JP5131533B2 - Battery charge / discharge control method and charge / discharge control apparatus - Google Patents

Description

  The present invention relates to a battery charge / discharge control method and a charge / discharge control apparatus, and more particularly to a battery charge / discharge control method and a charge / discharge control apparatus which are assembled batteries composed of a plurality of battery cells.

Conventionally, a discharge circuit provided for each of a plurality of battery cells (single cells) constituting a battery configured as an assembled battery, and cell balance control so that the capacity of each battery cell is uniform by controlling the discharge circuit. 2. Description of the Related Art A battery control device including a control unit for performing is known (for example, see Patent Documents 1 and 2).
In the cell balance control described in Patent Documents 1 and 2, control is performed so that the capacities of all the battery cells are uniform. Thereby, for example, the possibility that each battery cell may exceed the maximum voltage when energized during charging can be reduced.

JP 2007-244058 A JP 2001-190030 A

  However, when the battery is used for a long period of time, each battery cell deteriorates, and the internal resistance of the battery cell varies. Therefore, when the capacity of the battery cells of the battery is controlled to be uniform as in the above-described prior art, the increase in voltage at the time of charging is increased in a battery cell having a large internal resistance due to variation in internal resistance between the battery cells. . As a result, the battery cell having an increased internal resistance has a problem that the maximum voltage is exceeded and deterioration is accelerated.

  Also, in order to prevent the cell voltage from exceeding the maximum voltage and promoting deterioration during such charging, the cell voltage will exceed the maximum voltage if the cell voltage is greatly reduced by balanced discharge by the discharge circuit. Even if it can suppress, the problem that the waste by balance discharge will become large arises.

  The present invention has been made to solve such a problem, and even if there is a variation in internal resistance among the battery cells constituting the battery, the deterioration of the battery cell by exceeding the maximum voltage during charging is promoted. It aims at providing the charging / discharging control method and charging / discharging control apparatus of a battery which can suppress and suppress useless balance discharge.

  In order to achieve the above object, the present invention provides a charge / discharge control method for a battery in which a plurality of battery cells are connected, the voltage setting step for setting the charge start voltage of each battery cell, and each battery cell A discharge step of discharging each battery cell until a set charge start voltage is reached using a discharge circuit connected to the battery, and in the voltage setting step, a battery cell having a higher internal resistance has a charge start voltage It is characterized by a low setting.

  According to the present invention configured as described above, even if the internal resistance of the battery cell varies, the charging start voltage that is the target voltage at the time of cell balance control is set lower for the battery cell having a higher internal resistance. Thus, it is possible to suppress the generation of battery cells exceeding the voltage limit value of the battery cell, particularly in the battery cell having a large internal resistance, when the voltage rise occurs when the charging current is supplied to the battery. Thereby, deterioration promotion by the overcharge of a battery cell can be suppressed. In addition, since the charging start voltage is set relatively high in a battery cell having a small internal resistance, useless balance discharge can be suppressed, and deterioration of power storage efficiency due to balancing control can be reduced.

Preferably, in the present invention, in the voltage setting step, when the battery is charged with the maximum limit charging current that can be energized that is set for the battery, the voltage of each battery cell is Set to a value that is approximately equal.
According to the present invention configured as described above, when the charging current to the battery is the maximum value, the charging start voltage of each cell is set so that the charging voltage of each cell becomes substantially equal. It is possible to prevent a part of the battery cells from exceeding the voltage limit value due to the voltage increase during charging.

Preferably, in the present invention, in the voltage setting step, the charging start voltage of each battery cell is increased as the maximum value of the charging current value during the predetermined period decreases according to the history of the charging current value of the battery during the predetermined period. Set.
According to the present invention configured as described above, each battery cell exceeds the voltage limit value during charging by setting the charging start voltage of each battery cell higher as the maximum charging current value during the predetermined period is smaller. Can be prevented, the amount of discharge by balancing control can be reduced, and the battery efficiency can be improved.

