Battery management device, battery pack, battery management method, and battery management program

Abstract

In a battery management device (10) according to an embodiment, a lower limit reference voltage determination unit (124) determines a lower limit reference voltage corresponding to a lower limit reference SOC of a use SOC (State Of Charge) range for estimating the full charge capacity of a battery pack (20). A relative SOC calculation unit (122) calculates a relative SOC for display in which the remaining capacity at the end of charging of the battery pack (20) is set to 100%. When the charging with a reduced charging end voltage is designated, a lower limit reference SOC correction unit (126) corrects the lower limit reference SOC on the basis of the ratio between the remaining capacity at the complete charging time and the remaining capacity at the time of the charging with the reduced charging end voltage.

Description

Battery management device, battery pack, battery management method, and battery management program

[0001] The present disclosure relates to a battery management device, a battery pack, a battery management method, and a battery management program that have a charging mode with a lowered end-of-charge voltage.

[0002] Some battery-equipped devices, such as laptop PCs (personal computers), are equipped with an eco-charging mode. In eco-charging mode, the battery is not fully charged to extend its life, but is instead charged at a lower end voltage. In addition, charging at a lower end voltage may be performed at high temperatures or when the SOH (State of Health) is decreasing.

[0003] Generally, the full charge capacity (FCC) of a battery is calculated using the following formula (1).

[0004] FCC = (discharge capacity from full charge to detection of lower limit reference voltage) / (100 - lower limit reference SOC) x 100 x discharge efficiency coefficient (Equation 1) Full charge in the above (Equation 1) refers to a state in which the battery is charged up to the charge end voltage.

[0005] If a user always uses a battery until it is fully discharged, the lower limit reference SOC (State Of Charge) may be 0%, but since a user does not always use a battery until it is fully discharged, the lower limit reference SOC is set to, for example, about 3 to 15%. Reaching the lower limit reference SOC is detected by reaching the lower limit reference voltage corresponding to the lower limit reference SOC.

[0006] The SOC includes errors due to current measurement errors, etc. The error can be reset by setting it to 100% when fully charged and to 0% when fully discharged, but if the user does not charge the battery to a fully charged state or discharge it to a fully discharged state, the SOC error will remain unreset.

[0007] Therefore, one possible operation is to set the SOC to the value of the lower limit reference SOC when the lower limit reference voltage is detected, even if the SOC has not reached the lower limit reference SOC, and to maintain the SOC at a value of (lower limit reference SOC + 1) until the lower limit reference voltage is detected, even if the SOC has reached the lower limit reference SOC, and to set the SOC to the value of the lower limit reference SOC when the lower limit reference voltage is detected.

[0008] However, if the same lower limit reference SOC is used uniformly in both the standard charging mode, in which charging is performed to a fully charged state, and the eco charging mode, in which charging is not performed to a fully charged state, errors will occur in the calculation of the FCC and the correction of the SOC.

[0009] Patent Document 1 discloses a method in which, when the operating mode is changed from the long-life mode (4.1 V / cell) to the high-capacity mode (4.2 V / cell), the FCC in the long-life mode is divided by a predetermined coefficient (90%) to obtain the FCC in the high-capacity mode. The lower reference SOC (lower discharge capacity limit) is set to 4% (a fixed value) (see Equation 2 below).

[0010] FCC = (discharge capacity from full charge to 4%) / (100-4) × discharge efficiency coefficient / 90% (Equation 2)

[0011] Patent No. 5512250

[0012] To reduce the errors during the FCC calculation and SOC correction, it is possible to store a parameter table of the lower limit reference voltage for each end-of-charge voltage. However, this increases the program size of the microcontroller. It also makes it difficult to respond to small changes in the end-of-charge voltage.

[0013] The present disclosure provides a technique for relatively easily and accurately estimating full charge capacity regardless of the end-of-charge voltage.

