Vehicle equipped with an LFP battery degradation detection device, and method for detecting LFP battery degradation.

Abstract

To determine the degradation of an LFP battery.SOLUTION: A controller performs a series of charge / discharge processing of charging an LFP battery to be charged to a fully charged state by a charger / discharger, discharging the LFP battery in the fully charged state by the charger / discharger until OCV of the LFP battery reaches predetermined OCV (pOCV) of the LFP battery that uniquely represents common capacity CC before and after degradation of the LFP battery, and acquiring a current integrated value ICV of a discharge current during the discharging. The controller performs the charge / discharge processing one or more times to acquire variation capacity VC of the LFP battery on the basis of one or more current integrated values (ICVs) acquired by the processing. The controller adds the variation capacity VC to the common capacity CC, calculates the full charge capacity of the LFP battery, and determines the degradation of the LFP battery on the basis of the calculated full charge capacity of the LFP battery and the initial full charge capacity IFCC of the LFP battery.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for determining the deterioration of an LFP battery, a deterioration determination device, and a vehicle equipped with the device.

Background Art

[0002] Conventionally, LFP (lithium iron phosphate) batteries have been known. An LFP battery is a lithium-ion secondary battery using lithium iron phosphate (LiFePO4) as a material for the positive electrode. LFP batteries are mounted on vehicles such as engine vehicles, electric vehicles, and hybrid vehicles, and are used as power sources for low-voltage applications or power sources for high-voltage applications (such as vehicle drive power sources).

[0003] Patent Document 1 discloses a method for detecting the full charge capacity of a battery. The method in this document includes a step of detecting the no-load voltage of the battery (the first and second no-load voltages V , , , , ,

[0004] , , , , , , , , ,

[0005] ,V OCV2 ) at two different timings (the first and second no-load timings), a step of obtaining the remaining capacity of the battery (the first and second remaining capacities SOC1, SOC2) corresponding to each of the first and second no-load voltages V OCV1 ,V OCV2 , a step of calculating the change rate (δS [%]) of the remaining capacity from the difference between the first and second remaining capacities SOC1, SOC2, a step of calculating the capacity change value (δAh) of the battery from the integrated value of the charge and discharge current of the battery during the period between the first and second no-load timings, and a step of calculating the full charge capacity (Ahf) of the battery from the change rate (δS [%]) of the remaining capacity and the capacity change value (δAh).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] For example, the degradation of a secondary battery is determined by the ratio of its full charge capacity [Ah] at the time of degradation to its initial (pre-degradation) full charge capacity [Ah]. This is called SOH (State of Health), and a lower SOH indicates that the secondary battery is more degraded. As in Patent Document 1, if the current full charge capacity of a secondary battery can be detected, the initial full charge capacity of the secondary battery can be known in advance, and therefore the degree of degradation of the secondary battery can be obtained (the SOH of the secondary battery can be calculated).

[0006] The method described in Patent Document 1 obtains the remaining charge (SOC: State of Charge) of a battery corresponding to the battery's no-load voltage (OCV: Open Circuit Voltage) in order to detect the battery's full charge capacity. This is called the OCV method, and in the OCV method, the correlation between the OCV and SOC of a secondary battery (SOC-OCV curve) is used to estimate the SOC from the voltage value (OCV) of the secondary battery obtained by a voltage sensor. The method described in Patent Document 1 detects two OCVs, estimates two SOCs from them, and detects the full charge capacity based on these two SOCs.

[0007] However, LFP batteries have an SOC region where the OCV hardly changes even when the SOC changes (an SOC region where there is almost no correlation between OCV and SOC). Therefore, it is difficult to detect the full charge capacity of an LFP battery using a method like the one in Patent Document 1 (a method of detecting the full charge capacity by estimating multiple SOCs from multiple OCVs). Thus, a method for detecting the full charge capacity suitable for LFP batteries is desired.

