Power storage device

Abstract

To provide a power storage device that can continue to operate even if some of power storage cells become abnormal.SOLUTION: A power storage device used in an air vehicle includes a plurality of battery circuits which are connected in series and through which a current flows when the power storage device is charged and discharged. Each of the plurality of battery circuits includes a first electric path, a power storage cell connected to an adjacent battery circuit through the first electric path, a first body which is provided in the first electric path so that the forward direction of a body diode matches a charging direction of the power storage device, a second electric path which is connected to the adjacent battery circuit in parallel with the power storage cell and the first switch, and a second switch which is provided in the second electric path so that the forward direction of the body diode matches a discharge direction of the power storage device, and is turned on when the first switch is off.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an electricity storage device. [Background technology]

[0002] Conventionally, electric aircraft have been developed. For example, it is envisioned to realize a high-altitude platform station (HAPS) by mounting a radio relay station on an electric aircraft. An aircraft used as a HAPS is equipped with solar cells and a power storage device, and is required to continue flying non-stop for a long period of time, such as six months. An aircraft used as a HAPS flies during the day using power generated by the solar cells and charges the power storage device, and flies at night using the power stored in the power storage device. Patent Document 1 discloses a technology for configuring a communication network using a HAPS. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-54490 A Summary of the Invention [Problem to be solved by the invention]

[0004] The energy storage devices used in HAPS require a high discharge capacity (full charge capacity). It is known that the discharge capacity of lithium-ion batteries can be significantly increased by changing the active material of the negative electrode from graphite to metallic lithium. In lithium-ion batteries that use metallic lithium as the active material of the negative electrode, metallic lithium can precipitate in the form of dendrites during charging, causing a short circuit inside the storage cell. The timing of the short circuit varies depending on the storage cell, and it is difficult to predict when a short circuit will occur in an individual storage cell. It is desirable for the energy storage devices used in HAPS to use a large number of storage cells in order to continue HAPS operation for a long period of time.

[0005] An object of the present invention is to provide a power storage device that can continue to operate even if some of the power storage cells become abnormal. [Means for solving the problem]

[0006] According to one aspect of the present invention, an energy storage device used in an aircraft includes a plurality of battery circuits connected in series through which a current flows when the energy storage device is charged and discharged, and each of the plurality of battery circuits includes a first electric path, a energy storage cell connected to an adjacent battery circuit through the first electric path, a first switch including a diode and provided in the first electric path such that the forward direction of the diode is the charging direction of the energy storage device, a second electric path connected to the adjacent battery circuit in parallel with the energy storage cell and the first switch, and a second switch including a diode and provided in the second electric path such that the forward direction of the diode is the discharging direction of the energy storage device, the second switch being on when the first switch is off. Effect of the Invention

[0007] With the above configuration, the power storage device can continue to operate even if some of the power storage cells are abnormal. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a schematic diagram showing an example of the arrangement of a power storage device. [Diagram 2] 1 is a block diagram showing an example of an internal functional configuration of a power storage device according to a first embodiment. [Diagram 3] 2 is a schematic cross-sectional view showing an example of the internal configuration of a storage cell; FIG. [Figure 4] 6 is a flowchart showing a procedure of a process in which the CMU controls the operation of the power storage device. [Diagram 5] 1 is a schematic circuit diagram showing an energy storage device that performs charging and discharging when all of the energy storage cells are normal. [Figure 6] 1 is a schematic circuit diagram showing a power storage device that performs charging and discharging when one power storage cell is abnormal. [Figure 7] 11 is a flowchart showing a procedure for a process in which the CMU diagnoses the second switch. [Figure 8] FIG. 11 is a schematic circuit diagram showing the battery circuit when diagnosing the second switch. [Figure 9] 11 is a flowchart showing a procedure for a process performed by the CMU to diagnose the first switch. [Figure 10] FIG. 4 is a schematic circuit diagram showing the battery circuit when diagnosing the first switch. [Figure 11] 10 is a block diagram showing an example of an internal functional configuration of a power storage device according to a second embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] An energy storage device used in an aircraft includes a plurality of battery circuits connected in series through which a current flows when the energy storage device is charged and discharged, and each of the plurality of battery circuits includes a first electric path, a storage cell connected to an adjacent battery circuit through the first electric path, a first switch including a diode and provided in the first electric path so that the forward direction of the diode is the charging direction of the energy storage device, a second electric path connected to the adjacent battery circuit in parallel with the storage cell and the first switch, and a second switch including a diode and provided in the second electric path so that the forward direction of the diode is the discharging direction of the energy storage device, the second switch being on when the first switch is off.

