Full charge capacity estimation method and full charge capacity estimation device

Abstract

To improve the accuracy of estimating the full charge capacity of a secondary battery.SOLUTION: A full charge capacity estimation method includes, during the execution of full charge capacity estimation processing, acquiring a result of subtracting a lower charging rate SL based on a frequency distribution FD indicating the correspondence relationship between the voltage and frequency of a secondary battery B at the start of charging, from an upper charging rate SU of the secondary battery B at the end of charging, as the charging rate difference ΔSOC between the charging rate of the secondary battery B at the end of charging and the charging rate of the secondary battery B at the start of charging, and estimating a result of multiplying, by 100, a value obtained by dividing an integrated value I of current flowing in the secondary battery B in a period from the start of charging until the end of charging by the charging rate difference ΔSOC, as the full charge capacity of the secondary battery B.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for estimating the full charge capacity of a secondary battery. [Background technology]

[0002] As a method for estimating the full charge capacity of a secondary battery, there is a method for estimating the full charge capacity of a secondary battery by a so-called current integration method, in which the integrated value of the current flowing through the secondary battery from the start of charging to the end of charging is divided by the difference between the charging rate corresponding to the open circuit voltage of the secondary battery at the end of charging and the charging rate corresponding to the open circuit voltage of the secondary battery at the start of charging, and the result is multiplied by 100 to obtain the full charge capacity of the secondary battery. This current integration method estimates the full charge capacity by directly determining the increase in the capacity of the secondary battery or the increase in the charging rate of the secondary battery, and has the advantage of being able to estimate the full charge capacity without considering the deterioration characteristics or temperature characteristics of the secondary battery, since it can estimate the full charge capacity by following the degree of deterioration and temperature changes of the secondary battery. An example of a related technique is Patent Document 1.

[0003] Incidentally, when estimating the charging rate corresponding to the open circuit voltage of a secondary battery at the end of charging or the charging rate corresponding to the open circuit voltage of a secondary battery at the start of charging, the SOC-OCV characteristic, which indicates the correspondence between the charging rate of the secondary battery and the open circuit voltage of the secondary battery, is usually used.

[0004] Therefore, when estimating the full charge capacity of a secondary battery having many change regions in which the change in open circuit voltage per unit charging rate is relatively large, such as a lithium ion battery that uses a ternary metal compound (NMC) as the positive electrode material, using the SOC-OCV characteristics, the charging rate can be estimated without being significantly affected by the error contained in the open circuit voltage, and therefore the full charge capacity can be estimated with high accuracy.

[0005] On the other hand, when estimating the full charge capacity of a secondary battery having many plateau regions in which the change in open circuit voltage per unit charge rate is relatively small, such as a lithium-ion battery that uses lithium iron phosphate (LFP (LiFePO4)) as a positive electrode material, using the SOC-OCV characteristics, the estimation accuracy of the charge rate may be reduced due to the influence of errors contained in the open circuit voltage, and therefore the estimation accuracy of the full charge capacity may be reduced.

[0006] Therefore, other methods for estimating the full charge capacity include estimating the full charge capacity of a secondary battery using a dQ / dV curve that shows the correspondence between the voltage of the secondary battery and the voltage derivative of the remaining capacity of the secondary battery, or the internal resistance of the secondary battery.

[0007] However, since the dQ / dV curve and the internal resistance of a secondary battery fluctuate depending on the degree of deterioration of the secondary battery and changes in temperature of the secondary battery, it is necessary to successively update or correct the dQ / dV curve and internal resistance taking into account the deterioration characteristics and temperature characteristics of the secondary battery.

[0008] Therefore, with the other full charge capacity estimation methods described above, there is a concern that it is necessary to acquire information indicating the deterioration characteristics and temperature characteristics of the secondary battery in advance, and that the accuracy of estimating the full charge capacity may decrease if the degree of deterioration indicated in the pre-acquired deterioration characteristic information differs from the actual degree of deterioration, or if the temperature change indicated in the pre-acquired temperature characteristic information differs from the actual temperature change. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2008-241358 A Summary of the Invention [Problem to be solved by the invention]

[0010] An object according to one aspect of the present invention is to provide a full charge capacity estimation method and a full charge capacity estimation device that are capable of improving the accuracy of estimating the full charge capacity of a secondary battery. [Means for solving the problem]

[0011] A full charge capacity estimation method according to one embodiment of the present invention is a full charge capacity estimation method implemented by a full charge capacity estimation device that estimates the full charge capacity of a secondary battery, wherein when the full charge capacity estimation device performs a full charge capacity estimation process, the full charge capacity estimation device subtracts a lower charging rate based on information indicating the correspondence between the voltage of the secondary battery at the start of charging from the upper charging rate of the secondary battery at the end of charging, obtains the result as the charging rate difference between the charging rate of the secondary battery at the end of charging and the charging rate of the secondary battery at the start of charging, and estimates the full charge capacity of the secondary battery as the result of dividing the integrated value of the current flowing through the secondary battery from the start of charging to the end of charging by the charging rate difference and multiplying the result by 100.

