Battery Management Unit

Abstract

To equalize voltages of a plurality of battery cells while reducing the influence of deterioration in the accuracy of voltage detection of the battery cells.SOLUTION: A battery management device for managing a battery mounted on a vehicle includes a plurality of voltage detection circuits which are connected to corresponding one out of a plurality of battery cells via a pair of voltage detection lines while detecting voltage of the corresponding battery cell, and a plurality of discharge circuits which are connected to corresponding one out of the plurality of battery cells via the pair of voltage detection lines while discharging the corresponding battery cell, and discharges a battery cell in which a voltage difference between a voltage of the battery cell and a reference voltage is equal to or higher than a predetermined first threshold and lower than a second threshold, which is higher than the first threshold during stopping of a vehicle system by a corresponding discharge circuit, while discharging a battery cell having a voltage difference equal to or higher than the second threshold while a vehicular system is being stopped or started up, by a corresponding discharge circuit.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a battery management device and method for managing a battery that includes a plurality of battery cells and is installed in a vehicle. [Background technology]

[0002] Conventionally, a management device that manages a battery module (battery) that includes a plurality of cells connected in series and exchanges power with a vehicle's driving motor is known (see, for example, Patent Document 1). This management device includes a voltage detection circuit that is connected to each node of the plurality of cells via a plurality of voltage detection lines and detects the voltage of each cell, a plurality of discharge circuits that are provided between two adjacent voltage detection lines and connected in parallel to corresponding cells, and a control unit that controls the plurality of discharge circuits based on the voltage detected by the voltage detection circuit to execute equalization control to equalize the SOC (voltage) of the plurality of cells. In addition, the control unit executes equalization control in a first mode that equalizes the actual chargeable capacity of the plurality of cells based on the current full charge capacity and the detected voltage of each cell before or during charging of the battery module from an external charging device. Furthermore, the control unit executes equalization control in a second mode that equalizes the actual dischargeable capacity of the plurality of cells based on the current full charge capacity and the detected voltage of each cell before or during driving by the driving motor (before or during discharging of the plurality of cells). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-156119 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional management device, when a current flows from a cell to a discharge circuit due to the execution of the equalization control, a voltage drop occurs in the voltage detection line due to the electrical resistance of the voltage detection line. In addition, the current flowing through the discharge circuit and the voltage drop amount in the voltage detection line also vary due to the temperature characteristics of the voltage detection line and the variation in the resistance of the discharge circuit. For this reason, it is not easy to reduce the voltage detection error due to the voltage drop in the voltage detection line by correction, and the voltage drop deteriorates the voltage detection accuracy of the cell in the management device. And, as in the case of a vehicle including the management device, if the equalization control is executed while the storage module is being charged with power from an external charging device or while the storage module is being discharged and the vehicle is running with the power from the running motor, there is a risk that the charging control of the storage module, the control of the running motor (discharging control), and the like cannot be executed appropriately due to the deterioration of the voltage detection accuracy.

[0005] Therefore, a primary object of the present disclosure is to equalize the voltages of a plurality of battery cells while reducing the effects of deterioration in accuracy of voltage detection of the battery cells. [Means for solving the problem]

[0006] The battery management device of the present disclosure is a battery management device that includes a plurality of battery cells and manages a battery mounted on a vehicle, and includes a plurality of voltage detection circuits, each connected to a corresponding one of the plurality of battery cells via a pair of voltage detection lines and detecting the voltage of the corresponding battery cell, a plurality of discharge circuits, each connected to a corresponding one of the plurality of battery cells via the pair of voltage detection lines and discharging the corresponding battery cell, a voltage difference acquisition unit that acquires a voltage difference between the voltage of the battery cell detected by the voltage detection circuit and a reference voltage for each of the plurality of battery cells, and a cell balance control unit that discharges the battery cell whose voltage difference is equal to or greater than a predetermined first threshold and less than a second threshold greater than the first threshold by the corresponding discharge circuit while the system of the vehicle is stopped, and discharges the battery cell whose voltage difference is equal to or greater than the second threshold by the corresponding discharge circuit at least either while the system is stopped or while the system of the vehicle is started.

