Cell balancing method and battery pack management system applying the same

Abstract

A cell balancing method for a battery pack containing multiple battery cells includes the steps of: determining which of the multiple battery cells is a balancing target cell that requires cell balancing; measuring a first voltage to 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 to 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; calculating the balancing current using the first voltage and the second voltage if the difference between the first pack current and the second pack current is within a predetermined range; calculating the balancing current using the first voltage, the second voltage and the voltage change due to the internal resistance of the balancing target cell if the difference between the first pack current and the second pack current exceeds a predetermined range; and estimating the SOC (state of charge) of the balancing target cell according to the balancing current.

Description

Technical Field

[0001] [Cross - reference to Related Applications] This application claims the benefit of priority based on Korean Patent Application No. 10 - 2024 - 0005557, filed on January 12, 2024, and all the contents disclosed in the document of the Korean patent application are incorporated herein by reference.

[0002] This disclosure relates to a cell balancing method and a battery pack management system applying the same.

Background Art

[0003] Battery cell balancing is a method of reducing the voltage difference between a plurality of cells generated during the charge - discharge voltage behavior of a plurality of cells connected in series. A circuit capable of discharging a plurality of cells is implemented in a battery management system (hereinafter referred to as "BMS"), and relatively high - voltage cells are selected and discharged for a certain period to reduce the voltage difference from low - voltage cells. Different from such a passive cell balancing method, there is also an active cell balancing method that charges other cells with the energy of the cells to be balanced. However, the difficulty of implementing a BMS circuit for the active cell balancing method is high, and in the case of lithium - ion batteries, the passive cell balancing method is mainly used.

[0004] When using the passive cell balancing method, the state of charge of the battery is measured using a coulomb counting method or the like, but there is a problem that errors may occur due to changes in the power usage environment such as battery degradation.

Summary of the Invention

Problems to be Solved by the Invention

[0005] This invention provides a cell balancing method that can more accurately estimate the State of Charge (SOC) of a cell, and a battery pack management system to which this method is applied. [Means for solving the problem]

[0006] A cell balancing method for a battery pack including a plurality of battery cells according to one feature of the invention, comprising the steps of: determining which of the plurality of battery cells is a balancing target cell that requires cell balancing; measuring a first voltage to 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 to 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; calculating the balancing current using the first voltage and the second voltage if the difference between the first pack current and the second pack current is within a predetermined range; calculating the balancing current using the first voltage, the second voltage and the voltage change due to the internal resistance of the balancing target cell if the difference between the first pack current and the second pack current exceeds a predetermined range; and estimating the SOC (state of charge) of the balancing target cell according to the balancing current.

[0007] If 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.

[0008] If the difference between the first pack current and the second pack current exceeds a predetermined range, the method may further include the step of calculating the voltage change based on the difference between the first pack current and the second pack current and the internal resistance of the balancing target cell.

[0009] The step of calculating the voltage change may include the step of calculating the voltage change by multiplying the difference between the first pack current and the second pack current by the internal resistance of the balancing target cell.

[0010] If the difference between the first pack current and the second pack current exceeds a predetermined range, the step of calculating the balancing current may include the step of subtracting the second voltage from the first voltage, adding the voltage change, and dividing the resulting value by the balancing resistor as the balancing current, wherein the balancing resistor can form a discharge path with the balancing target cell when the balancing switch is turned on.

[0011] The step of determining the balancing target cells may include estimating the State of Charge (SOC) of each of the plurality of battery cells, calculating the average value of the plurality of SOCs of the plurality of battery cells, and determining the battery cells having an SOC of a predetermined value or higher based on the average value as the balancing target cells.

[0012] A battery pack management system including multiple battery cells is connected to both ends of each of the multiple battery cells and measures the cell voltage of each of the multiple battery cells. The system determines which of the multiple battery cells require cell balancing, and if there are cells that require balancing, it transmits a command to the cell monitoring IC to turn on the balancing switch connected to the cells that require balancing. The system then balances the battery pack according to the difference between the first pack current flowing through the battery pack when the balancing switch is off and the second pack current flowing through the battery pack when the balancing switch is on. The system includes a main control circuit that determines a balancing current calculation method. The main control circuit calculates the balancing current using a first voltage measured with the balancing switch in the off state and a second voltage measured with the balancing switch in the on state if the difference between the first pack current and the second pack current is within a predetermined range. If the difference between the first pack current and the second pack current exceeds a predetermined range, the system calculates the balancing current using the first voltage, the second voltage, and the voltage change due to the internal resistance of the balancing cell. The system can then estimate the state of charge (SOC) of the balancing cell according to the balancing current.

