Method for calibrating state of charge of battery and battery management system

Abstract

Disclosed is a method and a battery management system for calibrating a state of charge of a battery. The method includes measuring a terminal voltage and a current of the battery, storing a measured voltage value indicating the terminal voltage and a measured current value indicating the current in a memory, updating a state of charge of the battery based on the measured current value, estimating an open-circuit voltage of the battery based on a first number of measured voltage values and a first number of measured current values in the order stored in the memory, storing an estimated voltage value indicating the open-circuit voltage in the memory, and calibrating the updated state of charge with a reference state of charge when a calibration condition is satisfied by a data set in which a second number of estimated voltage values sequentially stored in the memory are arranged in sequential order.

Claims

1. A method for calibrating a state of charge of a battery, the method comprising: measuring a terminal voltage and a current of the battery; storing, in a memory: a measured voltage value indicating the measured terminal voltage; and a measured current value indicating the measured current; updating a state of charge of the battery using current integration of the measured current value; determining in an n.sup.th measurement cycle if at least a first number of measured voltage values and at least the first number of measured current values are sequentially stored in the memory, the first number being 2 or greater; estimating a voltage value indicating an open-circuit voltage of the battery in the n.sup.th measurement cycle based on the first number of measured voltage values and the first number of measured current values in the order stored in the memory if at least the first number of measured voltage values and at least the first number of measured current values are determined to be sequentially stored in the memory, and if not, estimating the voltage value for the n.sup.th measurement cycle to be equal to a previously estimated voltage value for an (n−1).sup.th measurement cycle; storing the estimated voltage value for the n.sup.th measurement cycle in the memory; determining whether at least a second number of the estimated voltage values are sequentially stored in the memory, the second number being 2 or greater; generating a data set including the second number of estimated voltage values arranged in a sequential order from the second number of estimated voltage values in the order stored in the memory if at least the second number of estimated voltage values are determined to be sequentially stored in the memory; calibrating the updated state of charge for the n.sup.th measurement cycle by setting the updated state of charge for the n.sup.th measurement cycle to be equal to a reference state of charge if a calibration condition is satisfied by the data set; and turning off a contactor of the battery if the updated state of charge is outside of a preset normal operating range.

2. The method according to claim 1, wherein: the estimating the open-circuit voltage of the battery uses a least square method associated with an equivalent circuit model of the battery; and the equivalent circuit model includes a voltage source, an Ohmic resistance, and at least one parallel RC circuit, connected in series.

3. The method according to claim 2, wherein the estimating the open-circuit voltage of the battery is performed based on the first number of measured voltage values and the first number of measured current values in the order stored in the memory if an estimation condition is satisfied by the first number of current values, the estimation condition being whether a change of current for a predetermined time period causes a change in voltage across two ends of each of the Ohmic resistance and the at least one parallel RC circuit.

4. The method according to claim 3, wherein the estimating the open-circuit voltage of the battery comprises estimating that the open-circuit voltage for the n.sup.th measurement cycle is equal to a previously estimated open-circuit voltage for the (n−1).sup.th measurement cycle if the estimation condition is not satisfied by the first number of current values.

5. The method according to claim 3, wherein the estimation condition is satisfied if a difference between a maximum current value of the first number of current values and a minimum current value of the first number of current values is equal to or larger than a reference current value.

6. The method according to claim 1, wherein the calibration condition is satisfied if: a difference between a reference voltage value corresponding to the reference state of charge and the estimated voltage value is less than a first voltage difference value; and a difference between two directly sequential estimated voltage values in the data set is less than a second voltage difference value.

7. The method according to claim 6, wherein the first voltage difference value is smaller than the second voltage difference value.

8. The method according to claim 1, further comprising updating the reference state of charge based on the updated state of charge for the n.sup.th measurement cycle.

9. The method of claim 8, further comprising turning off the contactor of the battery if a difference between the reference state of charge and the updated reference state of charge is larger than a predetermined value.

10. The method of claim 8, wherein the updated reference state of charge corresponds to an average state of charge over a time period from a past measurement cycle to the n.sup.th measurement cycle.

