Method for estimating state of health (SOH) of battery and battery system providing same

Abstract

The present disclosure relates to a method for estimating a state of health (SOH) of a battery and a battery system providing the same. According to the present disclosure, the battery system comprises: a battery; and a battery management system (BMS) configured to obtain a deterioration condition related to deterioration of the battery at each predetermined monitoring period, determine a relational expression representing a relationship between a total amount of energy of the battery and a state of health (SOH) of the battery according to the deterioration condition at each monitoring period, and estimating the SOH of the battery according to the relational expression, in which the total energy amount of the battery is the sum of the charging energy and the discharging energy of the battery.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2023-0178549, filed on December 11, 2023, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

[0003] The present disclosure relates to a method for estimating the state of health (SOH) of a battery and a battery system providing the same. Background Art

[0004] Batteries installed in high-power products such as electric and hybrid vehicles consist of multiple cells connected in series or parallel because they need to supply high voltage to the load. In eco-friendly vehicles, battery performance is directly related to vehicle performance, making the role of a battery management system (BMS) that efficiently manages the battery's status crucial.

[0005] The BMS estimates a state of charge (SOC) of a battery (or a battery cell), a state of health (SOH) of the battery, energy used to charge and discharge the battery based on a battery current flowing through the battery, a plurality of cell voltages of a plurality of battery cells, and a battery temperature, and diagnoses a state of the battery based on the estimation results.

[0006] Meanwhile, due to the nonlinearity of the battery cells, the SOH of the battery, etc. cannot be directly measured. Therefore, the BMS includes a plurality of SOH estimation models, and each of the plurality of estimation models estimates the SOH of the battery, etc. based on battery data. Summary of the Invention

[0007] Technical issues

[0008] The present disclosure attempts to provide a method for estimating the state of health (SOH) of a battery and a battery system providing the method, which are capable of estimating the SOH of a battery according to the state of the battery that changes in real time.

[0009] Technical Solution

[0010] An exemplary embodiment of the present disclosure provides a battery system comprising: a battery; and a battery management system (BMS) configured to obtain a degradation condition related to degradation of the battery at each predetermined monitoring cycle, determine a relational expression representing a relationship between a total energy amount of the battery and a state of health (SOH) of the battery based on the degradation condition at each monitoring cycle, and estimate the SOH of the battery based on the relational expression, wherein the total energy amount of the battery is the sum of charge energy and discharge energy of the battery.

[0011] The degradation conditions may include the temperature of the battery, the charge rate of the battery, the discharge rate of the battery, the maximum SOC of the battery, and the minimum SOC of the battery.

[0012] The BMS may measure the temperature of the battery, the charge rate of the battery, and the discharge rate of the battery, and estimate the maximum SOC of the battery and the minimum SOC of the battery.

[0013] The BMS may calculate the SOH change rate of the battery based on a relational expression at each monitoring cycle, and estimate the current SOH of the battery by subtracting a value obtained by accumulating a plurality of SOH change rates calculated at each cycle from the initial SOH of the battery.

[0014] The BMS may estimate a first SOH of the battery based on the total energy amount of the battery at the beginning of a monitoring period, estimate a second SOH of the battery based on the total energy amount of the battery at the end of the monitoring period, and calculate the difference between the first and second SOHs as an SOH change rate.

[0015] Another exemplary embodiment of the present disclosure provides a method for estimating a state of health (SOH) of a battery, the method comprising: obtaining a degradation condition related to degradation of a battery at each predetermined monitoring cycle; calculating a total energy amount of the battery by adding a charging energy of the battery and a discharging energy of the battery; and determining a relational expression representing a relationship between the total energy amount of the battery and the state of health (SOH) of the battery based on the degradation condition at each monitoring cycle, and estimating the SOH of the battery based on the relational expression.

[0016] The degradation conditions may include the temperature of the battery, the charge rate of the battery, the discharge rate of the battery, the maximum SOC of the battery, and the minimum SOC of the battery.

[0017] Obtaining the degradation condition may include: measuring a temperature of the battery, a charge rate of the battery, and a discharge rate of the battery; and estimating a maximum SOC of the battery and a minimum SOC of the battery.

[0018] Estimating the SOH of the battery may include calculating an SOH change rate of the battery based on a relational expression at each monitoring cycle; and subtracting a value obtained by accumulating a plurality of SOH change rates calculated at each cycle from an initial SOH of the battery.

[0019] Calculating the SOH change rate of the battery may include: estimating a first SOH of the battery based on the total energy amount of the battery at the beginning of the monitoring period; estimating a second SOH of the battery based on the total energy amount of the battery at the end of the monitoring period; and calculating the difference between the first SOH and the second SOH as the SOH change rate.

