WIRELESS COMMUNICATION METHOD, AND BATTERY SYSTEM FOR PROVIDING METHOD

CROSS-REFERENCE TO RELATED APPLICATIONThis application claims priority to and the benefit ofKorean Patent Application No. 1 0-2022-0083730 filed in the Korean Intellectual Property Office on July 07, 2022, the entire contents of which are incorporated herein by reference.TECHNICAL FIELDThe present disclosure relates to a wireless communication method between a plurality of battery management systems (BMSs) and a battery system providing the same.[Background]A battery system applied to an electric vehicle or the like may include a plurality of battery packs, each including a battery module and a slave battery management system (BMS) managing the battery module. In addition, the battery system may further include a master battery management system (BMS) communicating with a vehicle system and managing the plurality of battery packs.Recently, in order to solve the problems of poor quality of electric wiring and frequent maintenance related to wire cables and connectors, and to increase a mileage by reducing a weight of an electric vehicle, research and development on a method for wireless communication between a master BMS and a plurality of slave BMSs are increasing.[Summary][Technical Problem]The present disclosure attempts to provide a wireless communication method capable of wireless communication between a plurality of battery management systems (BMSs) without adding a separate component for wireless communication, and a battery system providing the same.Further, the present disclosure attempts to provide a wireless communication method capable of wireless communication between a plurality of battery management systems (BMS) in various industrial scientific and medical (ISM) bands, and a battery system providing the same.[Technical Solution]An exemplary embodiment of the present disclosure provides a battery system including at least one battery pack including a battery module and a slave battery management system (BMS) managing the battery module includes: a communication unit of the slave BMS; a capacitor connected between the communication unit and a first ground; an inductor connected between a contact between the first ground and the capacitor and a second ground; and a controller configured to transmit an AC signal having a predetermined frequency to the communication unit in an antenna mode, wherein in the antenna mode, the slave BMS is configured to communicate with the outside.The inductor may be located between the battery module and the slave BMS.A length between the inductor and the first ground may correspond to 1/4 of a wavelength of the AC signal.The first ground may be a signal ground of the slave BMS, and the secondground may be a chassis ground of the battery module.The battery system may further include a monitoring unit electrically connected to each of a plurality of battery cells included in the battery module to collect battery data including at least one of a current, a voltage, and a temperature for each of the plurality of battery cells.In a monitoring mode in which the monitoring unit collects the battery data, the control unit may transmit a DC signal to the communication unit.The battery system may further include a master BMS communicating with the communication unit in a wireless manner to manage the at least one slave BMS.In the antenna mode, the controller may be further configured to transmit the collected battery data to the master BMS through the communication unit.Another exemplary embodiment of the present disclosure provides a wireless communication method in a battery system including a communication unit of a slave battery management system (BMS) managing a battery module, a capacitor connected between the communication unit and a first ground, and an inductor connected between a contact between the first ground and the capacitor and a second ground, the method includes transmitting an AC signal having a predetermined frequency to the communication unit to configure the slave BMS to communicate with the outside.The inductor may be located between the battery module and the slave BMS.A length between the inductor and the first ground may correspond to 1/4 of a wavelength of the AC signal.The first ground may be a signal ground of the slave BMS, and the second ground may be a chassis ground of the battery module.The battery system may further include a monitoring unit electrically connected to each of a plurality of battery cells included in the battery module to collect battery data including at least one of a current, a voltage, and a temperature for each of the plurality of battery cells.The wireless communication method may further include collecting the battery data by the monitoring unit, before the communication with the outside, wherein the collection of the battery data includes transmitting a DC signal to the communication unit.The communication with the outside may include transmitting the collected battery data to a master BMS managing the slave BMS through the communication unit.