Failure diagnosing device and battery pack

Abstract

According to the present invention, a control circuit diagnoses a short-circuit failure of a discharge switch inserted into a positive internal power line connecting the positive terminal of the discharge terminals of a battery pack and the positive terminal of a battery module within the battery pack. A capacitor is connected in parallel with a load on the load side of the discharge switch. The control circuit: controls the discharge switch to an ON state in a state in which the load is stopped; turns off the discharge switch in a state in which the capacitor is charged; measures a voltage between the discharge terminals; re-measures the voltage between the discharge terminals after a set time from when the discharge switch was turned off; and diagnoses that a short-circuit failure has occurred in the discharge switch if an amount of decrease in the voltage between the discharge terminals is less than a threshold.

Description

Fault diagnosis device and battery pack

[0001] The present disclosure relates to a fault diagnosis device that diagnoses a short circuit fault in a discharge switch in a battery pack, and the battery pack.

[0002] In recent years, electric mobility vehicles such as electric bicycles, electric motorcycles, and electric kick scooters have become popular. Electric mobility vehicles use battery packs that include battery modules in which multiple cells are connected in series.

[0003] As a method for diagnosing a short circuit fault in a discharge switch in a battery pack, Patent Document 1 discloses a method for diagnosing a fault in the discharge cutoff FET without stopping charging, by taking advantage of the fact that charging continues via the parasitic diode of the discharge cutoff FET when the discharge cutoff FET is turned off during charging.

[0004] When the discharge cutoff FET is turned off during charging, if the charging current passes through the parasitic diode of the discharge cutoff FET in a normal state, causing a voltage drop due to the parasitic diode. On the other hand, if the discharge cutoff FET has a short circuit, no voltage drop occurs due to the parasitic diode, so the voltage drop in the current path when the discharge cutoff FET is off during charging is smaller than normal. By detecting this voltage drop, it is possible to determine whether the discharge cutoff FET has a short circuit.

[0005] JP 2013-181822 A

[0006] However, because the above method requires the charging current to flow via a discharge cutoff FET and its parasitic diode, it is difficult to apply to battery packs with separate charging and discharging lines. Also, because the FET's parasitic diode has a low thermal capacity, in applications with large charging currents, it is necessary to increase the number of FETs connected in parallel as a measure against heat generation.

[0007] The present disclosure has been made in view of these circumstances, and its purpose is to provide a technique for diagnosing a fault in a discharge switch in a battery pack without relying on the current flowing through the discharge switch.

[0008] In order to solve the above problem, a fault diagnosis device according to one aspect of the present disclosure includes a discharge terminal voltage measurement circuit that measures the voltage between the discharge terminals of a battery pack to which an external power line for supplying power to a load is connected, and a control circuit that diagnoses a short-circuit fault in a discharge switch inserted in a positive internal power line that connects the positive terminal of the discharge terminal of the battery pack and the positive terminals of battery modules in the battery pack. A capacitor is connected in parallel with the load on the load side of the discharge switch, and the control circuit controls the discharge switch to an on state when the load is stopped, turns off the discharge switch when the capacitor is charged, measures the voltage between the discharge terminals, and remeasures the voltage between the discharge terminals after a set time has elapsed since the discharge switch was turned off. If the voltage drop between the discharge terminals is less than a threshold, the control circuit diagnoses a short-circuit fault in the discharge switch.

[0009] Any combination of the above components, and conversion of the expression of the present disclosure into an apparatus, system, method, computer program, etc., are also valid aspects of the present disclosure.

[0010] According to the present disclosure, it is possible to perform fault diagnosis of a discharge switch in a battery pack without relying on the current flowing through the discharge switch.

[0011] Fig. 1 is a diagram for explaining a first configuration example of a battery pack according to an embodiment. Fig. 2 is a diagram for explaining a second configuration example of a battery pack according to an embodiment. Fig. 3 is a flowchart showing the flow of a start condition determination process for a short-circuit fault diagnosis process for a discharge switch by a battery management device. Fig. 4 is a flowchart showing the flow of a short-circuit fault diagnosis process for a discharge switch by a battery management device.

