WIRELESS BATTERY MANAGEMENT SYSTEM, WIRELESS BATTERY MANAGEMENT METHOD AND ELECTRIC VEHICLE

Abstract

A wireless battery management system includes a master and a plurality of slaves. The master is configured to wirelessly transmit a first command packet and scan a response packet transmitted wirelessly from each slave that received the first command packet among the plurality of slaves. The response packet is transmitted wirelessly in a time slot allocated to each slave.

Claims

1. A wireless battery management system, comprising: a master; and a plurality of slaves, wherein the master is configured to: wirelessly transmit a first command packet, and scan a response packet transmitted wirelessly from each slave that received the first command packet among the plurality of slaves, and wherein the response packet is transmitted wirelessly in a time slot allocated to each slave.

2. The wireless battery management system according to claim 1, wherein the master is further configured to identify, based on a corresponding ID included in the corresponding response packet, each slave that transmitted the corresponding response packet, among the plurality of slaves.

3. The wireless battery management system according to claim 1, wherein the master is further configured to classify each slave from which a corresponding ID included in the corresponding response packet is received, among the plurality of slaves, as a first group.

4. The wireless battery management system according to claim 3, wherein the master is further configured to: classify each slave not classified as the first group, among the plurality of slaves, as a second group, and wirelessly transmit a second command packet including the corresponding ID of each of the at least one slave classified as the second group.

5. The wireless battery management system according to claim 4, wherein each respective slave, among the at least one slave classified as the second group, is further configured to wirelessly transmit the corresponding response packet when the second command packet includes the corresponding ID of the respective slave classified as the second group.

6. The wireless battery management system according to claim 4, wherein the master is further configured to reclassify as the first group each slave, among the at least one slave previously classified as the second group, from which the corresponding ID included in the corresponding response packet is received within the threshold time following the master's transmission of the second command packet.

7. The wireless battery management system according to claim 1, wherein each slave is further configured to initialize a time count of a corresponding watchdog timer when receiving the first command packet.

8. The wireless battery management system according to claim 1, wherein each slave is further configured to be reset by a corresponding watchdog timer when the time count of the corresponding watchdog timer reaches a timeout.

9. The wireless battery management system according to claim 1, wherein each slave, among the plurality of slaves, is further configured to: increase a reference signal strength of itself by a predetermined value each time it is reset by a corresponding watchdog timer; and wirelessly transmit the corresponding response packet with the increased reference signal strength.

10. An electric vehicle comprising the wireless battery management system according to claim 1.

11. A wireless battery management method using a wireless battery management system, the method comprising: wirelessly transmitting, by a master of the wireless battery management system, a first command packet; and scanning, by the master, a response packet transmitted wirelessly from each slave that received the first command packet among a plurality of slaves of the wireless battery management system, wherein the response packet is transmitted wirelessly in a time slot allocated to each slave.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings illustrate a preferred embodiment of the present disclosure, and together with the detailed description of the present disclosure described below, serve to provide a further understanding of the technical aspects of the present disclosure, and thus the present disclosure should not be construed as being limited to the drawings.

[0025] FIG. 1 is a diagram exemplarily showing a configuration of an electric vehicle including a wireless battery management system.

[0026] FIG. 2 is a diagram exemplarily showing a detailed configuration of a master and a slave of FIG. 1.

[0027] FIG. 3 is a timing chart for describing a process of collecting battery information through wireless communication of a master of FIG. 1 with a plurality of slaves.

[0028] FIG. 4 is a flowchart showing a wireless battery management method according to a first embodiment of the present disclosure.

[0029] FIG. 5 is a flowchart showing a wireless battery management method according to a second embodiment of the present disclosure.

[0030] FIG. 6 is a diagram exemplarily showing a look up table for the second embodiment.

DETAILED DESCRIPTION

[0031] Hereinafter, the preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Prior to the description, it should be understood that the terms or words used in the specification and the appended claims should not be construed as being limited to general and dictionary meanings, but rather interpreted based on the meanings and concepts corresponding to the technical aspects of the present disclosure on the basis of the principle that the inventor is allowed to define the terms appropriately for the best explanation.

[0032] The terms including the ordinal number such as first, second and the like, are used to distinguish one element from another among various elements, but not intended to limit the elements by the terms.

[0033] Unless the context clearly indicates otherwise, it will be understood that the term comprises when used in this specification, specifies the presence of stated elements, but does not preclude the presence or addition of one or more other elements. Additionally, the term control unit as used herein refers to a processing unit of at least one function or operation, and this may be implemented by hardware and software either alone or in combination.

[0034] In addition, throughout the specification, it will be further understood that when an element is referred to as being connected to another element, it can be directly connected to the other element or intervening elements may be present.

[0035] FIG. 1 is a diagram exemplarily showing a configuration of an electric vehicle 1 according to the present disclosure.

