KR20230163707A - A Pulse Charging System for Rechargeable Battery. - Google Patents

Abstract

One embodiment of the present invention provides a battery including a secondary battery capable of repeated charging and discharging; a pulse generator that delivers a pulse signal with a variable duty ratio to the battery; A sensing module that measures the terminal voltage and open circuit voltage of the battery and the charging current delivered to the battery, and determines status information of the battery; and a control module that changes the duty ratio of the pulse generator or changes the charging time of the battery based on the open circuit voltage or the charging current measured by the sensing module. there is.

Description

Secondary battery pulse charging system {A Pulse Charging System for Rechargeable Battery.}

This embodiment relates to a secondary battery pulse charging system, and more specifically, to a battery charging system that performs pulse charging with a variable charging time and variable duty ratio to improve charging efficiency and extend battery life at the same time, and to a battery charging method thereof. will be.

During the charging process of lithium-based batteries, the phenomenon of metallic lithium plating is caused by the overpotential state of the graphite anode, which destroys the solid electrolyte interface on the graphite surface, reducing cycle efficiency and dendritic lithium ( Dendritic Lithium may form and cause an internal short, which may cause a fire.

In order to improve the lithium plating phenomenon that occurs during the battery charging process, a method of sequentially performing constant current charging and constant voltage charging has been proposed as a charging protocol for lithium-based secondary batteries. The constant current-constant voltage battery charging protocol performs charging by supplying a constant current to the battery until the open circuit voltage of the battery reaches a certain voltage - for example, 4.2V. After that, a constant voltage is supplied to the battery to maintain a constant current. -For example, this refers to a method of performing charging until it reaches 0.05C-.

However, when charging above a certain current, metallic lithium plating may occur at the end of constant current charging. In this case, increasing the charging current no longer shortens the charging time, and increases the constant voltage charging time, which reduces battery performance as a result of an unwanted reaction between the plated metal lithium and the electrolyte components.

Against this background, the purpose of this embodiment is, in one aspect, to provide a battery control module that can improve battery charging efficiency through current pulse charging with a variable duty ratio depending on the internal impedance of the battery cell, and a battery charging system including the same. It is done.

The purpose of this embodiment is, from another aspect, a battery control module capable of evenly spreading the concentration distribution of lithium ions and reducing the gradient of the concentration distribution of lithium ions during the turn-off period of the current pulse, and including the same. The goal is to provide a battery charging system that

In another aspect, the purpose of this embodiment is to provide a battery control module that monitors the development circuit voltage of a battery cell in real time, counts the overvoltage state time, and provides a variable charging time accordingly, and a battery charging system including the same. will be.

In order to achieve the above-described object, the first embodiment includes a battery including a secondary battery capable of repeated charging and discharging; a pulse generator that delivers a pulse signal with a variable duty ratio to the battery; A sensing module that measures the open circuit voltage of the battery and the charging current delivered to the battery, and determines status information of the battery; and a control module that changes the duty ratio of the pulse generator or changes the charging time of the battery based on the open circuit voltage or the charging current measured by the sensing module. there is.

In the battery charging system, the control module can adjust the duty ratio of the charging pulse of the pulse generator according to the increase rate of the internal impedance of the battery.

In the battery charging system, the control module counts the overvoltage state time when the open circuit voltage measured by the sensing module exceeds the overvoltage reference voltage value, and adjusts the number of charging pulses of the pulse generator according to the overvoltage state time. there is.

In the battery charging system, the control module can maintain the ratio of the turn-on period and the turn-off period of the charging pulse of the pulse generator within a preset range.

The battery charging system may further include a power source that transmits a charging voltage of a certain magnitude to the pulse generator, or generates and transmits a charging current of a certain magnitude.

In a battery charging system, the pulse generator can prevent an overvoltage state of the battery by adjusting the duty ratio and turn-off timing of the constant current or constant voltage delivered by the power source.

Additionally, in the battery charging system, the control module may prevent a sudden change (gradient) in the lithium ion concentration distribution of the battery by adjusting the turn-off time of the pulse.

The battery charging system includes an initialization mode that initializes data regarding battery internal impedance value, duty ratio, overvoltage state time, and charging mode time; And it may include a setting mode for calculating the battery internal impedance value or the duty ratio after the initialization mode and setting the state of the pulse signal generated by the pulse generator in the next cycle.

The battery charging system may further include a charging mode in which the pulse generator operates according to the pulse duty ratio and charging time determined in the setting mode.

In the battery charging system, the setting mode supplies current at a duty ratio corresponding to the size of the minimum current when the overvoltage state time exceeds the first overvoltage time threshold.

