Control device, control method, and program

Abstract

The present technology relates to a control device, a control method, and a program, whereby deterioration of a battery and a decrease in the battery capacity that can be used by a user can be suppressed. The discharge of charge accumulated in a battery cell is controlled on the basis of a presence time, which is a time during which a state point, which represents the terminal voltage and temperature of the battery cell, is present in a discharge region, which includes a plurality of small regions and is defined on a two-dimensional plane in which one of two orthogonal axes represents the terminal voltage of the battery cell and the other axis represents the temperature. The present technology can be applied to, for example, a battery or the like.

Description

Control device, control method, and program

[0001] The present technology relates to a control device, a control method, and a program, and particularly relates to a control device, a control method, and a program that can suppress, for example, battery deterioration and a reduction in battery capacity available to a user.

[0002] When a battery constituted by a secondary battery serving as a battery cell, for example, a lithium-ion battery, is left standing for a long time, the battery deteriorates. For example, characteristics such as battery capacity and resistance components inside the battery cell deteriorate. Furthermore, for a battery constituted by a laminated-cell lithium-ion battery, for example, battery swelling may occur.

[0003] In order to suppress such battery deterioration, when the deterioration risk is high, the battery cell is discharged to lower the terminal voltage of the battery cell. Hereinafter, the discharge of the battery cell performed for the purpose of lowering the terminal voltage of the battery cell as described above is also referred to as voltage-lowering discharge.

[0004] Battery deterioration is accelerated as the temperature increases. For example, Patent Document 1 proposes voltage-lowering discharge in which the higher the temperature is, the lower the terminal voltage of the battery cell is set and the faster the discharge rate is made. In the voltage-lowering discharge described in Patent Document 1, the discharge rate is changed by changing the resistance value of a variable resistor.

[0005] Japanese Patent No. 7507097

[0006] For voltage-lowering discharge, there is a demand for proposal of a technology that can suppress battery deterioration and a reduction in battery capacity available to a user.

[0007] The present technology has been made in view of such circumstances, and is intended to enable suppression of battery deterioration and a reduction in battery capacity available to a user.

[0008] The control device of this technology includes a control unit that controls the discharge of charge accumulated in the battery cell based on the existence time, which is the time that a state point, which is a point representing the terminal voltage and temperature of the battery cell, exists in a discharge region, which is a region including multiple sub-regions defined on a two-dimensional plane on which one of two orthogonal axes represents the terminal voltage of the battery cell and the other axis represents the temperature.

[0009] The control method of this technology includes controlling the discharge of charge accumulated in a battery cell based on the existence time, which is the time that a state point, which is a point representing the terminal voltage and temperature of the battery cell, exists in a discharge region, which is a region including multiple sub-regions defined on a two-dimensional plane on which one of two orthogonal axes represents the terminal voltage of the battery cell and the other axis represents the temperature of the battery cell.

[0010] The program for this technology is a program that causes a computer to function as a control unit that controls the discharge of charge accumulated in a battery cell, based on the existence time, which is the time that a state point, which is a point representing the terminal voltage and temperature of the battery cell, exists in a discharge region, which is a region containing multiple sub-regions defined on a two-dimensional plane on which one of two orthogonal axes represents the terminal voltage of the battery cell and the other axis represents the temperature of the battery cell.

[0011] In this technology, the discharge of charge accumulated in the battery cell is controlled based on the existence time, which is the time that a state point, which represents the terminal voltage and temperature of the battery cell, exists in a discharge region, which is a region containing multiple sub-regions defined on a two-dimensional plane on which one of two orthogonal axes represents the terminal voltage of the battery cell and the other axis represents the temperature.

[0012] The control device may be a single independent device, or it may be an internal block that constitutes a single independent device. Furthermore, the control device can be composed of multiple independent devices.

[0013] The program can be provided by recording it on a recording medium or by transmitting it via a transmission medium.

[0014] This figure shows an example configuration of one embodiment of a battery to which this technology is applied. This figure illustrates the risk of battery degradation. This figure illustrates an example of setting the on / off duty cycle of switch SW1 to change the discharge speed of battery cell 11. This figure illustrates an example of a discharge region. This figure shows an example of a temperature / cell voltage plane representing a small region r1 to r5 when the full charge voltage FV has decreased. This figure illustrates an example of information set in a register built into the control unit 31. This figure shows an example of the movement of state points representing cell voltage and temperature in the temperature / cell voltage plane. This figure shows a schematic example of the time change of cell voltage due to voltage drop discharge control by the microcomputer 30. This is a flowchart illustrating an example of the processing of voltage drop discharge control by the microcomputer 30. This is a flowchart illustrating an example of the processing of voltage drop discharge control based on existence time performed in step S13. This figure shows a first example of the time change of cell voltage due to voltage drop discharge control by the microcomputer 30. This figure shows a second example of the time change of cell voltage due to voltage drop discharge control by the microcomputer 30. This figure illustrates another example of a discharge region. This figure shows a third example of the time change of cell voltage due to voltage drop discharge control by the microcomputer 30. This is a diagram illustrating yet another example of the discharge region. This is a diagram illustrating an example of calculating the remaining charge calculation current used for calculating the remaining charge when voltage drop discharge is performed. This is a flowchart illustrating an example of cell balancing control. This is a diagram illustrating an example of the configuration of another embodiment of a battery to which this technology is applied. This is a diagram illustrating an example of the configuration of yet another embodiment of a battery to which this technology is applied. This is a diagram illustrating a specific example of the discharge current used as the remaining charge calculation current when voltage drop discharge is performed in battery 10. This is a diagram illustrating a specific example of the discharge current used as the remaining charge calculation current when voltage drop discharge is performed in battery 110. This is a diagram illustrating a specific example of the discharge current used as the remaining charge calculation current when voltage drop discharge is performed in battery 210. This is a flowchart illustrating an example of processing based on the degradation stage. This is a diagram illustrating an example of the relationship between the degradation stage and the duty cycle. This is a diagram illustrating an example of the relationship between the duty cycle and the time change of the cell voltage during voltage drop discharge.This is a block diagram showing an example configuration of one embodiment of a computer to which this technology is applied.

[0015] <One embodiment of a battery to which this technology is applied>

[0016] Figure 1 shows an example configuration of one embodiment of a battery to which this technology is applied.

[0017] In Figure 1, the battery 10 includes battery cells 11 and 21, resistors R11 and R12, capacitors C11 and C12, and a microcomputer 30. The battery 10 can be configured to be detachable from various electronic devices such as smartphones, laptop computers, and cameras, or it can be configured to be built into electronic devices.

[0018] Battery cells 11 and 21 are secondary batteries such as lithium-ion batteries. In Figure 1, battery cells 11 and 21 are connected in series by connecting the positive terminal of battery cell 11, whose negative terminal is connected to ground (GND), to the negative terminal of battery cell 21. Battery 10 can supply the voltage of the series-connected battery cells 11 and 21 as a power source.

[0019] The negative terminal of the battery cell 11 is connected to the GND terminal of the microcomputer 30, and the positive terminal of the battery cell 11 is connected to one end of resistor R11. The other end of resistor R11 is connected to the VIN1 terminal of the microcomputer 30. One end of capacitor C11 is connected to the connection point between resistor R11 and the VIN1 terminal of the microcomputer 30, and the other end of capacitor C11 is connected to the GND terminal of the microcomputer 30. Therefore, the battery cell 11 is connected via resistor R11 between the VIN1 terminal, where capacitor C11 is located, and the GND terminal.

[0020] The negative terminal of battery cell 21 is connected to the connection point between the positive terminal of battery cell 11 and resistor R11, and the positive terminal of battery cell 21 is connected to one end of resistor R21. The other end of resistor R21 is connected to the VIN2 terminal of microcomputer 30. One end of capacitor C21 is connected to the connection point between resistor R21 and the VIN2 terminal of microcomputer 30, and the other end of capacitor C21 is connected to the VIN1 terminal of microcomputer 30. Therefore, battery cell 21 is connected between the VIN2 terminal and the VIN1 terminal, where capacitor C21 is located, via resistors R11 and R21.

[0021] Here, resistors R11 and R21 can be, for example, 100Ω resistors. Capacitors C11 and C21 can be, for example, 0.1μF capacitors.

[0022] The microcomputer 30 includes a control unit 31, a switch control unit 32, switches SW1 to SW4, and resistors R1 to R4, and functions as a control device for controlling the battery 10.

[0023] The control unit 31 is supplied with information indicating the terminal voltages of the battery cells 11 and 21 connected to the microcomputer 30, as well as information indicating their temperature.

[0024] Here, the terminal voltage of the battery cell may be the terminal voltage of each individual battery cell constituting the battery, or it may be the terminal voltage of some or all of the battery cells constituting the battery (the voltage supplied by the battery to electronic devices). Here, we will use the terminal voltage of each individual battery cell constituting the battery (hereinafter also referred to as the cell voltage) as the terminal voltage of the battery cell.

[0025] The control unit 31 receives sequentially information indicating the cell voltage and temperature of each battery cell 11 and 21, measured by a sensor (not shown) which is a measuring unit, after being converted from analog to digital by an analog-to-digital (AD) converter (not shown). The control unit 31 acquires the information indicating the cell voltage and temperature of each battery cell 11 and 21, and controls the discharge of the charge accumulated in each battery cell 11 and 21 as a voltage drop discharge (controlling the voltage drop discharge for each battery cell) based on the cell voltage information (the cell voltage indicated by) and temperature information (the temperature indicated by). For example, for each battery cell 11 and 21, the control unit 31 counts the time that a state point of the battery cell exists in the discharge region, and controls the voltage drop discharge of the battery cell based on that time. The discharge region is a region where the voltage of a battery cell drops during discharge, defined on the temperature / cell voltage plane, which is a two-dimensional plane where one of two orthogonal axes (a vertical axis and a horizontal axis) represents cell voltage and the other axis (a horizontal axis) represents temperature. This region includes multiple sub-regions. The state point of a battery cell is a point on the temperature / cell voltage plane that represents the cell voltage and temperature of the battery cell. The temperature / cell voltage plane may also be a two-dimensional plane where the vertical axis represents temperature and the horizontal axis represents cell voltage.

[0026] The control unit 31 can control different voltage drop discharges for each sub-region included in the discharge area. For example, the control unit 31 can control different voltage drop discharges for each sub-region, such as different discharge speeds and speed change times for changing the discharge speed.

[0027] In controlling the voltage drop discharge of the battery cell, the control unit 31 generates a control signal CONDS#k to control switch SW#k and supplies it to the switch control unit 32. In Figure 1, k = 1, 2, 3, 4. For example, the control signal CONDS2, where k = 2, is the control signal output from the control unit 31 when controlling the on / off state of switch SW2.

[0028] The switch control unit 32 turns the switch SW#k on or off according to the control signal CONDS#k from the control unit 31.

[0029] Switches SW1 to SW4 are, for example, semiconductor switches. Switch SW#k and resistor R#k are connected in series. Switch SW1 and resistor R1, connected in series, are connected between the GND terminal and the VIN1 terminal of the microcomputer 30. Switch SW2 and resistor R2, connected in series, are connected between the VIN1 terminal and the VIN2 terminal of the microcomputer 30. Furthermore, switch SW3 and resistor R3, connected in series, are connected between the VIN2 terminal and the VIN3 terminal of the microcomputer 30. Switch SW4 and resistor R4, connected in series, are connected between the VIN4 terminal and the VIN3 terminal of the microcomputer 30. Note that in Figure 1, the VIN4 terminal and the VIN3 terminal are connected to the VIN2 terminal.

[0030] When only battery cell 11 is subjected to a voltage drop discharge, switch SW1 is turned on. As a result, a voltage drop discharge current flows from battery cell 11 through resistor R11, VIN1 terminal, resistor R1, switch SW1, and GND terminal to battery cell 11.

[0031] When only battery cell 21 is subjected to a voltage drop discharge, switch SW2 is turned on. As a result, a voltage drop discharge current flows from battery cell 21 through resistor R21, VIN2 terminal, switch SW2, resistor R2, VIN1 terminal, and resistor R11 to battery cell 21.

[0032] When both battery cells 11 and 21 are subjected to a voltage drop discharge, switches SW1 and SW2 are turned on. As a result, the discharge current for the voltage drop discharge flows from the series-connected battery cells 11 and 21 through resistor R21, the VIN2 terminal, switch SW2, resistors R2 and R1, switch SW1, and the GND terminal.

[0033] Here, the microcomputer 30 supports a battery configuration in which up to four battery cells are connected in series. In Figure 1, the first battery cell 11 and the second battery cell 21 are connected in series. When the battery 10 is configured with three battery cells connected in series, the second battery cell 21 is connected between the VIN2 terminal and the VIN1 terminal, where capacitor C21 is provided, via resistors R11 and R21, and similarly, the third battery cell is connected between the VIN3 terminal and the VIN2 terminal. When the battery 10 is configured with four battery cells connected in series, the fourth battery cell is similarly connected between the VIN4 terminal and the VIN3 terminal. Note that multiple battery cells connected in parallel can be used as each of the first to fourth battery cells.

