Battery cell deterioration diagnosis method and battery system using the same

Abstract

A method for diagnosing a degree of deterioration of a plurality of battery cells constituting a battery pack by a battery management system may include: calculating accumulated energy for the battery pack using a battery pack current flowing through the battery pack and a battery pack voltage that is a voltage of the battery pack; calculating a cell capacity of each of the plurality of battery cells for each predetermined cell capacity calculation period; calculating a cell capacity deviation for each of the plurality of battery cells for each accumulation period in which the accumulated energy increases by a predetermined unit; and diagnosing whether each battery cell is abnormal based on a result of comparing the calculated degree of change in the cell capacity deviation for each accumulation period with a predetermined critical value.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0116272, filed on September 15, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present disclosure relates to a battery cell deterioration diagnosis method and a battery system using the same. [Background technology]

[0003] A battery includes a plurality of battery cells, and the capacity of each of the plurality of battery cells deteriorates with use of the battery. If the deterioration rates of the plurality of battery cells are similar, the deviation in cell capacity among the plurality of battery cells may be within an acceptable range. However, if there is a defective battery cell among the plurality of battery cells, the deviation in cell capacity between the defective battery cell and the other battery cells may increase.

[0004] The battery management system monitors the cell capacity degradation of each of a plurality of battery cells, and when a deviation between the cell capacity degradations of the plurality of battery cells is equal to or greater than a predetermined critical value, the battery management system can diagnose a battery cell with a higher cell capacity degradation than the other battery cells as a defective cell. However, because battery cell degradation progresses over a considerable period of time, it takes a considerable amount of time for the cell capacity of a battery cell to deteriorate to a diagnostic condition corresponding to a defective cell. During this period, a battery cell with a higher cell capacity degradation may damage other battery cells with a relatively lower cell capacity degradation, which may ultimately result in damage to the entire battery. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a battery cell deterioration diagnosis method capable of detecting a defective battery cell before damage occurs to the battery, and a battery system using the same. [Means for solving the problem]

[0006] A battery management system according to an embodiment of the present invention may include a battery pack including a plurality of battery cells; a current sensor that measures a current flowing through the battery pack and generates a current detection signal indicating the measured battery pack current; a cell monitoring IC that measures a battery pack voltage of the battery pack and a cell voltage of each of the plurality of battery cells and generates a voltage detection signal indicating the measured battery pack voltage and the plurality of cell voltages; and a main control circuit that calculates accumulated energy for the battery pack using the current detection signal and the voltage detection signal, calculates a cell capacity of each of the plurality of battery cells for each predetermined cell capacity calculation period, calculates a degree of change in cell capacity deviation for each of the plurality of battery cells for each accumulation period in which the accumulated energy increases by a predetermined unit, and diagnoses whether each battery cell is abnormal based on a result of comparing the degree of change in the cell capacity deviation calculated for each accumulation period with a predetermined critical value.

[0007] The main control circuit may include an energy accumulation unit that calculates one of charge energy and discharge energy of the battery pack as the accumulated energy, using the battery pack current indicated by the current detection signal and the battery pack voltage indicated by the voltage detection signal.

[0008] The energy accumulator may calculate charge energy by multiplying a battery pack current by a battery pack voltage for each monitoring period during a charging period in which the battery pack is charged, and calculate accumulated energy by integrating the calculated charge energy for the charging period, or may calculate discharge energy by multiplying a battery pack current by a battery pack voltage for each monitoring period during a discharging period in which the battery pack is discharged, and calculate accumulated energy by integrating the calculated discharge energy for the discharging period.

[0009] The main control circuit may include a cell capacity calculation unit that calculates the cell capacity of each of the plurality of battery cells in units of the cell capacity calculation period and stores the calculated cell capacities, and the cell capacity calculation period may be a period from when the main control circuit is turned on to when it is turned off.

[0010] The cell capacity calculation unit may calculate an integrated current amount for each of the plurality of battery cells by integrating a current flowing through each of the plurality of battery cells during the cell capacity calculation period, calculate an SOC change amount for each of the plurality of battery cells during the cell capacity calculation period, and calculate a cell capacity for each of the plurality of battery cells by dividing the integrated current amount for the cell capacity calculation period by the SOC change amount.

[0011] The cell capacity calculation unit can estimate an SOC at the start of the cell capacity calculation cycle and an SOC at the end of the cell capacity calculation cycle based on the cell voltages of the plurality of battery cells indicated by the voltage detection signal or an OCV (Open Circuit Voltage) based on the cell voltages, and calculate the difference between the SOC at the end and the SOC at the start as the SOC change amount.

