Cell balancing method and battery system to which the same is applied

Abstract

The present invention relates to a cell balancing method and a battery system to which the same is applied, and the battery system of the present invention includes a battery including a plurality of battery cells, a monitoring unit that wakes up at short cycles and performs cell balancing for each of the plurality of battery cells based on predetermined first cell balancing execution conditions, and a monitoring unit that, when a period extension condition is met, wakes up at long cycles that are longer than the short cycle and performs cell balancing for each of the plurality of battery cells based on second cell balancing execution conditions, and a control unit that, when a low power mode entry condition is met, instructs the monitoring unit to enter the first low power mode, and then enters a sleep mode in which no previously set operations are performed.

Description

Technical Field

[0005]

[0001] [Cross - Reference to Related Applications] This application claims the benefit of priority based on Korean Patent Application No. 10 - 2023 - 0074193 filed on June 9, 2023, and all the contents disclosed in the literature of the Korean patent application are included as part of this specification.

[0002] The present invention relates to a cell balancing method and a battery system to which the same is applied.

Background Art

[0003] Battery cell balancing is a method for reducing the voltage difference between a plurality of cells generated during the charge - discharge voltage operation of a plurality of cells connected in series. A circuit that allows a plurality of cells to be discharged is implemented in a battery management system (hereinafter referred to as "BMS"). For example, passive cell balancing is a method of discharging a cell with a relatively high voltage for a certain period of time to reduce the voltage difference from a cell with a lower voltage. As another example, active cell balancing is a method of supplying the power of a cell with a relatively high voltage to a cell with a relatively low voltage to reduce the voltage difference between the plurality of cells.

[0004] However, when charging a battery as an external power source or when an upper - level system equipped with the battery is not operating, the BMS does not perform cell balancing in the sleep mode or shutdown mode, and there is a problem that the voltage difference between the plurality of cells increases.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention provides a cell balancing method and a battery management system to which this method can be applied, which can reduce the voltage difference between multiple battery cells using less power even in sleep mode or shutdown mode. [Means for solving the problem]

[0006] A battery system according to one feature of the present invention includes a battery containing a plurality of battery cells, a monitoring unit that wakes up at short cycles and performs cell balancing for each of the plurality of battery cells based on predetermined first cell balancing execution conditions, and a monitoring unit that, when a period extension condition is met, wakes up at long cycles that are a predetermined period longer than the short cycle and performs cell balancing for each of the plurality of battery cells based on second cell balancing execution conditions, and a control unit that, when a low power mode entry condition is met, instructs the monitoring unit to enter the first low power mode and then enters a sleep mode in which no previously set operations are performed.

[0007] If the monitoring unit does not satisfy the first cell balancing execution condition or the second cell balancing execution condition, it accumulates a first count without performing cell balancing on the plurality of battery cells. If the monitoring unit satisfies the first cell balancing execution condition or the second cell balancing execution condition, it can perform cell balancing on the battery cells among the plurality of battery cells that require cell balancing and accumulate a second count.

[0008] The aforementioned period extension condition is that the cumulative number of the first counts can exceed the first reference value.

[0009] The low-power mode entry conditions may include at least one of the following: a charging mode entry in which the battery is charged with power from an external device, and an operation interruption mode entry in which the operation of the higher-level system on which the battery is installed is interrupted.

[0010] When the low-power mode entry conditions are met, the control unit transmits the short-term cycle, the first cell balancing execution conditions, the long-term cycle, and the second cell balancing execution conditions to the monitoring unit, instructs the unit to enter the first low-power mode, and then enters the sleep mode or a shutdown mode in which no drive power is supplied.

[0011] The monitoring unit can wake up the control unit and terminate the first low-power mode or the second low-power mode when it satisfies at least one of the following conditions: a first condition in which the cell voltage of at least one of the plurality of battery cells falls below the discharge lower limit voltage, and a second condition in which the cumulative number of the second count exceeds a predetermined second reference value.

[0012] The monitoring unit can switch from the second low-power mode to the first low-power mode when the cumulative number of the first count and the second count exceeds the third reference value, thus fulfilling the condition for shortening the period.