[0034] As described above, the microcomputer 30 is compatible with batteries configured to connect up to four battery cells in series. Therefore, the microcomputer 30 can be commonly used in the manufacture of batteries configured to connect up to four battery cells in series.

[0035] The microcomputer 30 (control unit 31) performs the same processing for each of the battery cells 11 and 21 as control for voltage drop discharge. Therefore, unless otherwise necessary, the following explanation will focus on one of the battery cells 11 and 21, for example, battery cell 11.

[0036] <Battery degradation risk>

[0037] Figure 2 illustrates the risk of battery degradation.

[0038] For example, if the lithium-ion battery cell 11 is left unattended for a long time with a high cell voltage, the battery 10 (and its characteristics) will deteriorate. In addition to the cell voltage, the temperature of the battery 10 (battery cell 11) is also related to the deterioration of the battery 10. As shown in Figure 2, the higher the cell voltage and the higher the temperature, the higher the risk of deterioration.

[0039] A high risk of degradation affects the safety and reliability of the battery 10. Therefore, the microcomputer 30 that controls (manages) the battery 10 performs a voltage-reducing discharge of the battery cells 11. Specifically, the microcomputer 30 turns on switch SW1 to allow the discharge current from the battery cells 11 to flow through resistor R1, etc. In this way, the microcomputer 30 reduces the cell voltage of the battery cells 11 and suppresses the degradation (risk) of the battery 10.

[0040] While voltage drop discharge can suppress the degradation of battery 10, excessive voltage drop discharge reduces the battery capacity usable by the user (electronic device), also known as battery life (stamina). Hereafter, the battery capacity usable by the user will also be referred to as disposable capacity.

[0041] Therefore, the microcomputer 30 controls the voltage drop discharge of the battery cell 11 based on the duration for which a state point representing the cell voltage and temperature of the battery cell 11 exists in a discharge region where voltage drop discharge of the battery cell 11 is performed, which is defined on a two-dimensional plane representing the cell voltage and temperature of the battery cell 11. For example, the microcomputer 30 changes (controls) the discharge rate of voltage drop discharge based on the duration. This makes it possible to suppress the degradation of the battery 10 (battery cell 11) and the decrease in disposable capacity.

[0042] The discharge speed of a voltage drop discharge can be changed by any method. For example, as described in Patent Document 1, a variable resistor can be used as the resistor through which the discharge current of the voltage drop discharge flows, and the discharge speed can be changed by changing the resistance value of the variable resistor.

[0043] When changing the discharge rate by changing the resistance value of a variable resistor, controlling the voltage drop discharge requires a microcomputer capable of controlling the resistance value of the variable resistor, rather than a microcomputer 30 that controls the on / off state of switch SW#k.

[0044] In contrast, when employing the microcomputer 30 that controls the on / off of the switch SW#k, changing the discharge rate (magnitude of the discharge current) can be achieved by, for example, setting the on / off duty ratio of the switch SW1 that turns on / off the discharge current flowing from the battery cell 11.

[0045] <Changing of Discharge Rate>

[0046] FIG. 3 is a diagram illustrating an example of setting the on / off duty ratio of the switch SW1 for changing the discharge rate of the battery cell 11.

[0047] In FIG. 3, the on / off duty ratio N / M of the switch SW1 is set by setting an 8-bit variable M that represents the on / off cycle of the switch SW1 and an 8-bit variable N that represents the on-period of the switch SW1. For example, M×10 seconds is defined as the on / off cycle of the switch SW1, and N×10 seconds is defined as the on-period of the switch SW1.

[0048] The discharge rate can be changed by setting the on / off duty ratio N / M of the switch SW1.

[0049] <Discharge Region>

[0050] FIG. 4 is a diagram illustrating an example of the discharge region.

[0051] In FIG. 4, the horizontal axis represents temperature, and the vertical axis represents cell voltage.

[0052] The discharge region of the battery cell 11 is a region where voltage-reducing discharge of the battery cell 11 is performed, which is defined on a temperature / cell voltage plane with the vertical axis representing cell voltage and the horizontal axis representing temperature. The discharge region can include a plurality of small regions r#i. When a state point representing the cell voltage and temperature of the battery cell 11 exists within the discharge region, the microcomputer 30 performs voltage-reducing discharge of the battery cell 11. On the other hand, when the state point does not exist within the discharge region, the microcomputer 30 does not perform voltage-reducing discharge of the battery cell 11.

[0053] In FIG. 4, the small region r#i is a region divided based on temperature. On the temperature / cell voltage plane, a region with a higher temperature range is defined as a region with a higher degradation risk, and thus the small region r#i has a larger region number #i.

[0054] In FIG. 4, the discharge region includes five small regions r1 to r5. Each of the small regions r1 to r5 is divided by a threshold temperature (hereinafter also referred to as a temperature threshold). If the five temperature thresholds are represented as TM1 to TM5 (TM1<TM2<TM3<TM4<TM5)), the region between temperature thresholds TM1 and TM2 is the small region r1, and the region between temperature thresholds TM2 and TM3 is the small region r2. The region between temperature thresholds TM3 and TM4 is the small region r3, and the region between temperature thresholds TM4 and TM5 is the small region r4. The region above temperature threshold TM5 is the small region r5.

[0055] The number of small regions r#i (and temperature thresholds TM#i), the values of temperature thresholds TM#i, and some or all of other parameters related to voltage drop discharge can be set by any method such as simulation or an AI (artificial intelligence) model, for example, so as to balance the suppression of degradation of battery cells 11 and reduction of disposable capacity against the manufacturing cost of the battery 10. Further, for example, some of the parameters related to voltage drop discharge can be set from the perspective of the manufacturing cost of the battery 10, and the remaining parameters can be set from the perspective of suppressing degradation of the battery cells 11 and reduction of disposable capacity. In addition, parameters related to voltage drop discharge can be set by any method.

[0056] In FIG. 4, in the plurality of small regions r#i included in the discharge region, the cell voltage at which voltage drop discharge (at the discharge rate set for the small region r#i) ends, that is, the end voltage which is the cell voltage for switching between execution and stop of voltage drop discharge, is different from each other. Since there is a tendency that the degradation risk is high regardless of whether the cell voltage is high or the temperature is high, the end voltage of another small region r#i'(>i) having a higher temperature range than a given small region r#i is lower than the end voltage of the small region r#i.

[0057] The microcomputer 30 performs a voltage-down discharge of the battery cell 11 when the state points representing the cell voltage and temperature of the battery cell 11 are within the discharge region. Therefore, according to the small region r#i, which has multiple regions with different termination voltages, it can be said that the cell voltage at which the voltage-down discharge ends is divided into several stages for each temperature range.

[0058] The termination voltage can be set as a relative voltage, for example, a relative value based on the fully charged voltage.

[0059] The termination voltage can also be set as the absolute value of the cell voltage. However, if the termination voltage is set as the absolute value of the cell voltage, problems may arise, such as when the full charge voltage drops, the full charge voltage falling below the termination voltage, and even if the cell voltage is at or close to the full charge voltage, no voltage drop discharge occurs at all.

[0060] Here, the microcomputer 30 can control the full charge voltage based on the degradation of the battery cell 11 in order to allow the battery cell 11 to be used until a predetermined lifespan is reached. For example, the microcomputer 30 can estimate the degradation of the battery cell 11 based on the operating environment of the battery cell 11, and based on that operating environment (and the degree of degradation of the battery cell 11 estimated thereto), it can lower the full charge voltage, thereby suppressing a shortening of the battery cell 11's lifespan.

[0061] For example, the microcomputer 30 converts the operating time of the battery cell 11 (battery 10) at each temperature into an operating time at a predetermined temperature, and based on the cumulative value of the operating time at the predetermined temperature, the larger the cumulative value, the more the fully charged voltage can be reduced.

[0062] For example, the microcomputer 30 counts the number of times the battery 10 has been charged, and based on that number of charges, it can lower the full charge voltage more as the number of charges increases.

[0063] For example, the microcomputer 30 converts the charging time of the battery 10 at each charging voltage into a charging time at a predetermined voltage, and based on the cumulative value of the charging time at the predetermined voltage, the larger the cumulative value, the more the full charge voltage can be reduced.

[0064] In addition, the microcomputer 30 can reduce the full charge voltage based on two or more of the following: the cumulative value of the operating time at a predetermined temperature, the number of charging cycles, and the cumulative value of the charging time at a predetermined voltage.

[0065] Furthermore, the method for controlling the full charge voltage is not limited to the method described above.

[0066] In Figure 4, the termination voltage of the small region r#i is set as a relative voltage HV#i with respect to the full charge voltage FV (set by the relative voltage HV#i), and is set to full charge voltage FV - relative voltage HV#i.

[0067] In this way, by setting the termination voltage to the relative voltage HV#i, which is based on the full charge voltage FV, it is possible to prevent problems such as the full charge voltage FV falling below the termination voltage when the full charge voltage FV decreases.

[0068] Figure 5 shows an example of a temperature / cell voltage plane representing a small region r1 to r5 when the full charge voltage FV has decreased.

[0069] In Figure 5, the horizontal axis represents temperature, and the vertical axis represents cell voltage.

[0070] In Figure 4, the fully charged voltage FV is voltage V1, but in Figure 5, the fully charged voltage FV is voltage V2, which is lower than voltage V1.

[0071] By setting the termination voltage to the relative voltage HV#i, which is based on the full charge voltage FV, even if the full charge voltage FV decreases from voltage V1 to voltage V2, the full charge voltage FV will not fall below the termination voltage.

[0072] When the termination voltage is set as a relative voltage HV#i with respect to the full charge voltage FV, the termination voltage decreases as the full charge voltage FV decreases. Therefore, as the degradation of the battery cell 11 progresses and the full charge voltage FV decreases significantly, the termination voltage set as a relative voltage HV#i with respect to the full charge voltage FV also decreases significantly.

[0073] Furthermore, since the risk of degradation increases with higher temperatures, the relative voltage HV#i is set to a large value so that the termination voltage is lower in smaller regions r#i with higher temperature ranges.

[0074] Therefore, if the full charge voltage FV drops significantly, the termination voltage in the small region r#i with a high temperature range may become so small that it would result in over-discharge if a voltage drop discharge occurred.

[0075] Therefore, when setting the termination voltage as a relative voltage HV#i based on the fully charged voltage FV, a voltage limit value VL, which is an absolute voltage value that limits the termination voltage, can be set. In this case, if the termination voltage FV-HV#i, which is set as a relative voltage HV#i based on the fully charged voltage FV, falls below the voltage limit value VL, the termination voltage is set to the voltage limit value VL instead of the relative voltage HV#i. This prevents over-discharge due to voltage drop discharge.

[0076] In Figure 5, as the full charge voltage FV decreases to voltage V2, the termination voltage FV-HV#i, which is set as the relative voltage HV#i based on the full charge voltage FV in the high-temperature range subregions r4 and r5 among the subregions r1 to r5, falls below the voltage limit value VL. Therefore, the termination voltage in subregions r4 and r5 is set to the voltage limit value VL, not the voltage FV-HV#i.

[0077] <Information set in the register built into the control unit 31>

[0078] Figure 6 illustrates an example of information set in the registers built into the control unit 31.

[0079] The control unit 31 incorporates a register (not shown), in which parameters related to voltage drop discharge and other information necessary for controlling voltage drop discharge are set (stored). Note that various types of information can be set (stored) in any storage device instead of the register built into the control unit 31.

[0080] The registers built into the control unit 31 are set to a timer counter, as well as parameters related to voltage drop discharge, such as discharge speed information, speed change time information, number of regions information, termination voltage information, voltage limit value VL, and temperature threshold information.

[0081] The timer counter counts the duration for which state points representing the cell voltage and temperature of the battery cell 11 exist (continuously) within the discharge region. The timer counter is reset when a state point leaves the discharge region. Furthermore, the timer counter is also reset when charging of the battery 10 or normal discharge (discharge as battery 10 is used) begins. During charging of the battery 10 or during normal discharge, the timer counter does not count the duration.

[0082] As for the timer counter, one timer counter can be provided, that is, one timer counter common to all of the multiple sub-regions included in the discharge area. Alternatively, multiple timer counters can be provided, for example, a timer counter for each sub-region included in the discharge area. If one timer counter is provided, the storage capacity of the register built into the control unit 31 can be saved. If multiple timer counters are provided, finer control can be performed for voltage drop discharge control, for example, control that can more effectively suppress battery degradation and the decrease in disposable capacity of the battery 10.

