Electric vehicles

Abstract

This invention provides an electric vehicle that can calculate the allowable charging current according to the error contained in the estimated full charge capacity, thereby suppressing the prolongation of charging time. [Solution] The electric vehicle 1 comprises a battery 45 mounted on the electric vehicle 1, a charger 60 that charges the battery 45 with power supplied from an externally provided charging station 80, and a control unit 20. The control unit 20 estimates the fully charged capacity Ces of the battery 45 based on electrical characteristic information acquired between the first SOC at the start of charging and the second SOC at the completion of charging. The control unit 20 sets the allowable charging current Ia for the battery 45 based on the estimation error α1 of the fully charged capacity Ces corresponding to the charging interval CS from the first SOC to the second SOC, and the estimated SOH calculated from the fully charged capacity Ces.

Description

Technical Field

[0001] The present disclosure relates to an electric vehicle.

Background Art

[0002] When a deteriorated battery is charged with a charging current that does not change to a healthy battery, it is known that the battery characteristics deteriorate rapidly. Japanese Unexamined Patent Application Publication No. 2008-252960 (Patent Document 1) discloses an electric vehicle equipped with a charging system that calculates the SOH (State Of Health) indicating the degree of battery deterioration and reduces the charging current according to the decrease in SOH. Here, the SOH is calculated based on the initial full charge capacity and the actual full charge capacity. Here, it is difficult to directly obtain the actual full charge capacity of the battery. Therefore, in calculating the SOH, an estimated full charge capacity is used instead of the actual full charge capacity.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The estimated full charge capacity used by the electric vehicle disclosed in Japanese Unexamined Patent Application Publication No. 2008-252960 for SOH calculation includes an error with respect to the actual full charge capacity. Due to the estimation error, an estimated full charge capacity larger than the actual full charge capacity can be derived. In that case, the estimated SOH calculated from the estimated full charge capacity becomes higher than the actual SOH calculated from the actual full charge capacity. As a result, it is considered that the battery is charged with a charging current exceeding the upper limit at which the battery characteristics do not deteriorate, and the deterioration of the battery is promoted. To avoid this, the charging current is set on the safe side in consideration of the error included in the estimated full charge capacity. However, since the charging current is set overly on the safe side, the charging time has been prolonged.

[0005] This disclosure is made to solve the above-mentioned problems, and its purpose is to provide an electric vehicle that can calculate an allowable charging current according to the error contained in the estimated full charge capacity and suppress the prolongation of charging time. [Means for solving the problem]

[0006] The electric vehicle relating to the first aspect of this disclosure comprises a battery mounted on the electric vehicle, a charger that charges the battery with power supplied from an externally provided charging station, and a control unit. The control unit estimates the fully charged capacity of the battery based on electrical characteristic information acquired between the first State of Charge (SOC) at the start of charging and the second State of Charge (SOC) at the completion of charging. The control unit sets the allowable charging current to the battery based on the estimation error corresponding to the charging intervals from the first SOC to the second SOC and the estimated State of Health (SOH) calculated from the fully charged capacity.

[0007] The electrical characteristic information for an electric vehicle relating to the first aspect of this disclosure includes the open-circuit voltage at the start of charging and the integrated value of the open-circuit voltage and charging current at the end of charging.

[0008] The estimation error in the electric vehicle relating to the first aspect of this disclosure is the maximum value of the acquisition error of the multiple full-charge estimated capacity acquired in each charging section. [Effects of the Invention]

[0009] According to the electric vehicle described herein, it is possible to calculate the allowable charging current according to the error contained in the estimated full charge capacity, thereby suppressing the prolongation of charging time. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram of an electric vehicle according to an embodiment of the present disclosure. [Figure 2] This is a control flow diagram of an electric vehicle according to an embodiment of the present disclosure. [Figure 3] This is a table showing the estimated error corresponding to the charging section according to the embodiment of this disclosure. [Figure 4]The graphs showing the charging interval and acquisition error according to the embodiment of this disclosure are shown. [Figure 5] The graph shows the estimated SOH and the corrected value β according to the embodiment of this disclosure. [Modes for carrying out the invention]

[0011] 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. <Overall 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.

