JP2012191737A - Power storage system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide power storage system capable of effectively utilizing storage power even in emergency without complicating a control system and without damaging extendability.SOLUTION: Power storage units 1a and 1b include: battery packs 15, 16 and 17; AC/DC converters 11a and 11b for outputting an AC current to an AC line of a power distribution system 3, converting the AC current acquired from the AC line of the power distribution system to a DC current and outputting it; DC/DC converters 12a and 12b for converting a DC current of DC lines 5 and 6 from the AC/DC converters to a DC current of a prescribed value, outputting it to the battery packs, converting the DC current from the battery packs to the DC current of the prescribed value and outputting it to the DC lines of the AC/DC converters; and general controllers 20a and 20b for controlling the AC/DC converters and the DC/DC converters. An inter-power-storage-unit DC connection circuit 4 is provided between two power storage units selected from the plurality of power storage units, disconnects the DC lines inside the two power storage units at normal time and connects the DC lines inside the two power storage units at emergency time.

Description

  Embodiments described herein relate generally to a power storage system installed on a customer side for the purpose of system stabilization and load fluctuation suppression.

  In recent years, power generation equipment using renewable energy that does not emit greenhouse gases during power generation has been installed, and the reduction of carbon in power supply systems has been studied. In power generation using renewable energy, it is difficult to control the amount of power supply, and it is difficult to realize stable power supply. In the future, if the number of installed power generation facilities using such renewable energy increases, there is a risk that the short-term balance between power supply and demand will be disrupted and the frequency of power will deviate from an appropriate value. In addition, stable supply of power becomes difficult, and the quality of power may be deteriorated.

  Therefore, in addition to installing secondary batteries in the power distribution system that store surplus power from power generation facilities that use renewable energy, it is also possible to store and distribute power by using power storage facilities installed in consumers, etc. It is being considered.

JP 2005-86927 A JP-A-8-65895

  In power storage facilities installed on the customer side for the purpose of such system stabilization, load leveling, peak cut, emergency power supply, etc., a battery pack and a DC / DC converter and system for charge / discharge control thereof Specifications tailored to the scale of the customer by preparing multiple sets (hereinafter referred to as power storage units) with linked AC / DC converters and configuring a power storage system in which these are connected in parallel to the system AC line There is an advantage that it is easy to optimize.

  However, even if, for example, the power distribution system fails and power is supplied to the emergency circuit via the DC line using the battery pack's stored power, it is only used from a specific power storage unit that is DC-connected to the emergency circuit. There is a problem that power cannot be supplied to the circuit.

  On the other hand, the structure which always connects all the electrical storage units with a DC line is also considered. However, it is necessary to match the voltage of the DC line between the respective power storage units, and there is a concern that the control and communication of the system become complicated and hinder the scalability of the system scale.

  In addition, when configured as a single power storage unit, there is only one AC / DC converter, and the output capacity of the entire system is determined by the specifications of the converter. poor. Also, the DC line is long and there is a problem in voltage stability.

  An object of the present invention is to provide a power storage system that can effectively use stored power even in an emergency without complicating a control system and without impairing expandability.

  In order to solve the above-described problem, according to the power storage system according to the embodiment, the power storage system includes a plurality of power storage units, and each power storage unit includes a battery pack that houses a plurality of cell modules, and a power distribution system. An AC / DC converter that outputs an alternating current to the alternating current line and converts an alternating current obtained from the alternating current line of the distribution system into a direct current, and a direct current line that is output from the AC / DC converter. A direct current is converted into a predetermined value of direct current and output to the battery pack, and a direct current output from the battery pack is converted into a predetermined value of direct current and output to the direct current line of the AC / DC converter. A DC / DC converter; and an overall control device that controls the AC / DC converter and the DC / DC converter, and is selected from the plurality of power storage units. A connection circuit between power storage units that is provided between two power storage units, disconnects the DC lines in the two power storage units in a normal state, and connects the DC lines in the two power storage units in an emergency. It is provided.