[0014] A battery management device according to an aspect of the present disclosure includes a lower limit reference voltage determination unit that determines a lower limit reference voltage corresponding to a lower limit reference SOC of a usable SOC range for estimating the full charge capacity of a battery pack, and a relative SOC calculation unit that calculates a relative SOC for display, with the remaining capacity at the end of charging of the battery pack being 100%. The battery management device according to an aspect of the present disclosure also includes a lower limit reference SOC correction unit that, when charging with a lowered end-of-charge voltage is specified, corrects the lower limit reference SOC based on the ratio of the remaining capacity at full charge to the remaining capacity at charging with the lowered end-of-charge voltage.

[0015] Any combination of the above components, and conversion of the expression of the present disclosure into an apparatus, system, method, computer program, etc., are also valid aspects of the present disclosure.

[0016] According to the present disclosure, the full charge capacity can be estimated relatively easily and with high accuracy, regardless of the end-of-charge voltage.

[0017] FIG. 1 is a diagram for explaining the configuration of a battery pack according to an embodiment. FIG. 2 is a diagram showing an example of the data structure of a lower limit reference voltage table. FIG. 3 is a diagram showing an example of discharge curves in standard charge mode and eco charge mode when the lower limit reference SOC is set to 9%. FIG. 4 is a flowchart showing the flow of charge control by a battery management device. FIG. 5 is a flowchart showing the flow of discharge control according to a comparative example by a battery management device. FIG. 6 is a flowchart showing the flow of discharge control according to an example by a battery management device.

[0018] 1 is a diagram illustrating the configuration of a battery pack 1 according to an embodiment. In this embodiment, the battery pack 1 is assumed to be installed in a notebook PC, and the battery pack 1 supplies power to a load unit 2 of the notebook PC. Note that the device in which the battery pack 1 is installed is not limited to a notebook PC, and the battery pack 1 may also be used, for example, in an automotive application.

[0019] The battery pack 1 includes a battery pack 20 and a battery management device 10. The battery pack 20 includes multiple cells E1-E3 connected in series. While FIG. 1 shows an example of a three-series connection, the number of cells connected in series is determined by the specifications of the load unit 2. Lithium-ion battery cells, nickel-metal hydride battery cells, lead-acid battery cells, etc. can be used for the cells E1-E3. In the following description, we will assume an example in which lithium-ion battery cells (nominal voltage: 3.6-3.7 V) are used as the cells E1-E3. Note that in each series stage of cells, multiple cells may be connected in parallel to increase capacity.

[0020] A switch SW1 that switches between conduction and non-conduction with the load section 2 is inserted in the power line connecting the battery pack 20 and the load section 2. A semiconductor switch or a relay can be used as the switch SW1.

[0021] The battery management device 10 includes a measurement unit 11 and a control unit 12. The measurement unit 11 is configured as an analog front end integrated circuit (AFEIC) or an application specific integrated circuit (ASIC), and the control unit 12 is configured as a microcontroller.

[0022] The measurement unit 11 is connected to each node of the multiple cells E1-E3 connected in series by multiple voltage measurement lines, and measures the voltage of each cell E1-E3 by measuring the voltage between each two adjacent voltage measurement lines.

[0023] The measurement unit 11 includes a multiplexer and an analog-to-digital (A / D) converter. The multiplexer outputs the voltages of the multiple cells E1-E3 to the A / D converter in a predetermined order. The A / D converter converts the analog voltages input from the multiplexer into digital values. The measurement unit 11 transmits the converted digital voltage values ​​of the cells E1-E3 to the control unit 12 via a communication interface.

[0024] The measurement unit 11 measures the current flowing through the battery pack 20. A shunt resistor Rs is connected to the power line connecting the battery pack 20 and the load unit 2. A differential amplifier (not shown) amplifies the voltage across the shunt resistor Rs and outputs it to an A / D converter in the measurement unit 11. The A / D converter converts the analog voltage indicating the current flowing through the battery pack 20, which is input from the differential amplifier, into a digital value. The measurement unit 11 transmits the current value converted into a digital value to the control unit 12 via the communication interface.

