Display system

Abstract

Displays battery capacity with high accuracy. [Solution] The ECU performs a process that includes the steps of obtaining the maximum value of the SOC variation as a subtraction amount ΔC(0) (S100), obtaining an estimated value of the full charge capacity (S102), obtaining the usable SOC range (S104), subtracting the subtraction amount ΔC(0) from the usable SOC range (S106), calculating the display value of the full charge capacity (S108), and displaying the display value of the full charge capacity (S110).

Description

Technical Field

[0001] This disclosure relates to a display system.

Background Art

[0002] For example, Japanese Unexamined Patent Application Publication No. 2003-164006 (Patent Document 1) discloses a technique for calculating the degree of deterioration of a battery from voltage values and current values, correcting a capacity adjustment range according to the calculated degree of deterioration, and displaying the current battery capacity in segments.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When displaying the current capacity of a battery composed of a plurality of single cells as in the above-described technique, if the state where equalization processing for aligning the SOC (State Of Charge) among the plurality of single cells is not performed continues, variations in SOC may occur among the plurality of single cells. As a result, the entire capacity of the battery may not be fully utilized, and the actual value and the estimated value of the electrically drivable distance may deviate. Therefore, the current capacity and the fully charged capacity of the battery may not be accurately displayed in some cases.

[0005] This disclosure has been made to solve the above-described problems, and an object thereof is to provide a display system that accurately displays the capacity of a battery.

Means for Solving the Problems

[0006] A display system relating to a certain aspect of this disclosure is a display system that displays information regarding the full charge capacity of a battery including a plurality of lithium iron phosphate cells. This display system comprises a display device and a control device. The control device calculates the maximum variation in SOC among the plurality of cells as a subtraction amount using the charge and discharge history of each of the plurality of cells, and subtracts the subtraction amount from the usable SOC range of the battery. The display device displays information regarding the full charge capacity using the ratio of the value obtained by subtracting the subtraction amount from the SOC range to the SOC range.

[0007] In this way, by displaying information about the full charge capacity using the ratio of the usable SOC range to the usable SOC range minus the subtraction amount, it is possible to display the full charge capacity of the battery with high accuracy.

[0008] In one embodiment, the control device detects the step in the change of OCV (Open Circuit Voltage) in each of the multiple single cells and calculates the maximum value using the integrated current amount corresponding to the variation in the step between each of the multiple single cells.

[0009] In this way, the maximum value of the SOC variation can be calculated with high accuracy using the integrated current amount corresponding to the variation in the step detected in each individual cell.

[0010] In one further embodiment, the control device calculates the maximum value using the variation in the self-discharge amount of each of the multiple single cells over a predetermined period.

[0011] In this way, the maximum value of the SOC variation can be calculated with high accuracy using the variation in the self-discharge rate of each of the multiple individual cells.

[0012] In one further embodiment, the display system further comprises multiple monitoring circuits, each monitoring the state of a plurality of individual cells. The control device calculates a maximum value using the variation in power consumption of the multiple monitoring circuits in each of the plurality of individual cells over a predetermined period.

[0013] In this way, the maximum value of the SOC variation can be calculated with high accuracy using the variation in power consumption of the monitoring circuit in each individual cell.

[0014] Furthermore, in one embodiment, the control device calculates the subtraction amount using the State of Charge (SOC) range, which decreases due to the expansion of the single cell, in addition to the charge and discharge history.

[0015] This allows the full battery charge capacity to be displayed on the display device with even greater accuracy. [Effects of the Invention]

[0016] According to this disclosure, a display system can be provided that accurately displays the battery capacity. [Brief explanation of the drawing]

[0017] [Figure 1] This figure shows an example of the overall configuration of an electric vehicle equipped with the display system according to this embodiment. [Figure 2] This figure shows the relationship between OCV and remaining capacity in a single cell of this embodiment. [Figure 3] This flowchart shows an example of a process performed by the ECU. [Figure 4] This figure shows an example of the relationship between OCV, integrated current, and capacity of multiple single cells. [Figure 5] This figure shows the relationship between state of charge (SOC), temperature, and self-discharge rate in multiple single cells. [Modes for carrying out the invention]

[0018] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their description will not be repeated.

