Battery degradation indicator information acquisition device and method, battery pack, and electric vehicle

Abstract

An apparatus and method for obtaining battery degradation index information are provided. The apparatus includes a measuring unit that generates voltage sample values ​​and current sample values ​​of a battery cell, and a control unit that sets first to n ranges of interest and first to n sampling rates for the current charge-discharge process based on previous degradation index information associated with the previous charge-discharge process. The control unit acquires the voltage sample values ​​and current sample values ​​at at least one sampling rate selected from a reference sampling rate and the first to n sampling rates during the current charge-discharge process. The control unit determines current degradation index information by performing peak detection for at least one of the first to n ranges of interest from the current differential voltage profile of the battery cell, which is generated based on the voltage sample values ​​and current sample values ​​acquired during the course of the current charge-discharge process.

Description

Technical Field

[0001] The present invention relates to an apparatus and method for obtaining deterioration index information of a battery.

[0002] This application claims priority based on Korean Patent Application No. 10-2023-0107209 filed on August 16, 2023, and Korean Patent Application No. 10-2024-0095689 filed on July 19, 2024, and the contents disclosed in the specifications and drawings of the applications are all incorporated into this application.

Background Art

[0003] Recently, the demand for portable electronic products such as notebook computers, video cameras, and mobile phones has increased rapidly, and with the full-scale development of electric vehicles, energy storage batteries, robots, satellites, etc., research on high-performance batteries capable of repeated charging and discharging has been actively conducted.

[0004] Currently commercially available batteries include nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, lithium batteries, etc. Among these, lithium batteries are in the spotlight because they have almost no memory effect compared to nickel-based batteries, so they can be freely charged and discharged, have a very low self-discharge rate, and have a high energy density.

[0005] Generally, such batteries deteriorate with use. Therefore, in order to accurately estimate the state of charge (SOC) and state of health (SOH) of a deteriorated battery, or to control the extension of the life of a deteriorated battery, it is necessary to accurately judge the state of the battery.

[0006] Conventionally, after detecting at least two or more peaks from a differential voltage profile generated based on measured values of battery voltage and current, a method of estimating the degree of battery deterioration by comparing the peak characteristic information of the two peaks is used.

[0007] However, as the battery degrades, the shape of the differential voltage profile gradually changes, which can reduce the accuracy of detecting each peak in the differential voltage profile if the sampling rate for voltage and current measurements is low.

[0008] To improve this, it is necessary to increase the applied sampling rate, which not only requires a large amount of memory to record battery data, but also increases the power consumption required for sampling and places an excessive computational load on processing the battery data. [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention has been made to solve the above problems, and aims to provide an apparatus and method that can acquire degradation index information that sufficiently reflects the actual degradation state of battery cells, while reducing the computational load on the battery system by variably adjusting the sampling rate used to measure the voltage and current that form the basis for generating the differential voltage profile of battery cells, as well as a battery pack including the apparatus and an electric vehicle including the battery pack.

[0010] Other objectives and advantages of the present invention can be understood from the following description and will be understood more clearly from the embodiments of the present invention. Furthermore, it will be readily understood that the objectives and advantages of the present invention can be achieved by the means and combinations thereof set forth in the claims. [Means for solving the problem]

[0011] A battery degradation index information acquisition device according to one aspect of the present invention for achieving the above objective includes: a measuring unit configured to generate voltage sample values ​​and current sample values ​​of a battery cell; and a control unit configured to set first to n ranges of interest and first to n sampling rates for the current charge-discharge process based on previous degradation index information associated with the previous charge-discharge process, where n is a natural number of 2 or more. The control unit is configured to acquire voltage sample values ​​and current sample values ​​of the battery cell at at least one sampling rate selected from a reference sampling rate and the first to n sampling rates during the progress of the current charge-discharge process. The control unit is configured to determine current degradation index information by performing peak detection for at least one of the first to n ranges of interest from the current differential voltage profile of the battery cell, which is generated based on the voltage sample values ​​and current sample values ​​acquired during the progress of the current charge-discharge process.

[0012] The control unit may be configured to select the i-th sampling rate from the first to n sampling rates if, during the current charge / discharge process, the capacity value of the battery cell falls within the i-th range of interest among the first to n ranges of interest, where i is a natural number less than or equal to n. The control unit may also be configured to select the reference sampling rate if, during the current charge / discharge process, the capacity value of the battery cell falls outside all of the first to n ranges of interest.

[0013] Each of the first to n sampling rates may be greater than the reference sampling rate.

[0014] At least two of the first to n sampling rates can be the same as each other.

[0015] The aforementioned prior degradation index information may include at least one peak feature data from the first to nth peaks of interest already detected from the previous differential voltage profile. The peak feature data may represent at least one of capacitance values, differential voltage values, or kurtosis.

[0016] The control unit may be configured to set the size of the ith range of interest for the current charge / discharge process by applying a predetermined negative correspondence to the kurtosis of the ith peak of interest included in the previous degradation index information, where i is a natural number less than or equal to n.

[0017] The control unit may be configured to set an upper limit of the ith range of interest for the current charge / discharge process such that it is equal to the capacity value of the ith peak of interest among the first to nth peaks of interest included in the previous degradation index information, where i is a natural number less than or equal to n.

[0018] The control unit may be configured to set the ith sampling rate for the current charge / discharge process by applying a predetermined positive correspondence to the kurtosis of the ith peak of interest included in the previous degradation index information, where i is a natural number less than or equal to n.

[0019] Another embodiment of the present invention includes a battery degradation indicator information acquisition device.

[0020] An electric vehicle according to yet another aspect of the present invention includes the battery pack.

[0021] A method for obtaining battery degradation index information according to another aspect of the present invention includes the steps of: setting first to n ranges of interest and first to n sampling rates for the current charge-discharge process based on previous degradation index information associated with the previous charge-discharge process; acquiring voltage sample values ​​and current sample values ​​of the battery cell at at least one sampling rate selected from a predetermined reference sampling rate and the first to n sampling rates during the progress of the current charge-discharge process; and determining current degradation index information by performing peak detection for at least one of the first to n ranges of interest from the current differential voltage profile of the battery cell generated based on the voltage sample values ​​and current sample values ​​acquired during the progress of the current charge-discharge process, where n is a natural number greater than or equal to 2.