[0010] The energy storage device includes a plurality of battery circuits each having a storage cell and connected to each other. The battery circuit includes a storage cell, a first switch that opens and closes a first current path for connecting the storage cell to another battery circuit, and a second current path and a second switch that are parallel to the storage cell and the first switch. When the first switch is off, the second switch is on, and current bypasses the storage cell and flows through the second current path. Even if some of the multiple storage cells included in the energy storage device cannot be used, current flows through the multiple battery circuits, allowing the energy storage device to continue operating.

[0011] The power storage device may further include a control unit that controls the on / off switching of the first switch and the second switch so that the positive and negative terminals of the power storage cells in each battery circuit are not externally short-circuited. In this manner, the control unit switches the first switch and the second switch on and off, so that a current can bypass the power storage cells and flow through the second electric circuit.

[0012] The control unit may determine whether the storage cell is normal or abnormal, and in a battery circuit including the storage cell determined to be abnormal, turn off the first switch and then turn on the second switch. When the power storage device is abnormal, the control unit turns off the first switch and then turns on the second switch. When the storage cell is abnormal, the storage cell is disconnected from the other battery circuits and current flows through the second electric path. The first switch and the second switch are not turned on at the same time, and an external short circuit is prevented from occurring in the storage cell.

[0013] The control unit may determine whether the power storage cell is normal or abnormal based on the voltage of the power storage cell. When an internal short circuit occurs in the power storage cell, the voltage between the positive and negative terminals of the power storage cell decreases. The control unit can determine the abnormality of the power storage cell due to the internal short circuit based on the voltage of the power storage cell.

[0014] The control unit may determine whether the power storage cell is normal or abnormal based on a voltage of the power storage cell when the power storage cell is charged. Dendrites that cause internal short circuits in the power storage cell are likely to precipitate when the power storage cell is charged. The control unit can timely determine an abnormality in the power storage cell by making a determination based on the voltage of the power storage cell when the power storage cell is charged.

[0015] The first switch and the second switch may be configured using FETs, and the control unit may diagnose whether one of the first switch and the second switch is normal or abnormal during charging, and diagnose whether the other of the first switch and the second switch is normal or abnormal during discharging. It is possible to diagnose whether the first switch and the second switch are normal or abnormal from a voltage when the FET is turned on and a voltage when the FET is turned off and a current flows through a body diode (parasitic diode) of the FET. The direction of the current is opposite during charging and discharging. Fault diagnosis can be performed by reversing the polarity of the first switch and the second switch, and flowing a current through the body diode of one of the first switch and the second switch during charging and flowing a current through the body diode of the other switch during discharging.

[0016] The power storage device includes a plurality of battery circuits connected in series and through which a current flows when the power storage device is charged and discharged. Each of the plurality of battery circuits includes a first electric path, a power storage cell connected to an adjacent battery circuit through the first electric path, a first switch provided in the first electric path, a second electric path connected to the adjacent battery circuit in parallel with the power storage cell and the first switch, and a second switch provided in the second electric path and turned on when the first switch is off. One of the diodes of the first switch and the diode of the second switch is arranged so that the forward direction is the charging direction of the power storage device, and the other is arranged so that the forward direction is the discharging direction of the power storage device. Even in environments other than aircraft, when some of the power storage cells of the power storage device cannot be used, a current flows through the plurality of battery circuits, and the power storage device can continue to operate.

[0017] The negative electrode active material of the storage cell may be metallic lithium or an alloy containing lithium. A storage cell in which the negative electrode active material is metallic lithium or an alloy containing lithium has a large discharge capacity, but lithium is likely to precipitate in a dendrite shape, and an internal short circuit caused by the dendritic lithium is likely to occur. Since the storage device continues to operate even if an internal short circuit occurs in some of the storage cells, it is possible to operate for a long period of time even if a storage cell in which the negative electrode active material is metallic lithium or an alloy containing lithium is used. The storage device can increase the discharge capacity and discharge energy density by using a storage cell in which the negative electrode active material is metallic lithium or an alloy containing lithium.

[0018] The present invention will now be described in detail with reference to the drawings showing embodiments thereof. <Embodiment 1> FIG. 1 is a schematic diagram showing an example of the arrangement of a power storage device 1. The power storage device 1 is provided in an aircraft 2. For example, the aircraft 2 is a HAPS. The aircraft 2 is equipped with a load 21, such as a motor that generates power for flight and a communication device, and a solar cell 22. The load 21 and the solar cell 22 are each connected to the power storage device 1. The power storage device 1 is supplied with power generated by the solar cell 22 and charged. The power storage device 1 discharges and supplies power to the load 21. The power generated by the solar cell 22 and the power discharged by the power storage device 1 are supplied to a motor that generates power for flying the aircraft 2. The solar cell 22 and the power storage device 1 may be connected in parallel to the load 21.

