JP6729033B2 - Battery system - Google Patents

Description

The present invention relates to a battery system, and more particularly to a battery system including a nickel hydrogen battery containing a hydrogen storage alloy as a negative electrode active material.

In recent years, electric vehicles, such as hybrid vehicles, equipped with a battery system have become popular. In these battery systems, the battery may deteriorate due to various factors. Therefore, a technique for determining the degree of deterioration according to the factors has been proposed. For example, Japanese Unexamined Patent Application Publication No. 2011-228213 (Patent Document 1) discloses a method for determining cracks of a positive electrode active material in an active material layer formed on a positive electrode plate of a lithium ion battery. According to Patent Document 1, whether or not a crack in the positive electrode active material has occurred is determined using a graph in which pair data of the square root of the integrated value of the discharge amount of the lithium ion battery and the battery capacity is plotted.

JP, 2011-228213, A

The present inventor has found that in a nickel-hydrogen battery containing a hydrogen storage alloy as a negative electrode active material, the aspect of the occurrence and progress of cracks in the negative electrode active material is different from that in the negative electrode active material of another secondary battery (for example, a lithium ion battery). Focusing on the difference from the aspect (details will be described later). Then, when charging and discharging of the nickel-hydrogen battery are continued without considering the degree of progress of deterioration due to cracks in the negative electrode active material, deterioration due to cracks further progresses and battery performance deteriorates (specifically, the reaction resistance of the negative electrode It was noted that there is a possibility that increase or decrease in negative electrode capacity) may occur.

The present invention has been made to solve the above problems, and an object thereof is a battery system including a nickel-hydrogen battery containing a hydrogen storage alloy as a negative electrode active material, in which battery performance due to cracks generated in the negative electrode active material It is to provide a technology capable of suppressing the decrease.

A battery system according to an aspect of the present invention supplies electric power to an external device. The battery system consists of a nickel-hydrogen battery that contains a hydrogen-absorbing alloy as the negative electrode active material, a power converter that converts electric power between the nickel-hydrogen battery and external equipment, and the charging power to the nickel-hydrogen battery is the upper limit for controlling the charging power. And a control device that controls the power conversion device so that the discharge power from the nickel-hydrogen battery becomes less than the control upper limit value of the discharge power. The controller calculates an index value related to the degree of progress of deterioration due to cracks generated in the negative electrode active material, from the current input to and output from the nickel hydrogen battery and the temperature of the nickel hydrogen battery. When the index value indicates that the degree of progress of deterioration is larger than the predetermined amount, the control device compares the control upper limit of charging power with the case where the index value indicates that the degree of progress of deterioration is smaller than the predetermined amount. Decrease the control value and control upper limit of discharge power.

The greater the charging power or the discharging power, the greater the bias of the concentration of hydrogen (H) generated in the negative electrode active material. Since the local hydrogen amount (proton amount) in the negative electrode active material is different, the local volume change amount is also different. As a result, strain is generated in the crystal lattice and stress is generated. This stress also increases as the charging power or discharging power increases. According to the above configuration, the stress acting on the negative electrode active material can be reduced by reducing the control upper limit value of the charging power and the control upper limit value of the discharging power according to the index value. Therefore, it is possible to suppress further progress of deterioration due to cracks and suppress deterioration of battery performance.

FIG. 1 is a block diagram schematically showing an overall configuration of a hybrid vehicle equipped with the battery system according to the present embodiment. It is a figure which shows the structure of each cell contained in a battery in detail. It is a figure for demonstrating the crack which arises in the negative electrode active material of a secondary battery. 3 is a time chart for explaining the time course of internal resistance and battery capacity of a nickel-hydrogen battery. It is a figure for explaining a calculation processing of a crack index value. It is a figure which shows an example of a time change of a crack index value. It is a figure for demonstrating the limitation of the input/output electric power of a battery. It is a flowchart which shows the charging/discharging control of the battery which concerns on this Embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals and the description thereof will not be repeated.

Hereinafter, a configuration in which the battery system according to the embodiment of the present invention is mounted on a hybrid vehicle will be described as an example. However, the use of the battery system is not limited to the vehicle use, and may be the stationary use.

