Battery pack and diagnosis method

Abstract

To provide a battery pack capable of diagnosing whether a failure occurs or not.SOLUTION: A battery pack according to an embodiment of the present disclosure includes a storage battery having a plurality of battery cells connected in series, a plurality of switches respectively provided corresponding to the plurality of battery cells, each of the plurality of switches being provided in a first parallel path of a corresponding battery cell among the plurality of battery cells, a voltage detection circuit capable of detecting a voltage between both ends of each of the plurality of switches as a plurality of cell voltages respectively corresponding to the plurality of battery cells, and a diagnosis circuit capable of turning on one or more switches among the plurality of switches in a predetermined period and performing diagnosis processing based on a detection result of the voltage detection circuit before the predetermined period and a detection result of the voltage detection circuit after the predetermined period.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a battery pack including a storage battery and a method for diagnosing such a battery pack. [Background technology]

[0002] In devices equipped with storage batteries, diagnostic processing is often performed to check for malfunctions. For example, Patent Document 1 discloses a cell balancing control device that can detect breaks in wiring for detecting cell voltages. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-61717 Summary of the Invention [Problem to be solved by the invention]

[0004] As such, it is desirable to be able to diagnose whether or not a malfunction has occurred in devices equipped with storage batteries, and it is also expected that it will be possible to diagnose whether or not a malfunction has occurred in battery packs equipped with storage batteries.

[0005] It is desirable to provide a battery pack and a diagnostic method that can diagnose whether a malfunction has occurred. [Means for solving the problem]

[0006] A battery pack according to an embodiment of the present disclosure includes a storage battery, a plurality of switches, a voltage detection circuit, and a diagnostic circuit. The storage battery has a plurality of battery cells connected in series. The plurality of switches are provided corresponding to the plurality of battery cells, respectively, and each switch is provided in a first parallel path of a corresponding battery cell among the plurality of battery cells. The voltage detection circuit is capable of detecting voltages across each of the plurality of switches as a plurality of cell voltages corresponding to the plurality of battery cells, respectively. The diagnostic circuit is capable of turning on one or more of the plurality of switches for a predetermined period of time, and is capable of performing diagnostic processing based on a detection result of the voltage detection circuit before the predetermined period and a detection result of the voltage detection circuit after the predetermined period.

[0007] A diagnostic method according to one embodiment of the present disclosure includes, in a battery pack having a plurality of battery cells connected in series and a plurality of switches respectively corresponding to the plurality of battery cells and each switch being provided in a first parallel path of a corresponding battery cell among the plurality of battery cells, detecting voltages across each of the plurality of switches as first plurality of cell voltages respectively corresponding to the plurality of battery cells, turning on one or more switches for a predetermined period of time, detecting voltages across each of the plurality of switches after the predetermined period of time as second plurality of cell voltages respectively corresponding to the plurality of battery cells, and performing diagnostic processing based on the first plurality of cell voltages and the second plurality of cell voltages.

[0008] According to the battery pack and the diagnostic method in one embodiment of the present disclosure, it is possible to diagnose whether or not a malfunction has occurred. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram illustrating an example configuration of a battery pack according to an embodiment of the present disclosure. [Figure 2A] FIG. 2A is a flowchart illustrating an example of the operation of the battery pack shown in FIG. [Figure 2B] FIG. 2B is another flowchart illustrating an example of the operation of the battery pack shown in FIG. [Figure 3A] FIG. 3A is a flowchart illustrating an example of the voltage measurement operation shown in FIG. 2A. [Figure 3B] FIG. 3B is another flowchart illustrating an example of the operation of the voltage measurement shown in FIG. 2A. [Figure 4A] FIG. 4A is a flowchart illustrating an example of the operation of the disconnection determination process shown in FIG. 2A. [Figure 4B] FIG. 4B is another flowchart illustrating an example of the operation of the disconnection determination process shown in FIG. 2A. [Figure 5A] FIG. 5A is a flowchart illustrating an example of the voltage measurement operation shown in FIG. 2B. [Figure 5B] FIG. 5B is another flowchart illustrating an example of an operation of the voltage measurement shown in FIG. 2B. [Figure 6] FIG. 6 is a waveform diagram showing an example of voltage measurement in a battery pack in which no disconnection occurs. [Figure 7A] FIG. 7A is an explanatory diagram showing an example of the measurement results of the cell voltage and the storage battery voltage. [Figure 7B] FIG. 7B is another explanatory diagram showing an example of the measurement results of the cell voltage and the storage battery voltage. [Figure 8] FIG. 8 is an explanatory diagram showing an example of a battery pack in which a disconnection occurs. [Figure 9] FIG. 9 is a waveform diagram showing an example of voltage measurement in the battery pack shown in FIG. [Figure 10A] FIG. 10A is an explanatory diagram showing an example of the measurement results of the cell voltage and the storage battery voltage in the battery pack shown in FIG. [Figure 10B] FIG. 10B is another explanatory diagram showing an example of the measurement results of the cell voltage and the storage battery voltage in the battery pack shown in FIG. [Figure 11] FIG. 11 is a waveform diagram showing an example of the second voltage measurement in the battery pack shown in FIG. [Figure 12A]FIG. 12A is an explanatory diagram showing an example of the measurement results of the cell voltage and the storage battery voltage in the second voltage measurement in the battery pack shown in FIG. [Figure 12B] FIG. 12B is another explanatory diagram showing an example of the measurement results of the cell voltage and the storage battery voltage in the second voltage measurement in the battery pack shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0011] <Embodiment> [Configuration example] 1 shows an example of the configuration of a battery pack (battery pack 1) according to one embodiment. In this example, battery pack 1 is used in equipment that is primarily used outdoors and is frequently subjected to vibrations and shocks, such as outdoor power equipment such as a lawnmower or an electrically assisted bicycle. Battery pack 1 includes a positive terminal TP, a negative terminal TN, a storage battery 11, transistors DFET and CFET, a transistor 12, a fuse 13, resistors RG and R0 to R4, capacitors C0 to C4, and a microcontroller 20. The storage battery 11 is mounted in a cell holder 101, and the transistors DFET and CFET, the transistor 12, the fuse 13, resistors RG and R0 to R4, capacitors C0 to C4, and the microcontroller 20 are mounted on a substrate 102.

[0012] The positive terminal TP and the negative terminal TN are configured to transfer power between the battery pack 1 and a device to which the battery pack 1 is attached.

[0013] The storage battery 11 is provided in a path connecting the positive terminal TP and the negative terminal TN and is configured to store power. In this example, the storage battery 11 has ten battery cells BC. In this example, each of the ten battery cells BC is configured using a lithium-ion secondary battery. The ten battery cells BC are divided into five cell blocks CBL (cell blocks CBL0 to CBL4). In each cell block CBL, two battery cells BC are connected in parallel. The five cell blocks CBL are connected in series. Specifically, the positive electrodes of the two battery cells BC belonging to cell block CBL0 are connected to the negative electrodes of the two battery cells BC belonging to cell block CBL1, and the negative electrodes of the two battery cells BC belonging to cell block CBL0 are connected to the negative terminal TN of the battery pack 1. The positive electrodes of two battery cells BC belonging to cell block CBL1 are connected to the negative electrodes of two battery cells BC belonging to cell block CBL2, and the negative electrodes of two battery cells BC belonging to cell block CBL1 are connected to the positive electrodes of two battery cells BC belonging to cell block CBL0. The positive electrodes of two battery cells BC belonging to cell block CBL2 are connected to the negative electrodes of two battery cells BC belonging to cell block CBL3, and the negative electrodes of two battery cells BC belonging to cell block CBL2 are connected to the positive electrodes of two battery cells BC belonging to cell block CBL1. The positive electrodes of two battery cells BC belonging to cell block CBL3 are connected to the negative electrodes of two battery cells BC belonging to cell block CBL4, and the negative electrodes of two battery cells BC belonging to cell block CBL3 are connected to the positive electrodes of two battery cells BC belonging to cell block CBL2. The positive electrodes of two battery cells BC belonging to cell block CBL4 are connected to fuse 13, and the negative electrodes of two battery cells BC belonging to cell block CBL4 are connected to the positive electrodes of two battery cells BC belonging to cell block CBL3.

[0014] The ten battery cells BC in the cell holder 101 are connected to the wiring on the substrate 102 via six cell tabs CT (cell tabs CTG, CT0 to CT4). In FIG. 1, the wiring for the cell tabs CTG, CT0 to CT4 is indicated by thick lines. Each of the cell tabs CTG, CT0 to CT4 is a connection member made of a metal material. The negative electrodes of the two battery cells BC belonging to the cell block CBL0 are connected to the wiring on the substrate 102 via the cell tab CTG. Specifically, for example, the cell tab CTG is connected to the negative electrodes of the two battery cells BC by welding, and is also connected to the wiring on the substrate 102 by welding or soldering. Similarly, the positive electrodes of the two battery cells BC belonging to the cell block CBL0 and the negative electrodes of the two battery cells BC belonging to the cell block CBL1 are connected to the wiring on the substrate 102 via the cell tab CT0. The positive electrodes of the two battery cells BC belonging to cell block CBL1 and the negative electrodes of the two battery cells BC belonging to cell block CBL2 are connected to the wiring of the substrate 102 via cell tabs CT1. The positive electrodes of the two battery cells BC belonging to cell block CBL2 and the negative electrodes of the two battery cells BC belonging to cell block CBL3 are connected to the wiring of the substrate 102 via cell tabs CT2. The positive electrodes of the two battery cells BC belonging to cell block CBL3 and the negative electrodes of the two battery cells BC belonging to cell block CBL4 are connected to the wiring of the substrate 102 via cell tabs CT3. The positive electrodes of the two battery cells BC belonging to cell block CBL4 are connected to the wiring of the substrate 102 via cell tabs CT4.