11. The method of claim 10, wherein the updated reference state of charge is set as a reference state of charge for a next (n+1).sup.th measurement cycle.

12. The method of claim 1, wherein the generating of the data set and the calibrating of the updated state of charge for the for the n.sup.th measurement cycle are performed for the n.sup.th measurement cycle only if at least the second number of estimated voltage values are determined to be sequentially stored in the memory.

13. A battery management system for calibrating a state of charge of a battery, comprising: a memory; a sensing unit configured to measure a terminal voltage and a current of the battery; and a control unit operably coupled to the memory and the sensing unit, the control unit being configured to: store, in the memory: a measured voltage value indicating the measured terminal voltage; and a measured current value indicating the measured current; update a state of charge of the battery using current integration of the measured current value; determine in an n.sup.th measurement cycle if at least a first number of measured voltage values and at least the first number of measured current values are sequentially stored in the memory, the first number being 2 or greater; estimate a voltage value indicating an open-circuit voltage of the battery in the n.sup.th measurement cycle based on the first number of measured voltage values and the first number of measured current values in the order stored in the memory if at least the first number of measured voltage values and at least the first number of measured current values are determined to be sequentially stored in the memory, and if not, estimate the voltage value for the n.sup.th measurement cycle to be equal to a previously estimated voltage value for an (n−1).sup.th measurement cycle; store the estimated voltage value for the n.sup.th measurement cycle in the memory; determine whether at least a second number of the estimated voltage values are sequentially stored in the memory, the second number being 2 or greater; generate a data set including the second number of the estimated voltage values arranged in a sequential order from the second number of estimated voltage values in the order stored in the memory if at least the second number of estimated voltage values are determined to be sequentially stored in the memory; calibrate the updated state of charge for the n.sup.th measurement cycle by setting the updated state of charge for the n.sup.th measurement cycle to be equal to a reference state of charge if a calibration condition is satisfied by the data set; transmit a notification signal indicating that the state of charge of the battery is calibrated by setting the updated state of charge for the n.sup.th measurement cycle to be equal to the reference state of charge to an external device; and turn off a contactor of the battery the updated state of charge for the n.sup.th measurement cycle is outside of a preset normal operating range.

14. The battery management system according to claim 13, wherein the calibration condition is satisfied if: a difference between a reference voltage value corresponding to the reference state of charge and the estimated voltage value is less than a first voltage difference value; and a difference between two directly sequential estimated voltage values in the data set is less than a second voltage difference value.

15. The battery management system according to claim 13, wherein the control unit is further configured to update the reference state of charge based on the updated state of charge for the n.sup.th measurement cycle.

16. The battery management system of claim 15, wherein the control unit is further configured to turn off the contactor of the battery if a difference between the reference state of charge and the updated reference state of charge is larger than a predetermined value.

17. The battery management system of claim 15, wherein the updated reference state of charge corresponds to an average state of charge over a time period from a past measurement cycle to the n.sup.th measurement cycle.

18. The battery management system of claim 17, wherein the control unit is configured to use the updated reference state of charge as a reference state of charge for a next (n+1).sup.th measurement cycle.

19. A battery pack comprising the battery management system according to claim 13.

20. The battery management system of claim 13, wherein the control unit is configured to generate the data set and to calibrate the updated state of charge for the n.sup.th measurement cycle only if at least the second number of estimated voltage values are determined to be sequentially stored in the memory.

Description

DESCRIPTION OF DRAWINGS

(1) The accompanying drawings illustrate an embodiment of the present disclosure, and together with the following detailed description, serve to provide a further understanding of the technical aspects of the present disclosure, and thus the present disclosure should not be construed as limited to the drawings.

(2) FIG. 1 is a diagram showing the functional configuration of a battery pack according to an embodiment of the present disclosure.

(3) FIG. 2 is a diagram showing an exemplary equivalent circuit model of a battery shown in FIG. 1.

(4) FIGS. 3 and 4 are flowcharts showing a method for calibrating a state of charge of a battery according to another embodiment of the present disclosure.

