WO2022209244A1

WO2022209244A1 - Power storage device and equalization charging method

Info

Publication number: WO2022209244A1
Application number: PCT/JP2022/003399
Authority: WO
Inventors: 秀人中村; 雅進新垣; 彰田中; 敏幸佐藤
Original assignee: 古河電気工業株式会社; 古河電池株式会社
Priority date: 2021-03-30
Filing date: 2022-01-28
Publication date: 2022-10-06
Also published as: JPWO2022209244A1

Abstract

Provided is a power storage device having a simple device configuration and capable of equalization charging while inhibiting the occurrence of power peaks. Provided is a power storage device comprising a power storage battery group that has a plurality of strings (S1-S4), an AC/DC conversion device that is electrically connected to the power storage battery group and to an external power system, a power storage battery management unit that manages the state of each string, and a charge and discharge control unit that controls the AC/DC conversion device on the basis of a command from the power storage battery management part, said power storage device having: a plurality of switches (51-54) that categorize the plurality of strings into at least two sets and are inserted between each of the sets of the strings and the AC/DC conversion device; a switch control unit (4Cb) that provides an opening command to switches other than one switch selected from among the plurality of switches (51-54) upon determining that equalization charging is to be performed on the power storage battery group; and a switch reconnection unit (4Dc) that supplies a closing command to the plurality of switches (51-54) upon determining that the equalization charging of the power storage battery group has finished.

Description

Power storage device and equal charging method

The present invention relates to a power storage device, and in particular a technology related to equalization charging.

As a conventional power storage device (power storage device, power storage system), for example, there is a technique described in Patent Document 1.
At this time, if a plurality of strings are equally charged at the time of equalizing charging, the charging power required for equalizing charging increases. Therefore, even if equalization charging is performed late at night when power consumption is low, power peaks may occur.
On the other hand, in the power storage device of Patent Document 1, a chopper is provided for each string, and equal charging is performed for each string.
However, in the method described in Patent Literature 1, a chopper is provided and the chopper is controlled, which makes the apparatus expensive.

JP 2015-27158 A

The present invention has been made with a focus on the points as described above, and an object of the present invention is to provide a power storage device with a simple device configuration that enables equal charging while suppressing the occurrence of power peaks.

In order to solve the problem, one aspect of the present invention provides a storage battery group having a plurality of strings each including a storage battery row in which a plurality of storage batteries are connected in series, and an AC/DC converter that electrically connects the storage battery group and an external power system. a storage battery management unit that manages the state of each string; and a charge/discharge control unit that controls the AC/DC converter based on a command from the storage battery management unit, wherein the plurality of strings are classified into two or more sets, and it is determined that equal charging is to be performed for a plurality of switches interposed between the strings of each set and the AC/DC converter, and for the storage battery group, the plurality of A switch control unit that supplies an open command to switches other than one switch selected from the switches, and a switch reconnection unit that supplies a close command to the plurality of switches when it is determined that the equalization charge is completed. and

Further, according to another aspect of the present invention, there is provided an equalizing charging method for equalizing charging a storage battery group having a plurality of strings each including a storage battery train in which a plurality of storage batteries are connected in series, using an AC/DC converter, wherein the plurality of strings are classified into two or more sets, each set of strings is connected to the AC/DC converter via an individual switch, and when the storage battery group is uniformly charged, it is selected from the plurality of switches. In this equalizing charging method, only one switch is closed, and when it is determined that the equalizing charge is completed, all of the plurality of switches are closed.

According to aspects of the invention, during each equalization, only a particular set of strings is equalized. Therefore, it is possible to minimize the power and amount of power required for each equalization charge. Furthermore, an inexpensive switch is provided for each set of strings, and simple switching control (switching control only at the start and end of equalization control) is performed on the switch during each equalization charge. Therefore, the power storage device has a simple device configuration, and accordingly it is possible to provide an inexpensive power storage device.
Also, it is preferable to minimize the difference in S0C between the strings after the end of the equalizing charge and before supplying the closing command to the plurality of switches. By reducing the S0C difference, it is possible to prevent the circulating current from becoming large after equalization charging.

Further, it is preferable to minimize the voltage difference between the strings after the equalization charging is completed and before supplying the close command to the plurality of switches. By reducing the voltage difference, it is possible to prevent the circulating current from becoming large after equalization charging.
The number of strings in each set is, for example, one. As a result, the charging power of the charging voltage can be reliably suppressed, and power peaks can be further suppressed.
Each time it is determined that equalization charging is to be performed, the selected one switch is selected in a preset order. This makes it possible to sequentially perform uniform charging for all strings.