[0012] The electric vehicle 1 is, for example, an electric car. The electric vehicle 1 comprises a motor generator (MG) 11, which is a rotating electric machine, drive wheels 12, a power control unit (PCU) 13, a system main relay (SMR) 14, an ECU 20, a battery pack 40, a monitoring unit 50, a charger 60, and an inlet 70. The ECU 20 is communicatively connected to the PCU 13, the SMR 14, the monitoring unit 50, and the charger 60.

[0013] 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.

[0014] 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.

[0015] The PCU13 is a power conversion device that converts power bidirectionally between the MG11 and the battery pack 40. The PCU13 includes, for example, an inverter and a converter that operate based on a control signal from the ECU20. When the battery pack 40 is discharged, the converter boosts the voltage supplied from the battery pack 40 and supplies it to the inverter. The inverter converts the DC power supplied from the converter into AC power to drive the MG11. Note that the PCU13 may also be configured without the converter.

[0016] The SMR14 is electrically connected to the power line connecting the battery pack 40 and the PCU 13. When the SMR14 is closed (ON) (i.e., conducting) in response to a control signal from the ECU 20, power can be exchanged between the battery pack 40 and the PCU 13. On the other hand, when the SMR14 is open (OFF) (i.e., disconnected) in response to a control signal from the ECU 20, the electrical connection between the battery pack 40 and the PCU 13 is disconnected.

[0017] The ECU 20 includes a processor 21, memory 22, and storage 23. The processor 21 is an arithmetic unit such as a CPU (Central Processing Unit) or MPU (Micro-Processing Unit). The memory 22 is volatile memory (working memory) such as RAM (Random Access Memory). The storage 23 is rewritable non-volatile memory such as flash memory. The storage 23 stores a system program including an OS (Operating System) and a control program including computer-readable code necessary for control calculations. The processor 21 performs various processes by reading the system program and the control program, loading them into memory 22, and executing them. The ECU 20 may be divided into multiple ECUs according to function. Note that the ECU 20 is an example of a "control device" in this disclosure.

[0018] The battery pack 40 is mounted on the electric vehicle 1. The battery pack 40 has a plurality of power storage cells 45. The plurality of power storage cells 45 are electrically connected in series. The power storage cell 45 is a secondary battery such as a nickel-hydrogen battery or a lithium-ion battery. The secondary battery is, for example, a battery having a liquid electrolyte between a positive electrode and a negative electrode. Note that the power storage cell 45 is an example of the "battery" of the present disclosure.

[0019] The monitoring unit 50 has various sensors for detecting the states (for example, temperature, current, and voltage) of the battery pack 40 and each of the plurality of power storage cells 45. The monitoring unit 50 functions also as a BMS (Battery Management System) having a function of acquiring the OCV (Open Circuit Voltage) of each of the plurality of power storage cells 45, a SOC function of estimating the SOC (State Of Charge) of each of the plurality of power storage cells 45, a SOH estimation function of estimating the SOH (State of Health) of each of the plurality of power storage cells 45, and a communication function. The monitoring unit 50 outputs the detection result to the ECU 20.

[0020] The charger 60 converts the power supplied from the power source 80 via the charging cable and the inlet 70 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 60 includes, for example, an inverter and a converter (both not shown).

[0021] The inlet 70 is configured to be able to connect a charging cable. The inlet 70 receives power supply from a power source 80 provided outside the electric vehicle 1 via the charging cable. The power source 80 is, for example, a charging stand. <Control flow of electric vehicle> Next, the control flow of the electric vehicle 1 will be described with reference to FIG. 2.

[0022] In step S10 shown in Figure 2, the ECU 20 checks whether the power plug of the charging station is connected to the inlet 70. If it is connected (Yes in step S10), the ECU 20 proceeds to step S15. If it is not connected (No in step S10), the ECU 20 processes step S10 again.

[0023] In step S15, the ECU 20 starts charging the battery pack 40 with power supplied from the power supply 80 via the charger 60. The ECU 20 then proceeds to step S20.