[0013] The main control circuit can calculate the balancing current based on the difference between the first voltage and the second voltage if the difference between the first pack current and the second pack current is within a predetermined range.

[0014] 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 if the difference between the first pack current and the second pack current exceeds a predetermined range.

[0015] The main control circuit can calculate the voltage change by multiplying the difference between the first pack current and the second pack current by the internal resistance of the balancing target cell.

[0016] The battery pack management system may further include a balancing resistor that forms a discharge path with the cells to be balanced 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, and then dividing the result by the balancing resistor if the difference between the first pack current and the second pack current exceeds a predetermined range.

[0017] The main control circuit can estimate the State of Charge (SOC) of each of the plurality of battery cells, calculate the average value of the plurality of SOCs of the plurality of battery cells, and, based on the average value, determine which battery cells have an SOC of a predetermined value or higher as the balancing target cells. [Effects of the Invention]

[0018] This invention provides a cell balancing method that can take into account the internal resistance of a cell when estimating the state of charge (SOC) of that cell, and a battery pack management system to which this method is applied. [Brief explanation of the drawing]

[0019] [Figure 1] This is a diagram illustrating a battery pack system according to one embodiment. [Figure 2] This is a diagram illustrating a cell balancing circuit according to one embodiment. [Figure 3] This is a diagram illustrating a cell balancing circuit when the switch according to one embodiment is turned off. [Figure 4] This is a diagram illustrating a cell balancing circuit when the switch according to one embodiment is turned ON. [Figure 5]It is a flowchart showing a method for estimating the SOC of a cell according to the battery pack current according to an embodiment. [Figure 6] It is a flowchart showing a method for calculating a balancing current based on the internal resistance of a cell according to an embodiment.

Embodiments for Carrying Out the Invention

[0020] The embodiments described in this specification and the configurations illustrated in the drawings are a preferred example of the disclosed invention, and there may be various modifications that can replace the embodiments and drawings of this specification at the time of filing this application.

[0021] When explaining the embodiments disclosed in this specification, if it is determined that a specific description of related known technologies may obscure the gist of the embodiments disclosed in this specification, the detailed description will be omitted. Also, the attached drawings are for facilitating the understanding of the embodiments disclosed in this specification, and the technical idea disclosed in this specification is not limited by the attached drawings, and should be understood to include all modifications, equivalents or alternatives included in the idea and technical scope of the present invention.

[0022] Terms including ordinal numbers such as first, second, etc. can be used to explain various components, but the components are not limited to those terms. The above terms are only used for the purpose of distinguishing one component from another component.

[0023] When a certain component is referred to as "connected" or "connected to" another component, it should be understood that it may be directly connected or connected to the other component, but there may also be other components in between. On the other hand, when a certain component is referred to as "directly connected" or "directly connected to" another component, it should be understood that there are no other components in between.

[0024] In this application, terms such as "includes" or "has" indicate the presence of features, figures, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the presence or possibility of the presence or addition of one or more other features or figures, steps, actions, components, parts, or combinations thereof.

[0025] The embodiments disclosed herein will be described in detail below with reference to the attached drawings.

[0026] Figure 1 is a diagram showing a battery pack management system according to one embodiment.

[0027] Referring to Figure 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.

[0028] The two output terminals OUT1 and OUT2 of the battery pack management system 1 are connected to the battery pack 2. A relay 11 is connected between the positive terminal of the battery pack 2 and output terminal OUT1, and a current sensor 12 is connected between the negative terminal of the battery pack 2 and output terminal OUT2. The temperature sensor 13 can be located in a predetermined position within the battery pack management system 1, for example, in an area adjacent to the battery pack 2, or it can be physically coupled to the battery pack 2.

