阅读说明：本技术 管理装置、蓄电装置以及蓄电系统 (Management device, power storage device, and power storage system ) 是由 井上朋重 道永胜久 吉冈孝兼 池田隆志 濑户康太 于 2018-04-27 设计创作，主要内容包括：本发明提供一种管理装置、蓄电装置以及蓄电系统。管理装置(21)具备：主控制部(23),在被串联连接的多个蓄电元件(41)的充电中任意蓄电元件(41)的单电池电压成为第1阈值以上的情况下,对转换器(11)输出第1下拉信号以使得降低充电电压。(The invention provides a management device, a power storage device, and a power storage system. A management device (21) is provided with: when the cell voltage of any power storage element (41) becomes equal to or greater than the 1 st threshold value during charging of a plurality of power storage elements (41) connected in series, a main control unit (23) outputs a 1 st pull-down signal to the converter (11) so as to reduce the charging voltage.)

1. A management device is provided with:

the control unit notifies the charger of a pull-down of a charging voltage when a voltage of any of the plurality of power storage elements connected in series becomes equal to or higher than a 1 st threshold value during charging of the power storage elements.

2. The management device according to claim 1,

the charger controls charging in accordance with a total voltage of the plurality of electrical storage elements.

3. The management apparatus according to claim 1 or 2, wherein,

The control unit performs a step-down notification to the charger to further lower the charging voltage when the voltage of any of the power storage elements is equal to or higher than the 1 st threshold after the charging voltage is pulled down.

4. The management device according to claim 3,

The control unit performs the step pull-down notification a plurality of times to decrease the charging voltage in multiple steps.

5. The management device according to any one of claims 1 to 4,

The electricity storage element includes:

A low variation region in which a rate of change of an open circuit voltage with respect to a state of charge is relatively low; and

a high change region of a high charge state which is a high charge state compared to a charge state of the low change region and in which a rate of change of an open circuit voltage with respect to the charge state is relatively high compared to the low change region,

The 1 st threshold includes the high change region in the high charge state.

6. the management device according to any one of claims 1 to 5,

The control unit notifies the charger of a return of the charging voltage to an initial value when the voltages of all the power storage elements are equal to or lower than a 2 nd threshold value.

7. The management device of claim 6,

The control unit performs processing for notifying an abnormality when the charger repeats adjustment of the charging voltage a predetermined number of times or for a predetermined time or longer.

8. The management device according to any one of claims 1 to 5,

The control unit performs a return notification to return the charging voltage of the charger to an initial value when a voltage difference between the plurality of power storage elements is a predetermined value or less.

9. The management device of claim 8,

The control unit performs processing for notifying an abnormality when the state in which the charging voltage is pulled down continues for a predetermined time or longer.

10. The management device according to any one of claims 1 to 9,

Comprising: a discharge circuit that individually discharges the electric storage elements,

The control unit discharges only the electric storage element having a voltage equal to or higher than a 3 rd threshold value by the discharge circuit.

11. An electricity storage device is provided with:

One or a plurality of electricity storage blocks connected in series; and

The management device according to any one of claims 1 to 10,

The electricity storage block has a plurality of the electricity storage elements connected in series.

12. An electricity storage system is provided with:

A charger;

The power storage device according to claim 11; and

A charging path connecting the charger and the power storage device.

13. The power storage system according to claim 12,

The charger controls charging according to a total voltage of the electrical storage device.

14. The power storage system according to claim 12 or 13,

The charger pulls down the charging voltage from an initial value in response to the pull-down notification,

The pulled-down charge voltage is converted into a voltage of each of the storage elements and included in the high change region of the high charge state.

15. The power storage system according to any one of claims 12 to 14,

The charging path is not provided with a charging control circuit for controlling charging of the power storage device.

16. The power storage system according to any one of claims 12 to 14,

the disclosed device is provided with:

the power storage device is connected to a power supply line that supplies power from a main power supply to a load via a branch line; and

A power converter provided at the branch line,

the power converter is a bidirectional power converter that converts a part of electric power supplied from a main power supply to output a charging current to the power storage device and converts electric power supplied from the power storage device to output a discharging current to the load,

The control unit notifies the power converter of the pull-down for lowering the charging voltage when a voltage of any of the power storage elements of the power storage device becomes equal to or higher than the 1 st threshold.

Technical Field

the technology disclosed in the present specification relates to a technology for charging a plurality of power storage elements connected in series.

