Display system

Abstract

Displays battery capacity with high accuracy. [Solution] The ECU performs a process that includes the steps of obtaining an estimated value of the full charge capacity (S100), obtaining a subtraction amount ΔC(0) (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] The present disclosure relates to a display system.

Background Art

[0002] For example, Japanese Patent Application Laid-Open 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] [[ID=2३]]

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 of charge (SOC) equalization process is not performed and the state where the SOCs among the plurality of single cells are not aligned 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 electric driving range may deviate. Therefore, it may not be possible to accurately display the current capacity and the fully charged capacity of the battery.

[0005] The present 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 single cells of a lithium iron phosphate battery. This display system comprises a display device and a control device. The control device calculates a subtraction amount using a first SOC range corresponding to a dead zone based on a SOC set as the full charge state, and subtracts the subtraction amount from a second usable SOC range of the battery. The display device displays information regarding the full charge capacity using the ratio of the second SOC range to the value obtained by subtracting the subtraction amount from the second SOC range.

[0007] In this way, by displaying information about the full charge capacity using the ratio of the value obtained by subtracting a certain amount from the second SOC range to the second SOC range, the full charge capacity of the battery can be displayed with high accuracy.

[0008] In one embodiment, the control device sets a subtraction amount corresponding to the first SOC range when the estimated value of the full charge capacity is greater than a first value, sets a subtraction amount that decreases in proportion to the decrease in the estimated value when the estimated value is less than or equal to the first value and greater than a second value, and sets zero as the subtraction amount when the estimated value is less than a second value.

[0009] In this way, if the estimated full charge capacity is greater than the first value, the second SOC range corresponding to the dead zone is used as the subtraction amount, allowing for a more accurate display of the battery's full charge capacity.

[0010] Furthermore, in one embodiment, the control device calculates the subtraction amount using the SOC range that decreases due to the expansion of the single cell, in addition to the first SOC range.

[0011] This allows the full battery charge capacity to be displayed on the display device with even greater accuracy. [Effects of the Invention]

[0012] According to this disclosure, a display system can be provided that accurately displays the battery capacity. [Brief explanation of the drawing]

[0013] [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 diagram illustrates the relationship between detection error and the dead zone (SOC) range. [Figure 5] This figure shows an example of the relationship between the estimated full charge capacity and the subtraction amount ΔC(0). [Modes for carrying out the invention]

[0014] The embodiments of this disclosure will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0015] The following describes an example of the display system S according to this embodiment. Figure 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 rotating 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 configured by the ECU 300 and the display device 350.

[0016] MG10 is, for example, an embedded permanent magnet synchronous motor (IPM motor), which has functions as a motor and as a generator. The output torque of MG10 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.

[0017] During braking of the electric vehicle 1, MG10 is driven by the drive wheels 30, and MG10 operates as a generator. Thereby, MG10 also functions as a braking device that performs regenerative braking to convert the kinetic energy of the electric vehicle 1 into electric power. The regenerative power generated by the regenerative braking force in MG10 is stored in the battery 100.

[0018] PCU40 is a power conversion device that converts electric power bidirectionally between MG10 and the battery 100. PCU40 includes, for example, an inverter and a converter (both not shown) that operate based on a control signal from the ECU300.

[0019] The converter boosts the voltage supplied from the battery 100 during discharge of the battery 100 and supplies it to the inverter. The inverter converts the DC power supplied from the converter into AC power to drive MG10.

[0020] The inverter converts the AC power generated by MG10 into DC power during charging of the battery 100 and supplies it to the converter. The converter降压 the voltage supplied from the inverter to a voltage suitable for charging the battery 100 and supplies it to the battery 100.

[0021] SMR50 is electrically connected to the power line connecting the battery 100 and PCU40. When SMR50 is closed (ON) in response to a control signal from the ECU300, power can be exchanged between the battery 100 and PCU40. On the other hand, when SMR50 is opened (OFF) in response to a control signal from the ECU300, the electrical connection between the battery 100 and PCU40 is interrupted.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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 signals and vehicle speed signals), 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.

[0027] 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.

[0028] 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.

[0029] 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%.

[0030] 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.

[0031] Since the aforementioned battery 100 is composed of multiple individual cells 100a, variations in State of Charge (SOC) may occur among these individual cells 100a. In such cases, an equalization process is performed to eliminate the SOC variation by fully charging each of the individual cells 100a that make up the battery 100. 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.