[0012] The main control circuit may further include a cell capacity deviation calculation unit that calculates a cell capacity deviation for each cell capacity of the plurality of battery cells for each cell capacity calculation period, and the cell capacity deviation may be a change in cell capacity for each of the plurality of battery cells during the cell capacity calculation period.

[0013] The cell capacity deviation calculation unit calculates, for each of the plurality of battery cells, the difference between the cell capacity at the start of an n-th cell capacity calculation cycle and the cell capacity at the end of the n-th cell capacity calculation cycle as the cell capacity deviation of each battery cell, where "n" may be a natural number greater than or equal to 1 indicating the number of cell capacity calculation cycles that have elapsed since the battery pack began to be used until an arbitrary time point.

[0014] The main control circuit may include a degradation diagnosis unit that stores a cell capacity deviation for each of the plurality of battery cells during a cell capacity calculation period corresponding to a time point when the accumulated energy value increases by a predetermined reference energy unit, calculates a slope between a current cell capacity deviation corresponding to a current accumulation period and a previous cell capacity deviation corresponding to a previous accumulation period for each of the plurality of battery cells, and diagnoses a battery cell whose calculated slope is equal to or greater than a predetermined degradation threshold as an abnormal cell.

[0015] A method for diagnosing a degree of deterioration of a plurality of battery cells constituting a battery pack according to another embodiment of the present invention may include: calculating accumulated energy for the battery pack using a battery pack current flowing through the battery pack and a battery pack voltage that is a voltage of the battery pack; calculating a cell capacity of each of the plurality of battery cells for each predetermined cell capacity calculation period; calculating a cell capacity deviation for each of the plurality of battery cells for each accumulation period in which the accumulated energy increases by a predetermined unit; and diagnosing whether each battery cell is abnormal based on a result of comparing the degree of change in the cell capacity deviation calculated for each accumulation period with a predetermined critical value.

[0016] The step of calculating the cumulative energy may include the steps of: calculating charge energy by multiplying a battery pack current by a battery pack voltage for each monitoring period during a charging period in which the battery pack is charged, and integrating the calculated charge energy for the charging period to calculate the cumulative energy; and calculating discharge energy by multiplying a battery pack current by a battery pack voltage for each monitoring period during a discharging period in which the battery pack is discharged, and integrating the calculated discharge energy for the discharging period to calculate the cumulative energy.

[0017] The step of calculating the cell capacity may include the steps of: integrating currents flowing through each of the plurality of battery cells during the cell capacity calculation period to calculate an integrated current amount for each of the plurality of battery cells; calculating an SOC change amount for each of the plurality of battery cells during the cell capacity calculation period; and calculating the cell capacity for each of the plurality of battery cells by dividing the integrated current amount for the cell capacity calculation period by the SOC change amount. The cell capacity calculation period may be a period from when the main control circuit is turned on to when it is turned off.

[0018] The step of calculating the SOC change may include a step of estimating an SOC at a start point of the cell capacity calculation cycle and an SOC at an end point of the cell capacity calculation cycle based on the cell voltages of the plurality of battery cells indicated by the voltage sensing signal or an OCV (Open Circuit Voltage) based on the cell voltages, and calculating the difference between the SOC at the end point and the SOC at the start point as the SOC change.

[0019] The cell capacity deviation calculation step includes a step of calculating, for each of the plurality of battery cells, the difference between the cell capacity at the start of an n-th cell capacity calculation cycle and the cell capacity at the end of the n-th cell capacity calculation cycle as the cell capacity deviation of each battery cell, wherein the cell capacity deviation is the change in cell capacity between the cell capacity calculation cycles for each of the plurality of battery cells, and "n" may be a natural number greater than or equal to 1 indicating the number of cell capacity calculation cycles that have elapsed since the battery pack began to be used until an arbitrary time point.

[0020] The step of calculating the degree of change in the cell capacity deviation may include the steps of: storing the cell capacity deviation for each of the plurality of battery cells during a cell capacity calculation period corresponding to a time point at which the accumulated energy value increases by a predetermined reference energy unit; and calculating, for each of the plurality of battery cells, a slope between a current cell capacity deviation corresponding to the current accumulation period and a previous cell capacity deviation corresponding to a previous accumulation period. [Effects of the Invention]

[0021] The battery cell degradation diagnosis method and the battery system using the same according to the embodiment can detect an abnormal battery cell due to capacity degradation before damage occurs to the battery. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a diagram illustrating a battery system according to one embodiment. [Figure 2] FIG. 2 is a diagram showing a configuration of a part of an MCU according to an embodiment. [Figure 3] FIG. 3 is a flowchart illustrating a method for diagnosing a cell capacity degradation level of a battery cell according to an embodiment. [Figure 4] FIG. 4 is a graph illustrating the relationship between cell capacity deviation and accumulated energy according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] The suffixes "module" and / or "unit" for components used in the following description are given or used interchangeably solely for the convenience of writing the specification, and do not have any distinct meanings or roles. Furthermore, terms such as "unit," "device," and "module" used in the specification refer to a unit that processes at least one function or operation, and this can be realized by hardware, software, or a combination of hardware and software.