[0029] Battery pack 2 can supply the necessary power by connecting multiple battery cells in series or parallel. In Figure 1, battery pack 2 includes multiple battery cells Cell1 to Celln connected in series. The configuration and the connections between the configurations shown in Figure 1 are examples and the present invention is not limited thereto.

[0030] Relay 11 controls the electrical connection between the battery pack 2 and the external device. When relay 11 is turned on, the battery pack 2 and the external device are electrically connected, and charging or discharging occurs. When relay 11 is turned off, the battery pack 2 and the external device are electrically disconnected. The external device may be a load or a charger.

[0031] 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 measures the current flowing through the battery pack 2 (hereinafter referred to as "battery pack current") and can transmit a sensing signal IS indicating the measurement result to the main control circuit 30. The battery pack current may be the charging current that charges the battery pack 2, or the discharge current supplied from the battery pack 2 to the external device.

[0032] The temperature sensor 13 can sense the temperature of its location and transmit information TS indicating the sensed temperature to the main control circuit 30. The temperature sensor 13 is not limited to the one shown in Figure 1, and at least two can be provided to sense the temperature of multiple battery cells.

[0033] BMS3 includes a cell balancing circuit 10, a cell monitoring IC 20, and a main control circuit 30.

[0034] The cell balancing circuit 10 is connected to each of the multiple battery cells Cell1 to Celln, and can discharge the multiple battery cells Cell1 to Celln according to the signal received from the cell monitoring IC 20.

[0035] The cell monitoring IC20 is electrically connected to the positive and negative terminals of each of the multiple battery cells Cell1 to Celln, and measures the voltage of each of the multiple battery cells Cell1 to Celln.

[0036] The cell monitoring IC 20 transmits information regarding the measured cell voltages of multiple battery cells, Cell1 to Celln, to the main control circuit 30. Specifically, during rest periods when no charging or discharging occurs, the cell monitoring IC 20 measures the cell voltages of multiple battery cells, Cell1 to Celln, at predetermined intervals and transmits the measured cell voltages to the main control circuit 30.

[0037] The cell monitoring IC20 can discharge the cell to be balanced from among the multiple battery cells Cell1 to Celln via the cell balancing circuit 10 in response to the cell balancing control signal transmitted from the main control circuit 30.

[0038] During the rest period, the main control circuit 30 estimates the state of charge (SOC) of each of the multiple battery cells Cell1 to Celln based on the cell voltages of each of the multiple battery cells Cell1 to Celln received from the cell monitoring IC 20, calculates the average value of the multiple SOCs of the multiple battery cells Cell1 to Celln, and uses the average value as a reference to determine which battery cells have an SOC of a predetermined value or higher to be balanced. This method of determining which batteries to balance in the main control circuit 30 is one example, and there are various ways to determine which batteries to balance among the multiple battery cells Cell1 to Celln. For example, instead of SOC, the main control circuit 30 can determine a reference voltage based on the multiple cell voltages of the multiple battery cells Cell1 to Celln, and determine which battery cells have a cell voltage that is higher than a predetermined value compared to the reference voltage to be balanced.

[0039] Furthermore, the main control circuit 30 can calculate the degree of change in the battery pack current during the balancing period in accordance with the sensing signal IS received from the current sensor 12. The main control circuit 30 can calculate the balancing current, which is the current flowing through the cell balancing circuit 10, taking into account the degree of change in the battery pack current during the balancing period, and can estimate the State of Charge (SOC) of the cells to be balanced according to the balancing current.

[0040] The main control circuit 30 can store monitoring information such as the IS level of multiple cell voltages and currents received from the cell monitoring IC 20 and the sensing signals received from the sensors 12 in the memory 31 or the like.

[0041] The operation of the cell balancing circuit and the cell monitoring IC will be explained below with reference to Figures 2 to 4.

[0042] Figure 2 is a diagram illustrating a cell balancing circuit according to one embodiment.

[0043] Figure 3 is a diagram illustrating a cell balancing circuit when the switch is turned off according to one embodiment.

[0044] Figure 4 is a diagram illustrating a cell balancing circuit when the switch according to one embodiment is turned ON.

