System and method for determining state of charge of battery

Abstract

A method for estimating a state of charge of a battery may include determining a first estimated state of charge and a first estimated accuracy of the state of charge using a first estimation approach, determining a second estimated state of charge or a second estimated accuracy of the state of charge using a second estimation approach, and estimating the state of charge of the battery based on the first estimated state of charge, the first estimated accuracy of the state of charge, the second estimated state of charge, and the second estimated accuracy of the state of charge.

Description

Technical Field

[0001] The present disclosure generally relates to circuits for electronic devices, including but not limited to personal portable devices such as wireless telephones and media players, and more particularly, to determining the state of charge of a battery in real time. Background Art

[0002] Portable electronic devices, including wireless telephones (such as mobile / cellular phones), tablet computers, cordless telephones, mp3 players, and other consumer devices, are widely used. Such portable electronic devices are typically powered by a battery (e.g., a lithium-ion battery). In battery-powered devices, it is generally necessary to determine the state of charge of the battery, as this state of charge can indicate the remaining usage time of the battery.

[0003] An existing approach for determining the state of charge includes using a circuit called a coulomb counter that uses mathematical integration of a measured current to measure the amount of charge drawn from and delivered to the battery. While current integration may be accurate over short time periods, cumulative errors can occur after long-term measurements. Another existing approach is to use the measured voltage associated with the battery to determine the state of charge. However, this approach may be affected by transient errors introduced by voltage lookup. Some traditional approaches also use a combination of current integration and voltage-based approaches.

[0004] An approach that may overcome these disadvantages is needed. Summary of the Invention

[0005] In accordance with the teachings of the present disclosure, certain disadvantages and problems associated with existing approaches for determining the state of charge of a battery can be reduced or eliminated.

[0006] In accordance with an embodiment of the present disclosure, a method for estimating the state of charge of a battery may include using a first estimation approach to determine a first estimated state of charge and a first estimated accuracy of the state of charge, using a second estimation approach to determine a second estimated state of charge and a second estimated accuracy of the state of charge, and estimating the state of charge of the battery based on the first estimated state of charge, the first estimated accuracy of the state of charge, the second estimated state of charge, and the second estimated accuracy of the state of charge.

[0007] In accordance with these and other embodiments of the present disclosure, a system for estimating the state of charge of a battery may include logic for using a first estimation approach to determine a first estimated state of charge and a first estimated accuracy of the state of charge, logic for using a second estimation approach to determine a second estimated state of charge and a second estimated accuracy of the state of charge, and logic for estimating the state of charge of the battery based on the first estimated state of charge, the first estimated accuracy of the state of charge, the second estimated state of charge, and the second estimated accuracy of the state of charge.

[0008] Based on the accompanying drawings, the description, and the claims included herein, the technical advantages of the present disclosure may be apparent to those skilled in the art. The objectives and advantages of the embodiments will be achieved and attained at least by the elements, features, and combinations specifically pointed out in the claims.

[0009] It should be understood that the foregoing general description and the following detailed description are both exemplary and explanatory and do not limit the claims set forth in the present disclosure. Description of the Drawings

[0010] A more complete understanding of the examples, the embodiments, and some of their advantages can be obtained by reference to the following description in conjunction with the accompanying drawings, in which like reference numerals indicate like features, and in which:

[0011] Figure 1 A block diagram of an example battery-powered device in accordance with an embodiment of the present disclosure is shown;

[0012] Figure 2 A flowchart of an example method for determining the state of charge of a battery in accordance with an embodiment of the present disclosure is shown; and

[0013] Figure 3 A flowchart of another example method for determining the state of charge of a battery in accordance with an embodiment of the present disclosure is shown. Detailed Description

[0014] Figure 1 A block diagram of an example battery-powered device 10 in accordance with an embodiment of the present disclosure is shown. As Figure 1 shown, the device 10 may include a battery 12, a coulomb counter 18, a temperature sensor 20, and one or more power supply components 22. The device 10 may include any device that may include functional components powered by the battery 12, including but not limited to a smartphone, a tablet computer, a game controller, or other mobile devices.

[0015] The battery 12 may include any electrical energy source that includes one or more electrochemical cells 14 having external connections (such as the power supply component 22) for powering an electrical device, wherein such electrochemical cells 14 are configured to convert electrochemical energy into electrical energy. In some embodiments, the battery 12 may be a rechargeable battery that is capable of converting electrical energy received by the battery 12 into electrochemical energy stored within the electrochemical cells 14.