It is a figure explaining the structure of the electrical storage apparatus which concerns on embodiment based on this invention. It is a figure explaining the structure of EMS which concerns on embodiment based on this invention. It is a figure explaining the structure of BMU which concerns on embodiment based on this invention. FIG. 10 is a diagram of a sequence example up to the start of equalizing charging; FIG. 4 is a diagram showing an example of a method for determining the start of equalizing charging; FIG. 4 is a diagram showing an example of a method for determining strings to be evenly charged; FIG. 4 is a diagram of a sequence example from the start of equalizing charge to the end of equalizing charge; FIG. 10 is a diagram showing an example of SOC difference in each string; FIG. 10 is a diagram of a sequence example of performing post-processing after the end of equalizing charging; FIG. 10 is a diagram illustrating an example of SOC difference adjustment processing; It is a figure which shows the example of adjustment processing of a pressure difference. It is a figure which shows the voltage transition example after equalization charge. FIG. 4 is a diagram showing an example of power consumption during equalization charging;

Next, embodiments of the present invention will be described with reference to the drawings.
Here, the same components will be described with the same reference numerals unless there is a reason for convenience. In addition, in each drawing, the thickness and ratio of each component may be exaggerated, and the number of components may be different from the actual product. In addition, the present invention is not limited to the following embodiments as they are, and can be embodied by appropriate combinations and modifications as long as they do not deviate from the gist of the invention. can be included in

(Constitution)
As shown in FIG. 1, the power storage device of this embodiment includes a storage battery group (S1-S4) including a plurality of bipolar lead-acid batteries, a PCS2, an EMS3, a BMU4, and assembled battery sensors 61-64. Further, the power storage device of the present embodiment has switches 51-54.
<Battery group>
The storage battery group consists of a plurality of strings S1-S4. In this embodiment, as shown in FIG. 1, the number of strings N is four. Each string S1 to S4 is composed of a storage battery train in which a plurality of bipolar lead-acid batteries are connected in series.

<PCS2>
The PCS2 is an AC/DC conversion device, and is composed of, for example, a PWM converter. The PCS 2 is provided between the commercial system 1 (external power system) and the storage battery group, and converts alternating current into direct current and vice versa. PCS2 is connected in parallel to a plurality of strings S1-S4.
<Battery Sensors 61-64>
The assembled battery sensors 61 to 64 are arranged for each of the strings S1 to S4, acquire information on the state of the storage battery array such as the voltage and current of the target strings S1 to S4, and supply the acquired information to the BMU4.

<Switches 51 to 54>
The switches 51-54 are interposed between the strings S1-S4 and the PCS2, respectively. Each of the switches 51-54 is opened or closed according to the signal from the BMU4. Each of the switches 51 to 54 assumes a closed state as an initial state.
A plurality of strings S1 to S4 may be classified into two or more sets, and a switch may be interposed between the strings S1 to S4 and the AC/DC converter for each set of strings.

<EMS3>
EMS3 (Energy Management System) is a device that controls PCS2 to control charging/discharging of a storage battery group. As shown in FIG. 2, the EMS 3 includes a charge/discharge operation control section 3A, an equal charge execution processing section 3B, and a normal charge/discharge execution processing section 3C.
The charge/discharge operation control unit 3A performs charge/discharge control required as processing of the PCS 2 based on commands from the equal charge implementation processing unit 3B or the normal charge/discharge implementation processing unit 3C. For example, the charging operation is performed by delaying the phase of the output voltage of the PCS2 from the system input voltage, and the discharging operation is performed by leading the phase of the output voltage.

The normal charging/discharging execution processing unit 3C is a processing unit that executes PCS control for normal charging/discharging of the storage battery group. In normal charging control, for example, the storage battery is charged in the process of preliminary charging, CC charging (constant current charging), and CV charging (constant voltage charging).
The equalization charge implementation processing unit 3B is a processing unit that executes PCS control for equalization charge processing in accordance with a command from the BMU 4 . In equalizing charging, the storage battery is charged in the process of CC charging or CP charging (constant power charging) and CV charging. Specifically, CC charging or CP charging is performed until the voltage of the storage battery to be equalized reaches the start threshold voltage, and when the voltage of the storage battery to be equalized reaches the start threshold voltage or higher, CV charging is performed.

