WO2017169127A1

WO2017169127A1 - Secondary battery system

Info

Publication number: WO2017169127A1
Application number: PCT/JP2017/004293
Authority: WO
Inventors: 貴嗣上城
Original assignee: 株式会社日立製作所
Priority date: 2016-03-28
Filing date: 2017-02-07
Publication date: 2017-10-05
Also published as: JP2019114324A

Abstract

The purpose of the present invention is to prevent acceleration of degradation fluctuations in a battery system and prolong the life of the battery system. Provided is a secondary battery system in which multiple secondary batteries are connected in series and in parallel, wherein the system is characterized in that the voltage balancing function is separately set for each of the secondary batteries.

Description

Secondary battery system

The present invention relates to a secondary battery system.

In recent years, the market for battery systems using lithium ion batteries is increasing against the background of environmental measures. As the system operates, the capacity of the lithium-ion battery decreases and the internal resistance increases, and the deterioration accelerates as the temperature increases. In the battery system, a temperature distribution is generated and the temperature is high in the central portion, so that variation in deterioration occurs, and the deterioration further proceeds in the central portion. Since the amount of heat generated by the battery increases due to the increase in internal resistance accompanying the deterioration, the central portion becomes higher in temperature, and the deterioration accelerates. Thus, the deterioration variation in the battery system is accelerated as the system operation period elapses. Since the life of the battery system depends on the most deteriorated battery, the battery performance cannot be fully utilized and the life is shortened. Therefore, there is a need for a means for suppressing the acceleration of the deterioration in deterioration that occurs in the battery system and extending the life of the battery system. It is known that the deterioration of the lithium ion battery depends on the battery charging rate (hereinafter referred to as SOC) and the battery voltage in addition to the battery temperature. From this feature, in Patent Document 1, the cell controller sets the battery operating voltage range or the operating SOC range of the entire battery system according to the diagnosis result of the deterioration state (hereinafter referred to as SOH) of the assembled battery, and performs charge / discharge control. Secondary battery systems have been reported.

The technology of Patent Document 1 suppresses deterioration of the assembled battery and the battery system by shifting the operating SOC range of the assembled battery to the high SOC side or the low SOC side according to the SOH of the assembled battery, and has a long service life. It has become.

Japanese Patent Laying-Open No. 2015-065119

However, in Patent Document 1, since the battery system as a whole is similarly adjusted, acceleration of deterioration variation of each battery in the battery system cannot be suppressed, and the battery performance may not be used to the maximum extent. is there.

An object of the present invention is to suppress acceleration of deterioration variation in a battery system and extend the life of the battery system.

The means for solving the above problems are, for example, as follows.

In a secondary battery system in which a plurality of secondary batteries are connected in series or in parallel, the charging rate of the secondary battery is controlled by the voltage of the secondary battery, and the value of the voltage is determined for each secondary battery. Secondary battery system set individually.

The charging rate of the secondary battery is controlled by the use range of the voltage, and the use range is individually set for each secondary battery.

The voltage is a secondary battery system that is set according to the temperature in the secondary battery system or the degree of deterioration.

The voltage is a balancing voltage determined for each secondary battery, and the balancing voltage is at least one of a charge start voltage, a charge end voltage, a discharge start voltage, and a discharge end voltage of the secondary battery, The secondary battery system is a secondary battery system having an adjustment mechanism for adjusting the balancing voltage determined for each secondary battery for each secondary battery.

According to the present invention, acceleration of deterioration variation in the battery system can be suppressed, and the battery system can be extended in life. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is the schematic which shows the internal structure of the lithium ion secondary battery in one Embodiment of this invention. It is a characteristic view which shows the relationship between SOC of a lithium ion secondary battery in one Embodiment of this invention, battery temperature, and a capacity degradation coefficient. It is a characteristic view which shows the relationship between SOC of a lithium ion secondary battery in one Embodiment of this invention, battery temperature, and a resistance degradation coefficient. It is a characteristic view which shows the capacity degradation estimation curve in the place with different battery temperature of the lithium ion secondary battery system in one Embodiment of this invention. It is a characteristic view which shows the resistance deterioration estimation curve in the place with different battery temperature of the lithium ion secondary battery system in one Embodiment of this invention. It is a block diagram of the secondary battery system which has a battery balancing function in one Embodiment of this invention. It is a table | surface which shows the battery temperature in a conventional method in the place with a different battery temperature shown in Example 1 of this invention, a setting voltage, and a resistance degradation coefficient. It is a table | surface which shows the battery temperature to which this invention was applied in the place which has a different battery temperature shown in Example 1 of this invention, a setting voltage, and a resistance degradation coefficient. It is a flowchart which shows the battery balancing function in Example 1 of this invention. In Example 1 of this invention, it is a characteristic view which shows the deterioration estimation curve in the conditions where the technique of this invention and the technique of this invention were applied in the place which has a different battery temperature. It is a figure in Example 2 of this invention which shows the flow which updates each balancing voltage setting value from each battery degradation state. In Example 2 of this invention, it is a characteristic view which shows the deterioration estimation curve in the conditions where the technique of this invention and the technique of this invention were applied in the place which has a different battery temperature.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible. In all the drawings for explaining the present invention, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.

