Battery monitoring device

Abstract

To provide a battery monitoring device capable of quickly limiting current in response to detection of a disconnection in a battery pack.SOLUTION: A battery monitoring device that monitors a battery pack in which sets of battery cells that are connected in parallel with each other are connected in series includes an acquisition unit that acquires the voltage of the battery cells, a control unit that controls an upper limit value of a current flowing through the battery cells, and a detection unit that, when the upper limit value is greater than a predetermined value, detects an open circuit in the battery pack based on a comparison result between the voltage acquired by the acquisition unit and a first threshold value. When the detection unit detects an open circuit in the battery pack, the control unit controls the upper limit value to be equal to or less than the predetermined value.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a battery monitoring device. [Background technology]

[0002] Regarding the detection of disconnections in a battery pack in which multiple sets of battery cells connected in parallel are connected in series, for example, Patent Document 1 describes that disconnections are detected based on the resistance value of the battery cell being tested. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-125950 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, IV plotting is used as a method for calculating the resistance value of a battery cell. However, because it is necessary to collect the current and voltage of the battery cell for a certain period of time and calculate the resistance value using the least squares method, it takes a long time to detect an open circuit, and there is a risk that the battery cell or its peripheral components may fail due to overcurrent before the open circuit is detected.

[0005] SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to provide a battery monitoring device that can quickly limit current in response to the detection of a wire break in a battery pack. [Means for solving the problem]

[0006] The battery monitoring device of the present invention monitors an assembled battery in which sets of multiple battery cells connected in parallel with each other are connected in series, and includes an acquisition unit that acquires the voltage of the battery cells, a control unit that controls the upper limit value of the current flowing through the battery cells, and a detection unit that detects an open circuit in the assembled battery based on the result of comparing the voltage acquired by the acquisition unit with a first threshold value if the upper limit value is greater than a predetermined value, and when the detection unit detects an open circuit in the assembled battery, the control unit controls the upper limit value to be below the predetermined value.

[0007] In the above-described battery monitoring device, the battery pack may supply power to an electric motor that drives a vehicle, and the control unit may change the upper limit value to a second value that is greater than the first value in response to an operation by an occupant of the vehicle when the upper limit value is a first value that is greater than the predetermined value, and when the upper limit value is the second value, cut off the electrical connection between the electric motor and the battery pack when the detection unit detects a break in the battery pack.

[0008] In the battery monitoring device described above, when the upper limit value is the first value, the upper limit value may be controlled to the predetermined value when the detection unit detects a disconnection in the battery pack.

[0009] In the battery monitoring device, the acquisition unit acquires a voltage and a current of the battery cell, When the upper limit value is the predetermined value, the detection unit may calculate a resistance value of the battery cell from the voltage and current acquired by the acquisition unit, and detect a break in the battery pack when the resistance value is equal to or greater than a second threshold value.

[0010] In the battery monitoring device, when the upper limit value is the predetermined value and the resistance value is less than the second threshold value, the control unit may change the upper limit value to the first value. [Effects of the Invention]

[0011] According to the present invention, it is possible to quickly limit the current in response to the detection of a disconnection in the battery pack. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a configuration diagram showing an example of a system of a vehicle V. [Figure 2] FIG. 2 is a flowchart showing an example of a control process for the upper limit of current. [Figure 3] FIG. 3 is a diagram showing an example of the time required for a battery cell to fail when a wire is broken. [Figure 4] FIG. 4 is a flowchart showing an example of a process for transitioning to the launch mode. [Figure 5] FIG. 5 is a flowchart showing an example of the disconnection detection process. DETAILED DESCRIPTION OF THE INVENTION

[0013] (Vehicle system configuration) 1 is a configuration diagram showing an example of a system of a vehicle V. The vehicle V has a vehicle control device 1, a battery pack 2, a system main relay (SMR) 3, a boost converter 4, an inverter (INV) 5, an electric motor (MG) 6, an accelerator opening sensor 70, a launch switch (SW) 71, a display 72, a differential gear 80, a drive shaft 81, and drive wheels 82.