[0020] Beneficial effects

[0021] Provided are a method for estimating the state of health (SOH) of a battery and a battery system providing the method, which are capable of estimating the SOH of a battery in a highly reliable manner according to a state of the battery that changes in real time. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a diagram illustrating a battery system according to an exemplary embodiment.

[0023] Figure 2 is a flowchart illustrating a method for estimating a state of health (SOH) of a battery based on a relational expression representing a relationship between a total energy amount of the battery and the SOH of the battery according to an exemplary embodiment.

[0024] Figure 3 is a graph based on a relational expression representing the relationship between the total energy amount of a battery and the SOH of the battery according to an exemplary embodiment.

[0025] Figure 4 is a graph based on a relational expression representing the relationship between the total energy amount of a battery and the SOH of the battery according to an exemplary embodiment.

[0026] Figure 5 is a graph based on a relational expression representing the relationship between the total energy amount of a battery and the SOH of the battery according to an exemplary embodiment.

[0027] Figure 6 is a graph illustrating real-time varying SOH according to an exemplary embodiment. DETAILED DESCRIPTION

[0028] The exemplary embodiments described in this specification and the configurations shown in the drawings are preferred examples of the present disclosure, and there may be various modifications that may replace the exemplary embodiments of this specification and the drawings at the time of filing this application.

[0029] When describing the exemplary embodiments of this invention, if the detailed description of the related known technologies obscures the key points of the exemplary embodiments disclosed herein, such description will be omitted. In addition, the accompanying drawings are provided only to facilitate easy understanding of the exemplary embodiments disclosed herein, and it should be understood that the technical ideas disclosed herein are not limited by the accompanying drawings and cover all modifications, equivalents, and replacements that fall within the spirit and technical scope of the present invention.

[0030] Terms including ordinal numbers such as "first" and "second" may be used to describe various components, but these components are not limited by these terms. These terms are only used to distinguish one component from another.

[0031] It should be understood that when a component is referred to as being “connected to” or “coupled to” another component, the component may be directly connected or coupled to the other component, or connected or coupled to the other component with an intervening component. On the other hand, it should be understood that when a component is referred to as being “directly connected to” or “directly coupled to” another component, the component may be connected to the other component without any intervening components.

[0032] It should be understood that the terms "including", "having", etc. used in this document specify the existence of the features, numbers, steps, operations, components, parts or their combinations stated in the specification, but do not exclude the possibility of the existence or addition of one or more other features, numbers, steps, operations, components, parts or their combinations.

[0033] Hereinafter, the disclosed exemplary embodiments will be described in detail with reference to the accompanying drawings.

[0034] Figure 1 is a diagram illustrating a battery system according to an exemplary embodiment.

[0035] refer to Figure 1 , the battery system 100 includes a battery 110 , a relay 120 , a current sensor 130 , a temperature sensor 140 , and a battery management system (BMS) 150 .

[0036] The two terminals TE1 and TE2 of the battery system 100 are connected to the positive and negative terminals of the battery 110, the relay 120 is connected between the positive terminal of the battery 110 and the terminal TE1, and the current sensor 130 is connected between the negative terminal of the battery 110 and the terminal TE2. The temperature sensor 140 may be located at a predetermined position within the battery system 100, for example, in an area adjacent to the battery 110, or physically coupled to the battery 110.

[0037] The battery 110 may include a plurality of battery cells, and the plurality of battery cells may be connected in series / parallel. Figure 1 The battery 110 is shown to include a plurality of battery cells Cell 1 to Cell n connected in series, but Figure 1 The components and connection relationships between the components shown in FIG. 1 are merely examples, and the present disclosure is not limited thereto.

[0038] The relay 120 controls the electrical connection between the battery system 100 and an external device. When the relay 120 is turned on, the battery system 100 and the external device are electrically connected to each other for charging or discharging, and when the relay 120 is turned off, the battery system 100 and the external device are electrically disconnected from each other. The external device can be a load or a charger.

[0039] Current sensor 130 is connected in series to the current path between battery 110 and an external device. Current sensor 130 measures the current flowing through battery 110 and transmits a detection signal (CS) indicating the measurement result to the BMS. The current flowing through battery 110 can be a charging current for charging battery 110 or a discharging current supplied from battery 110 to an external device.

[0040] The temperature sensor 140 may detect the temperature of its location and transmit a signal TS indicating the detected temperature to the BMS. The temperature sensor 140 is not limited to Figure 1 , and at least two temperature sensors 140 may be provided to detect the temperatures of a plurality of battery cells.

