Battery SOC estimation system and estimation method

Abstract

The present invention relates to a system and method for estimating the State of Charge (SOC) of a battery, and more specifically, to a system for estimating the State of Charge (SOC) of a battery, comprising: a current sensor for measuring I_b, which is a current flowing through the battery; a voltage sensor for measuring V_t, which is a voltage across the ends of the battery; and an estimation unit for loading SOC_p, which is a SOC value from a previous point in time from the current point in time; determining whether the battery is charged or discharged based on I_b; and estimating an initial SOC according to the determination result. The estimation unit is characterized by estimating the initial SOC based on at least one of the time stored at the last point in time based on T_rest, which is a resting period of the battery, and T_stabilization, which is a stabilization time, the SOC_p, and State_p, which is a charging or discharging state at a previous point in time, when the conditions for determining whether the battery is charged or discharged are satisfied.

Description

Technology Field

[0001] The present invention relates to a battery SOC estimation system and estimation method, and more specifically, to a current integration-based battery charge state estimation system and estimation method. Background Technology

[0002] Estimating the State of Charge (SOC), a critical function of the Battery Management System (BMS), requires high accuracy for the safe and efficient use of batteries. Currently, ternary nickel-cobalt-manganese oxide (NCM) and lithium iron phosphate (LFP) batteries are widely used in the medium-to-large capacity battery application industry. In particular, the use of LFP batteries has been gradually expanding recently due to their advantages of long lifespan, high stability, and reasonable cost. Consequently, there is a growing industrial need for accurate SOC estimation technology for LFP batteries, and research on this is being conducted in recent years.

[0003] SOC estimation methods can be classified into model and data-based methods, Open Circuit Voltage (OCV), and current integration methods. Specifically, model and data-based methods require a significant amount of computation and battery data to estimate SOC with high accuracy. While the OCV method is the simplest approach, real-time SOC estimation is impossible because it requires a rest period for the battery to stabilize. The current integration method estimates SOC by integrating the current during charging and discharging with the initial SOC value and adding the results; compared to other real-time SOC estimation methods, it is relatively easy and simple to implement, making it convenient for system application. Furthermore, by combining this method with OCV to correct the initial SOC, it has been possible to improve the problem of cumulative error. The improved current integration method has recently been the most widely applied in commercial battery management systems, such as those for electric vehicles and ESS.

[0004] Figure 1 is a graph showing the SOC-OCV relationship of conventional NCM, and

[0005] Figure 2 is a graph showing the SOC-OCV relationship of a conventional LFP battery.

[0006] The current integration method combined with the OCV method utilizes a curve representing the relationship between SOC and OCV to update the initial SOC. Generally, the SOC-OCV relationship is obtained by charging from 0% to 100% and then discharging from 100% to 0% at regular SOC intervals; this is referred to as the Major Loop. However, due to the hysteresis effect of the battery, the charging OCV curve and the discharging OCV curve appear differently, and this must be appropriately reflected in the SOC estimation. As illustrated in Figures 1 and 2, LFP batteries exhibit lower operating voltages and a gradual OCV in the 10–90% SOC range compared to NCM batteries. In other words, since the deviation of OCV according to SOC is small, estimating the initial SOC based on this can lead to significant errors. Therefore, the average curve of the Major Loop is commonly used to account for hysteresis characteristics. However, this curve, where SOC and OCV correspond one-to-one, makes it difficult to account for different OCVs during charging and discharging. Therefore, to accurately estimate the SOC of the LFP, additional modeling reflecting hysteresis characteristics is required. Prior art literature

[0007] Korean Published Patent Application No. 10-2021-0074004 ("Battery management system, battery management method, battery pack and electric vehicle", Date of publication June 21, 2021) The problem to be solved

[0008] The present invention has been devised to solve the problems described above. The objective of the battery SOC estimation system and estimation method according to the present invention is to provide a battery SOC estimation system and estimation method capable of updating the initial SOC based on stored time, previous SOC, and previous charge / discharge state, and estimating the SOC by reflecting the initial SOC, current measurement error, and hysteresis characteristics. means of solving the problem

