WO2015025212A1

WO2015025212A1 - Electric storage system and full charge capacity estimation method for electric storage device

Info

Publication number: WO2015025212A1
Application number: PCT/IB2014/001575
Authority: WO
Inventors: Koji Aridome; Junta Izumi
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2013-08-23
Filing date: 2014-08-20
Publication date: 2015-02-26
Also published as: JP6197479B2; JP2015040832A

Abstract

An electric storage system includes ah, electric storage device. The electronic control unit executes estimation processing of calculating a present full charge capacity based on a decrease rate from an initial full charge capacity. The electronic control unit also calculates a decrease rate within a period of time in which full charge capacity is not estimated from after a previous full charge capacity has been calculated to a present time by using an average state of charge, an average battery temperature and a decrease rate map, and calculates a first elapsed period of time based on the decrease rate and the initial full charge capacity. The electronic control unit further calculates the present full charge capacity based on a present second elapsed period of time calculated from the first elapsed period and the non-estimation period of time, the decrease rate within the non-estimation period of time, and the initial full charge capacity.

Description

ELECTRIC STORAGE SYSTEM AND FULL CHARGE CAPACITY

ESTIMATION METHOD FOR ELECTRIC STORAGE DEVICE

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to a technique for estimating a full charge capacity of an electric storage device that is installed on a vehicle and supplies power to a drive motor.

2. Description of Related Art

[0002] Secondary batteries degrade and full charge capacity thereof decreases due to changes with time. Where the full charge capacity of a secondary battery decreases, the amount of power that can be used also decreases, and the running distance that can be traveled by a vehicle using electric power (EV running or the like) is shortened. Therefore, where the full charge capacity of a secondary battery under the usage environment cannot be determined with good accuracy, the full charge capacity can be, for example, underestimated. For this reason, the running distance of a vehicle using electric power is shortened by comparison with that corresponding to the decrease in full charge, capacity caused by changes with time.

[0003] Further, the state of charge (SOC) of a secondary battery represents a ratio of the present charge capacity to the full charge capacity, and the charge-discharge process of the secondary battery is controlled on the basis of the SOC. However, where the full charge capacity changes, the SOC also charges. Therefore, charge-discharge control exceeding the usable electric power amount can be performed unless the full charge capacity of the secondary battery is determined with good accuracy.

[0004] A method for accurately estimating the full charge capacity of a secondary battery is described, for example, in Japanese Patent Application Publication No. 2011-7564 (JP 2011-7564 A). In JP 2011-7564 A, the full charge capacity estimation accuracy is increased by calculating the integrated current value and SOC at the charging start time and charging end time during external charging in which a stable charging current is supplied and SOC fluctuations are small.

[0005] The full charge capacity can be estimated with good accuracy by performing full charge capacity estimation processing of a secondary battery during external charging, as described in JP 2011-7564 A, but where external charging is not performed (that is, unless at a specific timing such as external charging), the full charge capacity cannot be estimated. Therefore, where the period of time in which the external charging is not performed is long, the full charge capacity of a secondary battery that degrades with the passage of time cannot be adequately estimated according to the usage environment.

[0006] In other words, where there are few opportunities for (low- frequency of) estimating the full charge capacity decreasing due to changes with time, in addition to the problem associated with the estimation accuracy of the full charge capacity itself, the full charge capacity of a secondary battery under the usage environment cannot be adequately determined.

SUMMARY OF THE INVENTION

[0007] Accordingly, the invention provides an electric storage system and a method for estimating the full charge capacity of an electric storage device that make it possible to estimate accurately the present full charge capacity with reference to a previous full charge capacity at any timing within the usage period of time of the electric storage device, thereby increasing the estimation frequency (opportunities for estimation) of the full charge capacity and enabling adequate determination of full charge capacity.

[0008] According to a first aspect of the invention, ah electric storage system includes an electric storage device configured to perform charging and discharging and an electronic control unit, (a) The electronic control unit is configured to execute estimation processing of calculating a present full charge capacity based on a decrease rate from an initial full charge capacity that is defined in advance according to an elapsed period of time of the electric storage device, (b) The electronic control unit is further configured to calculate a decrease rate within a period of time in which full charge capacity is not estimated, by using an average state of charge over the period of time and an average battery temperature over the period of time, and a decrease rate map in which the decrease rate changes according to the average state of charge and the average battery temperature and the decrease rate is defined in advance. In the period of time, the full charge capacity is not estimated from after a previous full charge capacity has been calculated to a present time, (c) The electronic control unit is further configured to calculate a first elapsed period of time of the electric storage device at the time the previous full charge capacity has been calculated, based on the decrease rate in the period of time in which the full charge capacity is not estimated and the initial full charge capacity, (d) The electronic control unit is also configured to calculate the present full charge capacity based on a present second elapsed period of time of the electric storage device, the decrease rate within the period of time in which the full charge capacity is not estimated, and the initial full charge capacity, the present second elapsed period of time being calculated from the first elapsed period and the period of time in which the full charge capacity is not estimated.

[0009] With the above-described electric storage installed on a vehicle, the present full charge capacity, which changes with respect to the previous full charge capacity, is estimated on the basis of the usage environment (average state of charge and average battery temperature) within the period in which full charge capacity is not estimated from after the previous full charge capacity has been estimated to the present time. Therefore, the present full charge capacity can be estimated with good accuracy with reference to the previous full charge capacity at any timing within the usage period of time of the electric storage device, and the full charge capacity can be estimated not only at the specific timing in the usage period of time of the electric storage device. Therefore, the estimation frequency of full charge capacity can be increased while estimating the full charge capacity with good accuracy.

[0010] In the electric storage system, the ^' electronic control unit may be configured to execute first estimation processing of calculating the full charge capacity of the electric storage device on the basis of a difference in state of charge before and after external charging in which the electric storage device is charged by electric power supplied from an external power supply, and an integrated value of a charging current in the external charging. The electronic control unit may be also configured to execute the estimation processing within the period of time in which the full charge capacity is not estimated, from when the full charge capacity has been calculated during the external charging, until the present time by taking the full charge capacity estimated by the first estimation processing as the previous full charge capacity. In this case, the electronic control unit may be configured to calculate the full charge capacity in the first estimation processing by the following equation.

full charge capacity = current integrated value (∑I)/ASOC x 100

ASOC = SOC_e - SOC s, .

where: ASOC is a difference in SOC before and after charging;

SOC e is a state of charge when the charging is started; and

SOC_s is a state of charge when the charging is ended.

With the above-described electric storage system, the full charge capacity can be estimated with good accuracy even within the period of time in which the external charging is not performed, the number of opportunities for estimating the full charge capacity can be increased, and the full charge capacity of the electric storage device can be adequately determined.

[0011] Further, in the electric storage system, the electronic control unit may be configured to acquire a state of charge and a battery temperature of the electric storage device within the period of time in which full charge capacity is not estimated, a plurality of times at predetermined timings, regardless of whether the vehicle runs or stops. The electronic control unit may be also configured to store the acquired values of the state of charges and the battery temperature together with an elapsed time of the period of time in which the full charge capacity is not estimated, in a predetermined storage area. With the above-described electric storage system, the usage environment, which causes the decrease in full charge capacity, can be determined with good accuracy, and the estimation accuracy of full charge capacity is increased.

