Method for determining normal resistance range, and diagnostic device and battery system using same

Abstract

This diagnosis device may comprise: a direct current device for discharging a battery cell with a fixed current for a predetermined measurement period so as to measure a direct current resistance of the battery cell; an alternating current device for supplying an alternating current to the battery cell so as to measure an alternating current resistance of the battery cell; a voltage measurement device for measuring a voltage of the battery cell; a memory for storing, for each of a plurality of diagnosis periods, each of a plurality of resistance pairs in which the direct current resistance and the alternating current resistance are matched; and a diagnosis control circuit for calculating the direct current resistance and the alternating current resistance according to the voltage of the battery cell for each of the plurality of diagnosis periods, acquiring a graph for the plurality of resistance pairs on the basis of a plurality of dots corresponding to the plurality of resistance pairs, and determining a normal resistance range based on the graph on the basis of the graph and the uppermost dot and the lowermost dot, among the plurality of dots, that are farthest from the graph.

Description

Method for determining normal resistance range, and diagnostic device and battery system using the same

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0132604 dated September 30, 2024, and all contents disclosed in the document of said Korean patent application are incorporated herein as part of this specification.

[0003] The present disclosure relates to a method for determining a normal resistance range, and a diagnostic device and battery system using the same.

[0004] The DC resistance of a battery cell can be measured to diagnose abnormalities. A battery cell may be diagnosed as abnormal when there is a significant difference between its DC resistance value and that of other identical battery cells. However, since the DC resistance of a battery cell can vary depending on factors such as temperature and State of Charge (SOC), relying solely on DC resistance to determine abnormality may lead to diagnostic errors. Furthermore, errors may also occur in determining the appropriate measurement period for the DC resistance.

[0005] The present invention aims to provide a method for determining a normal resistance range that can improve the accuracy of diagnosing abnormalities in battery cells, as well as a diagnostic device and a battery system utilizing the same.

[0006] A diagnostic device according to one feature of the present invention may include a DC current device that discharges the battery cell with a fixed current for a predetermined measurement period to measure the DC resistance of the battery cell, an AC current device that supplies an AC current to the battery cell to measure the AC resistance of the battery cell, a voltage measuring device that measures the voltage of the battery cell, a memory that stores each of a plurality of resistance pairs in which the DC resistance and the AC resistance are matched for each of a plurality of diagnostic cycles, and a diagnostic control circuit that calculates the DC resistance and the AC resistance according to the voltage of the battery cell for each of the plurality of diagnostic cycles, obtains a graph for the plurality of resistance pairs based on a plurality of dots corresponding to the plurality of resistance pairs, and determines a normal resistance range based on the graph based on the graph and the upper dot and lower dot among the plurality of dots that are furthest from the graph.

[0007] The above diagnostic control circuit can implement the plurality of resistor pairs as a plurality of dots in a two-dimensional coordinate system and determine the graph according to the trend of the plurality of dots based on the positions of the plurality of dots.

[0008] The diagnostic control circuit can determine a correlation equation representing the graph, determine an upper limit line including the upper dot and having the slope of the correlation equation, set a lower limit line including the lower dot and having the slope of the correlation equation, and determine the area between the upper limit line and the lower limit line as a normal resistance range.

[0009] The above diagnostic control circuit controls the DC current device to discharge the battery cell with the fixed current during a first measurement period, controls the voltage measuring device at the start and end points of the first measurement period to measure the first voltage and the second voltage of the battery cell, and can calculate the DC resistance of the battery cell using the first voltage, the second voltage, and the fixed current.

[0010] The above diagnostic control circuit controls the alternating current device to supply a plurality of alternating currents for each frequency within a predetermined frequency range to the battery cell for a predetermined supply period, and after the predetermined supply period ends, controls the voltage measuring device to measure the alternating voltage of the battery cell, calculates the plurality of alternating currents for each frequency using the plurality of alternating currents for each frequency and the measured alternating voltage, and can determine the alternating resistance among the plurality of alternating resistances for each frequency within the frequency range, wherein the imaginary part resistance is 0, as the alternating resistance of the battery cell.