[0024] Furthermore, in describing the embodiments disclosed herein, if it is determined that a detailed description of related publicly known technology may obscure the gist of the embodiments disclosed herein, the detailed description will be omitted. Furthermore, the attached drawings are merely intended to facilitate understanding of the embodiments disclosed herein, and should not be construed as limiting the technical ideas disclosed herein, and should be understood to include any modifications, equivalents, or alternatives within the spirit and technical scope of the present invention.

[0025] Terms including ordinal numbers such as "first," "second," etc. may be used to describe various components, but the components are not limited by the terms. The terms are used only to distinguish one component from another.

[0026] When a component is referred to as being "coupled" or "connected" to another component, it should be understood that the component may be directly coupled or connected to the other component, but that there may be other components in between. Conversely, when a component is referred to as being "directly coupled" or "directly connected" to another component, it should be understood that there are no other components in between.

[0027] In this application, the use of terms such as "comprises" or "having" is intended to specify the presence of any feature, number, step, operation, component, part, or combination thereof described in the specification, but should be understood not to preclude the presence or additional possibility of one or more other embodiments, numbers, steps, operations, components, parts, or combinations thereof.

[0028] FIG. 1 is a diagram illustrating a battery system according to one embodiment.

[0029] 1, an external device 2 is connected between both output terminals (P+, P-) of the battery system 1, and when relays 21 and 22 are closed, the battery pack 10 and the external device 2 may be electrically connected. Although FIG. 1 shows the external device 2 connected to the battery system 1, this is an example to help understand the battery system 1, and the invention is not limited thereto.

[0030] If the external device 2 is an electrical load, the battery system 1 may discharge while operating as a power source that supplies energy to the electrical load 2. The electronic load may be a vehicle or an energy storage system (ESS), and the vehicle may be, for example, an electric vehicle, a hybrid vehicle, or smart mobility. If the external device 2 is a charger, the battery system 1 may be charged by receiving energy from a power grid through the charger 2.

[0031] The battery system 1 includes a battery pack 10 , two relays 21 and 22 , a current sensor 23 , and a battery management system (BMS) 100 .

[0032] The battery pack 10 includes a plurality of battery cells 10_1-10_4 connected in series. In Fig. 1, the battery pack 10 is shown as including four battery cells 10_1-10_4 connected in series, but this is an example and the present invention is not limited thereto. For example, five or more battery cells may be connected in series, or two or more battery cells connected in parallel may be connected in series.

[0033] The relay 21 is connected between the positive electrode of the battery pack 10 and the output terminal (P+), and the relay 22 is connected between the negative electrode of the battery pack 10 and the output terminal (P-). The opening and closing of the relays 21 and 22 may be controlled under the control of a main control unit (MCU) 130 of the BMS 100. For example, the MCU 130 may generate enable-level relay control signals SR1 and SR2 and transmit them to the relays 21 and 22, which may close in response to the enable-level relay control signals SR1 and SR2. Alternatively, the MCU 130 may generate disable-level relay control signals SR1 and SR2 and transmit them to the relays 21 and 22, which may open in response to the disable-level relay control signals SR1 and SR2. During charging or discharging of the battery pack 10, the relays 21 and 22 may close to form a charging current path or a discharging current path.

[0034] The current sensor 23 may detect a current flowing through the battery pack 10 (hereinafter, referred to as a battery pack current), generate a current detection signal IS indicating the detected battery pack current, and transmit the signal to the MCU 130. Hereinafter, the current flowing through the battery pack 10 is referred to as a battery pack current. Because the plurality of battery cells 10_1-10_4 are connected in series, the current flowing through the plurality of battery cells 10_1-10_4 may be the same as the battery pack current. When the plurality of battery cells are connected in parallel, a current sensor may be provided for each current path. Alternatively, when the battery system 1 includes a plurality of battery packs, a current sensor may be provided for each of the plurality of battery packs to measure the current flowing through each battery pack. The battery system 1 according to one embodiment may include current sensors for detecting the current flowing through each of the plurality of battery cells constituting the battery pack, and each current sensor may be connected in series to a corresponding battery cell at a position suitable for measuring the cell current of the corresponding battery cell.

