery system according to claim 1, wherein: When the final error value exceeds the predetermined reference range, the controller calibrates the initial SOC value by adding the SOC corresponding to the final error value to the initial SOC value.

6. The battery system according to claim 1, wherein: When the final error value exceeds the predetermined reference range, the controller divides the SOC corresponding to the final error value by a preset time and adds the divided SOC to the initial SOC value in units of the divided time, thereby calibrating the initial SOC value.

7. A battery system, the battery system being used to estimate the state of charge of the battery cell by integrating the cell current flowing in the battery cell, the battery system comprising: a memory configured to store mapping data, at each predetermined storage period, the mapping data mapping a state of charge (SOC) estimated based on an integrated value of the cell current and a first open circuit voltage estimated by a predetermined model simulating a cell voltage corresponding to the cell current; as well as A controller is configured to perform the following process, the process comprising: When the number of times the mapping data is stored reaches a predetermined reference number of times so that a calibration period arrives, estimating a plurality of second open circuit voltages corresponding to a plurality of SOCs stored in the memory based on a predetermined SOC open circuit voltage lookup table; calculating a final error value corresponding to a degree of difference between the plurality of first open-circuit voltages and the plurality of second open-circuit voltages based on a predetermined cost function that quantifies a degree of matching between the plurality of first open-circuit voltages and the plurality of second open-circuit voltages stored in the memory; and It is determined whether the final error value falls within a predetermined reference range to determine whether to calibrate the initial SOC value.

8. The battery system according to claim 7, wherein: The controller determines an error value corresponding to a minimum cost among a plurality of costs as the final error value, the plurality of costs being obtained by the following equation corresponding to the cost function, [Formula 1] Wherein, Cost is the cost, OCV_1 is the first open circuit voltage, OCV_2 is the second open circuit voltage, SOC is the state of charge, "k" is the storage cycle count, "n" is the reference number, and "ε" is the error value, "ε" corresponds to each of a plurality of integers within a predetermined range.

9. The battery system according to claim 7, wherein: When the Nth storage cycle arrives, the controller calculates the integral value by integrating the cell current measured in the time period from the N-1th storage cycle to the Nth storage cycle, and adds the integral value to the SOC corresponding to the N-1th storage cycle, thereby calculating the SOC corresponding to the Nth storage cycle.

10. The battery system according to claim 7, wherein: The memory stores a cell current curve calculated based on the cell current and a first cell voltage curve calculated based on a cell voltage for a storage duration, the cell voltage being a voltage at both ends of the battery cell, the storage duration being a time period between adjacent storage cycles, and The controller generates a second cell voltage curve corresponding to the cell current curve through a model including an open circuit voltage as a parameter based on an equivalent circuit of the battery cell.

11. The battery system according to claim 10, wherein: The controller calculates the magnitude of the open circuit voltage as the first open circuit voltage when the first cell voltage curve and the second cell voltage curve are fitted to be closest to each other.

12. The battery system according to claim 7, wherein: When the final error value exceeds the predetermined reference range, the controller calibrates the initial SOC value by adding the SOC corresponding to the final error value to the initial SOC value.

13. The battery system according to claim 7, wherein: When the final error value exceeds the predetermined reference range, the controller divides the SOC corresponding to the final error value by a preset time and adds the divided SOC to the initial SOC value in units of the divided time, thereby calibrating the initial SOC value.

14. A method for calibrating a state of charge, the method comprising the following steps: When a predetermined storage period arrives, estimating a state of charge (SOC) and a first open circuit voltage of the battery cell based on an integrated value of a cell current flowing in the battery cell and a predetermined model simulating a cell voltage corresponding to the cell current, respectively; storing mapping data mapping the SOC and the first open circuit voltage in a memory; When the number of times the mapping data is stored reaches a predetermined reference number of times so that a calibration period arrives, estimating a plurality of second open circuit voltages corresponding to a plurality of SOCs stored in the memory based on a predetermined SOC open circuit voltage lookup table; calculating a final error value corresponding to a degree of difference between the plurality of first open-circuit voltages and the plurality of second open-circuit voltages based on a predetermined cost function that quantifies a degree of matching between the plurality of first open-circuit voltages and the plurality of second open-circuit voltages stored in the memory; determining whether the final error value falls within a predetermined reference range; as well as When it is determined that the final error value exceeds the predetermined reference range, the initial SOC value is calibrated.

15. The method according to claim 14, wherein: The step of calculating the final error value comprises the following steps: Determine an error value corresponding to a minimum cost among a plurality of costs as the final error value, wherein the plurality of costs are obtained by the following formula corresponding to the cost function, [Formula 1] Wherein, Cost is the cost, OCV_1 is the first open circuit voltage, OCV_2 is the second open circuit voltage, SOC is the state of charge, "k" is the storage cycle count, "n" is the reference number, and "ε" is the error value, "ε" corresponds to each of a plurality of integers within a predetermined range.

16. The method according to claim 14, wherein: The step of estimating the SOC and the first open circuit voltage comprises the following steps: storing a cell current curve calculated based on the cell current and a first cell voltage curve calculated based on a cell voltage, the cell voltage being a voltage at both ends of the battery cell, for a storage duration, the storage duration being a time period between adjacent storage cycles; and generating a second cell voltage curve corresponding to the cell current curve through a model including an open circuit voltage as a parameter based on an equivalent circuit of the battery cell; and When the first cell voltage curve and the second cell voltage curve are fitted to be closest to each other, the magnitude of the open circuit voltage is calculated as the first open circuit voltage.

17. The method according to claim 14, wherein: The step of calibrating the initial SOC value comprises the following steps: The SOC corresponding to the final error value is added to the initial SOC value, thereby calibrating the initial SOC value.

18. The method according to claim 14, wherein: The step of calibrating the initial SOC value comprises the following steps: The SOC corresponding to the final error value is divided by a preset time, and the divided SOC is added to the initial SOC value in units of the divided time, thereby calibrating the initial SOC value.

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