Energy storage device

Abstract

The present invention provides an energy storage device that can perform capacitor failure detection in an energy storage device equipped with multiple energy storage cells connected in series. [Solution] The energy storage module 10 includes capacitors 20 and 21 connected in parallel to the energy storage cell 13 via positive and negative measurement lines 14, an AC wave generation switch 23 connected to the energy storage cell 13 side of the connection point of the capacitors 20 and 21 on the measurement line 14, which switches the energization of the capacitors 20 and 21 based on the voltage generated on the measurement line 14, and a control unit 17 which opens and closes the AC wave generation switch 23 at a predetermined switching frequency to apply a test voltage Vin to the capacitors 20 and 21 in order to determine if the capacitors 20 and 21 are faulty.

Description

Technical Field

[0004] ,

[0006] , , ,

[0005] , , ,

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

Background Art

[0002] Patent Document 1 describes a device that measures the current from a storage battery by a measurement unit and determines the state of the storage battery according to the measured current.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a power storage device including a plurality of power storage cells, for the purpose of smoothing the output from the power storage cells, it is conceivable to provide a capacitor in parallel to the power storage cells. However, the capacitor may fail due to continuous use of the power storage device, and it is desired to be able to determine the failure of the capacitor even after the product is shipped. Therefore, there is still room for improvement in the failure determination of the capacitor in the power storage device. <0​​​​​​​​​The energy storage device of this disclosure comprises a plurality of energy storage cells connected in series, a measurement unit that measures a measurement voltage corresponding to the voltage from 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, a switching element connected to the energy storage cells on the measurement line side of the capacitor connection point and switching the energization of the capacitor based on the voltage generated in the measurement lines, and a drive unit that opens and closes the switching element at a predetermined switching frequency to apply a test voltage to the capacitor in order to determine if the capacitor is faulty. [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 diagram illustrates how the attenuation of the capacitor's output voltage changes depending on the frequency of the input voltage. [Figure 4] This flowchart explains the procedures that the management device performs when a fault is detected. [Figure 5] This diagram illustrates the operation of the energy storage module when a capacitor failure is detected. [Figure 6] This figure shows the changes in each waveform during capacitor failure detection. [Figure 7] This figure shows the changes in the measured voltage corresponding to each capacitor during fault detection. [Figure 8] This figure shows the changes in the measured voltage corresponding to each capacitor during fault detection. [Figure 9] 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] 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 from 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, a switching element connected to the energy storage cells side of the connection point of the capacitor on the measurement line and switching the energization of the capacitor based on the voltage generated on the measurement line, and a drive unit that opens and closes the switching element at a predetermined switching frequency to apply a test voltage to the capacitor in order to determine if the capacitor is faulty.

[0010] When a capacitor malfunctions, its cutoff frequency changes, and the attenuation of the output voltage with respect to the input voltage at low frequencies becomes greater than when there is no malfunction. Therefore, by driving the switching element at a predetermined switching frequency, a test voltage corresponding to the switching frequency is applied to the capacitor. The value of the measured voltage obtained after passing through the capacitor changes according to the malfunction mode, and this measured voltage can be used to determine whether or not the capacitor is malfunctioning.

[0011] [2] The energy storage device described in [1] above may include a fault detection unit that determines whether or not a capacitor is faulty based on the measured voltage. By including a fault detection unit in the energy storage device, the operator does not need to use an external device to perform operations for fault detection of the capacitor, thereby reducing the workload on the operator.

[0012] [3] In the energy storage device described in [2] above, the fault detection unit may determine that the capacitor is short-circuited if the amplitude of the measured voltage is smaller than a predetermined threshold. When a capacitor is short-circuited, the attenuation of the output voltage is greater than when it is not faulty, provided that the frequency of the test voltage applied to the capacitor is the same. Therefore, the change in the amplitude of the measured voltage according to the switching frequency is determined using a threshold, and if the measured voltage is smaller than the threshold, it is determined that the capacitor is short-circuited. This makes it possible to determine a short-circuited capacitor using a simple method with a threshold.