[0013] A cell balancing method according to another feature of the present invention includes the steps of: receiving an instruction to enter a first low-power mode from the control unit when the low-power mode entry conditions are met, before the control unit enters a sleep mode in which it does not perform any previously set operations; performing the first low-power mode, which involves waking up at short intervals and performing cell balancing for each of the plurality of battery cells based on the first cell balancing execution conditions; and performing a second low-power mode, which involves waking up at long intervals that are a predetermined period longer than the short intervals and performing cell balancing for each of the plurality of battery cells based on the second cell balancing execution conditions, when the period extension conditions are met.

[0014] The steps for performing the first low-power mode include: when the short-term cycle arrives, the monitoring unit wakes up and determines whether the first cell balancing execution conditions are satisfied; if the determination shows that the first cell balancing execution conditions are not met, adding a first count corresponding to the number of times cell balancing was not performed; if the determination shows that the first cell balancing execution conditions are met, performing cell balancing on the battery cells among the plurality of battery cells that require cell balancing and adding a second count corresponding to the number of times cell balancing was performed; determining whether the cumulative number of the first counts exceeds a first reference value and thus satisfies the period extension condition; and if the determination shows that the period extension condition is met, proceeding to the step for performing the second low-power mode.

[0015] The cell balancing method may further include the steps of determining whether at least one of the following conditions is met: a first condition in which the cell voltage of at least one of the plurality of battery cells falls below the discharge lower limit voltage, and a second condition in which the cumulative number of the second count exceeds a second reference value; and if, as a result of the determination, at least one of the first condition and the second condition is met, waking up the control unit and terminating the first low-power mode.

[0016] The steps for performing the second low-power mode include, when the long-term cycle arrives, the monitoring unit wakes up and determines whether the second cell balancing execution condition is satisfied; if the determination shows that the second cell balancing execution condition is not met, the first count is added; if the determination shows that the second cell balancing execution condition is met, cell balancing is performed on the battery cells among the plurality of battery cells that require cell balancing and the second count is added; the determination shows whether the period shortening condition is satisfied, where the total cumulative number of the first count and the second count exceeds the third reference value; and if the determination shows that the period shortening condition is met, the system can proceed to perform the first low-power mode.

[0017] The cell balancing method may further include, before the step of determining whether the period shortening condition is satisfied, a step of determining whether at least one of the following is satisfied: a first condition in which the cell voltage of at least one of the plurality of battery cells falls below the discharge lower limit voltage, and a second condition in which the cumulative number of the second count exceeds a predetermined second reference value; and if, as a result of the determination, at least one of the first condition and the second condition is satisfied, a step of waking up the control unit and terminating the second low-power mode.

[0018] The low-power mode entry conditions may include at least one of the following: a charging mode entry in which the battery is charged with power from an external device, and an operation interruption mode entry in which the operation of the higher-level system on which the battery is installed is interrupted. [Effects of the Invention]

[0019] According to an embodiment of the present invention, even when the Battery Management System (BMS) is in sleep mode or shutdown mode, it can wake up at predetermined intervals and perform cell balancing to reduce the voltage difference between multiple cells.

[0020] According to an embodiment of the present invention, the power consumption of the battery management system (BMS) can be reduced by adjusting the wake-up period of the monitoring unit to a short-term or long-term period depending on the state of multiple cells. [Brief explanation of the drawing]

[0021] [Figure 1] This is a block diagram illustrating a battery system according to one embodiment. [Figure 2] This is a flowchart illustrating a cell balancing method using another embodiment. [Figure 3]It is a flowchart for explaining the first low power mode of FIG. 2 in detail. [Figure 4] It is a flowchart for explaining the second low power mode of FIG. 2 in detail.

Mode for Carrying Out the Invention

[0022] Hereinafter, the embodiments disclosed in this specification will be described in detail with reference to the attached drawings. For the same or similar components, the same or similar drawing numbers will be assigned, and duplicate descriptions thereof will be omitted. The suffixes "module" and / or "section" for the components used in the following description are given or mixed only for the convenience of preparing the specification, and do not have meanings or roles that are distinguishable from each other by themselves. In addition, when explaining the embodiments disclosed in this specification, if it is determined that a specific description of related known technologies will obscure the gist of the embodiments disclosed in this specification, the detailed description thereof will be omitted. In addition, the attached drawings are for the purpose of enabling easy understanding of the embodiments disclosed in this specification, and the technical idea disclosed in this specification is not limited by the attached drawings, and it must be understood that all modifications, equivalents or alternatives included in the idea and technical scope of the present invention are included.

