WO2024117022A1

WO2024117022A1 - Estimating device, electricity storage device, estimating method, and estimating program

Info

Publication number: WO2024117022A1
Application number: PCT/JP2023/042119
Authority: WO
Inventors: 佑介吉岡
Original assignee: 株式会社Ｇｓユアサ
Priority date: 2022-11-30
Filing date: 2023-11-24
Publication date: 2024-06-06
Also published as: JP2024078902A

Abstract

This estimating device comprises: an acquiring unit for acquiring time-series data of a voltage of an electricity storage element when the electricity storage element is energized using a unidirectional constant current; and an estimating unit for estimating an internal resistance value of each of a plurality of types of internal resistance component on the basis of the acquired time-series data of the voltage of the electricity storage element and a period of expression of the internal resistance components, obtained in advance by means of the unidirectional constant current energization.

Description

ESTIMATION DEVICE, POWER STORAGE DEVICE, ESTIMATION METHOD, AND ESTIMATION PROGRAM

The present invention relates to an estimation device, a power storage device, an estimation method, and an estimation program.

Energy storage elements such as lithium-ion secondary batteries are used as power sources for vehicles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

It is known that the internal resistance of energy storage elements increases as they are repeatedly charged and discharged. The internal resistance of a lithium-ion battery at a certain point after it starts to be used can be mainly classified into a positive electrode charge resistance component, a negative electrode charge resistance component, an ohmic resistance component (electrolyte resistance component), and a transport diffusion resistance component. There is a need to estimate the internal resistance value for each internal resistance component.

The battery diagnostic method disclosed in Patent Document 1 uses an AC impedance method to determine in advance the time when the electrolyte resistance component and the negative electrode charge resistance component appear, and further identifies the point at which the voltage rise changes from a curve to a linear shape. The diagnostic method measures the battery voltage during constant current charging and discharging, and separates the voltage rise into the electrolyte resistance component and the negative electrode charge resistance component, the positive electrode charge resistance component, and the transport diffusion resistance component.

Patent No. 6883742

The diagnostic method described in Patent Document 1 requires performing an AC impedance method in advance, and there is room for improvement in terms of easily estimating the internal resistance value for each internal resistance component.

The purpose of this disclosure is to provide a technology that can easily estimate the internal resistance value for each internal resistance component.

The estimation device according to one aspect of the present disclosure includes an acquisition unit that acquires time series data of the voltage of a storage element when a constant current is passed through the storage element in one direction, and an estimation unit that estimates an internal resistance value for each internal resistance component based on the acquired time series data of the voltage of the storage element and the occurrence periods of multiple types of internal resistance components that are previously determined by passing a constant current in one direction.

According to this disclosure, the internal resistance value for each internal resistance component can be easily estimated.

1 is a perspective view showing a configuration example of a power storage device including an estimation device; FIG. 2 is a block diagram showing a configuration example of an estimation device. 1 is a semi-logarithmic graph showing the internal resistance-time characteristics of an initial lithium ion battery and a degraded lithium ion battery. 1 is a semi-logarithmic graph showing internal resistance versus time characteristics for various currents. 1 is a semi-logarithmic graph showing internal resistance versus time characteristics for various temperatures. 1 is a semi-logarithmic graph showing internal resistance versus time characteristics for various SOCs. FIG. 13 is a diagram showing an example of the contents of boundary point information. FIG. 2 is a diagram illustrating an estimation method executed by the estimation device. 11 is a flowchart illustrating an example of a processing procedure executed by the estimation device.

(1) An estimation device according to one aspect of the present disclosure includes an acquisition unit that acquires time series data of a voltage of an energy storage element when a constant current is passed through the element in one direction, and an estimation unit that estimates an internal resistance value for each internal resistance component based on the acquired time series data of the voltage of the energy storage element and expression periods of multiple types of internal resistance components that are determined in advance by passing a constant current in one direction.
Here, "one direction" may refer to the discharging direction of the storage element, but is not limited thereto, and may refer to the charging direction of the storage element.
In this specification, the "constant current" may be a current that includes a certain degree of fluctuation due to the influence of ripple noise and the like.

The estimation device described in (1) above can easily estimate the internal resistance value for each internal resistance component of the storage element to be estimated based on the occurrence period of a known internal resistance component. The internal resistance is estimated, for example, using the voltage behavior of the storage element when the storage element is discharged at a constant current. Therefore, for example, for an in-vehicle storage element, the internal resistance can be estimated under a normal usage environment. Since no alternating current is used to estimate the internal resistance, estimation is easy. In addition to the internal resistance value for each internal resistance component, the estimation device may also estimate the power supply performance (SOF: State Of Function) of the storage element. In other words, other states and parameters, such as the SOF and the amount of deterioration of the storage capacity for each internal resistance component, may be estimated based on the internal resistance value for each internal resistance component.

For the estimation, the boundary points of the period during which the known internal resistance components are expressed can be used. The boundary points are determined in advance, for example, by a constant current discharge test of the storage element before it is installed in a moving body such as a vehicle or a stationary storage battery facility. In general, the output current of an AC impedance measuring device is limited to about 5 amperes (A) or less. In contrast, a high output of up to several hundred A is possible with constant current discharge (DC) from the storage element. Therefore, compared to the case where the AC impedance method is used, it is possible to determine the boundary points over a wider current range. In the case of AC, the current changes from moment to moment in a sinusoidal wave shape, so when the amplitude of the current becomes large, such as several hundred A, it is difficult to uniquely determine the position of the boundary point where the voltage changes. In the case of DC, the current is constant and not sinusoidal, so the position of the boundary point is easy to uniquely determine, and the internal resistance can be accurately separated into each resistance component.