[0012] A full charge capacity estimation method according to one embodiment of the present invention is configured to estimate the full charge capacity of a secondary battery using an increase in the capacity of the secondary battery or an increase in the charging rate of the secondary battery, as in the current integration method, and can estimate the full charge capacity following the degree of deterioration and temperature change of the secondary battery, so that the full charge capacity can be estimated without being affected by deterioration and temperature of the secondary battery, as compared with a case where the full charge capacity is estimated using the dQ / dV characteristic or internal resistance, and the estimation accuracy of the full charge capacity can be improved. Also, since the full charge capacity of the secondary battery can be successively estimated using an integrated value of the current flowing through the secondary battery, as in the current integration method, the full charge capacity of the secondary battery can be estimated while the secondary battery is in use.

[0013] In addition, the lower charging rate may be based on a frequency distribution indicating the correspondence between the voltage of the secondary battery and frequency, and the full charge capacity estimation device may be configured to update the frequency distribution using the voltage of the secondary battery at the start of charging each time the secondary battery is charged.

[0014] This makes it possible to update the frequency distribution in accordance with how the secondary battery is used, so that the full charge capacity can be estimated with high accuracy even if the way the secondary battery is used changes.

[0015] The full-charge capacity estimating device may be configured to correct the estimated full-charge capacity using a one-dimensional Kalman filter.

[0016] This allows the estimated full charge capacity to approach the true value.

[0017] The secondary battery may be a lithium ion battery having a plateau region in which the amount of change in open circuit voltage per unit charge rate is equal to or less than a predetermined value. For example, the unit charge rate is 10% and the predetermined value is 10 mV.

[0018] The secondary battery may be a lithium ion battery using lithium iron phosphate as a positive electrode material.

[0019] In addition, the full charge capacity estimation device may be configured to determine that the full charge capacity estimation condition is satisfied and to perform the full charge capacity estimation process when the voltage of the secondary battery at the start of charging is equal to or lower than a lower judgment threshold voltage and when the voltage of the secondary battery at the end of charging is equal to or higher than an upper judgment threshold voltage, or when it is determined that the secondary battery has reached a fully charged state.

[0020] In addition, the full charge capacity estimation device may be configured to set the charging rate corresponding to the most frequent value as the lower charging rate when a first voltage difference between the most frequent value of the frequency distribution and an over-discharge warning voltage is equal to or less than a first threshold value.

[0021] In addition, the full charge capacity estimation device may be configured to set the charging rate corresponding to the lower judgment threshold voltage as the lower charging rate when a second voltage difference between the most frequent value of the frequency distribution and an intermediate voltage between the minimum voltage and the maximum voltage of the frequency distribution is equal to or less than a second threshold.

[0022] In addition, a full charge capacity estimation device according to one embodiment of the present invention includes an acquisition unit that acquires the result of subtracting a lower charging rate based on a frequency distribution that shows the correspondence between the voltage of the secondary battery at the start of charging and frequency from an upper charging rate of the secondary battery at the end of charging as a charging rate difference between the charging rate of the secondary battery at the end of charging and the charging rate of the secondary battery at the start of charging, and an estimation unit that estimates the full charge capacity of the secondary battery by multiplying the result obtained by dividing the integrated value of the current flowing through the secondary battery from the start of charging to the end of charging by the charging rate difference, and 100.

[0023] A full charge capacity estimation device according to one embodiment of the present invention is configured to estimate the full charge capacity of a secondary battery using an increase in the capacity of the secondary battery or an increase in the charging rate of the secondary battery, as in the current integration method, and can estimate the full charge capacity by tracking the degree of deterioration and temperature changes of the secondary battery, so that the full charge capacity can be estimated without being affected by deterioration or temperature of the secondary battery, as compared to a case where the full charge capacity is estimated using the dQ / dV characteristic or internal resistance, and the estimation accuracy of the full charge capacity can be improved. Also, since the full charge capacity of the secondary battery can be successively estimated using an integrated value of the current flowing through the secondary battery, as in the current integration method, the full charge capacity of the secondary battery can be estimated while the secondary battery is in use. Effect of the Invention

[0024] According to the present invention, it is possible to improve the accuracy of estimating the full charge capacity of a secondary battery. [Brief description of the drawings]

[0025] [Figure 1] 1 is a diagram illustrating an example of a power storage device including a full charge capacity estimation device according to an embodiment; [Diagram 2] FIG. 4 is a diagram showing an example of voltage fluctuation of a secondary battery over time. [Diagram 3] FIG. 11 is a diagram showing the correspondence relationship between the voltage of a secondary battery and frequency. [Figure 4] 5 is a diagram showing an estimated value, a true value, and a corrected value of a full charge capacity. FIG. [Diagram 5]4 is a flowchart showing the operation of the full charge capacity estimating device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, the embodiments will be described in detail with reference to the drawings.