[0016] As Figure 1 shown, in addition to the electrochemical cells 14, the battery 12 may also include an internal equivalent impedance represented by a resistor 16 having a resistance R. Thus, in the presence of a current I drawn from the battery 12 BATIn the case of, the terminal voltage V measured across the terminals of the battery 12 TERM may be different from the open-circuit voltage V of the battery 12 OC (e.g., V TERM = V OC - R·I BAT ).

[0017] The coulomb counter 18 may include any system, device, or apparatus configured to accumulate the charge Q originating from or delivered to the battery 12. For example, as is known in the art, the coulomb counter 18 may use the mathematical integration of the current I BAT .

[0018] The temperature sensor 20 may include any system, device, or apparatus configured to sense the temperature TEMP near the battery 12, and may include a thermistor, a thermocouple, and / or other suitable devices.

[0019] The power supply assembly 22 may include one or more electrical and / or electronic devices, which may be adapted to perform the functions of the device 10, and may include, but are not limited to, one or more processors, memories, microphones, speakers, and / or touchscreen displays.

[0020] The fuel gauge 24 may include any suitable system, device, or apparatus (e.g., a correspondingly programmed digital signal processor) to receive the terminal voltage V TERM , the charge Q, and the temperature TEMP, and to determine the state of charge SOC of the battery 12 in real time based on these measurements. In addition to determining the state of charge SOC, the fuel gauge 24 may also determine the variance sSOC of the state of charge SOC based on the terminal voltage V TERM , the sensed voltage V SNS and the temperature TEMP. The fuel gauge 24 may further report the state of charge SOC and the state of charge variance sSOC to another component (not explicitly shown) of the device 10, which may further process these parameters.

[0021] The fuel gauge 24 may include an analog-to-digital conversion circuit configured to convert the measurements of the terminal voltage V TERM , the accumulated charge Q, and the temperature T into digital discrete measurements of the charge Q(k), the voltage V(k), and the temperature T(k). Thus, each of the charge Q(k), the voltage V(k), and the temperature T(k) may include a time series, where k = 1, 2, 3,... may be the running index of the time series. In addition, the time series of the current I(k) may also be derived based on the values of the charge Q(k) (e.g., I(k) ≈ Q(k) - Q(k - 1)). Thus, as described in more detail below, the fuel gauge 24 may determine and report the state of charge SOC(k) and the state of charge variance sSOC(k).

[0022] To determine the state of charge SOC(k) and the variance of the state of charge sSOC(k), the fuel gauge 24 can determine the state of the battery 12. For the purposes of this disclosure, the battery 12 can be in one of two states: an active state or a relaxation state. The battery 12 can be in the relaxation state when, at a particular time k, the following conditions exist: (a) the current has been zero for a predetermined amount of time (e.g., one hour) prior to time k; (b) the voltage difference dV(k) = V(k) - V(k - 1) is less than a threshold (e.g., 1 microvolt); and (c) the current I(k) = 0. If any of these conditions are not met, the battery 12 can be in the active state.

[0023] The consequence of the condition that the current must be zero for a predetermined amount of time means that the relaxation state is memory - dependent because whether the battery 12 is in the relaxation state can only be determined by knowing historical information about the current. Thus, the fuel gauge 24 can implement a counter C(k), which can be defined as storing a value indicative of the amount of time the current has been zero. Thus, the battery 12 can be said to be in the relaxation state when: (a) C(k)>C THRESH ; (b) dV(k)<V THRESH , and (c) I(k) = 0, where C THRESH is a counter threshold associated with the predetermined amount of time prior to time k, and V THRESH is a threshold for the voltage difference dV(k).

[0024] As Figure 1 shown, the fuel gauge 24 can store an open - circuit voltage meter 26 therein. The relationship between the open - circuit voltage V OC , the state of charge SOC, and the temperature TEMP can be obtained by characterization (e.g., during the manufacture and / or laboratory testing of the battery 12 and / or a battery substantially identical to the battery 12). Via a look - up table, for any given values of the open - circuit voltage V OC and the temperature TEMP, the state of charge SOC can be found, particularly during the relaxation period when I BAT = 0. Thus, during the relaxation period, SOC(k)=f(V(k),T(k)), where the open - circuit voltage meter 26 defines the function.