In order to achieve the above-mentioned object, the second embodiment is a method of charging a battery in a pulse manner through a variable duty ratio and a variable charging time, and the internal impedance value of the battery in the first time period and the second time period is Calculate, calculate the amount of change in the internal impedance value of the first time period and the second time period, and the duty ratio of the third time period is calculated by subtracting the product of the change in internal impedance value of the third time period and the proportionality coefficient to the duty ratio of the second time period. A duty ratio setting step of calculating the duty ratio of a third time period using a method; Measure the open circuit voltage value of the battery in the third time period, calculate the overvoltage state time when the open circuit voltage value exceeds the reference voltage value, and calculate the number of charging pulses delivered in the third time period according to the overvoltage state time, and A charging time determination step of determining the charging time; A battery charging step of charging the battery according to the duty ratio and charging time set in the third time period; and calculating the battery internal impedance based on the charging current and battery cell voltage measured in the battery charging step.

In the battery charging method, the internal impedance value is defined as the voltage value of the battery divided by the integrated average value of the charging current, and the duty ratio of the third time period is the duty ratio of the third time period and the change in the internal impedance value. It can be determined by the sum of the product of and the proportionality coefficient (k).

In the battery charging method, the internal impedance value is updated for each charging cycle of the battery, and can be corrected by reflecting the number of charge/discharge cycles and remaining capacity (SOC) of the battery.

In the battery charging method, the turn-on and turn-off ratios in the duty ratio setting step may be maintained within the range of 1:3 to 1:5.

In the battery charging method, the charging time may be reduced in inverse proportion to the overvoltage state time in the charging time determining step.

In the battery charging method, the duty ratio setting step recalculates the duty ratio when the overvoltage state time in which the open circuit voltage value exceeds the reference voltage value exceeds the first overvoltage time threshold, and the first overvoltage time threshold is It may be smaller than the second overvoltage time threshold for determining the charging completion state.

As described above, according to this embodiment, battery charging efficiency can be improved by monitoring the rate of increase in battery internal impedance and adjusting the duty ratio of the charging pulse.

According to this embodiment, the problem of reduced battery life due to battery overcharging can be solved by measuring the open circuit voltage of the battery cell, determining the overvoltage state of the open circuit voltage, and controlling the number of charging pulses.

According to this embodiment, in one battery charging cycle in which the setting mode and charging mode are repeated, the optimal battery charging state is maintained by updating information about the variable duty ratio and variable charging time in the setting mode after the previous charging mode ends. You can.

According to this embodiment, by providing a battery charging and discharging protocol, battery overvoltage can be minimized, metallic lithium plate reduction occurring within the battery can be reduced, and dendrite reduction can be reduced. there is. This can prevent insulation breakdown of the electrolyte separator and prevent fire accidents due to overcharging or malfunction of the battery.

1 is a diagram explaining a constant current-constant voltage battery charging method.
Figure 2 is a graph explaining the correlation between open circuit voltage and state of charge (SoC) in the constant current charging process.
Figure 3 is a graph explaining the pulse charging method.
Figure 4 is a diagram illustrating a battery charging system according to this embodiment.
Figure 5 is a diagram illustrating a battery charging method using current pulses according to this embodiment.
Figure 6 is a diagram illustrating time periods of the setting mode and charging mode according to this embodiment.
Figure 7 is a diagram illustrating a method for calculating internal impedance according to this embodiment.
Figure 8 is a diagram explaining parameters used in the internal impedance calculation process according to this embodiment.
9 is a flowchart of a battery charging method according to this embodiment.
Figure 10 is a diagram explaining parameters used in the initialization mode according to this embodiment.
11 is a detailed flowchart of the battery charging method according to this embodiment.
12 is a detailed flowchart of the charging mode according to this embodiment.

Hereinafter, some embodiments of the present invention will be described in detail through illustrative drawings. When adding reference numerals to components in each drawing, it should be noted that the same components are given the same reference numerals as much as possible even if they are shown in different drawings. Additionally, in describing the present invention, detailed descriptions of related known configurations or functions that are judged to be likely to obscure the gist of the present invention will be omitted.

Additionally, in describing the components of the present invention, terms such as first, second, a, and b may be used. These terms are only used to distinguish the component from other components, and the nature, order, or order of the component is not limited by the term. When a component is described as being “connected,” “coupled,” or “connected” to another component, that component may be directly connected or connected to that other component, but there is another component between each component. It will be understood that elements may be “connected,” “combined,” or “connected.”

1 is a diagram explaining a constant current-constant voltage battery charging method.

Referring to Figure 1, the battery charging method includes a method of delivering constant current (CC: Constant Current) to the battery, a method of delivering constant voltage (CV: Constant Voltage) to the battery, and charging by mixing constant current and constant voltage at a certain reference time. Methods for performing this are being proposed.