[0041] The BMS 150 includes a monitoring unit 151 , a main control unit (MCU) 152 , and a memory 153 .

[0042] The monitoring unit 151 is electrically connected to the positive electrode and the negative electrode of each of the plurality of battery cells Cell 1 to Cell n to measure the voltage of each of the plurality of battery cells Cell 1 to Cell n.

[0043] The monitoring unit 151 transmits information about the measured cell voltage of each of the plurality of battery cells Cell 1 to Cell n to the MCU 152. Specifically, the monitoring unit 151 may measure the cell voltage of each of the plurality of battery cells Cell 1 to Cell n at predetermined cycles during a rest period in which charging or discharging does not occur, and transmit the measured cell voltage to the MCU 152.

[0044] The MCU 152 may estimate a state of charge (SOC) of each of the plurality of battery cells using a cell voltage of each of the plurality of battery cells Cell 1 to Cell n received from the monitoring unit 151 during the rest period.

[0045] The MCU 152 may obtain a current level of current flowing through the battery 110 during a charge / discharge period of the battery 110 from the detection signal CS received from the current sensor 130 and obtain a temperature level of the battery 110 from the detection signal TS received from the temperature sensor 140 .

[0046] The memory 153 may store programs and data for controlling and managing components included in the BMS 150 , and store information obtained by the current sensor 130 , the temperature sensor 140 , and the monitoring unit 151 , and information calculated by the MCU 152 .

[0047] In the following, reference will be made to Figures 2 to 6A method of estimating the SOH of the battery by the MCU 152 using the information stored in the memory 153 is described.

[0048] Figure 2 is a flowchart illustrating a method for estimating the SOH of a battery based on a relational expression representing a relationship between a total energy amount of the battery and the SOH of the battery according to an exemplary embodiment.

[0049] Figures 3 to 5 are graphs each based on a relational expression representing a relationship between a total energy amount of a battery and an SOH of the battery according to an exemplary embodiment.

[0050] Figure 6 is a graph illustrating real-time varying SOH according to an exemplary embodiment.

[0051] refer to Figure 2 , the BMS may obtain the degradation condition at each predetermined monitoring period to estimate the SOH of the battery 110 that changes in real time according to the use of the battery 110 ( S1000 ).

[0052] As the battery 110 is used, the SOH of the battery 110 decreases, which is called degradation, and the condition of degradation of the battery 110 refers to factors involved in the degradation.

[0053] Specifically, the degradation condition may include the temperature of the battery 110 , the charge rate of the battery 110 , the discharge rate of the battery 110 , the highest SOC of the battery 110 , and the lowest SOC of the battery 110 .

[0054] The BMS 150 may obtain the temperature level of the battery 110 according to the detection signal TS received from the temperature sensor 140 .

[0055] In addition, the BMS 150 can obtain a current level of a current flowing through the battery 110 during a charge / discharge period of the battery 110 according to the detection signal CS received from the current sensor 130 , and can measure a charge rate (C-rate) of the battery 110 and a discharge rate (D-rate) of the battery 110 based on the current flowing through the battery 110 .

[0056] Specifically, the BMS 150 can measure the charge rate of the battery 110 by dividing the current flowing when the battery 110 is charged by the current capacity of the battery 110, and can measure the discharge rate of the battery 110 by dividing the current flowing when the battery 110 is discharged by the current capacity of the battery 110. The current capacity of the battery 110 can be determined as a value obtained by subtracting the capacity reduction according to the current degree of degradation of the battery 110 from the initial capacity of the battery 110. The initial capacity of the battery 110 is the capacity before the battery 110 is used, and can be determined based on the number of cells in the battery 110 and the chemical composition of the battery.

[0057] The BMS 150 may estimate the SOC of the battery 110 by using one of the following methods: a current integration method that integrates charge and discharge currents, an electrochemical modeling method that represents chemical reactions inside a cell in units of molecules, a mathematical formula technique that represents dynamic behaviors such as the operating time and state of charge (SOC) of the battery 110 as a purely mathematical empirical formula, and a voltage modeling method that uses the relationship between open circuit voltage (OCV) and state of charge (SOC).

[0058] In addition, the BMS 150 may determine the highest SOC of the battery 110 and the lowest SOC of the battery 110. The SOC range of the battery 110 according to the highest SOC of the battery 110 and the lowest SOC of the battery 110 refers to an SOC range in which the battery 110 is mainly charged and discharged.

[0059] The BMS 150 may determine the SOC at the start of charging of the battery 110 as the lowest SOC of the battery 110, and may determine the SOC at the end of charging of the battery 110 as the highest SOC of the battery 110. When the battery 110 is charged a plurality of times, the BMS 150 may determine an average of the plurality of lowest SOC values as the lowest SOC value, and determine an average of the plurality of highest SOC values as the highest SOC value.

