Battery pack and charge control circuit

Abstract

The present disclosure provides a technology for highly accurately estimating the SOC of a secondary battery even when the full charge capacity changes.　A battery pack (1) according to one aspect of the present disclosure comprises a secondary battery (5) and a charge control circuit (10), wherein the charge control circuit (10) keeps a first full charge capacity and a first SOC which are held, calculates a current second full charge capacity in the secondary battery (5), calculates a first battery remaining capacity from the first full charge capacity and the first SOC, calculates a second SOC from the second full charge capacity and the first battery remaining capacity, and, when the second SOC is more than 100%, sets the second SOC to 100%.

Description

Battery Pack and Charge Control Circuit

[0001] The present disclosure relates to a battery pack and a charge control circuit.

[0002] Patent Document 1 discloses a SOC estimation method for estimating the SOC value of a secondary battery. Patent Document 1 discloses that the charge and discharge current of a secondary battery is monitored and continuously integrated to obtain a first integrated value, and the result obtained by dividing the first integrated value by the capacity value of the secondary battery is added to the SOC initial value to continuously calculate the first SOC value. Patent Document 1 discloses detecting the timing at which charging and discharging in the secondary battery switch, and obtaining the terminal voltage of the secondary battery at that timing at that timing. Patent Document 1 discloses obtaining a correction value for converting the terminal voltage into the open-circuit voltage in the equilibrium state of the secondary battery, and obtaining a second SOC value based on the result of adding the correction value to the terminal voltage. Further, Patent Document 1 discloses that every time the second SOC value is obtained, the SOC initial value is updated with the second SOC value and the integration calculation of the first integrated value is restarted. Patent Document 1 discloses obtaining the current capacity value of the secondary battery from the difference between the second SOC value obtained previously and the second SOC value obtained this time, and the integrated value of the charge and discharge current in the time interval corresponding to the difference. Further, Patent Document 1 discloses updating the capacity value used for calculating the first SOC value with the current capacity value.

[0003] Patent Document 2 discloses a battery state estimation device for estimating the charge rate of a battery. Patent Document 2 discloses including a SOC determination unit that determines whether to estimate the charge rate of the battery based on either the full charge capacity or the dischargeable capacity of the battery, and a full charge capacity estimation unit that estimates the full charge capacity. Further, Patent Document 2 discloses including a discharge capacity estimation unit that estimates the dischargeable capacity, and a current integration estimation unit that estimates the charge rate of the battery based on the full charge capacity or the dischargeable capacity.

[0004] International Publication No. 2008 / 026476, International Publication No. 2016 / 129212

[0005] When estimating the State of Charge (SOC) of a battery, the full charge capacity is used. If the full charge capacity is used as a fixed parameter when estimating the SOC, changes (decreases) in the full charge capacity, such as when the battery degrades, will affect the SOC estimation result. This impact on the SOC estimation result leads to a deterioration in the accuracy of the SOC estimation.

[0006] This disclosure provides a technology for estimating the State of Charge (SOC) of a secondary battery with high accuracy, even when the full charge capacity changes.

[0007] One aspect of the present disclosure provides a battery pack comprising a secondary battery and a charging control circuit, wherein the charging control circuit holds a held first full charge capacity and a first state of charge (SOC), calculates the current second full charge capacity of the secondary battery, calculates a first remaining battery charge from the first full charge capacity and the first SOC, calculates a second SOC from the second full charge capacity and the first remaining battery charge, and if the second SOC exceeds 100%, sets the second SOC to 100%.

[0008] According to this disclosure, the State of Charge (SOC) of a secondary battery can be estimated with high accuracy even when the full charge capacity changes.

[0009] Figure 1 is a diagram showing a schematic example of a battery pack according to this embodiment. Figure 2 is a diagram showing an example of the charging process of the charging control circuit included in the battery pack according to this embodiment. Figure 3 is a flowchart showing an example of the process executed by the SOC estimation unit in the charging control circuit included in the battery pack according to this embodiment. Figure 4 is a flowchart showing an example of the process executed by the full charge capacity calculation unit in the charging control circuit included in the battery pack according to this embodiment. Figure 5 is a flowchart showing an example of the process executed by the capacity update unit in the charging control circuit included in the battery pack according to this embodiment.

