Voltage detection device

Abstract

To provide a voltage detection device for detecting a drift fault of a discharge resistor.SOLUTION: A voltage detection device for detecting each cell voltage of a secondary battery composed of a plurality of battery cells connected in series, includes: an estimation unit for estimating a discharge circuit voltage that is supposed to be detected by a discharge circuit voltage detection unit when a battery cell is discharged, based on a cell voltage detected by a cell voltage detection unit; and a determination unit for determining presence / absence of a fault in a discharge circuit using the discharge circuit voltage detected by the discharge circuit voltage detection unit when the battery cell is actually discharged and an estimation value of the discharge circuit voltage estimated by the estimation unit.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a voltage detection device.

Background Art

[0002] For the purpose of preventing a decrease in the chargeable capacity of a battery pack due to an imbalance in the voltages (cell voltages) of a plurality of battery cells constituting the battery pack, discharge control of the battery cells is performed so that each cell voltage becomes uniform.

[0003] For example, in Patent Document 1, a discharge circuit composed of a resistor and a discharge switch is connected in parallel for each battery cell, and discharge control is performed by turning the discharge switch on and off.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the invention described in Patent Document 1, a failure of the discharge circuit is detected by comparing the cell voltage when the discharge switch is in the on state with the cell voltage when the discharge switch is in the off state. However, with this method, although it is possible to detect an on / off failure of the discharge switch or a disconnection failure in the discharge circuit, it is not possible to detect a drift failure in which the discharge current fluctuates due to a change in the resistance value of the discharge resistor.

[0006] The present invention has been made in view of such circumstances, and an object thereof is to provide a voltage detection device that detects a drift failure of a discharge resistor.

Means for Solving the Problems

[0007] (1) A voltage detection device for detecting each cell voltage of a secondary battery composed of a plurality of battery cells connected in series, comprising: a discharge circuit connected in parallel to each of the plurality of battery cells and capable of forming a discharge path for discharging the battery cells; a discharge circuit voltage detection unit for detecting a discharge circuit voltage which is the voltage on the discharge path; a cell voltage detection unit for detecting the cell voltage without passing through the discharge circuit; and a failure determination unit for determining a failure of the discharge circuit. The failure determination unit includes an estimation unit for estimating the discharge circuit voltage that is assumed to be detected by the discharge circuit voltage detection unit when the battery cells are discharged, based on the cell voltage detected by the cell voltage detection unit, and a determination unit for determining the presence or absence of a failure of the discharge circuit by using the discharge circuit voltage detected by the discharge circuit voltage detection unit when the battery cells are actually being discharged and the estimated value of the discharge circuit voltage estimated by the estimation unit.

[0008] (2) The voltage detection device according to (1) above, wherein the discharge circuit has a discharge resistor and a discharge switch, the discharge path is a path through which a discharge current from the battery cell passes through the discharge switch and the discharge resistor when the discharge switch is in an on state, and the discharge circuit voltage may be a voltage generated when the discharge current flows through the discharge path.

[0009] (3) The voltage detection device according to (2) above, wherein the discharge circuit voltage may be the voltage between the terminals of the discharge switch generated when the discharge current flows through the discharge switch.

[0010] (4) The voltage detection device according to any one of (2) or (3) above, wherein when the discharge circuit voltage detected by the discharge circuit voltage detection unit is outside a predetermined range including the estimated value when the battery cells are actually being discharged, the determination unit may determine that the discharge resistor has failed.

Advantages of the Invention

[0011] As described above, according to the present invention, it is possible to provide a voltage detection device that detects a drift failure of a discharge resistor.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described through embodiments of the invention. However, the following embodiments do not limit the invention according to the claims. Also, not all combinations of features described in the embodiments are essential for the solution means of the invention. In the drawings, the same or similar parts may be denoted by the same reference numerals, and redundant descriptions may be omitted. Also, the shapes and sizes of the elements in the drawings may be exaggerated for clearer explanation.

[0014] Hereinafter, the voltage detection device 100 according to the present embodiment will be described with reference to the drawings.

[0015] The voltage detection device 100 according to the present embodiment is configured to detect the assembled battery 200 as shown in FIG. 1. The voltage detection device 100 is mounted on a vehicle having a motor as a driving power source, such as an electric vehicle or a hybrid vehicle, together with the assembled battery 200, and detects and manages the voltage of the assembled battery 200.

