Cell balancing method and battery pack management system using same

Abstract

This cell balancing method for a battery pack comprising a plurality of battery cells comprises the steps of: determining a balancing target cell requiring cell balancing among the plurality of battery cells; measuring a first voltage for the balancing target cell and measuring a first pack current flowing through the battery pack; turning on a balancing switch connected to the balancing target cell; measuring a second voltage for the balancing target cell and measuring a second pack current flowing through the battery pack; determining a balancing current calculation method according to the difference between the first pack current and the second pack current; if the difference between the first pack current and the second pack current is within a predetermined range, calculating a balancing current by using the first voltage and the second voltage; if the difference between the first pack current and the second pack current is outside of the predetermined range, calculating the balancing current by using the first voltage, the second voltage, and a voltage change amount resulting from an internal resistance of the balancing target cell; and estimating a state of charge (SOC) of the balancing target cell according to the balancing current.

Description

Cell balancing method and battery pack management system applying the same

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

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0005557, filed January 12, 2024, the entire contents of which are incorporated herein by reference.

[0003] The present disclosure relates to a cell balancing method and a battery pack management system using the same.

[0004] Battery cell balancing is a method for reducing the voltage difference between multiple cells that occurs during the charge / discharge voltage behavior of multiple cells connected in series. A circuit capable of discharging multiple cells is implemented in the Battery Management System (BMS), and cells with relatively high voltages are selected and discharged for a certain period of time to reduce the voltage difference with lower voltage cells. Unlike this passive cell balancing method, there is also an active cell balancing method that charges the energy of the target cell to other cells. However, due to the high difficulty of implementing a BMS circuit for the active cell balancing method, the passive cell balancing method is mainly used for lithium-ion batteries.

[0005] When using a passive cell balancing method, the state of charge of the battery is measured using a coulomb counting method, etc., but this has the problem that errors may occur depending on changes in the power usage environment, such as battery deterioration.

[0006] The present invention aims to provide a cell balancing method capable of estimating the SOC (State Of Charge) of a cell more accurately and a battery pack management system to which this method is applied.

[0007] A cell balancing method for a battery pack including a plurality of battery cells according to one aspect of the invention, comprising: a step of determining a balancing target cell that requires cell balancing among the plurality of battery cells; a step of measuring a first voltage for the balancing target cell and measuring a first pack current flowing in the battery pack; a step of turning on a balancing switch connected to the balancing target cell; a step of measuring a second voltage for the balancing target cell and measuring a second pack current flowing in the battery pack; a step of determining a balancing current calculation method according to a difference between the first pack current and the second pack current; a step of calculating a balancing current using the first voltage and the second voltage when the difference between the first pack current and the second pack current is within a predetermined range; a step of calculating a balancing current using the first voltage, the second voltage, and a voltage change amount due to the internal resistance of the balancing target cell when the difference between the first pack current and the second pack current is outside the predetermined range. It includes a step of estimating the SOC (state of charge) of the balancing target cell according to the step and the balancing current.

[0008] When the difference between the first pack current and the second pack current is within a predetermined range, the balancing current can be calculated based on the difference between the first voltage and the second voltage.

[0009] If the difference between the first pack current and the second pack current is outside a predetermined range, the method may further include calculating the voltage change amount based on the difference between the first pack current and the second pack current and the internal resistance of the balancing target cell.

[0010] The step of calculating the voltage change amount may include a step of calculating the voltage change amount by multiplying the difference between the first pack current and the second pack current by the internal resistance of the balancing target cell.

[0011] When the difference between the first pack current and the second pack current is outside a predetermined range, the step of calculating the balancing current may include a step of calculating a value obtained by subtracting the second voltage from the first voltage and adding the voltage change amount and dividing the result by a balancing resistor as the balancing current, and the balancing resistor may form a discharge path with the balancing target cell when the balancing switch is turned on.