[0012] FIG. 1 is a diagram illustrating a first configuration example of a battery pack 1 according to an embodiment. The battery pack 1 includes a battery module 20 and a battery management device 10. The battery module 20 includes multiple cells E1-En connected in series. The number of cells connected in series is determined by the specifications of the load 2. For example, if the load 2 is an electric bicycle, a battery module 20 including approximately 7-10 cells in series is used. The cells may be lithium-ion battery cells, nickel-metal hydride battery cells, lead-acid battery cells, or the like. In the following description, an example using lithium-ion battery cells (nominal voltage: 3.6-3.7 V) is assumed.

[0013] A large-capacitance capacitor C1 (e.g., an electrolytic capacitor) is connected in parallel with the load 2. An external power line for supplying power to the load 2 is connected to the charge / discharge terminals of the battery pack 1. A discharge switch Q1 and a charge switch Q2 are inserted in a positive internal power line connecting the positive terminal of the charge / discharge terminal of the battery pack 1 and the positive terminal of the battery module 20 inside the battery pack 1.

[0014] In this embodiment, an N-channel MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is used for each of the discharge switch Q1 and the charge switch Q2. In an N-channel MOSFET, a parasitic diode is formed in the source-to-drain direction. By connecting two N-channel MOSFETs in series in the reverse direction, it is possible to block current passing through the parasitic diode and form a bidirectional switch. By turning off the discharge switch Q1, it is possible to cut off the discharge current from the battery module 20, and by turning off the charge switch Q2, it is possible to cut off the charge current to the battery module 20.

[0015] The battery management device 10 is composed of multiple circuit components, including an IC, and the multiple circuit components are mounted on a circuit board. In this embodiment, the focus is on the fault diagnosis function of the battery management device 10, so in this specification the battery management device 10 is also referred to as a fault diagnosis device.

[0016] The battery management device 10 includes a measurement circuit 11, a control circuit 12, and a discharge terminal voltage measurement circuit 13. The measurement circuit 11 is configured as an AFE (Analog Front End) IC or an ASIC (Application Specific Integrated Circuit). The measurement circuit 11 is connected to each node of a plurality of series-connected cells E1-En via multiple voltage measurement lines, and measures the voltage of each cell E1-En by measuring the voltage between each two adjacent voltage measurement lines. The measurement circuit 11 can measure the overall voltage of the battery module 20 by adding up the voltages of each cell E1-En. Note that a resistive voltage divider circuit for measuring the overall voltage of the battery module 20 may be connected between the positive and negative terminals of the battery module 20.

[0017] The measurement circuit 11 includes a multiplexer and an A / D converter. The multiplexer outputs the measurement voltages of the multiple cells E1-En to the A / D converter in a predetermined order. The A / D converter converts the analog measurement voltages input from the multiplexer into digital values. The measurement circuit 11 transmits the converted digital voltage values ​​of the cells E1-En to the control circuit 12 via the communication interface.

[0018] The measurement circuit 11 can measure the current flowing through the battery module 20. A shunt resistor Rs is connected to an internal power line connecting the battery module 20 and the load 2. As an example of a current measurement system, a differential amplifier (not shown) amplifies the voltage across the shunt resistor Rs and outputs it to an A / D converter in the measurement circuit 11. The A / D converter converts the analog voltage indicating the current flowing through the battery module 20, which is input from the differential amplifier, into a digital value. The measurement circuit 11 transmits the current value converted into a digital value to the control circuit 12 via the communication interface. Note that a Hall element may be used instead of the shunt resistor Rs.

[0019] At least one thermistor T1 is installed on the surface of the battery module 20. The thermistor T1 is a temperature-sensitive element whose resistance value changes depending on the temperature. A voltage divided by the thermistor T1 and a voltage-dividing resistor (not shown) is output to an A / D converter in the measurement circuit 11. The A / D converter converts the input analog voltage indicating the surface temperature of the battery module 20 into a digital value. The measurement circuit 11 transmits the converted digital temperature value to the control circuit 12 via the communication interface.