[0019] Hereinafter, an example of a display system S according to this embodiment will be described. FIG. 1 is a diagram showing an example of the overall configuration of an electric vehicle 1 equipped with the display system S according to this embodiment. In this embodiment, the electric vehicle 1 is, for example, an electric car. The electric vehicle 1 includes a motor generator (MG) 10 which is a rotary electric machine, a power transmission gear 20, drive wheels 30, a power control unit (PCU) 40, a system main relay (SMR) 50, a battery 100, a monitoring unit 200, an electronic control unit (ECU) 300 which is an example of a control device, and a display device 350. The display system S is constituted by the ECU 300 and the display device 350.

[0020] The MG 10 is, for example, an embedded permanent magnet synchronous motor (IPM motor), and has functions as an electric motor and a generator. The output torque of the MG 10 is transmitted to the drive wheels 30 via a power transmission gear 20 configured to include a reduction gear, a differential device, and the like.

[0021] When the electric vehicle 1 is braked, the MG 10 is driven by the drive wheels 30 and the MG 10 operates as a generator. Thereby, the MG 10 also functions as a braking device that performs regenerative braking for converting the kinetic energy of the electric vehicle 1 into electric power. The regenerative electric power generated by the regenerative braking force in the MG 10 is stored in the battery 100.

[0022] The PCU 40 is a power conversion device that converts electric power bidirectionally between the MG 10 and the battery 100. The PCU 40 includes, for example, an inverter and a converter (both not shown) that operate based on a control signal from the ECU 300.

[0023] The converter, when the battery 100 is discharged, boosts the voltage supplied from the battery 100 and supplies it to the inverter. The inverter converts the DC power supplied from the converter into AC power to drive the MG10.

[0024] The inverter converts the AC power generated by the MG10 into DC power when charging the battery 100 and supplies it to the converter. The converter steps down the voltage supplied from the inverter to a voltage suitable for charging the battery 100 and supplies it to the battery 100.

[0025] The SMR50 is electrically connected to the power line connecting the battery 100 and the PCU 40. When the SMR50 is closed (ON) in response to a control signal from the ECU 300, power can be exchanged between the battery 100 and the PCU 40. On the other hand, when the SMR50 is opened (OFF) in response to a control signal from the ECU 300, the electrical connection between the battery 100 and the PCU 40 is interrupted.

[0026] Battery 100 stores power to drive MG10. Battery 100 is a rechargeable DC power source (secondary battery) and is composed of multiple single cells 100a stacked and electrically connected in series, for example. The single cells 100a may be composed of lithium-ion batteries, for example. In this embodiment, the single cells 100a are lithium iron phosphate batteries (LFP batteries) using lithium iron phosphate as the positive electrode active material.

[0027] The monitoring unit 200 includes a voltage sensor 210, a current sensor 220, and a temperature sensor 230. The voltage sensor 210 detects the voltage VB of the single cell 100a (the voltage VB between each terminal of the single cell 100a). The current sensor 220 detects the current IB that is input to and output from the battery 100 (single cell 100a). The current IB may be positive (+) for the current charging the battery 100 and negative (-) for the current discharging from the battery 100. The temperature sensor 230 detects the temperature TB of each single cell 100a. The monitoring unit 200 outputs the detection results from each detection unit to the ECU 300.

[0028] The electric vehicle 1 is equipped with a DC inlet 60, and the battery 100 is capable of rapid charging from an external DC power source, which is a charging device. The DC inlet 60 is configured to be connectable to a connector 420 located at the end of the charging cable 410 of the external DC power source (charging device) 400. The charging relay 70 is electrically connected to the power line connecting the DC inlet 60 and the battery 100. The charging relay 70 switches between supplying and cutting off power between the DC inlet 60 and the battery 100 in response to a control signal from the ECU 300. When the charging relay 70 is closed, external charging (rapid charging) of the battery 100 is performed.

[0029] The electric vehicle 1 is equipped with an AC inlet 80, and the battery 100 is capable of normal charging from an external AC power source, which is a charging facility. The AC inlet 80 is configured to be connectable to a connector 520 located at the end of the charging cable 510 of the external AC power source (charging facility) 500. An onboard charger 130 is provided in the power line between the AC inlet 80 and the battery 100, which converts the AC power supplied from the external AC power source into DC power and also converts it to a voltage that allows the battery 100 to be charged. A charging relay 90 is electrically connected to the power line connecting the onboard charger 130 and the battery 100. The charging relay 90 switches between supplying and cutting off power between the onboard charger 130 and the battery 100 in response to a control signal from the ECU 300. When the charging relay 90 is closed, external charging (normal charging) of the battery 100 is performed.