[0013] [4] In the energy storage device described in [3] above, there is a first threshold and a second threshold that is greater than the first threshold. The fault determination unit may determine that the capacitor has a short circuit failure when the amplitude of the measured voltage is less than the first threshold, and determine that the capacitor has an open circuit failure when the amplitude of the measured voltage is greater than the second threshold. When the capacitor has an open circuit failure, the amplitude of the measured voltage is greater than when the capacitor is not faulty. Therefore, the unit determines that the capacitor has an open circuit failure when the amplitude of the measured voltage is greater than the second threshold, which is different from the first threshold used to determine a short circuit failure. This makes it possible to determine not only short circuit failures but also open circuit failures in the capacitor, thereby increasing the reliability of fault determination.

[0014] [5] In the energy storage device described in any one of the above items [1] to [4], the drive unit may open and close the switching element at a switching frequency corresponding to the cutoff frequency when it is assumed that the capacitor is not faulty. In the above configuration, by using a known cutoff frequency to determine a short circuit fault, it becomes easier to capture the change in the measured voltage before and after the capacitor failure, and the accuracy of fault detection can be improved.

[0015] [Embodiment] Hereinafter, the energy storage device according to this embodiment will be described by taking the ESS (abbreviation of Energy Storage System) 1 as an example while referring to the drawings. The ESS 1 shown in FIG. 1 includes a plurality of energy storage modules 10 and is a device capable of supplying power from each energy storage module 10 to a load. The ESS 1 mainly includes, in addition to the plurality of energy storage modules 10, a management device 50 that manages each energy storage module 10. The ESS 1 includes a housing (not shown), and the energy storage module 10 and the management device 50 are housed in this housing.

[0016] The plurality of energy storage modules 10 are connected by wiring (not shown) to form a plurality of groups (banks). In the example shown in FIG. 1, three banks are formed, and each bank is configured by connecting a plurality of energy storage modules 10 in series. In addition to being connected in series, the plurality of energy storage modules 10 constituting each bank may be connected in parallel. The number of energy storage modules constituting each bank can be arbitrarily selected. Also, by connecting the energy storage modules 10 constituting each bank in parallel, a domain is formed. That is, the plurality of energy storage modules 10 are hierarchically structured by banks and domains that aggregate these banks.

[0017] The energy storage module 10 constituting each bank is connected to the power line 3 via an electromagnetic switch 55. The power line 3 is connected to, for example, a load (not shown). The electromagnetic switch 55 can switch the presence or absence of power supply from each bank to the power line 3 by controlling its 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 energy storage module 10 is provided for each bank and each domain. Hereinafter, when distinguishing between the management device 50 provided for the bank and the management device 50 provided for the domain, the former will be referred to as the management device 50A and the latter as the management device 50B for distinction.

[0019] The management device 50A installed in the bank can communicate via serial communication through a communication line with the battery monitoring board 12 with communication function built into each energy storage module 10 in the bank, via a communication unit. As will be described later, the management device 50A acquires status data (such as the measured voltage Vm described later) of the energy storage cells 13 inside the energy storage module 10. The management device 50A also acquires temperature data measured in the energy storage module 10 and current data measured separately for each bank. In addition to the above, the management device 50A may also perform management processing such as detecting abnormalities in the communication status.

[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 and capacitors 20 and 21, 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, and a communication IF 18 for communicating with the bank management device 50A. 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 of the energy storage cell 13 is referred to as the "positive side measurement line," and the measurement line 14 connected to the negative terminal 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.

[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] In the energy storage cell 13, a pair of capacitors 20 and 21 are connected to the positive and negative measurement lines 14 to smooth the voltage generated in the measurement lines 14. In this embodiment, the voltage generated in the measurement lines 14 is smoothed by two capacitors 20 and 21 connected in series. In other words, the capacitors 20 and 21 are provided in parallel with the energy storage cell 13 via the positive and negative measurement lines 14. In this embodiment, capacitor 20 is a ceramic capacitor. Hereafter, the pair of capacitors connected in series will also be referred to as "capacitors 20 and 21".