[0009] A battery SOC estimation system according to various embodiments of the present invention for solving the problems described above is a battery SOC estimation system for estimating the SOC (State of Charge) of a battery, comprising a current sensor for measuring I_b, which is a current flowing through the battery; a voltage sensor for measuring V_t, which is a voltage across the ends of the battery; and an estimation unit for loading SOC_p, which is a SOC value from a previous point in time from the current point in time, determining whether the battery is charged or discharged based on I_b, and estimating an initial SOC according to the determination result, wherein the estimation unit estimates the initial SOC based on at least one of the time stored at the last point in time based on T_rest, which is a resting period of the battery, and T_stabilization, which is a stabilization time, the SOC_p, and State_p, which is a charging or discharging state at a previous point in time, when the conditions for determining whether the battery is charged or discharged are satisfied.

[0010] In addition, the estimation unit estimates the SOC_p as the initial SOC when I_b is not 0, and estimates the initial SOC by comparing T_rest and T_stabilization when I_b is 0.

[0011] In addition, the estimation unit estimates the initial SOC by comparing T_rest and T_stabilization when I_b is 0, and when T_rest is longer than T_stabilization, estimates the initial SOC based on one of a plurality of hysteresis curves, and when T_rest is shorter than T_stabilization, estimates SOC_p as the initial SOC.

[0012] Additionally, the estimation unit loads the OCV, which is the terminal voltage of the battery measured at the last point in the rest period after the battery has stabilized, selects one of the loops among the plurality of hysteresis curves based on either SOC_p or State_p, calculates V_oc based on the previously extracted constant values ​​R_i, I_b, and V_t, defines a plurality of points closest to the reference based on V_oc in the selected curve, and estimates the initial SOC based on the plurality of points and linear interpolation.

[0013] In addition, the estimation unit is characterized by selecting one of a plurality of minor loops when the x-axis of the hysteresis curve represents SOC and the y-axis represents OCV, and selecting one of a plurality of major loops when the SOC is less than 10% or greater than 90%.

[0014] In addition, the estimation unit selects a loop of the hysteresis curve within the SOC range corresponding to the SOC_p, wherein if State_p is in a charged state, it selects a charging curve, and if State_p is in a discharged state, it selects a discharging curve.

[0015] In addition, the estimation unit is characterized by reducing the noise of I_b through a moving average filter.

[0016] In addition, a method for estimating an SOC of a battery comprising a current sensor, a voltage sensor, and an estimation unit comprises the following steps: the estimation unit (a) loading SOC_p, which is an SOC value from a previous point in time to a current point in time; the current sensor and the voltage sensor each (b) measuring I_b and V_t, which are the current and voltage of the battery, respectively; the estimation unit (c) determining whether the battery is charged or discharged based on I_b; and (d) estimating an initial SOC based on the determination result, wherein step (d) is characterized by estimating the initial SOC based on at least one of the time stored at the last point in time based on T_rest, which is the resting period of the battery, and T_stabilization, which is the stabilization time, the SOC_p, and State_p, which is the charging or discharging state at a previous point in time, when the conditions for determining whether the battery is charged or discharged are satisfied.

[0017] Additionally, the above step (d) is characterized by including (d-1) a step of estimating the SOC_p as the initial SOC when the I_b is not 0, and (d-2) a step of estimating the initial SOC by comparing the T_rest and T_stabilization when the I_b is 0.

[0018] Additionally, the above step (d-2) is characterized by estimating the initial SOC by comparing T_rest and T_stabilization when I_b is 0, and estimating the initial SOC based on one of a plurality of hysteresis curves when T_rest is longer than T_stabilization, and estimating the SOC_p as the initial SOC when T_rest is shorter than T_stabilization.