<BMU4>
The BMU 4 (Battery Management Unit) is a device that manages (monitors) the states of the strings S1-S4 based on signals from the assembled battery sensors 61-64. BMU4 of this embodiment has the process for providing EMS3 with the information for equalization charge.
The BMU 4, as shown in FIG. 3, includes a normal battery management unit 4A, an equalization charge necessity determination unit 4B, an equalization charge implementation start processing unit 4C, and an equalization charge post-processing unit 4D.

The normal battery management unit 4A manages the states of the strings S1-S4 based on the signals from the assembled battery sensors 61-64, and provides the information to the EMS3. In addition, the normal battery management unit 4A supplies a protective cutoff signal to the switches 51 to 54 in the event of overcharge or overdischarge at the charge/discharge value, and temporarily opens the switches 51 to 54 for protection. control may be exercised.
The equalization charge necessity determination unit 4B determines whether equalization charge is necessary based on preset conditions. Well-known conditions may be adopted as the preset conditions. For example, the equal charging necessity determination is executed by the process shown in FIG.

The equalization charge necessity determination shown in FIG. 5 will be described. The process of FIG. 5 is for determining the number of days elapsed since the previous equalizing charge.
That is, in step S10, it is determined whether or not the number of days elapsed since the previous equalizing charge is equal to or greater than a preset threshold value. If the determination is satisfied, the process proceeds to step S11, and if the determination is not satisfied, the process proceeds to step S12.
In step S11, it is determined that the equalization charge is required, and the process proceeds to the equalization charge implementation start processing section 4C. When the equalization charge is completed and the post-processing is also completed, the counter is reset and the process returns to step S10.
In step S12, it is determined that equalization charging is unnecessary, and after a predetermined sampling time, the process returns to step S10, and the process of step S10 is repeated.

The equalization charge execution start processing unit 4C executes processing for starting equalization charge.
As shown in FIG. 3, the equalization charge implementation start processing unit 4C includes an equalization implementation string determination unit 4Ca, a switch control unit 4Cb, and an equalization charge command unit 4Cc.
The equalization execution string determination unit 4Ca determines the strings (number N of the strings S1 to S4) to be equalized in the current equalization charge process. When the equalization string determination unit 4Ca determines that equalization charging is to be performed for the storage battery group, the string to be equalized charging is selected in order from the plurality of strings S1 to S4 that make up the assembled battery group in a preset order. to run.

The switch control unit 4Cb supplies a closing command to one switch selected from the plurality of switches 51 to 54 before starting equalization charging based on the determination of the equalization string determination unit 4Ca, and also supplies the closing command to the other switches. supply an open command to the
The processing of the equal implementation string judgment section 4Ca and the switch control section 4Cb is executed by the method shown in FIG. 6, for example. That is, serial numbers are assigned in advance to a plurality of strings S1 to S4. Then, in step S20, the number N of the string for which equalization was performed last time is obtained.

Next, in step S21, 1 is added to the string number N, and N is reset to 1 when the number N exceeds the maximum number of strings (4 in this example).
Next, in step S22, an open command is supplied to the switches 51-54 provided for the strings S1-S4 other than the string number N.
The equalizing charge command unit 4Cc supplies the equalizing charge command value to the EMS 3 after the processing of the switch control unit 4Cb is completed. EMS3 will perform equalization charge processing, if an equalization charge command value is input. Note that the equalizing charge command value includes a set voltage for equalizing charging (threshold value for switching to CV charging).

Further, when the equalizing charge command unit 4Cc determines that the equalizing charge is completed based on the detection values of the assembled battery sensors 61 to 64 of the strings S1 to S4 that are being equalized and charged, it notifies the EMS 3 to stop the equalizing charge.
For example, a termination condition is set such that the CV charging time is equal to or greater than a threshold value, the charging current is equal to or less than the threshold value, or the charging rate is equal to or greater than the threshold value.

The post-equalization charge processing unit 4D is activated when it is determined that the equalization charge is completed based on the equalization charge command value, and executes post-equalization charge processing.
The post-equalization charge processing unit 4D includes an SOC adjustment unit 4Da, a voltage difference adjustment unit 4Db, and a switch reconnection unit 4Dc.
The SOC adjustment unit 4Da reduces (for example, minimizes) the difference in S0C between the strings S1 to S4 after the current equalization charge is completed and before closing the switches 51 to 54 that were in the open state. Execute the process.