[0025] In the energy storage cell 13, the positive and negative measurement lines 14 are connected to an AC wave generation switch 23 and a first resistor 24 for switching the energization of capacitors 20 and 21. The AC wave generation switch 23 is, for example, an N-channel FET, with its drain connected to one end of the first resistor 24 and its source connected to the negative measurement line 14. In other words, the drain of the AC wave generation switch 23 is connected to the positive measurement line 14, prior to capacitors 20 and 21, via the first resistor 24. The other end of the first resistor 24, which is not connected to the AC wave generation switch 23, is connected to the positive measurement line 14. The gate of the AC wave generation switch 23 is connected to the control unit 17, and it opens and closes in response to a drive signal from the control unit 17. The AC wave generation switch 23 and the first resistor 24 are also elements for adjusting the balance of the SOC (State of Charge) for each energy storage cell 13. In this embodiment, the control unit 17 is an example of a drive unit. Note that the AC wave generation switch 23 may be a P-channel FET in addition to an N-channel FET.

[0026] A second resistor 25 is provided between the first resistor 24 and capacitors 20 and 21 on the positive measurement line 14. The resistance value R2 of the second resistor 25 is greater than the resistance value R1 of the first resistor 24 (R2 > R1). As a result, as will be described later, during the period when the AC wave generation switch 23 is closed, more current tends to flow to the first resistor 24 on the positive measurement line 14.

[0027] 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.

[0028] In the energy storage module 10 with the above configuration, the voltage from the energy storage cell 13 causes current to flow to the second resistor 25, allowing the measurement unit 16 to acquire a measured voltage Vm that has been smoothed by capacitors 20 and 21. The acquired measured voltage Vm is then transmitted to the bank management device 50A via the communication IF 18.

[0029] Due to deterioration from use, capacitors 20 and 21 in the energy storage module 10 may fail. Therefore, the management device 50A performs a fault detection to determine whether or not capacitors 20 and 21 have failed, based on the change in the measured voltage Vm output from the energy storage module 10. Here, if capacitors 20 and 21 are considered as low-pass filters, the frequency characteristics of capacitors 20 and 21 can be shown by a graph with the vertical axis as the gain [dB], which is a value corresponding to the ratio of the input voltage to the output voltage, and the horizontal axis as the frequency of the input voltage, as shown in Figure 3. In Figure 3, it is shown that the attenuation of the output voltage relative to the input voltage increases as the frequency of the input voltage increases. In this case, the cutoff frequency fc is the frequency of the input voltage at which the gain [dB] is reduced to a predetermined value (for example, -3dB).

[0030] If at least one of capacitors 20 or 21 shorts out, the combined capacitance of capacitors 20 and 21 increases, causing the cutoff frequency fc to shift to a lower frequency. In the example shown in Figure 3, the cutoff frequency changes from fc to a lower frequency fc' due to the increase in combined capacitance, and in the waveform showing the frequency response (shown by the dashed line), the return region and attenuation region shift to the lower frequency side. Therefore, after a short-circuit failure, capacitors 20 and 21 are more likely to attenuate the output voltage at lower frequencies compared to capacitors 20 and 21 before the failure. In the example in Figure 3, when comparing at the cutoff frequency fc before the failure, the output voltage attenuation of capacitors 20 and 21 before the failure is -3dB, while the output voltage attenuation of capacitors 20 and 21 after the failure is greater than -3dB, at -MdB. In other words, when comparing at the same input voltage frequency, the output voltage attenuation is greater before and after the failure of capacitors 20 and 21.

[0031] Therefore, the control device 50A opens and closes the AC wave generation switch 23 at a predetermined test frequency Fa, thereby applying a test voltage Vin, which is an input voltage that changes at this test frequency Fa, to capacitors 20 and 21. Then, it determines whether or not capacitors 20 and 21 are faulty from the measured voltage Vm corresponding to the output voltage after attenuation.