[0011] A method for determining a normal resistance range required for diagnosing abnormalities in a battery cell according to another feature of the invention may include: discharging the battery cell with a fixed current for a predetermined measurement period and calculating the DC resistance of the battery cell with the voltage change during the measurement period and the fixed current; supplying a plurality of frequency-specific AC currents to the battery cell within a predetermined frequency range for a predetermined supply period and measuring the AC voltage of the battery cell by supplying the AC current to determine the AC resistance of the battery cell; repeating the DC resistance calculation step and the AC resistance calculation step for each of the plurality of diagnosis cycles and storing a plurality of resistance pairs by matching the DC resistance and AC resistance calculated for each of the diagnosis cycles; obtaining a graph for the plurality of resistance pairs based on a plurality of dots corresponding to the plurality of resistance pairs; and determining a normal resistance range based on the graph based on the graph and the upper dot and lower dot among the plurality of dots that are furthest from the graph.

[0012] The step of obtaining the above graph may include the step of implementing the plurality of resistance pairs as a plurality of dots in a two-dimensional coordinate system and determining the graph according to the trend of the plurality of dots based on the positions of the plurality of dots.

[0013] The step of determining the normal resistance range may include the step of determining a correlation equation representing the graph, the step of determining an upper limit line including the upper dot and having the slope of the correlation equation, the step of setting a lower limit line including the lower dot and having the slope of the correlation equation, and the step of determining the area between the upper limit line and the lower limit line as the normal resistance range.

[0014] The step of determining the AC resistance of the battery cell may include the step of calculating the AC resistances for a plurality of frequencies using the AC currents for a plurality of frequencies and the measured AC voltages, and the step of determining the AC resistance among the AC resistances for a plurality of frequencies within the frequency range, in which the imaginary part resistance is zero, as the AC resistance of the battery cell.

[0015] A battery system according to another feature of the invention may include a battery pack comprising a plurality of battery cells and a battery management system that calculates the DC resistance and AC resistance of a target battery cell among the plurality of battery cells, and diagnoses the target battery cell as an abnormal cell when the resistance pair of the DC resistance and the AC resistance deviates from a normal resistance range. The normal resistance range may be determined according to the normal resistance range determination method.

[0016] The embodiments of the present disclosure can provide a method for determining a normal resistance range that can improve the accuracy of diagnosing whether a battery cell is abnormal, and a diagnostic device and battery system using the same.

[0017] Figure 1 is a block diagram showing the configuration of a diagnostic device for diagnosing abnormalities in a battery cell.

[0018] FIG. 2 is a graph showing the change in cell voltage of a reference battery cell according to CC discharge during a first measurement period according to some embodiment.

[0019] Figure 3 is a graph showing the AC resistance values ​​calculated by the diagnostic control circuit in an impedance plane.

[0020] FIG. 4 is a diagram showing a graph implemented based on a plurality of resistor pairs by a diagnostic control circuit according to a certain embodiment.

[0021] FIG. 5 is a graph for explaining a method of determining a normal resistance range in a graph according to a certain embodiment.

[0022] FIG. 6 is a flowchart illustrating a method for a diagnostic device according to a certain embodiment to determine a normal resistance range.

[0023] FIG. 7 is a block diagram showing a battery system utilizing a normal resistance range determined by a diagnostic device according to some embodiment.

[0024] FIG. 8 is a flowchart illustrating a method for diagnosing battery cell abnormalities in a battery management system according to a certain embodiment.

[0025] In describing the embodiments disclosed in this specification, detailed descriptions of related prior art are omitted if it is determined that such detailed descriptions may obscure the essence of the embodiments disclosed in this specification. Furthermore, the attached drawings are intended only to facilitate understanding of the embodiments disclosed in this specification, and the technical concept disclosed in this specification is not limited by the attached drawings; it should be understood that they include all modifications, equivalents, and substitutions that fall within the spirit and technical scope of the invention.

[0026] Terms including ordinal numbers, such as first, second, etc., may be used to describe various components, but said components are not limited by said terms. These terms are used solely for the purpose of distinguishing one component from another.

[0027] When it is stated that one component is "connected" or "connected" to another component, it should be understood that while it may be directly connected or connected to that other component, there may also be other components in between. On the other hand, when it is stated that one component is "directly connected" or "directly connected" to another component, it should be understood that there are no other components in between.