[0010] The embodiments for carrying out the invention will be described below with reference to the drawings. In each drawing, the same reference numerals are used for identical components, and redundant explanations may be omitted.

[0011] A battery pack according to this embodiment will now be described. The battery pack according to this embodiment comprises a secondary battery and a charging control circuit. The charging control circuit in the battery pack according to this embodiment maintains a first full charge capacity and a first state of charge (SOC), calculates the current second full charge capacity of the secondary battery, and calculates the first remaining battery charge from the first full charge capacity and the first SOC. Furthermore, the charging control circuit in the battery pack according to this embodiment calculates the second SOC from the second full charge capacity and the first remaining battery charge. In addition, if the second SOC exceeds 100%, the charging control circuit in the battery pack according to this embodiment sets the second SOC to 100%.

[0012] Details of the battery pack according to this embodiment will be explained with reference to the drawings. Figure 1 is a schematic example of a battery pack 1, which is an example of a battery pack according to this embodiment.

[0013] Battery pack 1 stores electricity by being charged from an external source. Battery pack 1 also supplies the stored power to devices. Devices that use battery pack 1 include, for example, information devices such as personal computers, smartphones, and tablet terminals; vehicles such as bicycles and automobiles; home appliances; and energy storage devices. Battery pack 1 is used by repeatedly charging and discharging. Battery pack 1 comprises a secondary battery 5, a charging control circuit 10, and a charging circuit 20.

[0014] The individual components that make up the battery pack 1 will be described in detail below.

[0015] [Secondary Battery 5] Secondary battery 5 is a battery that can be used by repeatedly charging and discharging. Secondary battery 5 is, for example, a lithium-ion battery.

[0016] [Charging Control Circuit 10] The charging control circuit 10 controls the charging in the charging circuit 20. The charging control circuit 10 also estimates the full charge capacity of the secondary battery 5.

[0017] The charging control circuit 10 includes, for example, a computer. The charging control circuit 10 includes, for example, a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), auxiliary storage device, etc. The CPU operates based on a program stored in the ROM or auxiliary storage device.

[0018] The charging control circuit 10 includes a measurement value acquisition unit 11, an SOC estimation unit 12, a full charge capacity calculation unit 13, a capacity update unit 14, a storage unit 15, and a charging control unit 16.

[0019] (Measurement Value Acquisition Unit 11) The measurement value acquisition unit 11 acquires the measurement values ​​measured by the current sensor 21 and the voltage sensor 22, which are provided in the charging circuit 20. The measurement value acquisition unit 11 also acquires the measurement values ​​measured by the temperature sensor 41, which is attached to the secondary battery 5 and measures the temperature in the secondary battery 5.

[0020] The measurement value acquisition unit 11 outputs the acquired current value, voltage value, and temperature to the SOC estimation unit 12. The measurement value acquisition unit 11 also calculates the integrated current amount by accumulating the current value over a predetermined period of time, for example. The measurement value acquisition unit 11 then outputs the calculated integrated current amount to the SOC estimation unit 12.

[0021] (SOC Estimation Unit 12) The SOC estimation unit 12 estimates the State of Charge (SOC) of the secondary battery 5. The SOC estimation unit 12 obtains, for example, current value, voltage value, temperature, and integrated current from the measurement value acquisition unit 11. Then, the SOC estimation unit 12 calculates the SOC (SOC) using, for example, the acquired current value, voltage value, temperature, and integrated current.

[0022] (Full charge capacity calculation unit 13) The full charge capacity calculation unit 13 calculates the current full charge capacity of the secondary battery 5.

[0023] (Capacity update unit 14) The capacity update unit 14 updates the full charge capacity stored in the memory unit 15.

[0024] (Storage Unit 15) The storage unit 15 stores each parameter. The storage unit 15 stores the current full charge capacity FCCa, which is used in the SOC estimation unit 12, and the new full charge capacity FCCb, which is calculated in the full charge capacity calculation unit 13. Hereinafter, the current full charge capacity FCCa may be referred to as the current full charge capacity. Also, the new full charge capacity FCCb may be referred to as the new full charge capacity.