[0022] The step of obtaining voltage and current sample values ​​of the battery cell may include the following steps, which are repeated during the current charge / discharge process: if the capacity value of the battery cell falls within the i-th range of interest among the first to n ranges of interest, the step of obtaining voltage and current sample values ​​of the battery cell at the i-th sampling rate among the first to n sampling rates; and if the capacity value of the battery cell falls outside all of the first to n ranges of interest, the step of obtaining voltage and current sample values ​​of the battery cell at the reference sampling rate, where i is a natural number less than or equal to n.

[0023] The aforementioned prior degradation index information may include at least one peak feature data from the first to nth peaks of interest already detected from the previous differential voltage profile. The peak feature data may represent at least one of capacitance values, differential voltage values, or kurtosis.

[0024] The upper limit value of the i-th range of interest for the current charge-discharge process can be set equal to the capacitance value of the i-th peak of interest included in the previous degradation index information. i can be a natural number less than or equal to n.

[0025] The i-th sampling rate for the current charge-discharge process can be set to have a predetermined positive correlation with the sharpness of the i-th peak of interest included in the previous degradation index information. i is a natural number.

Advantages of the Invention

[0026] According to at least one embodiment of the present invention, when measuring the voltage and current of a battery cell that serves as a basis for generating a differential voltage profile, by dynamically changing the sampling rate, in addition to reducing the computational load, it is possible to improve the detection accuracy of peaks on the differential voltage profile, which is a degradation index of the battery cell.

[0027] Further, according to at least one embodiment of the present invention, within the entire capacitance range, the range of interest, which is the capacitance range in which each peak is predicted to appear, is distinguished from the remaining capacitance range, and by setting the sampling rate applied to the range of interest to be larger than the sampling rate applied to the remaining capacitance range, it is possible to suppress an excessive increase in the amount of computation and data storage space required to obtain the differential voltage profile.

[0028] The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

[0029] The following drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further understand the technical idea of the present invention together with the detailed description of the invention. Therefore, the present invention should not be construed as being limited only to the matters described in the drawings.

Brief Description of the Drawings

[0030] [Figure 1] This diagram illustrates the configuration of an electric vehicle according to the present invention. [Figure 2] This graph is used to compare two voltage profiles generated by two adjacent charge / discharge processes. [Figure 3] This graph is referenced to compare two differential voltage profiles that have a one-to-one correspondence with the two voltage profiles shown in Figure 2. [Figure 4] This is a diagram referenced to illustrate the procedure for defining the scope of interest for a specific charge-discharge process. [Figure 5a] This figure is referenced to illustrate the change in peak detection power in response to changes in the applied sampling rate. [Figure 5b] This figure is referenced to illustrate the change in peak detection power in response to changes in the applied sampling rate. [Figure 5c] This figure is referenced to illustrate the change in peak detection power in response to changes in the applied sampling rate. [Figure 6] This flowchart is used to illustrate, in part, a method for obtaining battery degradation indicator information according to another embodiment of the present invention. [Figure 7] This flowchart is referenced to illustrate the subroutine in step S610 of Figure 6. [Figure 8] This flowchart is referenced to illustrate the subroutine in step S611 of Figure 6. [Modes for carrying out the invention]

[0031] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. Prior to this, terms and words used in this specification and in the claims shall not be interpreted in their usual and dictionary sense, but rather in a sense and concept appropriate to the technical idea of ​​the present invention, in accordance with the principle that the inventor himself may appropriately define the concept of terms in order to best describe the invention.

[0032] Therefore, it should be understood that the configurations shown in the embodiments described herein represent only one of the most preferred embodiments of the present invention and do not represent the entire technical concept of the present invention, and that there are various equivalents and modifications that can be substituted therein at the time of filing this application.

[0033] Terms that include ordinal numbers, such as "first," "second," etc., are used to distinguish one of the various components from the rest, and are not used to limit the components by such terms.

[0034] Throughout the specification, when a part "includes" a component, this means, unless otherwise stated, that it may include other components rather than excluding them. Furthermore, terms such as <control unit> in the specification mean a unit that processes at least one function or operation, which can be implemented by hardware, software, or a combination of hardware and software.

[0035] Furthermore, throughout the specification, when one part is described as being "connected" to another part, this includes not only cases where they are "directly connected," but also cases where they are "indirectly connected" to each other through other elements.

[0036] Figure 1 is a diagram illustrating the configuration of an electric vehicle according to the present invention.

[0037] Referring to Figure 1, the electric vehicle 1 includes a vehicle controller 2, a battery pack 10, a switching device 20, an inverter 30, and an electric motor 40.

[0038] The charge and discharge terminals P+ and P- of the battery pack 10 can be electrically coupled to the inverter 30 and / or charger 3 via a charging cable or the like. The charger 3 is included in the electric vehicle 1 or is provided at a charging station.

[0039] The vehicle controller 2 (e.g., ECU: Electronic Control Unit) is configured to transmit a key-on signal to the battery management system 100 in response to the user switching a start button (not shown) on the electric vehicle 1 to the ON position. The vehicle controller 2 is also configured to transmit a key-off signal to the battery management system 100 in response to the user switching the start button to the OFF position. The charger 3 can communicate with the vehicle controller 2 to supply charging power in constant current charging mode, constant voltage charging mode, and / or constant power charging mode to the battery 11 via the charge / discharge terminals P+ and P- of the battery pack 10.

[0040] The battery pack 10 includes a battery 11 and a battery management system 100. The battery management system 100 corresponds to the "battery degradation indicator information acquisition device" as described in the claims of this specification.

[0041] The battery 11 includes a cell group 12 and a case 13. The case 13 defines the overall shape of the battery 11 and provides the internal space in which the cell group 12 is arranged. The case 13 is fixedly fastened to the battery room provided in the electric vehicle 1 using bolts or the like.

[0042] The cell group 12 is arranged (housed) in an internal space provided by the case 13 and includes at least one battery cell BC. The type of battery cell BC is not particularly limited, as long as it is capable of repeated charging and discharging, such as a lithium-ion cell.

[0043] If cell group 12 includes multiple battery cells, these battery cells can be connected in series, parallel, or in a series-parallel combination.

[0044] The switching device 20 is electrically connected in series with the battery 11 via a power path connecting the battery 11 and the inverter 30. In Figure 1, the switching device 20 is shown connected between the positive terminal and the charge / discharge terminal P+ of the battery 11. The switching device 20 is controlled on / off in response to a switching signal from the battery management system 100. The switching device 20 may be a mechanical contactor that is switched on / off by the magnetic force of a coil, or a semiconductor switch such as a MOSFET (Metal Oxide Semiconductor Field Effect transistor).

