Electrical storage system

Abstract

Electrical storage system, including: an electrical storage device (10) configured to be charged by external charging, wherein the external charging is used to perform charging with electrical power from an external power supply (29); a voltage sensor (21) configured to detect a voltage value of the electrical storage device (10); a current sensor (22) configured to detect a current value of the electrical storage device (10); and a controller (30) that is configured to (a) to calculate a full charge capacity of the electrical storage device (10) based on a state of charge of the electrical storage device (10) at the time when external charging is started, a state of charge of the electrical storage device (10) at the time when external charging is finished, and an accumulated value of the current value during the period when external charging is performed, (b) to set a polarization elimination time, wherein the polarization elimination time is used to determine an eliminated state of a polarization that occurs as a result of charging or discharging the electrical storage device (10), (c) to consider a voltage value of the electrical storage device (10) at the time of at least one of the start of external charging or the termination of external charging as an open-circuit voltage of the electrical storage device (10), wherein the voltage value is detected by the voltage sensor (21) if a stopped time during the period when charging or discharging of the electrical storage device (10) is stopped is longer than the polarization elimination time, (d) to calculate the state of charge according to the voltage value detected by the voltage sensor (21) as the state of charge used to calculate the full charge capacity, using a correlation between an open-circuit voltage and the state of charge, and (e) to shorten the polarization elimination time when a rate of change increases, where the rate of change is a ratio of a fluctuation in the open-circuit voltage to a fluctuation in the state of charge.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The invention relates to an electrical storage system that calculates a full charge capacity of an electrical storage device. 2. Description of the state of the art

[0002] In Japanese Patent Application Laid-Open No. 2013-101072 (JPJP 2013-101072 A), when a battery pack is charged with electric power from an external power supply (referred to as external charging), a full charge capacity of the battery pack is calculated. The full charge capacity of the battery pack is calculated based on a state of charge (SOC) of the battery pack at the start of external charging, an SOC of the battery pack at the completion of external charging, and an accumulated current value during the period when external charging is performed. Because there is a predetermined correlation between an SOC and an open circuit voltage (OCV), the SOC of the battery pack is calculated from the OCV of the battery pack.

[0003] JP 2013-214371 A discloses a battery system comprising a battery unit (1) that performs charging and discharging, voltage sensors (201, 201a) for detecting the voltage of the battery unit, and controllers (300, 310) for estimating the state of the battery unit. The controller calculates the concentration distribution in the active material of the battery unit using a diffusion equation and calculates the polarization elimination time until the concentration distribution falls within an allowable range, assuming that no charging / discharging of the battery unit is performed. If the time during which no charging / discharging of the battery unit is performed is equal to or longer than the polarization elimination time, the controller detects the open-circuit voltage of the battery unit using the voltage sensor (see the abstract of document D1).

[0004] The document JP 2005-83 970 A discloses a secondary battery monitoring method for detecting the condition of the secondary battery carried in a vehicle by correctly estimating the degree of polarization. SUMMARY OF THE INVENTION

[0005] When polarization occurs as a result of charging or discharging the battery pack, a voltage value of the battery pack detected by a voltage sensor (referred to as the detected voltage value) includes a voltage fluctuation resulting from the polarization. Therefore, the detected voltage value deviates from the OCV by the amount of the voltage fluctuation resulting from the polarization. If charging or discharging of the battery pack remains stopped, it is possible to eliminate the polarization. Thus, after the polarization is eliminated, the detected voltage value can be considered the OCV.

[0006] By obtaining a time during the period when charging or discharging of the battery pack is stopped, it is possible to determine whether polarization has been eliminated. Specifically, the time during the period when polarization is eliminated (referred to as the polarization elimination time) is set in advance as a fixed value. If the time during the period when charging or discharging of the battery pack is stopped is longer than the polarization elimination time, it is determined that polarization has been eliminated. Polarization changes in response to the course of charging or discharging of the battery pack. Therefore, if the polarization elimination time (a fixed value) is set considering a possible maximum polarization, it is possible to determine that polarization has been eliminated regardless of the polarization state.

[0007] However, if the polarization elimination time (fixed value) is set with the greatest polarization in mind, the polarization elimination time (fixed value) tends to be long. Accordingly, the time required to determine that polarization has been eliminated also tends to be long, resulting in difficulty in obtaining the OCV of the battery pack. Specifically, if charging or discharging of the battery pack is started before the polarization elimination time (fixed value) has elapsed, the OCV of the battery pack cannot be obtained. As a result, it is not possible to calculate the SOC of the battery pack from the OCV of the battery pack, so it is not possible to calculate the full charge capacity of the battery pack from the SOC of the battery pack.

[0008] One aspect of the invention provides an electrical storage system. The electrical storage system includes an electrical storage device, a voltage sensor, a current sensor, and a controller. The electrical storage system is configured to be charged by external charging. External charging is for performing charging with electrical power from an external power supply. The voltage sensor is configured to detect a voltage value of the electrical storage device. The current sensor is configured to detect a current value of the electrical storage device. The controller is configured to calculate (estimate) a full charge capacity of the electrical storage device.

[0009] The controller is configured to calculate the full charge capacity of the electric storage device based on a charge state of the electric storage device at the time when external charging is started, a charge state of the electric storage device at the time when external charging is completed, and an accumulated value of the current value during the period when external charging is performed. The controller is configured to consider the voltage value of the electric storage device when a stopped time during the period when charging or discharging of the electric storage device is stopped is longer than a polarization elimination time. The voltage value is detected by the voltage sensor as an open-circuit voltage.The controller is configured to calculate the state of charge according to the voltage value detected by the voltage sensor as the state of charge used to calculate the full charge capacity, using a correlation between the open-circuit voltage and the state of charge. The controller is configured to set a polarization elimination time. The polarization elimination time is used to determine an eliminated state of polarization that occurs as a result of charging or discharging the electrical storage device.

[0010] When a ratio of the fluctuation in the open-circuit voltage to a fluctuation in the state of charge is defined as a rate of change, the polarization elimination time depends on the rate of change. The controller is configured to shorten the polarization elimination time as the rate of change increases when calculating the state of charge from the voltage value detected by the voltage sensor at the time of at least one of the start of external charging and the termination of external charging. Specifically, the rate of change is a value obtained by dividing the fluctuation in the open-circuit voltage by the fluctuation in the state of charge.

[0011] When calculating (estimating) the full charge capacity of an electric storage device, it is necessary to ensure the estimation accuracy of the state of charge at the start and end of external charging to ensure the estimation accuracy of the full charge capacity. If the state of charge calculated (estimated) from the voltage value is within the range of an allowable estimation error, it is possible to ensure the estimation accuracy of the state of charge.

[0012] Because there is a predetermined correlation between the state of charge and the open-circuit voltage, when the range of the state of charge estimation error is identified, it is possible to identify the allowable range of the open-circuit voltage corresponding to the range of the estimation error. With the progress of polarization elimination, the voltage value of the electric storage device approaches the open-circuit voltage and is within the above-described allowable range of the open-circuit voltage. When the voltage value of the electric storage device is within the allowable range of the open-circuit voltage, it is possible to ensure the estimation accuracy of the state of charge by calculating the state of charge based on the voltage value.That is, when the voltage value of the electric storage device is within the allowable range of the open-circuit voltage, it is possible to ensure the estimation accuracy of the state of charge even if the state of charge is calculated in a situation that a voltage value deviating from the open-circuit voltage is regarded as the open-circuit voltage.

[0013] In this way, the voltage value of the electric storage device only needs to be within the allowable range of the open-circuit voltage, and polarization does not need to be eliminated to such an extent that the voltage value of the electric storage device reaches the open-circuit voltage. In other words, as long as the voltage value of the electric storage device is within the allowable range of the open-circuit voltage, polarization can remain to ensure the estimation accuracy of the state of charge. When eliminating polarization by stopping charging or discharging of the electric storage device, a time from a time when charging or discharging is stopped to a time when polarization still remains is shorter than a time from the time when charging or discharging is stopped to the time when polarization is eliminated.

[0014] In the invention, the polarization elimination time is set by focusing on the above-described point. The polarization elimination time according to the invention is a time required until the voltage value of the electric storage device falls within the allowable range of the open-circuit voltage, and is a time from a time when charging or discharging is stopped to a time when polarization still remains. In the invention, using the polarization elimination time, the above-described state in which polarization still remains (polarization eliminated state) is determined.

