Method for estimating full charge capacity of battery

Abstract

A method for estimating the full charge capacity of a battery, which estimates the full charge capacity of the battery, includes: a first step of charging the battery until the battery is in a full charge state; a second step in which the battery having the first charge capacity in the fully charged state is discharged to a second charge capacity; a third step of calculating a discharge capacity discharged from the battery during a discharge period from the first charge amount to the second charge amount; and a fourth step for estimating the full charge capacity of the battery on the basis of the discharge capacity and the difference between the first charge capacity and the second charge capacity.

Description

Technical Field

[0001] The present disclosure relates to a method for inferring the full charge capacity of a battery mounted on a vehicle. Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2008-261669 discloses a method capable of accurately detecting the full charge capacity of a battery without fully discharging and fully charging the battery. In the method described in Japanese Unexamined Patent Application Publication No. 2008-261669, the full charge capacity of the battery is calculated based on the change value of the battery capacity and the change rate of the stored electricity (remaining capacity) during the charging process from the lower open circuit voltage (no-load voltage) to the upper open circuit voltage.

[0003] The above-mentioned Japanese Unexamined Patent Application Publication No. 2008-261669 is a technique for calculating the full charge capacity of a battery based on the open circuit voltage (OCV: Open Circuit Voltage) that changes with the change in the stored electricity (SOC: State Of Charge) of the battery. This technique is effective for a ternary system battery or the like in which it is easy to understand the change in the open circuit voltage corresponding to the stored electricity of the battery. However, for example, there is a problem that it is difficult to apply to a lithium iron phosphate-based lithium-ion battery (LFP battery) or the like that has a flat region in the SOC-OCV characteristics and for which it is difficult to understand the change in the open circuit voltage corresponding to the stored electricity of the battery. Summary of the Invention

[0004] The present disclosure has been made in view of the above problems, and an object thereof is to provide a full charge capacity inference method capable of suitably inferring the full charge capacity of a battery even for a battery having a flat region in the SOC-OCV characteristics.

[0005] In order to solve the above problems, one aspect of the technique of the present disclosure is a method for inferring the full charge capacity of a battery, which infers the full charge capacity of the battery, and includes:

[0006] A first step of charging the battery until it becomes a fully charged state;

[0007] A second step of discharging the battery having the first stored electricity in the fully charged state until it is reduced to the second stored electricity;

[0008] A third step of calculating the discharge capacity discharged from the battery during the discharge period from the first stored electricity to the second stored electricity; and

[0009] A fourth step of inferring the full charge capacity of the battery based on the discharge capacity and the difference between the first stored electricity and the second stored electricity.

[0010] According to the method for inferring the full charge capacity of the battery of the present disclosure described above, for a battery having a flat region in the SOC-OCV characteristic, the full charge capacity of the battery can also be appropriately inferred. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The features, advantages, and technical and industrial significance of the exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals represent like elements, where

[0012] Figure 1 is a schematic diagram of the functional modules of a power supply system for implementing the method for inferring the full charge capacity of a battery according to an embodiment of the present disclosure;

[0013] Figure 2 is a flowchart of the process of the method for inferring the full charge capacity of a battery according to an embodiment of the present disclosure;

[0014] Figure 3 is a diagram showing an example of a SOC-OCV characteristic curve having a flat region. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] The method for inferring the full charge capacity of the battery of the present disclosure performs a discharge process on the battery from the stored electricity in the fully charged state to a specified low stored electricity outside the flat region of the SOC-OCV characteristic, and infers the full charge capacity of the battery based on the discharge capacity and the change amount (change amplitude) of the stored electricity during the discharge period.

[0016] Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings.

[0017] Embodiment

[0018] Structure

[0019] Figure 1 is a schematic diagram showing an example of the functional modules of a power supply system 1 for implementing the method for inferring the full charge capacity of a battery according to an embodiment of the present disclosure. Figure 1 The illustrated power supply system 1 includes a solar power generation module 10, an auxiliary battery 20, a main battery 30, a DCDC converter 40, and a control device 50. In this Figure 1 figure, the connection lines indicating the flow of electric power are represented by solid lines, and the connection lines indicating the flow of detection signals, control signals, etc. are represented by dashed lines.

[0020] Figure 1The illustrated power supply system 1 can be mounted on a vehicle that uses an electric motor as a power source. Such vehicles include hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), and the like.

[0021] The solar power generation module 10 is a power generation device that receives sunlight and generates electricity, and outputs the generated electricity to the auxiliary battery 20 and the DCDC converter 40 connected to the solar power generation module 10. The solar power generation module 10 includes a solar panel 11 and an MPPT 12. The solar panel 11 is an aggregate of solar cell elements. The MPPT 12 includes a DCDC converter that outputs the electricity generated by the solar panel 11 at a prescribed voltage based on maximum power point tracking (MPPT) control.