[0012] The step of determining the balancing target cell may include the step of estimating the SOC of each of the plurality of battery cells, calculating an average value of the SOCs of the plurality of battery cells, and determining a battery cell having an SOC greater than or equal to a predetermined value based on the average value as the balancing target cell.

[0013] A battery pack management system including a plurality of battery cells includes a cell monitoring IC connected to both ends of each of the plurality of battery cells and measuring a cell voltage of each of the plurality of battery cells, and a main control circuit that determines a balancing target cell requiring cell balancing among the plurality of battery cells, and, if there is a balancing target cell, transmits a command to turn on a balancing switch connected to the balancing target cell to the cell monitoring IC, and determines a balancing current calculation method according to a difference between a first pack current flowing in the battery pack when the balancing switch is in an off state and a second pack current flowing in the battery pack when the balancing switch is in an on state, and the main control circuit calculates a balancing current using a first voltage for the balancing target cell measured when the balancing switch is in an off state and a second voltage for the balancing target cell measured when the balancing switch is in an on state, when the difference between the first pack current and the second pack current is within a predetermined range. When the difference between the first pack current and the second pack current is outside a predetermined range, the balancing current is calculated using the voltage change amount due to the first voltage, the second voltage, and the internal resistance of the balancing target cell, and the SOC (state of charge) of the balancing target cell can be estimated based on the balancing current.

[0014] The main control circuit can calculate the balancing current based on the difference between the first voltage and the second voltage when the difference between the first pack current and the second pack current is within a predetermined range.

[0015] The main control circuit can calculate the voltage change amount based on the difference between the first pack current and the second pack current and the internal resistance of the balancing target cell when the difference between the first pack current and the second pack current is outside a predetermined range.

[0016] The above main control circuit can calculate the voltage change amount by multiplying the difference between the first pack current and the second pack current by the internal resistance of the balancing target cell.

[0017] The battery pack management system may further include a balancing resistor that forms a discharge path with the balancing target cell when the balancing switch is turned on, and the main control circuit may calculate the balancing current by subtracting the second voltage from the first voltage and adding the voltage change amount and dividing the result by the balancing resistor when the difference between the first pack current and the second pack current is outside a predetermined range.

[0018] The above main control circuit can estimate the SOC of each of the plurality of battery cells, calculate an average value of the SOCs of the plurality of battery cells, and determine a battery cell having an SOC greater than a predetermined value based on the average value as the balancing target cell.

[0019] A cell balancing method that can consider internal cell resistance in estimating the state of charge (SOC) of a cell and a battery pack management system to which this method is applied are provided.

[0020] FIG. 1 is a diagram illustrating a battery pack system according to one embodiment.

[0021] FIG. 2 is a diagram illustrating a cell balancing circuit according to one embodiment.

[0022] FIG. 3 is a diagram illustrating a cell balancing circuit when a switch is turned off according to one embodiment.

[0023] FIG. 4 is a diagram showing a cell balancing circuit when a switch is turned on according to one embodiment.

[0024] FIG. 5 is a flowchart illustrating a method for estimating the SOC of a cell based on a battery pack current according to one embodiment.

[0025] FIG. 6 is a flowchart illustrating a method for calculating a balancing current based on internal cell resistance according to one embodiment.

[0026] The embodiments described in this specification and the configurations illustrated in the drawings are preferred examples of the disclosed invention, and there may be various modified examples that can replace the embodiments and drawings of this specification at the time of filing of this application.

[0027] In describing the embodiments disclosed in this specification, detailed descriptions of related known technologies will be omitted if it is determined that such detailed descriptions may obscure the gist of the embodiments disclosed in this specification. In addition, the attached drawings are provided solely to facilitate understanding of the embodiments disclosed in this specification, and the technical concepts disclosed in this specification are not limited by the attached drawings, and should be understood to include all modifications, equivalents, and substitutes included within the spirit and technical scope of the present invention.

[0028] Terms that include ordinal numbers, such as first, second, etc., may be used to describe various components, but the components are not limited by these terms. These terms are used solely to distinguish one component from another.