[0023] Terms including ordinal numbers such as first and second can be used to describe various components, but the components are not limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

[0024] When a certain component is referred to as being "connected" or "connected to" another component, it should be understood that it can be directly connected or connected to the other component, but other components can also exist in the middle. On the other hand, when a certain component is referred to as being "directly connected" or "directly connected to" another component, it should be understood that there are no other components in the middle.

[0025] In this application, terms such as “includes” or “having” should be understood to indicate the presence of features, figures, steps, actions, components, parts, or combinations thereof described in the specification, without prejudice to the presence or possibility of adding one or more other features, figures, steps, actions, components, parts, or combinations thereof.

[0026] Figure 1 is a block diagram illustrating a battery system according to one embodiment.

[0027] As shown in Figure 1, the battery system 1 includes a battery 2, a BMS (Battery Management System) 3, a relay 11, and a current sensor 12.

[0028] Battery 2 consists of multiple battery cells connected in series / parallel, capable of supplying the necessary power. In Figure 1, Battery 2 includes multiple battery cells (Cell1-Celln) connected in series and is connected between the two output terminals (OUT1, OUT2) of Battery System 1. Relay 11 is connected between the positive terminal of Battery System 1 and output terminal (OUT1), and current sensor 12 is connected between the negative terminal of Battery System 1 and output terminal (OUT2). The configuration and connections between the configurations shown in Figure 1 are examples only, and the invention is not limited thereto.

[0029] Relay 11 controls the electrical connection between the battery system 1 and the external device. When relay 11 is turned on, the battery system 1 and the external device are electrically connected for charging or discharging, and when relay 11 is turned off, the battery system 1 and the external device are electrically isolated. The external device may be a load or a charger.

[0030] The current sensor 12 is connected in series to the current path between the battery 2 and the external device.

[0031] The current sensor 12 can measure the current flowing through the battery 2, i.e., the charging current and the discharging current, and transmit the measurement results to the BMS 3.

[0032] The BMS3 includes a cell balancing circuit 10, a monitoring unit 20, a communication unit 30, and a control unit 40.

[0033] The cell balancing circuit 10 includes a plurality of switches (SW1-SWn) and a plurality of resistors (R1-Rn). Each of the plurality of switches (SW1-SWn) switches in accordance with the corresponding switching signal from a plurality of switching signals (SC[1]-SC[n]) supplied from the monitoring unit 20. For each of the plurality of cells (Cell1-Celln), the corresponding switch (SWi) and resistor (Ri) are connected in series between the positive and negative terminals of the cell (Celli). When the switch (SWi) is turned on, a discharge path is formed between the cell (Celli), the switch (SWi), and the resistor (Ri), and the cell (Celli) discharges. At this time, i is one of the natural numbers from 1 to n.

[0034] The monitoring unit 20 is electrically connected to the positive and negative terminals of each of the multiple cells (Cell1-Celln) and measures the cell voltage. The current value (hereinafter referred to as battery current) measured by the current sensor 12 can be transmitted to the monitoring unit 20. The monitoring unit 20 transmits information on the measured cell voltage and battery current to the control unit 40. Specifically, the monitoring unit 20 measures the cell voltage of each of the multiple cells (Cell1-Celln) at predetermined intervals during rest periods when no charging or discharging occurs, and transmits the measured cell voltage to the control unit 40.

[0035] As demonstrated in this embodiment, even when the BMS3 is in sleep mode (not performing a pre-configured operation) or in shutdown mode (not receiving drive power) (the control unit 40 is in shutdown mode), the monitoring unit 20 can wake up at predetermined intervals and perform cell balancing. This will be explained in more detail below with reference to Figures 2 to 4.

[0036] The communication unit 30 can communicate with the higher-level system on which the battery system 1 is installed, transmit battery data, and receive control signals from the higher-level system.