[0025] Furthermore, the memory unit 15 stores the charge rate SOCa, which is the current charge rate of the secondary battery 5 used when the SOC estimation unit 12 estimates the SOC, and the charge rate SOCb, which is the newly estimated charge rate by the SOC estimation unit 12. Hereinafter, the charge rate SOCa, which is the current charge rate of the secondary battery 5, may be referred to as the current charge rate. Also, the charge rate SOCb, which is the newly estimated charge rate, may be referred to as the new charge rate.

[0026] Furthermore, the memory unit 15 stores the charge rate SOCva, which is the charge rate at the first voltage Va, and the charge rate SOCvb, which is the charge rate at the second voltage Vb.

[0027] (Charging Control Unit 16) The charging control unit 16 controls the charging of the secondary battery 5. The charging control unit 16 controls the charging circuit 20 to control the charging of the secondary battery 5. The charging of the secondary battery 5 by the charging control unit 16 will now be described. Figure 2 is a diagram showing an example of the charging process of the charging control circuit 10 provided in a battery pack 1, which is an example of a battery pack according to this embodiment.

[0028] The charging control unit 16 performs pre-charging at the start of charging. Time T1 is the charging start time. The charging control unit 16 starts pre-charging at time T1 in Figure 2. For example, as pre-charging, the charging control unit 16 charges with a relatively low current, I2. Current I2 is about 0.3 times the current I3 in constant current charging, which will be described later. The charging control unit 16 also performs trickle charging with current I1 as pre-charging. Current I1 is about 0.1 times the current I3 in constant current charging.

[0029] The charging control unit 16 performs pre-charging until the battery voltage reaches voltage V1 at time T2. Rapid charging when the secondary battery 5 has low charge capacity may accelerate the deterioration of the secondary battery. Therefore, as pre-charging, the charging control unit 16 charges the secondary battery 5 while controlling the charging current to a small current.

[0030] At time T2 in Figure 2, when the preliminary charging is complete, the charging control unit 16 starts the main charging. Specifically, the charging control unit 16 starts the main charging when the battery voltage exceeds voltage V1. Voltage V1 is, for example, 3.0 volts.

[0031] The charging control unit 16 first performs constant current charging (CC charging) with a constant current as the main charging process. The charging control unit 16 charges the secondary battery 5 with a constant current I3.

[0032] Then, when the battery voltage (including the open-circuit voltage) reaches a predetermined voltage V3, the charging control unit 16 performs constant voltage charging (CV charging). The voltage V3 is, for example, 4.2 volts. Note that the battery voltage may also be measured in an open-circuit state by temporarily stopping the charging current. In Figure 2, at time T3, the charging control unit 16 terminates constant current charging (CC charging) and starts constant voltage charging (CV charging).

[0033] When constant voltage charging (CV charging) is started, the charging current gradually decreases. In constant voltage charging (CV charging), the charging control unit 16 stops charging when the charging current falls below a predetermined current I1. In Figure 2, at time T4, the charging control unit 16 stops constant voltage charging (CV charging).

[0034] As described above, the charging control unit 16 controls the system to perform constant current charging (CC charging) before constant voltage charging (CV charging). Then, during constant current charging (CC charging), the charging control unit 16 controls the system to perform constant voltage charging (CV charging) when the voltage of the secondary battery 5 reaches the determination voltage (voltage V3).

[0035] Constant current charging (CC charging) is fast, but there is a risk of the secondary battery degrading if the voltage exceeds a predetermined level. On the other hand, constant voltage charging (CV charging) is slower, but it allows for highly precise control of the charging process. Therefore, the charging control unit 16 rapidly charges the secondary battery 5 using constant current charging (CC charging), and then, once it reaches the determination voltage V3, switches to constant voltage charging (CV charging) to control the charging of the secondary battery 5 with high precision.

[0036] Furthermore, the charging control unit 16 stops charging at time T4, and then when the battery voltage falls below voltage V2 (at time T5), it restarts charging. Voltage V2 is, for example, 3.97 volts. In order to restart charging, the charging control unit 16, after a certain period of time has elapsed from time T5, performs charging with current I3 from time T6 to time T7, in the same way as during constant current charging (CC charging).

[0037] In Figure 2, constant current charging (CC charging) is an example of the first constant current charging, constant voltage charging (CV charging) is an example of constant voltage charging, voltage V2 is an example of the first threshold, and recharging is an example of the second constant current charging.

