Electricity storage device and battery deterioration state estimation method

Abstract

This electricity storage device comprises: a chargeable / dischargeable secondary battery; a control unit that controls charging / discharging of the secondary battery; and a storage unit that stores deterioration characteristic information relating to the deterioration characteristics of the secondary battery. The secondary battery is a nickel-zinc secondary battery in which a discharge depth and a capacity deterioration rate per charge / discharge are in a predetermined linear relationship. The storage unit stores information indicating the linear relationship as the deterioration characteristic information. The control unit estimates the deterioration state of the secondary battery on the basis of the number of charge / discharge times for each discharge depth of the secondary battery and the deterioration characteristic information stored in the storage unit.

Description

Power storage device and method for estimating battery deterioration state

[0001] The present invention relates to a power storage device and a method for estimating a battery degradation state.

[0002] Conventionally, backup power storage devices have been known that are connected to a power supply device that supplies power to various electrical devices, store the power supplied from the power supply device, and, if the power supply from the power supply device is interrupted, supply power to the various electrical devices using the stored power instead of the power supply device. The secondary batteries used in such power storage devices generally gradually deteriorate with repeated charging and discharging, resulting in a gradual decrease in battery capacity. Therefore, in order to properly operate the power storage device, it is necessary to accurately estimate the battery capacity deterioration rate (the rate at which the battery capacity remains relative to its initial state).

[0003] A known technique for estimating the degradation rate of battery capacity in a secondary battery is described, for example, in Patent Document 1. Patent Document 1 describes a method for detecting the internal state of a secondary battery, which calculates a capacity degradation coefficient D for a secondary battery with reduced storage capacity from a change in open circuit voltage Voc before and after charging or before and after discharging and the increase or decrease in the amount of stored electricity at that time, or a change in battery voltage Vc during charging or battery voltage Vd during discharging and the increase or decrease in the amount of stored electricity at that time.

[0004] Japanese Patent Application Publication No. 2011-257411

[0005] In recent years, nickel-zinc batteries using zinc as the negative electrode have been developed to be usable as secondary batteries by adopting a structure that allows repeated charging and discharging. These nickel-zinc secondary batteries have the characteristic of exhibiting smaller voltage changes due to differences in the amount of stored charge than conventional secondary batteries such as lithium-ion batteries. Therefore, when a power storage device is constructed using nickel-zinc secondary batteries, it is difficult to accurately estimate the rate of deterioration of the battery capacity using the method described in Patent Document 1.

[0006] In view of the above-mentioned problems, an object of the present invention is to accurately estimate the state of battery degradation in an electricity storage device using nickel-zinc secondary batteries.

[0007] The present invention provides a power storage device comprising: a rechargeable secondary battery; a control unit that controls charging and discharging of the secondary battery; and a memory unit that stores degradation characteristic information relating to the degradation characteristics of the secondary battery, wherein the secondary battery is a nickel-zinc secondary battery having a predetermined linear relationship between its depth of discharge and its capacity degradation rate per charge and discharge, the memory unit stores information representing the linear relationship as the degradation characteristic information, and the control unit estimates the degradation state of the secondary battery based on the number of charge and discharge cycles of the secondary battery for each depth of discharge and the degradation characteristic information stored in the memory unit. The present invention also provides a method for estimating the degradation state of a rechargeable secondary battery, wherein the secondary battery is a nickel-zinc secondary battery having a predetermined linear relationship between its depth of discharge and its capacity degradation rate per charge and discharge, and the method estimates the degradation state of the secondary battery based on the number of charge and discharge cycles of the secondary battery for each depth of discharge and the information representing the linear relationship.

[0008] According to the present invention, it is possible to accurately estimate the state of battery degradation in an electricity storage device using nickel-zinc secondary batteries.

[0009] 1 is a schematic diagram of an energy storage device according to an embodiment of the present invention; a graph showing an example of degradation characteristic information; a flowchart showing a processing flow of an energy storage device according to an embodiment of the present invention; a flowchart showing details of a charge control process; a flowchart showing details of a discharge control process; and a flowchart showing details of a capacity maintenance rate calculation process.

