Energy storage device

Abstract

The present invention provides an energy storage device equipped with multiple energy storage cells connected in series, which can perform capacitor failure detection even after the product has been shipped. [Solution] The energy storage module 10 comprises a plurality of energy storage cells 13 connected in series, a measurement unit 16 that measures a measurement voltage corresponding to the voltage of the energy storage cells 13, positive and negative measurement lines 14 that connect the energy storage cells 13 and the measurement unit 16, a capacitor 20 provided in parallel with the energy storage cells 13 via the measurement lines 14, and a boost circuit 30 that charges the capacitor 20 by applying a test voltage higher than the voltage from the plurality of energy storage cells 13 connected in series to the positive measurement line 14.

Description

Technical Field

[0001] The present invention relates to a power storage device including a power storage cell.

Background Art

[0002] Patent Document 1 describes a power storage device including a plurality of power storage cells connected in series. The power storage device includes a measurement unit that monitors the voltage of each power storage cell, and the state of the power storage cell can be determined using the voltage monitored by this measurement unit.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a power storage device, in order to smooth the output from the power storage cell, it is conceivable to provide a capacitor in parallel with the power storage cell. However, due to continuous use of the power storage device, the capacitor may fail. In particular, when microcracks that are difficult to detect in the inspection at the shipment stage occur in the capacitor, the cracks may grow during use of the power storage device, and eventually, a short circuit failure may occur. Therefore, there is still room for improvement in the failure determination of the capacitor in the power storage device.

[0005] The present invention has been made in view of the above problems, and provides a power storage device including a plurality of power storage cells connected in series, which can perform failure determination of a capacitor provided in parallel with the power storage cell even after shipment.

Means for Solving the Problems

[0006] The power supply device of the present disclosure is an energy storage device comprising: a plurality of energy storage cells connected in series; a measurement unit that measures a measurement voltage corresponding to the voltage of the energy storage cells; positive and negative measurement lines connecting the energy storage cells and the measurement unit; a capacitor provided in parallel with the energy storage cells via the measurement lines; and a boost circuit that charges the capacitor by applying a test voltage higher than the voltage from the plurality of energy storage cells connected in series to the positive measurement line in order to determine if the capacitor has failed. [Effects of the Invention]

[0007] The present invention provides an energy storage device comprising multiple energy storage cells connected in series, which allows for fault detection of capacitors connected in parallel to the energy storage cells even after shipment. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram illustrating the configuration of ESS. [Figure 2] This is a diagram illustrating the configuration of an energy storage module. [Figure 3] This is a flowchart explaining the procedure for diagnosing capacitor failure. [Figure 4] This is a timing chart illustrating the operation of the energy storage module during fault detection. [Figure 5] This figure shows the changes in the measured voltage corresponding to each capacitor during fault detection. [Figure 6] This figure shows the changes in the measured voltage corresponding to each capacitor during fault detection. [Figure 7] This diagram illustrates the configuration of the energy storage module according to the second embodiment. [Figure 8] This figure shows the changes in the measured voltage corresponding to each capacitor during fault detection. [Modes for carrying out the invention]

[0009] [Summary of this invention] [1] An energy storage device according to one embodiment of the present invention comprises a plurality of energy storage cells connected in series, a measuring unit that measures a measurement voltage corresponding to the voltage of the energy storage cells, positive and negative measurement lines connecting the energy storage cells and the measuring unit, a capacitor provided in parallel with the energy storage cells via the measurement lines, and a boost circuit that charges the capacitor by applying a test voltage higher than the voltage from the plurality of energy storage cells connected in series to the positive measurement line in order to determine if the capacitor has failed.

[0010] If a capacitor has microcracks, applying a test voltage higher than the voltage from multiple energy storage cells to the capacitor can cause the microcracks to grow, intentionally inducing a short-circuit failure. If a short-circuit failure can be induced in the capacitor, it becomes possible to determine the capacitor's failure by observing the change in the measured voltage, thus enabling capacitor failure detection even after the energy storage device has been shipped.

[0011] [2] The energy storage device described in [1] above may include a discharge switch that switches between a capacitor and a discharge unit for discharging the capacitor. The discharge switch may connect the discharge unit to the capacitor by switching operation prior to applying the test voltage from the boost circuit to the capacitor, thereby discharging the capacitor. By applying the test voltage to the capacitor after it has been discharged, the change in the rise waveform of the capacitor's charge can be greatly increased, making it easier to grow microcracks. This makes it easier to intentionally cause a short-circuit failure when microcracks have occurred in the capacitor.

[0012] [3] In the energy storage device described in [1] or [2] above, the boost circuit may generate a test voltage based on the voltages from multiple energy storage cells connected in series. By having the boost circuit generate a high-voltage test voltage based on the voltages from multiple energy storage cells, the test voltage can be generated using existing power, eliminating the need to add a new power source to the energy storage device.

