WO2015011534A2

WO2015011534A2 - Control device and control method for electrical storage device

Info

Publication number: WO2015011534A2
Application number: PCT/IB2014/001292
Authority: WO
Inventors: Hironori Harada
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2013-07-25
Filing date: 2014-07-08
Publication date: 2015-01-29
Also published as: WO2015011534A3; JP5765375B2; JP2015026478A

Abstract

A control device and control method for an electrical storage device are provided. The control device includes an electronic control unit. The electronic control unit estimates a degradation degree based on a change in full charge capacity of the electrical storage device that is charged or discharged by using a usage history including a frequency of each usage environment in a period of use of the electrical storage device, and controls input/output of the electrical storage device based on the degradation degree. When the usage history in the period of use is unavailable, the electronic control unit calculates an estimated period of use of the electrical storage device by using a full charge capacity and estimated degradation information, and generates an estimated usage history in the estimated period of use for calculating a degradation degree based on an estimated frequency of each usage environment, defined in advance based on the estimated degradation information.

Description

CONTROL DEVICE AND CONTROL METHOD FOR

ELECTRICAL STORAGE DEVICE

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to the estimation of degradation of an electrical storage device and input/output control based on the degradation. 2. Description of Related Art

[0002] In International Application Publication No. 2010/005079, when a lithium ion secondary battery is charged, an allowable input current value is set in order to suppress precipitation of lithium metal. The allowable input current value may be corrected based on the degradation degree of the secondary battery in consideration of aged degradation of the secondary battery. At this time, in International Application Publication No. 2010/005079, the degradation degree is estimated (calculated) from a charge/discharge history, such as a full charge capacity and an internal resistance that are calculated from a voltage value and a current value during charging or discharging.

[0003] On the other hand, as a method of estimating the degradation degree of a secondary battery, as described in Japanese Patent Application Publication No. 2012-181066 (JP 2012-181066 A), it is possible to estimate the degradation degree by using the usage history (a battery temperature frequencies, battery voltage (SOC) frequencies, an elapsed time, and the like) of a secondary battery, indicating a battery load condition in each usage environment. The estimation of the degradation degree using the usage history of a secondary battery suppresses detection errors of sensors as compared to the case where the degradation degree is estimated from a charge/discharge history, such as a voltage value and a current value that are detected by the sensors, so it is possible to accurately estimate the degradation degree of the secondary battery.

[0004] However, if the usage history, such as battery temperature frequencies from the past to the present in a period of use, of an electrical storage device, such as a secondary battery, is lost and unavailable or if the usage history is unavailable because of battery replacement, or the like, it is not possible to estimate the degradation degree of the electrical storage device based on the usage history. Therefore, there is a concern that it is not possible to appropriately control the input/output of the electrical storage device based on the degradation degree. SUMMARY OF THE INVENTION

[0005] In view of the above inconvenience, the invention provides a control device and control method for an electrical storage device, which are able to appropriately control the input/output of the electrical storage device based on the degradation degree that is accurately calculated even when a usage history of the electrical storage device in a period of use is unavailable at the time of estimating the degradation degree using the usage history.

[0006] An aspect of the invention provides a control device for an electrical storage device that is charged or discharged. The control device includes an electronic control unit configured to estimate a degradation degree based on a change in full charge capacity of the electrical storage device by using a usage history including a frequency of each usage environment in a period of use of the electrical storage device, and control input/output of the electrical storage device based on the degradation degree, the electronic control unit being configured to calculate an estimated period of use of the electrical storage device by using the full charge capacity and estimated degradation information when the usage history in the period of use is unavailable, the full charge capacity being calculated from a charge/discharge history of the electrical storage device, the estimated degradation information defining in advance a correlation between a period of use of the electrical storage device and a change in full charge capacity, and the electronic control unit being configured to generate an estimated usage history in the estimated period of use for calculating the degradation degree based on an estimated frequency of each usage environment, the estimated frequency being defined in advance based on the estimated degradation information.

[0007] With the thus configured control device for an electrical storage device, the estimated period of use of the electrical storage device is calculated by using the full charge capacity that is calculated based on the charge/discharge history of the electrical storage device and the estimated degradation information, and the estimated usage history in the estimated period of use is calculated. Therefore, even when an actual usage history of the electrical storage device in the period of use is unavailable, it is possible to accurately estimate (calculate) the degradation degree by using the estimated usage history, so it is possible to appropriately control the input/output of the electrical storage device based on the degradation degree.

[0008] In the control device, the electronic control unit may be configured to update the estimated usage history by using measured results of a measuring device that measures the usage environment of the electrical storage device, and calculate the degradation degree based on the estimated usage history, in the estimated usage history the measured results being reflected. With this configuration, the actually measured results of the usage environment of the electrical storage device are reflected into the estimated usage history, so it is possible to carry out accurate estimation of degradation based on the usage environments in an actual usage of the electrical storage device.

[0009] In the control device, the electronic control unit may be configured to compare the estimated usage history before the measured results are reflected with an additional usage history including the frequency of each usage environment based on the measured results, and the electronic control unit may be configured to generate the re-estimated usage history based on the additional usage history when the mutual frequencies of each usage environment differ from each other by a predetermined value or larger. With this configuration, a deviation between the estimated usage history and the usage history of the usage environments in an actual usage of the electrical storage device is suppressed, so it is possible to accurately estimate the degradation degree based on the usage environments in an actual usage.

[0010] More specifically, the electronic control unit may be configured to generate an additional usage history as follows. That is, the electronic control unit may be configured to calculate a first estimated period of use of the electrical storage device by using the full charge capacity and first estimated degradation information when the estimated usage history before the measured results are reflected and the additional usage history differ from each other by the predetermined value or larger, the full charge capacity being calculated from the charge/discharge history of the electrical storage device, the first estimated degradation information corresponding to a frequency of each usage environment of the additional usage history and defining in advance a correlation between a period of use of the electrical storage device and a change in full charge capacity, the correlation being different from the estimated degradation information, and the electronic control unit may be configured to generate a first estimated usage history in the first estimated period of use for calculating the degradation degree based on an estimated frequency of each usage environment, the estimated frequency being defined in advance based on the first estimated degradation information.

[0011] In the control device, each usage environment may be any one of a temperature of the electrical storage device, a level of charge of the electrical storage device and a temperature at each level of charge, and the usage history may include any one of a frequency of each temperature, a frequency of each level of charge and a frequency of each temperature at each level of charge.

[0012] In the control device, the electrical storage device may be a non-aqueous secondary battery. In this case, the electronic control unit may be configured to control input of the non-aqueous secondary battery while reducing an allowable input current value, the allowable input current value being a maximum current value up to which the input of the non-aqueous secondary battery is allowed, based on the degradation degree.

[0013] In the control device, the electronic control unit may be configured to reduce the allowable input current value based on a first degradation degree based on the usage history and a second degradation degree based on the charge/discharge history of the non-aqueous secondary battery.

[0014] Another aspect of the invention provides a control method for an electrical storage device that is charged or discharged. The control method includes: determining whether a usage history of the electrical storage device in a period of use is unavailable; calculating an estimated period of use of the electrical storage device by using a full charge capacity and estimated degradation information when the usage history in the period of use is unavailable, the full charge capacity being calculated from a charge/discharge history of the electrical storage device in the period of use, the estimated degradation information defining in advance a correlation between a period of use of the electrical storage device and a change in full charge capacity; generating an estimated usage history in the estimated period of use based on an estimated frequency of each usage environment, the estimated frequency being defined in advance based on the estimated degradation information; calculating the degradation degree by using the generated estimated usage history; and controlling input/output of the electrical storage device based on the calculated degradation degree. With the above-described control method for an electrical storage device, similar advantageous effects to those of the above-described control device for an electrical storage device are obtained.

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 is a view that shows the configuration of a battery system according to a first embodiment of the invention;

FIG. 2 is a graph that shows a variation in positive electrode potential and a variation in negative electrode potential, depending on a state of charge according to the first embodiment;

FIG. 3 is a graph for illustrating the process of limiting an allowable input power of a battery pack according to the first embodiment;

FIG. 4 is a graph that shows the correlation between a degradation degree D and a degradation coefficient η according to the first embodiment;

FIG. 5 is a graph that shows an example of a usage history including the frequency of each battery temperature (usage environment) in a period of use of the battery pack according to the first embodiment;

FIG. 6 is an example of a degradation behavior map that shows the correlation of a full charge capacity decrease amount (degradation degree) to a use time at each battery temperature according to the first embodiment;

FIG. 7 is a graph that shows the correlation between a full charge capacity decrease amount calculated from the usage history and a current period of use according to the first embodiment;

FIG. 8 is a flowchart that illustrates the process of calculating the degradation degree

D by using the usage history of the battery pack according to the first embodiment;

FIG. 9 is an example of a degradation behavior map that defines the correlation between a total period of use of the battery pack and a full charge capacity decrease amount according to the first embodiment;

FIG. 10 is a graph that shows an example of a presence probability distribution of battery temperatures corresponding to the predetermined degradation behavior map shown in FIG. 9;

FIG. 11 is a graph that shows an example of estimated battery temperature frequencies (estimated usage history) calculated based on the predetermined degradation behavior map and the presence probabilities of the battery temperature frequencies;

FIG. 12 is a flowchart that illustrates the process of producing estimated battery temperature frequencies (estimated usage history) due to a lost or unavailability of the usage history according to the first embodiment;

FIG. 13 is a flowchart that illustrates the process of setting an allowable input current value in the process of controlling the charging or discharging of the battery pack according to the first embodiment;

FIG. 14 is a graph that shows an example of a comparison between estimated battery temperature frequencies and an additional usage history according to the first embodiment;

FIG. 15 is a graph that shows an example of re-calculation of a total use time of the battery pack by using a degradation behavior map based on the additional usage history according to the first embodiment;

FIG. 16 is a graph that shows an example of estimated battery temperature frequencies newly produced in accordance with an estimated period of use based on the additional usage history;

FIG. 17 is a flowchart that illustrates the process of updating (regenerating) the estimated usage history based on the additional usage history according to the first embodiment;

FIG. 18 is a view that shows the process of controlling the charging or discharging of a battery pack according to a second embodiment of the invention, and is a flowchart that illustrates the process of setting an allowable input current value by using a first degradation degree based on a usage history and a second degradation degree based on a charge/discharge history;

FIG. 19 is a graph that shows the correlation between an internal resistance and degradation degree Dr (second degradation degree) of single cells (battery pack) according to the second embodiment; and

FIG. 20 is a graph that shows the correlation of a (corrected) degradation degree Dh that incorporates the degradation degree based on the usage history to the degradation degree Dr based on the charge/discharge history according to the second embodiment. DETAILED DESCRIPTION OF EMBODIMENTS

[0016] A first embodiment of the invention will be described. FIG. 1 is a view that shows the configuration of a battery system according to the first embodiment. The battery system according to the first embodiment may be mounted on a vehicle. The vehicle may be a hybrid vehicle or an electric vehicle. The hybrid vehicle includes an engine or a fuel cell in addition to a battery pack (described later) as a power source for propelling the vehicle. The electric vehicle includes only the battery pack (described later) as a power source for propelling the vehicle.

