Full charge capacity estimation method for battery

Abstract

To provide a full charge capacity estimation method capable of suitably estimating a full charge capacity of a battery even when the battery has a flat region for a SOC-OCV characteristic.SOLUTION: A method for estimating a full charge capacity of a battery includes: a first step for charging a battery until it becomes a fully-charged state; a second step for discharging the battery of a first power storage amount in the fully-charged state until it lowers to a second power storage amount; a third step for calculating a discharge capacity discharged from the battery during a discharge period from the first power storage amount to the second power storage amount; and a fourth step for estimating a full charge capacity of the battery on the basis of difference between the discharge capacity, the first power storage amount and the second power storage amount.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for estimating the full charge capacity of a battery installed in a vehicle. [Background technology]

[0002] Patent Document 1 discloses a method for accurately detecting the full charge capacity of a battery without fully discharging or fully charging the battery. The method described in Patent Document 1 calculates the full charge capacity of a battery based on the change in capacity of the battery and the rate of change in the amount of stored electricity (remaining capacity) during the charging process from the lower limit open circuit voltage (no-load voltage) to the upper limit open circuit voltage. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-261669 Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned Patent Document 1 describes a technology for calculating the full charge capacity of a battery based on the open circuit voltage (OCV), which varies with the battery's state of charge (SOC). This technology is effective for ternary batteries, etc., in which the change in open circuit voltage according to the battery's state of charge is easy to understand, but has the problem that it is difficult to apply to, for example, iron phosphate-based lithium-ion batteries (LFP batteries), which have a flat region in the SOC-OCV characteristic and in which the change in open circuit voltage according to the battery's state of charge is difficult to understand.

[0005] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a full charge capacity estimation method that can suitably estimate the full charge capacity of a battery even for a battery that has a flat region in its SOC-OCV characteristics. [Means for solving the problem]

[0006] In order to solve the above problem, one aspect of the disclosed technology is a method for estimating the full charge capacity of a battery, the method including: a first step of charging the battery until it is in a fully charged state; a second step of discharging the battery with a first stored amount of electricity that has reached the fully charged state until the stored amount drops to a second stored amount; a third step of calculating the discharge capacity released from the battery during the discharge period from the first stored amount to the second stored amount; and a fourth step of estimating the full charge capacity of the battery based on the discharge capacity and the difference between the first stored amount and the second stored amount. [Effects of the Invention]

[0007] According to the method for estimating the full charge capacity of a battery disclosed above, the full charge capacity of a battery can be suitably estimated even for a battery having a flat region in the SOC-OCV characteristic. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of functional blocks of a power supply system that implements a method for estimating a full charge capacity of a battery according to an embodiment of the present disclosure; [Figure 2] A processing flowchart of a method for estimating a full charge capacity of a battery according to an embodiment of the present disclosure. [Figure 3] FIG. 10 is a diagram showing an example of an SOC-OCV characteristic curve having a flat region. DETAILED DESCRIPTION OF THE INVENTION

[0009] The method for estimating the full charge capacity of a battery disclosed herein performs a discharge process on the battery from the amount of charge stored in the fully charged state to a predetermined low amount of charge that is outside the flat region of the SOC-OCV characteristic, and estimates the full charge capacity of the battery based on the amount of change (variation range) between the discharge capacity and the amount of charge stored during the discharge period. Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings.

[0010] <Embodiment> [composition] Fig. 1 is a schematic diagram showing an example of functional blocks of a power supply system 1 that realizes a method for estimating a battery full charge capacity according to an embodiment of the present disclosure. The power supply system 1 illustrated in Fig. 1 includes a solar power generation module 10, an auxiliary battery 20, a main battery 30, a DC-DC converter 40, and a control device 50. In Fig. 1, connection lines through which power flows are indicated by solid lines, and connection lines through which detection signals, control signals, etc. flow are indicated by dotted lines.

[0011] The power supply system 1 illustrated in FIG. 1 can be mounted on vehicles that use an electric motor as a power source, such as a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and a battery electric vehicle (BEV).

[0012] The solar power generation module 10 is a power generation device that generates electricity by receiving irradiation from sunlight and outputs the generated power to an auxiliary battery 20 and a DC-DC converter 40 connected to the solar power generation module 10. This solar power generation module 10 includes a solar panel 11, which is an assembly of solar battery cells, and a maximum power point tracking (MPPT) 12 that includes a DC-DC converter that outputs the power generated by the solar panel 11 at a predetermined voltage based on MPPT control.