[0019] 2 is a block diagram showing an example of an internal functional configuration of the energy storage device 1 according to the first embodiment. The energy storage device 1 includes a plurality of battery circuits 11. Each battery circuit 11 includes one storage cell 12, and is a circuit through which a current flows when the energy storage device 1 charges and discharges. The plurality of battery circuits 11 are connected in series. The plurality of storage cells 12 are connected to a load 21 and a solar cell 22 external to the energy storage device 1. When the energy storage device 1 charges and discharges, a current flows through the plurality of battery circuits 11, and the plurality of storage cells 12 charges and discharges.

[0020] The battery circuit 11 includes a first electric circuit 13, a storage cell 12 provided in the first electric circuit 13, and a first switch 14 provided in the first electric circuit 13 and connected in series to the storage cell 12. The storage cell 12 is connected to another (adjacent) battery circuit 11 via the first electric circuit 13 and the first switch 14. The first switch 14 is configured using a field effect transistor (FET). The first switch 14 is provided in the first electric circuit 13 such that the forward direction of its body diode is the charging direction of the storage device 1. The first switch 14 makes the first electric circuit 13 conductive when on, and makes the first electric circuit 13 non-conductive when off in the discharging direction of the storage device 1. Specifically, when the first switch 14 is on, the storage cell 12 is connected to the other battery circuit 11 through the first electric circuit 13, and can be charged and discharged. When the first switch 14 is off, no current flows through the storage cell 12 in the discharging direction, but a current flows through the body diode of the first switch 14 in the charging direction.

[0021] The battery circuit 11 further includes a second current path 15 connected to another battery circuit 11 in parallel with the storage cell 12 and the first switch 14, and a second switch 16 provided on the second current path 15. The second switch 16 is configured using a FET. The first switch 14 and the second switch 16 are connected in the battery circuit 11 so as to have mutually opposite polarities. The second switch 16 is provided on the second current path 15 so that the forward direction of its body diode is the discharging direction of the energy storage device 1. In a certain battery circuit 11, when the first switch 14 is turned off and the second switch 16 is turned on, the charging current does not flow to the storage cell 12, and the second current path 15 becomes a bypass and the charging current flows to the other battery circuit while bypassing the storage cell 12.

[0022] The second switch 16 is turned on when the first switch 14 is turned off. When the second switch 16 is turned on, it brings the second electric circuit 15 into a conductive state, and when the second switch 16 is turned off, it brings the second electric circuit 15 into a non-conductive state in the charging direction of the energy storage device 1. When the first switch 14 is turned on and the second switch 16 is turned off, the energy storage cell 12 is connected to the other battery circuit 11 through the first electric circuit 13.

[0023] FIG. 3 is a schematic cross-sectional view showing an example of the internal configuration of the storage cell 12. The storage cell 12 is an energy storage element of a secondary battery such as a lithium ion battery. The storage cell 12 is configured by storing a positive electrode 125, a separator 127, a negative electrode 126, and an electrolyte (electrolytic solution) in a rectangular parallelepiped container 121 with one side open, and attaching a lid 122 to the container 121. A positive electrode terminal 123 and a negative electrode terminal 124 for electrical connection with a circuit are provided on the outside of the lid 122. Alternatively, the container 121 may be configured using a laminate film. The positive electrode terminal 123 is connected to the positive electrode 125 in the container 121, and the negative electrode terminal 124 is connected to the negative electrode 126 in the container 121.

[0024] The positive electrode 125, the separator 127, and the negative electrode 126 are formed in a rectangular plate or sheet shape. The positive electrode 125, the separator 127, and the negative electrode 126 are stacked, and the separator 127 is interposed between the positive electrode 125 and the negative electrode 126. For example, the positive electrode 125 is made of a material containing a lithium transition metal oxide, and the negative electrode 126 is made of a metallic lithium or an alloy containing lithium. The alloy containing lithium is, for example, an alloy of tin or silicon and lithium. When the negative electrode 126 is made of metallic lithium or an alloy containing lithium, the active material of the negative electrode 126 is metallic lithium or an alloy containing lithium. The separator 127 is, for example, a glass cloth or a resin formed into a porous shape. The separator 127 is impregnated with an electrolyte. The positive electrode 125, the separator 127, and the negative electrode 126 may be wound or stacked. The shape of the storage cell 12 may be a shape other than a rectangular parallelepiped (prismatic), and may be a pouch shape or a cylindrical shape.

[0025] When the active material of the negative electrode 126 is metallic lithium or an alloy containing lithium, the discharge capacity is significantly increased compared to when the active material of the negative electrode is graphite, but dendritic lithium metal is likely to precipitate from the negative electrode 126. Dendritic lithium metal is particularly likely to precipitate when the power storage cell 12 is charged. The dendritic lithium metal from the negative electrode 126 grows with each charge and discharge, penetrates the separator 127, and comes into contact with the positive electrode 125. When the dendritic lithium metal from the negative electrode 126 comes into contact with the positive electrode 125, a short circuit occurs inside the power storage cell 12. The power storage cell 12 in which an internal short circuit has occurred enters an abnormal state in which it cannot operate normally.