(5) FIG. 5 is a graph showing a correlation between an open-circuit voltage and a state of charge of a battery.

MODE FOR DISCLOSURE

(6) Hereinafter, the preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Prior to the description, it should be understood that the terms or words used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present disclosure on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation.

(7) Therefore, the embodiments described herein and illustrations shown in the drawings are just a most preferred embodiment of the present disclosure, but not intended to fully describe the technical aspects of the present disclosure, so it should be understood that a variety of other equivalents and variations could be made thereto at the time of filing the application.

(8) Additionally, in describing the present disclosure, when it is deemed that a detailed description of relevant known elements or functions renders the key subject matter of the present disclosure ambiguous, the detailed description is omitted herein.

(9) The terms including the ordinal number such as “first”, “second” and the like, may be used to distinguish one element from another among various elements, but not intended to limit the elements by the terms.

(10) Unless the context clearly indicates otherwise, it will be understood that the term “comprises” or “includes” when used in this specification, specifies the presence of stated elements, but does not preclude the presence or addition of one or more other elements. Additionally, the term <control unit> as used herein refers to a processing unit of at least one function or operation, and this may be implemented in hardware or software alone or in combination.

(11) In addition, throughout the specification, it will be further understood that when an element is referred to as being “connected to” another element, it can be directly connected to the other element or intervening elements may be present.

(12) FIG. 1 is a diagram showing the functional configuration of a battery pack 10 according to an embodiment of the present disclosure.

(13) Referring to FIG. 1, the battery pack 10 includes a battery 20, a contactor 30 and a battery management system 100.

(14) The battery 20 includes a positive terminal B+ and a negative terminal B−. The battery 20 may include at least one unit cell. When the battery 20 includes a plurality of unit cells, the plurality of unit cells may be electrically connected in series or in parallel. Each unit cell may be, for example, a lithium ion battery, a lithium polymer battery, a nickel cadmium battery, a nickel hydrogen battery and a nickel zinc battery. Of course, the type of the unit cell is not limited to the list of types described above, and includes any type of battery that can be recharged repeatedly.

(15) The contactor 30 is installed on a high current path of the battery pack 10 to adjust the charge/discharge current of the battery pack 10. The high current path of the battery pack 10 may include a path between the positive terminal B+ of the battery 20 and a positive terminal P+ of the battery pack 10 and a path between the negative terminal B− of the battery 20 and a negative terminal P− of the battery pack 10. Although FIG. 1 shows that the contactor 30 is installed between the positive terminal P+ of the battery pack 10 and the positive terminal B+ of the battery 20, the installation location of the contactor 30 is not limited thereto. For example, the contactor 30 may be installed between the negative terminal P− of the battery pack 10 and the negative terminal B− of the battery 20.

(16) The contactor 30 may be turned on or off according to a switching signal from the battery management system 100 to adjust the current of the battery 20.

(17) The battery management system 100 may include a memory 110, a sensing unit 120 and a control unit 130, and optionally, may further include a communication unit 140.

(18) The memory 110 is not limited to a particular type and includes any storage medium capable of recording and erasing information. For example, the memory 110 may include at least one type of storage medium of flash memory type, hard disk type, Solid State Disk (SSD) type, Silicon Disk Drive (SDD) type, multimedia card micro type, random access memory (RAM), static random access memory (SRAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM) and programmable read-only memory (PROM). Additionally, the memory 110 may store programs including various control logics that can be executed by the control unit 130. Additionally, the memory 110 may store data indicating the results of the control logics executed by the control unit 130.

(19) The sensing unit 120 may include a voltage sensor and a current sensor, and optionally, may further include a temperature sensor. Each of the voltage sensor 121, the current sensor 122 and the temperature sensor may be operably connected to the control unit 130.

(20) The voltage sensor 121 measures a terminal voltage of the battery 20 and transmits a voltage signal indicating the measured terminal voltage to the control unit 130. The terminal voltage corresponds to a potential difference between the positive terminal B+ and the negative terminal B−. The control unit 130 stores a measured voltage value indicating the measured terminal voltage in the memory 110 based on the voltage signal transmitted from the voltage sensor 121.