[0014] The battery pack 2 supplies power to the electric motor 6. The battery pack 2 has a plurality of battery cells 20 such as lithium ion batteries, a plurality of voltage sensors 21, and a current sensor 22. The plurality of battery cells 20 are connected in parallel in pairs, for example. A voltage sensor 21 is further connected in parallel to each pair of battery cells 20 connected in parallel. The voltage sensor 21 detects the voltage of each pair of battery cells 20 and outputs the voltage to the vehicle control device 1.

[0015] A set of two battery cells 20 connected in parallel to each other is connected in series to each other. The plurality of battery cells 20 connected in this manner constitutes a battery pack B. A current sensor 22 is further connected to the plurality of sets of battery cells 20 connected in series to each other. The current sensor 22 detects the current flowing through the set of two battery cells 20 and outputs the detected current to the vehicle control device 1.

[0016] The SMR 3 is connected between the battery pack 2 and the boost converter 4. When the vehicle V is running (when Ready is on), the SMR 3 is controlled to the on state by the vehicle control device 1, electrically connecting the battery pack 2 and the boost converter 4. When the vehicle V is parked (when Ready is off), the SMR 3 is controlled to the off state by the vehicle control device 1, cutting off the electrical connection between the battery pack 2 and the boost converter 4.

[0017] The boost converter 4 boosts the output voltage of the battery pack 2 and applies it to the inverter 5. The boost converter 4 is a switching circuit including an IGBT (Insulated Gate Bipolar Transistor) and performs boost operation by being on / off controlled based on a PWM (Pulse Width Modulation) signal input from the vehicle control device 1.

[0018] The inverter 5 converts the output current of the battery pack 2 from DC current to three-phase AC current and outputs it to the electric motor 6. The inverter 5 is a switching circuit including an IGBT and performs conversion operation by being on / off controlled based on a PWM signal input from the vehicle control device 1.

[0019] The electric motor 6 has a stator and a rotor (not shown), and an output shaft 60 is integrally provided at the center of the rotor. The electric motor 6 can operate as either a motor or a generator. When the electric motor 6 operates as a motor, the battery pack 2 supplies power to the electric motor 6 via the inverter 5. When the electric motor 6 operates as a generator, the electric motor 6 charges each battery cell 20 of the battery pack 2 via the inverter 5.

[0020] The output shaft 60 is connected to a differential gear 80 via a power transmission mechanism (not shown). The differential gear 80 is connected to a drive shaft 81 of drive wheels 82. This allows the electric motor 6 to drive the drive wheels 82.

[0021] The accelerator opening sensor 70 detects the opening of an accelerator pedal (not shown) and outputs the detected opening to the vehicle control device 1. The SW71 is used to operate the launch start of the vehicle V. By executing a launch start, the vehicle V can start moving with a torque greater than normal. When a passenger in the vehicle V turns on the SW71, a launch request signal is output from the SW71 to the vehicle control device 1. The display 72 is, for example, a liquid crystal panel, and displays various information based on data signals input from the vehicle control device 1.

[0022] The vehicle control device 1 is an example of a battery monitoring device. The vehicle control device 1 is a computer such as an ECU (Electronic Control Unit), and includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory), none of which are shown. The vehicle control device 1 controls the output torque of the electric motor 6 in accordance with the detection value of an accelerator opening sensor 70, thereby controlling the drive of the vehicle V.

[0023] The vehicle control device 1 has, for example, as software functions that drive a CPU, an acquisition unit 11, a disconnection detection unit 12, and a control unit 13. Note that the acquisition unit 11, the disconnection detection unit 12, and the control unit 13 may be realized by hardware such as an integrated circuit (IC).

[0024] The acquisition unit 11 acquires the voltage of each battery cell 20 from a plurality of voltage sensors 21. The acquisition unit 11 also acquires from a current sensor 22 the current flowing through a pair of two battery cells 20.

[0025] The open circuit detection unit 12 is an example of a detection unit. The open circuit detection unit 12 detects open circuits within the battery pack B. An example of an open circuit is when one of a set of two battery cells 20 connected in parallel to each other is open (see the x mark). In this case, as shown by the symbol d, the current of the battery pack B is concentrated in the other battery cell 20 of the set of two battery cells 20.