[0028] In this application, terms such as “comprising” or “having” are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0029] Figure 1 is a block diagram showing the configuration of a diagnostic device for diagnosing abnormalities in a battery cell.

[0030] As illustrated in FIG. 1, the diagnostic device (1) may include a direct current device (10), an alternating current device (20), a voltage measuring device (30), two conversion switches (15, 25), a diagnostic control circuit (40), and a charging / discharging device (50). The diagnostic device (1) may perform a diagnosis on a battery pack (2) comprising a plurality of battery cells (21, 22, 23).

[0031] In FIG. 1, a voltage measuring device (30) is shown connected between the positive and negative electrodes of a battery cell (22), but the voltage measuring device (30) may be connected between the positive and negative electrodes of another battery cell (e.g., 21 or 23) among the plurality of battery cells constituting the battery pack (2). In FIG. 1, a first terminal (TR1) of a conversion switch (15) is shown connected to the positive electrode of the battery cell (22) and a first terminal (TR4) of a conversion switch (25) is shown connected to the negative electrode of the battery cell (22), but the first terminal (TR1) of the conversion switch (15) may be connected to the positive electrode of another battery cell (e.g., 21 or 23) among the plurality of battery cells constituting the battery pack (2), and the first terminal (TR4) of the conversion switch (25) may be connected to the negative electrode of another battery cell (e.g., 21 or 23).

[0032] The second terminal (TR2) of the conversion switch (15) is connected to one end (DC1) of the DC current device (10), and the third terminal (TR3) of the conversion switch (15) is connected to one end (AC1) of the AC current device (20). The second terminal (TR5) of the conversion switch (25) is connected to the other end (DC2) of the DC current device (10), and the third terminal (TR6) of the conversion switch (25) is connected to the other end (AC2) of the AC current device (20).

[0033] The diagnostic control circuit (40) is a circuit that includes control logic for controlling the operation of the components (15, 20, 25, 30, 50) of the diagnostic device (1). The diagnostic control circuit (40) can generate and transmit control signals to perform control on each of the components (15, 20, 25, 30, 50) according to the control logic. The diagnostic control circuit (40) can receive a voltage measurement signal (VS) in response to a control signal (OS3) from the voltage measurement device (30) and determine a normal resistance range based on the received voltage measurement signal (VS). The diagnostic control circuit (40) can determine whether the battery cell is abnormal based on the determined normal resistance range. The diagnostic control circuit (40) can be implemented as a combination of software for implementing the control logic and hardware for executing the software.

[0034] The diagnostic control circuit (40) can generate two switch control signals (SC1, SC2) to control the connection status of each of the two conversion switches (15, 25). Depending on the switch control signal (SC1), the conversion switch (15) can connect the first stage (TR1) and the second stage (TR2), connect the first stage (TR1) and the third stage (TR3), or float the first stage (TR1). Depending on the switch control signal (SC2), the conversion switch (25) can connect the first stage (TR4) and the second stage (TR5), connect the first stage (TR4) and the third stage (TR6), or float the first stage (TR4).

[0035] The charging / discharging device (50) can charge and discharge the battery pack (2) to be diagnosed. When the charging / discharging device (50) charges and discharges the battery pack (2), the diagnostic control circuit (40) can generate two switch control signals (SC1, SC2) that float the first stage (TR1) of the conversion switch (15) and the first stage (TR4) of the conversion switch (25). Each of the conversion switch (15) and the conversion switch (25) floats the first stage (TR1) and the first stage (TR4), respectively, according to each of the two switch control signals (SC1, SC2).

[0036] In the following description, the DC resistance and AC resistance of the battery cell (22) are used to determine the normal resistance range necessary to determine whether the battery cell is abnormal. However, the invention is not limited thereto, and the DC resistance and AC resistance of two or more battery cells constituting the battery pack (2) may also be used. Hereinafter, the battery cell used to determine the normal resistance range is referred to as the reference battery cell.