[0019] Additionally, the above step (d-2) is characterized by including: (d-2-1) a step of loading the OCV, which is the terminal voltage of the battery measured at the last point in time during the rest period after the battery has stabilized; (d-2-2) a step of selecting one of the loops of the plurality of hysteresis curves based on either SOC_p or State_p; (d-2-3) a step of calculating V_oc based on R_i, which is a constant value extracted in advance, I_b, and V_t; (d-2-4) a step of defining a plurality of points closest to the reference based on V_oc in the selected curve; and (d-2-5) a step of estimating the initial SOC based on the plurality of points and linear interpolation.

[0020] Additionally, the above step (d-2-2) is characterized by selecting one loop from a plurality of minor loops in the interval where the SOC is between 10% and 90%, and selecting one loop from a plurality of major loops in the interval where the SOC is less than 10% or greater than 90%.

[0021] Additionally, the above step (d-2-2) is characterized by selecting a loop of the hysteresis curve in the SOC range corresponding to the above SOC_p, wherein if the State_p is in a charged state, a charging curve is selected, and if the State_p is in a discharged state, a discharge curve is selected.

[0022] In addition, the method is characterized by further including a step of reducing the noise of I_b through a moving average filter after step (b) and before step (c). Effects of the invention

[0023] According to the battery SOC estimation system and estimation method of various embodiments of the present invention as described above, by updating the initial SOC by reflecting hysteresis characteristics, there is an effect of reducing cumulative errors caused by initial SOC errors, current measurement errors, etc., of existing current integration methods.

[0024] In addition, applying the Major Loop and Minor Loop, which are the hysteresis characteristics of the battery, to the initial SOC estimation improves the accuracy of the initial SOC, thereby having the effect of improving SOC estimation performance.

[0025] Furthermore, accurate estimation of SOC enables users to utilize the battery efficiently through precise information, ensuring stable battery operation and enhancing user safety. Brief explanation of the drawing

[0026] Figure 1 is a graph showing the SOC-OCV relationship of conventional NCM, and Figure 2 is a graph showing the SOC-OCV relationship of a conventional LFP battery, and Figure 3 is a graph showing the hysteresis error calculated based on the charge and discharge OCV curves of a conventional NCM, and Figure 4 is a graph showing the hysteresis error calculated based on the charge and discharge OCV curves of a conventional LFP battery, and Figure 5 is a graph showing the minor loop of a conventional LFP battery, and FIG. 6 is a schematic diagram illustrating a battery SOC estimation system according to the present invention, and FIG. 7 is a graph showing a hysteresis curve according to the present invention, and FIG. 8 is a flowchart illustrating an estimation method of a battery SOC estimation system according to the present invention, and FIG. 9 is a flowchart illustrating an initial SOC estimation method according to the present invention. Specific details for implementing the invention

[0027] In order to explain the present invention, the operational advantages of the present invention, and the objectives achieved by the implementation of the present invention, preferred embodiments of the present invention are illustrated below and examined with reference thereto.

[0028] First, the terms used in this application are used merely to describe specific embodiments and are not intended to limit the invention; singular expressions may include plural expressions unless the context clearly indicates otherwise. Furthermore, in this application, terms such as "comprising" or "having" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0029] In describing the present invention, if it is determined that a detailed description of related known components or functions may obscure the essence of the invention, such detailed description is omitted.

[0030] Figure 3 is a graph showing the hysteresis error calculated based on the charge and discharge OCV curves of a conventional NCM, and

[0031] Figure 4 is a graph showing the hysteresis error calculated based on the charge and discharge OCV curves of a conventional LFP battery, and

[0032] Figure 5 is a graph showing the minor loop of a conventional LFP battery.

