Electric vehicles

Abstract

To provide an electric vehicle that can reduce the discrepancy between the driving range expected by the user and the actual driving range that is possible. [Solution] The electric vehicle 1 comprises batteries 50 and 51 mounted on the electric vehicle 1 and a control unit 20. The control unit 20 stores information on the full charge capacity ΔC0 and the SOH correction value ΔSOHcv of the batteries 50 and 51, and estimates the fully charged capacity ΔC1 based on the battery characteristic information of the batteries 50 and 51. The full charge capacity ΔC0 is the difference between the capacity of the batteries 50 and 51 when the SOC is 100% and the capacity when the SOC is at the lower limit SOC in the initial state. The fully charged capacity ΔC1 is the difference between the capacity of the batteries 50 and 51 when the SOC is 100% and the capacity when the SOC is at the lower limit SOC after degradation of the batteries 50 and 51. The control unit 20 calculates the SOH by dividing the fully charged capacity ΔC1 by the full charge capacity ΔC0, and corrects the SOH using the SOH correction value ΔSOHcv to calculate the actual SOH.

Description

Technical Field

[0001] The present disclosure relates to electric vehicles. Background Art

[0002] Various methods have been proposed for estimating SOH (State of Health), which indicates the degree of deterioration of a battery mounted on a vehicle. The vehicle estimates the distance that the vehicle can travel based on the value of SOH by using the battery when charging is completed. For example, Japanese National Publication of International Patent Application No. 2016-530573 (Patent Document 1) discloses a method for calculating SOH from the ratio of battery capacity at the completion of charging before and after deterioration. The battery capacity is calculated from, for example, the open circuit voltage before the start of plug-in charging, the open circuit voltage after the end of plug-in charging, and the integrated value of current flowing between the start of plug-in charging and the end of plug-in charging. Prior Art Documents Patent Documents

[0003] Patent Document 1 Japanese National Publication of International Patent Application No. 2016-530573 Summary of the Invention Problems to be Solved by the Invention

[0004] In order to avoid battery deterioration, a battery mounted on a vehicle is operated to avoid over-discharging. Accordingly, when the battery reaches the discharge end voltage, the vehicle stops traveling even if the battery capacity has not reached the lower limit of use. Particularly, a deteriorated battery is more affected by voltage drop due to polarization than a battery before deterioration.

[0005] A user expects that a fully charged vehicle can travel a distance corresponding to the SOH. On the other hand, due to the influence of polarization occurring during traveling, the vehicle cannot always travel the travelable distance corresponding to the SOH. This is for avoiding battery deterioration. That is, a deviation occurs between the travelable distance expected by the user and the actually possible travel distance.

[0006] This disclosure was made to solve the above-mentioned problems, and its purpose is to provide an electric vehicle that can suppress the discrepancy between the driving range expected by the user and the driving range that is actually possible. [Means for solving the problem]

[0007] The electric vehicle according to the first aspect of this disclosure comprises a battery mounted on the electric vehicle and a control unit. The control unit stores information on the battery's full charge capacity and SOH correction value, and estimates the full charge capacity based on the battery's battery characteristic information. The full charge capacity is the difference between the capacity when the SOC is 100% and the capacity when the SOC is at the lower limit SOC in the initial state of the battery. The degraded capacity is the difference between the capacity when the SOC is 100% and the capacity when the SOC is at the lower limit SOC after the battery has degraded. The control unit calculates the SOH by dividing the degraded capacity by the full charge capacity, and then corrects the SOH using the SOH correction value to calculate the actual SOH.

[0008] The control unit of the electric vehicle relating to the first aspect of this disclosure may store information of a SOH correction map. The SOH correction map may show the relationship between SOH and SOH correction value. The control unit may determine the SOH correction value from the information of the SOH correction map.

[0009] The battery characteristic information of the electric vehicle relating to the first aspect of this disclosure may include current information and voltage information. The control unit may store SOH correction map information. The SOH correction map may show the relationship between internal resistance and SOH correction value. Internal resistance may be calculated based on the slope of a data set plotted with current information and voltage information. The control unit may determine the SOH correction value from the information in the SOH correction map.