[0027] FIG. 1 is a diagram illustrating an example of a power storage device including a full charge capacity estimation device according to an embodiment.

[0028] The power storage device BP (battery pack) shown in FIG. 1 is mounted on a vehicle Ve, such as a forklift or an electric vehicle, and includes a full charge capacity estimation device (battery ECU (Electronic Control Unit)) 1, a secondary battery B, an ammeter 2, a voltmeter 3, and switches SW1, SW2, and SW3.

[0029] In addition to the power storage device BP, the vehicle Ve is equipped with a motor M for driving the vehicle, an inverter circuit Inv that drives the motor M, and a vehicle ECU 4 that controls the operation of the inverter circuit Inv and communicates with a charger Ch provided outside the vehicle Ve.

[0030] The inverter circuit Inv includes a plurality of switches, and by repeatedly turning on and off each switch, it converts the DC power supplied from the secondary battery B into AC power and supplies it to the motor M. Also, by repeatedly turning on and off each switch, the inverter circuit Inv converts the AC power (regenerative power) supplied from the motor M into DC power and supplies it to the secondary battery B.

[0031] The vehicle ECU 4 changes the duty ratio of a control signal that controls the on / off of each switch of the inverter circuit Inv, thereby changing the power supplied from the secondary battery B to the inverter circuit Inv or the power supplied from the inverter circuit Inv to the secondary battery B.

[0032] The secondary battery B is, for example, composed of one or more lithium ion batteries. For example, a ternary system or lithium iron phosphate is used as the positive electrode material in the lithium ion battery. A lithium ion battery using a ternary system as the positive electrode material has a change region in the entire region of the SOC-OCV characteristics. On the other hand, a lithium ion battery using lithium iron phosphate as the positive electrode material has a hysteresis in the SOC-OCV characteristics between charging and discharging, and has more plateau regions than change regions in the charging side SOC-OCV characteristics and the discharging side SOC-OCV characteristics. The change region is the range of open circuit voltage or the range of charging rate when the change amount of the open circuit voltage per unit charging rate becomes larger than a predetermined value. The plateau region is the range of open circuit voltage or the range of charging rate when the change amount of the open circuit voltage per unit charging rate becomes equal to or smaller than a predetermined value. For example, the unit charging rate is 10[%], and the predetermined value is 10[mV]. The positive terminal of the secondary battery B is connected to the positive input terminal of the inverter circuit Inv and the positive output terminal of the charger Ch. The negative terminal of the secondary battery B is connected to the negative input terminal of the inverter circuit Inv via the ammeter 2, the switch SW1, and the switch SW3. The negative terminal of the secondary battery B is also connected to the negative output terminal of the charger Ch via the ammeter 2, the switch SW1, and the switch SW2.

[0033] The ammeter 2 is configured with a shunt resistor or the like, detects the current flowing through the secondary battery B, and sends the detected current to the full charge capacity estimation device 1.

[0034] The voltmeter 3 is configured with a voltage dividing resistor and the like, detects the voltage of the secondary battery B, and sends the detected voltage to the full charge capacity estimation device 1.

[0035] Each of the switches SW1, SW2, and SW3 is configured by a semiconductor relay (for example, a Metal Oxide Semiconductor Field Effect Transistor (MOSFET)), an electromagnetic relay, or the like.

[0036] When switches SW1 and SW3 are conductive and switch SW2 is cut off, a state is established in which power can be supplied from the secondary battery B to the inverter circuit Inv, and power can also be supplied from the inverter circuit Inv to the secondary battery B. When power is supplied from the secondary battery B to the inverter circuit Inv, the secondary battery B is discharged and the capacity, charging rate, or voltage of the secondary battery B decreases, and when power is supplied to the secondary battery B from the inverter circuit Inv or the charger Ch, the secondary battery B is charged and the capacity, charging rate, or voltage of the secondary battery B increases.

[0037] Furthermore, when switches SW1 and SW2 are conductive and switch SW3 is cut off, a state is achieved in which power can be supplied from charger Ch to secondary battery B. When secondary battery B is charged by the AC charging method, in vehicle Ve, AC power supplied from charger Ch is converted to DC power, and the DC power is supplied to secondary battery B, thereby charging secondary battery B.

[0038] The full charge capacity estimation device 1 includes a memory 11 and a processor 12 .