[0015] The transistor DFET is an N-channel field-effect transistor that can be turned on and off based on a control signal supplied from the microcontroller 20. The drain of the transistor DFET is connected to the drain of the transistor CFET, the source is connected to the positive terminal TP of the battery pack 1, and the control signal supplied from the microcontroller 20 is applied to the gate of the transistor DFET. As shown in FIG. 1 , the transistor DFET has a body diode. The anode of this body diode is connected to the source of the body of the transistor DFET, and the cathode is connected to the drain of the body of the transistor DFET. The transistor DFET is turned off based on the control signal supplied from the microcontroller 20, for example, when the storage battery 11 should not be discharged or when an abnormality occurs in the battery pack 1 and the battery pack 1 should be permanently disabled. This causes the transistor DFET to cut off the discharge current in the battery pack 1.

[0016] The transistor CFET is an N-channel field-effect transistor that can be turned on and off based on a control signal supplied from the microcontroller 20. The drain of the transistor CFET is connected to the drain of the transistor DFET, the source is connected to the fuse 13, and the control signal supplied from the microcontroller 20 is applied to the gate of the transistor CFET. As shown in FIG. 1 , the transistor CFET has a body diode, similar to the transistor DFET. The transistor CFET is turned off based on the control signal supplied from the microcontroller 20, for example, when the storage battery 11 should not be charged or when an abnormality occurs in the battery pack 1 and the battery pack 1 should thereafter be permanently disabled. In this way, the transistor CFET cuts off the charging current in the battery pack 1.

[0017] The transistor 12 is an N-channel field effect transistor, and is configured to pass a current through the fuse 13 by being turned on and off based on a control signal supplied from the microcontroller 20. The drain of the transistor 12 is connected to the control terminal of the fuse 13, the source is grounded, and the control signal supplied from the microcontroller 20 is applied to the gate.

[0018] The fuse 13 is configured to be able to be cut off based on the current supplied from the transistor 12. One end of the fuse 13 is connected to the source of the transistor CFET, the other end is connected to the cell tab CT4, and the control terminal is connected to the drain of the transistor 12. For example, when an abnormality occurs in the battery pack 1 and it is desired to make the battery pack 1 permanently unusable, the fuse 13 is blown and set to a disconnected state. In this way, the fuse 13 cuts off the charging current and discharging current in the battery pack 1.

[0019] One end of resistor RG is connected to cell tab CTG and the negative terminal TN of the battery pack 1, and the other end is connected to node NG. One end of resistor R0 is connected to cell tab CT0 and the other end is connected to node N0. One end of resistor R1 is connected to cell tab CT1 and the other end is connected to node N1. One end of resistor R2 is connected to cell tab CT2 and the other end is connected to node N2. One end of resistor R3 is connected to cell tab CT3 and the other end is connected to node N3. One end of resistor R4 is connected to cell tab CT4 and the fuse 13, and the other end is connected to node N4.

[0020] One end of capacitor C0 is connected to node N0, and the other end is connected to node NG. That is, capacitor C0 is provided in a parallel path of two battery cells BC belonging to cell block CBL0. Similarly, one end of capacitor C1 is connected to node N1, and the other end is connected to node N0. One end of capacitor C2 is connected to node N2, and the other end is connected to node N1. One end of capacitor C3 is connected to node N3, and the other end is connected to node N2. One end of capacitor C4 is connected to node N4, and the other end is connected to node N3.

[0021] The microcontroller 20 is configured to monitor the state of the battery pack 1 and to control the operations of the transistors CFET, DFET, and the fuse 13. The microcontroller 20 has five switches SW (switches SW0 to SW4), a voltage detection unit 21, and a diagnosis unit 22.

[0022] One end of switch SW0 is connected to node N0, and the other end is connected to node NG. That is, switch SW0 is provided in a parallel path of two battery cells BC belonging to cell block CBL0. Similarly, one end of switch SW1 is connected to node N1, and the other end is connected to node N0. One end of switch SW2 is connected to node N2, and the other end is connected to node N1. One end of switch SW3 is connected to node N3, and the other end is connected to node N2. One end of switch SW4 is connected to node N4, and the other end is connected to node N3. Each of switches SW0 to SW4 can be individually set to an ON state or an OFF state based on a control signal supplied from diagnostic unit 22.

[0023] The voltage detection unit 21 includes an AD converter and is configured to detect cell voltages VC0 to VC4 and a storage battery voltage VB based on the voltages at nodes NG and N0 to N4. Cell voltage VC0 is the voltage at node N0 relative to the voltage at node NG and corresponds to the cell voltages VC of two battery cells BC belonging to cell block CBL0. Cell voltage VC1 is the voltage at node N1 relative to the voltage at node N0 and corresponds to the cell voltages VC of two battery cells BC belonging to cell block CBL1. Cell voltage VC2 is the voltage at node N2 relative to the voltage at node N1 and corresponds to the cell voltages VC of two battery cells BC belonging to cell block CBL2. Cell voltage VC3 is the voltage at node N3 relative to the voltage at node N2 and corresponds to the cell voltages VC of two battery cells BC belonging to cell block CBL3. Cell voltage VC4 is the voltage at node N4 relative to the voltage at node N3 and corresponds to the cell voltages VC of two battery cells BC belonging to cell block CBL4. The battery voltage VB is the voltage of the node N4 relative to the voltage of the node NG, and corresponds to the voltage of the entire battery 11.

[0024] The diagnostic unit 22 is configured to perform diagnostic processing based on the detection result of the voltage detection unit 21.

[0025] For example, if the cell voltages VC0 to VC4 are unbalanced, the diagnostic unit 22 controls the operation of the switches SW0 to SW4 so that these cell voltages VC0 to VC4 are approximately the same voltage. Specifically, for example, if the cell voltage VC1 is higher than the cell voltages VC0, VC2, VC3, and VC4, the diagnostic unit 22 turns on the switch SW1. As a result, current flows through the resistor element R1, switch SW1, and resistor element R0 in the parallel paths of the two battery cells BC belonging to the cell block CBL1, discharging these two battery cells BC and lowering the cell voltage VC1. As a result, the diagnostic unit 22 adjusts the cell voltage VC1 so that it is the same voltage as the cell voltages VC0, VC2, VC3, and VC4. In this way, the diagnostic unit 22 adjusts the state of the storage battery 11 so that the cell voltages VC0 to VC4 are approximately the same voltage.

[0026] Furthermore, for example, the diagnostic unit 22 diagnoses whether or not there is a disconnection in the path from the battery cell BC via the cell tabs CT0 to CT3 to the voltage detection unit 21. For example, if the battery pack 1 is used in outdoor equipment such as a lawnmower or an electric-assisted bicycle, vibrations may cause the cell tab CT itself to break and become disconnected, or the cell tab CT may become disconnected and become disconnected from the battery cell BC, or the cell tab CT may become disconnected and become disconnected from the wiring on the substrate 102. As described below, the diagnostic unit 22 turns on, for example, the even-numbered switches and the odd-numbered switches among the switches SW0 to SW4, for different periods. Then, the diagnostic unit 22 detects a disconnection and identifies the location of the disconnection based on the cell voltages VC0 to VC4 before and after the period in which the even-numbered switches are turned on and the cell voltages VC0 to VC4 before and after the period in which the odd-numbered switches are turned on. If there is a disconnection, the diagnostic unit 22 fixes the transistors CFET and DFET in the off state. However, the present invention is not limited to this, and the diagnostic unit 22 may, for example, turn on the transistor 12 to blow the fuse 13. This makes it possible to make the battery pack 1 permanently unusable.

[0027] Here, the storage battery 11 corresponds to a specific example of a "storage battery" in the present disclosure. The battery cell BC corresponds to a specific example of a "battery cell" in the present disclosure. The switches SW0 to SW4 correspond to a specific example of a "plurality of switches" in the present disclosure. The voltage detection unit 21 corresponds to a specific example of a "voltage detection circuit" in the present disclosure. The cell voltages VC0 to VC4 correspond to a specific example of a "plurality of cell voltages" in the present disclosure. The diagnosis unit 22 corresponds to a specific example of a "diagnosis circuit" in the present disclosure. The storage battery voltage VB corresponds to a specific example of a "storage battery voltage" in the present disclosure. The capacitors C0 to C4 correspond to a specific example of a "plurality of capacitors" in the present disclosure. The positive terminal TP corresponds to a specific example of a "first terminal" in the present disclosure. The negative terminal TN corresponds to a specific example of a "second terminal" in the present disclosure. The transistors CFET and DFET correspond to a specific example of a "shutoff switch" in the present disclosure.

[0028] [Actions and Actions] Next, the operation and function of the battery pack 1 of this embodiment will be described.

[0029] (Overview of overall operation) First, referring to FIG. 1, an overview of the overall operation of the battery pack 1 will be described. The storage battery 11 stores power. The microcontroller 20 monitors the state of the battery pack 1 and controls the operation of the transistors CFET and DFET and the fuse 13. The switches SW0 to SW4 of the microcontroller 20 are individually set to an on or off state based on a control signal supplied from the diagnostic unit 22. The voltage detection unit 21 detects the cell voltages VC0 to VC4 and the storage battery voltage VB based on the voltages at the nodes NG and N0 to N4. For example, when the cell voltages VC0 to VC4 are unbalanced, the diagnostic unit 22 controls the operation of the switches SW0 to SW4 so that these cell voltages VC0 to VC4 become approximately the same voltage. Furthermore, for example, the diagnostic unit 22 diagnoses for breaks in the path from the battery cell BC to the voltage detection unit 21 via the cell tabs CT0 to CT3. The transistors CFET and DFET are turned on or off based on the control signal supplied from the microcontroller 20. The transistor 12 causes a current to flow through the fuse 13 based on a control signal supplied from the microcontroller 20, and the fuse 13 is blown by this current.