[0013] [4] Any of the energy storage devices described in [1] to [3] above may be equipped with a fault detection unit that determines whether or not a capacitor is faulty based on the measured voltage. If a short-circuit fault can be caused in the capacitor, the fault of the capacitor can be determined from the change in the measured voltage. In this respect, by equipping the energy storage device with a fault detection unit, when determining a capacitor fault, the operator does not need to use an external device to perform operations for fault detection, thereby reducing the workload on the operator.

[0014] [5] In the energy storage device described in [4] above, the fault detection unit may compare the measured voltage with a threshold and determine whether or not a capacitor is faulty based on the comparison result. Since the presence or absence of a capacitor fault can be determined by a simple method using a threshold, it is not necessary to configure the fault detection unit with a complex circuit.

[0015] (First Embodiment) Hereinafter, the energy storage device according to this embodiment will be described with reference to the drawings, using ESS (Energy Storage System) 1 as an example. ESS1 shown in Figure 1 is a device equipped with multiple energy storage modules 10, capable of supplying power from each energy storage module 10 to a load. In addition to the multiple energy storage modules 10, ESS1 mainly comprises a management device 50 that manages each energy storage module 10. ESS1 has a housing (not shown), and the energy storage modules 10 and the management device 50 are housed within this housing.

[0016] Multiple energy storage modules 10 are connected by wiring (not shown) to form multiple groups (banks). In the example shown in Figure 1, three banks are formed, and each bank is composed of multiple energy storage modules 10 connected in series. Note that the multiple energy storage modules 10 that make up each bank may be connected in parallel as well as in series. The number of energy storage modules that make up each bank can be arbitrarily selected. Furthermore, when the energy storage modules 10 that make up each bank are connected in parallel, a domain is formed. In other words, the multiple energy storage modules 10 are structured hierarchically in terms of banks and domains that aggregate these banks.

[0017] The power storage modules 10 that make up each bank are connected to the power line 3 via electromagnetic switches 55. The power line 3 is connected to, for example, a load not shown. The electromagnetic switches 55 can switch the presence or absence of power supply from each bank to the power line 3 by controlling the open / closed state by the management device 50.

[0018] The management device 50 is a device including a CPU, ROM, RAM, and a communication unit. A management device 50 for managing the power storage modules 10 is provided for each bank and each domain. Hereinafter, when distinguishing between the management device 50 provided in the bank and the management device 50 provided in the domain, the former is described as the management device 50A and the latter as the management device 50B to distinguish between the two.

[0019] The management device 50A provided in the bank can communicate with the battery monitoring board 12 with a communication function built into each power storage module 10 in the bank by serial communication via a communication line by means of the communication unit. As will be described later, the management device 50A acquires state data (such as the measured voltage Vm described later) of the power storage cells 13 inside the power storage module 10. The management device 50A also acquires data on the temperature measured by the power storage module 10 and data on the current measured for each bank. In addition to this, the management device 50A may execute management processes such as detection of communication state abnormalities.

[0020] The management device 50B located in the domain can communicate with the management device 50A located in the bank via a communication bus. The communication bus is, for example, a CAN (Controller Area Network) bus. Alternatively, the communication bus may be a LAN cable or an ECHONET / ECHONETLite® compatible communication medium. The management device 50B aggregates the status data acquired by the management device 50A and transmits the aggregated status data to an external device via a communication device 2. The communication device 2 may be a network card type device (network interface card) or another type of device.

[0021] (Regarding the configuration of the energy storage module) Next, the configuration of the energy storage module will be explained using Figure 2. The energy storage module 10 mainly comprises a plurality of energy storage cells 13 and a battery monitoring board 12. The plurality of energy storage cells 13 are connected in series between the positive terminal Tp and the negative terminal Tn, with N energy storage cells 13 forming a single battery pack 11. The energy storage cells 13 are, for example, lithium-ion battery cells, and their shape may be a prismatic cell, a cylindrical cell, or a laminated cell. In the following, when distinguishing each series-connected energy storage cell 13, the symbol "#n (where n is a number from 1 to N)" will be added to the designation to distinguish each energy storage cell 13. The same applies to the measurement line 14, Zener diode 19, and capacitor 20, which will be described later.

[0022] The battery monitoring board 12 mainly comprises a measurement unit 16 for measuring the voltage from each energy storage cell 13, a control unit 17, a communication IF 18 for communicating with the bank management device 50A, and a boost circuit 30. The positive and negative terminals of each energy storage cell 13 are connected to the measurement unit 16 via measurement lines 14 provided on the battery monitoring board 12. The measurement line 14 connected to the positive terminal side of an energy storage cell 13 is referred to as the "positive side measurement line," and the measurement line 14 connected to the negative terminal side is also referred to as the "negative side measurement line." For example, in energy storage cell 13#1, the negative side measurement line 14#2 is also the positive side measurement line 14#2 in energy storage cell 13#2. Furthermore, the positive side measurement line 14#1 connected to the positive terminal side of the energy storage cell 13#1, which is the highest-voltage energy storage cell 13, is also referred to as the "high-voltage side measurement line."