[0083] The discharge rate information indicates the discharge rate of the voltage drop discharge. For example, the duty cycle of the pulse that turns switch SW#i on / off (represented by M and N in Figure 3) can be used. The discharge rate can be set for each sub-region. Furthermore, multiple discharge rates can be set for a single sub-region. That is, multiple discharge rates can be set for a single sub-region. For example, a sub-region can have two discharge rates: a first discharge rate and a second discharge rate that is faster than the first discharge rate. In this case, a rate change time is set to change the discharge rate from the first discharge rate to the second discharge rate. When a state point enters a sub-region, if the existence time is less than (or less than) the rate change time, discharge is performed at the first discharge rate. When the existence time becomes equal to the rate change time, the discharge rate is changed from the first discharge rate to the second discharge rate.

[0084] Therefore, the discharge rate of a voltage drop discharge can be varied by a small region, i.e., the cell voltage and / or temperature (range). Furthermore, the discharge rate of a voltage drop discharge can be varied by the time the state point exists in the discharge region. As described above, the discharge rate can be changed when the state point moves from one small region to another, and can also be changed by the time it exists.

[0085] Furthermore, the discharge rate information can be set to zero, meaning that voltage drop discharge will not be performed.

[0086] Furthermore, the discharge rate of another sub-region r#i' (>i) with a higher temperature range than a given sub-region r#i can be set to a speed equal to or greater than the discharge rate of sub-region r#i, or to a speed faster than the discharge rate of sub-region r#i. This is because sub-regions r#i' with a higher temperature range have a higher risk of degradation than sub-regions r#i with a lower temperature range, and therefore, it is possible to perform a faster voltage drop discharge in sub-regions r#i' with a higher temperature range than in sub-regions r#i with a lower temperature range.

[0087] The speed change time information indicates the speed change time. The speed change time is the threshold for the duration at which the discharge rate of the voltage drop discharge is changed. The speed change time can be set for each sub-region, for example. For a single sub-region, the number of speed change times set in the speed change time information is the number of discharge rates set in the discharge rate information minus one. The speed change time of another sub-region r#i' with a higher temperature range than a certain sub-region r#i can be set to a time less than or equal to the speed change time of sub-region r#i, or to a time shorter than the speed change time of sub-region r#i. This is because sub-regions r#i' with a higher temperature range have a higher risk of degradation than sub-regions r#i with a lower temperature range, and therefore allow for faster voltage drop discharge in sub-regions r#i' with a higher temperature range at an earlier timing than in sub-regions r#i with a lower temperature range.

[0088] The domain number information indicates the number of subdomains.

[0089] Termination voltage information indicates the termination voltage. The termination voltage is the lower limit of the cell voltage at which voltage drop discharge occurs (the lower edge of the small region). In addition to using the absolute voltage that becomes the termination voltage (voltage relative to ground), the relative voltage HV#i relative to the full charge voltage FV can also be used as termination voltage information. When the relative voltage HV#i is used as the termination voltage information, the termination voltage is set to the relative voltage HV#i relative to the full charge voltage FV, i.e., full charge voltage FV - relative voltage HV#i. Termination voltage information can be set, for example, for each small region (each temperature range). In other words, termination voltage information indicates the voltage range that defines each small region.

[0090] The voltage limit value VL is the absolute voltage that limits the termination voltage. If the termination voltage, which is set as a relative value based on the full charge voltage FV, falls below the voltage limit value VL, the termination voltage is set to the voltage limit value VL. In other words, if the full charge voltage FV minus the relative voltage HV#i is less than the voltage limit value VL, the termination voltage will be the voltage limit value VL, not the full charge voltage FV minus the relative voltage HV#i.

[0091] The temperature threshold information is set to indicate the temperature threshold (TM#i). The temperature threshold is the temperature threshold that divides the discharge area into multiple sub-regions. The temperature threshold can be set for each sub-region, for example. In other words, the temperature threshold information is information that indicates the temperature range that defines each sub-region.

[0092] Of the above information, the discharge rate information, speed change time information, number of regions information, termination voltage information, voltage limit value VL, and temperature threshold information, excluding the timer counter, are set, for example, during the manufacturing of the battery 10.

[0093] Furthermore, the registers built into the control unit 31 can store various other information, such as the voltage drop discharge status of the battery 10. For example, it can store information such as the total time that each state point has existed in each sub-region r#i up to the present time, and the number of times the discharge rate has been changed. Based on this information, the battery development company can understand the use cases (usage conditions) of the battery 10 and utilize this information for future battery development.

[0094] <Movement of state points>

[0095] Figure 7 shows an example of the movement of state points representing the cell voltage and temperature of the battery cell 11 in the temperature / cell voltage plane.

[0096] In Figure 7, the horizontal axis represents temperature, and the vertical axis represents cell voltage.

[0097] Hereafter, unless otherwise specified, it will be assumed that a single timer counter common to all sub-regions is provided as the timer counter. Furthermore, for each sub-region, two discharge speeds are set as discharge speed information: a first discharge speed and a second discharge speed that is faster than the first discharge speed. In this case, one speed change time is set as the speed change time information, which is the time required to change the discharge speed from the first discharge speed to the second discharge speed.

[0098] In Figure 7, the state points move chronologically in the order of points P1, P2, P3, P4, and P5.

[0099] When the state point is at point P1, voltage drop discharge does not occur because point P1 is a point outside the discharge region.

[0100] For example, when the temperature rises and the state point moves from point P1 to point P2, the state point enters the small region r2 from outside the discharge region at point P2. Therefore, the timer counter starts counting the time the state point is in the discharge region. Furthermore, a voltage drop discharge at the first discharge rate is started in the small region r2 where the state point is located. In addition, the voltage drop discharge of the battery cell is controlled based on the time recorded by the timer counter.

[0101] As voltage drop discharge begins, the cell voltage starts to decrease.

[0102] Subsequently, for example, if the temperature rises further and the state point moves from point P2 to point P3, the state point moves from small region r2 to small region r3 at point P3. At the time the state point enters small region r3, the existence time measured by the timer counter is assumed not to exceed the speed change time in small region r3. In this case, due to entering small region r3, the discharge speed is changed from the first discharge speed in small region r2 to the first discharge speed in small region r3.

[0103] The first discharge rate in small region r3, which has a higher temperature range than small region r2, is faster than the first discharge rate in small region r2. Therefore, when the discharge rate changes from the first discharge rate in small region r2 to the first discharge rate in small region r3, which is faster than the first discharge rate in small region r2, the rate at which the cell voltage decreases also increases.

[0104] Since the state point that moved to point P3 is not outside the discharge region, the timer counter continues to count its existence time.

[0105] While the timer counter continues to count the existence time, the state point moves from point P3 to point P4 within the subregion r3. When the existence time exceeds the velocity change time in subregion r3 at the moment it moves to point P4, the discharge velocity is changed from the first discharge velocity in subregion r3 to a second discharge velocity in subregion r3 that is faster than the first discharge velocity in subregion r3.

[0106] As the discharge rate changes from the first discharge rate in small region r3 to the second discharge rate in small region r3, the rate at which the cell voltage decreases also increases. As a result, in Figure 7, the state point (represented by the cell voltage) that was within small region r3 moves to point P5, where it falls below (or becomes equal to) the termination voltage FV-HV3 of small region r3, and moves out of the discharge region.

[0107] The voltage drop discharge ends when the state point moves out of the discharge region. Furthermore, the timer counter (and its duration) is reset.

[0108] <Time-dependent changes in cell voltage due to voltage drop discharge control>

[0109] Figure 8 is a schematic diagram showing an example of the time change of the cell voltage due to the control of voltage drop discharge by the microcomputer 30.

[0110] In Figure 8, the horizontal axis represents time, and the vertical axis represents cell voltage.

[0111] Regarding the time evolution of the cell voltage, time 0 is defined as the moment when the state point enters the discharge region. The same applies hereafter.

[0112] In Figure 8, graph L1 shows an example of the time evolution of the cell voltage when the state point enters a small region r#i within a certain temperature range, but does not enter another small region r#j (≠i), and thus leaves the discharge region.

[0113] When the state point enters the small region r#i, the timer counter starts counting the existence time, and a voltage-decaying discharge occurs at the first discharge rate in the small region r#i. When comparing at similar voltages, the temperature range of the small region r#i has a lower degradation risk compared to the temperature range of the small region r#i', which will be described later. Therefore, the first discharge rate in the small region r#i is relatively slow. As a result, the cell voltage decreases very slowly.

[0114] When the time elapsed since the state point entered the small region r#i reaches time t11, which is equal to the speed change time in the small region r#i, the discharge rate is changed from the first discharge rate in the small region r#i to the second discharge rate in the small region r#i. In this case, the battery 10 has been left in the temperature range of the small region r#i for longer than the speed change time. Therefore, in order to lower the cell voltage more quickly, the discharge rate is changed from the first discharge rate in the small region r#i to the second discharge rate in the small region r#i, which is faster than the first discharge rate.

[0115] When the discharge rate is changed to the second discharge rate in the small region r#i, the cell voltage decreases somewhat more sharply than before the change in discharge rate.

[0116] In graph L1, the state point does not enter another sub-region r#j, and at time t12, the cell voltage falls below the termination voltage of sub-region r#i, causing it to exit the discharge region. Therefore, at time t12, the voltage drop discharge ends, and thereafter, the cell voltage at the end of the voltage drop discharge is (almost) maintained.

[0117] In Figure 8, graph L2 shows an example of the time evolution of the cell voltage when the state point enters a sub-region r#i' (>i) which is set to a higher temperature than the sub-region r#i, and does not enter any other sub-region r#j' (≠i'), thus leaving the discharge region.

[0118] When the state point enters sub-region r#i', which is set to a higher temperature than sub-region r#i, the timer counter starts counting the existence time, and a voltage drop discharge occurs at the first discharge rate in sub-region r#i'. Since sub-region r#i', which is set to a higher temperature than sub-region r#i, has a higher risk of degradation than sub-region r#i, which is set to a lower temperature than sub-region r#i', the first discharge rate in sub-region r#i' is faster than the first discharge rate in sub-region r#i. As a result, the cell voltage drops sharply.

[0119] When the time elapsed since the state point entered the small region r#i' reaches time t21, which is equal to the speed change time in the small region r#i', the discharge rate is changed from the first discharge rate in the small region r#i' to the second discharge rate in the small region r#i'. In this case, the battery 10 is in a state where it has been left for longer than the speed change time in the temperature range of small region r#i', which is set to be higher than the temperature of small region r#i. Therefore, in order to lower the cell voltage more quickly, the discharge rate is changed from the first discharge rate in the small region r#i' to the second discharge rate in the small region r#i', which is faster than the first discharge rate.

[0120] Furthermore, in the temperature range of sub-region r#i', which is set to a higher temperature than sub-region r#i, the risk of degradation is higher than in the temperature range of sub-region r#i. Therefore, the speed change time (t21) in sub-region r#i' is shorter than the speed change time (t11) in sub-region r#i.

[0121] When the discharge rate is changed to the second discharge rate in the small region r#i', the cell voltage decreases even more sharply than before the change in discharge rate.

[0122] In graph L2, the state point does not enter any other sub-region r#j', and at time t22, the cell voltage falls below the termination voltage of sub-region r#i', causing it to exit the discharge region. Therefore, at time t22, the voltage drop discharge ends, and thereafter, the cell voltage at the end of the voltage drop discharge is (almost) maintained.

[0123] As described above, voltage-dropping discharge is performed to suppress the degradation of the battery cell 11, and the cell voltage is reduced.

[0124] However, in the temperature range of small region r#i, the risk of degradation is lower than in the temperature range of small region r#i', which is set to a higher temperature than small region r#i. Therefore, voltage drop discharge is performed at a slower discharge rate than in small region r#i', and the reduction in disposable capacity is suppressed. Furthermore, even in a state with a low risk of degradation, if such a state continues for a long time, the possibility of degradation increases. Therefore, even in the temperature range of small region r#i, if the time spent in the discharge region is a relatively long rate change time, such as several days, the discharge rate is changed to a faster rate than the rate before the rate change time has elapsed in order to suppress degradation.

[0125] On the other hand, in the temperature range of small region r#i', which is set to a higher temperature than small region r#i', the risk of degradation is higher than in the temperature range of small region r#i, which is set to a lower temperature than small region r#i'. Therefore, voltage drop discharge is performed at a faster discharge rate than in the case of small region r#i, and degradation is suppressed. Furthermore, if a state with a high risk of degradation continues for a certain period of time, the possibility of degradation will increase significantly. Therefore, in the temperature range of small region r#i', if the time spent in the discharge region is a relatively short rate change time, such as a few hours, the discharge rate is changed to an even faster rate than the rate before the rate change time has elapsed in order to suppress degradation.