[0017] The battery pack 10 corresponding to an electrical storage device includes a plurality of single cells 11 connected in series with each other. For example, a non-aqueous electrolyte secondary battery, such as a lithium ion secondary battery, may be used as each single cell 11. The number of the single cells 11 that constitute the battery pack 10 may be set as needed in consideration of a required output, or the like, of the battery pack 10. In the first embodiment, the battery pack 10 is formed by connecting all the single cells 11 in series with each other. Instead, the battery pack 10 may include a plurality of the single cells 11 connected in parallel with each other. [0018] For example, the positive electrode of each single cell 11 is formed of a material that is able to occlude and release ions (for example, lithium ions). For example, lithium cobaltate or lithium manganate may be used as the material of the positive electrode. The negative electrode of each single cell 11 is formed of a material that is able to occlude and release ions (for example, lithium ions). For example, carbon may be used as the material of the negative electrode. When each single cell 11 is charged, the positive electrode releases ions into an electrolytic solution, and the negative electrode occludes ions in the electrolytic solution. When each single cell 11 is discharged, the positive electrode occludes ions in the electrolytic solution, and the negative electrode releases ions into the electrolytic solution.

[0019] A monitoring unit 21 detects the terminal voltage of the battery pack 10, and detects the voltage of each single cell 11. The monitoring unit 21 outputs the detected result to a controller 30 that is an electronic control unit (ECU). The monitoring unit 21 is able to detect the voltage value of each of the plurality of single cells 11 one by one and detect the voltage of a single cell group formed of a serially connected predetermined number of the single cells as one block. The number of the single cells 11 included in one block may be selectively set.

[0020] A current sensor 22 detects a current flowing through the battery pack 10, and outputs the detected result to the electronic control unit 30. In the first embodiment, the current sensor 22 is provided in a positive electrode line PL connected to the positive electrode terminal of the battery pack 10; however, the location of the current sensor 22 is not limited to this configuration. The current sensor 22 just needs to be able to detect a current flowing through the battery pack 10, and the location in a current path at which the current sensor 22 is provided may be set as needed. For example, the current sensor 22 may be provided in a negative electrode line NL connected to the negative electrode terminal of the battery pack 10. A plurality of the current sensors 22 may be used.

[0021] In the first embodiment, a negative value (IB < 0) is used as a current value detected by the current sensor 22 at the time when the battery pack 10 is being charged. A positive value (IB > 0) is used as a current value detected by the current sensor 22 at the time when the battery pack 10 is being discharged.

[0022] A temperature sensor 23 detects the temperature (battery temperature) of the battery pack 10. The temperature sensor 23 outputs the detected result to the electronic control unit 30. The temperature sensor 23 may be provided at one location in the battery pack 10 or may be provided at mutually different multiple locations in the battery pack 10. When a plurality of detected temperatures are used, the minimum value, maximum value, median value, averaged value, or the like, of the plurality of detected temperatures may be used as the temperature of the battery pack 10 as needed.

[0023] A capacitor C is connected to the positive electrode line PL and the negative electrode line NL, and smoothes voltage fluctuations between the positive electrode line PL and the negative electrode line NL.

[0024] 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. Each of the system main relays SMR-B, SMR-G switches between an on state and an off state upon reception of a control signal from the electronic control unit 30.

[0025] A system main relay SMR-P and a current-limiting resistor R are connected in parallel with the system main relay SMR-G. Here, the system main relay SMR-P and the current-limiting resistor R are connected in series with each other. The system main relay SMR-P switches between an on state and an off state upon reception of a control signal from the electronic control unit 30. The current-limiting resistor R is used to inhibit flow of inrush current to the capacitor C at the time when the battery pack 10 is connected to a load (specifically, an inverter 24).

[0026] When the battery pack 10 is connected to the inverter 24, the electronic control unit 30 initially switches the system main relays SMR-B, SMR-P from the off state to the on state. Thus, current flows through the current-limiting resistor R.

[0027] Subsequently, the electronic control unit 30 switches the system main relay SMR-G from the off state to the on state, and then switches the system main relay SMR-P from the on state to the off state. Thus, connection of the battery pack 10 with the inverter 24 completes, and the battery system shown in FIG. 1 enters an activated state (ready-on state). Information about the on/off state (IG-ON/IG-OFF) of an ignition switch of the vehicle is input to the electronic control unit 30. The electronic control unit 30 activates the battery system in response to switching of the ignition switch from the off state to the on state.

[0028] On the other hand, when the ignition switch switches from the on state to the off state, the electronic control unit 30 switches the system main relays SMR-B, SMR-G from the on state to the off state. Thus, connection of the battery pack 10 with the inverter 24 is interrupted, and the battery system enters a stopped state (ready-off state).

[0029] The inverter 24 converts direct-current power, output from the battery pack 10, to alternating-current power, and outputs the alternating-current power to a motor generator (MG) 25. For example, a three-phase alternating-current motor may be used as the motor generator 25. The motor generator 25 generates kinetic energy for propelling the vehicle upon reception of alternating-current power from the inverter 24. The motor generator 25 is connected to wheels, and kinetic energy generated by the motor generator 25 is transmitted to the wheels. Thus, it is possible to cause the vehicle to travel.

[0030] When the vehicle is decelerated or the vehicle is stopped, the motor generator 25 converts kinetic energy that is generated during braking of the vehicle to electric energy (alternating-current power). The inverter 24 converts alternating-current power, output from the motor generator 25, to direct-current power, and outputs the direct-current power to the battery pack 10. Thus, it is possible to store regenerated electric power in the battery pack 10.

[0031] In the battery system according to the first embodiment, the battery pack

10 is connected to the inverter 24; however, the battery pack 10 is not limited to this configuration. Specifically, a step-up circuit may be provided in a current path between the battery pack 10 and the inverter 24. When the step-up circuit is used, it is possible to step up the output voltage of the battery pack 10 and output the stepped-up electric power to the inverter 24. By using the step-up circuit, it is possible to step down the output voltage of the inverter 24 and output the stepped-down electric power to the battery pack 10.

[0032] The electronic control unit 30 includes a memory 31. The memory 31 stores information that is used when the electronic control unit 30 executes a specific process (particularly, a process described in the first embodiment). In the first embodiment, the memory 31 is incorporated in the electronic control unit 30; instead, the memory 31 may be provided outside the electronic control unit 30.

[0033] The electronic control unit 30 according to the first embodiment may include a timer 32. The timer 32 is able to count a period (time, age) of use of the battery pack 10 and count the duration of each usage environment in the period of use of the battery pack 10 (described later). The timer 32 as well as the memory 31 may be provided outside the electronic control unit 30 or may be incorporated in the electronic control unit 30.

[0034] Next, charge/discharge control over the battery pack 10 according to the first embodiment will be described. FIG. 2 is a graph that shows a variation in positive electrode potential and a variation in negative electrode potential, depending on the SOC of the battery pack 10.

[0035] When the single cells 11 are charged, the voltage value VB of the single cells 11 rises. As shown in FIG. 2, the voltage value VB of the single cells 11 is a difference between the positive electrode potential and the negative electrode potential. Therefore, as the charging of the single cells 11 advances, the positive electrode potential rises, and the negative electrode potential decreases. Here, when the negative electrode potential decreases below a reference potential (for example, 0 [V]), lithium metal may precipitate on the surfaces of the negative electrodes.

[0036] When the single cells 11 are in an energized state, an overvoltage occurs.

The overvoltage is a voltage variation amount associated with the internal resistance of the single cells 11, and the overvoltage decreases when energization of the single cells 11 is stopped. When the single cells 11 are charged, the voltage value VB (closed circuit voltage (CCV)) of the single cells 11 rises by the amount of the overvoltage with respect to the open voltage value (open circuit voltage (OCV)) of the single cells 11. Therefore, there is a concern that the negative electrode potential decreases below the reference potential depending on the overvoltage.

[0037] Therefore, in the first embodiment, in order to suppress precipitation of lithium metal, an allowable input current value is set, and an input current value (charge current value) of the single cells 11 (battery pack 10) does not exceed the allowable input current value. The allowable input current value is a maximum current value that is allowed at the time when the single cells 11 are charged.

[0038] When the allowable input current value increases, the current value at the time of charging the single cells 11 is allowed to be increased, so it is possible to improve the input performance of the single cells 11. On the other hand, when the allowable input current value reduces, the current value at the time of charging the single cells 11 is not allowed to be increased, so the charging of the single cells 11 is easily limited.

[0039] The allowable input current value is set as described below, and the process of setting the allowable input current value is executed by the electronic control unit 30.

[0040] When there is no charge/discharge history of the battery pack 10, in other words, when the battery pack 10 is charged or discharged for the first time, an allowable input current value Iii_m[t] is calculated based on the following mathematical expression (1).

[0041] In the above mathematical expression (1), lu_m[0] denotes a maximum allowable input current value at or below which it is possible to suppress precipitation of lithium metal within a unit time when charged from a state where there is no charge/discharge history. The allowable input current value ln_m[0] may be obtained in advance through an experiment, or the like, and information about the allowable input current value lii_m[0] may be stored in the memory 31.

[0042] The second term on the right-hand side of the above mathematical expression (1) is expressed as a function F of the current value IB, the battery temperature TB and the state of charge (SOC). Therefore, the value of the function F is calculated by identifying the current value IB, the battery temperature TB and the SOC. Here, values at time t are respectively used as the current value IB, the battery temperature TB and the SOC. The SOC indicates the percentage of a current level of charge with respect to a full charge capacity.