[0037] For example, the charging / discharging device (10) can charge the battery pack (2) at a first C-rate for a first time period, rest for a second time period, and then discharge it at a second C-rate for a third time period. “C-rate” is a ratio in which the charging current [A] or the discharging current [A] is divided by the rated capacity value [Ah] of the battery pack. Charging is performed by at least one of constant current (CC) charging and constant voltage charging, or a combination of both, and discharging can be performed by at least one of CC discharge and CV discharge, or a combination of both. The charging / discharging device (10) can charge and discharge the battery pack (2) in units of charging / discharging cycles. The charging / discharging cycle may be the sum of the first to third times.

[0038] The voltage measuring device (30) can measure a DC voltage or an AC voltage between the positive and negative electrodes of a reference battery cell (22). The diagnostic control circuit (40) transmits a control signal (OS3) instructing the voltage measuring circuit (30) to measure the DC voltage or AC voltage, and the voltage measuring circuit (30) can transmit a signal (VS) instructing the measured DC voltage or AC voltage according to the control signal (OS3) to the diagnostic control circuit (40).

[0039] The diagnostic control circuit (40) can transmit a control signal (OS1) instructing a DC current device (10) to perform CC discharge in order to calculate the DC resistance of the reference battery cell, and transmit a control signal (OS3) instructing a voltage measurement device (30) to perform voltage measurement during a first measurement period in which CC discharge is performed. For DC resistance measurement, the diagnostic control circuit (40) generates a switch control signal (SC1) connecting the first stage (TR1) and the second stage (TR2), and a switch control signal (SC2) connecting the first stage (TR4) and the second stage (TR5). Each of the conversion switch (15) and the conversion switch (25) can connect the first stage (TR1, TR4) and the second stage (TR2, TR5) according to each of the two switch control signals (SC1, SC2). Then, the reference battery cell (22) and the DC current device (10) can be electrically connected.

[0040] The DC current device (10) can discharge the reference battery cell (22) with a fixed current of a predetermined level during the first measurement period according to the control signal (OS1). The voltage measuring device (30) can measure the cell voltage of the reference battery cell (22) at the start and end points of the first measurement period, respectively, according to the control signal (OS2). At this time, the cell voltage is the DC voltage difference between the positive and negative electrodes of the battery cell.

[0041] FIG. 2 is a graph showing the change in cell voltage of a reference battery cell according to CC discharge during a first measurement period according to some embodiment.

[0042] In FIG. 2, period TP1 is a first measurement period, and CC discharge can be started at time T1 and terminated at time T2. The DC current device (10) can CC discharge a reference battery cell with a predetermined fixed current during the first measurement period (TP1). At time T1, the State of Charge (SOC) of the reference battery cell (22) can be controlled to a specific value.

[0043] As illustrated in FIG. 2, the cell voltage of the reference battery cell (22) can be reduced from voltage (V1) to voltage (V2) by CC discharge with a fixed current during the first measurement period (TP1). The voltage measuring device (30) can measure the cell voltage (V1) of the reference battery cell (22) at time T1 and transmit a signal (VS) indicating the cell voltage (V1) to the diagnostic control circuit (40). The voltage measuring device (30) can measure the cell voltage (V2) of the reference battery cell (22) at time T2 and transmit a signal (VS) indicating the cell voltage (V2) to the diagnostic control circuit (40).

[0044] The diagnostic control circuit (40) can calculate the voltage difference between voltage (V1) and voltage (V2) according to the signal (VS) and calculate the DC resistance by dividing it by the fixed current during the first measurement period (TP1). The diagnostic control circuit (40) can calculate the DC resistance at a predetermined diagnostic cycle. For example, the diagnostic cycle can be set to 100 cycles based on the charging / discharging cycle performed by the charging / discharging device (10). The diagnostic control circuit (40) can stop the charging / discharging device (50) at each diagnostic cycle and calculate the DC resistance and AC resistance. The charging / discharging device (50) can transmit a charging / discharging count signal (CDC) indicating the result of counting the number of charging / discharging cycles to the diagnostic control circuit (40). The diagnostic control circuit (40) can stop the charging / discharging device (50) and calculate the DC resistance and AC resistance whenever the charging / discharging count signal (CDC) indicates 100 cycles.

[0045] The diagnostic control circuit (40) can generate and transmit a control signal (OS1) instructing a DC current device (10) to perform a CC discharge during a first measurement period in order to calculate the DC resistance, and generate and transmit a control signal (OS3) instructing a voltage measuring device (30) to perform voltage measurements at the start and end points of the first measurement period, respectively.