[0010] The electric vehicle relating to the second aspect of this disclosure comprises a battery mounted on the electric vehicle and a control unit. The control unit stores information on the battery's full charge capacity and capacity correction value, and estimates the full charge capacity based on the battery's battery characteristic information. The full charge capacity is the difference between the capacity when the SOC is 100% and the capacity when the SOC is at the lower limit SOC in the initial state of the battery, or the difference between the capacity when the SOC is 100% and the capacity when the terminal voltage of the battery reaches the lower limit voltage. The final charge capacity is the difference between the capacity when the SOC is 100% and the capacity when the SOC is at the lower limit SOC after the battery has deteriorated. The control unit calculates the corrected capacity by correcting the final charge capacity with a capacity correction value, and calculates the actual SOH by dividing the corrected capacity by the full charge capacity.

[0011] The control unit of the electric vehicle relating to the second aspect of this disclosure may store information of a capacity correction map. The capacity correction map may show the relationship between the fully charged capacity and the capacity correction value. The control unit may determine the capacity correction value from the information of the capacity correction map.

[0012] The control unit of the electric vehicle relating to the second aspect of this disclosure may store known information showing the relationship between the open-circuit voltage of the battery and the state of charge (SOC). The battery characteristic information may include information on the open-circuit voltage and information on the integrated current value. The control unit may estimate the fully charged capacity based on the known information and the battery characteristic information. [Effects of the Invention]

[0013] According to this disclosure, it is possible to provide an electric vehicle that can suppress the discrepancy between the driving range expected by the user and the actual driving range that is possible. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram of an electric vehicle according to an embodiment of the present disclosure. [Figure 2] This figure shows the time changes of the current, capacity, and terminal voltage of an electric vehicle according to an embodiment of this disclosure. [Figure 3] This is a flowchart of the actual SOH calculation control performed by an electric vehicle according to the embodiment of this disclosure. [Figure 4] This is a modified example of the actual SOH calculation control flow performed by an electric vehicle according to the embodiment of this disclosure. [Modes for carrying out the invention]

[0015] 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. <Outline configuration of electric vehicles> Figure 1 is a diagram showing a schematic configuration of an electric vehicle according to an embodiment of the present disclosure. The electric vehicle 1 is, for example, an electric automobile. The electric vehicle 1 comprises a motor generator (MG) 11, drive wheels 12, a power control unit (PCU) 13, a system main relay (SMR) 14, an ECU 20, a battery pack 40, a charger 70, and an inlet 80. The ECU 20 is communicatively connected to the PCU 13, the SMR 14, the battery pack 40, and the charger 70.

[0016] MG11 is, for example, an embedded permanent magnet synchronous motor (IPM motor) that has both the function of an electric motor and a generator. The output torque of MG11 is transmitted to the drive wheels 12 via a power transmission system that includes a reduction gear and a differential gear.

[0017] When the electric vehicle 1 is braked, the MG11 is driven by the drive wheels 12, and the MG11 operates as a generator. In this way, the MG11 also functions as a braking device that performs regenerative braking, converting the kinetic energy of the electric vehicle 1 into electrical power. The regenerative power generated by the regenerative braking force in the MG11 is stored in the battery pack 40.

[0018] PCU 13 is a power conversion device that bidirectionally converts power between MG 11 and battery pack 40. PCU 13 includes, for example, an inverter and a converter that operate based on a control signal from ECU 20. When the battery pack 40 is discharging, the converter boosts the voltage supplied from the battery pack 40 and supplies the boosted voltage to the inverter. The inverter converts DC power supplied from the converter into AC power to drive MG 11. Note that PCU 13 may have a configuration in which the converter is omitted.