The constant current (CC)-constant voltage (CV) charging method initially charges the battery by constant current, and thereafter charges the battery by constant voltage. As a charging protocol for lithium-based secondary batteries, a constant current is initially supplied to the battery to charge it until the open circuit voltage of the battery reaches a certain reference voltage, for example, 4.2V. After the open circuit voltage of the battery reaches a certain reference voltage, a constant voltage is supplied to charge the battery. In this case, the charging current of the battery decreases, and constant voltage charging can be performed until the charging current of the battery decreases and reaches a constant current (for example, 0.05C). For example, if the current reaches 0.05C, it can be determined that the battery is fully charged. Here, C, defined as the unit of battery current, can be defined as the rate of change in battery cell capacity (Rated Capacity of Cell).

To prevent lithium plating from occurring on the positive electrode during the battery charging process, when the cell voltage reaches a certain voltage (e.g., 4.2V) during constant current charging, the charging current is reduced to a predetermined value (e.g., 4.2V). , CC-CV charging technique is used, which performs constant voltage charging until it reaches 0.05C-. However, in the CC-CV charging method, if charging current exceeds a certain level, metallic lithium plating may occur at the end of constant voltage (CC) mode. In this case, an increase in charging current no longer shortens the charging time and increases the constant voltage (CV) charging time, resulting in a decrease in battery performance as a result of an unwanted reaction between plated metallic lithium and electrolyte components.

Metallic Lithium Plating can occur due to the overpotential state of the graphite anode, which not only destroys the solid electrolyte interface on the graphite surface, reducing cycle efficiency but also forming dendritic lithium. This may cause an internal short circuit and cause a fire.

Figure 2 is a graph explaining the correlation between open circuit voltage and state of charge (SoC) in the constant current charging process.

Figure 2 is a graph showing the correlation between open circuit voltage (Voc) and state of charge (SoC) during a constant current charging process.

As the state of charge (SoC) increases, especially when the SoC approaches 100%, the battery voltage increases rapidly. If you overcharge the battery voltage to a certain voltage (e.g., 4.2V) or higher with constant current (CC) charging, the constant voltage (CV) increases. The charging capacity increases.

It is known from Reference 1 that when the constant voltage (CV) charging capacity increases above a certain level (0.3), the decrease in battery cell capacity due to high polarization accelerates.

Figure 3 is a graph explaining the pulse charging method.

Referring to Figure 3, a pulse charging method can be identified to improve the shortcomings of the constant current-constant voltage charging method.

According to Reference 2, the duty ratio can be adjusted to improve charging efficiency. According to Reference 3, the pulse charging technique can improve charging speed and battery life by providing a rest period for electrolyte ions to spread evenly with each pulse.

One battery charging cycle consists of Full Charge Detection Mode (FCDM), Search Mode (SM), and Charging Mode (CM), and the time of each mode is fixed to a predetermined time. do.

In full charge detection mode (FCDM), the open circuit voltage of the battery is measured, and in search mode (SM), pulses with different duty ratios (D1 to Dn) (n is an integer greater than 1) are generated to determine the maximum charge indicator (charging). You can find the duty ratio with factor)(η=Ib/D). Here, Ib may be the battery charging current.

In charging mode (CM), the battery can be charged by generating pulses during the charging mode time determined by the optimal duty ratio found in search mode (SM). This improves the charging speed by 14% and charging efficiency by 3.4% compared to CC-CV. It was confirmed that this was the case.

However, this method lacks consideration for battery performance degradation and shortened lifespan due to overvoltage of battery cells. Additionally, there is a limitation that charging mode (CM) and search mode (SM) are always required for a certain period of time (Tc, Ts) regardless of the charging state until the battery is fully charged.

In addition, as a charging technique proposed to improve the shortcomings of CC-CV charging and pulse charging, as in the US Patent Registration (US 5442274), an initial charging method is used to prevent the increase in battery impedance caused by high-speed pulse charging and the resulting performance degradation and shortened lifespan. A method was devised to perform CC charging, then pulse charging, and then CV charging at the end. This can also be defined as a CC-Pulse-CV charging method.

According to this, to extend battery life, it is recommended to charge the first 10% and last 10% of the state of charge (SoC) with low current. The first 10% low current charging is to prevent a rapid increase in internal impedance. The final 10% low current charging is to prevent overvoltage of battery cells and reduce constant voltage (CV) charging capacity. However, there is a limitation that the control circuit becomes more complicated as CC charging and CV charging modes are added to pulse charging.

Figure 4 is a diagram illustrating a battery charging system according to this embodiment.

Referring to FIG. 4, the battery charging system 100 may include a power source 110, a pulse generator 120, a battery 130, a sensing module 140, a control module 150, etc.

The power source 110 may be a power device that generates and transmits voltage or current to be delivered to the battery. The voltage or current generated by the power source 110 may be pulsed through the pulse generator 120 and transmitted to the battery in the form of a square wave. Depending on the switching timing, the same magnitude of voltage or current is transformed into different frequencies to be transmitted to the battery. It may be delivered to the cell 130.

The power source 110 may transmit a charging voltage of a certain magnitude to the pulse generator 120, or may generate and transmit a charging current of a certain magnitude.