[0016] The battery pack 200 is a secondary battery such as a lithium-ion battery or a nickel-metal hydride battery, for example. The battery pack 200 may be an all-solid-state battery. The battery pack 200 includes a plurality of battery cells C-1 to C-n (n is an integer of 2 or more) connected in series. That is, in the battery pack 200, n battery cells C-1 to C-n are connected in series. When not distinguishing each of the battery cells C-1 to C-n, it is simply labeled as "battery cell C". In the example shown in FIG. 1, for convenience of explanation, the case where the battery pack 200 includes two battery cells C-1 and battery cell C-2 is shown, but the number of battery cells C is not limited to two and may be three or more. The number of battery cells C depends on the vehicle body size of the vehicle on which the secondary battery 110 is mounted, and the number of battery cells C may vary depending on the vehicle.

[0017] The voltage detection device 100 detects the inter-terminal voltage (hereinafter referred to as "cell voltage") Vcell of each of the battery cells C-1 to C-n and performs cell balance control to equalize each cell voltage Vcell.

[0018] The voltage detection device 100 is electrically connected to each of the battery cells C-1 to C-n via a plurality of connection lines L and detects the cell voltage Vcell of each of the battery cells C-1 to C-n. For example, a fuse F is provided in each connection line L between the voltage detection device 100 and each of the battery cells C-1 to C-n.

[0019] The connection line L is connected to the output terminals (the positive and negative terminals of the battery cell C) of each of the battery cells C-1 to C-n, respectively. For example, one end of the connection line L-1 is connected to the positive terminal of the battery cell C-1, and the other end is connected to the voltage detection device 100. Also, one end of the connection line L-2 is connected to the positive terminal of the battery cell C-2, and the other end is connected to the voltage detection device 100. Thus, the connection line L-k (k is an integer from 1 to n) has one end connected to the positive terminal of the battery cell C-k and the other end connected to the voltage detection device 100.

[0020] Next, an example of the schematic configuration of the voltage detection device 100 according to the present embodiment will be described.

[0021] The voltage detection device 100 includes a plurality of discharge circuits 10-1 to 10-n, filter circuits 20-1 to 20-n, a plurality of discharge circuit voltage detection units 30-1 to 30-n, a plurality of cell voltage detection units 40-1 to 40-n, and a control unit 50. Note that the symbols below the hyphen are used to distinguish a plurality of components of the same type from each other. When distinguishing between a plurality of components of the same type is not necessary, the symbols below the hyphen may be omitted.

[0022] The plurality of discharge circuits 10 are provided on each connection line L between the battery pack 200 and the voltage detection device 100. The discharge circuit 10 is connected in parallel to each of the plurality of battery cells C and can form a discharge path 13 for discharging the battery cell C. The number of discharge circuits 10 is the same as the number of battery cells C connected in series in the battery pack 200.

[0023] For example, the discharge circuit 10-1 is connected in parallel to the battery cell C-1 by being connected between the connection line L-1 and the connection line L-2. The discharge circuit 10-1 can discharge the battery cell C-1 based on the control from the control unit 50. The discharge circuit 10-2 is connected in parallel to the battery cell C-2 by being connected between the connection line L-2 and the connection line L-3. The discharge circuit 10-2 can discharge the battery cell C-2 based on the control from the control unit 50. Thus, the discharge circuit 10-k is connected in parallel to the battery cell C-k by being connected between the connection line L-n and the connection line L-(n + 1). The discharge circuit 10-k can discharge the battery cell C-k based on the control from the control unit 50.

[0024] The discharge circuit 10 includes two discharge resistors 11 (11a, 11b) and a discharge switch 12. The discharge resistors 11a, 11b and the discharge switch 12 are connected in series, respectively. When the discharge switch 12 is turned on, the discharge path 13 is formed, and the battery cells C connected in parallel are discharged. Note that in the example of this embodiment, the discharge circuit 10 has two discharge resistors 11a, 11b, but the number of discharge resistors 11 is not limited. The discharge circuit 10 may have only one discharge resistor 11 or may have three or more discharge resistors 11.