[0036] Referring to FIG. 1, the electric vehicle 1 includes a battery pack 10, a relay 11, an inverter 12 and an electric motor 13.

[0037] The battery pack 10 includes N battery modules 20 and a wireless battery management system 30. N is a natural of 2 or greater. In the drawing, to distinguish the N battery modules 20, the numbers 20_120_N are sequentially given to the N battery modules 20 in a descending order of potential. In describing the common elements between the N battery modules 20_120_N, the numbers 20 or 20_i are given. The battery pack 10 may supply power required to drive the electric motor 13 of the electric vehicle 1.

[0038] The relay 11 is installed on a power line PL connecting the battery pack 10 to the inverter 12. The relay 11 is controlled to be turned on/off in response to a switching signal from a master 100 of the wireless battery management system 30 (hereinafter referred to as system).

[0039] The inverter 12 is provided to convert the direct current from the battery pack 10 to an alternating current in response to a control signal from the system 30 while the relay 11 is in a turn-on state. The electric motor 13 is a 3-phase alternating motor, and works by the alternating current power generated by the inverter 12.

[0040] The N battery modules 20_120_N are connected in series and/or in parallel. The battery module 20 includes at least one battery cell 21. The battery cell 21 may be a lithium ion battery cell. The battery cell 21 includes any type of repeatedly rechargeable battery and is not limited to a particular type.

[0041] The system 30 includes the master 100 and N slaves 200. In the drawing, to distinguish the N slaves 200, the numbers 200_1200_N are sequentially given to the N slaves 200. In describing the common elements between the N slaves 200_1200_N, the numbers 200 or 200_i are given.

[0042] The master 100 is configured to integratedly control the battery pack 10 through wireless communication with the N slaves 200_1200_N. Each of the plurality of slaves 200_1200_N is configured to wirelessly communicate with the master 100 using the slave's ID pre-allocated from the master 100. The master 100 stores the IDs allocated to the plurality of slaves 200_1200_N. The ID is identification information for distinguishing the plurality of slaves 200_1200_N.

[0043] The master 100 may communicate with a vehicle controller of the electric vehicle 1 via a wired network such as Controller Area Network (CAN). The master 100 may wirelessly communicate with each slave 200 through an antenna MA.

[0044] The plurality of slaves 200_1200_N is connected to a plurality of battery modules 20_120_N in a one-to-one relationship to collect and control battery information of the plurality of battery modules 20_120_N. Where i=1N, the slave 200_i is configured to monitor the state (for example, voltage, current, temperature) of the battery module 20_i. The power required for the operation of the slave 200_i may be supplied from the battery module 20_i.

[0045] The slave 200_i may wirelessly transmit data (hereinafter referred to as battery information) indicating the monitored state (for example, voltage, temperature and so on) of the battery module 20_i to the master 100 in response to a command wirelessly transmitted from the master 100.

[0046] The master 100 may calculate the state of charge (SOC) and the state of health (SOH) of the battery module 20_i or determine whether overvoltage, undervoltage, overcharge or overdischarge occurred in the battery module 20_i based on the battery information from the slave 200_i.

[0047] The plurality of slaves 200_1200_N is positioned at different areas in the battery pack 10 for different wireless communication distances from the master 100. The wireless communication distance between the slave 200_i and the master 100 may refer to a straight line distance between the antenna SA_i of the slave 200_i and the antenna MA of the master 100. Hereinafter, assume that the communication distance between the slave 200_i and the master 100 is shorter than the communication distance between the slave 200_i+1 and the master 100. For example, referring to FIG. 1, the antenna SA_i of the slave 200_i is positioned closer to the antenna MA of the master 100 than the antenna SA_i+1 of the slave 200_i+1. The antenna SA_i of the slave 200_i may be positioned on the upstream side of the antenna SA_i+1 of the slave 200_i+1, and the antenna SA_i+1 of the slave 200_i+1 may be positioned on the downstream side of the antenna SA_i of the slave 200_i.

[0048] Hereinafter, assume that a higher rank ID is allocated to a slave having a shorter wireless communication distance from the master 100. For example, the ID of the slave 200_i has a higher rank than the ID of the slave 200_i+1.

[0049] In the present disclosure, a command packet is wirelessly transmitted by the master 100, and may be classified into a main command packet and a sub command packet.

[0050] The master 100 wirelessly transmits the main command packet every reference time. The reference time (for example, 1 sec) is preset, considering the number of slaves 200_1200_N and the wireless communication distance from each slave 200. The main command packet may include information requesting the plurality of slaves 200_1200_N to transmit the battery information of the plurality of battery modules 20_120_N to the master 100.