[0008] The objective of this invention is to enable detection of the full charge capacity of an LFP battery and to determine the degradation of the LFP battery. [Means for solving the problem]

[0009] Apparatus for determining degradation of LFP battery according to the present invention Vehicles equipped with teeth, A vehicle comprising an LFP battery and a device for determining the degradation of the LFP battery, wherein the degradation determination device isThe system includes a charger / discharger for charging and discharging an LFP battery, and a controller for controlling the charger / discharger. The controller performs a series of charge / discharge processes, including charging the LFP battery to a fully charged state using the charger / discharger, discharging the fully charged LFP battery using the charger / discharger until the OCV of the LFP battery reaches a predetermined OCV of the LFP battery that uniquely represents the common battery capacity before and after the degradation of the LFP battery, and acquiring the integrated value of the discharge current during that time. The vehicle comprises a load to which power is constantly supplied regardless of whether the vehicle's ignition switch is on or off, and a main battery that supplies power to the load. The controller performs the charge / discharge process while the vehicle is parked with the vehicle's ignition switch off, and in the charge / discharge process, controls the charge / discharge unit to charge the LFP battery by supplying power from the main battery, and controls the charge / discharge unit to supply power to the load by discharging from the LFP battery to the load instead of the main battery. The controller performs the charge / discharge process one or more times, obtains the variable battery capacity of the LFP battery based on one or more integrated current values ​​obtained therefrom, and calculates the full charge capacity of the LFP battery by adding the variable battery capacity to the common battery capacity. The controller determines the degradation of the LFP battery based on the calculated full charge capacity of the LFP battery and the initial full charge capacity of the LFP battery.

[0010] Apparatus for determining degradation of LFP battery according to the present invention Vehicles equipped with In this configuration, the controller may perform the charge / discharge process two or more times to obtain two or more integrated current values, and use the average value of the two or more integrated current values ​​as the variable battery capacity.

[0012] Furthermore, the method for determining the degradation of an LFP battery according to the present invention is: A method for determining the degradation of an LFP battery, applicable to a vehicle equipped with an LFP battery, Charger / discharger The aforementioned The charging and discharging process includes the steps of: charging the LFP battery to a fully charged state; and discharging the fully charged LFP battery using the charger / discharger until the OCV of the LFP battery reaches a predetermined OCV of the LFP battery that uniquely represents the common battery capacity before and after the degradation of the LFP battery, and acquiring the integrated value of the discharge current during that time. The vehicle comprises a load to which power is constantly supplied, regardless of whether the vehicle's ignition switch is on or off, and a main battery that supplies power to the load. The charging and discharging process is performed while the vehicle is parked and the vehicle's ignition switch is off. During the charging and discharging process, power is supplied from the main battery to charge the LFP battery, and power is supplied to the load by discharging from the LFP battery instead of the main battery.The degradation determination method comprises the steps of: obtaining the variable battery capacity of the LFP battery based on one or more current integrated values ​​obtained by performing the charge-discharge process once or more times; calculating the full charge capacity of the LFP battery by adding the variable battery capacity to the common battery capacity; and determining the degradation of the LFP battery based on the calculated full charge capacity of the LFP battery and the initial full charge capacity of the LFP battery. [Effects of the Invention]

[0013] According to the present invention, it is possible to determine the degradation of an LFP battery. [Brief explanation of the drawing]

[0014] [Figure 1] This figure shows a schematic configuration of the deterioration determination device 12 according to the embodiment. [Figure 2] This flowchart shows the processes performed by controller 20. [Figure 3] This figure shows an example of a discharge curve for an LFP battery. [Modes for carrying out the invention]

[0015] Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the embodiments described herein. In all drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0016] Figure 1 shows a schematic configuration of a degradation detection device 12 according to an embodiment. The degradation detection device 12 is mounted on a vehicle 10. The vehicle 10 is, for example, an engine vehicle, an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, etc. The degradation detection device 12 determines the degradation of the LFP battery 14 mounted on the vehicle 10.

[0017] The LFP battery 14 is a single LFP cell (unit cell) or a battery pack composed of multiple LFP cells. In this embodiment, the LFP battery 14 is used as a power source for low-voltage applications. Note that in another embodiment, the LFP battery 14 may be used as a power source for high-voltage applications, for example, as a power source for a vehicle drive motor.

[0018] The vehicle 10 includes a first load 32, a main battery 30, an LFP battery 14, and a second load 34.

[0019] The first load 32 is a load that is constantly supplied with power regardless of the on / off state of the ignition switch of the vehicle 10. The first load 32 includes electronic devices that are supplied with power during parking, for example, a drive recorder with a parking monitoring function. Note that the parking monitoring function includes a function of recording the surroundings of the vehicle with a camera in order to prevent vandalism, contact with objects, intrusion into the vehicle, etc. while the vehicle is parked.