[0037] The control unit 40 can control the cell balancing circuit 10 so that cell balancing is performed while the higher-level system (not shown) on which the battery system 1 is installed is in operation. In this embodiment, when the low-power mode entry conditions are met, the control unit 40 transmits the short-term cycle, the first cell balancing execution conditions, the long-term cycle, and the second cell balancing execution conditions to the monitoring unit 20, instructs the system to enter the first low-power mode, and then enters sleep mode or shutdown mode. This will be explained in more detail below with reference to Figures 2 to 4.

[0038] Figure 2 is a flowchart illustrating a cell balancing method according to another embodiment, Figure 3 is a flowchart illustrating the first low-power mode of Figure 2 in detail, and Figure 4 is a flowchart illustrating the second low-power mode of Figure 2 in detail.

[0039] Referring to Figure 2, when the conditions for entering low-power mode are met, the control unit 40 decides to enter low-power mode (S100).

[0040] The conditions for entering low-power mode may include entering charging mode, in which battery 2 is charged with power from an external device, and entering operation interruption mode, in which the operation of the higher-level system on which battery 2 is installed is interrupted.

[0041] The low-power mode is a mode in which all devices in the BMS3 are in sleep mode or shutdown mode, and the monitoring unit 20 wakes up at short-term or long-term intervals to perform cell balancing. In other words, in low-power mode, other components in the BMS3 remain in sleep or shutdown state, but the monitoring unit 20 can wake up at predetermined intervals to perform cell balancing.

[0042] For example, in low-power mode, the monitoring unit 20 initially wakes up at short intervals to perform cell balancing, and if the voltage difference between multiple battery cells is not large, it wakes up at long intervals to perform cell balancing. Subsequently, the power consumption required for cell balancing can be reduced. In this case, the first low-power mode is a mode in which the monitoring unit 20 wakes up at short intervals to perform cell balancing, and the second low-power mode is a mode in which the monitoring unit 20 wakes up at long intervals to perform cell balancing.

[0043] When the conditions for entering low-power mode are met, the control unit 40 instructs the monitoring unit 20 to enter the first low-power mode, and then enters a sleep mode in which no previously set operations are performed, or a shutdown mode in which the supply of drive power is cut off. In this embodiment, the control unit 40 can transmit the short-term cycle, the first cell balancing execution conditions, the long-term cycle, and the second cell balancing execution conditions to the monitoring unit 20 to instruct it to enter the first low-power mode, and then enter a sleep mode or a shutdown mode.

[0044] Next, the monitoring unit 20 performs the first low-power mode (S200).

[0045] In the first low-power mode, the monitoring unit 20 can wake up at short intervals and perform cell balancing for each of the multiple battery cells (Cell-Celln) based on the first cell balancing execution conditions.

[0046] Referring to Figure 3, in step S200, when a short cycle arrives, the monitoring unit 20 wakes up and determines whether the conditions for executing the first cell balancing are satisfied (S210, S220).

[0047] For example, the first cell balancing execution condition may include a case where the cell voltage difference between multiple battery cells (Cell-Celln) is 0.5V or greater. However, it is not limited to this, and the first cell balancing execution condition can include a variety of cell balancing execution conditions.

[0048] In step S200, if the determination is made and the first cell balancing execution condition is not met (S230, No), the monitoring unit 20 does not perform cell balancing and adds the first count (S240).

[0049] In step S200, if the determination results in the first cell balancing execution condition being met (S230, Yes), the monitoring unit 20 performs cell balancing and adds the second count (S250, S260).

[0050] The first count can correspond to the number of times balancing was not performed. The second count can correspond to the number of times balancing was performed. Specifically, after a short cycle or a long cycle as described below has arrived, the monitoring unit 20 can add the first count if cell balancing is not performed, and add the second count if cell balancing is performed.

[0051] Cell balancing can be performed only on the battery cells (Cell-Celln) that are determined to require cell balancing. For example, even if only one battery cell among several battery cells requires cell balancing, the monitoring unit 20 can perform cell balancing and add a second count. As another example, if cell balancing is not required for all of the battery cells (Cell-Celln), the monitoring unit 20 can add a first count without performing cell balancing.

[0052] In step S200, the monitoring unit 20 determines whether the conditions for extending the period are met (S270).