In LFP-Gr lithium-ion batteries, which contain lithium iron phosphate in the positive electrode material and graphite in the negative electrode material, there is a tendency for the timing at which multiple types of internal resistance components appear to be separated in time when a constant current is passed through them. In particular, for energy storage elements that have similar tendencies to LFP-Gr lithium-ion batteries, it is easy to identify the boundary points, and this estimation method can be used effectively.

(2) In the estimation device described in (1) above, the estimation unit may estimate the internal resistance value for each internal resistance component using a boundary point of the period during which the internal resistance component occurs, which is determined based on the internal resistance-time characteristic obtained by passing a constant current through the storage element.

The estimation device described in (2) above can easily, accurately and frequently identify boundary points based on changes in the internal resistance-time characteristics. The boundary points may be found, for example, based on changes in the slope of the internal resistance-time characteristics. When the internal resistance value is small, it is difficult to identify boundary points based on the internal resistance value itself, but by using changes in the slope of the internal resistance-time characteristics, it is possible to properly identify boundary points even when the internal resistance value is small. Multiple types of internal resistance components can be accurately estimated based on changes in the internal resistance-time characteristics.

(3) In the estimation device described in (1) or (2) above, the internal resistance component may include a first resistance component and a second resistance component, and the boundary point of the expression period may include a first boundary point corresponding to the first resistance component and a second boundary point corresponding to the second resistance component. Furthermore, the internal resistance component may include a third resistance component, and the boundary point of the expression period may include a third boundary point corresponding to the third resistance component. The estimation unit may estimate an internal resistance value of the first resistance component based on the amount of change in the voltage of the storage element from the start of current flow through the storage element to the first boundary point, and after estimating the internal resistance value of the first resistance component, estimate an internal resistance value of the second resistance component based on the amount of change in the voltage of the storage element up to the second boundary point. The estimation unit may further estimate an internal resistance value of the third resistance component based on the amount of change in the voltage of the storage element up to the third boundary point after estimating the internal resistance value of the second resistance component.

The estimation device described in (3) above can estimate the internal resistance value of each resistance component sequentially. Since the target resistance component can be estimated at the boundary point corresponding to each resistance component, distributed processing is possible and the calculation load is lighter than when the internal resistance value of each resistance component is estimated all at once at a certain point in time. In addition, the internal resistance value of each resistance component can be grasped at an earlier stage.

(4) In the estimation device described in any one of (1) to (3) above, the boundary point of the onset period may be obtained in response to the current flowing through the storage element or the temperature of the storage element.

The estimation device described in (4) above can estimate the internal resistance value of each resistance component by taking into account the current or temperature of the storage element, i.e., the usage environment of the storage element. The internal resistance can be estimated with high accuracy for storage elements that may be used under a variety of current or temperature conditions. The boundary point of the manifestation period may be found for each current and temperature of the storage element. By taking into account both the current and temperature of the storage element, the estimation accuracy of the internal resistance can be further improved.

(5) In the estimation device described in any one of (1) to (4) above, a derivation unit may be provided that uses a data table indicating the relationship between the current of the storage element and the boundary point of the onset period to derive the boundary point according to the current of the storage element acquired by the acquisition unit.

The estimation device described in (5) above can easily and accurately identify the boundary point using a data table showing the relationship between the current and the boundary point. The boundary point is found corresponding to the current of the storage element. The acquisition unit of the estimation device may further acquire the temperature of the storage element, and the derivation unit may use a data table showing the relationship between the current and temperature and the boundary point to derive the boundary point of the manifestation period corresponding to the current and temperature of the storage element acquired by the acquisition unit. For a storage element that may be used under various current or current and temperature conditions, the boundary point can be accurately derived and the internal resistance can be estimated.

(6) In the estimation device described in any one of (1) to (5) above, the internal resistance component may include a total component of an ohmic resistance component and a negative electrode charge transfer resistance component, a positive electrode charge resistance component, and a transport diffusion resistance component.

The estimation device described in (6) above can separate the internal resistance of the storage element into the total ohmic resistance component and the negative electrode charge transfer resistance component, the positive electrode charge resistance component, and the transport diffusion resistance component, and estimate the value of each internal resistance.

(7) A power storage device according to one aspect of the present disclosure includes an estimation device according to any one of (1) to (6) above, and a power storage element.

According to the energy storage device described in (7) above, the internal resistance can be separated into each internal resistance component within the energy storage device. Responsiveness can be improved by performing processing locally in a short time without communicating with a higher-level device (e.g., the vehicle's ECU (Electronic Control Unit), a monitoring device installed remotely, a cloud server, etc.). Edge computing, which estimates the internal resistance value for each internal resistance component as well as the SOF and other conditions and parameters in the energy storage device, allows a mobile object or facility in which the energy storage device is mounted to use the energy storage device more safely and stably.

(8) The power storage device described in (7) above may be a 12V battery or a 48V battery.

The power storage device described in (8) above can be used suitably for mobile applications such as vehicles. In recent years, mobile objects have been required to have an automatic driving function. The automatic driving function can be realized by the power storage device outputting status information such as SOF to a higher-level device (i.e., outputting whether or not a specified amount of power can be supplied for a specified period of time without causing an excessive voltage drop in the power storage device).

