JP2021027726A - Residual capacity adjustment device of battery pack - Google Patents

Abstract

To provide a residual capacity adjustment device of a battery pack, which adjusts a capacity of the battery pack, while suppressing variations of a capacity deterioration level.SOLUTION: A residual capacity adjustment device 106 of a battery pack, which adjusts a residual capacity of each unit battery in a battery pack 105 in which a plurality of unit batteries as a secondary battery is serially connected, comprises: a target cross point SOC setting part that sets a target cross point SOC as a target value of the SOC in a cross point where each unit battery becomes equalization in a charge and discharge step of the battery pack; a discharge capacity setting part that sets a discharge capacity for discharging a large deterioration unit battery so that the SOC in the cross point becomes the target cross point SOC in regard to a large deterioration unit battery of which a deterioration level of a battery capacity is relatively large and a small deterioration unit battery of which the deterioration level is relatively small; and a discharge part that discharges the large deterioration unit battery in accordance with the discharge capacity set by the discharge capacity setting part.SELECTED DRAWING: Figure 1

Description

The present invention relates to a residual capacity adjusting device for an assembled battery mounted on a hybrid electric vehicle (HEV) or the like.

Conventionally, in order to expand the usable range of the assembled battery, the capacity deterioration degree is relatively large so that the voltage or SOC after adjusting the remaining capacity of the single battery having a relatively large capacity deterioration degree is increased by a predetermined amount. A device for adjusting the remaining capacity of an assembled battery that limits the discharge processing of a cell is known (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2011-061955

However, when the voltage or SOC after adjusting the remaining capacity of a cell having a relatively large degree of capacity deterioration is adjusted to increase by a predetermined amount as described above, the usable range of the assembled battery when discharging after that is limited. Although it is expanded, in that case, the cell cell having a large degree of capacity deterioration is used in a state where the SOC is relatively large. For this reason, a cell having a large degree of capacity deterioration is more likely to be deteriorated than a cell having a small degree of capacity deterioration, and the variation in the degree of deterioration is larger.

The present invention has been made in view of the above points, and an object of the present invention is to make it possible to adjust the capacity of an assembled battery while suppressing variations in the degree of capacity deterioration.

To achieve the above objectives
The present invention
It is a residual capacity adjusting device for an assembled battery that adjusts the remaining capacity of each of the above-mentioned unit batteries in an assembled battery in which a plurality of unit batteries that are secondary batteries are connected in series.
In the charging / discharging process of the assembled battery, the target crosspoint SOC setting unit that sets the target crosspoint SOC, which is the target value of the SOC at the crosspoint where the SOCs of the above unit batteries become equal,
For a large deterioration unit battery in which the degree of deterioration of the battery capacity is relatively large and a small deterioration unit battery in which the battery capacity is relatively small, the large deterioration unit battery is discharged so that the SOC at the cross point becomes the target cross point SOC. Discharge capacity setting unit that sets the discharge capacity for
A discharge unit that discharges the large deterioration unit battery according to the discharge capacity set by the discharge capacity setting unit, and a discharge unit that discharges the large deterioration unit battery.
With
The target cross-point SOC setting unit is characterized in that the target cross-point SOC is set according to the upper limit of the SOC in the usage range based on the usage history of the assembled battery.

As a result, the target cross-point SOC is set according to the upper limit of the SOC of the usage range based on the usage history of the assembled battery, and the discharge of the unit battery having a large degree of deterioration is adjusted, so that the unit battery having a large degree of deterioration is adjusted. However, it is used in a state where the SOC is small, that is, in a state where the degree of deterioration is slow, and the progress of the degree of deterioration can be slowed down to reduce the variation in the degree of deterioration of each unit battery.

In the present invention, the capacity of the assembled battery can be adjusted while suppressing the variation in the degree of capacity deterioration.