[0023] The measurement unit 16 is connected to the positive measurement line 14 in each energy storage cell 13 and can acquire a measured voltage Vm corresponding to the voltage generated in the positive measurement line 14. The control unit 17 is, for example, a microcomputer equipped with a CPU, ROM, RAM, etc., and can control the operation of the energy storage module 10 according to commands from the bank management device 50A acquired via the communication IF 18. In this embodiment, the measurement unit 16 and the control unit 17 are described as separate circuits, but the measurement unit 16 and the control unit 17 may be configured as a single circuit block that realizes each function.

[0024] The positive measurement line 14 is equipped with a power switch 21 that switches the connection between the energy storage cell 13 and the measurement unit 16. The power switch 21 is a PNP transistor, with its emitter side connected to the energy storage cell 13 and its collector side connected to the measurement unit 16. The base of the power switch 21 is connected to the control unit 17, and by switching its open / closed state in response to a drive signal from the control unit 17, it is possible to switch the electrical connection between the energy storage cell 13 and the measurement unit 16 via the positive measurement line 14. Note that the power switch 21 only needs to be capable of switching the connection between the energy storage cell 13 and the measurement unit 16, and may be an NPN transistor, a circuit with back-to-back FETs, or a similar component with the same function, in addition to a PNP transistor.

[0025] In the energy storage cell 13, capacitors 20 are connected to the positive and negative measurement lines 14 to smooth the voltage generated in the measurement lines 14. In other words, the capacitors 20 are provided in parallel with the energy storage cell 13 via the positive and negative measurement lines 14. In this embodiment, the capacitors 20 are ceramic capacitors.

[0026] In the energy storage cell 13, a protection circuit 15 is connected to the positive and negative measurement lines 14 to protect the measurement unit 16. In this embodiment, the protection circuit 15 is composed of a plurality of Zener diodes 19 provided in parallel with the energy storage cell 13 via the positive and negative measurement lines 14. Each Zener diode 19 has its cathode connected to the positive measurement line 14 and its anode connected to the negative measurement line 14, thereby generating a constant Zener voltage Vz when the reverse voltage exceeds a predetermined voltage.

[0027] In the energy storage cell 13, a discharge switch 22 and a discharge resistor 23, which is an example of a discharge section, are connected to the positive and negative measurement lines 14. The discharge switch 22 is an N-channel FET, with its drain connected to one end of the discharge resistor 23 and its source connected to the negative measurement line 14. The other end of the discharge resistor 23 that is not connected to the discharge switch 22 is connected to the positive measurement line 14. The gate of the discharge switch 22 is connected to the control unit 17, and by switching its open / closed state in response to a drive signal from the control unit 17, it is possible to switch between energizing and not energizing the discharge resistor 23 with the voltage generated in the positive measurement line 14.

[0028] In the energy storage module 10 with the above configuration, when the power switch 21 is closed, the voltage from each energy storage cell 13 is applied to the positive measurement line 14. Since a capacitor 20 is connected in parallel to each energy storage cell 13 via the positive and negative measurement lines 14, as the capacitor 20 charges, a smoothed voltage is input to the input terminal of the measurement unit 16. As a result, the measurement unit 16 can obtain a measured voltage Vm corresponding to the voltage from each energy storage cell 13. The obtained measured voltage Vm corresponding to each energy storage cell 13 is then transmitted to the bank management device 50A via the communication IF 18.

[0029] On the battery monitoring board 12, a boost circuit 30 is connected to the high-voltage measurement line 14#1, which is the highest-voltage side. As will be described later, the boost circuit 30 is a circuit for generating a test voltage Vis used to determine if the capacitor 20 is faulty. The test voltage Vis is also a voltage used to charge the capacitor 20 and promote the growth of microcracks if microcracks have occurred in the capacitor 20.

[0030] The boost circuit 30 has its input side connected via the voltage input line 24 to connection point K1 on the high-voltage side measurement line 14#1, prior to the power switch 21#1 (i.e., on the emitter side), and its output side connected via the voltage output line 25 to connection point K2 on the power switch 21, later than the power switch 21 (i.e., on the collector side). Connection point K1 is also the point on the high-voltage side measurement line 14#1 between the positive terminal side of the energy storage cell 13#1 and the emitter side of the power switch 21. Connection point K2 is also the point on the high-voltage side measurement line 14#1 between the collector side of the power switch 21 and the capacitor 20.