For example, when equalization charging is performed on string S1, as shown in FIG. 8, only the SOC of string S1 increases, resulting in a state in which the difference from the SOCs of the other strings S2 to S4 is large. In this state, if the strings are connected by closing all the switches 51 to 54, a large circulating current may flow between the strings S1 to S4. In order to prevent this, the processing of the SOC adjuster 4Da is executed.
Note that the SOCs of the strings S2 to S4 other than the string S1 that has undergone the equalization charge are generally substantially the same.

The SOC adjuster 4Da obtains the SOC difference between the string S1 that has been evenly charged and the other strings S2 to S4 based on the signals from the assembled battery sensors 61 to 64, and if the SOC difference is less than the threshold, adjusts the SOC. The process of part 4Da ends. On the other hand, when it is determined that the SOC difference is greater than or equal to the threshold value, the EMS 3 is sequentially supplied with adjustment discharge commands necessary for minimizing the SOC difference.
FIG. 10 shows a processing example of the SOC adjustment unit 4Da. The process of FIG. 10 is executed at a predetermined sampling period after the adjustment discharge command is supplied to the EMS 3. First, in step S30, the SOC of the string S1 that has undergone the equalizing charge and the SOC of the strings S2 to S4 other than that are determined. The SOC difference, which is the difference from the average value, is obtained. If the SOC difference is equal to or less than the determination threshold, the process proceeds to step S32. On the other hand, when it is determined that the SOC difference is larger than the determination threshold value, the process proceeds to step S31.

The determination threshold for adjusting the SOC difference is obtained by, for example, the following formula.
Judgment threshold [%] = allowable current × internal resistance × safety factor / SOC difference voltage conversion value For example, the conditions for each storage battery group (S1 to S4) are
・Allowable current: 100 [A]
・Storage battery group S1 internal resistance 20 [mΩ]
・Safety factor: 0.8
・SOC difference voltage conversion value: 0.2 [V]/SOC1 [%]
in the case of,
Judgment threshold = allowable current x internal resistance x safety factor/SOC difference voltage conversion value = 100 [A] x 20 [mΩ] x 0.8/0.2 [V/%]
= 8 [%]
becomes.

In step S31, a continuation command of adjustment discharge is supplied to EMS3, and it transfers to step S30.
On the other hand, in step S32, an adjustment discharge end signal is supplied to the EMS 3, and the processing of the SOC adjustment unit 4Da is ended.
The voltage difference adjustment unit 4Db executes a process of minimizing the voltage difference between the strings S1 to S4 after the current equalization charge is completed and before closing the switches 52 to 54 that were in the open state. In this embodiment, the voltage difference adjuster 4Db executes after the processing of the SOC adjuster 4Da.

The voltages of the string S1 (the number of strings N) subjected to the equalizing charge and the other strings S2 to S4 show voltage transitions as shown in FIG. 12 over time from the end of the equalizing charge. At this time, if all the strings S1 to S4 are connected to the PCS2 while the voltage difference between the strings S1 to S4 is large, a large circulating current flows. Therefore, the voltage difference adjustment unit 4Db executes processing to wait until the voltage difference falls within the threshold range.
When the switch reconnection unit 4Dc determines that the processing of the voltage difference adjustment unit 4Db is completed, it supplies a close command to all the switches 51-54. As a result, normal charge/discharge processing (normal operation) is resumed.

FIG. 11 shows a processing example of the voltage difference adjustment unit 4Db and the switch reconnection unit 4Dc.
In FIG. 11, first, in step S40, based on the detection values of the assembled battery sensors 61 to 64, the average value of the voltage of the string S1 (the number of strings N) that has been equally charged this time and the voltage of the other strings S2 to S4. , and it is determined whether or not the determined voltage difference is equal to or less than the determination threshold. If the obtained voltage difference is equal to or less than the determination threshold, the process proceeds to step S42. If the obtained voltage difference is greater than the determination threshold, the process proceeds to step S41.

The determination threshold value for adjusting the voltage difference is obtained by, for example, the following formula.
Judgment threshold [V] = allowable current x internal resistance x safety factor For example, the condition for each storage battery group (S1 to S4) is
・Allowable current: 100 [A]
・Storage battery group S1 internal resistance 20 [mΩ]
・Safety factor: 0.8
in the case of,
Judgment threshold = allowable current x internal resistance x safety factor = 100 [A] x 20 [mΩ] x 0.8
= 1.6 [V]
becomes.