[0015] As the above-described rate of change increases, the allowable range of the open-circuit voltage can be easily expanded with respect to the range of the state of charge estimation error. As the allowable range of the open-circuit voltage expands, the time required for the voltage value of the electric storage device to fall within the allowable range of the open-circuit voltage is shortened when eliminating polarization by stopping charging or discharging the electric storage device. In the invention, as the rate of change increases, the polarization elimination time is shortened.

[0016] In the invention, when the stopped time is longer than the polarization elimination time, the state of charge of the electric storage device is calculated in a situation where the voltage value detected by the voltage sensor is regarded as the open-circuit voltage of the electric storage device. As the rate of change increases, it is possible to increase the opportunity to calculate the state of charge from the voltage value by shortening the polarization elimination time. Accordingly, it is possible to increase the opportunity to calculate the full-charge capacity of the electric storage device using the state of charge calculated from the voltage value.

[0017] In the above aspect, the controller may be configured to, when charging or discharging of the electric storage device is stopped, calculate a fluctuation in the state of charge and a fluctuation in the open-circuit voltage based on the state of charge and the open-circuit voltage in a period until charging or discharging is stopped. Additionally, the controller may be configured to calculate the change rate and calculate the polarization elimination time according to the calculated change rate using a correlation between the change rate and the polarization elimination time. When the fluctuation in the state of charge and the fluctuation in the open-circuit voltage are calculated, it is possible to calculate the change rate.If the behavior (change) of the state of charge in a period until charging or discharging of the electrical storage device is stopped, that is, the behavior (change) of the state of charge while charging or discharging of the electrical storage device is in progress, is obtained, it is possible to calculate the fluctuation in the state of charge. Similarly, if the behavior (change) of the open-circuit voltage in a period until charging or discharging of the electrical storage device is stopped, that is, the behavior (change) of the open-circuit voltage while charging or discharging of the electrical storage device is in progress, is obtained, it is possible to calculate the fluctuation in the open-circuit voltage.

[0018] By using the correlation between the change rate and the polarization elimination time, it is possible to calculate the polarization elimination time according to the calculated change rate. The thus calculated polarization elimination time is compared with the stopped time. If the stopped time is longer than the polarization elimination time, it is possible to calculate the state of charge of the electrical storage device in a situation where the voltage value detected by the voltage sensor is considered the open-circuit voltage of the electrical storage device, as described above.

[0019] As described above, there is a correlation between the change rate and the polarization elimination time. The change rate is the ratio of the fluctuation in the open-circuit voltage to the fluctuation in the state of charge, so there is also a correlation between the change rate and the state of charge. In the above aspect, the controller may be configured to calculate the state of charge at the time when charging or discharging of the electrical storage device is stopped. The controller may be configured to calculate the polarization elimination time corresponding to the calculated state of charge using a correlation between the change rate and the polarization elimination time and a correlation between the change rate and the state of charge.By calculating the state of charge at the time when charging or discharging of the electrical storage device is stopped, it is possible to identify the change rate corresponding to the calculated state of charge using the correlation between the change rate and the state of charge. It is possible to identify the polarization elimination time corresponding to the change rate using the correlation between the change rate and the polarization elimination time. Thus, by calculating the state of charge at the time when charging or discharging of the electrical storage device is stopped, it is possible to calculate the polarization elimination time corresponding to the state of charge.

[0020] In the above aspect, the controller may be configured to, while charging or discharging of the electric storage device is stopped, calculate the polarization elimination time corresponding to the voltage value detected by the voltage sensor using a correlation between the change rate and the polarization elimination time and a correlation between the change rate and the voltage value. The change rate is the ratio of the fluctuation in the open-circuit voltage to the fluctuation in the state of charge, so there is also a correlation between the change rate and the state of charge. If the voltage value at the time when charging or discharging of the electric storage device is stopped is regarded as the open-circuit voltage, it is possible to identify the change rate corresponding to the open-circuit voltage using the correlation between the change rate and the open-circuit voltage.It is possible to identify the polarization elimination time according to the rate of change by using the correlation between the rate of change and the polarization elimination time. Thus, by detecting the voltage value at the time when charging or discharging of the electrical storage device is stopped, it is possible to calculate the polarization elimination time according to the voltage value.

[0021] In the above aspect, the controller may be configured to repeat detection of the voltage value by the voltage sensor while charging or discharging of the electrical storage device is stopped. The controller may be configured to calculate the polarization elimination time corresponding to the detected voltage value each time the voltage value is detected. While charging or discharging of the electrical storage device is stopped, it is possible to repeat detection of the voltage value of the electrical storage device using the voltage sensor. Each time the voltage value is detected, it is possible to calculate the polarization elimination time corresponding to the voltage value. Thus, it is possible to compare the last calculated polarization elimination time with the stopped time.

[0022] As the stopping time increases, polarization elimination continues, and the voltage value of the electric storage device approaches the open-circuit voltage. By using the voltage value approaching the open-circuit voltage, it is possible to obtain a more accurate rate of change and identify a more accurate allowable range of the open-circuit voltage. Thus, it is possible to calculate a more accurate polarization elimination time. When the stopping time is longer than the polarization elimination time, the fact that the voltage value of the electric storage device is within the allowable range of the open-circuit voltage can be easily identified, so that the estimation accuracy of the state of charge can be easily ensured. Accordingly, the estimation accuracy of the full-charge capacity calculated from the state of charge can be easily ensured.

[0023] In the above aspect, the electrical storage system may further include a temperature sensor. The temperature sensor may be configured to detect a temperature of the electrical storage device. The controller may be configured to shorten the polarization elimination time as the temperature increases. Polarization of the electrical storage device also depends on the temperature of the electrical storage device. Specifically, as the temperature of the electrical storage device increases, polarization increases with difficulty, and polarization can be easily eliminated. In other words, as the temperature of the electrical storage device decreases, polarization increases with ease, and polarization can be easily eliminated. As the temperature of the electrical storage device increases, it is possible to shorten the polarization elimination time.The temperature of the electrical storage device can be detected by the temperature sensor.

[0024] Another aspect of the present invention provides an electrical storage system for a vehicle. The electrical storage system includes an electrical storage device, a voltage sensor, and a controller. The electrical storage device is configured to be charged with electrical power from an external power supply. The external power supply is installed outside the electrical storage device, separate from the electrical storage device. The voltage sensor is configured to detect a voltage value of the electrical storage device. The controller is configured to calculate a change rate of an electromotive voltage at at least one of a first time point and a second time point. The controller is configured to calculate a predetermined standby time based on the change rate of the electromotive voltage.The controller is configured to calculate a state of charge of the electric storage device when the predetermined standby time has elapsed from the first time or the second time. The controller is configured to calculate a full charge capacity of the electric storage device using the calculated state of charge. The controller is configured to shorten the predetermined standby time as the change rate of the electromotive voltage increases. The first time is a predetermined time in a period from the time when an ignition switch of the vehicle is turned off to a time when charging of the electric storage device with electric power from the external power supply is started.The second time point is a predetermined time point during the period when the vehicle is stopped after charging the electric storage device with electric power from the external power supply is completed. The rate of change of the electromotive voltage is a ratio of a fluctuation in the open-circuit voltage to a fluctuation in the state of charge of the electric storage device. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Features, advantages and technical and industrial significance of exemplary embodiments of the invention are described below with reference to the accompanying drawings, in which like reference numerals designate like elements and in which: Fig. 1 a view showing the configuration of a battery system; Fig. 2 a graph showing the correlation (OCV curve) between an OCV and a SOC; Fig. 3 is a graph showing the correlation between a change rate of an electromotive voltage and a polarization elimination time; Fig. 4 is a flowchart illustrating the process of calculating a full charge capacity of the battery pack according to a first embodiment; Fig. 5 is a graph illustrating a method of calculating an OCV; Fig. 6 is a timing diagram showing the behavior of the SOC of the battery pack; Fig. 7 is a graph showing the correlation between an SOC and the rate of change of electromotive voltage; Fig. 8 is a flowchart illustrating the process of calculating a full charge capacity of a battery pack according to a second embodiment; Fig. 9 is a graph showing the correlation between an OCV and a rate of change of the electromotive voltage; and Fig. 10 is a flowchart illustrating the process of calculating a full charge capacity of a battery pack according to a third embodiment. DETAILED DESCRIPTION OF EMBODIMENTS

[0026] Embodiments of the invention are described below.