[0025] For example, one end of the discharge resistor 11a-1 is connected to the positive electrode terminal of the battery cell C-1 via the connection line L-1, and the other end is connected to the first terminal of the discharge switch 12-1. One end of the discharge resistor 11b-1 is connected to the second terminal of the discharge switch 12-1, and the other end is connected to the negative electrode terminal of the battery cell C-1 via the connection line L-2. By turning on the discharge switch 12-1, a discharge path 13-1 is formed in which the discharge current from the positive electrode terminal of the battery cell C-1 passes through the discharge resistor 11a-1, the discharge switch 12-1, and the discharge resistor 11b-1 and returns to the negative electrode terminal of the battery cell C-1.

[0026] Thus, one end of the discharge resistor 11a-k is connected to the positive electrode terminal of the battery cell C-k via the connection line L-k, and the other end is connected to the first terminal of the discharge switch 12-k. One end of the discharge resistor 11b-k is connected to the second terminal of the discharge switch 12-k, and the other end is connected to the negative electrode terminal of the battery cell C-k via the connection line L-(k + 1). By turning on the discharge switch 12-k, a discharge path 13-k is formed in which the discharge current from the positive electrode terminal of the battery cell C-k passes through the discharge resistor 11a-k, the discharge switch 12-k, and the discharge resistor 11b-k and returns to the negative electrode terminal of the battery cell C-k.

[0027] The filter circuits 20-1 to 20-n are low-pass filters for noise removal connected to each of the plurality of connection lines L, and are composed of a filter resistor 21a and a filter capacitor 21b. In the example shown in FIG. 1, the filter circuit 20-1 is connected to the connection line L-1, and the filter circuit 20-2 is connected to the connection line L-2.

[0028] The filter resistor 21a-k is connected in series to the connection line L-k. One end of the filter resistor 21a-k is connected to one end of the discharge resistor 11a-k, and the other end is connected to one end of the filter capacitor 21b-k.

[0029] One end of the filter capacitor 21b-k is connected to the cell voltage detection unit 40-k, and the other end is connected to GND (ground potential).

[0030] The discharge circuit voltage detection unit 30 is provided for each of the plurality of discharge circuits 10-1 to 10-n. The discharge circuit voltage detection unit 30-1 is connected to the discharge circuit 10-1 and detects the discharge circuit voltage Vr-1 which is the voltage on the discharge path 13 of the discharge circuit 10-1. Similarly, the discharge circuit voltage detection unit 30-2 is connected to the discharge circuit 10-2 and detects the discharge circuit voltage Vr-2 which is the voltage on the discharge path 13 of the discharge circuit 10-2. In this way, the discharge circuit voltage detection unit 30-k is connected to the discharge circuit 10-k and detects the discharge circuit voltage Vr-k which is the voltage on the discharge path 13 of the discharge circuit 10-k. The discharge circuit voltage detection unit 30-k directly or indirectly transmits the detected discharge circuit voltage Vr-k to the control unit 50.

[0031] The discharge circuit voltage Vr is a voltage generated when the discharge current from the battery cell C flows through the discharge path 13, and is, for example, the voltage between the terminals of the discharge switch 12 or the voltage across the discharge resistor 11. That is, the discharge circuit voltage Vr-k may be the voltage at any location on the discharge path 13-k. In this embodiment, as an example, the discharge circuit voltage Vr-k will be described as the voltage between the terminals of the discharge switch 12-k generated when the discharge current flows through the discharge switch 12-k.

[0032] The cell voltage detection unit 40-k detects the cell voltage of the battery cell C-k without passing through the discharge circuit 10-k. The cell voltage detection unit 40-k is electrically connected to the positive terminal of the battery cell C-k via the filter circuit 20-k and is connected to the negative terminal of the battery cell C-k via the filter circuit 20-(k + 1). The cell voltage detection unit 40-k detects the cell voltage Vcell which is the voltage between the positive terminal and the negative terminal of the battery cell C-k. The cell voltage detection unit 40-k directly or indirectly transmits the detected cell voltage Vcell to the control unit 50.

[0033] The control unit 50 controls the discharge switch 12 of each discharge circuit 10 to be in an on state or an off state. The control unit 50 causes the discharge circuit 10-k to discharge the battery cell C-k by controlling the discharge switch 12-k from the off state to the on state. For example, the control unit 50 detects the cell voltages Vcell of the plurality of battery cells C, and performs cell balance control to control each discharge switch 12 to be in an on state or an off state so as to equalize each cell voltage Vcell. Since the method of cell balance control is well-known, detailed description thereof is omitted.

