JP2016170885A - Battery control device, battery control method and lower limit voltage determining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery control device, a battery control method and a lower limit voltage determining method that can more properly set a lower limit voltage for regulating discharge of a battery.SOLUTION: A battery control device 50 for controlling discharging of a secondary battery 10 having a positive electrode containing a main active material and a metal compound as an additive includes, an SOC calculation unit 51 for achieving a charge state representing the rate of the remaining capacity to the full charge capacity of the secondary battery 10, a temperature obtaining unit 52 for obtaining the temperature of the secondary battery 10, and a lower limit voltage setting unit 53 for setting the lower limit voltage of the secondary battery 10. The lower limit voltage setting unit 53 sets the lower limit voltage as a higher value as the latest SOC of the secondary battery 10 is lower, and sets the lower limit voltage as a higher value as the temperature obtained under the condition that the latest SOC of the secondary battery 10 is the same is higher.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a battery control device, a battery control method, and a lower limit voltage determination method used for controlling a battery mounted on a vehicle such as an electric vehicle or a hybrid vehicle.

  A secondary battery such as a nickel metal hydride battery has a lower limit voltage for suppressing deterioration of battery characteristics such as a decrease in capacity and an increase in internal resistance. Generally, this lower limit voltage is a fixed value, and the discharge is controlled so that the battery voltage does not fall below the lower limit voltage. Patent Document 1 proposes a battery control device that sets a lower limit voltage of an input / output voltage of a battery according to a battery temperature and controls discharge of a secondary battery based on the lower limit voltage. This battery control device sets the lower limit voltage when the battery temperature is low to be equal to or lower than the lower limit voltage when the battery temperature is high.

Japanese Patent No. 4200256

  According to the battery control device described in Patent Literature 1, the secondary battery is prevented from being deteriorated by being regulated such that the voltage during discharging does not fall below the lower limit voltage. However, in recent years, there has been a demand for more effective use of the amount of power stored in the secondary battery. However, if the lower limit voltage is set lower than necessary, there is a high possibility that the secondary battery will deteriorate when a sudden discharge or the like occurs. Therefore, it is required to set the lower limit voltage that restricts the discharge more appropriately.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a battery control device, a battery control method, and a lower limit voltage determination method that can more appropriately set a lower limit voltage that regulates battery discharge. Is to provide.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
A battery control device that solves the above problem is a battery control device that controls the discharge of a secondary battery having a positive electrode including a main active material and a metal compound as an additive, with respect to the full charge capacity of the secondary battery. A charge state acquisition unit that acquires a charge state indicating a ratio of the remaining capacity, a temperature acquisition unit that acquires a temperature of the secondary battery, and a lower limit voltage setting unit that sets a lower limit voltage of the secondary battery, The lower limit voltage setting unit sets the lower limit voltage as a higher value as the charged state of the secondary battery is lower, and the acquired temperature is higher under the condition that the charged state of the secondary battery is the same. Set a higher value.

  A battery control method for solving the above problem is a battery control method for controlling discharge of a secondary battery having a positive electrode containing a main active material and a metal compound as an additive by a battery control device, wherein the battery control device is The lower limit voltage of the secondary battery is set as a higher value as the state of charge indicating the ratio of the remaining capacity to the full charge capacity of the secondary battery is lower, and the state of charge of the secondary battery is the same Below, it sets as a high value, so that the said acquired temperature is high.

  According to the above configuration or the above method, the lower limit voltage is set based on the state of charge of the secondary battery in addition to the temperature of the secondary battery. Thereby, the lower limit voltage which regulates the discharge of the secondary battery is set more appropriately. And by setting such a lower limit voltage, deterioration of the performance of the secondary battery is also suppressed, and the battery life can be extended. In addition, since the lower limit voltage is not set higher than necessary, the output range of the secondary battery is widened, more power output is possible, and the output performance of the secondary battery is enhanced.

  The battery control device includes a discharge time measuring unit that measures a discharge time that is a time during which the secondary battery is continuously discharged, and the lower limit voltage setting unit has the same charge state and temperature of the secondary battery. Under certain conditions, it is preferable to set a lower value as the measured discharge time is shorter.

  According to the above configuration, the lower limit voltage is set based on the discharge time in addition to the charge state and temperature of the secondary battery. Thus, by setting the lower limit voltage, the lower limit voltage can be set in accordance with the situation where the secondary battery is discharged. Therefore, the lower limit voltage can be set appropriately.

  A method for determining a lower limit voltage for solving the above problem is a method for determining a lower limit voltage for determining a lower limit voltage used for discharge control of a secondary battery having a positive electrode including a main active material and a metal compound as an additive. Measuring the potential of the positive electrode and the battery voltage while discharging the secondary battery under a plurality of conditions with different combinations of charge state and temperature indicating the ratio of the remaining capacity to the full charge capacity of the secondary battery, The lower limit voltage for regulating the discharge of the secondary battery is determined in advance based on the battery voltage when the potential reaches the starting potential of the metal elution reaction of the metal compound.

  A secondary battery having a positive electrode containing a main active material and a metal compound is likely to deteriorate when the potential of the positive electrode reaches the starting potential of the metal elution reaction of the metal compound. Further, when the secondary battery is discharged with a large current, the lower the charged state of the secondary battery, the sharper the potential of the positive electrode is compared to the increase of the potential of the negative electrode. Therefore, the battery voltage, which is the difference between the potential of the positive electrode and the potential of the negative electrode when the potential of the positive electrode reaches the starting potential of the metal elution reaction, becomes higher as the charged state of the secondary battery is lower. According to the above method, the lower limit voltage is predetermined based on the battery voltage when the potential of the positive electrode reaches the starting potential of the metal elution reaction of the metal compound, and is determined for each combination of the charge state and temperature. . If the lower limit voltage is set according to the charging state and temperature of the secondary battery whose charging and discharging are controlled based on the predetermined lower limit voltage in this way, the deterioration of the performance of the secondary battery is also suppressed. As a result, the battery life can be extended. In addition, since the lower limit voltage is not set higher than necessary, the output range of the secondary battery is widened, more power output is possible, and the output performance of the secondary battery is enhanced.

  Regarding the determination method of the lower limit voltage, a discharge time which is a time during which the discharge of the secondary battery is continued is obtained, a charging state of the secondary battery, a temperature of the secondary battery, and the secondary battery Preferably, the lower limit voltage is determined in advance under a plurality of conditions having different combinations with the discharge time.

  When the discharge time of the secondary battery is different, the potential of the negative electrode is different when the potential of the positive electrode reaches the starting potential of the metal elution reaction of the metal compound. Therefore, the lower limit voltage, which is the difference between the positive electrode potential and the negative electrode potential, also varies depending on the length of the discharge time. According to the above method, the secondary battery in which the combination of the charging state, the temperature, and the discharge time is different from each other is discharged, and when the potential of the positive electrode reaches the starting potential of the metal elution reaction of the metal compound, The lower limit voltage is predetermined based on the voltage. Thus, if the lower limit voltage is set based on the discharge time in addition to the charge state and temperature, the lower limit voltage can be set in accordance with the secondary battery whose discharge and charge are controlled. Therefore, the lower limit voltage can be set appropriately.

  About the determination method of the said lower limit voltage, it is preferable to preset previously the battery voltage of the said secondary battery as a lower limit voltage, when the electric potential of the said positive electrode reaches the starting electric potential of the metal elution reaction of a metal compound.