  In the present invention, it is preferable that the discharging step is performed when there is a battery cell having a voltage that exceeds a predetermined voltage and is larger than an average voltage value of the voltage of each battery cell. According to the present invention configured as described above, balancing control can be performed when the variation in the voltage value of each battery cell is large.

  In order to achieve the above object, the present invention provides a battery charge / discharge control apparatus in which a plurality of battery cells are connected, and includes a discharge circuit connected to each battery cell, and the interior of each battery cell. An internal resistance detecting means for detecting resistance; and a discharging means for discharging each battery cell to a charging start voltage by a discharging circuit. The discharging means sets the charging start voltage lower as the battery cell has a higher internal resistance. It is characterized by that.

  In the present invention, it is preferable that the discharging means is configured to reduce the voltage of each battery cell when the battery is charged with the charging start voltage of each battery cell with the maximum limited charging current that can be energized that is set for the battery. Set the value to be equal.

In the present invention, preferably, it has a current value detection means for detecting a current value energized to the battery, and a current value history acquisition means for obtaining a history of a current value energized to the battery in a predetermined period, The discharging means sets the charging start voltage of each battery cell to be higher as the maximum value of the charging current value during the predetermined period is smaller according to the history of the charging current value of the battery during the predetermined period.
Preferably, in the present invention, the discharge means discharges each battery cell by the discharge circuit when there is a battery cell having a voltage exceeding a predetermined voltage higher than the average voltage value of the voltage of each battery cell.

  According to the battery charge / discharge control method and the charge / discharge control apparatus of the present invention, even if each battery cell constituting the battery has a variation in internal resistance, the deterioration of the battery cell due to exceeding the maximum voltage during charging is suppressed. In addition, useless balance discharge can be suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 11. FIG. 1 is an explanatory diagram of a battery charge / discharge control device, FIG. 2 is an explanatory diagram of a discharge circuit of the battery charge / discharge control device, FIG. 3 is an explanatory diagram of a cell voltage change during charging, and FIG. FIG. 5 is an explanatory diagram of balancing control, FIG. 6 is a diagram showing a change in charging current over time including rapid charging, FIG. 7 is an explanatory diagram of balancing control by rapid charging control, and FIG. 8 is a cell open voltage. 9 is an explanatory diagram of map data showing the relationship between the SOC and the SOC, FIG. 9 is a diagram showing a time change of the charging current not including the time of quick charging, FIG. 10 is an explanatory diagram of balancing control by non-rapid charging control, and FIG. It is a flowchart of a control process.

In the present embodiment, an example in which the battery charge / discharge control method and charge / discharge control apparatus of the present invention are applied to a high-voltage battery mounted on a hybrid vehicle or the like will be described.
As shown in FIG. 1, the battery pack 1 of the present embodiment includes a battery 10 that is an assembled battery in which a plurality of single cells (battery cells) 11 are connected in series, and a charge / discharge control device 20 that controls the battery 10. It has.

The charge / discharge control device 20 includes a discharge circuit 21 provided corresponding to each battery cell 11, a voltage detection unit 23, an internal resistance detection unit 25, a charge / discharge determination unit 27, and a control unit 29 for controlling them. It has.
As shown in FIG. 2, each discharge circuit 21 has a configuration in which a series connection of a resistor 22 a and a switch 22 b is connected in parallel with each battery cell 11. The switch 22b is ON / OFF controlled between an open state and a closed state by a control signal from the control unit 29. By turning on the switch 22b (closed state), a closed circuit composed of the battery cell 11 and the resistor 22a is formed, and the current flowing through the closed circuit causes resistance according to the on time (discharge time) of the switch 22b. Electric power is consumed by the container 22a, and the capacity of the battery cell 11 can be reduced.

The charge / discharge determination unit 27 is connected between the positive terminal of the battery 10 and the positive terminal of the battery pack 1, detects the current direction of the charge / discharge current of the battery 10, and from this state, the charge state, the discharge state, and the rest state And the determination result is output to the control unit 29.
The voltage detection unit 23 is connected to the positive and negative terminals of each battery cell 11, and is configured to measure both terminal voltages of each battery cell 11 and output the voltage value to the control unit 29.