[0020] The discharge terminal voltage measurement circuit 13 measures the voltage between the charge and discharge terminals of the battery pack 1. The discharge terminal voltage measurement circuit 13 includes a first resistor voltage divider circuit (a series connection of a first resistor R1 and a second resistor R2) and a first measurement switch Q3, which are connected in series between the charge and discharge terminals of the battery pack 1. In the example shown in Fig. 1, an N-channel MOSFET is also used for the first measurement switch Q3.

[0021] The control circuit 12 controls the battery pack 1 based on the voltage values ​​of the cells E1-En, the current values ​​flowing through the battery module 20, and the temperature values ​​of the battery module 20 received from the measurement circuit 11. The control circuit 12 is composed of a microcontroller, and the microcontroller executes a firmware program to perform the following processes.

[0022] The control circuit 12 estimates the SOC (State of Charge) by combining the OCV (Open Circuit Voltage) method and the current integration method. The OCV method estimates the SOC based on the measured cell OCV and the cell's SOC-OCV curve. The cell's SOC-OCV curve is created in advance by the battery manufacturer based on characteristic tests and is registered in the control circuit 12 at the time of shipment.

[0023] The current integration method is a method for estimating the SOC based on the OCV at the start of cell charging and discharging and the integrated value of the measured current. With the current integration method, current measurement errors accumulate as the charging and discharging time increases. Therefore, it is preferable to use a weighted average of the SOC estimated by the current integration method and the SOC estimated by the OCV method.

[0024] When the control circuit 12 detects any of the abnormalities of overcharging, overdischarging, overcurrent, or overtemperature based on the voltage values, current values, and temperature values ​​of the multiple cells E1-En received from the measurement circuit 11, it sends a shut-off signal for the discharge switch Q1 and the charge switch Q2 to the measurement circuit 11, causing the measurement circuit 11 to turn off the discharge switch Q1 and the charge switch Q2.

[0025] The control circuit 12 can enable the discharge terminal voltage measurement circuit 13 by controlling the first measurement switch Q3 to the on state, and can disable the discharge terminal voltage measurement circuit 13 by controlling the first measurement switch Q3 to the off state. During the period when it is not necessary to measure the voltage between the charge and discharge terminals, current consumption can be reduced by controlling the first measurement switch Q3 to the off state.

[0026] The control circuit 12 can diagnose a short circuit failure of the discharge switch Q1 based on the voltage measured by the discharge terminal voltage measurement circuit 13. When the load 2 is stopped, the control circuit 12 controls the discharge switch Q1 to an on state to charge the capacitor C1. When the capacitor C1 is charged, the control circuit 12 turns off the discharge switch Q1 and turns on the first measurement switch Q3 to enable the discharge terminal voltage measurement circuit 13. The control circuit 12 acquires the output voltage of the discharge terminal voltage measurement circuit 13 and measures the voltage between the charge and discharge terminals of the battery pack 1. The control circuit 12 remeasures the voltage between the charge and discharge terminals a set time after the discharge switch Q1 is turned off, and if the drop in the voltage between the charge and discharge terminals is less than a threshold, it diagnoses that a short circuit failure has occurred in the discharge switch Q1.

[0027] Fig. 2 is a diagram illustrating a second configuration example of a battery pack 1 according to an embodiment. In the first configuration example shown in Fig. 1, the battery module 20 in the battery pack 1 is discharged and charged using the same terminal of the battery pack 1. When the load 2 is an electric bicycle, Fig. 1 shows a state in which the charge / discharge terminals of the detachable, portable battery pack 1 are connected to a mounting slot of the electric bicycle. To charge the battery pack 1, the battery pack 1 is removed from the mounting slot of the electric bicycle, and the charge / discharge terminals of the battery pack 1 are connected to a mounting slot of a charger to charge the battery module 20.

[0028] 2 has separate charging terminals and discharging terminals. A charger 3 can be connected between the charging terminals of the battery pack 1, and a load 2 can be connected between the discharging terminals of the battery pack 1. In the second configuration example of the battery pack 1, the battery management device 10 further includes a charging terminal voltage measurement circuit 14 in addition to the measurement circuit 11, the control circuit 12, and the discharging terminal voltage measurement circuit 13.