Background

In a battery pack in which a plurality of power storage elements are connected in series, the cell voltage (state of charge) varies due to a difference in characteristics. When the variation in the cell voltage (state of charge) is large, the voltage of some of the power storage elements may rise as compared to other power storage elements during charging. Patent document 1 describes that charging is interrupted when the voltage of some of the power storage elements exceeds a set value during charging.

Prior art documents

Patent document

Patent document 1: japanese laid-open patent publication No. 4-331425

Disclosure of Invention

Problems to be solved by the invention

The present specification addresses the problem of suppressing the electric storage element from exceeding the protection voltage during charging, thereby enabling continuous charging.

Means for solving the problems

The management device is provided with: the control unit notifies the charger of a pull-down of a charging voltage when a voltage of any of the plurality of power storage elements connected in series becomes equal to or higher than a 1 st threshold value during charging of the power storage elements.

Effects of the invention

The control unit performs pull-down notification to the charger when the voltage of any of the power storage elements is equal to or higher than the 1 st threshold. If the charger receives the pull-down notification, the charging voltage is decreased. By reducing the charging voltage, it is possible to suppress a voltage increase of the power storage element that is equal to or greater than the 1 st threshold value, as compared with a case where the charging voltage is not reduced. Therefore, the storage element can be prevented from exceeding the protection voltage, and the charging can be continued.

Drawings

fig. 1 is a block diagram showing an electrical configuration of a UPS in embodiment 1.

fig. 2 is a circuit diagram of a discharge circuit.

fig. 3 is a graph showing the SOC-OCV correlation of the battery pack.

Fig. 4 is a flowchart of the voltage management process.

Fig. 5 is a diagram showing changes in cell voltage of the storage element, cell voltage of the battery pack, and charging current in constant-current constant-voltage charging.

Fig. 6 is a diagram showing charging characteristics in the case where the charging voltages are different.

Fig. 7 is a diagram showing charging characteristics in a case where the charging voltage is included in the low variation region.

Fig. 8 is a diagram showing a charging characteristic in a case where the charging voltage is pulled down halfway.

Fig. 9 is a flowchart of the charging voltage recovery process.

Fig. 10 shows a waveform of a cell voltage of the storage element and a waveform of a charging current.

fig. 11 shows a waveform of a cell voltage of the electric storage element and a waveform of a charging current.

Fig. 12 is a waveform of a cell voltage of the electric storage element, a waveform of a cell voltage of the battery pack, and a waveform of a charging current.

Fig. 13 is an enlarged view of a main portion of fig. 10.

Fig. 14 is a flowchart of the voltage management processing in embodiment 2.

Fig. 15 is a view corresponding to fig. 4 in embodiment 2.

Fig. 16 is a block diagram showing an electrical configuration of a UPS according to embodiment 3.

Fig. 17 shows a waveform of a charging voltage of the converter and a voltage waveform of the storage element.

Fig. 18 shows a waveform of a charging voltage of the converter and a voltage waveform of the storage element.

Fig. 19 shows a waveform of a charging voltage of the converter and a voltage waveform of the storage element.

Fig. 20 is a block diagram showing an electrical configuration of a UPS according to embodiment 4.

fig. 21 is a block diagram showing an electrical configuration of a UPS according to another embodiment.

Fig. 22 is a diagram of a UPS showing another charging control method.

Detailed Description

(outline of the present embodiment)

The management device is provided with: the control unit notifies the charger of a pull-down of a charging voltage when a voltage of any of the plurality of power storage elements connected in series becomes equal to or higher than a 1 st threshold value during charging of the power storage elements.

When a plurality of power storage elements are connected in series, if the voltage (state of charge) of each power storage element varies greatly, the voltage of the power storage element having a high voltage rises sharply when charged by the charger.

The present inventors have studied whether or not a voltage increase in some of the power storage elements can be suppressed when a plurality of power storage elements are charged.

As a result of the study, the present inventors have conceived to reduce the charging voltage of the charger when the voltage of any power storage element becomes equal to or higher than the 1 st threshold. By reducing the charging voltage, it is possible to suppress a voltage increase of the power storage element that is equal to or greater than the 1 st threshold value, as compared with a case where the charging voltage is not reduced. Therefore, the electric storage element can be suppressed from exceeding the protection voltage. Charging can be continued while suppressing occurrence of a failure in the power storage element.

with regard to the plurality of electric storage elements, the charger may control charging in accordance with a total voltage of the plurality of electric storage elements, without finely controlling charging using a voltage of each electric storage element so that a voltage of an electric storage element having a highest voltage becomes fixed.