[0046] The diagnostic control circuit (40) can transmit a control signal (OS2) instructing AC charging to the AC current device (20) to calculate AC resistance following the DC resistance calculation, and transmit a control signal (OS3) instructing AC voltage measurement to the voltage measurement device (30). The diagnostic control circuit (40) can calculate AC resistance along with DC resistance at each diagnostic cycle. The diagnostic control circuit (40) can generate a control signal (OS2) containing information regarding the frequency and level of the AC current and the supply period for supplying the AC current. The diagnostic control circuit (40) can transmit a control signal (OS3) instructing AC voltage measurement to the voltage measurement device (30) for each frequency. For AC resistance measurement, the diagnostic control circuit (40) generates a switch control signal (SC1) connecting the first stage (TR1) and the third stage (TR3), and a switch control signal (SC2) connecting the first stage (TR4) and the third stage (TR6). Each of the conversion switch (15) and the conversion switch (25) can connect the first stage (TR1, TR4) and the third stage (TR3, TR6) according to each of the two switch control signals (SC1, SC2). Then, the reference battery cell (22) and the alternating current device (20) can be electrically connected.

[0047] The diagnostic control circuit (40) can transmit a control signal (OS2) to the AC current device (20) instructing that, for each of the plurality of frequencies, an AC current of a predetermined level be supplied to the reference battery cell (22) for a predetermined supply period. At the same time, the diagnostic control circuit (40) can transmit a control signal (OS3) to the voltage measuring device (30) instructing that, for each of the plurality of frequencies, an AC voltage be measured in synchronization with the end of the predetermined supply period. The AC current device (20) can supply an AC current of each frequency and a predetermined level to the reference battery cell (22) for a predetermined supply period according to the control signal (OS2). The voltage measuring device (30) can measure the AC cell voltage of the reference battery cell (22) according to the control signal (OS3). The voltage measuring device (30) can transmit a signal (VS) indicating the measured AC cell voltage of the reference battery cell to the diagnostic control circuit (40). At the start of the supply period, the SOC of the reference battery cell (22) can be set to a specific value and can be the same value as the SOC set when calculating the DC resistance.

[0048] The diagnostic control circuit (40) generates a control signal (OS3) and thus knows the frequency and level of the alternating current. The diagnostic control circuit (40) can calculate the frequency-specific alternating resistance based on the received signal (VS) and the alternating current. The diagnostic control circuit (40) can calculate the frequency-specific alternating resistance by dividing the alternating cell voltage of the reference battery cell (22) indicated by the received signal (VS) by the level of the alternating current. The diagnostic control circuit (40) can determine the alternating resistance with an imaginary part resistance value of 0 among the multiple alternating resistances calculated for multiple frequencies as the alternating resistance of the reference battery cell. The alternating resistance with an imaginary part resistance value of 0 can represent the ohmic resistance of the reference battery cell.

[0049] Figure 3 is a graph showing the AC resistance values ​​calculated by the diagnostic control circuit in an impedance plane.

[0050] In FIG. 3, the resistance value (R0) is a value determined by the electrolyte resistance of the reference battery cell and may be an ohmic resistance. In the present disclosure, the AC resistance of the battery cell may refer to a resistance in which the imaginary part resistance value is 0, such as the resistance value (R0). For reference, the first resistance region (RA1) may represent the resistance caused by the Solid Electrolyte Interphase (SEI) generated on the surface of the internal electrode particles of the reference battery cell. The second resistance region (RA2) may represent the charge transfer resistance in charge movement at the electrode material interface. The third resistance region (RA3) may represent the chemical diffusion resistance of lithium ions as Warburg impedance. In the present disclosure, the third resistance region (RA3) is a low-frequency region, and the diagnostic control circuit (40) calculates the AC resistance for each frequency within a predetermined frequency range, and among a plurality of AC resistances, the AC resistance in which the imaginary part resistance is 0 may be calculated as the AC resistance of the reference battery cell.