[0025] Although the open - circuit voltage meter 26 is shown in Figure 1 as integrated into the fuel gauge 24, in some embodiments, the open - circuit voltage meter 26 can be stored in a memory external to the fuel gauge 24 and can be accessed by the fuel gauge 24.

[0026] In addition to according to the open - circuit voltage V OCIn addition to estimating the state of charge SOC based on the temperature TEMP, for a known voltage V(k) and the variance sV(k) of the voltage, the fuel gauge 24 can also estimate the variance sSOC(k) based on the open-circuit voltage meter 26.

[0027] In addition to the variance sSOC(k) present in the voltage-based lookup approach, by using the known error p of the hardware specification from the coulomb counter 18, the variance sQ(t) of the charge accumulated by the coulomb counter 18 can be given by sQ(t) = f(p).

[0028] Using the state of charge estimation based on both the voltage-based lookup approach and the coulomb counter approach as well as the variances of these two approaches, which can actually serve as an "confidence" score for the estimation, the fuel gauge 24 can estimate the state of charge SOC(k) and its variance sSOC(k) based on the voltage-based lookup state of charge SOC(k) and variance sSOC(k) and the state of charge SOC(k) and variance sSOC(k) based on the coulomb counter. The following refers to V (k) and variance sSOC V (k) and the state of charge SOC based on the coulomb counter Q (k) and variance sSOC Q (k). To estimate the state of charge SOC(k) and its variance sSOC(k). The following refers to Figure 2 and Figure 3 describes an example of a method for estimating the state of charge SOC(k) and its variance sSOC(k) based on SOC V (k), sSOC V (k), SOC Q (k) and sSOC Q (k).

[0029] Figure 2 FIG. shows a flowchart of an example method 200 for determining the state of charge of a battery according to an embodiment of the present disclosure. According to certain embodiments, method 200 may begin at step 202. As described above, the teachings of the present disclosure may be implemented in various configurations of device 10. Therefore, the preferred initialization point of method 200 and the order of the steps including method 200 may depend on the selected implementation. In these and other embodiments, method 200 may be implemented as firmware, software, an application, a function, a library, or other instructions.

[0030] At step 202, the fuel gauge 24 can determine whether the battery 12 is in a relaxation state. During this determination, the fuel gauge 24 may not output an estimate of the state of charge SOC(k). At the first moment when the battery 12 is in a relaxation state, method 200 may proceed to step 204 and may remain at step 202 until then.

[0031] At step 204, the fuel gauge 24 may reset the time index k = 1 and use a voltage-based lookup approach to estimate the initial state of charge SOC(1) and variance sSOC(1) (e.g., SOC(1) = SOC V (1) and sSOC(1) = sSOC V (1)). When the battery 12 remains in the relaxation state, the fuel gauge 24 may use a voltage-based lookup approach to estimate the state of charge SOC(k) and variance sSOC(k) (e.g., SOC(k) = SOC V (k) and sSOC(k) = sSOC V (k)).

[0032] At step 206, the fuel gauge 24 may determine whether the battery 12 remains in the relaxation state. If the battery 12 remains in the relaxation state, the method 200 may proceed back to step 204. Otherwise, if it is active, the method 200 may proceed to step 208.

[0033] At step 208, for any moment when it is active, the fuel gauge 24 may use a coulomb counter-based approach to estimate the state of charge SOC(k) and variance sSOC(k) (e.g., SOC(k) = SOC Q (k) and sSOC(k) = sSOC Q (k)), where SOC Q (k) = SOC(k - 1)+Q(k) / Q max and sSOC Q (k) = sSOC(k - 1)+p / Q max , where Q max is a known constant parameter representing the maximum charge amount.

[0034] At step 210, the fuel gauge 24 may determine whether the battery 12 is in the relaxation state. If the battery 12 remains in the relaxation state, the method 200 may proceed to step 212. Otherwise, if it is active, the method 200 may proceed back to step 208.