[0033] First, the current integration method estimates the State of Charge (SOC) by integrating the charging and discharging currents and time to calculate the remaining capacity of the battery. Accordingly, the current integration method can be defined as shown in the following formula. While the current integration method has the advantage of simple implementation, errors accumulate due to factors such as initial SOC errors and current measurement errors. Therefore, an improved current integration method has been studied that applies the Open Circuit Voltage (OCV) method, which estimates SOC based on battery voltage, to the existing current integration method. Through this, the error is reduced by updating SOC_0 in the following formula. To apply OCV to the existing current integration method, an SOC-OCV relationship derived through preliminary experiments is required, and accurate SOC-OCV modeling is necessary to reduce OCV errors.

[0034]

[0035] Meanwhile, the battery SOC-OCV relationship does not correspond simply one-to-one due to hysteresis characteristics. Therefore, reflecting the battery hysteresis effect allows for more accurate modeling of the battery and SOC estimation. Figures 3 and 4 illustrate the maximum error in SOC caused by hysteresis in the Major Loop at the same OCV. In the OCV-SOC characteristic curve with OCV as the x-axis variable, the Major Loop hysteresis characteristic and the slope of the SOC / OCV for LFP batteries become significantly larger compared to NCM batteries. Consequently, this implies that in the improved current integration method using OCV voltage as the initial value for SOC, even a small OCV error in the LFP battery can lead to a large SOC estimation error. Therefore, to improve the accuracy of SOC estimation based on the current integration method for LFP, an additional method reflecting hysteresis characteristics is required.

[0036] In addition, as shown in Figure 5, the Minor Loop, which is a small hysteresis loop curve obtained by charging or discharging at an arbitrary SOC, can subdivide the Major Loop, thereby better explaining the hysteresis phenomenon of the battery. Accuracy is increased when the SOC is estimated by adding a Minor Loop in the OCV range, and since applications such as actual EVs repeatedly charge and discharge within a small SOC range due to discharge and regenerative braking, it is effective to apply multiple small hysteresis loops, called Minor Loops, to the SOC estimation.

[0037] In the current integration method, if the rest period is longer than the stabilization time, the OCV voltage based on the SOC-OCV characteristic curve is used to adjust the initial value (SOC_0). Generally, a single average SOC-OCV curve is generated by averaging the charge and discharge curves of the Major Loop, and then the SOC value corresponding to the OCV value during the rest period is used. However, as shown in Figure 4, this method results in a very large error in the most commonly used SOC range of 10–90% for LFP batteries. Therefore, hysteresis characteristics due to the Minor Loop must be reflected in this range.

[0038] FIG. 6 is a schematic diagram illustrating a battery SOC estimation system according to the present invention, and

[0039] Figure 7 is a graph showing a hysteresis curve according to the present invention.

[0040] As illustrated in FIG. 6, a battery SOC estimation system (1000) for estimating the SOC of a battery according to the present invention may include a current sensor (100), a voltage sensor (200), and an estimation unit (300).

[0041] The current sensor (100) can measure the current I_b flowing through the battery.

[0042] The voltage sensor (200) can measure the voltage V_t across the battery.

[0043] The estimation unit (300) retrieves SOC_p, which is the SOC value from the previous point in time from the current point in time, and can determine whether the battery is charged or discharged based on I_b measured by the current sensor (100). Afterwards, the initial SOC can be estimated based on the result of the determination.

[0044] Specifically, when the estimation unit (300) satisfies the condition for determining whether the battery is charged or discharged, it can estimate the initial SOC based on at least one of the time stored at the last point in time, SOC_p, and the charging or discharging state at the previous point in time, based on T_rest, which is the battery's rest period, and T_stabilization, which is the stabilization time.

[0045] More specifically, the estimation unit (300) determines whether the battery is charged or discharged based on I_b measured by the current sensor (100). If I_b is not zero, SOC_p can be estimated as the initial SOC. Subsequently, the estimated initial SOC can be substituted into the formula described above to calculate the final SOC. (Here, C_n may be a battery capacity extracted in advance.) The value I_b used at this time may be a value in which the noise of the current has been reduced by a moving average filter.

[0046]

[0047] Meanwhile, when I_b is 0, the estimation unit (300) can estimate the initial SOC by comparing T_rest and T_stabilization.