[0051] The diagnostic control circuit (40) can store DC resistance-AC resistance pairs (hereinafter referred to as 'resistance pairs') in memory (41) by matching the DC resistance and AC resistance calculated for each diagnostic cycle. When the number of multiple resistance pairs stored in memory (41) is greater than or equal to a predetermined threshold, the diagnostic control circuit (40) can implement the multiple resistance pairs as multiple dots in a two-dimensional coordinate system, determine a graph representing the trend of the multiple dots, and derive a correlation equation representing the determined graph. Specifically, the diagnostic control circuit (40) can calculate the DC resistance and AC resistance for each diagnostic cycle and store multiple resistance pairs that match the DC resistance and AC resistance in memory (41).

[0052] FIG. 4 is a diagram showing a graph implemented based on a plurality of resistor pairs by a diagnostic control circuit according to a certain embodiment.

[0053] In the two-dimensional coordinate system shown in Fig. 4, the x-axis may be the axis for DC resistance and the y-axis may be the axis for AC resistance.

[0054] In FIG. 4, multiple dots represent multiple pairs of resistors stored in memory (41). The diagnostic control circuit (40) can implement the multiple pairs of resistors as multiple dots (e.g., 43) in a two-dimensional coordinate system and determine a graph for the multiple pairs of resistors based on the positions of the multiple dots. In FIG. 4, a graph (42) indicated by a dashed line is shown. The diagnostic control circuit (40) can determine the graph (42) according to the trend of the multiple dots shown in FIG. 4 and determine a one-dimensional correlation equation representing the graph (42). The slope between the DC resistance and the AC resistance according to the one-dimensional correlation equation is 0.6735, and the R-squared value of the one-dimensional correlation equation is 0.9513.

[0055] The diagnostic control circuit (40) can determine an upper limit line and a lower limit line by considering the distribution of multiple dots based on the graph of FIG. 4.

[0056] FIG. 5 is a graph for explaining a method of determining a normal resistance range in a graph according to a certain embodiment.

[0057] As illustrated in FIG. 5, the diagnostic control circuit (40) can determine an upper limit line (52) that includes the upper dot (51) furthest from the graph (42) and has a slope between the DC resistance and the AC resistance. The diagnostic control circuit (40) can set a lower limit line (54) that includes the lower dot (53) furthest from the graph (42) and has a slope between the DC resistance and the AC resistance.

[0058] The diagnostic control circuit (40) can determine the area between the upper limit line (52) and the lower limit line (54) as the normal resistance range.

[0059] FIG. 6 is a flowchart illustrating a method for a diagnostic device according to a certain embodiment to determine a normal resistance range.

[0060] A diagnostic device (1) according to one embodiment can calculate the DC resistance and AC resistance for a reference battery cell at every diagnostic cycle.

[0061] The diagnostic device (1) can discharge a reference battery cell with a fixed current for a predetermined measurement period and calculate the DC resistance of the reference battery cell with the voltage change during the measurement period and the fixed current (S1).

[0062] The diagnostic device (1) can supply a plurality of frequency-specific alternating currents within a predetermined frequency range to a reference battery cell for a predetermined supply period, and measure the alternating voltage of the reference battery cell due to the alternating current supply to determine the alternating resistance of the reference battery cell (S2). Specifically, the diagnostic device (1) can calculate a plurality of alternating resistances for a plurality of frequency-specific reference battery cells and determine the alternating resistance among the plurality of alternating resistances, in which the imaginary part resistance is 0, as the alternating resistance of the reference battery cell.

[0063] The diagnostic device (1) can repeat steps S1 and S2 for each of the multiple diagnostic cycles.

[0064] The diagnostic device (1) can store multiple pairs of resistors by matching the DC resistance and AC resistance calculated for each of the multiple diagnostic cycles (S3).

[0065] The diagnostic device (1) can determine whether the number of stored multiple resistor pairs reaches a threshold (S4). If, as a result of the determination in step S4, the number of stored multiple resistor pairs reaches a threshold, the diagnostic device (1) can proceed with steps to determine a normal resistance range using the stored multiple resistor pairs. Otherwise, the diagnostic device (1) repeats steps S1 and S2.

[0066] The diagnostic device (1) can obtain a graph of multiple pairs of resistors based on multiple dots corresponding to multiple pairs of resistors (S5).