[0045] The inverter 30 is provided to convert the DC current from the cell group 12 into AC current in response to a command from the battery management system 100 or the vehicle controller 2.

[0046] The electric motor 40 is driven using AC power from the inverter 30. For example, a three-phase AC motor 40 can be used as the electric motor 40.

[0047] The battery management system 100 includes a measuring unit, a control unit 130, and a storage unit 140. The battery management system 100 may further include an ambient temperature sensor 117. The battery management system 100 may further include a communication circuit 150.

[0048] The measuring unit includes a voltage sensor 111 and a current sensor 113. The measuring unit may further include a temperature sensor 115. For the sake of explanation, the following description will assume that the measuring unit includes the voltage sensor 111, the current sensor 113, and the temperature sensor 115.

[0049] The voltage sensor 111 is connected in parallel to the battery 11 and is configured to detect the battery voltage, which is the voltage across the battery 11, and to generate a voltage signal representing the detected battery voltage.

[0050] Of course, the voltage sensor 111 can also be connected to the positive and negative terminals of each battery cell BC included in the battery 11, detect the cell voltage which is the voltage across both ends of each battery cell BC, and output a further voltage signal representing the cell voltage to the control unit 130.

[0051] The current sensor 113 is connected in series with the battery 11 via a current path between the battery 11 and the inverter 30. The current sensor 113 is configured to detect the battery current, which is the current flowing through the battery 11, and to generate a current signal representing the detected battery current. The current sensor 113 can be implemented by one or more known current sensing elements, such as a shunt resistor or a Hall effect element.

[0052] The temperature sensor 115 is configured to detect the battery temperature and generate a temperature signal representing the detected battery temperature. The temperature sensor 115 may be positioned within the case 13 so as to be able to detect a temperature close to the actual temperature of the battery 11. For example, the temperature sensor 115 may be mounted on the surface of at least one battery cell BC included in the cell group 12, so that the surface temperature of the battery cell BC can be detected as the battery temperature. For reference, when the term "temperature detected value" is used herein, it may refer to the battery temperature detected value.

[0053] The ambient temperature sensor 117 is configured to detect the ambient temperature (atmospheric temperature), which is the temperature at a predetermined location away from the battery 11, and to generate a temperature signal representing the detected ambient temperature. The ambient temperature sensor 117 may be placed at a predetermined location outside the case 13 where heat exchange between the battery 11 and the outside air takes place.

[0054] Each of the temperature sensor 115 and the ambient temperature sensor 117 can be implemented using one or more known temperature detection elements such as thermocouples, thermistors, and bimetals.

[0055] The communication circuit 150 is configured to support wired or wireless communication between the control unit 130 and the vehicle controller 2. Wired communication may be, for example, CAN (controller area network) communication, and wireless communication may be, for example, Zigbee® or Bluetooth® communication. Of course, the type of communication protocol is not particularly limited as long as it supports wired or wireless communication between the control unit 130 and the vehicle controller 2. The communication circuit 150 may include an output device (e.g., a display, a speaker) that provides information received from the control unit 130 and / or the vehicle controller 2 in a user-recognizable format.

[0056] The control unit 130 is operably coupled to at least one of the switching device 20, voltage sensor 111, current sensor 113, temperature sensor 115, ambient temperature sensor 117, and communication circuit 150. Operatable coupling of two components means that the two components are directly or indirectly connected to enable the transmission and reception of signals in one direction or bidirectionally.

[0057] The control unit 130 can collect a voltage signal from the voltage sensor 111, a current signal from the current sensor 113, a temperature signal from the temperature sensor 115 (sometimes called the "battery temperature signal"), and / or a temperature signal from the ambient temperature sensor 117 (sometimes called the "ambient temperature signal"). The control unit 130 can use an internally installed ADC (Analog to Digital Converter) to convert and record the analog signals collected from sensors 111, 113, 115, and 117 into digital values.

[0058] The control unit 130 may also be called a "control circuit" or "battery controller," and can be implemented in hardware using at least one of the following: ASICs (application-specific integrated circuits), DSPs (digital signal processors), DSPDs (digital signal processing devices), PLDs (programmable logic devices), FPGAs (field programmable gate arrays), microprocessors, or other electrical units for performing functions.

[0059] The storage unit 140 may include, for example, at least one type of storage medium from among flash memory type, hard disk type, SSD type (Solid State Disk type), SDD type (Silicon Disk Drive type), multimedia card micro type, RAM (random access memory), SRAM (static random access memory), ROM (read-only memory), EEPROM (electrically erasable programmable read-only memory), and PROM (programmable read-only memory). The storage unit 140 can store data and programs required for the calculation operations performed by the control unit 130. The storage unit 140 can store data indicating the results of the calculation operations performed by the control unit 130. Although Figure 1 shows the storage unit 140 as being physically independent of the control unit 130, it can also be incorporated into the control unit 130.

[0060] The control unit 130 can turn on the switching device 20 in response to a key-on signal. The control unit 130 can also turn off the switching device 20 in response to a key-off signal. The key-off signal is a signal that induces a switch from the cycle state to the idle state. Alternatively, the vehicle controller 2 can be responsible for the on / off control of the switching device 20 instead of the control unit 130.

[0061] When the switching device 20 is turned on and the inverter 30 or charger 3 is operating, the battery 11 enters a cycle state. Conversely, when the switching device 20 is turned off, or when the inverter 30 and charger 3 are stopped, the battery 11 enters a dormant state.

[0062] The term "cycle state" refers to the state in which the battery 11 is being charged and discharged, while the term "dormant state" refers to the state in which the charging and discharging of the battery 11 has stopped. When the battery 11 is in a cycle state or dormant state, it means that each battery cell BC contained within the battery 11 is also in a cycle state or dormant state.

[0063] For reference, the charge-discharge process described herein refers to a procedure that follows a protocol for charging and / or discharging a battery cell BC over a predetermined voltage range. The charge-discharge process includes at least one of a charging procedure and a discharging procedure for the battery cell BC, and may further include a resting procedure. As an example, the charge-discharge process may be a procedure for constantly charging the battery cell BC until its voltage reaches the upper limit of a predetermined voltage range. As another example, the charge-discharge process may be a procedure for constantly discharging the battery cell BC until its voltage reaches the lower limit of a predetermined voltage range. Of course, the charge-discharge process may also include only one of the constant-current discharging function and the constant-current charging function.