[Advantageous Effects]According to the present invention, there is no need to add a component (e.g., an antenna) for wireless communication inside a printed circuit board (PCB) for the BMS, and as a result, the size of the PCB for the BMS can be reduced.According to the present invention, the cost can be reduced because there is no need to purchase a component (e.g., an antenna) for wireless communication.According to the present invention, there is no need to change the PCB for the BMS according to a frequency band, and accordingly, a design of the PCB for the BMS can be commonized.[Brief Description of the Drawings]FIG. 1is a block diagram illustrating a battery system according to an exemplary embodiment.FIG. 2is a block diagram illustrating a battery pack ofFIG. 1in detail.FIG. 3is a block diagram illustrating the battery pack ofFIG. 1when operating in a monitoring mode in detail.FIG. 4is a block diagram illustrating the battery pack ofFIG. 1when operating in an antenna mode in detail.FIG. 5is a block diagram illustrating an antenna ofFIG. 4in detail.FIG. 6is a flowchart illustrating a wireless communication method according to an exemplary embodiment.[Detailed Description]Hereinafter, exemplary embodiments will be described in detail with reference to the accompanying drawings. The same or similar components will be denoted by the same or similar reference signs, and overlapping descriptions thereof will be omitted. The suffixes "module" and "unit" for components used in the description below are assigned or mixed in consideration of easiness in writing the specification and do not have distinctive meanings or roles by themselves. In addition, in describing exemplary embodiments in the present specification, detailed descriptions of relevant known technologies will be omitted if they unnecessarily obscure the gist of the exemplary embodiments disclosed in the present specification. Further, the accompanying drawings are provided only to help easily understand exemplary embodiments disclosed in the present specification. It should be understood that the technical idea disclosed in the present specification is not limited by the accompanying drawings, and includesall modifications, equivalents, and substitutions within the spirit and the technical scope of the present disclosure.Terms including ordinal numbers such as first and second may be used to describe various components, but these components are not limited by these terms. These terms are used only for the purpose of distinguishing one component from another component.It is to be understood that when one component is referred to as being "connected to" or "coupled to" another component, one component may be connected or coupled directly to another component, or one component may be connected or coupled to another component with an intervening component therebetween. On the other hand, it is to be understood that when one component is referred to as being "directly connected to" or "directly coupled to" another component, one component may be connected to another component with no intervening component therebetween.It should be understood that terms "include", "have", and the like used in the present application specify the presence of features, numerals, steps, operations, components, parts, or combinations thereof mentioned in the specification, but do not preclude the presence or addition of one or more other features, numerals, steps, operations, components, parts, or combinations thereof.FIG. 1is a block diagram illustrating a battery system according to an exemplary embodiment.FIG. 2is a block diagram illustrating a battery pack ofFIG. 1in detail.Referring toFIG. 1, a battery system 1 includes a battery 10 and a masterbattery management system (hereinafter referred to as a master BMS) 20.The battery 10 includes at least one battery pack. InFIG. 1, a plurality of battery packs 10_1 to 10_n are illustrated, but the number of battery packs is not limited thereto, and the battery 10 may include one battery pack 10_1.Hereinafter, reference sign "10_j" will be used to denote a specific battery pack among the plurality of battery packs 10_1 to 10_n, and reference signs "100j" and "200j" will be used to denote a battery module and a slave BMS included in the battery pack 10_j, respectively. In addition, reference signs "Cj", "Lj", "Nj", and "200_Aj" will be used to denote a capacitor, an inductor, a contact, and an antenna included in the battery pack 10_j, respectively, to be described below.The battery pack 10_j includes a battery module 100j and a slave BMS 200j.The battery module 100j may include a plurality of battery cells connected to each other in series and/or in parallel. In some exemplary embodiments, the battery cell may be a rechargeable secondary battery. InFIGS. 