[0027] Fig. 1 is a view showing the configuration of a battery system according to a first embodiment (which corresponds to an electric storage system according to the invention). Fig. The battery system shown in Figure 1 is mounted on a vehicle. The vehicle is, for example, a plug-in hybrid vehicle (PHV) or an electric vehicle (EV). The PHV includes another power source in addition to a battery pack 10 as a power source for driving the vehicle. The other power source is an engine or a fuel cell. The EV includes only the battery pack 10 as the power source for driving the vehicle.

[0028] In the present embodiment, the battery pack 10 is mounted on the vehicle; however, the battery pack 10 is not limited to this arrangement. That is, as long as a system is capable of charging the battery pack 10, the invention is applicable.

[0029] The battery pack (which corresponds to an electrical storage device according to the invention) 10 comprises a plurality of serially connected individual cells 11.

[0030] A secondary battery such as a nickel-metal hydride battery and a lithium-ion battery can be used as each of the individual cells 11. An electric double-layer capacitor can be used instead of the secondary battery. The number of individual cells 11 can be adjusted as needed based on a required output or the like of the battery pack 10. The battery pack 10 may include a plurality of the individual cells 11 connected in parallel.

[0031] A voltage sensor 21 detects the voltage value Vb of the battery pack 10 and outputs the detected result to a controller 30. A current sensor 22 detects the current value Ib of the battery pack 19 and outputs the detected result to the controller 30. In the present embodiment, the current value Ib at the time when the battery pack 10 is discharging is defined as a positive value. The current value Ib at the time when the battery pack 10 is charging is defined as a negative value. A temperature sensor 23 detects the temperature (battery temperature) Tb of the battery pack 10 and outputs the detected result to the controller 30.

[0032] The controller 30 includes a memory 31 and a timer 32. The memory 31 stores various pieces of information used by the controller 30 to execute a predetermined process (specifically, a process described in the present embodiment). The timer 32 is used to measure time. In the present embodiment, the memory 31 and the timer 32 are built into the controller 30; instead, at least one of the memory 31 and the timer 32 may be provided externally to the controller 30. The controller 30 may operate upon receiving electric power from a power supply other than the battery pack 10. The power supply is, for example, an auxiliary battery mounted on the vehicle. The auxiliary battery may be charged with electric power discharged from the battery pack 10.

[0033] A positive electrode line PL is connected to the positive electrode terminal of the battery pack 10. A negative electrode line NL is connected to the negative electrode terminal of the battery pack 10. A system main relay SMR-B is provided in the positive electrode line PL. A system main relay SMR-G is provided in the negative electrode line NL. The system main relays SMR-B, SMR-G each switch between an on state and an off state upon receiving a drive signal from the controller 30.

[0034] Information about the on / off state of an ignition switch is input to the controller 30. When the ignition switch switches from the off state to the on state, the controller 30 outputs control signals to switch the system main relays SMR-B, SMR-G to the on state. When the ignition switch switches from the on state to the off state, the controller 30 outputs control signals to switch the system main relays SMR-B, SMR-G to the off state.

[0035] The battery pack 10 is connected to an inverter 24 via the positive electrode line PL and the negative electrode line NL. When the system main relays SMR-B, SMR-G are in the on state, the battery pack 10 is connected to the inverter 24 and the battery system, which is in Fig. 1, assumes an activated state (a ready-on state). When the system main relays SMR-B, SMR-G are in the off state, the connection of the battery pack 10 to the inverter 24 is interrupted and the Fig. The battery system shown in Figure 1 assumes a stopped state (rest or ready-off state).

[0036] The inverter 24 converts DC power output from the battery pack 10 into AC power and outputs the AC power to a motor generator (MG) 25. The motor generator 25 generates kinetic energy (power) to drive the vehicle after receiving the AC power output from the inverter 24. The kinetic energy generated by the motor generator 25 is transmitted to the wheels, thereby enabling the vehicle to drive.

[0037] When the vehicle is decelerated or stopped, the motor generator 25 converts the kinetic energy generated during vehicle braking into electrical energy (AC power). The inverter 24 converts the AC power generated by the motor generator 25 into DC power and outputs the DC power to the battery pack 10. Thus, the battery pack 10 stores regenerative electrical power.

[0038] In the battery system according to the present embodiment, a booster circuit or "step-up circuit" can be provided in a current path between the battery pack 10 and the inverter 24. The booster circuit is capable of boosting the output voltage of the battery pack 10 and then outputting the boosted electrical power to the inverter 24. The booster circuit is capable of lowering the output voltage of the inverter 24 ("step down") and then outputting the reduced electrical power to the battery pack 10.

[0039] A charging line CHL1 is connected to the positive electrode line PL between the positive electrode terminal of the battery pack 10 and the system main relay SMR-B. A charging line CHL2 is connected to the negative electrode line NL between the negative electrode terminal of the battery pack 10 and the system main relay SMR-G. A charger 26 is connected to the charging lines CHL1, CHL2. A charging relay CHR-B is provided in the charging line CHL1 between the charger 26 and the positive electrode line PL. A charging relay CHR-G is provided in the charging line CHL2 between the charger 26 and the negative electrode line NL.

[0040] The charging relays CHR-B, CHR-G each switch between an on state and an off state upon receiving a control signal from the controller 30. An inlet (so-called connector) 27 is connected to the charger 26 via the charging lines CHL1, CHL2. A plug (so-called connector) 28 is connected to the inlet 27. That is, the plug 28 can be connected to the inlet 27, or the plug 28 can be disconnected from the inlet 27.

[0041] The connector 28 is connected to an AC power supply (which corresponds to an external power supply according to the invention) 29. For example, a commercial power supply can be used as the AC power supply 29. The connector 28 and the AC power supply 29 are installed outside the vehicle, separate from the vehicle. When the connector 28 is connected to the inlet 27 and the charging relays CHR-B, CHR-G are in the on state, it is possible to charge the battery pack 10 with electric power from the AC power supply 29. This charging is called external charging.

[0042] When external charging is performed, the charger 26 converts AC power from the AC power supply 29 into DC power and outputs the DC power to the battery pack 10. The charger 26 is capable of boosting the output voltage of the AC power supply 29 and then outputting the boosted electrical power to the battery pack 10. The controller 30 controls the operation of the charger 26.

[0043] A system that supports external charging is not limited to the Fig. 1. Specifically, as long as a system is capable of charging the battery pack 10 with electrical power from a power supply installed outside the vehicle (external power supply), the invention is applicable.

[0044] For example, the charging line CHL1 can be connected to the positive electrode line PL between the system main relay SMR-B and the inverter 24. The charging line CHL2 can be connected to the negative electrode line NL between the system main relay SMR-G and the inverter 24. In this case, when external charging is performed, not only the charging relays CHR-B, CHR-G, but also the system main relays SMR-B, SMR-G must be switched to the on state.

[0045] In the present embodiment, the AC power supply 29 is used. Instead of the AC power supply 29, a DC power supply (which corresponds to the external power supply according to the invention) may be used. In this case, the charger 26 may be omitted. Supplying electric power from the external power supply is not limited to supplying electric power using a cable. Instead, a so-called contactless charging system may be used. In the contactless charging system, it is possible to supply electric power using electromagnetic induction or a resonance phenomenon without any cable. A known configuration can be adopted as the contactless charging system as needed.

[0046] In the present embodiment, when external charging is performed, the full charge capacity of the battery pack 10 is calculated (estimated). The full charge capacity of the battery pack 10 is calculated based on the following mathematical expression (1). FCC=∑IbSOC_e−SOC_s

[0047] In the above mathematical expression (1), FCC is the full charge capacity of the battery pack 10. SOC_s is the state of charge (SOC) of the battery pack 10 at the time when external charging is started. SOC_e is the SOC of the battery pack 10 at the time when external charging is finished. ΣIb is a value obtained by accumulating the current value (charging current) Ib (accumulated current value) in a period from the start of external charging to the end of external charging. The current value Ib is detected by the current sensor 22. As described above, the current value (charging current) Ib is a negative value, so when calculating the accumulated current value ΣIb, the absolute value of the current value (charging current) Ib is used.

[0048] The SOC indicates the ratio of a charge level to the full charge capacity FCC. Because there is a correlation between the SOC and the open circuit voltage (OCV), if the correlation is obtained in advance, it is possible to calculate (estimate) the SOC of the battery pack 10 from the OCV of the battery pack 10. Specifically, using the voltage value Vb detected by the voltage sensor 21, it is possible to calculate the SOC of the battery pack 10. If the voltage value Vb is detected while the battery pack 10 is not being charged or discharged, a voltage fluctuation resulting from charging or discharging (energization) is not included in the voltage value Vb, and the voltage value Vb approaches the OCV.