The pulse generator 120 can adjust the charging voltage or charging current delivered from the power source 110 in the form of a pulse through switching of the internal circuit. The pulse generator 120 can vary the period, intensity, waveform, etc. of the signal, and can change the duty ratio of the pulse signal in real time or periodically with a variable duty ratio. The operation of the pulse generator 120 may be controlled by the control module 150.

The pulse generator 120 can prevent an overvoltage state of the battery 130 by adjusting the duty ratio and turn-off timing of the constant current or constant voltage delivered by the power source 110.

The battery 130 may include one or more battery cells and may be a battery capable of repeatedly charging and discharging a secondary battery series. The state of the battery may be defined by the charging current (Ic) and open circuit voltage (Voc) supplied to the battery 130.

The sensing module 140 may be a module that measures the charging current (Ic), open circuit voltage (Voc), or terminal voltage of the battery 9130. The sensing module 140 can measure the state of the battery in real time or periodically and transmit and receive data to the control module 150.

The control module 150 changes the duty ratio of the pulse generator 120 or changes the charging time of the battery 130 based on the open circuit voltage (Voc) or charging current (Ic) measured by the sensing module 140. You can change it. Adjusting the charging time of the battery 130 can be defined as adjusting the time to reach the target current or voltage by adjusting the pulse cycle or the number of pulses.

The control module 150 may adjust the duty ratio of the charging pulse of the pulse generator 120 according to the internal impedance value or the internal impedance increase rate of the battery 130. Here, the duty ratio may be determined by turn-on and turn-off periods and turn-on and turn-off timing. The control module 150 can perform operations in real time or periodically by calculating the amount of increase and decrease in the internal impedance value of the battery and driving at an appropriate duty ratio.

The control module 150 counts the overvoltage state time (Tov) when the open circuit voltage (Voc) measured by the sensing module 140 exceeds the overvoltage reference voltage value (Voc_thd), and generates a pulse according to the overvoltage state time (Tov). The operation time or number of charging pulses of the generator 120 can be adjusted.

The control module 150 may maintain the ratio of the turn-on period and the turn-off period of the charging pulse of the pulse generator 120 within a preset range to improve battery charging efficiency.

The control module 150 may prevent a sudden change (gradient) in the lithium ion concentration distribution of the battery by adjusting the turn-off time of the charging pulse of the pulse generator 120. The control module 150 may calculate the degree of change in the battery lithium ion concentration distribution based on the measurement data of the sensing module 140, or may utilize data stored in a storage device such as an internally preset register or memory.

The battery charging system of FIG. 4 may be implemented by an information processing device such as a battery management system (BMS) or a computer with computing capabilities, but is not limited thereto.

Figure 5 is a diagram illustrating a battery charging method using current pulses according to this embodiment.

Referring to FIG. 5, the battery charging system may adopt a method of charging by transferring a current pulse to the battery.

The battery charging system can distinguish the battery charging time period through Initialization Mode, Setup Mode, and Charging Mode.

In the initialization mode, data regarding battery internal impedance value, duty ratio, overvoltage state time, charging mode time, etc. can be initialized.

In the setting mode, the control module 150 calculates the battery internal impedance value and duty ratio during the setting mode time (Ts) after the initialization mode, and sets the state of the pulse signal generated by the pulse generator 120 in charging mode. .

In the charging mode, the battery can be charged through the operation of the pulse generator 120 according to the duty ratio and charging time of the pulse determined in the setting mode within the charging mode time (Tc).

In the battery charging process, the current is in the form of a pulse, and the operation may be determined by the turn-on time (Ton) and the turn-off time (Toff), and a plurality of pulses may be included within the charging mode time (Tc).

As shown in Figure 5, the charging current can be maintained at a constant size, and in the case of voltage, the sizes of the rising edge and falling edge can vary. For example, the battery's voltage may exceed the reference voltage - for example, 4.2V - at some periods of time.

In Figure 5, it can be understood that the pulse charging through the setting mode and charging mode is exemplified, and the initialization mode is omitted.

Figure 6 is a diagram illustrating time periods of the setting mode and charging mode according to this embodiment.

Referring to FIG. 6, each of the setting mode and charging mode may have different time periods, and the first to third time periods may have different time periods.

In the above-described battery charging system, different calculation times may be required depending on the amount of calculation of the sensing module 140 and control module 150, and the charging time defined in the pulse generator 120 may vary, resulting in overvoltage of the battery cell. Since the state time may vary, for optimal battery charging efficiency and low-power operation, it is necessary to implement different cycles and operation times for each mode rather than a fixed charging cycle.

Figure 7 is a diagram illustrating a method for calculating internal impedance according to this embodiment.

Figure 8 is a diagram explaining parameters used in the internal impedance calculation process according to this embodiment.