[0064] During the charging and discharging process, the control unit 130 can periodically or aperiodically collect voltage and current signals representing the voltage and current of the battery cell BC. Based on the collected voltage and current signals, the control unit 130 determines voltage sample values ​​and current sample values, and by integrating the current sample values ​​over time, it can determine the capacity value of the battery cell BC at each sampling timing during the charging and discharging process. This allows the voltage time series and capacity time series, which reflect the changes in the voltage sample values ​​and capacity values ​​over time, to be updated in accordance with the sampling timing of the voltage and current signals.

[0065] The control unit 130 can generate a voltage profile showing the correspondence between the voltage and capacity of a battery cell BC based on the voltage time series and capacity time series over a period from the start of the charge / discharge process to a specific point in time during the charge / discharge process or to the completion of the charge / discharge process. The control unit 130 can also generate a differential voltage profile showing the correspondence between the capacity and differential voltage of the battery cell BC from the voltage profile of the battery cell BC. The voltage time series, current time series, and capacity time series are sometimes referred to as voltage history, current history, and capacity history, respectively.

[0066] Figure 2 is a graph referenced to compare two voltage profiles generated by two adjacent charge / discharge processes. In Figure 2, the X-axis (horizontal axis) represents charge / discharge capacity, and the Y-axis (vertical axis) represents voltage. In this invention, the symbol m used as an ordinal number is assumed to be a natural number greater than or equal to 1, representing the number of cycles in the previous charge / discharge process. For example, if a total of 99 charge / discharge processes have been completed from the time of shipment of the battery cell BC to the present, then m is 99. The m-th charge / discharge process may also be called the "previous charge / discharge process" or "previous charge / discharge process," and the (m+1)th charge / discharge process may also be called the "current charge / discharge process" or "current charge / discharge process." For reference, a voltage profile may also be called a voltage curve, QV profile, or QV curve.

[0067] The m-th voltage profile 201 represents the correspondence between the capacity and voltage of battery cell BC, based on the capacity history and voltage history of battery cell BC during the progression of the m-th charge-discharge process.

[0068] Similarly, the (m+1) voltage profile 202 represents the correspondence between the capacity and voltage of battery cell BC, based on the capacity history and voltage history of battery cell BC during the progression of the (m+1) charge-discharge process.

[0069] For reference, capacity history can show the time-series change in the charge or discharge capacity of battery cell BC from the start to the end of a charge or discharge event. Similarly, voltage history can show the time-series change in the voltage of battery cell BC from the start to the end of a charge or discharge event.

[0070] Referring to Figure 2, when comparing the m-th voltage profile 201 and the (m+1)th voltage profile 202, the voltage change in the (m+1)th voltage profile 202 is greater than the voltage change in the m-th voltage profile 201 within the same capacity range. This difference is thought to be due to a higher degree of degradation of the battery cell BC, caused by potential capacity loss of the positive and / or negative electrodes, lithium deposition, etc., that may occur as the charge and discharge process of the battery cell BC progresses.

[0071] Figure 3 is a graph referenced to compare two differential voltage profiles that have a one-to-one correspondence with the two voltage profiles shown in Figure 2.

[0072] In Figure 3, the X-axis (horizontal axis) shows the same charge / discharge capacity as in Figure 2, and the Y-axis (vertical axis) shows the differential voltage. The differential voltage dV / dQ represents the ratio of the change in voltage dV to the change in charge or discharge capacity dQ.

[0073] Referring to Figures 2 and 3, the control unit 130 can obtain the mth differential voltage profile 301 by differentiating the voltage history of the battery cell BC acquired during the progress of the mth charge-discharge process with respect to the corresponding capacity history. That is, the mth voltage profile 201 can be seen as a function of either capacity or voltage to the other, and the mth differential voltage profile 301 may be the result of taking the first derivative of the voltage of the mth voltage profile 201 with respect to capacity. The mth differential voltage profile 301 is sometimes called the "previous differential voltage profile" or "previous differential voltage profile".

[0074] Similarly, the control unit 130 can obtain the (m+1)th differential voltage profile 302 by differentiating the voltage history of the battery cell BC acquired during the progress of the (m+1)th charge-discharge process with respect to the corresponding capacity history. The (m+1)th differential voltage profile 302 may be the result of taking the first derivative of the voltage of the (m+1)th voltage profile 202 with respect to capacity.

[0075] Referring to Figure 3, the (m+1)th differential voltage profile 302 has the shape of the mth differential voltage profile 301 contracted to the left along the X-axis. Even if the mth differential voltage profile 301 and the (m+1)th differential voltage profile 302 have the same voltage range, the capacitance history of the mth differential voltage profile 301 and the capacitance history of the (m+1)th differential voltage profile 302 do not have the same capacitance range. The (m+1)th differential voltage profile 302 is sometimes called the "current differential voltage profile" or "the current differential voltage profile".

[0076] For reference, the (m+1)th charge-discharge process performed to obtain the (m+1)th differential voltage profile 302 can be performed after the battery cell BC has been further charged and discharged to some extent since the end of the mth charge-discharge process performed to obtain the mth differential voltage profile 301. Therefore, the degradation index of battery cell BC reflected in the (m+1)th differential voltage profile 302 may be more advanced than the degradation index of battery cell BC reflected in the mth differential voltage profile 301.

[0077] Compared to the two voltage profiles 201 and 202 in Figure 2, the two differential voltage profiles 301 and 302 shown in Figure 3 have multiple peaks. These multiple peaks can be distinguished from one another by their order and / or position (capacity value), etc. For example, the multiple peaks may be ranked (in descending or ascending order) according to their respective capacity values. In this regard, the total number of peaks located in the differential voltage profile for a particular voltage range and / or a particular capacity range may be determined by the types of positive and negative electrode active materials of the battery cell BC, etc.

[0078] The term "peak" in any profile may refer collectively to either the maximum point or the minimum point, or both, that appear on that profile.

[0079] In the present invention, the peak feature information may include at least one peak parameter that represents the characteristics of at least one peak appearing in the differential voltage profile.