First, the lithium ion secondary battery installed in the secondary battery system will be described. In FIG. 1, the schematic of the internal structure of the lithium ion secondary battery in one Embodiment of this invention is shown. In the lithium ion secondary battery 100, an electrode group including a positive electrode 101, a separator 103, and a negative electrode 102 is installed and configured in a battery case 106.

The positive electrode 101 and the negative electrode 102 are arranged away from each other through a separator 103 containing an electrolytic solution, and the positive electrode 101 and the negative electrode 102 have no electron conductivity and have ionic conductivity.

When a current flows from the positive electrode 101 to the negative electrode 102, lithium ions are desorbed from the active material in the negative electrode 102, and a reaction in which lithium ions are inserted into the active material in the positive electrode 101 proceeds.

The electrode group has a configuration in which the positive electrode 101, the separator 103, the negative electrode 102, and the separator 103 are alternately stacked and wound, or the positive electrode 101, the separator 103, the negative electrode 102, and the separator 103 are alternately stacked. Yes. The shape of the battery includes a cylindrical shape, a flat oval shape, and a square shape when the electrode group is wound, and a rectangular shape and a laminate shape when the electrode group is wound. The shape may be selected.

The positive electrode terminal 104 and the negative electrode terminal 105 are energized with the positive electrode 101 and the negative electrode 102, respectively, and the lithium ion secondary battery 100 is charged / discharged from an external circuit via the positive electrode terminal 104, the negative electrode terminal 105, and the electronic circuit 110. A voltage sensor 111 is connected to the positive terminal 104 and the negative terminal 105, and a current sensor 112 is incorporated in the electronic circuit 110, and the current value flowing in the lithium ion secondary battery 100, the potential difference between the positive and negative electrodes, That is, the battery voltage is detected.

When using lithium ion secondary batteries, the capacity decreases and the internal resistance increases. It is known that such battery deterioration depends on environmental temperature and SOC, that is, battery voltage. Regarding the relationship between the SOC and the battery voltage, the higher the SOC, the higher the battery voltage.

FIG. 2 shows an example of a characteristic diagram showing the relationship between the SOC of the lithium ion secondary battery and the capacity deterioration coefficient with respect to the battery temperature, and FIG. 3 shows a characteristic diagram showing the relation between the SOC of the lithium ion secondary battery and the resistance deterioration coefficient with respect to the battery temperature. An example is shown. The capacity deterioration coefficient and the resistance deterioration coefficient each indicate an index of the deterioration rate, and the relationship between the deterioration and the deterioration coefficient is expressed by, for example, Expression (1).

In Equation (1), y is the battery deterioration amount, k is the deterioration coefficient, t is the test time, and a and b are constants. Expression (1) is a deterioration prediction expression based on a root rule that utilizes the fact that the battery deterioration amount is proportional to the ½ of the test time. This formula is based on a mechanism in which the speed of the side reaction in the battery is inversely proportional to the thickness of the film formed by the side reaction.
FIG. 2 and FIG. 3 are diagrams obtained from the results of calculating battery deterioration when a battery charged in each SOC is stored at various temperatures in a lithium ion secondary battery according to one embodiment. As an example, FIG. 2 shows the capacity deterioration coefficient as an index of the capacity deterioration rate, and FIG. 3 shows the capacity deterioration coefficient as an index of the resistance deterioration speed for the results of 35 ° C., 45 ° C., and 55 ° C. The horizontal axis indicates the SOC, and the vertical axis indicates the respective degradation coefficients. From the results of FIGS. 2 and 3, it can be seen that the battery deterioration is remarkable at high temperatures, but the deterioration coefficients are relatively moderate at low temperatures. It can also be seen that each degradation coefficient depends on the SOC. Therefore, the deterioration coefficient k in the equation (1) is expressed by an equation depending on the environmental temperature T and the SOC as in the equation (2).