[0012] In the electric storage system, the electronic control unit may be configured to execute the estimation processing and also change a predetermined period according to the previous full charge capacity, when the period of time in which the full charge capacity is not estimated exceeds the predetermined period. In this case, an allowed period of time of the period of time in which the full charge capacity is not estimated may be set smaller in relation to a non-estimation period of time for larger previous full charge capacity. With the above-described electric storage system, the full charge capacity can be estimated at any timing by using the period of time, in which full charge capacity is not estimated, as a trigger, and the increase in the period of time in which full charge capacity is not estimated, in other words, the increase in a period of time in which full charge capacity, which changes with time, cannot be determined can be suppressed. Further, since the decrease amount of full charge capacity increases in a state with a large full charge capacity, for example, changes in the full charge capacity can be accurately determined by setting a smaller (shorter) predetermined period of time which is the allowed period of time of the period of time in which full charge capacity is not estimated and increasing the full charge capacity estimation frequency for larger fuel charge capacity.

[0013] Further, in the electric storage system, in the decrease rate map, the decrease rate may be set to be higher as the average state of charge and the average battery temperature, become higher. With such a configuration, where the usage environment factors, which cause the decrease in full charge capacity of the electric storage device, are high, the decrease rate of fuel charge capacity is also set high. Therefore, the full charge capacity can be estimated with good accuracy according to the usage environment of the electric storage device.

[0014] According to a second aspect of the invention, provided is a full charge capacity estimation method for calculating a present full charge capacity based on a decrease rate from an initial full charge capacity that has been defined in advance according to an elapsed period of time of an electric storage device installed on a vehicle. The full charge capacity estimation method includes: a step of calculating an average state of charge over a period of time and an average battery temperature over the period of time, in the period of time the full charge capacity of the electric storage device being not estimated from after a previous full charge capacity has been calculated to a present time; a step of calculating a decrease rate within the period of time in which the full charge capacity is not estimated by using a decrease rate map in which the decrease rate changes according to the average state of charge and the average battery temperature and the decrease rate is defined in advance; a step of calculating a first elapsed period of time of the electric storage device at the time the previous full charge capacity has been calculated, based on the decrease rate within the period of time in which the full charge capacity being not estimated and_' the initial full charge capacity; and a step of calculating a present full charge capacity based on a present second elapsed period of time of the electric storage device, the decrease rate within the period of time in which the full charge capacity is not estimated, and the initial full charge capacity, the present second elapsed period of time being calculated from the first elapsed period of time and the period of time in which the full charge capacity is not estimated. The effects obtained with such a full charge capacity estimation method are the same as those obtained with the above-described power storage system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 shows the configuration of an electric storage system according an embodiment of the invention;

FIG. 2 is a flowchart showing the external charging operation and computation of full charge capacity during the external charging in the electric storage system of the present embodiment; FIG. 3 shows the relationship between the usage period of time of a secondary battery and the decrease in full charge capacity;

FIG. 4 shows the variation of the decrease amount (decrease rate) of full charge capacity for each usage environment of a secondary battery;

FIG. 5 shows the relationship between the usage environment and the decrease rate (slope) of full charge capacity, which is the relationship between the average SOC and average battery temperature of the secondary battery within the period of time in which full charge capacity is not estimated and the decrease rate of full charge capacity;

FIG. 6 illustrates a method for estimating the full charge capacity of a secondary battery in a subsequent period of time in which full charge capacity is not estimated on the basis of the previous estimated full charge capacity in the electric storage system of the present embodiment;

FIG. 7 shows the allowed number of days for the period of time in which full charge capacity is not estimated after the previous full charge capacity has been estimated in the electric storage system of the present embodiment;

FIG. 8 shows the first half of the flowchart illustrating the processing of estimating the present full charge capacity on the basis of the usage environment of the secondary battery within the period of time in which full charge capacity is not estimated after the previous full charge capacity has been estimated in the electric storage system of the present embodiment; and

FIG. 9 is a flowchart illustrating ,the second half of the processing for estimating the present full charge capacity, which follows the processing shown in FIG. 8.

DETAILED DESCRIPTION OF EMBODIMENTS

[0016] Embodiments of the invention are described below.

FIG. 1 shows the configuration of a battery system according to the present embodiment. The battery system shown in FIG. 1 can be installed, for example, on a vehicle. The vehicle is, for example, a plug-in hybrid vehicle (PHV) or an electric vehicle (EV). [0017] In the PHV, in addition to the below-described battery pack, another power source such as an engine or a fuel cell is provided as a power source for driving the vehicle. In the PHV, the battery pack can be charged using electric power from an external power supply. In the PHV equipped with an engine, the battery pack can be also charged by converting the mechanical energy generated by the engine into electric energy and using the obtained electric energy.

[0018] In the EV, only a battery pack is provided as a power source for the vehicle, and the battery pack can be charged by receiving electric power supplied from an external power supply. The external power supply, as referred to herein, is a power supply (for example, a commercial power supply) disposed outside the vehicle and separately therefrom.

[0019] A battery pack (corresponds to an electric storage device) 100 has a plurality of unit cells (correspond to electric storage elements) 10 connected in series. A secondary battery such as a nickel hydride battery or a lithium ion battery can be used as the unit cell 10. Further, an electric double layer capacitor can be used instead of the secondary battery.

[0020] The number of unit cells 10 can be set, as appropriate, according to the required output of the battery pack 100 and the like. In the battery pack 100 of the present embodiment, all of the unit cells 10 are connected in series, but the battery pack 100 may also include a plurality of unit cells 10 connected in parallel.

[0021] A monitoring unit 200 detects a voltage between the terminals of the battery pack 100, or detects a voltage between the terminals of each unit cell 10, and outputs the detection result to an electronic control unit (ECU) 300.

[0022] A temperature sensor 201 detects the temperature of the battery pack 100 (unit cell 10) and outputs the detection result to the ECU 300. In this case, the temperature sensor 201 can be provided at one location of the battery pack 100, or can be provided in a plurality of different locations in the battery pack 100. When the temperatures detected by a plurality of temperature sensors 201 differ from each other, for example, a center value of a plurality of detected temperatures can be used as the temperature of the battery pack 100.

[0023] A current sensor 202 detects an electric current flowing in the battery pack 100 and outputs the detection result to the ECU 300. In the present embodiment, an electric current value detected by the current sensor 202 when the battery pack 100 is discharged is taken as a positive value. An electric current value detected by the current sensor 202 when the battery pack 100 is charged is taken as a negative value.

[0024] In the present embodiment, the current sensor 202 is provided in a positive electrode line PL connected to a position electrode terminal of the battery pack 100, but a position for providing the current sensor 202 can be set, as appropriate, provided that the current sensor 202 can detect the electric current flowing in the battery pack 100. For example, the current sensor 202 can be provided in a negative electrode line NL connected to a negative electrode terminal of the battery pack 100. A plurality of current sensors 202 can be also used.

[0025] The ECU (corresponds to a controller) 300 has a memory 301, and the memory 301 stores various types of information necessary for the ECU 300 to perform predetermined processing (for example, the processing described in the present embodiment). In the present embodiment, the memory 301 is incorporated in the ECU 300, but the memory 301 can be also provided outside the ECU 300.