[0031] The voltage output line 25 is provided with a changeover switch 26 that can switch between connecting the boost circuit 30 and the high-voltage side measurement line 14#1. The changeover switch 26 is, for example, a P-channel FET, and its open / closed state is switched by a drive signal from the control unit 17.

[0032] The boost circuit 30 generates a test voltage Vis having twice the voltage value of the module voltage VCm by boosting the output of the multiple series-connected energy storage cells 13, i.e., the output from the battery pack 11. The boost circuit 30 mainly comprises an additive voltage generation unit 31 that generates an additive voltage Vp for generating the test voltage Vis, and a charge / discharge switching unit 32 that switches between charging and discharging by the additive voltage generation unit 31 in response to a drive signal from the control unit 17.

[0033] The summing voltage generation unit 31 includes a pair of forward-connected diodes 33 and 34, a buffer capacitor 35, and a summing voltage generation capacitor 36. The anode of diode 33 is connected to the voltage input line 24, and the cathode of diode 34 is connected to the voltage output line 25. One end of the buffer capacitor 35 is connected to the connection point of diodes 33 and 34, and one end of the summing voltage generation capacitor 36 is connected to the cathode of diode 34. The other ends of the summing voltage generation capacitor 36 and the buffer capacitor 35 are connected to the charge / discharge switching unit 32. In addition, a branch line 37 is connected to the anode side of diode 33, which supplies the module voltage VCm applied to the voltage input line 24 to the charge / discharge switching unit 32.

[0034] The charge / discharge switching unit 32 includes switches 38, 39, and 40 for switching the charging and discharging of the summing voltage generating capacitor 36 and the buffer capacitor 35. In this embodiment, switches 38 and 39 are N-channel FETs, and switch 40 is a P-channel FET. The drains of switches 39 and 40 are connected to each other via a resistor 41, and the gates of each are connected to a branch line 37. Switch 38 has its drain connected to a branch line 37 with a resistor 42, and its gate is connected to the control unit 17. The sources of switches 38 and 39 are connected to ground. In the charge / discharge switching unit 32 with the above configuration, the open / closed state of switch 38 is switched according to the value of the drive signal from the control unit 17, thereby switching the period in which switch 39 is open and the period in which switch 40 is open. This makes it possible for the charge / discharge switching unit 32 to switch the charging and discharging between the summing voltage generating capacitor 36 and the buffer capacitor 35, as will be described later.

[0035] Specifically, in the boost circuit 30, during the period when the power supply switch 21 is open, a drive signal from the control unit 17 causes switch 38 to open, and a voltage corresponding to the module voltage VCm is applied to the gates of switches 39 and 40 via the resistor 42 of the branch line 37. As a result, switch 39, which is an N-channel FET, closes (ON), and switch 40, which is a P-channel FET, opens (OFF), and a voltage corresponding to the module voltage VCm is input to the buffer capacitor 35 via the diode 33. This charges the buffer capacitor 35. After a predetermined period, the drive signal from the control unit 17 changes, causing switch 38 to close, which changes switch 39 from closed to open, and switch 40 from open to closed. In this state, the summing voltage generation capacitor 36 is charged by the discharge of the buffer capacitor 35 via the resistor 41. Subsequently, the drive signal from the control unit 17 changes at a predetermined cycle, switching the open / closed state of each switch 38-40 in the charge / discharge switching unit 32. This repeatedly charges the buffer capacitor 35 and charges the summation voltage generating capacitor 36 due to the discharge of the buffer capacitor 35. When the summation voltage generating capacitor 36 is fully charged, the voltage between the input and output sides of the boost circuit 30 (i.e., the voltage across both ends) becomes the summation voltage Vp, which is the same voltage as the module voltage VCm.

[0036] (Regarding capacitor failure detection) Next, using Figure 3, the process executed by the management device 50A when determining whether a capacitor 20 is faulty will be explained. The management device 50A determines whether a capacitor 20 in each energy storage module 10 is faulty by executing the process shown in Figure 3 during periods when the module voltage VCm, which is the output of the energy storage module 10, is not being used. Furthermore, since the process shown in the flowchart of Figure 3 is performed for one energy storage module 10 to be inspected, if the management device 50A wants to determine whether a capacitor 20 is faulty for all energy storage modules 10 that make up the bank, it will execute each of the processes shown in Figure 3 for all energy storage modules 10. In this embodiment, since ESS1 is an example of an energy storage device, the management device 50A is an example of a fault determination unit.

[0037] Figures 4(a), (b), and (c) are timing charts illustrating the operation of the energy storage module 10 when a fault detection of capacitor 20 is performed. Note that in Figures 4(a), (b), and (c), switches 21, 22, and 26 are schematically shown. As shown in Figure 4(a), in the normal state in the energy storage module 10 when a fault detection of capacitor 20 is not performed, the power supply switch 21 is in the closed state, the discharge switch 22 is in the open state, and the changeover switch 26 is in the open state. Therefore, the voltage from each energy storage cell 13 is applied to the positive electrode measurement line 14.