[0020] The main battery 30 is a secondary battery such as a lead-acid battery. The main battery 30 supplies power to the first load 32. Also, the main battery 30 supplies power to the second load 34 and the LFP battery 14 via the DCDC converter 26. Note that the main battery 30 is charged by power from a generator (not shown) that generates power using the power of the engine. Note that when the vehicle 10 is an electric vehicle or the like, the main battery 30 may be charged by power supplied from a high-voltage battery for vehicle driving or the like.

[0021] The LFP battery 14 is redundantly provided as a sub-battery for backing up the main battery 30 when an abnormality occurs in the main battery 30. The LFP battery 14 is configured to be able to supply power to the second load 34.

[0022] The second load 34 is a load that requires a more stable power supply than the first load 32. The second load 34 can continue to operate by power supplied from the backup LFP battery 14 in the event of a malfunction in the main battery 30. In other words, the second load 34 is a load with redundant power supplies. Examples of the second load 34 include electronic equipment related to airbags and electronic equipment related to advanced driver-assistance systems (ADAS).

[0023] Vehicle 10 is equipped with a degradation detection device 12 for the LFP battery 14. The degradation detection device 12 comprises a controller 20, a DC-DC converter 26, a relay 36, a current sensor 16, and a voltage sensor 18.

[0024] The controller 20 includes a microcomputer. The controller 20 comprises a processor 22 such as a CPU, memory 24, and an input / output interface (not shown). The memory 24 can be RAM (random access memory), ROM (read-only memory), or a non-volatile storage device (e.g., flash memory). The processor 22 uses RAM to perform processing according to programs and data pre-stored in the ROM or non-volatile storage device, thereby realizing the various controls and functions described below. A DC-DC converter 26, a relay 36, a current sensor 16, and a voltage sensor 18 are electrically connected to the controller 20. The controller 20 also receives a signal indicating the status of the ignition switch of the vehicle 10.

[0025] The DC-DC converter 26 is a bidirectional DC-DC converter that combines the functions of outputting power from the main battery 30 to the second load 34 and outputting power from the LFP battery 14 to the first load 32. The DC-DC converter 26 has multiple switching elements inside. The controller 20 controls the DC-DC converter 26 by switching the switching elements of the DC-DC converter 26 on and off.

[0026] Relay 36 is located between the main battery 30 and the DC-DC converter 26. Relay 36 is configured to switch between open and closed states under the control of the controller 20.

[0027] The current sensor 16 is a device that detects the charging current and discharging current of the LFP battery 14. The detected value from the current sensor 16 is output to the controller 20. The voltage sensor 18 is a device that detects the OCV (open-circuit voltage) of the LFP battery 14. The detected value from the voltage sensor 18 is output to the controller 20.

[0028] In typical vehicle conditions where degradation of the LFP battery 14 is not checked, the controller 20 closes the relay 36 to supply power from the main battery 30 to the first load 32, and also controls the DCDC converter 26 to supply power from the main battery 30 to the second load 34.

[0029] On the other hand, if the ignition switch of the vehicle 10 is in the off state, the controller 20 determines that the vehicle 10 is in a parked state and performs a degradation determination process for the LFP battery 14 (Figure 2). In the degradation determination process, the controller 20 charges (S102) and discharges (S104) the LFP battery 14. When the controller 20 charges the LFP battery 14 (S102), it closes the relay 36 and controls the DC-DC converter 26 to output power from the main battery 30 to the LFP battery 14. When the controller 20 discharges the LFP battery 14 (S104), it opens the relay 36 and controls the DC-DC converter 26 to output power from the LFP battery 14 to the first load 32. In the degradation determination process, the DC-DC converter 26 and the relay 36 function as a charger / discharger 25 for the LFP battery 14.

[0030] Figure 2 is a flowchart showing the degradation determination process performed by the controller 20. Figure 3 is a graph showing an example of the capacity-OCV curve (discharge curve) when discharging from a fully charged state of the LFP battery 14. In Figure 3, the horizontal axis is battery capacity (charge amount) [Ah], and the vertical axis is OCV [V]. In the same figure, the solid line shows the discharge curve of the initial (pre-degradation) LFP battery, and the dashed line shows the discharge curve of the LFP battery after degradation. IFCC is the full charge capacity of the initial LFP battery, and DFCC is the full charge capacity of the LFP battery after degradation. As shown in Figure 3, DFCC is smaller than IFCC. The LFP battery has a region where the OCV hardly changes even if the capacity changes, in the region where the capacity (charge amount) is relatively large.