[0026] System main relays SMR-B and SMR-G are provided in the positive electrode line PL and the negative electrode line NL, respectively. The system main relays SMR-B and SMR-G switch between ON and OFF by receiving control signals from the ECU 300. A system main relay SMR-P and a current limiting resistor 203 are connected in parallel to the system main relay SMR-G, and the system main relay SMR-P and the current limiting resistor 203 are connected in series.

[0027] When the battery pack 100 is connected to an inverter 204 (load), the ECU 300 first switches the system main relay SMR-B from OFF to ON and also switches the system main relay SMR-P from OFF to ON. As a result, an electric current flows in the current limiting resistor 203. In other words, the current limiting resistor 203 is used for suppressing an inrush current when the battery pack 100 is connected to the inverter 204. [0028] Then, the ECU 300 switches the system main relay SMR-G from OFF to ON and then switches the system main relay SMR-P from ON to OFF. As a result, the connection of the battery pack 100 and the inverter 204 is completed, and the battery system shown in FIG. 1 assumes a Ready-On state. Information relating to ON/OFF state of an ignition switch (IG-ON/IG-OFF) of the vehicle is inputted to the ECU 300, and the ECU 300 starts the battery system when the ignition switch is switched from OFF to ON.

[0029] Meanwhile, when the ignition switch is switched from ON to OFF, the ECU 300 switches the system main relays SMR-B and SMR-G from ON to OFF. As a result, the battery pack 100 and the inverter 204 are disconnected from each other, and the battery system assumes a Ready-Off state.

[0030] The inverter 204 converts DC power outputted from the battery pack 100 into AC power, and outputs the converted AC power to a motor generator 205. For example, a three-phase AC motor can be used as the motor generator 205. The motor generator 205 receives the AC power outputted from the inverter 204 and generates kinetic energy for driving the vehicle. The kinetic energy generated by the motor generator 205 is transmitted to wheels, thereby causing the vehicle to run.

[0031] Where the vehicle is decelerated or stopped, the motor generator 205 converts the kinetic energy generated when the vehicle is braked into electric energy (AC power). The inverter 204 converts the AC power generated by the motor generator 205 into DC power and outputs the DC power to the battery pack 100. As a result, the battery pack 100 can store the regenerated power.

[0032] In the present embodiment, the battery pack 100 is connected to the inverter 204, but such a configuration is not limiting. More specifically, the battery pack 100 can be connected to a boosting circuit, and the boosting circuit can be connected to the inverter 204. By using the boosting circuit, it is possible to boost the output voltage of the battery pack 100. Further, the boosting circuit can lower the voltage outputted from the. inverter 204 to the battery pack 100.

[0033] A charger 206 is connected to the positive electrode line PL and the negative electrode line NL. More specifically, the charger 206 is connected to both the positive electrode line PL and the negative electrode line NL. In this case, the positive electrode line PL connects the positive electrode terminal of the battery pack 100 to the system main relay SMR-B. The negative electrode line NL connects the negative terminal of the battery pack 100 to the system main relay SMR-G. An inlet (connector 207) is connected to the charger 206.

[0034] Charging relays Rchl and Rch2 are provided in the lines connecting the charger 206 to the lines PL and NL. The charging relays Rchl and Rch2 switch between ON and OFF by receiving control signals from the ECU 300.

[0035] A charging plug (connector) extended from an external power supply 208 is connected to the inlet 207. By connecting the charging plug to the inlet 207, it is possible to supply electric power from the external power supply 208 to the battery pack 100 through the charger 206. As a result, the battery pack 100 can be charged by the external power supply 208. When the external power supply 208 supplies AC power, the charger 206 converts the AC power from the external power supply (208) into DC power and supplies the DC power to the battery pack 100. The ECU 300 can control the operation of the charger 206.

[0036] When the electric power is supplied from the external power supply 208 to the battery pack 100, the charger 206 can also convert the voltage. In this case, the operation of supplying the electric power from the external power supply 208 to the battery pack 100 and charging the battery pack 100 when the vehicle is stopped is called "external charging". In the battery system of the present embodiment, the electric power is supplied from the external power supply 208 to the battery pack 100 when the charging relays Rchl and Rch2 are ON. When the external charging is performed, a constant current can be supplied to the battery pack 100, and the battery pack 100 can be charged by the constant current. During the external charging, the system main relays SMR-B and SMR-G can be set OFF.

[0037] The system that supplies the electric power from the external power supply 208 to the battery pack 100 is not limited to that shown in FIG 1. For example, the charger 206 can be connected to the battery pack 100 through the system main relays SMR-B, SMR-P, and SMR-G. More specifically, the charger 206 can be connected through the charging relays Rchl and Rch2 to the positive electrode line PL connecting the system main relay SMR-B and the inverter 204, and the negative electrode line NL connecting the system main relay SMR-G and the inverter 204. In this case, the external charging can be performed by switching the charging relays Rchl and Rch2 and the system main relays SMR-B and SMR-G from OFF to ON.

[0038] In the present embodiment, the external charging is performed by connecting the charging plug to the inlet 207, but such a configuration is not limiting. More specifically, the electric power of the external power supply 208 can be supplied to the battery pack 100 by using the so-called contactless charging system. In the contactless charging system, electric power can be supplied by using electromagnetic induction or a resonance effect, without using a cable. Conventional configurations can be used, as appropriate, as the contactless charging system.

[0039] In the present embodiment, the charger 206 is installed on the vehicle, but such a configuration is not limiting. Thus, the charger 206 may be disposed outside of the vehicle and separately therefrom. In this case, the ECU 300 can control the operation of the charger 206 by communication between the ECU 300 and the charger 206.

[0040] The ECU 300 can calculate (estimate) the SOC of the battery pack 100 on the basis of the voltage value detected by the monitoring unit 200, battery temperature detected by the temperature sensor 201, and current value detected by the current sensor 202, and can perform charge-discharge control of the battery pack 100 on the basis of the calculated SOC and estimated value of full charge capacity. The ECU 300 can be configured to include the functions of a SOC estimation unit, a full charge capacity calculation unit, and an external charging control unit.

[0041] The SOC of the battery pack 100 is a ratio (stage of charge) of the present charge capacity to the full charge capacity of the battery pack 100. The full charge capacity is thus the upper limit value of SOC. The SOC can be specified on the basis of the open circuit voltage (OCV) of the battery pack 100. For example, the correspondence relationship between the OCV and SOC of the battery pack 100 is stored in advance in a memory 301 as an OCV-SOC map. The ECU 300 can calculate the OCV of the battery pack 100 from the voltage (closed circuit voltage (CCV)) detected by the monitoring unit 200, and then calculate the SOC from the OCV-SOC map.

[0042] The correspondence relationship of OCV and SOC of the battery pack 100 varies according to the battery temperature. Therefore, the OCV-SOC map may be stored in the memory 301 for each battery temperature, and the SOC of the battery pack 100 may be estimated by switching (selecting) the SOC-OCV map according to the battery temperature when the SOC is estimated from the OCV of the battery pack 100.