[0013] The auxiliary battery 20 is a chargeable and dischargeable secondary battery for supplying power to auxiliary loads (not shown) of the vehicle. An example of the auxiliary battery 20 is a lithium-ion battery (e.g., an LFP battery) having an SOC-OCV characteristic with a flat region in which the absolute value of the rate of change of the open circuit voltage (OCV) relative to the state of charge (SOC) is equal to or less than a predetermined value. FIG. 3 shows an example of an SOC-OCV characteristic curve with a flat region. The auxiliary battery 20 is connected to the solar power generation module 10 so that it can be charged with power generated by the solar panel 11. The auxiliary battery 20 is also connected to the DC-DC converter 40 so that it can charge the main battery 30 with the power stored in the auxiliary battery 20.

[0014] The main battery 30 is a secondary battery configured to be chargeable and dischargeable for supplying power to a main load (not shown) of the vehicle. An example of this main battery 30 is a lithium-ion battery. The main battery 30 is connected to the solar power generation module 10 and the auxiliary battery 20 via a DC-DC converter 40 so that it can be charged using power generated by the solar panel 11 and power from the auxiliary battery 20. The main battery 30 is a battery (such as a drive battery) with a higher rated voltage than the auxiliary battery 20.

[0015] The DC-DC converter 40 is a power converter that can convert input power into power of a predetermined voltage and output it. One end (primary side) of this 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 (pumping charge) the power output by 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. The DC-DC converter 40 can also supply (pumping charge) 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 this DC-DC converter 40 is controlled by a control device 50.

[0016] The control device 50 is configured to control the power supply system 1. The control device 50 in this embodiment performs various processes and controls related to estimating the full charge capacity of the auxiliary battery 20. The control device 50 acquires information on the power generation from the solar power generation module 10, acquires information on physical quantities (voltage, current, stored power amount, etc.) from the auxiliary battery 20, and acquires information on physical quantities (voltage, current, stored power amount, etc.) from the main battery 30. A detection device such as a sensor is used to acquire this information. The control device 50 also controls the operation of the DC-DC converter 40 based on the acquired information.

[0017] A part or all of this control device 50 can be configured as an electronic control unit (ECU) that typically includes a processor, a memory, an input / output interface, etc. This electronic control unit achieves predetermined functions by having the processor read and execute programs stored in the memory.

[0018] [control] Next, a method for estimating the full charge capacity of a battery according to an embodiment of the present disclosure will be described with further reference to Fig. 2. Fig. 2 is a flowchart showing the processing procedure of the control device 50 for estimating the full charge capacity of the auxiliary battery 20.

[0019] 2 is initiated when the power stored in the main battery 30 falls below a predetermined reference power (power shortage). This reference power is, for example, the power that needs to be charged to prevent the battery from running out, and is appropriately set based on the power consumption of the main load that uses the main battery 30 as a power source.

[0020] (Step S201) The control device 50 charges the auxiliary battery 20 with the power generated by the solar power generation module 10 until the auxiliary battery 20 is fully charged. The fully charged state of the auxiliary battery 20 typically refers to a state in which the amount of stored power (or the power storage rate) of the auxiliary battery 20 is 100%. When the auxiliary battery 20 is fully charged, the process proceeds to step S202.

[0021] (Step S202) After the auxiliary battery 20 reaches a fully charged state, the control device 50 discharges the power stored in the auxiliary battery 20 to the main battery 30 via the DC-DC converter 40. In other words, power is transferred from the auxiliary battery 20 to the main battery 30. This discharge is performed until the first stored power amount (100%) of the fully charged auxiliary battery 20 drops to at least a predetermined second stored power amount (31% in the example of FIG. 3 ), which is the lower limit of the flat region of the SOC-OCV characteristic. Note that the discharge may continue even if the stored power amount drops below the second stored power amount. When the auxiliary battery 20 is discharged from the first stored power amount to the second stored power amount, which is the lower limit of the flat region, the process proceeds to step S203.

[0022] (Step S203) The control device 50 calculates the discharge capacity [Ah (ampere-hours)] discharged from the auxiliary battery 20 to the main battery 30 during the discharge period from the first stored amount to the second stored amount in step S202. This discharge capacity can be calculated based on a well-known current integration method, etc. In the example of FIG. 3, the discharge period from the first stored amount to the second stored amount (hereinafter referred to as "section SOC") is 69% (=100%-31%). Once the discharge capacity in the section SOC is calculated, the process proceeds to step S204.

[0023] (Step S204) The control device 50 calculates the full charge capacity of the auxiliary battery 20. This full charge capacity [Ah] can be calculated according to the following formula [1] based on the section SOC [%] and the discharge capacity [Ah] in that section SOC. Once the full charge capacity of the auxiliary battery 20 has been calculated, the process proceeds to step S205. Full charge capacity = discharge capacity of section SOC × (section SOC / 100) … [1]

[0024] (Step S205) The control device 50 determines whether the full charge capacity of the auxiliary battery 20 calculated in step S204 is less than a predetermined threshold. This determination is made to check whether the auxiliary battery 20 has deteriorated. Therefore, this threshold is appropriately set based on the standard performance of the auxiliary battery 20, the frequency of use of the vehicle in which it is installed, and the like. If the full charge capacity of the auxiliary battery 20 is less than the threshold (step S205, Yes), the process proceeds to step S206. On the other hand, if the full charge capacity of the auxiliary battery 20 is equal to or greater than the threshold (step S205, No), the process proceeds to step S207.