[0035] At step 212, for any moment in the relaxation state during step 204 other than the first relaxation moment, the fuel gauge 24 may calculate both the voltage-based lookup state of charge SOC V (k) and its variance sSOC V (k) and the coulomb counter-based state of charge SOC Q (k) and its variance sSOC Q (k), and then based on the variances sSOC V (k) and sSOC Q(k) Estimate the state of charge SOC(k) as SOC V (k) and SOC Q (k) as a weighted average (i.e., such that the path with lower variance is given a heavier weight in the weighted average). For example, in some embodiments, the fuel gauge 24 may use a known inverse variance weighted average algorithm or any other suitable approach to determine the weighted average. In addition to estimating the state of charge SOC(k), the fuel gauge 24 may also use any suitable approach to estimate the variance sSOC V (k) and variance sSOC Q (k) based on variance sSOC(k). After completing step 212, method 200 may proceed back to step 210 again.

[0036] Although Figure 2 a specific number of steps to be taken by method 200 are disclosed, method 200 may be performed with more or fewer steps than Figure 2 those depicted. Additionally, although Figure 2 a specific order of the steps to be taken by method 200 is disclosed, the steps comprising method 200 may be completed in any suitable order.

[0037] Method 200 may be implemented using the fuel gauge 24, its components, or any other system operable to implement method 200. In certain embodiments, method 200 may be implemented in part or in whole as software and / or firmware embodied in a computer-readable medium.

[0038] Figure 3 FIG. shows a flowchart of an example method 300 for determining the state of charge of a battery according to an embodiment of the present disclosure. According to certain embodiments, method 300 may begin at step 302. As described above, the teachings of the present disclosure may be implemented in various configurations of device 10. Accordingly, the preferred initialization point of method 300 and the order of the steps comprising method 300 may depend on the implementation selected. In these and other embodiments, method 300 may be implemented as firmware, software, an application, a function, a library, or other instructions.

[0039] At step 302, the fuel gauge 24 may determine whether the battery 12 is in a relaxation state. During this determination, the fuel gauge 24 may not output an estimate of the state of charge SOC(k). At the first moment when the battery 12 is in a relaxation state, method 300 may proceed to step 304 and may remain at step 302 until then.

[0040] At step 304, the fuel gauge 24 may reset the time index k = 1 and use a voltage-based lookup approach to estimate the initial state of charge SOC(1) and variance sSOC(1) (e.g., SOC(1) = SOCV (1) and sSOC(1) = sSOC V (1)). When the battery 12 is maintained in a relaxed state, the fuel gauge 24 can use a voltage-based lookup approach to estimate the state of charge SOC(k) and variance sSOC(k) (e.g., SOC(k) = SOC V (k) and sSOC(k) = sSOC V (k)).

[0041] At step 306, the fuel gauge 24 can determine whether the battery 12 is maintained in a relaxed state. If the battery 12 is maintained in a relaxed state, the method 300 can proceed back to step 304. Otherwise, if it is in an active state, the method 300 can proceed to step 308.

[0042] At step 308, for any moment in an active state, the fuel gauge 24 can use a coulomb counter-based approach to estimate the state of charge SOC(k) and variance sSOC(k) (e.g., SOC(k) = SOC Q (k) and sSOC(k) = sSOC Q (k)), where SOC Q (k) = SOC(k - 1) + Q(k) / Q max and sSOC Q (k) = sSOC(k - 1) + p / Q max , where Q max is a known constant parameter representing the maximum charge amount.

[0043] At step 310, the fuel gauge 24 can determine whether the battery 12 is in a relaxed state. If the battery 12 remains in a relaxed state, the method 300 can proceed to step 312. Otherwise, if it is in an active state, the method 300 can proceed back to step 308.

[0044] At step 312, for any moment in a relaxed state during step 304 other than the first relaxation moment, the fuel gauge 24 can calculate both the voltage-based lookup state of charge SOC V (k) and its variance sSOC V (k) and the coulomb counter-based state of charge SOC Q (k) and its variance sSOC Q (k), and then if sSOC V (k) < sSOC Q (k), estimate the state of charge SOC(k) as SOC V (k), and if sSOC V (k) > sSOC Q (k), estimate it as SOCQ (k). After completing step 312, method 300 can proceed to step 310 again.

[0045] Although Figure 3 a specific number of steps to be taken by method 300 are disclosed, method 300 can be implemented with more or fewer steps than Figure 3 those depicted. Additionally, although Figure 3 a specific order of the steps to be taken by method 300 is disclosed, the steps of method 300 can be completed in any suitable order.