[0032] (Regarding capacitor failure detection) Next, using Figure 4, the process executed by the management device 50A when determining whether a capacitor 20 is faulty will be explained. During periods when no processing such as SOC balance adjustment is being performed on the energy storage modules 10, that is, during periods when the AC wave generation switch 23 is not opening or closing, the management device 50A determines whether a capacitor 20 or 21 in each energy storage module 10 is faulty by the process shown in Figure 4. Furthermore, since the process shown in the flowchart of Figure 4 is performed on one energy storage module 10 to be inspected, if the management device 50A wants to determine whether a capacitor 20 or 21 is faulty for all energy storage modules 10 that make up the bank, it will execute the processes shown in Figure 4 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.

[0033] Figures 5(a) and 5(b) are timing charts illustrating the operation of the energy storage module 10 when a fault detection of capacitor 20 is performed. In Figures 5(a) and 5(b), the AC wave generation switch 23 is schematically shown. As shown in Figure 5(a), in the normal state in the energy storage module 10 when a fault detection of capacitor 20 is not performed, the AC wave generation switch 23 is in the open state, and the voltage from each energy storage cell 13 is applied to the positive electrode measurement line 14.

[0034] In step 10, the control device 50A opens and closes the AC wave generation switch 23 at the test frequency Fa for the energy storage module 10 to be inspected, thereby applying a test voltage Vin to the capacitors 20 and 21. Hereafter, this step will also be referred to as "S". In this embodiment, the test frequency Fa is the expected cutoff frequency fc for the capacitors 20 and 21 when no faults occur.

[0035] Figures 6(a), (b), and (c) are diagrams illustrating the processing in S10. Of these, Figure 6(a) shows the transition of the gate-source voltage Vgs generated at the gate of the AC wave generation switch 23 by the drive signal output from the control unit 17. Figure 6(b) shows the transition of the input voltage applied to capacitors 20 and 21, i.e., the test voltage Vin. Figure 6(c) shows the transition of the voltage across capacitors 20 and 21, i.e., the measured voltage Vm, in response to the application of the test voltage Vin to capacitors 20 and 21. Hereafter, among the drive signals output from the control unit 17, the signal applied to the gate of the AC wave generation switch 23 will be referred to as the test signal and distinguished from other drive signals.

[0036] The control unit 17 outputs a pulsed test signal corresponding to the test frequency Fa, causing the gate-source voltage Vgs generated at the gate of the AC wave generation switch 23 to change according to the test frequency Fa, as shown in Figure 6(a). During the period when the gate-source voltage Vgs is below the gate threshold of the AC wave generation switch 23, the AC wave generation switch 23 is in an open state (as shown in Figure 5(a)). On the other hand, during the period when the gate-source voltage Vgs is above the gate threshold of the AC wave generation switch 23, the AC wave generation switch 23 is in a closed state (as shown in Figure 5(b)). Here, by opening and closing the AC wave generation switch 23 at the test frequency Fa, the switching period Tsw of the AC wave generation switch 23 becomes a period corresponding to the test frequency Fc (Tsw = 1 / Fc). In one switching period Tsw, the period during which the AC wave generation switch 23 is in a closed state is referred to as the on period Ton, and the period during which the AC wave generation switch 23 is in an open state is also referred to as the off period Toff.

[0037] As shown in Figure 6(a), during the off period Toff, the AC wave generation switch 23 is in the open state. Therefore, as shown in Figure 5(a), the voltage from the energy storage cell 13 is input to capacitors 20 and 21 as a test voltage Vin via the second resistor 25. As a result, as shown in Figures 6(b) and (c), capacitors 20 and 21 are charged in accordance with the test voltage Vin applied to them, and the voltage across them (i.e., the measured voltage Vm) increases.

[0038] On the other hand, as shown in Figure 6(b), during the ON period Ton, the AC wave generation switch 23 is closed. Therefore, as shown in Figure 5(b), more current flows through the first resistor 24 than through the second resistor 25 due to the voltage from the energy storage cell 13. As a result, as shown in Figures 6(b) and (c), the test voltage Vin via the second resistor 25 is not applied to the capacitors 20 and 21. Note that in Figure 6(b), for the sake of explanation, the input voltage Vin applied to the capacitors 20 and 21 during the ON period Ton is set to "0".