[0029] The charging terminal voltage measurement circuit 14 measures the voltage between the charging terminals of the battery pack 1. The charging terminal voltage measurement circuit 14 includes a second resistance voltage divider circuit (a series connection of a third resistor R3 and a fourth resistor R4) and a second measurement switch Q4, which are connected in series between the charging terminals of the battery pack 1. In the example shown in Fig. 2, an N-channel MOSFET is also used for the second measurement switch Q4.

[0030] The control circuit 12 can enable the charging terminal voltage measurement circuit 14 by controlling the second measurement switch Q4 to the on state, and can disable the charging terminal voltage measurement circuit 14 by controlling the second measurement switch Q4 to the off state. In the second configuration example of the battery pack 1, the discharging terminal voltage measurement circuit 13 measures the voltage between the discharging terminals of the battery pack 1.

[0031] 3 is a flowchart showing the flow of the start condition determination process for the short circuit fault diagnosis process for the discharge switch Q1 by the battery management unit 10. As a premise, the short circuit fault diagnosis for the discharge switch Q1 can be performed while the load 2 is stopped, but cannot be performed while the load 2 is operating. The control circuit 12 may perform the short circuit fault diagnosis for the discharge switch Q1 periodically, or may perform it immediately after the load 2 is stopped. In the former case, if the load 2 is operating when the periodic diagnosis timing arrives, the fault diagnosis for that time is skipped.

[0032] The control circuit 12 acquires the voltage of the entire battery module 20 from the measurement circuit 11, and compares the acquired voltage of the entire battery module 20 with the first set voltage V1 (S10). In this embodiment, the operating principle is to determine whether or not a short circuit fault has occurred in the discharge switch Q1 by observing whether or not the charge stored in the capacitor C1 before the power supply from the battery module 20 is released and the voltage of the capacitor C1 decays when the power supply from the battery module 20 is interrupted.

[0033] If the voltage of the battery module 20 is low, the capacitor C1 cannot be charged to a high voltage, the voltage drop of the capacitor C1 becomes slow, and the risk of erroneous diagnosis increases. Therefore, in this embodiment, the voltage of the battery module 20 being equal to or higher than the first set voltage V1 is included as a start condition for diagnosing a short circuit fault in the discharge switch Q1. For example, if a battery module 20 including seven series cells E1-E7 is used, the first set voltage V1 may be set to, for example, 27.5 V.

[0034] In step S10, if the voltage of the entire battery module 20 is less than the first set voltage V1 (N in S10), the diagnosis start condition is not satisfied, and the control circuit 12 skips the short circuit failure diagnosis process.

[0035] If the overall voltage of the battery module 20 is equal to or greater than the first predetermined voltage V1 (Y in S10), the control circuit 12 acquires the voltage between the charging terminals of the battery pack 1 from the charging terminal voltage measurement circuit 14 and compares the acquired voltage between the charging terminals with the second predetermined voltage V2 (S11). If the charging terminal and the discharging terminal are short-circuited, the voltage between the discharging terminals may not decrease even when the discharging switch Q1 is turned off, which may lead to an erroneous diagnosis. Therefore, in this embodiment, the voltage between the charging terminals being less than the second predetermined voltage V2 is included as a condition for starting a short-circuit fault diagnosis for the discharge switch Q1. For example, if a battery module 20 including seven series cells E1-E7 is used, the second predetermined voltage V2 may be set to, for example, 27.5 V.

[0036] In step S11, if the voltage between the charging terminals is equal to or higher than the second set voltage V2 (N in S11), the diagnosis start condition is not satisfied, and the control circuit 12 skips the short circuit fault diagnosis process. Note that in the configuration example 1 of the battery pack 1 shown in FIG. 1, the process of step S11 is omitted.

[0037] If the voltage between the charging terminals is less than the second set voltage V2 (Y in S11), the control circuit 12 checks whether the discharge switch Q1 is in the ON state (S12). If the discharge switch Q1 is in the OFF state (N in S12), the control circuit 12 turns on the discharge switch Q1 (Y in S12). When diagnosing a short circuit fault in the discharge switch Q1 immediately after the load 2 is stopped, the discharge switch Q1 is basically in the ON state. If a certain amount of time has passed since the load 2 was stopped, the discharge switch Q1 is basically in the OFF state, so the control circuit 12 needs to turn on the discharge switch Q1.