[0030] (Detailed operation) The battery pack 1 diagnoses whether or not there is an open circuit in the path from the battery cell BC through the cell tabs CT0 to CT3 to the voltage detection unit 21. If an open circuit is detected, the battery pack 1 fixes the transistors CFET and DFET in the OFF state. This makes the battery pack 1 permanently unusable. This operation will be described in detail below.

[0031] 2A and 2B show an example of the disconnection diagnosis process. In this example, the battery pack 1 is charged with the transistors CFET and DFET turned on. As a result, the cell voltages VC0 to VC4 gradually increase. During this charging period, the battery pack 1 temporarily stops charging and performs a disconnection diagnosis.

[0032] First, the diagnosing unit 22 checks whether the maximum value of the cell voltages VC0 to VC4 is within a predetermined voltage range (step S101). In this example, the predetermined voltage range is equal to or greater than 3900 mV and less than 4050 mV. In the storage battery 11, the higher the state of charge, the higher the cell voltages VC0 to VC4. In this example, when the state of charge is about 70%, each of the cell voltages VC0 to VC4 is about 3900 mV. When the state of charge is low, the cell voltages VC0 to VC4 vary greatly, which may result in an erroneous diagnosis of a disconnection. Therefore, the diagnosing unit 22 performs a disconnection diagnosis when the state of charge reaches about 70%. If the maximum value of the cell voltages VC0 to VC4 is not within the predetermined voltage range (step S101), this step S101 is repeated until the maximum value of the cell voltages VC0 to VC4 becomes a voltage within the predetermined voltage range.

[0033] If the maximum value of the cell voltages VC0 to VC4 is within the predetermined voltage range ("Y" in step S101), the diagnosis unit 22 turns off the transistor CFET (step S102), causing the battery pack 1 to stop charging.

[0034] For example, if the battery pack 1 is being charged while connected to a device, stopping the charging in this manner allows the battery pack 1 to supply power to the device. Specifically, in the battery pack 1, a discharge current flows in the following order: negative terminal TN, storage battery 11, fuse 13, body diode of transistor CFET, transistor DFET, and positive terminal TP. During this open-circuit diagnosis process, the battery pack 1 monitors the discharge current. If the discharge current is equal to or greater than a predetermined current (e.g., 200 mA), the battery pack 1 stops the open-circuit diagnosis process, turns on transistor CFET, and resumes charging. In other words, if the discharge current is high, the cell voltage VC drops, reducing the diagnostic accuracy of the open-circuit diagnosis process. Therefore, when the discharge current is high, the battery pack 1 stops the open-circuit diagnosis process and resumes charging.

[0035] Next, the diagnosis unit 22 starts the operation of a timer (step S103).

[0036] Then, the diagnostic unit 22 checks whether each of the cell voltages VC0 to VC4 remains within ±10 mV for 10 consecutive seconds (step S104). That is, the diagnostic unit 22 checks whether the cell voltages VC0 to VC4 are stable. If each of the cell voltages VC0 to VC4 does not remain within ±10 mV for 10 consecutive seconds ("N" in step S104), the diagnostic unit 22 checks whether 30 seconds have elapsed since the timer started operating in step S103 (step S105). If 30 seconds have not yet elapsed ("N" in step S105), the process returns to step S104.

[0037] In step S104, if each of the cell voltages VC0 to VC4 remains within ±10 mV for 10 consecutive seconds, and in step S105, if 30 seconds have passed since the timer started operating, the microcontroller 20 performs voltage measurement A1 (step S106).

[0038] 3A and 3B show an example of a subroutine for voltage measurement A1.

[0039] First, the microcontroller 20 resets the retry counter (step S201). Specifically, the microcontroller 20 sets the count value of the retry counter to "0."

[0040] Next, the microcontroller 20 turns on the even-numbered switches SW (switches SW0, SW2, and SW4) among the switches SW0 to SW4 for a predetermined period of time and detects the cell voltages VC0 to VC4 and the storage battery voltage VB before and after the predetermined period of time (step S202). Specifically, first, while the switches SW0 to SW4 are in the off state, the voltage detection unit 21 detects the cell voltages VC0 to VC4 and the storage battery voltage VB. Then, the diagnosis unit 22 turns on the even-numbered switches SW (switches SW0, SW2, and SW4) for the predetermined period of time. The switches SW1 and SW3 are maintained in the off state. The length of this predetermined period of time can be set to, for example, 5 milliseconds. Then, after the predetermined period of time has elapsed and the even-numbered switches SW (switches SW0, SW2, and SW4) have returned to the off state, the voltage detection unit 21 detects the cell voltages VC0 to VC4 and the storage battery voltage VB, for example, 30 milliseconds later.

[0041] Next, the diagnosis unit 22 checks whether the voltage change amount of each of the cell voltages VC0 to VC4 before and after the predetermined period is within ±1 V (step S203). If the voltage change amount of each of the cell voltages VC0 to VC4 is within ±1 V ("Y" in step S203), the microcontroller 20 waits 0.25 seconds (step S204). If the voltage change amount of one or more of the cell voltages VC0 to VC4 exceeds ±1 V ("N" in step S202), the microcontroller 20 waits 1 second (step S205).

[0042] That is, as will be described later, if the voltage change amount of one or more of the cell voltages VC0 to VC4 exceeds ±1 V, there is a possibility that a disconnection has occurred. Therefore, in this case, the microcontroller 20 waits one second to ensure time for the voltage to return to a certain extent to its original voltage. On the other hand, if the voltage change amount of each of the cell voltages VC0 to VC4 is within ±1 V, there is a low possibility that a disconnection has occurred. Therefore, in this case, the microcontroller 20 waits 0.25 seconds to shorten the time for the disconnection diagnosis process.

[0043] Next, the microcontroller 20 turns on the odd-numbered switches SW (switches SW1 and SW3) among the switches SW0 to SW4 for a predetermined period of time and detects the cell voltages VC0 to VC4 and the storage battery voltage VB before and after the predetermined period of time (step S206). Specifically, first, while the switches SW0 to SW4 are in the off state, the voltage detection unit 21 detects the cell voltages VC0 to VC4 and the storage battery voltage VB. Then, the diagnosis unit 22 turns on the odd-numbered switches SW (switches SW1 and SW3) for the predetermined period of time. The switches SW0, SW2, and SW4 are maintained in the off state. The length of this predetermined period of time can be set to, for example, 5 milliseconds. Then, after the predetermined period of time has elapsed and the odd-numbered switches SW (switches SW1 and SW3) have returned to the off state, the voltage detection unit 21 detects the cell voltages VC0 to VC4 and the storage battery voltage VB, for example, 30 milliseconds later.

[0044] Next, the diagnosis unit 22 checks whether the voltage change amount of each of the cell voltages VC0 to VC4 before and after the predetermined period is within ±1 V (step S207). If the voltage change amount of each of the cell voltages VC0 to VC4 is within ±1 V ("Y" in step S207), the microcontroller 20 waits 0.25 seconds (step S208). If the voltage change amount of one or more of the cell voltages VC0 to VC4 exceeds ±1 V ("N" in step S207), the microcontroller 20 waits 1 second (step S209).

[0045] Next, the diagnostic unit 22 calculates the rate of change ΔVBev of the battery voltage VB when the even-numbered switch SW is operated in step S202, and the rate of change ΔVBod of the battery voltage VB when the odd-numbered switch SW is operated in step S206 (step S210). Specifically, the diagnostic unit 22 calculates the rate of change ΔVBev by dividing the battery voltage VB after the even-numbered switch SW is operated by the battery voltage VB before the even-numbered switch SW was operated in step S202. Furthermore, the diagnostic unit 22 calculates the rate of change ΔVBod by dividing the battery voltage VB after the odd-numbered switch SW is operated by the battery voltage VB before the odd-numbered switch SW was operated in step S206.

[0046] Next, the diagnosing unit 22 checks whether the rate of change ΔVBev of the battery voltage VB is greater than 0.9 and less than 1.1, and whether the rate of change ΔVBod of the battery voltage VB is greater than 0.9 and less than 1.1 (step S211). That is, in steps S202 and S206, it is expected that the battery voltage VB will not change significantly. However, for example, the battery voltage VB may change significantly due to the influence of noise from outside the battery pack 1. In this case, the detection results of the cell voltages VC0 to VC4 in steps S202 and S206 are also likely to be affected by noise, and therefore a diagnosis of a disconnection should not be made based on these detection results. Therefore, in step S211, the diagnosing unit 22 checks that the battery voltage VB has not changed significantly.

[0047] In step S211, if one or more of the change rates ΔVBev and ΔVBod of the storage battery voltage VB do not satisfy the condition ("N" in step S211), the diagnosis unit 22 checks whether the count value of the retry counter is 2 or more (step S212). If the count value of the retry counter is less than 2 ("N" in step S212), the diagnosis unit 22 increments the count value of this retry counter (step S213) and returns to step S202. This causes the microcontroller 20 to perform measurement again. If the count value of the retry counter is 2 or more, the microcontroller 20 makes a skip determination to skip the disconnection diagnosis process (step S214). This ends the voltage measurement A1 subroutine.