[This Embodiment]
<Battery system configuration>
FIG. 1 is a block diagram schematically showing an overall configuration of a hybrid vehicle equipped with the secondary battery system according to the present embodiment. The vehicle 1 includes a secondary battery system 2, motor generators (MG) 10 and 20, a power split mechanism 30, an engine 40, and drive wheels 50. The secondary battery system 2 includes a battery 100, a system main relay (SMR) 150, a power control unit (PCU) 200, and an electronic control unit (ECU) 300. Prepare

Each of motor generators 10 and 20 is a three-phase AC rotating electric machine. The motor generator 10 is connected to the crankshaft of the engine 40 via the power split mechanism 30. When starting the engine 40, the motor generator 10 uses the power of the battery 100 to rotate the crankshaft of the engine 40. The motor generator 10 can also generate power using the power of the engine 40. The AC power generated by motor generator 10 is converted into DC power by PCU 200 and charged in battery 100. Further, the AC power generated by the motor generator 10 may be supplied to the motor generator 20.

Motor generator 20 rotates the drive shaft using at least one of the electric power from battery 100 and the electric power generated by motor generator 10. Further, the motor generator 20 can also generate power by regenerative braking. The AC power generated by motor generator 20 is converted into DC power by PCU 200 and charged in battery 100.

The power split mechanism 30 is, for example, a planetary gear mechanism, and mechanically connects the three elements of the crankshaft of the engine 40, the rotation shaft of the motor generator 10, and the drive shaft. The engine 40 is an internal combustion engine such as a gasoline engine, and generates a driving force for the vehicle 1 to travel in response to a control signal from the ECU 300.

PCU 200 converts electric power between battery 100 and motor generators 10 and 20. Although not shown in any of the drawings, an inverter and a converter are included. The inverter is a general three-phase inverter. During the boosting operation, the converter boosts the voltage supplied from the battery 100 and supplies it to the inverter. During the step-down operation, the converter steps down the voltage supplied from the inverter to charge the battery 100. SMR 150 is electrically connected to a current path connecting battery 100 and PCU 200. When SMR 150 is closed in response to a control signal from ECU 300, electric power can be exchanged between battery 100 and PCU 200. The motor generators 10 and 20 correspond to the "external device" according to the present invention, and the PCU 200 corresponds to the "power conversion device" according to the present invention.

Battery 100 includes a plurality of cells 101, each of which is a nickel hydrogen battery. The configuration of each cell 101 will be described with reference to FIG. The battery 100 is provided with a voltage sensor 110, a current sensor 120, and a temperature sensor 130. The voltage sensor 110 detects the voltage Vb of the battery 100. The current sensor 120 detects the current Ib input/output to/from the battery 100. The temperature sensor 130 detects the temperature Tb of the battery 100. Each sensor outputs the detection result to ECU 300. ECU 300 calculates the SOC (State Of Charge) of battery 100 based on the detection result of each sensor.

The ECU 300 includes a CPU (Central Processing Unit) 301, a memory 302, an input/output buffer (not shown), and the like. ECU 300 controls each device so that vehicle 1 is in a desired state based on a signal received from each sensor and a map and a program stored in memory 302. The main control executed by the ECU 300 is charge/discharge control of the battery 100. For example, for the purpose of protecting the battery 100, the ECU 300 determines that the charging power to the battery 100 does not exceed the charging power upper limit value (control upper limit value) Win, and the discharging power from the battery 100 is the discharging power upper limit value (control upper limit value). ) The charge/discharge of the battery 100 is controlled so as not to exceed Wout. This charge/discharge control will be described in detail later.

FIG. 2 is a diagram showing a configuration of the cell 101 included in the battery 100. Since the configuration of each cell 101 is common, only one cell 101 is representatively shown in FIG. The cell 101 is, for example, a prismatic closed cell, and includes a case 102, a safety valve 103 provided in the case 102, an electrode body 104 housed in the case 102, and an electrolytic solution (not shown). In addition, in FIG. 2, the electrode body 104 is shown by seeing through a part of the case 102.