[0043] The SOC of the battery pack 10 and the SOC of each single cell 11 may be estimated by using a known method. For example, by accumulating the current value IB at the time when the battery pack 10 (single cells 11) is charged or discharged, it is possible to estimate the SOC of the battery pack 10 (single cells 11). On the other hand, the OCV and the SOC have a predetermined correlation. Therefore, when the correlation is obtained in advance, it is possible to identify the SOC corresponding to the OCV by measuring the OCV of the battery pack 10 (single cells 11).

[0044] When charging is continued from the state where there is no charge/discharge history to the time t, the value of the second term on the right-hand side of the mathematical expression (1) indicates an amount by which the allowable input current value Iu_m is reduced per unit time, and is subtracted from the allowable input current value lii_m[0]. On the other hand, when discharging is continued from the state where there is no charge/discharge history to the time t, the value of the second term on the right-hand side of the mathematical expression (1) indicates an amount by which the allowable input current value Iii_m is increased (recovered) per unit time, and is added to the allowable input current value lii_m[0].

[0045] The third term on the right-hand side of the mathematical expression (1) is expressed as a function G of the time t, the battery temperature TB and the SOC. Therefore, by identifying the time t, the battery temperature TB and the SOC, the value of the function G is calculated. Here, values at time t are respectively used as the battery temperature TB and the SOC. The value of the third term on the right-hand side of the mathematical expression (1) indicates an amount by which the allowable input current value Iu_m is increased (recovered) per unit time when the battery pack 10 is continuously left standing. Here, leaving the battery pack 10 standing is a state (non-energized state) where the charging or discharging of the battery pack 10 is stopped. [0046] On the other hand, when there is a charge/discharge history of the battery pack 10, in other words, after the battery pack 10 is charged or discharged, the allowable input current value lu_m[t] is calculated based on the following mathematical expression (2).

[0047] In the above mathematical expression (2), Iii_m[t] is an allowable input current value at time t (this time), and Iii_m[t-1] is an allowable input current value at time (t-1) (last time). The second term on the right-hand side of the mathematical expression (2) is expressed as a function f of the current value IB, the battery temperature TB and the SOC.

[0048] The function f depends on the current value IB, the battery temperature TB and the SOC. That is, the value of the second term on the right-hand side of the mathematical expression (2) may be calculated by identifying the current value IB, the battery temperature TB and the SOC. Here, values at time t are respectively used as the current value IB, the battery temperature TB and the SOC.

[0049] When the battery pack 10 is charged, the value of the second term on the right-hand side of the mathematical expression (2) indicates an amount (reduction amount) by which the allowable input current value Iii_m is reduced per unit time, and is subtracted from the allowable input current value Iij_m[t-1]. As described above, the current value IB is a negative value during charging, so the allowable input current value lu_m approaches 0 [A] when the allowable input current value Iii_m is reduced.

[0050] On the other hand, when the battery pack 10 is discharged, the value of the second term on the right-hand side of the mathematical expression (2) indicates an amount (recovery amount) by which the allowable input current value Iu_m is increased (recovered) per unit time, and is added to the allowable input current value Iij_m[t-1]. Here, when the allowable input current value Iu_m is increased, the allowable input current value Ii_im leaves from 0 [A].

[0051] The third term on the right-hand side of the mathematical expression (2) is expressed by a function g of the battery temperature TB and the SOC, the allowable input current value Iu_m[0], and the allowable input current value Iu_m[t-1]. As shown in the above mathematical expression (3), the function g is expressed as a coefficient β, and the coefficient β depends on the battery temperature TB and the SOC. Therefore, by obtaining a map showing the correlation among the coefficient β, the battery temperature TB and the SOC in advance, it is possible to identify the coefficient β corresponding to the battery temperature TB and the SOC. Values at time t are respectively used as the battery temperature TB and the SOC.

[0052] Here, the map that shows the correlation among the coefficient β, the battery temperature TB and the SOC may be stored in the memory 31. The value of the third term on the right-hand side of the mathematical expression (2) indicates an amount (recovery amount) by which the allowable input current value Iii_m is increased (recovered) per unit time when the battery pack 10 is continuously left standing. The value of the third term on the right-hand side of the mathematical expression (2) is added to the allowable input current value Iu_m[t-1].

[0053] When the allowable input current value Iii_m[t] is 0 [A], lithium ions in a negative electrode active material in each single cell 11 is in a saturated state. Therefore, the value of "Iu_m[0] - Iii_m[t]" indicates the amount of lithium ions in the negative electrode active material. Here, it is possible to increase the above-described recovery amount as the amount of lithium ions in the negative electrode active material reduces.

[0054] The recovery amount at time t depends on the recovery amount at time (t-1). The recovery amount at time (t-1) is expressed by "lii_m[0] - Iij_m[t-1]". Here, at the third term on the right-hand side of the mathematical expression (2), "lu_m[0] - Iii_m[t-1]" is divided by in_m[0] in order to make the value of "ln_m[0] - Iii_m[t-1]" be dimensionless. By multiplying the divided value by the coefficient β, it is possible to obtain the recovery amount per unit time.

[0055] Limiting control over charge electric power of the battery pack 10 according to the first embodiment by using the thus set allowable input current value Iii_m[t] may be executed as follows, and is executed by the electronic control unit 30.

[0056] The allowable input current value Iii_m[t] is calculated at predetermined intervals when the battery pack 10 is being charged or discharged or when the battery pack 10 is left standing. That is, each time a predetermined time corresponding to the interval between time t and time (t-1) elapses, the allowable input current value In_m[t] is updated. Here, the allowable input current value Iij_m[t] is used only when the charging of the battery pack 10 is controlled.

[0057] After the allowable input current value Iu_m[t] is calculated, the electronic control unit 30 controls the input/output (charging or discharging) of the battery pack 10 based on the allowable input current value Iii_m[t]. In the first embodiment, the charging or discharging (input/output) of the battery pack 10 is controlled by the battery input or battery output of a base electric power, and the electronic control unit 30 is able to set an input limit value Win[t] based on the allowable input current value Iij_m[t], and control the input electric power of the battery pack 10 by using the set input limit value Win[t]. For example, when the input of the battery pack 10 is controlled, the input limit value Win[t] is set based on the allowable input current value I|j_m[t], and the input electric power of the battery pack 10 is controlled such that the input electric power of the battery pack 10 does not exceed the input limit value Win[t]. The input limit value Win[t] may be, for example, set as will be described below.

[0058] A positive value is also used for the limit value of discharge electric power of the battery pack 10 when the battery pack 10 is discharged, while a negative value is also used for the limit value of charge electric power of the battery pack 10 when the battery pack 10 is charged. That is, an output limit value Wout is 0 or a positive value (Wout≥ 0), and the input limit value Win is 0 or a negative value (Win≤ 0).

[0059] FIG. 3 is a graph that shows the correlation between the current value IB and input/output electric power of the battery pack 10 in lithium precipitation suppressing control, and shows an example in which the input electric power of the battery pack 10 is limited in accordance with the allowable input current value Iii_m[t]. Initially, the electronic control unit 30 calculates an input current limit value Itag based on the allowable input current value Iii_m[t].

[0060] The input current limit value Itag is a value for specifying the input limit value Win[t]. Specifically, as shown in FIG. 3, the electronic control unit 30 calculates the input current limit value Itag by shifting the allowable input current value Iii_m[t] toward 0 [A] by a predetermined amount. Thus, the input current limit value Itag becomes a value closer to 0 [A] than the allowable input current value Iu_m[t], so the input of the battery pack 10 is more easily limited.

[0061] In this way, by providing a margin between the allowable input current value Iii_m[t] and the input current limit value Itag, it is possible to make it hard for the current value IB to exceed the allowable input current value I]i_m[t]. When the input of the battery pack 10 is controlled based on the input current limit value Itag, limiting the input of the battery pack 10 is started at the time when the current value IB has reached the input current limit value Itag. Here, even when the current value IB exceeds the input current limit value Itag because of a control delay, it is possible to inhibit the current value IB from reaching the allowable input current value Iu_m[t].

[0062] Subsequently, the electronic control unit 30 calculates the input limit value Win[t] based on the input current limit value Itag. When the input current limit value Itag is set, it is possible to set the input limit value Win[t]. When the input limit value Win[t] is set, the electronic control unit 30 adjusts a torque command for the motor generator 25 such that the input electric power of the battery pack 10 becomes lower than or equal to the input limit value Win[t].

[0063] For example, the input limit value Win[t] may be calculated based on the followine mathematical exoression 4 .

[4-K, xl{lB[t]- I_lag2 [t)}dt ...(4)

[0064] In the above mathematical expression (4), SWin[t] denotes an upper limit value of the input limit value Win preset in consideration of the input characteristics, and the like, of the battery pack 10, and denotes the base electric power shown in FIG. 3. Information about the input limit value SWinft] may be stored in the memory 31.

[0065] The input limit value SWinft] may be, for example, changed based on the battery temperature TB and the SOC. It is known that the degradation of the battery pack 10 is facilitated as the temperature of the battery pack 10 rises. Therefore, the input limit value SWinft] may be set so as to be lower as the temperature rises in a high temperature condition. Charging at the time when the battery temperature TB is high is carried out in consideration of a decrease in charging efficiency and a rise in temperature resulting from the decrease in charging efficiency.

[0066] When the battery pack 10 has a low temperature, the internal resistance increases. At this time, the voltage value VB of the battery pack 10 rises as a large charging current flows. Therefore, in order not to flow large current in a low temperature condition for the purpose of protecting the battery pack 10 and energization components, the input limit value SWinft] may be set so as to decrease as the battery temperature TB decreases.

[0067] On the other hand, as the SOC of the battery pack 10 rises, a decrease in charging efficiency, generation of heat due to heat of reaction resulting from the decrease in charging efficiency, and the like, occur. In order to suppress this situation, the input limit value SWinft] may be set so as to be lower as the SOC of the battery pack 10 rises.

[0068] In this way, the input limit value SWinft] may be set based on the battery temperature TB and the SOC, and, when the correlation between the input limit value SWinft] and the battery temperature TB (or/and the SOC) is obtained in advance, it is possible to identify the input limit value SWin[t] by detecting the battery temperature TB (or/and the SOC).