[0029] When a component is referred to as being "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components intervening. Conversely, when a component is referred to as being "directly connected" or "connected" to another component, it should be understood that there are no other components intervening.

[0030] In this application, terms such as “include” or “have” are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but should be understood not to exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0031] Hereinafter, embodiments disclosed in this specification will be described in detail with reference to the attached drawings.

[0032] FIG. 1 is a diagram illustrating a battery pack management system according to one embodiment.

[0033] Referring to FIG. 1, the battery pack management system (1) includes a battery pack (2), a BMS (3), a relay (11), a current sensor (12), and a temperature sensor (13).

[0034] Two output terminals (OUT1, OUT2) of the battery pack management system (1) are connected to the battery pack (2), a relay (11) is connected between the positive pole of the battery pack management system (1) and the output terminal (OUT1), and a current sensor (12) is connected between the negative pole of the battery pack management system (1) and the output terminal (OUT2). A temperature sensor (13) may be located at a predetermined location within the battery pack management system (1), for example, in an area adjacent to the battery pack (2), or may be located by being physically coupled to the battery pack (2).

[0035] The battery pack (2) can supply the required power by connecting multiple battery cells in series / parallel. In Fig. 1, the battery pack (2) includes multiple battery cells (Cell1-Celln) connected in series. The configurations and connection relationships between the configurations illustrated in Fig. 1 are merely examples, and the invention is not limited thereto.

[0036] The relay (11) controls the electrical connection between the battery pack management system (1) and an external device. When the relay (11) is turned on, the battery pack management system (1) and the external device are electrically connected to perform charging or discharging. When the relay (11) is turned off, the battery pack management system (1) and the external device are electrically disconnected. The external device may be a load or a charger.

[0037] The current sensor (12) is connected in series to the current path between the battery pack (2) and the external device. The current sensor (12) can measure the current flowing in the battery pack (2) (hereinafter referred to as “battery pack current”) and transmit a detection signal (IS) indicating the measurement result to the main control circuit (30). The battery pack current may be a charging current for charging the battery pack (2) or a discharging current supplied from the battery pack (2) to the external device.

[0038] The temperature sensor (13) can detect the temperature of the location and transmit information (TS) indicating the detected temperature to the main control circuit (30). The temperature sensor (13) is not limited to that shown in Fig. 1, and at least two temperature sensors may be provided to detect the temperature of cells of multiple batteries.

[0039] BMS (3) includes a cell balancing circuit (10), a cell monitoring IC (20), and a main control circuit (30).

[0040] The cell balancing circuit (10) is connected to each of a plurality of battery cells (Cell1-Celln) and can discharge the plurality of battery cells (Cell1-Celln) according to a signal received from the cell monitoring IC (20).

[0041] The cell monitoring IC (20) is electrically connected to the positive and negative poles of each of the plurality of battery cells (Cell1-Celln) and measures the voltage of each of the plurality of battery cells (Cell1-Celln).

[0042] The cell monitoring IC (20) transmits information about the cell voltage of each of the measured plurality of battery cells (Cell1-Celln) to the main control circuit (30). Specifically, the cell monitoring IC (20) can measure the cell voltage of each of the plurality of battery cells (Cell1-Celln) at predetermined intervals during a rest period in which no charging or discharging occurs, and transmit the measured cell voltage to the main control circuit (30).

[0043] The cell monitoring IC (20) can discharge a cell balancing target cell among a plurality of battery cells (Cell1-Celln) through the cell balancing circuit (10) according to a cell balancing control signal transmitted from the main control circuit (30).