[0035] The BMS 20 includes a cell monitoring IC 110, a cell balancing unit 120, and an MCU 130. The BMS 20 is connected to the plurality of battery cells 10_1-10_4, and can control the charge / discharge current of the battery pack 10 and control the cell balancing operation for the plurality of battery cells 10_1-10_4 based on information such as the cell voltages and battery pack currents of the plurality of battery cells 10_1-10_4.

[0036] For example, the cell monitoring IC 110 may measure the cell voltages of each of the battery cells 10_1-10_4 and the voltage of the battery pack 10 (hereinafter, referred to as the battery pack voltage) at each monitoring period and transmit voltage detection signals (CVS, PVS) indicating the measured cell voltages and battery pack voltage to the MCU 130. The MCU 130 may determine whether cell balancing is necessary based on the voltage detection signal CVS. The lowest cell voltage among the battery cells 10_1-10_4 may be lower than the other cell voltages by a predetermined threshold or more, or the highest cell voltage may be higher than the other cell voltages by a predetermined threshold or more. In this way, when the deviation between the cell voltages of the battery cells 10_1-10_4 is equal to or greater than a predetermined threshold, the MCU 130 may determine that cell balancing is necessary. If the MCU 130 determines that cell balancing is necessary, it may control the cell balancing unit 120 to perform the cell balancing operation. For example, the MCU 130 may generate a control signal CBM to discharge a battery cell having a cell voltage higher than a predetermined reference voltage among the plurality of cell voltages and transmit the control signal CBM to the cell balancing unit 120. The cell balancing unit 120 may form a discharge path capable of discharging the corresponding battery cell, and discharge the corresponding battery cell, or store energy generated while discharging the corresponding battery cell. The MCU 130 may generate a control signal CBM to charge a battery cell having a voltage lower than a predetermined reference voltage among the plurality of cell voltages and transmit the control signal CBM to the cell balancing unit 120. The cell balancing unit 120 may form a charge path capable of charging the corresponding battery cell, and charge the corresponding battery cell. Energy transferred from the discharged battery cell may be used for charging for cell balancing. The predetermined reference voltage may be determined based on the plurality of cell voltages. For example, an average value of the plurality of cell voltages or a median value of the plurality of cell voltages may be determined as the reference voltage.

[0037] The MCU 130 may diagnose the degree of cell capacity degradation for the battery cells 10_1-10_4. The MCU 130 may calculate accumulated energy by accumulating either the charge energy or the discharge energy for the battery pack 10, and may calculate the degree of change (e.g., slope) of the cell capacity deviation for each of the battery cells 10_1-10_4 each time the accumulated energy of the battery pack 10 increases by a predetermined unit. A period during which the accumulated energy increases by a reference energy unit is referred to as an accumulation period. The MCU 130 may diagnose whether a corresponding battery cell is abnormal based on the result of comparing the slope calculated for each accumulation period with a predetermined critical value. The degree of cell capacity degradation may be considered to increase as the degree of change in the cell capacity deviation increases. In other words, if the cell capacity of a battery cell decreases due to battery cell degradation, the degree of change in the cell capacity deviation may be used to diagnose the degree of cell capacity degradation based on the increase in the degree of change in the cell capacity deviation. In one embodiment, the degree of change in the cell capacity deviation refers to the difference between the cell capacity deviation in a current accumulation period and the cell capacity deviation in a previous accumulation period for each battery cell. The previous accumulation period may be immediately before the current accumulation period. The MCU 130 may calculate the cell capacity of each of the plurality of battery cells 10_1-10_4 for each predetermined cell capacity calculation period in order to calculate the cell capacity deviation. The MCU 130 may calculate the cell capacity of each battery cell based on the cell voltage of each of the plurality of battery cells 10_1-10_4.

[0038] The MCU 130 may be realized by a semiconductor IP (intellectual property), for example, an ASIC (application specific IC), and a program consisting of a set of control instructions for diagnosing the cell capacity deterioration degree for each of the plurality of battery cells 10_1-10_4 may be installed in the ASIC. In the following description, each of the components of the MCU 130 may be realized by a set of control instructions for performing a certain same operation among the overall control instructions.

[0039] FIG. 2 is a diagram showing a configuration of a part of an MCU according to an embodiment.

[0040] FIG. 3 is a flowchart illustrating a method for diagnosing a cell capacity degradation level of a battery cell according to an embodiment.

[0041] FIG. 2 shows a configuration for diagnosing the degree of cell capacity degradation for a battery cell.

