KR102284872B1 - Cell balancing apparatus and method - Google Patents

Abstract

A cell balancing apparatus and method are disclosed. The cell balancing apparatus and method are for balancing a state of charge between a plurality of battery cells connected in series in a battery module. The cell balancing device may include: a monitoring unit configured to detect voltages at both ends of each of the battery cells at predetermined intervals; a balancing unit including a plurality of balancing circuits; and a control unit operatively coupled to the monitoring unit and each of the balancing circuits. The control unit determines a balancing target of any one of the plurality of battery cells based on the voltages at both ends of the respective battery cells, and constantly controls the balancing current flowing through the balancing target every predetermined period as a reference balancing current. .

Description

Cell balancing apparatus and method {Cell balancing apparatus and method}

The present invention relates to a cell balancing apparatus and method, and more particularly, to an apparatus for equalizing the state of charge of a plurality of battery cells connected in series in a battery module.

Recently, as the demand for portable electronic products such as notebook computers, video cameras, and portable telephones has rapidly increased, and development of electric vehicles, energy storage batteries, robots, satellites, etc. is in full swing, high-performance secondary batteries that can be repeatedly charged and discharged research is being actively conducted.

Currently commercialized secondary batteries include nickel cadmium batteries, nickel hydride batteries, nickel zinc batteries, and lithium secondary batteries. Among them, lithium secondary batteries have almost no memory effect compared to nickel-based secondary batteries, so charging and discharging are free, The self-discharge rate is very low and the energy density is high, attracting attention.

Recently, as high output is required in electric vehicles, etc., a battery pack mounted thereon generally includes a plurality of battery cells connected in series with each other. However, since the battery cells cannot have completely the same characteristics, as charging and discharging of the battery pack are repeated, an imbalance in the state of charge between the battery cells is inevitable. If charging and discharging of the battery pack are continuously repeated without suppressing such imbalance, the usable capacity of the battery pack is reduced and deterioration of battery cells included therein is accelerated.

'Cell balancing' to solve the above problem is a technology that equalizes the state of charge between battery cells by forcibly discharging those having a relatively high state of charge among the battery cells by controlling a balancing circuit connected in parallel to each battery cell. . Accordingly, a target discharge capacity for equalization must be determined based on the open-circuit voltage of each battery cell, and each battery cell must be individually discharged by the determined target discharge capacity. In this case, as the actual discharge capacity due to cell balancing approaches the target discharge capacity, the variation in the state of charge between the battery cells may be precisely suppressed as desired.

However, even if the resistance value of the balancing circuit is constant, since the voltage of each battery cell changes while the cell balancing is in progress, the discharge current flowing through the balancing circuit cannot be kept constant. In order to calculate the actual discharge capacity, accurate monitoring of the discharge current is required, but the accuracy of the actual discharge capacity calculated based on the discharge current that is frequently changed during cell balancing is deteriorated.

An object of the present invention is to provide an apparatus and method for constantly maintaining an average discharge current per cycle for each battery cell while cell balancing is in progress.

Other objects and advantages of the present invention may be understood by the following description, and will become more clearly understood by the examples of the present invention. In addition, it will be readily apparent that the objects and advantages of the present invention can be realized by means and combinations thereof indicated in the claims.

Various embodiments of the present invention for achieving the above object are as follows.

A cell balancing device according to an aspect of the present invention is for balancing a state of charge between a plurality of battery cells connected in series in a battery module. The cell balancing device may include: a monitoring unit configured to detect voltages at both ends of each of the battery cells at predetermined intervals; a balancing unit including a plurality of balancing circuits; and a control unit operatively coupled to the monitoring unit and each of the balancing circuits. Each of the balancing circuits includes a resistance element and a switching element connected in series, and is connected in parallel to each of the battery cells. The control unit determines a balancing target of any one of the plurality of battery cells based on the voltages at both ends of each battery cell, and at every predetermined period, a balancing current of a balancing circuit connected in parallel to the balancing target is referenced The balancing unit is controlled to keep the current constant.