[0010] Fig. 1 is a schematic diagram of a power storage device according to one embodiment of the present invention. The power storage device 1 shown in Fig. 1 is a device that stores power supplied from an external source and is capable of discharging the stored power to supply it to various electrical devices, and is used, for example, as a backup power source for various electrical devices and for adjusting supply and demand in a power grid. Below, an example will be described in which the power storage device 1 is connected to a power generation system (not shown) (for example, a solar power generation system, a wind power generation system, etc.) and an electrical device, and performs cyclic operation in which charging and discharging are repeated between them to adjust supply and demand in a power grid, but the device can also be used for other purposes.

[0011] The power storage device 1 includes a secondary battery 10 , a control unit 11 , a switch 12 , a voltage detection unit 14 , a current detection unit 15 , and a storage unit 17 .

[0012] The secondary battery 10 is connected to a power generation system and electrical equipment (not shown) via a switch 12. When power is supplied from the power generation system, the secondary battery 10 is charged under the control of the control unit 11, thereby storing power in the secondary battery 10. On the other hand, when the operation of the power generation system is stopped, the secondary battery 10 is discharged under the control of the control unit 11, and power is supplied from the secondary battery 10 to the electrical equipment. A nickel-zinc secondary battery using zinc as the anode is used as the secondary battery 10.

[0013] The switch 12 is provided between the secondary battery 10 and the power generation system and electrical equipment, and is switched between a conductive state and a cut-off state under the control of the control unit 11. The switch 12 is configured using, for example, a relay, an IGBT (Insulated Gate Bipolar Transistor), an FET (Field Effect Transistor), or the like.

[0014] The voltage detection unit 14 detects the voltage between the positive and negative electrodes of the secondary battery 10 as the battery voltage and outputs the detection result to the control unit 11. The current detection unit 15 detects the charge / discharge current flowing through the secondary battery 10 and outputs the detection result to the control unit 11.

[0015] The control unit 11 controls charging and discharging of the secondary battery 10. The control unit 11 has the following functional blocks: a charge / discharge amount calculation unit 111, a state-of-charge calculation unit 112, a degradation state estimation unit 113, an alarm unit 114, and a switching control unit 115. The control unit 11 is configured using, for example, a microcomputer, and can realize these functional blocks by executing a predetermined program. Note that the control unit 11 may also be configured using a logic circuit such as an FPGA (Field Programmable Gate Array) instead of a microcomputer.

[0016] The charge / discharge amount calculation unit 111 calculates the charge / discharge amount (the amount of power stored in or discharged from the secondary battery 10) during charging and discharging of the secondary battery 10. The charge / discharge amount calculation unit 112 calculates a state of charge (SOC) value representing the state of charge of the secondary battery 10 based on the charge / discharge amount calculated by the charge / discharge amount calculation unit 111. The degradation state estimation unit 113 estimates the degradation state of the secondary battery 10 based on the charge / discharge history of the secondary battery 10 and estimates the current battery capacity of the secondary battery 10 according to the estimation result. The warning unit 114 determines whether degradation of the secondary battery 10 is progressing based on the estimation result of the degradation state of the secondary battery 10 by the degradation state estimation unit 113, and outputs a warning to the user if it is determined that degradation is progressing. The switching control unit 115 controls the switching state of the switch 12 according to a predetermined operation switching condition to switch the operation state of the power storage device 1 to a charging operation, a discharging operation, or a standby state. Specific details of these processes will be described later.

[0017] The storage unit 17 is configured using a storage medium such as a RAM or a flash memory, and stores various information used in the processing of the control unit 11. For example, the storage unit 17 stores information such as a program executed by the control unit 11, the latest SOC value of the secondary battery 10 calculated by the state-of-charge calculation unit 112, and the current battery capacity of the secondary battery 10 estimated by the degradation state estimation unit 113. The storage unit 17 also stores degradation characteristic information, which is information related to the degradation characteristics of the secondary battery 10. When the degradation state estimation unit 113 estimates the degradation state of the secondary battery 10, this degradation characteristic information is used.