[0048] In step S211, if the change rates ΔVBev and ΔVBod of the storage battery voltage VB each satisfy the condition ("Y" in step S211), the diagnosis unit 22 checks whether the processes of steps S201 to S211 have been repeated twice (step S215). If these processes have not yet been repeated twice ("N" in step S215), the process returns to step S201.

[0049] In step S215, if the processing of steps S201 to S211 has been repeated twice ("Y" in step S215), the diagnostic unit 22 calculates, for each of the cell voltages VC0 to VC4, the average value of two voltages before the even-numbered switches SW (switches SW0, SW2, SW4) are operated, the average value of two voltages after the even-numbered switches SW are operated, the average value of two voltages before the odd-numbered switches SW (switches SW1 and SW3) are operated, and the average value of two voltages after the odd-numbered switches SW are operated (step S216). Specifically, the diagnostic unit 22 calculates the average value of the cell voltages VC0, VC1, VC2, VC3, and VC4 detected in the first and second step S202 before the even-numbered switches SW are turned on. The diagnostic unit 22 also calculates the average values ​​of cell voltages VC0, VC1, VC2, VC3, and VC4 detected in the first and second steps S202 after the even-numbered switches SW are turned on. The diagnostic unit 22 also calculates the average values ​​of cell voltages VC0, VC1, VC2, VC3, and VC4 detected in the first and second steps S206 before the odd-numbered switches SW are turned on. The diagnostic unit 22 also calculates the average values ​​of cell voltages VC0, VC1, VC2, VC3, and VC4 detected in the first and second steps S206 after the odd-numbered switches SW are turned on.

[0050] Next, based on the calculation result in step S216, diagnostic unit 22 calculates, for each of cell voltages VC0 to VC4, the rate of change ΔVCev of voltage when even-numbered switches SW are operated (rates of change ΔVC0ev, ΔVC1ev, ΔVC2ev, ΔVC3ev, ΔVC4ev) and the rate of change ΔVCod of voltage when odd-numbered switches SW are operated (rates of change ΔVC0od, ΔVC1od, ΔVC2od, ΔVC3od, ΔVC4od) (step S217). Specifically, diagnostic unit 22 calculates the rate of change ΔVC0ev of cell voltage VC0 by dividing the average value of two cell voltages VC0 after operating an even-numbered switch SW by the average value of two cell voltages VC0 before operating an even-numbered switch SW. Similarly, the diagnostic unit 22 calculates the rate of change ΔVC1ev of the cell voltage VC1, the rate of change ΔVC2ev of the cell voltage VC2, the rate of change ΔVC3ev of the cell voltage VC3, and the rate of change ΔVC4ev of the cell voltage VC4 when the even-numbered switch SW is operated. Furthermore, the diagnostic unit 22 calculates the rate of change ΔVC0od of the cell voltage VC0 by dividing the average value of the cell voltage VC0 for two operations after the odd-numbered switch SW is operated by the average value of the cell voltage VC0 for two operations before the odd-numbered switch SW is operated. Similarly, the diagnostic unit 22 calculates the rate of change ΔVC1od of the cell voltage VC1, the rate of change ΔVC2od of the cell voltage VC2, the rate of change ΔVC3od of the cell voltage VC3, and the rate of change ΔVC4od of the cell voltage VC4 when the odd-numbered switch SW is operated.

[0051] This completes the voltage measurement A1 subroutine.

[0052] Next, as shown in FIG. 2A, the diagnostic unit 22 checks whether a skip determination was made in step S214 of the voltage measurement A1 (FIGS. 3A and 3B) (step S107). If a skip determination was made ("Y" in step S107), the diagnostic unit 22 turns on the transistor CFET (step S108). This causes the battery pack 1 to suspend the open circuit diagnosis process and resume charging. This is the end of the flow.

[0053] If the skip determination has not been performed ("N" in step S107), the microcontroller 20 performs the disconnection determination process B1 (step S109).

[0054] 4A and 4B show an example of a subroutine of the disconnection determination process B1.

[0055] First, the diagnostic unit 22 checks whether the change rates ΔVC1ev, ΔVC0ev of the cell voltages VC1, VC0 when the even-numbered switches SW (switches SW0, SW2, SW4) are operated satisfy "ΔVC1ev-ΔVC0ev>0.9" and whether the change rates ΔVC1od, ΔVC0od of the cell voltages VC1, VC0 when the odd-numbered switches SW (switches SW1, SW3) are operated satisfy "ΔVC1od-ΔVC0od<-0.9" (step S301). Note that these "0.9" and "-0.9" are just examples and can be changed as appropriate depending on the circuit configuration, for example.

[0056] If the condition of step S301 is met ("Y" in step S302), the diagnosis unit 22 determines that the path from the battery cell BC via the cell tab CT0 to the voltage detection unit 21 is broken (step S303). Then, the process proceeds to step S304. On the other hand, if the condition of step S301 is not met ("N" in step S302), the process proceeds to step S304.

[0057] Next, the diagnostic unit 22 checks whether the change rates ΔVC3ev, ΔVC2ev of the cell voltages VC3, VC2 when the even-numbered switches SW (switches SW0, SW2, SW4) are operated satisfy "ΔVC3ev-ΔVC2ev>0.9" and whether the change rates ΔVC3od, ΔVC2od of the cell voltages VC3, VC2 when the odd-numbered switches SW (switches SW1, SW3) are operated satisfy "ΔVC3od-ΔVC2od<-0.9" (step S304).

[0058] If the condition of step S304 is met ("Y" in step S305), the diagnosis unit 22 determines that the path from the battery cell BC via the cell tab CT2 to the voltage detection unit 21 is broken (step S306). Then, the process proceeds to step S307. On the other hand, if the condition of step S304 is not met ("N" in step S305), the process proceeds to step S307.

[0059] Next, the diagnostic unit 22 checks whether the change rates ΔVC2ev, ΔVC1ev of the cell voltages VC2, VC1 when the even-numbered switches SW (switches SW0, SW2, SW4) are operated satisfy "ΔVC2ev-ΔVC1ev<-0.9", and whether the change rates ΔVC2od, ΔVC1od of the cell voltages VC2, VC1 when the odd-numbered switches SW (switches SW1, SW3) are operated satisfy "ΔVC2od-ΔVC1od>0.9" (step S307).

[0060] If the condition of step S307 is met ("Y" in step S308), the diagnosis unit 22 determines that the path from the battery cell BC via the cell tab CT1 to the voltage detection unit 21 is broken (step S309). Then, the process proceeds to step S310. On the other hand, if the condition of step S307 is not met ("N" in step S308), the process proceeds to step S310.

[0061] Next, the diagnostic unit 22 checks whether the change rates ΔVC4ev, ΔVC3ev of the cell voltages VC4, VC3 when the even-numbered switches SW (switches SW0, SW2, SW4) are operated satisfy "ΔVC4ev-ΔVC3ev<-0.9", and whether the change rates ΔVC4od, ΔVC3od of the cell voltages VC4, VC3 when the odd-numbered switches SW (switches SW1, SW3) are operated satisfy "ΔVC4od-ΔVC3od>0.9" (step S310).

[0062] If the condition of step S310 is met ("Y" in step S311), the diagnosis unit 22 determines that there is a break in the path from the battery cell BC via the cell tab CT3 to the voltage detection unit 21 (step S312). Then, the subroutine of the break determination process B1 ends. On the other hand, if the condition of step S310 is not met ("N" in step S311), the subroutine of the break determination process B1 ends.

[0063] Next, as shown in FIG. 2A, the diagnostic unit 22 checks whether it has been determined that a disconnection has occurred in the disconnection determination process B1 (FIGS. 4A and 4B) (step S110). If no disconnection has occurred ("N" in step S110), the diagnostic unit 22 turns on the transistor CFET (step S108). This causes the battery pack 1 to resume charging. This is the end of the flow. That is, since the diagnostic unit 22 has confirmed that no disconnection has occurred in the disconnection diagnosis process, the diagnostic unit 22 ends this disconnection diagnosis process.

[0064] In step S110, if a break has occurred ("Y" in step S110), the microcontroller 20 performs the same processing as the processing in steps S103 to S110 with higher accuracy to check again whether a break has occurred.

[0065] First, the diagnosis unit 22 starts the operation of a timer (step S111).

[0066] Then, the diagnostic unit 22 checks whether each of the cell voltages VC0 to VC4 remains within ±5 mV for 30 consecutive seconds (step S112). The conditions in steps S112 and S113 are set to be stricter than the conditions in steps S104 and S105. This allows the diagnostic unit 22 to check whether the cell voltages VC0 to VC4 are stable. If each of the cell voltages VC0 to VC4 does not remain within ±5 mV for 30 consecutive seconds ("N" in step S112), the diagnostic unit 22 checks whether five minutes have elapsed since the timer started operating in step S111 (step S113). If five minutes have not yet elapsed ("N" in step S113), the process returns to step S112.

[0067] In step S112, if each of the cell voltages VC0 to VC4 remains within ±5 mV for 30 consecutive seconds, and if 5 minutes have passed since the timer started operating in step S113, the microcontroller 20 performs voltage measurement A2 (step S114).

[0068] 5A and 5B show an example of a subroutine for voltage measurement A2. Steps S401 to S414 in this voltage measurement A2 are the same as steps S201 to S214 in voltage measurement A1 shown in FIGS.

[0069] In this voltage measurement A2, the processing of steps S401 to S411 is repeated four times. That is, in voltage measurement A1 (FIGS. 3A and 3B), in step S215, diagnostic unit 22 checked whether the processing of steps S201 to S211 was repeated twice, but in voltage measurement A2, in step S415, diagnostic unit 22 checks whether the processing of steps S401 to S411 was repeated four times.