[0025] A temperature sensor T1 (e.g., a thermistor) is installed on the surface of the battery pack 20. A divided voltage between the temperature sensor T1 and a voltage dividing resistor (not shown) is input to the measurement unit 11. An A / D converter in the measurement unit 11 converts the input analog voltage indicating the temperature into a digital value. The measurement unit 11 transmits the converted digital temperature value to the control unit 12 via a communication interface.

[0026] The control unit 12 manages the states of the cells E1-E3 based on the voltage values ​​of the cells E1-E3, the current values ​​flowing through the battery pack 20, and the temperature values ​​of the battery pack 20 received from the measurement unit 11. When the control unit 12 detects overcharge, overdischarge, overcurrent, abnormally high temperature, or abnormally low temperature, it sends a shutoff signal for the switch SW1 to the measurement unit 11 to turn off the switch SW1.

[0027] The control unit 12 includes an SOC estimation unit 121, a relative SOC calculation unit 122, an FCC estimation unit 123, a lower limit reference voltage determination unit 124, an SOC adjustment unit 125, and a lower limit reference SOC correction unit 126. These functional blocks are realized by executing a program such as firmware in the microcontroller.

[0028] The SOC estimation unit 121 estimates the SOC by combining the OCV (Open Circuit Voltage) method and the current integration method. The OCV method estimates the SOC based on the measured cell OCV and the cell's SOC-OCV curve. The cell's SOC-OCV curve is created in advance based on characteristic tests conducted by the battery manufacturer and registered in the control unit 12 at the time of shipment.

[0029] The current integration method is a method for estimating the SOC based on the OCV at the start of cell charging and discharging and the integrated value of the measured current. With the current integration method, current measurement errors accumulate as the charging and discharging time increases. Therefore, it is preferable to use a weighted average of the SOC estimated by the current integration method and the SOC estimated by the OCV method.

[0030] The SOC estimation unit 121 converts the SOC of each cell E1-E3 into an actual capacity, combines these actual capacities to calculate the actual capacity of the battery pack 1, and can estimate the SOC of the battery pack 1 based on the actual capacity and the current FCC of the battery pack 1.

[0031] The relative SOC calculation unit 122 calculates the relative SOC for display of the battery pack 1, with the remaining capacity at the end of charging of the battery pack 1 set to 100%. The end-of-charge voltage per cell in the standard charging mode is generally 4.2 V (SOC = 100%), but the end-of-charge voltage per cell in the eco charging mode is specified to be lower than 4.2 V (SOC = 100%), such as 4.0 V or 3.8 V.

[0032] Hereinafter, in this specification, we consider a cell with an SOC of 80% when the end-of-charge voltage per cell is 4.0 V and an SOC of 60% when it is 3.8 V. In a three-series battery pack 1 using this cell, when eco-charging with an end-of-charge voltage of 12.0 V is specified, the original SOC is 80%, but the relative SOC displayed to the user is set to 100%. Similarly, when eco-charging with an end-of-charge voltage of 11.4 V is specified, the original SOC is 60%, but the relative SOC displayed to the user is set to 100%.

[0033] The relative SOC calculation unit 122 calculates the relative SOC by multiplying the original SOC by 100 / (original SOC corresponding to the end-of-charge voltage in eco charging mode). The relative SOC calculation unit 122 transmits the calculated relative SOC to the upper control unit 50 of the load unit 2 via the communication interface. The upper control unit 50 displays the relative SOC received from the battery pack 1 on the display unit 51. The display unit 51 may be a liquid crystal display, an organic electroluminescence (EL) display, a micro-LED (light emitting diode) display, or the like.