[0053] The condition for extending the period can be that the cumulative number of first counts exceeds the first reference value. For example, let's assume that the cumulative number of first counts, which is the number of times cell balancing was not performed, is 100. If cell balancing is not performed every 100 short cycles, it means that the magnitude of the voltage difference between multiple battery cells (Cell-Celln) is not large. This allows for a determination of whether or not cell balancing is possible in a long cycle that is a predetermined period longer than the short cycle, and reduces the power consumption used by the monitoring unit 20 to wake up and determine whether or not to perform cell balancing.

[0054] In step S200, if the result of the determination is that the period extension condition is not met (S270, NO), the monitoring unit 20 determines whether the wake-up condition for the control unit 40, which is in sleep mode or shutdown mode, is satisfied (S280).

[0055] The wake-up conditions of the control unit 40 may include at least one of the following: a first condition in which the cell voltage of at least one of the multiple battery cells (Cell-Celln) drops below the discharge limit voltage, and a second condition in which the cumulative number of second counts exceeds a second reference value. In this case, the discharge limit voltage (or cut-off voltage) can be the minimum cell voltage that ensures the stability of the battery cell.

[0056] If, as a result of the determination in step S200, the wake-up condition is not met (S280, No), the monitoring unit 20 goes back to sleep. Then, it restarts from step S210.

[0057] In step S200, if the determination results in the wake-up condition being met (S280, Yes), the monitoring unit 20 wakes up the control unit 40, which is in sleep mode or shutdown mode, and terminates the first low-power mode (S400).

[0058] The embodiment demonstrates that when the control unit 40 wakes up, the entire BMS3 wakes up from sleep mode. For example, in the first condition where the cell voltage of at least one of the multiple battery cells (Cell-Celln) drops below the discharge lower limit voltage, the monitoring unit 20 has difficulty resolving this problem. This is because the control unit 40 needs to wake up, monitor the overall state of the battery 2, and take substantial action regarding the battery cell whose voltage has dropped below the discharge lower limit voltage. As another example, the second condition, where the cumulative number of times cell balancing has been performed exceeds the second reference value, indicates that cell balancing has been performed frequently. Frequent cell balancing indicates a problem where the voltage difference between multiple battery cells (Cell-Celln) does not decrease. In this case, the control unit 40 can wake up, monitor the overall state of the battery 2, and control cell balancing for the multiple battery cells (Cell-Celln) through the monitoring unit 20 based on the monitoring results.

[0059] In step S200, if the judgment determines that the period extension conditions are met (S270, Yes), the monitoring unit 20 proceeds to the step of performing the second low-power mode (S300).

[0060] Next, the monitoring unit 20 performs a second low-power mode (S300).

[0061] In the second low-power mode, the monitoring unit 20 can wake up at long-term cycles and perform cell balancing for each of the multiple battery cells (Cell1-Celln) based on the second cell balancing execution conditions. For example, if the short-term cycle is 1 second, the long-term cycle may be about 2 seconds. However, it is not limited to this, and the short-term and long-term cycles can be determined with various cycles.

[0062] Referring to Figure 4, in step S300, when a long-term cycle arrives, the monitoring unit 20 wakes up and determines whether the conditions for executing the second cell balancing are satisfied (S310, S320).

[0063] For example, the first cell balancing execution condition may be that the cell voltage difference between multiple battery cells is 0.5V or more, and the second cell balancing execution condition may include that the cell voltage difference between multiple battery cells is 0.4V or more. Specifically, instead of determining whether or not to perform cell balancing in the long term, the criteria for the cell balancing execution condition can be raised. In this case, instead of saving power consumption by operating in low-power mode in the short term and long term, it is possible to prevent the voltage difference between multiple battery cells (Cell1-Celln) from widening significantly. However, the first and second cell balancing execution conditions can be set in various ways, and are not limited to this.

[0064] In step S300, if the result of the determination does not satisfy the conditions for executing the second cell balancing (S330, No), the monitoring unit 20 does not perform cell balancing and adds the first count (S340).

[0065] In step S300, if the result of the determination satisfies the conditions for executing the second cell balancing (S330, Yes), the monitoring unit 20 performs cell balancing and adds the second count (S350, S360).