[0024] In step S20, the ECU20 obtains the first SOC at the start of charging and the OCV1, which is the open-circuit voltage at the start of charging, from the monitoring unit 50. The ECU20 stores the obtained information on the first SOC and OCV1 in the storage 23. After that, the processing of the ECU20 proceeds to step S25.

[0025] In step S25, the ECU 20 performs a charging current integration process to integrate the charging current of the battery pack 40 detected at predetermined time intervals obtained from the monitoring unit 50 while the battery pack 40 is charging. The ECU 20 continues the charging current integration process until charging is completed (Yes in step S30). The ECU 20 then terminates the charging current integration process and stores the information of the integrated value of the charging current obtained by the charging current integration process in the storage 23.

[0026] In step S30, the ECU20 checks if charging is complete. If charging is complete (Yes in step S30), the ECU20 proceeds to step S35. If charging is not complete (No in step S30), the ECU20 processes step S25 again.

[0027] In step S35, the ECU 20 obtains the second SOC at the end of charging and the OCV2, which is the open-circuit voltage at the end of charging, from the monitoring unit 50. The ECU 20 stores the obtained information on the second SOC and OCV2 in the storage 23. After that, the processing of the ECU 20 proceeds to step S40.

[0028] In step S40, the ECU20 calculates the charging interval CS. The charging interval CS is the difference between the second state of charge (SOC) and the first state of charge (SOC). After that, the ECU20 proceeds to step S45.

[0029] In step S45, the ECU 20 obtains an estimated error α1 based on the charging interval CS. The ECU 20 then proceeds to step S50. The estimated error α1 is obtained from the charging interval CS-estimated error α1 table shown in Figure 3, which is pre-stored in the ECU 20's storage 33. The charging interval CS-estimated error α1 table shows the correspondence between the charging interval CS and the estimated error α1. The charging interval CS-estimated error α1 table is derived, for example, from experimentally obtained charging intervals CS and the obtained error α.

[0030] Figure 4 shows a graph plotting the acquisition error α experimentally obtained for each charging section CS. The acquisition error α is calculated using equation (1).

[0031] α = (Ces / Cac-1) × 100 ... (1) The acquisition error α[%] is calculated from the estimated full charge capacity Ces[mAh] and the actual full charge capacity Cac[mAh]. The estimated full charge capacity Ces is the full charge capacity estimated from the open-circuit voltage at the start of charging, the open-circuit voltage at the end of charging, and the integrated value of the charging current, for example, using a known OCV-SOC graph. The actual full charge capacity Cac is the actual full charge capacity of the battery.

[0032] In Figure 4, the smaller the charging interval CS, the greater the variability in the acquisition error α. In other words, the estimated full-charge capacity Ces derived in the region of small charging interval CS deviates significantly from the actual full-charge capacity Caac. In particular, when the acquisition error α is a positive value, the battery is evaluated as healthy relative to the actual battery's SOH. The estimated error α1 is the maximum value of the acquisition error α for each charging interval CS in Figure 4. Figure 3 shows the charging interval CS-estimated error α1 table, which summarizes the estimated error α1, which is the maximum value of the acquisition error α for each charging interval CS.

[0033] Referring again to Figure 2, in step S50, the ECU 20 calculates the estimated full charge capacity Ces and the estimated SOH. After that, the ECU 20 proceeds to step S55. The estimated full charge capacity Ces may be derived, for example, based on the information of the SOC-OCV graph and electrical characteristic information pre-stored in storage 23. The electrical characteristic information is, for example, the integrated value of OCV1, OCV2, and charging current obtained in the previous step.

[0034] The estimated SOH is calculated using equation (2). Estimated SOH=Ces / Co×100 (2) The estimated State of Health (SOH) [%] is calculated from the estimated full charge capacity Ces [mAh] and the initial full charge capacity Co [mAh]. The initial full charge capacity Co is the full charge capacity when no battery degradation has occurred.

[0035] In step S55, the correction value β is calculated from the estimated error α1 and the estimated SOH. After that, the ECU20 proceeds to step S60. When the relationship between the estimated SOH and the correction value β when the estimated error α1 is not considered (estimated error α1=0) is given by equation (3), the relationship between the estimated SOH and the correction value β according to the estimated error α1 when α1 is considered (estimated error α1≠0) is calculated by equation (4).

