Abnormality detection device, power storage device, abnormality detection method, and program

Abstract

To provide an abnormality detection device, a power storage device, an abnormality detection method, and a program that can detect an abnormality in an early stage to prevent power generation of a secondary battery due to an overcurrent.SOLUTION: The abnormality detection device includes: a voltage detection unit that detects an output voltage from a secondary battery to a power load; a current detection unit that detects a discharge current from the secondary battery to the power load; and a control unit that detects presence / absence of an abnormality of the power load based on a result of a comparison between output power obtained based on the output voltage and the discharge current and an overpower threshold value set previously.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an abnormality detection device, a power storage device, an abnormality detection method, and a program.

Background Art

[0002] Conventionally, in a system that supplies power from a power source to a load, in the event of a power outage of the power source or the like, a power storage device equipped with a secondary battery capable of charging and discharging is used to appropriately supply power to the load in place of the power source.

[0003] In such a power storage device, it is necessary to protect the circuits in the system and ensure safety in the event of an abnormality such that power exceeding the rating is supplied to the load. Therefore, in the power storage device, an overvoltage limit value or an overcurrent limit value is set for the output voltage or output current from the secondary battery (see, for example, Patent Document 1). Further, the overvoltage limit value or overcurrent limit value in this case is generally set to about 110% to 130% of the normal output voltage or output current in order to prevent malfunction of overvoltage or overcurrent protection.

[0004] As a result, when the output voltage or output current from the secondary battery exceeds the overvoltage limit value or overcurrent limit value, the overvoltage or overcurrent protection function operates and the supply of power to the load is cut off. Therefore, it is possible to suppress heat generation due to abnormal power being supplied to the load.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, in a power storage device equipped with a secondary battery, usually, the power that becomes a load is specified in advance, and the power of the secondary battery is supplied to the load. Therefore, since the power supplied to the load is constant, immediately after the start of discharge, the load is supplied with power at a high voltage and a small current. Also, immediately before the end voltage, the load is supplied with power at a low voltage and a large current.

[0007] Here, when an overcurrent limit is set, it is impossible to detect an abnormality of the load until the output current of the secondary battery exceeds the overcurrent limit. Therefore, for example, even if the power supplied to the load exceeds the specified value immediately after the start of discharge, an abnormality cannot be detected until the output voltage of the secondary battery decreases and the output current increases and exceeds the overcurrent limit value.

[0008] Therefore, there has been a problem that even if the output current from the secondary battery becomes excessive due to a failure of the load or the like and the temperature becomes high, the abnormality of the load cannot be detected early and the heat generation of the secondary battery due to the abnormality cannot be suppressed.

[0009] The present disclosure has been made in view of the problems in the above-described conventional technology, and an object thereof is to provide an abnormality detection device, a power storage device, an abnormality detection method, and a program that can detect an abnormality early and suppress heat generation of a secondary battery due to an overcurrent.

Means for Solving the Problems

[0010] The abnormality detection device according to the present disclosure includes a voltage detection unit that detects an output voltage from a secondary battery to a power load, a current detection unit that detects a discharge current from the secondary battery to the power load, and a control unit that detects the presence or absence of an abnormality of the power load based on a comparison result between an output power obtained based on the output voltage and the discharge current and a preset over-power threshold value. is provided.

[0011] Also, the power storage device according to the present disclosure A rechargeable secondary battery and, the above-described abnormality detection device, and are provided.

[0012] Furthermore, the abnormality detection method according to the present disclosure detects an output voltage from the secondary battery to the power load, detects a discharge current from the secondary battery to the power load, and based on a comparison result between the output power obtained based on the output voltage and the discharge current and a preset over-power threshold value, detects the presence or absence of an abnormality in the power load.

[0013] Moreover, the program according to the present disclosure causes a computer to execute the above-described abnormality detection method.

Advantages of the Invention

[0014] According to the present disclosure, an abnormality can be detected early, and heat generation of the secondary battery due to overcurrent can be suppressed.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments, and various modifications can be made without departing from the gist of the present disclosure. Further, the present disclosure includes all combinations of configurations that can be combined among the configurations shown in the following embodiments. In each figure, those denoted by the same reference numerals are the same or corresponding ones, which is common throughout the entire specification.

[0017] [Configuration of Power Storage System 100] FIG. 1 is a schematic diagram showing an example of the configuration of the power storage system 100 according to the present embodiment. As shown in FIG. 1, the power storage system 100 includes a BBU (Battery Backup Unit) 1 which is a power storage device, a power source 2, and a load device 3 which is a power supply target.