[0030] The ECU 300 includes a CPU (Central Processing Unit) 301 and memory (including, for example, ROM (Read Only Memory) and RAM (Random Access Memory)) 302. Based on signals received from the monitoring unit 200, signals from various sensors (not shown) (for example, accelerator opening signal, vehicle speed signal, etc.), and information such as maps and programs stored in the memory 302, the ECU 300 controls each device so that the electric vehicle 1 reaches a desired state. The ECU 300 also performs processes such as estimating the full charge capacity.

[0031] The display device 350 is configured to display textual information as a visual message to the user of the electric vehicle 1 in response to a control command from the ECU 300. The display device 350 is composed of, for example, a display unit of a touch panel display provided around the driver's seat. The display unit is composed of, for example, an LCD (Liquid Crystal Display) or an organic EL (Electro-Luminescence). The display device 350 may be provided, for example, in a combination meter (not shown) that is visible when the user of the electric vehicle 1 is seated in the driver's seat.

[0032] Figure 2 shows the relationship between OCV (Open Circuit Voltage) and remaining capacity in the single cell 100a (LFP battery) of this embodiment. In Figure 2(A), the vertical axis is the OCV [V] of the single cell 100a, and the horizontal axis is the remaining capacity (charge capacity) [Ah] of the single cell 100a. As shown in Figure 2(A), the relationship between OCV and remaining capacity (hereinafter, this relationship will also be referred to as the OCV curve) has a wide region where the change in the OCV curve is small (voltage flat region). If we refer to the point where the OCV curve increases from the voltage flat region and then returns to the voltage flat region as a "step", then in the single cell 100a of this embodiment, there are two steps P1 and P2.

[0033] At the first stage (where OCV is on the low-voltage side), step P1, the SOC of a new 100A cell is approximately 30%. At the second stage (where OCV is on the high-voltage side), step P2, the SOC of a new 100A cell is approximately 60%.

[0034] Figure 2(B) shows the relationship between the voltage change ΔVB of the voltage VB during charging of battery 100 and the remaining capacity, and shows the relationship when charging or discharging with a constant current. The voltage change ΔVB is the change in voltage VB with respect to the remaining capacity (charge capacity) [V / Ah], or the change in voltage VB with respect to time (charging time or discharging time) [V / s]. As shown in Figure 2(B), the voltage change ΔVB reaches a maximum value of M1 at the remaining capacity corresponding to step P1, and a maximum value of M2 at the remaining capacity corresponding to step P2. Therefore, the remaining capacity at which the voltage change ΔVB reaches a maximum value of M2 is stored as the reference capacity C2, and the charging current from when the voltage change ΔVB reaches a maximum value of M2 until full charge is calculated, and by adding this calculated value to the reference capacity C2, the full charge capacity of battery 100 (single cell 100a) can be estimated.

[0035] Since the aforementioned battery 100 is composed of multiple individual cells 100a, variations in State of Charge (SOC) may occur among the individual cells 100a. In such cases, an equalization process is performed to eliminate the SOC variations by fully charging the battery 100 and then fully charging each of the individual cells 100a. However, if the equalization process is not performed, the variation in SOC among the individual cells will increase, making it impossible to fully utilize the entire capacity of the battery 100, and causing a discrepancy between the actual and estimated electric driving range. Therefore, it may not be possible to display the current capacity or full charge capacity of the battery 100 with high accuracy.

[0036] Therefore, in this embodiment, the ECU 300 calculates the maximum variation in SOC among the multiple single cells 100a using the charge and discharge history of each of the multiple single cells 100a as a subtraction amount ΔC(0), subtracts the subtraction amount ΔC(0) from the usable SOC range of the battery 100, and displays information regarding the full charge capacity using the ratio of the value obtained by subtracting the subtraction amount ΔC(0) from the SOC range to the said SOC range.

[0037] In this way, by displaying information about the full charge capacity using the ratio of the usable SOC range to the usable SOC range minus the subtraction amount, the full charge capacity of battery 100 can be displayed with high accuracy.

[0038] The following describes an example of the processes performed by the ECU300, with reference to Figure 3. Figure 3 is a flowchart showing an example of the processes performed by the ECU300. For example, when connector 420 is connected to DC inlet 60, or when connector 520 is connected to AC inlet 80, external charging of battery 100 begins. When external charging of battery 100 begins, the processes shown in this flowchart are executed.