[0038] The control circuit 12 determines whether it is possible to stop discharging from the battery module 20 (S13). According to the above-described operating principle, a sufficient charge must be stored in the capacitor C1 before diagnosing a short circuit fault in the discharge switch Q1.

[0039] If the discharge switch Q1 remains turned on for a certain period of time or longer, the control circuit 12 determines that it is possible to stop discharging from the battery module 20 (Y in S13) and starts a short circuit fault diagnosis process for the discharge switch Q1. The certain period of time is determined according to the capacitance of the capacitor C1.

[0040] 4 is a flowchart showing the flow of the short circuit failure diagnosis process for the discharge switch Q1 performed by the battery management unit 10. The control circuit 12 turns off the discharge switch Q1 (S20). The control circuit 12 turns on the first measurement switch Q3 to enable the discharge terminal voltage measurement circuit 13 (S21). The control circuit 12 measures the discharge terminal voltage Vd(0) immediately after the discharge switch Q1 is turned off based on the output of the discharge terminal voltage measurement circuit 13 (S22).

[0041] Immediately after the discharge switch Q1 is turned off, charge remains in the capacitor C1 from the battery module 20 or the load 2, and the voltage of the capacitor C1 is higher than or equal to the voltage of the battery module 20. When the discharge terminal voltage measurement circuit 13 is enabled, the charge stored in the capacitor C1 is gradually released via the discharge terminal voltage measurement circuit 13.

[0042] After the first set time T1 has elapsed since the discharge switch Q1 was turned off (Y in S23), the control circuit 12 measures the current discharge terminal voltage Vd(x) of the discharge switch Q1 based on the output of the discharge terminal voltage measurement circuit 13 (S24). Because it takes some time for the voltage of the capacitor C1 to decrease after the discharge switch Q1 is turned off, the control circuit 12 waits for the first set time T1 as the time from the turn-off of the discharge switch Q1 until the start of fault determination. The first set time T1 may be set to, for example, 3 seconds. The first set time T1 depends on the capacitance of the capacitor C1, and is set to a longer time when the capacitance is large.

[0043] The control circuit 12 compares the difference voltage obtained by subtracting the currently measured discharge terminal voltage Vd(x) from the discharge terminal voltage Vd(0) measured immediately after turn-off with the threshold voltage Vth (S25). If the discharge switch Q1 does not have a short-circuit failure, turning off the discharge switch Q1 cuts off the power supply from the battery module 20 to the capacitor C1, causing the discharge terminal voltage Vd to decrease. The threshold voltage Vth is determined taking into account the capacitance of the capacitor C1, the discharge power from the battery module 20, the tolerances of the resistive components in the battery pack 1 and the components on the load 2 side, and the like. The threshold voltage Vth may be set to, for example, 1.2 V.

[0044] The differential voltage indicates the amount of voltage drop across capacitor C1. If the differential voltage is equal to or greater than the threshold voltage Vth (Y in S25), it can be determined that the power supply from battery module 20 to capacitor C1 has been cut off, and control circuit 12 diagnoses discharge switch Q1 as not having a short circuit (S26).

[0045] The control circuit 12 continues measuring the discharge terminal voltage Vd(x) (S24) and comparing the differential voltage Vd(x) with the threshold voltage Vth (S25) until the second set time T2 has elapsed since the discharge switch Q1 was turned off (N in S27). Even if the second set time T2 has elapsed since the discharge switch Q1 was turned off (Y in S27), if the differential voltage Vd(x) is less than the threshold voltage Vth (N in S25), it is determined that the power supply from the battery module 20 to the capacitor C1 has not been interrupted, and the control circuit 12 diagnoses the discharge switch Q1 as having a short-circuit fault (S28). Setting the second set time T2 ensures sufficient time for a fault to be determined, reducing misdiagnosis. The second set time T2 may be set to, for example, 10 seconds.

[0046] If the control circuit 12 diagnoses that the discharge switch Q1 has a short circuit fault (S28), the control circuit 12 may return to step S10 in Fig. 3 and perform the short circuit fault diagnosis of the discharge switch Q1 multiple times in the same sequence. If the control circuit 12 diagnoses that the discharge switch Q1 has a short circuit fault multiple times in succession, the control circuit 12 confirms the diagnosis of the short circuit fault.