[0018] The power source 2 is provided to supply power to the load device 3 and the BBU 1. The load device 3 receives power from the power source 2 or the BBU 1. In the present embodiment, the load device 3 is a power load whose rating is defined by power.

[0019] The BBU 1 stores the power supplied from the power source 2 during charging. Further, when the power from the power source 2 is cut off due to a power failure or the like, the BBU 1 supplies the stored power to the load device 3. The BBU 1 includes a secondary battery 11, a charging switch circuit 12, a discharging switch circuit 13, an output voltage detection unit 14, a battery voltage detection unit 15, a charge / discharge current detection unit 16, a current detection resistor 17, a thermal fuse 18, and a microcomputer (hereinafter, appropriately referred to as "microcontroller") 20.

[0020] The secondary battery 11 is, for example, a nickel-metal hydride secondary battery and is composed of one or a plurality of secondary battery cells. When the secondary battery 11 is composed of a plurality of secondary battery cells, the secondary battery 11 is configured, for example, by connecting the secondary battery cells in series.

[0021] The charging switch circuit 12 is arranged on a charging path (the dashed arrow in FIG. 1) through which current flows during charging, and switches the connection and disconnection of the charging path based on the control by the microcomputer 20. The charging switch circuit 12 includes, for example, a charging control FET and a diode. The charging control FET is a switching element that operates according to a charging control signal supplied from the microcomputer 20. The diode is a reverse current prevention element for preventing reverse current when a discharge current, which is an output current from the secondary battery 11, flows through the charging path.

[0022] The discharging switch circuit 13 is arranged on a discharging path (the solid arrow in FIG. 1) through which current flows during discharging, and switches the connection and disconnection of the discharging path based on the control by the microcomputer 20. The discharging switch circuit 13 includes, for example, a discharging control FET. The discharging control FET is a switching element that operates according to a discharging control signal supplied from the microcomputer 20.

[0023] In this way, by controlling the charging switch circuit 12 and the discharging switch circuit 13, charging and discharging of the secondary battery 11 are switched.

[0024] The output voltage detection unit 14 is a voltage sensor that detects the output voltage of the secondary battery 11 during discharging. The output voltage detection unit 14 supplies the detected output voltage of the secondary battery 11 to the microcomputer 20.

[0025] The battery voltage detection unit 15 is a voltage sensor that detects the battery voltage of the secondary battery 11. The battery voltage detection unit 15 supplies the detected battery voltage of the secondary battery 11 to the microcomputer 20.

[0026] The charge / discharge current detection unit 16 detects the voltage applied to the current detection resistor 17 disposed on the current path. The charge / discharge current detection unit 16 calculates the charge / discharge current flowing through the current path based on the detected voltage and the resistance value of the current detection resistor 17. The charge / discharge current detection unit 16 supplies the calculated charge / discharge current to the microcomputer 20.

[0027] The thermal fuse 18 cuts off the current flowing through the current path by melting when it reaches a predetermined temperature due to overcurrent or the like.

[0028] The microcomputer 20 controls the entire BBU1. In the present embodiment, the microcomputer 20 performs an abnormality detection process for detecting an abnormality in the power load. Details of the abnormality detection process will be described later.

[0029] FIG. 2 is a functional block diagram showing an example of the configuration of the microcomputer 20 in FIG. 1. In FIG. 2, only the processing units related to the abnormality detection process among the functions provided in the microcomputer 20 are shown. As shown in FIG. 2, the microcomputer 20 includes an information acquisition unit 21, an arithmetic unit 22, a comparison determination unit 23, a switch control unit 24, and a storage unit 25.

[0030] The information acquisition unit 21 acquires the output voltage, battery voltage, and charge / discharge current of the secondary battery 11 detected by the output voltage detection unit 14, the battery voltage detection unit 15, and the charge / discharge current detection unit 16, respectively. The acquired output voltage, battery voltage, and charge / discharge current are supplied to the arithmetic unit 22.

[0031] The arithmetic unit 22 performs various arithmetic operations based on the output voltage, battery voltage, and charge / discharge current supplied from the information acquisition unit 21. In the present embodiment, the arithmetic unit 22 calculates the output power of the secondary battery 11 based on the output voltage and the discharge current among the charge / discharge currents. The calculated output power is supplied to the comparison determination unit 23.