[0049] On the other hand, polarization occurs when the battery pack 10 is charged or discharged, with the result that a voltage fluctuation resulting from the polarization is included in the voltage value Vb detected by the voltage sensor 21. Thus, the voltage value Vb deviates from the OCV. After the polarization is eliminated, the voltage value Vb at that time can be regarded as the OCV of the battery pack 10. If the voltage value Vb at the time when the polarization remains is regarded as the OCV, a voltage fluctuation resulting from the polarization becomes an estimation error of the OCV.

[0050] When charging or discharging of the battery pack 10 remains stopped, it is possible to eliminate the polarization. Therefore, a time for eliminating the polarization (referred to as the polarization elimination time) is set in advance, and if a time during the period when charging or discharging of the battery pack 10 is stopped is longer than the polarization elimination time, it can be determined that the polarization has been eliminated.

[0051] In the present embodiment, the polarization elimination time is changed based on a change rate of the electromotive voltage (which corresponds to a change rate according to the invention). The polarization elimination time according to the present embodiment is not equal to a time required to completely eliminate polarization, as described below. The change rate of the electromotive voltage is the ratio of a fluctuation in the OCV (ΔOCV) to a fluctuation in the SOC (ΔSOC). Specifically, the change rate of the electromotive voltage is a value (ΔOCV / ΔSOC) obtained by dividing the fluctuation ΔOCV by the fluctuation ΔSOC. The SOC is the SOC of the battery pack 10. The OCV is the OCV of the battery pack 10.

[0052] In the present embodiment, the polarization elimination time is shortened as the change rate of the electromotive voltage increases. In other words, as the change rate of the electromotive voltage decreases, the polarization elimination time is lengthened. The reason why the polarization elimination time is changed in this way will be described below.

[0053] When calculating (estimating) the full charge capacity FCC of the battery pack 10 based on the mathematical expression (1) described above, it is necessary to bring an estimation error (an error with respect to a true value) of each of the SOC_s and the SOC_e into an allowable range ΔSOC_err. This is because, for each of the SOC_s and the SOC_e, when a difference between an estimated value and a true value is outside the allowable range ΔSOC_err, it is difficult to ensure the estimation accuracy of the full charge capacity FCC. By narrowing the allowable range ΔSOC_err, it is possible to improve the estimation accuracy of the full charge capacity FCC. It is possible to adjust the allowable range ΔSOC_err as needed, taking into account the accuracy of estimating the full charge capacity FCC.

[0054] Because there is a correlation between SOC and OCV, it is possible to set an allowable range of the OCV corresponding to the allowable range ΔSOC_err. When the voltage value Vb of the battery pack 10 is within the allowable range of the OCV, the SOC corresponding to the voltage value Vb calculated using the correlation between OCV and SOC is within the allowable range ΔSOC_err. That is, when the voltage value Vb is within the allowable range of the OCV, it is possible to calculate the SOC by considering the voltage value Vb as the OCV. Because the thus calculated SOC is within the allowable range ΔSOC_err, it is possible to ensure the estimation accuracy of the full charge capacity FCC.

[0055] As in Fig. 2, the allowable range of the OCV varies according to the allowable range ΔSOC_err with the change rate of the electromotive voltage. Fig. 2 shows the correlation (so-called OCV curve) between an OCV and a SOC. In Fig. 2 represents the ordinate axis OCV and represents the abscissa axis SOC.

[0056] As in Fig. As shown in Figure 2, the rate of change of the electromotive voltage in a region R1 of the OCV curve is lower than the rate of change of the electromotive voltage in a region R2 of the OCV curve. To bring the estimation error of the SOC in the region R1 within the allowable range ΔSOC_err, the voltage value Vb used to calculate (estimate) the SOC must be within the allowable range ΔOCV1. The allowable range ΔOCV1 corresponds to the allowable range ΔSOC_err in the region R1. The OCV of the battery pack 10 is included in the allowable range ΔOCV1.

[0057] The voltage value Vb shortly after charging or discharging of the battery pack 10 is stopped may be outside the allowable range ΔOCV1. In this case, polarization only needs to be eliminated until the voltage value Vb is within the allowable range ΔOCV1. Polarization may remain as long as the voltage value Vb is within the allowable range ΔOCV1. The polarization elimination time according to the present embodiment is a time required until the voltage value Vb is within the allowable range ΔOCV1. Using the polarization elimination time, a state in which the voltage value Vb is within the allowable range ΔOCV1 (polarization eliminated state) is determined even though polarization still remains.

[0058] To bring the SOC estimation error in the range R2 within the allowable range ΔSOC_err, the voltage value Vb used to calculate (estimate) the SOC must be within the allowable range ΔOCV2. The allowable range ΔOCV2 corresponds to the allowable range ΔSOC_err in the range R2. The OCV of the battery pack 10 is included in the allowable range ΔOCV2. The allowable range ΔSOC_err in the range R2 is the same as the allowable range ΔSOC_err in the range R1. Depending on the OCV curve, a region may arise where the fluctuation ΔOCV becomes "0" with respect to the fluctuation ΔSOC. At this time, only a specific OCV can correspond to the allowable range ΔSOC_err.

[0059] The voltage value Vb, shortly after charging or discharging of the battery pack 10 is stopped, may be outside the allowable range ΔOCV2. In this case, the polarization only needs to be eliminated until the voltage value Vb is within the allowable range ΔOCV2. Polarization may remain as long as the voltage value Vb is within the allowable range ΔOCV2. As Fig. As can be seen from Figure 2, the allowable range ΔOCV2 is wider than the allowable range ΔOCV1. The polarization elimination time according to the present embodiment is a time required until the voltage value Vb falls within the allowable range ΔOCV2. Using the polarization elimination time, a state in which the voltage value Vb falls within the allowable range ΔOCV2 (polarization elimination state) is determined even though polarization still remains.

[0060] Because the allowable range ΔOCV1 is narrower than the allowable range ΔOCV2, it is not possible to bring the voltage value Vb in the range R1 into the allowable range ΔOCV1 unless the polarization is eliminated by a greater amount than in the range R2. In other words, in the range R1, it is not possible to bring the voltage value Vb into the allowable range ΔOCV1 unless a time during the period when charging or discharging of the battery pack 10 is stopped is longer than in the range R2.

[0061] The change rate of the electromotive voltage in the region R1 is lower than the change rate of the electromotive voltage in the region R2. The polarization elimination time needs to be extended as the change rate of the electromotive voltage decreases. In other words, as the change rate of the electromotive voltage increases, it is possible to shorten the polarization elimination time. As described above, the polarization elimination time according to the present embodiment is a time during the period when polarization is eliminated until the voltage value Vb is within the allowable range (ΔOCV1, ΔOCV2) of the OCV.

[0062] By considering the allowable range ΔSOC_err to ensure the estimation accuracy of the full charge capacity FCC, it is possible to change the polarization elimination time according to the change rate of the electromotive voltage. Once it is determined whether polarization has been eliminated, it is possible to adjust the polarization elimination time according to the change rate of the electromotive voltage.

[0063] In the present embodiment, when setting the polarization elimination time, not only the change rate of the electromotive voltage but also the battery temperature Tb is taken into account. A polarization occurrence state, or a polarization occurrence state, and a polarization elimination state, or a polarization elimination state, depend on the battery temperature Tb. Specifically, as the battery temperature Tb decreases, polarization increases more easily or becomes more difficult to eliminate. In other words, as the battery temperature Tb increases, it becomes more difficult for polarization to increase or more difficult to eliminate polarization.

[0064] Therefore, the polarization elimination time is set taking into account not only the rate of change of the electromotive voltage, but also the battery temperature Tb. Especially when a correlation (an example) that is Fig. 3 is obtained in advance through an experiment or the like, it is possible to adjust the polarization elimination time by identifying the rate of change in the electromotive voltage and the battery temperature Tb. In Fig. 3, the ordinate axis represents a polarization elimination time and the abscissa axis represents a change rate of the electromotive voltage.

[0065] As in Fig. As shown in Figure 3, the polarization elimination time shortens as the change rate of the electromotive voltage increases. In other words, as the change rate of the electromotive voltage decreases, the polarization elimination time lengthens. For the same change rate of the electromotive voltage, as the battery temperature Tb decreases, the polarization elimination time lengthens. In other words, for the same change rate of the electromotive voltage, as the battery temperature Tb increases, the polarization elimination time shortens.