[0019] SMR 14 is electrically connected to a power line connecting battery pack 40 and PCU 13. When SMR 14 is closed (ON) in response to a control signal from ECU 20 (that is, in a conductive state), power can be transmitted and received between battery pack 40 and PCU 13. On the other hand, when SMR 14 is opened (OFF) in response to a control signal from ECU 20 (that is, in a disconnected state), the electrical connection between battery pack 40 and PCU 13 is disconnected.

[0020] ECU 20 includes a processor 21, a memory 22, and a storage 23. The processor 21 is an arithmetic device such as a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The memory 22 is a volatile memory (working memory) such as a RAM (Random Access Memory). The storage 23 is a rewritable non-volatile memory such as a flash memory. A system program including an OS (Operating System) and a control program including computer-readable code required for control calculation are stored in the storage 23. The processor 21 implements various processes by reading the system program and the control program, developing the programs in the memory 22, and executing the programs. The ECU 20 stores voltage information and current information acquired from a monitoring unit 60, which will be described later, together with time information. The ECU 20 may be divided into a plurality of ECUs each corresponding to one function. Note that the ECU 20 is an example of the "control unit" in the present disclosure.

[0021] A battery pack 40 is mounted on an electric vehicle 1. The battery pack 40 includes an assembled battery 50 and a monitoring unit 60. The assembled battery 50 includes a plurality of power storage cells 51. The plurality of power storage cells 51 are electrically connected in series. The power storage cell 51 is a secondary battery such as a nickel-hydrogen battery or a lithium-ion battery. Each of the assembled battery 50 and the power storage cell 51 is an example of the "battery" in the present disclosure.

[0022] The monitoring unit 60 includes various sensors that detect the states (e.g., temperature, current, and voltage) of the assembled battery 50 and each of the plurality of power storage cells 51. The monitoring unit 60 has a function of acquiring the temperature of each of the assembled battery 50 and the plurality of power storage cells 51 (hereinafter referred to as a temperature acquisition function). The monitoring unit 60 has a function of acquiring the current flowing through each of the assembled battery 50 and the plurality of power storage cells 51 (hereinafter referred to as a current acquisition function). The monitoring unit 60 has a function of acquiring the OCV (Open Circuit Voltage) of each of the assembled battery 50 and the plurality of power storage cells 51 (hereinafter referred to as an OCV acquisition function). The monitoring unit 60 has a function of estimating the SOC (State Of Charge) of each of the assembled battery 50 and the plurality of power storage cells 51 (hereinafter referred to as an SOC acquisition function). The monitoring unit 60 has a function of estimating the SOH (State of Health) of each of the assembled battery 50 and the plurality of power storage cells 51 (hereinafter referred to as an SOH acquisition function). The monitoring unit 60 has a function of communicating with the ECU 20. That is, the monitoring unit 60 functions as a BMS (Battery Management System). The monitoring unit 60 outputs detection results to the ECU 20.

[0023] A charger 70 converts power supplied from a power source 90 via a charging cable and an inlet 80 into power suitable for charging the battery pack 40 according to a control signal from the ECU 20, and charges the battery pack 40. The charger 70 is configured to include, for example, an inverter and a converter (neither of which is shown).

[0024] The inlet 80 is configured to accept a charging cable. The inlet 80 receives power from a power source 90 located outside the electric vehicle 1 via the charging cable. The power source 90 is, for example, a charging station.

[0025] Electric vehicles with this configuration can have their actual State of Health (SOH) calculated. Actual SOH is the SOH calculated considering the usable capacity during actual operation. <Method for calculating actual SOH (State of Health)> The method for calculating the actual SOH will be explained using Figure 2. Figure 2 shows the time progression of the capacity C and terminal voltage V of the energy storage cell 51 when the electric vehicle 1 is driven in an arbitrary pattern. In Figure 2, the initial battery B0 shows the energy storage cell 51 before degradation, and the degraded battery B1 shows the energy storage cell 51 that has degraded due to use compared to the initial battery B0.