  The internal resistance detection unit 25 is also connected to both positive and negative terminals of each battery cell 11, and is configured to measure the internal resistance of each battery cell 11 and output the internal resistance value to the control unit 29. The internal resistance detection unit 25 energizes each battery cell 11 with a current generated inside, detects a voltage value and a current value at that time, and calculates an internal resistance value of each battery cell 11 from the detected values. Is configured to do.

  The internal resistance detection unit 25 is not limited to the above configuration. For example, the internal resistance detection unit 25 receives an input / output current value (charge / discharge current value) Im of the battery 10 from the current sensor 30 provided in the battery system including the battery pack 1, and each battery is supplied from the voltage detection unit 23. You may comprise so that the voltage value of the cell 11 may be received and the internal resistance value of each battery cell 11 may be calculated from these time changes.

  The control unit 29 is constituted by a microcomputer including a CPU, a ROM storing a control program, and a RAM used as a work area. As will be described below, the control unit 29 controls the discharge circuit 21 based on the voltage detection unit 23, the internal resistance detection unit 25, the charge / discharge determination unit 27, and signals from the outside, and charges / recharges each battery cell 11. It is configured to perform discharge control. The external signal includes a charge / discharge current value Im from the current sensor 30 that measures the input / output current of the battery 10, an ignition signal IG from the ignition switch, and the like.

Next, the voltage change of the battery cell 11 at the time of charge is demonstrated based on FIG.
In FIG. 3, it is assumed that a stepped charging current I _C flows through the battery cell 11 from time t _S to time t _E. When the time t _S charging current I _C begins to flow, the battery cell 11, a voltage rise RI _C due to the internal resistance R, and the SOC rise ΔSOC by the charging current, rise Vp and is before charging by polarization voltage It is added to the open circuit voltage OCV _S. That is, the open circuit voltage OCV of the battery cell 11 is expressed as OCV = OCV _S + RI _C + ΔSOC + Vp. And SOC rise ΔSOC by the charging current, the polarization voltage rise Vp is gradually increased as time elapses, the voltage rise RI _C is due to the internal resistance R, it can be considered as not time varying. The SOC increase ΔSOC can be estimated by I _C · (t _E −t _S ).

When the charging current I _C disappears at time t _E , the voltage increase R _C due to the internal resistance R disappears, and the polarization voltage increase V p also decreases with the passage of time from time t _E. As a result, the voltage increase due to RI _C and Vp disappears, and the open circuit voltage OCV of the battery cell 11 decreases to OCV = OCV _S + ΔSOC. Thus, the open circuit voltage OCV of the battery cell 11 by the charging current I _C rises from OCV _S in OCV _S + [Delta] SOC (charged).

However, the open circuit voltage OCV of the battery cell 11 being charged rises to OCV = OCV _S + RI _C + ΔSOC + Vp. Therefore, it is necessary to perform charging control so that the maximum voltage during charging does not reach the maximum voltage Vmax or the upper limit voltage HCV when the battery cell 11 is energized (operated). Here, the energized maximum voltage Vmax is a use limit value set in consideration of cell deterioration, and if it exceeds this, overcharge occurs and cell deterioration is promoted. HCV is an upper limit voltage value that can be used in the battery cell 11.

Next, an outline of conventional charge / discharge control will be described with reference to FIG.
In FIG. 4, for easy understanding, it is assumed that the battery 10 includes _three battery cells 11 (battery cell 11 ₁ , battery cell 11 ₂ , battery cell 11 ₃ ). Also, the internal resistances of the battery cells 11 ₁ , battery cells 11 ₂ , and battery cells 11 ₃ are R ₁ , R ₂ , and R ₃ (R ₁ <R ₂ <R ₃ ), respectively, and each cell is set to the maximum limited charging current ( It is assumed that charging is performed for a time t at the standard maximum charging current (Imax). Here, the maximum limited charging current Imax is an upper limit current value set as the charging current of the battery 10, and the charging current value does not exceed the maximum limited charging current Imax on the charging device (generator) side for device protection. Limited to

