SOC Estimation Device, Program, and SOC Estimation Method

Abstract

Provided are an SOC estimation device, a program, and an SOC estimation method with which it is possible to precisely estimate the SOC on the basis of the OCV. This SOC estimation device (7) comprises: an OCV calculation unit (76) for acquiring a voltage value of a storage battery (3) being sampled within a prescribed period, determining a fitting function that includes the bottom e of a natural logarithm having the square root of a time t as an exponent on the basis of the sampled voltage value, and, unless an exception condition is met, calculating the OCV using the determined fitting function; and an SOC estimation unit (77) for estimating the SOC on the basis of the calculated OCV.

Description

Technical Field

[0001] The present disclosure relates to a SOC estimation device, a program, and a SOC estimation method.

Background Art

[0002] Rechargeable batteries are used in various fields such as household battery systems, automotive batteries, and mobile device batteries. When using a rechargeable battery, it is necessary to manage the SOC (State of Charge). The SOC represents the ratio of the charged amount of electricity to the full charge capacity of the rechargeable battery. Conventionally, various methods for estimating the SOC have been proposed. For example, the technique of Patent Document 1 calculates the resistance ratio between the resistance when the energy storage element charges and the resistance when it discharges, and estimates the SOC based on the relationship between the resistance ratio and the SOC.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, there is a method of estimating or correcting the SOC based on the correlation between the OCV (Open Circuit Voltage) of the rechargeable battery and the SOC (SOC-OCV curve). In the method using the SOC-OCV curve, in order to improve the accuracy of the SOC, which is the final estimation result, it is required to improve the estimation accuracy of the OCV.

[0005] In view of such circumstances, an object of the present disclosure is to provide a SOC estimation device, a program, and a SOC estimation method capable of accurately estimating the SOC based on the OCV.

Means for Solving the Problems

[0006] The SOC estimation device according to an embodiment of the present disclosure acquires the voltage value of the storage battery sampled within a predetermined time, determines a fitting function including a term of the base e of the natural logarithm having the square root of time t as an exponent based on the sampled voltage value, and calculates the OCV using the determined fitting function when an exception condition is not satisfied, and an OCV calculation unit; and an SOC estimation unit that estimates the SOC based on the calculated OCV.

[0007] A program according to an embodiment of the present disclosure causes a computer to acquire the voltage value of the storage battery sampled within a predetermined time, determine a fitting function including a term of the base e of the natural logarithm having the square root of time t as an exponent based on the sampled voltage value, and calculate the OCV using the determined fitting function when an exception condition is not satisfied, and an OCV calculation unit; and an SOC estimation unit that estimates the SOC based on the calculated OCV, and function as such.

[0008] An SOC estimation method according to an embodiment of the present disclosure is an SOC estimation method executed by an SOC estimation device having a control unit, wherein the control unit acquires the voltage value of the storage battery sampled within a predetermined time, determines a fitting function including a term of the base e of the natural logarithm having the square root of time t as an exponent based on the sampled voltage value, calculates the OCV using the determined fitting function when an exception condition is not satisfied, and estimates the SOC based on the calculated OCV.

Advantages of the Invention

[0009] According to the present disclosure, it is possible to provide a SOC estimation device, a program, and a SOC estimation method that can accurately estimate SOC based on OCV.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0011] Hereinafter, a SOC estimation device and a SOC estimation method according to an embodiment of the present disclosure will be described with reference to the drawings.

[0012] (Configuration of Battery System) FIG. 1 is a schematic configuration diagram showing an example of a battery system 1 including a SOC estimation device 7 according to an embodiment of the present disclosure. The battery system 1 includes a power conditioner 2, a battery 3, a current sensor 4, a temperature sensor 5, a voltage sensor 6, and a SOC estimation device 7. The SOC estimation device 7 estimates the SOC of the battery 3, and the charge state of the battery 3 in the battery system 1 is managed based on the estimated SOC. The SOC estimation device 7 may be configured as part of a battery management device (BMS: Buttery Management System) that manages charging and discharging of the battery 3, or may be configured as an independent device from the battery management device. Also, the power conditioner 2 is also referred to as a PCS (Power Conditioning System). In the battery system 1, the battery 3 is connected to the outside of the battery system 1, such as a power grid 8 and a load 9, via the power conditioner 2. Thereby, the battery system 1 can supply the power charged in the battery 3 to the power grid 8 and the load 9, etc. Also, the battery system 1 can charge the battery 3 with the power supplied from the power grid 8, etc.