[0080] As an example, the peak feature information of any given peak includes at least one peak parameter. Here, the positional information of the peak (i.e., 2D coordinates), such as capacitance and differential voltage, and kurtosis, may be included as individual peak parameters in the peak feature information.

[0081] In this invention, the degradation index information of the battery cell BC may include peak feature information for each of the first to nth peaks of interest located on the differential voltage profile, where n is a natural number greater than or equal to 2.

[0082] In this invention, the peak of interest can refer to two or more predetermined peaks among a plurality of peaks located on the differential voltage profile. In this regard, each of the plurality of peaks may indicate a particular type of degradation state, either individually or in comparison with other peaks. Therefore, each peak related to the degradation state to be diagnosed may be programmed to be set as the peak of interest.

[0083] In Figure 3, the labels P11 to P17 represent multiple peaks located on the m-th differential voltage profile 301. P21 to P27 represent multiple peaks located on the (m+1)-th differential voltage profile 302. If k is a natural number less than or equal to the total number of peaks, then peak P2k in the (m+1)-th differential voltage profile 302 is a left-shifted version of peak P1k in the m-th differential voltage profile 301. Therefore, the two peaks P1k and P2k are associated with the same type of degradation state.

[0084] Furthermore, k corresponds to the order in which multiple peaks appear in a particular differential voltage profile. For example, assuming that the mth voltage profile 201 was obtained by constant current discharge, P11 is the first peak with the lowest capacitance to appear in the mth differential voltage profile 301, and P17 is the last (seventh) peak with the highest capacitance to appear in the mth differential voltage profile 301.

[0085] Among the multiple peaks in each differential voltage profile, n peaks located in a specific order can be set as the first to nth peaks of interest of that differential voltage profile.

[0086] Figure 3 shows that four of the multiple peaks P11 to P17 that appeared in the m-th differential voltage profile 301—P12, P13, P14, and P16—were set as the first to fourth peaks of interest P[1] to P[4], respectively. Therefore, we will assume n=4 below.

[0087] Assuming that the multiple peaks P11 through P17 are ranked in descending order based on their volume values, the peak of interest P[1] is the second peak (the first maximum point), the peak of interest P[2] is the third peak (the second minimum point), the peak of interest P[3] is the fourth peak (the second maximum point), and the peak of interest P[4] is the sixth peak (the third maximum point).

[0088] The peaks P22, P23, P24, and P26 on the (m+1)th differential voltage profile 302 correspond, respectively, to the peaks of interest P[1] to P[4] on the mth differential voltage profile 301, and each of the peaks P22, P23, P24, and P26 is a peak of interest to be detected from the (m+1)th differential voltage profile 302.

[0089] Hereinafter, i is assumed to be a natural number less than or equal to n. The control unit 130 can set a specific capacitance range, including the capacitance value of the ith peak of interest on the differential voltage profile 301 associated with the mth charge-discharge cycle, as the ith range of interest associated with the (m+1)th charge-discharge cycle. That is, each time a charge-discharge process is performed, the first to nth ranges of interest, individually associated with the first to nth peaks of interest, can be set. The ith range of interest is for detecting the ith peak of interest.

[0090] Figure 4 is a diagram referenced to illustrate the procedure for setting the scope of interest for a specific charge-discharge process.

[0091] The first to fourth regions of interest R#1 to R#4 shown in Figure 4 are for the (m+1) charge-discharge process.

[0092] When setting the scope of interest for the (m+1)th charge / discharge process, it is possible to utilize battery cell BC degradation index information (sometimes called "previous degradation index information," "previous degradation index information," or "mth degradation index information") that has been updated based on the results of the already completed mth charge / discharge process.

[0093] Referring to Figure 4, the control unit 130 can set first to fourth interest ranges R#1 to R#4 that correspond one-to-one with first to fourth interest peaks P[1] to P[4] based on peak feature information for first to fourth interest peaks P[1] to P[4] acquired through the m-th charge-discharge process, before starting the (m+1) charge-discharge process.

[0094] The control unit 130 can determine the size of the range of interest corresponding to each of the first to nth peaks of interest P[1] to P[4], and / or its upper and lower limits, based on the peak feature information for each of the first to nth peaks of interest.

[0095] The control unit 130 can set the size of the i-th range of interest R#i by applying a predetermined negative correspondence to the kurtosis of the i-th peak of interest P[i] obtained in the m-th charge / discharge process. That is, the larger the kurtosis of the i-th peak of interest P[i], the smaller the size of the i-th range of interest R#i can be. Here, the kurtosis of any peak means the degree of sharpness of the peak. For example, the kurtosis of a particular peak can be determined in the same way as the difference between the mean differential voltage in a certain capacitance range with the capacitance value of a particular peak as the median value and the differential voltage of a particular peak.

[0096] As an example, referring to Figure 4, the magnitude of the fourth region of interest R#4 may be the result of applying a predetermined negative correspondence to the kurtosis of the fourth peak of interest P[4] obtained through the mth charge-discharge process.

[0097] When setting the i-th range of interest R#i, the control unit 130 can set the upper limit of the i-th range of interest R#i to be equal to the capacity value of the i-th peak of interest P[i] included in the degradation index information of the battery cell BC acquired in the m-th charge / discharge process. As an example, Figure 4 can be seen to confirm that the upper limit of the second range of interest R#2 matches the capacity value of the second peak of interest P[2] of the m-th differential voltage profile 301.

[0098] This is because, as battery cells BC degrade, their differential voltage profile tends to contract to the left (towards lower capacity) along the X-axis.

[0099] When setting the i-th range of interest R#i for the (m+1)th charge / discharge process, the control unit 130 can also set the upper limit of the i-th range of interest R#i by setting the capacity value of the i-th peak of interest P[i] acquired in the m-th charge / discharge process, and set the size of the i-th range of interest R#i so that it has a predetermined negative correspondence with the kurtosis of the i-th peak of interest P[i]. Referring to Figure 4, for example, the control unit 130 can set the upper limit of the second range of interest R#2 in the same way as the capacity value of the second peak of interest P[2] acquired in the m-th charge / discharge process, and set the size of the second range of interest R#2 in the same way as the value obtained by applying a predetermined negative relationship to the kurtosis of the second peak of interest P[2].

[0100] In the (m+1) charge-discharge process, the control unit 130 can determine the first to n sampling rates to be individually used for the first to n ranges of interest R#1 to R#4, based on the degradation index information of the battery cell BC acquired in the m charge-discharge process.