[0069] In the first embodiment, the input limit value SWin[t] that is set based on the battery temperature TB and SOC of the battery pack 10 is set as the base electric power (upper limit value) of the input limit value of the battery pack 10, and the input limit value Win[t] based on the allowable input current value Iii_m[t] is calculated. That is, the electronic control unit 30 executes first input control for controlling the battery input of the battery pack 10 while updating the base electric power (input limit value SWin) based on the battery temperature TB or/and SOC of the battery pack 10 and second input control for controlling the battery input of the battery pack 10 based on the input limit value Win[t] that is set by using the allowable input current value Iii_m[t] while updating the allowable input current value Iu_m[t] based on the state of charge of the battery pack 10. Therefore, the input limit value SWin[t] is the maximum value (upper limit value) of input electric power that is allowed for the battery pack 10, and the input limit value Win[t] that is set based on the allowable input current value Iij_m[t] is an input limit value limited by a larger amount (smaller amount as an absolute value) within the range in which the input limit value Win[t] does not exceed the input limit value SWin[t] that is the base electric power.

[0070] In the above mathematical expression (4), Kp, Ki each denote a preset gain. Itagl, Itag2 each denote an input current limit value, and each correspond to the above-described input current limit value Itag. In the above mathematical expression (4), the two input current limit values Itagl, Itag2 are set as the input current limit value Itag. Here, the input current limit values Itagl, Itag2 may be equal to each other or may be different from each other.

[0071] In the above description, the input current limit value Itag is set; however, the invention is not limited to this configuration. Specifically, the input limit value Win[t] may be set based on the allowable input current value Iu_m[t] without setting the input current limit value Itag.

[0072] According to the first embodiment, as shown in the above mathematical expression (2), the allowable input current value Iii_m[t] is set in consideration of the reduction amount per unit time and the recovery amount per unit time. Thus, it is possible to set the allowable input current value In_m[t] that incorporates the charge/discharge history of the single cells 11 until present time. By controlling the battery input of the battery pack 10 by using the input limit value Win[t] that is set based on the allowable input current value Iii_m[t], it is possible to suppress a decrease in the negative electrode potential below the reference potential. [0073] Here, the above mathematical expressions (1), (2) express the allowable input current value Iii_m[t] at the time when the degradation of the single cells 11 is not taken into consideration, and the degradation degree of the single cells 11 (battery pack 10) is not taken into consideration. Therefore, by taking into consideration the fact that the single cells 11 degrade because of usage (charging or discharging), it is possible to set the allowable input current value Iu_m[t] that incorporates the degradation of the single cells 11. An allowable input current value In_m_d[t] that incorporates the degradation of the single cells 11 is allowed to be calculated based on the following mathematical expression (5).

*M ^{= /}._im [']x 7 -⁽⁵⁾ [0074] In the above mathematical expression (5), η denotes a degradation coefficient. By multiplying the allowable input current value Iii_m[t], shown in the above mathematical expressions (1), (2), by the degradation coefficient η, it is possible to identify the allowable input current value Iij_m_d[t] that incorporates the degradation of the single cells 11. Here, the degradation coefficient η may be set in advance, and information about the degradation coefficient η may be stored in the memory 31.

[0075] The degradation coefficient η is a correction coefficient by which the allowable input current value Iu_m[t] is corrected based on the degradation degree D of the battery, and may be, for example, calculated by using the degradation degree of the single cells 11.

[0076] FIG. 4 is a graph that shows the correlation between the degradation coefficient η and the degradation degree D. For example, a value smaller than 1 may be used as the degradation coefficient η. As the degradation of the single cells 11 advances, lithium metal can easily precipitate, so it is desirable to limit the input of the single cells 11. When the degradation coefficient η that is a value smaller than 1 is used, it is possible to set the allowable input current value Iii_m_d[t] such that the allowable input current value Iiim_d[t] is smaller than the allowable input current value Iii_m[t], so it is possible to limit the input of the single cells 11. By controlling the input of the single cells 11 (battery pack 10) based on the allowable input current value Iii_m_d[t], precipitation of lithium metal is easily suppressed.

[0077] In the example shown in FIG. 4, the degradation coefficient η is set such that the degradation coefficient η is a constant degradation coefficient r\2 (< 1) until a degradation degree Da and gradually decreases with the degradation degree from the degradation degree Da to a degradation degree Db (ηΐ < η2 < 1). After the degradation degree Db, the degradation coefficient η may be set to a constant degradation coefficient ηΐ.

[0078] In the example shown in FIG. 4, the same value, that is, the degradation coefficient η2, is used from an initial stage after manufacturing (the initial stage of use) to the degradation degree Da. This is because the battery pack is used on the assumption that the battery pack is able to keep a certain function until the degradation degree Da, and stable control is executed by using the same degradation coefficient. After the degradation degree Da, the degradation coefficient η is gradually changed to decrease with the degree of degradation of the battery pack 10. After the degradation degree Db, in order to prevent a collapse of charge/discharge control over the battery pack 10, the degradation coefficient η is fixed to ηΐ as a lower limit guard value even when the degradation of the battery pack 10 advances as shown in FIG. 4. The correlation between the degradation degree D and the degradation coefficient η may be determined based on actually measured values, measured values through an experiment, or the like. Not limited to the example of FIG. 4, the correlation between the degradation degree D and the degradation coefficient η may be set as needed in order to suppress precipitation of lithium metal.

[0079] In the first embodiment, the correlation is set such that the degradation of the battery reduces as the degradation coefficient η increases and the degradation of the battery increases as the degradation coefficient η reduces. The allowable input current value Iu_m_d[t] that incorporates the degradation of the single cells 11 in the above mathematical expression (5) increases because a larger degradation coefficient η is applied as the degradation of the battery reduces, and reduces because a smaller degradation coefficient η is applied as the degradation of the battery increases.

[0080] Next, a method of calculating the degradation degree of the single cells 11 (battery pack 10) according to the first embodiment will be described in detail. The degradation degree D is a parameter that specifies a degradation state of the single cells 11, and indicates the degree of degradation based on the usage history of the single cells 11 (battery pack 10). The degradation degree D according to the first embodiment may be, for example, calculated by using a usage history including the frequency of each usage environment in a period of use of the single cells 11.

[0081] As described above, the rate of increase, or the like, in the internal resistance of the battery pack 10 is acquired in real time by using a charge/discharge history, such as a voltage value, a current value, and the like, that are detected by sensors, and it is possible to estimate the degradation state of the battery pack 10. For example, by acquiring the period of use (age of service) and the increasing tendency of the internal resistance in advance through an experiment, or the like, it is possible to acquire the degradation state of the battery pack 10.

[0082] However, the charge/discharge history, such as the voltage value, the current value, and the like, that are detected by the sensors include sensor errors. Therefore, the estimation of degradation using the charge/discharge history of the battery pack 10 may not be able to acquire the degradation degree of the battery pack 10.

[0083] On the other hand, elements for estimating the degree of degradation of the battery pack 10, in other words, factors that influence degradation, include the battery temperature, SOC (voltage) and elapsed time under a usage environment of the battery pack 10. By using the frequency of use of the battery pack 10 based on the factors that influence degradation, for example, the usage history associated with a battery load, indicating that the battery pack has been used under an environment of what battery temperature in the period of use and the battery pack has been used under an environment of what SOC state, it is possible to accurately acquire the degree of degradation of the battery pack 10.

[0084] The period of use is a period from an initial stage after manufacturing to current timing. The period of use includes a state where charge/discharge operation is being carried out (for example, the ignition switch of the vehicle is in the on state) and a state where charge/discharge operation is not being carried out (for example, the ignition switch of the vehicle is in the off state). This is because, even when charge/discharge operation is not being carried out, the degradation of the battery pack 10 is facilitated under an environment, such as a high battery temperature state and a high SOC state.

[0085] FIG. 5 is a view that shows one example of the usage history of the battery pack 10 according to the first embodiment. The abscissa axis represents a temperature, and the ordinate axis represents a duration at each temperature. In the example of FIG. 5, the usage history of the battery pack 10, formed of the frequency of each battery temperature, is shown as the frequency of each usage environment. For example, the battery temperature may be measured by the temperature sensor 23 at intervals of a predetermined period, and the duration of each battery temperature to which the battery pack 10 is exposed may be stored as the usage history of the battery pack 10. A total period of use (Tjotal) of the battery pack 10 in the period of use is a value obtained by accumulating the duration of each battery temperature shown in FIG. 5.

[0086] The electronic control unit 30 may store the battery temperature detected by the temperature sensor 23 and the duration of each battery temperature, detected by the timer 32, in the memory 31 as the usage history. For example, temperatures Tl to T7 are set in advance, the temperature corresponding to the detected battery temperature is determined, and a time [hour] detected by the timer 32 for the determined temperature is accumulated. Thus, the usage history is allowed to be generated (updated). Each temperature frequency may be set so as to have a predetermined temperature region. For example, a usage history may also be configured such that the range of a temperature tl to a temperature t2 is regarded as the battery temperature Tl and is included in the duration of the battery temperature Tl.

[0087] FIG. 6 is a graph that shows the correlation of a full charge capacity decrease amount to a use time at each battery temperature of the battery pack 10. In FIG. 6, the abscissa axis represents the square root of the duration (^(Duration)) of each battery temperature, and the ordinate axis represents a capacity retention rate of the full charge capacity of the battery pack 10. The capacity retention rate of the full charge capacity is the percentage of the current full charge capacity to the full charge capacity at the initial stage after manufacturing, and may be calculated by "Capacity Retention Rate = Current Full Charge Capacity / Full Charge Capacity at Initial Stage after Manufacturing". That is, where the capacity retention rate of the full charge capacity at the initial stage after manufacturing is 1, the current full charge capacity decrease amount (degradation degree) is "1 - Current Capacity Retention Rate".

[0088] As shown in FIG. 6, the full charge capacity decrease amount for a use time varies at each battery temperature, so the correlation of the full charge capacity decrease amount to a use time may be held as a degradation behavior map that varies at each battery temperature. A degradation behavior of a decrease in full charge capacity for a use time, which varies at each battery temperature shown in FIG. 6 may be obtained in advance by an experiment, or the like.