[0034] The FCC estimation unit 123 estimates the current FCC based on the discharge capacity from the fully charged state at the end of charging to the lower limit reference voltage, (100 - lower limit reference SOC), and the discharge efficiency coefficient (see Equation 1 above). The discharge capacity from the fully charged state at the end of charging to the lower limit reference voltage can be calculated by integrating the current value from the fully charged state at the end of charging to the lower limit reference voltage. (100 - lower limit reference SOC) corresponds to the usable SOC range, i.e., DOD (Depth Of Discharge). The lower limit reference SOC corresponds to the lower limit SOC of the usable SOC range.

[0035] The lower limit reference SOC is a given value, and is set in advance by a designer depending on the equipment to which the battery pack 1 is to be mounted. If the user continues to use the equipment for a predetermined period without the SOC decreasing to the lower limit reference SOC, the FCC estimation unit 123 may increase the value of the lower limit reference SOC by adding a predetermined value to the value of the lower limit reference SOC.

[0036] An SOH calculation unit (not shown) calculates the SOH of the battery pack 1 by calculating the following (Equation 3).

[0037] SOH = current FCC / initial FCC (Equation 3) The lower limit reference voltage determination unit 124 determines the lower limit reference voltage corresponding to the lower limit reference SOC by referring to a lower limit reference voltage table based on the temperature of the battery pack 20 and the discharge current flowing from the battery pack 20.

[0038] FIG. 2 shows an example of the data structure of the lower limit reference voltage table. The lower limit reference voltage table describes the combination of cell temperature and discharge current and the lower limit reference voltage for each lower limit reference SOC. The basic relationship between cell voltage and SOC is determined by the cell type. Furthermore, the relationship between cell voltage and SOC during discharge also depends on the temperature and current during discharge. Even with the same SOC, the higher the temperature, the lower the internal resistance, resulting in a higher voltage. Furthermore, even with the same SOC, the higher the discharge current, the lower the voltage. The designer creates a lower limit reference voltage table for cells E1-E3 used in the battery pack 20 based on the results of experiments or simulations and writes it into the program in advance. The lower limit reference voltage of the battery pack 1 is calculated by multiplying the lower limit reference voltage of the cell by the number of series connections.

[0039] The SOC adjustment unit 125 adjusts the relative SOC of the battery pack 1 to the value of the lower limit reference SOC when the voltage of the battery pack 1 reaches the lower limit reference voltage. In the standard charging mode, the relative SOC and the original SOC match. In the standard charging mode, when the lower limit reference voltage is detected, the SOC adjustment unit 125 sets the SOC to the value of the lower limit reference SOC even if the SOC has not reached the lower limit reference SOC. In the standard charging mode, even if the SOC has reached the lower limit reference SOC, the SOC adjustment unit 125 maintains the SOC at a value of (lower limit reference SOC + 1)% until the lower limit reference voltage is detected, and sets the SOC to the value of the lower limit reference SOC when the lower limit reference voltage is detected. This makes it possible to correct SOC errors.

[0040] 3 shows an example of discharge curves in the standard charging mode and the eco charging mode when the lower reference SOC is set to 9%. The end-of-charge voltage per cell in the standard charging mode is 4.2 V (SOC = 100%, RSOC = 100%), and the end-of-charge voltage per cell in the eco charging mode is 4.0 V (SOC = 80%, RSOC = 100%). In FIG. 3, RSOC represents the relative SOC, and LV represents the lower reference voltage corresponding to the lower reference SOC of 9%.

[0041] The FCC calculated from the discharge curve in the standard charge mode is obtained by substituting 9 for the lower limit reference SOC in the above equation (1), as shown below (equation 4).

[0042] FCC = (discharge capacity from full charge to LV detection) / (100% - 9%) × 100 × discharge efficiency coefficient = (discharge capacity from full charge to LV detection) / 91% × 100 × discharge efficiency coefficient (Equation 4) First, consider the case where the lower limit reference voltage LV is constant regardless of the end-of-charge voltage at full charge. In the eco charge mode (SOC = 80%) shown in Figure 3, the original lower limit reference SOC at LV detection is 11.3% (≈ 9% × 100% / 80%), and the original usable SOC range should be 88.7% (= 100% - 11.3%).