[0013] As shown by the dashed line in FIG. 1, the power conditioner 2, the battery 3, the current sensor 4, the temperature sensor 5, the voltage sensor 6, and the SOC estimation device 7 are connected to be communicable with each other by wire or wirelessly via a network such as CAN (Controller Area Network). In the present embodiment, as shown in FIG. 1, the battery system 1 is described as including one each of the power conditioner 2, the battery 3, the current sensor 4, the temperature sensor 5, the voltage sensor 6, and the SOC estimation device 7, but the number of each of these may be any number. Also, in the present embodiment, the SOC estimation device 7 is configured as part of the battery management device, but when it is an independent device from the battery management device, the battery system 1 may further include a battery management device.

[0014] The power conditioner 2 converts the DC power discharged from the storage battery 3 to AC power. Further, the power conditioner 2 converts the AC power supplied from the outside to the storage battery 3 to DC power.

[0015] The storage battery 3 is a rechargeable battery such as a lithium-ion battery, for example. The storage battery 3 includes a battery module 32 composed of one or more cells 31. The storage battery 3 can store electricity in the cells 31 constituting the battery module 32 and discharge from the cells 31. In the present embodiment, although it is described that a plurality of cells 31 are connected in series in the battery module 32, the cells 31 may be connected in parallel. Further, in the storage battery 3, a plurality of battery modules 32 may be connected in series or in parallel.

[0016] The current sensor 4 measures the current value flowing through the storage battery 3. The current value flowing through the storage battery 3 includes at least one of the current value input to the storage battery 3 and the current value output from the storage battery 3. The current sensor 4 transmits the measured current value as the current value flowing through the storage battery 3 to, for example, the SOC estimation device 7 or the like. In the present embodiment, the current sensor 4 is connected in series with one terminal of the battery module 32. However, the current sensor 4 is not limited to one terminal of the battery module 32 and may be connected at any position where the current value flowing through the storage battery 3 can be measured.

[0017] The temperature sensor 5 measures the temperature of the storage battery 3. The temperature sensor 5 transmits the measured temperature as the temperature of the storage battery 3 to, for example, the SOC estimation device 7 or the like. In the present embodiment, the temperature sensor 5 is installed on the outer surface of one terminal of the battery module 32. However, the temperature sensor 5 is not limited to the outer surface of one terminal of the battery module 32 and may be installed at any position where the temperature of the storage battery 3 can be measured.

[0018] The voltage sensor 6 measures the voltage value of the storage battery 3. The voltage sensor 6 transmits the measured voltage value as the voltage value of the storage battery 3 to, for example, the SOC estimation device 7 or the like. The voltage value of the storage battery 3 includes, for example, the voltage values during charging and discharging, and the value of the open-circuit voltage in a state where no current is flowing. In the present embodiment, the voltage sensor 6 is connected in parallel with both terminals of the battery module 32. However, the voltage sensor 6 is not limited to both terminals of the battery module 32 and may be installed at any position where the voltage value of the storage battery 3 can be measured.

[0019] The SOC estimation device 7 estimates the SOC of the storage battery 3 for the management of the storage battery 3. In the present embodiment, the SOC estimation device 7 communicates with the current sensor 4, the voltage sensor 6, etc., and acquires the current value flowing through the storage battery 3 and the voltage value of the storage battery 3. The SOC estimation device 7 may further communicate with the temperature sensor 5 to acquire the temperature of the storage battery 3. In the present embodiment, the voltage value of the storage battery 3 is given as the average voltage of the cells 31, but it is not limited thereto.