(9) In one aspect of the present disclosure, the estimation method acquires time series data of the voltage of a storage element when a constant current is passed through the storage element in one direction, and the computer executes a process of estimating the internal resistance value for each internal resistance component based on the acquired time series data of the voltage of the storage element and the occurrence periods of multiple types of internal resistance components that are previously determined by passing a constant current in one direction.

(10) An estimation program according to one aspect of the present disclosure acquires time series data of the voltage of a storage element when a constant current is passed through the storage element in one direction, and causes a computer to execute a process of estimating an internal resistance value for each internal resistance component based on the acquired time series data of the voltage of the storage element and the occurrence periods of multiple types of internal resistance components previously determined by passing a constant current in one direction.

This disclosure will be specifically described with reference to drawings showing its embodiments.

FIG. 1 is a perspective view showing an example configuration of a power storage device 1 including an estimation device 3. The power storage device 1 includes a plurality of power storage elements 2 (e.g., a plurality of power storage cells) and an estimation device 3. The power storage elements 2 and the estimation device 3 are housed, for example, in a housing case (not shown).

The storage element 2 is a secondary battery that can be charged and discharged, for example a lithium ion battery with a liquid electrolyte. The storage element 2 has a positive electrode in which a positive electrode active material layer is formed on a long strip of positive electrode substrate foil made of, for example, aluminum, an aluminum alloy, etc., and a negative electrode in which a negative electrode active material layer is formed on a long strip of negative electrode substrate foil made of, for example, copper or a copper alloy, etc. As the positive electrode active material used in the positive electrode active material layer or the negative electrode active material used in the negative electrode active material layer, any known material can be used as long as it is a positive electrode active material or a negative electrode active material capable of absorbing and releasing lithium ions. From the viewpoint of easily identifying the boundary point described later, the storage element 2 is preferably an LFP-Gr cell in which the positive electrode active material contains lithium iron phosphate and the negative electrode active material contains graphite.

Alternatively, the energy storage element (cell) 2 may be a laminated (pouch) type lithium ion battery, a lithium ion battery with a gel electrolyte, an all-solid-state lithium ion battery, a bipolar lithium ion battery (a battery in which the electrodes are electrically connected in series), a zinc-air battery, a sodium ion battery, or other electrochemical cells. The energy storage device 1 may have a single cell, or may have a module in which multiple cells are connected in series and/or parallel, a bank in which multiple modules are connected in series, or a domain in which multiple banks are connected in parallel.

The power storage device 1 of this embodiment is mounted on an engine vehicle having an internal combustion engine (engine) as a driving source, or an EV, HEV, or PHEV. The power storage device 1 is a 12 volt (V) battery or a 48 V battery. The 12 V battery can be, for example, a battery pack in which four LFP-Gr cells 2 are connected in series, or a battery pack in which four cell units in which two LFP-Gr cells 2 are connected in parallel are connected in series. Alternatively, a battery pack in which four cell units in which three LFP-Gr cells 2 are connected in parallel are connected in series may be used. The power storage device 1 is connected to electrical loads such as a vehicle ECU, a starter motor for starting the engine, and electrical equipment. When the starter motor is rotated or the vehicle is started, the power storage device 1 discharges and supplies power to the electrical loads.

The estimation device 3 is, for example, a battery management system (BMS). The estimation device 3 acquires measurement data including the voltages of the storage element 2 and the storage device 1, and the current flowing through the storage element 2, and estimates the internal resistance of the storage element 2 and the storage device 1 for each internal resistance component based on the acquired measurement data.

In the example of FIG. 1, the estimation device 3 is a flat circuit board installed on the top surface of the energy storage device 1. Alternatively, the estimation device 3 may be installed on the side of the energy storage device 1, or may be installed away from the energy storage device 1. The estimation device 3 may be located away from the energy storage device 1 and may include a server device that is communicatively connected to the BMS, or a vehicle ECU. In this case, the measurement data measured regarding the energy storage device 1 may be transmitted to the server device, etc., via communication.

FIG. 2 is a block diagram showing an example configuration of the estimation device 3. The estimation device 3 includes a control unit 31, a storage unit 32, an input unit 33, and an output unit 34. In this embodiment, the estimation device 3 is realized by a circuit board, but alternatively, the estimation device 3 may be configured to perform distributed processing by using multiple computers, may be realized by multiple virtual machines provided in a single server, or may be realized using a cloud server.

The control unit 31 is an arithmetic circuit equipped with a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. The CPU or GPU equipped in the control unit 31 executes various computer programs stored in the ROM or the storage unit 32, and controls the operation of each of the hardware components mentioned above. The control unit 31 may also have functions such as a timer that measures the elapsed time from when an instruction to start measurement is given to when an instruction to end measurement is given, a counter that counts numbers, and a clock that outputs date and time information.

The storage unit 32 includes a non-volatile storage device such as a flash memory or a hard disk drive. The storage unit 32 stores various computer programs and data referenced by the control unit 31. The storage unit 32 may be an external storage device connected to the estimation device 3.

The storage unit 32 of this embodiment stores an estimation program 321 for causing a computer to execute processing related to internal resistance estimation, and boundary point information 322 as data necessary for executing the estimation program 321. The boundary point information 322 stores information on boundary points that are the boundaries between the periods during which multiple types of internal resistance components are expressed. Details of the boundary point information 322 will be described later.