The case 102 includes a case main body and a lid body, both of which are made of metal, and is hermetically sealed by welding the entire circumference of the lid body on the opening of the case book. When the pressure inside the case 102 exceeds a predetermined value, the safety valve 103 discharges a part of the gas (hydrogen gas or the like) inside the case 102 to the outside. The electrode body 104 includes a positive electrode plate, a negative electrode plate, and a separator. The positive electrode plate is inserted in the bag-shaped separator, and the positive electrode plate and the negative electrode plate inserted in the separator are alternately laminated. The positive electrode plate and the negative electrode plate are electrically connected to a positive electrode terminal and a negative electrode terminal (not shown), respectively.

As the material of the electrode body 104 and the electrolytic solution, various conventionally known materials can be used. In this embodiment, as an example, an electrode plate including a positive electrode active material layer containing nickel hydroxide (Ni(OH) ₂ or NiOOH) and an active material support such as foamed nickel is used as the positive electrode plate. To be For the negative electrode plate, an electrode plate containing a hydrogen storage alloy (eg, LaNi ₅ or ReNi ₅ ) as a negative electrode active material is used. As the separator, a nonwoven fabric made of hydrophilized synthetic fibers is used. An alkaline aqueous solution containing potassium hydroxide (KOH) or sodium hydroxide (NaOH) is used as the electrolytic solution.

<Degradation due to cracks>
In a hydrogen storage alloy generally used as a negative electrode active material of a nickel hydrogen battery, a bias (distribution) of hydrogen concentration may occur in the negative electrode active material as the nickel hydrogen battery is charged and discharged. Since the local hydrogen amount (proton amount) in the negative electrode active material is different, the local volume change amount is also different, and as a result, strain may occur in the crystal lattice and stress may be generated. As described above, when the stress generated in the negative electrode active material exceeds the mechanical limit strength of the negative electrode active material, cracks may occur. This crack will be described below in comparison with the crack generated in the negative electrode active material of the lithium ion battery.

FIG. 3 is a diagram for explaining a crack generated in the negative electrode active material of the secondary battery. FIG. 3(A) schematically shows the negative electrode active material 4 (eg graphite or silicon) of a lithium ion battery, and FIG. 3(B) schematically shows the negative electrode active material (eg LaNi ₅ ) of a nickel hydrogen battery.

FIG. 4 is a time chart for explaining the internal resistance and the battery capacity of a nickel-hydrogen battery over time. In FIG. 4, the horizontal axis represents elapsed time. The initial time (0) is, for example, the time immediately after the manufacture of the nickel hydrogen battery (battery 100). The vertical axis represents the internal resistance (more specifically, the reaction resistance of the negative electrode) and the battery capacity (more specifically, the negative electrode capacity) of the nickel-hydrogen battery from the top.

As shown in FIG. 3A, a coating (SEI (Solid Electrolyte Interphase) film) 42 is formed on the negative electrode active material 4 of the lithium ion battery. When a crack 41 occurs in the negative electrode active material 4 due to the uneven concentration of lithium in the negative electrode active material 4 due to charge and discharge of the lithium ion battery and the volume of the negative electrode active material 4, a new surface is exposed. A new coating 42 is formed on the exposed surface by the reaction between the negative electrode active material 4 and the electrolytic solution. As a result, the internal resistance of the lithium-ion battery (more specifically, the reaction resistance of the negative electrode) can increase.

On the other hand, as shown in FIG. 3(B), even if a crack 51 is generated in the negative electrode active material 5 of the nickel-hydrogen battery and a new surface is exposed, the influence of the film formation is extremely small. That is, in the nickel-hydrogen battery, the reaction surface of the negative electrode active material 5 that can simply contribute to the battery reaction increases, so that the internal resistance can decrease as shown in the period T1 of FIG.

However, as the deterioration due to the cracks 51 progresses, the cracks 51 become gradually deeper, and finally, as shown by the diagonal lines in FIG. 3B, a part of the particles of the original negative electrode active material 5 is pulverized. Can be. That is, a part of the particles of the negative electrode active material 5 may be in a state of being isolated from the rest of the particles and other particles (not electrically connected) that are not shown. Then, the reaction area that can contribute to the battery reaction is reduced, and thus the internal resistance may increase and the battery capacity may decrease as shown in period T2 of FIG.

Therefore, in the present embodiment, a configuration is adopted in which a crack index value X indicating the degree of progress of deterioration due to cracks in the negative electrode active material 5 is calculated, and charging/discharging of the battery 100 is controlled based on the crack index value X. More specifically, there is a correlation between the degree of deterioration progressed by the crack 51 and the stress Fs acting on the negative electrode active material 5. Therefore, the stress Fs is estimated from the current Ib and the temperature Tb of the battery 100, and the crack index value X is calculated using the estimation result of the stress Fs.