[0047] When the control circuit 12 determines that the discharge switch Q1 has a short circuit, it turns off the charge switch Q2 and turns on an abnormality notification lamp (not shown) to notify the outside of the occurrence of the abnormality. The control circuit 12 sends an unusable signal to the control circuit (not shown) on the load 2 side to cause the control circuit (not shown) on the load 2 side to prohibit use of the load 2.

[0048] As described above, according to this embodiment, by observing the behavior of the voltage between the discharge terminals when the discharge switch Q1 is turned off, it is possible to diagnose a short circuit failure of the discharge switch Q1 without depending on the current flowing through the discharge switch Q1. In other words, since a short circuit failure diagnosis can be performed without depending on the current flowing through the parasitic diode of the discharge switch Q1, it is not necessary to consider heat generation by the parasitic diode, which has a small thermal capacity, and it is not necessary to increase the number of parallel connections of the discharge switch Q1 in order to increase the thermal capacity.

[0049] Furthermore, the method of diagnosing by detecting a voltage drop due to current flowing through the parasitic diode of the discharge switch Q1 cannot be applied to a battery pack 1 in which the charge line and the discharge line are separated, as shown in Figure 2. This is because the charging current from the charger 3 does not pass through the discharge switch Q1. Note that in the configuration example 2 shown in Figure 2, it is possible to diagnose a short circuit fault in the discharge switch Q1 while the charger 3 is charging the battery module 20, without stopping the charging.

[0050] The present disclosure has been described above based on the embodiments. The embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of the respective components and processing steps, and that such modifications are also within the scope of the present disclosure.

[0051] In the above-described embodiment, an example has been described in which N-channel MOSFETs are used for the discharge switch Q1 and the charge switch Q2. However, other types of semiconductor switches, such as bipolar transistors or IGBTs (Insulated Gate Bipolar Transistors), may be used for the discharge switch Q1 and the charge switch Q2. Furthermore, since a parasitic diode or an external diode is not required, relays may be used for the discharge switch Q1 and the charge switch Q2. Similarly, other types of semiconductor switches or relays may be used for the first measurement switch Q3 and the second measurement switch Q4.

[0052] In the above-described embodiment, the presence or absence of a short circuit failure in the discharge switch Q1 is diagnosed by storing charge in the capacitor C1 connected externally to the battery pack 1 and observing the behavior of the voltage between the discharge terminals when the discharge switch Q1 is turned off. In this regard, a capacitor connected inside the battery pack 1 can also be used as long as it is connected on the load 2 side of the discharge switch Q1. In this case, diagnosis is possible even when the battery pack 1 is not connected to the load 2.

[0053] In the above-described embodiment, an example has been described in which the battery pack 1 according to the present disclosure is mounted on an electric mobility such as an electric bicycle. In this regard, the battery pack 1 according to the present disclosure can also be mounted on a full-size electric vehicle, a low-speed electric vehicle (such as a golf cart or a land car), an electric ship, a rail vehicle, a multicopters (drones), a stationary power storage system, or a consumer electronic device (such as a smartphone or a notebook PC).

[0054] The embodiment may be specified by the following items.

[0055] [Item 1] A battery pack (1) includes: a discharge terminal voltage measurement circuit (13) that measures the voltage between the discharge terminals of the battery pack (1) to which an external power line for supplying power to a load (2) is connected; and a control circuit (12) that diagnoses a short circuit failure of a discharge switch (Q1) inserted in a positive internal power line that connects the positive terminal of the discharge terminal of the battery pack (1) and the positive terminal of a battery module (20) in the battery pack (1), wherein a capacitor (C1) is connected in parallel with the load (2) on the load (2) side of the discharge switch (Q1), and the control circuit (12) controls the discharge switch (Q1) to an on state when the load (2) is stopped, turns off the discharge switch (Q1) when the capacitor (C1) is charged, and measures the voltage between the discharge terminals, and remeasures the voltage between the discharge terminals after a set time has elapsed since the discharge switch (Q1) was turned off. If the drop in voltage between the discharge terminals is less than a threshold, the fault diagnosis device (10) diagnoses that a short circuit fault has occurred in the discharge switch (Q1).