[0026] The open circuit detection is performed for each pair of two battery cells 20 connected in parallel to each other within the battery pack B. The open circuit detection unit 12 detects the open circuit using a method according to the driving mode of the vehicle V. The driving modes include a normal mode, a launch mode, and a limited mode, as will be described later, and the upper limit value of the current flowing through each battery cell 20 differs between the modes.

[0027] In the limit mode, the open circuit detection unit 12 calculates the resistance value of the battery cell 20 from the voltage and current acquired by the acquisition unit 11, and detects an open circuit in the battery pack B when the resistance value is equal to or greater than a threshold value. In the limit mode, the upper limit value of the current flowing through the battery pack B is lower than in the normal mode and launch mode. Therefore, when current concentrates in a battery cell 20 due to an open circuit as described above, the time required for that battery cell 20 to fail is longer than in the normal mode and launch mode. Therefore, the open circuit detection unit 12 can reliably detect an open circuit before a battery cell 20 fails, even if, for example, an IV plot of the voltage and current is performed for a predetermined period and the resistance value is calculated using the least squares method.

[0028] On the other hand, in normal mode and launch mode, the upper limit of the current flowing through battery pack B is higher than in limited mode, so the time required for a battery cell 20 to fail in the event of a wire breakage is shorter than in limited mode, making it difficult to detect a wire breakage based on the resistance value described above. Therefore, in normal mode and launch mode, the wire breakage detection unit 12 detects a wire breakage in battery pack B based on the result of comparing the voltage acquired by the acquisition unit 11 with a threshold value. When a wire breakage causes current to concentrate in a battery cell 20, the voltage of that battery cell 20 rises. For this reason, the wire breakage detection unit 12 can quickly detect a wire breakage, for example, when the amount of change over time in the voltage of the voltage sensor 21 is equal to or greater than a threshold value.

[0029] The control unit 13 determines the output torque of the electric motor 6 according to the detected value of the accelerator opening sensor 70, and controls the boost converter 4 and the inverter 5 according to the output torque. Further, the control unit 13 controls the driving mode of the vehicle V (normal mode, launch mode, and limit mode). When the SW71 is operated to be on by the occupant in the normal mode, the control unit 13 controls the driving mode to the launch mode. Further, when the disconnection detection unit 12 detects a disconnection in the normal mode or the launch mode, the control unit 13 controls the driving mode to the limit mode.

[0030] (Control of the upper limit value of the current) The control unit 13 controls the upper limit value of the current flowing through the battery cell 20 according to the driving mode. The control unit 13 controls the upper limit value of the current in the limit mode to IL, the upper limit value of the current in the normal mode to IM, and the upper limit value of the current in the launch mode to IH. Here, the relationship IL < IM < IH holds. The upper limit value is controlled by, for example, the settings of Win and Wout.

[0031] FIG. 2 is a flowchart showing an example of the control process of the upper limit value of the current. This process is executed, for example, at a fixed cycle.

[0032] First, the control unit 13 determines whether the driving mode is the normal mode (step St1). The normal mode is used for normal driving when there is no possibility of disconnection in the assembled battery B. When the driving mode is the normal mode (Yes in step St1), the control unit 13 controls the upper limit value to IM (step St2).

[0033] When the driving mode is not the normal mode (No in step St1), the control unit 13 determines whether the driving mode is the launch mode (step St3). The launch mode is used for driving the vehicle V with a higher output torque than the normal mode. When the driving mode is the launch mode (Yes in step St3), the control unit 13 controls the upper limit value to IH (step St4).

[0034] If the traveling mode is not the launch mode (No in step St3), the control unit 13 determines whether the traveling mode is the limited mode (step St5). The limited mode is used for traveling when there is a possibility of a disconnection in the battery pack B. If the traveling mode is the limited mode (Yes in step St5), the control unit 13 controls the upper limit value to IL (step St6). If the traveling mode is not the limited mode (No in step St5), this process ends. In this manner, the control process for the upper limit value of the current is executed.