[0007] The battery management device of the present disclosure includes a plurality of voltage detection circuits each connected to a corresponding one of the plurality of battery cells, and a plurality of discharge circuits each connected to a corresponding one of the plurality of battery cells, and the voltage detection circuit and the discharge circuit corresponding to one battery cell share a pair of voltage detection lines. Therefore, when the battery cell is discharged by the discharge circuit to adjust the voltage of the battery cell to a reference voltage, a voltage drop occurs in the pair of voltage detection lines due to the electrical resistance of each voltage detection line, and the voltage drop deteriorates the voltage detection accuracy of the electric cell. In light of this, the cell balance control unit discharges a battery cell whose voltage difference between the battery cell voltage acquired by the voltage difference acquisition unit and the reference voltage is equal to or greater than a first threshold value and less than a second threshold value greater than the first threshold value, by the corresponding discharge circuit while the vehicle system is stopped. This limits the opportunity to discharge a battery cell whose voltage difference with the reference voltage is relatively small, by the discharge circuit, to when the vehicle system is stopped, i.e., when the vehicle is not in use or when the battery is not charged using an external charging device, and the like, thereby making it possible to reduce the influence of deterioration in the voltage detection accuracy of the battery cell during the activation of the vehicle system. Furthermore, the cell balance control unit discharges the battery cells whose voltage difference is equal to or greater than the second threshold value by the corresponding discharge circuit at least during either the vehicle system shutdown or the vehicle system startup. This ensures sufficient opportunities to discharge the voltage of the battery cells whose voltage difference from the reference voltage is relatively large, thereby making it possible to equalize the voltages of the multiple battery cells. As a result, the battery management device of the present disclosure makes it possible to equalize the voltages of the multiple battery cells while reducing the effects of deterioration in the accuracy of voltage detection of the battery cells.

[0008] Furthermore, the cell balance control unit may be configured to, when discharging the battery cells having the voltage difference equal to or greater than the second threshold value by the discharge circuit, lengthen the discharge time of the battery cells having the large voltage difference compared to the discharge time of the battery cells having the small voltage difference. This reduces the chances that the discharge circuit discharges the battery cells and the voltage detection circuit detects the voltage simultaneously (in parallel) during startup of the vehicle system, thereby effectively reducing the effects of deterioration in accuracy of voltage detection of the battery cells.

[0009] Furthermore, the voltage detection circuit may detect the voltage of the corresponding battery cell at a predetermined cycle, and the cell balance control unit may discharge the battery cell whose voltage difference is equal to or greater than the second threshold and less than a third threshold greater than the second threshold by the discharge circuit when the system is running and the voltage detection circuit is not detecting the voltage, and discharge the battery cell whose voltage difference is equal to or greater than the third threshold by the discharge circuit during the system startup regardless of whether the voltage detection circuit detects the voltage. This makes it possible to promote equalization of the voltages of a plurality of battery cells while minimizing the effect of deterioration in battery cell voltage detection accuracy when discharging a battery cell whose voltage difference from a reference voltage is equal to or greater than the second threshold by the discharge circuit during startup of the vehicle system.

[0010] The voltage detection circuit may include a resistor connected in series to the battery cell, a capacitor connected in parallel to the battery cell, and a voltage sensor that detects the terminal voltage of the capacitor, and the cell balancing control unit may cause the discharge circuit to discharge the battery cell whose voltage difference is equal to or greater than the second threshold and less than the third threshold from the time when the voltage detection circuit finishes detecting the voltage until a timing before the voltage detection circuit starts detecting the voltage. This makes it possible to ensure good voltage detection accuracy by the voltage detection circuit by charging the capacitor of the voltage detection circuit that has been discharged in conjunction with the discharge of the battery cell by the discharge circuit until the voltage detection circuit starts (resumes) detecting the voltage.

[0011] Furthermore, the detection value of the voltage detection circuit may be limited between an upper limit voltage and a lower limit voltage, and the cell balancing control unit may change the range between the upper limit voltage and the lower limit voltage according to the voltage difference when the battery cell whose voltage difference is equal to or greater than the second threshold is discharged by the discharge circuit. This makes it possible to effectively reduce the influence of deterioration in accuracy of voltage detection of the battery cell due to discharge of the battery cell by the discharge circuit.

[0012] The reference voltage may be a minimum value of voltages of the plurality of battery cells.

[0013] The battery management method disclosed herein is a battery management method for managing a battery that includes a plurality of battery cells, a plurality of voltage detection circuits, each connected to a corresponding one of the plurality of battery cells via a pair of voltage detection lines and detecting the voltage of the corresponding battery cell, and a plurality of discharge circuits, each connected to a corresponding one of the plurality of battery cells via the pair of voltage detection lines and discharging the corresponding battery cell, and that manages the battery that is mounted on a vehicle, wherein a voltage difference between the voltage of the battery cell detected by the voltage detection circuit and a reference voltage is obtained for each of the plurality of battery cells, and the battery cell whose voltage difference is equal to or greater than a predetermined first threshold and less than a second threshold greater than the first threshold is discharged by the corresponding discharge circuit while the system of the vehicle is stopped, and the battery cell whose voltage difference is equal to or greater than the second threshold is discharged by the corresponding discharge circuit at least either while the system is stopped or while the system of the vehicle is started.

