Charging system

Abstract

To properly shorten a charging time while suppressing deposition of lithium.SOLUTION: An ECU 40 controls external charging for charging a battery 20 using power supplied from a power facility 5 that is external to a vehicle 1. A memory 42 stores a plurality of maps each of which indicates correspondence between a prescribed parameter of the battery 20 and an electric current set value SV of the supplied power and is associated with a negative potential which is a potential of a negative electrode of the battery 20. The ECU 40 acquires a charging start negative potential which is a negative potential at the time of establishment of a charging start condition for starting external charging, selects a map associated with the charging start negative potential from among the plurality of maps, and controls the external charging in accordance with the set value SV corresponding to the parameter in the selected map.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a charging system. [Background technology]

[0002] Japanese Patent Application Laid-Open Publication No. 2022-147323 (Patent Document 1) discloses a charge control device. The charge control device is mounted on a vehicle capable of external charging (rapid charging), which charges an on-board power storage device using power supply (charging current) from power equipment external to the vehicle, and includes a calculation unit and a charge control unit. The calculation unit calculates a damage accumulation amount that indicates the amount of accumulated damage to the power storage device caused by rapid charging of the power storage device. The charge control unit permits rapid charging of the power storage device when the damage accumulation amount is less than a threshold, and when the damage accumulation amount is equal to or greater than the threshold, restricts rapid charging of the power storage device more than when the damage accumulation amount is less than the threshold. The damage accumulation amount is calculated after rapid charging begins, and increases the longer the period during which the charging current value, which is the current value of the power storage device during rapid charging, is greater than a predetermined value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-147323 Summary of the Invention [Problem to be solved by the invention]

[0004] Lithium ion secondary batteries can experience lithium deposition on the surface of their negative electrodes. Lithium deposition is likely to occur, for example, when the lithium ion secondary battery is charged at a high current (high rate), resulting in a decrease in the thermal stability of the battery.

[0005] Whether or not lithium deposition occurs depends not only on whether a large current is supplied to the power storage device during external charging, but also on the state of the power storage device at the start of external charging (charging history). Specifically, if the power storage device was overcharged until immediately before the start of external charging, lithium deposition is more likely to occur after the start of external charging than if charging of the power storage device was stopped for a long period of time from the start of external charging until immediately before the start of external charging. Patent Document 1 does not consider this point. Under the assumption that lithium deposition is always likely to occur after the start of external charging, lithium deposition can be suppressed by performing external charging while always limiting the magnitude of the current of the power supply. However, in this case, the charging current of the battery may be excessively limited, potentially prolonging external charging.

[0006] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to provide a charging system for appropriately shortening the charging time while suppressing lithium deposition. [Means for solving the problem]

[0007] A charging system according to the present disclosure includes a control device and a storage device. The control device controls external charging, which charges a lithium-ion battery using supply power from a power facility external to a vehicle equipped with the lithium-ion battery. The storage device stores a plurality of maps, each of which represents a correspondence relationship between a predetermined parameter of the lithium-ion battery and a set value of the current of the supply power and is associated with a negative electrode potential, which is the potential of the negative electrode of the lithium-ion battery. The control device acquires a charge start negative electrode potential, which is the negative electrode potential when a charge start condition for starting external charging is met, selects a map associated with the charge start negative electrode potential from the plurality of maps, and controls the external charging in accordance with a set value corresponding to the parameter in the selected map.

[0008] Lithium deposition occurs when the negative electrode potential falls below the reference potential. Therefore, when the negative electrode potential at the start of charging is low, lithium deposition is likely to occur after the start of external charging, whereas when the negative electrode potential at the start of charging is high, lithium deposition is unlikely to occur after the start of external charging. The negative electrode potential at the start of charging reflects the state (charging history) of the energy storage device before the start of external charging. Specifically, if the energy storage device was overcharged until immediately before the start of external charging, the negative electrode potential at the start of charging is relatively low. On the other hand, if charging of the energy storage device was stopped for a long period of time from the start of external charging until immediately before the start of external charging, the negative electrode potential at the start of charging is relatively high. By adopting the above configuration, the negative electrode potential at the start of charging is reflected in the set value. For example, when the negative electrode potential at the start of charging is low (when lithium deposition is likely to occur), the set value is set smaller than when the negative electrode potential at the start of charging is high, thereby limiting the magnitude of the current of the power supply. This limits the charging current of the energy storage device, reducing the number of electrons that enter the active material of the negative electrode and mitigating cathodic polarization of the negative electrode. As a result, the decrease in the negative electrode potential after the start of charging is suppressed, and lithium deposition can be effectively suppressed. On the other hand, when the negative electrode potential is high (lithium deposition is less likely to occur), the charging current is increased by setting a larger value than when the negative electrode potential is low. This prevents the charging current from being excessively limited, and the charging time can be shortened. As described above, with the above configuration, it is possible to appropriately shorten the charging time while effectively suppressing lithium deposition.