[0089] In FIG. 6, because the duration (temperature frequency) of the temperature region T2 is allowed to be acquired from the usage history shown in FIG. 5, it is possible to calculate a current capacity retention rate Cap(T2) of the battery pack 10 for the duration of the temperature region T2 from the square root of the duration of the temperature region T2 in the period of use by consulting the degradation behavior map of the temperature region T2. At this time, a degradation degree D2 of the battery pack 10 based on the duration of the temperature region T2 may be expressed by a full charge capacity decrease amount ACap(T2) from the initial stage after manufacturing, and may be calculated by "Degradation Degree D2 (ACap(T2)) = 1 - Cap(T2)". Degradation degrees Dl, D3, D4, ... respectively corresponding to the other temperature regions Tl, T3, T4, ... are allowed to be calculated based on the usage history and a pre-obtained degradation behavior of a decrease in full charge capacity for to a use time at each battery temperature.

[0090] In the first embodiment, a degradation degree D based on the total usage history of the battery pack 10 is calculated by integrating the degradation degrees Dl to D7, calculated respectively for the temperature frequencies of the usage history. The degradation degree D based on the total usage history of the battery pack 10 may be regarded as the one in which the degradation degrees Dl to D7 in the respective temperature regions are present at the percentages of the durations with respect to the total use time of the battery pack 10. Therefore, the degradation degree in each temperature region may be multiplied by the percentage of the duration with respect to the total use time as a weighted value, and a value obtained by adding the degradation degrees at the respective battery temperatures to which the weighted values are applied may be calculated as the total degradation degree D of the battery pack 10. For example, the degradation degree D may be obtained as the following mathematical expression (6). In the mathematical expression (6), n denotes a number (temperature region number) assigned to each battery temperature. ( Duration of Tn \ . ..

Degradation Degree D = Degradation Degree D(Tn) x ... (6)

I T _total J

[0091] FIG. 7 is a graph that shows the correlation between a retention rate (decrease amount) of the full charge capacity of the battery pack 10 and a current period of use. In FIG. 7, the abscissa axis represents a period (age) of use of the battery pack 10, and the ordinate axis represents a capacity retention rate.

[0092] As shown in FIG. 7, the current capacity retention rate and period of use of the battery pack 10 are allowed to be plotted, and it appears that the capacity retention rate decreases from the capacity retention rate (= 1) at the initial stage after manufacturing as the period of use extends. It is found that the differential (ACap) between the capacity retention rate at the initial stage after manufacturing and the current capacity retention rate is the degradation degree of the battery pack 10. That is, the degradation degree D indicates the amount of decrease in the capacity retention rate of the battery pack 10 with respect to the current use time. In other words, the degradation degree D indicates the full charge capacity decrease amount of the battery pack 10 with respect to the full charge capacity at the initial stage after manufacturing, and it is possible to calculate the current full charge capacity by subtracting the degradation degree D (ACap) from the full charge capacity at the initial stage after manufacturing. A change in the capacity retention rate of the full charge capacity with the period of use, shown in FIG. 7, is a degradation behavior map based on the usage history of the battery pack 10.

[0093] FIG. 8 is a flowchart for illustrating the process of calculating the degradation degree D by using the usage history of the battery pack 10 according to the first embodiment.

[0094] Initially, the electronic control unit 30 acquires the battery temperature TB of the battery pack 10 from the temperature sensor 23 in a period from when the ignition switch of the vehicle is turned on to when the ignition switch is turned off. At this time, the timer 32 counts the duration of each battery temperature. The electronic control unit 30 incorporates the acquired battery temperatures TB and the durations corresponding to the battery temperatures into the usage history stored in the memory 31. The battery temperatures TB and the durations corresponding to the battery temperatures in a period from when the ignition switch of the vehicle is turned off to when the ignition switch is turned on may also be reflected into the usage history.

[0095] The electronic control unit 30 loads the usage history stored in the memory 31 (S101). Subsequently, the electronic control unit 30 calculates a capacity retention rate corresponding to the duration of each temperature region by using the degradation behavior map of the full charge capacity for the use time at each battery temperature, shown in FIG. 6 (S102).

[0096] The electronic control unit 30 calculates a differential between the capacity retention rate at the initial stage after manufacturing and the capacity retention rate corresponding to each temperature frequency, that is, a degradation degree D (Tn) of the battery pack 10 based on the duration of each battery temperature (S103). The electronic control unit 30 multiplies the degradation degree D(Tn) at each battery temperature by the percentage of the duration with respect to the total use time T_total as a weighted value based on the above mathematical expression (6). A value obtained by adding the degradation degrees D(Tn) at the respective battery temperatures to which the weighted values are applied is calculated as the total degradation degree D of the battery pack 10 (S104). The electronic control unit 30 stores the calculated degradation degree D and the total use time T_total of the battery pack 10 in the memory 31 in association with each other.

[0097] The degradation degree D based on the thus calculated usage history correlates with the degradation coefficient η of the battery pack 10 shown in FIG. 4 as described above, and the electronic control unit 30 is able to specify the allowable input current value Iii_m_d[t] that incorporates degradation by using the degradation degree D. [0098] The process of calculating the degradation degree D using the usage history according to the first embodiment, shown in FIG. 8, may be, for example, executed at any timing in a period from when the ignition switch of the vehicle is turned off to when the ignition switch is turned on. Input/output control over the battery pack 10 from when the ignition switch of the vehicle is turned on to when the ignition switch is turned off is allowed to use the degradation degree D calculated before the ignition switch of the vehicle is turned on. Each time the ignition switch of the vehicle is turned off, a new degradation degree D is calculated based on the updated usage history. Input/output control over the battery pack 10 after the ignition switch of the vehicle is turned on may be executed in a period until the ignition switch is turned off by using the degradation degree D calculated at the latest.

[0099] In input/output control over the battery pack 10 after the ignition switch of the vehicle is turned on, the electronic control unit 30 is able to update the usage history by using the battery temperature TB, and the like, acquired as needed. Therefore, the electronic control unit 30 may be configured to calculate the degradation degree D in real time at predetermined timing in accordance with input/output control over the battery pack 10.

[0100] In the above description, the degradation degree D is calculated by using the usage history including the frequency of each battery temperature (temperature frequency) as the usage environment of the battery pack 10; however, another usage history may also be used. That is, the usage environment of the battery pack 10 may include the battery temperature of the battery pack 10, the SOC (level of charge) of the battery pack 10 or the temperature at each SOC. Thus, the usage history may include the frequency of each battery temperature, the frequency of each SOC or the frequency of each battery temperature at each SOC. The degradation degree D may be configured to be obtained by calculating the degradation degree of the battery pack 10 for each usage history including one or a plurality of usage environments and then integrating the calculated degradation degrees.

[0101] By using the usage history associated with a battery load that influences degradation, such as the battery temperature, SOC (voltage) and elapsed time, under the usage environment of the battery pack 10, it is possible to accurately acquire the degree of degradation of the battery pack 10. However, if the usage history from the past to the present in the period of use of the battery pack 10 becomes unavailable, there is a concern that the estimation of degradation degree cannot be carried out different from the estimation of degradation degree based on the charge/discharge history. [0102] For example, if a component of the electronic control unit 30 is replaced or the usage history stored in the memory 31 is cleared, the usage history is lost. . When the battery pack 10 is replaced, the usage history that has been stored in the memory 31 and used in order to calculate the degradation degree D so far is the usage history of the pre-replaced battery pack 10, so the usage history is unavailable. In the battery system in which a plurality of the battery packs 10 are connected, when at least one battery pack 10 is replaced, the usage environment of each battery pack 10 varies, so the usage history that has been used so far is unavailable.

[0103] Therefore, in the first embodiment, in estimation of the degradation degree using the usage history of the battery pack 10, even when the usage history of the battery pack 10 in a period of use is unavailable, input/output control over the battery pack 10 based on the degradation degree is allowed to be appropriately executed by accurately calculating the degradation degree.

[0104] Specifically, the electronic control unit 30 determines whether the usage history of the battery pack 10 in the period of use is unavailable. For example, when component replacement of the electronic control unit 30, replacement of the battery pack 10, or the like, has been carried out, the electronic control unit 30 carries out initialization operation. It is possible to determine that the current usage history is unavailable based on this initialization operation. When the usage history in the memory 31 disappears, it may be determined that the usage history is unavailable.

[0105] When the electronic control unit 30 determines that the current usage history is unavailable, the electronic control unit 30 calculates an estimated period of use of the battery pack 10 by using a full charge capacity, which is calculated from the charge/discharge history of the battery pack 10, and a predetermined degradation behavior map (which corresponds to estimated degradation information). The predetermined degradation behavior map defines in advance the correlation between a period of use of the battery pack 10 and a change in full charge capacity. An estimated usage history in the estimated period of use for calculating the degradation degree D is generated based on an estimated frequency of each usage environment, defined in advance based on the predetermined degradation behavior map.

[0106] FIG. 9 is an example of the degradation behavior map that defines the correlation between a total period of use of the battery pack 10 and a change in full charge capacity. The abscissa axis represents a period of use, and the ordinate axis represents a full charge capacity. The degradation behavior map shown in FIG. 9 is a degradation behavior map defined in advance based on an experimental usage history or actually used usage history of the battery pack 10. For example, as in the case of the correlation between a retention rate (decrease amount) of the full charge capacity of the battery pack 10 in actual usage and a current period of use, shown in FIG. 7, the degradation behavior map shown in FIG. 9 is allowed to be generated by setting the ordinate axis as the full charge capacity.

[0107] One or a plurality of degradation behavior maps defined in advance may be prepared. The electronic control unit 30 is able to extract an appropriate degradation behavior map based on user information (such as a traveling region and a traveling environment) that is allowed to be acquired in advance, from a plurality of degradation behavior maps. The single same degradation behavior map may be uniformly applied. In this case, in order to deal with various usage environments, a degradation behavior map of a condition in which the battery temperature, and the like, of the battery pack 10 in a usage environment, which are factors that influence degradation, are strict (for example, a degradation behavior map of which the battery temperature frequency is high in a high temperature environment) may be applied.

[0108] In the example shown in FIG. 9, CO denotes the full charge capacity at the initial stage after manufacturing, and CI denotes the current full charge capacity of the battery pack 10. The current full charge capacity CI of the battery pack 10 is allowed to be calculated from the charge/discharge history of the battery pack 10. The full charge capacity of the battery pack 10 may be, for example, calculated by "Full Charge Capacity = 100÷(SOC_e-SOC_s)x Accumulated Current Value". SOC_s denotes the SOC of the battery pack 10 at the time when current accumulation is started. SOC_e denotes the SOC of the battery pack 10 at the time when current accumulation is ended. The accumulated current value is a value obtained by accumulating a charge/discharge current of the battery pack 10 from when the SOC_s is calculated to when the SOC_e is calculated where a discharge current is a positive value and a charge current is a negative value.

