Apparatus and method for cell balancing

Abstract

A cell balancing device and method are disclosed. A cell balancing device according to one aspect of the present invention includes a plurality of DC / DC converters connected to each of a plurality of battery cells and outputting a voltage that is adjusted in magnitude from an individual battery cell according to a voltage control command from a controller, and a controller that generates a voltage control command to control the output voltage magnitude of each DC / DC converter based on the voltage magnitude of each battery cell and transmits the voltage control command to the corresponding DC / DC converter.

Description

Technology Field

[0001] The present invention relates to a cell balancing device and method, and more specifically, to a cell balancing device and method that can improve the energy efficiency and increase the lifespan of a battery pack by reducing the design cost for cell balancing and independently controlling the battery cells within the battery pack. Background Technology

[0002] Recently, as the demand for portable electronic products such as laptops, video cameras, and mobile phones has increased rapidly, and the development of electric vehicles, energy storage batteries, robots, and satellites has accelerated, research on high-performance batteries capable of repeated charging and discharging is actively underway.

[0003] Currently commercialized batteries include nickel-cadmium, nickel-hydrogen, nickel-zinc, and lithium batteries. Among these, lithium batteries are gaining attention for their advantages, such as the ability to freely charge and discharge with almost no memory effect compared to nickel-based batteries, a very low self-discharge rate, and high energy density.

[0004] A battery pack may include a plurality of battery cells and a battery management system. The battery management system is provided to manage the status of the plurality of battery cells. As the battery pack's usage period increases, differences in internal characteristics intensify, resulting in an imbalance of characteristics within the battery pack. Since this imbalance within the battery pack adversely affects performance, such as the battery pack's capacity, power output, and lifespan, cell balancing technology is essential to reduce the imbalance.

[0005] Conventional active cell balancing technology performs balancing through energy transfer, unlike passive cell balancing which consumes energy, but it has the disadvantage of being difficult to apply to actual mass production due to the complex design structure and significantly increased design costs.

[0006] In addition, the method of balancing battery cells using resistance has the problem of low efficiency because it consumes excess energy, and also has the limitation that it is impossible for the battery to always be in a 100% charged state due to the consumed energy.

[0007] Accordingly, there is a demand for a cell balancing technique that can reduce design costs for cell balancing and independently control battery cells within a battery pack, thereby improving the energy efficiency and increasing the lifespan of the battery pack.

[0008] The background technology of the present invention is disclosed in Korean Registered Patent Publication No. 10-1632694 (published June 22, 2016). The problem to be solved

[0009] The present invention has been devised to improve the above-mentioned problems, and the objective of the present invention is to provide a cell balancing device and method that can improve the energy efficiency and increase the lifespan of a battery pack by reducing the design cost for cell balancing and independently controlling the battery cells within the battery pack.

[0010] The problems that the present invention aims to solve are not limited to the problem(s) mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0011] A cell balancing device according to one aspect of the present invention includes a plurality of DC / DC converters connected to each of a plurality of battery cells and outputting a voltage magnitude that is adjusted from each individual battery cell according to a voltage control command from a controller, and a controller that generates a voltage control command to control the output voltage magnitude of each DC / DC converter based on the voltage magnitude of each battery cell and transmits the voltage control command to the corresponding DC / DC converter.

[0012] In the present invention, the controller compares a reference carrier wave having a constant frequency with the voltage of each battery cell, determines the PWM duty of each DC / DC converter based on the comparison result, and can generate the determined PWM duty of each DC / DC converter as a voltage control command and transmit it to the corresponding DC / DC converter.

[0013] In the present invention, the controller can determine a PWM duty cycle that turns on the switch when the voltage of the battery cell becomes greater than the reference carrier wave.

[0014] In the present invention, the controller can generate a voltage control command that increases the PWM duty cycle as the battery cell has a higher voltage.

[0015] In the present invention, the controller can determine the PWM duty of each DC / DC converter so that the total voltage output from a plurality of DC / DC converters becomes the voltage of a preset battery pack.

[0016] In the present invention, each of the plurality of DC / DC converters can control the voltage magnitude of the corresponding battery cell according to the PWM duty included in the voltage control command.