  For example, the timing at which the value for calculating the state of charge of the secondary battery, such as the magnitude of the current and the voltage, is measured may be delayed with respect to the timing for obtaining those parameters in the step of determining the lower limit voltage. There is sex. Further, when the secondary battery is discharged with a large current, the voltage of the secondary battery tends to decrease as the discharge continues. Therefore, if the timing for acquiring the value for calculating the state of charge of the secondary battery is delayed, the lower limit voltage is set to be lower. In the above method, when the lower limit voltage is determined in advance, the battery voltage of the secondary battery a predetermined time before the potential of the positive electrode reaches the start potential of the metal elution reaction of the metal compound is determined as the lower limit voltage. If it does in this way, a lower limit voltage will be set high compared with the case where it sets as a battery voltage when the electric potential of a positive electrode reaches the starting electric potential of a metal elution reaction. Therefore, depending on the setting of the predetermined time, even if the timing at which the value for calculating the state of charge of the secondary battery is measured is delayed with respect to the measurement timing in the step of determining the lower limit voltage in advance, the potential of the positive electrode is It is possible to suppress the battery voltage from dropping below the starting potential of the metal elution reaction. For this reason, at least deterioration of the secondary battery can be suppressed.

  According to the present invention, the lower limit voltage for regulating battery discharge can be set more appropriately.

The block diagram which shows the outline of the structure about 1st Embodiment of a battery control apparatus. The graph which shows the relationship between a lower limit voltage and temperature when discharge time is a short time including the relationship with SOC. The graph which shows the relationship between a lower limit voltage and temperature when discharge time is long including the relationship with SOC. The block diagram which shows the outline of the structure for measuring a lower limit voltage. The figure which shows the specific example of the calculation method of a minimum voltage. The graph which shows the specific example of the lower limit voltage when discharge time is a short time, and the lower limit voltage when discharge time is long time. 5 is a flowchart showing a procedure of processing for setting a lower limit voltage in the embodiment. 4 is a flowchart illustrating a procedure for low temperature setting processing in the embodiment. 4 is a flowchart illustrating a procedure for high temperature setting processing in the embodiment. The figure which shows the specific example of the calculation method of a lower limit voltage about 2nd Embodiment of a battery control apparatus.

(First embodiment)
Hereinafter, a first embodiment of a battery control device, a battery control method, and a lower limit voltage determination method will be described.

  First, a secondary battery 10 mounted on a vehicle such as an electric vehicle or a hybrid vehicle will be described with reference to FIG. In the present embodiment, the secondary battery 10 is connected to an electric motor that is a load. Further, the secondary battery 10 is connected to an in-vehicle charger that can be connected to an external power source, and is charged by electric power supplied via the in-vehicle charger. Alternatively, when the vehicle is a hybrid vehicle equipped with an engine, the secondary battery 10 is charged with electric power generated by driving a generator mounted on the vehicle.

  The secondary battery 10 is an assembled battery in which a plurality of battery modules 11 are electrically connected in series or in parallel. The battery module 11 includes a plurality of unit cells 100 made of nickel metal hydride secondary batteries, and the unit cell 100 includes a negative electrode including a hydrogen storage alloy and a positive electrode including nickel hydroxide.

  The positive electrode includes a foamed nickel substrate that is a metal porous body, a positive electrode active material mainly composed of nickel oxide, nickel oxyhydroxide, or the like filled in the foamed nickel substrate, and an additive (such as a conductive agent). Have. The conductive agent is a cobalt compound such as cobalt oxyhydroxide and covers the surface of the nickel oxide.

The negative electrode has an electrode support made of punching metal or the like and a hydrogen storage alloy applied to the electrode support.
In the initial state, which is the state when the unit cell 100 is shipped, the positive electrode regulation is set such that the negative electrode capacity is larger than the positive electrode capacity. Thereby, the negative electrode capacity is provided with a charge reserve and a discharge reserve, which are capacity provided in excess of the positive electrode capacity. Therefore, the state in which the active material of the positive electrode has no uncharged portion, that is, the state in which the full charge is reached is also the fully charged state in the unit cell 100. In addition, the state in which the charged portion of the active material of the positive electrode is eliminated is a state where the remaining capacity of the single battery 100 is “0”.

  The battery module 11 is provided with six battery cases by partitioning the space inside the integrated battery case with a partition wall. Each battery case corresponds to the first cell 101 to the sixth cell 106 which are the unit cells 100. The battery module 11 includes a positive electrode terminal 12 and a negative electrode terminal 13 formed by electrically connecting the first cell 101 to the sixth cell 106 in series as input / output terminals used for charging and discharging. A positive side wiring PL and a negative side wiring NL, which are external wirings, are connected to the positive terminal 12 and the negative terminal 13, respectively. An electric motor, a power source, and the like are connected to the positive terminal 12 and the negative terminal 13 through a positive side wiring PL and a negative side wiring NL.

  In the battery module 11, a voltmeter 40 that measures the voltage between terminals is electrically connected between the positive terminal 12 and the negative terminal 13, and an ammeter 41 that measures input / output current is electrically connected to the negative wiring NL. Are connected in series. The voltmeter 40 outputs a signal corresponding to the measured inter-terminal voltage, and the ammeter 41 outputs a signal corresponding to the measured current to the battery control device 50, respectively.

  In FIG. 1, one voltmeter 40 is connected to each battery module 11, but one voltmeter 40 may be connected to a plurality of battery modules 11. In that case, the voltage measured by the voltmeter 40 is divided by the number of battery modules 11 to which the voltmeter 40 is connected, and the divided value is used as the voltage across the terminals of one battery module 11. The ammeter 41 may also be connected to the plurality of battery modules 11 and may be obtained as a current for each battery module 11 from the current measured by the ammeter 41.

  The battery control device 50 includes a computer having a calculation unit and a storage unit, and sets a lower limit voltage that regulates the discharge of the secondary battery through a calculation process in a calculation unit of a program stored in the storage unit or the like. Various processing such as processing is performed. The battery control device 50 calculates a state of charge (hereinafter referred to as SOC) indicating a charging rate of the secondary battery 10 and measures the temperature of the secondary battery 10. The battery control device 50 includes a calculation unit, a storage unit in which a program and the like are stored, and the calculation unit and the storage unit perform various calculations, whereby the SOC calculation unit 51, the temperature acquisition unit 52, and the lower limit voltage setting unit. 53 functions. The storage unit stores lower limit voltage data 54.

  The SOC calculation unit 51 inputs a signal corresponding to the voltage at a predetermined time interval from the voltmeter 40. Further, the SOC calculation unit 51 inputs a signal corresponding to the current from the ammeter 41 at a predetermined time interval. The SOC calculation unit 51 calculates the SOC for each battery module 11 from these signals and the like. The charging and discharging of the secondary battery are controlled so that charging and discharging is performed within the SOC range defined as the control range in the vehicle. The temperature acquisition unit 52 acquires the temperature of the secondary battery 10 based on the signal input from the thermometer 20. In addition, the lower limit voltage setting unit 53 determines whether or not the discharge of the secondary battery 10 is started from the current input from the ammeter 41 or the like.

  When the discharge of the secondary battery 10 is started, the lower limit voltage setting unit 53 acquires the latest SOC (hereinafter referred to as the latest SOC) and temperature measured before the discharge calculated by the SOC calculation unit 51 is started. The lower limit voltage of the battery module 11 is set according to the temperature acquired by the unit 52 and the discharge time during which the discharge has continued since the discharge was started. The “lower limit voltage” is the lower limit of the voltage at which the secondary battery 10 is allowed to discharge.