[0032] Therefore, in this embodiment, the ECU 300 calculates a subtraction amount ΔC(0) using a first SOC range corresponding to the dead zone based on the SOC set as the fully charged state, subtracts the subtraction amount from the usable second SOC range of the battery, and displays information regarding the full charge capacity on the display device 350 using the ratio of the value obtained by subtracting the subtraction amount from the second SOC to the second SOC range.

[0033] This method allows for a highly accurate display of the full charge capacity of battery 100.

[0034] 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.

[0035] In step 100 (hereinafter referred to as S), the ECU 300 obtains an estimated value of the full charge capacity. The ECU 300 obtains an estimated value of the full charge capacity from, for example, the monitoring unit 200. The monitoring unit 200 calculates an 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 the battery 100. The monitoring unit 200 calculates an 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 calculate the estimated value of the full charge capacity. The process then moves to S102.

[0036] In S102, the ECU300 obtains the subtraction amount ΔC(0). More specifically, the ECU300 calculates the capacity variation (i.e., the subtraction amount ΔC(0)) using the SOC width corresponding to the dead zone, based on the SOC set as the fully charged state. For example, the SOC equivalent to the dead zone is calculated in advance when the SOC is set to 95% as the fully charged state. The SOC width equivalent to the dead zone represents the SOC width corresponding to the voltage range formed by the detection error of the voltage sensor 210, and is adapted through experiments, etc.

[0037] Figure 4 is a diagram illustrating the relationship between detection error and dead zone SOC range. The vertical axis in Figure 4 represents OCV. The horizontal axis in Figure 4 represents SOC. Figure 4 shows an example of the change in OCV in response to a change in SOC of a single cell 100a. C2 in Figure 4 is the SOC corresponding to the step P2 described above, for example, 60%. As the step P2 has been described above, a detailed explanation will not be repeated. C3 in Figure 4 is the SOC set as the fully charged state, for example, 95%. As shown in Figure 4, when the state where the SOC is 95% is set as the fully charged state, and the OCV corresponding to the SOC of 95% (C3 in Figure 4) is assumed to be OCV(0), the detection error of the voltage sensor 210 that detects OCV is shown by the voltage range of the positive error and the negative error with respect to OCV(0). The range of SOC corresponding to this voltage range is set as the dead zone SOC range (corresponding to the first SOC range). In the following explanation, we will assume that the size of the first SOC range of this dead zone is S(1).

[0038] For example, the memory 302 of the ECU 300 stores a map showing the relationship between a pre-set estimated full charge capacity and the subtraction amount. The ECU 300 uses the acquired estimated full charge capacity and the map to calculate the subtraction amount ΔC(0).

[0039] Figure 5 shows an example of the relationship between the estimated full charge capacity and the subtraction amount ΔC(0). The vertical axis in Figure 5 represents the subtraction amount ΔC(0). The horizontal axis in Figure 5 represents the estimated full charge capacity. As shown in Figure 5, the relationship between the estimated full charge capacity and the subtraction amount ΔC(0) is as follows: When the estimated full charge capacity is greater than P(0), S(1) is set as the subtraction amount ΔC(0). Furthermore, when the estimated full charge capacity is less than or equal to P(0) and within the range of P(1) or greater, the subtraction amount ΔC(0) is set to decrease from S(1) in proportion to the decrease in the estimated value. For example, when the estimated value is less than or equal to P(0) and P(2) is greater than or equal to P(1), the ECU300 sets S(2) from the map as the subtraction amount ΔC(0). Furthermore, when the estimated full charge capacity is less than P(1), zero is set as the subtraction amount ΔC(0).

[0040] The ECU300 sets the subtraction amount ΔC(0) based on the acquired estimated full charge capacity and the map shown in Figure 5. The process then moves to S104.

[0041] In S104, the ECU 300 obtains the usable SOC range (corresponding to the second 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 the 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.

[0042] In S106, the ECU300 subtracts the subtraction amount ΔC(0) from the usable SOC range. The process then moves to S108.