A computer program (program product) including the estimation program 321 may be provided by a non-transitory recording medium 3A on which the computer program is readably recorded. The recording medium 3A is, for example, a portable memory such as a magnetic disk, an optical disk, or a semiconductor memory. The control unit 31 reads the desired computer program from the recording medium 3A using a reading device (not shown) and stores the read computer program in the memory unit 32. Alternatively, the computer program may be provided by communication. The estimation program 321 may be a single computer program or may be composed of multiple computer programs, and may be executed on a single computer or on multiple computers interconnected by a communication network.

The input unit 33 has an interface for connecting various sensors. The sensors connected to the input unit 33 include, for example, a current sensor 41, a voltage sensor 42, and a temperature sensor 43.

The current sensor 41 is, for example, a shunt resistor, a current transformer, or a Hall effect current sensor, and measures the magnitude and direction (charging or discharging) of the current flowing through the storage element 2 in a time series. The voltage sensor 42 detects the terminal voltage of the storage element (cell) 2 in a time series. The temperature sensor 43 is, for example, a thermocouple or a thermistor, and measures the temperature of the storage element 2 in a time series. The control unit 31 acquires current data measured by the current sensor 41, voltage data measured by the voltage sensor 42, and temperature data measured by the temperature sensor 43 via the input unit 33 at any time. A temperature estimation unit that estimates the temperature of the storage element 2 in a time series using the measurement value by the temperature sensor 43 may be realized by the estimation device 3.

The output unit 34 may include an interface for connecting a display device 5. An example of the display device 5 is a liquid crystal display device.

Alternatively, the output unit 34 may be provided with a communication interface for communicating with an external device. The external device communicatively connected to the output unit 34 may be a higher-level device (e.g., a vehicle ECU). When an estimation result is obtained, the control unit 31 transmits information based on the estimation result from the output unit 34 to the external device. The external device receives the information transmitted from the output unit 34, for example, and displays the estimation result on a display of the own device based on the received information.

A method for estimating the internal resistance according to this embodiment will be described.
The inventors have studied the analysis of the internal resistance based on the voltage behavior when a constant direct current is passed through the energy storage element 2. The internal resistance of the energy storage element 2 includes a plurality of types of internal resistance components. In this embodiment, the internal resistance of the energy storage element 2 is classified into a first resistance component, a second resistance component, and a third resistance component. The first resistance component is a composite component of an ohmic resistance component and a negative electrode charge resistance component. The second resistance component is a positive electrode charge resistance component. The third resistance component is a transport diffusion resistance component. When the energy storage element 2 is discharged for a predetermined time, it is presumed that the negative electrode charge resistance usually appears earlier than the positive electrode charge resistance, and the transport diffusion resistance appears last (appearing in the order of the first resistance component, the second resistance component, and the third resistance component).

The internal resistance-time characteristic of the energy storage element 2 will now be described. The internal resistance-time characteristic may be a characteristic (profile) shown as a curve that represents the relationship between the internal resistance and time in the energy storage element 2. The inventors considered that by identifying the point at which the slope of the internal resistance-time characteristic changes, the internal resistance can be separated into each internal resistance component. The point at which the slope changes may be the point at which the slope of the internal resistance-time characteristic changes by a predetermined threshold value or more. The point at which the slope changes corresponds to a boundary point. The boundary point is the boundary of the expression period in which each internal resistance is expressed. In the internal resistance-time characteristic, the type of internal resistance component changes before and after the boundary point. In this embodiment, the boundary point is represented by the time corresponding to the boundary point, and hereinafter the boundary point is also referred to as the boundary time. The boundary point and boundary time may have a certain width.

Based on the internal resistance-time characteristics shown in Figure 3, it is possible to identify the first boundary time T1, which is the time when the slope changes for the first time after the start of discharge, the second boundary time T2, which is the time when the slope changes next, and the third boundary time T3, which is the time when the slope changes after that. The internal resistance can be separated into each resistance component: the internal resistance appearing from the start of discharge to the first boundary time T1 is the first resistance component, the internal resistance appearing from the first boundary time T1 to the second boundary time T2 is the second resistance component, and the internal resistance appearing from the second boundary time T2 to the third boundary time T3 is the third resistance component. After the third boundary time T3, the internal resistance hardly increases and remains almost constant.

The inventors conducted constant current discharge tests under various conditions on LFP-Gr type lithium ion batteries in which the first boundary time T1, the second boundary time T2, and the third boundary time T3 are relatively far apart (the intervals between each boundary time are relatively wide), and investigated the factors that affect the boundary times.

Figure 3 is a semi-logarithmic graph showing the internal resistance-time characteristics of an initial lithium-ion battery and a degraded lithium-ion battery. Figures 3 to 6, which will be described below, show the results of a constant-current discharge test using an LFP-Gr test cell (energy storage element). The vertical axis of the graphs shown in Figures 3 to 6 is the internal resistance (DCR, in mΩ), and the horizontal axis is the logarithm of the time (in seconds) that has elapsed since the start of discharge. The internal resistance (R) is the value (ΔV) obtained by subtracting the cell terminal voltage (open circuit voltage: OCV) before the start of discharge from the cell terminal voltage measured after a predetermined constant current discharge, divided by the current (I). Figures 3 to 6 show the first boundary time T1, second boundary time T2, and third boundary time T3, which are determined from the slope of the internal resistance-time characteristics in correspondence with the internal resistance-time characteristics.