[0035] (Time required for battery cell failure) 3 is a diagram showing an example of the time required for a battery cell 20 to fail when a disconnection occurs. The horizontal axis shows the current value (A) flowing through the battery cell 20, and the vertical axis shows the time (seconds) required for the battery cell 20 to fail due to an overcurrent when the disconnection occurs. The vertical axis is scaled logarithmically.

[0036] The operating range of the current is 0 to IL in limited mode, 0 to IM in normal mode, and 0 to IH in launch mode. The time required for a fault becomes shorter as the current increases. Here, the time required when the current is in the range of 0 to IL is much longer than when the current is in other ranges. Therefore, in limited mode (operating range: 0 to IL), the effect of the time required on open circuit detection can be practically ignored.

[0037] On the other hand, in normal mode (usage range: 0 to IM), the required time is the shortest value T1 at the upper current limit value IM, and in launch mode (usage range: 0 to IH), the required time is the shortest value T2 at the upper current limit value IH. Here, the relationship T1>T2 holds between the shortest values ​​T1 and T2.

[0038] In this way, in the normal mode and the launch mode, the upper limit values ​​IM and IH of the current are greater than the upper limit value IL in the limited mode, and therefore the time required for failure of the battery cell 20 is short. Therefore, by comparing the voltage of the battery cell 20 with the threshold value, the control unit 13 can shorten the time required for open circuit detection, and determine the possibility of an open circuit before a battery cell 20 fails, although the accuracy of open circuit detection is lower than detection using resistance values.

[0039] Furthermore, in the limited mode, the upper limit value IL of the current is lower than the upper limits IM and IH in the normal mode and the launch mode, so the time required for failure of the battery cell 20 is very long. For this reason, the control unit 13 detects an open circuit from the resistance value of the battery cell 20, which enables more reliable open circuit detection, although the time required for open circuit detection is longer than the above-mentioned detection using voltage. Note that the upper limit value IL is an example of a predetermined value, the upper limit value IM is an example of a first value, and the upper limit value IH is an example of a second value.

[0040] (Transition to launch mode) 4 is a flowchart showing an example of a process for transitioning to the launch mode. This process is executed, for example, at regular intervals.

[0041] First, the control unit 13 determines whether or not a launch request has been made (step St11). As described above, a launch request is issued when the passenger turns on the SW 71. If there is no launch request (No in step St11), this process ends.

[0042] If there is a launch request (Yes in step St11), the control unit 13 determines whether the driving mode of the vehicle V is the normal mode (step St12). If the driving mode is the normal mode (Yes in step St12), the control unit 13 transitions the driving mode from the normal mode to the launch mode (step St13). If the driving mode is the launch mode or the limited mode (No in step St12), the control unit 13 rejects the launch request (step St14). In this case, the driving mode does not change. In this way, the transition process to the launch mode is executed.

[0043] (Open Circuit Detection Process) FIG. 5 is a flowchart showing an example of the open circuit detection process. This process is executed in parallel with the above-described transition process to the launch mode.

[0044] The open circuit detection unit 12 determines whether the running mode is the normal mode (step St21). When the running mode is the normal mode (Yes in step St21), the open circuit detection unit 12 acquires the amount of change ΔV in the voltage of the battery cell 20 over time (step St22). At this time, the open circuit detection unit 12 calculates, for example, the difference between two voltage values (= latest voltage value - previous voltage value) continuously acquired by the acquisition unit 11 as the amount of change ΔV in voltage over time.

[0045] Next, the open circuit detection unit 12 compares the amount of change ΔV in voltage over time with the threshold value ThA (step St23). When ΔV < ThA holds (No in step St23), the open circuit detection unit 12 determines that there is no possibility of an open circuit and executes each process after step St21 again.

[0046] Also, when ΔV ≧ ThA holds (Yes in step St23), the open circuit detection unit 12 determines that there is a possibility of an open circuit (step St24). Here, the threshold value ThA is an example of the first threshold value and is appropriately determined based on, for example, the current usage range in the normal mode and the electrical characteristics of the battery cell 20.