Referring to FIGS. 7 and 8, the internal impedance value of the battery can be calculated using the battery cell voltage (V) and charging current (Ic).

The charging current average value (Ic_av) can be calculated through the equation in FIG. 8 using the switching period (Tsw), duty ratio (Dn), individual charging current (Ic,k), and number of pulses (Np).

The cell voltage deviation (ΔVb) can be calculated by the voltage (Vb,1) of the reference point (P2) and the voltage (Vb,on) of the reference point (P1), and each reference point may vary in response to individual pulses. In particular, if the impedance is calculated based on the voltage (Vb,1) measured at the first point (P2) of the charging mode, the impedance calculation can be simplified regardless of the change in voltage over time.

Here, since the falling edge of the pulse is not vertical, a different reference point (P3) can be adopted as a reference point for impedance calculation. The reference point (P3) may be defined as a point after a certain period of time (Tintrpt) or a point where the voltage decreases at a certain rate, but is not limited thereto.

The internal impedance value of the battery can be defined by dividing the cell voltage deviation (ΔVb) by the charging current average value (Ic_av).

9 is a flowchart of a battery charging method according to this embodiment.

Referring to FIG. 9, the battery charging method may include an initialization mode (S210), a setup mode (S220), a charging mode (S230), and a full charge search mode (S240).

The initialization mode (S210) may be a step to initialize the battery internal impedance value (Rin), duty ratio (D), overvoltage time threshold (Tov_th), battery cell voltage (V), charging mode time (Tc), etc. In the initialization mode (S210), all or part of the above-described parameters can be initialized, and parameters such as those shown in FIG. 10 can be initialized, but are not limited thereto.

The setting mode (S220) may be a mode that determines the duty ratio and charging time for charging the battery cell.

In the setting mode (S220), a duty ratio setting step can be performed in which the internal impedance increase or decrease of the battery is calculated and the duty ratio of the current pulse is determined based on this.

In addition, the setting mode (S220) measures the open circuit voltage value of the battery in the first time period, calculates the overvoltage state time when the open circuit voltage value exceeds the reference voltage value, and transmits the value to the second time period according to the overvoltage state time. A charging time determination step may be performed to determine the number of charging pulses and the charging time.

In the charging time determination step, the charging time of the second time period may be reduced in inverse proportion to the overvoltage state time of the first time period. For example, the correlation between the overvoltage state time, the charging capacity of the battery, and the charging time can be calculated in advance, and the charging time corresponding to the overvoltage state time can be reduced.

Here, the internal impedance value can be defined as the cell voltage value of the battery divided by the integrated average value of the charging current. Additionally, the duty ratio of the second time period may be determined by the sum of the product of the duty ratio of the first time period, the amount of change in the internal impedance value, and the proportionality coefficient (k).

In the duty ratio setting step, the turn-on and turn-off ratios may be maintained within the range of 1:3 to 1:5, but various ratios that are not limited thereto may be defined.

The charging mode (S230) may perform a battery charging step in which battery charging is performed in a first time period and battery charging is performed according to a duty ratio and charging time set in a second time period.

The full charge search mode (S240) can perform a step of detecting whether the battery is fully charged by comparing the open circuit voltage (Voc) of the battery and the fully charged battery cell voltage (Vfc).

If necessary, the setup mode (S220) can be performed again after the full charge search mode (S240).

Figure 10 is a diagram explaining parameters used in the initialization mode according to this embodiment.

The initial battery impedance value (Rin_0) may be an updated battery impedance value measured precisely at the beginning of each charging cycle, or may be the last impedance value measured in the previous charging/discharging cycle. It can be used to increase or decrease battery impedance (ΔRin).

The initial duty ratio value (D0) is the initial value of the duty ratio that is set in advance because the duty ratio is adjusted according to the impedance difference value from the previous charging mode. The battery internal impedance value (Rin) gradually decreases as the state of charge (SoC) increases, and as the number of charge and discharge cycles (Nc) increases, it gradually increases throughout the entire state of charge (SoC) due to aging phenomenon. I do it. The control module 150 can calculate the correlation between the state of charge (SoC) of the battery and the number of charge and discharge cycles (Nc) in advance or in real time and use it in the battery charging process. For example, a calibration process may be further performed to adjust the increase/decrease range of the duty ratio or the increase/decrease range of the charging time in response to the state of charge (SoC). Considering these points, the initial duty ratio value (D0) may be determined based on the state of charge (SoC), the number of charge/discharge cycles (Nc), and the initial value of battery impedance (Rin_0).

The duty ratio maximum value (Dmax) and the duty ratio minimum value (Dmin) can be used to increase the duty ratio. For example, the maximum duty ratio (Dmax) may be set to 60%, and the minimum duty ratio (Dmin) may be set to 10%, which may be any appropriate value for battery operation efficiency and fire prevention. can be used If necessary, the minimum duty ratio value (Dmin) can be defined as a duty ratio that produces an average current corresponding to the reference current, and the duty ratio can be inverted based on changing current data.