[0038] In step 10, the control device 50A initiates a discharge process to discharge the capacitor 20 of the energy storage module 10 to be inspected. Hereinafter, steps will also be referred to as "S". In this embodiment, by applying the inspection voltage Vis to the capacitor 20 through the process of S13 described later, microcracks are grown in capacitors 20 that have microcracks. At this time, if the charge of the capacitor 20 is low, applying the inspection voltage Vis can make the slope of the charge rise steeper than when there is residual charge, making it easier to grow microcracks. Therefore, in the discharge process, the control unit 17 of the energy storage module 10 outputs a drive signal as shown in Figure 4(b), opening the power supply switch 21 and closing the discharge switch 22. As a result, the charge of the capacitor 20 is discharged through the discharge resistor 23, and the measured voltage Vm measured by the measurement unit 16 decreases over time.

[0039] The control device 50A monitors the measured voltage Vm transmitted from the energy storage module 10 under inspection via the communication IF 18, and in S11, it determines whether the measured voltage Vm from all energy storage cells 13 in the energy storage module 10 under inspection has become less than or equal to the discharge judgment value Th1. The discharge judgment value Th1 is a value used to determine when the discharge of the capacitor 20 is complete, and is, for example, a value indicating approximately 0[V]. If the measured voltage Vm from all energy storage cells 13 is not less than or equal to the discharge judgment value Th1 (S11:NO), the control device 50A remains in standby mode.

[0040] When the control device 50A determines that the measured voltage Vm from all energy cells 13 in the energy storage module 10 under inspection has fallen below the discharge judgment value Th1 (S11: YES), it proceeds to S12 and sends a command to the energy storage module 10 under inspection to terminate the discharge process. As a result, the control unit 17 of the energy storage module 10 under inspection changes the drive signal to open the discharge switch 22 from the closed state, thereby stopping the discharge of the capacitor 20.

[0041] In S13, the control device 50A sends a command to the energy storage module 10 to be inspected to start charging the capacitor 20 with the inspection voltage Vis. The control unit 17 first outputs a drive signal to open the power supply switch 21 and the changeover switch 26. Then, the control unit 17 changes the drive signal output to the gate of the switch 38 at a predetermined period to start the generation of the summation voltage Vp by the summation voltage generation unit 31. As already explained, the drive signal output from the control unit 17 to the gate of the switch 38 changes at a predetermined period, causing the charging of the buffer capacitor 35 and the charging of the summation voltage generation capacitor 36 due to the discharge of the buffer capacitor 35 to be repeated.

[0042] The control unit 17 determines whether the summation voltage Vp, which is the voltage across the terminals of the summation voltage generation capacitor 36, has risen to the target voltage (i.e., the module voltage VCm). The control unit 17 may, for example, determine that the summation voltage Vp has reached the target voltage based on the output from a voltage sensor provided in the boost circuit 30. Alternatively, the control unit 17 may determine that the summation voltage Vp has reached the target voltage after a predetermined time has elapsed since the start of generation of the summation voltage Vp in response to a command from the management device 50A.

[0043] When the control unit 17 determines that the summation voltage Vp has reached the target voltage, it changes the drive signal to close the changeover switch 26, thereby starting to charge the capacitors 20 with the test voltage Vis. Specifically, as shown in Figure 4(c), when the changeover switch 26 is closed, the output side of the boost circuit 30, which is connected in series with the battery pack 11 via the voltage input line 24, is connected to the connection point K2 of the high-voltage side measurement line 14#1 via the voltage output line 25. As a result, each capacitor 20 is subjected to a test voltage Vis(VCm+Vp), which is the sum of the module voltage VCm from the battery pack 11 and the summation voltage Vp from the boost circuit 30, and starts to charge.

[0044] In S14, the control device 50A determines whether or not the capacitor 20 is faulty in the energy storage module 10 under inspection by using a threshold voltage determination value Th2 to determine the change in the rising waveform of the measured voltage Vm associated with the charging of the capacitor 20. Here, the voltage determination value Th2 is a value that indicates the lower limit of the terminal voltage of the capacitor 20 that is expected when a short circuit fault has not occurred in the capacitor 20.

[0045] Figures 5 and 6 show the changes in the measured voltage Vm corresponding to each capacitor 20 during fault detection. As an example, only the changes in the measured voltages Vm#1, Vm#2, and Vm#N corresponding to capacitors 20#1, 20#2, and 20#N are shown. In this embodiment, the control device 50A compares the magnitude of the measured voltage Vm and the voltage determination value Th2, and uses the opening width ΔV when the measured voltage Vm exceeds the voltage determination value Th2 to determine whether a capacitor 20 is faulty and, if so, the type of fault (short circuit fault, open circuit fault).