In addition, the controller may determine a duty cycle correction value for each predetermined period based on the reference balancing current, the resistance value of the resistance element, and the voltage across both ends of the balancing target detected at each predetermined period. The controller may update a target duty cycle of a switching signal applied to a switching element of a balancing circuit connected in parallel to the balancing target at every predetermined period based on the duty cycle correction value.

In addition, the control unit, the following formula:

는 상기 기준 밸런싱 전류,

은 상기 밸런싱 대상의 양단 전압,

는 상기 저항 소자의 저항값,

는 미리 정해진 기준 듀티 사이클,

는 상기 듀티 사이클 보정값)(

is the reference balancing current,

is the voltage across the balancing target,

is the resistance value of the resistive element,

is the predetermined reference duty cycle,

is the duty cycle correction value)

may be used to determine the duty cycle correction value.

In addition, the monitoring unit may be configured to detect the temperature of each battery cell at each predetermined period. The controller may determine the duty cycle correction value for each predetermined period based on the temperature of the balancing target.

In addition, the controller may determine the charging state of each battery cell based on the voltage across the battery cells, and determine the balancing target based on the charging state of each battery cell.

In addition, the control unit determines the smallest one among the charging states of the plurality of battery cells as the target charging state, and based on the difference between the charging state of the balancing target and the target charging state, the target discharge capacity for the balancing target can be decided

Also, the controller may determine a target balancing time for the balancing target based on the reference balancing current and the target discharge capacity.

A battery pack according to another aspect of the present invention may include the cell balancing device.

Cell balancing method according to another aspect of the present invention, based on the initial voltage across the plurality of battery cells, determining the state of charge of the plurality of battery cells; determining a balancing target of any one of the plurality of battery cells based on the state of charge of the plurality of battery cells; determining a target state of charge for the balancing target based on initial voltages across the plurality of battery cells; determining a target discharge capacity for the balancing target based on a difference between the balancing target's charging state and the target charging state; determining a target balancing time for the balancing target based on a reference balancing current and the target discharge capacity; and constantly controlling the balancing current of the balancing target as a reference balancing current during the target balancing time.

According to at least one of the embodiments of the present invention, while the cell balancing is in progress, even if the voltage of each battery cell changes, the average discharge current per cycle (hereinafter, referred to as a 'balancing current') may be constantly maintained.

Accordingly, the actual discharge capacity calculated based on the balancing current may be closer to the target discharge capacity. In addition, it is possible to reduce the number of calculations required to compare whether the actual discharge capacity has reached the target discharge capacity.

Effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

The following drawings attached to the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical spirit of the present invention together with the detailed description of the present invention to be described later, so the present invention is a matter described in such drawings should not be construed as being limited only to
1 is a diagram showing a functional configuration of a cell balancing apparatus according to an embodiment of the present invention.
2 is a flowchart showing steps of a cell balancing method according to an embodiment of the present invention.
3 is a timing chart showing a voltage across both ends of a balancing target, a target duty cycle, and a balancing current while the cell balancing method of FIG. 2 is executed.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor should properly understand the concept of the term in order to best describe his invention. Based on the principle that can be defined, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

Therefore, the configuration shown in the embodiments and drawings described in the present specification is only the most preferred embodiment of the present invention and does not represent all of the technical spirit of the present invention, so at the time of the present application, various It should be understood that there may be equivalents and variations.

In addition, in the description of the present invention, if it is determined that a detailed description of a related well-known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

Terms including an ordinal number such as 1st, 2nd, etc. are used for the purpose of distinguishing any one of various components from the others, and are not used to limit the components by such terms.

Throughout the specification, when a part "includes" a certain element, it means that other elements may be further included, rather than excluding other elements, unless otherwise stated. In addition, a term such as <control unit> described in the specification means a unit that processes at least one function or operation, which may be implemented as hardware or software, or a combination of hardware and software.