[0034] The control unit 50 is directly or indirectly connected to each discharge circuit voltage detection unit 30, and acquires the discharge circuit voltage Vr from each discharge circuit voltage detection unit 30. The control unit 50 is directly or indirectly connected to each cell voltage detection unit 40, and acquires the cell voltage Vcell from each cell voltage detection unit 40. The control unit 50 executes a failure determination process for determining the failure of each discharge circuit 10.

[0035] The control unit 50 is, for example, a processor. This processor is a microprocessor, a microcontroller, a microcomputer, a CPU (Central Processing Unit), or a DSP (Digital Signal Processor). The control unit 50 is operable to execute computer program instructions and perform operations described by the computer program instructions. The control unit 50 is an example of a "failure determination unit".

[0036] For example, the control unit 50 includes an estimation unit 51 and a determination unit 52.

[0037] The estimation unit 51 estimates a discharge circuit voltage Vr that is assumed to be detected by the discharge circuit voltage detection unit 30 when the battery cell C is discharged, based on the cell voltage Vcell of the battery cell C detected during discharge. For example, the estimation unit 51 acquires the cell voltage Vcell of the battery cell C-k from the cell voltage detection unit 40-k. Then, the estimation unit 51 estimates a discharge circuit voltage Vr-k that is assumed to be detected by the discharge circuit voltage detection unit 30 due to the discharge of the battery cell C-k, based on the acquired cell voltage Vcell. This cell voltage Vcell of the battery cell C-k is the voltage detected by the discharge circuit voltage detection unit 30 when the battery cell C is being discharged, but is not limited thereto, and may be the voltage detected by the discharge circuit voltage detection unit 30 immediately before the discharge of the battery cell C.

[0038] The determination unit 52 determines the presence or absence of a failure in the discharge circuit 10-k using the discharge circuit voltage Vr-k (hereinafter referred to as the "detection value") detected by the discharge circuit voltage detection unit 30-k when the battery cell C-k is actually being discharged, and the estimated value of the discharge circuit voltage Vr-k estimated by the estimation unit 51. For example, when the detection value of the discharge circuit voltage Vr-k is outside a predetermined range ΔV including the estimated value of the discharge circuit voltage Vr-k when the battery cell C is actually being discharged, the determination unit 52 determines that the discharge resistor 11 has failed. The failure of the discharge resistor 11 includes a drift failure of the discharge resistor 11. This predetermined range ΔV is a range for determining whether the detection value of the discharge circuit voltage Vr-k is normal or abnormal, and may be calculated from the above estimated value and may include an error. Here, the abnormality of the discharge circuit voltage Vr-k is a state in which the discharge circuit voltage Vr has deviated from the normal range due to the drift failure of the discharge resistor 11. For example, the predetermined range ΔV may be the range of the theoretical value of the discharge circuit voltage Vr-k, and may be calculated by the determination unit 52 or the estimation unit 51.

[0039] The failure determination process according to this embodiment will be described below with reference to FIG. 2. FIG. 2 is a diagram for explaining the flow of the failure determination process according to this embodiment. For convenience of explanation, the failure determination process of the discharge circuit 10-1 will be described, but the present invention is not limited thereto, and the failure determination process may be performed for one or more or all of the discharge circuits 10 that discharge the battery cell C. The failure determination process may be performed one or more times during the discharge of the battery cell C. Further, the failure determination process is performed a plurality of times during the discharge of the battery cell C, so that the accuracy of the failure determination process is improved.

[0040] When the control unit 50 discharges the battery cell C-1 by cell balance control or the like, the control unit 50 controls the discharge switch 12-1 of the discharge circuit 10-1 to be in the on state (step S101). When the discharge switch 12-1 shifts to the on state, the discharge of the battery cell C-1 is started.

[0041] When the control unit 50 controls the discharge switch 12-1 to be in the on state, the control unit 50 detects the cell voltage Vcell of the battery cell C-1 from the cell voltage detection unit 40-1 (step 102).