[0020] The SOC estimation device 7 estimates the OCV of the storage battery 3 and estimates the SOC based on the correlation between the OCV and the SOC (SOC-OCV curve). In the present embodiment, the SOC estimation device 7 calculates the SOC of the storage battery 3 (hereinafter referred to as the initial SOC) based on the acquired current value of the storage battery 3 by the current integration method, which is a known method. Then, the SOC estimation device 7 corrects the initial SOC calculated by the current integration method based on the estimated OCV and outputs it as the final SOC of the storage battery 3 (hereinafter sometimes referred to as the final SOC). The SOC estimation device 7 may further output an OCV flag indicating that the output SOC is corrected based on the estimated OCV. In the current integration method, the SOC estimation device 7 may correct the current value of the storage battery 3 based on the acquired temperature of the storage battery 3 by a known method and then calculate the initial SOC. As another configuration example, a device different from the SOC estimation device 7 may calculate the initial SOC, and the SOC estimation device 7 may acquire the calculated initial SOC. At this time, the SOC estimation device 7 may calculate (estimate) the final SOC by correcting the acquired initial SOC based on the OCV. Here, instead of the initial SOC and the final SOC, which are ratios to the full charge capacity of the storage battery 3, the initial current integration value and the final current integration value may be calculated.

[0021] (Configuration of SOC Estimation Device) Referring to FIG. 1, the schematic configuration of the SOC estimation device 7 according to the present embodiment will be described. As shown in FIG. 1, the SOC estimation device 7 includes a control unit 71, a communication unit 72, and a storage unit 73. The control unit 71 includes an OCV calculation unit 76 and an SOC estimation unit 77. The control unit 71, the communication unit 72, and the storage unit 73 are connected to each other so as to be communicable, either wired or wirelessly. The SOC estimation device 7 may be implemented by a computer.

[0022] The control unit 71 includes one or more processors. The processor may be, for example, a general-purpose processor such as a CPU (Central Processing Unit) or a dedicated processor specialized for specific processing. The control unit 71 is not limited to a processor and may include one or more dedicated circuits. The dedicated circuit may be, for example, an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). The control unit 71 controls the communication unit 72 and the storage unit 73 in order to realize the functions of the SOC estimation device 7.

[0023] The OCV calculation unit 76 calculates the OCV based on the acquired voltage value of the storage battery 3 and outputs the calculated OCV to the SOC estimation unit 77. In the present embodiment, the OCV calculation unit 76 acquires the voltage values of the storage battery 3 sampled within a predetermined time, and based on the sampled voltage values, determines a fitting function including a term of the base e of the natural logarithm with the square root of time t as an exponent. Then, when the exception condition is not satisfied, the OCV calculation unit 76 calculates the OCV using the determined fitting function, and when the exception condition is satisfied, uses the last sampled voltage value as the OCV. Details of the fitting function and the exception condition will be described later.

[0024] The SOC estimation unit 77 estimates the SOC based on the OCV calculated by the OCV calculation unit 76. In the present embodiment, the SOC estimation unit 77 calculates the initial SOC of the storage battery 3 based on the acquired current value of the storage battery 3, and estimates the final SOC by correcting the initial SOC based on the acquired OCV. The correlation relationship (SOC-OCV curve) used by the SOC estimation unit 77 for correction is stored, for example, in the storage unit 73. The SOC estimation unit 77 reads out the correlation relationship between the OCV and the SOC from the storage unit 73 during correction.

[0025] Here, the SOC estimation device 7 may have the following software configuration. One or more programs used for controlling the operation of the SOC estimation device 7 are stored in the storage unit 73. When the program stored in the storage unit 73 is read by the processor of the control unit 71, the control unit 71 functions as the OCV calculation unit 76 and the SOC estimation unit 77.

[0026] The communication unit 72 includes one or more communication modules. The communication module is, for example, a CAN communication module, a wired LAN (Local Area Network) communication module, a wireless LAN communication module, or the like. In the present embodiment, the SOC estimation device 7 can communicate with the power conditioner 2, the storage battery 3, the current sensor 4, the temperature sensor 5, the voltage sensor 6, etc. included in the storage battery system 1 via the communication unit 72.

[0027] The storage unit 73 is, for example, a semiconductor memory, a magnetic memory, an optical memory, or the like. The storage unit 73 may be a cache memory of the processor included in the control unit 71. The storage unit 73 may be a volatile storage device or a non-volatile storage device. The storage unit 73 stores a system program, an application program, embedded software, information, etc. for realizing the functions of the SOC estimation device 7. In the present embodiment, the storage unit 73 stores information such as the correlation between the above OCV and SOC and the fitting function.