[0109] When the current usage history becomes unavailable, the electronic control unit 30 is able to calculate the current full charge capacity by causing a predetermined discharge operation through battery diagnosis, or the like, and calculate the current full charge capacity through external charging from an external power supply, such as a commercial power supply. When only the current usage history is lost without battery replacement, or the like, the existing full charge capacity calculated at the latest and stored in the memory 31 may be used as the current full charge capacity CI without executing the full charge capacity estimation process.

[0110] When the current usage history becomes unavailable, the electronic control unit 30 acquires the current full charge capacity of the battery pack 10, and calculates an estimated period of use of the battery pack 10 based on the degradation behavior map shown in FIG. 9. As shown in FIG. 9, an estimated period of use T_tol of the corresponding battery pack 10 is allowed to be calculated from the full charge capacity CI of the battery pack 10 based on the charge/discharge history.

[0111] FIG. 10 is a graph that shows a presence probability distribution of the battery temperatures corresponding to the predetermined degradation behavior map shown in FIG. 9. As described above, the degradation behavior map that defines the correlation between a total period of use of the battery pack 10 and a change in full charge capacity is generated based on an experimental usage history or actually used usage history of the battery pack 10, so it is possible to acquire a time (duration) in which the battery pack 10 is exposed to each battery temperature in the period of use of the battery pack 10 in advance.

[0112] Therefore, as shown in FIG. 10, the presence probabilities of the battery temperatures corresponding to the predetermined degradation behavior map shown in FIG. 9 may be defined in advance, and the electronic control unit 30 generates estimated battery temperature frequencies (estimated usage history) in the estimated period of use T_tol based on the estimated period of use T_tol calculated from the predetermined degradation behavior map and presence probabilities P (which correspond to the estimated frequencies) of the battery temperatures shown in FIG. 10.

[0113] FIG. 11 is a graph that shows an example of the estimated usage history.

The duration of each temperature region is allowed to be calculated by P(n)xT_tol. As shown in FIG. 10 and FIG. 11, the presence probability of the temperature region T3 is P3, so the estimated battery temperature frequency of the temperature region T3 is calculated by P3xT_tol. Similarly, the estimated temperature frequency of each of the temperature regions Tl, T2, T4, ... is allowed to be obtained by multiplying each temperature frequency by the estimated period of use T_tol, so it is possible to generate the estimated usage history including the estimated frequency of each temperature region in the estimated period of use T_tol.

[0114] FIG. 12 is a flowchart that illustrates the process of generating the estimated usage history. The electronic control unit 30 determines whether the current usage history is lost, unavailable or not (S301). As described above, it is determined whether the current usage history becomes unavailable by determining whether there is component replacement of the electronic control unit 30, a loss of the usage history in the memory 31, replacement of the battery pack 10, or the like.

[0115] When it is determined that the current usage history becomes unavailable, the electronic control unit 30 acquires or calculates the current full charge capacity of the battery pack 10 from the detected values of the current value IB and voltage value VB (S302). The electronic control unit 30 calculates the current full charge capacity CI by causing the predetermined discharge operation through battery diagnosis, or the like, or acquires the existing full charge capacity calculated at the latest and stored in the memory 31 as the current full charge capacity CI.

[0116] The electronic control unit 30 calculates the estimated period of use T_tol corresponding to the current full charge capacity CI of the battery pack 10 by using the degradation behavior map that defines in advance the correlation between a total period of use of the battery pack 10 and a change in full charge capacity, the degradation behavior map being stored in the memory 31 (S303).

[0117] Subsequently, the electronic control unit 30 calculates the presence probability of each battery temperature by consulting the presence probability distribution of the battery temperatures corresponding to the degradation behavior map used to calculate the estimated period of use T_tol (S304). The presence probabilities may be respectively calculated in advance from the presence probability distribution from a plurality of predetermined battery temperatures, and may be stored in the memory 31.

[0118] The electronic control unit 30 generates the estimated battery temperature frequencies in the estimated period of use T_tol based on the estimated period of use T_tol and the presence probability P of each battery temperature (S305). The generated estimated battery temperature frequencies are stored in the memory 31 as the estimated usage history for calculating the degradation degree D.

[0119] In this way, by using the degradation behavior map (estimated degradation information) that defines in advance the correlation between a total period of use of the battery pack 10 and a change in full charge capacity, the estimated period of use corresponding to the current full charge capacity measured value is calculated, and the estimated usage history in the estimated period of use is calculated. Therefore, even when an actual usage history in the period of use of the battery pack 10 becomes unavailable, it is possible to accurately estimate (calculate) the degradation degree D by using the estimated usage history based on the current full charge capacity measured value, so it is possible to appropriately control the input of the battery pack 10 in response to the degradation degree.

[0120] Next, the process of controlling the charging or discharging of the battery pack 10 in the battery system according to the first embodiment will be described. FIG. 13 is a flowchart that illustrates the process of setting the allowable input current value Ii_im. The process shown in FIG. 13 is executed by the electronic control unit 30.

[0121] In step S501, the electronic control unit 30 detects the current value IB of the battery pack 10 based on the output of the current sensor 22. The electronic control unit 30 detects the temperature TB of the battery pack 10 based on the output of the temperature sensor 23. Furthermore, the electronic control unit 30 detects the voltage VB of the battery pack 10 based on the output of the monitoring unit 21. In step S502, the electronic control unit 30 estimates the SOC of the battery pack 10. A method of estimating the SOC is as described above.

[0122] In step S503, the electronic control unit 30 updates the usage history of the battery pack 10. The battery temperature TB detected by the temperature sensor 23 in step S501 and the duration of each battery temperature TB, detected by the timer 32, are stored in the memory 31 as the usage history. At this time, the electronic control unit 30 updates the current usage history of the battery pack 10 in the period of use or the estimated usage history after the current usage history becomes unavailable by using the detected battery temperature TB and the duration of the battery temperature TB.

[0123] Subsequently, the electronic control unit 30 acquires the degradation degree D from the memory 31 in step S504, and calculates the degradation coefficient η of the battery pack 10 based on the usage history by using the degradation degree D (S505).

[0124] In step S506, the electronic control unit 30 calculates the allowable input current value Iii_m[t] based on the above mathematical expression (2). The allowable input current value Iii_m[t] is calculated at predetermined intervals when the battery pack 10 is being charged or discharged or when the battery pack 10 is left standing. That is, each time the predetermined time corresponding to the interval between time t and time (t-1) elapses, the allowable input current value Iii_m[t] is updated. Here, the allowable input current value Iu_m[t] is used only when the charging of the battery pack 10 is controlled.

[0125] In step S507, the electronic control unit 30 calculates the allowable input current value Iii_m_d[t] based on the above mathematical expression (5). Here, the allowable input current value Iii_m[t] calculated in the process of step S506 is used as the allowable input current value Iii_m[t] shown in the above mathematical expression (5). The degradation coefficient η is the one calculated in step S505.

[0126] After the allowable input current value Iij_m_d[t] is calculated, the electronic control unit 30 controls the input/output (charging or discharging) of the battery pack 10 based on the allowable input current value Iii_m_d[t]. The electronic control unit 30 sets the input limit value (electric power) Win[t] based on the allowable input current value Iij_m_d[t] as shown in the mathematical expression (5), and controls the input of the battery pack 10 such that the input electric power of the battery pack 10 does not exceed the set input limit value Win[t]. The details are as described above.

[0127] Here, the electronic control unit 30 is able to update the estimated usage history of the battery pack 10 in step S503, That is, the electronic control unit 30 updates the estimated usage history by using the measured results of a measuring device, such as the temperature sensor 23, that measures the usage environment of the battery pack 10, and calculates the degradation degree D based on the estimated usage history into which the measured results are reflected. Therefore, after the usage history is lost, the actually measured results of the usage environment of the battery pack 10 are reflected into the estimated usage history, so it is possible to carry out accurate estimation of degradation based on the usage environments in an actual usage of the battery pack 10.

[0128] On the other hand, because the measured results of the usage environment of the battery pack 10 are reflected in the estimated usage history, it is possible to carry out more accurate estimation of degradation based on the usage environments in an actual usage of the battery pack 10 as the period of use of the battery pack 10 elapses in the estimated usage history. However, when the estimated usage history significantly differs from the usage environments (battery temperatures) in an actual usage of the battery pack 10, it is not possible to accurately estimate the degradation degree D. That is, it takes time until the actually measured results of the usage environment of the battery pack 10 are reflected into the estimated usage history and then the estimated usage history becomes close to a usage history in an actually used environment, so the degradation degree D that deviates from the usage environments (battery temperatures) in an actual usage of the battery pack 10 is calculated.

[0129] The usage history may be generated by storing measured results in a predetermined period from current timing to a set period before. That is, the usage history may be configured as the frequencies of battery temperatures stored within the set period. After the battery temperature frequencies have been stored for the set period, the battery temperature frequencies are allowed to be generated so as not to include the battery temperature frequencies older the set period before each time the actually measured results of the usage environment of the battery pack 10 are reflected. With this configuration, it is possible to accurately calculate the degradation of the battery in response to a change in usage environment.

[0130] Not limited to the battery temperature frequencies within the set period, the battery temperature frequencies may be generated by storing all the battery temperature frequencies from the initial stage after manufacturing to current timing. In this case, the usage history may be generated such that the battery temperature frequencies older the set period before from the current timing are reflected into the usage history at a predetermined percentage. This is because the past usage history also influences the degradation of the battery.

[0131] Therefore, in the first embodiment, when the estimated usage history deviates from the actually measured results of the usage environment thereafter by a predetermined amount or larger, the degradation degree D suitable for an actual usage environment of the battery pack 10 is allowed to be accurately estimated by generating the estimated period of use generated in order to calculate the degradation degree D again.

[0132] FIG. 14 is a graph that shows a comparative example between estimated battery temperature frequencies that constitute the estimated usage history and actually measured additional usage history based on the actually measured results. The electronic control unit 30, for example, is able to separately store an additional usage history including the frequencies of usage environments based on the measured results while holding the estimated usage history before the measured results are reflected, in the memory 31 in addition to the process of incorporating the measured results into the estimated usage history in step S503 shown in FIG. 13.