[0043] However, if the lower limit reference SOC is uniformly set to 9%, the usable SOC range will be 91%, as shown in Equation 4 above. Therefore, the FCC calculated from the discharge curve in eco charging mode will be smaller than the actual value. This error becomes larger as the end-of-charge voltage at full charge decreases.

[0044] Furthermore, the relative SOC adjustment unit 125 sets the relative SOC of the battery pack 1 to 9% at the time of LV detection. The relative SOC at the time of LV detection in the eco charging mode shown in FIG. 3 should be around 11.3%, and SOC adjustment causes the remaining battery charge display of the battery pack 1 to jump significantly from around 11.3% to 9%. This jump in value increases as the end-of-charge voltage at full charge decreases. Such discrete numerical changes result in an unnatural remaining battery charge display for the user. Therefore, in this embodiment, a mechanism is introduced to correct the error in the FCC calculated in the eco charging mode and the unnatural jump in the remaining battery charge display.

[0045] When charging with a lowered end-of-charge voltage is specified, lower-limit reference SOC correction unit 126 corrects the lower-limit reference SOC based on the ratio between the remaining capacity at full charge and the remaining capacity at charge with the lowered end-of-charge voltage. The remaining capacity may be considered in terms of SOC or actual capacity. For example, lower-limit reference SOC correction unit 126 refers to the SOC-OCV curve of the cell to identify the SOC corresponding to the end-of-charge voltage (OCV).

[0046] The SOC-OCV curve of the cell may be defined as discrete data in a table. In this case, the remaining capacity corresponding to the end-of-charge voltage not listed in the table is estimated by linear interpolation. If the end-of-charge SOC is specified by the upper control unit 50, the above ratio can be calculated from the end-of-charge SOC.

[0047] If the SOC at full charge is 100% and the SOC at full charge with a lowered end-of-charge voltage is 80%, the above ratio is 1.25. In this case, the corrected lower limit reference SOC is 11.3% (≈9% × 1.25). The FCC estimation unit 123 calculates the following (Equation 5) to estimate a new FCC. The relative SOC adjustment unit 125 sets the relative SOC of the battery pack 1 to 11.3% at the time of LV detection. The relative SOC of the battery pack 1 should be near 11.3% at the time of LV detection, and SOC adjustment will prevent the remaining charge display of the battery pack 1 from jumping significantly.

[0048] FCC = (discharge capacity from full charge to LV detection) / (100% - 11.3%) × 100 × discharge efficiency coefficient (Equation 5) Furthermore, if the SOC at full charge is 100% and the SOC at full charge when charging with a lowered end-of-charge voltage is 60%, the above ratio is approximately 1.67. In this case, the corrected lower limit reference SOC is 15.0% (≈9% × 1.67). The FCC estimation unit 123 calculates the following (Equation 6) to estimate a new FCC. The relative SOC adjustment unit 125 sets the relative SOC of the battery pack 1 to 15.0% at the time of LV detection. The relative SOC of the battery pack 1 should be near 15.0% at the time of LV detection, and SOC adjustment will prevent the remaining charge display of the battery pack 1 from jumping significantly.

[0049] FCC = (discharge capacity from full charge to LV detection) / (100% - 15.0%) × 100 × discharge efficiency coefficient (Equation 6). Figure 4 is a flowchart showing the flow of charge control by the battery management unit 10. Assume that the battery pack 1 is connected to a charger. The upper-level control unit 50 on the load unit 2 (main unit) side determines a charge mode as charge control to lower the charge voltage. The charge execution unit (not shown) of the battery management unit 10 receives the charge mode from the upper-level control unit 50 (step S10). The charge execution unit determines a charge end voltage (step S11). If the upper-level control unit 50 specifies a charge end SOC instead of a charge end voltage as the charge mode, the charge execution unit refers to the cell's SOC-OCV curve to identify the charge end voltage corresponding to the charge end SOC. Note that the charge mode may be determined by the battery management unit 10 itself.