When the voltages (states of charge) of the respective power storage elements vary, if the total voltage of the plurality of power storage elements is monitored and charging is performed, the voltage of the power storage element having the highest voltage may rise and exceed the protection voltage. When the voltage of any of the power storage elements is equal to or higher than the 1 st threshold, the charging voltage is reduced, whereby it is possible to suppress the voltage of the power storage element having the highest voltage from rising and the voltage of the power storage element from reaching the protection voltage.

The control unit may be configured to perform a step-down notification to the charger to further lower the charge voltage, when the voltage of the power storage element is equal to or higher than the 1 st threshold after the pull-down of the charge voltage. The control unit may perform the step pull-down notification a plurality of times to decrease the charging voltage in multiple steps. By performing the pull-down notification from the control unit to the charger, the charging voltage drops, and the voltage of the power storage element can be prevented from temporarily reaching the protection voltage. When the voltage of the storage element becomes equal to or higher than the 1 st threshold again after the pull-down of the charging voltage, the control unit notifies the charger of the step-down, and further lowers the charging voltage. This operation is performed over a plurality of times, so that the voltage of the electric storage element can be suppressed from reaching the protection voltage.

the power storage element may include: a low variation region in which a rate of change of an open circuit voltage with respect to a state of charge is relatively low; and a high change region of a high charge state which is a high charge state compared to a charge state of the low change region and in which a change rate of an open circuit voltage with respect to the charge state is relatively high compared to the low change region, the 1 st threshold being included in the high change region of the high charge state.

The higher the charging voltage, the faster the charging speed in the electric storage element. The present inventors tried to charge a storage element with a high voltage by setting the 1 st threshold to a voltage included in a high change region of a high charge state until the voltage of any storage element becomes the 1 st threshold or more. A method has been found in which, after the voltage of any of the storage elements becomes equal to or higher than the 1 st threshold, a notification is sent to the charger to pull down the charging voltage, thereby lowering the charging voltage. This can shorten the charging time as compared with the case where the charging voltage is reduced from the beginning. In the high variation region, the charge capacity variation ratio with respect to the variation of the open circuit voltage is smaller than in the low variation region. Therefore, as compared with the case where the 1 st threshold is included in the low variation region, the state of charge of the power storage element can be maintained at the high state of charge while the voltage of the power storage element is reduced.

the control unit may perform a return notification to return the charging voltage of the charger to an initial value when the voltages of all the power storage elements are equal to or lower than a 2 nd threshold value.

by recovering the charging voltage, the charging speed of the power storage element can be accelerated. In addition, when the discharged battery pack is recharged, the plurality of power storage elements can be charged at a normal charging voltage, and the charging time can be shortened.

The control unit may notify an abnormality when the charger repeats the adjustment of the charging voltage a predetermined number of times or for a predetermined time or longer. By notifying the abnormality, it is possible to suppress the power storage device that is not suitable for use from being continuously used.

The control unit may be configured to perform a return notification to return the charging voltage of the charger to an initial value when a voltage difference between the plurality of power storage elements is equal to or less than a predetermined value.

By recovering the charging voltage, the charging speed of the power storage element can be accelerated. In addition, when the discharged battery pack is recharged, the plurality of power storage elements can be charged at a normal charging voltage, and the charging time can be shortened.

The control unit may notify an abnormality when the state in which the charging voltage is pulled down continues for a predetermined time or more. By notifying the abnormality, it is possible to suppress the power storage device that is not suitable for use from being continuously used.

The control unit may include a discharge circuit that discharges the power storage elements individually, and the control unit may discharge the power storage elements having a voltage equal to or higher than a 3 rd threshold value by the discharge circuit. The charging voltage is reduced by the charger and the electric storage element is discharged by the discharging circuit, so that the voltage rise of the electric storage element having a value equal to or higher than the 3 rd threshold can be further suppressed. Instead of using the 3 rd threshold, the discharge circuit may discharge the electric storage elements so that the voltage difference is smaller than the 4 th threshold when the difference between the voltage of each electric storage element and the lowest voltage is equal to or greater than the 4 th threshold.