[0070] In step S415, if the processes of steps S401 to S411 have been repeated four times ("Y" in step S415), the diagnostic unit 22 calculates, for each of the cell voltages VC0 to VC4, the average value of two voltages excluding the maximum and minimum values ​​of the four voltages before operating the even-numbered switches SW (switches SW0, SW2, SW4), the average value of two voltages excluding the maximum and minimum values ​​of the four voltages after operating the even-numbered switches SW, the average value of two voltages excluding the maximum and minimum values ​​of the four voltages before operating the odd-numbered switches SW (switches SW1, SW3), and the average value of two voltages excluding the maximum and minimum values ​​of the four voltages after operating the odd-numbered switches SW (step S416). In this way, the diagnostic unit 22 calculates the average value of the remaining two voltages excluding the maximum and minimum values ​​of the four voltages, thereby improving the accuracy of the disconnection diagnosis.

[0071] Next, based on the calculation results of step S416, the diagnostic unit 22 calculates, for each of the cell voltages VC0 to VC4, the rate of change ΔVCev of the voltage when the even-numbered switch SW is operated and the rate of change ΔVCod of the voltage when the odd-numbered switch SW is operated (step S417). Specifically, the diagnostic unit 22 calculates the rate of change ΔVCev of the cell voltage VC0 (rate of change ΔVC0ev) by dividing the average value of the cell voltage VC0 for two times after the even-numbered switch SW is operated by the average value of the cell voltage VC0 for two times before the even-numbered switch SW is operated. Similarly, the diagnostic unit 22 calculates the rate of change ΔVCev of the cell voltage VC1 (rate of change ΔVC1ev), the rate of change ΔVCev of the cell voltage VC2 (rate of change ΔVC2ev), the rate of change ΔVCev of the cell voltage VC3 (rate of change ΔVC3ev), and the rate of change ΔVCev of the cell voltage VC4 (rate of change ΔVC4ev) when the even-numbered switch SW is operated. Furthermore, the diagnostic unit 22 calculates the rate of change ΔVCod of the cell voltage VC0 (rate of change ΔVC0od) by dividing the average value of the cell voltage VC0 for two operations after the odd-numbered switch SW is operated by the average value of the cell voltage VC0 for two operations before the odd-numbered switch SW is operated. Similarly, the diagnostic unit 22 calculates the rate of change ΔVCod of the cell voltage VC1 (rate of change ΔVC1od), the rate of change ΔVCod of the cell voltage VC2 (rate of change ΔVC2od), the rate of change ΔVCod of the cell voltage VC3 (rate of change ΔVC3od), and the rate of change ΔVCod of the cell voltage VC4 (rate of change ΔVC4od) when the odd-numbered switch SW is operated.

[0072] This completes the voltage measurement A2 subroutine.

[0073] Next, as shown in FIG. 2B, the diagnostic unit 22 checks whether a skip determination was made in step S414 of voltage measurement A2 (FIGS. 5A and 5B) (step S115). If a skip determination was made ("Y" in step S115), the diagnostic unit 22 turns on the transistor CFET (step S116). This causes the battery pack 1 to suspend the open circuit diagnosis process and resume charging. This is the end of the flow.

[0074] If a skip determination has not been made in voltage measurement A2 ("N" in step S115), the microcontroller 20 performs disconnection determination processing B2 (step S117). This disconnection determination processing B2 is similar to the disconnection determination processing B1 shown in FIGS. 4A and 4B.

[0075] Next, the diagnostic unit 22 checks whether it has been determined in the disconnection determination process B2 that a disconnection has occurred (step S118). If no disconnection has occurred ("N" in step S118), the diagnostic unit 22 turns on the transistor CFET (step S116). This causes the battery pack 1 to resume charging. This completes the flow. That is, the diagnostic unit 22 has confirmed that no disconnection has occurred in the second diagnosis, which was performed with higher accuracy than the first diagnosis, and therefore terminates the disconnection diagnosis process.

[0076] In step S119, if a disconnection has occurred ("Y" in step S118), the diagnostic unit 22 fixes the transistors CFET and DFET in the OFF state (step S119), thereby making the battery pack 1 permanently unusable.

[0077] This completes the process.

[0078] Here, for example, the predetermined period in step S202 corresponds to a specific example of a "first predetermined period" in the present disclosure. For example, the predetermined period in step S206 corresponds to a specific example of a "second predetermined period" in the present disclosure. The rate of change ΔVCev corresponds to a specific example of a "first rate of change" in the present disclosure. The rate of change ΔVCod corresponds to a specific example of a "second rate of change" in the present disclosure.

[0079] (Example) Next, a specific example will be given to explain the disconnection diagnosis process for the battery pack 1. First, the disconnection diagnosis process for the battery pack 1 in which no disconnection has occurred will be explained, and then the disconnection diagnosis process for the battery pack 1 in which a disconnection has occurred will be explained.

[0080] (In the case of battery pack 1 with no disconnection) Figure 6 shows an example of voltage measurement A1 in a battery pack 1 where no open circuit has occurred, where (A) shows the waveform of cell voltage VC4, (B) shows the waveform of cell voltage VC3, (C) shows the waveform of cell voltage VC2, (D) shows the waveform of cell voltage VC1, and (E) shows the waveform of cell voltage VC0. In Figure 6, the horizontal axis represents time.

[0081] In the first step S202 (FIG. 3A), the diagnostic unit 22 turns on the even-numbered switches SW (switches SW0, SW2, and SW4) for a short period starting at time t1. The length of the period during which the switches SW are turned on is, for example, 5 milliseconds, which is very short in the time scale of FIG. 6. For example, when the switch SW0 turns on, the node N1 and the node N0 are connected to each other via the switch SW0, and the cell voltage VC0 decreases (FIG. 6(E)). In this way, at time t1 when the switches SW0, SW2, and SW4 turn on, the cell voltages VC0, VC2, and VC4 transiently decrease slightly and then return to their original voltages (FIGS. 6(A), (C), and (E)). On the other hand, the cell voltages VC1 and VC3 transiently increase slightly at time t1 and then return to their original voltages (FIGS. 6(B) and (D)).

[0082] In this example, the cell voltages VC0 to VC4 hardly change before and after the period in which the even-numbered switches SW are turned on, so the amount of change in each of the cell voltages VC0 to VC4 is within ±1 V. Therefore, the microcontroller 20 waits for 0.25 seconds (step S204).

[0083] Next, in the first step S206 (FIG. 3A), the diagnosis unit 22 turns on the odd-numbered switches SW (switches SW1, SW3) for a short period starting from timing t2. The cell voltages VC1 and VC3 transiently decrease slightly at timing t2 and then return to their original voltages (FIGS. 6B and 6D). On the other hand, the cell voltages VC0, VC2, and VC4 transiently increase slightly at timing t2 and then return to their original voltages (FIGS. 6A, 6C, and 6E). In this example, the amount of change in each of the cell voltages VC0 to VC4 is within ±1 V before and after the period in which the odd-numbered switches SW are turned on. Therefore, the microcontroller 20 waits 0.25 seconds (step S208).

[0084] Next, in step S202 for the second time, the diagnostic unit 22 turns on the even-numbered switches SW (switches SW0, SW2, SW4) for a short period starting from timing t3. This operation is almost the same as the operation at timing t1. Then, the microcontroller 20 waits for 0.25 seconds (step S204).

[0085] Next, in step S206 for the second time, the diagnostic unit 22 turns on the odd-numbered switches SW (switches SW1 and SW3) for a short period starting from timing t4. This operation is almost the same as the operation at timing t2. Then, the microcontroller 20 waits for 0.25 seconds (step S208).

[0086] Figure 7A shows an example of the cell voltages VC0 to VC4 and the storage battery voltage VB when the even-numbered switches SW are turned on. Figure 7B shows an example of the cell voltages VC0 to VC4 and the storage battery voltage VB when the odd-numbered switches SW are turned on. In Figures 7A and 7B, the voltages are expressed in mV.

[0087] 7A shows data in step S202 for the first time and data in step S202 for the second time. In FIG. 7A, "before" indicates before the even-numbered switches SW are turned on, and "after" indicates after the even-numbered switches SW are turned on. Similarly, FIG. 7B shows data in step S206 for the first time and data in step S206 for the second time. In FIG. 7B, "before" indicates before the odd-numbered switches SW are turned on, and "after" indicates after the odd-numbered switches SW are turned on.

[0088] In step S210 (FIG. 3(B)), diagnostic unit 22 calculates the rate of change ΔVBev of storage battery voltage VB when even-numbered switches SW are operated, and the rate of change ΔVBod of storage battery voltage VB when odd-numbered switches SW are operated. Then, in step S211, diagnostic unit 22 checks whether the rate of change ΔVBev of storage battery voltage VB is greater than 0.9 and less than 1.1, and whether the rate of change ΔVBod of storage battery voltage VB is greater than 0.9 and less than 1.1.

[0089] In this example, as shown in Fig. 7A, when the even-numbered switch SW is operated, the rate of change ΔVBev of the battery voltage VB the first time and the rate of change ΔVBev of the battery voltage VB the second time are greater than 0.9 and less than 1.1. Also, as shown in Fig. 7B, when the odd-numbered switch SW is operated, the rate of change ΔVBod of the battery voltage VB the first time and the rate of change ΔVBod of the battery voltage VB the second time are greater than 0.9 and less than 1.1. Therefore, the diagnosing unit 22 determines that there is no influence of noise from outside the battery pack 1 and that it is possible to perform a diagnosis of an open circuit based on the detection results of the cell voltages VC0 to VC4.