Next, a secondary battery system equipped with a lithium ion secondary battery will be described. The secondary battery system is a system in which a plurality of lithium ion secondary batteries are connected in series and in parallel. When the secondary battery system is operated, current flows through the system circuit, and the battery generates heat according to Joule's law. The temperature in the secondary battery system rises due to the battery heat generation, but the heat distribution varies depending on the location inside the system, and thus a temperature distribution occurs in the secondary battery system. Generally, the temperature at the center of the system is high and the temperature at the end of the system is low. In one embodiment, it was about 10 ° C.

Since the deterioration of the lithium ion secondary battery depends on the temperature, variation in the deterioration occurs in the secondary battery system. For example, in a secondary battery system in which secondary batteries are stacked and stacked, the temperature in the central part of the system is generally high, and therefore, the secondary battery disposed in the central part of the system promotes more deterioration. Further, since the amount of heat generated by the battery increases due to the increase in internal resistance accompanying the deterioration, the central part of the system becomes higher in temperature and the deterioration is accelerated.

4 and 5 show capacity deterioration estimation curves and resistance deterioration estimation curves at different battery temperatures in the secondary battery system. The operation period and the vertical axis indicate the capacity change rate and the resistance change rate. A is assumed to be the end of the system, and B is assumed to be the center of the system. The temperature difference between A and B is about 10 ° C., A is 45 ° C., and B is 35 ° C., and the results of estimating the respective deterioration are shown. From the results of FIGS. 4 and 5, it is estimated that the battery deterioration estimated value is remarkably different depending on the temperature difference, and the deterioration variation is accelerated. Thus, the deterioration variation in the secondary battery system is accelerated as the system operation period elapses. Since the life of the secondary battery system depends on the most deteriorated battery, the battery performance cannot be fully utilized and the life is shortened.

Therefore, it is necessary to provide a means for suppressing the acceleration of deterioration variation occurring in the secondary battery system and extending the life of the secondary battery system.

FIG. 6 is a configuration diagram of a secondary battery system having a battery balancing function in one embodiment for suppressing the acceleration of deterioration variation occurring in the secondary battery system.

6, the secondary battery system 400 has a configuration in which a plurality of sets are arranged in parallel, with the power conditioner 410, the battery panel 430, and the battery management unit 420 connected to the battery panel 430 as one series set. In the secondary battery system 400, the flowing AC wave is converted to DC by the power conditioner 410, and a DC current flows through the battery panel 430. The battery management unit 420 is connected to the battery panel 430 and has a function of storing, analyzing, and managing each battery information transmitted from the battery panel 430.

In the battery panel 430, battery modules 440 composed of a plurality of lithium ion secondary batteries 100 connected in series are connected in series. The lithium ion secondary batteries 100 are stacked and arranged, for example, and in many cases, a temperature difference occurs depending on the position of the lithium ion secondary battery 100. The value of the current flowing through each lithium ion secondary battery 100, the battery voltage, and the battery temperature are respectively obtained from a current sensor 451 connected in series with the battery, a voltage sensor 452 connected in parallel with the battery, and a temperature sensor 453 attached to the battery surface. Detected. The current sensor 451, voltage sensor 452, and temperature sensor 453 are connected to the cell controller 456 and transmit each detected value to the battery management unit 420. A bypass circuit is provided between the lithium ion secondary batteries 100 and is connected to the transistor 454 and the resistor 455. Using this bypass circuit, each lithium ion secondary battery 100 can be adjusted to a predetermined voltage. This function is hereinafter referred to as a voltage balancing function.

The flow of the battery balancing function is shown below. First, when the lithium ion secondary battery 100 is larger than a predetermined voltage, a command is issued from the cell controller 456 to the transistor 454, and the switch is turned on. When the switch is turned on, the lithium ion secondary battery 100 is discharged and discharged to a predetermined voltage as time passes. When the lithium ion secondary battery becomes a predetermined voltage or lower, a command is issued from the cell controller 456 to the transistor 454, and the switch is turned OFF. With the above flow, the voltage of each lithium ion secondary battery 100 can be adjusted.