[0133] In FIG. 14, the temperature frequencies indicated by the dotted lines are the estimated usage history before the actually measured results of the usage environment are reflected, and the temperature frequencies indicated by the continuous lines are the additional usage history based on only the actually measured results of the usage environment. The abscissa axis represents a battery temperature, and the ordinate axis represents a duration.

[0134] As shown in FIG. 14, the estimated usage history before the actually measured results of the usage environment are reflected has a distribution in which the temperature frequencies (durations) in the region from the temperature T3 to the temperature T5 are large, and the additional usage history has a distribution in which the temperature frequencies (durations) in the region from the temperature T2 to the temperature T4 is large. Such variations in temperature frequency are calculated through statistical processing, such as standard deviation, and, when the battery temperature frequencies of the estimated usage history before the actually measured results of the usage environment are reflected differ from the battery temperature frequencies of the additional usage history by a predetermined value or larger, the electronic control unit 30 executes regenerating process so as to generate the re-estimated usage history based on the additional usage history formed of only the actually measured results of the usage environment.

[0135] When the battery temperature frequencies of the estimated usage history before the actually measured results of the usage environment are reflected differ from the battery temperature frequencies of the additional usage history by the predetermined value or larger, the electronic control unit 30 calculates the estimated period of use (which corresponds to the first estimated period of use) corresponding to the full charge capacity that is calculated from the charge/discharge history of the battery pack 10 by using the degradation behavior map corresponding to the battery temperature frequencies of the additional usage history.

[0136] FIG. 15 is a graph that shows an example in which the total use time of the battery pack 10 is re-calculated by using the degradation behavior map based on the additional usage history formed of only the actually measured results of the usage environment. In FIG. 15, the continuous line indicates a degradation behavior map 1 (which corresponds to first estimated degradation information) at the battery temperature frequencies of the additional usage history. The alternate long and short dashed line indicates a degradation behavior map 2 used at the time when the estimated usage history before the actually measured results of the usage environment are reflected is calculated. The abscissa axis represents a use time, and the ordinate axis represents a full charge capacity.

[0137] As shown in FIG. 15, the degradation behavior map 1 differs from the degradation behavior map 2, and has a different estimated period of use of the battery pack 10, corresponding to the current full charge capacity C2 of the battery pack 10. In the example shown in FIG. 15, the degradation behavior map 1, as compared to the degradation behavior map 2, has a degradation behavior in which the full charge capacity is hard to decrease even when the use time extends. That is, in the estimated value of the total period of use of the battery pack 10 up to the present for the same full charge capacity C2, the T_to3 of the degradation behavior map 1 is longer than the T_to2 of the degradation behavior map 2.

[0138] In this way, in the first embodiment, the estimated period of use corresponding to the full charge capacity that is calculated from the charge/discharge history of the battery pack 10 by using the degradation behavior map 1 that defines in advance the correlation between a period of use of the battery pack 10 and a change in full charge capacity, corresponding to the battery temperature frequencies of the additional usage history, and, as in the case of the presence probability distribution of the battery temperatures, shown in FIG. 10, the estimated usage history (which corresponds to the first estimated usage history) is regenerated for calculating the degradation degree D based on the presence probability distribution of the battery temperatures, defined in advance based on the degradation behavior map 1.

[0139] FIG. 16 is a graph that shows an example of the estimated usage history newly generated based on the total use time based on the additional usage history and the presence probability distribution of the battery temperatures of the degradation behavior map 1. The electronic control unit 30 is able to generate the estimated battery temperature frequencies in the estimated period of use T_to3 based on the calculated estimated period of use T_to3 and the presence probabilities P of the battery temperatures, defined in advance based on the degradation behavior map 1. The regenerated estimated battery temperature frequencies are stored in the memory 31 as the estimated usage history for calculating the degradation degree D.

[0140] FIG. 17 is a flowchart that illustrates the process of regenerating the estimated usage history based on the additional usage history. As shown in FIG. 17, in the regenerating process, when the additional usage history is stored the predetermined value or larger (S701), the electronic control unit 30 determines whether the battery temperature frequencies of the estimated usage history before the actually measured results of the usage environment are reflected differ from the battery temperature frequencies of the additional usage history by the predetermined value or larger (S702). In step S701, when the additional usage history is not stored the predetermined value or larger, that is, when the actually measured results of the usage environment for updating the estimated usage history generated based on the degradation behavior map 2 are not reflected the predetermined value or larger, the regenerating process is not executed. This is because, when the number of the battery temperature frequencies based on the actually measured results of the usage environment, which constitute the additional usage history, is small, it is not possible to accurately determine an actual usage environment of the battery pack 10.

[0141] When the additional usage history is stored the predetermined value or larger and the battery temperature frequencies of the estimated usage history before the actually measured results of the usage environment are reflected differ from the battery temperature frequencies of the additional usage history by the predetermined value or larger, the electronic control unit 30 acquires or calculates the current full charge capacity C2 of the battery pack 10 as in the case of step S302 shown in FIG. 12 (S703).

[0142] The electronic control unit 30 extracts the degradation behavior map 1 having a presence probability distribution of the battery temperatures corresponding to the battery temperature frequencies of the additional usage history from among the plurality of degradation behavior maps that define in advance the correlation between a total period of use of the battery pack 10 and a change in full charge capacity, stored in the memory 31 (S704).

[0143] The electronic control unit 30 calculates the estimated period of use T_to3 corresponding to the current full charge capacity C2 of the battery pack 10 by using the degradation behavior map 1 corresponding to the battery temperature frequencies of the extracted additional usage history (S705).

[0144] Subsequently, the electronic control unit 30 calculates the presence probabilities of the battery temperatures by consulting the presence probability distribution of the battery temperatures, corresponding to the degradation behavior map 1 used to calculate the estimated period of use T_to3 (S706).

[0145] The electronic control unit 30 generates the estimated battery temperature frequencies in the estimated period of use T_to3 based on the calculated estimated period of use T_to3 and the presence probabilities P of the battery temperatures (S707). The estimated battery temperature frequencies based on the regenerated additional usage history are stored in the memory 31 as the estimated usage history for calculating the degradation degree D (S708).

[0146] In the first embodiment, when the current usage history of the battery pack 10 in the period of use becomes unavailable, it is possible to accurately estimate (calculate) the degradation degree D by using the estimated usage history based on the current full charge capacity measured value, and it is possible to appropriately control the input/output of the battery pack 10 based on the estimated degradation degree. Therefore, it is possible to accurately carry out battery abnormality determination or remaining service life determination for the battery pack 10 thereafter. For example, the estimated period of use obtained from the full charge capacity measured value is compared with the actual period of use of the vehicle, and it may be determined that the battery is abnormal when the estimated period of use is longer than the actual period of use. By comparing the estimated period of use with a preset period of use upper limit value of the battery pack 10, it is possible to determine the remaining service life of the battery pack 10 (for example, how long does the battery pack 10 last until it becomes unusable). A determination result as to battery abnormality or remaining service life may be informed to a user through a display device, an alarm lamp, or the like, mounted on the vehicle.

[0147] Next, a second embodiment of the invention will be described. FIG. 18 is a view that shows the process of controlling the charging or discharging of the battery pack 10 according to the second embodiment, and is a flowchart that illustrates the process of setting an allowable input current value by using a first degradation degree based on the usage history and a second degradation degree based on the charge/discharge history.

[0148] In the second embodiment, for the degradation coefficient η that uses the degradation degree Dr based on the charge/discharge history of the battery pack 10, the degradation coefficient η is calculated in consideration of the degradation degree D based on the usage history according to the first embodiment.

[0149] As shown in FIG. 18, the electronic control unit 30 detects the current value IB of the battery pack 10 based on the output of the current sensor 22 in step S901.

The electronic control unit 30 detects the temperature TB of the battery pack 10 based on the output of the temperature sensor 23. In addition, the electronic control unit 30 detects the voltage VB of the battery pack 10 based on the output of the monitoring unit 21. In step S902, the electronic control unit 30 estimates the SOC of the battery pack 10.

[0150] In step S903, the electronic control unit 30 updates the usage history of the battery pack 10 as in the case of step S503 in FIG. 13. In step S904, the electronic control unit 30 calculates the age of service of the battery pack 10. The age of service of the battery pack 10 may be, for example, acquired through a time counting process by the timer 32 with reference to the age of service 0 years (initial stage after manufacturing).

Information about the age of service may be stored (updated) in the memory 31 as needed.

The electronic control unit 30 acquires the age of service (for example, in years) from the memory 31.

[0151] In step S905, the electronic control unit 30 calculates the internal resistance R of the single cells 11 based on the detected current value IB and voltage value VB. As a method of calculating the internal resistance R, for example, the internal resistance R of the single cells 11 may be estimated by detecting the current value IB and voltage value VB of the single cells 11.

[0152] Specifically, the current value IB and the voltage value VB are detected, and the detected current value IB and voltage value VB are plotted in a coordinate system having a current value and a voltage value as coordinate axes. When a straight line approximated to a plurality of plots, the slope of the approximate straight line is allowed to be calculated as the internal resistance (calculated internal resistance value) R of the single cells 11.

[0153] In step S906, the electronic control unit 30 calculates the degradation degree Dr by using the calculated internal resistance R. FIG. 19 is a graph that shows the correlation between the internal resistance of the single cells 11 (battery pack 10) and the degradation degree Dr. It is known that the internal resistance R increases as the single cells 11 degrade, and, for example, an increase in the internal resistance R based on the age of service and the degradation degree Dr may be caused to correlate with each other with reference to the internal resistance RO in the initial stage after manufacturing at the age of service 0 years. In FIG. 19, numerals assigned to the internal resistances R indicate the ages of service (periods of use) of the battery pack 10.

[0154] In the example of FIG. 19, for example, a degradation parameter map that associates the degradation degree Dr with each internal resistance R at each age of service may be generated such that the degradation degree Dr increases with an increase in the internal resistance R.

[0155] Subsequently, the electronic control unit 30 acquires the degradation degree D based on the usage history from the memory 31 in step S907, calculates a correction value D' based on a deviation (differential) between the degradation degree Dr based on the charge/discharge history and the degradation degree D based on the usage history, and calculates the corrected degradation degree Dh of the battery pack 10 by adding the correction value D' to the degradation degree Dr. At this time, the electronic control unit 30 may determine whether the degradation degree Dr and the degradation degree D deviate from each other by a predetermined value or larger, and may be configured to calculate the corrected degradation degree Dh when it is determined that the degradation degree Dr and the degradation degree D deviate from each other by the predetermined value or larger, and may be configured to calculate the corrected degradation degree Dh when it is determined that the deviation is larger than or equal to the predetermined value.