[0090] Then, in steps S216 and S217 (FIG. 3(B)), the diagnostic unit 22 calculates the change rates ΔVC0ev, ΔVC1ev, ΔVC2ev, ΔVC3ev, ΔVC4ev) of the cell voltages VC0 to VC4 when the even-numbered switches SW are operated, and the change rates ΔVC0od, ΔVC1od, ΔVC2od, ΔVC3od, ΔVC4od of the cell voltages VC0 to VC4 when the odd-numbered switches SW are operated.

[0091] Then, in the disconnection determination process B1 (FIGS. 4A and 4B), the diagnostic unit 22 checks whether the change rates ΔVC0ev, ΔVC1ev, ΔVC2ev, ΔVC3ev, and ΔVC4ev of the cell voltages VC0 to VC4 when the even-numbered switches SW are operated, and the change rates ΔVC0od, ΔVC1od, ΔVC2od, ΔVC3od, and ΔVC4od of the cell voltages VC0 to VC4 when the odd-numbered switches SW are operated, satisfy the conditions of steps S301, S304, S307, and S310.

[0092] 7A and 7B, none of the conditions in steps S301, S304, S307, and S310 are satisfied, so the diagnosing unit 22 determines that no disconnection has occurred.

[0093] (In the case of battery pack 1 with a disconnection) 8 shows an example of a battery pack 1 in which a disconnection has occurred. In this example, as shown in FIG. 8, the disconnection has occurred at a disconnection location W of the cell tab CT0.

[0094] Figure 9 shows an example of voltage measurement A1 in the battery pack 1 shown in Figure 8, where (A) shows the waveform of cell voltage VC4, (B) shows the waveform of cell voltage VC3, (C) shows the waveform of cell voltage VC2, (D) shows the waveform of cell voltage VC1, and (E) shows the waveform of cell voltage VC0. In Figure 9, the horizontal axis represents time.

[0095] In the first step S202 (FIG. 3A), the diagnostic unit 22 turns on the even-numbered switches SW (switches SW0, SW2, and SW4) for a short period starting from timing t11. In this example, an open circuit occurs in the cell tab CT0. Therefore, when switch SW0 turns on, for example, the voltage at node N0 changes toward the voltage at node NG, so that cell voltage VC0 decreases (FIG. 9(E)) and cell voltage VC1 increases (FIG. 9(D)). Then, when switch SW0 turns off, the voltage at node N0 slowly changes toward its original voltage. As a result, cell voltages VC0 and VC1 slowly change toward their original voltages. The cell voltages VC2 to VC4 are the same as when no open circuit occurs (FIG. 6) (FIGS. 9(A) to 9(C)).

[0096] In this example, the amount of change in each of the cell voltages VC0 to VC4 before and after the period in which the even-numbered switches SW are in the on state is greater than ±1 V. Therefore, the microcontroller 20 waits for one second (step S205).

[0097] Next, in the first step S206 (FIG. 3A), the diagnostic unit 22 turns on the odd-numbered switches SW (switches SW1 and SW3) for a short period starting from timing t12. In this example, since an open circuit occurs in the cell tab CT0, for example, when switch SW1 turns on, the voltage at node N0 changes toward the voltage at node N1, so that cell voltage VC1 decreases (FIG. 9(D)) and cell voltage VC0 increases (FIG. 9(E)). Then, when switch SW1 turns off, the voltage at node N0 slowly changes toward its original voltage. As a result, cell voltages VC0 and VC1 slowly change toward their original voltages. Then, the microcontroller 20 waits for one second (step S209).

[0098] Next, in step S202 for the second time, the diagnostic unit 22 turns on the even-numbered switches SW (switches SW0, SW2, SW4) for a short period starting from timing t13. This operation is almost the same as the operation at timing t11. Then, the microcontroller 20 waits for one second (step S205).

[0099] Next, in step S206 for the second time, the diagnosis unit 22 turns on the odd-numbered switches SW (switches SW1 and SW3) for a short period starting from timing t14. This operation is almost the same as the operation at timing t12. Then, the microcontroller 20 waits for one second (step S209).

[0100] Fig. 10A shows an example of the cell voltages VC0 to VC4 and the storage battery voltage VB when the even-numbered switches SW are turned on. Fig. 10B shows an example of the cell voltages VC0 to VC4 and the storage battery voltage VB when the odd-numbered switches SW are turned on.

[0101] In this example, as shown in Fig. 10A, when the even-numbered switch SW is operated, the rate of change ΔVBev of the battery voltage VB the first time and the rate of change ΔVBev of the battery voltage VB the second time are greater than 0.9 and less than 1.1. Also, as shown in Fig. 10B, when the odd-numbered switch SW is operated, the rate of change ΔVBod of the battery voltage VB the first time and the rate of change ΔVBod of the battery voltage VB the second time are greater than 0.9 and less than 1.1. Therefore, the diagnosing unit 22 determines that there is no influence of noise from outside the battery pack 1 and that it is possible to diagnose an open circuit based on the detection results of the cell voltages VC0 to VC4.

[0102] Then, in the disconnection determination process B1 (FIGS. 4A and 4B), the diagnostic unit 22 checks whether the change rates ΔVC0ev, ΔVC1ev, ΔVC2ev, ΔVC3ev, and ΔVC4ev of the cell voltages VC0 to VC4 when the even-numbered switches SW are operated, and the change rates ΔVC0od, ΔVC1od, ΔVC2od, ΔVC3od, and ΔVC4od of the cell voltages VC0 to VC4 when the odd-numbered switches SW are operated, satisfy the conditions of steps S301, S304, S307, and S310.

[0103] 10A and 10B, the conditions of step S301 are met. That is, "ΔVC1ev - ΔVC0ev > 0.9" and "ΔVC1od - ΔVC0od < -0.9" are met. Therefore, in step S303, the diagnosis unit 22 determines that the path from the battery cell BC via the cell tab CT0 to the voltage detection unit 21 is broken.

[0104] Since the diagnosing unit 22 has thus determined that a disconnection has occurred ("Y" in step S110 of FIG. 2A), it will again confirm with higher accuracy that a disconnection has occurred.

[0105] FIG. 11 shows the results of voltage measurement A2 in the battery pack 1 shown in FIG. 8, where (A) shows the waveform of cell voltage VC4, (B) shows the waveform of cell voltage VC3, (C) shows the waveform of cell voltage VC2, (D) shows the waveform of cell voltage VC1, and (E) shows the waveform of cell voltage VC0.

[0106] In the first step S202 (FIG. 3A), the diagnostic unit 22 turns on the even-numbered switches SW (switches SW0, SW2, and SW4) for a short period starting at timing t21. This operation is almost the same as the operation at timing t11 in voltage measurement A1 (FIG. 9). Then, the microcontroller 20 waits for one second (step S205).

[0107] In the first step S206 (FIG. 3A), the diagnostic unit 22 turns on the odd-numbered switches SW (switches SW1 and SW3) for a short period starting at timing t22. This operation is almost the same as the operation at timing t12 in voltage measurement A1 (FIG. 9). Then, the microcontroller 20 waits for one second (step S209).

[0108] The same applies to the subsequent operations at timings t23 to t28. In this example, the operation of step S202 is performed four times and the operation of step S206 is performed four times alternately.

[0109] Fig. 12A shows an example of the cell voltages VC0 to VC4 and the storage battery voltage VB when the even-numbered switches SW are turned on. Fig. 12B shows an example of the cell voltages VC0 to VC4 and the storage battery voltage VB when the odd-numbered switches SW are turned on.

[0110] In this example, as shown in Fig. 12A, when the even-numbered switches SW are operated, the change rates ΔVBev of the four storage battery voltages VB are each greater than 0.9 and less than 1.1. Also, as shown in Fig. 12B, when the odd-numbered switches SW are operated, the change rates ΔVBod of the four storage battery voltages VB are each greater than 0.9 and less than 1.1. Therefore, the diagnosing unit 22 determines that there is no influence of noise from outside the battery pack 1 and that it is possible to diagnose an open circuit based on the detection results of the cell voltages VC0 to VC4.

[0111] Then, in the disconnection determination process B2, the diagnostic unit 22 checks whether the change rates ΔVC0ev, ΔVC1ev, ΔVC2ev, ΔVC3ev, ΔVC4ev of the cell voltages VC0 to VC4 when the even-numbered switches SW are operated, and the change rates ΔVC0od, ΔVC1od, ΔVC2od, ΔVC3od, ΔVC4od of the cell voltages VC0 to VC4 when the odd-numbered switches SW are operated, satisfy the conditions of steps S301, S304, S307, S310.

[0112] 12A and 12B, the conditions of step S301 are met. That is, "ΔVC1ev - ΔVC0ev > 0.9" and "ΔVC1od - ΔVC0od < -0.9" are met. Therefore, in step S303, the diagnosis unit 22 determines that the path from the battery cell BC via the cell tab CT0 to the voltage detection unit 21 is broken.

[0113] In this way, the diagnosis unit 22 can identify the disconnection location W as shown in FIG.