1and2, it is illustrated that the battery module 100j includes three battery cells Cell1, Cell2, and Cell3 connected to each other in series, but the number of battery cells is not limited thereto. The battery module 100j may include any number of battery cells.The slave BMS 200j may collect battery data for the battery module 100j and transmit the collected battery data to a master BMS 20 through wireless communication. In this case, the battery data may include at least one of a cell voltage, a cell current, and a cell temperature for each of the plurality of batterycells Cell1, Cell2, and Cell3. In addition, the battery data may include at least one of a module voltage, which is a voltage at both ends of the battery module 100j, and a module current, which is a current flowing through the battery module 100j.Referring toFIG. 2, the slave BMS 200j may include a monitoring unit 210, a communication unit 220, a control unit 230, a capacitor Cj, and an inductor Lj.The monitoring unit 210 is electrically connected to the battery module 100j to collect battery data. For example, the monitoring unit 210 is an integrated circuit (IC) capable of collecting battery data, and may include an application specific IC (ASIC), a battery monitoring IC (BMIC), or the like.Referring toFIG. 2, as an example, the monitoring unit 210 is electrically connected to positive and negative electrodes of each of the plurality of battery cells Cell1, Cell2, and Cell3, and the plurality of battery cells Cell1, Cell2, and Cell3 measure a cell voltage of each of the plurality of battery cells Cell1, Cell2, and Cell3. As another example, the monitoring unit 210 may receive information about a cell current and a cell temperature measured by a current sensor (not shown) and a temperature sensor (not shown), respectively. As another example, the monitoring unit 210 may measure a cell voltage of each of the plurality of battery cells Cell1, Cell2, and Cell3 at every predetermined cycle during a rest period in which charging and discharging does not occur, and calculate a cell current based on the measured cell voltage. The monitoring unit 210 may collect battery data at every predetermined cycle or in real time, and transmit the collected battery data to the control unit 230.The communication unit 220 may be an analog signal processing devicethat processes data to be transmitted. For example, the communication unit 220 may include a radio frequency IC (RFIC), but is not limited thereto.According to an exemplary embodiment, the control unit 230 may convert a digital signal into an analog signal (alternating current signal, AC signal) and transmit the converted signal to the communication unit 220. Then, the communication unit 220 processes the analog signal by amplifying and filtering the analog signal, and transmits the processed analog signal to the antenna. The antenna may convert the processed analog signal into an electromagnetic wave and transmit the electromagnetic wave into the air. According to an exemplary embodiment, the antenna may be an antenna generated in an antenna mode, and the antenna will be described in detail with reference toFIGS. 4and5below.The control unit 230 may control an overall operation of the slave BMS 200j. For example, the monitoring unit 210 may be controlled to collect battery data, and the communication unit 220 may be controlled to transmit the collected battery data to the master BMS 20.A capacitor Cj may be connected between the communication unit 220 and a first ground GND1. In this case, the first ground GND1 may be a signal ground located in the slave BMS 200j, but is not limited thereto. For example, the first ground GND1 may be implemented by an earth ground or a chassis ground.An inductor Lj may be connected between a second ground GND2 and a contact Nj between the first ground GND1 and the capacitor Cj. In this case, the second ground GND2 may be a chassis ground located in the battery module100j, but is not limited thereto. For example, the second ground GND2 may be implemented by an earth ground or a signal ground.According to an exemplary embodiment, referring toFIG. 2, the inductor Lj may be located in an external space between the battery module 100j and the slave BMS 200j. Specifically, one end of the inductor Lj connected to the contact Nj may be located outside a housing of the slave BMS 200j.The master BMS 20 may communicate with a superordinate control unit 2 to receive commands and information, and manage and control the slave BMS 200j included in at least one battery pack 10_j according to the received commands. In this case, the superordinate control unit 2 may be a control unit of a superordinate system (e.g., a vehicle, an ESS system, etc.) in which the battery system 1 is mounted.Referring back toFIG. 