[0067] The diagnostic device (1) can determine the normal resistance range based on the graph obtained in step S5, and based on the upper dot and lower dot that are furthest from the graph among the plurality of dots (S6).

[0068] Specific examples of the plurality of steps S1-S6 shown in FIG. 6 have been previously explained with reference to FIG. 1 to FIG. 5, so redundant explanations are omitted.

[0069] FIG. 7 is a block diagram showing a battery system utilizing a normal resistance range determined by a diagnostic device according to some embodiment.

[0070] As illustrated in FIG. 7, the battery system (100) includes a battery pack (110) and a battery management system (120). The battery system (100) can transmit and receive information through communication with an external system. For example, the battery system (100) can transmit and receive information through CAN communication with an Electronic Control Unit (ECU) (200) of a vehicle equipped with the battery system (100).

[0071] The battery management system (120) can perform a diagnosis for each of the plurality of battery cells (111~11n) constituting the battery pack (110) by internally setting a normal resistance range determined by the diagnostic control circuit (40). The battery management system (120) can perform a diagnosis for the plurality of battery cells (111~11n) by calculating the DC resistance and AC resistance of each of the plurality of battery cells (111~11n) at a predetermined diagnostic cycle.

[0072] FIG. 8 is a flowchart illustrating a method for diagnosing battery cell abnormalities in a battery management system according to a certain embodiment.

[0073] As illustrated in FIG. 8, the battery management system (120) can calculate the DC resistance of a target battery cell (e.g., 111 in FIG. 7) to be diagnosed (S11). The method for calculating the DC resistance of the target battery cell (111) is the same as the method for calculating the DC resistance of the reference battery cell (22) described above.

[0074] Next, the battery management system (120) can calculate the AC resistance of the target battery cell (111) (S12). The method for calculating the AC resistance of the target battery cell is the same as the method for calculating the AC resistance of the reference battery cell (22) described above.

[0075] The battery management system (120) can determine whether the coordinates of the target dot corresponding to the DC resistance and AC resistance of the target battery cell (21) are within the normal resistance range (S13).

[0076] If the target dot is within the normal resistance range in step S13, the battery management system (120) can determine that the target battery cell (111) is normal (S14).

[0077] If the target dot deviates from the normal resistance range in step S13, the battery management system (120) may determine that the target battery cell (111) is abnormal (S15). If the target battery cell (111) is abnormal, the battery management system (120) may notify the ECU (200) via CAN communication (S16).

[0078] In this way, diagnosing battery cell abnormalities by considering both DC and AC resistance can improve accuracy compared to diagnosis using only DC resistance. Consequently, battery cell abnormalities that may occur during durability testing or actual vehicle driving can be detected more accurately.

[0079] Although embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims also fall within the scope of the present invention.

Claims

1. A DC current device that discharges the battery cell with a fixed current for a predetermined measurement period to measure the DC resistance of the battery cell; An alternating current device that supplies alternating current to the battery cell to measure the alternating resistance of the battery cell; A voltage measuring device for measuring the voltage of the above battery cell; A memory that stores each of a plurality of resistor pairs in which the DC resistance and the AC resistance are matched for each of a plurality of diagnostic cycles; and A diagnostic control circuit comprising: calculating DC resistance and AC resistance according to the voltage of the battery cell for each of the plurality of diagnostic cycles; obtaining a graph for the plurality of resistance pairs based on a plurality of dots corresponding to the plurality of resistance pairs; and determining a normal resistance range based on the graph based on the graph and the upper dot and lower dot among the plurality of dots that are furthest from the graph. Diagnostic device.

2. In Paragraph 1, The above diagnostic control circuit is, The above plurality of resistance pairs are implemented as a plurality of dots in a two-dimensional coordinate system, and the graph is determined according to the trend of the plurality of dots based on the positions of the plurality of dots. Diagnostic device.

3. In Paragraph 2, The above diagnostic control circuit is, Determine the correlation equation representing the above graph, and Determining an upper limit line that includes the upper dot and has the slope of the correlation equation, and setting a lower limit line that includes the lower dot and has the slope of the correlation equation, Determining the area between the upper limit line and the lower limit line as the normal resistance range, Diagnostic device.