[0014] According to this method, it is possible to equalize the voltages of a plurality of battery cells while reducing the effects of deterioration in accuracy of battery cell voltage detection. [Brief description of the drawings]

[0015] [Figure 1] 1 is a schematic configuration diagram showing a vehicle equipped with a battery management device according to the present disclosure. [Diagram 2] 1 is a schematic configuration diagram showing a battery management device according to the present disclosure; [Diagram 3] 5 is a time chart showing a change in the detection value of a voltage sensor when a battery cell is discharged by a discharge circuit of the battery management device of the present disclosure. [Figure 4] 4 is a flowchart illustrating an example of a routine executed by a battery management device of the present disclosure. [Diagram 5]4 is a time chart for explaining a procedure for discharging a battery cell by a discharge circuit of a battery management device of the present disclosure. [Figure 6] 4 is a time chart for explaining a procedure for discharging a battery cell by a discharge circuit of a battery management device of the present disclosure. [Figure 7] 4 is a time chart for explaining a procedure for discharging a battery cell by a discharge circuit of a battery management device of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Next, an embodiment of the present disclosure will be described with reference to the drawings.

[0017] 1 is a schematic diagram showing a vehicle 100 equipped with a battery management device 10 of the present disclosure. The vehicle 100 shown in the figure is an electric vehicle (BEV) or a hybrid vehicle (HEV, PHEV) including a battery 1 managed by the battery management device 10, and a motor generator (three-phase AC motor) MG that is connected to the battery 1 via a power control device including an inverter and a system main relay (neither of which are shown), and that can exchange power with the battery 1 to output driving power and regenerative braking power.

[0018] As shown in the figure, the battery 1 is a so-called high-voltage battery including a plurality of battery cells 2 connected in series, for example. The plurality of battery cells 2 may be dispersed and housed in module cases of a plurality of battery modules (not shown), and the plurality of battery modules may be connected in series, for example. The battery cells 2 constituting the battery module are ternary, NCA, or iron phosphate lithium-ion secondary batteries.

[0019] As shown in Fig. 2, the battery management device 10 of the vehicle 100 includes a microcomputer (hereinafter referred to as "microcomputer") 11 including a CPU, a ROM, a RAM, etc., one or more management ICs 15 each including a plurality of switching elements (e.g., transistors) Sw and a voltage sensor V and connected to the microcomputer 11, a plurality of filter resistors Rf and discharge resistors Rb, and a plurality of filter capacitors Cf. The number of switching elements Sw, the number of voltage sensors V, and the number of filter capacitors Cf in the battery management device 10 are all the same as the total number of battery cells 2 of the battery 1. As shown in the figure, the battery management device 10 is connected to each of the plurality of battery cells 2 via a plurality of voltage detection lines Lv. The plurality of voltage detection lines Lv are each connected to the positive electrode of the battery cell 2 on one end side, the negative electrode of the battery cell 2 on the other end side, or a node between adjacent battery cells 2.

[0020] Furthermore, two (a pair) of voltage detection lines Lv connected to both ends of one battery cell 2 are connected to each other via a filter resistor Rf, a filter capacitor Cf, and a filter resistor Rf. That is, a filter capacitor Cf is connected in parallel to each battery cell 2 via a pair of voltage detection lines Lv and a filter resistor Rf. Then, each voltage sensor V of the management IC 15 detects the terminal voltage of the corresponding filter capacitor Cf. As a result, the pair of voltage detection lines Lv, the two filter resistors Rf, the filter capacitor Cf, and the voltage sensor V form a voltage detection circuit 16 that detects the voltage (terminal voltage) of the corresponding battery cell 2, and the battery management unit 10 includes a plurality of voltage detection circuits 16 (the same number as the battery cells 2) provided for each of the plurality of battery cells 2.

[0021] Furthermore, a discharge resistor Rb is connected in parallel to the filter resistor Rf to each voltage detection line Lv, and a pair of voltage detection lines Lv connected to both ends of one battery cell 2 is connected to a corresponding switching element Sw of the management IC 15 via the discharge resistor Rb. As a result, by turning on the switching element Sw, a current from the battery cell 2 flows through the two discharge resistors Rb to reduce the voltage of the battery cell 2, and the voltages of the multiple battery cells 2 can be equalized. In other words, the pair of voltage detection lines Lv, the two discharge resistors Rb, and the switching element Sw form a discharge circuit 17 that discharges the corresponding battery cell 2, and the battery management unit 10 includes a plurality of discharge circuits 17 (the same number as the battery cells 2) provided for each of the multiple battery cells 2.