[0126] As a result, the degradation of the battery 10 (battery cell 11) and the reduction in disposable capacity can be suppressed more effectively than with conventional technologies. For example, in actual use cases, the battery 10 is often left unused for several hours. In such cases, the discharge rate of voltage drop discharge is suppressed, thereby prioritizing disposable capacity. On the other hand, if the battery 10 is left unused for several days or longer, or exposed to high temperatures with a high risk of degradation, such as the temperature range of small region r#i' which is set to a higher temperature than small region r#i, the discharge rate of voltage drop discharge is made faster than in the case of small region r#i, thereby suppressing degradation.

[0127] <Control of voltage drop discharge by microcomputer 30>

[0128] Figure 9 is a flowchart illustrating an example of the process for controlling voltage drop discharge by the microcomputer 30.

[0129] In step S11, the control unit 31 of the microcomputer 30 determines whether the state point of the battery cell 11 has entered the discharge region. If it determines that it has not entered the discharge region, it returns to step S11.

[0130] Then, in step S11, if it is determined that the state of the battery cell 11 has entered the discharge region, the process proceeds to step S12.

[0131] In step S12, the control unit 31 starts counting the time the state point is in the discharge region using a timer counter, and the process proceeds to step S13.

[0132] In step S13, the control unit 31 performs voltage drop discharge control of the battery cell 11 based on its existence time. For example, the control unit 31 performs voltage drop discharge (on / off of switch SW1) of the battery cell 11 at a discharge rate based on the small region in which the state point exists. Then, the control unit 31 changes the discharge rate of the voltage drop discharge of the battery cell 11 based on its existence time.

[0133] In step S13, the voltage drop discharge control based on existence time includes a voltage drop discharge termination determination that determines whether to terminate the voltage drop discharge. If the voltage drop discharge termination determination in step S13 determines that the voltage drop discharge should be terminated, the process proceeds from step S13 to step S14.

[0134] In step S14, the control unit 31 terminates the voltage drop discharge of the battery cell 11 and resets the existence time on the timer counter. Then, the process returns from step S14 to step S11, and the same process is repeated thereafter.

[0135] Figure 10 is a flowchart illustrating an example of the voltage drop discharge control process based on existence time, which is performed in step S13 of Figure 9.

[0136] In step S21, the control unit 31 determines whether the existence time measured by the timer counter is equal to or greater than the speed change time in the small region r#i where the state point of the battery cell 11 exists (or is greater than the speed change time).

[0137] If, in step S21, it is determined that the existence time is not greater than or equal to the speed change time in the small region r#i where the state point of the battery cell 11 exists, the process proceeds to step S22.

[0138] In step S22, the control unit 31 initiates a voltage drop discharge (on / off of switch SW1) at a first discharge rate in the small region r#i where the state point of the battery cell 11 exists, and the process proceeds to step S23.

[0139] In step S23, the control unit 31 determines whether the existence time measured by the timer counter is equal to or greater than the speed change time in the small region r#i where the state point of the battery cell 11 exists.

[0140] If, in step S23, it is determined that the existence time is not greater than or equal to the speed change time in the small region r#i where the state point of the battery cell 11 exists, the process proceeds to step S24.

[0141] In step S24, the control unit 31 determines whether the state point of the battery cell 11 has entered another sub-region r#j, that is, whether the sub-region in which the state point exists has changed.

[0142] In step S24, if it is determined that the state point has entered (exists in) another sub-region r#j, the process returns to step S21, and the same process is performed thereafter. This causes a voltage reduction discharge at the discharge rate in the other sub-region r#j.

[0143] Furthermore, if it is determined in step S24 that the state point is not in another sub-region r#j, the process proceeds to step S25.

[0144] In step S25, the control unit 31 determines whether the voltage drop discharge has ended. Specifically, the control unit 31 determines whether the state point of the battery cell 11 has moved out of the discharge region, or whether charging of the battery 10 or discharge for use of the battery 10 (normal discharge) has started.

[0145] In step S25, if it is determined that the state point has not moved outside the discharge region and neither charging nor normal discharging of the battery 10 has started, the control unit 31 determines not to terminate the voltage drop discharge, and the process returns to step S23. In this case, the voltage drop discharge at the first discharge rate in the small region r#i where the state point of the battery cell 11 is located, which was started in step S22, continues.

[0146] Furthermore, in step S25, if it is determined that the state point has moved out of the discharge region, or that charging or normal discharge of the battery 10 has started, the control unit 31 determines that the voltage drop discharge will end, and the process returns to step S14.

[0147] On the other hand, if it is determined in step S21 or step S23 that the existence time has become greater than or equal to the speed change time in the small region r#i where the state point of the battery cell 11 exists, the process proceeds to step S26.

[0148] In step S26, the control unit 31 starts a voltage drop discharge at a second discharge rate in the small region r#i where the state point of the battery cell 11 is located, and the process proceeds to step S27. If the process proceeds from step S23 to step S26, in step S26, the discharge rate of the voltage drop discharge is changed from the first discharge rate in the small region r#i where the state point of the battery cell 11 is located to the second discharge rate in that small region r#i.

[0149] In step S27, the control unit 31 determines whether the state point of the battery cell 11 has entered another sub-region r#j, that is, whether the sub-region where the state point exists has changed.

[0150] In step S27, if it is determined that the state point has entered another sub-region r#j, the process returns to step S21, and the same process is performed thereafter. This causes a voltage reduction discharge at the discharge rate in the other sub-region r#j.

[0151] Furthermore, if it is determined in step S27 that the state point is not in another sub-region r#j, the process proceeds to step S28.

[0152] In step S28, the control unit 31 performs a determination of the end of the voltage drop discharge, similar to the case in step S25.

[0153] If it is determined in step S28 that the voltage drop discharge should not be terminated, the process returns to step S27. In this case, the voltage drop discharge at the second discharge rate in the small region r#i where the state point of the battery cell 11 is located, which was started in step S26, continues.

[0154] Furthermore, if it is determined in step S28 that the voltage drop discharge has ended, the process returns and proceeds to step S14.

[0155] <Time-dependent changes in cell voltage due to voltage drop discharge control>

[0156] Figure 11 shows a first example of the time change of the cell voltage due to voltage drop discharge control by the microcomputer 30.

[0157] In Figure 11, the horizontal axis represents time, and the vertical axis represents cell voltage.

[0158] Figure 11 shows an example of the time change of cell voltage due to voltage drop discharge control when only one timer counter is provided in common for all the sub-regions included in the discharge area.

[0159] In Figure 11, graph L11 shows an example of the time change of the cell voltage when the state point enters small region r3 and remains in small region r3 at all times until the cell voltage of the battery cell 11 falls below the termination voltage, that is, when it leaves the discharge region without entering the other small regions r1, r2, r4, and r5.

[0160] When the state point enters the small region r3, the timer counter starts counting the existence time, and a voltage drop discharge occurs at the first discharge rate in the small region r3. As a result, the cell voltage decreases at a rate corresponding to the first discharge rate in the small region r3.

[0161] When the time elapsed since the state point entered the discharge region (small region r3) reaches time tr3, which is the time of the rate change in small region r3, the discharge rate changes from the first discharge rate in small region r3 to a second discharge rate in small region r3 that is faster than the first discharge rate. As a result, the cell voltage decreases at a faster rate than in the case of the first discharge rate, corresponding to the second discharge rate in small region r3.

[0162] In graph L11, the state point is outside the discharge region because the cell voltage falls below the termination voltage FV-HV3 of the sub-region r3, without entering any other sub-region r#j. Therefore, when the cell voltage falls below the termination voltage FV-HV3 of the sub-region r3, the voltage drop discharge ends, and thereafter, the cell voltage at the end of the voltage drop discharge is (almost) maintained.

[0163] In Figure 11, graph L12 shows an example of the time change of the cell voltage when the state point enters small region r4 and remains in small region r4 at all times until the cell voltage of the battery cell 11 falls below the termination voltage, that is, when it leaves the discharge region without entering the other small regions r1 to r3 and r5.

[0164] When the state point enters the small region r4, the timer counter starts counting the existence time, and a voltage drop discharge occurs in the small region r4 at a first discharge rate. As a result, the cell voltage decreases at a rate corresponding to the first discharge rate in the small region r4.

[0165] In small region r4, where the temperature range is higher and the risk of degradation is higher than in small region r3, the first discharge rate is faster than the first discharge rate in small region r3. Therefore, in graph L12, the cell voltage decreases at a faster rate than in graph L11.

[0166] When the time elapsed since the state point entered the discharge region (small region r4) reaches time tr4, which is equal to the rate change time tr4 in small region r4, the discharge rate changes from the first discharge rate in small region r4 to a second discharge rate in small region r4 that is faster than the first discharge rate. As a result, the cell voltage decreases at a faster rate than in the case of the first discharge rate, corresponding to the second discharge rate in small region r4.

[0167] In the small region r4, which has a higher temperature range and a higher risk of degradation than the small region r3, the speed change time tr4 is shorter than the speed change time tr3 in the small region r3 in order to reduce the high risk of degradation early on.

[0168] Subsequently, in graph L12, the state point exits the discharge region because the cell voltage falls below the termination voltage FV-HV4 of the sub-region r4, without entering any other sub-region r#j. Therefore, when the cell voltage falls below the termination voltage FV-HV4 of the sub-region r4, the voltage drop discharge ends, and thereafter, the cell voltage at the end of the voltage drop discharge is maintained.

[0169] In Figure 11, graph L13 shows an example of the time change of the cell voltage when the state point enters small region r3, moves to small region r4 due to a change in the temperature of the battery cell 11, and then moves out of the discharge region.

[0170] When the state point enters the small region r3, the timer counter starts counting the existence time, and a voltage drop discharge occurs at the first discharge rate in the small region r3. As a result, the cell voltage decreases at a rate corresponding to the first discharge rate in the small region r3, similar to graph L11.

[0171] Subsequently, as the temperature rises, at time t131, when the state point moves from small region r3 to small region r4, the discharge rate changes from the first discharge rate in small region r3 to the discharge rate in small region r4.

[0172] Time t131 is the time after the speed change time tr4 in small region r4 has elapsed from time t=0, when the state point entered small region r3. Therefore, since the existence time measured by the timer counter has exceeded the speed change time tr4 in small region r4, at time t131, the discharge speed is changed from the first discharge speed in small region r4 to the second discharge speed. As a result, the cell voltage decreases at a rate corresponding to the second discharge speed in small region r4.

[0173] Subsequently, in graph L13, the state point moves out of the discharge region because the cell voltage falls below the termination voltage FV-HV4 of the small region r4. Therefore, when the cell voltage falls below the termination voltage FV-HV4 of the small region r4, the voltage drop discharge ends, and thereafter the cell voltage at the end of the voltage drop discharge is maintained.

[0174] In Figure 11, graph L14 shows an example of the time change of the cell voltage when the state point enters small region r4, moves to small region r3 due to a change in the temperature of the battery cell 11, and then moves out of the discharge region.

[0175] When the state point enters the small region r4, the timer counter starts counting the existence time, and a voltage drop discharge occurs at the first discharge rate in the small region r4. As a result, the cell voltage decreases at a rate corresponding to the first discharge rate in the small region r4, similar to graph L12.

[0176] When the time elapsed since the state point entered the small region r4 reaches time tr4, which is equal to the rate change time tr4 in the small region r4, the discharge rate changes from the first discharge rate in the small region r4 to a second discharge rate in the small region r4 that is faster than the first discharge rate, similar to graph L12. As a result, the cell voltage decreases at a faster rate than in the case of the first discharge rate, corresponding to the second discharge rate in the small region r4.

[0177] Subsequently, as the temperature decreases and the state point moves from small region r4 to small region r3 at time t141, the discharge rate changes from the second discharge rate in small region r4 to the discharge rate in small region r3.

[0178] Time t141 is a time that has not exceeded the speed change time tr3 in small region r3 since time t=0 when the state point entered small region r4. Therefore, since the existence time measured by the timer counter has not elapsed beyond the speed change time tr3 in small region r3, at time t141, the discharge speed is changed from the second discharge speed in small region r4 to the first discharge speed in small region r3. As a result, the cell voltage decreases at a rate corresponding to the first discharge speed in small region r3. The first discharge speed in small region r3 is slower than the discharge speed before the change, i.e., the second discharge speed in small region r4.

[0179] Subsequently, in graph L14, the state point moves out of the discharge region because the cell voltage falls below the termination voltage FV-HV3 of the small region r3. Therefore, when the cell voltage falls below the termination voltage FV-HV3 of the small region r3, the voltage drop discharge ends, and thereafter the cell voltage at the end of the voltage drop discharge is maintained.