[0017] A cell balancing method according to another aspect of the present invention is a cell balancing method for a battery pack having a plurality of battery modules, each having one battery cell and one DC / DC converter connected thereto, wherein the method comprises the steps of: a controller generating a voltage control command based on the voltage magnitude of each battery cell and transmitting the voltage control command to the corresponding DC / DC converter; and each DC / DC converter adjusting and outputting the magnitude of the voltage input from the battery cell according to the voltage control command.

[0018] In the step of transmitting the voltage control command to the corresponding DC / DC converter, the controller compares a reference carrier wave having a certain frequency with the voltage of each battery cell, determines the PWM duty of each DC / DC converter based on the comparison result, and generates the determined PWM duty of each DC / DC converter as the voltage control command and transmits it to the corresponding DC / DC converter.

[0019] In the step of transmitting the voltage control command to the corresponding DC / DC converter, the present invention can determine a PWM duty cycle that turns on the switch when the voltage of the corresponding battery cell becomes greater than the reference carrier wave.

[0020] In the step of transmitting the voltage control command to the corresponding DC / DC converter, the present invention can generate a voltage control command that increases the PWM duty cycle as the battery cell has a higher voltage.

[0021] In the step of transmitting the voltage control command to the corresponding DC / DC converter, the present invention allows the controller to determine the PWM duty of each DC / DC converter such that the total voltage output from the plurality of DC / DC converters becomes the voltage of a preset battery pack.

[0022] In the step of adjusting and outputting the magnitude of the voltage, the present invention allows each DC / DC converter to control the magnitude of the voltage of the corresponding battery cell according to the PWM duty included in the voltage control command. Effects of the invention

[0023] A cell balancing device and method according to one embodiment of the present invention performs a balancing function by controlling a switch duty based on a battery cell voltage, and by individually controlling the output voltage of the battery cell through the switch duty, it is possible to reduce design costs for cell balancing and independently control the battery cells within the battery pack, thereby improving the energy efficiency and increasing the lifespan of the battery pack.

[0024] A cell balancing device and method according to one embodiment of the present invention can not only perform cell balancing within a battery pack but also function as a power converter that controls the output voltage by determining the voltage output of the entire battery pack based on a voltage controlled by a PWM control method. Furthermore, since it can perform the function of a power converter as well as cell balancing performed by a BMS, battery system development costs can be effectively reduced, and the voltage output of the entire battery pack can be changed by varying the number of battery modules to meet required specifications.

[0025] Meanwhile, the effects of the present invention are not limited to those mentioned above, and various effects may be included within the scope obvious to a person skilled in the art from the contents described below. Brief explanation of the drawing

[0026] FIG. 1 is a block diagram schematically showing the configuration of a cell balancing device according to one embodiment of the present invention. FIG. 2 is an exemplary diagram illustrating voltage control of a battery cell in one balancing module according to one embodiment of the present invention. FIG. 3 is an example diagram illustrating the PWM duty cycle for each battery cell according to the present embodiment. FIG. 4 is an illustrative diagram for explaining the voltage boost ratio according to the PWM duty cycle according to one embodiment of the present invention. FIG. 5 is a diagram illustrating a cell balancing method according to an embodiment of the present invention. Specific details for implementing the invention

[0027] Hereinafter, a cell balancing device and method according to an embodiment of the present invention will be described with reference to the attached drawings. In this process, the thickness of the lines or the size of the components shown in the drawings may be exaggerated for clarity and convenience of explanation.

[0028] Additionally, the implementations described herein may be implemented, for example, as methods or processes, devices, software programs, data streams, or signals. Even if discussed only in the context of a single form of implementation (e.g., discussed only as a method), implementations of the discussed features may also be implemented in other forms (e.g., devices or programs). Devices may be implemented in appropriate hardware, software, and firmware, etc. Methods may be implemented in devices such as processors, which generally refer to processing devices including, for example, computers, microprocessors, integrated circuits, or programmable logic devices. Processors also include communication devices such as computers, cell phones, portable / personal digital assistants ("PDAs"), and other devices that facilitate the communication of information between end-users.

[0029] Furthermore, the terms used in this specification are used merely to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, terms such as "comprising" or "having" are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof. Terms such as "first," "second," etc., may be used to describe various components, but the components should not be limited by these terms. These terms are used solely for the purpose of distinguishing one component from another.

[0030] Hereinafter, embodiments according to the present invention will be described in detail with reference to the attached drawings. In describing with reference to the attached drawings, identical or corresponding components are given the same reference numerals, and redundant descriptions thereof will be omitted.