[0042] Based on the cell voltage of the battery cell C-1 detected in step S102, the estimation unit 51 estimates the discharge circuit voltage Vr-1 generated by the discharge of the battery cell C-1 (step S103). For example, assume that the cell voltage Vcell detected in step S102 is 3 [V]. In this case, the estimation unit 51 estimates the discharge circuit voltage Vr-1 using the following formula (1). The estimated value of this discharge circuit voltage Vr-1 (hereinafter referred to as "Vr estimated value") is the theoretical value of the so-called discharge circuit voltage Vr-1 calculated from the cell voltage Vcell, the resistance value R1 of the discharge resistor 11a, the resistance R2 of the discharge resistor 11b, and the on-resistance value Ron of the discharge switch 12.

[0043] Vr estimated value = 3 [V] × Ron / (R1 + R2 + Ron)…(1)

[0044] During the discharge of the battery cell C-1, the discharge circuit voltage detection unit 30-1 detects the discharge circuit voltage Vr-1 (step S104). The discharge circuit voltage detection unit 30-1 transmits the detected discharge circuit voltage Vr-1 to the control unit 50. The determination unit 52 compares the detected value of the discharge circuit voltage Vr-1 obtained from the discharge circuit voltage detection unit 30-1 (hereinafter referred to as "Vr detection value") with the Vr estimated value. The determination unit 52 determines whether the Vr detection value is within a predetermined range ΔV including the Vr estimated value (step S105). When the Vr detection value is within the predetermined range ΔV, the determination unit 52 determines that the discharge resistor 11 is normal (step S106). When the determination unit 52 determines that the discharge resistor 11 is normal, it determines whether the discharge of the battery cell C-1 has ended (step S107). If in step S107 the determination unit 52 determines that the discharge of the battery cell C-1 has ended, the failure determination process ends. If in step S107 the determination unit 52 determines that the discharge of the battery cell C-1 has not ended, the process proceeds to step S102.

[0045] In step S105, when the determination unit 52 determines that the Vr detection value is not within the predetermined range ΔV, it determines that the discharge resistor 11 is abnormal (step S108) and outputs a flag indicating an abnormality (step S109). When a flag indicating an abnormality is output, for example, the voltage detection device 100 outputs a display or information indicating the abnormality of the discharge resistor 11.

[0046] For example, when the cell voltage Vcell is 3V, R1 = R2 = 30Ω, and Ron = 5Ω, the Vr estimated value becomes 0.23V. And, for example, when the determination unit 52 sets the predetermined range ΔV to the range of 0.207V to 0.253V in consideration of variations such as the resistance value of the discharge resistor and the resistance value of the on-resistance, if the Vr detection value falls within the range of 0.207V to 0.253V, it is determined that the discharge resistor 11 is normal, and if it does not fall within the range, it is determined that the discharge resistor 11 has a drift failure.

[0047] As described above, the voltage detection device 100 includes a discharge circuit 10 that is connected in parallel to each of a plurality of battery cells C and can form a discharge path 13 for discharging the battery cell C, a discharge circuit voltage detection unit 30 that detects a discharge circuit voltage Vr that is the voltage on the discharge path 13, a cell voltage detection unit 40 that detects a cell voltage Vcell without going through the discharge circuit 10, and a control unit 50 that determines a failure of the discharge circuit 10. The control unit 50 estimates a discharge circuit voltage Vr that is assumed to be detected by the discharge circuit voltage detection unit 30 when the battery cell C is discharged, based on the cell voltage Vcell detected by the cell voltage detection unit 40. Further, the control unit 50 determines the presence or absence of a failure of the discharge circuit 10 using the discharge circuit voltage Vr detected by the discharge circuit voltage detection unit 30 when the battery cell C is actually being discharged and the estimated value of the discharge circuit voltage Vr.

[0048] With such a configuration, the voltage detection device 100 can detect a drift failure of the discharge resistor 11.

[0049] As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and designs and the like within the scope not departing from the gist of the present invention are also included.

[0050] For example, when detecting the first cell voltage Vcell after starting the failure determination process, in the example shown in FIG. 2, it is executed after the discharge switch 12 is turned on, but it is not limited to this. For example, step S102 may be performed immediately before the discharge switch 12 is turned on. In this case, after detecting the cell voltage Vcell, the discharge switch 12 is quickly controlled to the on state, and the discharge circuit voltage Vr is estimated.

[0051] In the flow shown in FIG. 2, the order of step S103 and step S104 may be swapped. That is, the processing may be executed in the order of step S102, step S104, and step S103.