[0018] 2 is a graph showing an example of deterioration characteristic information stored in the storage unit 17. In FIG. 2, a solid line graph 21 and a dashed line graph 22 represent deterioration characteristic information when the upper limit SOC of the secondary battery 10 is 100% and 80%, respectively. Specifically, the line graph 21 shows the deterioration characteristic of the secondary battery 10 when the secondary battery 10 is charged to an SOC value of 100% and then discharged. The line graph 22 shows the deterioration characteristic of the secondary battery 10 when the secondary battery 10 is charged to an SOC value of 80% and then discharged. In these line graphs 21 and 22, the horizontal axis represents the depth of discharge (DOD) of the secondary battery 10, and the vertical axis represents the capacity deterioration rate of the secondary battery 10 per charge / discharge (the ratio of the amount of decrease in battery capacity to the initial battery capacity). In FIG. 2, the values ​​on the vertical axes of the linear graphs 21 and 22 are normalized by setting the capacity deterioration rate per discharge of the secondary battery 10 from 100% to 80% as 1.

[0019] As shown by the linear graphs 21 and 22 in Fig. 2, the secondary battery 10 has a characteristic of a nickel-zinc secondary battery, in which the depth of discharge and the capacity degradation rate per charge / discharge are linearly related. That is, the secondary battery 10 has a degradation characteristic in which the battery capacity decreases at a constant rate according to the depth of discharge at each charge / discharge. Such degradation characteristic of the secondary battery 10 does not change significantly even with an increase in the number of charge / discharge cycles, and the relationship between the number of charge / discharge cycles of the secondary battery 10 and the capacity retention rate (the ratio of the battery capacity after degradation to the battery capacity in the initial state) is expressed by a linear equation with a slope that depends on the depth of discharge.

[0020] The inventors of the present invention have found through experiments and the like that when a nickel-zinc secondary battery is used as the secondary battery 10, the secondary battery 10 has the above-described deterioration characteristics. In the energy storage device 1 of this embodiment, this deterioration characteristic is utilized to perform the processing described below, thereby estimating the current deterioration state from the charge / discharge history of the secondary battery 10, calculating the battery capacity according to the deterioration state, and controlling the charge / discharge of the secondary battery 10.

[0021] 3 is a flowchart showing a flow of processing in the power storage device according to one embodiment of the present invention. The power storage device 1 controls charging and discharging of the secondary battery 10 by causing the control unit 11 to execute the processing shown in the flowchart in FIG. 3 at predetermined processing intervals.

[0022] In step S10, the control unit 11 determines whether or not to start charging the secondary battery 10. If it is determined that charging should be started, the process proceeds to step S20. If it is determined that charging should not be started, the process proceeds to step S30. The determination in step S10 can be made based on a predetermined determination condition. For example, the control unit 11 can determine that charging of the secondary battery 10 should be started when a preset date and time arrives, or when the power generated by a power generation system (not shown) reaches a predetermined value or more.

[0023] In step S20, the control unit 11 switches the switch 12 from OFF (disconnected state) to ON (conductive state) using the switching control unit 115. This allows power from the power generation system to be input to the power storage device 1 to charge the secondary battery 10. After the switch 12 is switched ON in step S20, the process proceeds to step S40.

[0024] In step S30, the control unit 11 determines whether the secondary battery 10 is being charged. If the secondary battery 10 is being charged, that is, if the switch 12 has been switched from OFF to ON in step S20 in the previous or previous processing and has not been switched OFF since, the process proceeds to step S40. On the other hand, if the secondary battery 10 is not being charged, that is, if the switch 12 has been switched OFF in the previous or previous processing, the process proceeds to step S50.