[0156] FIG. 20 is a graph that shows the correlation of the corrected degradation degree Dh that incorporates the degradation degree D based on the usage history to the degradation degree Dr based on the charge/discharge history. The corrected degradation degree Dh is calculated by adding (or subtracting) the correction value D' to the degradation degree Dr based on the charge/discharge history.

[0157] The correction value D' of the degradation degree may be, for example, calculated based on a difference between the degradation degree Dr and the degradation degree D. As described above, the degradation degree Dr based on the charge/discharge history can be estimated to be lower (or higher) although degradation has advanced because the voltage value, the current value, and the like, detected by the sensors include sensor errors.

[0158] Therefore, in the second embodiment, the correction value D' of the degradation degree is associated in advance with a differential value between the degradation degree Dr based on the charge/discharge history and the degradation degree D based on the usage history. When the differential value is large, the estimation of degradation of the degradation degree Dr is corrected to increase by increasing the correction value D'. When the differential value is small, the estimation of degradation of the degradation degree Dr is corrected to reduce by reducing the correction value D'. The differential value between the degradation degree Dr based on the charge/discharge history and the degradation degree D based on the usage history and the correction value D' of the degradation degree may be set as a map in advance based on actually measured values, shown in FIG. 7, an experiment, or the like.

[0159] In step S909, the electronic control unit 30 calculates the degradation coefficient η of the battery pack 10 by using the degradation degree Dh calculated in step S908. The degradation coefficient η may be calculated by using the correlation between the degradation degree D and the degradation coefficient η, shown in FIG. 4.

[0160] When the differential value is a deviation that falls within a predetermined value, the degradation coefficient η may be calculated by using only the degradation degree Dr based on the charge/discharge history without incorporating the correction value D'.

[0161] In step S910, the electronic control unit 30 calculates the allowable input current value Iu_m[t] based on the above mathematical expression (2) as in the case of step S506 in FIG. 13. In step S911, the electronic control unit 30 calculates the allowable input current value I_lim_d [t] based on the above mathematical expression (4) as in the case of step S507 in FIG. 13. Here, the value calculated in step S909 is used as the degradation coefficient η for obtaining the allowable input current value Iii_m_d[t].

[0162] After the allowable input current value Iii_m_d[t] is calculated, the electronic control unit 30 controls the input/output (charging or discharging) of the battery pack 10 based on the allowable input current value Iij_m_d[t]. As expressed by the mathematical expression (5), the electronic control unit 30 sets the input limit value (electric power) Win[t] of the battery pack 10 based on the allowable input current value Iii_m_d[t], and controls the battery input of the battery pack 10 such that the input electric power of the battery pack 10 does not exceed the set input limit value Win[t].

[0163] In this way, in the second embodiment, the estimation of degradation of the battery pack 10 is carried out by a plurality of methods, the first degradation degree calculated based on the usage history is compared with the second degradation degree calculated based on the charge/discharge history, and, the mutual degradation degrees deviate from each other by the predetermined value or larger, the degradation degree for calculating the degradation coefficient η is corrected based on the degree of deviation from the other degradation degree, and the input of the battery pack 10 is controlled such that the allowable input current value is decreased with the corrected degradation degree Dh.

[0164] That is, in the second embodiment, at the time of updating the allowable input current value Iii_m[t], the charging (battery input) of the battery pack 10 is controlled while reducing the allowable input current value Iu_m[t] by applying the degradation coefficient η (< 1) based on the degradation state of the battery pack 10, and the rate of reduction (degradation coefficient η) at the time of reducing the allowable input current value Iii_m[t] is changed based on the degradation degree based on the charge/discharge history (which corresponds to the second degradation degree) and the degradation degree based on the usage history (first degradation degree). With this configuration, even when the degradation degree Dr based on the charge/discharge history is estimated to be low, it is possible to accurately estimate the degradation degree of the battery pack 10 based on the degradation degree D based on the usage history.

[0165] In the above description, the first degradation degree D calculated based on the usage history is compared with the second degradation degree Dr calculated based on the charge/discharge history, and, when the mutual degradation degrees deviate from each other by the predetermined value or larger, the degradation degree Dh is calculated by correcting the degradation degree Dr. Instead, the degradation degree Dh may be calculated by correcting the degradation degree D. That is, the degradation degree D for calculating the degradation coefficient η may be corrected based on the degree of deviation with respect to the other degradation degree Dr, and the input of the battery pack 10 may be controlled such that the allowable input current value is reduced based on the corrected degradation degree Dh.

[0166] In the above description, the estimation of degradation that uses the internal resistance R of the battery pack 10 is described as one example of a degradation estimation method for the battery pack 10 based on the charge/discharge history. Instead, the estimation of degradation based on the charge/discharge history that is calculated based on the full charge capacity, the OCV (OCV fluctuations in the single cells 11 with respect to SOC fluctuations), or the like may be carried out.

[0167] For example, as the single cells 11 degrade, the full charge capacity reduces, so the degradation parameter map that associates the degradation degree with each full charge capacity of each age of service is allowed to be generated such that the degradation degree increases with a decrease in full charge capacity. The degradation parameter map that associates the degradation degree with each percentage of OCV fluctuations with respect to the SOC fluctuation width of each age of service is allowed to be generated such that the degradation degree increases with an increase in the percentage of OCV fluctuations with respect to the SOC fluctuation width.

[0168] In the above-described first embodiment and second embodiment, an example of the estimation of degradation of the battery pack 10 mounted on the vehicle and input control over the battery pack 10 is described; however, the invention is not limited to this configuration. That is, as long as a system controls the charging of a lithium ion secondary battery in order to suppress precipitation of lithium metal, the invention is applicable.

[0169] The lithium ion secondary battery is illustrated as each of the single cells 11 that constitute the battery pack 10. Instead, it is also possible to estimate the degradation degree based on a usage history including the frequency of each usage environment even in another secondary battery, such as a nickel-metal hydride battery. In this case, by applying the invention, even when an actual usage history of the battery pack 10 in a period of use becomes unavailable, it is possible to accurately estimate (calculate) a degradation degree by using an estimated usage history.

Claims

CLAIMS:

1. A control device for an electrical storage device that is charged or discharged, the control device comprising:

an electronic control unit configured to:

(a) estimate a degradation degree based on a change in full charge capacity of the electrical storage device by using a usage history including a frequency of each usage environment in a period of use of the electrical storage device,

(b) control input/output of the electrical storage device based on the degradation degree,

(c) calculate an estimated period of use of the electrical storage device by using the full charge capacity and estimated degradation information when the usage history in the period of use is unavailable, the full charge capacity being calculated from a charge/discharge history of the electrical storage device, the estimated degradation information defining in advance a correlation between a period of use of the electrical storage device and a change in full charge capacity, and

(d) generate an estimated usage history in the estimated period of use for calculating the degradation degree based on an estimated frequency of each usage environment, the estimated frequency being defined in advance based on the estimated degradation information.

2. The control device according to claim 1, wherein

the electronic control unit is configured to update the estimated usage history by using measured results of a measuring device that measures the usage environment of the electrical storage device, and

the electronic control unit is configured to calculate the degradation degree based on the estimated usage history in which the measured results is reflected.

3. The control device according to claim 2, wherein

the electronic control unit is configured to compare the estimated usage history before the measured results are reflected with an additional usage history including the frequency of each usage environment based on the measured results, and

the electronic control unit is configured to generate the re-estimated usage history based on the additional usage history when the mutual frequencies of each usage environment differ from each other by a predetermined value or larger.

4. The control device according to claim 3, wherein

the electronic control unit is configured to calculate a first estimated period of use of the electrical storage device by using the full charge capacity and first estimated degradation information when the estimated usage history before the measured results are reflected and the additional usage history differ from each other by the predetermined value or larger,

the full charge capacity is calculated from the charge/discharge history of the electrical storage device,

the first estimated degradation information corresponds to a frequency of each usage environment of the additional usage history and the first estimated degradation information defines in advance a correlation between a period of use of the electrical storage device and a change in full charge capacity, the correlation is different from the estimated degradation information, and

the electronic control unit is configured to generate a first estimated usage history in the first estimated period of use for calculating the degradation degree based on an estimated frequency of each usage environment, the estimated frequency is defined in advance based on the first estimated degradation information.

5. The control device according to any one of claims 1 through 4, wherein each usage environment is any one of a temperature of the electrical storage device, a level of charge of the electrical storage device and a temperature at each level of charge, and

the usage history includes any one of a frequency of each temperature, a frequency of each level of charge and a frequency of each temperature at each level of charge.

6. The control device according to any one of claims 1 through 5, wherein the electrical storage device is a non-aqueous secondary battery, and

the electronic control unit is configured to control input of the non-aqueous secondary battery while reducing an allowable input current value based on the degradation degree, the allowable input current value is a maximum current value up to which the input of the non-aqueous secondary battery is allowed.

7. The control device according to claim 6, wherein the electronic control unit is configured to reduce the allowable input current value on the basis of a first degradation degree based on the usage history and a second degradation degree based on the charge/discharge history of the non-aqueous secondary battery.

8. The control device according to claim 7, wherein

the electronic control unit is configured to compare the first degradation degree with the second degradation degree,

the electronic control unit is configured to calculate a corrected degradation degree when the mutual degradation degrees deviate from each other by a predetermined value or larger, and

the electronic control unit is configured to reduce the allowable input current value based on the corrected degradation degree.

9. A control method for an electrical storage device that is charged or discharged, the control method comprising:

determining whether a usage history of the electrical storage device in a period of use is unavailable;

calculating an estimated period of use of the electrical storage device by using a full charge capacity and estimated degradation information when the usage history in the period of use is unavailable, the full charge capacity being calculated from a charge/discharge history of the electrical storage device in the period of use, and the estimated degradation information defining in advance a correlation between a period of use of the electrical storage device and a change in full charge capacity;

generating an estimated usage history in the estimated period of use based on an estimated frequency of each usage environment, the estimated frequency being defined in advance based on the estimated degradation information;

calculating the degradation degree by using the generated estimated usage history; and

controlling input/output of the electrical storage device based on the calculated degradation degree.