[0043] As a result, the ECU 300 can determine the overcharge state or overdischarge state of the battery pack 100 by monitoring the voltage value (CCV) detected by the monitoring unit 200 during charging and discharging. For example, the charging of the battery pack 100 can be restricted such that the calculated SOC does not become higher than a predetermined upper_^limit SOC corresponding to the full charge capacity, or the charge-discharge control can be performed to restrict discharging such that the calculated SOC does not become lower than a lower-limit SOC. ,

[0044] The ECU 300 can be also provided for each inverter 204 and motor generator 205, and a separate ECU for performing the SOC estimation processing, full charge capacity estimation processing, and external charging processing can be provided independently from the vehicle control. In other words, a configuration in which a central control device that controls the entire vehicle controls each unit, or a configuration in which individual ECU is provided for controlling each unit and the central control device is connected to each individual ECU may be used.

[0045] The full charge capacity of the battery pack 100 can be calculated by Eq. (1) below.

Eq. (1) Full charge capacity = current integrated value (∑I)/(SOC_e - SOC_s) x 100.

[0046] In Eq. (1), the full charge capacity is the full charge capacity of the battery pack 100 based on actually measured values from the monitoring unit 200 or the current sensor 202. The SOC s (SOC at the start of charging) is the SOC of the battery pack 100 when the integration of current is started in the external charging, and the SOC_e is the SOC of the battery pack 100 at the time the integration of current is ended. The integrated current value is a value obtained by integrating the external charging current of the battery pack 100 over an interval of time from after the SOC s is calculated until the SOC_e is calculated. A value obtained by subtracting the SOC_s from the SOC e represents the change in SOC during the external charging (SOC difference = ASOC), and the full charge capacity of the battery pack 100 can be calculated from the ratio of the current value to the change in SOC.

[0047] In the SOC estimation processing during the external charging, a voltage between the terminals of the battery pack 100 in a state immediately before or immediately after connection to the load or the charger 206 is detected with the monitoring unit 200, thereby making it possible to use the voltage value detected by the monitoring unit 200 as the OCV and calculating the SOC from the OCV-SOC map.

[0048] FIG. 2 is a flowchart showing the external charging operation and computation of full charge capacity in the present embodiment. As shown in FIG. 2, the ECU 300 can perform the full charge capacity computational processing as the external charging proceeds. The ECU 300 detects whether or not the charging plug connected to the external power supply 208 is connected to the inlet 207 (S I 01), and can start the external charging when the connection of the charging plug is detected (S I 02).

[0049] Initially, the ECU 300 calculates the SOC at the charging start timing, at which the battery pack 100 is to be charged, from a voltage value OCV1 detected by the monitoring unit 200 when the charging is started, and stores the calculated SOC1 as the SOC_s in the memory 301 (S103). Then, the ECU 300 starts the input of charging power by supplying the power of the external power supply 208 to the battery pack 100 through the charger 206, and also starts the integration processing of the charging current flowing in the battery pack 100 (S104). The ECU 300 monitors the voltage value in the battery pack 100, and when a voltage value corresponding to the predetermined SOC upper limit value corresponding to charging end is reached, ends the supply of electric power from the external power supply 208 to the battery pack 100 (YES in SI 05) and ends the integration processing of the charging current. [0050] Then, the ECU 300 calculates a SOC2 at the charging end time from a voltage value OCV2 detected by the monitoring unit 200 when the charging is ended, and stores the SOC2 calculated after the charging is ended as the SOC e in the memory 301 (S106). ¹

[0051] The ECU 300 calculates the full charge capacity of the battery pack 100 as shown by Eq. (1) above on the basis of a difference (ASOC = SOC_e - SOC_s) between SOC before and after the external charging and the integrated value of the charging current during the external charging (S I 07). The ECU 300 then starts measuring a period of time in which full charge capacity is not estimated after the end of estimation processing of the full charge capacity during the external charging and until the full charge capacity estimation processing at the time of the next external charging is performed, and performs preparatory processing for full charge capacity estimation processing performed outside the external charging time within the period of time in which full charge capacity is not estimated (SI 08).

[0052] During the external charging, a constant charging current flows to the battery pack 100 and, therefore, the integrated current value can be calculated with good accuracy. Further, in the external charging performed when the vehicle is stopped, a state is assumed in which large SOC fluctuations in the battery pack 100 are suppressed. Therefore, the SOCl at the charging start time and the SOC2 at the charging end time can be calculated with good accuracy. As a result, the full charge capacity can be estimated with good accuracy on the basis of charging-discharging history during the external charging.

[0053] However, as mentioned hereinabove, where the estimation frequency of full charge capacity is small-, the full charge capacity at the present time, which decreases (degrades) due to changes with time, cannot be adequately determined. In other words, where the period from after the full charge capacity has been estimated until the next estimation of the full charge capacity (the period of time in which full charge capacity is not estimated; referred to hereinbelow as "non-estimation period of time") is long, the charge and discharge of the battery pack 100 is controlled in a state in which the full charge capacity cannot be adequately determined.

[0054] For example, where the charge-discharge control is performed with reference to the previously estimated full charge capacity, despite the fact that the present full charge capacity is less than the previously estimated full charge capacity, an underestimated SOC is calculated with respect to the charged power and an overestimated SOC is calculated with respect to the discharged power. Where the SOC is underestimated with respect to the charged power, the usable power decreases, and the running distance (EV running) of the vehicle using the electric power of the battery pack 100 is shortened. Where the SOC is overestimated with respect to the discharged power, overdischarge occurs that exceeds the lower limit value of SOC.

[0055] Thus, where the number of opportunities for (frequency of) estimation processing of the full charge capacity decreasing with the passage of time decreases, a state is reached in which the present full charge capacity of the secondary battery under the usage environment cannot be determined with good accuracy. In particular, when the estimation processing of full charge capacity is performed at a specific timing, such as during the external charging, where the external charging is not performed, the full charge capacity cannot be estimated and the number of opportunities for estimating the full charge capacity decreases. Therefore, the charge-discharge control cannot be performed in a state with an adequately determined full charge capacity.

[0056] Accordingly, in the present embodiment, the estimation of full charge capacity, which decreases in response to the usage environment of the battery pack 100, is enabled in the non-estimation period of time after the previous full charge capacity has been estimated. Thus, although the external charging is not performed frequently, in other words, although the estimation processing of full charge capacity based on charge-discharge history associated with the external charging is not performed frequently, the estimation of full charge capacity based on the usage environment of the battery pack 100 is performed within the period from after the previous full charge capacity has been calculated until the next full charge capacity is estimated. Thus, the number of opportunities for estimating the full charge capacity is increased and the full charge Capacity can be determined adequately and with good accuracy.

[0057] FIG. 3 shows the relationship between the usage period of time of the battery pack 100 and the decrease in full charge capacity. In FIG. 3, the usage period of time (for example, the number of days) of the battery pack 100 is plotted against the abscissa, and the full charge capacity is plotted against the ordinate. In the figure, CO is a full charge capacity at the initial stage of production of the battery pack 100.