It is a block diagram which shows the drive system of an automobile to which the residual capacity adjusting device of an assembled battery is applied. It is a circuit diagram which shows the example of the discharge circuit of a unit cell. It is a graph which shows the relationship between the remaining capacity of a unit cell and a cross point. It is a graph which shows the progress example of the deterioration of a unit cell. It is a graph which shows the magnitude relationship between the residual capacity adjustment of a unit cell and SOC. It is a flowchart which shows the example of the remaining capacity adjustment operation.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Schematic configuration of automobile drive system)
The assembled battery 105 to be adjusted for the remaining capacity of the present embodiment is mounted on an automobile such as a hybrid electric vehicle (HEV) or an electric vehicle (EV). For example, as shown in FIG. 1, the drive system of the automobile. Incorporated as part of the system. More specifically, the automobile is provided with a motor 102 for driving the load 101, so that the DC power supplied from the assembled battery 105 is converted into three-phase AC power by the inverter 103 and supplied to the motor 102. It has become. The electric power supplied to the motor 102 is controlled based on the required torque output from the vehicle controller 104.

(Structure of assembled battery 105)
The assembled battery 105 is configured by connecting a plurality of unit cells 105a (a plurality of unit batteries which are secondary batteries) using, for example, a lithium ion battery or a nickel hydrogen battery, in series. It should be noted that each unit cell 105a may be configured by connecting a plurality of battery cells having a smaller unit in series and / or in parallel. The assembled battery 105 is provided with a current sensor 111, a temperature sensor 112, and a voltage sensor 113. By these, the voltage of the entire assembled battery 105 and each unit cell 105a, and the input / output current (charge / discharge current) to these are detected, and the battery controller 106 (residual capacity adjusting device, target crosspoint SOC setting unit, discharge capacity setting unit). ), The remaining capacity of the assembled battery 105 and each unit cell 105a, the degree of deterioration, and the like are required. Further, the temperature of the assembled battery 105 and the unit cell 105a is detected, and the temperature sensitivity of the battery performance is corrected and abnormal heat generation is monitored. In the battery controller 106, for example, the input / output possible power of the assembled battery 105 is calculated and given to the vehicle controller 104 to be used for vehicle traveling control and the like.

As shown in FIG. 2, for example, a discharge switch 105b (discharge unit) and a discharge resistor 105c connected in series are connected to each unit cell 105a of the assembled battery 105. The discharge switch 105b is turned on and off by the battery controller 106, and can be discharged for each unit cell 105a as described later.

(About the degree of deterioration of the unit cell 105a and the change in SOC)
The SOC of each unit cell 105a is represented by the remaining capacity / fully charged capacity, and increases or decreases according to the change in the remaining capacity due to charging / discharging, for example, as shown in FIG. Further, when the full charge capacity decreases due to the deterioration of the unit cell 105a, the amount of change in SOC becomes large when the same charge / discharge current flows for the same time.

Therefore, for example, a large deterioration unit cell with a relatively large degree of deterioration (S_cell with a relatively small full charge capacity) and a small deterioration unit cell with a relatively small degree of deterioration (L_cell with a relatively large full power receiving capacity). ) And the same SOC (Crosspoint SOC) at a certain point in time as the charging / discharging progresses, the magnitude relation of the SOCs of the two unit cells is reversed before and after that point. Further, as shown in FIGS. 3A and 3B, the size of the crosspoint SOC itself is determined according to the degree of deterioration of each unit cell 105a and the remaining capacity at a certain point in time.

On the other hand, the degree of deterioration of the unit cell 105a may vary from unit cell to unit cell 105a. In such a case, for example, as shown in FIG. 4, the life of the entire assembled battery 105 is until the full charge capacity of S_cell reaches a predetermined lower limit. Here, the degree of progress of the deterioration can change depending on various factors, but also changes depending on the magnitude of the SOC when charging / discharging is performed. That is, when charging / discharging is performed with a large SOC, deterioration is more likely to proceed than when charging / discharging is performed with a small SOC. Therefore, for example, by increasing the SOC of S_cell and L_cell when charging and discharging are performed, the degree of deterioration of S_cell is suppressed to a small level and the degree of deterioration of L_cell is slightly increased, as shown by the broken line in FIG. Can be done. In this case, the life of the entire assembled battery 105 can be extended by increasing the time until the full charge capacity of S_cell reaches a predetermined lower limit.