[0066] The Fig. The correlation shown in Figure 3 can be expressed as a summary or an arithmetic expression and can be stored in the memory 31. When the polarization elimination time is calculated using the Fig. To calculate the correlation shown in Figure 3, it is necessary to identify the change rate of the electromotive voltage and the battery temperature Tb. The battery temperature Tb can be detected by the temperature sensor 23. When the fluctuation ΔSOC and the fluctuation ΔOCV are calculated, the change rate of the electromotive voltage can be calculated. By obtaining the behavior (change) of the SOC of the battery pack 10, the fluctuation ΔSOC can be calculated. By obtaining the behavior (change) of the OCV of the battery pack 10, the fluctuation ΔOCV can be calculated.

[0067] In the present embodiment, the polarization elimination time is calculated based on the change rate of the electromotive voltage and the battery temperature Tb; however, the calculation of the polarization elimination time is not limited to this configuration. Specifically, it is possible to calculate the polarization elimination time from the change rate of the electromotive voltage without considering the battery temperature Tb.

[0068] When the full charge capacity FCC of the battery pack 10 is calculated as described above, the full charge capacity FCC is used to calculate (estimate) the SOC of the battery pack 10 during vehicle travel. Specifically, the SOC of the battery pack 10 during vehicle travel can be calculated based on the following mathematical expression (2). SOC_cur=SOC_ref+∑IbFCC

[0069] In the above mathematical expression (2), SOC_cur is the instantaneous SOC of the battery pack 10. SOC_ref is the SOC of the battery pack 10 at the time the ignition switch switches from the off state to the on state. If the OCV of the battery pack 10 at the time the ignition switch is switched to the on state is identified, it is possible to calculate SOC_ref based on the correlation between OCV and SOC. ΣIb is a value obtained by accumulating the current value Ib of the battery pack 10 (accumulated current value) after the ignition switch is switched to the on state. FCC is the full charge capacity of the battery pack 10.

[0070] According to the mathematical expression (2) described above, after the ignition switch switches to the on state, it is possible to acquire the SOC_cur of the battery pack 10 by continuing to detect the current value Ib of the battery pack 10. That is, it is possible to acquire the SOC (SOC_cur) of the battery pack 10 while the vehicle is running.

[0071] For the full charge capacity FCC shown in the above-described mathematical expression (2), only the last calculated full charge capacity FCC could be used, or a value obtained by correcting the previous full charge capacity FCC with the last full charge capacity FCC could be used. When the previous full charge capacity FCC is corrected with the last full charge capacity FCC, it is possible, for example, to assign weights to the previous full charge capacity FCC and the last full charge capacity FCC and then add these full charge capacities FCC together. The added full charge capacity FCC can be used as the full charge capacity FCC shown in the above-described mathematical expression (2).

[0072] Next, the process of calculating the full charge capacity FCC with reference to the Fig. 4 is described. The flow chart shown in Fig. 4 is executed by the controller 30. When the connector 28 is connected to the inlet 27 and the battery system is put into a stopped state in response to the ignition switch being turned off, the Fig. The process shown in Figure 4 is started.

[0073] In step S101, the controller 30 calculates a polarization elimination time ts from the change rate of the electromotive voltage and the battery temperature Tb. As described above, using the Fig. 3, it is possible to calculate the polarization elimination time ts from the change rate of the electromotive voltage and the battery temperature Tb. The battery temperature Tb is detected by the temperature sensor 23. For example, the change rate of the electromotive voltage can be calculated by a method described below.

[0074] When the fluctuation ΔSOC and the fluctuation ΔOCV are calculated within a predetermined time required until the ignition switch is turned off, the change rate of the electromotive voltage can be calculated. When calculating the fluctuation ΔSOC, when the current value Ib at which the battery pack 10 is charged or discharged is detected within the predetermined time, a value (accumulated current value) ΣIb obtained by accumulating these current values ​​Ib can be calculated. When the calculated accumulated current value ΣIb is divided by the full charge capacity FCC of the battery pack 10, the fluctuation ΔSOC can be calculated.

[0075] On the other hand, if a change in the OCV of the battery pack 10 is obtained within the predetermined time required until the ignition switch is turned off, the fluctuation ΔOCV can be calculated. The OCV of the battery pack 10 can be calculated from the current value Ib and the voltage value Vb. Specifically, when the battery pack 10 is being charged or discharged, the current value Ib and the voltage value Vb are detected. As shown in Fig. 5, pairs of current values ​​Ib and voltage values ​​Vb are plotted in a coordinate system whose coordinate axes represent the current value Ib and the voltage value Vb, respectively. When a line L approximating the plurality of plot points is calculated, the voltage value Vb on the line L in the case where the current value Ib is equal to 0 [A] is the OCV.

[0076] In step S102, the controller 30 measures an elapsed time (corresponding to a stopped time according to the invention) tm_s using the timer 32. The elapsed time tm_s is an elapsed time from the time when charging or discharging of the battery pack 10 is stopped as a result of the ignition switch being turned off. When the system main relays SMR-B, SMR-G are turned off from the on state, the measurement of the elapsed time tm_s is started.

[0077] In step S103, the controller 30 determines whether an instruction to execute external charging has been issued. The controller 30 measures the elapsed time tm_s until an instruction to execute external charging is issued. When the connector 28 is connected to the inlet 27, an instruction to execute external charging can be input to the controller 30. Thus, the controller 30 is able to determine that an instruction to execute external charging has been issued.

[0078] On the other hand, the connector 28 is connected to the inlet 27, and then the time at which external charging is started (referred to as the charging start time) can be set. In this case, when the current time becomes the charging start time, the controller 30 determines that an instruction to execute external charging has been issued. Not the charging start time, but a scheduled time for starting the vehicle (referred to as the start time) can be set. At this time, the charging start time is set so that external charging is completed before the start time.

[0079] When an instruction to execute external charging is issued, the controller 30 determines in step S104 whether the elapsed time tm_s is longer than the polarization elimination time ts. The elapsed time tm_s is a time from the time when measuring the time tm_s is started to a time when an instruction to execute external charging is issued. The polarization elimination time ts is a time calculated in the process of step S101. If the elapsed time tm_s is longer than the polarization elimination time ts, the controller 30 executes the process of step S105. On the other hand, if the elapsed time tm_s is shorter than or equal to the polarization elimination time ts, the controller 30 executes the process of step S106.

[0080] In step S105, the controller 30 detects the voltage value Vb of the battery pack 10 using the voltage sensor 21 and regards the voltage value Vb as the OCV of the battery pack 10. This voltage value Vb can be considered to be in the above-described allowable range (ΔOCV1, ΔOCV2 shown in Fig. 2) of the OCV. Thus, the controller 30 calculates the SOC corresponding to the voltage value Vb, which is considered the OCV (which corresponds to the SOC_s described above), using the correlation between an OCV and an SOC.

[0081] In step S106, the controller 30 sets the SOC of the battery pack 10 at the end of the trip as the SOC_s. In other words, the controller 30 sets the SOC of the battery pack 10 at the time the ignition switch is turned from the on state to the off state as the SOC_s. As described above, while the vehicle is traveling, the SOC of the battery pack 10 is calculated (estimated), so it is possible to identify the SOC of the battery pack 10 at the time the ignition switch is turned from the on state to the off state.

[0082] In step S107, the controller 30 starts external charging by operating the charger 26 by switching the charging relays CHR-B, CHR-G to the on state. In step S108, the controller 30 calculates the accumulated current value XIb by accumulating the current value (charging current) Ib detected by the current sensor 22 during external charging.

[0083] In step S109, the controller 30 determines whether to stop external charging. For example, when the voltage value Vb of the battery pack 10 detected by the voltage sensor 21 has reached a target voltage value at which external charging is stopped, the controller 30 may determine to stop external charging. The target voltage value at which external charging is stopped can be set as needed. For example, the voltage value Vb at the time when the battery pack 10 is in a full charge state may be set as the target charge value at which external charging is stopped. On the other hand, when the accumulated current value ΣIb has reached a target accumulation value, the controller 30 may determine to stop external charging. The target accumulation value can be set as needed.

[0084] Until it is determined to stop external charging, the accumulated current value ΣIb is calculated in the process of step S108. When it is determined to stop external charging, the controller 30 stops external charging in step S110. Specifically, the controller 30 stops the operation of the charger 26 and switches the charging relays CHR-B, CHR-G from the on state to the off state. In step S110, the controller 30 calculates a polarization elimination time te from the rate of change in the electromotive voltage and the battery temperature Tb.