Balancing is performed by controlling the charging rate of the secondary battery. The charging rate is controlled by the voltage of the secondary battery. In particular, it is preferable to perform balancing by adjusting the operating voltage range of the secondary battery. The working voltage range can be adjusted by an adjusting mechanism that determines and adjusts the balancing voltage (VBk) to each secondary battery.

As the balancing voltage, for example, a charge start voltage, a charge end voltage, a discharge start voltage, and a discharge end voltage can be set. By adjusting these voltages, you can use a secondary battery in a wide voltage range, use a secondary battery in a narrow range, or use a secondary battery in a low voltage range. Use can be adjusted and the burden on the secondary battery can be adjusted.

For example, adjustment by a bypass circuit can be used as an adjustment mechanism for performing the operation (balancing) for adjusting these voltages. The resistor 455 used for the bypass circuit is used to control the current value flowing through the bypass circuit. The resistance value of the resistor 455 is not limited. However, if the resistance value is too large, it takes time to adjust the voltage. If the resistance value is too small, the discharge current is high and the battery is loaded. Therefore, although it depends on the application, it is desirable that the resistor 455 has a resistance value such that the value of the current flowing through the bypass circuit is about 0.5 C to 2 C. Further, a variable resistor whose resistance value varies depending on the value of the current flowing through the bypass circuit may be used for the resistor 455.

When using transistors and resistors in this way, the voltage can be lowered by discharging from the secondary battery. When adjusting to increase the voltage, the charging is continued until the secondary battery exceeds the balancing voltage value through the power generation device provided in the secondary battery system or an external power source. It can be adjusted by a method such as operating the voltage balancing function.

It is desirable to activate this voltage balancing function when there is no current load in the system, such as when system operation starts, ends, or during regular system maintenance.

Balancing is preferably performed, for example, at the end of charging, at the end of discharging, or during maintenance. At this time, the balancing is preferably performed until the next charging or discharging is started.

Next, a means for suppressing the acceleration of deterioration variation occurring in the secondary battery system and extending the life of the secondary battery system will be described. In general, in a secondary battery system, a predetermined voltage value determined when a command is transmitted to the transistor 454 has a common value. The purpose is to eliminate the voltage variation of each battery in the secondary battery system caused by operation. In the present invention, a predetermined voltage value serving as a determination criterion is set in each lithium ion secondary battery.

In the secondary battery system, the temperature in the central part of the system is high, and the deterioration is accelerated in the central part of the system. In order to eliminate the deterioration variation, it is necessary to suppress deterioration at the center of the system. 2 and 3, it is known that the battery deterioration depends on the SOC, that is, the battery voltage. Therefore, it is preferable to set the SOC of the battery in the central part of the system so as to suppress the deterioration of the battery in the central part of the system where the deterioration is promoted. To set the SOC, for example, it can be set by appropriately changing the start / end voltage of charge / discharge. When the SOC setting of the battery is changed, the battery voltage changes and the output changes. Therefore, in order not to change the rated output performance of the battery panel 430, not only the SOC setting change of the battery at the center of the system but also the SOC setting of the battery at the end of the system can be performed.

For example, using the results shown in FIGS. 2 and 3, the SOC of the battery at the center of the system with high temperature and large deterioration may be set low, and the SOC of the battery at the end of the system with low temperature and low deterioration may be set high. Here, “low SOC” means, for example, that the SOC range to be used is narrowed (for example, a battery used in the range of 30 to 70% is used in the range of 32 to 68%), or a low SOC is used. It is possible to use such a setting that the battery is used (for example, the battery used in the range of 30 to 70% is used in the range of 28 to 68%). The latter is preferable from this viewpoint because the usable capacity decreases.

As described above, the precaution when re-setting the SOC is that the maximum output and energy capacity of the battery change when the SOC of the battery is changed. For example, when the SOC is lowered, the maximum output and energy capacity are reduced. Therefore, the maximum output and energy capacity after the SOC change satisfy the design values, and the estimated maximum output and energy capacity after SOC reset after long-term operation are the estimated maximum output and energy capacity during normal operation. It is necessary to determine the SOC setting value in consideration of whether the value is exceeded.