It is a block diagram which shows the structure of the electrical storage system which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of each electrical storage unit in the electrical storage system which concerns on 1st Embodiment shown in FIG. It is a figure which shows operation | movement at the time of a power failure in a power distribution system in the electrical storage system which concerns on 1st Embodiment shown in FIG. It is a figure which shows operation | movement at the time of the power failure of the A / D converter in the electrical storage system which concerns on 1st Embodiment shown in FIG. It is a figure which shows the structure in the case of connecting the some electrical storage unit of the electrical storage system which concerns on 1st Embodiment shown in FIG. 1 with a some switch. It is a block diagram which shows the structure of the electrical storage system which concerns on the 2nd Embodiment of this invention. It is a figure which shows operation | movement at the time of a power failure in a power distribution system in the electrical storage system which concerns on 2nd Embodiment shown in FIG. It is a figure which shows the structure in the case of connecting the some electrical storage unit of the electrical storage system which concerns on 2nd Embodiment shown in FIG. 6 with a some diode. It is a block diagram which shows the structure of the electrical storage system which concerns on the 3rd Embodiment of this invention. It is a figure which shows operation | movement at the time of a power failure in a power distribution system in the electrical storage system which concerns on 3rd Embodiment shown in FIG. It is a figure which shows operation | movement at the time of the power failure of the A / D converter in the electrical storage system which concerns on 3rd Embodiment shown in FIG. It is a figure which shows the structure in the case of connecting the some electrical storage unit of the electrical storage system which concerns on 3rd Embodiment shown in FIG. 9 with a some thyristor.

  Hereinafter, a power storage system according to an embodiment of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram showing a configuration of a power storage system according to the first embodiment of the present invention. FIG. 2 is a block diagram showing a configuration of each power storage unit in the power storage system according to the first embodiment shown in FIG.

This power storage system is a system connected to a power distribution system 3 that is a power system in a building,
It is comprised from the two electrical storage units 1a and 1b connected to the power distribution system 3. FIG. The two power storage units 1a and 1b include a detection device 2, overall control devices 20a and 20b that perform overall control of the entire system, AC / DC converters 11a and 11b, and DC / DC converters 12a, 13a, 12b, 13b, and 14b. And an emergency circuit 13a and battery packs 15a, 15b, 15c, 15d, and 17b. The detection device 2 is, for example, a current sensor that detects a current of the distribution system 3 or an EMS (Energy Management system) receiving terminal. EMS is an energy management system provided outside the system.

  The overall control device 20 (20a, 20b) includes a management unit 22 and a communication unit 21. The management unit 22 has a load distribution control function for controlling the charge / discharge amounts for the battery packs 15a to 17b based on the battery information of the battery packs 15a to 17b. Moreover, the state of the power distribution system 3 and the operation status of the entire system are monitored, and commands are given to the AC / DC converter 11 (11a, 11b) and the DC / DC converters 12a, 12b, 13a, 13b, 14b as necessary. Do.

  The communication unit 21 acquires battery information of each of the battery packs 15a to 17b by communication via the AC / DC converter 11 (11a, 11b) and the DC / DC converters 12a, 12b, 13a, 13b, 14b, The operation information of each converter is received and the control command information is transmitted to each converter.

The AC / DC converter 11 (11a, 11b) includes a bidirectional inverter 111, a control unit 112, and a communication unit 113.
The bidirectional inverter 111 has a switching element capable of pulse width modulation PWM (Pulse Width Modulation) control, converts AC power from the power distribution system 3 into DC power, and converts the DC power lines of the DC / DC converters 12 and 13 ( DC line), or DC power of the DC line from the DC / DC converters 12 and 13 is converted into AC power and output to the distribution system 3.
The control unit 112 controls the operation of the bidirectional inverter 111 based on a communication command from the overall control device 20. The communication unit 112 transmits and receives information to and from the DC / DC converters 12 and 13. The communication unit 113 transmits / receives information to / from the overall control device 20.

The DC / DC converter 12 includes a voltage step-up / step-down unit 121, a control unit 122, and a communication unit 123. The voltage step-up / down unit 121 has a switching element capable of PWM control, performs voltage conversion of DC power from the AC / DC converter 11 and charges the secondary batteries of the battery packs 15a to 17b, Voltage conversion of the electric power stored in the battery is performed and the AC / DC converter 11 is discharged.
The control unit 122 controls the voltage step-up / down unit 121 based on communication commands from the overall control device 20 and the AC / DC converter 11. The communication unit 123 transmits and receives information to and from the overall control device 20, the AC / DC converter 11, and the battery packs 15a to 17b.