[0044] The main control circuit (30) estimates the SOC (state of charge) of each of the plurality of battery cells based on the cell voltages of each of the plurality of battery cells (Cell1-Celln) received from the cell monitoring IC (20) during the rest period, calculates an average value of the SOCs of the plurality of battery cells (Cell1-Celln), and determines a battery cell having an SOC higher than a predetermined value based on the average value as a balancing target cell. This method of determining a balancing target cell of the main control circuit (30) is one example, and various methods of determining a balancing target cell among the plurality of battery cells (Cell1-Celln) can be implemented. For example, the main control circuit (30) may determine a reference voltage based on the cell voltages of the plurality of battery cells (Cell1-Celln) instead of the SOC, and determine a battery cell having a cell voltage higher than a predetermined value than the reference voltage as a balancing target cell.

[0045] In addition, the main control circuit (30) can calculate the degree of change in the battery pack current during the balancing period based on the detection signal (IS) received from the current sensor (12). The main control circuit (30) can calculate the balancing current, which is the current flowing in the cell balancing circuit (10), by considering the degree of change in the battery pack current during the balancing period, and can estimate the SOC of the cell to be balanced based on the balancing current.

[0046] The main control circuit (30) can store monitoring information such as the detection signal (IS) level received from a plurality of cell voltage and current sensors (12) received from the cell monitoring IC (20) in a memory (31), etc.

[0047] Hereinafter, with reference to FIGS. 2 to 4, the operation of the cell balancing circuit and the operation of the cell monitoring IC will be described.

[0048] FIG. 2 is a diagram illustrating a cell balancing circuit according to one embodiment.

[0049] FIG. 3 is a diagram illustrating a cell balancing circuit when a switch is turned off according to one embodiment.

[0050] FIG. 4 is a diagram showing a cell balancing circuit when a switch is turned on according to one embodiment.

[0051] Referring to Fig. 2, the cell balancing circuit (10) includes a plurality of balancing resistors (RB1_1-RBn_1, RB1_2-RBn_2) and a plurality of balancing switches (SC1-SCn). The cell monitoring IC (20) includes a plurality of terminals (VC1-VCn+1) for sensing cell voltage and a plurality of terminals (SD1-SDn) for controlling the balancing switches. (n is a natural number)

[0052] A balancing resistor (RBi_1) is connected between the positive electrode of the cell (Celli) and the terminal (VCi) for cell voltage sensing, and a balancing resistor (RBi+1_1) is connected between the negative electrode of the cell (Celli) and the terminal (VCi+1) for cell voltage sensing (i is a natural number from 1 to n).

[0053] One end of the balancing resistor (RBi_1) is connected to the positive pole of the cell (Celli), the other end of the balancing resistor (RBi_1) is connected to one end of the balancing resistor (RBi_2) and the terminal (VCi), and the other end of the balancing resistor (RBi_2) is connected to one end of the balancing switch (SCi). One end of the balancing resistor (RBi+1_1) is connected to the negative pole of the cell (Celli) and the other end of the balancing switch (SCi), and the other end of the balancing resistor (RBi+1_1) is connected to the terminal (VCi+1).

[0054] A switching signal (SWCi) for controlling the switching operation of the balancing switch can be provided to the balancing switch (SCi) from a terminal (SDi) for controlling the balancing switch.

[0055] The switching signal (SWCi) has an on level or an off level, and the balancing switch (SCi) can be turned on by the switching signal at the on level, and the balancing switch (SCi) can be turned off by the switching signal at the off level.

[0056] The cell monitoring IC (20) can measure the voltage between two adjacent terminals among a plurality of terminals (VC1-VCn+1) and transmit the measured cell voltage to the main control circuit (30).

[0057] Referring to FIG. 3, a third cell (Cell3), a balancing resistor (RB3_1), a balancing resistor (RB3_2), a balancing switch (SC3), a balancing resistor (RB4_1), a cell monitoring IC (20), and a main control circuit (30) are illustrated.

[0058] One end of the balancing resistor (RB3_1) is connected to the positive pole of the third cell (Cell3), the other end of the balancing resistor (RB3_1) is connected to one end of the balancing resistor (RB3_2) and the terminal (VC3), the other end of the balancing resistor (RB3_2) is connected to one end of the balancing switch (SC3), the other end of the balancing switch (SC3) is connected to the negative pole of the third cell (Cell3) and one end of the balancing resistor (RB4_1), and the other end of the balancing resistor (RB_1) is connected to the terminal (VC4).