The overvoltage time threshold (Tov_th) may be a threshold value of the time during which the open-circuit voltage of the battery exceeds the reference voltage value. For battery operation, a plurality of thresholds, such as a first overvoltage time threshold (Tov_th1) and a second overvoltage time threshold (Tov_th2), can be set. The control module 150 stores the threshold value of the overvoltage state time and can control the operation of the pulse generator 120 in response to the overvoltage state time.

The fully charged battery cell voltage (Vfc) can be set to an appropriate threshold to prevent an overvoltage condition in the battery cell. For example, the fully charged battery cell voltage (Vfc) may be set to 4.1V or 4.2V, but various standards, but not limited thereto, may be set depending on the charging capacity or purpose of the battery cell.

The charging mode time (Tc) may be the time for driving the battery cell charging mode. For example, the initial value of the charging mode time (Tc_0) may be defined as an integer multiple of the switching time (Tsw).

The maximum and minimum values (Tc_max, Tc_min) of the charging mode time can be used to increase the charging mode time.

FIG. 10 is an example of parameters initialized in the initialization mode (S210) of FIG. 9, and the present embodiment can store and calculate various variables, but are not limited thereto.

11 is a detailed flowchart of the battery charging method according to this embodiment.

Referring to FIG. 11, the battery charging method may include an initialization mode (S210), a setup mode (S220), a charging mode (S230), and a full charge search mode (S240).

The initialization mode (S210) may include the step of initializing the overvoltage state time (Tov,n).

The setting mode (S220) includes measuring the open circuit voltage (S221), comparing the open circuit voltage and the fully charged battery cell voltage (S222), adjusting the duty ratio (S223), and adjusting the charging time. (S224), etc. may be included.

The step of measuring the open circuit voltage (S221) may be a step of measuring the open circuit voltage of the battery cell using sensors included in the sensing module 130.

The step of comparing the open circuit voltage and the fully charged battery cell voltage (S222) may be a step of comparing the measured open circuit voltage (Voc) and the fully charged battery cell voltage (Vfc). When the open circuit voltage (Voc) does not exceed the fully charged battery cell voltage (Vfc), the duty ratio adjustment step (S223) or the charging time adjustment step (S224) can be performed.

The step of adjusting the duty ratio (S223) may include calculating an increase or decrease in the internal impedance of the battery cell. The internal impedance change (ΔRin) may be the difference between the battery impedance value measured in the (n-1)th setting mode and the battery impedance value measured in the (n-2)th setting mode, and can be calculated by Equation 1 below. You can. Here, n may be an integer of 2 or more.

(Equation 1)

Applying Equation 1, the amount of impedance change in the third time period in FIG. 6 can be calculated through the impedance value calculated in the second time period and the impedance value calculated in the first time period.

Next, the (n)th charging mode duty ratio can be calculated by (Equation 2) below. Here, Dn is the duty ratio of the (n)th charging mode, and k_R may be a proportionality coefficient.

(Equation 2)

Applying Equation 2, the duty ratio of the third time period in FIG. 6 can be calculated through the duty ratio of the second time period, the impedance change amount of the third time period, and the proportionality coefficient of the third time period.

The step of adjusting the duty ratio (S223) may further include measuring the overvoltage state time and comparing it with a threshold value. If the measured overvoltage state time (Tov,n) exceeds the overvoltage time threshold (Tov_th), the duty ratio can be recalculated. For example, the duty ratio may be reduced in response to the overvoltage state time, but is not limited thereto.

If the measured overvoltage state time (Tov,n) exceeds the first overvoltage time threshold (Tov_th1), the duty ratio can be recalculated. At this time, the first overvoltage time threshold (Tov_th1) may have a value smaller than the second overvoltage time threshold (Tov_th2). Additionally, when the measured overvoltage state time (Tov,n) exceeds the first overvoltage time threshold (Tov_th1), the minimum current may be supplied. For example, the battery can be charged with a duty ratio corresponding to 0.1C current, but is not limited to this.

The step of adjusting the duty ratio (S223) may further include increasing the duty ratio between the maximum duty ratio value and the minimum duty ratio value.

In addition, the step of adjusting the duty ratio (S223) changes the duty ratio according to the internal impedance value while maintaining the ratio of the switch turn-on period and turn-off period within the range of 1:3 to 1:5 to improve charging efficiency. can do.

The step of adjusting the charging time (S224) may include calculating the (n)th charging mode time (Tc,n), and updating the next charging mode time according to the calculation formulas in Equations 3 and 4 below. You can.

(Equation 3)

(Equation 4)

Here, the overvoltage state time change amount (ΔTov) can be defined as the difference between the overvoltage state time of the (n)th setting mode and the overvoltage state time of the (n-1)th setting mode.