[0058] Factors affecting the decrease in full charge capacity of the battery pack 100 (battery degradation) include the battery temperature, SOC (voltage), and elapsed time under the usage environment of the battery pack 100. Therefore, by determining the usage environment of the battery pack 100 corresponding to the factors affecting the degradation, for example, the battery temperature environment under which the battery pack has been used and the SOC state environment under which the battery pack has been used in the usage period of time, it is, possible to determine the usage period of time of the battery pack 100 and the decrease in full charge capacity and also to determine the full charge capacity from the present usage period of time.

[0059] The usage period of time, as referred to herein, is a period from the initial stage of production until the present time. The. usage period of time also includes a state in which the charge-discharge operation is performed (for example, the ON state of the ignition switch of the vehicle) and a state in which the charge-discharge operation is not performed (for example, the OFF state of the ignition switch of the vehicle). This is because, for example, under the environment with a high battery temperature or a high SOC, the degradation of the battery pack 100 advances even when the charge-discharge operation is not performed.

[0060] As shown in FIG 3, where a plurality of values of full charge capacity of the battery pack 100 and the usage period of time at the corresponding time is plotted, it is clear that the full charge capacity decreases from the full charge capacity CO at the initial stage of production with the increase in the usage period of time. The degradation curve in FIG. 3 shows the decrease amount of the full charge capacity of the battery pack 100 against the time elapsed before the present time, in other words, the decrease amount (degree of degradation) of the present full charge capacity with respect to the full charge capacity CO at the initial stage of production.

[0061] In FIG. 3, a first degradation transition and a second degradation transition, which are shown by curves, represent the transition of degradation in states with different usage environments. For example, the degradation curves differ correspondingly to the average battery temperature or average SOC of the battery pack 100 in the usage period of time. This is because, as described above, the change in the full charge capacity with time becomes a degradation transition map that differs for each factor (usage environment of the battery pack 100) affecting the degradation.

[0062] FIG. 4 shows the relationship between the variation of the decrease amount (decrease rate) of full charge capacity and the usage period of time for each usage environment of the battery pack 100. In FIG. 4 the square root of the time elapsed under each usage environment (A/(usage period of time)) is plotted against the abscissa, and the full charge capacity of the battery pack 100 is plotted against the ordinate. The straight lines in the figure correspond to the first degradation transition and second degradation transition shown in FIG. 3.

[0063] As shown in FIG. 4, the decrease rate of the full charge capacity against the elapsed time in the battery pack 100 can be represented by a straight line, which has a negative slope with respect to the full charge capacity CO at the initial stage of production, by plotting a square root of elapsed time, rather than the elapsed time as in FIG. 3, on the abscissa. In other words, the change in full charge capacity of the battery pack 100 is a transition against the elapsed time, which has a predetermined slope (decrease rate) which differs according to the battery temperature and SOC. The decrease rate of full charge capacity against the elapsed time, which differs according to the battery temperature and SOC, as shown in FIG. 4 can be determined by preliminary tests, or the like. The results can be saved in the memory 301 as a degradation transition map that differs according to the battery temperature and SOC.

[0064] In FIG. 4, for example, where the full charge capacity of the previous estimation is denoted by C 1 , the full charge capacity of the battery pack 100 decreases by AC (= CO - CI) with respect to the full charge capacity CO at the initial stage of production. Where the decrease rate of full charge capacity, such as shown in FIG. 4, is obtained, the decrease amount of full charge capacity corresponding to the elapsed time from the point of time at which the previous full charge capacity has been estimated until the present time can be determined and the full charge capacity at the present time can be calculated.

[0065] However, as mentioned hereinabove, where the usage environment of the battery pack 100 is different, the decrease rate from the full charge capacity CO to the full charge capacity CI is also different. Since the slope (decrease rate) of the second degradation transition is larger than that of the first degradation transition, the full charge capacity C 1 can be reached earlier than with the first degradation transition with respect to the usage period of time of the battery pack 100. In other words, as shown in FIG. 4, the decrease amount of full charge capacity against the elapsed time of the battery pack 100 before the present time is different at the decrease rate (first slope) following the first degradation transition from a point X and the decrease rate (second slope) following the second degradation transition from a point Y even at the same full charge capacity CI .

[0066] Thus, where the decrease rate of full charge capacity at which the present full charge capacity is reached from the point of time at which the previous full charge capacity has been estimated cannot be determined, in other words, the slope at which the full charge capacity of the battery pack 100 decreases cannot be determined, the decrease amount of full , charge capacity against the usage period of time of the battery pack 100 cannot be accurately determined.

[0067] Accordingly, in the present embodiment, the decrease rate of full charge capacity is determined on the basis of the average battery temperature and average SOC of the battery pack 100 from after the full charge capacity has been estimated on the basis of the charge-discharge history during the external charging until the present full charge capacity is calculated, that is, on the basis of the usage environment of the battery pack 100, and the transition in decrease from the previously calculated full charge capacity to the present time, at which the present full charge capacity is calculated, is estimated with consideration for the usage environment of the battery pack 100. [0068] FIG. 5 shows the relationship (corresponds to the decrease rate map) between the average battery temperature, average SOC and decrease rate of full charge capacity of the battery pack 100. In this case, the average battery temperature is a value obtained by averaging the battery temperature of the battery pack 100, which is measured at predetermined intervals, by the measurement frequency of battery temperature, time, number of days and the like. For example, the average battery temperature can be calculated by adding up battery temperatures measured at predetermined intervals and calculating the time average of the sum of battery temperatures (∑ of battery temperatures).

[0069] Similarly to the average battery temperature, the average SOC is a value obtained by averaging the SOC of the battery pack 100, which is measured at predetermined intervals (detection timing same as or different from that of the battery temperature), by the SOC measurement frequency, time, number of days and the like. For example, the average SOC can be calculated by adding up SOC measured at predetermined intervals and calculating the time average of the sum of SOC (∑SOC).

[0070] As shown in FIG. 5, the higher is the average battery temperature, the larger is the decrease rate of full charge capacity, and the higher is the average SOC, the larger is the decrease rate of full charge capacity. In other words, as mentioned hereinabove, where the deterioration factors (factors decreasing the full charge capacity) of the battery pack 100 under the usage environment produce a large effect, a large decrease rate (slope) of full charge capacity is set. Meanwhile, where the degradation factors of the battery pack 100 under the usage environment produce a small effect when the average battery temperature is low and the average SOC is low, a small decrease rate of full charge capacity is set. With such a configuration, it is possible to estimate the full charge capacity with good accuracy according to the usage environment of the battery pack 100. The relationship between the average battery temperature, average SOC, and decrease rate of full charge capacity of the battery pack 100, which is shown in FIG. 5, can be determined by preliminary tests or the like and can be stored in the memory 301.

[0071] FIG. 6 illustrates a method for estimating the full charge capacity of the battery pack 100 in the subsequent non-estimation period of time on the basis of the full charge capacity estimated during the previous external charging. In FIG. 6, the square root of the elapsed time under the usage environments (V(usage period of time)) is plotted against the abscissa, and the full charge capacity of the battery pack 100 is plotted against the ordinate.

[0072] The previous full charge capacity estimated during external charging is denoted by CI . The point X in FIG. 6 indicates the previous full charge capacity CI , but the relationship between the full charge capacity CI and the decrease rate of full charge capacity before the present time at which the present full charge capacity is calculated is unclear. Therefore, although the point X is associated with the full charge capacity CI, it is not associated with the V(usage period of time) of the battery pack 100.