[0059] The balancing switch (SC3) can perform a switching operation according to a switching signal (SWC3) provided from the cell monitoring IC (20). A switching signal (SWC3) for controlling the switching operation of the balancing switch can be provided to the balancing switch (SC3) from the terminal (SD3).

[0060] The switching signal (SWC3) has an On level or an Off level, and the balancing switch (SC3) can be turned On by the switching signal at the On level, and the balancing switch (SC3) can be turned Off by the switching signal at the Off level.

[0061] The positive voltage of the third cell (Cell3) can be provided to the terminal (VC3) through the balancing resistor (RB3_1), and the negative voltage of the third cell (Cell3) can be provided to the terminal (VC4) through the balancing resistor (RB4_1).

[0062] The cell monitoring IC (20) can measure the cell voltage of the third cell (Cell3) according to the voltage difference between two terminals (VC3, VC4).

[0063] The cell monitoring IC (20) can transmit the first voltage (V1) for the balancing target cell to the main control circuit (30) when the balancing switch (SCi) is in the off state. For example, when the balancing target cell is the third cell (Cell3), the cell monitoring IC (20) can transmit the voltage of the third cell (Cell3) measured when the balancing switch (SC3) is in the off state as the first voltage (V1) to the main control circuit (30). The cell monitoring IC (20) can transmit the voltage across the balancing resistor (RB3_2) measured when the balancing switch (SCi) is in the on state as the second voltage (V2) to the main control circuit (30).

[0064] The main control circuit (30) can determine the cell internal resistance based on the cell voltage of each of the plurality of battery cells and the cell temperature measured from the temperature sensor (13). For example, the cell monitoring IC (20) can measure the voltage of a battery cell in a resting state where no charging or discharging is performed, and the main control circuit (30) can determine the OCV voltage based on the measured cell voltage and the internal resistance of the corresponding cell corresponding to the cell temperature. The main control circuit (30) can store a look-up table, function, etc. that define the relationship between the OCV, temperature, and internal resistance, and use the same to determine the internal resistance. However, the method for determining the cell internal resistance is not limited thereto and can be implemented according to various known technologies.

[0065] Additionally, the main control circuit (30) can receive the battery pack current from the current sensor (12). For example, the main control circuit (30) can receive a detection signal (IS) from the current sensor (12) and determine the value of the battery pack current (I1) flowing to the third cell (Cell3) according to the detection signal (IS).

[0066] Referring to FIG. 4, when the balancing switch (SC3) is turned on, the third cell (Cell3) is discharged along a discharge path (BP) consisting of the third cell (Cell3), two balancing resistors (RB3_1, RB3_2), and the balancing switch (SC3).

[0067] The cell is discharged as the balancing current (IB) flows along the discharge path (BP). Specifically, the third cell (Cell3) is discharged as the balancing current (IB) passes through two balancing resistors (RB3_1, RB3_2) in the discharge path (BP).

[0068] At some point during the period in which cell balancing is performed along the discharge path (BP), the cell monitoring IC (20) can measure the second voltage (V2), which is the voltage across the balancing resistor (RB3_2). The point in time is a predetermined period of time after the start of cell balancing, and may be changed depending on the design.

[0069] At some point during the period in which cell balancing is performed, a voltage at one end of the balancing resistor (RB3_2) may be provided to a terminal (VC3), and a voltage at the other end of the balancing resistor (RB3_2) may be provided to a terminal (VC4).

[0070] The cell monitoring IC (20) can measure the second voltage (V2) based on the voltage difference between the two terminals (VC3, VC4). In addition, the cell monitoring IC (20) can provide the second voltage (V2) to the main control circuit.

[0071] The main control circuit (30) can determine the value of the battery pack current (I2) flowing to the third cell (Cell3) based on the detection signal (IS) provided from the current sensor (12) at any point during the period in which cell balancing is performed.