In the secondary battery system, deterioration in the secondary battery system is established by setting a predetermined voltage value to be determined at the time of command transmission to the transistor 454 in each battery so that the SOC of each battery determined in this way is obtained. Variations can be eliminated and the life of the secondary battery system can be extended.

For these results, a control method will be described using the following examples.

In the first embodiment, a predetermined voltage value (hereinafter referred to as a balancing voltage value) that is determined when a command is sent to the transistor 454 in the secondary battery system in consideration of the relationship of the battery deterioration with respect to the SOC and the battery temperature in the lithium ion secondary battery. Was set for each battery depending on the position of the battery.

Since Example 1 uses a system applied to a hybrid vehicle (hereinafter referred to as HEV), the estimated value of the maximum output after long-term operation is higher in the method according to the present invention than in the conventional method and the method according to the present invention. In consideration of the above, a predetermined voltage value that is determined when a command is transmitted to the transistor 454 is set in each battery. For the setting, for example, an optimum balancing voltage value of each battery was calculated using a deterioration prediction formula calculated from the results of FIGS. 2 and 3, a database of deterioration results, and the like. The calculation method is specifically shown below.

From Equations (1) and (2), the resistance deterioration prediction equation is as shown in Equation (3), such as environmental temperature T, SOC,
It is expressed by an expression that depends on the operating time t.

Further, the relationship between the battery voltage V and the SOC is expressed by equation (4), and the calculation formula for the maximum output P _max is expressed by equation (5).
Shown in (6). I _max indicates the maximum current value in a certain SOC.

By combining the equations (3) to (6), the maximum output deterioration prediction formula P _max (T, SOC, t) at a certain environmental temperature, SOC, and operation time is expressed as the equation (7).

Here, limiting conditions are provided as in equations (8) and (9), and the optimum value of SOC is calculated so that the maximum output value after long-term operation is maximized. The maximum output _{P max} in SOC in equation (8) is a limiting condition that meets the design output value _{P A.} Equation (9) is a limiting condition that the estimated value of the maximum output in a certain SOC after long-term operation in a high temperature environment of the secondary battery system is higher than the estimated value of the maximum output after long-term operation in the conventional method. . In Formula (9), it calculated as 45 degreeC as high temperature environmental conditions, and 3650 days as long-term operation period. The initial setting SOC of the conventional method is 50%.

FIG. 7 and FIG. 8 show the results reflecting the calculated values of the SOC optimum values using the equations (7), (8), and (9).

FIG. 7 shows the battery temperature, the set voltage, and the resistance deterioration coefficient in the conventional method in a place having different battery temperatures. It can be seen that in the place B where the temperature is high, the resistance deterioration coefficient is higher than in the place A where the temperature is low, and the deterioration easily proceeds.
FIG. 8 shows the battery temperature, the set voltage, and the resistance deterioration coefficient to which the method according to the present invention is applied in a place having different battery temperatures. The values of the system end A and the system center B are shown as representative points. Here, the “set voltage” can be, for example, a voltage that is reached when balancing starts and ends, or can be a center SOC.

The location B of high temperature is used under milder conditions than the location A of low temperature, or the location A of low temperature is used under stricter conditions than the location B of high temperature. Can be reduced.

FIG. 9 is a flowchart for explaining voltage balancing control in the first embodiment. The process shown in this control flowchart is called from the main routine and executed at a predetermined time when there is no current load in the system, such as at the start or end of system operation, or during periodic system maintenance.

The control flowchart of FIG. 9 will be described.

<Step S1>
Each battery voltage V _K detected from the voltage sensor 452 is compared with the balancing voltage value V _BK in each battery, and it is determined whether each battery voltage V _K is larger than each balancing voltage value V _BK . As each cell voltage _{V K} is determined to be greater than the balancing voltage value _{V BK} (in step S1 YES), the processing proceeds to step S4. Each battery voltage _{V K} is smaller than the balancing voltage value _{V BK} (in step S1 NO), the process proceeds to step S2.

<Step S2>
It is determined from the value of the current sensor 453 whether or not the battery panel 430 is charged. If battery panel 430 is charged (YES in step S2), the process returns to the start, and the process starts again from step S1. If battery panel 430 is not charged (NO in step S2), the process proceeds to step S3.

<Step S3>
Charging of the battery panel 430 is started. Thereafter, the process returns to the start, and the process starts again from step S1.