[0180] Figure 12 shows a second example of the time change of the cell voltage due to the control of voltage drop discharge by the microcomputer 30.

[0181] In Figure 12, the horizontal axis represents time, and the vertical axis represents cell voltage.

[0182] Figure 12 shows an example of the time change of cell voltage due to voltage drop discharge control when a timer counter is provided individually for each sub-region. Note that if the sub-regions r#i included in the discharge region are regions divided based on temperature (only), then providing a timer counter individually for each sub-region r#i is equivalent to providing a timer counter for each temperature range.

[0183] A timer counter in a subregion r#i counts the existence time of that subregion r#i and the subregions in the temperature range higher than r#i. That is, the timer counter in subregion r#i counts the existence time d#i of the state point when it is (consecutively) in subregions r#i+1, r#i+2, ... which are higher temperature ranges (with a higher risk of degradation than subregion r#i) than subregion r#i.

[0184] Therefore, if a state point exists in a sub-region r#i, the existence times d#i, d#i-1

[0185] Subsequently, when the existence time d#i of the small region r#i where the state point exists, as determined by the timer counter, becomes the speed change time tr#i of the small region r#i, the discharge speed is changed according to the discharge speed information of the small region r#i.

[0186] In Figure 12, graph L21 shows an example of the time change of the cell voltage when the state point enters small region r3 and remains in small region r3 at all times until the cell voltage of the battery cell 11 falls below the termination voltage, that is, when it leaves the discharge region without entering the other small regions r1, r2, r4, and r5.

[0187] Graph L22 shows an example of the time change of the cell voltage when the state point enters small region r4 and remains in small region r4 at all times until the cell voltage of the battery cell 11 falls below the termination voltage, that is, when it leaves the discharge region without entering the other small regions r1 to r3 and r5.

[0188] Graph L23 shows an example of the time evolution of the cell voltage when the state point enters small region r3, moves to small region r4 due to a change in the temperature of the battery cell 11, and then moves out of the discharge region.

[0189] Graphs L21 and L22 are identical to graphs L11 and L12 in Figure 11, respectively.

[0190] In graph L23, when the state point enters small region r3, the timer counters for small region r3 and small regions r1 and r2 in the temperature range lower than small region r3 begin counting the existence time d1 to d3. Furthermore, a voltage drop discharge is performed at the first discharge rate in small region r3. As a result, the cell voltage decreases at a rate corresponding to the first discharge rate in small region r3, similar to graph L11. Graph L23 up to this point is identical to graph L13 in Figure 11.

[0191] Subsequently, as the temperature rises, at time t231, when the state point moves from small region r3 to small region r4, the timer counter for small region r4, and for small regions r1 to r3 in the temperature range lower than small region r4, which has not yet started counting, begins counting the existence time d4. The timer counters for small regions r1 to r3 continue counting the existence times d1 to d3. Furthermore, the discharge rate is changed from the first discharge rate in small region r3 to the discharge rate in small region r4.

[0192] Time t231 is the time after the speed change time tr4 in sub-region r4 has elapsed from time t=0, when the state point entered sub-region r3. Therefore, the existence times d1 to d3, as measured by the timer counters of each of the sub-regions r1 to r3, have all exceeded the speed change time tr4 in sub-region r4.

[0193] However, the existence time d4 of the small region r4 where the state point exists at time t231, as measured by the timer counter, starts counting at time t231. Therefore, at time t231, the speed change time tr4 in the small region r4 has not yet elapsed.

[0194] Therefore, at time t231, the discharge rate is changed to the first discharge rate in small region r4. As a result, the cell voltage decreases at a rate corresponding to the first discharge rate in small region r4.

[0195] Then, while the state point remains in the small region r4, when the time d4 of the small region r4 where the state point exists, as measured by the timer counter, becomes the speed change time tr4 in the small region r4, at time t232, when the time d4 becomes the speed change time tr4, the discharge speed is changed from the first discharge speed in the small region r4 to the second discharge speed. As a result, the cell voltage decreases at a rate corresponding to the second discharge speed in the small region r4.

[0196] Subsequently, in graph L23, the state point moves out of the discharge region because the cell voltage falls below the termination voltage FV-HV4 of the small region r4. Therefore, when the cell voltage falls below the termination voltage FV-HV4 of the small region r4, the voltage drop discharge ends, and thereafter the cell voltage at the end of the voltage drop discharge is maintained.

[0197] Figure 13 illustrates another example of a discharge region.

[0198] Figure 13, like Figure 4, shows a discharge region defined on a temperature / cell voltage plane, where the vertical axis represents cell voltage and the horizontal axis represents temperature.

[0199] Assuming the cell voltage is constant, when considering temperature, the risk of degradation increases as the temperature rises. Assuming the temperature is constant, when considering cell voltage, the risk of degradation increases as the cell voltage rises. In Figure 13, the sub-region r#ij included in the discharge region is a region divided based on both temperature and cell voltage, and the discharge region is set considering that the region where at least one of the temperature and cell voltage of the battery cell 11 is high is a region where the risk of degradation of the battery cell 11 is high (or tends to be high) (taking into consideration that it is a region where the risk of degradation is considered high). In Figure 13, the region number #ij of the sub-region r#ij is composed of the temperature number #i and the voltage number #j, and the higher the temperature range of the sub-region r#ij is, the larger the temperature number #i is, and the higher the cell voltage range of the sub-region r#ij is, the larger the voltage number #j is. Therefore, if voltage number #j is fixed, the subregion #ij is a region with a higher risk of degradation as temperature number #i increases, and if temperature number #i is fixed, the subregion #ij is a region with a higher risk of degradation as voltage number #j increases.

[0200] In Figure 13, the direction of temperature and cell voltage are each divided into five sections, and the discharge region includes 13 sub-regions: sub-regions r1-5, sub-regions r2-5, sub-regions r3-3 and r3-5, sub-regions r4-2 to r4-5, and sub-regions r5-1 to r5-5. The 13 sub-regions r1-5 to r5-5 are divided by threshold temperatures and cell voltages.

[0201] As described above, when the sub-region r#ij is a region divided based on both temperature and cell voltage, the timer counter can be provided as a single unit common to all sub-regions included in the discharge region, as shown in Figure 11, or it can be provided individually for each sub-region, as shown in Figure 12. In addition, timer counters can be provided for each temperature or cell voltage range, or for each of multiple sub-regions.

[0202] Figure 14 shows a third example of the time change of the cell voltage due to voltage drop discharge control by the microcomputer 30.

[0203] In Figure 14, the horizontal axis represents time, and the vertical axis represents cell voltage.

[0204] Figure 14 shows an example of the time variation of the cell voltage due to voltage drop discharge control when the small region r#ij is divided into regions based on both temperature and cell voltage, as shown in Figure 13, and a timer counter is provided individually for each small region.

[0205] As shown in Figure 13, each sub-region r#ij is a region divided based on both temperature and cell voltage. If a timer counter is provided individually for each sub-region, the timer counter for a given sub-region r#ij counts the time the state point exists in a sub-region with a degradation risk equal to or greater than that of that sub-region r#ij. In other words, the timer counter for a sub-region r#ij counts the time the state point exists in that sub-region r#ij and the time it exists in a sub-region with a higher degradation risk than that sub-region r#ij. A high degradation risk for a battery cell 11 means that at least one of the temperature and cell voltage of the battery cell 11 is high, and the sub-regions located in the upward, rightward, or upper-right directions on the temperature / cell voltage plane have a higher degradation risk. A timer counter in a small region r#ij can count the time a state point exists in a small region with a degradation risk equal to or greater than that of small region r#ij, where the temperature range is greater than or equal to the minimum value of the temperature range of small region r#ij, and the cell voltage range is greater than or equal to the minimum value of the cell voltage range of small region r#ij (all or part of this region). Alternatively, a timer counter in a small region r#ij can count the time a state point exists in a small region with a degradation risk equal to or greater than that of small region r#ij, where the temperature range is greater than or equal to the minimum value of the temperature range of small region r#ij, and the cell voltage range is greater than or equal to the minimum value of the cell voltage range of small region r#ij, where the temperature range is greater than or equal to that of small region r#ij, and the cell voltage range is greater than or equal to that of small region r#ij.

[0206] In Figure 14, graph L31 shows an example of the time change of the cell voltage when the state point enters small region r3-5 and remains in small region r3-j, which has the same temperature number as small region r3-5, until the cell voltage of battery cell 11 falls below the termination voltage (i.e., when moving within small region r3-j).

[0207] Graph L32 shows an example of the time change of the cell voltage when the state point enters small region r4-5 and remains in small region 4-j, which has the same temperature number as small region r4-5, until the cell voltage of battery cell 11 falls below the termination voltage (i.e., when moving within small region r4-j).

[0208] In graph L31, when the state point enters the sub-region r3-5, the timer counters for each sub-region with degradation risk equal to or less than that of sub-region r3-5 begin counting the existence time. Furthermore, a voltage drop discharge occurs at the first discharge rate in sub-region r3-5. As a result, the cell voltage decreases at a rate corresponding to the first discharge rate in sub-region r3-5.

[0209] Subsequently, in graph L31, the state point remains in the small region r3-5, and the time t311 represents the time elapsed from t=0 when the state point entered the small region r3-5 to the time t311 when the speed change time in the small region r3-5 has elapsed. At time t311, the discharge rate changes from the first discharge rate in the small region r3-5 to the second discharge rate in the small region r3-5. As a result, the cell voltage decreases at a rate corresponding to the second discharge rate in the small region r3-5.

[0210] In graph L31, due to the subsequent decrease in cell voltage, at time t312, the state point moves from sub-region r3-5 to sub-region r3-3, which has a lower degradation risk. When the state point moves from sub-region r3-5 to sub-region r3-3, the timer counters that have been counting up to that point—that is, the timer counters for each sub-region with a degradation risk equal to or less than that of sub-region r3-5, and the timer counters for each sub-region with a higher degradation risk than that of sub-region r3-3—stop counting the existence time (or stop and reset). For example, the timer counter for sub-region r3-5, which has a higher degradation risk than that of sub-region r3-3, stops counting its existence time from time t312. Furthermore, the discharge rate changes from the second discharge rate in sub-region r3-5 to the discharge rate in sub-region r3-3.

[0211] At time t312, if the time elapsed in sub-region r3-3 according to the timer counter has not exceeded the time for speed change in sub-region r3-3, the discharge speed is changed from the second discharge speed in sub-region r3-5 to the first discharge speed in sub-region r3-3. Also, at time t312, if the time elapsed in sub-region r3-3 according to the timer counter has exceeded the time for speed change in sub-region r3-3, the discharge speed is changed from the second discharge speed in sub-region r3-5 to the second discharge speed in sub-region r3-3. The cell voltage decreases at a rate corresponding to the changed discharge speed.

[0212] Subsequently, in graph L31, at time t313, the cell voltage falls below the termination voltage FV-HV3 of the small region r3-3, causing the state point to move out of the discharge region. Therefore, when the cell voltage falls below the termination voltage FV-HV3 of the small region r3-3, the voltage drop discharge ends, and thereafter, the cell voltage at the end of the voltage drop discharge is maintained.

[0213] On the other hand, in graph L32, when the state point enters the sub-region r4-5, the timer counters for each sub-region with degradation risk equal to or less than that of sub-region r4-5 begin counting the existence time. Furthermore, a voltage drop discharge is performed at the first discharge rate in sub-region r4-5. As a result, the cell voltage decreases at a rate corresponding to the first discharge rate in sub-region r4-5.

[0214] In graph L32, due to the subsequent decrease in cell voltage, at time t321, the state point moves from sub-region r4-5 to sub-region r4-4, which has a lower degradation risk. When the state point moves from sub-region r4-5 to sub-region r4-4, the timer counters that have been counting up to that point—that is, the timer counters for each sub-region with a degradation risk equal to or less than that of sub-region r4-5, and for each sub-region with a degradation risk higher than that of sub-region r4-4—stop counting the existence time. For example, the timer counter for sub-region r4-5, which has a higher degradation risk than that of sub-region r4-4, stops counting its existence time from time t321. Furthermore, the discharge rate is changed from the first discharge rate in sub-region r4-5 to the first discharge rate in sub-region r4-4. The cell voltage decreases at a rate corresponding to the changed discharge rate.

[0215] Subsequently, in graph L32, at time t322, the state point moves from sub-region r4-4 to sub-region r4-3, which has a lower degradation risk, and then at time t323, after time t322, it moves from sub-region r4-3 to sub-region r4-2, which also has a lower degradation risk.

[0216] At time t322, as in the case at time t321, the counting of existence time by the timer counters of each sub-region whose degradation risk is higher than that of sub-region r4-3, among the sub-regions whose degradation risk is equal to or less than that of sub-region r4-4, is stopped. Furthermore, the discharge rate is changed from the discharge rate in sub-region r4-4 to the discharge rate in sub-region r4-3.