  When the lower limit voltage is set by the lower limit voltage setting unit 53, the load is set so that the secondary battery is discharged and charged from the lower limit voltage setting unit 53 within the range of the lower limit voltage or more and the separately set upper limit voltage or less. A command signal is transmitted to the control device that controls

  Next, with reference to FIG. 2 and FIG. 3, the lower limit voltage data 54 stored in the battery control device 50 will be described in detail in a two-dimensional map. The lower limit voltage data 54 may not be a map but may be stored in a table format, and the data format is not limited.

  The map shown in FIG. 2 is a map of short-time characteristics indicating the lower limit voltage when the discharge time is shorter than a predetermined time. The horizontal axis of the map is the temperature, and the vertical axis of the map is the lower limit voltage. The temperature is divided into a “low temperature region” and a “high temperature region” with the specific temperature Tp1 as a boundary. For example, the specific temperature Tp1 is “0 ° C.”, the “low temperature region” is a temperature range below 0 ° C., and the “high temperature region” is a temperature range of 0 ° C. or higher.

In the low temperature range, the lower limit voltage is determined by one lower limit voltage change line L1. The lower limit voltage change line L1 increases as the temperature increases.
In the high temperature range, as with the low temperature range, the lower limit voltage is determined to increase as the temperature increases, but the lower limit voltage change lines L2 to L4 are determined for each range of the latest SOC. The range of the latest SOC is divided into the latest SOC “low”, the latest SOC “medium”, and the latest SOC “high”. For example, when the latest SOC is “0% or more and less than 30%”, the latest SOC is “low”, and when it is “30% or more and less than 60%”, the latest SOC is “medium” or “60% or more and less than 100%”. In some cases, the latest SOC is “high”. In the high temperature range, the lower limit voltage becomes higher as the latest SOC becomes lower.

  The map shown in FIG. 3 is a long-time characteristic map indicating the lower limit voltage when the discharge time is equal to or longer than a predetermined time. The horizontal axis of the map is the temperature, and the vertical axis of the map is the lower limit voltage. The temperature is divided into a “low temperature region” and a “high temperature region” with the specific temperature Tp1 as a boundary.

  In the low temperature range, the lower limit voltage is determined by one lower limit voltage change line L5 that changes with a temperature change. The lower limit voltage change line L5 when the discharge time is long is higher than the lower limit voltage change line L1 when the discharge time is short under a condition where the temperature is the same.

  In the high temperature range, as in the case where the discharge time is short, the lower limit voltage change lines L6 to L8 are defined for the latest SOC “low”, the latest SOC “medium”, and the latest SOC “high”. In the high temperature range, the lower limit voltage becomes higher as the latest SOC becomes lower.

  Further, under the condition of the same temperature, the lower limit voltage change line L6 when the latest SOC is “low” and the discharge time is long is the lower limit voltage change line L6 when the latest SOC is “low” and the discharge time is short. The lower limit voltage is higher than the lower limit voltage change line L2. Under the condition of the same temperature, the lower limit voltage change line L7 when the latest SOC is “medium” and the discharge time is long is the lower limit voltage change line L7 when the latest SOC is “medium” and the discharge time is short. The lower limit voltage is higher than the change line L3. Under the condition of the same temperature, the lower limit voltage change line L8 when the latest SOC is “high” and the discharge time is long is the lower limit voltage change line L8 when the latest SOC is “high” and the discharge time is short. The lower limit voltage is higher than the change line L4.

  The lower limit voltage setting unit 53 refers to such a map, the latest SOC calculated by the SOC calculation unit 51, the temperature acquired by the temperature acquisition unit 52, and the discharge that has been discharged after the discharge is started. Set the lower limit voltage corresponding to time. For example, when the discharge time is less than a predetermined time, the short-time characteristic map of FIG. 2 is referred to. Further, when the latest SOC is “60%” and the temperature is “20 ° C.”, the lower limit voltage corresponding to the temperature “20 ° C.” is read out from the lower limit voltage change line L3 of the latest SOC “medium” and the reading is performed. Based on the lower limit voltage, it is set as the lower limit voltage at that time.

<Determination method of lower limit voltage>
Next, a method for determining the lower limit voltage for creating the lower limit voltage data 54 described with reference to FIGS. 2 and 3 will be described with reference to FIG.

  The unit cell 100 is an electrode in which a predetermined number of negative electrodes 111 containing a hydrogen storage alloy and a predetermined number of positive electrodes 112 containing nickel hydroxide are laminated via a separator (not shown) made of an alkali-resistant resin nonwoven fabric. A group 113 is provided. In the cell 100, the negative electrode 111 of the electrode group 113 is connected to the current collector plate 114 on the negative electrode side, the positive electrode 112 of the electrode group 113 is connected to the current collector plate 115 on the positive electrode side, and the electrolytic solution (not shown) is used. It is configured to be housed in a resin battery case. The lower limit voltage data 54 is created by obtaining the lower limit voltage of the unit cell 100. Therefore, when setting the lower limit voltage of the battery module 11, the lower limit voltage read from the lower limit voltage data 54 is multiplied by the same multiple (6 times in this embodiment) as the number of the single cells 100, and the multiplication is performed. The obtained value is set as the lower limit voltage of the battery module 11.

  As described above, the positive electrode contains a cobalt compound as a conductive agent. When a metal elution reaction in which cobalt elutes occurs, the metal elution reaction proceeds irreversibly, so that the possibility of deterioration of the positive electrode increases.

  Even when the latest SOC is within the control range of the secondary battery 10, when the voltage of the unit cell 100 decreases due to the discharge of a large current, the voltage at which the positive electrode potential Vp, which is the potential of the positive electrode 112, starts the cobalt elution reaction. (Hereinafter referred to as metal elution potential αV). The metal elution potential αV is, for example, “0.28V”. For this reason, in order to suppress deterioration, it is preferable to set the lower limit voltage of the unit cell 100 to the metal elution potential αV.

  The configuration of a measuring device that measures the lower limit voltage will be described. Here, a case will be described as an example where the third cell 103 of the battery cells 11 of the battery module 11 is the measurement target. For the other cells 101, 102, 104, 105 and 106, the lower limit voltage can be measured in the same manner as the third cell 103.

  A measuring device 60 that measures the lower limit voltage is connected to the third cell 103 via each measuring instrument. In the third cell 103, a positive electrode pin 63P is electrically connected to the current collector plate 115 on the positive electrode side, and a negative electrode pin 63N is electrically connected to the current collector plate 114 on the negative electrode side. A reference electrode 63C for measuring the positive electrode potential Vp and the negative electrode potential Vn is provided. As the reference electrode 63C, an electrode suitable for an electrolytic solution is usually used. In this embodiment, a mercury oxide reference electrode (Hg / HgO) suitable for an alkaline electrolyte is used.

  The third cell 103 is connected to a voltmeter 65P that measures the positive electrode potential Vp with respect to the reference electrode 63C and a voltmeter 65N that measures the negative electrode potential Vn with respect to the reference electrode 63C. The voltmeter 65P is electrically connected between the positive electrode pin 63P (wiring 64P) and the reference electrode 63C (wiring 64N), and the voltmeter 65N includes the negative electrode pin 63N (wiring 64N) and the reference electrode 63C (wiring). 64N). Further, a discharge circuit 69 for discharging the third cell 103 and an ammeter 68 for measuring a current flowing through the discharge circuit 69 are connected to the third cell 103. The discharge circuit 69 and the ammeter 68 are connected in series between the positive electrode pin 63P (wiring 64P) and the negative electrode pin 63N (wiring 64N).