(21) The current sensor 122 measures a current of the battery 20 and transmits a current signal indicating the measured current to the control unit 130. The control unit 130 stores a current value indicating the measured current in the memory 110 based on the current signal transmitted from the current sensor 122.

(22) The temperature sensor 123 measures a temperature of the battery 20 and transmits a temperature signal indicating the measured temperature to the control unit 130. The control unit 130 stores a temperature value indicating the measured temperature in the memory 110 based on the temperature signal transmitted from the temperature sensor 123.

(23) The control unit 130 may be operably connected to the memory 110, the sensing unit 120, the communication unit 140 and the contactor 30 to individually control the operation of each of the memory 110, the sensing unit 120, the communication unit 140 and the contactor 30. The control unit 130 may be physically implemented using at least one of application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), microprocessors and electrical units for performing other functions.

(24) The control unit 130 may update the state of charge (SOC) of the battery 20 based on the current value stored in the memory 110 using current integration. Assume that the current value indicating the current measured during charging of the battery 20 has the positive sign and the current value indicating the current measured during discharging of the battery 20 has the negative sign, the current integration may be expressed as the following Equation 1.

(25) $\begin{array}{cc}\mathrm{SOC}\left(t_n\right)=\mathrm{SOC}\left(t_{n-1}\right)+\frac{I_{\mathrm{bat}}\left(t_n\right)\Delta t}{Q_{\mathrm{full}}}\times 100& \text{<}\mathrm{Equation}1\text{>}\end{array}$

(26) In Equation 1, Δt is a given measurement cycle (e.g., 0.001 sec), t.sub.n is the time point after nΔt has elapsed from an initial time point (i.e., the measurement time point at the n.sup.th cycle), t.sub.n-1 is the time point after (n−1)Δt has elapsed from the initial time point, I.sub.bat(t.sub.n) is the measured current value indicating the current measured at t.sub.n, QUI is the full charge capacity of the battery 20, SOC(t.sub.n-1) is the SOC at t.sub.n-1, and SOC(t.sub.n) is the SOC at t.sub.n. Those skilled in the art will easily understand t.sub.i=initial time point+iΔt, and Δt=t.sub.i-t.sub.i-1. The initial time point may be the time point at which a predetermined initialization event occurred. The initialization event may be, for example, an event that charging or discharging of the battery 20 starts in no-load condition, or an event that the SOC of the battery 20 is calibrated.

(27) FIG. 2 is a diagram showing an exemplary equivalent circuit model 200 of the battery 20 shown in FIG. 1.

(28) Referring to FIG. 2, the equivalent circuit model 200 includes a voltage source 205, an Ohmic resistance R.sub.0 and a parallel RC circuit 210, electrically connected in series to each other. The voltage source 205 is used to indicate the open-circuit voltage (OCV) of the battery 20. The Ohmic resistance R.sub.0 is used to indicate an internal resistance of the battery 20. The parallel RC circuit 210 is used to indicate a polarization voltage of the battery 20, and includes resistance R.sub.1 and capacitance C.sub.1 electrically connected in parallel. Of course, the equivalent circuit model 200 may further include one or more additional parallel RC circuits (not shown).

(29) As shown in FIG. 2, when the number of parallel RC circuits 210 included in the equivalent circuit model 200 is one, a model voltage value indicating a terminal voltage of the equivalent circuit model 200 at t.sub.n may be expressed as the following Equation 2.
V.sub.mod(t.sub.n)=V.sub.oc(t.sub.n)+R.sub.0I.sub.bat(t.sub.n)+V.sub.1(t.sub.n)  <Equation 2>

(30) V.sub.oc(t.sub.n) is the OCV of the battery 20 at t.sub.n, R.sub.0 is the internal resistance of the battery 20, V.sub.1(t.sub.n) is the polarization voltage at t.sub.n, and V.sub.mod(t.sub.n) is the model voltage value at t.sub.n.