[0073] For this reason, the decrease rate of full charge capacity, which changes against the usage period of time of the battery pack- 100, is specified (calculated) in order to determine the nature of the transition by which the full charge capacity decreases after the previous full charge capacity has been estimated until the present time. This decrease ratio of full charge capacity is calculated (see FIG. 5) on the basis of a map in which the relationship between the average battery temperature, average SOC, and decrease rate of full charge capacity of the battery pack 100 has been defined in advance. As mentioned hereinabove, the average battery temperature and average SOC of the battery pack 100 are average values of battery temperature and SOC measured within a period of time in which full charge capacity is not estimated, namely, from after the previous full charge capacity has been estimated until the present time.

[0074] Where the decrease rate of full charge capacity is specified, the decrease transition of full charge capacity corresponding to the usage period of time of the battery pack 100, for which the full charge capacity CO at the initial stage of production is taken as a reference, can be specified. As shown in FIG. 6, a straight line represented by the decrease rate of a third slope can be determined as a third degradation transition corresponding to the average battery temperature and average SOC in the non-estimation period of time.

[0075] The previous full charge capacity CI is then associated with the degradation transition of the third slope. As shown in FIG. 6, the crossing point Y of the straight line that is parallel to the abscissa and determined between two points, namely, the full charge capacity CI and the point X, and the straight line determined by the full charge capacity CO and the third slope becomes the full charge capacity CI in which the full charge capacity decreases at a decrease rate of the third slope. By using the point Y, it is possible to calculate the " (usage period of time Tl)" of the battery pack 100 corresponding to the full charge capacity C 1 in the relationship between the usage time and the variation in full charge capacity determined by the third slope.

[0076] In other words, the "V(usage period of time Tl)" of the battery pack 100 corresponding to the full charge capacity CI corresponds to the elapsed time of the battery pack 100 at the time the previous full charge capacity CI has been estimated. For example, the previous full charge capacity becomes as follows:

Eq. (2): CI = CO - Q ^χ V(usage period of time Tl).

Here, Q is the decrease rate (third slope) of the full charge capacity specified by the average battery temperature and average SOC.

[0077] In this case, where Eq. (2): CI = CO - Q x V(usage period of time Tl) is transformed with respect to the (usage period of time Tl),

Eq. (3): V(usage period of time Tl) = (CO - Cl)/Q is obtained.

Since the full charge capacity CO at the initial stage of production, decrease rate Q, and previous full charge capacity CI can be determined in advance, the V(usage period of time Tl) can be calculated.

[0078] By adding the non-estimation period of time to the calculated (usage period of time Tl) corresponding to the previous full charge capacity CI , it is possible to calculate the V(usage period of time T2) at the present time at which the present full charge capacity is calculated. By calculating the V(usage period of time T2) at the present time, it is possible to calculate a full charge capacity C2 at the present time, which corresponds to the decrease rate Q of full charge capacity determined by the third slope. In the example shown in FIG. 6, by calculating the V(usage period of time T2), it is possible to specify a point Z on the straight line of full charge capacity having the third slope and calculate the full charge capacity C2 corresponding to the point Z. For example, the present full charge capacity C2 can be calculated from such a relationship by the following equation.

Eq. (4): C2 = CO - Q x V(usage period of time T2)

[0079] The usage period of time corresponding to the V(usage period of time T2) can be calculated by adding up the second power of the V(usage period of time Tl) corresponding to the previously calculated full charge capacity CI and the non-estimation period of time. The V(usage period of time T2) corresponding to the third slope can be calculated by calculating the root square of the calculated value.

[0080] FIG. 7 shows the allowed number of days for the period of time in which full charge capacity is not estimated after the previous full charge capacity has been estimated. In FIG. 7, the allowed period of time in which full charge capacity is not estimated is plotted against the ordinate, and the full charge capacity is plotted against the abscissa.

[0081] The allowed period of time defines a period of time, after the previous full charge capacity has been estimated, in which the full charge capacity should be estimated. In the present embodiment, the elapsed time of the non-estimation period of time after the full charge capacity estimation during the external charging is taken as a trigger, the full charge capacity estimation is periodically performed even though the external charging is not performed, and the full charge capacity is determined with good accuracy while ensuring the opportunity for estimating the full charge capacity.

[0082] As shown in FIG. 7, the full charge capacity CO at the initial stage of production is taken as a reference for the allowed period of time, the allowed period of time extends with the decrease in full charge capacity, and where the full charge capacity becomes less than a threshold C_th (< CO), a constant allowed period of time is set. Such settings are selected so that in a state with a large full charge capacity, since the decrease amount is large, the spacing between the full charge capacity estimation processing operations could be shortened by setting a short allowed period of time, and the full charge capacity could be adequately determined. As shown in the example in FIG. 3, the full charge capacity decreases from the full charge capacity CO at the initial stage of production due to changes with time as the usage period of time of the battery pack 100 elapses, but the larger is the full charge capacity, the larger is the decrease amount of the full charge capacity in the usage period of time, and as the full charge capacity decreases, the decrease amount of the full charge capacity in the usage period of time becomes small. Therefore, as shown in FIG. 7, the amount of the full charge capacity for which the allowed period of time B is set is larger than the full charge capacity C2 for which the allowed period of time A, Which is longer than the allowed period of time B, is set. As the full charge capacity of the battery pack 100 decreases, a longer allowed period of time is set and the spacing of the estimation processing operations of the full charge capacity is increased.

[0083] Thus, in the present embodiment, the full charge capacity can be accurately estimated at any timing after the previous full charge capacity estimation by using the elapsed time of the non-estimation period of time as a trigger, and the increase in the non-estimation period of time, in other words, the increase in a period of time in which the full charge capacity, which changes with time, cannot be determined can be suppressed. Further, in a state with a larger previous full charge capacity, changes in the full charge capacity can be accurately determined by setting a shorter allowed period of time for the non-estimation period of time and increasing the full charge capacity estimation frequency.

[0084] The allowed period of time can be set after the full charge capacity estimation processing during the external changing. In the full charge capacity estimation processing during the external charging that is shown in FIG. 2, the ECU 300 executes step SI 07. In the preparatory processing of step SI 07, the allowed period of time is calculated from the newest full charge capacity that has been estimated during the external charging by using the map shown in FIG. 7, and the allowed period of time for the non-estimation period of time after the full charge capacity estimation can be set.

[0085] The preparatory processing can be executed not only during the external charging, but also after the full charge capacity estimation processing that is executed using the allowed period of time as a trigger. In other words, the ECU 300 executes the preparatory processing each time the full charge capacity is estimated during the external charging or each time the full charge capacity is estimated not necessarily during the external charging, and the full charge capacity can be estimated at a predetermined timing within the non-estimation period of time after the full charge capacity estimation.

[0086] FIG. 8 is a flowchart showing the processing of estimating the present full charge capacity on the basis of the usage environment of the battery pack 100 within the non-estimation period of time after the previous full charge capacity has been estimated. FIG. 9 is a flowchart illustrating the estimation processing of full charge capacity following the processing shown in FIG. 8.

[0087] The processing shown in FIGS. 8 and 9 is executed by the ECU 300 regardless of the ON/OFF state of the ignition switch of the vehicle and regardless of whether or not the external charging is performed.