The power storage device includes one or a plurality of power storage blocks connected in series, each of the power storage blocks having a plurality of the power storage elements connected in series, and a management device.

The power storage system is provided with a charger, the power storage device, and a charging path connecting the charger and the power storage device.

With regard to the plurality of power storage elements, the charger may control charging in accordance with a total voltage of the power storage device, without finely controlling charging using a voltage of each power storage element so that a voltage of a power storage element having a highest voltage becomes constant.

The charger may pull down the charge voltage from an initial value in response to the pull-down notification, and the pulled-down charge voltage may be converted into a voltage of each of the power storage elements and included in the high change region of the high charge state.

Since the charge voltage after the pull-down is converted into the voltage of each storage element and included in a high change region in the high charge state, the charge time can be shortened even after the charge voltage is lowered.

The charging path may not include a charging control circuit for controlling charging of the power storage device. The charging voltage can be controlled without using a charging control circuit, and the number of components can be reduced.

The power storage system includes: the power converter includes a power storage device connected to a power supply line for supplying electric power from a main power supply to a load via a branch line, and a power converter provided in the branch line, wherein the power converter is a bidirectional power converter that converts a part of the electric power supplied from the main power supply to output a charging current to the power storage device and converts the electric power supplied from the power storage device to output a discharging current to the load, and the control unit notifies the power converter of the pull-down for lowering the charging voltage when a voltage of any of the power storage elements of the power storage device becomes equal to or higher than the 1 st threshold. The charging can be controlled without stopping the power converter.

The charging method comprises the following steps: a step of performing pull-down notification from a management device of an electric storage element to a charger when a voltage of any electric storage element becomes a 1 st threshold or more during charging of a plurality of electric storage elements connected in series; and a step of lowering the charging voltage by the charger.

(embodiment mode 1)

Embodiment 1 disclosed in the present specification is explained with reference to fig. 1 to 13.

the present embodiment exemplifies an uninterruptible power supply (hereinafter, also referred to as "UPS") 10 installed in facilities such as buildings, stations, and hospitals. As shown in fig. 1, the UPS10 includes: a power supply line 15 for connecting a load 70 installed in a building or a factory, not shown, to an ac power supply 80, a converter (an example of a "charger") 11, an inverter 12, and a power storage device 20. The converter 11 and the inverter 12 are provided on the power supply line 15. The uninterruptible power supply 10 corresponds to a power storage system.

The UPS10 is an inverter-always-on UPS. The UPS10 converts the electric power output from the ac power supply 80 from ac to dc by the converter 11, and supplies the converted electric power to the inverter 12. The inverter 12 converts the electric power supplied from the converter 11 from a direct current to an alternating current and supplies the converted electric power to the load 70.

A part of the dc current output from the converter 11 is supplied to the power storage device 20 as a charging current. The power storage device 20 is charged by the charging current from the converter 11.

converter 11 controls charging of power storage device 20 with the total voltage. The charging control based on the total voltage is a charging control for maintaining the total voltage of power storage device 20 at a target value, and control corresponding to the voltage of each power storage element 41, such as maintaining the highest cell voltage of power storage element 41 constant, is not performed. The total voltage of the power storage device 20 is the sum (total voltage) of the voltages of the plurality of power storage elements 41 connected in series. In power storage device 20, 5 power storage blocks 30 are connected in series, and each power storage block 30 has 4 power storage elements 41 connected in series. Therefore, the power storage device 20 is the sum of the voltages of the 20 power storage elements 41 connected in series.

The converter 11 will be described about the control of charging the power storage device 20. Converter 11 receives information on the total voltage, information on the capacity such as the SOC, and information on the voltage of each power storage element 41 from power storage device 20. When the remaining capacity of the power storage device 20 is small, the converter 11 performs constant-current charging control on the power storage device 20. With the constant-current charging control, if the total voltage of the electrical storage device 20 reaches a given value, switching is made to constant-voltage charging control (charging control based on the total voltage) so that the total voltage of the electrical storage device 20 is maintained at a target value. Hereinafter, the voltage of each power storage element (single cell) is referred to as a cell voltage.

In the constant-voltage charging control, an initial value Yo of a charging voltage Y of the converter 11 (an output voltage of the converter) is expressed by the following expression (1).