[0009] In one aspect, the parameters include the SOC and temperature of the lithium ion battery. In one aspect, the charge starting negative electrode potential includes first to Nth potentials. The i-th potential (2≦i≦N) is higher than the (i−1)th potential for each value of i. The multiple maps include first to Nth maps associated with the first to Nth potentials, respectively. For each value of i, the set value in the i-th map is equal to or higher than the set value in the (i−1)th map for the same SOC and temperature.

[0010] In one aspect, in each of the plurality of maps, the set value is determined so that the negative electrode potential is higher than a reference potential that is a potential at which lithium is deposited on the negative electrode.

[0011] In one aspect, the power facility is a DC power facility configured to supply DC power as feed power to the vehicle, and external charging is charging the lithium-ion battery using DC power from the DC power facility. [Effects of the Invention]

[0012] According to the present disclosure, it is possible to appropriately shorten the charging time while suppressing lithium deposition. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram schematically showing the overall configuration of a vehicle system according to an embodiment of the present invention; [Figure 2] FIG. 2 is a diagram showing in detail the hardware configuration of a vehicle and power equipment. [Figure 3] FIG. 2 is a diagram showing an example of changes over time in the positive electrode potential and the negative electrode potential of a battery during external charging. [Figure 4] FIG. 2 is a diagram for explaining a group of maps stored in an ECU (Electronic Control Unit). [Figure 5] FIG. 2 is a diagram showing an example of the change over time in the negative electrode potential of a battery during external charging. [Figure 6] 3 is a flowchart illustrating a process executed by an ECU. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts in the drawings will be denoted by the same reference numerals, and the description thereof will not be repeated. The embodiments and their modifications may be combined with each other as appropriate.

[0015] 1 is a diagram showing a schematic overall configuration of a vehicle system according to the present embodiment. Referring to FIG. 1, vehicle system 100 includes vehicle 1 and power equipment 5.

[0016] The vehicle 1 is an electric vehicle equipped with a battery 20, for example, an electric vehicle (BEV: Battery Electric Vehicle). The vehicle 1 may be another type of electric vehicle, such as a plug-in hybrid electric vehicle (PHEV). The vehicle 1 is electrically connected to an electric power facility 5 via a charging cable 6. The vehicle 1 is configured to perform external charging, in which the battery 20 is charged using power supplied from an electric power facility external to the vehicle 1, such as the electric power facility 5.

[0017] The power equipment 5 is provided outside the vehicle 1. The power equipment 5 is a DC power equipment configured to supply DC power as feed power to the battery 20 via a charging cable 6 during external charging. The above-described external charging using DC power is also referred to as "DC charging (rapid charging)." During DC charging, the battery 20 is charged with a large current.

[0018] 2 is a diagram showing in detail the hardware configuration of vehicle 1 and power equipment 5. Referring to FIG. 2, power equipment 5 includes an AC / DC converter 51, an HMI (Human Machine Interface) device 53, and a control circuit 55.

[0019] The AC / DC converter 51 converts AC power from the power grid (AC power supply) 7 into DC power. This DC power is used to charge the battery 20. The HMI device 53 receives various user operations from the user of the vehicle 1. The user operations include a charge start operation that instructs the start of external charging of the vehicle 1. The control circuit 55 detects the charge start operation, controls the AC / DC converter 51, and exchanges various information with the vehicle 1, for example, via CAN (Controller Area Network) communication.

[0020] The vehicle 1 includes an inlet 11, charging relays 131 and 132, a PCU (Power Control Unit) 16, and a motor 17. The vehicle 1 further includes a battery 20, SMRs (System Main Relays) 141 and 142, a voltage sensor 21, a current sensor 22, a temperature sensor 23, and an ECU 40.

[0021] Inlet 11 is configured to be connectable to a charging connector 61 of a charging cable 6. When charging connector 61 is connected to inlet 11, a signal indicating this (a PISW signal, not shown) is output from charging connector 61 through inlet 11 to ECU 40 (described later). Charging relay 131 is connected between charging line PL0 and power line PL1. Charging relay 132 is connected between charging line NL0 and power line NL1.