[0026] As shown in FIG. 2, the energy storage device 1 includes a CMU (Cell Monitoring Unit) 3. The CMU 3 is a circuit board mounted on a battery module or a battery pack (energy storage device 1). In this embodiment, the CMU 3 corresponds to a control unit. The CMU 3 measures the states of the multiple storage cells 12 and controls the multiple battery circuits 11. The CMU 3 includes a calculation unit 31, a memory 32, a storage unit 33, a voltage measurement unit 34, a temperature measurement unit 35, a switching unit 36, and an output unit 37. The calculation unit 31 is, for example, a CPU (Central Processing Unit). The memory 32 stores information required for calculation in the calculation unit 31. The storage unit 33 is nonvolatile and stores programs and data. For example, the storage unit 33 is a nonvolatile semiconductor memory. The calculation unit 31 executes processing according to the program stored in the storage unit 33. The voltage measurement unit 34 measures the voltage between the positive and negative terminals of each of the storage cells 12. For example, the voltage measurement unit 34 includes a voltmeter connected to the positive terminal and the negative terminal of each of the storage cells 12. The temperature measurement unit 35 measures the temperature of each of the storage cells 12. The output unit 37 outputs a signal to the outside of the power storage device 1.

[0027] The CMU 3 is connected to each of the first switch 14 and the second switch 16, and controls the operation of the first switch 14 and the second switch 16. The switching unit 36 ​​switches each of the first switch 14 and the second switch 16 between on and off. The switching unit 36 ​​applies a voltage between the source and gate of the FET constituting the first switch 14 and the second switch 16, for example. When the switching unit 36 ​​applies a voltage exceeding a predetermined voltage, the first switch 14 and the second switch 16 are turned on, and when the applied voltage is reduced, the first switch 14 and the second switch 16 are turned off. When the FET is intentionally turned off, the applied voltage may be set to zero or may be a negative voltage. The voltage measurement unit 34 measures the voltage of each of the first switch 14 and the second switch 16. For example, the voltage measurement unit 34 measures the voltage between the source and drain of the first switch 14 and the second switch 16.

[0028] FIG. 4 is a flowchart showing a procedure of a process in which the CMU 3 controls the operation of the energy storage device 1. In an initial state, all of the first switches 14 are on, and all of the second switches 16 are off. The voltage measurement unit 34 measures the voltage of the energy storage cell 12, and the temperature measurement unit 35 measures the temperature of the energy storage cell 12 (S11). The calculation unit 31 determines whether or not the energy storage cell 12 is abnormal based on the measured voltage and temperature (S12). When a short circuit (internal short circuit) occurs inside the energy storage cell 12, the voltage of the energy storage cell 12 decreases, and the temperature of the energy storage cell 12 increases. For example, in S12, the calculation unit 31 determines that the energy storage cell 12 is abnormal when the measured voltage is less than a predetermined threshold voltage or the measured temperature is equal to or greater than a predetermined threshold temperature. The calculation unit 31 may determine that the energy storage cell 12 is abnormal when the measured voltage is equal to or less than a predetermined threshold voltage or the measured temperature exceeds a predetermined threshold temperature. If the storage cell 12 is normal (S12: NO), the CMU 3 ends the process.

[0029] If the energy storage cell 12 is abnormal (S12: YES), the calculation unit 31 causes the switching unit 36 ​​to turn off the first switch 14 in the battery circuit 11 including the energy storage cell 12 determined to be abnormal (S13). During the period from when S13 is performed until when S14 is performed, the first switch 14 and the second switch 16 are both off. When the energy storage device 1 is charging, if the first switch 14 and the second switch 16 are both off, a charging current temporarily flows through the body diode of the first switch 14. When the energy storage device 1 is discharging, if the first switch 14 and the second switch 16 are both off, a discharging current temporarily flows through the body diode of the second switch 16.

[0030] The calculation unit 31 then turns on the second switch 16 in the battery circuit 11 including the storage cell 12 determined to be abnormal by the switching unit 36 ​​(S14). The second circuit 15 becomes conductive, and the abnormal storage cell 12 becomes disconnected from the other battery circuits 11 and does not charge or discharge. If the storage cell 12 in which an internal short circuit has occurred continues to charge or discharge, the dendritic lithium metal will grow further and may ignite when exposed to air. Since the abnormal storage cell 12 does not charge or discharge, the risk of ignition is reduced and the safety of the storage device 1 is improved. The calculation unit 31 performs the process of S14 after a predetermined time has elapsed since the first switch 14 was turned off in S13. If the first switch 14 and the second switch 16 are turned on at the same time, an external short circuit occurs in the storage cell 12. If an external short circuit occurs, a large current will flow through the battery circuit 11, and the storage device 1 may be damaged. The CMU 3 turns off the first switch 14 and then turns on the second switch to prevent the occurrence of an external short circuit. The CMU 3 then ends the processing. The CMU 3 repeatedly executes the processing of S11 to S14 for each of the multiple storage cells 12. For a storage cell 12 that has once been determined to be abnormal, the CMU 3 does not need to execute the processing of S11 to S14 thereafter.