<Calculation of crack index value>
FIG. 5 is a diagram for explaining a process of calculating the crack index value X. In FIG. 5, the horizontal axis represents the elapsed time and the vertical axis represents the stress Fs acting on the negative electrode active material 5. It is considered that when the stress Fs exceeds the mechanical limit strength (typically the tensile limit strength) Flim of the negative electrode active material 5, cracks 51 occur. Therefore, as shown by hatching, the degree of progress of damage due to cracks within a predetermined period is calculated by performing time integration of the excess amount (in other words, the damage amount) ΔF in which the stress Fs exceeds the limit strength Flim. can do.

More specifically, as shown in the following formula (1), the crack index value X(t2) at the time t2 when the period Δt has elapsed from the time t1 is the crack index value (increase amount) ΔX increased during Δt. It is calculated by adding to the crack index value X(t1) at time t1.

X(t2)=X(t1)+ΔX (1)
In the above formula (1), the increase amount ΔX can be calculated by multiplying the crack generation coefficient k per unit time based on the stress excess amount ΔF at time t2 (or time t1) by the period Δt (see below). See formula (2)).

ΔX=k×Δt (2)
Regarding the relationship between the excess amount of stress ΔF and the crack generation coefficient k per unit time, the durability test of the battery 100 is performed in advance under various conditions in which the combination (Ib, Tb) of the current Ib of the battery 100 and the temperature Tb is different. It can be quantified by carrying out. Hereinafter, this quantification method will be described in more detail.

After performing the durability test under various conditions, the battery 100 is disassembled, the negative electrode active material 5 is observed by using an SEM (Scanning Electron Microscope), and various image processing is performed, so that the battery 100 It is possible to quantify the amount of cracks generated according to the combination of conditions (Ib, Tb). On the other hand, during the durability test of each combination (Ib, Tb), the stress Fs generated in the negative electrode active material 5 is calculated by model formula (for example, hydrogen concentration distribution calculation by diffusion equation and stress calculation by Hooke's law). It is possible to calculate it by such as refining). That is, the limit strength Flim can be specified from the crack occurrence determination result in the SEM observation after the durability test or the image processing, and the amount (ΔF) of the stress Fs exceeding the limit strength Flim and the unit time per unit time. The relationship with the crack generation coefficient k can be specified in advance. However, the limit strength Flim may be determined based on theoretical material properties (for example, tensile strength limit). In this way, the correlation between the excess amount ΔF defined in advance and the crack generation coefficient k per unit time can be prepared in advance as a map MP1 (or a relational expression) and stored in the memory 302.

Further, by mounting a model formula in which the above-mentioned substance diffusion and stress prediction are refined in the ECU 300, the stress Fs generated under arbitrary traveling conditions on the vehicle 1 can be calculated in accordance with the control cycle. Is possible. By successively calculating the excess amount ΔF which is the difference between the stress Fs and the limit strength Flim, the crack generation coefficient k can be calculated by referring to the map MP1. When the stress Fs is less than or equal to the limit strength Flim, the excess amount ΔF becomes 0 and the crack generation coefficient k also becomes 0. Therefore, it is determined that the crack generation has not progressed.

<Charge/discharge control according to crack index value>
FIG. 6 is a diagram showing an example of the change over time in the crack index value X. In FIG. 6, the horizontal axis represents elapsed time. The initial time (0) is, for example, the time immediately after the battery 100 is manufactured. The vertical axis represents the crack index value X.

As the crack index value X, a threshold value Xth and an allowable upper limit value Xp are set by experiment or simulation. As described with reference to FIGS. 3 and 4, the allowable upper limit value Xp means that a part of the particles of the negative electrode active material 5 are isolated from other particles, and as a result, the internal resistance increases and the battery capacity decreases. Is a value that can cause. The threshold value Xth is a value lower than the allowable upper limit value Xp and corresponds to the “predetermined value” according to the present invention.