[0039] The memory 11 is configured with a RAM (Random Access Memory) or a ROM (Read Only Memory), etc. The memory 11 stores an upper determination threshold voltage and a lower determination threshold voltage, which will be described later. The information stored in the memory 11 can be obtained by testing, simulation, etc. The memory 11 may be provided in the processor 12.

[0040] The processor 12 includes a charge / discharge control unit 121, a determination unit 122, an acquisition unit 123, an estimation unit 124, and a correction unit 125. When the processor 12 executes a program stored in the memory 11, the charge / discharge control unit 121, the determination unit 122, the acquisition unit 123, the estimation unit 124, and the correction unit 125 are realized.

[0041] When the charge / discharge control unit 121 receives a notification from the vehicle ECU 4 that the ignition switch of the vehicle Ve is turned on, it turns on switches SW1 and SW3 and turns off switch SW2, thereby enabling power to be supplied from the secondary battery B to the inverter circuit Inv and enabling power to be supplied from the inverter circuit Inv to the secondary battery B, and when it receives a notification that the ignition switch is turned off, it turns off switches SW1 to SW3.

[0042] Furthermore, when the charge / discharge control unit 121 receives a charge start instruction from the vehicle ECU 4 or the like, it turns on the switches SW1 and SW2 and turns off the switch SW3, and then starts the charge control process for the secondary battery B. When it determines that the secondary battery B has reached a fully charged state, it ends the charge control process for the secondary battery B and turns off the switches SW1 to SW3. For example, when the charge / discharge control unit 121 receives a charge start instruction, it executes a constant-current constant-voltage charge control process. That is, when it starts the constant-current constant-voltage charge control process, the charge / discharge control unit 121 keeps the current flowing through the secondary battery B constant until the voltage of the secondary battery B reaches a predetermined voltage Vc, and when the voltage of the secondary battery B reaches the predetermined voltage Vc, it gradually reduces the current flowing through the secondary battery B until the current flowing through the secondary battery B becomes equal to or less than the end current If, and when the current flowing through the secondary battery B becomes equal to or less than the end current If, it determines that the secondary battery B has reached a fully charged state, reduces the current flowing through the secondary battery B to zero, and ends the constant-current constant-voltage charge control process.

[0043] When the determination unit 122 receives a charging start instruction, the determination unit 122 determines whether or not the full charge capacity estimation condition is satisfied. For example, the determination unit 122 determines that the full charge capacity estimation condition is satisfied when the voltage of the secondary battery B at the start of charging is equal to or lower than the lower determination threshold voltage and the voltage of the secondary battery B at the end of charging is equal to or higher than the upper determination threshold voltage, or when it is determined that the secondary battery B is in a fully charged state.

[0044] FIG. 2 is a diagram showing an example of the change in the voltage of the secondary battery B over time. The horizontal axis of the two-dimensional coordinate system shown in FIG. 2 indicates time, and the vertical axis indicates voltage. The solid line shown in FIG. 2 indicates the change in the voltage (closed circuit voltage) of the secondary battery B over time. The charging control process is started at times t1, t3, and t5, respectively, and ends at times t2, t4, and t6, respectively. The lower limit voltage<over-discharge warning voltage<lower side judgment threshold voltage<upper side judgment threshold voltage. The lower limit voltage is a voltage that is preset to protect the secondary battery B so that the voltage of the secondary battery B does not fall below the lower limit voltage. The over-discharge warning voltage is a voltage that is preset to warn the user when the secondary battery B is likely to be in an over-discharge state. The lower side judgment threshold voltage is a voltage that is preset in consideration of the trade-off between the frequency at which the full charge capacity estimation condition is satisfied and the full charge capacity estimation error. The upper determination threshold voltage is a voltage that is set in advance based on the closed circuit voltage of the secondary battery B in a fully charged state, and is, for example, a predetermined voltage Vc in the constant current constant voltage charging control process.

[0045] The judgment unit 122 judges that the full charge capacity estimation condition is satisfied during the charging control processing period from time t1 to time t2 because the voltage of secondary battery B at the start of charging at time t1 is below the lower judgment threshold voltage and the voltage of secondary battery B at the end of charging at time t2 is above the upper judgment threshold voltage.

[0046] Furthermore, the determination unit 122 determines that the full charge capacity estimation condition was not satisfied during the charge control processing period from time t3 to time t4 because the voltage of secondary battery B at the start of charging at time t3 was higher than the lower determination threshold voltage.

[0047] In addition, the judgment unit 122 determines that the full charge capacity estimation condition is satisfied during the charging control processing period from time t5 to time t6, because the voltage of secondary battery B at the start of charging at time t5 is below the lower judgment threshold voltage and the voltage of secondary battery B at the end of charging at time t6 is above the upper judgment threshold voltage.