[0028] (Processing example of SOC estimation device) With reference to FIG. 2, an example of the process of estimating the SOC of the storage battery 3 executed by the SOC estimation device 7 according to the present embodiment will be described. This process corresponds to the SOC estimation method according to the present embodiment. FIG. 2 shows a flowchart of an example of the process of the SOC estimation device 7.

[0029] As described above, the SOC estimation device 7 communicates with the current sensor 4, the voltage sensor 6, etc., and acquires the current value flowing through the storage battery 3 and the voltage value of the storage battery 3. The OCV calculation unit 76 starts calculating the OCV when the storage battery 3 is not in the charge / discharge operation, that is, when it is in a standby state. In the present embodiment, the OCV calculation unit 76 starts calculating the OCV when the magnitude of the current value flowing through the storage battery 3 is equal to or less than a predetermined value (Yes in step S1). When the magnitude of the current value is greater than the predetermined value (No in step S1), the OCV calculation unit 76 waits until it becomes equal to or less than the predetermined value. Here, the predetermined value is set according to specifications such as the standby current of the storage battery 3.

[0030] The OCV calculation unit 76 acquires the voltage values sampled within a predetermined time (step S2). The predetermined time may be the wait time used in general OCV measurements. The wait time is, for example, 3 hours. Assuming that the sampled voltage value is V, V may be associated with t which is the sampled time. For example, when sampling is performed at 6 points, the OCV calculation unit 76 is the sampled voltage value (t 0 , V 0 ), (t 1 , V 1 ), (t 2 , V 2 ), (t 3 , V 3 ), (t 4 , V 4 ) and (t 5 , V 5 ) and obtains them. At this time, assuming that the wait time is 3 hours (3h), t 0 < t 1 < t 2 < t 3 < t 4 < t 5 < 3h holds. FIG. 3 is a diagram illustrating the time change of the voltage value of the storage battery 3 that has become inactive. The horizontal axis indicates the elapsed time since the storage battery 3 became inactive. The vertical axis indicates the voltage value of the storage battery 3.

[0031] The OCV calculation unit 76 determines a fitting function for modeling the voltage change of the storage battery 3 using these sampled voltage values (step S3). As a result of the intensive research by the present inventor, it has been found that when using a fitting function including a term of the base e of the natural logarithm having the square root of time t as an exponent, the voltage change of the storage battery 3 can be accurately approximated. In the present disclosure, the fitting function is represented by f(t) of the following formula (1) with time as t, voltage value as V, and coefficient as v.

[0032]

Equation

[0033] In the present embodiment, the OCV calculation unit 76 determines v which is the coefficient in formula (1) using the sampled voltage values. Here, FIG. 4 is a plot obtained by calculating values related to √ω in formula (1) based on the measured values of the actual storage battery 3. The horizontal axis represents the square root of time t. The vertical axis is the natural logarithm (ln) of (dV / d√t). It is estimated that the voltage value of the storage battery 3 has become a value (estimated value) sufficiently close to the OCV after sufficient time has elapsed. As shown in FIG. 4, the relational expression of these values related to √ω shows a change that linearly decreases until the estimated value is reached. Therefore, in f(t) of formula (1), V which is the voltage value at t when √ω changes negatively can be estimated as the OCV.

[0034] Here, it is preferable that values of the natural logarithm of (dV / d√t) are obtained corresponding to a constant interval at √t in FIG. 4. Therefore, the voltage value of the storage battery 3 is preferably sampled, for example, every (A×n) 2 seconds where n is an integer of 1 or more. Here, the coefficient A is 10 as an example.

[0035] However, the values related to √ω may not show the changes as shown in FIG. 4. At this time, the OCV calculation unit 76 may estimate the OCV without using f(t) in Equation (1) assuming that the exception condition is satisfied. Specifically, the OCV calculation unit 76 may determine that the exception condition is satisfied when (dV / d√t) = 0 or √ω ≤ 0 during the sampling period. For example, in the case of the above six-point sampling, the sampling period is t 0 ~t 5 in the time range of.

[0036] That is, when the exception condition is satisfied (Yes in step S4), the OCV calculation unit 76 uses the last sampled voltage value as the OCV (step S5). For example, in the case of the above six-point sampling, the OCV calculation unit 76 uses the "V 5 " sampled at the last time "t 5 " as the OCV. When the exception condition is not satisfied (No in step S4), the OCV calculation unit 76 calculates the OCV using the determined fitting function (step S6).