(About setting the target crosspoint SOC)
As described above, the degree of deterioration of S_cell is more likely to be suppressed as the SOC of S_cell at the time of charging / discharging is smaller than that of L_cell. However, for example, when charging / discharging is performed in a state where a cross point does not occur in the charging / discharging process and the SOC of L_cell is always large, the assembled battery 105 reaches the charging limit when L_cell reaches the charging upper limit during charging. At the time of discharge, when S_cell reaches the lower limit of discharge, the assembled battery 105 reaches the discharge limit, which causes a decrease in the usable capacity of the assembled battery 105.

Therefore, by setting the cross point SOC to the SOC of the upper limit of charging, that is, by setting the target cross point SOC to the upper limit of charging, the usable capacity of the assembled battery 105 is kept large, and the degree of deterioration of S_cell is suppressed to a small level. Therefore, it is possible to maintain a large usable capacity until the assembled battery 105 reaches the end of its life.

Here, the upper limit of charging may be set when each unit cell 105a is fully charged, that is, when the SOC reaches 100%, but when the assembled battery 105 is applied to an automobile or the like, the SOC is usually set. It is not always fully used in the range of 0 to 100% or in the range where a predetermined margin is expected, and the SOC is used only in the range of 20 to 80% depending on the usage pattern of the user, for example. There are many things to do. Therefore, if the target cross-point SOC is set at the upper limit of the SOC of the usage range (for example, the SOC is 80%) based on the usage history of the assembled battery 105, the usable capacity of the assembled battery 105 is increased and actually used. In the range where the SOC is 80% or less, the SOC of S_cell is always kept smaller than the SOC of L_cell, so that the degree of deterioration of S_cell can be easily suppressed to a small level.

(Specific setting example of target crosspoint SOC and adjusted discharge current capacity)
For example, as shown in FIG. 5, at a certain time t1, the SOCs of L_cell and S_cell are 50% and 48%, respectively, and the SOC of the usage range based on the usage history of the assembled battery 105 is 20 to 80%. To do. Further, it is assumed that the full charge capacities of L_cell and S_cell are 12Ah and 10Ah, respectively.

After that, if the charging of the assembled battery 105 progresses and 1.2Ah is charged by the time t2, the SOC of L_cell increases by 1.2Ah / 12Ah = 10%, and 50% + 10% = 60%. It becomes. Further, the SOC of S_cell increases by 1.2Ah / 10Ah = 12% to 48% + 12% = 60%. That is, the cross point SOC before discharge adjustment is 60%.

Further, if charging progresses further and the SOC of L_cell reaches 80% at time t3, it will increase by 20% from the above cross point SOC (60%), so in the meantime, 12Ah × 20%. = 2.4Ah will be charged. On the other hand, when S_cell is charged by the same amount, its SOC increases by 2.4Ah / 10Ah = 24% to 84%.

Therefore, if the SOC of S_cell is lowered by 4%, the target crosspoint SOC can be reduced to 80%. For that purpose, it is preferable to discharge S_cell by 10 Ah × 4% = 0.4 Ah.

In the above description, for convenience, the SOC of the current crosspoint is once obtained, but in reality, the SOC of the current crosspoint is not obtained, and for example, if the SOCs of S_cell and L_cell at a certain point in time are known. , The adjusted discharge current capacity may be obtained directly. Further, the graph of FIG. 5 shows an example in which the S_cell is charged until the target crosspoint SOC is reached after the adjustment discharge of S_cell as an example for explaining the calculation example. Even if charging and discharging are performed in such a pattern, when the crosspoint SOC is reached, the SOC will be 80% of the target crosspoint SOC.

(Example of adjustment operation)
Hereinafter, a specific example of the adjustment operation will be described with reference to FIG.

(S101) First, the open circuit voltage for each unit cell 105a before and after the elapse of a predetermined time is acquired.