(31) FIGS. 3 and 4 are flowcharts showing a method for calibrating the SOC of the battery 20 according to another embodiment of the present disclosure, and FIG. 5 is a graph showing a correlation between the OCV and the SOC of the battery 20. The method shown in FIGS. 3 and 4 may be periodically performed for a predetermined period (e.g., Δt).

(32) Referring to FIGS. 1 to 4, in step S300, the control unit 130 measures the terminal voltage and the current of the battery 20 at t.sub.n using the sensing unit 120. Optionally, the control unit 130 may further measure the temperature of the battery 20 at t.sub.n.

(33) In step S310, the control unit 130 stores a measured voltage value indicating the terminal voltage measured at t.sub.n and a measured current value indicating the current measured at t.sub.n in the memory 110. In this instance, (n−1) measured voltage values and (n−1) measured current values measured for the period from t.sub.1 to t.sub.n-1 are stored in the memory 110. Optionally, the control unit 130 may store a measured temperature value indicating the temperature measured at t.sub.n in the memory 110.

(34) In step S320, the control unit 130 updates the SOC of the battery 20 based on the measured current value measured at t.sub.n using current integration. That is, the control unit 130 may estimate SOC(t.sub.n), i.e., the SOC of the battery 20 at t.sub.n (see Equation 1). In this instance, the control unit 130 may use the above-described Equation 1. Data indicating the previous SOC, i.e., SOC(t.sub.n-1), may be stored in the memory 110.

(35) In step S330, the control unit 130 determines whether a first number or more of measured voltage values and a first number or more of measured current values are sequentially stored in the memory 110. Hereinafter, assume that the first number a is 2 or greater. n measured voltage values and n measured current values are each stored in the memory 110 through the step S310, and thus, in step S330, the control unit 130 determines whether n≥a. The first number a is a minimum number (e.g., 2000) required to estimate the OCV of the battery 20 with a predetermined level of accuracy or above, and it may be an experimentally preset value. For example, in case that first number a=2000, when t.sub.n≥t.sub.2000, the value of the step S330 is “YES”. In contrast, when t.sub.n<t.sub.2000, the value of the step S330 is “NO”. When the value of the step S330 is “YES”, the step S340 is performed. When the value of the step S330 is “NO”, the step S360 is performed.

(36) In step S340, the control unit 130 determines whether a preset estimation condition is satisfied by the first number of measured current values. The estimation condition may be satisfied, for example, when (i) a difference between the maximum current value of the first number of measured current values and the minimum current value of the first number of measured current values is equal to or larger than a reference current value (e.g., 90A) and/or (ii) each of the number of negative values of the first number of measured current values and the number of positive values of the first number of measured current values is equal to or larger than a predetermined number. Each of the estimation conditions (i) and (ii) is used to check whether a change of current for the period from t.sub.n-a+1 to t.sub.n sufficiently causes a change in voltage across two ends of each of the Ohmic resistance R.sub.0 and the parallel RC circuit 210. When the value of the step S340 is “YES”, step S350 is performed. When the value of the step S340 is “NO”, step S360 is performed.

(37) In step S350, the control unit 130 estimates the OCV of the battery 20 based on the first number of measured voltage values and the first number of measured current values in the order lately stored in the memory 110.

(38) V.sub.1(t.sub.n) in Equation 2 may be expressed as the following Equation 3.

(39) $\begin{array}{cc}{V}_1\left(t_n\right)=V_1\left(t_{n-a}\right){\exp }^{-\frac{t_n}{{\tau }_1}}+\underset{i=n-a+1}{\overset{n}{.Math.}}\left\{R_1{I}_{\mathrm{bat}}\left(t_i\right)\left({\exp }^{-\frac{t_{n-i}}{{\tau }_1}}-{\exp }^{-\frac{t_{n-i+1}}{{\tau }_1}}\right)\right\}& \text{<}\mathrm{Equation}3\text{>}\end{array}$

(40) In Equation 3, τ.sub.1 is a given time constant for the parallel RC circuit 210. In Equations 2 and 3, V.sub.oc(t.sub.n), R.sub.0, R.sub.1 and V.sub.1(t.sub.n) may be each an unknown value that can be estimated as described below. Of course, the voltage V.sub.1(t.sub.n) of the parallel RC circuit 210 may be differently expressed from Equation 3.