[0217] At time t323, as at time t321, the counting of existence time by the timer counters of each sub-region whose degradation risk is higher than that of sub-region r4-2, among the timer counters of each sub-region whose degradation risk is equal to or less than that of sub-region r4-3, is stopped. Furthermore, the discharge rate is changed from the discharge rate in sub-region r4-3 to the discharge rate in sub-region r4-2. In Figure 14, at time t323, the discharge rate has been changed to the first discharge rate in sub-region r4-2.

[0218] Subsequently, in graph L32, the state point remains in sub-region r4-2, and the time t324 represents the elapsed time since time 0 when the state point first entered a sub-region (sub-region r4-5) with a degradation risk equal to or greater than that of sub-region r4-2. At time t324, the discharge rate changes from the first discharge rate in sub-region r4-2 to the second discharge rate in sub-region r4-2. As a result, the cell voltage decreases at a rate corresponding to the second discharge rate in sub-region r4-2.

[0219] In graph L32, at time t325, the cell voltage falls below the termination voltage FV-HV4 of small region r4-2, causing the state point to move out of the discharge region. Therefore, when the cell voltage falls below the termination voltage FV-HV4 of small region r4-2, the voltage drop discharge ends, and thereafter the cell voltage at the end of the voltage drop discharge is maintained.

[0220] It should be noted that the graph showing the time change of cell voltage due to the control of voltage drop discharge described above is an example and does not necessarily represent the optimal change in cell voltage due to the control of voltage drop discharge. Furthermore, a level representing the degree of degradation risk can be set for each sub-region included in the discharge region, taking into account the range of temperature and / or cell voltage. For example, in Figure 13, a level of degradation risk, as shown by the intensity of the color, can be set for each sub-region r#ij, which is divided based on both temperature and cell voltage. For example, by assigning a larger value to the higher the degradation risk, a level 1 degradation risk can be set for sub-regions r1-5, r2-5, r3-3, r4-2, and r5-1; a level 2 degradation risk can be set for sub-regions r3-5, r4-3, and r5-2; a level 3 degradation risk can be set for sub-regions r4-4 and r5-3; a level 4 degradation risk can be set for sub-regions r4-5 and r5-4; and a level 5 degradation risk can be set for sub-region r5-5. In this case, a timer counter can be provided individually for each degradation risk level. When a timer counter is provided individually for each degradation risk level, the number of timer counters will be less than or equal to the number of sub-regions included in the discharge area. A timer counter for a degradation risk level counts the time that a state point exists in a sub-region of degradation risk equal to or higher than that level. For example, a timer counter for degradation risk level 3 counts the time that a state point exists in a sub-region of degradation risk equal to or higher than level 3, i.e., sub-regions r4-4 and r4-5, and sub-regions r5-3 to r5-5, enclosed by thick lines in Figure 13. If a state point exists in sub-region r#ij, the discharge rate is changed from the first discharge rate in sub-region r#ij to the second discharge rate in sub-region r#ij based on the time that state point exists in that sub-region r#ij according to the timer counter for that degradation risk level. When setting degradation risk levels, all sub-regions with the same degradation risk level can be treated as one new sub-region, and the discharge rate (information) and rate change time (information) can be set for each new sub-region.Setting the discharge rate and rate change time for each new sub-region is equivalent to setting the discharge rate and rate change time for each level of degradation risk.

[0221] Figure 15 illustrates yet another example of a discharge region.

[0222] Figure 15, similar to Figure 4, shows a discharge region defined on a temperature / cell voltage plane, where the vertical axis represents cell voltage and the horizontal axis represents temperature.

[0223] In Figure 15, the small region r#j is a region divided based on the cell voltage. In the temperature / cell voltage plane, regions with a higher cell voltage range (voltage range) are considered to have a higher risk of degradation, and these regions have a larger region number (voltage number) #j.

[0224] In Figure 15, the discharge region includes five sub-regions r1 to r5. Each of these sub-regions r1 to r5 is separated by a threshold cell voltage.

[0225] For the sub-regions r#j divided based on the cell voltage as described above, the higher the voltage range (and thus the risk of degradation), the faster the discharge rate can be set compared to the lower voltage range in order to reduce the risk of degradation earlier. In addition, a single timer counter can be provided for all sub-regions included in the discharge region, or a separate timer counter can be provided for each sub-region (each voltage range).

[0226] <Calculation of current for remaining charge calculation>

[0227] Figure 16 illustrates an example of calculating the remaining battery capacity calculation current used when performing a voltage drop discharge.

[0228] For example, in calculating the remaining charge of the battery 10, the microcomputer 30 detects and integrates the total current flowing from the two battery cells 11 and 21 of the battery 10 to calculate the total charge (amount) flowing from the two battery cells 11 and 21 of the battery 10.

[0229] The current path of the discharge current during low-voltage discharge differs from the current path when the battery 10 is being charged or discharged under normal conditions. Therefore, the discharge current during low-voltage discharge cannot be detected using the current detection means used during charging or normal discharge of the battery 10.

[0230] For example, the microcomputer 30 calculates a remaining charge calculation current used to calculate the remaining charge of the battery 10 when voltage drop discharge is performed, based on the discharge current that flows due to voltage drop discharge, which is calculated from the resistance of the circuit through which the discharge current flows due to voltage drop discharge and the cell voltage of the battery cell that has undergone voltage drop discharge. The cell voltage is supplied sequentially to the control unit 31, as explained in Figure 1. The resistance (resistance value) of the circuit through which the discharge current flows due to voltage drop discharge is stored in a register built into the control unit 31 as one of the parameters related to voltage drop discharge.

[0231] In Figure 16, the current path through which the discharge current (discharge current flowing due to voltage drop discharge) flows in the battery 10 is shown by a dashed line.

[0232] If voltage drop discharge does not occur in battery cells 11 and 21, switches SW1 and SW2 are turned off, and no discharge current flows for voltage drop discharge. In other words, the discharge current for voltage drop discharge is 0. When the discharge current for voltage drop discharge is 0, the current for calculating remaining charge is also 0.

[0233] When only battery cell 11 of battery cells 11 and 21 undergoes a voltage drop discharge, switch SW1 is turned ON and switch SW2 is turned OFF. As a result, the current Icell1, which is the discharge current for the voltage drop discharge, flows from battery cell 11 back to battery cell 11 via resistor R11, VIN1 terminal, resistor R1, switch SW1, and GND terminal.

[0234] In this case, the discharge current Icell1 during voltage drop discharge is calculated using the resistance (resistance value) R11+R1 of the closed circuit through which the discharge current Icell1 flows, and the cell voltage Vcell1 of the battery cell 11, according to the formula Icell1=Vcell1 / (R11+R1). The current I for remaining charge calculation is calculated based on the discharge current Icell1 during voltage drop discharge, according to the formula I=(Icell1×Vcell1) / V, assuming that it is the total current flowing from the two battery cells 11 and 21 of the battery 10 (total cell-based current) that is integrated in the remaining charge calculation of the battery 10. V represents the voltage of the series connection of the two battery cells 11 and 21 of the battery 10. When the cell voltage of battery cell 21 is represented by Vcell2, the voltage V is expressed by the formula V=Vcell1+Vcell2.

[0235] When only battery cell 21 of battery cells 11 and 21 experiences a voltage drop discharge, switch SW1 is turned off and switch SW2 is turned on. As a result, the current Icell2, which is the discharge current for the voltage drop discharge, flows from battery cell 21 back to battery cell 21 via resistor R21, VIN2 terminal, switch SW2, resistor R2, VIN1 terminal, and resistor R11.

[0236] In this case, the discharge current Icell2 for voltage drop discharge is calculated using the closed circuit resistance R21+R2+R11 through which the discharge current Icell2 flows, and the cell voltage Vcell2 of the battery cell 21, according to the formula Icell2 = Vcell2 / (R21+R2+R11). The remaining charge calculation current I is calculated based on the discharge current Icell2 for voltage drop discharge, according to the formula I = (Icell2 × Vcell2) / V, similar to the case where only the battery cell 11 undergoes voltage drop discharge.

[0237] When both battery cells 11 and 21 are subjected to a voltage drop discharge, switches SW1 and SW2 are turned on. This causes a current Iv, which is the discharge current for the voltage drop discharge, to flow from battery cells 11 and 21 (connected in series) through resistor R21, the VIN2 terminal, switch SW2, resistor R2, resistor R1, switch SW1, and the GND terminal back to the battery cells 11 and 21 in a closed circuit.

[0238] In this case, the discharge current Iv for voltage drop discharge is calculated using the resistance R21+R2+R1 of the closed circuit through which the discharge current Iv flows, and the voltage V=Vcell1+Vcell2 across the series connection of battery cells 11 and 21, according to the formula Iv=V / (R21+R2+R1). The discharge current Iv is the total current flowing from the two battery cells 11 and 21 of the battery 10 (the current on a total cell basis), and is used as the current I for calculating the remaining charge.

[0239] As described above, by calculating the current used for calculating the remaining charge when voltage drop discharge occurs, and using that remaining charge calculation current to calculate the remaining battery capacity, it is possible to calculate the remaining battery capacity that reflects the amount of charge lost due to voltage drop discharge.

[0240] <Cell Balancing>

[0241] Figure 17 is a flowchart illustrating an example of cell balancing control.

[0242] In battery 10, when both battery cells 11 and 21 undergo voltage drop discharge simultaneously, the discharge current Icell1 of battery cell 11 and the discharge current Icell2 of battery cell 12 may differ (vary). In this case, an imbalance in cell voltage occurs, where the cell voltage of battery cell 11 and the cell voltage of battery cell 12 are different.

[0243] An imbalance in cell voltage can lead to various adverse effects. For example, variations in degradation may occur between battery cells. Also, for example, if, in battery 10, the full charge determination is made based on the higher of the two cell voltages of battery cells 11 and 21, the battery capacity at full charge may decrease. Furthermore, for example, in battery 10, the cell voltage of the lower of the two battery cells 11 and 21 may drop sharply during discharge, making it easier to reach the discharge stop voltage. Also, for example, if, in battery 10, the cell voltages of battery cells 11 and 21 are monitored individually, overcharge protection (stopping charging due to overcharging) is more likely to be triggered.

[0244] Therefore, the battery 10 can perform cell balancing control to balance the cell voltages of battery cells 11 and 21 to approximately the same level.

[0245] In cell balancing control, in step S111, the microcomputer 30 calculates the voltage difference (absolute value of the voltage difference) between the cell voltages of the two battery cells 11 and 21, and the process proceeds to step S112.

[0246] In step S112, the microcomputer 30 determines whether the voltage difference is large, that is, whether the voltage difference is above a predetermined threshold.

[0247] In step S112, if it is determined that the voltage difference is not above a predetermined threshold, the cell balancing control is terminated.

[0248] On the other hand, if it is determined in step S112 that the voltage difference is greater than or equal to a predetermined threshold, the process proceeds to step S113. In step S113, the microcomputer 30 sets the cell with the larger voltage among the two battery cells 11 and 21 as the target for voltage drop discharge, performs voltage drop discharge, and terminates the cell balancing control.

[0249] According to the cell balancing control, if the voltage difference between the cell voltages is large (above a predetermined threshold), a voltage drop discharge is performed on the cell with the higher voltage among the two battery cells 11 and 21. This balances the cell voltages of both battery cells 11 and 21 to approximately the same level.

[0250] In the cell balancing described above, the cell with the higher voltage among the two battery cells 11 and 21 is subjected to a voltage drop discharge. This causes the energy (charge) corresponding to the voltage difference between the two battery cells 11 and 21 to be discarded as heat loss through the resistor. This type of cell balancing is called passive cell balancing.

[0251] Battery 10 can perform both passive and active cell balancing. In active cell balancing, the charge from the battery cell with the higher voltage is supplied to the cell with the lower voltage. Active cell balancing requires a dedicated circuit, but it allows for the effective utilization of energy corresponding to the voltage difference without wasting it.

[0252] In Figure 17, a large voltage difference (above a predetermined threshold) was used as a condition for performing cell balancing; however, other conditions can be added to the conditions for performing cell balancing.

[0253] <Another embodiment of a battery to which this technology is applied>

[0254] Figure 18 shows an example configuration of another embodiment of a battery to which this technology is applied.

[0255] In the figures, parts corresponding to those in Figure 1 are denoted by the same reference numerals, and their explanations will be omitted as appropriate below. Also, in Figure 18, parts related to voltage drop discharge are shown, while other parts are omitted from the illustration.

[0256] In Figure 18, the battery 110 includes battery cells 11 and 21, a microcomputer 130, a switch 141, and a resistor 142. Like the battery 10, the battery 110 can be configured to be detachable from various electronic devices, or it can be configured to be built into electronic devices.