[0032] The comparison and determination unit 23 compares the output power of the secondary battery 11 calculated by the calculation unit 22 with the over-power threshold value pre-stored in the storage unit 25, and determines the presence or absence of an abnormality in the power load. Information indicating the determination result is supplied to the switch control unit 24. The over-power threshold value is a threshold value set for the output power of the secondary battery 11 so that power exceeding the rating is not supplied to the load device 3.

[0033] The switch control unit 24 controls the charge switch circuit 12 and the discharge switch circuit 13. In particular, when the comparison and determination unit 23 determines that there is an abnormality in the power load, the switch control unit 24 outputs a discharge control signal for cutting off the discharge path to the discharge switch circuit 13.

[0034] The storage unit 25 stores various types of information used by the microcomputer 20. For example, in the present embodiment, the storage unit 25 stores the over-power threshold value used by the comparison and determination unit 23.

[0035] FIG. 3 is a block diagram showing an example of the main part of the control system of the microcomputer 20 in FIG. 1. As shown in FIG. 3, the microcomputer 20 includes a CPU (Central Processing Unit) 1001, a ROM (Read Only Memory) 1002, a RAM (Random Access Memory) 1003, and the like. Each part constituting the microcomputer 20 is connected by a bus 1005. Further, a storage device 1004 corresponding to the storage unit 25 in FIG. 2 is also connected to the bus 1005.

[0036] The CPU 1001 reads a program corresponding to the processing content from the ROM 1002 and expands it in the RAM 1003, and controls the operation of the power storage system 100 in cooperation with the expanded program. The storage device 1004 stores various types of data used for the calculation of the CPU 1001 and the like.

[0037] [Detection of Abnormality] Next, a method for detecting an abnormality in the power storage system 100 having the above configuration will be described. In a conventional power storage system 100, an abnormality in a load is detected based on the discharge current of the secondary battery 11. Specifically, for example, in a conventional power storage system 100, an overcurrent threshold value, which is a threshold value for detecting an abnormality with respect to the discharge current, is set. Then, when the discharge current becomes equal to or greater than the overcurrent threshold value, it is determined that an abnormality has occurred in the load.

[0038] Here, when the load device 3 is an electric load, the discharge current increases as the battery voltage decreases. The change in the battery voltage with respect to the capacity of the secondary battery 11 at this time varies depending on the discharge characteristics of the secondary battery 11.

[0039] FIG. 4 is a graph for explaining the discharge characteristics according to the type of the secondary battery 11. In FIG. 4, the horizontal axis represents the capacity of the secondary battery 11, and the vertical axis represents the battery voltage of the secondary battery 11. In this example, the change in the battery voltage with respect to the capacity in each of the nickel-metal hydride secondary battery, the lithium-ion secondary battery, and the lead storage battery is shown.

[0040] As shown in FIG. 4, the lithium-ion secondary battery and the lead storage battery have a characteristic in which the battery voltage decreases at a substantially constant rate with respect to the capacity. Due to such discharge characteristics, the battery voltage decreases according to the capacity of the secondary battery 11, and as a result, the discharge current becomes equal to or greater than the overcurrent threshold value. Therefore, in the lithium-ion secondary battery and the lead storage battery, an abnormality is detected relatively early.

[0041] On the other hand, in the nickel-metal hydride secondary battery, as shown in FIG. 4, there is a flat region where the battery voltage remains substantially constant even when the capacity changes. In this flat region, since the battery voltage is substantially constant, the current supplied to the electric load also remains substantially constant.

[0042] Therefore, for example, when an abnormality occurs in the power load, since the battery voltage is substantially constant in the flat region, more discharge current than normal will be supplied to the load device 3. However, if the discharge current at this time is less than the overcurrent threshold value, the abnormality will not be detected. The abnormality is detected, for example, near the discharge cut-off voltage at which the battery voltage decreases due to further reduction in the capacity of the nickel-metal hydride secondary battery. Therefore, in the case of a nickel-metal hydride secondary battery, even when an abnormality occurs in the power load, it takes time to detect the abnormality.

[0043] Here, regarding the fact that it takes time to detect an abnormality based on the discharge current, a specific example will be given for explanation. Fig. 5 is a graph for explaining the relationship between the discharge current and the battery voltage when detecting an abnormality based on the discharge current in the power storage system 100. In Fig. 5, the horizontal axis represents the discharge current of the secondary battery 11, and the vertical axis represents the battery voltage of the secondary battery 11. Also, the graph indicated by the broken line shows the change in the discharge current at rated conditions. The graph indicated by the solid line shows the change in the discharge current during an abnormality. In this example, assume that the secondary battery 11 mounted on the BBU1 is composed of 40 secondary battery cells connected in series, and the rated power of the load device 3 is 1 kW.