[0046] Method 300 can be implemented using fuel gauge 24, its components, or any other system operable to implement method 300. In some embodiments, method 300 can be implemented partially or fully in software and / or firmware embodied in a computer-readable medium.

[0047] As used herein, when two or more elements are referred to as being "coupled" to each other, the term indicates that the two or more elements are in electrical communication or mechanical communication, as applicable, either directly or indirectly connected, with or without intermediate elements.

[0048] This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that would be understood by a person of ordinary skill in the art. Similarly, where appropriate, the appended claims encompass all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that would be understood by a person of ordinary skill in the art. Additionally, in the appended claims, a reference to a device or system or a component of a device or system that is adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function includes the device, system, or component, whether or not the particular function is activated, turned on, or unlocked, so long as the device, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. Accordingly, the systems, devices, and methods described herein can be modified, added to, or omitted without departing from the scope of this disclosure. For example, the components of the systems and devices can be integrated or separated. Additionally, the operations of the systems and devices disclosed herein can be performed by more, fewer, or other components, and the methods described can include more, fewer, or other steps. Further, the steps can be performed in any suitable order. As used in this document, "each" refers to each member of a set or each member of a subset of a set.

[0049] Although the exemplary embodiments are shown in the drawings and described below, the principles of this disclosure can be implemented using any number of techniques, whether currently known or not. This disclosure should not in any way be limited to the exemplary embodiments and techniques shown in the drawings and described above.

[0050] Unless otherwise specifically noted, the items depicted in the drawings are not necessarily drawn to scale.

[0051] All of the examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the disclosure and the concepts contributed by the inventor to further the art, and are to be construed as not being limited to such specifically recited examples and conditions. Although the embodiments of the disclosure have been described in detail, it should be understood that various changes, substitutions, and alterations can be made to the disclosure without departing from the spirit and scope of the disclosure.

[0052] While specific advantages have been enumerated above, various embodiments may include some, none, or all of the enumerated advantages. In addition, other technical advantages may become apparent to one of ordinary skill in the art after reading the foregoing drawings and description.

[0053] To assist the Patent Office and any readers of any patent issued on this application in interpreting the appended claims, the applicant wishes to note that unless the words “means for” or “step for” are expressly used in a particular claim, they are not intended to invoke 35 U.S.C. § 112(f) for any of the appended claims or claim elements.

Claims

1. A method for estimating the state of charge of a battery, comprising: Determine a first estimated state of charge and a first estimated accuracy of the state of charge using a first estimation approach; Determine a second estimated state of charge and a second estimated accuracy of the state of charge using a second estimation approach; And Estimate the battery state of charge based on the first estimated state of charge, the first estimated accuracy of the state of charge, the second estimated state of charge, and the second estimated accuracy of the state of charge.

2. The method according to claim 1, further comprising estimating the accuracy of the state of charge of the battery based on a first estimation accuracy of the state of charge and a second estimation accuracy of the state of charge.

3. The method according to claim 1 or 2, wherein, The first estimation approach includes voltage-based lookups of the first estimated state of charge and the first estimated accuracy of the state of charge from a table constructed based on characteristics of the battery, and further wherein: Determining the first estimated state of charge includes looking up the first estimated state of charge based on a measured voltage associated with the battery; and Determining the first estimated accuracy of the state of charge includes looking up the first estimated accuracy of the state of charge based on a measured voltage associated with the battery.

4. The method according to any one of claims 1-3, wherein, The second estimation approach includes a coulomb-counter-based estimation of charge flowing into and out of the battery, and further wherein: Determining the second estimated state of charge includes estimating the second estimated state of charge based on charge flowing into and out of the battery; and Determining the second estimated accuracy of the state of charge includes estimating the second estimated accuracy of the state of charge based on charge flowing into and out of the battery.

5. The method according to any one of claims 1-4, wherein: The first estimated accuracy of the state of charge includes a first estimated variance of the state of charge; and The second estimated accuracy of the state of charge includes a second estimated variance of the state of charge.