In addition, throughout the specification, when a part is "connected" with another part, it is not only "directly connected" but also "indirectly connected" with another element interposed therebetween. include

1 is a diagram illustrating a functional configuration of a cell balancing apparatus 100 according to an embodiment of the present invention.

The cell balancing apparatus 100 balances a state of charge between _{a plurality of battery cells Cell 1} to Cell _n connected in series in the battery module 20 of the battery pack 10 . Referring to FIG. 1 , the cell balancing apparatus 100 includes a monitoring unit 110 , a balancing unit 120 , and a control unit 130 .

The monitoring unit 110 may include a voltage detection circuit and optionally further include a temperature detection circuit. The voltage detection circuit may include at least one voltage sensor. The voltage detection circuit is electrically connected to both ends (ie, positive and negative) of each of the plurality of battery cells (Cell ₁ to Cell _{n) included in the battery module 20 through a sensing line, so that each battery cell (Cell)} It is possible to detect the voltage across both ends of , every predetermined period, and transmit a voltage signal representing the detected voltage across both ends to the controller 130 . The temperature detection circuit may include at least one temperature sensor. Preferably, the temperature detection circuit may include the same number of temperature sensors TS ₁ to TS _{n as the number of balancing circuits BC 1} to BC _n . The temperature sensor TS _i , i = 1 to n may be installed adjacent to the switching element SW _{i of the balancing circuit BC i included in the balancing unit 120 .} The temperature detection circuit detects the temperatures of the plurality of balancing circuits BC ₁ to BC _{n every predetermined period using the temperature sensors TS 1} to TS _n , and sends a temperature signal indicating the detected temperature to the controller 130 . can be transmitted

The balancing unit 120 may include a plurality of balancing circuits BC ₁ to BC _n . The number of balancing circuits BC included in the balancing unit 120 may be the same as the number of battery cells included in the battery module 20 . The balancing circuit BC _i may include a resistance element R _i and a switching element SW _i connected in series with each other, and may be connected in parallel to the battery cell Cell _{i .} The resistance element R _i may have a predetermined resistance value. The switching element SW _i may be a semiconductor switch controllable by a switching signal (eg, a pulse width modulation signal). When the switching element (SW _i) of the turn-on state, thereby forming the closed circuit of the battery cell (Cell _i), a resistance element (R _i) and a switching element (SW _i), the battery cell (Cell _i) is discharged.

The control unit 130 is operatively coupled to the monitoring unit 110 and the plurality of balancing circuits BC ₁ to BC _{n .} The controller 130, in hardware, ASICs (application specific integrated circuits), DSPs (digital signal processors), DSPDs (digital signal processing devices), PLDs (programmable logic devices), FPGAs (field programmable gate arrays), microprocessors (microprocessors) and may be implemented using at least one of electrical units for performing other functions. The control unit 300 may include a memory. The memory stores data, commands, and software required for the overall operation of the cell balancing device 100 , and includes a flash memory type, a hard disk type, and a solid state disk (SSD) type. type), SDD type (Silicon Disk Drive type), multimedia card micro type, random access memory (RAM), static random access memory (SRAM), read-only memory (ROM), The storage medium may include at least one type of electrically erasable programmable read-only memory (EEPROM) and programmable read-only memory (PROM).

The controller 130 may receive a voltage signal and a temperature signal from the monitoring unit 110 , and individually control the _{plurality of balancing circuits BC 1} to BC _{n based on the voltage signal and the temperature signal.} A cell balancing method by the controller 130 will be described in more detail with reference to FIG. 2 below.

2 is a flowchart showing steps of a cell balancing method according to an embodiment of the present invention.

Referring to FIGS. 1 and 2 , in step S200 , the controller 130 receives a voltage signal representing an initial voltage across the _{plurality of battery cells Cell 1} to Cell _{n from the monitoring unit 110 .} In this case, the initial voltage across both ends may represent an open circuit voltage (OCV) of each battery cell detected in the no-load state of the battery module 20 .