[0032] FIG. 1 is a block diagram schematically showing the configuration of a cell balancing device according to one embodiment of the present invention, FIG. 2 is an illustrative diagram for explaining voltage control of a battery cell in one balancing module according to one embodiment of the present invention, FIG. 3 is an illustrative diagram for explaining the PWM duty for each battery cell according to one embodiment of the present invention, and FIG. 4 is an illustrative diagram for explaining the voltage boost ratio according to the PWM duty according to one embodiment of the present invention.

[0033] Referring to FIG. 1, a cell balancing device according to one embodiment of the present invention includes a plurality of battery cells (110a, 110b, ..., 110n, hereinafter referred to as '110'), a plurality of DC / DC converters (120a, 120b, ..., 120n, hereinafter referred to as '120') connected to each battery cell (110), and a controller (130).

[0034] Multiple battery cells (110) can be connected to each other in series or in parallel.

[0035] The battery cell (110) is not particularly limited in type as long as it is rechargeable, such as a lithium-ion cell.

[0036] Multiple DC / DC converters (120) can be connected to each of the multiple battery cells (110).

[0037] Each DC / DC converter (120) can be connected to a battery cell (110) to form a single battery module (10). Multiple battery modules (10) can be connected in series or in parallel to form a battery pack (1). Each battery module (10) can be controlled by a controller (130) as shown in FIG. 2. Referring to FIG. 2, the controller (130) can transmit a voltage control command (Signal) to the DC / DC converter (120) to control the PWM duty cycle based on the voltage of the battery cell (110). Then, the DC / DC converter (120) can control the output voltage (Vout) by controlling the switch according to the PWM duty cycle.

[0038] A plurality of DC / DC converters (120) may be devices for converting DC input from a connected battery cell (110) into a higher or lower DC to create or stabilize the required voltage.

[0039] To this end, a plurality of DC / DC converters (120) can adjust (boost or step down) the voltage of an incoming battery cell (110) and output it according to a voltage control command from a controller (130). Here, the voltage control command may include PWM.

[0040] The DC / DC converter (120) can output a different voltage magnitude of the corresponding battery cell (110) according to the PWM duty included in the voltage control command from the controller (130). That is, the voltage output of the DC / DC converter (120) can be determined by the PWM duty (switching duty ratio). Here, the PWM duty (switching duty ratio) is a ratio to the time during which the switch conducts, and the voltage of the DC / DC converter (120) can be controlled according to the ratio of the time during which the switch is turned on.

[0041] The DC / DC converter (120) has an input / output ratio determined by the PWM duty as shown in Equation 1 below, and can control the output through the PWM duty (D).

[0042] [Mathematical Formula 1]

[0043]

[0044] The DC / DC converter (120) is connected to each battery cell (110) so that the required voltage can be independently adjusted for each battery cell (110).

[0045] These DC / DC converters (120) can be implemented in various ways, such as a Buck converter (step-down), a Boost converter (step-up), and a Buck-Boost converter (step-down), to convert a DC voltage into a higher or lower DC voltage.

[0046] The controller (130) can generate a voltage control command to control the output voltage magnitude of each DC / DC converter (120) based on the voltage magnitude of each battery cell (110) and transmit the voltage control command to the corresponding DC / DC converter (120). Here, the voltage control command may include a PWM duty cycle.

[0047] The controller (130) senses the voltage of each battery cell (110), compares the sensed voltage of each battery cell (110) with a reference carrier wave having a constant frequency, determines the PWM duty of each DC / DC converter (120) based on the comparison result, and generates the determined PWM duty of each DC / DC converter (120) as a voltage control command and transmits it to the corresponding DC / DC converter (120). At this time, the controller (130) can determine the PWM duty to turn on the switch when the voltage of the corresponding battery cell (110) becomes greater than the reference carrier wave.

[0048] For example, five battery cells form a battery pack (1), and a method for determining the PWM duty cycle is described when a reference sawtooth wave and the voltages of the first to fifth battery cells (vb1 to vb5) are input as shown in FIG. 3 (a). In this case, the controller (130) can compare the reference sawtooth wave with each of the voltages of the first to fifth battery cells (vb1 to vb5). Based on the comparison result, the controller (130) can increase the PWM duty cycle in order from the first battery cell (vb1), which has the lowest battery cell voltage, to the fifth battery cell (vb15), which has the highest battery cell voltage, as shown in FIG. 3 (b).