Here, the (n)th charging mode time (Tc,n) is the proportionality coefficient (k_ov), overvoltage state time change (ΔTov), and PWM switching cycle ( It can be calculated by subtracting the value multiplied by Tsw).

Here, the initial charging mode time value (Tc,0) may be defined as the switching period (Tsw) multiplied by an integer (k_t).

In the step of adjusting the charging time (S224), the charging mode time can be rounded up by the maximum and minimum values of the charging mode time (Tc,n). For example, the minimum value of the charging mode time (Tc,n) may be set to be equal to the switching period (Tsw).

Additionally, in the step of adjusting the charging time (S224), the number of pulses (Np) for the (n)th charging mode can be determined by the charging mode time (Tc,n) and the switching cycle (Tsw).

(Equation 5)

The switching period (Tsw) is a switch period of a power device and may be defined as the sum of duty-on time and duty-off time, but is not limited thereto.

During most of the entire charging time during the battery charging process, the open circuit voltage (Voc) is less than the full charge voltage (Vfc), so the charging mode time (Tc,n) is constant without the influence of the overvoltage state time (Tov). That is, the initial charging mode time (Tc,0) can be maintained.

If the state of charge (SoC) increases beyond a certain level - for example, the closer the SoC is to 100%, or the closer to CV in CC-CV charging - the open circuit voltage (Voc) is higher than the full charge voltage (Vfc). As the equal or greater time increases, the charging mode time gradually decreases.

The charging mode (S230) may be a step of charging the battery based on the variable duty ratio and variable charging time determined in the setting mode (S220).

The full charge search mode (S240) updates the overvoltage time (S241), and if the overvoltage state time (Tov,n) is less than the second overvoltage time threshold (Vov_th2), it returns to the step of measuring the open-circuit voltage (S242). ) may include. If the open circuit voltage (Voc) is equal to or greater than the full charge voltage (Vfc) and at the same time the overvoltage state time (Tov,n) exceeds the second overvoltage time threshold (Vov_th2), the charging is judged to be complete. You can do it, and you can end charging. Here, the second overvoltage time threshold (Vov_th2) may be defined as a value greater than the first overvoltage time threshold (Vov_th1).

FIG. 11 functionally divides the operating method of the battery charging system, and this embodiment may include various modified embodiments such as some steps being omitted or some sequences being modified.

12 is a detailed flowchart of the charging mode according to this embodiment.

Referring to FIG. 12, the charging mode (S230) includes charging the battery by generating a current pulse (S231), measuring the battery charging current (Ic) (S232), updating the pulse sequence (S233), It may include a step of checking the elapse of charging mode time (S234) and a step of calculating the internal impedance of the battery (S235).

The step of charging the battery by generating a current pulse (S231) may be a step of supplying current in the form of a pulse to the battery by repeating turn-on and turn-off of the current through the pulse generator 120.

The step of measuring the battery charging current (Ic) (S232) may be a step of measuring the charging current (Ic) of the battery by the sensing module 140.

The step of updating the pulse sequence (S233) may be a step of sequentially updating the number of pulses as the pulses pass.

The step of checking the elapse of charging mode time (S234) checks whether the time of the battery charging mode has elapsed. If it has not elapsed, the step returns to the current pulse generation and battery charging step (S231). A step (S235) of calculating the battery internal impedance (Rin_n) is performed.

The step of calculating the battery internal impedance (S235) may be a step of calculating the battery internal impedance through the cell voltage (V) and current average value (Ic_ac) of the battery using the method of FIG. 8 described above.

The step of calculating the battery internal impedance (S235) calculates the deviation (ΔVb) of the battery voltage based on the cell voltage measured at the start point of the first pulse of the charging mode - for example, point P2 in FIG. 7, and calculates the internal impedance can be calculated.

According to another embodiment, the battery voltage measured at the end point of the last pulse (Ton) - for example, point P1 in FIG. 7, the point when the last pulse of the charging mode starts to turn off (Toff), and the interruption time (Tintrpt) ) can be defined as the battery voltage deviation (ΔVb) measured at the point in time (P3).

Additionally, the interruption time (Tintrpt) is the current interrupt time, which refers to the time required for the reactance component of the battery's internal impedance to become 0, and can vary depending on the chemical characteristics of the inlet that makes up the battery. For example, the interruption time (Tintrpt) may be defined as 0.5 seconds, but is not limited thereto.

The step of calculating the battery internal impedance value in step S235 of FIG. 12 may be performed in the charging mode, but is not limited thereto and may also be performed in the setting mode of FIG. 11, and the order of calculation is not limited thereto and can be varied. can be set.

The average charging current (Ic_av) in charging mode can be the average current value of multiple pulses, and the internal impedance value of the battery can be calculated by dividing the average current value (Ic_av) by the voltage deviation (ΔVb).