(41) When the measured voltage value indicating the terminal voltage measured at t.sub.i is indicated as ‘V.sub.bat(t.sub.i)’, the first number of measured voltage values are expressed as a×1 matrix as shown in the following Equation 4.
V.sub.bat_v=[V.sub.bat(t.sub.n−a+1)V.sub.bat(t.sub.n−a+2)V.sub.bat(t.sub.n−a+3) . . . V.sub.bat(t.sub.n-1)V.sub.bat(t.sub.n)].sup.T  <Equation 4>

(42) When the measured current value indicating the current measured at t.sub.i is indicated as ‘I.sub.bat(t.sub.i)’, the first number of measured current values are expressed as a×1 matrix as shown in the following Equation 5.
I.sub.bat_v=[I.sub.bat(t.sub.n−a+1)I.sub.bat(t.sub.n−a+2)I.sub.bat(t.sub.n−a+3) . . . I.sub.bat(t.sub.n-1)I.sub.bat(t.sub.n)].sup.T  <Equation 5>

(43) When the model voltage value at t.sub.i is indicated as ‘V.sub.mod(t.sub.i)’, the first number of model voltage values are expressed as a×1 matrix as shown in the following Equation 6 from Equation 2.
V.sub.mod_v=[V.sub.mod(t.sub.n−a+1)V.sub.mod(t.sub.n−a+2)V.sub.mod(t.sub.n−a+3) . . . V.sub.mod(t.sub.n-1)V.sub.mod(t.sub.n)].sup.T  <Equation 6>

(44) Let us define r, K.sub.v, J.sub.v, l.sub.v as below.

(45) $r=\exp \left(-\frac{\Delta t}{{\tau }_1}\right)$$K_v={\left[r{r}^2{r}^3\mathrm{.Math.}{r}^a\right]}^T$$J_v=\left(1-r\right)\left[\begin{array}{ccccc}1& 0& 0& \mathrm{.Math.}& 0\\ r& 1& 0& \mathrm{.Math.}& 0\\ r^2& r& 1& \mathrm{.Math.}& 0\\ \mathrm{.Math.}& \mathrm{.Math.}& \mathrm{.Math.}& \ddots & \mathrm{.Math.}\\ r^{a-1}& a^{a-2}& r^{a-3}& \mathrm{.Math.}& 1\end{array}\right]I_{\mathrm{bat}\_v}$$1_v={\left[111\mathrm{.Math.}1\right]}^T$

(46) r is the constant, and each of K.sub.v, J.sub.v, l.sub.v is a×1 matrix.

(47) Assume that OCV V.sub.oc(t.sub.i) by the voltage source 205 is constant as V.sub.oc_n for the period from t.sub.n-a to t.sub.n, Equation 6 may be expressed as the following Equation 7 by the above assumptions.
V.sub.mod_v=[l.sub.vI.sub.bat_vK.sub.vJ.sub.v][V.sub.oc_nR.sub.0V.sub.1(t.sub.n-a)R.sub.1].sup.T  <Equation b 7>

(48) In Equation 7, when a×4 matrix [l.sub.v I.sub.bat_v K.sub.v J.sub.v] including known values is indicated as ‘H’ and 4×1 matrix [V.sub.oc_n R.sub.0V.sub.1(t.sub.n-a) R.sub.1].sup.T including unknown values is indicated as ‘x’, Equation 7 may be simplified as the following Equation 8.
V.sub.mod_v=Hx<Equation 8>

(49) The least square method associated with the equivalent circuit model 200, used for the control unit 130 to estimate the OCV of the battery 20, may be expressed as the following Equation 9.