[0101] The control unit 130 can select one of the reference sampling rate and the first to n sampling rates at each sampling timing during the (m+1)th charge / discharge process, and sample the voltage and current of the battery cell BC at the selected sampling rate. The selected sampling rate is sometimes called the "representative sampling rate".

[0102] In this invention, the sampling rate is a term that refers to the number of samples (sampling count) taken per unit time (e.g., 1 second) from a continuous signal in order to generate a discrete signal.

[0103] In this invention, the reference sampling rate is a sampling rate different from the first to nth sampling rates, and may be a basic value of a sampling rate applicable to sampling timings where the first to nth sampling rates are not applied. The reference sampling rate may be a predetermined constant.

[0104] Alternatively, the reference sampling rate may be a variable that depends on the State of Health (SOH) of the battery cell BC. Since the SOH of the battery cell BC can be estimated using various known logics, a detailed explanation of this will be omitted.

[0105] The relationship data between SOH and the reference sampling rate may be pre-recorded in the storage unit 140 in the form of a lookup table or function (e.g., SOH-sampling rate relationship curve). For example, the relationship data between SOH and the reference sampling rate defines a negative correspondence in which the reference sampling rate increases as SOH decreases, which reflects the characteristics of battery cell BC where the rate of voltage change increases as SOH increases.

[0106] In the present invention, the representative sampling rate can be used to collect voltage and current signals representing the voltage and current of the battery cell BC during the progress of the (m+1) charge-discharge process.

[0107] At each sampling timing during the (m+1)th charge / discharge process, the control unit 130 can determine whether there is a range of interest to which the capacity value of the battery cell BC belongs among the first to nth ranges of interest (for example, R#1 to R#4 in Figure 4). If the capacity value of the battery cell BC belongs to the ith range of interest R#i, the control unit 130 can set the ith sampling rate as the representative sampling rate. On the other hand, if the capacity value of the battery cell BC falls outside all of the first to nth ranges of interest R#1 to R#4, the control unit 130 can set the reference sampling rate as the representative sampling rate.

[0108] The control unit 130 can set at least one of the first to n sampling rates to be greater than the reference sampling rate. This is to precisely detect the ith peak of interest P[i] from a portion of the (m+1)th differential voltage profile 302 corresponding to the ith range of interest R#i.

[0109] The control unit 130 can set at least two of the first to nth sampling rates to be the same as each other. That is, it can apply a sampling rate of the same size to at least two or more of the first to nth ranges of interest R#1 to R#4.

[0110] In the (m+1)th charge / discharge process, the control unit 130 can set the ith sampling rate by applying a predetermined positive correspondence to the kurtosis of the ith peak of interest P[i] included in the previous degradation index information. As an example, the control unit 130 can determine the fourth sampling rate by multiplying the kurtosis of the fourth peak of interest P[4] by a predetermined positive coefficient.

[0111] Figures 5a to 5c are referenced to illustrate the change in peak detection power in response to a change in the representative sampling rate. In each of Figures 5a, 5b, and 5c, the X-axis represents time and the Y-axis represents amplitude.

[0112] Specifically, Figure 5a is a graph illustrating the raw signal that will be sampled. This raw signal can represent, for example, an analog signal showing the change over time of the voltage, current, or differential voltage of a battery cell BC. In Figure 5a, the labels P1a to P7a represent the actual peaks of the raw signal.

[0113] Figure 5b is a graph showing multiple discrete signal values ​​(ra) obtained by applying a low sampling rate (more than 1) to the low signal shown in Figure 5a. In Figure 5b, the multiple peaks indicated by symbols P1b to P7b are peaks that appear on the curve connecting the multiple discrete signal values ​​(ra).

[0114] Comparing Figure 5a and Figure 5b, it can be seen that based on the multiple discrete signal values ​​shown in Figure 5b, it is difficult to accurately obtain the peak feature information of the low signal shown in Figure 5a. Specifically, none of the multiple peaks P1b to P7b in Figure 5b match the peaks P1a to P7a in Figure 5a. In other words, referring to Figures 5a and 5b, it is difficult to obtain sufficiently precise peak feature information of the actual low signal peak when applying a low sampling rate. Also, similar to the case of Figure 5b, the peak feature information of the curve obtained by applying a low sampling rate (P1b to P7b in the case of Figure 5b) cannot accurately reflect the degradation index information of the battery cell BC.

[0115] On the other hand, Figure 5c is a graph illustrating multiple discrete signal values ​​(r) obtained by applying a high sampling rate (greater than 2.5 times / minute) to the low signal shown in Figure 5a. In Figure 5c, the symbols P1c to P7c are peaks that appear on the curve connecting the multiple discrete signal values ​​(r) obtained with a high sampling rate (greater than 2.5 times / minute).

[0116] Comparing Figure 5a and Figure 5c, when a one-to-one correspondence is established between the X-axis values ​​corresponding to the multiple peaks P1a to P7a shown in Figure 5a and the X-axis values ​​corresponding to the multiple peaks P1c to P7c shown in Figure 5c, the difference in X-axis values ​​between corresponding peaks becomes smaller as the applied sampling rate increases. In other words, by applying a high sampling rate per unit time, it can be confirmed that in Figure 5c, signal values ​​were obtained that more faithfully reflect the peak characteristic information of the continuous low signals shown in Figure 5a.

[0117] Referring to Figures 5a, 5b, and 5c, it can be seen that applying a high sampling rate is advantageous in order to obtain discrete signal values ​​( ) containing peak feature information of the low signal at each sampling timing.

[0118] Figure 6 is a flowchart referenced to illustrate an exemplary method for obtaining battery degradation index information according to another embodiment of the present invention. The method in Figure 6 can be used to perform a new charge-discharge cycle after the initial charge-discharge process for the battery cell BC has been completed.

[0119] When performing the current charge-discharge process, the (m+1) charge-discharge process, the control unit 130 can utilize the battery cell BC degradation index information updated in the previous charge-discharge process, the m charge-discharge process, which has already been completed.

[0120] Prior to the current charge-discharge process, the previous degradation index information stored in the memory unit 140 may include peak feature information for the first to nth peaks of interest P[1] to P[4] located on the differential voltage profile (301 in Figure 4) obtained through the mth charge-discharge process.