[0072] FIG. 5 is a flowchart illustrating a method for estimating the SOC of a cell based on a battery pack current according to one embodiment.

[0073] FIG. 6 is a flowchart illustrating a method for calculating a balancing current based on internal cell resistance according to one embodiment.

[0074] Hereinafter, referring to FIGS. 5 and 6, the main control circuit (30) will be described for calculating the balancing current (IB) and estimating the SOC of the cell based on the received information.

[0075] The main control circuit (30) can receive a first voltage (V1) for a cell measured before a balancing operation from the cell monitoring IC (20) and can receive a battery pack current (hereinafter, first pack current) flowing in the cell measured before a balancing operation from the current sensor (12) (S1000). The main control circuit (30) can also store this in a memory (31), etc. Specifically, the main control circuit (30) can receive and store the cell voltage of each of a plurality of battery cells (Cell1-Celln) received from the cell monitoring IC (20).

[0076] The main control circuit (30) can estimate the SOC of each of the plurality of battery cells based on the cell voltage of each of the plurality of battery cells (Cell1-Celln), and determine the balancing target cell according to the SOC of each of the plurality of battery cells (S1100).

[0077] For example, the main control circuit (30) can calculate the average value of multiple SOCs of multiple battery cells (Cell1-Celln) and select a battery cell having an SOC greater than a predetermined value based on the average value as a balancing target cell.

[0078] When the main control circuit (30) determines that a balancing target cell is selected and a balancing operation is necessary, it can transmit a balancing switch On command connected to the balancing target cell to the cell monitoring IC (20) (S1200).

[0079] The cell monitoring IC (20) can generate an on-level switching signal (SWCi) to turn on a balancing switch (e.g., SCi) corresponding to a balancing target cell (e.g., Celli) according to an ON command of the main control circuit (30), and transmit the signal to the balancing switch (SCi).

[0080] The main control circuit (30) can receive a second voltage (V2), which is a voltage across the balancing resistor (RBi_2), from the cell monitoring IC (20) and a detection signal (IS) from the current sensor (12) while the balancing switch is turned on and cell balancing is performed along the discharge path (BP). The main control circuit (30) can receive a battery pack current (hereinafter, second pack current) flowing in the cell during the balancing operation based on the detection signal (IS) (S1300). The main control circuit (30) can also store the second voltage (V2) and the battery pack current (I2) in a memory, etc.

[0081] The main control circuit (30) can determine a method for calculating the balancing current by comparing (S1400) the first pack current (I1) and the second pack current (I2).

[0082] The main control circuit (30) can determine a method for calculating a balancing current value by comparing the difference between the first pack current (I1) and the second pack current (I2) with a predetermined range.

[0083] Specifically, the main control circuit (30) can calculate the balancing current using the voltage change amount due to the first voltage (V1), the second voltage (V2) and the internal resistance of the balancing target cell (hereinafter, cell internal resistance) when the difference between the first pack current (I1) and the second pack current (I2) exceeds a predetermined range (S1500).

[0084] The main control circuit (30) can calculate the balancing current using the first voltage (V1) and the second voltage (V2) when the difference between the first pack current (I1) and the second pack current (I2) is within a predetermined range (S1600).

[0085] Referring to FIG. 6, a method for calculating a balancing current by the main control circuit (30) when the difference between the first pack current (I1) and the second pack current (I2) exceeds a predetermined range is described.

[0086] The main control circuit (30) can determine the internal resistance of the balancing target cell when the difference between the first pack current (I1) and the second pack current (I2) is outside a predetermined range (S1510).