[0022] Furthermore, the management IC 15 causes each voltage sensor V to detect the voltage of the corresponding filter capacitor Cf, i.e., the battery cell 2, in a predetermined period (e.g., 150 ms), and completes the detection of the voltage of each battery cell 2 and the self-diagnosis process of the management IC 15 within a time period (e.g., 100 ms) shorter than the period from the start of voltage detection. Furthermore, the management IC 15 transmits the detection value of each voltage sensor V to the microcomputer 11. The microcomputer 11 limits the detection value of each voltage sensor V of the management IC 15 between a predetermined upper limit voltage (positive value) and a predetermined lower limit voltage (negative value), and calculates the open circuit voltage (OCV) of each battery cell 2 based on the detection value, and calculates the SOC of each battery cell 2 based on the open circuit voltage. Furthermore, the management IC 15 controls the on / off of the corresponding switching element Sw according to a command signal from the microcomputer 11.

[0023] Here, in the battery management device 10, the voltage detection circuit 16 and the discharge circuit 17 corresponding to one battery cell 2 share a pair of voltage detection lines Lv as shown in FIG. 2. Therefore, when the switching element Sw is turned on to discharge the battery cell 2 by the discharge circuit 17, a voltage drop (for example, about several tens of mV) occurs in the pair of voltage detection lines Lv due to the electrical resistance of each voltage detection line Lv (see the dotted line in FIG. 2), and the detection value of the voltage sensor V becomes smaller according to the voltage drop as shown in FIG. 3. In addition, due to the temperature characteristics of the voltage detection line Lv and the variation of the discharge resistor Rb of the discharge circuit 17, the current (equalization current) flowing through the discharge circuit 17 and the voltage drop amount in the voltage detection line Lv also vary. For this reason, it is not easy to reduce the detection error of each voltage sensor V due to the voltage drop in the voltage detection line Lv by correction, and when equalizing the voltages of the multiple battery cells 2, it is necessary to consider the influence of the deterioration of the voltage detection accuracy of the battery cells 2 caused by the voltage drop in the voltage detection line Lv.

[0024] Based on this, in order to equalize the voltages of the multiple battery cells 2 while minimizing the effect of deterioration in the voltage detection accuracy of the battery cells 2 caused by a voltage drop in the voltage detection line Lv, the battery management unit 10 executes the routine shown in Fig. 4 to determine the execution conditions for discharging by the discharge circuit 17 for each battery cell 2. The routine in Fig. 4 is repeatedly executed at predetermined time intervals (very short time intervals) by the microcomputer 11 serving as a cell balance control unit while a start switch (IG switch) (not shown) of the vehicle 100 is turned on and the system of the vehicle 100 is started up.

[0025] At the start of the routine of FIG. 4, the microcomputer 11 (CPU) detects the voltages V of the multiple battery cells 2 detected by the voltage sensors V of the management IC 15. n (where "n" indicates the number of the battery cell 2, and n=1, 2, . . . , N-1, N, where "N" is the total number of the battery cells 2) (step S100). Furthermore, the microcomputer 11 acquires the voltage V 1 ,V 2 ,…V N The minimum voltage V min(step S110), and sets the value 1 to a variable n (the number of the battery cell 2) (step S120).

[0026] Next, the microcomputer 11 as the voltage difference acquisition unit calculates the voltage V n and the minimum voltage V as the reference voltage min Voltage difference ΔV n (=V n -V min ) is calculated (obtained) (step S130), and the voltage difference ΔV n It is determined whether the voltage difference ΔV is equal to or greater than a predetermined first threshold value Vref1 (a relatively small positive value) (step S140). n is less than the first threshold value Vref1 (step S140: NO), the microcomputer 11 n is the minimum voltage V min The voltage V of the n-th battery cell 2 is close to n In order to indicate that it is not necessary to reduce the charge-discharge potential by discharging, the first discharge flag and the second discharge flag are both turned off for the nth battery cell 2 (step S145).

[0027] The first discharge flag is turned on when the discharge circuit 17 discharges the battery cell 2 while the system of the vehicle 100 is stopped with the start switch turned off, and the second discharge flag is turned on when the discharge circuit 17 discharges the battery cell 2 while the system of the vehicle 100 is running. After the process of step S145, the microcomputer 11 increments the variable n (step S190) and determines whether the variable n is greater than the total number N of the battery cells 2 described above (step S200). If it is determined that the variable n is equal to or less than the total number N (step S200: NO), the microcomputer 11 repeatedly executes the processes from step S130 onwards.

[0028] In addition, the microcomputer 11 detects the voltage difference ΔV n is equal to or greater than the first threshold value Vref1 (step S140: YES), nIt is determined whether the voltage difference ΔV is equal to or greater than a second threshold value Vref2 that is greater than the first threshold value Vref1 (step S150). n is less than the second threshold value Vref2 (step S150: NO), the microcomputer 11 n Although it is necessary to reduce the charge / discharge voltage by discharging, it is determined that discharging is unnecessary while the system of the vehicle 100 is running, and the first discharge flag is turned on and the second cell discharge flag is turned off for the n-th battery cell 2 (step S155). After the process of step S155, the microcomputer 11 increments the variable n (step S190) and determines whether the variable n is greater than the total number N of the battery cells 2 described above (step S200). If it is determined that the variable n is equal to or less than the total number N (step S200: NO), the microcomputer 11 repeatedly executes the processes from step S130 onwards.