Each of the battery packs 15a to 17b includes a secondary battery array that accommodates a plurality of cell modules and a battery management device BMU (Battery Management Unit) 152. The BMU 152 includes a control unit 153, a communication unit 154, and a management unit 155. .
The secondary battery array is obtained by connecting secondary batteries such as lithium ion, NiMH, and lead in series and parallel. The control unit of the BMU 152 controls the secondary battery train based on the communication command from the DC / DC converters 12 and 13 to charge / discharge the battery. The communication unit 154 transmits and receives information to and from the DC / DC converters 12 and 13. The management unit 155 manages battery information such as the voltage, current, temperature, SOC (State Of Charge) value, internal resistance, charge / discharge integrated current, etc. of the secondary battery string, so that the secondary battery string is abnormal. And the remaining life of charge / discharge cycles is detected.

  In the first embodiment, one DC / DC converter 12 and 13 is provided for each of two battery packs. Specifically, DC / DC converters 12 and 13 are provided between the AC / DC converter 11 and the two battery packs. Of course, the number of battery packs connected to the DC / DC converters 12 and 13 may be changed within a controllable range.

  Further, another DC / DC converter and a battery pack set can be connected to the DC line between the AC / DC converter 11 and the DC / DC converters 12 and 13. Further, the emergency circuit 14a can be connected so that power can be supplied from the battery through the DC line in an emergency. It is assumed that such emergency circuit 14a is connected to important equipment such as an elevator, an emergency light, and a data center in a building.

  By configuring such a system, for example, when the detection device 2 detects that there is surplus power from solar power generation, the battery packs 15a, 15b, 16a, 16b, and 17b are charged, and conversely the summer When the power consumption is large, such as during the daytime, discharging from the battery packs 15a, 15b, 16a, 16b, and 17b makes it possible to stabilize the power system and level the load fluctuations.

  Further, the storage capacities of the battery packs 15a, 15b, 16a, 16b, and 17b can be changed according to the scale of a customer who arranges the storage system, so that a plurality of systems can be expanded.

  Further, as shown in FIG. 1, the output capacity of the system can be changed by connecting a plurality of power storage units 1a, 1b in parallel with AC lines and connecting the overall control devices 20a, 20b with communication lines to cooperate. It becomes possible to give the system expandability.

  Next, the inter-storage-unit DC connection circuit 4 shown in FIG. 1 will be described. The inter-storage unit DC connection circuit 4 includes a switch 41, a control unit 42, and a communication unit 43 between the DC line 5 of the storage unit 1a and the DC line 6 of the storage unit 1b. One end of the switch 41 is connected to the DC line 5 in the first power storage unit 1a via the connector CN1, and the other end of the switch 41 is connected to the DC line 6 in the second power storage unit 1b via the connector CN2. .

  The communication unit 42 receives information from the overall control devices 20a and 20b. The control unit 43 controls opening and closing of the switch 41 based on communication commands from the overall control devices 20a and 20b. The switch 41 has an intercept SW, and opens and closes the DC line based on a control command from the control unit 43 by the intercept SW. When outputting the DC lines 5 and 6 from the power storage units 1a and 1b to the outside, a circuit protector such as a circuit breaker may be provided.

  By opening the switch SW of the switch 41 during normal operation, the DC lines 5 and 6 between the power storage units 1a and 1b are not electrically connected. By controlling in this way, the DC line 5 between the AC / DC converter 11a and the DC / DC converters 12a and 13a is closed in the power storage unit 1a, and the AC / DC converter 11b and the DC / DC converter are closed. Since the DC line 6 between 12b and 13b is closed in the power storage unit 1b, there is an advantage that voltage control of the DC lines 5 and 6 and the like can be easily performed.

  Next, opening / closing control of the switch 41 when a power failure occurs in the distribution system 3 will be described. As shown in FIG. 3, when the power distribution system 3 fails, the detection device 2 in the power storage units 1a and 1b first detects that the power distribution system 3 has failed and transmits the detected information to the overall control devices 20a and 20b. To do.

  Based on the detected information, the overall control devices 20 a and 20 b transmit a control command for closing the switch 41 to the communication unit 42 in the inter-storage-unit DC connection circuit 4. The control unit 43 receives a command from the communication unit 42 and performs control to close the switch 41.

  By closing the switch 41 in this way, the DC lines 5 and 6 between the power storage units 1a and 1b are electrically connected. By controlling in this way, it becomes possible to exchange power between the power storage units 1a and 1b. For this reason, for example, the power stored in the battery packs 15b, 16b, and 17b of the second power storage unit 1b can be supplied to the emergency circuit 14a connected to the first power storage unit 1a in FIG. Can effectively use the stored electricity.

  However, since it is necessary to equalize and control the DC voltage of each power storage unit 1a, 1b, communication is performed between the power storage units 1a, 1b via the overall control devices 20a, 20b to stabilize the DC lines 5, 6. It is better to perform control.