[0114] Thus, the battery pack 1 includes a storage battery 11 having a plurality of battery cells BC connected in series, a plurality of switches SW provided corresponding to each of the plurality of battery cells BC and each provided in a first parallel path of a corresponding battery cell BC, a voltage detection circuit (voltage detection unit 21) capable of detecting the voltages across each of the plurality of switches SW as a plurality of cell voltages VC corresponding to each of the plurality of battery cells BC, and a diagnostic circuit (diagnostic unit 22) capable of turning on one or more of the plurality of switches SW (e.g., even-numbered switches SW0, SW2, SW4) for a predetermined period of time and capable of performing diagnostic processing based on the detection results of the voltage detection circuit (voltage detection unit 21) before and after the predetermined period. This allows the battery pack 1 to diagnose, for example, whether a break has occurred in the path from the battery cell BC through the cell tabs CT0 to CT3 to the voltage detection unit 21, thereby diagnosing whether a malfunction has occurred.

[0115] In particular, the battery pack 1 performs diagnostic processing based on the detection results of the voltage detection circuit (voltage detection unit 21) before and after a predetermined period. This allows for a shorter diagnostic time than when diagnostic processing is performed based on the detection results of the voltage detection unit 21 during the period when the switch SW is turned on. That is, for example, when detecting the voltage during the period when the switch SW is turned on, the period during which the switch SW is turned on needs to be extended to some extent in order to perform AD conversion more reliably. Furthermore, if the period during which the switch SW is turned on is extended in this way, it takes longer for the voltage to stabilize after the switch SW is turned off from the on state. As a result, the diagnostic time increases. On the other hand, the battery pack 1 detects the voltage during the periods before and after the period during which the switch is turned on. This allows for a shorter period during which the switch SW is turned on and a shorter period during which the voltage to stabilize after the switch SW is turned off from the on state. As a result, the battery pack 1 can effectively diagnose whether a malfunction has occurred in a short time.

[0116] In addition, in the battery pack 1, two adjacent battery cells BC among the multiple battery cells BC are connected to each other via a connection node, and the diagnostic circuit (diagnostic unit 22) is configured to diagnose a break in the path from the connection node to the voltage detection circuit (voltage detection unit 21) during diagnostic processing. This makes it possible to diagnose a break if any of the cell tabs CT0 to CT3 occurs. That is, for example, if a break occurs in the cell tab CT4 or the cell tab CTG, the battery pack 1 becomes unable to charge or discharge, making it easy to diagnose the break. However, if a break occurs in any of the cell tabs CT0 to CT3, the battery pack 1 can still charge and discharge, making it difficult to diagnose the break. Furthermore, for example, if a break occurs in the cell tab CT0, the voltage at node N0 may become a voltage between the voltages at nodes NG and N1 due to capacitors C0 and C1. Therefore, if a break occurs in any of the cell tabs CT0 to CT3, it is difficult to diagnose the break. In the battery pack 1, one or more of the switches SW are turned on for a predetermined period of time, and a diagnostic process is performed based on the detection results of the voltage detection circuit before and after the predetermined period, so that it is possible to diagnose disconnections in the cell tabs CT0 to CT3. Therefore, it is possible to diagnose whether a malfunction has occurred in the battery pack 1.

[0117] Furthermore, in the battery pack 1, the voltage detection circuit (voltage detection unit 21) can detect the storage battery voltage VB of the storage battery 11, and the diagnostic circuit (diagnostic unit 22) can further perform diagnostic processing based on the storage battery voltage VB before a predetermined period and the storage battery voltage VB after the predetermined period. This allows the battery pack 1 to check, for example, whether there is an influence of noise from outside the battery pack 1, thereby improving the accuracy of the diagnostic processing.

[0118] The battery pack 1 further includes a plurality of capacitors C0 to C4, each of which is provided corresponding to a plurality of battery cells BC and is provided in the second parallel path of a corresponding one of the plurality of battery cells BC. This allows the battery pack 1 to stabilize the cell voltages VC0 to VC4, making it easier for the voltage detection unit 21 to detect the cell voltages VC0 to VC4, for example.

[0119] In addition, in the battery pack 1, the diagnostic circuit (diagnostic unit 22) can turn on one or more even-numbered switches SW among the multiple switches SW during a first predetermined period, and can turn on one or more odd-numbered switches SW among the multiple switches SW during a second predetermined period. The diagnostic circuit (diagnostic unit 22) can perform diagnostic processing based on the multiple cell voltages VC before the first predetermined period, the multiple cell voltages VC after the first predetermined period, the multiple cell voltages VC before the second predetermined period, and the multiple cell voltages VC after the second predetermined period. This allows the battery pack 1 to perform diagnostic processing effectively in a short time. That is, for example, if the diagnostic circuit sequentially selects one of the multiple switches SW and turns on the selected switch SW, the diagnostic processing would take a long time. On the other hand, in the battery pack 1, the diagnostic circuit turns on one or more even-numbered switches SW among the multiple switches SW, and turns on one or more odd-numbered switches SW among the multiple switches SW during the second predetermined period. This allows the battery pack 1 to reduce the number of periods during which the switch SW is in the ON state, thereby enabling the diagnostic process to be performed effectively in a short time.

[0120] Furthermore, in the battery pack 1, the diagnostic circuit (diagnostic unit 22) is capable of calculating a first rate of change (rate of change ΔVCev) of each of the plurality of cell voltages VC before and after a first predetermined period, and performing diagnostic processing based on the difference between the first rate of change (rate of change ΔVCev) of two cell voltages VC corresponding to two adjacent battery cells BC among the plurality of battery cells BC, and is capable of calculating a second rate of change (rate of change ΔVCod) of each of the plurality of cell voltages VC before and after a second predetermined period, and performing diagnostic processing based on the difference between the second rate of change (rate of change ΔVCod) of two cell voltages VC corresponding to two adjacent battery cells BC among the plurality of battery cells BC. As a result, in the battery pack 1, the location of the disconnection can be identified as shown in FIGS. 4A and 4B , and diagnostic processing can be performed effectively.

[0121] Furthermore, in the battery pack 1, the diagnostic circuit (diagnostic unit 22) can change the length of the waiting time after the first predetermined period depending on whether the amount of change in one or more cell voltages VC among the multiple cell voltages VC before and after the first predetermined period exceeds a predetermined amount, and can change the length of the waiting time after the second predetermined period depending on whether the amount of change in one or more cell voltages VC among the multiple cell voltages VC before and after the second predetermined period exceeds a predetermined amount. For example, if the amount of change in one or more of the cell voltages VC0 to VC4 exceeds ±1 V, there is a possibility of a disconnection. Therefore, in this case, the microcontroller 20 waits 1 second to ensure time for the voltage to return to its original voltage to some extent. On the other hand, if the amount of change in each of the cell voltages VC0 to VC4 is within ±1 V, there is little possibility of a disconnection. Therefore, in this case, the microcontroller 20 waits 0.25 seconds to shorten the time required for the disconnection diagnosis process. This allows the battery pack 1 to perform the diagnosis process effectively.

[0122] [effect] As described above, this embodiment includes a storage battery having a plurality of battery cells connected in series, a plurality of switches provided corresponding to the plurality of battery cells, each switch being provided in a first parallel path of a corresponding battery cell among the plurality of battery cells, a voltage detection circuit capable of detecting the voltage across each of the plurality of switches SW as a plurality of cell voltages corresponding to the plurality of battery cells, and a diagnostic circuit capable of turning on one or more of the plurality of switches for a predetermined period of time and capable of performing diagnostic processing based on the detection result of the voltage detection circuit before the predetermined period and the detection result of the voltage detection circuit after the predetermined period, thereby making it possible to diagnose whether a malfunction has occurred.

[0123] In this embodiment, two adjacent battery cells among the plurality of battery cells are connected to each other via a connection node, and the diagnostic circuit is capable of diagnosing a break in the path from the connection node to the voltage detection circuit during diagnostic processing, so that it is possible to diagnose whether a malfunction has occurred.

[0124] In this embodiment, the voltage detection circuit is capable of detecting the battery voltage of the battery, and the diagnostic circuit is further capable of performing diagnostic processing based on the battery voltage before a specified period and the battery voltage after a specified period, thereby improving the accuracy of the diagnostic processing.

[0125] In this embodiment, the diagnostic circuit is capable of turning on one or more even-numbered switches SW among the multiple switches during a first predetermined period, and turning on one or more odd-numbered switches SW among the multiple switches during a second predetermined period. The diagnostic circuit is also capable of performing diagnostic processing based on the multiple cell voltages before the first predetermined period, the multiple cell voltages after the first predetermined period, the multiple cell voltages before the second predetermined period, and the multiple cell voltages after the second predetermined period. This allows for efficient diagnostic processing in a short time.

[0126] In this embodiment, the diagnostic circuit is capable of calculating a first rate of change of each of the plurality of cell voltages before and after a first predetermined period, and performing diagnostic processing based on the difference between the first rate of change of two cell voltages corresponding to two adjacent battery cells among the plurality of battery cells, and is capable of calculating a second rate of change of each of the plurality of cell voltages VC before and after a second predetermined period, and performing diagnostic processing based on the difference between the second rate of change of two cell voltages corresponding to two adjacent battery cells among the plurality of battery cells, so that diagnostic processing can be performed effectively.

[0127] In this embodiment, the diagnostic circuit is capable of changing the length of the waiting time after the first predetermined period depending on whether the amount of change in one or more of the multiple cell voltages before and after the first predetermined period exceeds a predetermined amount, and is capable of changing the length of the waiting time after the second predetermined period depending on whether the amount of change in one or more of the multiple cell voltages before and after the second predetermined period exceeds a predetermined amount, thereby enabling diagnostic processing to be performed effectively.

[0128] Although the present technology has been described above by giving embodiments, the present technology is not limited to these embodiments and can be modified in various ways.

[0129] For example, in the above embodiment, five cell blocks CBL0 to CBL4 are provided, but the number of cell blocks CBL is not limited to five, and instead may be, for example, two or more and four or less, or six or more.