The upper graph in Figure 3 shows the characteristics of a degraded product, and the lower graph shows the characteristics of an initial product. When comparing the boundary times of an initial storage element that has not been repeatedly charged and discharged with a degraded storage element that has been repeatedly charged and discharged, it was found that the times at which each internal resistance component appears are almost the same. The first boundary time T1, second boundary time T2, and third boundary time T3 are all almost the same for new and degraded products, and each boundary time does not depend on the degree of degradation of the storage element 2.

Figure 4 is a semi-logarithmic graph showing the correlation between internal resistance and time for various currents. From the top of the graph, the characteristics of the test cell when discharging DC currents of 5A, 10A, 15A, 30A, 60A, and 150A are shown. As is clear from Figure 4, the time at which each internal resistance component appears changes depending on the magnitude of the current flowing through the storage element 2. The larger the current, the shorter the first boundary time T1, second boundary time T2, and third boundary time T3.

Figure 5 is a semi-logarithmic graph showing the correlation between internal resistance and time at various temperatures. From the top of the graph, the characteristics of the test cell when discharging the same DC current at temperatures of -30°C, -20°C, -10°C, 0°C, and 25°C are shown. As is clear from Figure 5, the time at which each internal resistance component appears changes depending on the temperature of the storage element 2. The higher the temperature, the shorter the first boundary time T1, second boundary time T2, and third boundary time T3.

Figure 6 is a semi-logarithmic graph showing the correlation between internal resistance and time for various SOCs (State of Charge). From the top of the graph, it shows the characteristics of the test cell when discharging the same DC current from SOCs of 10%, 30%, 70%, and 90%. As is clear from Figure 6, the time at which each internal resistance component appears is roughly the same, and each boundary time is independent of the SOC of the storage element 2 at the start of discharge.

In consideration of the above characteristics, in this embodiment, boundary point information 322 is generated in advance, which specifies the above-mentioned first boundary time T1, second boundary time T2, and third boundary time T3 for each current and temperature of the storage element 2. The obtained boundary point information 322 is used to estimate the internal resistance of the storage element 2 in the usage environment. The estimation method of this embodiment will be described in detail below.

FIG. 7 is a diagram showing an example of the contents of the boundary point information 322. The boundary point information 322 is information that indicates the relationship between the current and temperature of the storage element 2 and the boundary time. In this embodiment, the boundary point information 322 includes a first boundary time table 3221, a second boundary time table 3222, and a third boundary time table 3223, and stores the relationship between the current and temperature and the boundary time in a data table format.

The first boundary time table 3221 is, for example, a two-dimensional table, and indicates a first boundary time T1 associated with temperature and current. A plurality of first boundary times T1 are stored for a plurality of temperatures at predetermined intervals of current. Similarly, the second boundary time table 3222 indicates a second boundary time T2 associated with temperature and current. The third boundary time table 3223 indicates a third boundary time T3 associated with temperature and current.

The first boundary time table 3221, the second boundary time table 3222, and the third boundary time table 3223 may further store boundary times by SOC. For example, in the case of a storage element 2 whose boundary time is SOC-dependent, the accuracy of separation of the internal resistance components is improved by setting the boundary time taking into account the SOC in addition to the temperature and current.

The boundary point information 322 shown in FIG. 7 is an example and is not limited to this example. The boundary point information 322 may store the relationship between the boundary point and the current and temperature using a function formula, graph, etc. The boundary time may be indicated by the discharge rate (C rate) instead of the current (amperes). The boundary point information 322 may be information indicating the relationship between the boundary time and at least one of the current and temperature.

The boundary point information 322 can be generated by performing a constant current discharge test in advance. A graph of the internal resistance-time characteristics is generated from the voltage-time characteristics (discharge curve) when the test cell is discharged. The internal resistance-time characteristics are semi-logarithmic graphs with the internal resistance on the vertical axis and the logarithm of time on the horizontal axis, as shown, for example, in Figures 3 to 6. Alternatively, the internal resistance-time characteristics may be a graph with the internal resistance on the vertical axis and the time on the horizontal axis.

The first boundary time T1, the second boundary time T2, and the third boundary time T3 are obtained by determining the points (times at which the slope changes) where the slope of the internal resistance changes based on the generated internal resistance-time characteristic. There are no particular limitations on the method for determining the points where the slope of the graph changes, but for example, the points can be determined by analyzing the graph shape (waveform) to identify the points before and after which the slope of the graph changes by more than a predetermined threshold value. The points where the slope changes may also be determined using other known methods such as graph analysis and fitting. Tests are performed under different currents and temperatures, and each boundary time is identified for each current and temperature, thereby obtaining boundary point information 322 as shown in FIG. 7.

The boundary point information 322 may be generated using a test cell that is the same as the storage element 2 whose internal resistance is to be estimated, or a test cell that has a structure, type, composition, etc. similar to that of the storage element 2.

The estimation device 3 acquires the boundary point information 322, for example, by communicating with an external server, and stores the acquired boundary point information 322 in the storage unit 32. The boundary point information 322 may be written to the estimation device 3 at the time of manufacturing the energy storage device 1 or at the time of shipment from the factory, etc.