[0048] When the charging control process starts, the acquisition unit 123 stores in the memory 11 the voltage of the secondary battery B at the start of charging.

[0049] Furthermore, the acquisition unit 123 obtains an integrated value [Ah] of the current flowing through the secondary battery B at each predetermined cycle during the charge control processing period.

[0050] Furthermore, when the charge control process ends, the acquisition unit 123 stores in the memory 11 the voltage of the secondary battery B at the end of charging and the integrated value I of the current last calculated during the charge control process.

[0051] Furthermore, when the determination unit 122 determines that the full charge capacity estimation condition is satisfied, the acquisition unit 123 acquires the result of subtracting the lower side charging rate SL based on the frequency distribution FD (information) indicating the correspondence relationship between the voltage of the secondary battery B at the start of charging and the frequency (the ratio of the number of times the voltage of the secondary battery B is currently acquired to the total number of times the voltage of the secondary battery B is acquired at the start of charging) from the upper side charging rate SU of the secondary battery B at the end of charging as the charging rate difference ΔSOC between the charging rate of the secondary battery B at the end of charging and the charging rate of the secondary battery B at the start of charging. Note that the charging rate is the ratio [%] of the remaining capacity to the full charge capacity of the secondary battery B. The upper side charging rate SU is a fixed value, for example, 100 [%].

[0052] 3(a) and 3(b) are diagrams showing an example of a frequency distribution FD indicating the correspondence relationship between the voltage of secondary battery B at the start of charging and frequency. Note that the horizontal axis of the two-dimensional coordinate system shown in Fig. 3(a) and Fig. 3(b) indicates voltage, and the vertical axis indicates frequency.

[0053] The frequency distribution FD1 shown in Fig. 3(a) shows the frequency distribution FD when the secondary battery B (vehicle Ve) is used in such a manner that a first voltage difference between the mode (the voltage corresponding to the highest frequency) and the over-discharge warning voltage is equal to or less than a first threshold, that is, in such a manner that the secondary battery B is often discharged until it is just before it reaches an over-discharged state. When the secondary battery B is used as in the frequency distribution FD1 shown in Fig. 3(a), it is assumed that the charging rate of the secondary battery B corresponding to the mode is stored in advance in the memory 11 as a lower charging rate SL.

[0054] 3(b) shows a frequency distribution FD when the secondary battery B (vehicle Ve) is used in such a manner that a second voltage difference between the mode and the intermediate voltage between the minimum and maximum voltages of the secondary battery B at the start of charging is equal to or less than a second threshold, that is, the secondary battery B in a fully charged state is often used until the remaining capacity is about half. When the secondary battery B is used as in the frequency distribution FD2 shown in FIG. 3(b), it is assumed that the charging rate of the secondary battery B corresponding to the lower determination threshold voltage is stored in the memory 11 as a lower charging rate SL.

[0055] When the judgment unit 122 judges that the full charge capacity estimation condition is satisfied and when the secondary battery B is used in such a manner that the frequency distribution FD becomes the frequency distribution FD1 shown in Figure 3(a), i.e., when the first voltage difference between the mode and the over-discharge warning voltage is equal to or less than the first threshold, the acquisition unit 123 acquires the lower charging rate SL corresponding to the mode from the memory 11.

[0056] In addition, when the judgment unit 122 judges that the full charge capacity estimation condition is satisfied and the secondary battery B is used in such a manner that the frequency distribution FD becomes the frequency distribution FD2 shown in Figure 3(b), that is, when the second voltage difference between the mode and the intermediate voltage is equal to or less than the second threshold, the acquisition unit 123 acquires from the memory 11 the lower charging rate SL corresponding to the lower judgment threshold voltage.

[0057] That is, one of the lower charging rate SL corresponding to frequency distribution FD1 and the lower charging rate SL corresponding to frequency distribution FD2 is pre-stored in memory 11 depending on how secondary battery B is used, and when it is determined that the full charge capacity estimation condition is satisfied, the acquisition unit 123 acquires the lower charging rate SL stored in memory 11.

[0058] In addition, the lower charging rate SL corresponding to the frequency distribution FD1 and the lower charging rate SL corresponding to the frequency distribution FD2 may be stored in advance in the memory 11, and the acquisition unit 123 may be configured to acquire one of the two lower charging rates SL stored in the memory 11 depending on how the secondary battery B is used when it is determined that the full charge capacity estimation condition is satisfied.

[0059] When the judgment unit 122 judges that the full charge capacity estimation condition is satisfied, the estimation unit 124 subtracts the lower charging rate SL from the upper charging rate SU to obtain the charging rate difference ΔSOC, and estimates the full charge capacity of the secondary battery B by multiplying the result obtained by dividing the integrated value I stored in the memory 11 by the charging rate difference ΔSOC by 100.