[0066] The first count can correspond to the number of times balancing was not performed. The second count can correspond to the number of times balancing was performed. Specifically, after a short-term or long-term cycle has arrived, the monitoring unit 20 can add the first count if cell balancing is not performed, and add the second count if cell balancing is performed.

[0067] Cell balancing can only be performed on battery cells (Cell1-Celln) that are determined to require it. For example, even if cell balancing is required for only one of the battery cells, the monitoring unit 20 can perform cell balancing and add a second count. As another example, if cell balancing is not required for all of the battery cells, the monitoring unit 20 can skip cell balancing and add a first count.

[0068] In step S300, the monitoring unit 20 determines whether the wake-up conditions for the control unit 40, which is in sleep mode or shutdown mode, are met (S370).

[0069] The wake-up conditions of the control unit 40 may include at least one of the following: a first condition in which the cell voltage of at least one of the multiple battery cells drops below the discharge lower limit voltage, and a second condition in which the cumulative number of second counts exceeds a second reference value. In this case, the discharge lower limit voltage (or cut-off voltage) can be the minimum cell voltage that ensures the stability of the battery cell.

[0070] In step S300, if the determination results in the wake-up condition being met (S370, Yes), the monitoring unit 20 wakes up the control unit 40, which is in sleep mode or shutdown mode, and terminates the second low-power mode (S400).

[0071] The embodiment demonstrates that when the control unit 40 wakes up, the entire BMS 3 wakes up in sleep mode. For example, under the first condition where the cell voltage of at least one of the multiple battery cells (Cell-Celln) drops below the discharge lower limit voltage, the monitoring unit 20 has difficulty resolving this problem. This is because the control unit 40 needs to wake up to monitor the overall state of the battery 2 and take substantial action regarding the battery cell whose voltage has dropped below the discharge lower limit voltage. As another example, the second condition, where the cumulative number of times cell balancing has been performed exceeds the second reference value, indicates that cell balancing has been performed frequently. Frequent cell balancing indicates a problem where the voltage difference between multiple battery cells (Cell-Celln) does not decrease. In this case, the control unit 40 can wake up to monitor the overall state of the battery 2 and, based on the monitoring results, control cell balancing for the multiple battery cells (Cell-Celln) through the monitoring unit 20.

[0072] In step S300, if the result of the judgment is that the wake-up condition is not met (S370, No), the monitoring unit 20 determines whether the period shortening condition is satisfied (S380).

[0073] The condition for shortening the duration can be that the cumulative number of first and second counts exceeds the third threshold value. For example, a high cumulative number of first and second counts indicates a longer duration in the second low-power mode. After a certain period, the system may be configured to re-enter the first low-power mode for system stability.

[0074] In step S300, if the determination is that the time reduction condition is not met (S280, No), the monitoring unit 20 goes back to sleep. Then, it restarts from step S310.

[0075] In step S300, if the determination results in the condition for shortening the period being met (S280, Yes), the monitoring unit 20 goes back to sleep. Then, step S200 is restarted from the beginning.

[0076] 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 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. A battery containing multiple battery cells, A monitoring unit that wakes up at short intervals and performs cell balancing for each of the plurality of battery cells based on predetermined first cell balancing execution conditions, and when the period extension condition is met, wakes up at long intervals that are a predetermined period longer than the short interval and performs cell balancing for each of the plurality of battery cells based on second cell balancing execution conditions, A battery system including a control unit that, upon meeting the conditions for entering a low-power mode, instructs the monitoring unit to enter the first low-power mode, and then enters a sleep mode in which no previously set operations are performed.

2. The monitoring unit, If the first cell balancing execution condition or the second cell balancing execution condition is not met, cell balancing is not performed on the plurality of battery cells and the first count is accumulated. The battery system according to claim 1, wherein when the first cell balancing execution condition or the second cell balancing execution condition is met, cell balancing is performed on the battery cells among the plurality of battery cells that require cell balancing and a second count is accumulated.

3. The aforementioned conditions for extending the period are: The battery system according to claim 2, wherein the cumulative number of the first count exceeds a first reference value.