  The voltmeters 65P and 65N, the discharge circuit 69, and the ammeter 68 are connected to the measuring device 60. The voltmeter 65P and the voltmeter 65N output a signal corresponding to each measured voltage, and the ammeter 68 outputs a signal corresponding to the measured current to the measuring device 60, respectively. The cell voltage Vc between the positive electrode pin 63P and the negative electrode pin 63N of the third cell 103 can be calculated from the measurement results of the voltmeters 65P and 65N.

  The third cell 103 is provided with a thermometer 67 for measuring the temperature in the battery case. The thermometer 67 outputs a signal corresponding to the measured battery temperature to the measuring device 60. The measuring device 60 includes a computer having a calculation unit and a storage unit, and performs various processes such as a lower limit voltage measurement process through a calculation process in a calculation unit of a program stored in the storage unit or the like. Further, the measuring device 60 acquires the positive electrode potential Vp, the negative electrode potential Vn, the discharge current, and the battery temperature of the third cell 103 from each input signal. Further, the measuring device 60 outputs an instruction for the amount of current to be discharged, and discharges a current corresponding to the output from the discharge circuit 69. At this time, a large current (for example, 7C to 30C) that is the largest current value or higher value required on the vehicle is discharged.

  The measuring device 60 includes an SOC calculation unit 61 and a lower limit voltage acquisition unit 62. The SOC calculation unit 61 calculates the latest SOC before flowing a large current of the third cell 103 by a known method. The SOC calculation unit 61 may use an inter-terminal voltage, an input / output current, or the like of the battery module 11 as necessary.

  The lower limit voltage acquisition unit 62 acquires the lower limit voltage of the third cell 103 according to the processing procedure for acquiring the lower limit voltage. The lower limit voltage acquisition unit 62 sets the condition for acquiring the lower limit voltage as a condition in which the temperature range of the temperature, the SOC, and the discharge time are combined, and acquires the lower limit voltage by making the combination different from each other as shown below. . For example, “the latest SOC“ high ”/ long time” in the “high temperature region” indicates a condition that the high temperature region, the latest SOC “high”, and the discharge time are long.

<High temperature range>
Latest SOC “High”, Long Time Latest SOC “High”, Short Time Latest SOC “Medium”, Long Time Latest SOC “Medium”, Short Time Latest SOC “Low”, Long Time Latest SOC “Low”, Short Time <Low Temperature Range>
Latest SOC “High”, Long Time Latest SOC “High”, Short Time Latest SOC “Medium”, Long Time Latest SOC “Medium”, Short Time Latest SOC “Low”, Long Time Latest SOC “Low”, Short Time Lower limit voltage For example, the latest SOC “high” is set to “80%”, the latest SOC “medium” is set to “60%”, and the latest SOC “low” is set to “20%”. Further, even in a high temperature range where the battery temperature is equal to or higher than the specific temperature Tp, the temperature is changed, for example, “0 ° C.”, “5 ° C.”, “10 ° C.”, etc. For example, since the temperature is changed like “−5 ° C.”, “−10 ° C.”, “−15 ° C.”, etc., the lower limit voltage is actually acquired under more conditions than the above 12 conditions. . Further, the discharge time is adjusted by changing the magnitude of the current flowing through the third cell 103.

  In addition, when the current SOC is the same as that of the latest SOC and the current of the same magnitude is passed, the time for the positive electrode potential Vp to reach the metal elution potential αV does not change. Therefore, when the lower limit voltage is acquired under conditions of different discharge times, the magnitude of the current flowing through the third cell 103 is changed. Specifically, when the discharge time is shortened, the discharge is performed with a large current, and when the discharge time is lengthened, the discharge is performed with a small current. Even in actual vehicle control, the discharge rate tends to increase when the discharge time of the secondary battery 10 is short, and the discharge rate tends to decrease when the discharge time is long. . In actual vehicle control, constant current discharge is not performed as in the process of determining the lower limit voltage, and the current value varies finely according to the output required for the motor. Yes. Therefore, the discharge conditions in the step of determining the lower limit voltage cannot be made exactly the same as the discharge conditions in actual vehicle control. Therefore, in this step, it is only necessary to obtain the lower limit voltage reflecting the tendency of the relationship between the discharge time and the lower limit voltage.

  First, for the third cell 103 adjusted to one combination condition, the lower limit voltage acquisition unit 62 starts acquiring the positive electrode potential Vp, the negative electrode potential Vn that is the negative electrode potential, and the lower limit voltage. When acquisition of the lower limit voltage is started, the lower limit voltage acquisition unit 62 discharges the power stored in the third cell 103 from the discharge circuit 69 with a large current. In the third cell 103, the SOC of the third cell 103 decreases as the discharge with a large current continues, the positive electrode potential Vp of the third cell 103 decreases, and the negative electrode potential Vn of the third cell 103 decreases. Rises. The cell voltage Vc is a potential difference between the positive electrode potential Vp and the negative electrode potential Vn, and decreases when the potential difference becomes smaller due to the decrease in the positive electrode potential Vp and the increase in the negative electrode potential Vn.

  And the lower limit voltage acquisition part 62 acquires the cell voltage Vc when the positive electrode potential Vp reaches the metal elution potential αV as the lower limit voltage. That is, the lower limit voltage is set to the lowest battery voltage in the battery voltage range in which the elution reaction of the cobalt compound that progresses irreversibly can be suppressed. For this reason, the lower limit voltage is not set larger than necessary. In addition, since the metal elution reaction occurs in the positive electrode of the unit cell 100 that has been subjected to the process of obtaining the lower limit voltage, the unit cell 100 becomes a new one each time the combination of the temperature, the latest SOC, and the discharge time is changed. Exchanged. And this acquisition of a lower limit voltage is performed for every combination condition.

  FIG. 5 shows the positive electrode potential Vp, the negative electrode potential Vn, and the cell voltage Vc when the discharge time is short among the positive electrode potential Vp, the negative electrode potential Vn, and the cell voltage Vc obtained by each combination condition described above. Show. That is, the latest SOC “high” / short time in the high temperature region, the latest SOC “medium” / short time, the latest SOC “low” / short time, and the latest SOC “high” / short time in the low temperature region The graph shows the changes in the positive electrode potential Vp, the negative electrode potential Vn, and the cell voltage Vc for the three combinations of SOC “medium” / short time and latest SOC “medium” / short time.

  The positive electrode potential Vp decreases as the large current continues and reaches the metal elution potential αV. For example, as shown in the graphs of the latest SOC “low”, “medium”, and “high” in “high temperature region” in FIG. 5, the time until the positive electrode potential Vp reaches the metal elution potential αV is low. It is getting shorter.

  Further, for example, as shown in the graph of the high temperature region and the graph of the low temperature region in the latest SOC “high” in FIG. 5, the time until the positive electrode potential Vp reaches the metal elution potential αV is shorter as the temperature is lower. .

  On the other hand, the negative electrode potential Vn rises while the positive electrode potential Vp reaches the metal elution potential αV. As shown in the graphs of the latest SOC “low”, “medium”, and “high” in the “high temperature region” in FIG. 5, the rate of change (slope) at which the negative electrode potential Vn increases increases as the latest SOC decreases. In addition, as shown in the graph of the high temperature region and the graph of the low temperature region in the latest SOC “high” in FIG. 5, the rate of change in which the negative electrode potential Vn increases increases as the battery temperature decreases.