[0039] The peak value of the measured voltage Vm is determined by the attenuation amount corresponding to the frequency characteristics of capacitors 20 and 21, as explained earlier. Therefore, in S11, the control device 50A determines whether or not there is a fault in capacitor 20 of the energy storage module 10 under inspection by determining the measured voltage Vm using threshold values ​​Th1 and Th2.

[0040] Figures 7, 8, and 9 show the changes in the measured voltage Vm corresponding to each capacitor 20 and 21 during fault determination in S14. As an example, only the changes in the measured voltages Vm#1, Vm#2, and Vm#N corresponding to each set of capacitors 20#1 and 21#1, 20#2 and 21#2, and 20#N and 21#N are shown. In Figures 7 to 9, the test voltage Vin applied to each capacitor 20 and 21 is shown by a dashed line. In this embodiment, the control device 50A determines whether or not a capacitor 20 is faulty and, if so, the type of fault (short circuit fault, open circuit fault) by comparing the amplitude ΔV of the measured voltage Vm with the determination values ​​Th1 and Th2.

[0041] First, let's explain the case where capacitors 20 and 21 are not faulty, using Figure 7. The control device 50A determines that capacitors 20 and 21 are not faulty if the amplitude ΔV of the measured voltage Vm is greater than or equal to the first judgment value Th1 and less than or equal to the second judgment value Th2. Here, the amplitude ΔV of the measured voltage Vm is the voltage difference between the peak value Vmax and the bottom value Vmin of the measured voltage Vm in one switching cycle Tsw. As described above, when a pulsed test voltage Vin is applied to capacitors 20 and 21, charging and discharging occur in capacitors 20 and 21 in one switching cycle Tsw, and the measured voltage Vm changes between the peak value Vmax and the bottom value Vmin. At this time, the peak value Vmax of the measured voltage Vm will be a value corresponding to the test frequency Fa. Note that in Figures 7 to 9, the bottom value Vmin is set to a value close to 0 for the sake of explanation, but the actual bottom value Vmin will be a value corresponding to the charge of capacitors 20 and 21.

[0042] For example, each time the test voltage Vin is applied to capacitors 20 and 21, the control device 50A detects the peak value Vmax and the bottom value Vmin of the measured voltage Vm within one switching cycle Tsw. The control device 50A may then use the average value of the multiple peak values ​​Vmax and bottom values ​​Vmin obtained as a value for calculating the amplitude ΔV. The first judgment value Th1 is the lower limit of the expected amplitude ΔV of the measured voltage Vm when the test voltage Vin is applied to capacitors 20 and 21 that are not faulty. The second judgment value Th2 is a value greater than the first judgment value Th1 and is the upper limit of the expected amplitude ΔV of the measured voltage Vm when the test voltage Vin is applied to capacitors 20 and 21 that are not faulty.

[0043] As shown in Figure 3, if capacitors 20 and 21 are not faulty, their capacitance and combined capacitance do not change. Therefore, the peak value Vmax of the measured voltage Vm obtained by applying the test voltage Vin to capacitors 20 and 21 corresponds to the test frequency Fa. For this reason, the control device 50A determines that there is no short-circuit fault in capacitors 20 and 21 if the amplitude ΔV of the measured voltage Vm is greater than or equal to the first determination value Th1. In the example shown in Figure 7, since no fault has occurred in any pair of capacitors 20 and 21, the amplitude ΔV of each measured voltage Vm♯1, Vm♯2, and Vm♯N is greater than or equal to the first determination value Th1.

[0044] If a short circuit occurs in capacitors 20 and 21, the combined capacitance of capacitors 20 and 21 increases, and the cutoff frequency fc shifts to the lower frequency side. Therefore, after a failure, the peak value Vmax of the measured voltage Vm is attenuated more significantly when the same test voltage Vin at the same test frequency Fa is applied to capacitors 20 and 21 before the failure. Note that a short circuit occurs in capacitors 20 and 21, including cases where either one of the pair of capacitors 20 and 21 has a short circuit failure, and cases where both capacitors 20 and 21 have short circuit failures. For this reason, the control device 50A determines that a pair of capacitors 20 and 21 has a short circuit failure if the amplitude ΔV of the measured voltage Vm is below the first judgment value Th1. Note that for capacitors 20 and 21 that do not have a short circuit failure, as explained above, the amplitude ΔV of the measured voltage Vm is greater than or equal to the first judgment value Th1.