<Step S4>
It is determined from the value of the current sensor 453 whether or not the battery panel 430 is charged. If battery panel 430 is charged (YES in step S4), the process proceeds to step S5. If battery panel 430 is not charged (NO in step S4), the process proceeds to step S6.

<Step S5>
Charging of the battery panel 430 is started. Thereafter, the process proceeds to step S6.

<Step S6>
It is determined whether or not the transistor 454 (k) installed in the bypass circuit of each battery is OFF. If each transistor 454 (k) is OFF (YES in step S6), the process proceeds to step S7. If each transistor 454 (k) is ON (NO in step S6), the process proceeds to step S8.

<Step S7>
Each transistor 454 (k) is turned on. By turning on each transistor 454 (k), the balancing function of each battery is turned on, and the battery is discharged until the respective balancing voltage _VBK is reached. Thereafter, the process proceeds to step S8.

<Step S8>
Each battery voltage V _K detected from the voltage sensor 452 is compared with the balancing voltage value V _BK in each battery, and it is determined whether or not each battery voltage V _K is smaller than each balancing voltage value V _BK . As each cell voltage _{V K} is determined to be smaller than the balancing voltage value _{V BK} (in step S8 YES), the processing proceeds to step S9. Each battery voltage _{V K} is smaller than the balancing voltage value _{V BK} (in step S8 NO), the process proceeds to step S6.

<Step S9>
Each transistor 454 (k) is turned off. By turning off each transistor 454 (k), the voltage balancing function of each battery is turned off. Thereafter, the battery balancing process ends.

By the control according to the flowchart of FIG. 9, in the secondary battery system, each battery voltage is periodically adjusted to the balancing voltage value, and the SOC distribution is taken depending on the location in the secondary battery system. The acceleration can be eliminated and the life of the secondary battery system can be extended.

FIG. 10 shows the estimation results of the maximum output change at the system end A and the system center B in the secondary battery system. The horizontal axis indicates the operation period, and the vertical axis indicates the maximum output change rate. A result of the system end A according to the conventional method is shown as A1, a result of the system center B as B1, a result of the system end A according to the method of the present invention as A2, and a result of the system center B as B2. As shown in FIG. 7 and FIG. 8, by applying the method of the present invention, the set voltage is lowered so as to suppress the deterioration of the system center B, and the set voltage value of the system end A so as to maintain the rated output of the battery panel. Therefore, the maximum output initial value of the system central portion B to which the method of the present invention is applied is lower than the maximum output initial value of the system central portion B in the conventional method. However, as the operation period elapses, the maximum output of the system central part B to which the method of the present invention is applied increases, and it has been shown that the life of the secondary battery system can be extended by the method of the present invention.

In the second embodiment, in addition to the setting of the balancing voltage value of each battery in the secondary battery system in the first embodiment, the setting value of each balancing voltage is updated according to the SOH of each battery calculated periodically. . The update period of the balancing voltage (VBk) may be any period, and may be one month, two months, or half a year.

Fig. 11 shows the flow of updating the setting value of the balancing voltage. First, the current value, voltage value, and battery temperature of each battery are detected from the current sensor 451, voltage sensor 452, and temperature sensor 453, and transmitted to each cell controller 456. Each cell data is transmitted from each cell controller 456 to the battery management unit 420, and the battery management unit 420 calculates the SOC and SOH of the battery using those data. The calculation method of the SOC is calculated using, for example, the result of the accumulated charge / discharge capacity calculated from the battery voltage from a certain point in time and the transition of the current value from the certain point in time. The SOH estimation method is calculated from, for example, a current value, a battery temperature, an estimated resistance value at the battery temperature, a difference value between the battery voltage and the open circuit voltage in the SOC calculated at that time, and the like.

Next, using the actual temperature and SOH value of each battery, and a deterioration prediction formula calculated from the results of FIGS. 2 and 3, for example, a database of deterioration results, etc., an updated value of the optimum balancing voltage value of each battery Is calculated.

The specific calculation method is basically the same as that of the first embodiment, and using the formulas (3) to (9), the set SOC, that is, the balancing voltage is set so that the maximum output value after long-term operation becomes maximum. Calculate the optimum value. The transition of the resistance deterioration depends on SOH at a certain operation time t in addition to the environmental temperature T, the SOC, and the operation time t. Therefore, by reflecting the SOH calculated periodically in the prediction formula, it is possible to calculate a more appropriate setting SOC, that is, a balancing voltage value. In this example, since the value of SOH is also used for the prediction of deterioration in Example 2, Expression (10) is used instead of Expression (3).