In step S205, the control unit 130, based on the plurality of initial voltage across the battery cell (Cell ₁ Cell ~ _n), it is possible to determine the state of charge of the plurality of battery cells (Cell ₁ Cell ~ _n). When the initial both-end voltage is the open-circuit voltage, the controller 130 uses the open-circuit voltage-state of charge (SOC) curve data pre-recorded in the memory embedded therein, and the initial open-circuit voltage of each battery cell (Cell). It is possible to determine a state of charge corresponding to .

In step S210, the control unit 130, and which can determine the one of the balancing target charging a plurality of (Cell ₁ ~ Cell _n) battery cell on the basis, the status of the plurality of battery cells (Cell ₁ ~ Cell _n). In this case, the controller 130 may determine, as a balancing target, the one having the highest state of charge (Cell _{k , k=1 to n) among the plurality of battery cells (Cell 1} to Cell _{n ).} Of course, the controller 130 may simultaneously determine two or more of the _{plurality of battery cells Cell 1} to Cell _{n as the balancing target.} For example, the controller 130 may _{determine two or more of the plurality of battery cells Cell 1} to Cell _n as the balancing target except for those having the lowest state of charge.

In step S215 , the controller 130 may determine a target charging state for a balancing target. For example, the controller 130 may determine the smallest one among the charging states of the _{plurality of battery cells Cell 1} to Cell _{n as the target charging state.} The reason is that, to equalize the charge state of the balancing unit 120 (Cell ₁ ~ Cell _n), the plurality of battery cells selectively, (Cell ₁ ~ Cell _n), the plurality of battery cells, because only be discharged to the minimum value of those it is for

In step S220, the control unit 130, based on the difference between the charge state and the target state of charge of the balancing target (Cell _k), determines the target discharge capacity for the target balancing (Cell _k). For example, if the maximum capacity given in advance is 3000mAh, the _{state of charge of the balancing target (Cell k} ) is 80%, and the target state of charge is 70%, the state of charge of the balancing target (Cell _k ) is 80% and the target state of charge is 70% 3000mAh × 10% = 300mAh, which is a capacity corresponding to a difference of 10%, may be determined as the target discharge capacity.

In step S225 , the controller 130 may determine a reference balancing current based on a difference between the charging state of the _{balancing target Cell k and the target charging state.} For example, balancing the target if more than 15% higher than the charge is at a target state of charge of the (Cell _k) is to increase the reference balancing current proportional to the charge state and the target state of charge of the balancing target (Cell _k), otherwise It can be kept constant with a fixed value given in advance. Of course, the controller 130 may use a predetermined fixed value as the reference balancing current regardless of the difference between the charging state of the _{balancing target Cell k and the target charging state.}

In step S230 , the controller 130 determines a target balancing time for the _{balancing target Cell k} based on the reference balancing current and the target discharge capacity. In this case, there is a relationship of [balancing duration = target discharge capacity / reference balancing current].

When the target discharge capacity, the reference balancing current, and the target balancing time are determined, the controller 130 determines the balancing current of the balancing circuit (BC _{k ) connected in parallel to the balancing target (Cell k ) through steps S230 to S245 to be described later.} The balancing unit 120 is controlled to keep the current constant. In this case, _{the balancing current of the balancing circuit BC k} may be an average value of the discharge current flowing through the balancing circuit BC connected in parallel to the balancing target during a predetermined period.

In step S235 , the controller 130 determines a duty cycle correction value for each predetermined period based on the voltage across both ends of _{the balancing target Cell k detected for each predetermined period.} In this case, the controller 130 may use Equation 1 or Equation 2 below.