[0050] The charging execution unit starts charging (step S12). The charging execution unit charges the battery pack 20, for example, by CC-CV (Constant Current Constant Voltage) charging. The charging execution unit ends charging when the voltage of the battery pack 1 reaches the charging end voltage (Y in step S13). In the description of FIG. 4, an example was assumed in which the charging execution unit controls a DC (Direct Current) / DC converter (not shown) on the battery management unit 10 side to control the voltage or current during charging, but the upper control unit 50 may control a DC / DC converter (not shown) on the load unit 2 (main body) side to control the voltage or current during charging.

[0051] 5 is a flowchart showing the flow of discharge control according to a comparative example performed by the battery management device 10. The relative SOC calculation unit 122 calculates the relative SOC according to the charge mode, with the remaining capacity of the battery pack 1 at the end of charge being 100% (step S20). The relative SOC calculation unit 122 transmits the calculated relative SOC to the upper control unit 50 as a display SOC (step S21). The upper control unit 50 causes the display unit 51 to display the received relative SOC.

[0052] The lower limit reference voltage determination unit 124 determines a lower limit reference voltage corresponding to the lower limit reference SOC by referring to a lower limit reference voltage table based on the temperature of the battery pack 20 and the discharge current flowing from the battery pack 20 (step S23). If the voltage of the battery pack 1 has not reached the lower limit reference voltage (N in step S24), the process proceeds to step S20. If the voltage of the battery pack 1 reaches the lower limit reference voltage (Y in step S24), the SOC adjustment unit 125 forcibly sets the relative SOC of the battery pack 1 to the lower limit reference SOC (step S25). The FCC estimation unit 123 estimates the current FCC based on the discharge capacity from the fully charged state at the end of charging until the lower limit reference voltage is reached, the used SOC range, and the discharge efficiency coefficient (step S26).

[0053] The relative SOC calculation unit 122 continues to calculate the relative SOC according to the charging mode (step S27). The relative SOC calculation unit 122 transmits the calculated relative SOC to the upper control unit 50 as an SOC for display (step S28). The upper control unit 50 displays the received relative SOC on the display unit 51. The processes of steps S27 to S28 are repeatedly executed (step S29: No) until the discharge is completed (step S29: Y). The timing of the discharge completion is determined when the battery reaches a fully discharged state or when a new charge is started.

[0054] FIG. 6 is a flowchart showing the flow of discharge control according to an embodiment of the present invention performed by the battery management device 10. The flowchart of discharge control according to the embodiment shown in FIG. 6 is the flowchart of discharge control according to the comparative example shown in FIG. 5 , to which step S22 has been added. The lower limit reference SOC corrector 126 multiplies the set lower limit reference SOC by the ratio of the remaining capacity at full charge to the remaining capacity at eco-charging to calculate the corrected lower limit reference SOC (step S22). The lower limit reference voltage determiner 124 determines the lower limit reference voltage corresponding to the corrected lower limit reference SOC by referencing a lower limit reference voltage table based on the temperature of the battery pack 20 and the discharge current flowing from the battery pack 20 (step S23). The remaining processing is the same as that of the flowchart shown in FIG. 5.

[0055] As described above, according to this embodiment, the FCC can be estimated relatively easily and with high accuracy regardless of the charging mode, and large numerical value jumps can be suppressed during SOC matching. Furthermore, there is no need to store a lower limit reference voltage table for each end-of-charge voltage, which can suppress an increase in program size. Furthermore, it is also possible to accommodate small changes in the end-of-charge voltage. In this way, with a simple program structure, it is possible to achieve relatively high-accuracy FCC estimation and suppress large numerical value jumps during SOC matching.

[0056] The present disclosure has been described above based on the embodiments. The embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of the respective components and processing steps, and that such modifications are also within the scope of the present disclosure.