[0025] In step S40, the control unit 11 executes a charging control process for the secondary battery 10 during charging. Details of this process will be described later with reference to Fig. 4. After the charging control process is executed in step S40, the process proceeds to step S90.

[0026] In step S50, the control unit 11 determines whether or not to start discharging the secondary battery 10. If it is determined that discharging should be started, the process proceeds to step S60. If it is determined that discharging should not be started, the process proceeds to step S70. The determination in step S50 can be made based on a predetermined determination condition, as in step S10. For example, it can be determined that discharging of the secondary battery 10 should be started when a preset date and time arrives, or when the power generated by a power generation system (not shown) falls below a predetermined value.

[0027] In step S60, control unit 11 switches switch 12 from OFF (disconnected state) to ON (conductive state) using switching control unit 115. This causes the power stored in secondary battery 10 to be discharged and supplied to the electrical equipment from power storage device 1. After switch 12 is switched ON in step S60, the process proceeds to step S80.

[0028] In step S70, the control unit 11 determines whether the secondary battery 10 is discharging. If the secondary battery 10 is discharging, that is, if the switch 12 has been switched from OFF to ON in step S60 in the previous or previous processing and has not been switched OFF since, the process proceeds to step S80. On the other hand, if the secondary battery 10 is not discharging, that is, if the switch 12 has been switched OFF in the previous or previous processing, the process proceeds to step S90.

[0029] In step S80, the control unit 11 executes a discharge control process for the discharging secondary battery 10. Details of this process will be described later with reference to Fig. 5. After the discharge control process is executed in step S80, the process proceeds to step S90.

[0030] In step S90, the control unit 11 causes the degradation state estimation unit 113 to execute a capacity maintenance rate calculation process for calculating a capacity maintenance rate according to the current degradation state of the secondary battery 10. In this process, the control unit 11 estimates the current degradation state of the secondary battery 10 based on the degradation characteristic information of the secondary battery 10 stored in the storage unit 17, and calculates the capacity maintenance rate of the secondary battery 10 according to the estimation result. Details of the capacity maintenance rate calculation process executed in step S90 will be described later with reference to FIG. 6 .

[0031] In step S100, the control unit 11 determines whether the capacity maintenance rate of the secondary battery 10 calculated in step S90 is less than a predetermined threshold (e.g., 50%). If the capacity maintenance rate of the secondary battery 10 is less than the threshold, i.e., if the deterioration of the secondary battery 10 has progressed beyond a predetermined deterioration state and the battery capacity has decreased to an extent that interferes with the operation of the energy storage device 1, the process proceeds to step S110. On the other hand, if the capacity maintenance rate of the secondary battery 10 is equal to or greater than the threshold, i.e., if the deterioration state of the secondary battery 10 is within an acceptable range and the battery capacity is maintained to an extent that does not cause problems in the operation of the energy storage device 1, the process shown in the flowchart of FIG. 3 is terminated without executing step S110, and the process waits until the next processing cycle.

[0032] In step S110, the control unit 11 causes the alarm unit 114 to output a predetermined alarm to the user of the power storage device 1. Here, the alarm is output to notify the user of the ongoing deterioration of the secondary battery 10, for example, by outputting a predetermined sound or image (video) from a speaker or display device (not shown) provided in the power storage device 1, or by turning on a warning lamp installed in a position visible to the user. In addition to these, as long as it is possible to notify the user of the deterioration of the secondary battery 10, the alarm can be output to the user by any method in step S110.

[0033] After the warning is output in step S110, the process shown in the flowchart of FIG. 3 ends and the process waits until the next processing cycle.

[0034] FIG. 4 is a flowchart showing the details of the charge control process executed in step S40 of FIG.

[0035] In step S410, the charge / discharge amount calculation unit 111 acquires the current value of the secondary battery 10 from the current detection unit 15. Here, the current value acquired indicates the magnitude of the charging current in the secondary battery 10 during charging.