[0038] (Processing in the SOC estimation unit 12) The processing in the SOC estimation unit 12 will now be explained. Figure 3 is a flowchart showing an example of the processing performed by the SOC estimation unit 12 in the charging control circuit 10 of a battery pack 1, which is an example of a battery pack according to this embodiment.

[0039] The SOC estimation unit 12 estimates the State of Charge (SOC). The SOC estimation unit 12 estimates the SOC using, for example, the Kalman filter method, which estimates the SOC using a Kalman filter; the current integration method, which estimates the SOC using the integrated current amount; or the voltage method, which estimates the SOC using the battery voltage. Here, we will explain the case in which the SOC estimation unit 12 estimates the SOC using the current integration method.

[0040] (Step S10) The SOC estimation unit 12 acquires the measured results from the measurement value acquisition unit 11. Specifically, the SOC estimation unit 12 acquires the current value I measured by the current sensor 21.

[0041] (Step S20) The SOC estimation unit 12 acquires the fully charged capacity FCCa (current fully charged capacity), which is the fully charged capacity at the current time, from the storage unit 15.

[0042] (Step S30) The SOC estimation unit 12 acquires the charging rate SOCa (current SOC), which is the charging rate at the current time, from the storage unit 15.

[0043] (Step S40) Next, the SOC estimation unit 12 calculates a new charging rate SOCb (new SOC) from the acquired current value I, charging rate SOCa, and fully charged capacity FCCa. The charging rate SOCb is obtained, for example, by Equation 1.

[0044] SOCb = SOCa + (I × Δt) / FCCa ··· (Equation 1)

[0045] Note that Δt is the time from when the previous current value was measured until the current current value is acquired.

[0046] (Step S50) If the charging rate SOCb is 100% or more, the SOC estimation unit 12 changes the charging rate SOCb to 100%.

[0047] (Step S60) Next, the SOC estimation unit 12 stores the calculated charging rate SOCb in the storage unit 15 as the charging rate SOCa. By storing the charging rate SOCb in the storage unit 15 as the charging rate SOCa, the SOC estimation unit 12 updates the charging rate SOCa to the charging rate SOCb. In other words, the SOC estimation unit 12 replaces the charging rate SOCa with the charging rate SOCb.

[0048] By performing the above processing, the SOC estimation unit 12 estimates the charging rate.

[0049] (Processing of the fully charged capacity calculation unit 13) The processing in the fully charged capacity calculation unit 13 will be described. FIG. 4 is a flowchart showing an example of the processing executed by the fully charged capacity calculation unit 13 in the charge control circuit 10 included in the battery pack 1, which is an example of the battery pack according to the present embodiment.

[0050] The fully charged capacity calculation unit 13 acquires the SOC change amount and current integration amount during a specific period during charging and calculates the fully charged capacity.

[0051] When performing the following processes, the charging control unit 16 controls the charging circuit 20 to perform CC charging.

[0052] (Step S110) The full charge capacity calculation unit 13 obtains the result of voltage measurement from the measurement value acquisition unit 11 and determines whether the acquired voltage is the first voltage Va. In other words, the full charge capacity calculation unit 13 determines whether the first voltage Va has been detected. If the first voltage Va is detected (YES in step S110), the full charge capacity calculation unit 13 proceeds to step S120. If the first voltage is not detected (NO in step S110), the full charge capacity calculation unit 13 proceeds to step S140.

[0053] (Step S120) The full charge capacity calculation unit 13 determines whether the SOC at the first voltage Va has not been acquired. In other words, the full charge capacity calculation unit 13 determines whether the SOC at the first voltage Va has not been acquired. The full charge capacity calculation unit 13 checks, for example, whether an appropriate value is stored in the storage unit 15 for the charge rate SOCva. For example, if a negative value is stored as the charge rate SOCva, the full charge capacity calculation unit 13 determines that the SOC at the first voltage Va has not been acquired. Note that the method by which the full charge capacity calculation unit 13 determines whether the SOC at the first voltage Va has not been acquired is not limited to the above. For example, the full charge capacity calculation unit 13 may determine whether the SOC at the first voltage Va has not been acquired by checking a flag.