[0029] On the other hand, the voltage difference ΔV n is equal to or greater than the second threshold value Vref2 (step S150: YES), the microcomputer 11 n It is determined whether the voltage difference ΔV is equal to or greater than a third threshold Vref3 that is greater than the second threshold Vref2 (step S160). n is less than the third threshold value Vref3 (step S160: NO), the microcomputer 11 n It is deemed necessary to discharge the n-th battery cell 2 both while the system of the vehicle 100 is stopped and while the system is running, and both the first and second discharge flags are turned on for the n-th battery cell 2 (step S165).

[0030] In addition, the voltage difference ΔV nis less than the third threshold value Vref3 (step S160: NO), in order to ensure the voltage detection accuracy of each voltage sensor V of the management IC 15, in step S165, the microcomputer 11 turns on a discharge temporary prohibition flag for the n-th battery cell 2. When the discharge temporary prohibition flag is on, the discharge of the battery cell 2 by the discharge circuit 17 is prohibited while the system of the vehicle 100 is starting up and the voltage of the battery cell 2 is being detected and the self-diagnosis process is being executed, in order to ensure the voltage detection accuracy of the voltage sensor V.

[0031] Next, the microcomputer 11 sets the standby time tw and the upper and lower limit voltages for limiting the detection value of the voltage sensor V (step S167). The standby time tw is the time that should be secured between the end of discharging the battery cell 2 by the discharge circuit 17 during the system startup of the vehicle 100 and the start (restart) of detection of the voltage of the battery cell 2 by the voltage sensor V. That is, when the switching element Sw of the management IC 15 is turned on and the discharge circuit 17 discharges the battery cell 2, a voltage drop occurs in a pair of voltage detection lines Lv, and the filter capacitor Cf of the voltage detection circuit 16, which shares the voltage detection line Lv with the discharge circuit 17, is discharged to a voltage determined by a time constant based on the capacitance of the filter capacitor Cf and the resistance value of the filter resistor Rf, and the on-time of the switching element Sw.

[0032] Therefore, in order to ensure the voltage detection accuracy of the voltage sensor V, it is necessary to charge the filter capacitor Cf by the amount discharged while the battery cell 2 was discharged by the discharge circuit 17 before the voltage sensor V starts (resumes) voltage detection. For this reason, in step S167, a waiting time tw is set as the time for charging the filter capacitor Cf by the amount discharged by the filter capacitor Cf accompanying the discharge of the battery cell 2. In this embodiment, the waiting time tw set in step S167 is a constant value that is determined in advance based on the capacitance of the filter capacitor Cf and the resistance value of the filter resistor Rf of the voltage detection circuit 16, the time from the end of voltage detection by the voltage sensor V and the end of the self-diagnosis process of the management IC 15 to the start of the next voltage detection by the voltage sensor V, etc.

[0033] Furthermore, in step S167, the microcomputer 11 sets the upper limit voltage to a positive value smaller than the value used when the battery cell 2 is not discharged by the discharge circuit 17, and sets the lower limit voltage to a negative value larger than the value used when the battery cell 2 is not discharged by the discharge circuit 17, thereby narrowing the range between the upper limit voltage and the lower limit voltage. After the process of step S167, the microcomputer 11 increments the variable n (step S190) and determines whether the variable n is greater than the total number N of the battery cells 2 described above (step S200). If it is determined that the variable n is equal to or less than the total number N (step S200: NO), the microcomputer 11 repeatedly executes the processes from step S130 onwards.

[0034] And the microcontroller 11 detects the voltage difference ΔV n is equal to or greater than the third threshold value Vref3 (step S160: YES), n It is deemed necessary to discharge the voltage difference ΔV both during system shutdown and during system startup of the vehicle 100, and both the first and second discharge flags are turned on (step S170). nis equal to or higher than the third threshold Vref3, the microcomputer 11 turns off the temporary discharge prohibition flag in step S170 to prioritize discharging the battery cells 2, i.e., equalizing the voltages of the multiple battery cells 2, over the voltage detection accuracy of each voltage sensor V of the management IC 15.