(50) $\begin{array}{cc}\mathrm{SSE}=\underset{i=n-a+1}{\overset{n}{.Math.}}{\left\{V_{\mathrm{bat}}\left(t_i\right)-V_{\mathrm{mod}}\left(t_i\right)\right\}}^2={.Math.V_{\mathrm{bat}\_v}-\mathrm{Hx}.Math.}^2& \text{<}\mathrm{Equation}9\text{>}\end{array}$

(51) In Equation 9, SSE is the sum of squared errors between V.sub.bat_v and V.sub.mod_v. The control unit 130 may estimate x by minimizing the SSE of Equation 9 using the following Equation 10.
x=(H.sup.TH).sup.−1H.sup.TV.sub.bat_v  <Equation 10>

(52) V.sub.oc_n that is a component included in x estimated using Equation 10 is the estimated voltage value indicating the OCV of the battery 20 estimated at t.sub.n.

(53) In step S360, the control unit 130 estimates that the OCV of the battery 20 is equal to the previously estimated OCV. In other words, when the estimated voltage value indicating the previously estimated OCV is V.sub.oc_n-1, the control unit 130 sets V.sub.oc_n to the same value as V.sub.oc_n-1.

(54) In step S365, the control unit 130 stores the estimated voltage value V.sub.oc_n indicating the estimated OCV of the battery 20 in the memory 110.

(55) In step S370, the control unit 130 determines whether a second number or more of estimated voltage values are sequentially stored in the memory 110. The second number may be 2 or greater. For example, in case that the second number is 5, when at least V.sub.oc_n-4, V.sub.oc_n-3, V.sub.oc_n-2, V.sub.oc_n-1 and V.sub.oc_n are sequentially stored in the memory 110, the value of the step S370 is “YES”. When the value of the step S370 is “YES”, the step S380 is performed. When the value of the step S370 is “NO”, the step S394 may be performed. Hereinafter, assume that the second number is 5 for convenience of description.

(56) In step S380, the control unit 130 generates a data set including the second number of estimated voltage values V.sub.oc_n-4, V.sub.oc_n-3, V.sub.oc_n-2, V.sub.oc_n-1 and V.sub.oc_n arranged in a sequential order from the second number of estimated voltage values V.sub.oc_n-4, V.sub.oc_n-3, V.sub.oc_n-2, V.sub.oc_n-1 and V.sub.oc_n in the order lately stored in the memory 110.

(57) In step S385, the control unit 130 determines whether a calibration condition is satisfied by the data set. The calibration condition may be satisfied when (i) a difference (e.g., |3.3V−V.sub.oc_n|) between a reference voltage value (e.g., 3.3V) corresponding to a reference SOC (e.g., 50%) and the estimated voltage value V.sub.oc_n is less than a preset first voltage difference value (e.g., 0.005V), and (ii) a difference (e.g., |V.sub.oc_n-2−V.sub.oc_n-1|) between two adjacent estimated voltage values (e.g., V.sub.oc_n-4 and V.sub.oc_n-3, V.sub.oc_n-3 and V.sub.oc_n-2, V.sub.oc_n-2 and V.sub.oc_n-1, V.sub.oc_n-1 and V.sub.oc_n) in the data set is less than a preset second voltage difference value (e.g., 0.01V).

(58) The memory 110 may store OCV-SOC curve data corresponding one-to-one to each of a plurality of temperature ranges. The control unit 130 may select any one piece of OCV-SOC curve data corresponding to any one temperature range to which a measured temperature value indicating the temperature measured at to belongs, and a correlation between OCV and SOC indicated by the selected OCV-SOC curve data may be represented as the graph shown in FIG. 5. The reference voltage value (‘reference OCV’ in FIG. 5) corresponding to the reference SOC may be determined from the selected OCV-SOC curve data. The first voltage difference value may be smaller than the second voltage difference value. When the value of the step S385 is “YES”, the step S390 is performed. When the value of the step S385 is “NO”, the step S394 is performed.

(59) In step S390, the control unit 130 calibrates the updated SOC with the reference SOC. Accordingly, SOC(t.sub.n) indicating the SOC updated in the step S320 may be changed to the same value as the reference SOC.

(60) In step S392, the control unit 130 transmits a notification signal indicating that the SOC of the battery 20 is calibrated to an external device 1 using the communication unit 140. The external device 1 may be, for example, an electronic control unit (ECU) of an electric vehicle in which the battery pack 10 is mounted.