[0054] If the State of Charge (SOC) at the first voltage Va has not been obtained (YES in step S120), the full charge capacity calculation unit 13 proceeds to step S130. If the SOC at the first voltage Va has been obtained (NO in step S120), the full charge capacity calculation unit 13 proceeds to step S140.

[0055] (Step S130) The full charge capacity calculation unit 13 obtains the current time ta. The full charge capacity calculation unit 13 also obtains the current charge rate SOCva from the SOC estimation unit 12. For example, the SOC estimation unit 12 estimates the charge rate SOCva using the voltage method. When the secondary battery 5 is charged by constant current charging (CC charging), it is known that the charge rate SOC is proportional to the open-circuit voltage. That is, the charge rate SOC satisfies the following equation 2.

[0056] SOC (V) = α×V×100 (Formula 2)

[0057] SOC(V) is the rate of charge (in %) at the estimated open-circuit voltage V, where α is a constant (in volts), and V is the open-circuit voltage (in volts) of the secondary battery 5. Therefore, for example, the rate of charge SOCva at the first voltage Va can be calculated using Equation 3.

[0058] SOCva = α×Va×100 (Formula 3)

[0059] (Step S140) Next, the full charge capacity calculation unit 13 obtains the voltage measurement result from the measurement value acquisition unit 11 and determines whether the acquired voltage is the second voltage Vb. In other words, the full charge capacity calculation unit 13 determines whether it has detected the second voltage Vb. The second voltage Vb is assumed to be a voltage higher than the first voltage Va. If the second voltage Vb is detected (YES in step S140), the full charge capacity calculation unit 13 proceeds to step S150. If the second voltage is not detected (NO in step S140), the full charge capacity calculation unit 13 terminates processing.

[0060] (Step S150) The full charge capacity calculation unit 13 obtains the current time tb. The full charge capacity calculation unit 13 also obtains the current charge rate SOCvb from the SOC estimation unit 12.

[0061] Using Equation 2, the charge level (SOCvb) can be calculated using Equation 4.

[0062] SOCvb = α×Vb×100 (Formula 4)

[0063] (Step S160) The full charge capacity calculation unit 13 calculates the cumulative current amount ΔQ accumulated between time ta and time tb based on time ta and time tb. For example, if time ta is in seconds, time tb is in seconds, the current value Ic in CC charging is in amperes, and the cumulative current amount ΔQ is in ampere-seconds, the full charge capacity calculation unit 13 calculates the cumulative current amount ΔQ based on equation 5.

[0064] ΔQ = Ic×(tb-ta) (Formula 5)

[0065] Furthermore, the full charge capacity calculation unit 13 calculates the SOC difference ΔSOC, which is the difference in the charge rate. Specifically, the full charge capacity calculation unit 13 calculates the SOC difference ΔSOC using Equation 6.

[0066] ΔSOC = SOCvb - SOCva ... (Formula 6) = α (Vb - Va) x 100

[0067] (Step S170) The full charge capacity calculation unit 13 calculates the full charge capacity FCCb, which is the newly calculated full charge capacity. The full charge capacity calculation unit 13 calculates the full charge capacity FCCb based on Equation 7.

[0068] FCCb = ΔQ / (ΔSOC / 100) ... (Formula 7) = {Ic×(tb-ta)} / {α(Vb-Va)}

[0069] The full charge capacity calculation unit 13 stores the calculated full charge capacity FCCb in the storage unit 15.

[0070] Note that time ta is an example of the first charging time, and time tb is an example of the second charging time.

[0071] Furthermore, although the above example describes an example of calculating the full charge capacity using two times, ta and tb, the above process may be repeated. To illustrate with two examples, for instance, the full charge capacity may be calculated by calculating the charge rate at time tc when the third voltage Vc is higher than the second voltage Vb, and then calculating the charge rate at time td when the fourth voltage Vd is higher than the third voltage Vc. For example, the full charge capacity may be calculated using two times, ta and tb, and then calculated using two times, tc and td, and these full charge capacities may be averaged to calculate the full charge capacity.

[0072] Time tc is an example of the third charging time, and time dd is an example of the fourth charging time.