[0048] Specifically, when T_rest is longer than T_stabilization, the estimation unit (300) can estimate the initial SOC based on any one of the multiple hysteresis curves. On the other hand, when T_rest is shorter than T_stabilization, SOC_p can be estimated as the initial SOC.

[0049] More specifically, the estimation unit (300) can read the OCV, which is the terminal voltage of the battery measured at the end of the rest period after the battery has stabilized, as illustrated in FIG. 7. Subsequently, one of the loops among a plurality of hysteresis curves can be selected based on SOC_p and State_p. The hysteresis curves mentioned here may have SOC on the x-axis and OCV on the y-axis, and when selecting one of the loops among the plurality of hysteresis curves, in the range where SOC is 10% to 90%, one of the loops among the plurality of minor loops can be selected based on either SOC_p or State_p. Additionally, in the range where SOC is less than 10% or greater than 90%, one of the loops among the plurality of major loops can be selected based on SOC_p and State_p. In addition, the estimation unit (300) selects a loop of the hysteresis curve within the SOC range corresponding to SOC_p, and if State_p is in a charged state, it selects a charging curve, and if State_p is in a discharged state, it selects a discharge curve. Furthermore, based on the previously extracted constant values ​​R_i, I_b, and V_t, V_oc can be calculated using the following formula. V_oc = V_t + I_b x R_i (where R_i represents the internal resistance of the battery, which is determined in advance for each SOC through a preliminary experiment or calibration process, V_t is the terminal voltage across the battery measured by a voltage sensor, and I_b is the current flowing across the battery measured by a current sensor.) The above formula is intended to derive the actual open circuit voltage (V_oc) by correcting for the voltage drop caused by the internal resistance that occurs when current flows through the battery. In particular, since no voltage drop occurs when the current (I_b) is zero, such as during the rest period after the battery has stabilized, the calculated V_oc has a physically identical value to the terminal voltage (OCV) measured at that time.Subsequently, in the selected hysteresis curve, multiple points closest to the OCV, which is the terminal voltage of the battery measured at the end of the rest period after the battery has stabilized, can be selected. Accordingly, the initial SOC can be estimated by applying linear interpolation to the selected points. Here, when the selected points are denoted as P_1(SOC_1, OCV_1) and P_2(SOC_2, OCV_2), the initial SOC(SOC(OCV)) can be calculated as follows.

[0050]

[0051] FIG. 8 is a flowchart illustrating an estimation method of a battery SOC estimation system according to the present invention, and

[0052] FIG. 9 is a flowchart illustrating an initial SOC estimation method according to the present invention.

[0053] A battery SOC estimation method according to another embodiment of the present invention relates to an estimation method of a battery SOC estimation system comprising a current sensor, a voltage sensor, and an estimation unit.

[0054] As illustrated in FIG. 8, a battery SOC estimation method according to another embodiment of the present invention can have an estimation unit load SOC_p, which is the SOC value of the previous time point before the current time point, in step S100, a current sensor and a voltage sensor each measure I_b and V_t, which are the current and voltage of the battery, respectively, in step S200, and the estimation unit determine whether the battery is charged or discharged based on I_b in step S300, and can estimate the initial SOC according to the determination result in step S400.

[0055] At this time, after step S200 and before S300, a step of reducing the noise of I_b based on a moving average filter may be further included.

[0056] Specifically examining the estimation method of a battery SOC estimation system according to another embodiment of the present invention, the estimation unit may estimate an initial SOC based on at least one of the time stored at the last point in time, SOC_p, and the charging or discharging state at the previous point in time, when the condition for determining whether the battery is charged or discharged is satisfied in step S400, based on the battery's rest period T_rest and stabilization time T_stabilization.

[0057] More specifically, in determining whether the battery is charged or discharged based on I_b measured by the current sensor, if I_b is not zero in step S410, the estimation unit may estimate SOC_p as the initial SOC. Subsequently, in step 500, the estimated initial SOC can be substituted into the formula described above to calculate the final SOC. (Here, C_n may be a battery capacity extracted in advance.)