In step S41, it is determined that reconnection is impossible, and after a predetermined sampling time, the process proceeds to step S40.
In step S42, the closing command is supplied to all the switches 51 to 54 in the processing of the switch reconnection unit 4Dc, and the processing of the voltage difference adjustment unit 4Db and the switch reconnection unit 4Dc is terminated.
4, 7, and 9 show examples of sequence diagrams relating to the equalization charging based on the present embodiment.
The sequence diagram of FIG. 4 is a sequence diagram showing an example of the determination of the need to start equalizing charging and the processing at the time of starting equalizing charging. That is, it is a sequence diagram for performing the processes of the equalization charge necessity determination unit 4B and the equalization charge implementation start processing unit 4C.

FIG. 7 is a sequence diagram from the start of equalizing charge to SOC adjustment control after the end of equalizing charge.
FIG. 9 is a sequence diagram from SOC adjustment control to return to normal operation.
Here, EMS3 comprises a charge/discharge control part. BMU4 comprises a storage battery management part. Also, the configuration of each device may not be the processing configuration described above.

(Other operations)
In this embodiment, equalization charging is performed only for a specific set of strings during each equalization charging process. For this reason, it is possible to reduce the power and amount of power required for each equalization charge. Furthermore, inexpensive switches 51 to 54 are provided for each set of strings S1 to S4, and simple opening/closing control (opening/closing control only at the start and end of equalization control) is performed for each equalization charge. is. As a result, the power storage device has a simple device configuration, and accordingly it is possible to provide an inexpensive power storage device.

Here, lead-acid batteries, including bipolar batteries, require periodic equalization charging. However, if equal charging is performed for the entire storage battery group, power consumption will increase and power peaks may occur, as in the case of equal charging with four strings in FIG. 13 . On the other hand, in the present embodiment, by equalizing charging only one string or a part of the strings, the power consumption can be brought closer to the power consumption during normal operation without equalizing charging, as in the case of equalizing charging with one string in FIG. be able to. Therefore, in this embodiment, it is possible to suppress the power and the amount of power required for equalization charging. Note that the number of strings for which each equalization charge is performed need not be one. All the strings S1 to S4 may be classified into a plurality of groups, and equal charging may be performed for each of the strings S1 to S4 of each group.

Equalization charging may be set at a time when normal operation (power demand) is low, as shown in FIG.
Further, when the SOC difference or voltage difference between the strings S1 to S4 is large, if the strings S1 to S4 are electrically connected, the circulating current becomes a large current, which may damage the equipment.
On the other hand, in the present embodiment, a process of reducing the SOC difference and voltage difference between the strings S1 to S4 is executed as the post-processing of the equalization charging. As a result, when the equalization charging operation returns to the normal operation, the circulating current is prevented from becoming large, and the equipment is prevented from being damaged.

Also, if the number of strings for which each equalization charge is executed is 1, the charging power of the charging voltage required for each equalization charge can be minimized, and power peaks can be suppressed more reliably. becomes.
In addition, each time it is determined that equalization charging is to be performed, the selected one of the switches 51 to 54 is selected in a preset order, whereby equalization charging can be performed in order for all the strings S1 to S4. becomes.

(others)
The present disclosure can also take the following configuration.
(1) A storage battery group having a plurality of strings each composed of a storage battery train in which a plurality of storage batteries are connected in series, an AC/DC converter electrically connecting the storage battery group and an external power system, and managing the state of each string. A power storage device comprising: a storage battery management unit; and a charge/discharge control unit that controls the AC/DC converter based on a command from the storage battery management unit, wherein the plurality of strings are classified into two or more sets, each A plurality of switches interposed between the set of strings and the AC/DC converter, and when it is determined that equal charging is to be performed for the storage battery group, switches other than the switch selected from the plurality of switches are selected. and a switch reconnection unit that supplies a close command to the plurality of switches when it is determined that the equalization charge is completed.

(2) An SOC adjustment unit is provided for reducing the SOC difference between the strings after the equalization charge is completed and before the close command is supplied to the plurality of switches by the switch reconnection unit.
(3) A voltage difference adjustment section is provided for reducing the voltage difference between strings after the equalization charge is completed and before the close command is supplied to the plurality of switches by the switch reconnection section.
(4) The number of strings in each set is one.
(5) The switch control unit sequentially selects the selected one switch from the plurality of switches in a preset order each time it determines that equalization charging is to be performed.