In FIG. 4, the battery cells 11 ₁ , 11 ₂ , and 11 ₃ are discharged after the open circuit voltages OCV ₁ , OCV ₂ , and OCV ₃ are adjusted to the same balancing target voltage Vbal by the discharge circuit 21 (OCV ₁ = OCV ₂ = OCV). ₃ ) Charged. The balancing target voltage corresponds to the charging start voltage.
Here, as shown in FIG. 4, when the charge in the voltage of the battery cell 11 ₂ has reached the energization time of the maximum voltage Vmax, the control is performed so as to end the charging, the charging immediately before the end, the battery cell 11 ₁ Is Vbal + R ₁ · Imax + ΔSOC + Vp (<Vmax), the voltage of the battery cell 11 ₂ is Vbal + R ₂ · Imax + ΔSOC + Vp (= Vmax), and the voltage of the battery cell 11 ₃ is Vbal + R ₃ · Imax + ΔSOC + Vp (> Vmax). In this case, in the battery cells 11 ₁ , 11 ₂ , and 11 ₃ , ΔSOC (= Imax · t) and Vp are substantially the same value.

Therefore, the voltage of the battery cell 11 ₁ does not reach Vmax and charging can be continued. On the other hand, the voltage of the battery cell 11 ₃ exceeds Vmax and is overcharged, which may promote deterioration.
To avoid overcharging of such a battery cell 11 _3, when the charging of the voltage of the battery cell 11 ₃ reaches the energization time of the maximum voltage Vmax, the control is performed so as to end the charging, the battery cell 11 ₁ and the battery cell 11 ₂ cannot be sufficiently charged.

As described above, when the balancing target voltage Vbal of the battery cell 11 ₁ , the battery cell 11 ₂ , and the battery cell 11 ₃ is set to the same value, due to the nonuniformity of the internal resistance value between the cells, the cells that are overcharged or sufficiently There is a problem that a cell that cannot be charged is generated, deterioration of the battery is promoted, and battery capacity cannot be fully utilized as a whole.

Next, the outline of the charge / discharge control of this embodiment will be described with reference to FIG.
As in the example of FIG. 4, the battery cells 11 ₁ , battery cells 11 ₂ , and battery cells 11 ₃ having internal resistance values R ₁ , R ₂ , and R ₃ (R ₁ <R ₂ <R ₃ ) are connected to the maximum limited charging current. It shall be charged with Imax. Further, as described above, ΔSOC and Vp are approximately equal among the voltage rises due to the charging of the battery cells 11 ₁ , battery cells 11 ₂ , and battery cells 11 ₃ . On the other hand, among the voltage rises due to charging, R ₁ · Imax, R ₂ · Imax, R ₃ · Imax differ depending on the internal resistance value.

Therefore, if the balancing target voltages of the battery cells 11 ₁ , 11 ₂ , 11 ₃ are Vbal ₁ , Vbal ₂ , Vbal ₃ , respectively, the voltages of the cells 11 ₁ , 11 ₂ , 11 ₃ are Vbal ₁ + R ₁ · Imax, Vbal ₂ + R ₂ · Imax, and Vbal ₃ + R ₃ · Imax, respectively, and ΔSOC and Vp are added over time.

In the present embodiment, when the charging current flows, the voltages in the cells 11 ₁ , 11 ₂ , 11 ₃ become substantially equal, and the battery cells 11 ₁ , 11 ₂ , 11 ₃ are being charged immediately before the end of charging. Control is performed so that the voltage simultaneously reaches the maximum voltage Vmax when energized. That is, the larger the internal resistance value, the lower the balancing target voltage Vbal is set so that the voltages at the start of energization are equal. Therefore, a voltage difference represented by Vbal ₁ −Vbal ₂ = (R ₂ −R ₁ ) · Imax and Vbal ₁ −Vbal ₃ = (R ₃ −R ₁ ) · Imax is provided for each balancing target voltage.

By performing charge / discharge control in this way, it is possible to charge each battery cell 11 ₁ , 11 ₂ , 11 ₃ to the maximum voltage value Vmax that can be charged without overcharging. As a result, it is possible to suppress the deterioration of the battery cell 11 and to maximize the battery performance.