[0042] As shown in FIG. 2, the MCU 130 may include an energy accumulation unit 131, a cell capacity calculation unit 132, a cell capacity deviation calculation unit 133, and a degradation level diagnosis unit 134.

[0043] The energy accumulation unit 131 may calculate accumulated energy by accumulating either charge energy or discharge energy for the battery pack 10. For example, the energy accumulation unit 131 may calculate either charge energy or discharge energy for the battery pack 10 as accumulated energy using the battery pack current indicated by the current sensing signal IS and the battery pack voltage indicated by the voltage sensing signal PVS (S1). The measurement points of the battery pack current indicated by the current sensing signal IS and the battery pack voltage indicated by the voltage sensing signal PVS may be synchronized under the control of the MCU 130. For example, the MCU 130 may instruct the current sensor 23 to measure the current and the cell monitoring IC 110 to measure the battery pack voltage at every predetermined monitoring period.

[0044] Specifically, when the energy accumulation unit 131 calculates the accumulated energy according to the charge energy, it may calculate the charge energy by multiplying the battery pack current by the battery pack voltage for each monitoring period during a charging period in which the battery pack 10 is charged, and may calculate the accumulated energy by integrating the charge energy calculated during the charging period. Alternatively, when the energy accumulation unit 131 calculates the accumulated energy according to the discharge energy, it may calculate the discharge energy by multiplying the battery pack current by the battery pack voltage for each monitoring period during a discharging period in which the battery pack 10 is discharged, and may calculate the accumulated energy by integrating the discharge energy calculated during the discharging period. The energy accumulation unit 131 may transmit the calculated accumulated energy value ACCE to the deterioration degree diagnosis unit 134.

[0045] The cell capacity calculation unit 132 may calculate the cell capacity of each of the plurality of battery cells 10_1-10_4 at a predetermined cell capacity calculation cycle and store the calculated cell capacities (S2). The cell capacity indicates the amount of charge that the battery cell can hold, and may be expressed as a State of Health (SOH). In one embodiment, the SOH, which is the ratio of the current cell capacity of the battery cell to the initial cell capacity of the battery cell, may be used as a factor indicating the current cell capacity of the battery cell. The state of the battery cell before it is used may be referred to as "initial."

[0046] The cell capacity calculation period may be set in various ways depending on the design. For example, the period from when the BMS 100 is powered on to when it is powered off may be set as the cell capacity calculation period. Powering on means that a power source is connected to the BMS 100 and power required for the operation of the BMS 100 is supplied, and powering off means that the power source connected to the BMS 100 is cut off and power supply to the BMS 100 is cut off. When the BMS 100 is powered on, the MCU 130 may also be connected to a power source and turned on, and when the BMS 100 is powered off, the MCU 130 may also be turned off due to the power cut off. Powering on and powering off of the BMS 100 may be controlled by a user operation or a control command from an upper controller.

[0047] Specifically, the cell capacity calculation unit 132 may calculate an integrated current amount for each of the battery cells 10_1-10_4 by integrating the current flowing through each of the battery cells 10_1-10_4 during a cell capacity calculation period, calculate an SOC change amount for each of the battery cells 10_1-10_4 during the cell capacity calculation period, and calculate the cell capacity SOH for each of the battery cells 10_1-10_4 by dividing the integrated current amount for each of the battery cells 10_1-10_4 during the cell capacity calculation period by the SOC change amount. In one embodiment, the battery cells 10_1-10_4 are connected in series, and therefore the integrated current amounts for the battery cells 10_1-10_4 may be the same. However, unlike the embodiment, if the battery cells are connected in parallel, the battery system 1 may be provided with a current sensor for each current path, and the cell capacity calculation unit 132 may collect current measurement results for each current path to calculate the integrated current amount for each of the battery cells.

[0048] The cell capacity calculation unit 132 may estimate the SOC at the start of a cell capacity calculation cycle and the SOC at the end of the cell capacity calculation cycle based on the cell voltage or OCV (Open Circuit Voltage) of each of the battery cells 10_1-10_4, and calculate the difference between the SOC at the end and the SOC at the start as an SOC change amount. Various known techniques for estimating the SOC for each of the battery cells 10_1-10_4 may be applied to an embodiment. For example, the BMS 100 according to an embodiment may include a lookup table in which condition factors are cell temperature and OCV (or cell voltage), and factors determined by the condition factors are tabulated as SOC. The cell capacity calculation unit 132 may derive, from the lookup table, an SOC corresponding to the OCV (or cell voltage) calculated based on the cell voltage measured at the current cell temperature. If necessary, the cell capacity calculation unit 132 may estimate an SOC under conditions not recorded in the lookup table using interpolation.