[0257] In the battery 110, battery cell 11, whose negative terminal is connected to ground (GND), and battery cell 21 are connected in series by connecting the positive terminal of battery cell 11 to the negative terminal of battery cell 21, thereby forming a series connection circuit.

[0258] The switch 141 is provided to form a closed circuit with the series connection circuit of the battery cells 11 and 21.

[0259] The resistor 142 is located between the switch 141 and the positive terminal of the battery cell 21.

[0260] The microcomputer 130 is supplied with information indicating the cell voltage of battery cells 11 and 21, as well as information indicating the temperature, similar to the case of battery 10. Based on the information indicating the cell voltage (the cell voltage indicated by) and the information indicating the temperature (the temperature indicated by), the microcomputer 130 counts the time that one of the battery cells 11 and 21 (for example, either one or the one with the higher or lower cell voltage) exists in a discharge region defined on the temperature / cell voltage plane, and controls the voltage drop discharge of both battery cells 11 and 21 based on that time, similar to the microcomputer 30. The microcomputer 30 supplies an on / off signal, which is a control signal that controls the on / off state of switch 141, to switch 141 on / off, thereby controlling the simultaneous voltage drop discharge of both battery cells 11 and 21.

[0261] In the battery 110 configured as described above, when the switch 141 is turned on, a voltage drop discharge current flows from the series-connected battery cells 11 and 21 to the series-connected battery cells 11 and 21 via the resistor 142 and the switch 141.

[0262] Therefore, in the battery 110, voltage drop discharge occurs simultaneously for both battery cells 11 and 21.

[0263] Figure 19 shows an example of the configuration of yet another embodiment of a battery to which this technology is applied.

[0264] In the figures, parts corresponding to those in Figure 1 are denoted by the same reference numerals, and their explanations will be omitted as appropriate below. Also, in Figure 19, parts related to voltage drop discharge are shown, while other parts are omitted from the illustration.

[0265] In Figure 19, the battery 210 includes battery cells 11 and 21, a microcomputer 230, a switch 241, a resistor 242, a switch 251, and a resistor 252. Like the battery 10, the battery 210 can be configured to be detachable from various electronic devices, or it can be configured to be built into electronic devices.

[0266] In the battery 210, battery cell 11, whose negative terminal is connected to ground (GND), and battery cell 21 are connected in series by the positive terminal of battery cell 11 and the negative terminal of battery cell 21 being connected.

[0267] The switch 241 is provided to form a closed circuit with the battery cell 11.

[0268] The resistor 242 is located between the switch 241 and the positive terminal of the battery cell 11.

[0269] The switch 251 is provided to form a closed circuit with the battery cell 21.

[0270] The resistor 252 is located between the switch 251 and the positive terminal of the battery cell 21.

[0271] The microcomputer 230 is supplied with information indicating the cell voltage of each battery cell 11 and 21, as well as information indicating the temperature, similar to the case of the battery 10. Based on the information indicating the cell voltage (the cell voltage indicated by) and the information indicating the temperature (the temperature indicated by), the microcomputer 230 counts the time that each battery cell state point exists in the discharge region defined on the temperature / cell voltage plane, and controls the voltage drop discharge of each battery cell 11 and 21 based on that time, similar to the microcomputer 30.

[0272] The microcomputer 230 controls the voltage drop discharge of the battery cell 11 by supplying an on / off signal, which is a control signal to turn the switch 241 on or off, and by turning the switch 241 on or off. Similarly, the microcomputer 230 controls the voltage drop discharge of the battery cell 21 by supplying an on / off signal, which is a control signal to turn the switch 251 on or off, and by turning the switch 251 on or off.

[0273] In the battery 210 configured as described above, when switch 241 is turned on, a discharge current for voltage drop discharge flows from battery cell 11 through resistor 242 and switch 241 to battery cell 11. Similarly, when switch 251 is turned on, a discharge current for voltage drop discharge flows from battery cell 21 through resistor 252 and switch 251 to battery cell 21.

[0274] Therefore, in the battery 210, voltage drop discharge is performed individually (for each battery cell) for each of the battery cells 11 and 21.

[0275] In the battery 110 shown in Figure 18, voltage drop discharge is performed simultaneously on both battery cells 11 and 21 using switch 141 and resistor 142. Battery 110 using switch 141 and resistor 142 is advantageous in terms of cost and volume compared to battery 210 using switch 241 and resistor 242, and switch 251 and resistor 252. Furthermore, in battery 110, during voltage drop discharge, the discharge current Icell1 of battery cell 11 and the discharge current Icell2 of battery cell 21 become the same, suppressing the occurrence of variations in discharge current.

[0276] On the other hand, the battery 210 in Figure 19 uses switches 241 and resistors 242, and switches 251 and resistors 252, so that voltage drop discharge can be performed individually (for each battery cell) for each of the battery cells 11 and 21. Furthermore, this allows for cell balancing, where the cell with the higher voltage among the battery cells 11 and 21 is targeted for voltage drop discharge. Also, in the battery 210, if the cell voltages of battery cells 11 and 21 are the same, and the resistance values ​​of resistors 242 and 252 are the same, then during voltage drop discharge, the discharge current Icell1 of battery cell 11 and the discharge current Icell2 of battery cell 21 will be the same, and no variation in discharge current will occur.

[0277] <Specific examples of discharge current used for calculating remaining battery level>

[0278] Figure 20 shows a specific example of the discharge current used for calculating the remaining charge when a voltage drop discharge is performed in the battery 10.

[0279] In Figure 20, the discharge currents Icell1 of battery cell 11 and Icell2 of battery cell 21 are shown by dashed lines when two battery cells 11 and 21 in battery 10 are simultaneously subjected to voltage drop discharge (when both switches SW1 and SW2 are on).

[0280] For example, let's assume that the cell voltage Vcell1 of battery cell 11 and the cell voltage Vcell2 of battery cell 21 are both the same at 4.48V, and that the resistance values ​​of resistors R1, R2, R11, and R21 are all 100Ω.

[0281] In this case, the resistance values ​​are different in the closed circuit through which the discharge current Icell1 of battery cell 11 flows and in the closed circuit through which the discharge current Icell2 of battery cell 21 flows. Therefore, as shown in Figure 20, the discharge current Icell1 of battery cell 11 is 35.8mA, and the discharge current Icell2 of battery cell 21 is 26.9mA, so the discharge currents Icell1 and Icell2 are different.

[0282] Figure 21 shows a specific example of the discharge current used for calculating the remaining charge when a voltage drop discharge is performed in the battery 110.

[0283] In Figure 21, the discharge currents Icell1 of battery cell 11 and Icell2 of battery cell 21 are shown by dashed lines when two battery cells 11 and 21 in battery 110 are simultaneously subjected to voltage drop discharge (when switch 141 is on).

[0284] For example, let's assume that the cell voltage Vcell1 of battery cell 11 and the cell voltage Vcell2 of battery cell 21 are both the same at 4.48V, and that the resistance value Z of resistor 142 is 227Ω.

[0285] In battery 110, the discharge current Icell1 of battery cell 11 and the discharge current Icell2 of battery cell 21 are the same, resulting in 39mA.

[0286] Figure 22 shows a specific example of the discharge current used for calculating the remaining charge when a voltage drop discharge is performed in the battery 210.

[0287] In Figure 22, the discharge currents Icell1 of battery cell 11 and Icell2 of battery cell 21 are shown by dashed lines when two battery cells 11 and 21 in battery 210 are simultaneously subjected to voltage drop discharge (when switches 241 and 251 are on).

[0288] For example, the cell voltage Vcell1 of battery cell 11 and the cell voltage Vcell2 of battery cell 21 are both the same at 4.48V, and the resistance value Z1 of resistor 242 and the resistance value Z2 of resistor 252 are both 120Ω.

[0289] In battery 210, the discharge current Icell1 of battery cell 11 and the discharge current Icell2 of battery cell 21 are the same, resulting in 37mA.

[0290] In Figures 20 to 22, the discharge currents Icell1 and Icell2 are the values ​​when the duty cycle (N / M) for switching switches SW1, SW2, and switches 141, 241, and 251 on / off is set to 100% (1.0). Furthermore, the resistance values ​​of resistors R1, R2, R11, R21, and resistors 142, 242, and 252 are not limited to the values ​​mentioned above. Values ​​that allow the discharge rate when the duty cycle is 100% to be greater than or equal to the maximum discharge rate required for voltage drop discharge can be adopted. In reality, the cell voltage Vcell1 of battery cell 11 and the cell voltage Vcell2 of battery cell 21 are not constant values ​​such as 4.48V mentioned above, but change with charging and discharging.

[0291] <Processing based on the deterioration stage>

[0292] Figure 23 is a flowchart illustrating an example of processing based on degradation stages.

[0293] In battery 10 (and similarly in batteries 110 and 210), the microcomputer 30 can perform processing based on degradation stages, which represent the degree of degradation of battery 10 (and its battery cells 11 and 21) as discrete values. Figure 23 shows such processing based on degradation stages.

[0294] In the degradation stage-based processing, in step S121, the microcomputer 30 sequentially records the degradation status of the battery 10 (battery cells 11 and 21). In step S122, the microcomputer 30 updates the degradation stage, which represents the degree of degradation, at a specific timing based on the degradation status of the battery. In step S123, the microcomputer 30 performs predetermined control based on the degradation stage.

[0295] In step S123, a predetermined control based on the degradation stage can be, for example, a control that changes the full charge voltage FV based on the degradation stage. For example, as the degradation stage progresses (as the battery 10 degrades), the full charge voltage FV can be set to a lower voltage than the current voltage.

[0296] In addition, in step S123, a predetermined control based on the degradation stage may be, for example, a control that changes the duty cycle based on the degradation stage.

[0297] The duty cycle coefficient is a coefficient used to correct the duty cycle ratio (N / M), which is information about the discharge rate.

[0298] The duty cycle for turning on / off the switch SW1 (switch SW2, switches 141, 241, 251) that determines the discharge rate can be the duty cycle N / M, which is the discharge rate information, or a corrected duty cycle obtained by correcting the duty cycle N / M, which is the discharge rate information, can be used. In the microcomputer 30, the correction of the duty cycle N / M, which is the discharge rate information, can be performed, for example, by multiplying the duty cycle N / M by a duty coefficient.

[0299] Figure 24 shows an example of the relationship between the degradation stage and the duty cycle.

[0300] In Figure 24, degradation stages 0 to 7 are defined, and each degradation stage #i is associated with a duty cycle coefficient a#i.

[0301] The degradation stage #i indicates the degree of degradation; a larger number #i represents a greater degree of degradation. The duty cycle a#i associated with degradation stage #i is, for example, a value of 1.0 or greater, and the larger the number #i, the larger the value.

[0302] The duty cycle N / M, which is discharge rate information, is corrected according to, for example, the formula N × A#i / M.

[0303] For example, if the duty cycle N / M, which is discharge rate information, is 3 / 10 (=30%) when N=3 and M=10, and the duty coefficient a#i associated with the degradation stage is 1.20, then the corrected duty cycle will be 3 × 1.20 / 10 = 3.6 / 10 = 36%.

[0304] Furthermore, if calculations are performed in the microcomputer 30 while truncating or rounding decimal places, it is desirable to express the numerical values ​​in a way that prevents large errors from occurring due to truncation or rounding decimal places, and to perform the calculation of the formula N × A#i / M as a correction for the duty cycle N / M.

[0305] For example, as mentioned above, if the duty cycle N / M is 30% and the duty coefficient a#i = 1.20, then the corrected duty cycle should be 36%.

[0306] However, if a 30% duty cycle is expressed as 3 / 10, the calculation of the formula N×A#i / M, which is a correction using the duty cycle coefficient a#i=1.20, is performed according to the formula (3×(120 / 100)) / 10, and when the calculation of the numerator is completed, it becomes 3.6 / 10. For example, if rounding to the nearest whole number is performed, the 3.6 in the numerator of 3.6 / 10 is rounded to 4, and as a result, the corrected duty cycle becomes 4 / 10 = 40%.

[0307] Therefore, a 30% duty cycle can be expressed as 30 / 100 by increasing the number of decimal places. In this case, the calculation of the formula N × A#i / M as a correction by the duty cycle coefficient a#i = 1.20 is performed according to the formula (30 × (120 / 100)) / 100, and when the calculation of the numerator is completed, it becomes 36 / 100. Since there are no decimal places in the numerator or denominator of 36 / 100, no rounding to the decimal point is performed, and the corrected duty cycle is 36 / 100 = 36%.

[0308] Figure 25 shows an example of the relationship between the duty cycle and the time change of the cell voltage during voltage drop discharge.

[0309] The relationship between the duty cycle and the time variation of the cell voltage in Figure 25 assumes that the state point remains within a single small region and that no speed change time has elapsed.