[0045] Referring to Figure 2, the cell balancing circuit 10 includes multiple balancing resistors RB1_1 to RBn_1, RB1_2 to RBn_2, and multiple balancing switches SC1 to SCn. The cell monitoring IC 20 includes multiple terminals VC1 to VCn+1 for cell voltage sensing and multiple terminals SD1 to SDn for controlling the balancing switches (n is a natural number).

[0046] A balancing resistor RBi_1 is connected between the positive terminal of cell Celli and terminal VCi for cell voltage sensing, and a balancing resistor RBi+1_1 is connected between the negative terminal of cell Celli and terminal VCi+1 for cell voltage sensing (where i is a natural number from 1 to n).

[0047] One end of balancing resistor RBi_1 is connected to the positive terminal of cell Celli, the other end of balancing resistor RBi_1 is connected to one end of balancing resistor RBi_2 and terminal VCi, and the other end of balancing resistor RBi_2 is connected to one end of balancing switch SCi. One end of balancing resistor RBi+1_1 is connected to the negative terminal of cell Celli and the other end of balancing switch SCi, and the other end of balancing resistor RBi+1_1 is connected to terminal VCi+1.

[0048] A switching signal SWCi for controlling the switching operation of the balancing switch may be provided to the balancing switch SCi from terminal SDi for controlling the balancing switch.

[0049] The switching signal SWCi has an on level or an off level. In response to the on-level switching signal, the balancing switch SCi can be turned on, and in response to the off-level switching signal, the balancing switch SCi can be turned off.

[0050] The cell monitoring IC20 can measure the voltage between two adjacent terminals from among the multiple terminals VC1 to VCn+1 and transmit the measured cell voltage to the main control circuit 30.

[0051] Referring to Figure 3, the third cell Cell3, balancing resistor RB3_1, balancing resistor RB3_2, balancing switch SC3, balancing resistor RB4_1, cell monitoring IC20, and main control circuit 30 are illustrated.

[0052] One end of balancing resistor RB3_1 is connected to the positive terminal of the third cell, Cell3. The other end of balancing resistor RB3_1 is connected to one end of balancing resistor RB3_2 and terminal VC3. The other end of balancing resistor RB3_2 is connected to one end of balancing switch SC3. The other end of balancing switch SC3 is connected to the negative terminal of the third cell, Cell3, and one end of balancing resistor RB4_1. The other end of balancing resistor RB_1 is connected to terminal VC4.

[0053] The balancing switch SC3 can operate in response to the switching signal SWC3 provided by the cell monitoring IC20. The switching signal SWC3 for controlling the switching operation of the balancing switch can be provided to the balancing switch SC3 from terminal SD3.

[0054] The switching signal SWC3 has an ON level or an OFF level. An ON level switching signal can turn the balancing switch SC3 ON, and an OFF level switching signal can turn the balancing switch SC3 OFF.

[0055] The positive voltage of the third cell, Cell3, may be supplied to terminal VC3 via balancing resistor RB3_1, and the negative voltage of the third cell, Cell3, may be supplied to terminal VC4 via balancing resistor RB4_1.

[0056] The cell monitoring IC20 can measure the cell voltage of the third cell, Cell3, according to the voltage difference between two terminals, VC3 and VC4.

[0057] The cell monitoring IC 20 can transmit a first voltage V1 to the balancing target cell to the main control circuit 30 when the balancing switch SCi is in the off state. For example, if the balancing target cell is the third cell, Cell 3, the cell monitoring IC 20 can transmit the voltage of the third cell, Cell 3, measured when the balancing switch SC3 is in the off state, to the main control circuit 30 as the first voltage V1. 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, to the main control circuit 30 as the second voltage V2.

[0058] The main control circuit 30 can determine the internal resistance of a cell based on the cell voltage of each of the multiple battery cells and the cell temperature measured by the temperature sensor 13. For example, the cell monitoring IC 20 measures the voltage of a certain battery cell in a dormant state where no charging or discharging is occurring, and the main control circuit 30 can determine the internal resistance of that cell corresponding to the OCV voltage and cell temperature based on the measured cell voltage. The main control circuit 30 can store lookup tables, functions, etc. that define the relationship between OCV, temperature, and internal resistance, and use these to determine the internal resistance. However, the method for determining the internal resistance of a cell is not limited to this and may be implemented by a variety of known techniques.