[0022] The auxiliary battery 20 is a secondary battery that is configured to be chargeable and dischargeable and is used to supply power to auxiliary loads (not shown) of the vehicle. As the auxiliary battery 20, a lithium-ion battery (e.g., an LFP battery) having an SOC-OCV characteristic can be exemplified. The SOC-OCV characteristic has a flat region in which the absolute value of the change rate of the open circuit voltage (OCV) with respect to the stored electricity (SOC) is equal to or less than a prescribed value. An example of an SOC-OCV characteristic curve having a flat region is shown in Figure 3 . The auxiliary battery 20 is connected to the solar power generation module 10 so as to be chargeable with the electricity generated by the solar panel 11. In addition, the auxiliary battery 20 is connected to the DCDC converter 40 so as to be able to charge the main battery 30 with the electricity stored in itself.

[0023] The main battery 30 is a secondary battery that is configured to be chargeable and dischargeable and is used to supply power to main loads (not shown) of the vehicle. As the main battery 30, a lithium-ion battery can be exemplified. The main battery 30 is connected to the solar power generation module 10 and the auxiliary battery 20 via the DCDC converter 40 so as to be chargeable with the electricity generated by the solar panel 11 and the electricity of the auxiliary battery 20. The main battery 30 is a battery (such as a driving battery) having a rated voltage higher than that of the auxiliary battery 20.

[0024] The DC-DC converter 40 is a power converter that can convert the input power into a specified voltage and output it. One end (primary side) of the DC-DC converter 40 is connected to the solar power generation module 10 and the auxiliary battery 20, and the other end (secondary side) is connected to the main battery 30. The DC-DC converter 40 can supply (pump charging) the power output from the solar power generation module 10 and the auxiliary battery 20 connected to the primary side to the main battery 30 connected to the secondary side. In addition, the DC-DC converter 40 can supply (draw charging) the power of the main battery 30 connected to the secondary side to the auxiliary battery 20 connected to the primary side. The operation of the DC-DC converter 40 is controlled by the control device 50.

[0025] The control device 50 is a structure for controlling the power supply system 1. In the present embodiment, the control device 50 performs various processes and controls related to inferring the full charge capacity of the auxiliary battery 20. The control device 50 obtains information on the generated power from the solar power generation module 10, obtains information on physical quantities (voltage, current, stored power, etc.) from the auxiliary battery 20, and obtains information on physical quantities (voltage, current, stored power, etc.) from the main battery 30. In order to obtain this information, detection devices such as sensors are used. In addition, the control device 50 controls the operation of the DC-DC converter 40 based on the obtained information and the like.

[0026] Typically, a part or all of the control device 50 can be configured as an electronic control unit (ECU: Electronic Control Unit) including a processor, a memory, an input / output interface, and the like. The electronic control unit realizes a specified function by the processor reading and executing a program stored in the memory.

[0027] Control

[0028] Next, with further reference to Figure 2 , a method for inferring the full charge capacity of a battery according to an embodiment of the present disclosure will be described. Figure 2 is a flowchart showing the processing sequence of the full charge capacity inference control of the auxiliary battery 20 executed by the control device 50.

[0029] Based on the situation that the power stored in the main battery 30 is lower than a predetermined reference power (power shortage), etc., the full charge capacity inference control of the auxiliary battery 20 exemplified in this appendix Figure 2 is started. This reference power is, for example, the power required for charging to prevent the battery from running out, and is appropriately set based on the power consumption of the main load using the main battery 30 as a power source.

[0030] S201

[0031] The control device 50 charges the auxiliary battery 20 with the generated power output from the solar power generation module 10 until the auxiliary battery 20 reaches a fully charged state. Typically, the fully charged state of the auxiliary battery 20 is a state where the stored power (or the state of charge rate) of the auxiliary battery 20 becomes 100%. When the auxiliary battery 20 reaches the fully charged state, the process proceeds to S202.

[0032] (S202)

[0033] After the auxiliary battery 20 reaches the fully charged state, the control device 50 discharges the power stored in the auxiliary battery 20 to the main battery 30 via the DCDC converter 40. That is, power is transmitted from the auxiliary battery 20 to the main battery 30. This discharge is performed until the first stored power (100%) of the auxiliary battery 20, which is in the fully charged state, decreases to a specified second stored power (in the Figure 3 example, 31%) that is at least the lower limit of the flat region in the SOC-OCV characteristic. Additionally, the discharge can continue below the second stored power. When the auxiliary battery 20 is discharged from the first stored power to the second stored power at the lower limit of the flat region, the process proceeds to S203.

[0034] S203

[0035] The control device 50 calculates the discharge capacity [Ah (ampere-hour)] discharged from the auxiliary battery 20 to the main battery 30 during the discharge period from the first stored power to the second stored power in the above S202. This discharge capacity can be calculated based on a well-known current integration method or the like. In the Figure 3 example, the discharge period from the first stored power to the second stored power (hereinafter referred to as "interval SOC") is 69% (= 100% - 31%). When the discharge capacity in the interval SOC is calculated, the process proceeds to S204.

[0036] S204

[0037] The control device 50 calculates the full charge capacity of the auxiliary battery 20. This full charge capacity [Ah] can be calculated based on the interval SOC [%] and the discharge capacity [Ah] in this interval SOC according to the following formula [1]. When the full charge capacity of the auxiliary battery 20 is calculated, the process proceeds to S205.