Next, the balancing target voltage setting process of this embodiment will be described.
First, with reference to FIGS. 6 and 7, a case where rapid acceleration / deceleration is frequently performed by vehicle operation (rapid charging control) will be described. Also in this example, for the sake of easy understanding, it is assumed that the battery 10 includes battery cells 11 ₁ , 11 ₂ , and 11 ₃ as in FIGS. 4 and 5.

  FIG. 6 shows the time change of the current value Im received from the current sensor 30 by the control unit 29. In this example, the current value Im reaches the maximum limited charging current Imax n times from the current time point to a predetermined time before (in this example, 10 hours before), and at that time, the maximum limited charging current Imax is , Each continues for time t1, t2,... Tn.

The control unit 29 is configured to store the number of times that the current value Im has reached the maximum limited charging current Imax and each duration in a memory during a predetermined period (for example, during the past 10 hours of operation time). . Then, the control unit 29 calculates the average value t _AVE of the duration time by dividing the sum of the duration times by the number of times the current value has reached the maximum limited charging current Imax during the operation time of the predetermined time.

In addition, the control unit 29 sets the charging current to the maximum limited charging current Imax and estimates the voltage increase due to the internal resistance. In this case, the voltage increases due to the internal resistance of the battery cells 11 ₁ , 11 ₂ , 11 ₃ are R ₁ · Imax, R ₂ · Imax, R ₃ · Imax, respectively (R ₁ <R ₂ <R ₃ ).
Further, the control unit 29 sets the charging time to the average duration t _AVE, and sets the SOC increase ΔSOC (= Imax · t _AVE ) due to charging and the offset amount (polarization voltage increase Vp) at this time. These values can be set to the same value in each battery cell 11. Note that the offset may be calculated as a function of the charging current and the charging time, or may be a predetermined constant value for easy calculation.

Then, the control unit 29 balances the voltage values obtained by subtracting the voltage increase due to the internal resistance, the SOC increase ΔSOC, and the offset from the maximum voltage Vmax during energization for each of the battery cells 11 ₁ , 11 ₂ , 11 ₃ . target voltage value Vbal _1, set to _{Vbal 2, Vbal 3 (Vbal 1} > Vbal 2> Vbal 3).

Moreover, the control part 29 has memorize | stored in the memory the map data showing the relationship between the electrical storage amount SOC of the battery cell 11, and the open circuit voltage value OCV as shown in FIG. The controller 29 calculates a discharge amount D _SOCn corresponding to the difference Dv _n between the open circuit voltage value OCV _n and the balancing target voltage value Vbal _{n of} each battery cell 11 from this map data (n = 1, 2, 3). This discharge amount D _SOCn is the target discharge amount for each battery cell 11. That is, the electricity storage amount SOC _n that the open circuit voltage value OCV _n of each battery cell 11 is equivalent to, the target discharge amount D _SOCn difference between the charged amount SOCbal _n is to be discharged corresponding the balancing target voltage value Vbal _n. Therefore, when the discharge amount D _{SOCn is} discharged, the open circuit voltage value OCV _n of the battery cell 11 reaches the balancing target voltage value Vbal _n in the calculation.

Further, the control unit 29 sets the target in each battery cell 11 based on the target discharge amount D _SOCn of each battery cell 11, the open circuit voltage value OCV _{n of} each battery cell 11, and the resistance value of the resistor 22 a of the discharge circuit 21. Calculate the discharge time. Then, the control unit 29 operates the switch 22b of the discharge circuit 21 corresponding to each battery cell 11 to be closed for the calculated target discharge time, and discharges each battery cell 11 by the target discharge amount. When the target discharge amount is discharged, the control unit 29 performs a process of returning the switch 22b of the discharge circuit 21 to the open state. Thus, the open circuit voltage OCV _n of all the battery cells 11 reaches the balancing target voltage value Vbal _n.