[0059] Furthermore, 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 sensing signal IS from the current sensor 12 and determine the value of the battery pack current I1 flowing to the third cell Cell 3 according to the sensing signal IS.

[0060] Referring to Figure 4, when the balancing switch SC3 is turned on, the third cell Cell3 is discharged along the discharge path BP, which consists of the third cell Cell3, two balancing resistors RB3_1 and RB3_2, and the balancing switch SC3.

[0061] The balancing current IB flows along the discharge path BP, and the cell is discharged. Specifically, the third cell, Cell3, is discharged while the balancing current IB passes through two balancing resistors RB3_1 and RB3_2 in the discharge path BP.

[0062] At some point during the period when cell balancing is performed by the discharge path BP, the cell monitoring IC20 can measure the second voltage V2, which is the voltage across the balancing resistor RB3_2. This point in time is a predetermined period of time that has elapsed since the start of cell balancing, and can be changed according to the design.

[0063] At some point during the cell balancing process, the voltage at one end of the balancing resistor RB3_2 may be supplied to terminal VC3, and the voltage at the other end of the balancing resistor RB3_2 may be supplied to terminal VC4.

[0064] The cell monitoring IC20 can measure a second voltage V2 according to the voltage difference between two terminals VC3 and VC4. Furthermore, the cell monitoring IC20 can supply the second voltage V2 to the main control circuit.

[0065] The main control circuit 30 can determine the battery pack current I2 value flowing to the third cell Cell 3 based on the sensing signal IS provided by the current sensor 12 at some point during the period in which cell balancing is performed.

[0066] Figure 5 is a flowchart showing a method for estimating the state of charge (SOC) of a cell according to the battery pack current in one embodiment.

[0067] Figure 6 is a flowchart showing a method for calculating the balancing current based on the internal resistance of a cell according to one embodiment.

[0068] The following explanation, with reference to Figures 5 and 6, describes how the main control circuit 30 calculates the balancing current IB and estimates the cell's SOC based on the received information.

[0069] The main control circuit 30 can receive a first voltage V1 for the cells measured before the balancing operation from the cell monitoring IC 20, and can also receive the battery pack current (hereinafter referred to as the first pack current) flowing through the cells measured before the balancing operation from the current sensor 12 (S1000). The main control circuit 30 may store these in a memory 31 or the like. Specifically, the main control circuit 30 can receive and store the cell voltages of each of the multiple battery cells Cell1 to Celln received from the cell monitoring IC 20.

[0070] The main control circuit 30 estimates the State of Charge (SOC) of each of the multiple battery cells (Cell1 to Celln) based on their respective cell voltages, and can determine which cell to balance according to the SOC of each of the multiple battery cells (S1100).

[0071] For example, the main control circuit 30 can calculate the average value of multiple SOCs of multiple battery cells Cell1 to Celln, and based on the average value, select battery cells with an SOC of a predetermined value or higher as balancing target cells.

[0072] When the main control circuit 30 has selected a cell to be balanced and determines that a balancing operation is necessary, it can transmit a balancing switch ON command connected to the cell to be balanced to the cell monitoring IC 20 (S1200).

[0073] The cell monitoring IC 20 can generate an on-level switching signal SWCi to turn on the balancing switch (e.g., SCi) corresponding to the cell to be balanced (e.g., Celli) in response to an ON command from the main control circuit 30, and transmit this signal to the balancing switch SCi.

[0074] The main control circuit 30 can receive a second voltage V2, which is the voltage across the balancing resistor RBi_2, from the cell monitoring IC 20 and a sensing signal IS from the current sensor 12 while the balancing switch is turned on and cell balancing is performed along the discharge path BP. Based on the sensing signal IS, the main control circuit 30 can receive the battery pack current (hereinafter referred to as the second pack current) flowing through the cells during the balancing operation (S1300). The main control circuit 30 may store the second voltage V2 and the battery pack current I2 in memory or elsewhere.