  The power storage system according to the first embodiment is also effective when the AC / DC converters 11a and 11b fail. As shown in FIG. 4, for example, when the AC / DC converter 11b of the second power storage unit 1b fails, the power stored in the second power storage unit 1b cannot supply power to another unit via the AC line. . For this reason, in performing system stabilization control, there is a possibility that the capacity of the storage battery is insufficient, and the entire system may have to be stopped.

  However, power is supplied from the second power storage unit 1b to the first power storage unit 1a via the DC lines 5 and 6 by closing the switch 41 of the DC lines 5 and 6 and connecting the DC line 5 and the DC line 6. By doing so, the power storage system can be operated continuously.

  However, since it is not preferable that electric power is supplied in the direction of the failed second power storage unit 1b, the DC voltage on the second power storage unit 1b side is set slightly higher than the DC voltage on the first power unit 1a side. It is preferable to perform communication control via the overall control devices 20a and 20b.

Further, the first embodiment can be extended not only to the connection of the DC line between the two power storage units 1a and 1b but also to the connection of the DC line between the plurality of power storage units 1a to 1d as shown in FIG. In the modification shown in FIG. 5, assuming that the number of power storage units is n, the number of switches 41 may be prepared as many as _n C ₂ and arranged between the DC lines as shown in FIG. In the example shown in FIG. _5, the number of 4 _{C 2,} i.e. may be prepared six switches 41a to 41f.

  Then, by arranging the six switches 41a to 41f in a matrix with respect to each DC line, any two power storage units can be selected and connected. Of course, a plurality of switches may be closed to connect three or more storage unit DC lines. Each switch 41a to 41f is opened and closed by a communication unit 42 that transmits / receives information to / from each power storage unit and a control unit 43 that receives the command and transmits a control signal to each switch. do it.

  As described above, according to the power storage system according to the first embodiment, during normal operation, the DC lines 5 and 6 between the power storage units 1a and 1b are electrically disconnected to manage the DC lines 5 and 6 in units. In an emergency, the DC lines 5 and 6 between the power storage units 1a and 1b are electrically connected by the switch 41 in an emergency, and power can be interchanged between the power storage units 1a and 1b without performing complicated control. Become.

(Second Embodiment)
FIG. 6 is a block diagram showing a configuration of a power storage system according to the second embodiment of the present invention. The power storage system of the second embodiment shown in FIG. 6 differs from the power storage system of the first embodiment shown in FIG. 1 in the configuration of the inter-storage unit DC connection circuit 4a. The inter-storage-unit DC connection circuit 4a includes only the diode D1.

  The diode D1 has an anode connected to the second power storage unit 1b side and a cathode connected to the first power storage unit 1a side so that a current flows only from the second power storage unit 1b to the first power storage unit 1a.

  Here, during normal operation, the DC line between the power storage units 1a and 1b is controlled by maintaining the DC voltage V1 of the first power storage unit 1a higher than the DC voltage V2 of the second power storage unit 1b. 5 and 6 are in a state in which no current flows. For example, when the allowable voltage range of the DC lines 5 and 6 is ± 5%, V1 may be + 5% to ± 0%, and V2 may be ± 0% to −5%.

  As a result, the diode D1 is in a reverse bias state, so that the DC line 5 between the AC / DC converter 11a and the DC / DC converters 12a and 13a is closed in the first power storage unit 1a, and the AC / DC converter 11b. Since the DC line 6 between the DC / DC converters 12b, 13b and 14b is closed in the first power storage unit 1b, there is an advantage that the voltage control of the DC lines 5 and 6 can be easily performed.

  Next, the operation when a power failure occurs in the distribution system 3 will be described. As shown in FIG. 7, when the power distribution system 3 fails, initially, no current flows from the second power storage unit 1b to the first power storage unit 1a due to the relationship of V1> V2. For this reason, the stored power of the battery packs 15a and 16a of the first power storage unit 1a is supplied to the emergency circuit 14a of the first power storage unit 1a. However, when the power storage capacity of the first power storage unit 1a decreases, the voltage V1 gradually decreases. However, when V1 <V2, the diode D1 becomes forward and a forward current flows. For this reason, power can be supplied to the emergency circuit 14a from the battery packs 15b, 16b, and 17b of the second power storage unit 1b.