[0130] For example, in the above embodiment, the cell block CBL has two battery cells BC connected in parallel, but this is not limited to this, and instead, for example, it may have one battery cell BC, or it may have three or more battery cells BC.

[0131] For example, in the above embodiment, the capacitors C0 to C4 are provided, but the present invention is not limited to this, and instead, the capacitors C0 to C4 may be omitted.

[0132] For example, in the above embodiment, the charging is stopped temporarily during the charging period to diagnose the disconnection, but the present invention is not limited to this and the disconnection can be diagnosed in various cases. Specifically, for example, when the battery pack 1 is removed from the device and stored, the battery pack 1 may be woken up from the power saving state intermittently to diagnose the disconnection.

[0133] For example, the various numerical values ​​such as the cell voltage VC, the storage battery voltage VB, the measurement waiting time, and the threshold value in the above embodiment are merely examples and can be changed as appropriate.

[0134] The effects described in this specification are merely examples, and the effects of the present disclosure are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present disclosure.

[0135] Furthermore, the present disclosure may take the following aspects. <1> a storage battery having a plurality of battery cells connected in series; a plurality of switches provided corresponding to the plurality of battery cells, each of the switches being provided in a first parallel path of a corresponding battery cell among the plurality of battery cells; a voltage detection circuit capable of detecting the voltage across each of the plurality of switches as a plurality of cell voltages respectively corresponding to the plurality of battery cells; a diagnostic circuit capable of turning on one or more of the plurality of switches for a predetermined period of time, and capable of performing diagnostic processing based on a detection result of the voltage detection circuit before the predetermined period of time and a detection result of the voltage detection circuit after the predetermined period of time; A battery pack equipped with <2> two adjacent battery cells among the plurality of battery cells are connected to each other via a connection node; The diagnostic circuit is capable of diagnosing a break in a path from the connection node to the voltage detection circuit in the diagnostic process. <1> The battery pack described. <3> the voltage detection circuit is capable of detecting a battery voltage of the storage battery; The diagnostic circuit is further capable of performing the diagnostic process based on the battery voltage before the predetermined period and the battery voltage after the predetermined period. <1> or <2> The battery pack described. <4> The power supply further includes a plurality of capacitors provided corresponding to the plurality of battery cells, each capacitor being provided in a second parallel path of a corresponding battery cell among the plurality of battery cells. <1> from <3> 10. The battery pack according to claim 9, wherein: <5> the predetermined period includes a first predetermined period and a second predetermined period; The diagnostic circuitry includes: During the first predetermined period, one or more even-numbered switches among the plurality of switches can be turned on; During the second predetermined period, one or more odd-numbered switches among the plurality of switches can be turned on; The diagnostic process can be performed based on the plurality of cell voltages before the first predetermined period, the plurality of cell voltages after the first predetermined period, the plurality of cell voltages before the second predetermined period, and the plurality of cell voltages after the second predetermined period. <1> from <4> 10. The battery pack according to claim 9, wherein: <6> a first rate of change of each of the plurality of cell voltages before and after the first predetermined period is calculated, and the diagnostic process can be performed based on a difference between the first rate of change of two of the cell voltages corresponding to two adjacent battery cells among the plurality of battery cells; It is possible to calculate a second rate of change of each of the plurality of cell voltages before and after the second predetermined period, and to perform the diagnostic process based on the difference between the second rate of change of two of the cell voltages corresponding to two adjacent battery cells among the plurality of battery cells. <5> The battery pack described. <7> The diagnostic circuitry includes: a length of a waiting time after the first predetermined period can be changed depending on whether a change amount of one or more cell voltages among the plurality of cell voltages before and after the first predetermined period exceeds a predetermined amount; The length of the waiting time after the second predetermined period can be changed depending on whether the amount of change in one or more cell voltages among the plurality of cell voltages before and after the second predetermined period exceeds a predetermined amount. <5> The battery pack described. <8> a first terminal connected to one end of the storage battery; a second terminal connected to the other end of the storage battery; a cutoff switch provided in a charge / discharge path of the storage battery connecting the first terminal and the second terminal; Furthermore, The diagnostic circuit can fix the cutoff switch in an OFF state based on the result of the diagnostic process. <1> from <7> 10. The battery pack according to claim 9, wherein: <9> In a battery pack including a plurality of battery cells connected in series and a plurality of switches respectively provided corresponding to the plurality of battery cells and each provided in a first parallel path of a corresponding battery cell among the plurality of battery cells, detecting voltages across each of the plurality of switches as first plurality of cell voltages respectively corresponding to the plurality of battery cells; turning on the one or more switches for a predetermined period of time; After the predetermined period, detecting voltages across each of the plurality of switches as a second plurality of cell voltages respectively corresponding to the plurality of battery cells; performing a diagnostic process based on the first plurality of cell voltages and the second plurality of cell voltages; A diagnostic method comprising: [Explanation of symbols]

[0136] 1... battery pack, 11... storage battery, 12... transistor, 13... fuse, 20... microcontroller, 21... voltage detection unit, 22... diagnostic unit, 101... cell holder, 102... circuit board, A1, A2... voltage measurement, B1, B2... open circuit determination processing, BC... battery cell, C0 to C4... capacitor, CBL, CBL0 to CBL4... cell block, CFET... transistor, CT, CT0 to CT4, CTG... cell tab, DFET... transistor N0~N4...nodes, R0~R4,RG...resistance elements, SW,SW0~SW4...switches, TN...negative terminal, TP...positive terminal, VB...battery voltage, VC,VC0~VC4...cell voltage, ΔVBev,ΔVBod...rate of change, ΔVC0ev,ΔVC0od,ΔVC1ev...rate of change, ΔVC1od,ΔVC2ev,ΔVC2od,ΔVC3ev,ΔVC3od,ΔVC4ev,ΔVC4od,ΔVCev,ΔVCod...rate of change.

Claims

1. a storage battery having a plurality of battery cells connected in series; a plurality of switches provided corresponding to the plurality of battery cells, each of the switches being provided in a first parallel path of a corresponding battery cell among the plurality of battery cells; a voltage detection circuit capable of detecting the voltage across each of the plurality of switches as a plurality of cell voltages respectively corresponding to the plurality of battery cells; a diagnostic circuit capable of turning on one or more of the plurality of switches for a predetermined period of time, and capable of performing diagnostic processing based on a detection result of the voltage detection circuit before the predetermined period of time and a detection result of the voltage detection circuit after the predetermined period of time; A battery pack equipped with

2. two adjacent battery cells among the plurality of battery cells are connected to each other via a connection node; The diagnostic circuit is capable of diagnosing a break in a path from the connection node to the voltage detection circuit in the diagnostic process. The battery pack according to claim 1 .

3. the voltage detection circuit is capable of detecting a battery voltage of the storage battery; The diagnostic circuit is further capable of performing the diagnostic process based on the battery voltage before the predetermined period and the battery voltage after the predetermined period. The battery pack according to claim 1 .

4. The power supply further includes a plurality of capacitors provided corresponding to the plurality of battery cells, each capacitor being provided in a second parallel path of a corresponding battery cell among the plurality of battery cells. The battery pack according to claim 1 .

5. the predetermined period includes a first predetermined period and a second predetermined period; The diagnostic circuitry includes: During the first predetermined period, one or more even-numbered switches among the plurality of switches can be turned on, During the second predetermined period, one or more odd-numbered switches among the plurality of switches can be turned on, The diagnostic process can be performed based on the plurality of cell voltages before the first predetermined period, the plurality of cell voltages after the first predetermined period, the plurality of cell voltages before the second predetermined period, and the plurality of cell voltages after the second predetermined period. The battery pack according to claim 1 .

6. a first rate of change of each of the plurality of cell voltages before and after the first predetermined period, and performing the diagnostic process based on a difference between the first rate of change of two of the cell voltages corresponding to two adjacent battery cells among the plurality of battery cells; A second rate of change of each of the plurality of cell voltages before and after the second predetermined period is calculated, and the diagnostic process can be performed based on the difference between the second rate of change of two of the cell voltages corresponding to two adjacent battery cells among the plurality of battery cells. The battery pack according to claim 5 .

7. The diagnostic circuitry includes: a length of a waiting time after the first predetermined period can be changed depending on whether a change amount of one or more cell voltages among the plurality of cell voltages before and after the first predetermined period exceeds a predetermined amount; The length of the waiting time after the second predetermined period can be changed depending on whether the amount of change in one or more cell voltages among the plurality of cell voltages before and after the second predetermined period exceeds a predetermined amount. The battery pack according to claim 5 .

8. a first terminal connected to one end of the storage battery; a second terminal connected to the other end of the storage battery; a cutoff switch provided in a charge / discharge path of the storage battery connecting the first terminal and the second terminal; Furthermore, The diagnostic circuit can fix the cutoff switch in an OFF state based on the result of the diagnostic process. The battery pack according to claim 1 .

9. a battery pack including a plurality of battery cells connected in series and a plurality of switches respectively provided corresponding to the plurality of battery cells and each provided in a first parallel path of a corresponding battery cell among the plurality of battery cells, detecting voltages across each of the plurality of switches as first plurality of cell voltages respectively corresponding to the plurality of battery cells; turning on the one or more switches for a predetermined period of time; After the predetermined period, detecting voltages across each of the plurality of switches as a second plurality of cell voltages respectively corresponding to the plurality of battery cells; performing a diagnostic process based on the first plurality of cell voltages and the second plurality of cell voltages; A diagnostic method comprising:

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