4. The aforementioned low-power mode entry conditions are: The battery system according to claim 1, comprising at least one of entering a charging mode in which the battery is charged by the power of an external device, and entering an operation interruption mode in which the operation of a higher-level system on which the battery is installed is interrupted.

5. The control unit, The battery system according to claim 4, wherein when the conditions for entering the low-power mode are met, the short-term cycle, the first cell balancing execution condition, the long-term cycle, and the second cell balancing execution condition are transmitted to the monitoring unit to instruct the entry into the first low-power mode, and then the system enters the sleep mode or a shutdown mode in which no drive power is supplied.

6. The monitoring unit, The battery system according to claim 2, wherein when at least one of the following conditions is met: a first condition in which the cell voltage of at least one of the plurality of battery cells falls below the discharge lower limit voltage, and a second condition in which the cumulative number of the second count exceeds a predetermined second reference value, the control unit is woken up to terminate the first low-power mode or the second low-power mode.

7. The monitoring unit, The battery system according to claim 2, wherein when the cumulative number of the first count and the second count exceeds a third reference value, the system changes from the second low-power mode to the first low-power mode.

8. When the conditions for entering low-power mode are met, the control unit receives an instruction to enter the first low-power mode before entering sleep mode in which it does not perform any previously set operations. The steps include performing a first low-power mode in which the system wakes up at short intervals and performs cell balancing for each of the multiple battery cells based on the first cell balancing execution conditions, A cell balancing method comprising the step of performing a second low-power mode in which, when the period extension condition is met, the system wakes up at long-term cycles that are a predetermined period longer than the short-term cycle, and performs cell balancing for each of the plurality of battery cells based on the second cell balancing execution condition.

9. The step of performing the first low-power mode is: When the aforementioned short cycle arrives, the monitoring unit wakes up and determines whether the first cell balancing execution conditions are satisfied. If, as a result of the above determination, the first cell balancing execution condition is not met, the first count corresponding to the number of times the cell balancing was not performed is added, If the above determination results in the first cell balancing execution condition being met, the process involves performing cell balancing on the battery cells among the plurality of battery cells that require cell balancing, and adding a second count corresponding to the number of times the cell balancing has been performed. A step of determining whether the cumulative number of the first count exceeds the first reference value satisfies the condition for extending the period, The cell balancing method according to claim 8, further comprising the step of entering the step of performing the second low-power mode if the conditions for extending the period are met as a result of the above determination.

10. If the above determination is not met, the step is to determine whether at least one of the following conditions is met: a first condition in which the cell voltage of at least one of the plurality of battery cells falls below the discharge lower limit voltage, and a second condition in which the cumulative number of the second count exceeds the second reference value. The cell balancing method according to claim 9, further comprising the step of waking up the control unit and ending the first low-power mode if, as a result of the above determination, at least one of the first condition and the second condition is met.

11. The step of performing the second low-power mode is: When the aforementioned long-term cycle arrives, the monitoring unit wakes up and determines whether the second cell balancing execution conditions are satisfied. If the result of the above determination does not satisfy the second cell balancing execution condition, the step of adding the first count is performed. If the result of the above determination satisfies the second cell balancing execution condition, the process involves performing cell balancing on the battery cells among the plurality of battery cells that require cell balancing, and adding the second count. A step of determining whether the condition for shortening the period is satisfied, where the total cumulative number of the first count and the second count exceeds the third reference value, A cell balancing method according to claim 9, comprising the step of entering the step of performing the first low-power mode if the condition for shortening the period is met as a result of the above determination.

12. Before the step of determining whether the conditions for shortening the period mentioned above are met, A step of determining whether at least one of the following is met: a first condition in which the cell voltage of at least one of the plurality of battery cells falls below the discharge lower limit voltage, and a second condition in which the cumulative number of the second count exceeds a predetermined second reference value. The cell balancing method according to claim 11, further comprising the step of waking up the control unit and terminating the second low-power mode if, as a result of the above determination, at least one of the first condition and the second condition is met.

13. The aforementioned low-power mode entry conditions are: The cell balancing method according to claim 9, comprising at least one of entering a charging mode in which a battery including the plurality of battery cells is charged with power from an external device, and entering an operation interruption mode in which the operation of a higher-level system on which the battery is installed is interrupted.

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