[0045] In the example shown in Figure 8, a short-circuit fault has occurred in the capacitor pair 20♯2 and 21♯2, and the amplitude ΔV of the measured voltage Vm♯2 is below the first judgment value Th1. On the other hand, since no fault has occurred in the capacitor pairs 20♯1 and 21♯1, and 20♯N and 21♯N, the amplitude ΔV of the respective measured voltages Vm♯1 and Vm♯N is greater than or equal to the first judgment value Th1.

[0046] Continued use of ESS1 may cause open faults in capacitors 20 and 21. When open faults occur in capacitors 20 and 21, the capacitance of capacitors 20 and 21 and the combined capacitance change significantly, resulting in a high peak value Vmax of the measured voltage Vm. Note that an open fault in capacitors 20 and 21 includes cases where either one of the pair of capacitors 20 and 21 has an open fault, and cases where both capacitors 20 and 21 have an open fault. Therefore, the control device 50A determines that an open fault has occurred in capacitors 20 and 21 if the amplitude ΔV of the measured voltage Vm is greater than the second determination value Th2.

[0047] In the example shown in Figure 9, an open fault occurs in the capacitor pair 20♯2 and 21♯2, and the measured voltage Vm♯2 is greater than the second judgment value Th2. In this embodiment, since a protection circuit 15 is provided on the measurement line 14, the measured voltage Vm in the case of an open fault converges to the Zener voltage Vz (>Th2) of the Zener diode 19. On the other hand, since capacitors 20♯1, 21♯1, and 20♯N, 21♯N are not faulty, the amplitude ΔV of each measured voltage Vm♯1, Vm♯N is greater than the first judgment value Th1, but smaller than the second judgment value Th2.

[0048] In S12, if the control device 50A determines that there are no faulty capacitors 20 or 21 among all the capacitors 20 or 21 in the energy storage module 10 under inspection (S12: YES), it proceeds to S13 and sends a command to the energy storage module 10 under inspection to start the recovery process. In the recovery process in S13, for example, the control unit 17 may open or close the AC wave generation switch 23 so that the charge of the faulty capacitors 20 or 21 becomes a predetermined voltage (for example, the voltage from the energy storage cell 13).

[0049] When the control device 50A completes the process in S13, it changes the energy storage module 10 in the bank to be inspected and executes processes S10 to S13, and the later-described processes S14 to S16, on the new energy storage module 10.

[0050] On the other hand, if the management device 50A determines that there is a faulty capacitor 20 or 21 among the capacitors 20 or 21 in the energy storage module 10 (S12: NO), it proceeds to S14 and updates the fault determination history, which records whether or not the capacitors 20 or 21 are faulty. The fault determination history contains information indicating whether or not a fault has occurred in the capacitors 20 or 21 in each energy storage module 10. When the management device 50A determines that a fault has occurred in the capacitors 20 or 21 of the energy storage module 10 under inspection, it changes the fault flag in the fault determination history to a value indicating that it is faulty. In addition to this, it is desirable that the fault determination history also contains information that can identify the energy storage module 10 in which a fault in the capacitors 20 or 21 has been determined.

[0051] In this embodiment, the update of the fault determination history in S14 is performed for each energy storage module 10 that constitutes the bank. Therefore, once a fault flag indicating that a fault has occurred has been set for the energy storage module 10 under inspection, the fault flag will remain at the same value even if a fault is determined for another capacitor 20 or 21 in the same energy storage module 10.

[0052] The management device 50A proceeds to S15 and performs notification processing. That is, the management device 50A prompts the replacement of the energy storage module 10 in which capacitors 20 and 21 have failed through 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 in which capacitor 20 has failed. In addition to this, the management device 50A may also notify the domain's management device 50B that a capacitor 20 in the energy storage module 10 has failed.