After the balance control, each battery cell 11 is charged to the maximum capacity at the same time without being overcharged when a charging current having a magnitude of the maximum limited charging current Imax continues to flow to the battery 10. Specifically, the control unit 29 monitors the voltage of the battery cell 11 having the highest balancing target voltage Vbal (in the case of FIG. 7, the battery cell 11 ₁ ), and when this voltage value reaches the maximum voltage Vmax during energization, A signal for terminating the charging is output to the charging device side to terminate the charging. Thereby, if the charging current is continuously the magnitude of the maximum limited charging current Imax, all the cells can be made to reach the maximum voltage Vmax during energization simultaneously during charging.

Next, with reference to FIG. 9 and FIG. 10, a case will be described in which rapid acceleration / deceleration is not frequently performed by a vehicle operation and quick charging is difficult to be performed as in the examples of FIG. 6 and FIG. 7 (non-rapid charging control). .
FIG. 9 shows the time change of the current value Im received from the current sensor 30 by the control unit 29, as in FIG. In this example, the current value Im does not reach the maximum limited charging current Imax between a current time and a predetermined time before (10 hours in this example), and the maximum current value detected by the control unit 29 during this time is It is assumed that the maximum charging current imax. The control unit 29 is configured to store the maximum charging current imax in a memory.

When the current value Im does not reach the maximum limited charging current Imax during the operation time from the current time point to a predetermined time before the current time point, the control unit 29 sets the charging current to the maximum charging current imax, Estimate voltage increase due to resistance. In this case, the voltage increase due to the internal resistance of the battery cells 11 ₁ , 11 ₂ , 11 ₃ is R ₁ · imax, R ₂ · imax, R ₃ · imax, respectively (R ₁ <R ₂ <R ₃ ).

Further, the control unit 29 sets the SOC increase ΔSOC due to charging and the offset (polarization voltage increase Vp) at this time. In this embodiment, ΔSOC is set to a fixed value.
Then, the control unit 29 balances the voltage values obtained by subtracting the voltage increase due to the internal resistance, the SOC increase ΔSOC, and the offset from the maximum voltage Vmax during energization for each of the battery cells 11 ₁ , 11 ₂ , 11 ₃ . The target voltage values Vbal ₁ ′, Vbal ₂ ′, and Vbal ₃ ′ are set.

Here, in the case of FIGS. 6 and 7 (rapid charging control), the charging current is set to the maximum charging current Imax, so that the voltage increase due to the internal voltage is Rn · Imax (n = 1, 2, 3). However, in the case of FIG. 9 and FIG. 10 (non-rapid charge control), the charging current is set to the maximum charging current imax, so that the voltage increase due to the internal voltage is Rn · imax (n = 1, 2). , 3). That is, in the case of FIGS. 9 and 10, the voltage increase due to the internal resistance is estimated to be smaller by Rn · (Imax−imax). Thereby, the magnitude of the balancing target voltage Vbal _n ′ of each cell can be set to be larger than Vbal _n by Rn · (Imax−imax). That is, Vbal _n ′ = Vbal _n + Rn · (Imax−imax).

  Thus, even if the balancing target voltage Vbal is set to be large, there is very little possibility that the charging current will increase to the maximum charging current Imax from the past operation history, so that a large charging current flows during charging and the voltage of each cell Does not exceed the maximum voltage Vmax during energization, and the amount of discharge of each cell in the balancing control can be reduced, so that battery efficiency can be improved.

Next, the process flow of the charge / discharge control apparatus 20 of this embodiment is demonstrated based on FIG.
First, the control unit 29 determines whether or not a condition for starting the discharge control is satisfied (step S1). This condition is to detect a state in which no charging / discharging current flows in each battery cell 11, and the control unit 29 is charged / discharged from the current sensor 30 when the ignition signal IG is received by, for example, ignition on. It is determined that the condition is satisfied, for example, when the current value is zero, or when the charge / discharge determination unit 27 detects that it is in a resting state.

When the condition is not satisfied (step S1; No), the control unit 29 ends the process and performs the process of step S1 again after a predetermined time.
On the other hand, when the condition is satisfied (step S1; Yes), the control unit 29 acquires the open circuit voltage OCV of each battery cell 11 from the voltage detection unit 23 in a state where the charge / discharge current is not flowing, and stores it in the memory. Store (step S2).