[0026] Referring to Figure 2(1), the initial battery B0 installed in the electric vehicle 1 discharges a current I during operation. Similarly, the degraded battery B1 installed in the electric vehicle 1 discharges a current I during operation. The current I fluctuates with time t.

[0027] Referring to Figure 2(2), the electric vehicle 1 is configured to output power from the initial battery B0 from full capacity C0full to the lower limit capacity CMinn. Full capacity C0full is the capacity C of the initial battery B0 when the State of Charge (SOC) is 100%. Lower limit capacity CMinn is the capacity C of the battery when the SOC is at the lower limit SOC. The lower limit capacity CMinn is set to avoid battery degradation and protect the vehicle. The difference between the capacity C of the initial battery B0 when the SOC is 100% and the capacity C when the SOC is at the lower limit SOC is called the full charge capacity ΔC0. In other words, the full charge capacity ΔC0 is the difference between full capacity C0full and the lower limit capacity CMinn.

[0028] Similarly, the electric vehicle 1 is configured to output power from the degraded battery B1 from its full capacity C1 to its lower limit capacity CMinn. The full capacity C1 is the capacity C of the degraded battery B1 when its State of Charge (SOC) is 100%. The difference between the capacity C of the degraded battery B1 when its SOC is 100% and the capacity C when its SOC is at its lower limit is called the fully charged capacity ΔC1. In other words, the fully charged capacity ΔC1 is the difference between the full capacity C1 and the lower limit capacity CMinn.

[0029] Here, referring to Figure 2(3), the terminal voltage of the battery decreases due to the effect of polarization over time. When the terminal voltage reaches the lower limit voltage VMin, the battery protection function of the electric vehicle 1 is activated to prevent battery degradation. In Figure 2(3), due to the action of the battery protection function, the electric vehicle 1 limits the output of current I before the degraded battery B1 reaches the lower limit SOC.

[0030] More specifically, referring to Figure 2(1), the degraded battery B1 mounted on the electric vehicle 1 discharges current I during operation. Referring to Figure 2(3), the terminal voltage V of the degraded battery B1 reaches the lower limit voltage VMin at time t1. Referring again to Figure 2(1), the electric vehicle 1 stops running at time t1, before the capacity C of the degraded battery B1 reaches the lower limit capacity CMin. Referring to Figure 2(2), the capacity C of the degraded battery B1 at time t1 when the operation is stopped is called the stop capacity C1end. The difference between the full capacity C1full and the stop capacity C1end is called the corrected capacity ΔC1'. The difference between the stop capacity C1end and the lower limit capacity CMin is called the capacity correction value ΔCcv. In other words, the corrected capacity ΔC1' is expressed as the difference between the fully charged capacity ΔC1 and the capacity correction value ΔCcv.

[0031] Note that the full charge capacity ΔC0 may be the difference between the capacity C of the initial battery B0 when its SOC is 100% and the capacity C of the initial battery B0 when its terminal voltage reaches the lower limit. This is because, when the electric vehicle 1 equipped with the initial battery B0 is running, the terminal voltage of the initial battery B0 may reach the lower limit voltage VMin before the initial battery B0 reaches the lower limit SOC, i.e., before time t3.

[0032] Conventional SOH is calculated using equation (1). SOH[-]=ΔC1 / ΔC0 ···(1) The actual SOH, which takes into account the usable capacity, is calculated using one of the following equations: (2) to (5).

[0033] Actual SOH[-] = ΔC1' / ΔC0 ···(2) =(ΔC1-ΔCcv) / ΔC0 ···(3) =ΔC1 / ΔC0-ΔCcv / ΔC0 (4) =SOH-ΔSOHcv ···(5) Information on the full charge capacity ΔC0, the capacity correction value ΔCcv, and the SOH correction value ΔSOHcv is pre-stored in the ECU20. The SOH correction value ΔSOHcv is a correction value used to calculate the actual SOH from the SOH. The ECU20 estimates the full charge capacity ΔC1 based on the battery characteristic information of the energy storage cell 51, for example, by a known method disclosed in Patent Document 1. More specifically, the battery characteristic information includes at least one piece of information obtained by the ECU20 through the monitoring unit 60, such as the temperature information of the battery pack 50 and the multiple energy storage cells 51, the integrated current value information, and the open-circuit voltage information. The ECU20 stores known information showing the relationship between the open-circuit voltage of the energy storage cell 51 and the SOC. The ECU20 estimates the full charge capacity ΔC1 based on the known information and the battery characteristic information.