[0049] The cell capacity deviation calculation unit 133 may calculate a cell capacity deviation dSOH for each of the plurality of battery cells 10_1-10_4 with respect to the cell capacity SOH for each of the plurality of battery cells 10_1-10_4 for each cell capacity calculation period (S3). The cell capacity deviation according to an embodiment may refer to a change in cell capacity for each of the plurality of battery cells 10_1-10_4 during a cell capacity calculation period. Therefore, the cell capacity deviation calculation unit 133 may calculate, for each of the plurality of battery cells 10_1-10_4, a difference SOH_n1-SOH_n2 between a cell capacity SOH_n1 at the start of an n-th cell capacity calculation period and a cell capacity SOH_n2 at the end of the n-th cell capacity calculation period as the cell capacity deviation dSOH_n of the corresponding battery cell. "n" may be a natural number equal to or greater than 1, indicating the number of cell capacity calculation periods that have elapsed since the battery pack 10 began to be used until an arbitrary time point (e.g., the current time point).

[0050] The deterioration level diagnosis unit 134 may calculate the degree of change in the cell capacity deviation for each of the plurality of battery cells 10_1 to 10_4 for each accumulation period in which the accumulated energy increases by a predetermined unit (S4).

[0051] The deterioration level diagnosis unit 134 receives the accumulated energy value from the energy accumulation unit 131, receives and stores the cell capacity deviation dSOH for each of the plurality of battery cells 10_1-10_4 during a cell capacity calculation period corresponding to a point in time when the accumulated energy value has increased by a predetermined reference energy unit from the cell capacity deviation calculation unit 133, and calculates the degree of change (e.g., slope) between the cell capacity deviation corresponding to the current accumulation period (hereinafter, current cell capacity deviation, dSOH_n) and the cell capacity deviation corresponding to the immediately preceding accumulation period (hereinafter, immediately preceding cell capacity deviation, dSOH_n-1) for each of the plurality of battery cells 10_1-10_4 (S4). The accumulation period is updated every time the accumulated energy value increases by the reference energy unit.

[0052] When the accumulation period is updated (when the accumulated energy value increases by a reference energy unit), the deterioration level diagnosis unit 134 may request the cell capacity deviation calculation unit 133 for each of the plurality of battery cells 10_1-10_4. The cell capacity calculation unit 132 may transmit the current cell capacity deviation dSOH_n, which is the cell capacity deviation calculated at the time closest to the time when the request was received, to the deterioration level diagnosis unit 134. The deterioration level diagnosis unit 134 may store the current cell capacity deviation dSOH_n received in response to the request. The deterioration level diagnosis unit 134 calculates the slope between the current cell capacity deviation dSOH_n and the previously stored cell capacity deviation dSOH_n-1 for each accumulation period. For example, the deterioration level diagnosis unit 134 may calculate the slope by dividing the value obtained by subtracting the previous cell capacity deviation dSOH_n-1 from the current cell capacity deviation dSOH_n by the reference energy. For your information, the cell capacity may be expressed in [%] because it is the ratio of the cell capacity at the time of calculation to the cell capacity of the initial battery cell. The unit of cumulative energy may be [J] (joule).

[0053] The deterioration level diagnosis unit 134 can diagnose whether each battery cell is abnormal based on the result of comparing the degree of change in the cell capacity deviation calculated for each accumulation period with a predetermined critical value (S5). The deterioration level diagnosis unit 134 can diagnose a battery cell, among the plurality of battery cells 10_1-10_4, whose calculated slope is equal to or greater than a predetermined deterioration critical value, as an abnormal cell.

[0054] FIG. 4 is a graph illustrating the relationship between cell capacity deviation and accumulated energy according to one embodiment.

[0055] 4 is an example for explaining the present invention, and the present invention is not limited thereto. In FIG. 4, the horizontal axis represents accumulated energy, and as the accumulated energy increases, the position representing the accumulated energy on the horizontal axis moves to the right, and the vertical axis represents cell capacity deviation, and as the cell capacity deviation increases, the position representing the cell capacity deviation on the vertical axis moves upward.

[0056] 4, the "dSOH_TH" shown on the vertical axis is a fixed value, which is a cell capacity deviation threshold value for determining whether a battery cell is normal. Conventionally, when the cell capacity deviation reaches "dSOH_TH," the cell can be diagnosed as an abnormal cell due to degradation.

[0057] A graph 300 shown in FIG. 4 is a graph showing the cell capacity deviation with respect to the accumulated energy of a certain battery cell among the plurality of battery cells 10_1-10_4.