(61) In step S394, the control unit 130 may update the reference SOC. The control unit 130 may update the reference SOC based on the updated SOC SOC(t.sub.n) using the following Equation 11.

(62) $\begin{array}{cc}\begin{array}{c}{\mathrm{SOC}}_{\mathrm{ref}}\left(t_n\right)=\frac{{\mathrm{SOC}}_{\mathrm{ref}}\left(t_{n-1}\right)\left\{\left(t_n-t_r\right)-\Delta t\right\}}{t_n-t_r}+\frac{\mathrm{SOC}\left(t_n\right)\Delta t}{t_n-t_r}\\ =\frac{{\mathrm{SOC}}_{\mathrm{ref}}\left(t_{n-1}\right)\left\{\left(n-r-1\right)\Delta t\right\}}{\Delta t\left(n-r\right)}+\frac{\mathrm{SOC}\left(t_n\right)\Delta t}{\Delta t\left(n-r\right)}\\ =\frac{{\mathrm{SOC}}_{\mathrm{ref}}\left(t_{n-1}\right)\left\{n-r-1\right\}+\mathrm{SOC}\left(t_n\right)}{n-r}\end{array}& \text{<}\mathrm{Equation}11\text{>}\end{array}$

(63) In Equation 11, t.sub.r is the past (i.e., r.sup.th cycle earlier than the n.sup.th cycle) measurement time point (e.g., t.sub.1), and SOC.sub.ref(t.sub.n-1) is the previous reference SOC. The updated reference SOC SOC.sub.ref(t.sub.n) may correspond to an average SOC for the period from t.sub.r to t.sub.n. The reference SOC SOC.sub.ref(t.sub.n) updated by the step S394 may be stored in the memory 110. SOC.sub.ref(t.sub.n) may be used as the previous reference SOC in the next cycle (i.e., n+1.sup.th cycle). According to Equation 11, an advantage is that the reference SOC is periodically updated dependent on the SOC change history of the battery 20. Of course, the reference SOC may not be updated in the step S394, and may be preset.

(64) In step S396, the control unit 130 may control the contactor 30 based on a control signal transmitted from the external device 1 or SOC(t.sub.n) obtained in the step S320. The control signal may be a response of the external device 1 to the notification signal transmitted in the step S392. When SOC(t.sub.n) is outside of a preset normal operating range (e.g., 20˜80 [%]), the control unit 130 may turn off the contactor 30 to protect the battery 20 from overcharge and overdischarge. When a difference between SOC.sub.ref(t.sub.n) and SOC.sub.ref(t.sub.n-1) is larger than a predetermined value (e.g., 0.3%), the control unit 130 may turn off the contactor 30. It is because a very large difference between SOC.sub.ref(t.sub.n) and SOC.sub.ref(t.sub.n-1) represents a high likelihood that an error occurred in at least one of the steps performed to determine SOC.sub.ref(t.sub.n).

(65) The embodiments of the present disclosure described hereinabove are not implemented only through the apparatus and method, and may be implemented through programs that realize the functions corresponding to the configurations of the embodiments of the present disclosure or recording media having the programs recorded thereon, and this implementation may be easily achieved by those skilled in the art from the disclosure of the embodiments previously described.

(66) While the present disclosure has been hereinabove described with regard to a limited number of embodiments and drawings, the present disclosure is not limited thereto and it is obvious to those skilled in the art that various modifications and changes may be made thereto within the technical aspects of the present disclosure and the equivalent scope of the appended claims.

(67) Additionally, many substitutions, modifications and changes may be made to the present disclosure described hereinabove by those skilled in the art without departing from the technical aspects of the present disclosure, and the present disclosure is not limited to the above-described embodiments and the accompanying drawings, and some or all the embodiments may be selectively combined together to make various modifications.

DESCRIPTION OF REFERENCE NUMERALS

(68) 1: external device 10: battery pack 20: battery 30: contactor 100: battery management system 110: memory 120: sensing unit 130: control unit 140: communication unit 200: equivalent circuit mode R0: Ohmic resistance 210: parallel RC circuit