[0047] In this way, in the normal mode, the open circuit detection unit 12 detects an open circuit according to the comparison result between the amount of change ΔV in voltage over time and the threshold value ThA. Therefore, compared with the case of detecting an open circuit by a method such as an I-V plot based on the resistance value, the time required for open circuit detection can be shortened.

[0048] Next, the control unit 13 shifts the driving mode from the normal mode to the restricted mode (step St25). As a result, the control unit 13 changes the upper limit value of the current flowing through the battery cell 20 from IM to IL. Therefore, if there is a possibility of disconnection, the current of the battery cell 20 is restricted to the usage range with the lowest current value among the usage ranges of the currents in the three modes, and thus a failure of the battery cell 20 due to overcurrent is suppressed.

[0049] Next, the control unit 13 outputs, to the display 72, message information for notifying the passenger that the driving mode has shifted to the restricted mode (step St26). After that, the processes after step St21 are executed again.

[0050] Also, when the driving mode is not the normal mode (No in step St21), the disconnection detection unit 12 determines whether the driving mode is the launch mode (step St27). When the driving mode is the launch mode (Yes in step St27), the disconnection detection unit 12 acquires the amount of change over time ΔV of the voltage of the battery cell 20 in the same manner as in step St22 (step St28).

[0051] Next, the disconnection detection unit 12 compares the amount of change over time ΔV of the voltage with the threshold value ThB (step St29). When ΔV < ThB holds (No in step St29), the disconnection detection unit 12 determines that there is no possibility of disconnection and executes the processes after step St21 again.

[0052] Also, when ΔV ≧ ThB holds (Yes in step St29), the disconnection detection unit 12 determines that there is a possibility of disconnection (step St30). Here, the threshold value ThB is an example of the first threshold value, and is appropriately determined based on, for example, the usage range of the current in the launch mode and the electrical characteristics of the battery cell 20. As described above, in the launch mode, a larger current than in the normal mode flows through the battery cell 20, so the time required for failure is short. For this reason, the threshold value ThB may be set to a value smaller than the threshold value ThA so that disconnection is detected more quickly than in the normal mode.

[0053] In this way, in the launch mode, the disconnection detection unit 12 detects a disconnection based on the result of comparing the time change ΔV of the voltage with the threshold value ThB. Therefore, as in the normal mode, the time required for disconnection detection can be shortened.

[0054] Next, the control unit 13 controls the SMR 3 to be turned off (step St31). This allows the control unit 13 to cut off the electrical connection between the electric motor 6 and the battery pack B. Therefore, by quickly limiting the current of the battery cells 20 to 0 (A), it becomes possible to effectively protect the battery cells 20 from the large current in the launch mode.

[0055] Next, the control unit 13 outputs message information to the display 72 to notify the passenger that the SMR 3 has been turned off (step St32), after which the process ends.

[0056] In this way, in the normal mode and launch mode, where the upper limit of the current flowing through the battery cell 20 is greater than IL, the disconnection detection unit 12 detects a disconnection based on the result of comparing the time change ΔV of the voltage of the battery cell 20 with the threshold value ThB. Furthermore, when the disconnection detection unit 12 detects a disconnection, the control unit 13 controls the upper limit of the current to be equal to or less than IL. Therefore, the vehicle control device 1 can quickly limit the current in response to the detection of a disconnection in the battery pack B.

[0057] If the running mode is not the launch mode (No in step St27), the disconnection detection unit 12 determines whether the running mode is the restricted mode (step St41). If the running mode is not the restricted mode (No in step St41), the control unit 13 shifts the running mode to the normal mode (step St38). Therefore, if the running mode is not set and is not one of the above three modes, such as in the initial state, the normal mode is set. Thereafter, each process from step St21 onwards is executed again.

[0058] Also, when the driving mode is the restricted mode (Yes in step St41), the disconnection detection unit 12 acquires the current and voltage of the battery cell 20 (step St33). At this time, the disconnection detection unit 12 collects the current and voltage acquired by the acquisition unit 11 for a certain period and performs an I-V plot. Next, the disconnection detection unit 12 calculates the resistance value of the battery cell 20 from the slope of the approximate straight line obtained by the I-V plot (step St34).