[0088] The ECU 300 measures the non-estimation period of time after the previous full charge capacity has been estimated and measures the battery temperature and SOC of the battery pack 100 for each elapsed hour. The ECU 300 increments the 1-h time counter C_lh each minute (S301). The ECU 300 determines whether or not 1 h has elapsed, in other words, whether or not the 1-h time counter C lh has exceeded 60 (S302). Where 1 h has not elapsed, the increment processing of the 1 -h time counter C_lh of step S301 is executed each minute.

[0089] Where it is determined in step S302 that 1 h has elapsed, the ECU 300 increments a non-estimation time counter C_24h (S303). The non-estimation time counter C_24h operates in 1 -h units corresponding to the 1-h time counter C lh, and is incremented each time 1 h elapses after the previous full charge capacity has been estimated.

[0090] The ECU 300 acquires the detected values of voltage and battery temperature of the battery pack 100 from the monitoring unit 200 and the temperature sensor 201 each time 1 h elapses after the previous full charge capacity has been estimated (S304). In step S305, the ECU 300 performs SOC estimation processing on the basis of the detected voltage value, and then performs SOC integration processing of calculating the∑SOC on the basis of the estimated SOC. Likewise, in step S360, the ECU 300 performs the battery temperature integration processing of calculating ∑(battery temperature) by using the calculated battery temperature.

[0091] In the present embodiment, the SOC and battery temperature of the battery pack 100 in the non-estimation period of time are acquired a plurality of times at predetermined timings, regardless of whether the vehicle runs or stops, and the acquired SOC and battery temperature are stored together with the elapsed time of the non-estimation period of time in the memory 301. Therefore, the usage environment, which causes the decrease in full charge capacity, can be determined with good accuracy, and the estimation accuracy of full charge capacity based on the average SOC and average battery temperature is increased.

[0092] The 1-h time counter C lh, non-estimation time counter C_24h,∑SOC, and∑(battery temperature) are each initialized (= 0) in the preparatory processing, of step Si 07. In other words, the processing of measuring the time after the full charge capacity has been estimated and the processing of determining the usage environment are used, and calculations are performed anew for full charge capacity estimation processing in the non-estimation period of time each time the newest full charge capacity is estimated.

[0093] The ECU 300 acquires the allowed period of time A that has been set by the preparatory processing in step S I 07 (S307), and determines whether or not the non-estimation period of time at the present time exceeds the allowed period of time following the increment processing of the non-estimation time counter C_24h, SOC integration processing, and battery temperature integration processing (S308). For example, where the units of the allowed period of time A are "days", it can be determined whether the allowed period of time Ax24 is equal to or greater than the value of the non-estimation time counter C_24h,

[0094] When it is determined that the time elapsed after the previous full charge capacity has been estimated exceeds the allowed period of time, the ECU 300 starts the estimation processing of full charge capacity based on the usage environment.

[0095] The ECU 300 calculates the average SOC and average battery temperature of the battery pack 100 in the non-estimation period of time (elapsed time) after the previous full charge capacity has been estimated (S309). The average SOC and average battery temperature can be calculated by dividing the ∑SOC calculated in the SOC integration processing of step S305 and the∑(battery temperature) calculated in the battery temperature integration processing of step S306 by the non-estimation time counter C_24h.

[0096] In step S310, the ECU 300 initializes the 1-h time counter C_lh, non-estimated time counter C_24h,∑SOC, and∑(battery temperature). The initialization processing of step S310 is performed with the same objective as the preparatory processing of step SI 07 in FIG. 2, and the counters and parameters are initialized as the preparatory processing of the full charge capacity estimation processing of the next cycle based on the usage environment of the battery pack 100.

[0097] Where the ECU 300 calculates the average SOC and average battery temperature of the battery pack 100 before the present time within the non-estimation period of time (elapsed time) after the previous full charge capacity has been estimated, the decrease rate of full charge capacity of the battery pack 100 that varies with the passage of time is calculated with reference to the map in which the relationship between the average battery temperature, average SOC, and decrease rate of full charge capacity of the battery pack 100 shown in FIG. 5 has been defined in advance (S311).

[0098] Where the decrease rate of full charge capacity is specified in S311 from the average battery temperature and average SOC of the battery pack 100 before the present time within the non-estimation period of time (elapsed time) after the previous full charge capacity has been estimated,, the ECU 300 then calculates the " A/(usage period of time Tl)" corresponding to the elapsed time of the battery pack 100 at the time the previous full charge capacity has been estimated (S312). The "V(usage period of time Tl)" can be calculated by

Eq. (5): "V(usage period of time Tl)" = (full charge capacity at the initial stage of production (CO) - previous full charge capacity (Cl))/decrease rate (Q).

[0099] Then, the ECU 300 calculates the usage period of time corresponding to the "V(usage period of time T2)" of the battery pack 100 at the present time at which the present full charge capacity is calculated (S313). The ECU 300 adds up the second power of the "V(usage period of time Tl)" calculated in step S312 and the non-estimation period of time A, and calculates the usage period of time corresponding to the "V(usage period of time T2)". Then, the ECU 300 calculates the square root of the calculated sum of the second power of the "V( usage period of time Tl)" and the non-estimation period of time A, and calculates the " (usage period of time T2)" corresponding to the third slope (S314). The present full charge capacity is then calculated by the following formula: "present full charge capacity (C2) = full charge capacity at the initial stage of production (CO) - decrease ratio (Q) x V(usage period of time T2)" (S315).

[0100] The ECU 300 stores the calculated present full charge capacity (C2) in the memory 301 and calculates the allowed period of time (A) corresponding to the present full charge capacity from the map which prescribes the allowed number of days for the non-estimation period of time after the previous full charge capacity has been estimated as a preparatory processing for the estimation processing of full charge capacity of the next cycle that is based on the usage environment of the battery pack 100 (S316). The ECU 300 then sets the allowed number of days calculated in S316 as the allowed period of time.

[0101] Thus, in the full charge capacity estimation processing of the present embodiment, the present full charge capacity is calculated on the basis of the decrease rate from the initial full charge capacity (CO) that has been defined in advance according to the elapsed period of time of the battery pack 100. In this case, the ECU 300 initially calculates the decrease rate (Q) within the period of time in which full charge capacity is not estimated by using the average SOC and average battery temperature over the period of time in which full charge capacity is not estimated from when the previous full charge capacity has been calculated until the present time and also the decrease rate map in which the decrease change that changes in response to the average SOC and average battery temperature has been defined in advance. , Then, the first elapsed period of time (A/(usage period of time Tl)) corresponding to the time at which the previous full charge capacity has been calculated is calculated on the basis of the decrease rate (Q) within the period of time in which full charge capacity is not estimated and the initial full charge capacity (CO). The present full charge capacity is then calculated on the basis of the present second elapsed period of time (V(usage period of time T2)) of the battery pack 100, which is calculated from the first elapsed period of time (V(usage period of time Tl)) and the period of time (A) in which the full charge capacity is not estimated, the decrease rate (Q) within the period of time in which the full charge capacity is not estimated, and the initial full charge capacity (CO).