When the crack index value X reaches the threshold value Xth, further increase of the stress Fs is suppressed (or the already generated stress Fs is relaxed) so that the crack index value X does not reach the allowable upper limit value Xp. It is desirable to do. Therefore, in the present embodiment, as described below, the restriction on the input/output power of battery 100 is strengthened in order to suppress the increase in stress Fs.

FIG. 7 is a diagram for explaining the limitation of the input/output power of the battery 100. FIG. 7 conceptually shows an example of a map MP2 for setting the charging power upper limit value Win and the discharging power upper limit value Wout. The horizontal axis represents the temperature Tb of the battery 100. The upper limit of the vertical axis indicates the discharge power upper limit value Wout of the battery 100, and the lower limit of the vertical axis indicates the charge power upper limit value Win of the battery 100.

If the temperature Tb is lower than the predetermined temperature Tf, the electrolyte of the battery 100 may be frozen, and thus charging/discharging of the battery 100 is prohibited. Therefore, both the discharge power upper limit value Wout and the charge power upper limit value Win are set to 0. Although not shown, the charging power upper limit value Win and the discharging power upper limit value Wout may be set to 0 at or above a predetermined temperature from the viewpoint of protecting the battery 100.

When the temperature Tb becomes equal to or higher than the predetermined temperature Tf, charging/discharging of the battery 100 is permitted. The absolute value of the discharge power upper limit value Wout increases as the temperature Tb increases. When the crack index value X is equal to or more than the allowable upper limit value Xp, the absolute value of the discharge power upper limit value Wout at the same temperature Tb is set smaller than when the crack index value X is less than the allowable upper limit value Xp.

Similarly, the absolute value of the charging power upper limit Win also increases as the temperature Tb increases. When the crack index value X is equal to or greater than the allowable upper limit value Xp, the absolute value of the charging power upper limit value Win at the same temperature Tb is set smaller than when the crack index value X is less than the allowable upper limit value Xp.

As described above, in the present embodiment, when the crack index value X becomes equal to or greater than the threshold value Xth, the charging power upper limit value Win (absolute value) is higher than when the crack index value X is less than the threshold value Xth. And the discharge power upper limit value Wout (absolute value) is set small. In other words, the charging power upper limit value Win and the discharging power upper limit value Wout are narrowed down. A correlation as an example shown in FIG. 7 is stored in the memory 302 of the ECU 300 as the map MP2.

<Charge/discharge control flow>
FIG. 8 is a flowchart showing charge/discharge control of battery 100 according to the present embodiment. This flowchart is called from the main routine and executed when a predetermined condition is satisfied or at predetermined time intervals. Note that each step (hereinafter abbreviated as “S”) included in these flowcharts is basically realized by software processing by the ECU 300, but is realized by dedicated hardware (electric circuit) created in the ECU 300. May be done.

The crack index value X is sequentially updated by repeatedly executing the process of the flowchart shown in FIG. This flowchart shows the n-th arithmetic processing, and it is assumed that the crack index value X(n-1) up to the (n-1)-th (previous) processing is stored in the memory 302.

In S10, the ECU 300 acquires the voltage Vb, the current Ib, and the temperature Tb from each sensor provided in the battery 100. The ECU 300 also calculates OCV from the voltage Vb. An example in which OCV is included as a parameter will be described here, but OCV is not an essential parameter for stress estimation.

In S20, the ECU 300 calculates the stress Fs by using the above-described model formula from the OCV, the current Ib, and the temperature Tb acquired in S10. Since this calculation method has already been described, detailed description will not be repeated.

In S30, the ECU 300 calculates the crack generation coefficient k by referring to the map MP1 from the excess amount ΔF of the stress Fs with respect to the limit strength Flim, and uses this to calculate the current crack generation amount ΔX(n). As described in the equation (2), the present crack generation amount ΔX(n) can be calculated as the product of the crack generation coefficient k and the excess period.

In S40, the crack index value X(n) up to this time (n-th) arithmetic processing is calculated. The crack index value X(n) is the crack index value X from the previous ((n-1)th) calculation process to the crack generation amount ΔX(n) in this calculation process, as shown in the following equation (3). It can be calculated by adding to (n-1).