FIG. 8 is a diagram for explaining the estimation method executed by the estimation device 3. The vertical axis in the upper graph of FIG. 8 indicates that the discharge current increases as it moves downward. FIG. 8 shows that a small current (e.g., 10 A) is discharged from the storage element 2 until time 0, and a large current (e.g., 110 A) is discharged after time 0. As shown in FIG. 8, the terminal voltage of the storage element 2 decreases over time due to the discharge from the time 0. From the start of discharge until the first boundary time T1 (t1 in FIG. 8) has passed, it is the first resistance component section in which the voltage behavior caused by the first resistance component appears. After the first boundary time T1, until the second boundary time T2 (t2 in FIG. 8) has passed, it is the second resistance component section in which the voltage behavior caused by the second resistance component appears. After the second boundary time T2, until the third boundary time T3 (t3 in FIG. 8) has passed, it is the third resistance component section in which the voltage behavior caused by the third resistance component appears.

The estimation device 3 acquires measurement data of the discharge current, voltage, and temperature of the storage element 2 through various sensors. The estimation device 3 stores the acquired measurement data in the memory unit 32. The estimation device 3 repeatedly acquires the measurement data at predetermined or appropriate intervals, and stores the data in chronological order in the memory unit 32. As a result, time series data of the current, voltage, and temperature is obtained, as shown in FIG. 8.

When new measurement data is acquired, the estimation device 3 determines whether or not to estimate the internal resistance. The estimation device 3 may determine whether or not to estimate the internal resistance by determining whether or not the current fluctuation ΔI is equal to or greater than a preset fluctuation threshold. The current fluctuation ΔI may be the difference between the current at the time of determination and the current at the measurement time immediately preceding the time of determination. In this specification, "difference" refers to the absolute value of the difference.

If the current fluctuation ΔI is equal to or greater than a preset fluctuation threshold, the estimation device 3 estimates the internal resistance. If the current fluctuation ΔI is less than a preset fluctuation threshold, the estimation device 3 does not estimate the internal resistance. The estimation device 3 may determine the direction of current flow based on the positive or negative of the obtained current, and estimate the internal resistance only if it is determined that discharging is occurring. The estimation device 3 may estimate the internal resistance when the above-mentioned current fluctuation ΔI is detected after the current in the storage element 2 has been substantially constant for a predetermined period of time or more (the current fluctuation has been substantially zero for a predetermined period of time or more).

For example, when the energy storage device 1 is mounted on an engine vehicle, the fluctuation threshold value may be set taking into consideration the current value during cranking, when the engine crankshaft is rotated by the starter motor to start the engine. When the energy storage device 1 is mounted on an EV, the fluctuation threshold value may be set taking into consideration the current value when the high-voltage system is started.

Alternatively, the estimation device 3 may estimate the internal resistance when a current fluctuation ΔI occurs, regardless of the fluctuation value of the current, or when an instruction is received from a higher-level device. The estimation device 3 may estimate the internal resistance when the current (absolute value of the current) at the time of determination is equal to or greater than a preset current threshold value.

When it is determined that the internal resistance is to be estimated, the estimation device 3 derives a first boundary time T1 that serves as a reference for estimating the internal resistance, based on the current and temperature at the time when it is determined that the internal resistance is to be estimated and the first boundary time table 3221 of the boundary point information 322. Based on the information stored in the first boundary time table 3221, the estimation device 3 reads out the first boundary time T1 (e.g., t1) that corresponds to the current and temperature at the time of determination.

The estimation device 3 waits until the first boundary time t1 has elapsed. The reference point (t=0) for starting to measure the elapsed time may be, for example, the time immediately before a current fluctuation is detected, that is, the measurement time immediately preceding the time at which it is determined that the internal resistance should be estimated. After the first boundary time t1 has elapsed, the estimation device 3 calculates the internal resistance value R1 of the first resistance component.

The internal resistance value R1 of the first resistance component is calculated by dividing the amount of change in voltage ΔV1 from the reference point to the point when the first boundary time t1 has elapsed (hereinafter also referred to as the first time point) by the current fluctuation ΔI. The amount of change in voltage ΔV1 is found by calculating the difference between the voltage at the reference point and the voltage at the first time point. To take into account minute current changes, the current fluctuation ΔI may also be found by calculating the difference between the average value of the current at each measurement time point before the first time point after the reference point and the current at the reference point (current before the fluctuation).

Similarly, the estimation device 3 derives the second boundary time T2 based on the current and temperature at the first time point and the second boundary time table 3222 of the boundary point information 322. The estimation device 3 reads out the second boundary time T2 (e.g., t2) corresponding to the current and temperature at the first time point based on the information stored in the second boundary time table 3222.

The estimation device 3 waits until the second boundary time t2 has elapsed. The reference point for starting to measure the elapsed time may be the same as the reference point for the first boundary time t1. After the second boundary time t2 has elapsed, the estimation device 3 calculates the internal resistance value R2 of the second resistance component. The internal resistance value R2 of the second resistance component is calculated by dividing the amount of change in voltage ΔV2 from the first time point to the time point at which the second boundary time t2 has elapsed (hereinafter also referred to as the second time point) by the current fluctuation ΔI. The amount of change in voltage ΔV2 is found by calculating the difference between the voltage at the second time point and the voltage at the first time point. The current fluctuation ΔI may be the difference between the average value of the current at each measurement time point before the second time point that is later than the first time point and the current at the reference point.

The estimation device 3 derives the third boundary time T3 based on the current and temperature at the second time point and the third boundary time table 3223 of the boundary point information 322. The estimation device 3 reads out the third boundary time T3 (e.g., t3) corresponding to the current and temperature at the second time point based on the information stored in the third boundary time table 3223.