[0037] Then, the SOC estimation unit 77 estimates the SOC based on the OCV calculated by the OCV calculation unit 76 (step S7).

[0038] As described above, the SOC estimation device 7 and the SOC estimation method according to the present embodiment can estimate the SOC with high accuracy based on the OCV by the above configuration and steps.

[0039] Here, as described above, in the present embodiment, the sampling period of the voltage value of the storage battery 3 is shorter than the weight time of general OCV measurement. For example, in the case of the above six-point sampling, the time until "t 5 " at which "V 5 " is sampled is earlier than the conventional weight time (for example, 3 hours). Therefore, the SOC estimation device 7 and the SOC estimation method according to the present embodiment can estimate the SOC earlier than the conventional SOC estimation method using OCV.

[0040] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications or corrections based on the present disclosure. Therefore, it should be noted that these modifications or corrections are included in the scope of the present disclosure. For example, the functions included in each component or each step, etc., can be rearranged so as not to be logically contradictory, and a plurality of components or steps, etc., can be combined into one or divided. The embodiments according to the present disclosure can also be realized as a program executed by a processor included in the device or a storage medium storing the program. It should be understood that these are also included in the scope of the present disclosure.

[0041] For example, in the above embodiment, the SOC estimation device 7 and the SOC estimation method estimate the SOC of the storage battery 3 included in the storage battery system 1, but are not limited to the storage battery system 1 and can be applied to other systems and devices including secondary batteries. For example, the SOC estimation device 7 and the SOC estimation method may be used in electronic devices such as portable terminals including lithium-ion batteries.

Description of Reference Numerals

[0042] 1 Storage battery system 2 Power conditioner (PCS) 3 Storage battery 4 Current sensor 5 Temperature sensor 6 Voltage sensor 7 SOC estimation device 8 Power grid 9 Load 31 Cell 32 Storage battery module 71 Control unit 72 Communication unit 73 Storage unit 76 OCV calculation unit 77 SOC estimation unit

Claims

1. An OCV calculation unit that acquires voltage values of a storage battery sampled within a predetermined time, determines a fitting function including a term of the base e of the natural logarithm having the square root of time t as an exponent based on the sampled voltage values, and calculates the OCV using the determined fitting function when an exception condition is not satisfied; An SOC estimation unit that estimates the SOC based on the calculated OCV, The fitting function is represented by f(t) of the following formula (1) with the voltage value as V and the coefficient as v, and is an SOC estimation device. 【Number 1】

2. The SOC estimation device according to claim 1, wherein when the exception condition is satisfied, the OCV calculation unit uses the voltage value sampled last as the OCV.

3. The SOC estimation device according to claim 1 or 2, wherein the SOC estimation unit estimates the final SOC by correcting the first SOC calculated by the current integration method based on the calculated OCV.

4. The exception condition is satisfied when (dV / d√t) = 0 or √ω ≤ 0 during the sampling period, and the SOC estimation device according to any one of claims 1 to 3.

5. A computer, An OCV calculation unit that acquires voltage values of a storage battery sampled within a predetermined time, determines a fitting function including a term of the base e of the natural logarithm having the square root of time t as an exponent based on the sampled voltage values, and calculates the OCV using the determined fitting function when an exception condition is not satisfied; An SOC estimation unit that functions to estimate the SOC based on the calculated OCV, The fitting function is represented by f(t) of the following formula (1) with the voltage value as V and the coefficient as v, and is a program. 【Number 2】

6. An SOC estimation method executed by an SOC estimation device having a control unit, wherein the control unit Performs a step of acquiring voltage values of a storage battery sampled within a predetermined time; Performs a step of determining a fitting function including a term of the base e of the natural logarithm having the square root of time t as an exponent based on the sampled voltage values; Performs a step of calculating the OCV using the determined fitting function when an exception condition is not satisfied; Performs a step of estimating the SOC based on the calculated OCV, and includes The fitting function is an SOC estimation method represented by f(t) in the following formula (1), where the voltage value is V and the coefficient is v. [Number 3]

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