[0022] PCU 16 is electrically connected between power lines PL1, NL1 and motor 17. PCU 16 includes an inverter (not shown) and is capable of driving motor 17 by converting the output power of battery 20 into AC power. Motor 17 is, for example, a permanent magnet synchronous motor equipped with a rotor in which a permanent magnet is embedded, and is capable of receiving AC power from PCU 16 to generate driving force for vehicle 1 to run.

[0023] Battery 20 is a lithium-ion battery in which the reactant in its negative electrode is lithium. The positive electrode of battery 20 is electrically connected to power line PL1 via SMR 141. The negative electrode of battery 20 is electrically connected to power line NL1 via SMR 142. When battery 20 is charged, lithium ions are released from its positive electrode active material into the electrolyte. The lithium ions enter the negative electrode active material of battery 20 and combine with electrons entering from the positive electrode active material of battery 20 through an external circuit, becoming absorbed in the negative electrode active material. As a result, the negative electrode potential of battery 20 during charging decreases due to cathode polarization. When battery 20 is charged at a large current via DC charging, or when battery 20 was overcharged immediately before charging, lithium ions may concentrate on the negative electrode surface, resulting in a significant decrease in the potential of the negative electrode (negative electrode potential) of battery 20. In this case, the negative electrode potential may fall below the lithium reference potential (described below).

[0024] The voltage sensor 21, current sensor 22, and temperature sensor 23 respectively detect the voltage VB, current IB, and temperature TB of the battery 20. The detection results are output to the ECU 40.

[0025] The ECU 40 includes a CPU 41 and a memory (storage device) 42. The CPU 41 executes various types of arithmetic processing. The memory 42 includes a ROM 42A and a RAM 42B. The ROM 42A stores programs executed by the CPU 41 and various types of data. The various types of data include a map group (described later). The memory 42 may be included in the vehicle 1 as an external component of the ECU 40.

[0026] The ECU 40 estimates the SOC (State of Charge) and negative electrode potential of the battery 20 based on the voltage VB, the current IB, and the temperature TB. The SOC is estimated, for example, according to the integrated value of the current IB, according to the voltage VB using an SOC-OCV (Open Circuit Voltage) curve of the battery 20, or using a known model such as the Newman model. The negative electrode potential is estimated, for example, using the Newman model. The ECU 40 sequentially calculates the load on the motor 17 and stores the calculation results in the memory 42.

[0027] The ECU 40 is a control device that controls various devices of the vehicle 1, such as the charging relays 131 and 132, the SMRs 141 and 142, and the PCU 16. The ECU 40 can exchange various information with the control circuit 55 via CAN communication. This information includes a charging start signal CS and a set value SV. The charging start signal CS indicates that the above-mentioned charging start operation has been performed and is transmitted from the control circuit 55 to the ECU 40. The set value SV is a set value (command value) for the current of the supply power and is transmitted from the ECU 40 to the control circuit 55. In response to receiving the charging start signal CS, the ECU 40 turns on the charging relays 131 and 132 and the SMRs 141 and 142. This causes supply power from the power equipment 5 to be supplied to the battery 20, and external charging begins. During external charging, the ECU 40 transmits the set value SV to the control circuit 55, thereby controlling external charging (the magnitude of the current of the supply power). A specific method for determining the set value SV will be described in detail later.

[0028] The vehicle 1 may further include a measuring device that measures the negative electrode potential of the battery 20. This measuring device measures the negative electrode potential with respect to the potential of a reference electrode of the battery 20.

[0029] The battery 20, the voltage sensor 21, the current sensor 22, the temperature sensor 23, the charging relays 131 and 132, the SMRs 141 and 142, and the ECU 40 form an example of a "charging system" of the present disclosure.

[0030] 3 is a diagram showing an example of changes over time in the positive electrode potential and the negative electrode potential of battery 20 during external charging. Referring to FIG. 3, the horizontal axis represents the elapsed time from the start of external charging. The vertical axis represents the potential relative to the potential of lithium, which is a reactant in the negative electrode of battery 20 (lithium reference potential Vref).

[0031] The positive electrode potential Vp and the negative electrode potential Vn are the potentials of the positive electrode and the negative electrode of the battery 20 with respect to the lithium reference potential Vref, respectively. The voltage VB corresponds to the potential difference between the positive electrode potential Vp and the negative electrode potential Vn. During external charging, the positive electrode potential Vp increases while the negative electrode potential Vn decreases. As a result, the voltage VB increases.