  Thus, in the temperature range, the rate of change of the positive electrode potential Vp and the negative electrode potential Vn increases as the latest SOC decreases, but the rate of decrease of the positive electrode potential Vp is shorter than the rate of increase of the negative electrode potential Vn. Therefore, as shown in the graphs of the latest SOCs “low”, “medium”, and “high” in the “high temperature region” in FIG. 5, when the positive electrode potential Vp reaches the metal elution potential αV in the high temperature region (time The cell voltage Vc at (T0) is “1.10 V”, “1.07 V”, and “1.05 V” in descending order of the latest SOC. That is, the cell voltage Vc when the positive electrode potential Vp reaches the metal elution potential αV increases as the latest SOC decreases.

  Further, as shown in the graph of the high temperature region and the graph of the low temperature region in the latest SOC “high” in FIG. 5, when the positive electrode potential Vp reaches the metal elution potential αV in the same immediate SOC (time T0). The cell voltage Vc becomes “0.88V” and “1.05V” in order of increasing temperature. That is, the cell voltage Vc when the positive electrode potential Vp reaches the metal elution potential αV increases as the temperature increases.

  In the low temperature range, the rising speed of the negative electrode potential Vn increases. Therefore, under the same SOC conditions, the cell voltage Vc when the positive electrode potential Vp reaches the metal elution potential αV decreases as the temperature decreases. In the low temperature range, the cell voltage Vc when the positive electrode potential Vp reaches the metal elution potential αV is substantially the same in the latest SOC “low”, the latest SOC “medium”, and the latest SOC “high”.

  FIG. 6 shows the positive electrode potential Vp, the negative electrode potential Vn and the cell voltage Vc when the discharge time is short, and the positive electrode when the discharge time is long when the temperature and the latest SOC are the same combination. A potential Vp, a negative potential Vn, and a cell voltage Vc are shown.

The time until the positive electrode potential Vp reaches the metal elution potential αV tends to be short when the discharge time is short, and tends to be long when the discharge time is long.
Further, the rising speed of the negative electrode potential Vn tends to increase when the discharge time is short, and tends to decrease when the discharge time is long. Therefore, the cell voltage Vc when the positive electrode potential Vp reaches the metal elution potential αV tends to be low when the discharge time is short, and tends to be high when the discharge time is long.

  That is, the cell voltage Vc when the positive electrode potential Vp reaches the metal elution potential αV is higher as the latest SOC is lower at the same temperature and the same discharge time. Further, the cell voltage Vc when the positive electrode potential Vp reaches the metal elution potential αV becomes higher as the battery temperature is higher if the current SOC is the same and the discharge time is the same. Furthermore, the cell voltage Vc when the positive electrode potential Vp reaches the metal elution potential αV is higher as the discharge time is longer at the same temperature and the latest SOC.

  Then, from the cell voltage Vc when the positive electrode potential Vp in each combination condition reaches the metal elution potential αV, the lower limit voltage change lines L1 to L4 in the short time discharge shown in FIG. 2 and the lower limit in the long time discharge shown in FIG. Voltage change lines L5 to L8 are obtained.

  Note that the manner in which the positive electrode potential Vp is reduced and the manner in which the negative electrode potential Vn is increased due to a large current discharge differs depending on the discharge amount, battery capacity, electrode configuration, nearest SOC, temperature, and the like. Also, the manner in which the SOC decreases due to the discharge of a large current also differs depending on the discharge amount, battery capacity, electrode configuration, nearest SOC, temperature, and the like. Therefore, the lower limit voltage is preferably set according to the discharge amount, battery capacity, electrode configuration, latest SOC, temperature, and the like.

<Lower voltage setting process>
With reference to FIG. 7, the procedure of the process of setting the lower limit voltage for the battery module 11 by the lower limit voltage setting unit 53 will be described. The process of setting the lower limit voltage is repeatedly performed as needed at a predetermined cycle or a predetermined interval. The process of setting the lower limit voltage may be performed at the timing when the latest SOC value or battery temperature is updated or changed. The interval between the repeated executions of the process may be regular or irregular, but is preferably performed at any time in response to a change in the battery state of the battery module 11.

  When the lower limit voltage setting process is started, the lower limit voltage setting unit 53 determines whether or not the discharge of the secondary battery 10 is started (step S1). When the discharge is not started (step S1: NO), the lower limit voltage setting unit 53 waits for the discharge to start.

  When the discharge is started (step S1: YES), the lower limit voltage setting unit 53 measures a discharge time Tm in which the discharge is continued from the start of the discharge (step S2). In addition, the lower limit voltage setting unit 53 acquires the temperature Tp measured by the temperature acquisition unit 52 (step S3). And the lower limit voltage setting part 53 judges whether the acquired temperature Tp is less than specific temperature Tp1 (step S4).

  When it is determined that the measured battery temperature is lower than the specific temperature Tp1 (step S4: YES), the lower limit voltage setting unit 53 performs a low temperature setting process that is a lower limit voltage setting process at a low temperature (step S5). . When the low temperature setting process is performed, the lower limit voltage setting unit 53 determines whether or not the discharge of the secondary battery 10 has ended (step S7), and when the discharge has not ended (step S7: NO) ), The process returns to step S2, and the measurement of the discharge time Tm is continued.

  On the other hand, when it is determined that the measured temperature Tp is equal to or higher than the specific temperature Tp1 (step S4: NO), the lower limit voltage setting unit 53 performs a high temperature setting process that is a setting process of the lower limit voltage at a high temperature (step S4). S6). When the high temperature setting process is performed, the lower limit voltage setting unit 53 determines whether or not the discharge of the secondary battery 10 has ended (step S7), and when the discharge has not ended (step S7: NO) ), The process returns to step S2, and the measurement of the discharge time Tm is continued.

  Next, the low temperature setting process will be described with reference to FIG. The lower limit voltage setting unit 53 determines whether or not the measured discharge time Tm is less than the predetermined time Tm1 (step S5-1). Immediately after the discharge is started at a low temperature, it is first determined that the discharge time Tm is less than the predetermined time Tm1.

  If it is determined that the discharge time Tm is less than the predetermined time Tm1 (step S5-1: YES), low temperature / short time characteristics are selected (step S5-2). Specifically, the lower limit voltage change line L1 in the graph of FIG. 2 is selected. The lower limit voltage setting unit 53 reads the lower limit voltage corresponding to the acquired temperature Tp from the lower limit voltage change line L1, and sets the read lower limit voltage as the lower limit voltage (step S5-4). When the lower limit voltage is set in this way, the lower limit voltage setting unit 53 determines whether or not the discharge has ended (step S7 in FIG. 7), and when the discharge has not ended, repeats step S2.

  When the predetermined time Tm1 has elapsed since the start of discharge, it is determined in step S5-1 that the discharge time Tm is equal to or longer than the predetermined time Tm1 (step S5-1: NO). In that case, the lower limit voltage setting unit 53 selects the low temperature / long time characteristic (step S5-3). Specifically, a lower limit voltage change line (not shown) in long-time discharge is selected. The lower limit voltage setting unit 53 reads the lower limit voltage corresponding to the acquired temperature Tp from the lower limit voltage change line, and sets the read lower limit voltage as the lower limit voltage (step S5-4). That is, at a low temperature, the short-term characteristic lower limit voltage is set first, and when the discharge continues thereafter, the short-term characteristic lower limit voltage is switched to the long-term characteristic lower limit voltage.