[0121] Referring to Figures 1 to 4 along with Figure 6, in step S610, the control unit 130 can set the first to nth ranges of interest (R#1 to R#4 in Figure 4) for the current charge-discharge process based on previous degradation index information associated with the previous charge-discharge process.

[0122] In step S611, the control unit 130 can set the first to nth sampling rates based on the previous degradation index information.

[0123] Steps S610 and S611 may be procedures performed to precisely detect the first to nth peaks of interest (P22, P23, P24, P26 in Figure 4) from the differential voltage profile 302 obtained through the current charge-discharge process, before initiating the current charge-discharge process.

[0124] The specific details regarding the setting of the i-th range of interest R#i and the i-th sampling rate will be described separately later, with reference to Figures 7 and 8.

[0125] In step S612, the control unit 130 can start the current charge / discharge process. For example, the control unit 130 can request the charger 3 to start a charging procedure according to a predetermined charging protocol, or request the inverter 30 or a separately provided discharge circuit (not shown) to start a discharge procedure according to a predetermined discharge protocol. For reference, the capacity value of the battery cell BC at the time of execution of step S612 can be initialized to 0 [Ah].

[0126] In step S613, the control unit 130 can determine a representative sampling rate that is the same as the reference sampling rate.

[0127] In step S614, the control unit 130 can acquire voltage sample values ​​and current sample values ​​of the battery cell BC according to a representative sampling rate. Each time step S614 is performed, the control unit 130 can further acquire a capacity value of the battery cell BC based on the current sample value by utilizing methods such as current integration.

[0128] In step S615, the control unit 130 can determine whether the capacity value of the battery cell BC belongs to any one of the first to nth ranges of interest R#1 to R#4. That is, in step S615, it is determined whether there is a range of interest to which the capacity value of the battery cell BC belongs among the first to nth ranges of interest R#1 to R#4.

[0129] If the capacity value obtained in step S614 belongs to the i-th range of interest R#i, which is one of the first to n-th ranges of interest R#1 to R#4, the method in Figure 6 can proceed to step S617. On the other hand, if the capacity value obtained in step S614 does not belong to any of the first to n-th ranges of interest R#1 to R#4, the method in Figure 6 can proceed to step S616.

[0130] In step S617, the control unit 130 can determine a representative sampling rate that is the same as the i-th sampling rate. After step S617, the method according to Figure 6 can proceed to step S614.

[0131] In step S616, the control unit 130 can determine whether or not the termination conditions for the current charge / discharge process are met. For example, if the current charge / discharge process is a constant current charging procedure, the termination conditions for the charge / discharge process are met if the voltage sample value obtained in step S614 is equal to or greater than the upper limit voltage (charging termination voltage) of a predetermined voltage range. As another example, if the current charge / discharge process is a constant current discharging procedure, the termination conditions for the charge / discharge process are met if the voltage sample value obtained in step S614 is equal to or less than the lower limit voltage (discharging termination voltage) of a predetermined voltage range.

[0132] If the value in step S616 is "no", the method in Figure 6 can return to step S613.

[0133] If the output value in step S616 is "yes", it indicates that the voltage of battery cell BC has changed from either the upper or lower voltage limit of a predetermined voltage range to the other due to the current charge / discharge process. If the value in step S616 is "yes", the method in Figure 6 can proceed to step S618.

[0134] In step S618, the control unit 130 can generate a current differential voltage profile (302 in Figure 4) for the current charge-discharge process. The current differential voltage profile represents the correspondence between the capacity of the battery cell BC and its differential voltage during the course of the current charge-discharge process.

[0135] In step S619, the control unit 130 determines the current degradation index information by performing peak detection on the current differential voltage profile (302 in Figure 4) for at least one of the first to n ranges of interest. For example, the previous degradation index information can be updated to the current degradation index information based on the first to n peaks of interest (P22, P23, P24, P26 in Figure 4) detected from the current differential voltage profile. The current degradation index information obtained as a result of step S619 may include the capacitance value, differential voltage value, and / or kurtosis of at least one of the newly detected peaks of interest P22, P23, P24, P26 from the current differential voltage profile 302.

[0136] Figure 7 is a flowchart referenced to illustrate the subroutine in step S610 of Figure 6.

[0137] In step S710, the control unit 130 can obtain the capacitance value and kurtosis of the i-th peak of interest P[i] from the previous degradation index information.

[0138] In step S711, the control unit 130 can set an upper limit of the i-th range of interest R#i based on the capacitance value of the i-th peak of interest P[i].

[0139] It is clear that during the current charge-discharge process, the degradation of the battery cell BC has progressed further compared to the previous charge-discharge process. As mentioned above, as the battery cell BC degrades, the differential capacity profile tends to contract to the left along the X-axis (horizontal axis). Therefore, considering that the capacity values ​​of the peaks of interest P22, P23, P24, and P26 detected from the differential voltage profile 302 obtained as a result of the (m+1) charge-discharge process are expected to be smaller than the capacity values ​​of the peaks of interest P[1] to P[4] already detected through the previous charge-discharge process, the upper limit of the i-th range of interest R#i can be set to be equal to the capacity value of the i-th peak of interest P[i] already detected through the previous charge-discharge process. Of course, the control unit 130 can variably set the first to n-th ranges of interest (R#1 to R#4 in Figure 4), and it is also possible to set a capacity value larger than the capacity value of the i-th peak of interest P[i] as the upper limit of the i-th range of interest R#i.

[0140] In step S712, the control unit 130 can determine the size of the i-th range of interest R#i based on the kurtosis of the i-th peak of interest P[i]. As an example, the control unit 130 can set the size of the i-th range of interest R#i based on the kurtosis of the i-th peak of interest P[i] using a predetermined negative correspondence.

[0141] In steps S711 and S712, if the size and upper limit of the i-th range of interest (R#i) among the first to n-th ranges of interest R#1 to R#4 are determined, the lower limit of the i-th range of interest R#i is equal to the upper limit minus the size.

[0142] Figure 8 is a flowchart referenced to illustrate the subroutine in step S611 of Figure 6.

[0143] In step S810, the control unit 130 can obtain the kurtosis of the i-th peak of interest P[i] from the previous degradation index information.