[0044] If the discharge cut-off voltage of one secondary battery cell at this time (hereinafter, N secondary battery cells will be appropriately referred to as "N cells") is "0.9 V", the discharge cut-off voltage of the secondary battery 11 with 40 cells connected in series will be "36 V" (= 0.9 V × 40). Also, the discharge current at this time will be "about 27.8 A" (= 1 kW / 36 V). Therefore, the overcurrent threshold value for the discharge current in this case is set to about "34 A" (= 27.8 A × 1.2) considering a predetermined margin from the perspective of avoiding false detection. Furthermore, when the full charge voltage per cell is 1.5 V, the battery voltage of the secondary battery 11 in the fully charged state will be about "60 V" (= 40 cells × 1.5 V).

[0045] When the power load is normal, as shown by the dashed-line graph in Fig. 5, even when the battery voltage of the secondary battery 11 decreases and reaches near the discharge cut-off voltage, the discharge current of the secondary battery 11 is about 27.8 A, which is smaller than the overcurrent threshold (about 34 A), and is less than the overcurrent threshold.

[0046] Here, when due to some abnormality the power load becomes 1.3 kW, which is larger than the normal time, the load device 3 is supplied with power exceeding the rated power. In this case, a higher-value discharge current is supplied to the load device 3 compared to the normal time.

[0047] For example, assuming that the battery voltage immediately after discharge from a full charge is about 50 V, the discharge current of the secondary battery 11 becomes about "26 A" (= 1.3 kW / 50 V). At this time, as shown by the solid-line graph in Fig. 5, the discharge current is smaller than the overcurrent threshold (about 34 A). Therefore, with the conventional method of detecting an abnormality based on the discharge current, even though an abnormality has occurred immediately after discharge, the abnormality cannot be detected. As shown in Fig. 5, the abnormality is detected when the battery voltage becomes about "38 V" (= 1.3 kW / 34 A), which is close to the discharge cut-off voltage.

[0048] Thus, in the case where the load is a power load, the abnormality detection method based on the discharge current of the secondary battery 11 cannot detect an abnormality early depending on the type of the secondary battery 11 used.

[0049] Therefore, the power storage system 100 according to the present embodiment performs an abnormality detection process capable of detecting an abnormality early even when the load is a power load. Specifically, in the abnormality detection process according to the present embodiment, an abnormality is detected based on the output power supplied from the secondary battery 11 to the load device 3.

[0050] FIG. 6 is a graph for explaining the relationship between the output power and the battery voltage when an abnormality is detected based on the output power in the power storage system 100. In FIG. 6, the horizontal axis represents the output power of the secondary battery 11, and the vertical axis represents the battery voltage of the secondary battery 11. The graph indicated by the broken line shows the change in the output power at the rated time. The graph indicated by the solid line shows the change in the output power during an abnormality.

[0051] In this example, similar to the example described above, it is assumed that the secondary battery 11 mounted on the BBU1 is composed of 40 secondary battery cells connected in series, and the rated power of the load device 3 is 1 kW.

[0052] For example, in the case of the above-described example, assuming that the battery voltage immediately after discharging from a full charge is about 50 V, the output power of the secondary battery 11 is about "1.3 kW" (= 26 A × 50 V). At this time, the output power is larger than the over-power threshold value (1.2 kW) as shown by the solid-line graph in FIG. 6. Therefore, in the method according to the present embodiment for detecting an abnormality based on the output power, an abnormality can be detected immediately after discharging.

[0053] Thus, when the load is an electric power load, the abnormality detection method based on the output voltage of the secondary battery 11 can detect an abnormality at an early stage even for a secondary battery 11 having a discharge characteristic including a flat region of the battery voltage such as a nickel-metal hydride secondary battery.

[0054] [Abnormality Detection Process] FIG. 7 is a flowchart showing an example of the flow of the abnormality detection process by the power storage system 100 according to the present embodiment. The abnormality detection process is performed during discharging of the secondary battery 11.

[0055] First, in step S1, the information acquisition unit 21 of the microcomputer 20 acquires the output voltage and the discharge current of the secondary battery detected by the output voltage detection unit 14 and the charge / discharge current detection unit 16, respectively. The information acquisition unit 21 supplies the acquired output voltage and discharge current to the calculation unit 22.