  In this way, effective use of the stored power can be achieved in an emergency. Further, unlike the power storage system of the first embodiment, the power storage system of the first embodiment does not require a troublesome control / communication system required for opening and closing the switch 41, and between the power storage units 1a and 1b. There is an advantage that it is not necessary to strictly adjust the DC line voltage. However, in the second embodiment, it is necessary to determine the power storage unit to which the emergency circuit 14a is connected and to set the direction of the diode D1 in advance.

  Moreover, since the bidirectional | two-way electric power supply between the electrical storage units 1a and 1b cannot be performed, the electrical storage system of 2nd Embodiment is a countermeasure against the failure of AC / DC converter 11a, 11b like 1st Embodiment. Is not suitable.

  The power storage system of the second embodiment can also be extended to DC line connection between a plurality of power storage units 1a to 1d as shown in FIG. For example, if an emergency circuit 14a is installed in each of the first power storage unit 1a and the second power storage unit 1b, the third power storage unit 1c and the fourth power storage unit 1d are changed to the first power storage unit 1a and the second power storage unit 1b. The diodes D1 to D4 may be installed so that the current flows.

(Third embodiment)
FIG. 9 is a block diagram showing a configuration of a power storage system according to the third embodiment of the present invention. The power storage system of the third embodiment shown in FIG. 9 differs from the power storage system of the first embodiment shown in FIG. 1 in the configuration of the inter-storage unit DC connection circuit 4b. The inter-storage-unit DC connection circuit 4 b includes two thyristors Th <b> 1 and Th <b> 2 connected in reverse direction, a communication unit 41, and a control unit 43.

  Here, during normal operation, no current flows through the DC lines 5 and 6 between the power storage units 1a and 1b by not applying a signal from the control unit 43 to the gates G1 and G2 of the thyristors Th1 and Th2. State. As a result, the DC line 5 between the AC / DC converter 11a and the DC / DC converters 12a and 13a is closed in the first power storage unit 1a, and the AC / DC converter 11b and the DC / DC converters 12b, 13b, Since the DC line 6 between 14b is closed in the 2nd electrical storage unit 1b, there exists an advantage that voltage control etc. of the DC lines 5 and 6 are easy to perform.

  Next, the operation when a power failure occurs in the distribution system 3 will be described. As shown in FIG. 10, when the detection device 2 detects that the power distribution system 3 has failed, the DC of the first power storage unit 1a side having the emergency circuit 14a is initially given by a command from the overall control devices 20a and 20b. Control is performed so that the voltage V1 is higher than V2. Further, a pulse-like signal is continuously given from the control unit 43 to the gate of the thyristor Th1, but at this time, the thyristor Th1 does not conduct because of the reverse voltage, and the emergency circuit 14a of the first power storage unit 1a The stored power of the first power storage unit 1a is supplied.

  However, as the power storage capacity of the first power storage unit 1a decreases, the voltage of V1 gradually decreases. Therefore, when V1 <V2, the voltage becomes a forward voltage, and the thyristor Th1 is turned on by a pulse signal to the gate. . Then, since a current flows from the second power storage unit 1b toward the first power storage unit 1a, power can be supplied from the battery packs 15b, 16b, and 17b of the second power storage unit 1b.

  In this way, effective use of the stored power can be achieved in an emergency. In addition, since the DC lines 5 and 6 can be gently connected using the voltage relationship between V1 and V2, there is an advantage that strict adjustment of the DC line voltage is not required as in the first embodiment. . If it is desired to disconnect the DC line for the convenience of the system, the thyristors Th1, Th2 are adjusted by adjusting the voltage with a DC / DC converter so that a reverse voltage of V1> V2 is temporarily applied. Just turn off.

  Furthermore, unlike the configuration of the second embodiment, the configuration of the third embodiment is also effective when the AC / DC converters 11a and 11b fail. As shown in FIG. 11, when the AC / DC converter 11b of the second power storage unit 1b fails, the power stored in the second power storage unit 1b cannot be supplied to another unit via the AC line. For this reason, there is a possibility that the capacity of the storage battery is insufficient in performing the system stabilization control, and there may be a situation where the entire system must be stopped.

  However, the system can be continuously operated by supplying power through the DC lines 5 and 6 from the second power storage unit 1b to the first power storage unit 1a by closing and connecting the switch of the DC line. Specifically, the thyristor Th1 may be turned on after controlling V1 and V2 as in the case of the power distribution system power failure. At this time, since the thyristor Th2 remains off, power is not supplied in the direction of the failed second power storage unit 1b.