[0052] In the above-described embodiment, the timing for estimating the discharge circuit voltage Vr-k by the estimation unit 51 is during the discharge of the discharge circuit voltage Vr-k, but it is not limited thereto, and it may be before the discharge of the battery cell C-k (preferably immediately before the discharge), or both.

[0053] Part or all of the voltage detection device 100 may be implemented as a system-on-a-chip. For example, as shown in FIG. 3, the discharge switch 12-k, the discharge circuit voltage detection unit 30-k, and the cell voltage detection unit 40-k may be configured as one integrated circuit 300. In this case, this integrated circuit 300 is provided for each battery cell C and may transmit and receive information by communicating directly or indirectly with the control unit 50. For example, a plurality of integrated circuits 300 may be daisy-chain connected, and only the integrated circuit on the lowest potential side among the plurality of integrated circuits 300 may be communicably connected to the control unit 50 via a communication line.

[0054] The term "… unit" described in the specification means a unit that processes at least one function or operation, which may be embodied as hardware or software, or a combination of hardware and software.

Explanation of Reference Numerals

[0055] 100… Voltage detection device, 200… Battery pack, C… Battery cell, 10… Discharge circuit, 20… Filter circuit, 30… Discharge circuit voltage detection unit, 40… Cell voltage detection unit, 50… Control unit

Claims

1. A voltage detection device for detecting each cell voltage of a secondary battery composed of a plurality of battery cells connected in series, comprising: a discharge circuit connected in parallel to each of the plurality of battery cells and capable of forming a discharge path for discharging the battery cells; a discharge circuit voltage detection unit for detecting a discharge circuit voltage which is a voltage on the discharge path; a cell voltage detection unit for detecting the cell voltage without passing through the discharge circuit; a failure determination unit for determining a failure of the discharge circuit; wherein the failure determination unit includes an estimation unit for estimating the discharge circuit voltage that is assumed to be detected by the discharge circuit voltage detection unit when the battery cells are discharged, based on the cell voltage detected by the cell voltage detection unit in a state where the battery cells are being discharged; and a determination unit for determining the presence or absence of a failure of the discharge circuit by using the discharge circuit voltage detected by the discharge circuit voltage detection unit when the battery cells are actually being discharged and the estimated value of the discharge circuit voltage estimated by the estimation unit. A voltage detection device comprising the above.

2. The discharge circuit has a discharge resistor and a discharge switch, the discharge path is a path through which a discharge current from the battery cell passes through the discharge switch and the discharge resistor when the discharge switch is turned on, and the discharge circuit voltage is a voltage generated when the discharge current flows through the discharge path. The voltage detection device according to Claim 1.

3. The discharge circuit voltage is a voltage between terminals of the discharge switch generated when the discharge current flows through the discharge switch. The voltage detection device according to Claim 2.

4. The determination unit determines that the discharge resistor has failed when the discharge circuit voltage detected by the discharge circuit voltage detection unit is outside a predetermined range including the estimated value when the battery cells are actually being discharged. The voltage detection device according to Claim 2 or 3.

5. A voltage detection device for detecting each cell voltage of a secondary battery composed of a plurality of battery cells connected in series, comprising: a discharge circuit connected in parallel to each of the plurality of battery cells and capable of forming a discharge path for discharging the battery cells; a discharge circuit voltage detection unit for detecting a discharge circuit voltage which is a voltage on the discharge path; a cell voltage detection unit for detecting the cell voltage without passing through the discharge circuit; a failure determination unit for determining a failure of the discharge circuit; wherein the failure determination unit An estimation unit that estimates the discharge circuit voltage that is assumed to be detected by the discharge circuit voltage detection unit when the battery cell is discharged, based on the cell voltage detected by the cell voltage detection unit; A determination unit that determines the presence or absence of a failure in the discharge circuit using the discharge circuit voltage detected by the discharge circuit voltage detection unit when the battery cell is actually being discharged and the estimated value of the discharge circuit voltage estimated by the estimation unit; Comprising; The discharge circuit has a discharge resistor and a discharge switch; The discharge path is a path through which the discharge current from the battery cell passes through the discharge switch and the discharge resistor when the discharge switch is turned on; The discharge circuit voltage is a voltage generated when the discharge current flows through the discharge path; The discharge circuit voltage is the voltage between the terminals of the discharge switch generated when the discharge current flows through the discharge switch; A voltage detection device.

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