  Next, it is determined whether any one of the open circuit voltages OCV of the battery cells 11 stored in the memory exceeds the predetermined open circuit voltage by a predetermined voltage value (step S3). That is, the control unit 29 calculates the average value of the open-circuit voltage OCV of each battery cell 11 stored in the memory for the presence or absence of the open-circuit voltage OCV of each cell, and the open circuit is larger than this average value by a predetermined voltage. Judgment is made by whether or not there is a battery cell 11 having the voltage OCV.

If there is no cell having an open circuit voltage OCV that exceeds the predetermined voltage value above the average open circuit voltage (step S3; No), the control unit 29 ends the process.
On the other hand, when there is a cell having an open circuit voltage OCV exceeding the predetermined open circuit voltage value than the average open circuit voltage (step S3; Yes), the control unit 29 determines the internal resistance value of each battery cell 11 from the internal resistance detection unit 25. Obtain (step S4).

Furthermore, the control unit 29 takes in history information of current values during operation for the past predetermined time (for example, 10 hours) (step S5). That is, the control unit 29 reads the maximum value imax of the current value within a predetermined period, and when the maximum current value is the maximum limited charging current Imax, the average duration t _AVE during which the maximum limited charging current Imax flows after reaching the maximum current value. Is read from memory.

And the control part 29 calculates the balancing target voltage Vbal of each battery cell 11 from the acquired internal resistance value of each battery cell 11, and the historical information of an electric current value (step S6).
Further, the control unit 29 determines the target discharge amount D _SOC of each battery cell 11 based on the map data shown in FIG. 8 from the open circuit voltage OCV and the balancing target voltage Vbal of each battery cell 11 (step S7). . Further, the control unit 29 calculates a target discharge time based on the open circuit voltage OCV of each battery cell 11, the balancing resistance value of the resistor 22a of the discharge circuit 21, the target discharge amount D _{SOC, and the} like (step S8).

Next, the controller 29 determines whether or not the battery 10 is not charged / discharged (step S9). In this process, for example, the control unit 29 determines whether the ignition is off and the charge / discharge determination unit 27 determines whether the engine is in a pause state based on an output or the like.
When the battery 10 is not in a state where it is not charged / discharged (step S9; No), the control unit 29 repeats the process of step S9. On the other hand, when the battery 10 is not charged / discharged (step S9; Yes), the control unit 29 starts balancing control (step S10).

  In this balancing control, the control unit 29 outputs a control signal to the discharge circuit 21 corresponding to each battery cell 11, operates the switch 22b, and closes it to measure the target discharge time. Thereby, each battery cell 11 is discharged, and electric power is consumed by the resistor 22a.

The control unit 29 determines whether there is a battery cell 11 whose discharge time has reached the target discharge time (step S11).
When there is no battery cell 11 whose discharge time has reached the target discharge time (step S11; No), the control unit 29 repeats step S11. On the other hand, when there is a battery cell 11 whose discharge time has reached the target discharge time (step S11; Yes), the control unit 29 ends the balancing control of the battery cell 11 whose discharge time has reached the target discharge time, and is still discharged. Balancing control of the battery cells 11 whose time has not reached the target discharge time is continued (step S12). In step S12, the control unit 29 controls the switch 22b of the corresponding discharge circuit 21 to the open state.

And the control part 29 determines whether balancing control was complete | finished in all the battery cells 11 (step S13).
When the balancing control is not finished in all the battery cells 11 (step S13; No), the control unit 29 repeats the process of step S11 again. On the other hand, when the balancing control is finished in all the battery cells 11 (step S13; Yes), the control unit 29 finishes the process.

  Thus, in the present embodiment, the charging start voltage (balancing target voltage Vbal) is set lower for the battery cell 11 having a higher internal resistance in accordance with the magnitude of the internal resistance of each battery cell 11. This prevents the voltage of some of the battery cells 11 from exceeding the voltage limit value (maximum voltage Vmax during energization) due to the voltage increase caused by the internal resistance when the charging current flows. And cell deterioration can be suppressed.