[0046] The control device 50A determines that all capacitors 20 are not faulty if, for all capacitors 20 being charged by the test voltage Vis, the measured voltage Vm exceeds the voltage determination value Th2 and the opening width ΔV is less than or equal to the difference determination value Th3. The "opening width ΔV" is the difference value (Vm-Th2) obtained by subtracting the voltage determination value Th2 from the measured voltage Vm when the measured voltage Vm exceeds the voltage determination value Th2, and in this embodiment, it is also a value used to determine the presence or absence of an open fault, which will be described later. The difference determination value Th3 is, for example, the upper limit of the difference value that can be expected when no open fault has occurred in the capacitor 20.

[0047] When the test voltage Vis is applied, microcracks in the capacitor 20 grow, causing a short circuit failure. In this case, the capacitor 20's ability to charge is significantly reduced. Therefore, the control device 50A determines that a short circuit failure has occurred in any capacitor 20 that is being charged by the test voltage Vis and whose measured voltage Vm is below the voltage judgment value Th2. In capacitors 20 that have not experienced a short circuit failure, the measured voltage Vm exceeds the voltage judgment value Th2, and the opening width ΔV converges to the difference judgment value Th3 or less.

[0048] In the example shown in Figure 5, a short-circuit fault has occurred in capacitor 20#1, and even after charging with the test voltage Vis, the measured voltage Vm#1 remains below the voltage judgment value Th2. On the other hand, capacitors 20#2 and 20#N do not have short-circuit faults, so their respective measured voltages Vm#2 and Vm#N are above the voltage judgment value Th2, and the opening width ΔV is less than or equal to the difference judgment value Th3.

[0049] Continued use of the energy storage module 10 may cause an open fault in the capacitor 20. When an open fault occurs in the capacitor 20, the capacitor 20 ceases to function, and the test voltage Vis applied to the positive measurement line 14 is input to the measurement unit 16. Therefore, the control device 50A determines that an open fault has occurred in any of the capacitors 20 that are being charged by the test voltage Vis, where the measured voltage Vm exceeds the voltage judgment value Th2 (Vm>Th2) and the opening width ΔV exceeds Th3 (ΔV>Th3).

[0050] Here, since a Zener diode 19 is connected to the measurement line 14 as a protection circuit 15, if the measured voltage Vm significantly exceeds the voltage judgment value Th2 due to an open fault, the measured voltage Vm will converge to the Zener voltage Vz. Also, at the capacitor 20 on the lower voltage side of the capacitor 20 where the open fault occurred, the measured voltage Vm will converge to a value less than or equal to the voltage judgment value Th2 ((Vis-Vz) / (N-1)).

[0051] In the example shown in Figure 6, an open fault has occurred in capacitor 20#2, with the measured voltage Vm#2 exceeding the voltage threshold Th2, and the opening width ΔV exceeding the differential threshold Th3. On the other hand, the measured voltages Vm#1 and Vm#N of the non-faulty capacitors 20#1 and 20#N are below the voltage threshold Th2.

[0052] In S15, if the control device 50A determines that there are no faulty capacitors 20 among all the capacitors 20 in the energy storage module 10 under inspection (S15: YES), it proceeds to S16 and sends a command to the energy storage module 10 under inspection to start the recovery process. As a result, the control unit 17 in the energy storage module 10 under inspection first opens the changeover switch 26 in response to a change in the output of the drive signal, thereby stopping the charging of each capacitor 20. Next, the control unit 17 closes the discharge switch 22 in response to a change in the output of the drive signal, thereby discharging the capacitors 20. In this embodiment, the control unit 17 stops the discharge of the capacitors 20 by opening the discharge switch 22 when the measured voltage Vm drops to a predetermined voltage (for example, a voltage equivalent to the voltage from the energy storage cell 13). The control unit 17 may also close the switch 38 for a certain period of time in response to the boost circuit 30 in response to the drive signal, thereby discharging the charge of the buffer capacitor 35 and the summing voltage generating capacitor 36 via the discharge resistor 23.

[0053] When the management device 50A finishes processing S16, it changes the energy storage module 10 in the bank to be inspected and performs processing S10 to S16, and S17 (described later), on the new energy storage module 10.

[0054] On the other hand, if the management device 50A determines that there is a faulty capacitor 20 in the energy storage module 10 (S15: NO), it proceeds to S17 and performs notification processing. In the notification processing, the management device 50A displays, for example, text or an image on an unillustrated display unit indicating that there is an energy storage module 10 with a faulty capacitor 20. In addition to this, the management device 50A may also notify the domain's management device 50B that a fault has occurred in one of the capacitors 20 in the energy storage module 10.