[0031] Dendritic lithium metal inside the storage cells 12 is likely to occur when the storage cells 12 are charged. The CMU 3 desirably performs the processes of S11 to S14 for each of the multiple storage cells 12 during charging. By performing the processes of S11 to S14 during charging, the energy storage device 1 can immediately find an abnormal storage cell 12 and effectively eliminate danger. The CMU 3 may perform a process of determining whether or not there is an abnormality in the storage cell 12 based on only one of the voltage or temperature of the storage cell 12. The CMU 3 that determines whether or not there is an abnormality in the storage cell 12 based only on the voltage of the storage cell 12 does not need to be equipped with a temperature measurement unit 35.

[0032] 5 is a schematic circuit diagram showing the energy storage device 1 that performs charging and discharging when all the storage cells 12 are normal. The current that flows during charging (charging current) is indicated by a solid arrow, and the current that flows during discharging (discharging current) is indicated by a dashed arrow. The multiple storage cells 12 are connected to each other via a first electric circuit 13. A current flows through the storage cells 12 and the first electric circuit 13, and all the storage cells 12 perform charging and discharging.

[0033] FIG. 6 is a schematic circuit diagram showing the energy storage device 1 that performs charging and discharging when one of the storage cells 12 is abnormal. The current that flows during charging is indicated by a solid arrow, and the current that flows during discharging is indicated by a dashed arrow. It is assumed that the second storage cell 12 from the top in FIG. 6 is abnormal. In the battery circuit 11 including the abnormal storage cell 12, the first switch 14 is turned off, and the storage cell 12 is not connected to the other battery circuits 11. The second switch 16 is turned on, and the second electric circuit 15 is in a conductive state. In the battery circuit 11 including the normal storage cell 12, the first switch 14 is turned on, and the storage cell 12 is connected to the other battery circuits 11 via the first electric circuit 13. The second switch 16 is turned off, and the second electric circuit 15 is in a non-conductive state.

[0034] In a battery circuit 11 including a normal storage cell 12, a current flows through the storage cell 12 and the first electric circuit 13, and the storage cell 12 charges and discharges. In a battery circuit 11 including an abnormal storage cell 12, a current does not flow through the storage cell 12 and the first electric circuit 13, but flows through the second electric circuit 15. In other words, a current does not flow through the abnormal storage cell 12, and the second electric circuit 15 acts as a bypass, allowing a current to flow through the second electric circuit 15. A current flows through the energy storage device 1 as a whole, and the normal storage cell 12 charges and discharges.

[0035] Thus, in this embodiment, even if some of the multiple storage cells 12 are abnormal, current flows bypassing the abnormal storage cells 12, the other storage cells 12 operate normally, and charging and discharging are performed as a whole in the energy storage device 1. Even if an internal short circuit occurs in some of the storage cells 12 and some of the storage cells 12 become abnormal, the energy storage device 1 can continue to operate.

[0036] The energy storage device 1 provided in the aircraft 2 used as a HAPS is required to have a high discharge capacity. The energy storage cell 12 in which the active material of the negative electrode 126 is metallic lithium or an alloy containing lithium has a large discharge capacity, but is prone to precipitation of dendritic lithium metal, and is prone to internal short circuit caused by the dendritic lithium metal. The precipitation of dendritic lithium metal is influenced by the current distribution in the negative electrode 126, and the current distribution in the negative electrode 126 differs for each energy storage cell 12. The timing and degree of precipitation of dendritic lithium metal differs for each energy storage cell 12, and the timing of occurrence of internal short circuit caused by dendritic lithium metal differs for each energy storage cell 12. It is difficult to predict the timing of occurrence of internal short circuit in each energy storage cell 12 and to perform control based on the prediction.

[0037] The energy storage device 1 according to the present embodiment continues to operate even if an internal short circuit occurs in some of the storage cells 12, and therefore can operate regardless of the timing of the occurrence of the internal short circuit. The aircraft 2 used as a HAPS is required to fly continuously for a long period of time, such as six months, and the energy storage device 1 provided in the aircraft 2 needs to operate for a long period of time without maintenance. The energy storage device 1 continues to operate even if an internal short circuit occurs in some of the storage cells 12, and therefore can operate for a long period of time without maintenance. Therefore, the energy storage device 1 according to the present embodiment can be used as an energy storage device provided in the aircraft 2 used as a HAPS. In addition, the energy storage device 1 continues to operate even if an internal short circuit occurs in some of the storage cells 12, and therefore can operate for a long period of time even if the storage cells 12 in which the active material of the negative electrode 126 is metallic lithium or an alloy containing lithium are used. The energy storage device 1 using the storage cells 12 in which the active material of the negative electrode 126 is metallic lithium or an alloy containing lithium has a high discharge capacity and is useful as an energy storage device provided in the aircraft 2 used as a HAPS.