[0058] When the accumulated energy reaches "ACCE_1", the degradation level diagnosis unit 134 calculates a slope DS1 between the cell capacity deviation dSOH_0 immediately before when the accumulated energy is "ACCE_0" and the current cell capacity deviation dSOH_1 when the accumulated energy is "ACCE_1". The slope DS1 is a value less than the degradation critical value, and the degradation level diagnosis unit 134 determines that the corresponding battery cell is normal.

[0059] When the accumulated energy reaches "ACCE_2," the degradation level diagnosis unit 134 calculates a slope DS2 between the cell capacity deviation dSOH_1 immediately before when the accumulated energy was "ACCE_1" and the current cell capacity deviation dSOH_2 when the accumulated energy was "ACCE_2." The slope DS2 is a value equal to or greater than the degradation threshold, and the degradation level diagnosis unit 134 determines that the corresponding battery cell is abnormal.

[0060] The degradation threshold may be a constant value or may vary depending on the accumulated energy. For example, the degradation threshold may increase as the accumulated energy increases.

[0061] Compared to the conventional method, even though the current cell capacity deviation dSOH_2 is less than "dSOH_TH," the battery cell can be determined to be abnormal in one embodiment. In the conventional method, the cell capacity deviation of the battery cell may affect other battery cells as it progresses from the current cell capacity deviation dSOH_2 to "dSOH_TH." In contrast, a battery system according to one embodiment can detect an abnormal battery cell with a large degree of cell capacity degradation at an early stage by calculating the degree of change in the cell capacity deviation.

[0062] When the BMS 100 detects an abnormal battery cell, it can notify the outside. The outside may include a terminal or server that manages the battery system 1, a higher-level controller of a device incorporating the battery system 1, etc. When an abnormal battery cell is detected and the corresponding battery cell is replaced in the battery pack 10, the influence on the cell capacity degradation of other battery cells can be prevented.

[0063] Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited to these, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the claims below also fall within the scope of the present invention.

Claims

1. a battery pack including a plurality of battery cells; a current sensor that measures a current flowing through the battery pack and generates a current sense signal indicative of the measured battery pack current; a cell monitoring IC that measures a battery pack voltage of the battery pack and a cell voltage of each of the plurality of battery cells, and generates a voltage sensing signal indicative of the measured battery pack voltage and the measured plurality of cell voltages; a main control circuit that calculates accumulated energy for the battery pack using the current sensing signal and the voltage sensing signal, calculates a cell capacity of each of the plurality of battery cells for each predetermined cell capacity calculation period, calculates a degree of change in cell capacity deviation for each of the plurality of battery cells for each accumulation period in which the accumulated energy increases by a predetermined unit, and diagnoses whether each battery cell is abnormal based on a result of comparing the degree of change in cell capacity deviation calculated for each accumulation period with a predetermined critical value. Battery system.

2. The main control circuit an energy accumulation unit that calculates, as the accumulated energy, one of charge energy and discharge energy of the battery pack using the battery pack current indicated by the current detection signal and the battery pack voltage indicated by the voltage detection signal; The battery system of claim 1 .

3. The energy accumulation unit calculating charge energy by multiplying a battery pack current by a battery pack voltage for each monitoring period during a charging period in which the battery pack is charged, and integrating the calculated charge energy during the charging period to calculate cumulative energy; or calculating discharge energy by multiplying a battery pack current by a battery pack voltage for each monitoring period during a discharge period in which the battery pack is discharged, and integrating the discharge energy calculated during the discharge period to calculate cumulative energy; The battery system of claim 2 .

4. The main control circuit a cell capacity calculation unit that calculates the cell capacity of each of the plurality of battery cells in a predetermined cell capacity calculation cycle and stores the calculated cell capacities; The battery system according to claim 1 , wherein the cell capacity calculation period is a period from when the main control circuit is turned on to when it is turned off.

5. The cell capacity calculation unit integrating currents flowing through each of the plurality of battery cells during the cell capacity calculation period to calculate an integrated current amount for each of the plurality of battery cells; calculating an SOC change amount for each of the plurality of battery cells during the cell capacity calculation period; and calculating a cell capacity for each of the plurality of battery cells by dividing the integrated current amount for the cell capacity calculation period by the SOC change amount. The battery system of claim 4.

6. The cell capacity calculation unit an SOC at a start point of the cell capacity calculation cycle and an SOC at an end point of the cell capacity calculation cycle are estimated based on the cell voltages of the plurality of battery cells indicated by the voltage sensing signals or an OCV based on the respective cell voltages; and a difference between the SOC at the end point and the SOC at the start point is calculated as the SOC change amount. The battery system of claim 5 .