[0102] With such a configuration, the present full charge capacity can be estimated with good accuracy with reference to the previous full charge capacity at any timing within the usage period of time of the battery pack 100, and the full charge capacity can be estimated not only at the specific timing in the usage period of time of the battery pack 100. Therefore, the estimation frequency of full charge capacity can be increased while estimating the full charge capacity with good accuracy.

[0103] In particular, even when the full charge capacity estimation processing is performed during the external charging, the full charge capacity can be estimated with good accuracy within the period of time in which the external charging is not performed, the number of opportunities for estimating the full charge capacity can be increased, and the full charge capacity of the electric storage device can be adequately determined.

[0104] Further, the full charge capacity estimation processing of the present embodiment in which the present full charge capacity is estimated with good accuracy with reference to the previous full charge capacity at any timing within the usage period of time of the battery pack 100 can be performed a plurality of times within the period of time in which full charge capacity is not estimated. In this case, the present full charge capacity can be calculated by using the full charge capacity obtained by the full charge capacity estimation processing based on the usage environment of the present embodiment as the previous full charge capacity. In other words, even when the previous full charge capacity has not been calculated on the basis of charge-discharge history during the external charging, the present full charge capacity can be estimated with good accuracy with reference to the previous full charge capacity at any timing within the usage period of time of the battery pack 100 on the basis, of the average SOC and average battery temperature from after the previous full charge capacity has been calculated until the present time.

[0105] The full charge capacity estimation processing shown in FIGS. 8 and 9 is configured such that the initialization is performed each time the full charge capacity is calculated by the full charge capacity estimation processing based on the charge-discharge history at the time of external charging. This is because the full charge capacity calculated by the full charge capacity estimation processing based on the charge-discharge history at the time of external charging has a high estimation accuracy, as mentioned hereinabove, and therefore the estimation accuracy of the full charge capacity based on the average SOC and average battery temperature, which is performed within the period of time in which full charge capacity is not estimated, is increased.

[0106] Further, in the present embodiment, charge-discharge control of the battery pack 100 can be performed using a full charge capacity learning value obtained by learning in time series the full charge capacity that is sequentially calculated. For example, the presently calculated full charge capacity and the learning value of full charge capacity that has been previously calculated can be used to perform the following calculation:

Eq. (6): Full charge capacity learning value = previous full charge capacity learning value x (1 - K) + full charge capacity (actually measured value) x K.

Here K is a reflection coefficient (learning parameter) determining the ratio of the actually measured full charge capacity and previous full charge capacity learning value included in the full, charge capacity learning value that is to be presently measured. K is a value within a range from 0 to 1, and the full charge capacity learning value can be calculated using any value thereof within this range.

[0107] In this case, the present full charge capacity estimation processing based on the usage environment of the battery pack 100 within the period of time in which full charge capacity is not estimated can. be configured to use the newest full charge capacity learning value for the previous full charge capacity and reflect the present full charge capacity, which has been estimated according to the usage environment, as the actually measured full charge capacity value in the full charge capacity learning value.

Claims

CLAIMS:

1. An electric storage system installed on a vehicle, the electric storage system comprising:

an electric storage device configured to perform charging and discharging; and an electronic control unit configured to

(a) execute estimation processing of calculating a present full charge capacity based on a decrease rate from an initial full charge capacity that is defined in advance according to an elapsed period of time of the electric storage device,

(b) calculate a decrease rate within a period of time in which full charge capacity is not estimated, by using an average state of charge over the period of time, an average battery temperature over the period of time, and a decrease rate map in which the decrease rate changes according to the average state of charge and the average battery temperature and the decrease rate is defined in advance, in the period of time the full charge capacity being not estimated from after a previous full charge capacity has been calculated to a present time, ;

(c) calculate a first elapsed period of time of the electric storage device at the time the previous the full charge capacity has been calculated, based on the decrease rate in the period of time in which full charge capacity is not estimated and the initial full charge capacity; and

(d) calculate the present full charge capacity based on a present second elapsed period of time of the electric storage device, the decrease rate within the period of time in which the full charge capacity is not estimated, and the initial full charge capacity, the present second elapsed period of time being calculated from the first elapsed period and the period of time in which the full charge capacity is not estimated.

2. The electric storage system according to claim 1, wherein

the electronic control unit is configured to execute first estimation processing of calculating the full charge capacity of the electric storage device on the basis of a difference in state of charge before and after external charging in which the electric storage device is charged by electric power supplied from an external power supply, and an integrated value of a charging current in the external charging; and

the electronic control unit is configured to execute the estimation processing within the period of time in which the full charge capacity is not estimated from when the full charge capacity has been calculated during the external charging until the present time, by taking the full charge capacity estimated by the first estimation processing as the previous full charge capacity.

3. The power storage system according to claim 2, wherein

the electronic control unit is configured to calculate the full charge capacity in the first estimation processing by the following equation:

full charge capacity = current integrated value (∑I)/ASOC x 100

ASOC = SOC_e - SOC_s,

where: ASOC is a difference in state of charge before and after charging;

SOC_e is a state of charge when charging is started; and

SOC_s is a state of charge when charging is ended.

4. The electric storage system according to any one of claims 1 through 3, wherein the electronic control unit is configured to acquire a state of charge and a battery temperature of the electric storage device within the period of time in which the full charge capacity is not estimated, a plurality of times at predetermined timings, regardless of whether the vehicle runs or stops; and

the electronic control unit is configured to store the acquired values of the state of charges and the battery temperatures together with an elapsed time of the period of time in which the full charge capacity is not estimated, in a predetermined storage area.

5. The electric storage system according to any one of claims 1 through 4, wherein the electronic control unit is configured to execute the estimation processing and also change a predetermined period according to the previous full charge capacity, when the period of time in which the full charge capacity is not estimated exceeds the predetermined period.

6. The electric storage system according to any one of claims 1 through 5, wherein an allowed period of time of the period of time in which the full charge capacity is not estimated is set smaller in relation to a non-estimation period of time for larger previous full charge capacity.

7. The electric storage system according to any one of claims 1 through 6, wherein in the decrease rate map, the decrease rate is set to be higher as the average state of charge and the average battery temperature become higher.

8. A full charge capacity estimation method for calculating a present full charge capacity based on a decrease rate from an initial full charge capacity that has been defined in advance according to an elapsed period of time of an electric storage device installed on a vehicle, the full charge capacity estimation method comprising:

calculating an average state of charge over a period of time and an average battery temperature over the period of time, in the period of time the full charge capacity of the electric storage device being not estimated from after a previous full charge capacity has been calculated to a present time; '

calculating a decrease rate within the period of time in which the full charge capacity is not estimated by using a decrease rate map in which the decrease rate changes according to the average state of charge and the average battery temperature and the decrease rate is defined in advance;

calculating a first elapsed period of time of the electric storage device at the time the previous full charge capacity has been calculated, based on the decrease rate within the period of time in which the full charge capacity is not estimated and the initial full charge capacity,; and calculating a present full charge capacity based on a present second elapsed period of time of the electric storage device, the decrease rate within the period of time in which the full charge capacity is not estimated, and the initial full charge capacity, the present second elapsed period of time being calculated from the first elapsed period of time and the period of time in which the full charge capacity is not estimated.