The estimation device 3 waits until the third boundary time t3 has elapsed. The reference point for starting to measure the elapsed time may be the same as the reference point for the first boundary time t1. After the third boundary time t3 has elapsed, the estimation device 3 calculates the internal resistance value R3 of the third resistance component. The internal resistance value R3 of the third resistance component is calculated by dividing the amount of change in voltage ΔV3 from the second time point to the time point at which the third boundary time t3 has elapsed (hereinafter also referred to as the third time point) by the current fluctuation ΔI. The amount of change in voltage ΔV3 is found by calculating the difference between the voltage at the third time point and the voltage at the second time point. The current fluctuation ΔI may be the difference between the average value of the current at each measurement time point before the third time point that is after the second time point and the current at the reference point.

In the above, each boundary time is determined using the temperature at each point in time. Alternatively, if it is assumed that the storage element 2 will be used in an environment with relatively little temperature change, each boundary time may be determined using the temperature at a common point in time. The temperature at the common point in time may be, for example, the temperature at a reference point.

In the above, the first boundary time T1, the second boundary time T2, and the third boundary time T3 are identified in sequence at the reference point, the first time point, and the second time point. The boundary times can be identified more accurately by taking into account the current at each time point, but alternatively, the boundary times may be identified at the same timing. For example, the estimation device 3 may refer to each table of the boundary point information 322 and identify the first boundary time T1, the second boundary time T2, and the third boundary time T3 based on the current and temperature at the reference point.

The estimation device 3 may estimate the first resistance component, the second resistance component, and the third resistance component together at the same time (e.g., the third time point). The estimation device 3 may estimate the first resistance component at any time point after the first time point, may estimate the second resistance component at any time point after the second time point, and may estimate the third resistance component at any time point after the third time point.

FIG. 9 is a flowchart showing an example of a processing procedure executed by the estimation device 3. The processing in the flowchart below may be executed by the control unit 31 in accordance with the estimation program 321 stored in the memory unit 32 of the estimation device 3, or may be realized by a dedicated hardware circuit (e.g., FPGA or ASIC) provided in the control unit 31, or may be realized by a combination of these. The estimation device 3 repeatedly executes the following processing, for example, at predetermined or appropriate intervals.

The control unit 31 of the estimation device 3 acquires the current, voltage, and temperature of the storage element 2 by functioning as an acquisition unit (step S11). The control unit 31 may acquire time series data of the current, voltage, and temperature by repeatedly acquiring the current, voltage, and temperature at a predetermined or appropriate interval. The control unit 31 may acquire time series data of the current, voltage, and temperature by accepting measurement data of the current, voltage, and temperature of the storage element 2 in time series via the input unit 33. The control unit 31 may read out the time series data stored in the memory unit 32.

The control unit 31 determines whether or not to estimate the internal resistance (step S12). For example, if it is determined that the internal resistance is not to be estimated because the current fluctuation ΔI is less than a preset fluctuation threshold (step S12: NO), the control unit 31 returns the process to step S12 and waits until the current fluctuation ΔI becomes equal to or greater than the fluctuation threshold.

If it is determined that the internal resistance is to be estimated because the current fluctuation ΔI is equal to or greater than a preset fluctuation threshold (step S12: YES), the control unit 31 derives a first boundary time T1 (step S13). The control unit 31 identifies the first boundary time T1 corresponding to the current and temperature at the determination time point when it is determined that the internal resistance is to be estimated, based on the current and temperature at the determination time point and the first boundary time table 3221.

The control unit 31 determines whether the first boundary time T1 has elapsed based on the time elapsed from the reference point (step S14). If it is determined that the first boundary time T1 has not elapsed (step S14: NO), the control unit 31 returns the process to step S14 and waits until the first boundary time T1 has elapsed.

If it is determined that the first boundary time T1 has elapsed (step S14: YES), the control unit 31, functioning as an estimation unit, estimates the internal resistance value R1 of the first resistance component (step S15). The control unit 31 divides the amount of change in voltage ΔV1 from the reference point to the first point in time by the current fluctuation ΔI to obtain the internal resistance value R1 of the first resistance component.

The control unit 31 derives the second boundary time T2 (step S16). The control unit 31 identifies the second boundary time T2 corresponding to the current and temperature at the first time point based on the current and temperature at the first time point and the second boundary time table 3222.

The control unit 31 determines whether the second boundary time T2 has elapsed based on the time elapsed from the reference point (step S17). If it is determined that the second boundary time T2 has not elapsed (step S17: NO), the control unit 31 returns the process to step S17 and waits until the second boundary time T2 has elapsed.

If it is determined that the second boundary time T2 has elapsed (step S17: YES), the control unit 31, functioning as an estimation unit, estimates the internal resistance value R2 of the second resistance component (step S18). The control unit 31 divides the amount of change in voltage ΔV2 from the first point in time to the second point in time by the current fluctuation ΔI to obtain the internal resistance value R2 of the second resistance component.

The control unit 31 derives the third boundary time T3 (step S19). The control unit 31 identifies the third boundary time T3 corresponding to the current and temperature at the second point in time based on the current and temperature at the second point in time and the third boundary time table 3223.

The control unit 31 determines whether or not the third boundary time T3 has elapsed based on the time elapsed from the reference point (step S20). If it is determined that the third boundary time T3 has not elapsed (step S20: NO), the control unit 31 returns the process to step S20 and waits until the third boundary time T3 has elapsed.