[0035] Furthermore, the microcomputer 11 sets the upper limit voltage to a positive value smaller than the value set in step S167, and sets the lower limit voltage to a negative value larger than the value set in step S167 (step S180). n is equal to or greater than the third threshold Vref3, the voltage difference ΔV n is determined to be equal to or greater than the second threshold value Vref2 and less than the third threshold value Vref3, the range between the upper limit voltage and the lower limit voltage is further narrowed. After the process of step S180, the microcomputer 11 increments the variable n (step S190) and determines whether or not the variable n is greater than the total number N of the battery cells 2 described above (step S200). If it is determined that the variable n is equal to or less than the total number N (step S200: NO), the microcomputer 11 repeatedly executes the processes from step S130 onwards.

[0036] 4 is executed as described above, and the conditions for discharging by the discharge circuit 17 are determined for all (N) battery cells 2, it is determined in step S200 that the variable n exceeds the total number N. When it is determined that the variable n exceeds the total number N (step S200: YES), the microcomputer 11 as the cell balance control unit ends the routine of FIG. 4, and in accordance with the conditions for discharging each battery cell 2, cooperates with the management IC 15 to set the voltages of the multiple battery cells 2 to the minimum voltage V min Equalize it to match.

[0037] That is, in accordance with the setting of the first and second discharge flags in step S155 of FIG. 4, the microcomputer 11 sets the minimum voltage V min Voltage difference ΔV nThe battery cells 2 whose minimum voltage V is equal to or greater than a first threshold Vref1 and less than a second threshold Vref2 are not discharged by the discharge circuit 17, but are discharged while the system is stopped with the start switch turned off. min Voltage difference ΔV n Opportunities for discharging the battery cells 2, which have a relatively small capacitance, by the discharge circuit 17 are limited while the system of the vehicle 100 is stopped, such as when the vehicle 100 is not in use or when the battery 1 is not being charged using an external charging device (when the system main relay is open). When discharging the battery cells 2 while the system is stopped, the system main relay is opened and power is supplied only to devices necessary for executing the discharge process, such as the battery management unit 10.

[0038] In addition, the microcomputer 11 determines whether the first and second discharge flags are set to the minimum voltage V min Voltage difference ΔV n The battery cells 2 whose minimum voltage Vref2 is equal to or higher than the second threshold value Vref2 are discharged by the corresponding discharge circuits 17 at least during either the system stop or the system startup of the vehicle 100. For example, if the system startup of the vehicle 100 continues after the routine of FIG. 4 ends, the microcomputer 11 min Voltage difference ΔV n The battery cells 2 whose voltage difference is equal to or greater than the second threshold value Vref2 are discharged by the corresponding discharge circuits 17. After the start switch is turned off, n The battery cells 2 whose voltages are equal to or higher than the second threshold value Vref2 are discharged by the corresponding discharge circuits 17 while the system is stopped.

[0039] Furthermore, in accordance with the setting of the discharge temporary prohibition flag in step S165 of FIG. 4, the microcomputer 11 sets the minimum voltage V min Voltage difference ΔV n When the voltage sensor V (voltage detection circuit 16) is not detecting any voltage during system startup, the microcomputer 11 causes the battery cells 2 whose minimum voltage V is equal to or greater than the second threshold value Vref2 and less than the third threshold value Vref3 to be discharged by the discharge circuit 17. In addition, the microcomputer 11 causes the battery cells 2 whose minimum voltage Vmin Voltage difference ΔV n The battery cells 2 whose minimum voltage Vref3 is equal to or higher than the third threshold Vref3 are discharged by the discharge circuit 17 during system startup, regardless of whether the voltage sensor V (voltage detection circuit 16) detects the voltage. As a result, as can be seen from FIGS. 6 and 7, the minimum voltage V min Voltage difference ΔV n When the battery cell 2 whose voltage difference is equal to or greater than the second threshold value Vref2 is discharged by the discharge circuit 17 during system startup (as well as during system shutdown), n is large (V n >Vref3) The discharge time of battery cell 2 is the voltage difference V n is small (V n ≦Vref3) The discharge time of battery cell 2 is longer than that of the battery cell 2.

[0040] As shown in FIG. 6, the microcomputer 11 monitors the voltage difference V n The battery cell 2 whose voltage Vref2 is equal to or higher than the second threshold value Vref2 and lower than the third threshold value Vref3 is discharged by the discharge circuit 17. This makes it possible to charge the filter capacitor Cf by the amount of discharge of the filter capacitor Cf accompanying the discharge of the battery cell 2 after the battery cell 2 is discharged by the discharge circuit 17 until the voltage sensor V resumes detecting the voltage.

[0041] As described above, the battery management device 10 of the vehicle 100 includes a plurality of voltage detection circuits 16 each connected to a corresponding one of the plurality of battery cells 2, and a plurality of discharge circuits 17 each connected to a corresponding one of the plurality of battery cells 2, and the voltage detection circuit 16 and the discharge circuit 17 corresponding to one battery cell 2 share a pair of voltage detection lines Lv. minWhen the battery cell 2 is discharged by the discharge circuit 17 to match the voltage detection line Lv, a voltage drop occurs in the pair of voltage detection lines Lv due to the electrical resistance of each voltage detection line Lv, and this voltage drop deteriorates the voltage detection accuracy of the battery cell 2.