[0036] β = Estimated SOH (α1=0)···(3) β = estimated SOH - α1 / 100 (α1≠0)···(4) The correction value β[%] is calculated from the estimated SOH[%] and the estimated error α1[%]. Equation (4) is derived based on a previously obtained graph of the correction value β when the estimated error α1=0. Figure 5 shows the graphs of equation (4) corresponding to each estimated error α1. Figure 5 shows the graphs for calculating β when the estimated errors α1=0, 2, 3, 5, and 6. The graph for estimated error α1=0 represents the case where there is no estimated error or the error is not considered. The graph for estimated error α1=5 is offset so that β is smaller compared to the case where the estimated error α1=0. The graph for estimated error α1=2 shows a reduced offset amount compared to the case where the estimated error α1=5.

[0037] In step S60, the allowable charging current Ia is calculated from the initial charging current Io and the correction value β. After that, the ECU 20 terminates the charging control processing for the battery pack 40. The allowable charging current Ia is calculated using equation (5).

[0038] Ia = Io × β / 100 ... (5) The allowable charging current Ia [A] is calculated from the initial charging current Io [A] and the correction value β [%]. The initial charging current Io is the maximum charging current at which the battery performance does not deteriorate when the SOH of the energy storage cell 45 is 100% (α=0).

[0039] Referring to Figure 5, in the embodiment of this disclosure, the ECU 20 calculates the allowable charging current Ia according to the estimated error α1. As a result, the allowable charging current Ia is set to the safe side (so that the charging current is smaller) compared to when the estimated error α1 is not considered (when the estimated error α1 = 0). More specifically, for example, if the initial charging current Io is 1A and the estimated SOH is 80%, the allowable charging current Ia when the estimated error α1 is not considered (when the estimated error α1 = 0) is 0.8A, and the allowable charging current Ia when the estimated error α1 = 5 is 0.75A. As a result, the allowable charging current Ia is set to the safe side by 0.05A.

[0040] In the embodiments of this disclosure, the estimation error α1 is set for each charging interval CS. The larger the charging interval CS, the closer the estimated SOH is to the actual SOH and the more reliable it is, and the smaller the estimation error α1 is set. That is, by considering the estimation error α1 according to the charging interval CS, the ECU 20 can set the allowable charging current Ia to a large value. As a result, the ECU 20 can suppress the prolongation of charging time.

[0041] In the embodiments of this disclosure, the estimated error α1 is the maximum value of the acquisition error α experimentally obtained in each charging interval CS shown in Figure 3, but this disclosure is not limited thereto. For example, in each charging interval CS, the estimated error α1 may be the value obtained by adding the standard deviation σ to the average acquisition error αave of the acquisition error α.

[0042] 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]

[0043] 1 Electric vehicle, 11 MG, 12 Drive wheels, 20 Control unit, 21 Processor, 22 Memory, 23 Storage, 33 Storage, 40 Battery pack, 45 Energy storage cell, 50 Monitoring unit, 60 Charger, 70 Inlet, 80 Power supply, Cac Actual capacity at full charge, Ces Estimated capacity at full charge, Co Initial capacity at full charge, CS Charging interval, Ia Allowable charging current, Io Initial charging current, α Acquisition error, α1 Estimated error, αave Average acquisition error, β Correction value.

Claims

1. The battery installed in the electric vehicle, A charger that charges the battery using power supplied from an externally located charging station, It includes a control unit, The control unit estimates the fully charged capacity of the battery based on the electrical characteristic information acquired between the first State of Charge (SOC) at the start of charging and the second State of Charge (SOC) at the completion of charging. The control unit sets the allowable charging current to the battery based on the estimation error corresponding to the charging interval up to the first SOC and the second SOC, and the estimated SOH calculated from the estimated full charge capacity, in an electric vehicle.

2. The electric vehicle according to claim 1, wherein the electrical characteristic information includes the open-circuit voltage at the start of charging, the open-circuit voltage at the end of charging, and the integrated value of the charging current.

3. The electric vehicle according to claim 1, wherein the estimation error is the maximum value of the acquisition error of the multiple full charge estimated capacity acquired in each charging section.

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