  Next, the high temperature setting process will be described with reference to FIG. The lower limit voltage setting unit 53 acquires the SOC from the SOC calculation unit 51 (step S6-1). The SOC acquired here is the latest SOC. The lower limit voltage setting unit 53 determines whether or not the acquired SOC is equal to or greater than the first SOC threshold value Sth1 (step S6-2). The first SOC threshold value Sth1 is a threshold value for discriminating between the latest SOC “high” and the latest SOC “medium”.

  When the latest SOC is equal to or higher than the first SOC threshold value Sth1 (step S6-2: YES), that is, when the latest SOC is “high”, the lower limit voltage setting unit 53 has the discharge time Tm less than the predetermined time Tm1. It is determined whether or not there is (step S6-3). When the discharge time is less than predetermined time Tm1 (step S6-3: YES), lower limit voltage setting unit 53 selects the latest SOC “high” and short-time characteristics (step S6-4). Specifically, the lower limit voltage change line L4 in FIG. 2 is selected. And the lower limit voltage setting part 53 reads the lower limit voltage corresponding to the acquired temperature Tp among the lower limit voltage change lines L4, and sets the read lower limit voltage as a lower limit voltage (step S6-6). Then, the lower limit voltage setting unit 53 returns to step S7 shown in FIG. 7 to determine whether or not the discharge has ended when the lower limit voltage is set (step S7 shown in FIG. 7). Returns to step S2 shown in FIG.

  Thus, after the latest SOC “high” / short-time characteristic is selected, the lower limit voltage based on the latest SOC “high” / short-time characteristic is repeatedly set while the discharge time Tm is less than the predetermined time Tm1. Eventually, when the discharge time Tm becomes equal to or longer than the predetermined time Tm1 (step S6-3: NO), the lower limit voltage setting unit 53 selects the latest SOC “high” / long-time characteristic (step S6-5). Specifically, the lower limit voltage change line L8 in FIG. 3 is selected. Then, the lower limit voltage corresponding to the acquired temperature Tp is read from the lower limit voltage change line L8, and the read lower limit voltage is set as the lower limit voltage (step S6-6). As a result, a lower limit voltage higher than the lower limit voltage set when the latest SOC is “high” and the discharge time Tm is less than the predetermined time Tm1 is set. When the lower limit voltage is set, it is determined whether or not the discharge is finished (step S7 shown in FIG. 7). If the discharge is continued, the process returns to step S2.

  On the other hand, when the latest SOC is less than the first SOC threshold value Sth1 in step S6-2 (step S6-2: NO), the lower limit voltage setting unit 53 determines that the latest SOC is equal to or greater than the second SOC threshold value Sth2. It is determined whether it is less than the SOC threshold value Sth1 (step S6-7). The second SOC threshold value Sth2 is a threshold value for discriminating between the latest SOC “middle” and the latest SOC “low”, and is smaller than the first SOC threshold value Sth1.

  When the lower limit voltage setting unit 53 determines that the latest SOC is equal to or greater than the second SOC threshold value Sth2 and less than the first SOC threshold value Sth1 (step S6-7: YES), the lower limit voltage setting unit 53 measures the discharge being measured. It is determined whether or not the time Tm is less than the predetermined time Tm1 (step S6-8). If the measured discharge time Tm is less than the predetermined time Tm1 (step S6-8: YES), the latest SOC “medium” / short-time characteristics are selected (step S6-9). Specifically, the lower limit voltage change line L3 shown in FIG. 2 is selected. Then, the lower limit voltage corresponding to the acquired temperature Tp is read from the lower limit voltage change line L3, and the read lower limit voltage is set as the lower limit voltage (step S6-6).

  Thus, after the latest SOC “medium” / short-time characteristics are selected, the lower limit voltage based on the latest SOC “medium” / short-time characteristics is repeatedly set while the discharge time Tm is less than the predetermined time Tm1. . Eventually, when the discharge time Tm becomes equal to or longer than the predetermined time Tm1 (step S6-8: NO), the lower limit voltage setting unit 53 selects the latest SOC “medium” / long-time characteristic (step S6-10). Specifically, the lower limit voltage change line L7 in FIG. 3 is selected. Then, the lower limit voltage corresponding to the acquired temperature Tp is read from the lower limit voltage change line L7, and the read lower limit voltage is set as the lower limit voltage (step S6-6). As a result, a lower limit voltage higher than the lower limit voltage set when the latest SOC is “medium” and the discharge time Tm is less than the predetermined time Tm1 is set. Further, a lower limit voltage higher than the lower limit voltage set when the latest SOC is “high” is set. When the lower limit voltage is set, it is determined whether or not the discharge is finished (step S7 shown in FIG. 7). If the discharge is continued, the process returns to step S2.

  On the other hand, when the lower limit voltage setting unit 53 determines in step S6-7 that the latest SOC is less than the second SOC threshold value Sth2 (step S6-7: NO), the discharge time Tm is less than the predetermined time Tm1. It is determined whether or not there is (step S6-11).

  If the measured discharge time Tm is less than the predetermined time Tm1 (step S6-11: YES), the latest SOC “low” / short-time characteristic is selected (step S6-12). Specifically, the lower limit voltage change line L2 shown in FIG. 2 is selected. Then, the lower limit voltage corresponding to the acquired temperature Tp is read from the lower limit voltage change line L2, and the read lower limit voltage is set as the lower limit voltage (step S6-6).

  Thus, after the latest SOC “low” / short-time characteristics are selected, the lower limit voltage based on the latest SOC “low” / short-time characteristics is repeatedly set while the discharge time Tm is within the predetermined time Tm1. . Eventually, when the discharge time Tm becomes equal to or longer than the predetermined time Tm1 (step S6-11: NO), the lower limit voltage setting unit 53 selects the latest SOC “low” / long-time characteristic (step S6-13). Specifically, the lower limit voltage change line L6 in FIG. 3 is selected. Then, the lower limit voltage corresponding to the acquired temperature Tp is read from the lower limit voltage change line L6, and the read lower limit voltage is set as the lower limit voltage (step S6-6). As a result, a lower limit voltage higher than the lower limit voltage set when the latest SOC is “low” and the discharge time Tm is less than the predetermined time Tm1 is set. Also, a lower limit voltage higher than the lower limit voltage set when the latest SOC is “medium” and “high” is set. When the lower limit voltage is set, the lower limit voltage setting unit 53 returns to step S7 shown in FIG. 7 to determine whether or not the discharge has ended (step S7 shown in FIG. 7). Return to step S2.

  Thus, when the lower limit voltage is set for the battery module 11, for example, when at least one of the plurality of battery modules 11 constituting the secondary battery 10 reaches the lower limit voltage, the discharge is restricted. Alternatively, when the voltage is measured for each block composed of the plurality of battery modules 11 by the voltmeter 40, the discharge is restricted when any block reaches the lower limit voltage.

  In addition, since the lower limit voltage corresponding to the current battery state of the battery module 11 is set as needed, an appropriate lower limit voltage is set even if a discharge with a large current is suddenly requested. And even if the discharge by a large current was made, discharge is controlled because the voltage between the terminals of the battery module 11 reaches the lower limit voltage, and the deterioration of the performance of the positive electrode is suppressed. As a result, the battery life is extended. Moreover, since the range of voltage output is expanded by setting the lower limit voltage appropriately and low, more power can be output from the battery module 11 and the output performance of the battery module 11 is enhanced.