[0038] The CMU 3 performs a process for diagnosing whether the first switch 14 and the second switch 16 are in a normal state in which they can open and close the first electric circuit 13 and the second electric circuit 15. Fig. 7 is a flowchart showing the procedure of the process in which the CMU 3 diagnoses the second switch 16. Fig. 8 is a schematic circuit diagram showing the battery circuit 11 when diagnosing the second switch 16. The CMU 3 diagnoses the second switch 16 when the energy storage device 1 is discharging.

[0039] In an initial state, the first switch 14 is on and the second switch 16 is off. During discharging, the calculation unit 31 turns off the first switch 14 by the switching unit 36 ​​(S21), and then turns on the second switch 16 by the switching unit 36 ​​in the battery circuit 11 including the first switch 14 that has been turned off (S22). When the second switch 16 is in the on state, a current flows through the second switch 16 as shown by the solid arrow in FIG. 8. The voltage measurement unit 34 measures the voltage between both ends of the second switch 16 (S23). When the second switch 16 is normal, the measured voltage is approximately 0V.

[0040] The calculation unit 31 then uses the switching unit 36 ​​to turn off the second switch 16 (S24). When the second switch 16 is in the off state, a current flows through a body diode included in the second switch 16, as indicated by the dashed arrow in FIG. 8. The voltage measurement unit 34 measures the voltage across the second switch 16 (S25). When the second switch 16 is normal, the measured voltage is higher than the voltage when the second switch 16 is on. For example, the voltage across the second switch 16 is 0.6 to 1 V.

[0041] The calculation unit 31 determines whether the second switch 16 is normal or not based on the voltages measured in S23 and S25 (S26). For example, the calculation unit 31 determines that the second switch 16 is normal if the voltage when the second switch 16 is turned on is a low value close to 0V and the voltage when the second switch 16 is turned off is within a higher predetermined range. For example, the calculation unit 31 determines that the second switch 16 is in an abnormal state in which the second switch 16 cannot reliably open or close the second electric circuit 15 if there is no difference between the voltage when the second switch 16 is turned on and the voltage when the second switch 16 is turned off.

[0042] If the second switch 16 is normal (S26: YES), the calculation unit 31 turns on the first switch 14 (S27) and ends the process. The time required for the processes of S21 to S27 is a short time of about one to several seconds, and there is no effect on the operation of the power storage device 1. If the second switch 16 is abnormal (S26: NO), the calculation unit 31 causes the output unit 37 to output abnormality information indicating that the second switch 16 is abnormal (S28) and ends the process. For example, the abnormality information is input to a control device of the aircraft 2, and processing such as notification to the outside of the aircraft 2 is performed.

[0043] FIG. 9 is a flowchart showing the procedure of the process in which the CMU 3 diagnoses the first switch 14. FIG. 10 is a schematic circuit diagram showing the battery circuit 11 when diagnosing the first switch 14. The CMU 3 diagnoses the first switch 14 when the power storage device 1 is charging. In the initial state, the first switch 14 is on and the second switch 16 is off. When the first switch 14 is on, a current flows through the first switch 14 as shown by the solid arrow in FIG. 10. During charging, the voltage measurement unit 34 measures the voltage between both ends of the first switch 14 (S31). When the first switch 14 is normal, the measured voltage is approximately 0V.

[0044] The calculation unit 31 then uses the switching unit 36 ​​to turn off the first switch 14 (S32). When the first switch 14 is in the off state, a current flows through a body diode included in the first switch 14, as indicated by a dashed arrow in FIG. 10. The voltage measurement unit 34 measures the voltage between both ends of the first switch 14 (S33). When the first switch 14 is normal, the measured voltage is higher than the voltage when the first switch 14 is on. For example, the voltage between both ends of the first switch 14 is 0.6 to 1 V.

[0045] The calculation unit 31 determines whether the first switch 14 is normal or not based on the voltages measured in S31 and S33 (S34). For example, the calculation unit 31 determines that the first switch 14 is normal if the voltage when the first switch 14 is turned on is a low value close to 0 V and the voltage when the first switch 14 is turned off is within a higher predetermined range. For example, the calculation unit 31 determines that the first switch 14 is in an abnormal state in which the first switch 14 cannot reliably open or close the first electric circuit 13 if there is no difference between the voltage when the first switch 14 is turned on and the voltage when the first switch 14 is turned off.