[0053] When the management device 50A finishes the notification process in S15, it proceeds to S16 and refers to the fault determination history to determine whether the number of fault flags is K or greater. Here, "K" is the number at which it can be determined that a bank can continue to be used even if there is a storage module 10 in a single bank where capacitors 20 and 21 have failed. In this embodiment, "K=2". The number of fault flags K at which a bank can continue to be used can be set appropriately according to the number of storage modules 10 that make up the bank. If the number of fault flags is less than K, the management device 50A proceeds to the recovery process in S13. That is, it continues to use the bank in question. This prevents the ESS1 from becoming unnecessarily unavailable by continuing to use the bank even if there is a storage module 10 in a single bank where capacitors 20 and 21 have failed, as long as it can continue to be used.

[0054] Furthermore, capacitors 20 and 21 that have been found to have a short-circuit failure have a higher combined capacitance than capacitors 20 and 21 that have not been found to have a short-circuit failure. Therefore, if continued use is to be performed, the increase in combined capacitance must be taken into consideration. For example, when adjusting the SOC balance for capacitors 20 and 21, it is expected that the voltage across the capacitors 20 and 21 that have been found to have a short-circuit failure will recover more slowly than the capacitors that have not been found to have a short-circuit failure. For this reason, it is desirable to take the increase in combined capacitance into consideration when adjusting the SOC balance and performing subsequent processing on capacitors 20 and 21 that have been found to have a short-circuit failure.

[0055] After completing the process in S13 for the current target energy storage module 10, the management device 50A changes the target energy storage module 10 and performs the processes in S10 to S12, which have already been described, for the new energy storage module 10. If the management device 50A determines that capacitors 20 and 21 are faulty based on the process in S12 for the new energy storage module 10 (S12: NO), it proceeds to S14 and increases the fault flag in the fault determination history by 1. After executing the notification process in S15, the management device 50A proceeds to S16, and if the value indicated by the fault flag is K or more, it enters a standby state.

[0056] In standby mode, the control device 50A prevents the use of the bank containing the energy storage module 10 with the faulty capacitors 20 and 21 until the faulty capacitors 20 and 21, including the faulty capacitors, are replaced. Specifically, the control 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 standby mode.

[0057] Furthermore, even in standby mode, the management device 50A may change the energy storage module 10 to be inspected and execute the processes S10 to S16 on the new energy storage module 10 that has not yet been subjected to fault detection.

[0058] The embodiment described above can achieve the following effects. The control device 50A opens and closes the AC wave generation switch 23 at the test frequency Fa, thereby applying a test voltage Vin, which changes according to this test frequency Fa, to capacitors 20 and 21. At this time, the measured voltage Vm that has passed through capacitors 20 and 21 changes due to the change in capacitance according to the failure mode of capacitors 20 and 21, and this measured voltage Vm can be used to determine whether or not capacitors 20 and 21 are faulty.

[0059] The control device 50A determines whether or not capacitors 20 and 21 are faulty, eliminating the need for operators to use external devices to perform fault detection operations and thus reducing the workload on operators.

[0060] The control device 50A determines that a short-circuit fault has occurred in capacitors 20 and 21 when the amplitude ΔV of the measured voltage Vm is smaller than the first determination value Th1. This allows the presence or absence of a short-circuit fault in capacitors 20 and 21 to be determined using a simple method with the threshold value Th1, thereby reducing the processing load on the control device 50A when determining the fault of capacitors 20 and 21.

[0061] The control device 50A (fault determination unit) determines that capacitors 20 and 21 have an open fault if the amplitude ΔV of the measured voltage Vm is greater than the second determination value Th2. This makes it possible to determine the presence or absence of open faults as well as short faults for capacitors 20 and 21, thereby improving the reliability of fault determination.

[0062] The control device 50A opens and closes the AC wave generation switch 23 at a test frequency Fa corresponding to the cutoff frequency fc when capacitors 20 and 21 are assumed not to be faulty, thereby applying a test voltage Vin to capacitors 20 and 21. By using the known cutoff frequency fc of the capacitors 20 and 21 under test to determine whether or not a fault exists, it becomes easier to capture the change in the measured voltage Vm before and after a fault in capacitors 20 and 21, thereby improving the accuracy of fault detection.