[0058]

[0059] Meanwhile, the estimation unit can estimate the initial SOC by comparing T_rest and T_stabilization when I_b is 0 in step S420.

[0060] Specifically, if T_rest is longer than T_stabilization, the estimator can estimate the initial SOC based on any one of the multiple hysteresis curves in step S420. On the other hand, if T_rest is shorter than T_stabilization, SOC_p can be estimated as the initial SOC in step S420.

[0061] More specifically, as illustrated in FIG. 9, the estimation unit can read the OCV, which is the terminal voltage of the battery measured at the end of the rest period after the battery has stabilized in step S421. Subsequently, in step S422, one of the loops among a plurality of hysteresis curves can be selected based on SOC_p and State_p. The hysteresis curves referred to here may have SOC on the x-axis and OCV on the y-axis, and when selecting one of the loops among the plurality of hysteresis curves, in the range where SOC is between 10% and 90%, one of the loops among the plurality of minor loops can be selected based on either SOC_p or State_p. Additionally, in the range where SOC is less than 10% or greater than 90%, one of the loops among the plurality of major loops can be selected based on SOC_p and State_p. In addition, the estimation unit selects a loop of the hysteresis curve within the SOC range corresponding to SOC_p, selecting a charging curve if State_p is in a charging state and a discharging curve if State_p is in a discharging state. Furthermore, V_oc can be calculated based on the constant values ​​R_i, I_b, and V_t extracted in advance in step S423. Subsequently, based on V_oc calculated from the hysteresis curve selected in step S424, multiple points closest to this criterion can be selected. Accordingly, the initial SOC can be estimated by applying linear interpolation to the points selected in step S425. Here, when the selected points are denoted as P_1 (SOC_1, OCV_1) and P_2 (SOC_2, OCV_2), the initial SOC(SOC(OCV)) can be calculated as follows.

[0062]

[0063] Although preferred embodiments of the present invention have been described above, the present invention is not limited to the specific embodiments described above. That is, those skilled in the art to which the present invention pertains can make numerous changes and modifications to the present invention without departing from the spirit and scope of the appended claims, and all such appropriate changes and modifications should be deemed to fall within the scope of the present invention as equivalents. Explanation of the symbols

[0064] 1000: Battery SOC Estimation System 100: Current sensor 200: Voltage sensor 300 : Estimation part