[0310] The duty cycle coefficient a#i associated with degradation stage #i is, for example, a value of 1.0 or greater, with larger numbers #i corresponding to larger values. For example, in Figure 25, duty cycle coefficient a0 is 1.0, duty cycle coefficient a1 is 1.2, and duty cycle coefficient a2 is 1.4.

[0311] Therefore, by correcting the duty cycle N / M, which is discharge rate information, using the duty coefficient a#i, the rate at which the cell voltage decreases can be made faster than before the degradation progressed, as the battery 10 deteriorates.

[0312] By correcting the duty cycle ratio N / M, which is discharge rate information, using the duty coefficient a#i, the cell voltage can be reduced more rapidly as the battery 10 deteriorates, compared to the case without correction. As a result, the deterioration of DCR (internal resistance of the battery cell) due to high temperature and high voltage can be suppressed. Furthermore, when the battery 10 deteriorates, by making the rate of decrease in cell voltage during voltage drop discharge faster than before the deterioration progressed, the state point can quickly escape the small region with a high risk of deterioration, and further deterioration of the battery 10 can be suppressed.

[0313] <Description of a computer using this technology>

[0314] The series of processes described above can be executed by hardware or by software. When the series of processes are executed by software, the programs that make up that software are installed on a computer. Here, a computer includes computers built into dedicated hardware, as well as general-purpose personal computers, for example, that can perform various functions by installing various programs.

[0315] Figure 26 is a block diagram showing an example of the hardware configuration of a computer that executes the series of processes described above using a program.

[0316] In a computer, the processing circuit 901, ROM (Read Only Memory) 902, and RAM (Random Access Memory) 903 are interconnected by a bus 904.

[0317] An input / output interface 905 is further connected to the bus 904. An input unit 906, an output unit 907, a storage unit 908, a communication unit 909, and a drive 910 are connected to the input / output interface 905.

[0318] The input unit 906 may include physical or virtual operating means that the user operates to input information, such as a keyboard, mouse, or touch panel, as well as means that the user inputs information through voice, eye gaze, etc. Furthermore, the input unit 906 may include sensors for inputting various physical quantities to the computer. For example, the input unit 906 may include sensors that acquire physical quantities such as light (including infrared light other than visible light) or sound, such as a camera or microphone. Also, for example, the input unit 906 may include sensors that acquire other physical quantities such as temperature, moisture content, acceleration, distance, etc. The output unit 907 may include means that present information to the user by stimulating the user's perception, such as a display, speaker, or haptic device. The storage unit 908 is composed of a hard disk, non-volatile or volatile memory, etc., and stores various types of information (including programs). The communication unit 909 is a network interface, etc., and performs wired or wireless communication with the outside. The drive 910 drives removable media 911 such as a magnetic disk, optical disk, magneto-optical disk, or semiconductor memory.

[0319] The processing circuit 901 includes a processor that executes programs such as a CPU (Central Processing Unit) and a DSP (Digital Signal Processor). The processing circuit 901 (its processor) performs the above-described series of processes by loading the program stored in the storage unit 908 into the RAM 903 via the input / output interface 905 and the bus 904 and executing it. The processing circuit 901 can output the processing results of the series of processes from the output unit 907 via the bus 904 and the input / output interface 905 as needed. The processing circuit 901 can also store the processing results in the storage unit 908 or transmit them from the communication unit 909.

[0320] The program executed by the computer (processing circuit 901) can be provided by recording it on a removable medium 911, such as a package medium. The program can also be provided via wired or wireless transmission media, such as a local area network, the internet, or digital satellite broadcasting.

[0321] In a computer, a program can be installed in the storage unit 908 via the input / output interface 905 by inserting a removable media 911 into the drive 910. Alternatively, a program can be received by the communication unit 909 from another device, such as a server, via a wired or wireless transmission medium, and installed in the storage unit 908. Furthermore, programs can be pre-installed in the ROM 902 or the storage unit 908.

[0322] The programs executed by the computer may be programs that are processed chronologically in the order described herein, or they may be programs that are processed in parallel or at necessary times, such as when a call is made.

[0323] The processes that a computer performs according to a program do not necessarily have to follow the order described in the flowchart. In other words, the processes that a computer performs according to a program include processes that are executed in parallel or individually (e.g., parallel processing and object-based processing).

[0324] The program may be processed by a single computer (processor), or it may be processed in a distributed manner by multiple computers. Furthermore, the program may be transferred to a remote computer and executed there.

[0325] When the above-described series of processes are performed by a computer executing a program, the processing circuit 901 (its processor) functions as a control unit 31 by executing the program.

[0326] Furthermore, the embodiments of this technology are not limited to those described above, and various modifications are possible without departing from the spirit of this technology.

[0327] For example, this technology can be configured as cloud computing, where a single function is shared and processed collaboratively by multiple devices via a network.

[0328] Furthermore, each step described in the flowchart above can be performed by a single device, or it can be divided and performed by multiple devices.

[0329] Furthermore, if a single step includes multiple processes, those processes can be executed by a single device or shared among multiple devices.

[0330] Furthermore, the effects described herein are merely illustrative and not limiting, and other effects may also occur.

[0331] Furthermore, this technology can take the following configuration.

[0332] <1> A control device comprising a control unit that controls the discharge of charge accumulated in a battery cell based on the existence time, which is the time a state point, which is a point representing the terminal voltage and temperature of the battery cell, exists in a discharge region, which is a region including a plurality of sub-regions defined on a two-dimensional plane on which one of two orthogonal axes represents the terminal voltage of the battery cell and the other axis represents the temperature. <2> The control device according to <1>, wherein the control unit performs different discharge control for each of the sub-regions. <3> The control device according to <1> or <2>, wherein the control unit changes the discharge rate when the state point moves from one sub-region to another sub-region. <4> The control device according to <3>, wherein the sub-regions are regions divided based on temperature, and the discharge rate in other sub-regions with a higher temperature range than one sub-region is faster than the discharge rate in one sub-region. <5> The control device according to <3> or <4>, wherein the control unit changes the discharge rate based on the on / off duty cycle of a switch that turns the current flowing from the battery cell on / off. <6> The control device according to any one of <1> to <5>, wherein the control unit changes the discharge rate based on the existence time. <7> The control device according to <6>, wherein the control unit increases the discharge rate based on the existence time. <8> The control device according to <6> or <7>, wherein the rate change time, which is a threshold for the existence time used to change the discharge rate, is set for each of the sub-regions. <9> The control device according to <8>, wherein the sub-regions are regions divided based on temperature, and the rate change time in other sub-regions with a higher temperature range than one sub-region is shorter than the rate change time in the first sub-region. <10> The control device according to any one of <1> to <9>, wherein the control unit resets the existence time when the state point moves out of the discharge region, or when the battery is charged or discharged as battery use occurs. <11> The control device according to any one of <1> to <10>, wherein the termination voltage, which is the terminal voltage used to terminate the discharge, is different for each of the sub-regions.<12> The control device according to <11>, wherein the subregion is a region divided based on temperature, and the termination voltage of other subregions with a higher temperature range than one subregion is lower than the termination voltage of the first subregion. <13> The control device according to any one of <1> to <12>, wherein the termination voltage is set as a relative value based on the fully charged voltage. <14> The control device according to <13>, wherein if the termination voltage set as a relative value based on the fully charged voltage falls below a voltage limit value that limits the termination voltage, the termination voltage is set to the voltage limit value. <15> The control device according to any one of <1> to <14>, wherein the existence time is counted by a single timer counter common to all of the multiple subregions. <16> The control device according to any one of <1> to <14>, wherein the existence time is counted by a timer counter for each subregion. <17> The control device according to <16>, wherein a high terminal voltage and temperature of the battery cell indicates a high risk of degradation of the battery cell, and a timer counter for one small region counts the time the state point exists in the one small region and when it exists in a small region with a higher risk of degradation than the one small region. <18> The control device according to any one of <1> to <17>, wherein for each battery cell, the control unit calculates a current for calculating the remaining battery capacity when the discharge is performed, based on the current that flows due to the discharge, calculated from the resistance of the circuit through which the discharge controls the discharge and the terminal voltage of the battery cell. <19> A control method that includes controlling the discharge of charge accumulated in a battery cell based on the time the state point, which is the time the state point exists in a discharge region, which is a region including a plurality of small regions defined on a two-dimensional plane on which one of two orthogonal axes indicates the terminal voltage of the battery cell and the other axis indicates the temperature, where the state point is a point representing the terminal voltage and temperature of the battery cell.<20> A program to cause a computer to function as a control unit that controls the discharge of charge accumulated in a battery cell, based on the existence time, which is the time that a state point, which is a point representing the terminal voltage and temperature of the battery cell, exists in a discharge region, which is a region including multiple subregions defined on a two-dimensional plane on which one of two orthogonal axes represents the terminal voltage of the battery cell and the other axis represents the temperature.

[0333] 10 Battery, 11, 21 Battery cell, 30 Microcomputer, 31 Control unit, 32 Switch control unit, 901 Processing circuit, 902 ROM, 903 RAM, 904 Bus, 905 Input / Output interface, 906 Input unit, 907 Output unit, 908 Storage unit, 909 Communication unit, 910 Drive, 911 Removable media

Claims

The system includes a control unit that controls the discharge of charge accumulated in a battery cell based on the existence time, which is the time that a state point, which represents the terminal voltage and temperature of the battery cell, exists in a discharge region, which is a region containing multiple sub-regions defined on a two-dimensional plane on which one of two orthogonal axes represents the terminal voltage of the battery cell and the other axis represents the temperature of the battery cell. Control device. 　 The control unit performs different discharge control for each of the sub-regions. The control device according to claim 1. 　 The control unit changes the discharge rate when the state point moves from one sub-region to another sub-region. The control device according to claim 1. 　 The aforementioned sub-region is a region defined based on temperature. The discharge rate in other sub-regions with a higher temperature range than sub-region 1 is faster than the discharge rate in sub-region 1. The control device according to claim 3. 　 The control unit changes the discharge rate by the on / off duty cycle of the switch that turns the current flowing from the battery cell on / off. The control device according to claim 3. 　 The control unit changes the discharge rate based on the existence time. The control device according to claim 1. 　 The control unit increases the discharge rate based on the existence time. The control device according to claim 6. 　 The rate change time, which is the threshold for the existence time that changes the discharge rate, is set for each of the small regions. The control device according to claim 6. 　 The aforementioned sub-region is a region defined based on temperature. The speed change time in other sub-regions with a higher temperature range than sub-region 1 is shorter than the speed change time in sub-region 1. The control device according to claim 8. 　 The control unit resets the existence time when the state point moves out of the discharge region, or when the battery is charged or discharged for use. The control device according to claim 1. 　 The termination voltage, which is the terminal voltage at which the discharge ends, differs for each of the small regions. The control device according to claim 1. 　 The aforementioned sub-region is a region defined based on temperature. The termination voltage in other small regions with a higher temperature range than small region 1 is lower than the termination voltage in small region 1. The control device according to claim 11. 　 The termination voltage is set as a relative value based on the fully charged voltage. The control device according to claim 11. 　 If the termination voltage, which is set as a relative value based on the fully charged voltage, falls below the voltage limit value that restricts the termination voltage, the termination voltage is set to the voltage limit value. The control device according to claim 13. 　 The existence time is counted by a single timer counter common to all of the aforementioned sub-regions. The control device according to claim 1. 　 The existence time is counted by the timer counter for each of the sub-regions. The control device according to claim 1. 　 If at least one of the terminal voltage and temperature of the battery cell is high, this indicates a high risk of degradation of the battery cell. The timer counter of the small region 1 counts the time the state point exists in the small region 1 and in a small region with a higher risk of degradation than the small region 1. The control device according to claim 16. 　 The control unit controls the discharge for each battery cell. Based on the current flowing due to the discharge, which is calculated from the resistance of the circuit through which the current flows due to the discharge and the terminal voltage of the battery cell, a current for calculating the remaining battery capacity after the discharge is calculated. The control device according to claim 1. 　 The discharge of charge accumulated in the battery cell is controlled based on the existence time, which is the time that a state point, which represents the terminal voltage and temperature of the battery cell, exists in a discharge region, which is a region containing multiple sub-regions defined on a two-dimensional plane on which one of two orthogonal axes represents the terminal voltage of the battery cell and the other axis represents the temperature. A control method that includes the following. 　 A control unit controls the discharge of charge accumulated in a battery cell based on the existence time, which is the time that a state point, which represents the terminal voltage and temperature of the battery cell, exists in a discharge region, which is a region containing multiple sub-regions defined on a two-dimensional plane on which one of two orthogonal axes represents the terminal voltage of the battery cell and the other axis represents the temperature of the battery cell. A program that makes a computer function.

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