[0087] The main control circuit (30) can determine the cell internal resistance based on the cell voltage of each of the plurality of battery cells and the cell temperature measured from the temperature sensor (13). For example, the cell monitoring IC (20) can measure the voltage of a battery cell in a resting state where no charging or discharging is performed, and the main control circuit (30) can determine the OCV voltage based on the measured cell voltage and the internal resistance of the corresponding cell corresponding to the cell temperature. The main control circuit (30) can store a look-up table, function, etc. that define the relationship between the OCV, temperature, and internal resistance, and use the same to determine the internal resistance. However, the method for determining the cell internal resistance is not limited thereto and can be implemented according to various known technologies.

[0088] The main control circuit (30) can calculate the voltage change amount based on the first pack current (I1), the second pack current (I2) and the cell internal resistance (S1520).

[0089] The voltage change refers to the difference in voltage that occurs in a cell when the battery pack current changes. Specifically, the voltage change may be the difference between the cell voltage when the first pack current (I1) flows in the cell and the cell voltage when the second pack current (I2) flows in the cell.

[0090] The main control circuit (30) can calculate the voltage change amount based on the difference between the first pack current (I1) and the second pack current (I2) and the internal resistance of the cell.

[0091] Specifically, the main control circuit (30) can calculate the voltage change amount by multiplying the difference between the first pack current (I1) and the second pack current (I2) by the cell internal resistance, and can store the voltage change amount in memory, etc.

[0092] The main control circuit (30) can calculate the balancing current (IB) using the first voltage (V1), the second voltage (V2), the voltage change amount, and the balancing resistor (RBi_1) (S1530).

[0093] Specifically, the main control circuit (30) can calculate the balancing current (IB) by dividing the value obtained by subtracting the second voltage (V2) from the first voltage (V1) and adding the voltage change amount by the balancing resistor (RBi_1) (S1530).

[0094] Referring to FIGS. 3 and 4, the main control circuit (30) can calculate the voltage change amount of the third cell (Cell3) by multiplying the difference between the first pack current (I1) and the second pack current (I2) by the internal resistance (R3) of the third cell (Cell3), and the main control circuit (30) can calculate the balancing current (IB) by dividing the value obtained by subtracting the second voltage (V2) from the first voltage (V1) and adding the voltage change amount of the third cell (Cell3) by the balancing resistor (RB3_1).

[0095] The main control circuit (30) can calculate the balancing current (IB) using only the first voltage (V1) and the second voltage (V2) because the influence of the cell internal resistance on the balancing current (IB) is small when the difference between the first pack current (I1) and the second pack current (I2) is within a predetermined range.

[0096] Specifically, the main control circuit (30) can calculate the balancing current (IB) based on the difference between the first voltage (V1) and the second voltage (V2) when the difference between the first pack current (I1) and the second pack current (I2) is within a predetermined range.

[0097] Referring to FIGS. 3 and 4, the main control circuit (30) can calculate the value obtained by dividing the difference between the first voltage (V1) and the second voltage (V2) by the balancing resistor (RB3_1) as the balancing current (IB).

[0098] The main control circuit (30) can estimate the SOC of the cell according to the balancing current (IB) (S1700).

[0099] The main control circuit (30) can estimate the SOC of the balancing target cell after the balancing operation by subtracting the discharge SOC of the battery cell (e.g., Celli) estimated according to the balancing current and balancing operation time from the SOC of the battery cell (e.g., Celli) before discharge according to the current integration method (coulomb counting).

[0100] Although the 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 made by a person having ordinary skill in the art to which the present invention pertains also fall within the scope of the present invention.

Claims

1. A cell balancing method for a battery pack including a plurality of battery cells, A step of determining a balancing target cell among the plurality of battery cells that requires cell balancing; A step of measuring a first voltage for the balancing target cell and measuring a first pack current flowing in the battery pack; A step of turning on a balancing switch connected to the above balancing target cell; A step of measuring a second voltage for the balancing target cell and measuring a second pack current flowing in the battery pack; A step of determining a balancing current calculation method according to the difference between the first pack current and the second pack current; A step of calculating a balancing current using the first voltage and the second voltage when the difference between the first pack current and the second pack current is within a predetermined range; When the difference between the first pack current and the second pack current is out of a predetermined range, a step of calculating the balancing current using the voltage change amount due to the first voltage, the second voltage, and the internal resistance of the balancing target cell; and A method comprising a step of estimating the state of charge (SOC) of the balancing target cell according to the balancing current.