4. In Paragraph 1, The above diagnostic control circuit is, The above direct current device is controlled to discharge the battery cell at the fixed current for a first measurement period, and At the start and end points of the first measurement period, respectively, the voltage measuring device is controlled to measure the first voltage and the second voltage of the battery cell, and Calculating the DC resistance of the battery cell using the first voltage, the second voltage, and the fixed current. Diagnostic device.

5. In Paragraph 1, The above diagnostic control circuit is, The above alternating current device controls to supply a plurality of frequency-specific alternating currents within a predetermined frequency range to the battery cell for a predetermined supply period, and After the above predetermined supply period ends, the voltage measuring device is controlled to measure the alternating voltage of the battery cell, and Calculate the multiple frequency-specific AC resistances using the multiple frequency-specific AC currents and measured AC voltages, and Determining the AC resistance of the battery cell as the AC resistance of the AC resistance having an imaginary part resistance of zero among a plurality of frequency-specific AC resistances within the above frequency range. Diagnostic device.

6. A method for determining the normal resistance range required for diagnosing abnormalities in a battery cell, A step of discharging the battery cell with a fixed current for a predetermined measurement period, and calculating the voltage change during the measurement period and the DC resistance of the battery cell with the fixed current; A step of supplying a plurality of frequency-specific alternating currents within a predetermined frequency range to the battery cell for a predetermined supply period, and measuring the alternating voltage of the battery cell due to the supply of the alternating currents to determine the alternating resistance of the battery cell; A step of repeating the DC resistance calculation step and the AC resistance calculation step for each of the multiple diagnostic cycles, and storing multiple resistance pairs by matching the DC resistance and AC resistance calculated for each diagnostic cycle; A step of obtaining a graph for the plurality of resistor pairs based on a plurality of dots corresponding to the plurality of resistor pairs; and A method comprising the step of determining a normal resistance range based on the graph, and based on the upper dot and lower dot among the plurality of dots that are furthest from the graph. Method for determining normal resistance range.

7. In Paragraph 6, The step of obtaining the above graph is, The method comprises the step of implementing the plurality of resistance pairs as a plurality of dots in a two-dimensional coordinate system, and determining the graph according to the trend of the plurality of dots based on the positions of the plurality of dots. Method for determining normal resistance range.

8. In Paragraph 6, The step of determining the above normal resistance range is, A step of determining a correlation equation representing the above graph; A step of determining an upper limit line that includes the upper dot and has the slope of the correlation equation; Step of setting a lower limit line including the lower dot and having the slope of the correlation equation; and A step including determining the area between the upper limit line and the lower limit line as the normal resistance range, Method for determining normal resistance range.

9. In Paragraph 6, The step of determining the AC resistance of the battery cell above is, A step of calculating the plurality of frequency-specific AC resistances using the plurality of frequency-specific AC currents and measured AC voltages; and A step comprising determining, among a plurality of frequency-specific AC resistances within the above frequency range, an AC resistance having an imaginary part resistance of 0 as the AC resistance of the battery cell, Method for determining normal resistance range.

10. A battery pack comprising a plurality of battery cells; and A battery management system comprising: calculating the DC resistance and AC resistance of a target battery cell among the plurality of battery cells; and diagnosing the target battery cell as an abnormal cell when the resistance pair of the DC resistance and the AC resistance deviates from a normal resistance range. The above normal resistance range is, A step of discharging a reference battery cell with a fixed current for a predetermined measurement period, and calculating the voltage change during the measurement period and the DC resistance of the reference battery cell with the fixed current; A step of supplying a plurality of frequency-specific alternating currents within a predetermined frequency range to the reference battery cell for a predetermined supply period, and measuring the alternating voltage of the reference battery cell due to the supply of the alternating currents to determine the alternating resistance of the reference battery cell; A step of repeating the DC resistance calculation step and the AC resistance calculation step for each of the multiple diagnostic cycles, and storing multiple resistance pairs by matching the DC resistance and AC resistance calculated for each diagnostic cycle; A step of obtaining a graph for the plurality of resistor pairs based on a plurality of dots corresponding to the plurality of resistor pairs; and Determined by a method comprising the step of determining a normal resistance range based on the graph, and based on the upper dot and lower dot furthest from the graph among the plurality of dots. Battery system.

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