[0046] If first switch 14 is normal (S34: YES), calculation unit 31 turns on first switch 14 (S35) and ends the process. The time required for the processes of S31 to S35 is a short time of about one to several seconds, and there is no effect on the operation of power storage device 1. If first switch 14 is abnormal (S34: NO), calculation unit 31 causes output unit 37 to output abnormality information indicating that first switch 14 is abnormal (S36), and ends the process.

[0047] The processes of S21 to S28 and S31 to S36 are performed sequentially for the multiple battery circuits 11. By diagnosing the first switch 14 and the second switch 16, the power storage device 1 can confirm that the first switch 14 and the second switch 16 are normal and continue charging and discharging. If it is determined that the first switch 14 or the second switch 16 is abnormal, a process for stopping the power storage device 1, such as landing the aircraft 2, can be performed.

[0048] Alternatively, the first switch 14 and the second switch 16 may be connected in the battery circuit 11 with polarities opposite to those shown in Figures 2, 5, 6, 8 and 10. In this case, the processes of S21 to S28 are performed during charging, and the processes of S31 to S36 are performed during discharging.

[0049] As described above in detail, in this embodiment, each of all the storage cells 12 is provided with the first switch 14 that opens and closes the first circuit 13 for connecting the storage cells 12 to the other storage cells 12, and the second circuit 15 and the second switch 16 that constitute a bypass. When the storage cell 12 is abnormal, the first switch 14 is turned off and the second switch 16 is turned on, and the current bypasses the storage cell 12 and flows through the second circuit 15. The storage device 1 can continue to operate even if some of the storage cells 12 are abnormal. For this reason, the storage device 1 can use storage cells 12 that are prone to internal short circuits. By using storage cells 12 that are prone to internal short circuits but have a high discharge capacity, the storage device 1 has a high discharge capacity and is useful as a storage device to be provided in an aircraft 2 used as a HAPS that requires a high discharge capacity.

[0050] <Embodiment 2> In the second embodiment, the configuration of the flying object 2 other than the power storage device 1 is the same as in the first embodiment. FIG. 11 is a block diagram showing an example of the internal functional configuration of the power storage device 1 according to the second embodiment. The power storage device 1 includes a plurality of power storage modules 10. The plurality of power storage modules 10 are connected in parallel to each other. The power storage module 10 includes a plurality of battery circuits 11 connected in series to each other. The configuration of the battery circuits 11 is the same as in the first embodiment. The power storage device 1 includes a CMU 3. The internal functional configuration of the CMU 3 is the same as in the first embodiment. The plurality of power storage modules 10 are connected to a load 21 and a solar cell 22 outside the power storage device 1. When the power storage device 1 charges and discharges, a current flows through the plurality of power storage modules 10, and each of the power storage cells 12 charges and discharges.

[0051] The CMU 3 executes the same process as in the first embodiment for each of the energy storage modules 10. In the second embodiment as well, if an abnormality occurs in an energy storage cell 12, the current bypasses the energy storage cell 12 and flows through the second electric circuit 15. The energy storage device 1 can continue to operate even if some of the energy storage cells 12 are abnormal. The energy storage device 1 can use energy storage cells 12 that are prone to internal short circuits but have a high discharge capacity, and is useful as an energy storage device to be provided in an aircraft 2 that requires a high discharge capacity.

[0052] Furthermore, in the second embodiment, even if the current is turned off when performing the process of diagnosing the first switch 14 or the second switch 16 in one power storage module 10, the current flows to the other power storage modules 10, and the power storage device 1 can continue to operate. The CMU 3 may perform a process of putting each power storage module 10 into a state of disconnection from the other power storage modules 10. For example, when the CMU 3 detects an abnormality in the first switch 14 or the second switch 16, the CMU 3 may perform a process of putting the power storage module 10 including the abnormal first switch 14 or second switch 16 into a state of disconnection, thereby allowing the power storage device 1 to continue to operate.

[0053] In the first and second embodiments, FETs are used as the first switch 14 and the second switch 16. Alternatively, the first switch 14 and the second switch 16 may be configured using elements other than FETs. The power storage cell 12 may be a battery other than a lithium ion battery. The aircraft 2 may be provided with a plurality of power storage devices 1.

[0054] In the first and second embodiments, the first switch 14 is provided in the first electric circuit 13 such that the forward direction of the diode is the charging direction of the energy storage device 1, and the second switch 16 is provided in the second electric circuit 15 such that the forward direction of the diode is the discharging direction of the energy storage device 1. With this configuration, when the energy storage device 1 is discharged, a process of flowing a current bypassing a specific energy storage cell 12 can be quickly performed. Alternatively, the diode of the first switch 14 and the diode of the second switch 16 may be reversed. In other words, the diode of the first switch 14 and the diode of the second switch 16 may be arranged such that one of them is arranged so that the charging direction of the energy storage device 1 is the forward direction, and the other is arranged so that the discharging direction of the energy storage device 1 is the forward direction.