6. The method according to claim 5, wherein, Estimating the battery state of charge based on the first estimated state of charge, the first estimated accuracy of the state of charge, the second estimated state of charge, and the second estimated accuracy of the state of charge includes: estimating the battery state of charge as a weighted average of the first estimated state of charge and the second estimated state of charge, as an inverse-variance weighted average, based on the first estimated accuracy of the state of charge and the second estimated accuracy of the state of charge.

7. The method according to any one of claims 1-6, wherein, Estimating the battery state of charge based on the first estimated state of charge, the first estimated accuracy of the state of charge, the second estimated state of charge, and the second estimated accuracy of the state of charge includes: estimating the battery state of charge as a weighted average of the first estimated state of charge and the second estimated state of charge, as an inverse-variance weighted average, based on the first estimated accuracy of the state of charge and the second estimated accuracy of the state of charge.

8. The method according to any one of claims 1-6, wherein, Estimating the battery state of charge based on the first estimated state of charge, the first estimated accuracy of the state of charge, the second estimated state of charge, and the second estimated accuracy of the state of charge includes: estimating the battery state of charge as the first estimated state of charge when the first estimated accuracy of the state of charge is greater than the second estimated accuracy of the state of charge, and estimating the battery state of charge as the second estimated state of charge when the first estimated accuracy of the state of charge is less than the second estimated accuracy of the state of charge.

9. A system for estimating the state of charge of a battery, comprising: Logic for using a first estimation approach to determine a first estimated state of charge and a first estimated accuracy of the state of charge; Logic for determining a second estimated state of charge and a second estimated accuracy of the state of charge using a second estimation approach; and Logic for estimating the state of charge of the battery based on the first estimated state of charge, the first estimated accuracy of the state of charge, the second estimated state of charge, and the second estimated accuracy of the state of charge.

10. The system according to claim 9, further comprising logic for estimating the accuracy of the state of charge of the battery based on a first estimation accuracy of the state of charge and a second estimation accuracy of the state of charge.

11. The system according to claim 9 or 10, wherein, The first estimation approach includes voltage-based lookups of the first estimated state of charge and the first estimated accuracy of the state of charge from a table constructed based on characteristics of the battery, and further wherein: Determining the first estimated state of charge includes looking up the first estimated state of charge based on a measured voltage associated with the battery; and Determining the first estimated accuracy of the state of charge includes looking up the first estimated accuracy of the state of charge based on a measured voltage associated with the battery.

12. The system according to any one of claims 9-11, wherein, The second estimation approach includes a coulomb-counter-based estimation of the charge flowing into and out of the battery, and further wherein: Determining the second estimated state of charge includes estimating the second estimated state of charge based on the charge flowing into and out of the battery; and Determining the second estimated accuracy of the state of charge includes estimating the second estimated accuracy of the state of charge based on the charge flowing into and out of the battery.

13. The system according to any one of claims 9 to 12, wherein: The first estimated accuracy of the state of charge includes the first estimated variance of the state of charge; and The second estimated accuracy of the state of charge includes the second estimated variance of the state of charge.

14. The system according to claim 13, wherein, Estimating the state of charge of the battery based on the first estimated state of charge, the first estimated accuracy of the state of charge, the second estimated state of charge, and the second estimated accuracy of the state of charge includes: estimating the state of charge of the battery as a weighted average of the first estimated state of charge and the second estimated state of charge, as an inverse-variance weighted average, based on the first estimated accuracy of the state of charge and the second estimated accuracy of the state of charge.

15. The system according to any one of claims 9 - 14, wherein, Estimating the state of charge of the battery based on the first estimated state of charge, the first estimated accuracy of the state of charge, the second estimated state of charge, and the second estimated accuracy of the state of charge includes: estimating the state of charge of the battery as a weighted average of the first estimated state of charge and the second estimated state of charge, as an inverse-variance weighted average, based on the first estimated accuracy of the state of charge and the second estimated accuracy of the state of charge.

16. The system according to any one of claims 9 - 14, wherein, Estimating the state of charge of the battery based on the first estimated state of charge, the first estimated accuracy of the state of charge, the second estimated state of charge, and the second estimated accuracy of the state of charge includes: when the first estimated accuracy of the state of charge is greater than the second estimated accuracy of the state of charge, estimating the state of charge of the battery as the first estimated state of charge, and when the first estimated accuracy of the state of charge is less than the second estimated accuracy of the state of charge, estimating the state of charge of the battery as the second estimated state of charge.

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