[0025] (Step S206) The control device 50 determines that the auxiliary battery 20 has deteriorated and therefore needs to be replaced. This determination result is preferably notified to the vehicle user, a server that centrally manages multiple vehicles, or the like. If it is determined that the auxiliary battery 20 needs to be replaced, the process proceeds to step S207.

[0026] (Step S207) The control device 50 determines whether the power shortage in the main battery 30 has been resolved (whether the stored power is equal to or greater than a predetermined reference power). That is, the control device 50 determines whether the power shortage in the main battery 30 has been resolved by the power transfer from the auxiliary battery 20 to the main battery 30 performed in step S202. If the power shortage in the main battery 30 has been resolved (step S207, Yes), the control for estimating the full charge capacity of the auxiliary battery 20 ends. On the other hand, if the power shortage in the main battery 30 has not yet been resolved (step S207, No), the control returns to step S201 and the control for estimating the full charge capacity of the auxiliary battery 20 is repeatedly performed.

[0027] <Actions and Effects> As described above, according to the method for estimating the full charge capacity of a battery according to an embodiment of the present disclosure, the auxiliary battery 20 is first charged until it reaches a fully charged state (first stored power amount), and then the fully charged auxiliary battery 20 is discharged until it reaches a low stored power amount (second stored power amount) at which the stored power amount can be accurately estimated from the open circuit voltage. Then, the discharge capacity discharged from the auxiliary battery 20 during this discharging period is calculated, and the full charge capacity of the auxiliary battery 20 is estimated based on the discharge capacity and the change in the stored power amount due to the discharge.

[0028] By this method, the full charge capacity of the auxiliary battery 20 can be suitably estimated even if the auxiliary battery 20 is an LFP battery or the like that has a flat region in the SOC-OCV characteristic.

[0029] In addition to charging the auxiliary battery 20 with the power generated by the solar power generation module 10 described above, other methods for fully charging the auxiliary battery 20 include charging it with regenerative power generated while the vehicle is running, charging it from an external charger connected when the vehicle is parked, or charging it by pumping power from the main battery 30.

[0030] In addition, as a method for discharging the auxiliary battery 20 from the first storage amount to the second storage amount, in addition to transferring power from the auxiliary battery 20 to the main battery 30 as described above, it is also possible to supply dark current to the on-board loads while the vehicle is parked.

[0031] The above describes one embodiment of the present disclosure. However, the present disclosure can be understood not only as the above-described method for estimating the full charge capacity of a battery, but also as a program for the method, a computer-readable non-transitory recording medium storing the program, or an apparatus for executing the method for estimating the full charge capacity. [Industrial Applicability]

[0032] The full charge capacity estimation method of the present disclosure can be used when it is desired to accurately estimate the full charge capacity of a battery. [Explanation of symbols]

[0033] 1 Power System 10 Solar power generation module 11. Solar Panels 12 MPPT 20 Auxiliary battery 30 Main engine battery 40 DC-DC converter 50 Control device

Claims

1. 1. A method for estimating a full charge capacity of a battery, comprising: a first step of charging the battery to a fully charged state; a second step of discharging the battery having the first charge amount in the fully charged state until the charge amount decreases to a second charge amount; a third step of calculating a discharge capacity discharged from the battery during a discharge period from the first stored amount to the second stored amount; a fourth step of estimating the full charge capacity of the battery based on the discharge capacity and a difference between the first stored charge amount and the second stored charge amount, A method for estimating the full charge capacity of a battery.

2. the battery is a lithium ion battery having an SOC-OCV characteristic with a flat region in which the rate of change of open circuit voltage with respect to the amount of stored charge is equal to or less than a predetermined value, the second step comprises discharging the battery to a second stored charge amount that is a lower limit of the flat region; The method for estimating a full charge capacity of a battery according to claim 1.

3. the battery is an auxiliary battery mounted on a vehicle equipped with a solar power generation module, the first step is charging the auxiliary battery with power generated by the solar power generation module; 3. The method for estimating a full charge capacity of a battery according to claim 1.

4. The vehicle further includes a main engine battery, the second step discharging the auxiliary battery to the main battery; The method for estimating a full charge capacity of a battery according to claim 3.

5. a fifth step of determining that the battery needs to be replaced when the full charge capacity of the battery is less than a predetermined threshold; 5. The method for estimating a full charge capacity of a battery according to claim 1.

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