[0060] The correction unit 125 corrects the full charge capacity estimated by the estimation unit 124 by filtering it with a predetermined filter. The predetermined filter may be, for example, a one-dimensional Kalman filter or a weighted average filter, but is not limited to this. The filter constant may be set to a value that prioritizes accuracy or a value that prioritizes tracking, depending on how the secondary battery B is used.

[0061] Here, Fig. 4 is a diagram showing the estimated full charge capacity, the true value of the full charge capacity, and the corrected full charge capacity. The horizontal axis of the two-dimensional coordinate system shown in Fig. 4 indicates time, and the vertical axis indicates the full charge capacity. Also, a circle shown in Fig. 4 indicates the estimated full charge capacity, a triangle shown in Fig. 4 indicates the true value of the full charge capacity, and a square shown in Fig. 4 indicates the corrected full charge capacity.

[0062] The estimated full charge capacity in the first charging control process is larger than the true value, the estimated full charge capacity in the second charging control process is smaller than the true value, and the corrected full charge capacity in the second charging control process is closer to the true value than the estimated full charge capacity in the second charging control process.

[0063] In addition, the estimated full charge capacity in the third charging control process is smaller than the true value, and the corrected full charge capacity in the third charging control process is closer to the true value than the estimated full charge capacity in the third charging control process. In addition, the corrected full charge capacity in the third charging control process is closer to the true value than the corrected full charge capacity in the second charging control process.

[0064] In addition, in the fourth charging control process, the full charge capacity estimation condition is not satisfied and the full charge capacity is not estimated by the estimation unit 124, so the corrected full charge capacity in the fourth charging control process is the same as the corrected full charge capacity in the third charging control process.

[0065] In addition, the estimated full charge capacity in the fifth charging control process is larger than the true value, and the corrected full charge capacity in the fifth charging control process is closer to the true value than the estimated full charge capacity in the fifth charging control process. In addition, the corrected full charge capacity in the fifth charging control process is closer to the true value than the corrected full charge capacity in the fourth charging control process.

[0066] In this way, the full charge capacity after correction can be made closer to the true value by correcting the full charge capacity by the correction unit 125. Also, as the number of times the full charge capacity is estimated increases, the corrected full charge capacity can be made closer to the true value.

[0067] FIG. 5 is a flowchart showing the operation of the full charge capacity estimation device 1.

[0068] First, when the charging control process starts (step S1: Yes), the acquisition unit 123 of the full charge capacity estimation device 1 stores the voltage of the secondary battery B at the start of charging in the memory 11 (step S2).

[0069] Next, the acquisition unit 123 obtains an integrated value of the current detected by the ammeter 2 at predetermined intervals (step S3) until the charging control process is completed (step S4: No).

[0070] Next, when the charge control process ends (step S4: Yes), the acquisition unit 123 stores in the memory 11 the voltage of the secondary battery B at the end of charging and the integrated value I last calculated during the charge control process (step S5).

[0071] Next, the determination unit 122 of the full charge capacity estimation device 1 determines whether or not the full charge capacity estimation condition is satisfied (step S6).

[0072] Next, when the determination unit 122 determines that the full charge capacity estimation condition is satisfied (step S6: Yes), the acquisition unit 123 starts a full charge capacity estimation process, acquires the upper side charging rate SU and the lower side charging rate SL from the memory 11 (step S7), and calculates the charging rate difference ΔSOC (step S8). When the upper side charging rate SU and the lower side charging rate SL are fixed values, the charging rate difference ΔSOC may be stored in advance in the memory 11. In this case, when the determination unit 122 determines that the full charge capacity estimation condition is satisfied, the acquisition unit 123 acquires the charging rate difference ΔSOC from the memory 11.

[0073] Next, the estimation unit 124 of the full charge capacity estimation device 1 estimates the full charge capacity of the secondary battery B by dividing the integrated value I obtained from the memory 11 by the charging rate difference ΔSOC, multiplying the result by 100 (step S9).

[0074] Then, the correction unit 125 of the full charge capacity estimation device 1 corrects the full charge capacity estimated by the estimation unit 124, and ends the full charge capacity estimation process (step S10).

[0075] 5 (determination unit 122 shown in FIG. 1) and step S10 (correction unit 125 shown in FIG. 1) may be omitted. When step S6 (determination unit 122) is omitted, the process of storing in memory 11 the voltage of secondary battery B at the start of charging and the voltage of secondary battery B at the end of charging can be omitted.