[0060] The BMS 150 may determine a relational expression representing a relationship between the total energy amount of the battery 110 and the SOH of the battery 110 according to the degradation condition at each monitoring period ( S1100 ).

[0061] The total energy amount of the battery 110 refers to the sum of the energy charged to the battery 110 (hereinafter referred to as battery charging energy) and the energy discharged from the battery 110 (hereinafter referred to as battery discharging energy).

[0062] According to an exemplary embodiment, a relational expression representing a relationship between a total energy amount of the battery 110 and the SOH of the battery 110 may be defined as Formula 1.

[0063] [Formula 1]

[0064] (Battery SOH) =

[0065] It can be defined as Equation 2.

[0066] [Formula 2]

[0067]

[0068] 、 、 、 、 is a parameter determined according to the chemical properties of the battery 110, which can be determined using a table stored in the memory 153. T represents the temperature of the battery 110, C represents the charge rate of the battery 110, D represents the discharge rate of the battery 110, represents the maximum SOC of the battery 110, and Indicates the minimum SOC of the battery 110 .

[0069] The BMS 150 may determine a relational expression representing the relationship between the total energy amount of the battery 110 and the SOH of the battery 110 according to a predetermined formula and a stored table.

[0070] refer to Figures 3 to 5 , a graph of batteries 110 having different chemical properties and different degradation conditions can be seen according to relational expressions, each of which represents a relationship between the total energy amount of each of the batteries 110 and the SOH of each of the batteries 110 .

[0071] Figure 4 According to the expression A graph f1 of a first relational expression of the relationship between the total energy amount of the battery 110 and the SOH of the battery 110 when the value is 2, Figure 5 According to the expression A graph f2 of a second relational expression of the relationship between the total energy amount of the battery 110 and the SOH of the battery 110 when the value is 3, and Figure 6 According to the expression A graph f3 is a graph of a third relational expression showing the relationship between the total energy amount of the battery 110 and the SOH of the battery 110 when φ is 10.

[0072] The BMS 150 may determine different relationship expressions according to the degradation condition that changes at each monitoring cycle. Figure 6 ,when When the first cycle T1 among the plurality of monitoring cycles is 2, the BMS 150 can estimate the SOH of the battery 110 using the graph f1 according to the first relational expression. When the second period T2 is 3, the SOH of the battery 110 can be estimated using the graph f2 according to the second relational expression, and when When the value is 10 at the third period T3 , the SOH of the battery 110 may be estimated using the graph f3 according to the third relational expression.

[0073] The BMS 150 may calculate the SOC change rate of the battery 110 during the monitoring period (S1200). Specifically, the BMS 150 may calculate the difference between the SOC of the battery 110 based on the total energy amount of the battery at the beginning of the monitoring period and the SOC of the battery 110 based on the total energy amount of the battery at the end of the monitoring period as the change rate of the SOC of the battery 110.

[0074] The BMS 150 may calculate the total amount of battery energy charged and discharged since the initial start of operation of the battery 110 as the total amount of energy of the battery 110. Specifically, the BMS 150 may calculate the charge energy of the battery 110 by multiplying the charge time by the product of the voltage and current used during the charge, and may calculate the discharge energy of the battery 110 by multiplying the discharge time by the product of the voltage and current used during the discharge. However, the method of obtaining the charge energy of the battery 110 and the discharge energy of the battery 110 is not limited thereto and may be implemented according to various known techniques.

[0075] refer to Figure 6 When the total energy amount of battery 110 is 0 [kWh], BMS 150 may set the SOH of battery 110 to 100% (P1). At the end of first period T1, BMS 150 may calculate the total energy amount of battery 110. When the total energy amount of battery 110 is 40 [kWh] at the end of first period T1, BMS 150 may estimate the SOH of battery 110 to be 77% (P2) and calculate the difference between the SOH of battery 110 at the beginning of first period T1 and the SOH of battery 110 at the end of first period T1 (which is 23%) as the SOH change rate ΔSOC1.

[0076] When the total energy amount of battery 110 is 40 kWh, BMS 150 may set the SOH of battery 110 to 77% (P2). When the total energy amount of battery 110 is 78 kWh at the end of second period T2, BMS 150 may estimate the SOH of battery 110 to be 48% (P3) and calculate the difference between the SOH of battery 110 at the beginning and the end of second period T2 (which is 29%) as SOH change rate ΔSOC2. Similarly, BMS 150 may calculate the difference between the SOH of battery 110 at the beginning and the end of third period T3 (which is 29%) as SOH change rate ΔSOC3.