[0057] In the above-described embodiment, eco-charging is assumed as charging with a lowered end-of-charge voltage, but the present disclosure can also be applied to life stage charging, in which the end-of-charge voltage is lowered from the viewpoint of safety as the SOH decreases. In this case, the accuracy of FCC estimation after the life stage transition can be improved.

[0058] In the above-described embodiment, an example has been described in which the battery pack 1 according to the present disclosure is mounted in a notebook PC. In this regard, the battery pack 1 according to the present disclosure can also be mounted in other consumer electronic devices (e.g., smartphones and tablets), electric vehicles, electric bicycles, electric motorcycles, electric kick scooters, multicopters (drones), and stationary power storage systems.

[0059] The embodiment may be specified by the following items.

[0060] [Item 1] The battery management device (10) of item 1 includes a lower limit reference voltage determination unit (124) that determines a lower limit reference voltage corresponding to a lower limit reference SOC of a usable SOC range for estimating the full charge capacity of the battery pack (20). The battery management device (10) of item 1 also includes a relative SOC calculation unit (122) that calculates a relative SOC for display, with the remaining capacity at the end of charging of the battery pack (20) set to 100%. The battery management device (10) of item 1 also includes a lower limit reference SOC correction unit (126) that, when charging with a lowered end-of-charge voltage is specified, corrects the lower limit reference SOC based on the ratio of the remaining capacity at full charge to the remaining capacity at charging with the lowered end-of-charge voltage.

[0061] This allows the full charge capacity to be estimated relatively easily and with high accuracy, regardless of the end-of-charge voltage.

[0062] [Item 2] The battery management device (10) of item 2 is the battery management device (10) according to item 1, further including an SOC adjustment unit (125) that adjusts the relative SOC to a lower-limit reference SOC when the voltage of the battery pack (20) reaches a lower-limit reference voltage.

[0063] This makes it possible to prevent large jumps in the SOC value when matching the SOC.

[0064] [Item 3] The battery management device (10) of item 3 is the battery management device (10) according to item 1, further comprising a full charge capacity estimation unit (123) that estimates a full charge capacity based on a discharge capacity from an end-of-charging state until a lower-limit reference voltage is reached, (100 - lower-limit reference SOC), and a discharge efficiency coefficient.

[0065] This allows the full charge capacity to be estimated relatively easily and with high accuracy.

[0066] [Item 4] In the battery management device (10) of Item 4, in the battery management device (10) described in Item 1, the lower limit reference voltage determination unit (124) determines the lower limit reference voltage by referring to a table that describes, for each lower limit reference SOC, the relationship between the combination of the temperature and discharge current of the battery pack (20) and the lower limit reference voltage.

[0067] This makes it possible to determine an optimum lower limit reference voltage corresponding to the lower limit reference SOC.

[0068] [Item 5] A battery pack (1) of item 5 includes a battery pack (20) and the battery management device (10) according to any one of items 1 to 4.

[0069] This makes it possible to realize a battery pack (1) that can estimate the full charge capacity relatively easily and with high accuracy regardless of the end-of-charge voltage and can suppress large numerical jumps when matching the SOC.

[0070] [Item 6] The battery management method of Item 6 includes a step of determining a lower limit reference voltage corresponding to a lower limit reference SOC of a usable SOC range for estimating a full charge capacity of the battery pack (20), and a step of calculating a relative SOC for display, in which the remaining capacity at the end of charging of the battery pack (20) is set to 100%.

[0071] The battery management method of item 6 also includes a step of adjusting the relative SOC to the lower limit reference SOC when the voltage of the battery pack (20) reaches the lower limit reference voltage. The battery management method of item 6 also includes a step of correcting the lower limit reference SOC based on the ratio of the remaining capacity at full charge to the remaining capacity at charge with the lowered end-of-charge voltage, when charging with a lowered end-of-charge voltage is specified.

[0072] This allows the full charge capacity to be estimated relatively easily and with high accuracy, regardless of the end-of-charge voltage.