[0042] Based on this, the microcomputer 11 calculates the voltage of the battery cell 2 acquired in step S130 of FIG. 4 and the minimum voltage V min Voltage difference V n The microcomputer 11 causes the battery cells 2 whose voltage difference V is equal to or greater than a predetermined first threshold value Vref1 and less than a second threshold value Vref2 that is greater than the first threshold value Vref1, to be discharged by the corresponding discharge circuit 17 while the vehicle 100 system is stopped (step S155). n The battery cells 2 whose charge voltages are equal to or higher than the second threshold value Vref2 are discharged by the corresponding discharge circuits 17 at least while the vehicle 100 system is stopped or while the system is running (steps S165, S170).

[0043] This results in a minimum voltage V min Voltage difference V n By limiting the opportunity for discharging the battery cell 2, which has a relatively small minimum voltage V, by the discharge circuit 17 to when the vehicle 100 system is stopped, i.e., when the vehicle 100 is not in use or when the battery 1 is not being charged using an external charging device, it is possible to reduce the effect of deterioration in the accuracy of detecting the voltage of the battery cell 2 while the vehicle 100 system is running. min Voltage difference V n This ensures sufficient opportunities to discharge the voltage of the battery cells 2 having a relatively large voltage, thereby equalizing the voltages of the multiple battery cells 2. As a result, the battery management unit 10 makes it possible to equalize the voltages of the multiple battery cells 2 while reducing the effects of deterioration in the accuracy of voltage detection of the multiple battery cells 2.

[0044] In addition, the microcontroller 11 detects the minimum voltage V min Voltage difference V n When the battery cell 2 whose voltage difference is equal to or greater than the second threshold value Vref2 is discharged by the discharge circuit 17, the voltage difference V nThe discharge time of the battery cell 2 for which the voltage difference V is equal to or greater than the third threshold Vref3 that is greater than the second threshold Vref2 is calculated by n The discharge time of the battery cell 2 is set to be longer than the discharge time of the battery cell 2 for which the discharge circuit 17 has a small value and is less than the third threshold value Vref3. This reduces the opportunities for the discharge of the battery cell 2 by the discharge circuit 17 and the detection of the voltage by the voltage detection circuit 16 (voltage sensor V) to be performed simultaneously (in parallel) during startup of the vehicle 100 system, thereby making it possible to effectively reduce the effects of deterioration in the accuracy of voltage detection of the battery cell 2.

[0045] That is, in the battery management unit 10, the voltage detection circuit 16 (voltage sensor V) detects the voltage of the corresponding battery cell 2 at a predetermined cycle, and the microcomputer 11 detects the voltage difference V n When the voltage detection circuit 16 is not detecting a voltage during system startup, the microcomputer 11 causes the battery cells 2 whose voltage difference V is equal to or greater than the second threshold value Vref2 and less than the third threshold value Vref3 to be discharged by the discharge circuit 17. n The battery cells 2 whose minimum voltage Vref3 is equal to or higher than the third threshold Vref3 are discharged by the discharge circuit 17 during system startup, regardless of whether the voltage detection circuit 16 detects the voltage. As a result, the minimum voltage V min Voltage difference V n When a battery cell 2 whose voltage is equal to or greater than the second threshold Vref2 is discharged by the discharge circuit 17, it is possible to promote equalization of the voltages of multiple battery cells 2 while minimizing the effects of deterioration in the voltage detection accuracy of the battery cell 2.

[0046] Each voltage detection circuit 16 of the battery management unit 10 includes a filter resistor Rf connected in series to the battery cell 2, a filter capacitor Cf connected in parallel to the battery cell 2, and a voltage sensor V that detects the terminal voltage of the filter capacitor Cf. The microcomputer 11 then monitors the voltage difference V from the time when the voltage sensor V (voltage detection circuit 16) finishes detecting the voltage until the time when the voltage sensor V starts (resumes) detecting the voltage by the waiting time tw set in step S167. nThe battery cells 2 whose voltages are equal to or greater than the second threshold value Vref2 and less than the third threshold value Vref3 are discharged by the discharge circuit 17. This allows the filter capacitor Cf of the voltage detection circuit 16, which is discharged as the discharge circuit 17 discharges the battery cells 2, to be charged before the voltage sensor V starts detecting the voltage, thereby ensuring good voltage detection accuracy by the voltage sensor V.