2. In paragraph 1, A cell balancing method for calculating the balancing current based on the difference between the first voltage and the second voltage when the difference between the first pack current and the second pack current is within a predetermined range.

3. In paragraph 1, A cell balancing method further comprising the step of calculating the voltage change amount based on the difference between the first pack current and the second pack current and the internal resistance of the balancing target cell when the difference between the first pack current and the second pack current is out of a predetermined range.

4. In paragraph 3, The steps for calculating the above voltage change amount are: A cell balancing method comprising the step of calculating the voltage change amount by multiplying the difference between the first pack current and the second pack current by the internal resistance of the cell to be balanced.

5. In paragraph 1, When the difference between the first pack current and the second pack current is outside a predetermined range, the step of calculating the balancing current is: It includes a step of calculating the balancing current by subtracting the second voltage from the first voltage and adding the voltage change amount and dividing the result by the balancing resistance. The above balancing resistor forms a discharge path with the balancing target cell when the balancing switch is turned on. Cell balancing method.

6. In paragraph 1, The step of determining the above balancing target cell is: A cell balancing method comprising the steps of estimating the SOC of each of the plurality of battery cells, calculating an average value of the plurality of SOCs of the plurality of battery cells, and determining a battery cell having an SOC greater than or equal to a predetermined value based on the average value as the balancing target cell.

7. In a battery pack management system including a plurality of battery cells, A cell monitoring IC connected to each end of the plurality of battery cells and measuring the cell voltage of each of the plurality of battery cells; and A main control circuit is included that determines a balancing target cell that requires cell balancing among the plurality of battery cells, and, if there is a balancing target cell, transmits a command to turn on a balancing switch connected to the balancing target cell to the cell monitoring IC, and determines a balancing current calculation method based on a difference between a first pack current flowing in the battery pack when the balancing switch is in an off state and a second pack current flowing in the battery pack when the balancing switch is in an on state. The above main control circuit, A battery pack management system for calculating a balancing current by using a first voltage for the balancing target cell measured when the balancing switch is in an off state and a second voltage for the balancing target cell measured when the balancing switch is in an on state when the difference between the first pack current and the second pack current is within a predetermined range, and calculating a balancing current by using the first voltage, the second voltage, and a voltage change amount due to the internal resistance of the balancing target cell when the difference between the first pack current and the second pack current is out of the predetermined range, and estimating a SOC (state of charge) of the balancing target cell according to the balancing current.

8. In paragraph 7, The above main control circuit, A battery pack management system that calculates the balancing current based on the difference between the first voltage and the second voltage when the difference between the first pack current and the second pack current is within a predetermined range.

9. In paragraph 7, The above main control circuit, A battery pack management system that calculates the voltage change amount based on the difference between the first pack current and the second pack current and the internal resistance of the balancing target cell when the difference between the first pack current and the second pack current is outside a predetermined range.

10. In paragraph 9, The above main control circuit, A battery pack management system that calculates the voltage change amount by multiplying the difference between the first pack current and the second pack current by the internal resistance of the balancing target cell.

11. In paragraph 7, Further comprising a balancing resistor that forms a discharge path with the balancing target cell when the balancing switch is turned on; The above main control circuit, A battery pack management system that calculates the balancing current by subtracting the second voltage from the first voltage, adding the voltage change amount, and dividing the result by the balancing resistor when the difference between the first pack current and the second pack current is outside a predetermined range.

12. In paragraph 7, The above main control circuit, A battery pack management system that estimates the SOC of each of the plurality of battery cells, calculates an average value of the plurality of SOCs of the plurality of battery cells, and determines a battery cell having an SOC higher than a predetermined value based on the average value as the balancing target cell.

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