[0056] In step S2, the arithmetic unit 22 calculates the output power of the secondary battery 11 based on the output voltage and discharge current of the secondary battery 11. The arithmetic unit 22 supplies the calculated output power to the comparison determination unit 23.

[0057] In step S3, the comparison determination unit 23 reads the over-power threshold value from the storage unit 25. Then, the comparison determination unit 23 compares the output power received from the arithmetic unit 22 with the over-power threshold value read from the storage unit 25.

[0058] As a result of the comparison, if the output power is equal to or greater than the over-power threshold value (step S3: Yes), the comparison determination unit 23 determines that the power load is abnormal, and supplies information indicating the determination result to the switch control unit 24. Then, the process proceeds to step S4.

[0059] In step S4, the switch control unit 24 controls the discharge switch circuit 13 based on the information received from the arithmetic unit 22. Since the information received at this time indicates an abnormality, the switch control unit 24 outputs a discharge control signal for turning off the discharge control FET included in the discharge switch circuit 13 to cut off the discharge path. Thereby, the discharge path is cut off and the discharge is stopped.

[0060] On the other hand, in step S3, if the output power is less than the over-power threshold value (step S3: No), the comparison determination unit 23 determines that the power load is normal. Then, the series of processes ends.

[0061] As described above, in the power storage system 100 according to the present embodiment, based on the comparison result between the output power supplied to the power load obtained based on the output voltage and discharge current of the secondary battery 11 and a preset over-power threshold value, the presence or absence of an abnormality in the power load is detected. Thereby, an abnormality in the power load can be detected at an early stage. And since the abnormality can be detected at an early stage, heat generation of the secondary battery 11 due to an overcurrent flowing can be suppressed.

[0062] As described above, although the present embodiment has been explained, the present disclosure is not limited to the above-described embodiment, and various modifications and applications are possible without departing from the gist of the present disclosure. For example, the power storage system 100 according to the present embodiment may perform the conventional abnormality detection process based on the discharge current in parallel with the abnormality detection process based on the output power of the secondary battery 11. By performing the two abnormality detection processes in parallel, it is possible to more reliably detect an abnormality in the load.

[0063] Also, in the present embodiment, it has been described that when the output power of the secondary battery 11 is equal to or greater than the over-power threshold value, an abnormality in the load is detected. However, if an abnormality is immediately determined in this way, for example, even when a measurement error or the like occurs, it will be determined that there is an abnormality. Therefore, for example, when the state where the output power is equal to or greater than the over-power threshold value is within a predetermined set time such as 1 second, the abnormality may not be determined.

Explanation of Signs

[0064] 1 BBU 2 Power supply 3 Load device 11 Secondary battery 12 Charge switch circuit 13 Discharge switch circuit 14 Output voltage detection unit 15 Battery voltage detection unit 16 Charge and discharge current detection unit 17 Current detection resistor 18 Thermal fuse 20 Microcomputer 21 Information acquisition unit 22 Calculation unit 23 Comparison and determination unit 24 Switch control unit 25 Storage unit 100 Power storage system

Claims

1. A voltage detection unit that detects the output voltage from the secondary battery to the power load; A current detection unit that detects the discharge current from the secondary battery to the power load; A control unit that detects the presence or absence of an abnormality in the power load based on the comparison result between the output power obtained based on the output voltage and the discharge current and a preset over-power threshold value An abnormality detection device comprising the above.

2. The control unit When the output power is equal to or greater than the over-power threshold value, determines that the power load is abnormal The abnormality detection device according to claim 1.

3. The control unit When the time during which the output power is equal to or greater than the over-power threshold value is within a set time, determines that the power load is normal The abnormality detection device according to claim 1.

4. The control unit Further detects the presence or absence of an abnormality in the power load based on the comparison result between the discharge current and a preset over-current threshold value The abnormality detection device according to claim 1.

5. The secondary battery is a nickel-metal hydride secondary battery The abnormality detection device according to claim 1.

6. A rechargeable secondary battery; The abnormality detection device according to claim 1; A power storage device comprising the above.

7. Detect the output voltage from the secondary battery to the power load; Detect the discharge current from the secondary battery to the power load; Detect the presence or absence of an abnormality in the power load based on the comparison result between the output power obtained based on the output voltage and the discharge current and a preset over-power threshold value An abnormality detection method.

8. A program for causing a computer to execute the abnormality detection method according to Claim 7.

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