[0077] The BMS 150 may accumulate a plurality of SOH change rates calculated at each cycle ( S1300 ). Specifically, the BMS 150 may accumulate a plurality of SOH change rates calculated each time each cycle ends.

[0078] refer to Figure 6 , the BMS 150 may calculate the sum of the SOH change rate ΔSOC1 of the first cycle and the SOH change rate ΔSOC2 of the second cycle as the final SOH change rate after the second cycle ends, and may update the final SOH change rate to the sum of the SOH change rate ΔSOC1 of the first cycle, the SOH change rate ΔSOC2 of the second cycle, and the SOH change rate ΔSOC3 of the third cycle after the third cycle ends.

[0079] The BMS 150 may estimate the current SOH by subtracting the accumulated SOH change rate from the initial SOH of the battery ( S1400 ).

[0080] For example, if the current time is the time point at the end of the third cycle, the current SOH of the battery 110 can be estimated to be 19% by subtracting 81% - which is the sum of the SOH change rate ΔSOC1 of the first cycle, the SOH change rate ΔSOC2 of the second cycle, and the SOH change rate ΔSOC3 of the third cycle - from 100%, which is the initial SOH of the battery 110.

[0081] In addition, when the SOC of the battery 110 decreases to a predetermined value or lower, the BMS 150 may communicate with the vehicle control unit to inform the user of this situation.

[0082] Although the exemplary embodiments of the present disclosure have been described in detail above, the scope of the present disclosure is not limited thereto, and various modifications and improvements made by those skilled in the art having ordinary knowledge in the art to which the present disclosure pertains also fall within the scope of the present disclosure.

Claims

1. A battery system comprising: Battery; as well as a battery management system (BMS) configured to obtain a degradation condition related to degradation of the battery at each predetermined monitoring period, determine a relational expression representing a relationship between a total energy amount of the battery and a state of health (SOH) of the battery based on the degradation condition at each monitoring period, and estimate the SOH of the battery based on the relational expression, The total energy of the battery is the sum of the charging energy and the discharging energy of the battery.

2. The battery system according to claim 1, wherein The degradation conditions include a temperature of the battery, a charge rate of the battery, a discharge rate of the battery, a maximum SOC of the battery, and a minimum SOC of the battery.

3. The battery system according to claim 2, wherein The BMS measures the temperature of the battery, the charge rate of the battery, and the discharge rate of the battery, and estimates the maximum SOC of the battery and the minimum SOC of the battery.

4. The battery system according to claim 1, wherein The BMS calculates the SOH change rate of the battery based on the relational expression at each monitoring cycle, and estimates the current SOH of the battery by subtracting a value obtained by accumulating a plurality of SOH change rates calculated at each cycle from an initial SOH of the battery.

5. The battery system according to claim 4, wherein The BMS estimates a first SOH of the battery based on the total energy amount of the battery at the beginning of the monitoring period, estimates a second SOH of the battery based on the total energy amount of the battery at the end of the monitoring period, and calculates a difference between the first SOH and the second SOH as the SOH change rate.

6. A method for estimating the state of health (SOH) of a battery, the method comprising: obtaining a degradation condition related to degradation of the battery at each predetermined monitoring period; calculating a total energy amount of the battery by adding the charging energy of the battery and the discharging energy of the battery; as well as A relational expression representing a relationship between a total energy amount of the battery and a state of health (SOH) of the battery is determined according to the degradation condition at each monitoring period, and the SOH of the battery is estimated according to the relational expression.

7. The method according to claim 6, wherein The degradation conditions include a temperature of the battery, a charge rate of the battery, a discharge rate of the battery, a maximum SOC of the battery, and a minimum SOC of the battery.

8. The method according to claim 7, wherein Obtaining the degradation condition includes: measuring the temperature of the battery, the charge rate of the battery, and the discharge rate of the battery; as well as The maximum SOC of the battery and the minimum SOC of the battery are estimated.

9. The method according to claim 6, wherein Estimating the SOH of the battery includes: Calculating the SOH change rate of the battery based on the relational expression at each monitoring period; as well as A value obtained by accumulating a plurality of SOH change rates calculated at each of the cycles is subtracted from the initial SOH of the battery.

10. The method according to claim 9, wherein Calculating the SOH change rate of the battery includes: estimating a first SOH of the battery according to a total energy amount of the battery at the beginning of the monitoring period; estimating a second SOH of the battery based on a total energy amount of the battery at the end of the monitoring period; as well as A difference between the first SOH and the second SOH is calculated as the SOH change rate.

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