[0047] Furthermore, the battery management unit 10 calculates the SOC of each battery cell 2 based on the detection value of the voltage sensor V (voltage detection circuit 16) limited between the upper limit voltage and the lower limit voltage. min Voltage difference V n When the battery cell 2 whose voltage difference is equal to or greater than the second threshold value Vref2 is discharged by the discharge circuit 17, the voltage difference V n In response to this, the range between the upper limit voltage and the lower limit voltage is changed (steps S167, S180). This makes it possible to effectively reduce the influence of deterioration in the accuracy of voltage detection of the multiple battery cells 2 caused by the discharge of the battery cells 2 by the discharge circuit 17.

[0048] In step S130 of FIG. 4, the minimum voltage V min Alternatively, for example, an average value of the voltages of the multiple battery cells 2 may be used as the reference voltage. Also, in step S130 of FIG. 4, instead of calculating the difference between the voltage of each battery cell 2 and the reference voltage, an SOC difference between the estimated SOC of each battery cell and a reference SOC (for example, the minimum value of the estimated SOC of the multiple battery cells 2) may be calculated, and in steps S140-S160 of FIG. 4, the SOC difference may be compared with first to third threshold values. This embodiment is particularly suitable for a battery 1 in which the battery cells 2 are iron phosphate-based lithium-ion secondary batteries (lithium iron phosphate batteries). Furthermore, in step S167 of FIG. 4, instead of setting the standby time tw to a constant value, the standby time tw may be set to a value that is inversely proportional to the voltage difference V n It may be changed depending on the above.

[0049] In addition, the invention of the present disclosure is not limited to the above embodiment, and various modifications can be made within the scope of the present disclosure. Furthermore, the above embodiment is merely a specific form of the invention described in the Summary of the Invention, and does not limit the elements of the invention described in the Summary of the Invention. [Industrial Applicability]

[0050] The invention of the present disclosure can be used in fields such as the manufacturing of battery management devices that include a plurality of battery cells and manage a battery mounted on a vehicle. [Explanation of symbols]

[0051] 1 battery, 2 battery cell, 10 battery management device, 11 microcontroller, 15 management IC, 16 voltage detection circuit, 17 discharge circuit, 100 vehicle, Cf filter capacitor, Rb discharge resistor, Rf filter resistor.

Claims

1. A battery management device that manages a battery that includes a plurality of battery cells and is mounted on a vehicle, a plurality of voltage detection circuits each connected to a corresponding one of the plurality of battery cells via a pair of voltage detection lines, and configured to detect the voltage of the corresponding battery cell at a predetermined cycle; a plurality of discharge circuits each connected to a corresponding one of the plurality of battery cells via the pair of voltage detection lines and discharging the corresponding battery cell; a voltage difference acquisition unit that acquires a voltage difference between the voltage of the battery cell detected by the voltage detection circuit and a reference voltage for each of the plurality of battery cells; a cell balance control unit that discharges the battery cells whose voltage difference is equal to or greater than a predetermined first threshold and less than a second threshold greater than the first threshold by the corresponding discharge circuit while a system of the vehicle is stopped, and discharges the battery cells whose voltage difference is equal to or greater than the second threshold by the corresponding discharge circuit at least either while the system is stopped or while the system of the vehicle is running; Equipped with The cell balance control unit is a battery management device that discharges, via the discharge circuit, the battery cells whose voltage difference is equal to or greater than the second threshold and less than a third threshold that is greater than the second threshold when the system is running and the voltage detection circuit is not detecting a voltage, and discharges, via the discharge circuit, the battery cells whose voltage difference is equal to or greater than the third threshold during the system startup, regardless of whether the voltage detection circuit is detecting a voltage.

2. 2. The battery management device according to claim 1, The cell balance control unit is a battery management device that, when discharging the battery cells whose voltage difference is equal to or greater than the second threshold value using the discharge circuit, extends the discharge time of the battery cells whose voltage difference is large compared to the discharge time of the battery cells whose voltage difference is small.

3. 3. The battery management device according to claim 1, the voltage detection circuit includes a resistor connected in series to the battery cell, a capacitor connected in parallel to the battery cell, and a voltage sensor that detects a voltage between terminals of the capacitor; The cell balance control unit is a battery management device that causes the discharge circuit to discharge the battery cell whose voltage difference is equal to or greater than the second threshold and less than the third threshold from the time when the voltage detection circuit finishes detecting the voltage to a timing before the voltage detection circuit starts detecting the voltage.

4. The battery management device according to any one of claims 1 to 3, the detection value of the voltage detection circuit is limited between an upper limit voltage and a lower limit voltage; The cell balance control unit is a battery management device that changes the range between the upper limit voltage and the lower limit voltage in accordance with the voltage difference when the battery cell whose voltage difference is equal to or greater than the second threshold is discharged by the discharge circuit.

5. 5. The battery management unit according to claim 1, wherein the reference voltage is a minimum value of voltages of the plurality of battery cells.

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