<Equation 1>

<Equation 2>

은 밸런싱 대상(Cell_k)의 양단 전압, R_CB는 저항 소자(R)의 미리 주어진 저항값, D_FIX

는 미리 정해진 기준 듀티 사이클(예, 0.5 = 50%), D_AD는 듀티 사이클 보정값이다. 상기 수학식 2의 α는 미리 주어진 상수이고, T는 밸런싱 회로(BC_k)의 온도이다.In Equations 1 and 2, I _CB is the reference balancing current, V _CELL

is the voltage across both ends of the balancing target (Cell _{k ), R CB} is the resistance value given in advance of the resistive element (R), D _FIX

is a predetermined reference duty cycle (eg, 0.5 = 50%), D _AD is the duty cycle correction value. In Equation 2, α is a constant given in advance, and T is the temperature of the _{balancing circuit BC k .}

In Equation 1, since I _CB , R _CB and D _FIX are constant values for the target balancing time, D _AD depends on V _{CELL .} In comparison, in Equation 2, since I _CB , R _CB and D _FIX are constant values for the target balancing time, D _AD depends not only on V _CELL but also on αT. According to Equation 2, _{R CB} may be corrected according to the temperature of the _{balancing circuit BC k .} That is, the control unit 130, the voltage across both ends of the _{balancing target (Cell k ) V CELL} And, based on the temperature T of the balancing circuit BC _k , the duty cycle correction value may be determined at every predetermined period.

_{As the balancing target Cell k} is discharged during the target balancing time, the control unit 130, _{V CELL} detected at every predetermined period gradually decreases. In Equations 1 and 2, since D _AD and V _CELL have an inverse relationship, _{D AD} increases as much as the decrease amount of _{V CELL.}

In step S240 , the controller 130 determines a target duty cycle for the _{balancing target Cell k based on the duty cycle correction value.} At this time, the control unit 130, Equation 3:

By using , _{the target duty cycle for the balancing target Cell k} may be updated every predetermined period.

In step S245 , the controller 130 outputs a switching signal having a target duty cycle to the balancing switch SW _{k of the balancing circuit BC k} connected in parallel to the _{balancing target Cell k .} Accordingly, the turn-on time and turn-off time per cycle of the _{balancing switch SW k can be adjusted.} When cell balancing for the balancing target (Cell _k ) is in progress, _{D SW} also increases as _{D AD} increases, so the turn-on time per cycle of the _{balancing switch SW k also increases.} As a result, the decrease amount of _{V CELL is canceled by the increase amount of D SW} , so that the balancing current for the target balancing time can be constantly maintained as the reference balancing current. In this case, that the balancing current is kept constant as the reference balancing current is not limited to the balancing current being completely the same as the reference balancing current, and it should be understood as encompassing even a difference between the two within an allowable value.

In step S250 , the controller 130 may determine whether the accumulated balancing time has reached a target balancing time. The accumulated balancing time may be a time elapsed from the time when cell balancing using the reference balancing current is started to the present. When the value of step S250 is "YES", the control unit 130 stops the output of the switching signal to the balancing switch, thereby ending the method. When the value of step S250 is "NO", the control unit 130 returns to step S235.

3 is a timing chart showing a voltage across both ends of a balancing target, a target duty cycle, and a balancing current while the cell balancing method of FIG. 2 is executed. For better understanding, it is assumed that the controller 130 periodically updates the target duty cycle based on the duty cycle correction value determined using Equation 1 among Equations 1 and 2.

Referring to FIG. 3A , it can be seen that the _{voltage V CELL} across both ends of the balancing target gradually decreases as the balancing target Cell _{k is discharged through successive periods P 1} to P _{m .}

_{As the control unit 130 increases D AD} in response to a decrease in the _{voltage V CELL} across both ends of the balancing target (Cell _k ), D _SW also _{gradually increases from P 1} to P _{m in} FIG. 3 (b) can be confirmed from Since the target duty cycle may be updated when one cycle ends and the next cycle starts, it may increase in a stepwise fashion as shown in FIG. 3B . Accordingly, as shown in (c) of FIG. 3 , the balancing current I of the _{balancing target Cell k} may be constantly maintained as the reference balancing current from _{P 1} to P _{m .}

The embodiment of the present invention described above is not implemented only through the apparatus and method, and may be implemented through a program for realizing a function corresponding to the configuration of the embodiment of the present invention or a recording medium in which the program is recorded. The implementation can be easily implemented by those skilled in the art to which the present invention pertains from the description of the above-described embodiments.