[0063] (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 a UPS (Uninterruptible Power System) in addition to ESS1. Furthermore, an energy storage module 10 may also be considered as an energy storage device.

[0064] In the above embodiment, the bank management device 50A performed fault detection on the capacitors 20 and 21 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 have the function of a fault detection unit for determining whether or not the capacitors 20 and 21 are faulty. In this case, the control unit 17 can perform the series of processes S10 to S16 in Figure 4. In addition, an external device such as a management PC that can communicate with the ESS1 via the communication device 2 may function as a fault detection unit.

[0065] In the above embodiment, the test frequency Fa used was the cutoff frequency fc assumed when capacitors 20 and 21 are not faulty. The test frequency Fa is not limited to the above cutoff frequency fc, and should be a value that can capture the change in the measured voltage Vm in response to the application of the test voltage Vin before and after the failure of capacitors 20 and 21.

[0066] In the above embodiment, the control device 50A determined whether capacitors 20 and 21 were faulty using only one test voltage Vin at a single test frequency Fa. Alternatively, the control device 50A may determine whether capacitors 20 and 21 are faulty using test voltage Vin at multiple different test frequencies Fa. For example, in S10, the control device 50A applies test voltage Vin at two different test frequencies Fa1 and Fa2 to capacitors 20 and 21, respectively. Then, it can determine whether a fault is present using the measured voltage Vm corresponding to each test frequency Fa1 and Fa2. In this case, in S11, the values ​​of the determination values ​​Th1 and Th2 can be changed according to the test frequencies Fa1 and Fa2 used. This increases the redundancy of fault determination for capacitors 20 and 21.

[0067] In the above embodiment, each energy storage module 10 had a pair of capacitors 20 and 21 connected in parallel to the energy storage cell 13. Alternatively, each energy storage module 10 may have only one capacitor connected in parallel to the energy storage cell 13.

[0068] In the above embodiment, the control device 50A determined in S11 that in addition to a short circuit fault of capacitors 20 and 21, there was also an open circuit fault. Alternatively, the control device 50A may determine in S11 only that there was a short circuit fault of capacitors 20 and 21.

[0069] In the above embodiment, the management device 50A entered a standby state in S16 if the number of energy storage modules 10 with faulty capacitors 20 and 21 was K or more. Alternatively, if the management device 50A determined in S12 that there was a fault in capacitors 20 and 21 (S12: NO), it may perform only the notification process in S15 without executing processes S14 and S16. [Explanation of Symbols]

[0070] 10: Energy storage module, 11: Battery pack, 12: Battery monitoring board, 13: Energy storage cell, 14: Measurement line, 15: Protection circuit, 16: Measurement unit, 17: Control unit (drive unit), 20, 21: Capacitor, 22: Power switch, 23: AC wave generation switch, 24: First resistor, 25: Second resistor, 50: Management device (fault detection unit), 55: Electromagnetic switch, Th1: First judgment value (first threshold), Th2: Second judgment value (second threshold), Vm: Measurement voltage

Claims

1. Multiple energy storage cells connected in series, A measuring unit that measures a measurement voltage corresponding to the voltage from 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, In the measurement line, a switching element is connected to the energy storage cell side of the capacitor connection point and switches the presence or absence of current flow to the capacitor based on the voltage generated in the measurement line, A power storage device comprising: a drive unit that opens and closes the switching element at a predetermined switching frequency to apply a test voltage to the capacitor in order to determine if the capacitor is faulty.

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

3. In the energy storage device according to claim 2, The fault determination unit determines that the capacitor is short-circuited when the amplitude of the measured voltage is smaller than a predetermined threshold.

4. In the energy storage device according to claim 3, The threshold includes a first threshold and a second threshold that is greater than the first threshold. The fault determination unit, If the amplitude of the measured voltage is smaller than the first threshold, it is determined that the capacitor is short-circuited. A power storage device that determines that the capacitor is in an open fault when the amplitude of the measured voltage is greater than the second threshold value.

5. In the energy storage device according to any one of claims 1 to 4, The drive unit is an energy storage device that opens and closes the switching element at a switching frequency corresponding to the cutoff frequency when it is assumed that the capacitor is not faulty.

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