1, according to an exemplary embodiment, the master BMS 20 may communicate with each of the plurality of slave BMSs 2001 to 200N in a wireless manner to transmit various control signals or receive battery data. An external device illustrated inFIG. 1may be a charger in a charging mode for charging the battery 10, or a load (e.g., a motor) in a discharging mode for discharging the battery 10.The slave BMS 200j according to an exemplary embodiment is capable of wireless communication with the master BMS 20 without including a separate antenna device. This will be described in detail with reference toFIGS. 4and5below.FIG. 3is a block diagram illustrating the battery pack ofFIG. 1when operating in a monitoring mode in detail.FIG. 4is a block diagram illustratingthe battery pack ofFIG. 1when operating in an antenna mode in detail.FIG. 5is a block diagram illustrating an antenna ofFIG. 4in detail.According to an exemplary embodiment, the battery pack 10_j may operate in a monitoring mode for collecting battery data or in an antenna mode for communicating with the outside. Hereinafter, a structure of the battery pack 10_j in the monitoring mode will be described in detail with reference toFIG. 3, and a structure of the battery pack 10_j in the antenna mode will be described in detail with reference toFIGS. 4and5.Referring toFIG. 3, in the monitoring mode, the control unit 230 may control the communication unit 220 to transmit a direct current (DC) signal to the capacitor Cj.When the DC signal is applied to the capacitor Cj, a circuit as illustrated inFIG. 3may be formed according to the electrical characteristics of the capacitor Cj that is opened in response to the DC signal. That is, one end of the inductor Lj may be connected to the first ground GND1, and the other end of the inductor Lj may be connected to the second ground GND2. At this time, external noise may be removed by the inductor Lj.Referring toFIG. 4, in the antenna mode, the control unit 230 may control the communication unit 220 to transfer an AC signal having a predetermined frequency to the capacitor Cj.When the alternating current (AC) signal is applied to the capacitor Cj, a circuit as illustrated inFIG. 4may be formed according to the electrical characteristics of the inductor Lj that is opened in response to the AC signal. Specifically, a transmission line (bolded portion) connecting a first terminalconnected to the capacitor Cj, a second terminal connected to the first ground GND1, and a third terminal adjacent to the inductor Lj to each other may function as an inverted-F antenna. That is, in the antenna mode for communicating with the outside (e.g., the master BMS), an antenna Aj corresponding to an inverted-F antenna structure may be formed in the slave BMS 200j.The inverted-F antenna is an antenna made to improve impedance matching of an inverted-L antenna. In this case, the inverted-L antenna may be an antenna made by horizontally bending about 80% of a length of a monopole antenna with respect to the upper side thereof to reduce its height.Referring toFIG. 4, as an example, the antenna 200_Aj may convert an AC signal input through the communication unit 220 into an electromagnetic wave, and transmit the converted electromagnetic wave into the air. As another example, the antenna Aj may receive an electromagnetic wave, convert the received electromagnetic wave into an AC signal, and transfer the converted AC signal to the communication unit 220.Referring toFIG. 5, according to an exemplary embodiment, the antenna 200_Aj may resonate at a frequency having a wavelength λ of four times the antenna length AL. Specifically, the inverted-F antenna may be configured to have an antenna length (AL=λ/4) corresponding to 1/4 of a wavelength (λ) of a signal to be transmitted and received. In this case, the antenna length AL may correspond to a length between the inductor Lj and the first ground GND1.As an example, in order to transmit and receive a signal corresponding to a frequency of 2.45 GHZ, the antenna length AL may be 30.61 mm. As another example, in order to transmit and receive a signal corresponding to a frequencyof 915 MHZ, the antenna length AL may be 81.97mm.According to an exemplary embodiment, the antenna length AL may be determined according to the position (mounting distance) of the inductor Lj. That is, by a simple manipulation of changing the position where the inductor Lj is mounted, the slave BMS 200j can perform wireless communication with the master BMS 20 in various industrial scientific and medical (ISM) frequency bands.FIG. 6is a flowchart illustrating a wireless communication method according to an exemplary embodiment.Hereinafter, a wireless communication method and a battery system providing the same will be described with reference toFIGS. 1 to 6.Referring toFIG. 