  Moreover, in this embodiment, since the battery cell 11 with smaller internal resistance can set the charge start voltage higher, the discharge amount due to balancing discharge using the discharge circuit 21 can be suppressed, and the battery efficiency is improved. It becomes possible.

It is explanatory drawing of the charging / discharging control apparatus of the battery by embodiment of this invention. It is explanatory drawing of the discharge circuit of the charging / discharging control apparatus of the battery of FIG. It is explanatory drawing of the cell voltage change at the time of charge by embodiment of this invention. It is explanatory drawing of the balancing control which concerns on a prior art example. It is explanatory drawing of balancing control by embodiment of this invention. It is a figure which shows the time change of the charging current including the time of the quick charge by embodiment of this invention. It is explanatory drawing of the balancing control by the quick charge control by embodiment of this invention. It is explanatory drawing of the map data which shows the relationship between the cell open circuit voltage and SOC by embodiment of this invention. It is a figure which shows the time change of the charging current which does not include the time of the quick charge by embodiment of this invention. It is explanatory drawing of the balancing control by the non-rapid charge control by embodiment of this invention. It is a flowchart of the charging / discharging control process by embodiment of this invention.

Explanation of symbols

1 battery pack 10 battery 11, 11 _1, 11 _2, 11 ₃ cell 20 charging and discharging control unit 21 discharge circuit 22a resistor 22b switch 23 voltage detector 25 detecting the internal resistance section (internal resistance detecting means)
27 Charge / Discharge Discrimination Unit 29 Control Unit (Discharge Unit)
30 Current sensor

Claims (8)

A charge / discharge control method for a battery in which a plurality of battery cells are connected,
A voltage setting step for setting the charging start voltage of each battery cell;
Using a discharge circuit connected to each battery cell, and discharging each battery cell until it reaches a set charge start voltage,
In the voltage setting step, the charging / discharging control method for a battery is characterized in that the charging start voltage is set lower for a battery cell having a larger internal resistance.   In the voltage setting step, the charging start voltage of each battery cell is set to a value such that the voltage of each battery cell becomes substantially equal when the battery is charged with the maximum limited charging current that can be energized that is set for the battery. The battery charge / discharge control method according to claim 1, wherein the battery charge / discharge control method is set.   In the voltage setting step, the charging start voltage of each battery cell is set higher as the maximum value of the charging current value during the predetermined period is smaller according to the history of the charging current value of the battery during the predetermined period. The charge / discharge control method for a battery according to claim 1.   The discharge process is performed when there is a battery cell having a voltage that exceeds a predetermined voltage and is larger than an average voltage value of the voltage of each battery cell, according to any one of claims 1 to 3. The charging / discharging control method of the battery as described. A battery charge / discharge control device comprising a plurality of battery cells connected,
A discharge circuit connected to each battery cell;
Internal resistance detection means for detecting the internal resistance of each battery cell;
Discharging means for discharging each battery cell to a charging start voltage by the discharge circuit,
The battery charging / discharging control device according to claim 1, wherein the discharging unit sets a lower charging start voltage for a battery cell having a larger internal resistance.   The discharging means sets the charging start voltage of each battery cell to such a value that the voltage of each battery cell becomes substantially equal when the battery is charged with the maximum limited charging current that can be energized that is set for the battery. The charge / discharge control device for a battery according to claim 5. Current value detection means for detecting a current value energized to the battery;
Current value history acquisition means for acquiring a history of a current value energized to the battery in a predetermined period;
The discharging means sets the charging start voltage of each battery cell to be higher as the maximum value of the charging current value during the predetermined period is smaller according to the history of the charging current value of the battery during the predetermined period. The battery charge / discharge control device according to claim 5.   The discharge means discharges each battery cell by the discharge circuit when there is a battery cell having a voltage that exceeds a predetermined voltage and is larger than an average voltage value of the voltage of each battery cell. The charging / discharging control apparatus of the battery of any one of thru | or 7.

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