If it is determined that the third boundary time T3 has elapsed (step S20: YES), the control unit 31, functioning as an estimation unit, estimates the internal resistance value R3 of the third resistance component (step S21). The control unit 31 divides the amount of change in voltage ΔV3 from the second point in time to the third point in time by the current fluctuation ΔI to obtain the internal resistance value R3 of the third resistance component.

The control unit 31 outputs the estimated results of the internal resistance, including the estimated internal resistance value R1 of the first resistance component, the estimated internal resistance value R2 of the second resistance component, and the estimated internal resistance value R3 of the third resistance component, to a higher-level device (step S22), and ends the series of processes. The higher-level device may be, for example, a vehicle ECU.

The estimation device 3 or higher-level device may determine the power supply performance (e.g., charge acceptance performance, discharge performance, etc.) of the energy storage element 2 or energy storage device 1 based on the estimated internal resistance. The estimation device 3 or higher-level device may estimate the voltage behavior of the energy storage element 2 and determine whether charging or discharging is possible, for example, by providing the estimated internal resistance values of the first resistance component, the second resistance component, and the third resistance component to an equivalent circuit model that simulates the voltage behavior of the energy storage element 2. By using the internal resistance value corresponding to the actual current and temperature of the energy storage element 2, the accuracy of the determination of the power supply performance can be improved.

According to this embodiment, the internal resistance value can be easily and accurately estimated by separating each internal resistance component using pre-prepared boundary point information 322. Since the boundary point information 322 is set for each current and temperature, the boundary time can be determined taking into account the current and temperature used by the storage element 2. By determining each boundary time based on the current and temperature at each specific time, the internal resistance corresponding to the actual usage state of the storage element 2 can be accurately estimated.

The timing for starting internal resistance estimation can be adjusted by setting it to the time when current fluctuation ΔI is equal to or greater than the fluctuation threshold. For example, internal resistance estimation can be performed when an amount of current suitable for estimating internal resistance flows, such as during cranking or when the high-voltage system starts up, or when an operation is repeated in a cycle suitable for estimating internal resistance, enabling necessary and sufficient estimation.

The estimation device, estimation method, and estimation program can be applied to applications other than vehicles, and may be applied to flying objects such as aircraft, flying vehicles, and HAPS (High Altitude Platform Stations), as well as to ships and submarines. The estimation device, estimation method, and estimation program are preferably applied to moving objects that require a high level of safety (requiring real-time calculations), but they may also be applied to stationary energy storage devices, not limited to moving objects.

The embodiments disclosed herein are illustrative in all respects and should not be considered as limiting. The technical features described in each embodiment can be combined with each other, and the scope of the present invention is intended to include all modifications within the scope of the claims and the scope equivalent to the claims.
The sequences shown in each embodiment are not limited, and the order of each process may be changed and multiple processes may be executed in parallel, as long as there is no contradiction. The subject of each process is not limited, and the process of each device may be executed by another device, as long as there is no contradiction.

　The matters described in each embodiment can be combined with each other. Furthermore, the independent claims and dependent claims described in the claims can be combined with each other in any and all combinations, regardless of the citation format. Furthermore, the claims use a format in which a claim cites two or more other claims (multi-claim format), but this is not limited to this. They may also be written in a format in which multiple claims cite at least one other claim (multi-multi-claim).

REFERENCE SIGNS LIST 1 Energy storage device 2 Energy storage element 3 Estimation device 31 Control unit 32 Storage unit 33 Input unit 34 Output unit 321 Estimation program 322 Boundary point information 3221 First boundary time table 3222 Second boundary time table 3223 Third boundary time table 3A Recording medium

Claims

an acquisition unit that acquires time series data of a voltage of the storage element when a constant current is applied to the storage element in one direction;
and an estimation unit that estimates an internal resistance value for each internal resistance component based on the acquired time series data of the voltage of the storage element and the occurrence periods of multiple types of internal resistance components that are previously obtained by passing a constant current in one direction.
The estimation device according to claim 1, wherein the estimation unit estimates the internal resistance value for each internal resistance component using a boundary point of a period during which the internal resistance component is expressed, the boundary point being determined based on an internal resistance-time characteristic obtained by passing a constant current through the storage element.
the internal resistance component includes a first resistance component and a second resistance component,
the boundary points of the onset period include a first boundary point corresponding to the first resistance component and a second boundary point corresponding to the second resistance component;
The estimation unit is
estimating an internal resistance value of the first resistance component based on an amount of change in voltage of the storage element from a time when current is started to be passed through the storage element to the first boundary point;
3 . The estimation device according to claim 1 , further comprising: a step of estimating an internal resistance value of the first resistance component, and then estimating an internal resistance value of the second resistance component based on an amount of change in voltage of the storage element up to the second boundary point.
The estimation device according to claim 1 or 2, wherein the onset period is determined in response to a current flowing through the power storage element or a temperature of the power storage element.
The estimation device according to claim 1 or 2;
A power storage device comprising: a power storage element.
Obtaining time series data of a voltage of the storage element when a constant current is applied to the storage element in one direction;
The estimation method includes a process in which a computer executes a process of estimating an internal resistance value for each internal resistance component based on the acquired time series data of the voltage of the storage element and the occurrence periods of multiple types of internal resistance components obtained in advance by passing a constant current in one direction.
Obtaining time series data of a voltage of the storage element when a constant current is applied to the storage element in one direction;
An estimation program that causes a computer to execute a process of estimating an internal resistance value for each internal resistance component based on the acquired time series data of the voltage of the storage element and the occurrence periods of multiple types of internal resistance components that are previously obtained by passing a constant current in one direction.