[0032] When the negative electrode potential Vn falls below the lithium reference potential Vref, lithium precipitation occurs and lithium precipitates on the negative electrode of the battery 20. Therefore, when the negative electrode potential Vn is low, lithium precipitation is likely to occur after the start of external charging. On the other hand, when the negative electrode potential Vn is high, lithium precipitation is unlikely to occur after the start of external charging.

[0033] FIG. 4 is a diagram for explaining the map group stored in the ROM 42A. Referring to FIG. 4, the map group MP includes a plurality of maps mp(1), mp(2), ··· mp(N).

[0034] Each map is associated with a charging start negative electrode potential Vns. The charging start negative electrode potential Vns is the negative electrode potential Vn when the condition for starting external charging (hereinafter, also referred to as "charging start condition") is satisfied. In this example, the charging start negative electrode potential Vns includes V(1), V(2), ··· V(N). V(i) (2 ≤ i ≤ N) is higher than V(i - 1) for each value of i (V(1) < V(2) < ··· < V(N)). The maps mp(1), mp(2), ··· mp(N) are respectively associated with V(1), V(2), ··· V(N). The charging start negative electrode potential Vns reflects the state (charging history) of the battery 20 before the start of external charging. Specifically, when the battery 20 has been overcharged until immediately before the start of external charging, lithium ions are concentrated on the negative electrode surface, so the charging start negative electrode potential Vns is relatively low. On the other hand, when the charging of the battery 20 has been stopped from a long time before the start of external charging until immediately before the start of external charging, lithium ions are not concentrated on the negative electrode surface as described above, so the charging start negative electrode potential Vns is relatively high. The charging start condition is, for example, that the ECU 40 receives a charging start signal CS.

[0035] Each map represents the correspondence relationship between predetermined parameters (in this example, temperature TB and SOC) of battery 20 and set value SV. For example, when charge start negative electrode potential Vns is Vi, temperature TB is Tj, and SOC is Xk, set value SV is SV(i,j,k) (in one example, i=1). In each map, each set value SV is determined so that negative electrode potential Vn during external charging is higher than lithium reference potential Vref.

[0036] For each value of i, the setpoint SV in map mp(i) (2≦i≦N) is greater than or equal to the setpoint SV in map mp(i−1) for the same SOC and temperature TB. In other words, for each value of i, SV(i,j,k)≧SV(i−1,j,k) holds (SV(N,j,k)≧SV(N−1,j,k)≧...≧SV(2,j,k)≧SV(1,j,k)).

[0037] When the negative electrode potential Vn falls below the lithium reference potential Vref, lithium deposition occurs. Lithium deposition is likely to occur when a large current is input to the battery 20 due to DC charging.

[0038] Whether or not lithium deposition occurs depends not only on whether a large current is supplied to the battery 20 as a charging current during external charging, such as DC charging, but also on the state of the battery 20 at the start of external charging (charging history). Specifically, if the battery 20 was overcharged immediately before the start of external charging, lithium deposition is more likely to occur after the start of external charging because lithium ions are concentrated on the negative electrode surface than if charging of the battery 20 was stopped long before the start of external charging and immediately before the start of external charging (for example, if the motor 17 was in an unloaded state). Under the assumption that lithium deposition is always likely to occur after the start of external charging, lithium deposition can be suppressed by performing external charging while always limiting the magnitude of the supplied power current (set value SV). However, in this case, the charging current of the battery 20 may be excessively limited, potentially prolonging external charging.

[0039] Therefore, the ECU 40 in this embodiment has a configuration to address the above problem. Specifically, the ECU 40 acquires the charge start negative electrode potential Vns when a charge start condition is met. "Acquiring the charge start negative electrode potential Vns" may mean estimating the charge start negative electrode potential Vns using a Newman model or the like, or acquiring a measured value of the charge start negative electrode potential Vns from the aforementioned measuring device that measures the negative electrode potential. The ECU 40 selects a map associated with the acquired charge start negative electrode potential Vns from the map group MP. The ECU 40 controls external charging (the magnitude of the current of the supplied power) according to a set value SV corresponding to a combination of temperature TB and SOC in the selected map. For example, if the charge start negative electrode potential Vns is V(1) and map mp(1) is selected, when temperature TB is Tj and SOC is Xk at a certain point during external charging, the ECU 40 transmits SV(1,j,k) as the set value SV to the power equipment 5.