[0036] In step S420, the charge / discharge amount calculation unit 111 calculates an integrated current value for the period from the previous processing to the current processing. Here, for example, the integrated current value can be calculated by multiplying the current value acquired in step S410 by a predetermined processing period. Alternatively, the integrated current value may be calculated by acquiring a current value multiple times at predetermined sampling periods during one processing period, multiplying each current value by the sampling period, and adding up the results.

[0037] In step S430, the state-of-charge calculation unit 112 updates the SOC value of the secondary battery 10 based on the current integrated value calculated in step S420. Here, for example, the increase in the SOC value due to charging between the previous processing and the current processing is calculated from the ratio between the current integrated value calculated in step S420 and the maximum capacity of the secondary battery 10, and this increase is added to the SOC value at the previous processing. This updates the SOC value of the secondary battery 10 to the latest value, reflecting the current integrated value during the period from the previous processing to the current processing. The SOC value updated in step S430 is stored in the storage unit 17. The SOC value at the previous processing refers to the SOC value calculated by the state-of-charge calculation unit 112 in the most recently executed charge control processing at step S40 or the most recently executed discharge control processing at step S80, and is stored in the storage unit 17.

[0038] In step S440, the latest SOC value calculated in step S430 is equal to or exceeds a predetermined upper limit S Ｈ It is determined whether the latest SOC value reaches the upper limit value S Ｈ When the upper limit S Ｈ If it is equal to or greater than the upper limit value S Ｈ If the upper limit S Ｈ If it is less than this, the process proceeds to step S450.

[0039] In step S450, it is determined whether a preset charge stop condition is satisfied. If the charge stop condition is satisfied, the process proceeds to step S460. If the charge stop condition is not satisfied, the process shown in the flowchart of FIG. 4 ends and charging of secondary battery 10 continues. Here, it can be determined whether to continue charging of secondary battery 10 based on preset charge stop conditions for, for example, the current date and time, the elapsed time since charging started, the power generated by the power generation system, the power consumption of electrical devices, etc.

[0040] In step S460, the switching control unit 115 switches the switch 12 from ON (conducting state) to OFF (disconnecting state) to stop charging the secondary battery 10. This switches the operating state of the power storage device 1 from charging to standby. After the charging of the secondary battery 10 is stopped by executing the processing of step S460, the processing shown in the flowchart of FIG. 4 ends.

[0041] 4 described above, after charging of the secondary battery 10 is stopped in step S460, the voltage value (OCV: Open Circuit Voltage) of the secondary battery 10 may be acquired from the voltage detection unit 14, and the cumulative error in the integrated current value included in the SOC value of the secondary battery 10 calculated in step S430 may be corrected based on this voltage value. In this way, the error included in the SOC value due to the cumulative error in the integrated current value during charging can be removed, and an accurate SOC value after charging is stopped can be calculated.

[0042] FIG. 5 is a flowchart showing the details of the discharge control process executed in step S80 of FIG.

[0043] In step S810, the charge / discharge amount calculation unit 111 acquires the current value of the secondary battery 10 from the current detection unit 15. Here, the current value acquired indicates the magnitude of the discharge current in the secondary battery 10 during discharge.

[0044] In step S820, the charge / discharge amount calculation unit 111 calculates an integrated current value for the period from the previous processing to the current processing. Here, similar to step S420 in Fig. 4 described above, the integrated current value can be calculated by multiplying the current value acquired in step S810 by a predetermined processing period. Alternatively, the integrated current value may be calculated by acquiring a current value multiple times at predetermined sampling periods during one processing period, multiplying each current value by the sampling period, and adding up the results.

[0045] In step S830, the state-of-charge calculation unit 112 updates the SOC value of the secondary battery 10 based on the integrated current value calculated in step S820. Here, for example, the amount of decrease in the SOC value due to discharge between the previous processing and the current processing is calculated from the ratio between the integrated current value calculated in step S820 and the maximum capacity of the secondary battery 10, and this decrease is subtracted from the SOC value at the time of the previous processing. As a result, the SOC value of the secondary battery 10 is updated to the latest value, reflecting the integrated current value during the period from the previous processing to the current processing, similar to step S430 in FIG. 4 described above. The SOC value updated in step S830 is stored in the storage unit 17.