When using a high current pulse to measure the internal impedance value (Rin), it may be measured differently from the actual value (Reference 4), but in this embodiment, when determining the duty ratio, the absolute value of the internal impedance value (Rin) is used instead of the absolute value. It is calculated using the impedance difference (ΔRin) from the previous charging mode, and the error resulting from the difference from the actual value can be adjusted using the proportionality coefficient (k_R).

Additionally, the battery's internal impedance value can be updated to an accurate measured value every charging cycle of the battery, or can be corrected by reflecting the number of charge/discharge cycles and remaining capacity (SOC) of the battery.

Battery charging efficiency can be improved by charging the battery with a current pulse with a variable duty ratio depending on the increase or decrease in internal impedance.

In addition, when charging during the variable charging mode time to prevent the overvoltage time from being excessively long when the state of charge (SoC) is above a certain level, the battery is charged with a high current pulse above a certain level to increase the charging speed. Lifespan can also be improved.

Reference 1: Sheng Sui Zhang, "The effect of the charging protocol on the cycle life of a Li-ion battery", 2006

Reference 2: Qi Li, "Understanding the molecular mechanism of pulse current charging for stable lithium-metal batteries", 2017

Reference 3: Liang-Rui Chen, "Design of Duty-Varied Voltage Pulse Charger for Improving Li-Ion Battery-Charging Response", 2009

Reference 4: Zeyang Geng, “Intermittent current interruption method for commercial lithium ion batteries aging characterization”, 2021

Claims (12)

A battery including a secondary cell capable of repeated charging and discharging;
a pulse generator that delivers a pulse signal with a variable duty ratio to the battery;
A sensing module that measures the terminal voltage and open circuit voltage of the battery and the charging current delivered to the battery, and determines status information of the battery; and
A battery charging system comprising a control module that changes the duty ratio of the pulse generator or changes the charging time of the battery based on the open circuit voltage or the charging current measured by the sensing module. According to claim 1,
The control module is a battery charging system that adjusts the duty ratio of the charging pulse of the pulse generator according to the internal impedance value of the battery. According to claim 1,
The control module counts the overvoltage state time in which the open circuit voltage measured by the sensing module exceeds the overvoltage reference voltage value, and adjusts the number of charging pulses of the pulse generator according to the overvoltage state time. A battery charging system . According to claim 1,
A battery charging system further comprising a power source that transmits a charging voltage of a certain magnitude to the pulse generator or generates and transmits a charging current of a certain magnitude. According to claim 1,
The control module is a battery charging system that adjusts the turn-off time of the charging pulse of the pulse generator to prevent a sudden change (gradient) in the lithium ion concentration distribution of the battery. According to claim 1,
The battery charging system is,
An initialization mode that initializes data regarding battery internal impedance value, duty ratio, overvoltage state time, and charging mode time; and
A battery charging system comprising a setting mode for calculating the duty ratio based on the battery internal impedance increase rate after the initialization mode and setting the state of the pulse signal generated by the pulse generator in the next cycle. According to claim 6,
The battery charging system is,
A battery charging system further comprising a charging mode in which the pulse generator operates according to the pulse duty ratio and charging time determined in the setting mode. According to claim 2,
The setting mode supplies current at a duty ratio corresponding to the size of the minimum current when the overvoltage state time exceeds the first overvoltage time threshold. In a method of charging a battery in a pulse manner through a variable duty ratio and variable charging time,
Calculate the internal impedance value of the battery in the first time period and the second time period, calculate the amount of change in the internal impedance value between the first time period and the second time period, and the duty ratio of the third time period is the duty ratio of the second time period. A duty ratio setting step of calculating the duty ratio of the third time period by subtracting the product of the change in the internal impedance value of the third time period and the proportional coefficient;
Measure the open circuit voltage value of the battery in the third time period, calculate the overvoltage state time when the open circuit voltage value exceeds the reference voltage value, and calculate the number of charging pulses delivered in the third time period according to the overvoltage state time, and A charging time determination step of determining the charging time;
A battery charging step of charging the battery according to the duty ratio and charging time set in the third time period; and
A battery charging method comprising calculating the battery internal impedance based on the charging current and battery cell voltage measured in the battery charging step. According to clause 9,
In the battery internal impedance calculation step, the deviation between the cell voltage (Vb,1) measured at the start of the first pulse of the charging mode and the peak value of the cell voltage (Vb,on) measured at the end of the final pulse of the charging mode is calculated. A battery charging method in which the internal impedance is determined by dividing the value by the average value of the charging current for the corresponding charging mode. According to clause 9,
A battery charging method that reduces the charging time in inverse proportion to the overvoltage state time in the charging time determining step. According to clause 9,
In the duty ratio setting step, when the overvoltage state time in which the open circuit voltage value exceeds the reference voltage value exceeds the first overvoltage time threshold, the duty ratio is recalculated,
The first overvoltage time threshold is smaller than the second overvoltage time threshold for determining a charging completion state.