[0038] Full charge capacity = Discharge capacity of interval SOC × (interval SOC / 100) … [1]

[0039] S205

[0040] The control device 50 determines whether the full charge capacity of the auxiliary battery 20 calculated in S204 above is less than a predetermined threshold value. This determination is made to confirm whether the auxiliary battery 20 is deteriorated. Therefore, this threshold value is appropriately set based on the specification performance of the auxiliary battery 20, the usage frequency of the vehicle equipped, etc. When the full charge capacity of the auxiliary battery 20 is less than the threshold value (S205, Yes), the process proceeds to S206. On the other hand, when the full charge capacity of the auxiliary battery 20 is equal to or greater than the threshold value (S205, No), the process proceeds to S207.

[0041] S206

[0042] Since the auxiliary battery 20 is deteriorated, the control device 50 determines that the auxiliary battery 20 needs to be replaced. It is preferable to notify the determination result to a server that centrally manages vehicle users, multiple vehicles, etc. If it is determined that the auxiliary battery 20 needs to be replaced, the process proceeds to S207.

[0043] S207

[0044] The control device 50 determines whether the power shortage of the main battery 30 has been eliminated (whether the stored power has become equal to or greater than a predetermined reference power). That is, the control device 50 determines whether the power of the main battery 30 has been sufficiently stored by the power transmission from the auxiliary battery 20 performed in S202 above. When the power shortage of the main battery 30 has been eliminated (S207, Yes), the inference control of the full charge capacity of the auxiliary battery 20 ends. On the other hand, when the power shortage of the main battery 30 has not been eliminated (S207, No), the process returns to S201, and the inference control of the full charge capacity of the auxiliary battery 20 is repeatedly executed.

[0045] Function and Effect

[0046] As described above, according to the method for inferring the full charge capacity of a battery according to an embodiment of the present disclosure, the auxiliary battery 20 is temporarily charged until it becomes a fully charged state (the first stored power). In addition, the fully charged auxiliary battery 20 is discharged until it becomes a low stored power state (the second stored power) where the stored power can be accurately inferred based on the open circuit voltage. Then, the discharge capacity discharged from the auxiliary battery 20 during this discharge period is calculated, and the full charge capacity of the auxiliary battery 20 is inferred based on the discharge capacity and the change amount of the stored power caused by the discharge.

[0047] By this method, even if the auxiliary battery 20 is an LFP battery or the like having a flat region in the SOC-OCV characteristic, the full charge capacity of the auxiliary battery 20 can be appropriately inferred.

[0048] In addition, as a method for bringing the auxiliary battery 20 into a fully charged state, in addition to charging with the electric power generated by the above-described solar power generation module 10, charging with the regenerative electric power generated during the running of the vehicle can also be cited. The auxiliary battery 20 can also be brought into a fully charged state by charging from an external charger or the like connected when the vehicle is parked, or by draw charging with the electric power of the main battery 30.

[0049] In addition, as a method for discharging the auxiliary battery 20 from the first stored power amount to the second stored power amount, in addition to supplying electric power from the above-described auxiliary battery 20 to the main battery 30, it can also be performed by supplying the dark current to the in-vehicle load while the vehicle is parked.

[0050] As described above, one embodiment of the present disclosure has been described. However, the present disclosure can be understood not only as the above-described method for inferring the full charge capacity of the battery, but also as a program for the method, a computer-readable non-temporary recording medium storing the program, or a device that executes the method for inferring the full charge capacity.

[0051] The method for inferring the full charge capacity of the present disclosure can be used in cases where it is desired to accurately infer the full charge capacity of the battery.

Claims

1. A method for inferring the full charge capacity of a battery, which infers the full charge capacity of the battery, wherein, Comprising: Step 1, charging the battery to a fully charged state; Step 2, discharging the battery with the first stored electricity amount in the fully charged state until it reduces to the second stored electricity amount; Step 3, calculating the discharge capacity discharged from the battery during the discharge period from the first stored electricity amount to the second stored electricity amount; And Step 4, inferring the fully charged capacity of the battery based on the discharge capacity and the difference between the first stored electricity amount and the second stored electricity amount.

2. The method for inferring the fully charged capacity of a battery according to claim 1, wherein the battery is a lithium-ion battery having an SOC-OCV characteristic, and the SOC-OCV characteristic has a flat region, in which the change rate of the open circuit voltage with respect to the stored electricity amount is below a specified value, in Step 2, discharging the battery until the stored electricity amount reaches the lower limit of the flat region as the second stored electricity amount.

3. The method for inferring the fully charged capacity of a battery according to claim 1 or 2, wherein the battery is an auxiliary battery mounted on a vehicle equipped with a solar power generation module, in Step 1, charging the auxiliary battery with the generated power of the solar power generation module.

4. The method for inferring the fully charged capacity of a battery according to claim 3, wherein the vehicle is further equipped with a main battery, in Step 2, discharging from the auxiliary battery to the main battery.

5. The method for inferring the fully charged capacity of a battery according to any one of claims 1 to 4, wherein it further includes Step 5, in which, when the fully charged capacity of the battery is less than a specified threshold value, it is determined that the battery needs to be replaced.

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