As described above, according to the first embodiment, the effects listed below can be obtained.
(1) The lower limit voltage of the battery module 11 is set based on the SOC of the secondary battery 10 in addition to the temperature Tp of the secondary battery 10. Thereby, the lower limit voltage which regulates the discharge of the secondary battery 10 is set more appropriately. And by setting such a lower limit voltage, the degradation of the performance of the secondary battery 10 is also suppressed, and the battery life can be extended. In addition, since the lower limit voltage is not set higher than necessary, the output range of the secondary battery 10 is expanded, more power output is possible, and the output performance of the secondary battery is enhanced.

  (2) The lower limit voltage is set based on the discharge time in addition to the SOC and temperature of the battery module 11. By setting the lower limit voltage in this manner, the lower limit voltage can be set in accordance with the usage status of the secondary battery 10. Therefore, the lower limit voltage can be set appropriately.

  (3) The secondary battery 10 having the positive electrode including the main active material and the metal compound is likely to deteriorate when the positive electrode potential Vp reaches the metal elution potential αV. When the secondary battery 10 is discharged with a large current, the positive electrode potential Vp decreases and reaches the metal elution potential αV. However, as the SOC of the secondary battery 10 decreases, the positive electrode potential Vp decreases to the negative electrode potential Vn. It decreases rapidly compared to the increase of. Therefore, the battery voltage, which is the difference between the positive electrode potential and the negative electrode potential when the positive electrode potential Vp reaches the metal elution potential αV, becomes higher as the charged state of the secondary battery is lower. According to the embodiment, the lower limit voltage is determined in advance with reference to the voltage when the positive electrode potential Vp reaches the metal elution potential αV, and the lower limit voltage is determined for each combination of the charge state and the temperature. Then, based on the lower limit voltage determined in advance as described above, the lower limit voltage is set according to the nearest SOC and temperature of the secondary battery 10. Thereby, the deterioration of the performance of the secondary battery 10 is also suppressed, and the battery life can be extended. In addition, since the lower limit voltage is not set higher than necessary, the output range of the secondary battery 10 is expanded, more power output is possible, and the output performance of the secondary battery is enhanced.

(Second Embodiment)
Next, a second embodiment embodying the present invention will be described. Since the second embodiment has a configuration in which a part of the determination method of the lower limit voltage of the first embodiment is changed, the same parts are denoted by the same reference numerals and detailed description thereof is omitted.

  With reference to FIG. 10, the determination method of the lower limit voltage for creating the lower limit voltage data 54 will be described. In this embodiment, the temperature is divided into a high temperature region, a middle temperature region, and a low temperature region by two specific temperatures. That is, the lower limit voltage is determined by 18 combinations obtained by adding the following six combinations to the 12 combinations in the first embodiment. Note that the graph of FIG. 10 is a table of short-time characteristics in which the discharge time is short.

<Medium temperature range>
Latest SOC “High” / Long Time Latest SOC “High” / Short Time Latest SOC “Medium” / Long Time Latest SOC “Medium” / Short Time Latest SOC “Low” / Long Time Latest SOC “Low” / Short Time By the way When discharging of the secondary battery 10 is started as described above, the battery control device 50 inputs a voltage detection signal corresponding to the voltage from the voltmeter 40 in order to calculate the latest SOC. At this time, the timing when the battery control device 50 inputs the voltage detection signal coincides with the timing when the measurement device 60 inputs the voltage detection signal corresponding to the voltage from the voltmeters 65P and 65N in order to create the lower limit voltage data 54. It is preferable to do. It is preferable that the timing at which the battery control device 50 inputs a current detection signal corresponding to the current from the ammeter 41 also coincides with the timing at which the measurement device 60 inputs a current detection signal corresponding to the current from the ammeter 68.

  However, actually, the timing at which the battery control device 50 inputs the voltage detection signal may be delayed with respect to the timing at which the measurement device 60 inputs the voltage detection signal due to the influence of the measurement interval of the voltmeter 40 and the like. is there. When the timing at which the battery control device 50 inputs the voltage detection signal is delayed with respect to the timing at which the measurement device 60 inputs the voltage detection signal, the difference between the actually set lower limit voltage and the lower limit voltage to be originally set is different. May grow. In particular, when the latest SOC is low, the cell voltage Vc changes abruptly when a large current is discharged.

  Since the cell voltage Vc decreases with discharge, if the timing at which the battery control device 50 inputs each signal is later than the timing at which the battery control device 50 inputs each signal, the lower limit voltage is set lower. And if discharge of the secondary battery 10 is controlled based on the set lower limit voltage, the positive electrode potential Vp may fall below the metal elution potential αV.

  Here, a threshold value larger than the metal elution potential αV may be set, and the cell voltage Vc when the positive electrode potential Vp reaches this threshold value may be set as the lower limit voltage. However, in this case, since the rate of change of the positive electrode potential Vp at the time of large current discharge differs under each combination condition, the difference between the time for the positive electrode potential Vp to reach the threshold and the time to reach the metal elution potential αV is It depends on each combination condition. Therefore, for example, under a combination condition where the change rate of the positive electrode potential Vp is large, the lower limit voltage can be set appropriately, but in a combination where the change rate of the positive electrode potential Vp is small, the lower limit voltage is set higher. The output range may be narrowed more than necessary.

  Therefore, in the present embodiment, the cell voltage Vc that is a certain time Tm1 before the time T0 when the positive electrode potential Vp reaches the metal elution potential αV is set as the lower limit voltage. When the lower limit voltage is set in this way, the lower limit voltage is set higher. As a result, the timing at which the battery control device 50 inputs each signal is delayed from the timing at which the battery control device 50 inputs each signal, and even if the secondary battery 10 is controlled based on the lower limit voltage, the positive electrode potential Vp is It is suppressed that it falls below the metal elution potential αV. Further, the fixed time Tm1 can be obtained in advance from the voltage measurement interval by the voltmeters 65P and 65N.

  As shown in the graphs of combinations in which the temperature and the latest SOC in FIG. 10 are different from each other, the cell of the time “T0-T1” that is back by a certain time T1 from the time T0 when the positive electrode potential Vp reaches the metal elution potential αV. The voltage Vc is the lower limit voltage.

  As in the first embodiment, the cell voltages Vc1 to Vc9 at time “T0-T1” are higher as the nearest SOC of the unit cell 100 is lower. Further, the higher the temperature is, the higher the SOC is in the same SOC of the unit cell 100.

  And the lower limit voltage change line in short-time discharge and the lower limit voltage change line in long-time discharge are calculated | required from the cell voltage Vc obtained by measuring on each combination condition. Further, the lower limit voltage of the unit cell 100 obtained as described above is set to 6 times that is the number of cells constituting the battery module 11 and set as the lower limit voltage for the battery module 11.

As described above, according to the second embodiment, in addition to the effects (1) to (3) described in the first embodiment, the effects listed below can be obtained.
(4) In setting the lower limit voltage, the timing at which the signal corresponding to the voltage of the secondary battery 10, the signal corresponding to the current, and the signal corresponding to the temperature are actually acquired are those signals when the lower limit voltage is determined in advance. There is a possibility that it will be delayed with respect to the timing of acquiring. Further, when large current discharge is started, the cell voltage Vc decreases as the discharge is continued. In the above-described embodiment, when the lower limit voltage is determined in advance, the cell voltage Vc a certain time Tm1 before the positive electrode potential Vp reaches the metal elution potential αV is determined as the lower limit voltage. That is, the lower limit voltage is set higher than the case where the lower limit voltage is set as the cell voltage Vc at the time T0 when the positive electrode potential Vp reaches the metal elution potential αV. Therefore, even if the timing at which each of the above signals is actually acquired is delayed from the timing at which each signal is acquired when the lower limit voltage is determined in advance, the lower limit voltage set at that time is the positive potential. Vp does not fall below the cell voltage Vc when the metal elution potential αV is reached. For this reason, at least deterioration of the secondary battery can be suppressed.