6, first, the monitoring unit 210 collects battery data (S100).The monitoring unit 210 may collect battery data at every predetermined cycle or in real time, and transmit the collected battery data to the control unit 230. In this case, the battery data may include at least one of a cell voltage, a cell current, and a cell temperature for each of the plurality of battery cells Cell1, Cell2, and Cell3. In addition, the battery data may include at least one of a module voltage, which is a voltage at both ends of the battery module 100j, and a module current, which is a current flowing through the battery module 100j.In step S100, the control unit 230 may control the communication unit 220 to transmit a DC signal to the capacitor Cj. Specifically, in a monitoring mode step in which the monitoring unit 210 collects battery data, when the direct current (DC) signal is applied to the capacitor Cj, a circuit as illustrated inFIG. 3may be formed according to the electrical characteristics of the capacitor Cj that isopened in response to the DC signal. That is, both ends of the inductor Lj may be connected to the first ground GND1 and the second ground GND2, respectively, such that the inductor Lj is positioned between the first ground GND1 and the second ground GND2. At this time, external noise may be removed by the inductor Lj. Then, the monitoring unit 210 may collect battery data less influenced by external noise.Next, the control unit 230 transmits the battery data collected through the communication unit 220 to the master BMS 20 (S200).According to an exemplary embodiment, the control unit 230 may transmit battery data to the BMS 20 through the communication unit 220. According to another exemplary embodiment, the control unit 230 may communicate with the outside in a wireless manner through the communication unit 220 to transmit various types of information or receive a control signalIn this case, the outside may be the master BMS 20, but is not limited thereto, and may include various devices located outside the slave BMS 200j.In step S200, the control unit 230 may control the communication unit 220 to transmit an AC signal having a predetermined frequency to the capacitor Cj. Specifically, when the alternating current (AC) signal is applied to the capacitor Cj, a circuit as illustrated inFIG. 4is formed according to the electrical characteristics of the inductor Lj that is opened in response to the AC signal. Specifically, a transmission line (bolded portion) connecting a first terminal connected to the capacitor Cj, a second terminal connected to the first ground GND1, and a third terminal adjacent to the inductor Lj to each other may function as an inverted-F antenna. That is, in an antenna mode step for communicatingwith the outside, an antenna 200_Aj corresponding to an inverted-F antenna structure may be formed in the slave BMS 200j.The inverted-F antenna is an antenna made to improve impedance matching of an inverted-L antenna. In this case, the inverted-L antenna may be an antenna made by horizontally bending about 80% of a length of a monopole antenna with respect to the upper side thereof to reduce its height.Referring toFIG. 4, as an example, the antenna 200_Aj may convert an AC signal input through the communication unit 220 into an electromagnetic wave, and transmit the converted electromagnetic wave into the air. As another example, the antenna Aj may receive an electromagnetic wave, convert the received electromagnetic wave into an AC signal, and transfer the converted AC signal to the communication unit 220.Referring back toFIG. 5, according to an exemplary embodiment, the antenna 200_Aj may resonate at a frequency having a wavelength λ of four times the antenna length AL. Specifically, the inverted-F antenna may be configured to have an antenna length (AL=λ/4) corresponding to 1/4 of a wavelength (λ) of a signal to be transmitted and received. In this case, the antenna length AL may correspond to a length between the inductor Lj and the first ground GND1.As an example, in order to transmit and receive a signal corresponding to a frequency of 2.45 GHZ, the antenna length AL may be 30.61 mm. As another example, in order to transmit and receive a signal corresponding to a frequency of 915 MHZ, the antenna length AL may be 81.97mm.According to an exemplary embodiment, the antenna length AL may be determined according to the position (mounting distance) of the inductor Lj. Thatis, by a simple manipulation of changing the position where the inductor Lj is mounted, the slave BMS 200j can perform wireless communication with the master BMS 20 in various industrial scientific and medical (ISM) frequency bands.Although the exemplary embodiments of the present disclosure have been described in detail above, the scope of the present disclosure is not limited thereto. Various modifications and improvements made by those skilled in the art also fall within the scope of the present disclosure. See more