[0046] In step S840, the latest SOC value calculated in step S830 is equal to or lower than the predetermined lower limit S Ｌ It is determined whether the latest SOC value reaches the lower limit value S Ｌ When the lower limit S Ｌ If it is equal to or less than the lower limit value S Ｌ If the lower limit S Ｌ If it is greater than , the process proceeds to step S850.

[0047] In step S850, it is determined whether a preset discharge stop condition is satisfied. If the discharge stop condition is satisfied, the process proceeds to step S860. If the discharge stop condition is not satisfied, the process shown in the flowchart of Fig. 5 is terminated and the discharge of secondary battery 10 is continued. Here, as in step S450 in Fig. 4 described above, it is possible to determine whether to continue the discharge of secondary battery 10 based on preset discharge stop conditions, for example, the current date and time, the elapsed time since the start of discharge, the power generated by the power generation system, the power consumption of electrical devices, etc.

[0048] In step S860, the switching control unit 115 switches the switch 12 from ON (conducting state) to OFF (blocking state) to stop discharging the secondary battery 10. This switches the operating state of the energy storage device 1 from discharging to a standby state.

[0049] In step S870, the state-of-charge calculation unit 112 calculates the depth of discharge of the secondary battery 10 in the current discharge. Here, the depth of discharge in the current discharge is calculated by calculating the difference between the SOC value at the start of discharge, i.e., the SOC value last calculated in the most recently executed charge control process in step S40, and the SOC value at the end of discharge, i.e., the SOC value calculated in the immediately preceding step S830. In this way, the depth of discharge of the secondary battery 10 is calculated for each charge / discharge cycle based on the states of charge of the secondary battery 10 at the start and end of discharge.

[0050] In step S880, the SOC value at the start of discharge used to calculate the depth of discharge in step S870 and the depth of discharge calculated in step S870 are recorded in association with the current number of charge / discharge cycles in storage unit 17. The current number of charge / discharge cycles is the total number of charge / discharge cycles of secondary battery 10 that have been performed since the start of operation of power storage device 1, and is counted up by one each time the process of step S880 is executed, and is stored in storage unit 17 together with the SOC value at the start of discharge and the depth of discharge. As a result, data on the SOC value at the start of discharge and the depth of discharge are recorded in storage unit 17 for each charge / discharge cycle.

[0051] After the SOC value and depth of discharge at the start of discharge are recorded in the storage unit 17 in step S880, the process shown in the flowchart of FIG. 5 ends.

[0052] 5 described above, after discharging of the secondary battery 10 is stopped in step S860, the voltage value (OCV) of the secondary battery 10 may be acquired from the voltage detection unit 14, and the cumulative error in the current integrated value included in the SOC value of the secondary battery 10 calculated in step S830 may be corrected based on this voltage value. In this way, the error included in the SOC value due to the cumulative error in the current integrated value during discharging can be removed, and an accurate SOC value after discharging is calculated.

[0053] FIG. 6 is a flowchart showing the details of the capacity maintenance rate calculation process executed in step S90 of FIG.

[0054] In step S910, the degradation state estimation unit 113 acquires, from the storage unit 17, the SOC value and the depth of discharge at the start of discharge in each charge / discharge cycle in the charge / discharge cycles that have been performed so far of the secondary battery 10. As described above, in the discharge control process of Fig. 5 , the depth of discharge is calculated each time the discharge of the secondary battery 10 is stopped, and the data is stored in the storage unit 17 together with the SOC value at the start of discharge. In step S910, by reading the data on the SOC value and the depth of discharge at the start of discharge from the storage unit 17, it is possible to acquire the SOC value and the depth of discharge at the start of discharge in each charge / discharge cycle in the charge / discharge cycles that have been performed so far on the secondary battery 10.