In the above, although the present invention has been described with reference to limited embodiments and drawings, the present invention is not limited thereto and will be described below with the technical idea of the present invention by those of ordinary skill in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of equivalents of the claims.

In addition, since the present invention described above can be various substitutions, modifications and changes within the scope that does not depart from the technical spirit of the present invention for those of ordinary skill in the art to which the present invention pertains, the above-described embodiments and attachments Not limited by the illustrated drawings, all or part of each embodiment may be selectively combined so that various modifications can be made.

10: battery pack
20: battery module
Cell: battery cell
100: cell balancer
110: monitoring unit
120: balancing unit
BC: balancing circuit
R: resistance element
SW: switching element
130: control unit

Claims (9)

An apparatus for balancing a state of charge between a plurality of battery cells connected in series in a battery module, the apparatus comprising:
a monitoring unit configured to detect the voltage across the battery cells at predetermined intervals;
a balancing unit including a plurality of balancing circuits; and
a control unit operatively coupled to the monitoring unit and each of the balancing circuits;
Each of the balancing circuits includes a resistance element and a switching element connected in series, and is connected in parallel to each of the battery cells,
The control unit is
Determine the state of charge of each battery cell based on the voltage across the battery cells,
Determining a balancing target of any one of the plurality of battery cells based on the state of charge of each battery cell,
The apparatus of controlling the balancing unit to constantly maintain a balancing current of a balancing circuit connected in parallel to the balancing target as a reference balancing current at every predetermined period.
According to claim 1,
The control unit is
Based on the reference balancing current, the resistance value of the resistance element, and the voltage across the balancing target detected at each predetermined period, a duty cycle correction value is determined for each predetermined period,
and updating a target duty cycle of a switching signal applied to a switching element of a balancing circuit connected in parallel to the balancing target at every predetermined period based on the duty cycle correction value.
3. The method of claim 2,
The control unit is
Equation:

(I _CB is the reference balancing current, V _CELL is the voltage across both ends of the balancing target, R _CB is the resistance value of the resistor, D _FIX is a predetermined reference duty cycle, D _AD is the duty cycle correction value)
to determine the duty cycle correction value.
3. The method of claim 2,
The monitoring unit,
configured to detect the temperature of each battery cell at each predetermined period;
The control unit is
Further based on the temperature of the balancing target, the apparatus determines the duty cycle correction value for each predetermined period.
delete According to claim 1,
The control unit is
Determining the smallest one among the charging states of the plurality of battery cells as the target state of charge,
determining a target discharging capacity for the balancing target based on a difference between a charging state of the balancing target and the target charging state.
7. The method of claim 6,
The control unit is
determining a target balancing time for the balancing target based on the reference balancing current and the target discharge capacity.
the device according to any one of claims 1 to 4, 6 and 7;
comprising, a battery pack.
A method of balancing a state of charge between a plurality of battery cells connected in series in a battery module, the method comprising:
determining the state of charge of the plurality of battery cells based on initial voltages across the plurality of battery cells;
determining a balancing target of any one of the plurality of battery cells based on the state of charge of the plurality of battery cells;
determining a target state of charge for the balancing target based on initial voltages across the plurality of battery cells;
determining a target discharge capacity for the balancing target based on a difference between the balancing target's charging state and the target charging state;
determining a target balancing time for the balancing target based on a reference balancing current and the target discharge capacity; and
constantly controlling the balancing current of the balancing target as a reference balancing current during the target balancing time;
A method comprising

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