[0085] The polarization elimination time te is calculated as in the case of the polarization elimination time ts. Specifically, using the Fig. 3, the polarization elimination time te is calculated according to the rate of change in the electromotive voltage and the battery temperature Tb. The battery temperature Tb is detected by the temperature sensor 23. When the fluctuation ΔSOC and the fluctuation ΔOCV are calculated within the predetermined time required until external charging is stopped, the rate of change in the electromotive voltage can be calculated.

[0086] If the current value Ib with which the battery pack 10 is charged is detected within the predetermined time required until external charging is stopped, a value (accumulated current value) ΣIb obtained by accumulating these current values ​​Ib can be calculated. If the calculated accumulated current value ΣIb is divided by the full charge capacity FCC of the battery pack 10, the fluctuation ΔSOC can be calculated. On the other hand, if a change in the OCV of the battery pack 10 is acquired within the predetermined time required until external charging is stopped, the fluctuation ΔOCV can be calculated. As described with reference to Fig. 5, the OCV can be calculated from the current value Ib and the voltage Vb. If the OCV is determined by the Fig. 5, it is necessary to change the current value Ib during external charging.

[0087] On the other hand, if the current value Vb of the battery pack 10 is detected while external charging is performed at a constant current, a change in the voltage value Vb can be obtained. Thus, a fluctuation in the voltage value Vb within the predetermined time required until external charging is stopped can be calculated, and the calculated fluctuation can be regarded as the fluctuation ΔOCV.

[0088] In step S111, the controller 30 measures the elapsed time (corresponding to the stopped time according to the invention) tm_e using the timer 32. The elapsed time tm_e is an elapsed time from the time when external charging is stopped. In step S112, the controller 30 determines whether the elapsed time tm_e is longer than the polarization elimination time te. The polarization elimination time te is a time calculated in the process of step S110. The elapsed time tm_e is a time from the time when external charging is stopped to the current time.

[0089] If the elapsed time tm_e is shorter than or equal to the polarization elimination time te, the controller 30 determines in step S113 whether an instruction to start the battery system set in Fig. 1 is issued. This instruction is used to switch the ignition switch to the on state. When an instruction to start the battery system is issued, the controller 30 terminates the Fig. 4. On the other hand, when no instruction to start the battery system is issued, the controller 30 continues measuring the elapsed time tm_e in the process of step S111.

[0090] If the elapsed time tm_e is longer than the polarization elimination time te, the controller 30 executes the process of step S114. In step S114, the controller 30 detects the voltage value Vb of the battery pack 10 using the voltage sensor 21 and regards the voltage value Vb as the OCV of the battery pack 10. The voltage value Vb can be considered to be within the above-described allowable range (ΔOCV1, ΔOCV2, Fig. 2) of the OCV. Thus, the controller 30 calculates the SOC corresponding to the voltage value Vb, which is considered the OCV (which corresponds to the SOC_e described above), using the correlation between an OCV and an SOC.

[0091] In step S115, the controller 30 calculates the full charge capacity FCC of the battery pack 10 based on the above-described mathematical expression (1). The SOC_s identified in the process of step S105 or step S106 is used as the SOC_s shown in the above-described mathematical expression (1). The SOC_e calculated in the process of step S114 is used as the SOC_e shown in the above-described mathematical expression (1). The accumulated current value ΣIb calculated in the process of step S108 is used as the accumulated current value ΣIb shown in the above-described mathematical expression (1).

[0092] In the Fig. 4, the polarization elimination times ts, te are calculated; instead, one of the polarization elimination times ts, te could be calculated. In this case, one of the processes of step S104 and step S112 shown in Fig. 4. In the processes of step S105 and step S114 shown in Fig. 4, an opportunity is obtained to calculate the SOC from the OCV. If the polarization elimination time ts is not calculated, a predetermined time (fixed value) can be used as the polarization elimination time ts. Similarly, if the polarization elimination time te is not calculated, a predetermined time (fixed value) can be used as the polarization elimination time te.

[0093] In the Fig. In the processes shown in Figure 4, when the elapsed time tm_e is less than or equal to the polarization elimination time te and an instruction to start the battery system is issued, the full charge capacity FCC of the battery pack 10 is not calculated. However, even in this case, the full charge capacity FCC of the battery pack 10 can be calculated.

[0094] For example, when calculating the SOC of the battery pack 10 during external charging, the SOC at the time when external charging is stopped can be used as the SOC_e. On the other hand, after external charging is stopped, the voltage value Vb of the battery pack 10 is detected using the voltage sensor 21, and the voltage value Vb can be regarded as the OCV of the battery pack 10. Using the correlation between an OCV and a SOC, the SOC corresponding to the OCV can be used as the SOC_e. Once the SOC_e is identified, it is possible to calculate the full charge capacity FCC of the battery pack 10 as described above.

[0095] Fig. 6 shows the behavior (an example) of the SOC of the battery pack 10. In Fig. In Figure 6, the ordinate axis represents the SOC of the battery pack 10, and the abscissa axis represents time. Between time t1 and time t2, the vehicle is traveling, and the battery pack 10 is being charged or discharged in response to the vehicle's traveling state. The ignition switch is switched from the on state to the off state at time t2. At time t2, the polarization elimination time ts is calculated, and measurement of the elapsed time tm_s is started. The polarization elimination time ts is calculated from the battery temperature Tb at time t2 and the rate of change in the electromotive voltage within the predetermined time until time t2.

[0096] Between time t2 and time t3, the vehicle is stopped, and charging or discharging of the battery pack 10 is stopped. At time t3, external charging is started after receiving an instruction to execute external charging. A time from time t2 to time t3 is the elapsed time tm_s. In the Fig. In the processes shown in Figure 4, it is determined whether the elapsed time tm_s is longer than the polarization elimination time ts. If the elapsed time tm_s is longer than the polarization elimination time ts, the OCV of the battery pack 10 at time t3 is identified, and the SOC_s is calculated according to the identified OCV. If the elapsed time tm_s is shorter than or equal to the polarization elimination time ts, the SOC of the battery pack 10 at time t2 is used as the SOC_s.

[0097] Between time t3 and time t4, external charging is performed. The SOC of battery pack 10 increases as a result of the external charging. At time t4, external charging is stopped. At time t4, the polarization elimination time te is calculated, and a measurement of the elapsed time tm_e is started. Between time t4 and time t5, the vehicle is stopped, and charging or discharging of battery pack 10 is stopped. At time t5, an instruction to start the battery system is issued.

[0098] A time from time t4 to time t5 is the elapsed time tm_e and in the Fig. In the processes shown in Figure 4, it is determined whether the elapsed time tm_e is longer than the polarization elimination time te. If the elapsed time tm_e is longer than the polarization elimination time te, the OCV of the battery pack 10 at time t5 is identified, and the SOC_e is calculated according to the OCV. If the elapsed time tm_e is shorter than or equal to the polarization elimination time te, the SOC_e is not calculated, and the full charge capacity FCC is also not calculated. However, even if the elapsed time tm_e is shorter than or equal to the polarization elimination time te, the full charge capacity FCC can be calculated as described above.

[0099] In the present embodiment, the polarization elimination times ts, te are changed in response to the rate of change in the electromotive voltage or the battery temperature Tb. As described with reference to Fig. 3, when the change rate in the electromotive voltage increases, the polarization elimination times ts, te can be shortened. Thus, an opportunity that the elapsed times tm_s, tm_e are correspondingly longer than the polarization elimination times ts, te increases, so that it is possible to obtain an opportunity to execute the processes of steps S105 and S114 described in Fig. 4 shown.

[0100] When estimating the SOC, in order to ensure the estimation accuracy of the SOC, it is preferable to calculate (estimate) the SOC from the OCV (including the voltage value Vb within the allowable range of the OCV). Therefore, it is also preferable to increase the opportunity to execute the processes of step S105 and step S114. On the other hand, if the estimation accuracy of the SOC is ensured, it is possible to ensure the estimation accuracy of the full charge capacity FCC. Thus, when calculating (estimating) the full charge capacity FCC, it is preferable to use the SOC calculated from the OCV (including the voltage value Vb within the allowable range of the OCV).By increasing an opportunity to execute the processes of step S105 and step S114, it is possible to increase an opportunity to calculate the full charge capacity FCC using the SOC calculated from the OCV (including the voltage value Vb within the allowable range of the OCV).

[0101] A second embodiment will be described. Similar reference numerals denote the same components as those described in the first embodiment, and a detailed description thereof will be omitted. The following mainly describes the difference from the first embodiment.