In addition, each said embodiment can also be suitably changed and implemented as follows.
In each of the above embodiments, the lower limit voltage is set higher as the latest SOC is lower. However, due to factors other than the elution reaction of cobalt, there is a possibility that the relationship that the lower limit voltage becomes higher as the latest SOC becomes lower may change. For example, when the latest SOC is low, the time required to reach the set lower limit voltage is faster than when the latest SOC is high. Therefore, when the latest SOC is low, the lower limit voltage is set higher than the above embodiments in consideration of safety, and when the latest SOC is high, the lower limit voltage is maintained as it is or the width is smaller than when the SOC is low. You may make it set high.

  In the first embodiment, the lower limit voltage is acquired for each of the three cases of “low”, “medium”, and “high” for the latest SOC for each of the “high temperature region” and the “low temperature region”. The case was illustrated. Further, in the second embodiment, the lower limit voltage has three values of “low”, “medium”, and “high” for the latest SOC for each of the “high temperature region”, “medium temperature region”, and “low temperature region”. The case where it was acquired about each case was illustrated. However, the present invention is not limited to this, and the combination of the battery temperature at which the lower limit voltage is acquired and the latest SOC may be more or less. For example, the battery temperature may be a plurality of arbitrary temperatures, and the nearest SOC combined with each battery temperature may be a plurality of arbitrary values. If the number of combinations when acquiring the lower limit voltage is small, the time required for acquisition can be shortened, and if it is large, the acquisition accuracy can be increased.

  In the above embodiment, the case where the active material constituting the positive electrode is a nickel compound and the additive is a cobalt compound is exemplified. However, the present invention is not limited thereto, and the positively active material or additive may be composed of other compounds.

  -In above-mentioned embodiment, the battery module 11 illustrated about the case where six cells were comprised in series. However, the present invention is not limited to this, and the battery module may be configured such that five or less cells or seven or more cells are connected in series. The battery module may be a single cell. In any case, the lower limit voltage may be set according to the number of cells connected in series constituting the battery module.

In the above embodiment, the secondary battery 10 is composed of a plurality of battery modules 11, but the secondary battery 10 may be a single battery module 11.
-In above-mentioned embodiment, it illustrated about the case where the charge state regarding the electrical storage amount of the secondary battery 10 is SOC. However, the present invention is not limited to this, and the state of charge of the secondary battery 10 may be the actual amount of charge (charge amount). Usually, the amount of charge (charge amount) and the SOC can be converted to each other. Similarly, regarding the data regarding the lower limit voltage, a relationship with the charged amount (charge amount) may be used instead of the relationship with the SOC.

  In each of the above embodiments, the secondary battery 10 is a power source for an electric motor, but may be a power source for other devices of the vehicle. In addition, the secondary battery 10 may be used as a power source other than the vehicle as long as it is used as a power source. In this case, for example, when the SOC control range is large, such as a stationary power supply, the chemical degradation of the battery per hour increases. Therefore, it is preferable to set the lower limit voltage higher from the viewpoint of securing the life. For example, a predetermined margin or the like may be added to the metal elution potential αV and set higher.

  In the above embodiment, the secondary battery is embodied as a nickel hydride storage battery, but may be embodied as another alkaline storage battery. For example, the present invention may be embodied in a nickel / cadmium storage battery, a nickel zinc storage battery, or the like. Moreover, you may actualize to other storage batteries, such as a lithium ion storage battery. In that case, a secondary reaction such as a potential of the positive electrode potential used as a reference for determining the lower limit voltage, a potential at which the compound contained in the positive electrode chemically degrades, or a potential at which electrolysis of the electrolyte starts to occur occurs. Cell voltage. At this time, the threshold value of the positive electrode potential or the negative electrode potential, which is a reference, varies depending on the combination of the positive electrode material, the negative electrode material, or the electrolyte.

  DESCRIPTION OF SYMBOLS 10 ... Secondary battery, 11 ... Battery module, 12 ... Positive electrode terminal, 13 ... Negative electrode terminal, 20 ... Thermometer, 37 ... Thermometer, 40 ... Ammeter 41 ... Voltmeter, 41 ... Ammeter, 50 ... Battery control apparatus DESCRIPTION OF SYMBOLS 51 ... SOC calculation part 52 ... Temperature acquisition part 53 ... Lower limit voltage setting part 54 ... Lower limit voltage data, 100 ... Single cell 101-106 ... 1st cell-6th cell, 111 ... Negative electrode, 112 ... Positive electrode 113 ... Electrode group, 114 ... Current collector plate, 115 ... Current collector plate.

Claims (6)

A battery control device for controlling discharge of a secondary battery having a positive electrode containing a main active material and a metal compound as an additive,
A charge state acquisition unit for acquiring a charge state indicating a ratio of a remaining capacity to a full charge capacity of the secondary battery;
A temperature acquisition unit for acquiring the temperature of the secondary battery;
A lower limit voltage setting unit for setting a lower limit voltage of the secondary battery,
The lower limit voltage setting unit sets the lower limit voltage as a higher value as the charged state of the secondary battery is lower, and the acquired temperature is higher under the condition that the charged state of the secondary battery is the same. The battery control device is characterized by being set to a higher value. A discharge time measuring unit for measuring a discharge time which is a time during which the discharge of the secondary battery is continued;
The battery control device according to claim 1, wherein the lower limit voltage setting unit sets a lower value as the measured discharge time is shorter under a condition in which the charge state and temperature of the secondary battery are the same. A battery control method for controlling discharge of a secondary battery having a positive electrode containing a main active material and a metal compound as an additive by a battery control device,
The battery control device sets the lower limit voltage of the secondary battery as a higher value as the state of charge indicating the ratio of the remaining capacity to the full charge capacity of the secondary battery is lower, and the state of charge of the secondary battery The battery control method is characterized in that a higher value is set as the acquired temperature is higher under the same condition. A method for determining a lower limit voltage for determining a lower limit voltage used for discharge control of a secondary battery having a positive electrode including a main active material and a metal compound as an additive,
The potential of the positive electrode and the battery voltage are measured while discharging the secondary battery under a plurality of conditions in which the combination of the state of charge and the temperature indicating the ratio of the remaining capacity to the full charge capacity of the secondary battery is different from each other. A method for determining a lower limit voltage, wherein a lower limit voltage for regulating discharge of the secondary battery is predetermined based on a battery voltage when the potential reaches a starting potential of a metal elution reaction of a metal compound. While obtaining a discharge time that is a time during which the secondary battery is continuously discharged, a combination of a charge state of the secondary battery, a temperature of the secondary battery, and a discharge time of the secondary battery is mutually The lower limit voltage determination method according to claim 4, wherein the lower limit voltage is determined in advance under a plurality of different conditions. The method for determining a lower limit voltage according to claim 4 or 5, wherein a battery voltage of the secondary battery a predetermined time before the potential of the positive electrode reaches a start potential of a metal elution reaction of a metal compound is preset as a lower limit voltage.

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