Yo＝Vsel×N……(1)

vsel is a target cell voltage for charging the power storage device 41, and is 3.5[ V ] as an example. N is the number of series-connected storage elements 41, and is 20 as an example. The initial value Yo of the charging voltage Y is, for example, 3.5 × 20[ V ].

the power storage device 20 is float-charged, and even if the charging current becomes almost zero at the charging voltage Y, the converter 11 maintains the charging state of the power storage device 20 by continuing the constant-voltage charging control. The total voltage of the power storage device 20 is maintained at the charging voltage Y as a target value by constant voltage charging control. Although the converter 11 has a function of stopping charging when the cell voltage of the power storage element 41 exceeds the protection voltage during charging, it is not preferable to stop charging.

The power storage device 20 includes: 5 power storage blocks 30 connected in series, a battery management apparatus (hereinafter referred to as "BMU") 21 that manages the plurality of power storage blocks 30, and a switch 22. The power storage device 20 is connected to the power supply line 15 via a branch line 16. The power supply line 15 and the branch line 16 are a charging path and a discharging path of the power storage device 20. The power storage device 20 is charged by the charging current from the converter 11. The charging current is supplied from the converter 11 to the power storage device 20 via the power supply line 15 and the branch line 16. When ac power supply 80 fails to supply electric power due to an abnormality, power storage device 20 supplies electric power to load 70 via inverter 12. The battery management device 21 corresponds to a management device.

The switch 22 is a normally closed relay. The switch 22 is provided to cut off the power storage device 20 from the power supply line 15 when the use of the power storage device 20 needs to be prohibited, for example, when the power storage element 41 exceeds a protection voltage.

Each power storage block 30 includes a battery pack 40 in which a plurality of (4 in the present embodiment) power storage elements 41 are connected in series, a discharge circuit 31, a battery monitoring device (hereinafter referred to as "CMU") 32, a current sensor, a temperature sensor, and the like (not shown).

the storage element 41 is a lithium ion cell using a negative electrode active material of a graphite material such as graphite, graphitizable carbon, or graphitizable carbon, and a positive electrode active material of an iron phosphate system such as lithium iron phosphate. The battery pack 40 as a lithium ion battery is 4 storage elements 41 connected in series. In the power storage device 20, 5 battery packs 40 are connected in series, and 20 total power storage elements 41 are connected in series.

The storage element 41, which is a lithium ion battery cell, has a correlation (hereinafter referred to as "SOC-OCV correlation") shown in fig. 3 between an Open Circuit Voltage (OCV) and a State Of Charge (SOC). In the SOC-OCV correlation in which the X axis is SOC [% ] and the Y axis is OCV, the range of SOC of 30 to 95% is a flat low variation region F in which the variation amount of OCV with respect to the variation amount of SOC is smaller than a given value, as shown in fig. 3. The low variation region F is a region in which the OCV varies by less than 2 to 6[ mV ] with respect to a 1 [% ] change in SOC.

The range in which the SOC is 95% or more and the range in which the SOC is 30% or less are high variation regions S in which the variation amount of OCV with respect to the variation amount of SOC is relatively higher than low variation regions F. A region of high state of charge (region of SOC of 95% or more) having a SOC greater than that of the low change region F (range of SOC of 30 to 95%) among the high change region S is set as the 1 st high change region S1. A low state of charge region (region having an SOC of 30% or less) having an SOC smaller than that of the low change region F (range having an SOC of 30 to 95%) among the high change region S is set as the 2 nd high change region S2. The 1 st and 2 nd high variation regions S1 and S2 are regions in which the OCV varies by 2 to 6 mV or more with respect to 1 [% ] change in SOC, for example. As shown in fig. 3, the 1 st high variation region S1 is a region in which the cell voltage is about 3.35V or more. The 1 st high variation region S1 is a high variation region of a high charge state.

SOC＝Cr/Co×100··········(2)

Co is the full charge capacity of the power storage device, and Cr is the remaining capacity of the power storage device.

As shown in fig. 1 and 2, the discharge circuit 31 is provided for each power storage element 41. The discharge circuit 31 is a circuit in which a discharge resistor R and a discharge switch SW are connected in series. Each discharge circuit 31 is connected in parallel to each power storage element 41. The discharge circuit 31 switches the discharge switch SW from open to closed in accordance with an instruction from the CMU32, thereby discharging the electric storage elements 41 individually.