[0056] This makes it possible to diagnose whether or not the discharge switch (Q1) has a short circuit failure, without depending on the current flowing through the discharge switch (Q1).

[0057] [Item 2] The fault diagnosis device (10) according to Item 1, wherein the discharge terminal voltage measurement circuit (13) includes a resistive voltage divider circuit (R1, R2) and a measurement switch (Q3) connected in series between the discharge terminals, and when diagnosing a short circuit fault in the discharge switch (Q1), the control circuit (12) controls the measurement switch (Q3) to an on state and acquires an output voltage of the resistive voltage divider circuit (R1, R2).

[0058] This allows the voltage between the discharge terminals to be measured while promoting a voltage drop across the capacitor (C1).

[0059] [Item 3] The fault diagnosis device (10) according to Item 1, wherein the control circuit (12) executes a diagnosis of a short circuit fault of the discharge switch (Q1) a plurality of times, and when it diagnoses that a short circuit fault has occurred a plurality of times consecutively, it confirms the diagnosis of a short circuit fault.

[0060] This can improve the accuracy of the fault diagnosis.

[0061] [Item 4] The fault diagnosis device (10) according to Item 1, further comprising a battery voltage measurement circuit (11) that measures the voltage of the battery module (20), wherein the control circuit (12) skips diagnosing a short circuit fault in the discharge switch (Q1) when the voltage of the battery module (20) is less than a certain value.

[0062] This makes it possible to prevent a decrease in the accuracy of the fault diagnosis.

[0063] [Item 5] A battery pack (1) comprising: a battery module (20); and the fault diagnosis device (10) according to any one of items 1 to 4.

[0064] This makes it possible to diagnose whether or not the discharge switch (Q1) has a short circuit failure, without depending on the current flowing through the discharge switch (Q1).

[0065] 1 Battery pack, 2 Load, 3 Charger, C1 Capacitor, 20 Battery module, E1-En Cells, 10 Battery management device, 11 Measurement circuit, 12 Control circuit, 13 Discharge terminal voltage measurement circuit, 14 Charging terminal voltage measurement circuit, Rs Shunt resistor, R1-R4 Resistor, T1 Thermistor, Q1 Discharge switch, Q2 Charging switch, Q3-Q4 Measurement switch.

Claims

1. A fault diagnosis device comprising: a discharge terminal voltage measurement circuit that measures the voltage between the discharge terminals of a battery pack to which an external power line for supplying power to a load is connected; and a control circuit that diagnoses a short-circuit fault in a discharge switch inserted in a positive internal power line that connects the positive terminal of the discharge terminal of the battery pack and the positive terminals of battery modules in the battery pack, wherein a capacitor is connected in parallel with the load on the load side of the discharge switch, and the control circuit: controls the discharge switch to an on state when the load is stopped; turns off the discharge switch when the capacitor is charged and measures the voltage between the discharge terminals; measures the voltage between the discharge terminals again after a set time has elapsed since the discharge switch was turned off; and diagnoses a short-circuit fault in the discharge switch if the drop in voltage between the discharge terminals is less than a threshold value.

2. The fault diagnosis device according to claim 1, wherein the discharge terminal voltage measurement circuit includes a resistive voltage divider circuit and a measurement switch connected in series between the discharge terminals, and when diagnosing a short circuit fault in the discharge switch, the control circuit controls the measurement switch to an on state and acquires the output voltage of the resistive voltage divider circuit.

3. The fault diagnosis device according to claim 1, wherein the control circuit diagnoses the discharge switch for a short circuit fault multiple times, and when it diagnoses that a short circuit fault has occurred multiple times in succession, it confirms the diagnosis of a short circuit fault.

4. The fault diagnosis device according to claim 1, further comprising a battery voltage measurement circuit that measures the voltage of the battery module, wherein the control circuit skips diagnosis of a short circuit fault in the discharge switch if the voltage of the battery module is less than a certain value.

5. A battery pack comprising: the fault diagnosis device according to any one of claims 1 to 4; and the battery module.

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