(S102) Next, using the open circuit voltage-SOC map obtained in advance, the SOC for each unit cell 105a before and after the elapse of a predetermined time is obtained.

(S103) From the difference in SOC (ΔSOC) before and after the lapse of the predetermined time and the integrated value of the charge / discharge current flowing through the assembled battery 105 during that period, the full charge capacity for each unit cell 105a can be obtained. That is, a value corresponding to the degree of deterioration of each unit cell 105a is obtained.

(S104) A minimum fully charged capacity cell, a maximum fully charged capacity cell, that is, a large deterioration unit battery (S_cell) in which the degree of deterioration of the battery capacity is relatively large, and a small small deterioration unit battery (L_cell) are required.

(S105) The degree of deterioration of the full charge capacity of the above S_cell and L_cell is required.

(S106) It is determined whether or not the difference in the degree of deterioration is equal to or greater than a predetermined difference in the degree of deterioration. That is, if the variation in the degree of deterioration is small, the effect of extending the life of the entire assembled battery 105 may not always be large. In such a case, the remaining capacity is not particularly adjusted (discharged). The adjustment operation may be terminated to prevent excessive and frequent discharge. On the other hand, when the variation in the degree of deterioration is large to some extent, the process proceeds to (S107) and the adjustment operation is continued. However, the difference in the degree of deterioration as described above is not limited to be determined, and control may be simplified so that discharge can always be performed.

(S107) The usage range of the SOC in the assembled battery 105 is obtained based on the information indicating the usage history of the assembled battery 105, which is recorded in advance. In addition, the maximum SOC of the usage range is set as the target crosspoint SOC.

(S108) For example, the calculation described above is performed, and the predicted SOC of S_cell when L_cell reaches the target crosspoint SOC can be obtained from the difference between the current SOC of L_cell and the target crosspoint SOC.

(S109) It is determined whether or not the predicted SOC of the above S_cell is larger than the target crosspoint SOC. That is, if the predicted SOC of S_cell is smaller than the target crosspoint SOC, the crosspoint SOC cannot be set to the target crosspoint SOC even if the discharge adjustment of S_cell is performed, so that the adjustment operation is terminated. On the other hand, when the predicted SOC of S_cell is larger than the target crosspoint SOC, the process proceeds to (S109) and the adjustment operation is continued. In order to make the same judgment, not limited to the above, for example, it is determined that the SOC at the cross point before discharging is smaller than the target cross point SOC, or whether the discharge current capacity is a positive value. You may decide whether or not. Further, for example, when the difference between the SOC at the cross point before the discharge and the target cross point SOC is equal to or larger than a predetermined SOC difference threshold value, that is, when the effect of suppressing deterioration variation is expected to be large to some extent. Discharge adjustment may be performed to prevent excessive and frequent discharge. Further, in such operations and determinations, various equivalent operations and determinations may be performed.

Further, when the predicted SOC is smaller than the target crosspoint SOC, L_cell may be discharged as necessary so that the usable capacity can be increased. That is, securing the usable capacity and suppressing deterioration of S_cell may be adjusted according to the usage status of the assembled battery 105 and the like.

(S110) The amount of discharge current for discharging S_cell is obtained so that the crosspoint SOC becomes the target crosspoint SOC.

(S111) The discharge of S_cell is adjusted according to the amount of the discharge current. Specifically, discharge is performed by closing the discharge switch 105b corresponding to S_cell for a time corresponding to the amount of discharge current.

As described above, the target cross-point SOC is set according to the upper limit of the SOC of the usage range based on the usage history of the assembled battery, and the discharge of the unit cell 105a having a large degree of deterioration is adjusted, so that the degree of deterioration is reduced. The large unit cell 105a is used in a state where the SOC is small, that is, the progress of the degree of deterioration is slow, and the progress of the degree of deterioration can be slowed down to reduce the variation in the degree of deterioration of each unit cell 105a. it can.