7. The main control circuit a cell capacity deviation calculation unit that calculates a cell capacity deviation for each of the plurality of battery cells for each cell capacity calculation period; The cell capacity deviation is a change in cell capacity for each of the plurality of battery cells during the cell capacity calculation period. The battery system of claim 4.

8. The cell capacity deviation calculation unit For each of the plurality of battery cells, a difference between a cell capacity at a start point of an n-th cell capacity calculation cycle and a cell capacity at an end point of the n-th cell capacity calculation cycle is calculated as a cell capacity deviation of each battery cell; The n is a natural number of 1 or more that indicates the number of cell capacity calculation cycles that have elapsed since the battery pack began to be used until an arbitrary time point. The battery system of claim 7.

9. The main control circuit a degradation diagnosis unit that stores a cell capacity deviation for each of the plurality of battery cells during a cell capacity calculation period corresponding to a time point when the accumulated energy value has increased by a predetermined reference energy unit, calculates a slope between a current cell capacity deviation corresponding to a current accumulation period and a previous cell capacity deviation corresponding to a previous accumulation period for each of the plurality of battery cells, and diagnoses a battery cell whose calculated slope is equal to or greater than a predetermined degradation critical value as an abnormal cell; The battery system of claim 1 .

10. A method for diagnosing a deterioration level of a plurality of battery cells constituting a battery pack by a main control circuit of a battery management system, comprising: Calculating cumulative energy for the battery pack using a battery pack current flowing through the battery pack and a battery pack voltage that is a voltage of the battery pack; calculating a cell capacity of each of the plurality of battery cells at each predetermined cell capacity calculation period; Calculating a cell capacity deviation for each of the plurality of battery cells at each cell capacity calculation period; calculating a degree of change in cell capacity deviation for each of the plurality of battery cells for each accumulation period in which the accumulated energy increases by a predetermined unit; and diagnosing whether each battery cell is abnormal based on a result of comparing the degree of change in the cell capacity deviation calculated for each accumulation period with a predetermined critical value. Battery cell deterioration diagnosis method.

11. The step of calculating the accumulated energy comprises: calculating a charge energy by multiplying a battery pack current by a battery pack voltage for each monitoring period during a charging period in which the battery pack is charged, and integrating the calculated charge energy during the charging period to calculate cumulative energy; calculating discharge energy by multiplying a battery pack current by a battery pack voltage for each monitoring period during a discharge period in which the battery pack is discharged, and integrating the discharge energy calculated during the discharge period to calculate cumulative energy; The battery cell deterioration diagnosis method according to claim 10.

12. The step of calculating the cell capacity includes: integrating currents flowing through each of the plurality of battery cells during the cell capacity calculation period to calculate an integrated current amount for each of the plurality of battery cells; Calculating an amount of change in SOC of each of the plurality of battery cells during the cell capacity calculation period; and calculating a cell capacity for each of the plurality of battery cells by dividing an integrated amount of current during the cell capacity calculation period by the amount of change in SOC, The cell capacitance calculation period is a period from when the main control circuit is turned on to when it is turned off. The battery cell deterioration diagnosis method according to claim 10.

13. The step of calculating the SOC change amount includes: estimating an SOC at a start point of the cell capacity calculation cycle and an SOC at an end point of the cell capacity calculation cycle based on the cell voltages of each of the plurality of battery cells or an OCV based on the cell voltages of each of the plurality of battery cells, and calculating a difference between the SOC at the end point and the SOC at the start point as the SOC change amount, The battery cell deterioration diagnosis method according to claim 12.

14. The step of calculating the cell capacity deviation includes: calculating, for each of the plurality of battery cells, a difference between a cell capacity at a start point of an n-th cell capacity calculation cycle and a cell capacity at an end point of the n-th cell capacity calculation cycle as a cell capacity deviation of each battery cell; the cell capacity deviation is a change in cell capacity for each of the plurality of battery cells during the cell capacity calculation period; The n is a natural number of 1 or more that indicates the number of cell capacity calculation cycles that have elapsed since the battery pack began to be used until an arbitrary time point. The battery cell deterioration diagnosis method according to claim 10.

15. The step of calculating the degree of change in the cell capacity deviation includes: storing a cell capacity deviation for each of the plurality of battery cells during a cell capacity calculation period corresponding to a time point at which the accumulated energy value increases by a predetermined reference energy unit; and calculating, for each of the plurality of battery cells, a slope between a current cell capacity deviation corresponding to a current cumulative period and a previous cell capacity deviation corresponding to a previous cumulative period. The battery cell deterioration diagnosis method according to claim 10.

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