[0040] With this configuration, the charge start negative electrode potential Vns (the charge history of the battery 20) is reflected in the set value SV. For example, when lithium deposition is likely to occur because the charge start negative electrode potential Vns is low (for example, when Vns = V(1) and the margin M (= M(1)) is small (see the solid line in FIG. 5 )), the magnitude of the current of the power supply is limited by setting the set value SV smaller than when the charge start negative electrode potential Vns is high. This limits the charge current of the battery 20, reduces the number of electrons entering the negative electrode active material during external charging, and reduces cathode polarization of the negative electrode. As a result, the decrease in the negative electrode potential Vn after the start of external charging is suppressed, and lithium deposition can be effectively suppressed. On the other hand, when lithium deposition is unlikely to occur because the charge start negative electrode potential Vns is high (for example, when Vns = V(N) and the margin M (= M(N)) is large (see the dashed-dotted line in FIG. 5 )), the charge current is increased by setting the set value SV larger than when the charge start negative electrode potential Vns is low. This prevents excessive limitation of the charging current and shortens the charging time. As described above, the above configuration makes it possible to appropriately shorten the charging time while effectively suppressing lithium deposition.

[0041] 6 is a flowchart illustrating a process executed by the ECU 40. This flowchart starts when the ECU 40 detects connection of the charging connector 61 to the inlet 11 in accordance with the above-mentioned PISW signal.

[0042] 6, the ECU 40 acquires the detected values of the voltage VB, the current IB, and the temperature TB from the voltage sensor 21, the current sensor 22, and the temperature sensor 23 (S102). The ECU 40 estimates the SOC and the negative electrode potential Vn according to these detected values (S104). The ECU 40 determines whether a charge start condition is met (S105). The charge start condition is, for example, that the ECU 40 receives a charge start signal CS. If the charge start condition is not met (NO in S105), the process returns to S102. As a result, the ECU 40 continues to estimate the SOC and the negative electrode potential Vn until the charge start condition is met. If the charge start condition is met (YES in S105), the process proceeds to S120.

[0043] The ECU 40 acquires (estimates in this example) the charge start negative electrode potential Vns (S120). The ECU 40 selects a map associated with the charge start negative electrode potential Vns from the map group MP (S125). For example, if the charge start negative electrode potential Vns is V(1), the map mp(1) ( FIG. 4 ) is selected. The ECU 40 determines a set value SV corresponding to the temperature TB and SOC in the selected map, transmits the set value SV to the power equipment 5, and controls external charging accordingly (S130). The control in S130 continues until external charging is completed.

[0044] As described above, according to the embodiment, it is possible to effectively suppress lithium deposition and appropriately shorten the charging time. [Other variations] The ECU 40 may estimate the charge start negative electrode potential Vns based on a map that shows a predetermined relationship between the time during which the load on the motor 17 has been less than a predetermined value before the start of external charging and the charge start negative electrode potential. The longer the time, the closer the charge start negative electrode potential Vns is to the open circuit potential of the battery 20. The map is determined in advance through evaluation tests or the like and is stored in the ROM 42A.

[0045] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0046] 1 vehicle, 5 power equipment, 20 batteries, 40 ECUs, 61 charging connectors, 100 vehicle systems.

Claims

1. a control device that controls external charging to charge the lithium-ion battery using power supplied from a power facility external to the vehicle on which the lithium-ion battery is mounted; a storage device that stores a plurality of maps, each of which represents a correspondence relationship between a predetermined parameter of the lithium ion battery and a set value of the current of the power supply, and which is associated with a negative electrode potential that is a potential of a negative electrode of the lithium ion battery; The control device a charge start negative electrode potential, which is the negative electrode potential when a charge start condition for starting the external charging is satisfied; selecting a map associated with the charge starting negative electrode potential from the plurality of maps; A charging system that controls the external charging in accordance with the set value corresponding to the parameter in the selected map.

2. The charging system of claim 1 , wherein the parameters include a state of charge (SOC) and a temperature of the lithium-ion battery.

3. The charge starting negative electrode potential includes first to Nth potentials, and the i-th potential (2≦i≦N) is higher than the (i−1)-th potential for each value of i; the plurality of maps include first to Nth maps respectively associated with the first to Nth potentials; 3. The charging system of claim 2, wherein for each value of i, the set value in the i-th map is greater than or equal to the set value in the (i-1)-th map for the same SOC and temperature.

4. 4. The charging system according to claim 1, wherein in each of the plurality of maps, the set value is determined so that the negative electrode potential is higher than a reference potential that is a potential at which lithium is deposited on the negative electrode.

5. the power facility is a DC power facility configured to supply DC power as the supply power to the vehicle, The charging system according to claim 1 , wherein the external charging is charging the lithium-ion battery using the DC power from the DC power facility.

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