[0049] As described above, the controller (130) can generate a voltage control command that increases the PWM duty as the battery cell (110) has a higher voltage. At this time, the controller (130) can determine the PWM duty of each DC / DC converter (120) so that the total voltage output from the plurality of DC / DC converters (120) becomes the voltage of the pre-set battery pack (1). Accordingly, the controller (130) can generate a voltage control command that controls the PWM duty based on the voltage of the battery cell (110) so that the PWM duty has a larger value as the battery cell (110) has a higher voltage. Then, the DC / DC converter (120) can output a different voltage magnitude of the connected battery cell (110) according to the PWM duty included in the voltage control command.

[0050] The controller (130) can control the multiple DC / DC converters (120) to output the voltage of the corresponding battery cells (110) with the same PWM duty cycle when the voltage of the multiple battery cells (110) constituting the battery pack (1) is constant (identical). When the voltage of the multiple battery cells (110) constituting the battery pack (1) is not constant (unbalanced), the controller (130) can control the DC / DC converters (120) to output the voltage magnitude of the battery cells (110) differently by varying the PWM duty cycle according to the voltage magnitude of each battery cell (110).

[0051] For example, if the DC / DC converter (120) is implemented as a boost converter, as shown in FIG. 4, the voltage of the boost converter increases as the PWM duty increases, so the battery cell (110) having a higher terminal voltage (output voltage) can be boosted at a higher voltage ratio, and the battery cell (110) having a high boost ultimately outputs a large current, thereby supplying more power.

[0052] The cell balancing device configured as described above can perform balancing on the unbalanced battery pack (1) according to the PWM duty cycle and can also control the voltage output. That is, the cell balancing device can perform cell balancing while simultaneously controlling the battery output.

[0053] Additionally, the cell balancing device can perform cell balancing by utilizing a DC-DC converter (120) to control the voltage of the battery pack (1). To this end, the cell balancing device can control the voltage of each battery cell (110) by utilizing a PWM control method that adjusts the duty ratio of the switch. Additionally, the cell balancing device can perform cell balancing simultaneously by determining the voltage output of the entire battery pack (1) based on the voltage controlled by the PWM control method, in combination with the voltage control technology of the DC / DC converter (120).

[0055] FIG. 5 is a diagram illustrating a cell balancing method according to an embodiment of the present invention.

[0056] Referring to FIG. 5, the controller (130) senses the voltage of each battery cell (110) (S502) and generates a voltage control command based on the sensed voltage of each battery cell (110) (S504). At this time, the controller (130) can generate a voltage control command by controlling the PWM duty based on the voltage of the battery cell (110) so that the PWM duty has a larger value for the battery cell (110) having a higher voltage. The controller (130) can determine the PWM duty of each DC / DC converter (120) so that the total voltage output from the plurality of DC / DC converters (120) becomes the voltage of the pre-set battery pack (1). Additionally, the controller (130) compares the voltage of each sensed battery cell (110) with a reference carrier wave having a constant frequency, determines the PWM duty of each DC / DC converter (120) based on the comparison result, and can generate a voltage control command based on the determined PWM duty of each DC / DC converter (120). The controller (130) can generate a voltage control command by controlling the PWM duty based on the voltage of the battery cell (110) so that the PWM duty has a larger value for the battery cell (110) having a higher voltage.

[0057] When step S504 is performed, the controller (130) transmits a voltage control command to the DC / DC converter (120) (S506).

[0058] When step S506 is performed, the DC / DC converter (120) outputs a voltage that is adjusted in magnitude from the battery cell (110) according to the voltage control command (S508). At this time, the DC / DC converter (120) can control the voltage magnitude of the corresponding battery cell (110) according to the PWM duty included in the voltage control command.

[0060] As described above, the cell balancing device and method according to one embodiment of the present invention perform a balancing function by controlling the switch duty based on the battery cell voltage, and by individually controlling the output voltage of the battery cell through the switch duty, the design cost for cell balancing can be reduced and the battery cells within the battery pack can be controlled independently, thereby improving the energy efficiency and increasing the lifespan of the battery pack.