[0039] In step 100 (hereinafter referred to as S), the ECU 300 obtains the maximum value of the variation in SOC among multiple single cells 100a as the subtraction amount ΔC(0). More specifically, the ECU 300 detects the step difference of each of the multiple single cells 100a. For example, the ECU 300 detects the step difference P2 by detecting the maximum value corresponding to the step difference P2 of the second stage of the OCV (where the OCV is on the high-voltage side).

[0040] In other words, the ECU300 may determine that a maximum value has been detected when the change in OCV ΔOCV is smaller than the previous change in ΔOCV(n-1) and ΔOCV(n) is smaller than the previous change in ΔOCV(n-1). Alternatively, the ECU300 may determine that a maximum value has been detected when the sign of the derivative of the change in ΔOCV changes from positive to negative. For example, the ECU300 starts integrating the current from the point when the first step P2 is detected among the multiple single cells 100a. The ECU300 calculates the total integrated current up to the point when the last step P2 is detected among the multiple single cells 100a. The ECU300 calculates the maximum variation in SOC from the total integrated current as the subtraction amount ΔC(0). For example, a map showing the relationship between the integrated current and the subtracted amount ΔC(0) may be pre-set through experiments or other means and stored in memory 302, and the ECU 300 may calculate the subtracted amount ΔC(0) using the integrated current and the map. The map may also include the battery temperature in addition to the integrated current and the subtracted amount ΔC(0).

[0041] Figure 4 shows an example of the relationship between OCV, integrated current, and capacity of multiple single cells 100a. The vertical axis of Figure 4(A) shows OCV. The horizontal axis of Figure 4(A) shows capacity. Furthermore, the vertical axis of Figure 4(B) shows integrated current. The horizontal axis of Figure 4(B) shows capacity. Figure 4(A) shows an example of the relationship between OCV and capacity of four single cells 100a out of multiple single cells 100a. LN1, LN2, LN3, and LN4 in Figure 4(A) show examples of the relationship between OCV and capacity of the first, second, third, and fourth single cells, respectively. In the following explanation, we will assume that LN1 in Figure 4 corresponds to the first single cell where the step was first detected, and LN4 in Figure 4 corresponds to the fourth single cell where the step was last detected.

[0042] As shown in LN1 of Figure 4(A), when a maximum value is detected in the OCV change of the first cell among the multiple single cells 100a during external charging, current integration begins as shown in Figure 4(B). Then, as shown in LN2 and LN3 of Figure 4(A), current integration continues when a maximum value is detected in the OCV change of the second and third cells, respectively. Then, as shown in LN4 of Figure 4(A), when a maximum value is detected in the OCV change of the fourth cell, current integration stops as shown in Figure 4(B), and the current integration amount S(0) is calculated. The ECU300 calculates the subtraction amount ΔC(0) using the current integration amount S(0) and the map. The subsequent processing moves to S102.

[0043] In S102, the ECU 300 obtains an estimated value of the full charge capacity. The ECU 300 obtains the estimated value of the full charge capacity from, for example, the monitoring unit 200. The monitoring unit 200 calculates the estimated value of the full charge capacity from, for example, the OCV(1) at the start of charging, the OCV(2) at the end of charging, and the integrated value of the charging current from the start to the end of charging during the most recent charging of battery 100. The monitoring unit 200 calculates the estimated value of the full charge capacity from, for example, the change in SOC ΔSOC calculated from the difference between OCV(1) and OCV(2), and the change in capacity due to the integrated value of the charging current. Alternatively, the ECU 300 may be configured to calculate the estimated value of the full charge capacity. The process then moves to S104.

[0044] In S104, the ECU 300 obtains the usable SOC range. The usable SOC range is calculated, for example, by subtracting the SOC at which the electric vehicle 1 stops running from the SOC corresponding to a fully charged state (95%). The SOC at which the electric vehicle 1 stops running is a predetermined value. The usable SOC range is a predetermined value and may be stored in the memory 302 of the ECU 300, obtained from the storage device (not shown) of the monitoring unit 200, or obtained from an external server. The process then moves to S106.

[0045] In S106, the ECU300 subtracts the subtraction amount ΔC(0) from the usable SOC range. The process then moves to S108.