[0031] The flowchart in Figure 2 will be explained while referring to the graph in Figure 3. When the controller 20 determines that the ignition switch of the vehicle 10 is in the off state and the vehicle 10 is in a parked state, it starts the flow in Figure 2. In S100, the controller 20 obtains the number of processes N. The number of processes N is the number of times the charge / discharge process (S102~S108) described below is performed. N is an integer of 1 or more. N is stored in memory 24 in advance.

[0032] Next, in S102, the controller 20 outputs power from the main battery 30 to the LFP battery 14 using the charger / discharger 25, and charges the LFP battery 14 until it is fully charged. The controller 20 determines that the LFP battery 14 is fully charged when, for example, the charging current detected by the current sensor 16 falls below a predetermined value.

[0033] In S104, the controller 20 discharges the LFP battery 14 to the first load 32 using the charger / discharger 25. At this time, the controller 20 also performs current integration of the discharge current to obtain the integrated current value ICV [Ah]. The integrated current value ICV [Ah] is calculated by multiplying the current value [A] of the discharge current detected by the current sensor 16 by the discharge time [h].

[0034] In S106, the controller 20 checks whether the OCV of the LFP battery 14 has reached a predetermined OCV (pOCV). The OCV of the LFP battery 14 is detected by the voltage sensor 18.

[0035] Here, the predetermined OCV (pOCV) is the OCV of the LFP battery, which uniquely represents the same capacity (also called common capacity CC or common battery capacity CC) before and after degradation of the LFP battery, as shown in Figure 3. As shown in Figure 3, when the OCV of the LFP battery reaches the predetermined OCV (pOCV), it is estimated that the capacity of the LFP battery is the common capacity CC, regardless of whether the LFP battery has degraded or not. The predetermined OCV (pOCV) and common capacity CC can be obtained in advance through experiments, etc., and are stored in memory 24 in advance.

[0036] If S106 is No, the controller 20 continues S104 (discharging the LFP battery 14 and obtaining the integrated current value ICV) until the OCV of the LFP battery 14 reaches a predetermined OCV (pOCV).

[0037] If S106 is answered with Yes, the controller 20 proceeds to S108. In S108, the controller 20 stores the integrated current value ICV in memory 24. This completes the first charge / discharge process.

[0038] In S110, the controller 20 decrements the number of processes N and checks if the number of processes N has become 0 (S112). If the number of processes N is not 0 (S112: No), the controller 20 returns to S102 and executes the charge / discharge process again (S102~S108). In this way, the controller 20 repeatedly executes the charge / discharge process the number of times determined by the number of processes N obtained in S100.

[0039] If S112 is Yes (if the number of processes N becomes 0), the controller 20 proceeds to S114. In S114, the controller 20 reads the integrated current value ICV from memory 24 and obtains the variable capacity VC of the LFP battery (also called variable battery capacity VC) based on the integrated current value ICV. Specifically, if the charge / discharge process is performed only once, the controller 20 uses the integrated current value ICV as is for the variable capacity VC. If the charge / discharge process is performed two or more times, the controller 20 calculates the average value of the integrated current value IVC obtained in each charge / discharge process and uses that average value for the variable capacity VC.

[0040] Next, in S116, the controller 20 adds the variable capacity VC to the common capacity CC to calculate the estimated full charge capacity EFCC [Ah] of the LFP battery 14.

[0041] Then, in S118, the controller 20 determines the degradation of the LFP battery 14 based on the estimated full charge capacity EFCC [Ah] of the LFP battery 14 and the initial full charge capacity IFCC [Ah] of the LFP battery 14. Specifically, the controller 20 calculates the ratio of the estimated full charge capacity EFCC to the initial full charge capacity IFCC ((EFCC / IFCC) × 100) to obtain the degradation level [%] of the LFP battery 14. The initial full charge capacity IFCC of the LFP battery 14 is stored in memory 24 beforehand.

[0042] According to the embodiments described above, the full charge capacity of the LFP battery 14 can be estimated, and the degradation of the LFP battery 14 can be determined.

[0043] Next, a modified example will be described. In the embodiment described above, the main battery 30 for charging the LFP battery 14 in the degradation determination process was a lead-acid battery. However, the main battery may be a high-voltage battery that supplies power to the vehicle's motor. Also, the discharge of the LFP battery in the degradation determination process may be performed on a load other than the first load 32 mounted on the vehicle.