Claims

Claim 1 A battery SOC estimation system for estimating the SOC (State of Charge) of a battery, comprising: a current sensor for measuring I_b, a current flowing through the battery; a voltage sensor for measuring V_t, a voltage across the battery; and an estimation unit for loading SOC_p, a SOC value from a previous point in time from the current point in time, determining whether the battery is charged or discharged based on I_b, and estimating an initial SOC according to the determination result; wherein, when the determination condition for whether the battery is charged or discharged is satisfied, the estimation unit estimates the initial SOC based on at least one of the time stored at the last point in time based on T_rest, a resting period of the battery, and T_stabilization, a stabilization time, the SOC_p, and State_p, a charging or discharging state at a previous point in time; if I_b is not zero, the estimation unit estimates the SOC_p as the initial SOC; and if I_b is zero, the estimation unit estimates the initial SOC by comparing T_rest and T_stabilization. Claim 2 delete Claim 3 A battery SOC estimation system according to claim 1, wherein the estimation unit estimates the initial SOC by comparing T_rest and T_stabilization when I_b is 0, and estimates the initial SOC based on one of a plurality of hysteresis curves when T_rest is longer than T_stabilization, and estimates the SOC_p as the initial SOC when T_rest is shorter than T_stabilization. Claim 4 In paragraph 3, the estimation unit loads the OCV, which is the terminal voltage of the battery measured at the last point in time during the rest period after the battery has stabilized, selects one loop of the plurality of hysteresis curves based on either SOC_p or State_p, calculates V_oc based on a prior extracted constant value R_i, I_b, and V_t, defines a plurality of points closest to the reference based on V_oc on the selected curve, and estimates the initial SOC based on the plurality of points and linear interpolation, a battery SOC estimation system. (Here, the prior extracted constant value R_i is the internal resistance of the battery.) Claim 5 A battery SOC estimation system according to claim 4, wherein the estimation unit selects one loop from a plurality of minor loops in the interval where the SOC is 10% to 90%, and selects one loop from a plurality of major loops in the interval where the SOC is less than 10% or greater than 90%. Claim 6 A battery SOC estimation system according to claim 5, wherein the estimation unit selects a loop of the hysteresis curve within the SOC range corresponding to the SOC_p, wherein if the State_p is in a charged state, the charging curve is selected, and if the State_p is in a discharged state, the discharge curve is selected. Claim 7 In claim 1, the estimation unit is a battery SOC estimation system that reduces the noise of I_b through a moving average filter. Claim 8 A method for estimating an SOC of a battery comprising a current sensor, a voltage sensor, and an estimation unit, wherein the estimation unit comprises: (a) a step of loading SOC_p, which is an SOC value from a previous time point to a current time point; (b) a step in which the current sensor and the voltage sensor each measure I_b and V_t, which are the current and voltage of the battery; and the estimation unit comprises: (c) a step of determining whether the battery is charged or discharged based on I_b; and (d) a step of estimating an initial SOC according to the determination result; wherein, if the condition for determining whether the battery is charged or discharged is satisfied, the initial SOC is estimated based on at least one of the time stored at the last time point based on T_rest, which is the resting period of the battery, and T_stabilization, which is the stabilization time, the SOC_p, and State_p, which is the charging or discharging state at a previous time point; and the step (d) comprises: (d-1) a step of estimating SOC_p as the initial SOC when I_b is not zero. and (d-2) a step of estimating the initial SOC by comparing T_rest and T_stabilization when I_b is 0; a method for estimating a battery SOC estimation system. Claim 9 delete Claim 10 In claim 8, the above step (d-2) is a method for estimating an SOC estimation system of a battery, wherein when I_b is 0, the initial SOC is estimated by comparing T_rest and T_stabilization, and when T_rest is longer than T_stabilization, the initial SOC is estimated based on one of a plurality of hysteresis curves, and when T_rest is shorter than T_stabilization, the SOC_p is estimated as the initial SOC. Claim 11 In claim 10, the above step (d-2) comprises: (d-2-1) loading the OCV, which is the terminal voltage of the battery measured at the last point in time during the rest period after the battery has stabilized; (d-2-2) selecting one loop of the plurality of hysteresis curves based on either SOC_p or State_p; (d-2-3) calculating V_oc based on a prior extracted constant value R_i, I_b, and V_t; (d-2-4) defining a plurality of points closest to the reference based on V_oc in the selected curve; and (d-2-5) estimating the initial SOC based on the plurality of points and linear interpolation; a method for estimating a battery SOC estimation system. (Here, the prior extracted constant value R_i is the internal resistance of the battery.) Claim 12 In claim 11, the above step (d-2-2) is a method for estimating a battery SOC estimation system, wherein, when the x-axis of the hysteresis curve represents SOC and the y-axis represents OCV, one loop is selected from a plurality of minor loops in the interval where the SOC is 10% to 90%, and one loop is selected from a plurality of major loops in the interval where the SOC is less than 10% or greater than 90%. Claim 13 In claim 12, the above step (d-2-2) selects a loop of the hysteresis curve in the SOC range corresponding to the above SOC_p, wherein if the State_p is in a charged state, a charging curve is selected, and if the State_p is in a discharged state, a discharge curve is selected, a method for estimating a battery SOC estimation system. Claim 14 A method for estimating a battery SOC estimation system, further comprising, in claim 8, a step of reducing the noise of I_b through a moving average filter after step (b) and before step (c).

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