[0046] In S108, the ECU300 calculates the display value of the full charge capacity. Specifically, the ECU300 calculates the ratio of the usable SOC range to the usable SOC range minus the subtraction amount ΔC(0). That is, the ECU300 calculates the ratio by dividing the usable SOC range minus the subtraction amount ΔC(0) by the usable SOC range. The ECU300 calculates the display value of the full charge capacity (corrected value of the capacity retention rate) by multiplying the calculated ratio by the current capacity retention rate. The ECU300 calculates the current capacity retention rate by, for example, dividing the estimated full charge capacity by the initial value of the full charge capacity. The initial value of the full charge capacity is the full charge capacity when no battery degradation has occurred. The initial value of the full charge capacity is, for example, a value predetermined by the type of battery 100, and may be stored in the memory 302 of the ECU300, obtained from the storage device (not shown) of the monitoring unit 200, or obtained from an external server. The subsequent processing is moved to S110.

[0047] In S110, the ECU300 displays the calculated full charge capacity value on the display device 350. The process is then terminated.

[0048] The operation of the ECU300 based on the structure and flowchart described above will now be explained. For example, when connector 420 is connected to DC inlet 60, external charging of battery 100 begins.

[0049] When external charging of battery 100 begins, ECU 300 obtains the maximum variation in SOC among multiple single cells 100a as a subtraction amount ΔC(0) (S100). As described above, ECU 300 detects the step difference in each of the multiple single cells 100a. It starts integrating the current from the time the first step difference is detected and uses the accumulated current up to the time the last step difference is detected to calculate the maximum variation in SOC as a subtraction amount ΔC(0).

[0050] Subsequently, the ECU 300 obtains an estimated value of the full charge capacity of the battery 100 from the monitoring unit 200 (S102) and obtains the usable SOC range of the battery 100 (S104).

[0051] The ECU 300 subtracts the subtraction amount ΔC(0) from the usable SOC range of the battery 100 (S106), and calculates the display value of the full charge capacity by multiplying the ratio of the usable SOC range minus the subtraction amount ΔC(0) to the usable SOC range by the current capacity retention rate (S108). The ECU 300 displays the calculated display value on the display device 350 (S110).

[0052] As described above, the display system S according to this embodiment can accurately display the full charge capacity of the battery 100 by correcting the current capacity retention rate using the subtraction amount ΔC(0), which is the maximum value of the variation in SOC among the multiple single cells 100a. Therefore, it is possible to provide a display system that displays the battery capacity with high accuracy.

[0053] Furthermore, the maximum value of the SOC variation can be calculated with high accuracy using the integrated current amount corresponding to the step detected in each 100a cell.

[0054] The following describes some variations. In the above-described embodiment, the case in which the maximum value of the SOC variation is calculated using the integrated current was explained as an example, but it is not limited to using the integrated current. For example, the ECU300 may calculate the maximum value of the SOC variation using the self-discharge amount of each single cell 100a when left idle.

[0055] Figure 5 shows the relationship between State of Charge (SOC), temperature, and self-discharge rate for multiple single cells 100a. Figure 5 shows the self-discharge rates corresponding to various SOCs and temperatures when the cells remain in a state of not being fully charged for a predetermined number of days (for example, 30 days). The left side of Figure 5 shows the maximum error (MAX) (%) of the self-discharge rates corresponding to various SOCs and temperatures for multiple single cells 100a. The right side of Figure 5 shows the average error (TYP) (%) of the self-discharge rates corresponding to various SOCs and temperatures for multiple single cells 100a. The various SOCs are described as including, but are not limited to, 10%, 40%, 70%, and 95%. Furthermore, the various temperatures are described as including, but are not limited to, -30°C, -20°C, -10°C, 0°C, 10°C, 20°C, 30°C, 40°C, and 50°C. The ECU300 acquires the self-discharge amount for each cell 100a after charging has been completed to a fully charged state. For example, the ECU300 acquires the self-discharge amount corresponding to the SOC and temperature in each cell 100a, provided that the SOC and temperature remain constant for a predetermined period until the next charge is performed. If a predetermined number of days has elapsed until the next charge is performed, the acquired self-discharge amount is reflected in the self-discharge amounts corresponding to various SOCs and temperatures shown in Figure 5. In other words, the ECU300 calculates the maximum error and average error of the self-discharge amount using the acquired self-discharge amount and updates the self-discharge amounts corresponding to various SOCs and temperatures shown in Figure 5.