[0055] When the management device 50A performs the notification process in S17, it enters a standby state. In this standby state, it prevents the use of the bank containing the energy storage module 10 with the faulty capacitor 20 until the faulty capacitor 20 and other components are replaced. Specifically, the management device 50A isolates the bank containing the energy storage module 10 with the faulty capacitor 20 from the other banks by opening the electromagnetic switch 55 (shown in Figure 1) that connects the banks in parallel. As a result, ESS1 can continue to be used by supplying power to the load from a bank where the capacitor 20 is not faulty. Alternatively, ESS1 itself may be made unusable in the standby state.

[0056] Furthermore, even when the management device 50A performs notification processing in S17, it may change the energy storage module 10 to be inspected and perform the processing in S10 to S17 for the new energy storage module 10 that has not yet been subjected to fault detection.

[0057] The embodiment described above can achieve the following effects. The energy storage module 10 is equipped with a capacitor 20 connected in parallel to the energy storage cell 13 via a measurement line 14. When a failure of the capacitor 20 is detected, the boost circuit 30 applies a test voltage Vis, which is higher than the module voltage VCm from the battery pack 11, to the positive measurement line 14#1 to charge the capacitor 20. This makes it possible to determine whether or not the capacitor 20 is faulty by applying the high-voltage test voltage Vis to the capacitor 20 after the ESS1 has been shipped, thereby causing the microcrack to grow.

[0058] The control unit 17 closes the discharge switch 22 to discharge the capacitor 20, and then applies the test voltage Vis from the boost circuit 30 to the capacitor 20. This increases the change in the rising edge waveform of the charge of the capacitor 20, making it easier to grow microcracks, and for capacitors 20 that have microcracks, it is possible to intentionally cause a short-circuit failure.

[0059] The boost circuit 30 generates a high-voltage test voltage Vis based on the module voltage VCm from the battery pack 11, thereby utilizing existing power to generate the test voltage Vis and eliminating the need to add a new power source within the energy storage module 10.

[0060] The management device 50A (fault detection unit) that manages the energy storage modules 10 that make up the bank determines whether or not there is a fault in the capacitor 20 provided in the energy storage module 10. This allows the fault detection of the capacitor 20 to be completed within the ESS1, eliminating the need for an operator to operate an external device for fault detection and reducing the workload on the operator.

[0061] The control device 50A compares the measured voltage Vm with the voltage determination value Th2 and determines whether or not the capacitor 20 is faulty based on the comparison result, thereby enabling the determination of whether or not the capacitor 20 is faulty in a simple method using the threshold voltage determination value Th2.

[0062] (Second Embodiment) In the second embodiment, the same reference numerals are used for the same components as in the first embodiment, and their descriptions are not repeated. In this embodiment, the configuration differs from the first embodiment in that two capacitors connected in series are provided in parallel in the energy storage cell 13.

[0063] As shown in Figure 7, two capacitors 60 and 61 connected in series are connected to the positive and negative measurement lines 14 of each energy storage cell 13. Therefore, one measurement voltage Vm is measured for each pair of capacitors 60 and 61 by the measurement unit 16. In this embodiment, the bank management device 50A determines whether or not there is a fault in a pair of capacitors 60 and 61 based on the comparison result of the measurement voltage Vm and the voltage determination value Th4 in the fault determination in S14 of Figure 3.

[0064] The control device 50A determines that all capacitors 60 and 61 are not faulty if the measured voltage Vm of a pair of capacitors 60 and 61, which are being charged by the test voltage Vis, exceeds the voltage determination value Th4, and the opening width ΔV is less than or equal to the difference determination value Th5. Note that the voltage determination value Th4 used in this embodiment is a different value from the voltage determination value Th2 used in the first embodiment, but they may be the same value. Similarly, the difference determination value Th5 used in this embodiment is a different value from the difference determination value Th3 used in the first embodiment, but they may be the same value.

[0065] If a short circuit occurs in at least one of a pair of capacitors 60 and 61, the combined capacitance of the pair of capacitors 60 and 61 changes, leading to a decrease in their ability to charge. For example, if one of a pair of capacitors 60 and 61 experiences a short circuit, the combined capacitance becomes larger than when no short circuit occurs, reducing the amount of charge stored in the pair of capacitors 60 and 61. Therefore, in this embodiment as well, the control device 50A determines that a pair of capacitors 60 and 61 being charged by the test voltage Vis has a short circuit if the measured voltage Vm is below the voltage determination value Th4. Note that a short circuit occurs in a pair of capacitors 60 and 61 if at least one of the capacitors 60 and 61 has a short circuit. The same applies to open circuit failures, which will be described later. In this case, for a pair of capacitors 60 and 61 that does not have a short circuit, the measured voltage Vm is above the voltage determination value Th4, and the opening width ΔV is less than or equal to the difference determination value Th5.