[0059] Next, the disconnection detection unit 12 compares the resistance value with the threshold value ThR (step St35). When the resistance value ≥ ThR holds (Yes in step St35), the disconnection detection unit 12 determines that a disconnection has occurred (step St36). Here, the threshold value ThR is an example of the second threshold value and is appropriately determined based on, for example, the current usage range in the restricted mode and the electrical characteristics of the battery cell 20 in the restricted mode.

[0060] In this way, the disconnection detection unit 12 detects a disconnection when the resistance value is greater than or equal to the threshold value ThR in the restricted mode where the upper limit value is IL. Therefore, it is possible to detect a disconnection more reliably than in the normal mode and the launch mode.

[0061] Next, the control unit 13 outputs message information for notifying the passenger that the driving mode has shifted to the restricted mode to the display 72 (step St37). Then, this process ends.

[0062] Also, when the resistance value < ThR holds (No in step St35), the disconnection detection unit 12 determines that no disconnection has occurred (step St39). Next, the control unit 13 shifts the driving mode from the restricted mode to the normal mode (step St40). Thereby, the control unit 13 changes the upper limit value of the current of the battery cell 20 from IL to IH. Therefore, when it is determined that no disconnection has occurred, it is possible to relax the restriction on the current of the battery cell 20. Thereafter, each process after step St21 is executed again. In this way, the disconnection detection process is executed.

[0063] The disconnection detection process is executed for each pair of two battery cells 20 connected in parallel. If a disconnection is detected in any one pair, the process for that pair when the disconnection is detected is executed with priority over the processes for the other pairs. For example, if the condition in step St23 is met in any one pair and it is determined that there is a possibility of a disconnection (step St24), the driving mode is shifted to the restricted mode in the processes for all pairs (step St25).

[0064] In this example, the disconnection detection unit 12 compares the current of the battery cell 20 with the thresholds ThA and ThB, but it may also compare the current with an estimated value of the current when there is no disconnection. In this case, the estimated value is an example of the first threshold. The estimated value can be obtained, for example, from the results of a numerical simulation performed in advance by modeling the battery pack B.

[0065] The above-described embodiment is a preferred example of the present invention, but the present invention is not limited to this and can be modified in various ways without departing from the spirit of the present invention. [Explanation of symbols]

[0066] 1 vehicle control device (battery monitoring device), 2 battery pack, 3 SMR, 6 electric motor, 11 acquisition unit, 12 disconnection detection unit (detection unit), 13 control unit, V vehicle, B assembled battery

Claims

1. A battery monitoring device that monitors a battery pack in which a plurality of sets of battery cells that are connected in parallel with each other are connected in series, an acquisition unit that acquires the voltage of the battery cell; a control unit that controls an upper limit value of a current flowing through the battery cell; a detection unit that detects a disconnection in the battery pack according to a comparison result between the voltage acquired by the acquisition unit and a first threshold value when the upper limit value is greater than a predetermined value; the control unit controls the upper limit value to be equal to or less than the predetermined value when the detection unit detects a disconnection in the battery pack. Battery monitoring device.

2. the assembled battery supplies power to an electric motor that drives a vehicle; The control unit When the upper limit value is a first value that is greater than the predetermined value, the upper limit value is changed to a second value that is greater than the first value in response to an operation by a passenger of the vehicle; When the upper limit value is the second value, if the detection unit detects a disconnection in the battery pack, the electrical connection between the electric motor and the battery pack is interrupted. The battery monitoring device according to claim 1 .

3. When the upper limit value is the first value, if the detection unit detects a disconnection in the battery pack, the upper limit value is controlled to the predetermined value. The battery monitoring device according to claim 2 .

4. the acquisition unit acquires a voltage and a current of the battery cell; When the upper limit value is the predetermined value, the detection unit calculates a resistance value of the battery cell from the voltage and current acquired by the acquisition unit, and when the resistance value is equal to or greater than a second threshold value, detects an open circuit in the battery pack. The battery monitoring device according to claim 3 .

5. When the upper limit value is the predetermined value and the resistance value is less than the second threshold value, the control unit changes the upper limit value to the first value. The battery monitoring device according to claim 4 .

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