[0043] In S108, the ECU 300 calculates the display value of the full charge capacity. Specifically, the ECU 300 calculates the ratio of the value obtained by subtracting the subtraction amount ΔC(0) from the second SOC range to the second SOC range. That is, the ECU 300 calculates the ratio value by dividing the value obtained by subtracting the subtraction amount ΔC(0) from the usable SOC range by the usable SOC range. The ECU 300 calculates the display value of the full charge capacity (corrected value of the capacity retention rate) by multiplying the calculated ratio value by the current capacity retention rate value. The ECU 300 calculates the current capacity retention rate value by, for example, dividing the estimated value of the 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 ECU 300, 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.

[0044] In S110, the ECU300 displays the calculated full charge capacity value on the display device 350. The process then terminates.

[0045] 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.

[0046] When external charging of battery 100 begins, ECU 300 obtains an estimated value of the full charge capacity from monitoring unit 200 (S100). Then, using the obtained estimated value of the full charge capacity and the map shown in Figure 5, the subtraction amount ΔC(0) is obtained (S102). For example, if the estimated value of the full charge capacity is greater than P(0), S(1) is obtained from the map shown in Figure 5 as the subtraction amount ΔC(0). Subsequently, ECU 300 obtains the usable SOC range of battery 100 from memory 302 (S104) and subtracts the subtraction amount ΔC(0) from the usable SOC range (S106). The display value of the full charge capacity is calculated 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), and information indicating the calculated display value is displayed on the display device 350 (S110).

[0047] As described above, the display system S according to this embodiment calculates the display value of the full charge capacity using the ratio of the usable SOC range to the value obtained by subtracting the subtraction amount ΔC(0) from the usable SOC range, and the calculated display value is displayed on the display device 350, thereby enabling a highly accurate display of the full charge capacity of the battery 100. Therefore, a display system that displays the battery capacity with high accuracy can be provided.

[0048] Furthermore, the ECU300 sets S(1) as the subtraction amount ΔC(0) when the estimated full charge capacity is greater than P(0). Also, when the estimated full charge capacity is less than or equal to P(0) and greater than or equal to P(1), the ECU300 sets the subtraction amount ΔC(0) to a value that increases proportionally to the increase in the estimated value. Furthermore, when the estimated full charge capacity is less than P(0), the ECU300 sets zero as the subtraction amount ΔC(0). In this way, when the estimated full charge capacity is greater than P(0), the SOC range corresponding to the dead zone is set as the subtraction amount ΔC(0), allowing for a highly accurate display of the full charge capacity of battery 100.

[0049] The following describes some variations. In the above-described embodiment, the SOC range corresponding to the dead zone was set as the subtraction amount ΔC(0), and the ratio to the usable SOC range was 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.

[0050] Furthermore, although the above-described embodiment explains that the subtraction amount ΔC(0) is calculated using an estimated value of the full charge capacity and the map shown in Figure 4, the map used to calculate the subtraction amount ΔC(0) is not particularly limited to the map shown in Figure 4. For example, the map shown in Figure 4 may be set so that the subtraction amount ΔC(0) decreases monotonically in a linear or nonlinear manner from the upper limit to the lower limit of the estimated value (the subtraction amount ΔC(0) decreases as the estimated value decreases). Alternatively, the size of the SOC range corresponding to the dead zone may be set as the subtraction amount ΔC(0) regardless of the change in the estimated value.

[0051] Furthermore, in the above-described embodiment, the SOC range corresponding to the voltage range indicating the detection error of the voltage sensor 210 was described as being set as the dead zone SOC range. However, the SOC range may be set as the dead zone SOC range by adding a certain margin to the upper or lower limit of the SOC range corresponding to the voltage range indicating the detection error.

[0052] Furthermore, in the above embodiment, we described an example where a state where the SOC is 95% is set as the fully charged state, but the SOC corresponding to the fully charged state is not limited to 95%.

[0053] 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]

[0054] 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 a subtraction amount using a first SOC range corresponding to the dead zone based on the SOC (State of Charge) set as the fully charged state, and subtracts the subtraction amount from the usable second 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 second SOC range to the second SOC range.

2. The display system according to claim 1, wherein the control device sets the subtraction amount corresponding to the first SOC range when the estimated value of the full charge capacity is greater than a first value, sets the subtraction amount to a value that decreases in proportion to the decrease in the estimated value when the estimated value is less than or equal to the first value and greater than a second value, and sets the subtraction amount to zero when the estimated value is less than a second value.

3. The display system according to claim 1 or 2, wherein the control device calculates the subtraction amount using the SOC range that decreases due to the expansion of the single cell in addition to the first SOC range.

Images