[0044] Furthermore, the embodiments described above were for determining the degradation of LFP batteries installed in a vehicle. However, the LFP battery may be removed from the vehicle and the degradation determination process may be performed in an environment outside the vehicle. Alternatively, the degradation determination process may be performed on LFP batteries used for purposes other than vehicles.

[0045] Furthermore, the degradation determination process may be performed individually for each LFP cell (single cell) or for a battery pack consisting of multiple LFP cells. [Explanation of Symbols]

[0046] 10 Vehicle, 12 Degradation detection device, 14 LFP battery, 16 Current sensor, 18 Voltage sensor, 20 Controller, 22 Processor, 24 Memory, 25 Charger / Discharger, 26 DC-DC converter, 30 Main battery, 32 First load, 34 Second load, 36 Relay, CC Common capacity (common battery capacity), VC Variable capacity (variable battery capacity).

Claims

1. A vehicle comprising an LFP battery and a device for determining the degradation of the LFP battery, The aforementioned deterioration determination device is A charger / discharger for charging and discharging the LFP battery, The system includes a controller for controlling the charger / discharger, The aforementioned controller, The LFP battery is charged to a fully charged state using the charger / discharger. The charger / discharger discharges the fully charged LFP battery until the OCV of the LFP battery reaches a predetermined OCV of the LFP battery that uniquely represents the common battery capacity before and after degradation of the LFP battery, and the integrated value of the discharge current during that time is obtained, thereby performing a series of charge / discharge processes. The aforementioned vehicle is A load that is always supplied with power, regardless of whether the ignition switch of the aforementioned vehicle is on or off, The system comprises a main battery that supplies power to the aforementioned load, The aforementioned controller, The charging and discharging process is performed while the vehicle is parked with the ignition switch of the vehicle turned off. In the aforementioned charging and discharging process, By controlling the charger / discharger, power is supplied from the main battery to charge the LFP battery. By controlling the charger / discharger, power is supplied to the load by discharging from the LFP battery instead of the main battery. The aforementioned controller, The charge-discharge process is performed one or more times, and the variable battery capacity of the LFP battery is obtained based on one or more current integrated values ​​obtained therefrom. The full charge capacity of the LFP battery is calculated by adding the variable battery capacity to the common battery capacity. Based on the calculated full charge capacity of the LFP battery and the initial full charge capacity of the LFP battery, the degradation of the LFP battery is determined. A vehicle equipped with a device for determining the degradation of an LFP battery, characterized by the following features.

2. A vehicle equipped with a degradation determination device for an LFP battery as described in claim 1, The aforementioned controller, The charge-discharge process is performed two or more times to obtain two or more integrated current values, and the average value of the two or more integrated current values ​​is taken as the variable battery capacity. A vehicle equipped with a device for determining the degradation of an LFP battery, characterized by the following features.

3. A method for determining the degradation of an LFP battery, applicable to a vehicle equipped with an LFP battery, A step of charging the LFP battery to a fully charged state using a charger / discharger, and The charge-discharge process includes a step of discharging the fully charged LFP battery using the charger / discharger until the OCV of the LFP battery reaches a predetermined OCV of the LFP battery that uniquely represents the common battery capacity before and after degradation of the LFP battery, and acquiring the integrated value of the discharge current during that time. The aforementioned vehicle is A load that is always supplied with power, regardless of whether the ignition switch of the aforementioned vehicle is on or off, The system comprises a main battery that supplies power to the aforementioned load, The charging and discharging process is performed while the vehicle is parked and the ignition switch of the vehicle is off. In the aforementioned charging and discharging process, The LFP battery is charged by power supplied from the main battery, Instead of the main battery, the LFP battery is discharged to the load and power is supplied to the load. The aforementioned deterioration determination method is: A step of obtaining the variable battery capacity of the LFP battery based on one or more current integrated values ​​obtained by performing the charge-discharge process one or more times, A step of calculating the full charge capacity of the LFP battery by adding the variable battery capacity to the common battery capacity, The method includes a step of determining the degradation of the LFP battery based on the calculated full charge capacity of the LFP battery and the initial full charge capacity of the LFP battery. A method for determining the degradation of an LFP battery, characterized by the features described above.

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