[0073] (Processing in the Capacity Update Unit 14) The processing in the capacity update unit 14 will now be explained. Figure 5 is a flowchart showing an example of the processing performed by the capacity update unit 14 in the charging control circuit 10 of a battery pack 1, which is an example of a battery pack according to this embodiment.

[0074] The capacity update unit 14 updates the full charge capacity if it has already calculated the new full charge capacity at a specified timing. Specifically, the capacity update unit 14 updates the full charge capacity, for example, when the battery is fully charged.

[0075] (Step S210) The capacity update unit 14 determines whether it is time to update the full charge capacity. In other words, the capacity update unit 14 determines whether it is time to update the full charge capacity. Basically, the capacity update unit 14 may determine that it is time to update the full charge capacity when charging is complete, i.e., when the battery is fully charged. Alternatively, the capacity update unit 14 may determine that it is time to update the full charge capacity each time the full charge capacity calculation unit 13 finishes calculating the full charge capacity. Furthermore, the capacity update unit 14 may determine that it is time to update the full charge capacity each time the SOC estimation unit 12 estimates the SOC. Also, the capacity update unit 14 may determine that it is time to update the full charge capacity after recharging has been performed. If it is time to update (YES in step S210), the capacity update unit 14 proceeds to step S220. If it is not time to update (NO in step S210), the capacity update unit 14 terminates processing.

[0076] (Step S220) The capacity update unit 14 determines whether the full charge capacity FCCb (new full charge capacity) has been calculated. The capacity update unit 14 checks, for example, whether an appropriate value is stored in the storage unit 15 for the full charge capacity FCCb. For example, if a negative value is stored for the full charge capacity FCCb, the capacity update unit 14 determines that the full charge capacity FCCb has not been calculated. Note that the method by which the capacity update unit 14 determines whether the full charge capacity FCCb has been calculated is not limited to the above. For example, the capacity update unit 14 may determine whether the full charge capacity FCCb has been calculated by checking a flag.

[0077] If the full charge capacity FCCb has already been calculated (YES in step S220), the capacity update unit 14 proceeds to step S230. If the full charge capacity FCCb has not already been calculated (NO in step S220), the capacity update unit 14 terminates the process.

[0078] (Step S230) The capacity update unit 14 calculates the remaining capacity of the secondary battery 5 at the present time. Based on the full charge capacity FCCa and the current charge rate SOC, the capacity update unit 14 calculates the remaining capacity Qr of the secondary battery 5.

[0079] (Step S240) Next, the capacity update unit 14 calculates the charge rate SOCb using the new full charge capacity FCCb and the remaining capacity Qr calculated in step S230. If the charge rate SOCb is 100% or more, the charge rate SOCb is set to 100%.

[0080] (Step S250) Next, the capacity update unit 14 updates the charge rate SOCa stored in the memory unit 15 with the charge rate SOCb. In other words, the capacity update unit 14 replaces the charge rate SOCa stored in the memory unit 15 with the charge rate SOCb.

[0081] (Step S260) Next, the capacity update unit 14 updates the full charge capacity FCCa stored in the memory unit 15 with the full charge capacity FCCb. In other words, the capacity update unit 14 replaces the full charge capacity FCCa stored in the memory unit 15 with the full charge capacity FCCb.

[0082] The current remaining battery capacity is calculated using the previous full charge capacity and the estimated SOC value. For example, if the current full charge capacity FCCa is 1000 milliamperes and the current charge rate SOC is 50%, then secondary battery 5 has a remaining capacity of 500 milliamperes. This 500 milliamperes is the current remaining battery capacity. If the new full charge capacity FCCb decreases to, for example, 950 milliamperes, the new charge rate SOCb is calculated from the remaining battery capacity of 500 milliamperes and the full charge capacity FCCb as 500 / 950 × 100 = 53%. The newly calculated charge rate SOCb is then updated to the charge rate SOCa.

[0083] In step S50 shown in Figure 3, the SOC estimation unit 12 changes the charge rate SOCb to 100% if it is 100% or higher. The effect of step S50 is as follows: If the full charge capacity is updated when the battery is fully charged and charging is complete, the charge rate SOCb can remain at 100%. That is, if the charge rate SOCa is 100%, calculating the charge rate SOCb from the remaining battery capacity and the full charge capacity FCCb may result in a charge rate SOCb exceeding 100%. Here, although the charge rate should not exceed 100% by definition, if the charge rate SOCb exceeds 100%, it will cause discomfort to the user. Also, the remaining battery capacity when the charge rate SOCb is set to 100% is the same as the updated full charge capacity. For example, if the remaining battery capacity calculated is 1000 milliamperes and the updated full charge capacity is 950 milliamperes, the remaining battery capacity is set to 950 milliamperes.