[0075] The main control circuit 30 can compare the first pack current I1 and the second pack current I2 (S1400) and determine a method for calculating the balancing current.

[0076] The main control circuit 30 can compare the difference between the first pack current I1 and the second pack current I2 with a predetermined range and determine a method for calculating the balancing current value. Specifically, if the difference between the first pack current I1 and the second pack current I2 exceeds a predetermined range, the main control circuit 30 can calculate the balancing current using the voltage change due to the first voltage V1, the second voltage V2, and the internal resistance of the cell to be balanced (hereinafter referred to as the cell internal resistance) (S1500).

[0077] The main control circuit 30 can calculate the balancing current using the first voltage V1 and the second voltage V2 if the difference between the first pack current I1 and the second pack current I2 is within a predetermined range (S1600).

[0078] Referring to Figure 6, we will now explain how the main control circuit 30 calculates the balancing current when the difference between the first pack current I1 and the second pack current I2 exceeds a predetermined range.

[0079] The main control circuit 30 can determine the internal resistance of the balancing target cell if the difference between the first pack current I1 and the second pack current I2 exceeds a predetermined range (S1510).

[0080] The main control circuit 30 can determine the internal resistance of a cell based on the cell voltage of each of the multiple battery cells and the cell temperature measured by the temperature sensor 13. For example, the cell monitoring IC 20 measures the voltage of a certain battery cell in a dormant state where no charging or discharging is occurring, and the main control circuit 30 can determine the internal resistance of that cell corresponding to the OCV voltage and cell temperature based on the measured cell voltage. The main control circuit 30 can store lookup tables, functions, etc., that define the relationship between OCV, temperature, and internal resistance, and use these to determine the internal resistance. However, the method for determining the internal resistance of a cell is not limited to this and may be implemented by a variety of known techniques.

[0081] The main control circuit 30 can calculate the voltage change based on the first pack current I1, the second pack current I2, and the cell internal resistance (S1520).

[0082] The voltage change refers to the difference in voltage generated in the cells 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 through the cells and the cell voltage when the second pack current I2 flows through the cells.

[0083] The main control circuit 30 can calculate the voltage change based on the difference between the first pack current I1 and the second pack current I2 and the internal resistance of the cell.

[0084] Specifically, the main control circuit 30 can calculate the voltage change by multiplying the difference between the first pack current I1 and the second pack current I2 by the cell's internal resistance, and can store the voltage change in memory or elsewhere.

[0085] The main control circuit 30 can calculate the balancing current IB using the first voltage V1, the second voltage V2, the voltage change, and the balancing resistor RBi_1 (S1530).

[0086] Specifically, the main control circuit 30 can calculate the balancing current IB by subtracting the second voltage V2 from the first voltage V1, adding the voltage change, and then dividing the result by the balancing resistor RBi_1 (S1530).

[0087] Referring to Figures 3 and 4, the main control circuit 30 can calculate the voltage change of the third cell Cell 3 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 Cell 3. The main control circuit 30 can also calculate the balancing current IB by subtracting the second voltage V2 from the first voltage V1, adding the voltage change of the third cell Cell 3, and dividing the result by the balancing resistor RB3_1.

[0088] 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's 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.

[0089] 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, provided that the difference between the first pack current I1 and the second pack current I2 is within a predetermined range.

[0090] Referring to Figures 3 and 4, the main control circuit 30 can calculate the balancing current IB as the value obtained by dividing the difference between the first voltage V1 and the second voltage V2 by the balancing resistor RB3_1.

[0091] The main control circuit 30 can estimate the state of charge (SOC) of the cell according to the balancing current IB (S1700).

[0092] The main control circuit 30 can estimate the state of charge (SOC) of the battery cell to be balanced after the balancing operation by subtracting the discharge SOC of the battery cell (e.g., Celli), which is estimated according to the balancing current and balancing operation time, from the state of charge (SOC) of the battery cell (e.g., Celli) before discharge, using the current integration method (coulomb counting).

[0093] Although embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto. Various modifications and improvements made by persons with ordinary skill in the art to which the present invention belongs also fall within the scope of the present invention.