The CMU32 has a voltage detection circuit 33 and a sub control unit 34. The voltage detection circuit 33 measures the cell voltage of each power storage element 41 and the cell voltage of the assembled battery 40 (the total voltage of 4 power storage elements 41), and outputs the cell voltage and the cell voltage to the sub-control unit 34. The sub-control unit 34 switches the discharge switch SW of the discharge circuit 31, and outputs the measurement values of the cell voltage of each power storage element 41 and the cell voltage of the battery pack 40 to the BMU 21.

The BMU21 is communicably connected to the converter 11 via the 1 st communication line 51. The BMU21 is communicably connected to the CMU32 of each power storage block 30 via the 2 nd communication line 52. Various communication methods such as CAN, LIN, RS232C, and RS485 CAN be adopted for communication between the BMU21 and the converter 11 and communication between the BMU21 and the CMU 32.

the BMU21 includes a main control unit 23. The main control unit 23 is an example of a control unit. The main control unit 23 monitors the output of the CMU32 from each power storage block 30. When the voltage of any power storage element 41 of the power storage device 20 exceeds the protection voltage, the BMU21 sends a signal to the switch 22 to switch the switch 22 from closed to open. By switching the switch 22, the power storage device 20 is cut off from the power supply line 15, and a failure of the power storage element 41 (the battery pack 40) is prevented. The protection voltage is a cell voltage at which there is a possibility of a failure in the power storage element 41 and it is desirable to prohibit the use of the power storage element 41. The protection voltage is 4.0[ V ] as an example.

The main control unit 23 performs the equalization process when there is a variation in voltage between the storage elements 41. The equalization process is a process of discharging the high-voltage power storage element 41 by the discharge circuit 31. The voltage difference between the respective power storage elements 41 is reduced by the equalization process to equalize the variation in the charge capacity between the power storage elements 41. The equalization process can be performed for each power storage block 30.

lithium ion cells, unlike lead storage batteries, are prone to cell voltage rise under high state of charge (high SOC). The following problems arise when the converter 11 controls the charging of the power storage device 20 with the total voltage of the power storage device 20 without finely controlling the charging using the cell voltage of each power storage element 41 so that the cell voltage of the power storage element having the highest voltage is constant. Even if the total voltage of power storage device 20 maintains charging voltage Y, a voltage difference exists between power storage elements 41, and the cell voltage of some of power storage elements 41 may increase compared to the assumed cell voltage. In particular, when the variation in cell voltage (state of charge) between the power storage elements 41 is large, the cell voltage of the power storage element 41 having a high charge rate may suddenly increase in the range of the 1 st high variation region S1 in the last stage of charging. In order to eliminate the cell voltage variation between the storage elements 41, even if the equalization process is performed, the discharge may not be performed in time during the voltage rise, and the cell voltage of the storage element 41 having a high charging rate may exceed the protection voltage.

When the cell voltage of the power storage element 41 exceeds the protection voltage, the power storage device 20 is disconnected from the power supply line 15 by the switch 22. When the power supply line 15 is cut, neither charging from the converter 11 to the power storage device 20 nor discharging from the power storage device 20 to the inverter 12 can be achieved.

the main control unit 23 of the BMU21 of the present embodiment executes a voltage management process for continuing the constant voltage charging control by the converter 11 while suppressing the cell voltage of each power storage element 41 from reaching the protection voltage.

The voltage management process will be described with reference to fig. 4 and 5.

Fig. 4 is a flowchart showing the flow of the voltage management process. The voltage management process is executed all the time or periodically during charging of the power storage device 20.

In the voltage management processing, first, the sub-control unit 34 of the CMU32 in each power storage block 30 of the power storage device 20 detects the cell voltage of each power storage element 41 from the output of the voltage detection circuit 33. After the detection of the cell voltage, the sub-control section 34 outputs the detection result to the main control section 23 of the BMU21 (S11).

The main control unit 23 of the BMU21 compares the input cell voltage of each power storage element 41 with the 1 st threshold value stored in the main control unit 23 in advance (S12). As a result of the comparison, when the cell voltages of all the power storage elements 41 of the power storage device 20 are smaller than the 1 st threshold value (S12: no), the voltage management processing is ended. The 1 st threshold is a charging voltage upper limit value at which the performance of the storage element 41 is likely to deteriorate. The upper limit of the charging voltage is the upper limit of the voltage of the storage element 41 in the charged state.

The 1 st threshold is a voltage included in the 1 st high change region S1, and is 3.7[ V ] as an example.

the magnitude relationship among the charging target cell voltage, the 1 st threshold value, and the protection voltage is as follows.