[0055] In step S920, the degradation state estimation unit 113 calculates the number of charge / discharge cycles for each depth of discharge of the secondary battery 10 based on the depth of discharge in each charge / discharge cycle obtained in step S910. Here, the number of charge / discharge cycles for each depth of discharge can be determined by grouping and aggregating the number of data on the depth of discharge obtained in step S910 by the depth of discharge value represented by the data.

[0056] In step S930, the degradation state estimation unit 113 acquires degradation characteristic information of the secondary battery 10 from the storage unit 17. As described above, the storage unit 17 pre-stores degradation characteristic information indicating the relationship between the number of charge / discharge cycles and the capacity maintenance rate of the secondary battery 10, as illustrated in Fig. 2. In step S930, the degradation characteristic information of the secondary battery 10 can be acquired by reading this degradation characteristic information from the storage unit 17.

[0057] In step S940, the degradation state estimation unit 113 calculates the battery capacity of the secondary battery 10 after degradation based on the number of charge / discharge cycles for each depth of discharge calculated in step S920 and the degradation characteristic information acquired in step S930. Here, for each combination of the SOC value at the start of discharge and the depth of discharge value, the degradation state estimation unit 113 acquires a corresponding capacity degradation rate by referring to the degradation characteristic information, and multiplies the capacity degradation rate by the number of charge / discharge cycles to obtain degradation capacity values, which are then totaled for all depths of discharge, thereby calculating the battery capacity after degradation according to the degradation state of the secondary battery 10. In this way, the degradation state of the secondary battery 10 can be estimated based on the number of charge / discharge cycles for each depth of discharge of the secondary battery 10 and the degradation characteristic information stored in the storage unit 17.

[0058] In step S950, the degradation state estimation unit 113 calculates a capacity maintenance rate according to the current degradation state of the secondary battery 10, based on the post-degradation battery capacity calculated in step S940. Here, the current capacity maintenance rate can be calculated by determining the ratio of the post-degradation battery capacity to the initial battery capacity. Note that the capacity maintenance rate calculated in step S950 is compared with a predetermined threshold value in step S100 of FIG. 3, as described above. If the capacity maintenance rate falls below the threshold value, an alarm is output in step S110 to notify the user.

[0059] Once the capacity maintenance rate is calculated in step S950, the process shown in the flowchart of FIG. 6 ends.

[0060] According to the embodiment of the present invention described above, the following advantageous effects are achieved.

[0061] (1) The energy storage device 1 includes a chargeable and dischargeable secondary battery 10, a control unit 11 that controls the charging and discharging of the secondary battery 10, and a memory unit 17 that stores degradation characteristic information related to the degradation characteristics of the secondary battery 10. The secondary battery 10 is a nickel-zinc secondary battery in which the depth of discharge and the capacity degradation rate per charge and discharge have a predetermined linear relationship as shown in FIG. 2 . The memory unit 17 stores information representing this linear relationship as degradation characteristic information. The control unit 11 estimates the degradation state of the secondary battery 10 based on the number of charge and discharge cycles of the secondary battery 10 for each depth of discharge and the degradation characteristic information stored in the memory unit 17 (step S940). This allows for accurate estimation of the degradation state of the energy storage device 1 that uses a nickel-zinc secondary battery as the secondary battery 10.

[0062] (2) The energy storage device 1 includes a current detection unit 15 that detects the current flowing through the secondary battery 10. The control unit 11 determines the state of charge of the secondary battery 10 based on the integrated value of the current detected by the current detection unit 15 (steps S430 and S830), and determines the depth of discharge of the secondary battery 10 for each charge / discharge cycle based on the state of charge at the start and end of discharge of the secondary battery 10 (step S870). Then, based on the depth of discharge of the secondary battery 10 determined for each charge / discharge cycle, the control unit 11 calculates the number of charge / discharge cycles for each depth of discharge of the secondary battery 10 (step S920). This allows the number of charge / discharge cycles for each depth of discharge required to estimate the degradation state of the secondary battery 10 to be accurately determined from the past charge / discharge history.