[0102] The rate of change in the electromotive voltage is a value obtained by dividing the fluctuation ΔOCV by the fluctuation ΔSOC, and depends on the correlation (OCV curve) between an OCV and a SOC, as described with reference to Fig. 2. Therefore, there is a correlation that can be Fig. 7, between a rate of change in the electromotive voltage and a SOC. The Fig. 7 can be calculated based on the correlation shown in Fig. 2. The gradient of a tangent to the OCV curve passing through the SOC (a point) of the OCV curve becomes the rate of change in the electromotive voltage. Thus, the Fig. The correlation shown in Figure 7 was obtained.

[0103] In the first embodiment, the polarization elimination times ts, te are calculated from the rate of change in the electromotive voltage; however, if the correlation shown in Fig. 7, the polarization elimination times ts, te can be calculated from the SOC of the battery pack 10. When the SOC of the battery pack 10 is calculated (estimated), the rate of change in the electromotive voltage corresponding to the SOC can be calculated using the Fig. 7. If the rate of change in the electromotive voltage is identified, it is possible to determine the polarization elimination times ts, te using the correlation shown in Fig. 3. As in the case of the first embodiment, when calculating the polarization elimination times ts, te, the battery temperature Tb can be taken into account.

[0104] In the present embodiment, the polarization elimination times ts, te are calculated from the SOC of the battery pack 10 without calculating the rate of change in the electromotive voltage. Fig. The flowchart shown in Fig. 8 shows the process of calculating the full charge capacity of the battery pack 10 in the present embodiment and corresponds to the flowchart shown in Fig. 4. Similar step numbers denote the same processes as the processes shown in Fig. 4, and a detailed description of them will be omitted.

[0105] In the present embodiment, instead of the process of step S101 shown in Fig. 4, the process of S116, which is shown in Fig. 8 is executed. In step S116, the controller 30 calculates the polarization elimination time ts based on the SOC of the battery pack 10 and the battery temperature Tb. The SOC of the battery pack 10 is the SOC at the time when charging or discharging of the battery pack 10 is stopped in response to the ignition switch being turned off. The SOC corresponds to the SOC_s described in the process of step S106. The battery temperature Tb is the battery temperature Tb at the time when charging or discharging of the battery pack 10 is stopped in response to the ignition switch being turned off, and is detected by the temperature sensor 23.

[0106] When calculating the SOC of the battery pack 10, the polarization elimination time ts can be calculated using the correlation between an SOC and a change rate in the electromotive voltage and the correlation between a change rate in the electromotive voltage and a polarization elimination time, as described above. In the process of step S116, the polarization elimination time ts is calculated taking into account not only the SOC of the battery pack 10 but also the battery temperature Tb. However, it is possible to calculate the polarization elimination time ts from the SOC of the battery pack 10 without considering the battery temperature Tb. The thus calculated polarization elimination time ts is used in the process of step S104.

[0107] In the present embodiment, instead of the process of step S110 shown in Fig. 4 is shown, which in Fig. 8 is executed. In step S117, the controller 30 stops external charging as in the first embodiment. The controller 30 calculates the polarization elimination time te based on the SOC of the battery pack 10 and the battery temperature Tb. The SOC of the battery pack 10 is the SOC at the time of termination of external charging.

[0108] The SOC is obtained by adding the fluctuation ΔSOC during the external charging period to the SOC at the start of external charging. The SOC_s described in the process of step S105 or step S106 can be used as the SOC at the start of external charging. On the other hand, the fluctuation ΔSOC can be calculated by dividing the accumulated current value ΣIb calculated in the process of step S108 by the full charge capacity FCC. The battery temperature Tb is the battery temperature Tb at the end of external charging and is detected by the temperature sensor 23.

[0109] When calculating the SOC of the battery pack 10, the polarization elimination time te can be calculated as described above. In the process of step S117, the polarization elimination time te is calculated taking into account not only the SOC of the battery pack 10 but also the battery temperature Tb. However, the polarization elimination time may be calculated from the SOC of the battery pack 10 without considering the battery temperature Tb. The thus calculated polarization elimination time te is used in the process of step S112.

[0110] One of the processes of step S116 and step S117 shown in Fig. 8 can be executed. If only the process of step S116 is executed, the process of step S110 shown in Fig. 4 may be performed instead of the process of step S117. Instead of the process of step S117, a predetermined time (fixed value) may be used as the polarization elimination time te.

[0111] If only the process of step S117 is executed, the process of step S101 shown in Fig. 4 may be performed instead of the process of step S116. Instead of the process of step S116, a predetermined time (fixed value) may be used as the polarization elimination time ts.

[0112] A third embodiment of the invention will be described. Like reference numerals denote like components as those described in the first embodiment, and detailed descriptions thereof will be omitted. The following mainly describes the difference from the first embodiment.

[0113] The rate of change in an electromotive voltage is a value obtained by dividing the fluctuation ΔOCV by the fluctuation ΔSOC and depends on the correlation (OCV curve) between an OCV and a SOC, as described with reference to Fig. 2. Therefore, there is a correlation that can be Fig. 9, between a rate of change in the electromotive voltage and an OCV. The Fig. The correlation shown in Figure 9 can be calculated based on the OCV curve shown in Fig. 2. The gradient of a tangent to the OCV curve passing through the OCV (a point) on the OCV curve becomes the rate of change in the electromotive voltage. Thus, the Fig. The correlation shown in Figure 9 was obtained.

[0114] In the first embodiment, the polarization elimination times ts, te are calculated from the rate of change in the electromotive voltage; however, if the Fig. Using the correlation shown in Figure 9, the polarization elimination times ts, te can be calculated from the OCV of the battery pack 10.

[0115] Once the OCV of the battery pack 10 is identified, the rate of change in the electromotive voltage corresponding to the OCV can be calculated using the formulas given in Fig. 9. Once the rate of change in the electromotive voltage is identified, the polarization elimination times ts, te can be calculated using the correlation shown in Fig. 3 can be identified. As in the case of the first embodiment, when calculating the polarization elimination times ts, te, the battery temperature Tb can be taken into account.

[0116] In the present embodiment, the polarization elimination times ts, te are calculated from the voltage value Vb of the battery pack 10 without calculating the rate of change in the electromotive voltage. Fig. The flowchart shown in Fig. 10 shows the process of calculating the full charge capacity of the battery pack 10 in the present embodiment and corresponds to the flowchart shown in Fig. 4. The same step numbers denote the same processes as the processes shown in the flowchart shown in Fig. 4, and the detailed description of these will be omitted.

[0117] In the present embodiment, instead of the process of step S101 shown in Fig. 4, the process of step S118 shown in Fig. 10 is executed. In step S118, the controller 30 calculates the polarization elimination time ts based on the voltage value Vb of the battery pack 10 and the battery temperature Tb. The voltage value Vb of the battery pack 10 is the voltage value Vb after charging or discharging of the battery pack 10 is stopped in response to the ignition switch being turned off, and is detected by the voltage sensor 21. The voltage value Vb is regarded as the OCV of the battery pack 10. The battery temperature Tb is the battery temperature Tb after charging or discharging of the battery pack 10 is stopped in response to the ignition switch being turned off, and is detected by the temperature sensor 23.

[0118] By considering the voltage value Vb of the battery pack 10 as the OCV, the polarization elimination time ts can be calculated using the correlation between an OCV and a change rate in the electromotive voltage and the correlation between a change rate in the electromotive voltage and a polarization elimination time, as described above. In the process of step S118, the polarization elimination time ts is calculated by considering not only the voltage value Vb (value regarded as the OCV) of the battery pack 10 but also the battery temperature Tb. However, the polarization elimination time ts can be calculated from the voltage value Vb of the battery pack 10 without considering the battery temperature Tb.

[0119] In the process from step S103, until it is determined that an instruction to execute external charging is issued, the processes from step S118 and step S102 are executed. When the process returns from the process from step S103 to the process from step S118, the polarization elimination time ts is repeatedly calculated based on the voltage value Vb and the battery temperature Tb at that time. That is, until an instruction to execute external charging is issued, detection of the voltage value Vb and the battery temperature Tb is repeated, and the calculation of the polarization elimination time ts is repeated. The polarization elimination time ts used in the process from step S104 is the polarization elimination time ts calculated from the voltage value Vb and the battery temperature Tb at the time when an instruction to execute external charging is issued.

[0120] As time elapses from the time the ignition switch is turned off, polarization that occurred as a result of charging or discharging the battery pack 10 before the ignition switch is turned off can be easily eliminated. Accordingly, the voltage value Vb changes and approaches the OCV. Thus, when the process returns from the process of step S103 to the process of step S118, the voltage value Vb has changed, and the polarization elimination time ts is calculated based on the changed voltage value Vb.