  Further, if the AC / DC converter 11a of the second power storage unit 1a fails, the stored power of the first power storage unit 1a cannot supply power to another unit via the AC line. For this reason, there is a possibility that the capacity of the storage battery is insufficient in performing the system stabilization control, and there may be a situation where the entire system must be stopped.

  However, by turning on and connecting the thyristor Th2 of the DC line, the system can be continuously operated by supplying power from the first power storage unit 1a to the second power storage unit 1b through the DC lines 5 and 6. it can. At this time, since the thyristor Th1 remains off, power is not supplied in the direction of the failed first power storage unit 1a.

  Also in the third embodiment, as shown in FIG. 12, expansion to DC connection between the plurality of power storage units 1 a to 1 d is also possible. Thus, by arranging thyristors in a matrix for each DC line, it is possible to select and connect any two power storage units. Of course, a plurality of thyristors may be closed to connect three or more storage unit DC lines.

  Each thyristor is opened and closed by a communication unit 42 that transmits / receives information to / from each of the power storage units 1a to 1d and a control unit 43 that receives the command and transmits a control signal to each switch, and is controlled collectively by the control unit 43. It ’s fine.

  In the third embodiment, there is an advantage over the first and second embodiments in that strict DC voltage adjustment is not necessary and it is possible to cope with an AC / DC converter failure. Since the gate control circuit of the thyristor is required, the device becomes large and the control is slightly complicated.

  As mentioned above, although the electrical storage system of 1st Embodiment thru | or 3rd Embodiment was demonstrated, since there are each a merit and a demerit, in view of the content of emergency countermeasures required, controllability, etc., as needed Just choose.

  As described above, according to the power storage systems of the first to third embodiments, the stored power can be effectively used even in an emergency without complicating the control system and without impairing the expandability. A power storage system can be provided.

  As mentioned above, although several embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1a 1st electrical storage unit 1b 2nd electrical storage unit 2 Detection apparatus 3 Distribution system 4 Inter-storage unit DC connection circuit 5, 6 DC line 11a, 11b AC / DC converter 12a, 12b, 13a, 13b DC / DC converter 14a Emergency Circuits 15a, 15b, 16a, 16b, 17b Battery packs 22, 155 Management units 41, 41a-41f Switches 21, 42, 113, 123, 154 Communication units 43, 112, 122, 153 Control units D1-D4 Diodes Th1- Th12 Thyristor 111 Bidirectional Inverter 121 Voltage Buck-Boost Unit

Claims (7)

A power storage system including a plurality of power storage units,
Each power storage unit
A battery pack containing a plurality of cell modules;
An AC / DC converter that outputs an alternating current to the alternating current line of the power distribution system and converts the alternating current acquired from the alternating current line of the power distribution system into a direct current;
The direct current of the direct current line output from the AC / DC converter is converted into a direct current of a predetermined value and output to the battery pack, and the direct current output from the battery pack is converted into a direct current of a predetermined value. A DC / DC converter that outputs to a DC line of the AC / DC converter;
An overall control device for controlling the AC / DC converter and the DC / DC converter;
Provided between two power storage units selected from the plurality of power storage units, and disconnects the DC lines in the two power storage units in a normal state. In an emergency, the DC lines in the two power storage units. A power storage system comprising a connection circuit between power storage units for connecting each other.   The storage unit connection circuit connects the DC lines in the two storage units in an emergency based on the emergency signal from the communication unit, the switch, and the communication unit that receives an emergency signal from the overall control device. The power storage system according to claim 1, further comprising a control unit that closes the switch.   The power storage system according to claim 2, wherein the switches are arranged in a matrix with respect to each DC line.   The connection circuit between the energy storage units is normally connected to the cathode when the potential of the DC line of one energy storage unit in the two energy storage units is set higher than the potential of the DC line of the other energy storage unit. The power storage system according to claim 1, further comprising: a diode connected to the DC line of the one power storage unit, and an anode connected to the DC line of the other power storage unit.   The power storage system according to claim 4, wherein the diodes are arranged in a matrix with respect to each DC line.   The storage unit connection circuit includes a communication unit that receives an emergency signal from the overall control device, a first thyristor and a second thyristor that are connected in reverse parallel, and the first signal based on the emergency signal from the communication unit. The power storage system according to claim 1, further comprising a control unit that turns on one of the thyristor and the second thyristor.   The power storage system according to claim 6, wherein the first thyristor and the second thyristor are arranged in a matrix with respect to each of the DC lines.

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