[0144] In step S812, the control unit 130 can determine the i-th sampling rate based on the kurtosis of the i-th peak of interest P[i]. For example, the control unit 130 can obtain a reference coefficient (which may be greater than 1) corresponding to the kurtosis of the i-th peak of interest P[i] from the storage unit 140, and then multiply the reference sampling rate by the obtained reference coefficient to determine the i-th sampling rate. There is a positive correspondence between the peak kurtosis and the reference coefficient, and relational data defining such a correspondence may be pre-stored in the storage unit 140.

[0145] In this regard, at least two of the first to n sampling rates can be set to be identical to one another. For example, at least two of the first to n sampling rates can be set to be identical to a value that is a predetermined value greater than the reference sampling rate or a predetermined ratio greater than the reference sampling rate. As another example, at least two of the first to n sampling rates may be equal to the value obtained by multiplying the reference sampling rate by the reference coefficient corresponding to the kurtosis of any one of the first to fourth peaks of interest P[1] to P[4].

[0146] The embodiments of the present invention described above are not limited to apparatus and methods, but can also be realized by a program that implements functions corresponding to the configuration of the embodiments of the present invention, or by a recording medium on which such a program is recorded. Such implementation can be easily carried out by experts in the technical field to which the present invention belongs, based on the description of the embodiments described above.

[0147] Although the present invention has been described above with reference to limited embodiments and drawings, it goes without saying that the present invention is not limited thereto, and various modifications and variations are possible within the equivalent scope of the technical idea of ​​the present invention and the claims described below by persons with ordinary skill in the art to which the present invention pertains.

[0148] Furthermore, the present invention described above can be substituted, modified, and altered in various ways by a person with ordinary skill in the art to which the present invention belongs, without departing from the technical spirit of the invention. Therefore, it is not limited to the embodiments described above and the accompanying drawings, and all or part of each embodiment can be selectively combined to form various modifications.

Claims

1. A measuring unit configured to generate voltage and current sample values ​​of a battery cell, Includes a control unit configured to set first to n ranges of interest and first to n sampling rates for the current charge-discharge process based on previous degradation index information associated with the previous charge-discharge process, The control unit, During the charging and discharging process described above, voltage sample values ​​and current sample values ​​of the battery cell are acquired at a reference sampling rate and at least one sampling rate selected from the first to n sampling rates. A battery degradation index information acquisition device configured to determine current degradation index information by detecting a peak in at least one of the first to n ranges of interest from the current differential voltage profile of the battery cell, which is generated based on the voltage sample value and current sample value acquired during the charging and discharging process, where n is a natural number of 2 or more.

2. The control unit, during the current charge / discharge process, If the capacity value of the battery cell falls within the i-th range of interest among the first to n-th ranges of interest, select the i-th sampling rate from the first to n-th sampling rates. The system is configured to select the reference sampling rate if the capacity value of the battery cell falls outside all of the first to nth ranges of interest. The battery degradation index information acquisition device according to claim 1, wherein i is a natural number less than or equal to n.

3. The battery degradation index information acquisition device according to claim 1, wherein each of the first to n sampling rates is greater than the reference sampling rate.

4. The battery degradation index information acquisition device according to claim 1, wherein at least two of the first to n sampling rates are the same as each other.

5. The aforementioned previous degradation indicator information is The data includes peak feature data from at least one of the first to nth peaks of interest already detected from the previous differential voltage profile, The battery degradation indicator information acquisition device according to claim 1, wherein the peak feature data represents at least one of capacity value, differential voltage value, or kurtosis.

6. The control unit, The battery degradation index information acquisition device according to claim 5, configured to set the size of the ith range of interest for the current charge / discharge process by applying a predetermined negative correspondence to the kurtosis of the ith peak of interest included in the aforementioned previous degradation index information, where i is a natural number less than or equal to n.

7. The control unit, The battery degradation index information acquisition device according to claim 5, configured to set an upper limit of the ith range of interest for the current charge / discharge process so as to be equal to the capacity value of the ith peak of interest among the first to nth peaks of interest included in the previous degradation index information, where i is a natural number less than or equal to n.

8. The control unit, The battery degradation index information acquisition device according to claim 5, configured to set the i-th sampling rate for the current charge / discharge process by applying a predetermined positive correspondence to the kurtosis of the i-th peak of interest included in the aforementioned previous degradation index information, wherein i is a natural number less than or equal to n.

9. A battery pack comprising a battery degradation indicator information acquisition device according to any one of claims 1 to 8.

10. An electric vehicle comprising the battery pack described in claim 9.

11. The steps include setting first to n ranges of interest and first to n sampling rates for the current charge-discharge process based on previous degradation index information associated with the previous charge-discharge process, During the aforementioned charging and discharging process, the steps include acquiring voltage sample values ​​and current sample values ​​of the battery cell at a predetermined reference sampling rate and at least one sampling rate selected from the first to n sampling rates, The steps include determining current degradation indicator information by detecting peaks in at least one of the first to n ranges of interest from the current differential voltage profile of the battery cell, which is generated based on the voltage sample values ​​and current sample values ​​acquired during the charging and discharging process, A method for obtaining battery degradation index information, wherein n is a natural number greater than or equal to 2.

12. The step of obtaining the voltage sample value and current sample value of the battery cell is: The following steps are repeated during the aforementioned charging and discharging process: If the capacity value of the battery cell falls within the i-th range of interest among the first to n-th ranges of interest, the step is to acquire the voltage sample value and current sample value of the battery cell at the i-th sampling rate among the first to n-th sampling rates, If the capacity value of the battery cell falls outside the range of interest from the first to the nth, the step is to acquire the voltage sample value and current sample value of the battery cell at the reference sampling rate. The method for obtaining battery degradation index information according to claim 11, wherein i is a natural number less than or equal to n.

13. The aforementioned previous degradation indicator information is The data includes peak feature data from at least one of the first to nth peaks of interest already detected from the previous differential voltage profile, The method for acquiring battery degradation index information according to claim 11, wherein the peak feature data represents at least one of capacity value, differential voltage value, or kurtosis.

14. The upper limit of the i-th range of interest for the aforementioned charge-discharge process is, The method for obtaining battery degradation index information according to claim 13, wherein the i is set to be equal to the capacity value of the ith peak of interest included in the aforementioned previous degradation index information, and i is a natural number less than or equal to n.

15. The i-th sampling rate for the charge-discharge process described above is: A method for acquiring battery degradation index information according to claim 13, wherein the kurtosis of the i-th peak of interest included in the aforementioned prior degradation index information is set to have a predetermined positive correspondence, and i is a natural number less than or equal to n.

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