[0061] A cell balancing device and method according to one embodiment of the present invention can not only perform cell balancing within a battery pack but also function as a power converter that controls the output voltage by determining the voltage output of the entire battery pack based on a voltage controlled by a PWM control method. Furthermore, since it can perform the function of a power converter as well as cell balancing performed by a BMS, battery system development costs can be effectively reduced, and the voltage output of the entire battery pack can be changed by varying the number of battery modules to meet required specifications.

[0062] Although the present invention has been described with reference to the embodiments illustrated in the drawings, this is merely illustrative, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible therefrom.

[0063] Therefore, the true technical scope of protection of the present invention should be determined by the following patent claims. Explanation of the symbols

[0064] 1 : Battery pack 10: Battery Module 110: Battery cell 120 : DC / DC converter 130 : Controller

Claims

Claim 1 A plurality of DC / DC converters connected to each of a plurality of battery cells, and outputting a voltage that adjusts the magnitude of the voltage input from each individual battery cell according to a voltage control command from a controller; and a controller that generates a voltage control command to control the output voltage magnitude of each DC / DC converter based on the voltage magnitude of each battery cell and transmits the voltage control command to the corresponding DC / DC converter, wherein the controller determines the PWM duty of each DC / DC converter so that the total voltage output from the plurality of DC / DC converters becomes the voltage of a preset battery pack, and generates a voltage control command that controls the PWM duty based on the voltage of each battery cell so that the PWM duty has a larger value for the battery cell having a higher voltage, and the DC / DC converter determines the input / output ratio according to the PWM duty (D) as shown in the following mathematical formula and controls the output through the PWM duty, [Mathematical Formula] A cell balancing device characterized in that Vo represents the output voltage and Vi represents the input voltage. Claim 2 A cell balancing device according to claim 1, wherein the controller compares a reference carrier wave having a constant frequency with the voltage of each battery cell, determines the Power Width Modulation Duty (PWM) of each DC / DC converter based on the comparison result, and generates the determined PWM duty of each DC / DC converter as a voltage control command and transmits it to the corresponding DC / DC converter. Claim 3 A cell balancing device according to paragraph 2, wherein the controller determines a PWM duty cycle to turn on the switch when the voltage of the battery cell becomes greater than the reference carrier wave. Claim 4 delete Claim 5 delete Claim 6 A cell balancing device according to claim 1, wherein each of the plurality of DC / DC converters controls the voltage magnitude of the corresponding battery cell according to the PWM duty included in the voltage control command. Claim 7 A cell balancing method for a battery pack comprising a plurality of battery modules, each connected to one battery cell and one DC / DC converter, wherein a controller generates a voltage control command based on the voltage magnitude of each battery cell and transmits the voltage control command to the corresponding DC / DC converter; Each DC / DC converter includes a step of adjusting and outputting the magnitude of the voltage input from the battery cell according to the voltage control command, and in the step of transmitting the voltage control command to the corresponding DC / DC converter, the controller generates a voltage control command that increases the PWM duty as the battery cell has a higher voltage, and in the step of transmitting the voltage control command to the corresponding DC / DC converter, the controller determines the PWM duty of each DC / DC converter so that the total voltage output from the plurality of DC / DC converters becomes the voltage of the preset battery pack, and in the step of adjusting and outputting the magnitude of the voltage, the DC / DC converter determines the input / output ratio according to the PWM duty (D) as shown in the following mathematical formula, and controls the output through the PWM duty, [Mathematical Formula] A cell balancing method characterized in that Vo represents the output voltage and Vi represents the input voltage. Claim 8 A cell balancing method according to claim 7, wherein, in the step of transmitting the voltage control command to the corresponding DC / DC converter, the controller compares the voltage of each battery cell with a reference carrier wave having a constant frequency, determines the PWM duty of each DC / DC converter based on the comparison result, and generates the determined PWM duty of each DC / DC converter as the voltage control command and transmits it to the corresponding DC / DC converter. Claim 9 A cell balancing method according to claim 8, wherein, in the step of transmitting the voltage control command to the corresponding DC / DC converter, the controller determines a PWM duty cycle to turn on the switch when the voltage of the corresponding battery cell becomes greater than the reference carrier wave. Claim 10 delete Claim 11 delete Claim 12 A cell balancing method according to claim 7, wherein, in the step of adjusting and outputting the magnitude of the voltage, each DC / DC converter controls the voltage magnitude of the corresponding battery cell according to the PWM duty included in the voltage control command.

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