As described above, the battery management unit 420 uses the equations (4) to (9) and (10) to regularly set SOC, that is, balancing voltage value so that the maximum output value after long-term operation becomes maximum. Update the optimal value of. The updated value of the balancing voltage value in each battery calculated by the battery management unit 420 is transmitted to each cell controller 456. After the transmission, each cell controller 456 activates the voltage balancing function using the updated balancing voltage value. The same voltage balancing control flow as that of the flowchart of FIG. 9 of the first embodiment can be used.

In the second embodiment, the balancing voltage value is set based on the SOH and the temperature. However, the balancing voltage value may be calculated based only on the SOH, or the balancing voltage value may be appropriately changed according to only the temperature.

FIG. 12 shows the estimation result of the maximum output change at the system end A and the system center B in the secondary battery system. The horizontal axis indicates the operation period, and the vertical axis indicates the maximum output change rate. A result of the system end A according to the conventional method is shown as A1, a result of the system center B as B1, a result of the system end A according to the method of the present invention as A2, and a result of the system center B as B2. In Example 2, the update period was calculated as 30 days. As shown in FIG. 12, by periodically updating the balancing voltage value to reflect the SOH of each battery, the acceleration of deterioration variation in a hot place is reduced as compared with the first embodiment, and the life of the secondary battery system is extended. Can do.

DESCRIPTION OF SYMBOLS 100 Lithium ion secondary battery 101 Positive electrode 102 Negative electrode 103 Separator 104 Positive electrode terminal 105 Negative electrode terminal 106 Battery case 110 Electronic circuit 111 Voltage sensor 112 Current sensor 400 Secondary battery system 410 Power conditioner 420 Battery management part 430 Battery panel 440 Battery module 451 Current Sensor 452 Voltage sensor 453 Temperature sensor 454 Transistor 455 Resistance 456 Cell controller

Claims

In a secondary battery system in which a plurality of secondary batteries are connected in series or in parallel,
The charging rate of the secondary battery is controlled by the voltage of the secondary battery,
The value of the voltage is a secondary battery system set individually for each secondary battery.
In claim 1,
The charging rate of the secondary battery is controlled by the usage range of the voltage,
The use range is a secondary battery system that is individually set for each of the secondary batteries.
In claim 1 or claim 2,
The said voltage is a secondary battery system set according to the temperature in a secondary battery system, or a degradation degree.
In claim 3,
The voltage is a balancing voltage determined for each secondary battery,
The balancing voltage is at least one of a charge start voltage, a charge end voltage, a discharge start voltage, and a discharge end voltage of the secondary battery,
The secondary battery system is a secondary battery system having an adjustment mechanism for adjusting the balancing voltage determined for each secondary battery for each secondary battery.
In claim 4,
Balancing to adjust the secondary battery to the balancing voltage is performed by the adjustment mechanism,
The adjustment mechanism is a current bypass circuit provided for each secondary battery,
The bypass circuit is a secondary battery system having a resistor and a transistor.
In claim 5,
The balancing is a secondary battery that is performed at the start of charging, at the end of charging, at the start of discharging, at the end of discharging, or during maintenance.
In claim 6,
Adjustment of the voltage at the time of balancing is made by turning the transistor on and off,
When the voltage of the secondary battery is higher than the balancing voltage value, balancing is performed by turning on the transistor, and when the voltage of the secondary battery reaches the balancing voltage value, the transistor is turned off. Next battery system.
In claim 7,
When adjusting the balance voltage higher than the voltage of the secondary battery,
The secondary battery system that performs the balancing after the end of charging and the charging by the power generation device provided in the secondary battery system or an external power source until the secondary battery exceeds each balancing voltage value.
In claim 8,
The secondary battery system includes a temperature detection unit that detects a temperature of the secondary battery, a voltage detection unit that detects a voltage of the secondary battery, and a current detection that detects a current value flowing through the secondary battery. And a battery management unit,
The battery management unit includes an SOC calculation unit that calculates a charge rate (SOC) of each of the secondary batteries, an SOH calculation unit that calculates a respective battery deterioration state (SOH),
A secondary battery system comprising a balancing voltage calculation unit that calculates a balancing voltage of each of the secondary batteries using at least the SOH of each of the secondary batteries.