[0076] That is, in the full charge capacity estimation device 1 of the embodiment, the lower charging rate SL based on the frequency distribution FD is subtracted from the upper charging rate SU of the secondary battery B at the end of charging to obtain the result as the charging rate difference ΔSOC between the charging rate of the secondary battery B at the end of charging and the charging rate of the secondary battery B at the start of charging, and the full charge capacity of the secondary battery B is estimated by dividing the integrated value I of the current flowing through the secondary battery B from the start of charging to the end of charging by the charging rate difference ΔSOC and multiplying the result by 100.

[0077] In this way, the full charge capacity estimation device 1 of the embodiment is configured to estimate the full charge capacity of secondary battery B using the increase in capacity of secondary battery B and the increase in the charging rate of secondary battery B, as in the current integration method, and can estimate the full charge capacity in accordance with the degree of deterioration and temperature changes of secondary battery B. Therefore, compared to estimating the full charge capacity using the dQ / dV characteristics or internal resistance, it is possible to estimate the full charge capacity without being affected by the deterioration or temperature of secondary battery B, and the estimation accuracy of the full charge capacity can be improved.

[0078] In addition, according to the full charge capacity estimation device 1 of the embodiment, the full charge capacity of the secondary battery B can be successively estimated using the integrated value I of the current flowing through the secondary battery B, as in the current accumulation method, so that the full charge capacity of the secondary battery B can be estimated while the secondary battery B is in use.

[0079] Furthermore, since the full charge capacity estimation device 1 of the embodiment is configured to estimate the full charge capacity using the charging rate difference ΔSOC based on the frequency distribution FD, it is possible to estimate the full charge capacity without being affected by errors contained in the open circuit voltage of the secondary battery B, compared to the case where the full charge capacity is estimated using the charging rate difference based on the SOC-OCV characteristics. Therefore, it is possible to accurately estimate the full charge capacity even for a secondary battery B that has a plateau region.

[0080] In addition, according to the full charge capacity estimation device 1 of the embodiment, in an environment where the secondary battery B is repeatedly discharged and charged, there is no need to provide special operational control for estimating the full charge capacity, thereby suppressing increases in manufacturing costs.

[0081] Furthermore, the full charge capacity estimation method implemented by the full charge capacity estimation device 1 of the embodiment does not require acquisition of the open circuit voltage of the secondary battery B, and therefore there is no restriction of waiting for the polarization elimination time after discharging the secondary battery B.

[0082] The present invention is not limited to the above-described embodiment, and various improvements and modifications are possible without departing from the gist of the present invention.

[0083] <Variation 1> In the above embodiment, the lower charging rate SL is stored in advance in the memory 11 and acquired from the memory 11 during the full charge capacity estimation process, but the frequency distribution FD shown in Fig. 3(a) or 3(b) may be stored in the memory 11, the frequency distribution FD may be updated based on the voltage of the secondary battery B acquired at the start of charging each time the charge control process is performed, and the lower charging rate SL may be acquired using the updated frequency distribution FD. This allows the frequency distribution FD to be updated according to how the secondary battery B is used, so that the full charge capacity can be accurately estimated even if the way the secondary battery B is used changes.

[0084] Note that SOC-CCV characteristic information indicating the correspondence relationship between the charging rate of secondary battery B and the closed circuit voltage of secondary battery B may also be stored in advance in the memory 11. In this case, the acquisition unit 123 acquires, as the lower charging rate SL, the charging rate corresponding to the voltage obtained from the frequency distribution FD (the mode in the case of the frequency distribution FD1 shown in FIG. 3(a) and the lower determination threshold voltage in the case of the frequency distribution FD2 shown in FIG. 3(b)) using the SOC-CCV characteristic information.

[0085] Also, SOC-OCV characteristic information indicating the correspondence relationship between the charging rate of secondary battery B and the open circuit voltage of secondary battery B may be stored in advance in memory 11. In this case, the acquisition unit 123 converts the voltage obtained by the frequency distribution FD based on the internal resistance of secondary battery B and the current flowing through secondary battery B into the open circuit voltage of secondary battery B, and acquires the charging rate corresponding to the converted open circuit voltage as the lower charging rate SL using the SOC-OCV characteristic information.

[0086] <Variation 2> In the above embodiment, the upper charging rate SU is set to, for example, 100%. However, the upper charging rate SU may be set to, for example, 99% or 98%, taking into account the decrease in the full charge capacity of the secondary battery B due to the increase in temperature of the secondary battery B.

[0087] <Variation 3> The upper determination threshold voltage may be an open circuit voltage equal to or higher than the upper open circuit voltage when the charging side SOC-OCV characteristic of secondary battery B using lithium iron phosphate as the positive electrode material transitions from the plateau region to the change region.

[0088] In addition, the lower judgment threshold voltage may be an open circuit voltage lower than the lower open circuit voltage when the charging side SOC-OCV characteristic of secondary battery B using lithium iron phosphate as the positive electrode material transitions from the plateau region to the change region.