[0084] Note that SOCa represents an example of the first state of charge (SOC), SOCb represents an example of the second state of charge (SOC), Qr represents an example of the first remaining battery charge, FCCa represents an example of the first full charge capacity, and FCCb represents an example of the second full charge capacity.

[0085] According to the battery pack of this embodiment, the State of Charge (SOC) of the secondary battery can be estimated with high accuracy even when the full charge capacity changes. Furthermore, according to the battery pack of this embodiment, it is possible to prevent the estimated charge rate from exceeding 100%.

[0086] Although the present disclosure has been described above based on examples, the present disclosure is not limited to the above examples, and various modifications are possible within the scope of the claims.

[0087] This application claims priority to Basic Patent Application No. 2024-189235, filed with the Japan Patent Office on October 28, 2024, the entire contents of which are incorporated herein by reference.

[0088] 1 Battery pack, 5 Secondary battery, 10 Charging control circuit, 11 Measurement value acquisition unit, 12 SOC estimation unit, 13 Full charge capacity calculation unit, 14 Capacity update unit, 15 Memory unit, 16 Charging control unit, 20 Charging circuit, SOCa, SOCb, SOCva, SOCvb Charge rate, FCCa, FCCb Full charge capacity, ΔSOC SOC difference, ΔQ Current integration amount

Claims

1. A battery pack comprising a secondary battery and a charging control circuit, wherein the charging control circuit maintains a first full charge capacity and a first state of charge (SOC), calculates the current second full charge capacity of the secondary battery, calculates the first remaining battery charge from the first full charge capacity and the first SOC, calculates the second SOC from the second full charge capacity and the first remaining battery charge, and if the second SOC exceeds 100%, sets the second SOC to 100%.

2. The battery pack according to claim 1, wherein the charging control circuit updates the held first full charge capacity to the second full charge capacity and updates the held first SOC to the second SOC.

3. The battery pack according to claim 2, wherein the charging control circuit updates the second full charge capacity when the secondary battery is fully charged.

4. The battery pack according to claim 1 or claim 2, wherein the secondary battery is charged by a first constant current charge and a constant voltage charge performed after the first constant current charge, the time when the voltage of the secondary battery reaches a first voltage is defined as the first charging time, the time when the voltage reaches a second voltage higher than the first voltage is defined as the second charging time, and the charging control circuit calculates the second full charge capacity using the first voltage, the second voltage, the first charging time, the second charging time, and the current value in the first constant current charge.

5. The battery pack according to claim 4, wherein the charging control circuit determines the cumulative amount of current charged between the first charging time and the second charging time based on the first charging time, the second charging time and the current value, and calculates the second full charge capacity based on the cumulative amount of current and the difference between the first voltage and the second voltage.

6. The battery pack according to claim 4, wherein the time when the voltage of the secondary battery becomes a third voltage higher than the second voltage is defined as the third charging time, the time when the voltage becomes a fourth voltage higher than the third voltage is defined as the fourth charging time, and the charging control circuit calculates the second full charge capacity using the first voltage, the second voltage, the third voltage, the fourth voltage, the first charging time, the second charging time, the third charging time, the fourth charging time, and the current value.

7. The battery pack according to claim 1 or claim 2, wherein the secondary battery is charged by a first constant current charge and a constant voltage charge performed after the first constant current charge, and a second constant current charge is performed when the voltage of the secondary battery falls below a first threshold after the constant voltage charge, and the charge control circuit updates the second full charge capacity after the second constant current charge.

8. A charging control circuit for controlling the charging of a secondary battery, which holds a first full charge capacity and a first state of charge (SOC), calculates the current second full charge capacity of the secondary battery, calculates the first remaining battery charge from the first full charge capacity and the first SOC, calculates the second SOC from the second full charge capacity and the first remaining battery charge, and if the second SOC exceeds 100%, sets the second SOC to 100%.

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