[0034] According to equation (3), the ECU 20 can calculate the corrected capacity ΔC1' by correcting the fully charged capacity ΔC1 with the capacity correction value ΔCcv, and then calculate the actual SOH by dividing the corrected capacity ΔC1' by the fully charged capacity ΔC0. The ECU 20 may store information from a capacity correction map. The capacity correction map is a lookup table that shows the relationship between the fully charged capacity ΔC1 and the capacity correction value ΔCcv. The ECU 20 may determine the capacity correction value ΔCcv based on the value of the fully charged capacity ΔC1 from the information in the capacity correction map.

[0035] According to equation (5), the ECU 20 can calculate the actual SOH by dividing the fully charged capacity ΔC1 by the maximum charged capacity ΔC0 and correcting the SOH with the SOH correction value ΔSOHcv. The ECU 20 may store information from an SOH correction map. The SOH correction map is a lookup table that shows the relationship between SOH and the SOH correction value ΔSOHcv. The ECU 20 may determine the SOH correction value ΔSOHcv from the information in the SOH correction map.

[0036] The SOH correction map, while illustrating an example showing the relationship between SOH and the SOH correction value ΔSOHcv, is not limited to this embodiment of the disclosure. The SOH correction map may also show the relationship between internal resistance and the SOH correction value ΔSOHcv. Battery characteristic information includes current information and voltage information, and internal resistance may be calculated based on the slope of the data set plotted from the current information and voltage information.

[0037] The actual State of Health (SOH) according to the embodiments of this disclosure is an index calculated by taking into account the effects of polarization generated during driving. Users expect that a fully charged vehicle can travel a distance corresponding to the SOH. On the other hand, due to the effects of polarization generated during driving, a vehicle may not be able to travel the distance corresponding to the SOH. An electric vehicle 1 that can calculate the driving distance based on the actual SOH can suppress the discrepancy between the driving distance expected by the user and the actually possible driving distance. <Actual SOH Calculation Control Flow for Electric Vehicles> Next, with reference to Figure 3, the actual SOH calculation control flow performed by the electric vehicle 1 will be described.

[0038] In step S11 shown in Figure 3, the ECU20 calculates the State of Health (SOH). The SOH is calculated using, for example, equation (1). After that, the ECU20 proceeds to step S12.

[0039] In step S12, the ECU20 determines the SOH correction value ΔSOHcv. For example, the ECU20 determines the SOH correction value ΔSOHcv based on information from an SOH correction map that shows the relationship between SOH and the SOH correction value ΔSOHcv. After that, the ECU20 proceeds to step S13.

[0040] In step S13, the ECU20 calculates the actual SOH. The actual SOH is calculated using, for example, equation (5). Note that the actual SOH is not limited to the difference between SOH and the SOH correction value ΔSOHcv. The actual SOH may also be calculated by multiplying SOH by the SOH correction value ΔSOHcv. After that, the ECU20 terminates the actual SOH calculation control flow.

[0041] Alternatively, the ECU20 may calculate the actual SOH based on the control flow shown in Figure 4. In step S21 shown in Figure 4, the ECU20 calculates the full charge capacity ΔC1. For example, the full charge capacity ΔC1 is calculated using battery characteristic information, including open-circuit voltage information and integrated current value information, based on known information showing the relationship between the open-circuit voltage and SOC. After that, the processing of the ECU20 proceeds to step S22.

[0042] In step S22, the ECU 20 determines the capacity correction value ΔCcv. For example, the ECU 20 determines the capacity correction value ΔCcv based on information from a capacity correction map that shows the relationship between the fully charged capacity ΔC1 and the capacity correction value ΔCcv. After that, the ECU 20 proceeds to step S23.