(6) An equalizing charging method for equalizing charging a storage battery group having a plurality of strings composed of a series of storage battery trains by using an AC/DC converter, wherein the plurality of strings are combined into two or more groups. , each set of strings is connected to the AC/DC converter via an individual switch, and one switch selected from the plurality of switches when performing equal charging of the storage battery group is closed, and when it is determined that the equalization charge is completed, all of the plurality of switches are closed.

(7) After the equalizing charge is completed, before closing all of the plurality of switches, a process for reducing the SOC difference between the strings is performed.
(8) After the equalization charge is completed, a process for reducing the voltage difference between the strings is performed before closing all of the plurality of switches.
(9) The number of strings in each set is one.
(10) Each time it is determined that equalization charging is to be performed, the selected one switch is sequentially selected from the plurality of switches in a preset order.

Here, the entire contents of Japanese Patent Application 2021-057385 (filed on March 30, 2021), to which this application claims priority, constitute a part of this disclosure by reference. Although described herein with reference to a limited number of embodiments, the scope of rights is not limited thereto, and modifications of each embodiment based on the above disclosure will be obvious to those skilled in the art.

1 Commercial system 2 PCS (AC/DC converter)
3 EMS
3A Charge/discharge operation control unit 3B Equal charge implementation processing unit 3C Normal charge/discharge implementation processing unit 4 BMU (battery management unit)
4A Normal battery management unit 4B Equalization charge necessity determination unit 4C Equalization charge execution start processing unit 4Ca Equalization execution string determination unit 4Cb Switch control unit 4Cc Equalization charge command unit 4D Equalization charge post-processing unit 4Da SOC adjustment unit 4Db Voltage difference adjustment unit 4Dc Switch reconnection parts 51 to 54 Switches 61 to 64 Battery pack sensor N String number S1 to S4 String (storage battery group)

Claims

a storage battery group having a plurality of strings composed of storage battery strings in which a plurality of storage batteries are connected in series;
an AC/DC converter that electrically connects the storage battery group and an external power system;
a storage battery management unit that manages the state of each string;
a charge/discharge control unit that controls the AC/DC converter based on a command from the storage battery management unit,
a plurality of switches that classify the plurality of strings into two or more sets and are interposed between each set of strings and the AC/DC converter;
a switch control unit that supplies an open command to switches other than one switch selected from the plurality of switches when it is determined that the storage battery group is to be uniformly charged;
a switch reconnection unit that supplies a close command to the plurality of switches when it is determined that the equalization charge has ended;
power storage device.
After the equalization charge is completed, before supplying a closing command to the plurality of switches at the switch reconnection unit, an SOC adjustment unit that reduces the difference in SOC between the strings,
The power storage device according to claim 1 .
a voltage difference adjustment unit that reduces the voltage difference between the strings after the equalization charge is completed and before supplying the closing command to the plurality of switches at the switch reconnection unit;
The power storage device according to claim 1 or 2.
The number of strings in each set is 1,
The power storage device according to any one of claims 1 to 3.
The switch control unit sequentially selects the selected one switch from the plurality of switches in a preset order each time it is determined that equalization charging is performed.
The power storage device according to any one of claims 1 to 4.
An equalizing charging method for equalizing charging a storage battery group having a plurality of strings consisting of a plurality of storage battery rows in which a plurality of storage batteries are connected in series using an AC/DC converter,
Classifying the plurality of strings into two or more sets, connecting each set of strings to the AC/DC converter via an individual switch,
When performing equal charging for the storage battery group, only one switch selected from the plurality of switches is closed,
When it is determined that the equalization charge has ended, all of the plurality of switches are closed,
Equal charging method.
After equalization charging is completed, before closing all of the plurality of switches, processing is performed to reduce the difference in SOC between the strings.
The equal charging method according to claim 6.
After equalization charging is completed, before closing all of the plurality of switches, processing is performed to reduce the voltage difference between the strings.
The equal charging method according to claim 6 or 7.
The number of strings in each set is 1,
The equal charging method according to any one of claims 6 to 8.
Each time it is determined that equalization charging is to be performed, the selected one switch is selected in order from the plurality of switches in a preset order,
The equal charging method according to any one of claims 6 to 9.