[0089] <Modification 4> The judgment unit 122 may be configured to turn on flag FL if the voltage of secondary battery B at the start of charging is equal to or lower than the lower judgment threshold voltage, and to turn on flag FU if the voltage of secondary battery B at the end of charging is equal to or higher than the upper judgment threshold voltage or if it is determined that secondary battery B has reached a fully charged state, and to judge that the full charge capacity estimation condition is satisfied when both flags FL and FU are on.

[0090] <Variation 5> When determining the lower charging rate SL, if the most frequent in the frequency distribution FD is lower than the lower judgment threshold voltage, the charging rate corresponding to the most frequent may be set as the lower charging rate SL, and if the most frequent in the frequency distribution FD is higher than the lower judgment threshold voltage, the charging rate corresponding to the lower judgment threshold voltage may be set as the lower charging rate SL. [Explanation of symbols]

[0091] 1 Full charge capacity estimation device 2 Ammeter 3. Voltmeter 4. Vehicle ECU 11. Memory 12 processors 121 Charge / discharge control unit 122 Judgment Department 123 Acquisition Department 124 Estimation Department 125 Correction section Vehicle BP power storage device Inv Inverter circuit Medium motor Ch charger SW1, SW2, SW3 switches

Claims

1. A full charge capacity estimation method implemented by a full charge capacity estimation device that estimates a full charge capacity of a secondary battery, comprising: When performing a full charge capacity estimation process, the full charge capacity estimation device subtracts a lower charging rate based on information indicating the correspondence between the voltage of the secondary battery at the start of charging from an upper charging rate of the secondary battery at the end of charging, obtains the result as a charging rate difference between the charging rate of the secondary battery at the end of charging and the charging rate of the secondary battery at the start of charging, and estimates the full charge capacity of the secondary battery as the result of dividing an integrated value of a current flowing through the secondary battery from the start of charging to the end of charging by the charging rate difference and multiplying the result by 100. Full charge capacity estimation method.

2. 2. The method for estimating a full charge capacity according to claim 1, The lower charging rate is based on a frequency distribution indicating a correspondence relationship between a voltage of the secondary battery and a frequency, The full-charge capacity estimation device updates the frequency distribution based on the voltage of the secondary battery at the start of charging each time the secondary battery is charged. Full charge capacity estimation method.

3. 2. The method for estimating a full charge capacity according to claim 1, The full charge capacity estimation device corrects the estimated full charge capacity using a one-dimensional Kalman filter. Full charge capacity estimation method.

4. 2. The method for estimating a full charge capacity according to claim 1, The secondary battery is a lithium ion battery having a plateau region in which the amount of change in open circuit voltage per unit charge rate is equal to or less than a predetermined value. Full charge capacity estimation method.

5. The method for estimating a full charge capacity according to claim 4, The unit charging rate is 10%. The predetermined value is 10 mV. Full charge capacity estimation method.

6. 2. The method for estimating a full charge capacity according to claim 1, The secondary battery is a lithium-ion battery that uses lithium iron phosphate as a positive electrode material. Full charge capacity estimation method.

7. 2. The method for estimating a full charge capacity according to claim 1, The full charge capacity estimation device determines that a full charge capacity estimation condition is satisfied and performs the full charge capacity estimation process when the voltage of the secondary battery at the start of charging is equal to or lower than a lower determination threshold voltage and when the voltage of the secondary battery at the end of charging is equal to or higher than an upper determination threshold voltage, or when it is determined that the secondary battery is in a fully charged state. Full charge capacity estimation method.

8. 2. The method for estimating a full charge capacity according to claim 1, When a first voltage difference between a mode of the frequency distribution and an over-discharge warning voltage is equal to or smaller than a first threshold, the full charge capacity estimation device determines a charging rate corresponding to the mode as the lower charging rate. Full charge capacity estimation method.

9. A method for estimating a full charge capacity according to claim 7, When a second voltage difference between a mode value of the frequency distribution and an intermediate voltage between a minimum voltage and a maximum voltage of the frequency distribution is equal to or smaller than a second threshold, the full charge capacity estimation device determines a charging rate corresponding to the lower determination threshold voltage as the lower charging rate. Full charge capacity estimation method.

10. an acquisition unit that acquires a result obtained by subtracting a lower side charging rate based on a frequency distribution that indicates a correspondence relationship between the voltage of the secondary battery and frequency at the start of charging from an upper side charging rate of the secondary battery at the end of charging as a charging rate difference between the charging rate of the secondary battery at the end of charging and the charging rate of the secondary battery at the start of charging; an estimation unit that estimates a full charge capacity of the secondary battery by dividing an integrated value of a current flowing through the secondary battery from a charging start time to a charging end time by the charging rate difference and multiplying the result by 100; A full charge capacity estimation device comprising:

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