[0121] When the process returns from the process of step S103 to the process of step S118, the battery temperature Tb may change. In this case, the polarization elimination time ts is calculated based on the changed battery temperature Tb.

[0122] As described above, when calculating the polarization elimination time ts, the voltage value Vb is regarded as the OCV. As the voltage value Vb approaches the OCV, it is possible to obtain a more accurate rate of change in the electromotive voltage, and it is possible to calculate a more accurate polarization elimination time ts. The thus calculated polarization elimination time ts is compared with the elapsed time tm_s. If the elapsed time tm_s is longer than the polarization elimination time ts, the process of step S105 can be executed. In the process of step S105, the SOC_s included in the allowable range ΔSOC_err specified in Fig. 2. Accordingly, the estimation accuracy of the full charge capacity FCC calculated from the SOC_s can be easily ensured.

[0123] In the present embodiment, instead of the process of step S110 shown in Fig. 4, the processes of step S119 and step S120 shown in Fig. 10 are executed. In step S119, the controller 30 stops external charging as in the case of the first embodiment. In step S120, the controller 30 calculates the polarization elimination time te based on the voltage value Vb of the battery pack 10 and the battery temperature Tb. The voltage value Vb of the battery pack 10 is the voltage value Vb after external charging is stopped and is detected by the voltage sensor 21. The voltage value Vb is regarded as the OCV of the battery pack 10. The battery temperature Tb is the battery temperature Tb after external charging is stopped and is detected by the temperature sensor 23.

[0124] By considering the voltage value Vb of the battery pack 10 as the OCV, the polarization elimination time te can be calculated using the correlation between an OCV and a change rate in the electromotive voltage and the correlation between a change rate in the electromotive voltage and a polarization elimination time, as described above. In the process of step S120, the polarization elimination time te is calculated by considering not only the voltage value Vb (value regarded as the OCV) of the battery pack 10 but also the battery temperature Tb. However, the polarization elimination time te can be calculated from the voltage value Vb of the battery pack 10 without considering the battery temperature Tb.

[0125] In the process of step S113, when no instruction to start the battery system is issued, the process of step S120 is executed. When the process returns from the process of step S113 to the process of step S120, the polarization elimination time te is repeatedly calculated based on the voltage value Vb and the temperature Tb at that time. That is, while no instruction to start the battery system is issued, the detection of the voltage value Vb and the battery temperature Tb is repeated, and the calculation of the polarization elimination time te is repeated. The thus calculated polarization elimination time te is used in the process of step S112. That is, in the process of step S112, the last calculated polarization elimination time te is used.

[0126] As time elapses from the time when external charging is stopped, the polarization that occurred as a result of external charging can be easily eliminated. Accordingly, the voltage value Vb changes and approaches the OCV. Thus, when the process returns from the process of step S113 to the process of step S120, the voltage value Vb has changed, and the polarization elimination time te is calculated based on the changed voltage value Vb.

[0127] When the process returns from the process of step S113 to the process of step S120, the battery temperature Tb may change. In this case, the polarization elimination time te is calculated based on the changed battery temperature Tb.

[0128] As described above, when calculating the polarization elimination time te, the voltage value Vb is regarded as the OCV. As the voltage value Vb approaches the OCV, it is possible to obtain a more accurate rate of change in the electromotive voltage, and it is possible to calculate a more accurate polarization elimination time te. The thus calculated polarization elimination time te is compared with the elapsed time tm_e. If the elapsed time tm_e is longer than the polarization elimination time te, the process of step S114 may be executed. In the process of step S114, the SOC_e included in the allowable range ΔSOC_err specified in Fig. 2. Accordingly, the estimation accuracy of the full charge capacity FCC calculated from the SOC_e can be easily ensured.

[0129] In the present embodiment, the process returns from the process of step S103 to the process of step S118; however, the process is not limited to this configuration. Specifically, when no instruction to execute external loading is issued, the process may return from the process of step S103 to the process of step S102. In this case, if the Fig. 10 is started, the process of step S118 is executed only once.

[0130] In the present embodiment, the process returns from the process of step S113 to the process of step S120; however, the process is not limited to this configuration. Specifically, when no instruction to start the battery system is issued, the process may return from the process of step S113 to the process of step S111. In this case, the process of step S120 is executed only once.

Claims

[1] Electrical storage system, with: an electrical storage device (10) configured to be charged by external charging, wherein the external charging is for carrying out charging with electrical power from an external power supply (29); a voltage sensor (21) configured to detect a voltage value of the electrical storage device (10); a current sensor (22) configured to detect a current value of the electrical storage device (10); and a controller (30) configured to (a) calculate a full charge capacity of the electrical storage device (10) based on a charge state of the electrical storage device (10) at the time when the external charging is started, a charge state of the electrical storage device (10) at the time when the external charging is finished, and an accumulated value of the current value during the period when the external charging is carried out, (b) setting a polarization elimination time, the polarization elimination time being used to determine an eliminated state of a polarization occurring as a result of charging or discharging the electrical storage device (10), (c) to regard a voltage value of the electric storage device (10) at the time of at least one of the start of the external charging or the termination of the external charging as an open-circuit voltage of the electric storage device (10), wherein the voltage value is detected by the voltage sensor (21) when a stopped time during the period when charging or discharging of the electric storage device (10) is stopped is longer than the polarization elimination time, (d) calculating the state of charge corresponding to the voltage value detected by the voltage sensor (21) as the state of charge used to calculate the full charge capacity using a correlation between an open circuit voltage and the state of charge, and (e) to shorten the polarization elimination time as a change rate increases, the change rate indicating a ratio of a variation in the open circuit voltage to a variation in the state of charge. [2] The electric storage system according to claim 1, wherein the controller (30) is configured to, when charging or discharging of the electric storage device (10) is stopped, calculate the variation in the state of charge and the variation in the open circuit voltage based on the state of charge and the open circuit voltage in a period until the charging or discharging is stopped, and also calculate the change rate, and calculate the polarization elimination time corresponding to the calculated change rate using a correlation between the change rate and the polarization elimination time. [3] The electric storage system according to claim 1, wherein the controller (30) is configured to calculate the state of charge at the time when charging or discharging of the electric storage device (10) is stopped, and calculate the polarization elimination time corresponding to the calculated state of charge using a correlation between the change rate and the polarization elimination time and a correlation between the change rate and the state of charge. [4] The electric storage system according to claim 1, wherein the controller (30) is configured to, while charging or discharging of the electric storage device (10) is stopped, calculate the polarization elimination time corresponding to the voltage value detected by the voltage sensor (21) using a correlation between the change rate and the polarization elimination time and a correlation between the change rate and the voltage value. [5] The electric storage system according to claim 4, wherein the controller (30) is configured to, while charging or discharging of the electric storage device (10) is stopped, repeat detection of the voltage value by the voltage sensor (21) and calculate the polarization elimination time corresponding to the detected voltage value each time the voltage value is detected. [6] Electrical storage system according to one of claims 1 to 5, further comprising: a temperature sensor (23) configured to detect a temperature of the electrical storage device (10), wherein the controller (30) is configured to shorten the polarization elimination time as the temperature increases. [7] An electrical storage system for a vehicle, the electrical storage system comprising: an electrical storage device (10) configured to be charged with electrical power from an external power supply (29), wherein the external power supply (29) is installed outside the electrical storage device (10) separately from the electrical storage device (10); a voltage sensor (21) configured to detect a voltage value of the electrical storage device (10); and a controller (30) configured to to calculate a rate of change in an electromotive voltage at at least a first time or a second time, to calculate a predetermined standby time based on the rate of change in the electromotive voltage, to calculate a state of charge of the electrical storage device (10) when the predetermined standby time has elapsed from the first time or the second time, to calculate a full charge capacity of the electrical storage device (10) using the state of charge, and to shorten the predetermined standby time when the rate of change in the electromotive voltage increases, wherein the first time point is a predetermined time point in a period from a time point when an ignition switch of the vehicle is switched to an off state to the time point when charging of the electric storage device (10) with electric power from the external power supply (29) is started, wherein the second time point is a predetermined time point during the period when the vehicle is left standing after charging of the electrical storage device (10) with electrical power from the external power supply (29) is completed, wherein the rate of change in the electromotive voltage is a ratio of a fluctuation in an open-circuit voltage to a fluctuation in a state of charge of the electrical storage device (10).

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