[0063] (3) The control unit 11 determines whether the state of charge of the secondary battery 10 reaches a predetermined lower limit S Ｌ (step S840: Yes), the discharge of the secondary battery 10 is stopped (step S860). This prevents the secondary battery 10 from being over-discharged, and effectively suppresses excessive deterioration of the secondary battery 10.

[0064] (4) The control unit 11 determines whether the charge state of the secondary battery 10 reaches a predetermined upper limit S Ｈ(step S440: Yes), charging of the secondary battery 10 is stopped (step S460). This prevents the secondary battery 10 from being overcharged, and effectively prevents the secondary battery 10 from deteriorating excessively.

[0065] (5) The control unit 11 calculates a capacity maintenance rate according to the deterioration state of the secondary battery 10 (step S950), and when this capacity maintenance rate falls below a predetermined threshold (step S100: Yes), outputs an alarm (step S110). As a result, when the deterioration of the secondary battery 10 is more advanced than the predetermined deterioration state and the battery capacity has decreased to the extent that it interferes with the operation of the energy storage device 1, it is possible to effectively notify the user of this.

[0066] The present invention is not limited to the above-described embodiment, and can be implemented using any components without departing from the spirit of the present invention.

[0067] The above-described embodiments and modifications are merely examples, and the present invention is not limited to these details as long as the features of the invention are not impaired. Furthermore, although various embodiments and modifications have been described above, the present invention is not limited to these details. Other aspects that can be considered within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention.

[0068] 1: Power storage device 10: Secondary battery 11: Control unit 12: Switch 14: Voltage detection unit 15: Current detection unit 17: Storage unit 111: Charge / discharge amount calculation unit 112: Capacity estimation unit 113: Degradation state estimation unit 114: Alarm unit 115: Switching control unit

Claims

1. A power storage device comprising a rechargeable secondary battery, a control unit that controls charging and discharging of the secondary battery, and a storage unit that stores degradation characteristic information regarding degradation characteristics of the secondary battery, wherein the secondary battery is a nickel-zinc secondary battery in which a depth of discharge and a capacity degradation rate per charge-discharge cycle have a predetermined linear relationship, the storage unit stores information representing the linear relationship as the degradation characteristic information, and the control unit estimates a degradation state of the secondary battery based on the number of charge-discharge cycles for each depth of discharge of the secondary battery and the degradation characteristic information stored in the storage unit.

2. The power storage device according to claim 1, further comprising a current detection unit that detects a current flowing through the secondary battery, wherein the control unit obtains a state of charge of the secondary battery based on an integrated value of the current detected by the current detection unit, obtains a depth of discharge of the secondary battery for each charge-discharge cycle based on the state of charge at the start and stop of discharge of the secondary battery, and calculates the number of charge-discharge cycles for each depth of discharge of the secondary battery based on the depth of discharge of the secondary battery obtained for each charge-discharge cycle.

3. The power storage device according to claim 2, wherein the control unit stops discharging of the secondary battery when the state of charge reaches a predetermined lower limit value during discharge of the secondary battery.

4. The power storage device according to claim 2, wherein the control unit stops charging of the secondary battery when the state of charge reaches a predetermined upper limit value during charging of the secondary battery.

5. The power storage device according to claim 1, wherein the control unit calculates a capacity maintenance rate according to the degradation state of the secondary battery, and outputs an alarm when the capacity maintenance rate becomes less than a predetermined threshold value.

6. A method for estimating a degradation state of a rechargeable secondary battery, wherein the secondary battery is a nickel-zinc secondary battery in which a depth of discharge and a capacity degradation rate per charge-discharge cycle have a predetermined linear relationship, and the degradation state of the secondary battery is estimated based on the number of charge-discharge cycles for each depth of discharge of the secondary battery and information representing the linear relationship.

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