X(n)=X(n-1)+ΔX(n) (3)
In S50, the ECU 300 determines whether the crack index value X(n) calculated in S40 is equal to or greater than the threshold value Xth. If the crack index value X(n) is less than the threshold value Xth (NO in S50), the ECU 300 advances the process to S70 and refers to the map MP2 (see FIG. 7) to determine the normal charging power upper limit Win and The discharge power upper limit value Wout is used. On the other hand, when crack index value X(n) is equal to or greater than threshold value Xth (YES in S50), ECU 300 advances the process to S60 and refers to map MP2 to determine charge power upper limit value Win and discharge power upper limit value Wout. The limit of the input/output power of the battery 100 is strengthened by lowering it from the normal time.

As described above, according to the present embodiment, the crack index value X indicating the degree of progress of deterioration due to the crack generated in the negative electrode active material 5 due to the stress Fs acting on the negative electrode active material 5 containing the hydrogen storage alloy is set as follows. calculate. When the crack index value X is equal to or greater than the threshold value Xth, the charging power upper limit value Win (absolute value) and discharge of the battery 100 are higher than when the crack index value X is less than the threshold value Xth. The power upper limit value Wout (absolute value) is set small. When the charge power or the discharge power increases, the distortion of the crystal lattice in the negative electrode active material 5 increases. By decreasing the charge power upper limit value Win and the discharge power upper limit value Wout, the strain generated in the negative electrode active material 5 is reduced. Therefore, the crack index value X is prevented from further increasing. Therefore, it is possible to suppress the progress of deterioration due to cracks, thereby suppressing an increase in the reaction resistance of the negative electrode and a decrease in the negative electrode capacity (that is, a decrease in battery performance).

In addition, in the above embodiment, the example using the tensile strength has been described. Generally, the parameter used to determine the presence or absence of cracks in the negative electrode active material is considered to be tensile strength, but the influence of compressive strength may be considered in addition to (or instead of) tensile strength. By considering the influences of both the tensile strength and the compressive strength, it becomes possible to more accurately determine whether or not a crack has occurred.

In addition, in FIG. 7, the configuration in which both the charging power upper limit value Win and the discharging power upper limit value Wout are limited has been described as an example, but only one of the charging power upper limit value Win and the discharging power upper limit value Wout is limited. May be.

Further, a rest period may be provided during charging/discharging of the battery 100 to suspend charging/discharging. Since the bias of the hydrogen concentration in the negative electrode active material 5 is alleviated during the rest period, and as a result, the strain of the crystal lattice in the negative electrode active material 5 is alleviated, cracks are less likely to occur in the negative electrode active material 5. Is. Alternatively, the battery 100 may be positively charged and discharged in order to promote the alleviation of the bias in the hydrogen concentration. That is, since the bias direction of the hydrogen concentration in the negative electrode active material 5 is opposite between the time of charging the battery 100 and the time of discharging the battery 100, for example, the battery 100 may be discharged for a certain time and then charged in reverse. It is possible to reduce the bias in hydrogen concentration. As a result, the generation of cracks can be suppressed.

It should be considered that the embodiments disclosed this time are exemplifications in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.

1 vehicle, 2 secondary battery system, 4,5 negative electrode active material, 10,20 motor generator, 30 power split mechanism, 40 engine, 41,51 crack, 42 coating, 50 drive wheel, 100 battery, 101 cell, 102 case , 103 safety valve, 104 electrode body, 110 voltage sensor, 120 current sensor, 130 temperature sensor, 150 SMR, 200 PCU, 300 ECU, 301 CPU, 302 memory.

Claims (1)

A battery system for supplying power to an external device,
A nickel-hydrogen battery containing a hydrogen storage alloy as a negative electrode active material,
A power converter that converts power between the nickel-hydrogen battery and the external device,
Control for controlling the power conversion device such that charging power to the nickel-hydrogen battery is less than a control upper limit value of the charging power, and discharging power from the nickel-hydrogen battery is less than a control upper limit value of the discharging power. Equipped with a device,
The control device is
From the current input to and output from the nickel-hydrogen battery, and the temperature of the nickel-hydrogen battery, calculate an index value related to the degree of progress of deterioration due to cracks generated in the negative electrode active material,
When the index value indicates that the degree of progress of the deterioration is larger than a predetermined amount, compared with the case where the index value indicates that the degree of progress of the deterioration is smaller than the predetermined amount, the charging power A battery system for reducing the control upper limit value and the control upper limit value of the discharge power.

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