Claims

1. In a cell balancing method for a battery pack containing multiple battery cells, A step of determining which of the plurality of battery cells is the one to be balanced and requires cell balancing; A step of measuring a first voltage to the balancing target cell and measuring a first pack current flowing through the battery pack; Steps include turning on the balancing switch connected to the cell to be balanced; A step of measuring a second voltage to the balancing target cell and measuring the second pack current flowing through 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; If the difference between the first pack current and the second pack current is within a predetermined range, the first voltage and the second voltage are used to calculate the balancing current; If the difference between the first pack current and the second pack current exceeds a predetermined range, the steps of calculating the balancing current using the first voltage, the second voltage, and the voltage change due to the internal resistance of the balancing target cell; and A cell balancing method comprising the step of estimating the state of care (SOC) of the cells to be balanced according to the balancing current.

2. The cell balancing method according to claim 1, wherein if the difference between the first pack current and the second pack current is within a predetermined range, the balancing current is calculated based on the difference between the first voltage and the second voltage.

3. The cell balancing method according to claim 1, 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 cell to be balanced, if the difference between the first pack current and the second pack current exceeds a predetermined range.

4. The step of calculating the voltage change is: The cell balancing method according to claim 3, comprising the step of calculating the voltage change 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. If the difference between the first pack current and the second pack current exceeds a predetermined range, the step of calculating the balancing current is as follows: The process includes the step of calculating the balancing current by subtracting the second voltage from the first voltage and adding the voltage change, and then dividing the result by the balancing resistor. The balancing resistor forms a discharge path with the balancing target cell when the balancing switch is turned on. A cell balancing method according to any one of claims 1 to 4.

6. The step of determining the cells to be balanced is: A cell balancing method according to any one of claims 1 to 4, comprising the steps of estimating the SOC of each of the plurality of battery cells, calculating the average value of the plurality of SOCs of the plurality of battery cells, and determining the battery cells having an SOC of a predetermined value or higher based on the average value as the cells to be balanced.

7. In a battery pack management system that includes multiple battery cells, A cell monitoring IC connected to each of the plurality of battery cells for measuring the cell voltage of each of the plurality of battery cells; and The main control circuit includes a function that determines which of the plurality of battery cells require cell balancing, transmits a command to the cell monitoring IC to turn on the balancing switch connected to the balancing cell if such a cell exists, and determines a balancing current calculation method based on the difference between a first pack current flowing through the battery pack when the balancing switch is off and a second pack current flowing through the battery pack when the balancing switch is on. The main control circuit described above is A battery pack management system that, when the difference between the first pack current and the second pack current is within a predetermined range, calculates the balancing current using a first voltage measured with the balancing switch off and a second voltage measured with the balancing switch on for the balancing target cell; when the difference between the first pack current and the second pack current exceeds a predetermined range, calculates the balancing current using the first voltage, the second voltage and the voltage change due to the internal resistance of the balancing target cell; and estimates the SOC of the balancing target cell according to the balancing current.

8. The main control circuit described above is The battery pack management system according to claim 7, wherein the balancing current is calculated 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. The main control circuit described above is The battery pack management system according to claim 7, wherein if the difference between the first pack current and the second pack current exceeds a predetermined range, the amount of voltage change is calculated based on the difference between the first pack current and the second pack current and the internal resistance of the balancing target cell.

10. The main control circuit described above is The battery pack management system according to claim 9, wherein the amount of voltage change is calculated by multiplying the difference between the first pack current and the second pack current by the internal resistance of the balancing target cell.

11. When the balancing switch is turned on, it further includes a balancing resistor that forms a discharge path with the cell to be balanced, The main control circuit described above is A battery pack management system according to any one of claims 7 to 10, wherein if the difference between the first pack current and the second pack current exceeds a predetermined range, the balance current is calculated by subtracting the second voltage from the first voltage and adding the voltage change amount, and then dividing the result by the balancing resistor.

12. The main control circuit described above is A battery pack management system according to any one of claims 7 to 10, comprising estimating the SOC of each of the plurality of battery cells, calculating the average value of the plurality of SOCs of the plurality of battery cells, and determining, based on the average value, battery cells having an SOC of a predetermined value or higher as the balancing target cells.

Images