[0056] The ECU300 may, for example, extract the self-discharge amount, maximum error, and average error of the self-discharge amount for the same SOC and the same temperature, calculate the difference between them, and use the calculated difference to calculate the maximum value of SOC variation. For example, the ECU300 extracts the maximum error of the self-discharge amount of 2.6% when the SOC is 70% and the temperature is 30°C, as shown in Figure 5(A), and the average error of the self-discharge amount of 1.6% when the SOC is 70% and the temperature is 30°C, as shown in Figure 5(B). The ECU300 calculates the maximum value of SOC variation using 1% of the difference between the extracted values. For example, a map showing the relationship between the difference and the maximum value of SOC variation may be set in advance, and the ECU300 may calculate the maximum value of SOC variation using the calculated difference and the map. In this way, the maximum value of SOC variation can be calculated with high accuracy.

[0057] Furthermore, while the above embodiment describes the case where the maximum value of the SOC variation is calculated using the integrated current as an example, it is not limited to using the integrated current. For example, the ECU 300 may calculate the maximum value of the SOC variation using the variation in power consumption of the monitoring IC (Integral Circuit). The monitoring unit 200 includes a plurality of monitoring ICs. The plurality of monitoring ICs monitor the state (current, voltage, and temperature) of a plurality of single cells 100a. The plurality of monitoring ICs operate using the power of each of the plurality of single cells 100a. The ECU 300 acquires the power consumption of the plurality of monitoring ICs. The ECU 300 calculates, for example, the difference between the maximum error in the power consumption of each monitoring IC and the average error in the power consumption over a predetermined number of days (for example, 30 days). The ECU 300 may use the calculated difference to calculate the maximum value of the SOC variation. For example, a map showing the relationship between the difference and the maximum value of the SOC variation may be set in advance, and the ECU300 may use the calculated difference and the map to calculate the maximum value of the SOC variation. In this way, the maximum value of the SOC variation can be calculated with high accuracy.

[0058] In the above-described embodiment, the maximum variation in SOC is calculated as a subtraction amount ΔC(0), and the ratio to the usable SOC range is calculated by subtracting the subtraction amount ΔC(0) from the usable SOC range. However, the correction is not limited to this method. For example, the ECU 300 may subtract the SOC range that decreases due to the swelling of the battery 100 in addition to the subtraction amount ΔC(0) from the usable SOC range. The SOC range that decreases due to swelling may be a predetermined value, or it may be set according to the degradation state of the single cell 100a. In this way, the full charge capacity of the battery 100 can be displayed with even greater accuracy.

[0059] Furthermore, the above-mentioned modifications may be implemented by combining all or part of them as appropriate. The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0060] 1 electric vehicle, 10 MG, 20 power transmission gears, 30 drive wheels, 60 DC inlet, 70 charging relay, 80 AC inlet, 90 charging relay, 100 battery, 100a single cell, 130 onboard charger, 200 monitoring unit, 210 voltage sensor, 220 current sensor, 230 temperature sensor, 300 ECU, 301 CPU, 302 memory, 350 display device, 400, 500 power supply, 410, 510 charging cable, 420, 520 connector.

Claims

1. A display system that displays information regarding the full charge capacity of a battery, which includes multiple single cells of a lithium iron phosphate battery, Display device and Equipped with a control device, The control device calculates the maximum variation in State of Charge (SOC) among the plurality of single cells using the charge and discharge history of each of the plurality of single cells as a subtraction amount, and subtracts the subtraction amount from the usable SOC range of the battery. The display device is a display system that displays information regarding the full charge capacity using the ratio of the value obtained by subtracting the subtraction amount from the SOC range to the SOC range.

2. The display system according to claim 1, wherein the control device detects steps in the change of OCV (Open Circuit Voltage) in each of the plurality of single cells, and calculates the maximum value using the integrated current amount corresponding to the variation in steps between each of the plurality of single cells.

3. The display system according to claim 1, wherein the control device calculates the maximum value using the variation in the self-discharge amount in each of the plurality of single cells over a predetermined period.

4. The display system further comprises a plurality of monitoring circuits that monitor the state of each of the plurality of single cells, The display system according to claim 1, wherein the control device calculates the maximum value using the variation in power consumption of the plurality of monitoring circuits in each of the plurality of single cells over a predetermined period.

5. The display system according to any one of claims 1 to 4, wherein the control device calculates the subtraction amount using the SOC range that decreases due to the swelling of the single cell in addition to the charge and discharge history.

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