[0073] [Item 7] The battery management program of item 7 causes a computer to execute a process of determining a lower limit reference voltage corresponding to a lower limit reference SOC of a usable SOC range for estimating the full charge capacity of the battery pack (20), and a process of calculating a relative SOC for display, in which the remaining capacity at the end of charging of the battery pack (20) is set to 100%. The battery management program of item 7 also causes the computer to execute a process of adjusting the relative SOC to the lower limit reference SOC when the voltage of the battery pack (20) reaches the lower limit reference voltage. The battery management program of item 7 also causes the computer to execute a process of correcting the lower limit reference SOC, when charging with a lowered end-of-charge voltage is specified, based on the ratio of the remaining capacity at full charge to the remaining capacity at charging with the lowered end-of-charge voltage.

[0074] This allows the full charge capacity to be estimated relatively easily and with high accuracy, regardless of the end-of-charge voltage.

[0075] REFERENCE SIGNS LIST 1 Battery pack 2 Load section 10 Battery management device 11 Measurement section 12 Control section 121 SOC estimation section 122 Relative SOC calculation section 123 FCC estimation section 124 Lower limit reference voltage determination section 125 SOC adjustment section 126 Lower limit reference SOC correction section 20 Assembled battery 50 Upper control section 51 Display section E1 Cell E2 Cell E3 Cell Rs Shunt resistor SW1 Switch T1 Temperature sensor

Claims

1. A battery management device comprising: a lower limit reference voltage determination unit that determines a lower limit reference voltage corresponding to a lower limit reference SOC of a usable SOC (State Of Charge) range for estimating the full charge capacity of a battery pack; a relative SOC calculation unit that calculates a relative SOC for display, with the remaining capacity at the end of charging of the battery pack being 100%; and a lower limit reference SOC correction unit that, when charging with a lowered end-of-charging voltage is specified, corrects the lower limit reference SOC based on the ratio between the remaining capacity at full charge and the remaining capacity at charging with the lowered end-of-charging voltage.

2. The battery management device according to claim 1, further comprising an SOC adjustment unit that adjusts the relative SOC to the lower limit reference SOC when the voltage of the battery pack reaches the lower limit reference voltage.

3. The battery management device of claim 1, further comprising a full charge capacity estimation unit that estimates a full charge capacity based on the discharge capacity from the end of charging state until the lower limit reference voltage is reached, (100 - the lower limit reference SOC), and a discharge efficiency coefficient.

4. A battery management device as described in claim 1, wherein the lower limit reference voltage determination unit determines the lower limit reference voltage by referring to a table which describes, for each lower limit reference SOC, the relationship between a combination of the temperature and discharge current of the battery pack and the lower limit reference voltage.

5. A battery pack comprising: the assembled battery; and the battery management device according to any one of claims 1 to 4.

6. A battery management method comprising: a step of determining a lower limit reference voltage corresponding to a lower limit reference SOC of a usable SOC range for estimating a full charge capacity of a battery pack; a step of calculating a relative SOC for display, in which the remaining capacity at the end of charging of the battery pack is set to 100%; a step of adjusting the relative SOC to the lower limit reference SOC when the voltage of the battery pack reaches the lower limit reference voltage; and a step of correcting the lower limit reference SOC based on the ratio of the remaining capacity at full charge to the remaining capacity at charging with the lowered end of charging voltage, when charging with a lowered end of charging voltage is specified.

7. A battery management program that causes a computer to execute the following processes: determining a lower limit reference voltage corresponding to the lower limit reference SOC of a usable SOC range for estimating the full charge capacity of a battery pack; calculating a relative SOC for display, in which the remaining capacity at the end of charging of the battery pack is set to 100%; adjusting the relative SOC to the lower limit reference SOC when the voltage of the battery pack reaches the lower limit reference voltage; and correcting the lower limit reference SOC based on the ratio of the remaining capacity at full charge to the remaining capacity at charging with the lowered end of charging voltage, when charging with a lowered end of charging voltage is specified.

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