[0055] In the first and second embodiments, the CMU 3 performs the function of the control unit. Alternatively, a higher-level management device capable of communicating with the CMU 3, or a remotely located management device capable of communicating with the power storage device 1 may perform the function of the control unit. In other words, the circuit board on which the first switch 14 and the second switch 16 are provided and the circuit board on which the control unit is provided may be provided physically separated from each other. The power storage device 1 may be mounted on a moving object other than the aircraft 2.

[0056] The present invention is not limited to the contents of the above-described embodiment, and various modifications are possible within the scope of the claims. In other words, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention. [Explanation of symbols]

[0057] 1. Energy storage device 10 Energy storage module 11 Battery circuit 12 Energy storage cells 13 1st electric circuit 14 First Switch 15 2nd electric circuit 16 Second Switch 2. Flying Objects 21 Load 22 Solar Cells 3. CMU

Claims

1. A power storage device for use in an aircraft, comprising: a plurality of battery circuits connected in series and through which a current flows when the power storage device is charged and discharged; Each of the plurality of battery circuits includes: A first circuit; A storage cell connected to an adjacent battery circuit through the first electric path; a first switch including a diode and provided on the first electric path such that a forward direction of the diode corresponds to a charging direction of the power storage device; a second electric circuit connected in parallel to the storage cell and the first switch to the adjacent battery circuit; a second switch including a diode, the second switch being provided in the second electric path such that a forward direction of the diode corresponds to a discharge direction of the power storage device, and being turned on when the first switch is turned off; a control unit that controls switching on and off of the first switch and the second switch so that a positive terminal and a negative terminal of the storage cell in each battery circuit are not externally short-circuited; The control unit is determining whether the storage cell is normal or abnormal, turning off the first switch in a battery circuit including the storage cell determined to be abnormal, and then turning on the second switch, and not controlling the first switch and the second switch after turning on the second switch; The first switch and the second switch are configured using FETs, The control unit diagnoses whether the first switch is normal or abnormal so as to determine that the first switch is abnormal when there is no difference between a voltage across the first switch when the first switch is turned on and a voltage across the first switch when the first switch is turned off during charging, and diagnoses whether the second switch is normal or abnormal so as to determine that the second switch is abnormal when there is no difference between a voltage across the second switch when the second switch is turned on and a voltage across the second switch when the second switch is turned off during discharging. Energy storage device.

2. The control unit is Based on the voltage of the storage cell, it is determined whether the storage cell is normal or abnormal. The power storage device according to claim 1 .

3. The control unit is A determination is made as to whether the storage cell is normal or abnormal based on a voltage of the storage cell when the storage cell is charged. The power storage device according to claim 1 .

4. a plurality of battery circuits connected in series and through which a current flows when the power storage device is charged and discharged; Each of the plurality of battery circuits includes: A first circuit; A storage cell connected to an adjacent battery circuit through the first electric path; A first switch provided in the first current path and configured using a FET; a second electric circuit connected in parallel to the storage cell and the first switch to the adjacent battery circuit; a second switch that is provided in the second electric circuit and is configured using a FET and is turned on when the first switch is turned off; one of the diodes of the first switch and the second switch is arranged so that a charging direction of the power storage device corresponds to a forward direction, and the other is arranged so that a discharging direction of the power storage device corresponds to a forward direction, a control unit that controls switching on and off of the first switch and the second switch so that a positive terminal and a negative terminal of the storage cell in each battery circuit are not externally short-circuited; The control unit is determining whether the storage cell is normal or abnormal, turning off the first switch in a battery circuit including the storage cell determined to be abnormal, and then turning on the second switch, and not controlling the first switch and the second switch after turning on the second switch; During charging, the one switch is diagnosed as normal or abnormal so that it is determined that the one switch is abnormal if there is no difference between the voltage across both ends of the one switch when the one switch of the first switch and the second switch having a diode with a forward charging direction is turned on and the voltage across both ends of the one switch when the one switch is turned off; during discharging, the other switch is diagnosed as normal or abnormal so that it is determined that the other switch is abnormal if there is no difference between the voltage across both ends of the other switch when the other switch of the first switch and the second switch having a diode with a forward discharging direction is turned on and the voltage across both ends of the other switch when the other switch is turned off. Energy storage device.

5. The active material of the negative electrode of the storage cell is metallic lithium or an alloy containing lithium. The power storage device according to claim 1 .

6. a plurality of power storage modules each including the plurality of battery circuits; The plurality of power storage modules are connected in parallel to each other, The control unit causes each of the power storage modules to be in a state of being disconnected from the other power storage modules. The power storage device according to claim 1 .

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