Charging target cell voltage < 1 st threshold < protection voltage (3)

as a result of the comparison, when the cell voltage of any of the electric storage elements 41 of the electric storage device 20 is equal to or greater than the 1 st threshold (S12: yes), the main control unit 23 outputs a signal to the sub control unit 34 so that the electric storage element 41 having the cell voltage equal to or greater than the 1 st threshold is discharged. The sub-control unit 34, to which the signal is input, discharges the electric storage element 41 having the cell voltage of 1 st or higher through the discharge circuit 31 (S13).

The main control part 23 outputs a 1 st pull-down signal for pulling down the charging voltage Y from the initial value Yo to the converter 11 at the same time as S13 (S14). The converter 11 to which the 1 st pull-down signal is input pulls down the charging voltage Y by a given value from the initial value Yo (S15), and continues the constant voltage charging control. The 1 st pull-down signal output from the main control unit 23 to the converter 11 corresponds to a pull-down notification.

By decreasing the charging voltage Y, the cell voltage of the power storage element 41 that is equal to or higher than the 1 st threshold can be decreased to be less than the 1 st threshold. This can keep charging while suppressing the power storage element 41 from exceeding the protection voltage.

Fig. 5 shows a waveform of a cell voltage of the storage device 41, a waveform of a cell voltage of the battery pack 40, and a waveform of a charging current in the constant-current constant-voltage charging.

the converter 11 performs constant-current charging control on the power storage device 20 after the start of charging. When the total voltage of the power storage device 20 reaches a predetermined voltage value (see V1 in fig. 5), the converter 11 switches from the constant-current charging control to the constant-voltage charging control. After switching to the constant-voltage charging control, the converter 11 charges the power storage device 20 at the charging voltage Yo. When the constant voltage charging control is switched, the charging current of power storage device 20 gradually decreases.

After switching to the constant voltage charging control, the average cell voltage (broken line Va) of the power storage device 20 is maintained at around the charging target cell voltage. When the variation in cell voltage (state of charge) between the power storage elements 41 is large, the maximum cell voltage (solid line Vh) of the power storage element 41 rises to reach the 1 st threshold value. The average cell voltage Va is an average cell voltage of all the power storage elements 41 constituting the power storage device 20. The highest cell voltage Vh is a cell voltage of the power storage element having the highest voltage among all the power storage elements 41 constituting the power storage device 20.

when the maximum cell voltage Vh of the power storage element 41 reaches the 1 st threshold, the discharge circuit 31 discharges the power storage element 41 that is equal to or higher than the 1 st threshold. At the same time, the 1 st pull-down signal is output from the main control section 23 to the converter 11. The converter 11 pulls down the charging voltage Y (V2 of fig. 5) from the initial value Yo.

By pulling down and discharging the charge voltage Y, the maximum cell voltage Vh of the electric storage element 41 can be suppressed from being equal to or higher than the 1 st threshold value. Therefore, the charging can be continued while suppressing the power storage element 41 from exceeding the protection voltage.

Differences between the UPS10 of embodiment 1 and the UPS400 of another charging control method will be described.

Fig. 22 is a circuit diagram of a UPS400 of another charging control method. The UPS400 includes a converter 11, an inverter 12, a power storage device 420, and a charge control circuit 450. Power storage device 420 includes a plurality of power storage blocks 430 and BMU421 connected in series. Power storage device 420 is connected to power supply line 15 from ac power supply 80 to load 70 via branch line 16. The charge control circuit 450 is provided at the branch line 16.

The charge control circuit 450 includes a 1 st path L1, a 2 nd path L2, a 1 st diode D1, a switch SW, and a 2 nd diode D2. The 1 st path L1 and the 2 nd path L2 are connected in parallel. The 1 st diode D1 charges in the forward direction. The 1 st diode D1 and the switch SW are connected in series and provided on the 1 st path L1. The discharge direction of the 2 nd diode D2 is the forward direction. The 2 nd diode D2 is disposed at the 2 nd path L2.

path 1L 1 is a path for charging power storage device 420. Path 2L 2 is a path for discharging power storage device 420. The switch SW is a switch that controls charging to the power storage block 430. Based on the output of CMU432, control unit 423 of BMU421 switches on and off switch SW while monitoring the cell voltages of power storage elements 41, and thereby charges power storage device 420 in a normal use-capable region (see fig. 5).