[0066] In the example shown in Figure 8, a short-circuit fault occurs in capacitor 60#1 of a pair of capacitors 60#1 and 61#1, and even after charging with the test voltage Vis, the measured voltage Vm#1 is below the voltage judgment value Th4. On the other hand, in the pair of capacitors 60#2 and 60#2, and the pair of capacitors 60#N and 60#N, which are not faulty, the measured voltages Vm#2 and Vm#N are above the voltage judgment value Th4, and the opening width ΔV is less than or equal to the difference judgment value Th5.

[0067] If an open fault occurs in a pair of capacitors 60 and 61, the procedure is the same as in the first embodiment. That is, the control device 50A determines that an open fault has occurred in a pair of capacitors 60 and 61 that are charged by the test voltage Vis, if the measured voltage Vm exceeds the voltage determination value Th4 (Vm > Th4) and the opening width ΔV exceeds Th5 (ΔV > Th5). In this case as well, the capacitor 20 that does not have an open fault will have a measured voltage Vm below the voltage determination value Th4.

[0068] In the embodiment described above, even in an energy storage module 10 equipped with two capacitors 60 and 61 connected in series, it is possible to determine whether or not the capacitors 60 and 61 have failed after the product has been shipped.

[0069] (Regarding other embodiments) The technologies disclosed herein are not limited to the embodiments described above, and the following embodiments, for example, are also included in the technical scope disclosed herein. In the above embodiment, ESS1 was described as an example of an energy storage device. The energy storage device can be configured to include multiple energy storage cells 13, and may be an emergency power supply such as a UPS (Uninterruptible Power System). Alternatively, an energy storage module 10 may be considered as an energy storage device.

[0070] In the above embodiment, prior to determining the capacitor failure in S14, the control device 50A discharged the capacitor 20(60,61) in S10. Alternatively, the control device 50A may perform the failure determination in S14 without discharging the capacitor 20(60,61).

[0071] In the above embodiment, the boost circuit 30 generated an added voltage Vp for generating the test voltage Vis using the module voltage VCm from the battery pack 11. Alternatively, the boost circuit 30 may generate the test voltage Vis using a voltage supplied from a power supply circuit (not shown).

[0072] In the above embodiment, the control device 50A determined in S14 that the capacitor 20 had both a short-circuit fault and an open-circuit fault. Alternatively, the control device 50A may be configured to determine only the short-circuit fault of the capacitor 20 in S14.

[0073] In the above embodiment, the bank management device 50A performed fault detection on the capacitors 20 in each energy storage module 10. Alternatively, if the energy storage module 10 is considered as an energy storage device, the control unit 17 of the energy storage module 10 may perform the fault detection unit for the capacitors 20. In this case, the control unit 17 only needs to execute the series of processes S10 to S17 in Figure 3. In addition, an external device that can communicate with the ESS1 via the communication device 2 may function as the fault detection unit. [Explanation of symbols]

[0074] 1:ESS, 10: Energy storage module, 12: Battery monitoring board, 13: Energy storage cell, 14: Measurement line, 15: Protection circuit, 16: Measurement unit, 17: Control unit, 20: Capacitor, 21: Power switch, 22: Discharge switch, 23: Discharge resistor, 26: Changeover switch, 30: Boost circuit, 50: Management device, 60, 61: Capacitors, Vis: Test voltage, Vm: Measurement voltage

Claims

1. Multiple energy storage cells connected in series, A measuring unit that measures a measurement voltage corresponding to the voltage of the energy storage cell, Positive and negative measurement lines connecting the energy storage cell and the measurement unit, A capacitor connected in parallel to the energy storage cell via the aforementioned measurement line, A power storage device comprising: a boost circuit that charges the capacitor by applying a test voltage higher than the voltage from a plurality of series-connected power storage cells to the positive measurement line in order to determine if the capacitor is faulty.

2. In the energy storage device according to claim 1, The capacitor is equipped with a discharge switch that switches between whether or not it is connected to a discharge unit that discharges the capacitor. The discharge switch is an energy storage device that, prior to the application of the test voltage by the boost circuit to the capacitor, connects the discharge section to the capacitor by an opening and closing operation to discharge the capacitor.

3. In the energy storage device according to claim 1 or claim 2, The boost circuit is a power storage device that generates the test voltage based on the voltages from a plurality of series-connected power storage cells.

4. In the energy storage device according to claim 1 or claim 2, A power storage device comprising a fault determination unit that determines whether or not the capacitor is faulty based on the measured voltage.

5. In the energy storage device according to claim 4, The fault determination unit compares the measured voltage with a threshold value and determines whether or not the capacitor is faulty based on the comparison result, in this energy storage device.

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