[0043] In step S23, the ECU20 calculates the actual SOH. The actual SOH is calculated based on the corrected capacity ΔC1' derived, for example, by equation (3). Note that the corrected capacity ΔC1' is not limited to the difference between the fully charged capacity ΔC1 and the capacity correction value ΔCcv. The corrected capacity ΔC1' may also be calculated by multiplying the fully charged capacity ΔC1 by the capacity correction value ΔCcv. After that, the ECU20 terminates the actual SOH calculation control flow.

[0044] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0045] 1 Electric vehicle, 11 MG, 12 Drive wheels, 20 ECU, 21 Processor, 22 Memory, 23 Storage, 40 Battery pack, 50 Battery set, 51 Energy cell, 60 Monitoring unit, 70 Charger, 80 Inlet, 90 Power supply, B0 Initial battery, B1 Degraded battery, C Capacity, C0full Full capacity, C1end Stop capacity, C1full Complete capacity, CMin Lower limit capacity, I Current, V Terminal voltage, VMin Lower limit voltage, ΔC0 Full charge capacity, ΔC1 Complete charge capacity, ΔC1' Corrected capacity, ΔCcv Capacity correction value, ΔSOHcv SOH correction value.

Claims

1. It comprises a battery mounted on an electric vehicle and a control unit, The control unit stores information on the full charge capacity of the battery and information on the SOH correction value, and estimates the full charge capacity based on the battery characteristic information of the battery. The full charge capacity is the difference between the capacity of the battery when the SOC is 100% and the capacity when the SOC is at the lower limit of SOC. The fully charged capacity is the difference between the capacity when the SOC is 100% and the capacity when the SOC is at the lower limit SOC after the battery has degraded. The control unit calculates the State of Health (SOH) by dividing the fully charged capacity by the maximum charge capacity, and corrects the SOH using the SOH correction value to calculate the actual SOH, in the electric vehicle.

2. The control unit stores information about the SOH correction map, The SOH correction map shows the relationship between the SOH and the SOH correction value. The electric vehicle according to claim 1, wherein the control unit determines the SOH correction value from the information of the SOH correction map.

3. The aforementioned battery characteristic information includes current information and voltage information, The control unit stores information about the SOH correction map, The SOH correction map shows the relationship between the internal resistance and the SOH correction value. The internal resistance is calculated based on the slope of the data set obtained by plotting the current information and the voltage information. The electric vehicle according to claim 1, wherein the control unit determines the SOH correction value from the information of the SOH correction map.

4. It comprises a battery mounted on an electric vehicle and a control unit, The control unit stores information on the full charge capacity of the battery and information on the capacity correction value, and estimates the fully charged capacity based on the battery characteristic information of the battery. The full charge capacity is the difference between the capacity of the battery when the SOC is 100% and the capacity when the SOC is at the lower limit SOC, or the difference between the capacity when the SOC is 100% and the capacity when the terminal voltage of the battery reaches the lower limit voltage. The fully charged capacity is the difference between the capacity when the SOC is 100% and the capacity when the SOC is at the lower limit SOC after the battery has degraded. The control unit calculates a corrected capacity by correcting the fully charged capacity with the capacity correction value, and calculates the actual State of Health (SOH) by dividing the corrected capacity by the fully charged capacity, in an electric vehicle.

5. The control unit stores information for the capacity correction map, The capacity correction map shows the relationship between the fully charged capacity and the capacity correction value. The electric vehicle according to claim 4, wherein the control unit determines the capacity correction value from the information in the capacity correction map.

6. The control unit stores known information indicating the relationship between the open-circuit voltage of the battery and the SOC. The aforementioned battery characteristic information includes information on the open-circuit voltage and information on the integrated current value. The electric vehicle according to claim 4, wherein the control unit estimates the fully charged capacity based on the known information and the battery characteristic information.

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