(Other matters)
In the above example, the description has been made focusing on S_cell, which has a relatively large degree of deterioration, and L_cell, which has a relatively small degree of deterioration. However, even when there are many unit cells 105a, the discharge adjustment as described above can be performed in relation to each of the two units. it can. On the other hand, for example, among all the unit cells 105a, the unit cell 105a having the smallest degree of deterioration is designated as L_cell as described above, and all the other unit cells 105a are designated as S_cell, and the discharge is adjusted so that many unit cells 105a It may be possible to prevent the deterioration of the product from progressing. On the contrary, even if the discharge is adjusted for one or a small number of unit cells 105a having a large degree of deterioration, the deterioration of the unit cell 105a having a large degree of deterioration is mainly suppressed. Good. In any case, if the deterioration of the unit cell 105a having a large degree of deterioration continues to be suppressed, it is expected that the unit cell 105a having a smaller degree of deterioration than the other unit cells 105a will eventually become the unit cell 105a. Therefore, the variation in the degree of deterioration can be reduced.

In the above example, how to obtain the open circuit voltage, SOC, and full charge capacity is an example, and various methods can be applied.

In addition, regarding the significance of the SOC upper limit of the usage history, even if the SOC exceeds the upper limit in the actual use after that, there is no big inconvenience as in the case of overcharging. The magnitude relationship between the SOCs of S_cell and L_cell may be reversed, and if the degree and frequency are small, the suppression of deterioration of S_cell is not hindered as a whole. Therefore, for example, depending on the degree of deterioration variation of the unit cell 105a and the degree to which suppression thereof is required, the SOC of the upper limit of the absolute usage history may be applied, or the SOC of the upper limit of the SOC equal to or higher than the predetermined frequency of appearance may be applied. May be applied, or may be set in consideration of a predetermined margin and a safety factor.

101 Load 102 Motor 103 Inverter 104 Vehicle controller 105 Group battery 105a Unit cell 105b Discharge switch 105c Discharge resistance 106 Battery controller 111 Current sensor 112 Temperature sensor 113 Voltage sensor

Claims (4)

It is a residual capacity adjusting device for an assembled battery that adjusts the remaining capacity of each of the above-mentioned unit batteries in an assembled battery in which a plurality of unit batteries that are secondary batteries are connected in series.
In the charging / discharging process of the assembled battery, the target crosspoint SOC setting unit that sets the target crosspoint SOC, which is the target value of the SOC at the crosspoint where the SOCs of the above unit batteries become equal,
For a large deterioration unit battery in which the degree of deterioration of the battery capacity is relatively large and a small deterioration unit battery in which the battery capacity is relatively small, the large deterioration unit battery is discharged so that the SOC at the cross point becomes the target cross point SOC. Discharge capacity setting unit that sets the discharge capacity for
A discharge unit that discharges the large deterioration unit battery according to the discharge capacity set by the discharge capacity setting unit, and a discharge unit that discharges the large deterioration unit battery.
With
The target cross-point SOC setting unit is configured to set the target cross-point SOC according to the upper limit of the SOC of the usage range based on the usage history of the assembled battery. Remaining capacity adjusting device. The remaining capacity adjusting device for the assembled battery according to claim 1.
The discharge unit of the assembled battery is characterized in that the small deterioration unit battery is discharged when the difference in the degree of deterioration between the large deterioration unit battery and the small deterioration unit battery is equal to or more than a predetermined deterioration degree difference threshold value. Remaining capacity adjusting device. The remaining capacity adjusting device for the assembled battery according to any one of claims 1 to 2.
The discharge unit is a residual capacity adjusting device for an assembled battery, characterized in that the small deterioration unit battery is discharged when the SOC at the cross point before the discharge is smaller than the target cross point SOC. The remaining capacity adjusting device for the assembled battery according to claim 3.
The discharge unit is a set characterized in that the small deterioration unit battery is discharged when the difference between the SOC at the cross point before the discharge and the target cross point SOC is equal to or larger than a predetermined SOC difference threshold value. Battery remaining capacity adjustment device.

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