[0051] The master 100 is configured to perform the operation of classifying each of the plurality of slaves 200_1200_N as a first group or a second group at least once for a standby period from the time point at which the master 100 transmitted the main command packet until the master 100 will transmit the next main command packet. The master 100 may scan a response packet from the second group during a threshold time (for example, 0.3 sec) from the time point at which the master 100 transmitted the main command packet.

[0052] When at least one of the plurality of slaves 200_1200_N is classified as the second group, the master 100 may be configured to wirelessly transmit the sub command packet at least once within the standby period. The sub command packet is for inducing each slave 200 of the second group to wirelessly transmit the response packet.

[0053] When the sub command packet includes the ID of the slave 200, the slave 200 may be configured to wirelessly transmit the response packet as a response to the sub command packet to the master 100.

[0054] The master 100 classifies each slave 200 that wirelessly transmitted the response packet within the threshold time from the time point at which the sub command packet was transmitted as the first group from the second group. Each of the remaining slaves 200 of the second group is maintained as the second group.

[0055] FIG. 2 is a diagram exemplarily showing the detailed configuration of the master 100 and the slave 200 of FIG. 1.

[0056] Referring to FIG. 2, the master 100 includes an antenna MA, a wireless communication circuit 110 and a control unit 120. The power required to operate the master 100 may be supplied from at least one of the plurality of battery modules 20_120_N or an external power source.

[0057] The wireless communication circuit 110 is configured to wirelessly transmit a command packet to the slave 200 through the antenna MA. Additionally, the wireless communication circuit 110 is configured to receive a response packet from the slave 200 through the antenna MA.

[0058] The control unit 120 is operably connected to the wireless communication circuit 110. The control unit 120 may determine a request for at least one of the plurality of slaves 200_1200_N based on a signal (for example, indicating the battery information) received through the antenna MA, and wirelessly transmit the command packet including data indicating the request to at least one of the plurality of slaves 200_1200_N.

[0059] The control unit 120 may be implemented in hardware using at least one of application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), microprocessors and electrical units for performing other functions. The control unit 120 may have a memory device embedded therein, and the memory device may include, for example, RAM, ROM, register, hard disk, optical recording media or magnetic recording media. The memory device may store, update and/or erase programs including a variety of control logics executed by the control unit 120 and/or data created when the control logics are executed.

[0060] The slave 200 includes an antenna SA, a sensing unit 210, a wireless communication circuit 220 and a control unit 230. The slave 200 may further include a watchdog timer 240.

[0061] The sensing unit 210 includes a voltage measurement circuit 211 and a temperature sensor 212. The sensing unit 210 may further include a current sensor (not shown). The voltage measurement circuit 211 includes at least one voltage sensor.

[0062] The voltage measurement circuit 211 measures a module voltage of the battery module 20. The module voltage is a voltage across the battery module 20. The voltage measurement circuit 211 may further measure a cell voltage of each battery cell 21 included in the battery module 20. The cell voltage is a voltage across the battery cell 21. The voltage measurement circuit 211 transmits a voltage signal indicating the module voltage and the cell 21 voltage to the control unit 230.

[0063] The temperature sensor 212 is positioned at a predetermined distance from the battery module 20 to transmit a temperature signal indicating the temperature of the battery module 20 to the control unit 230.

[0064] The current sensor is installed on a charge/discharge current path of the battery pack 10 to measure an electric current flowing during the charge/discharge of the battery pack 10, and transmit a current signal indicating the measured current to the control unit 230.

[0065] The wireless communication circuit 220 is connected to the control unit 230 and the antenna SA. The wireless communication circuit 220 may be implemented in hardware using RF System on Chip (SoC). The wireless communication circuit 220 may wirelessly transmit data to the master 100 or other slave 200 or wirelessly receive data from the master 100 or other slave 200 through the antenna SA.

[0066] The control unit 230 may be operably coupled to the sensing unit 210 and the wireless communication circuit 220 to individually control the operation of each of the sensing unit 210 and the wireless communication circuit 220. The control unit 230 may be implemented in hardware using at least one of application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), microprocessors and electrical units for performing other function. The control unit 230 may have a memory device embedded therein, and the memory device may include, for example, RAM, ROM, register, hard disk, optical recording media or magnetic recording media. The memory device may store, update and/or erase programs including a variety of control logics executed by the control unit 230 and/or data created when the control logics are executed.

[0067] The wireless communication circuit 220 is configured to selectively perform at least one of preset functions in response to a signal from the master 100 or other slave 200 wirelessly received through the antenna SA.

[0068] When a signal is received through the antenna SA, the wireless communication circuit 220 may measure the signal strength of the received signal. When the command packet is received from the master 100 through the antenna SA, the wireless communication circuit 220 may wirelessly transmit the response packet as a response to the command packet to the master 100. The response packet is a signal for reporting that the slave 200 succeeded to receive the command packet wirelessly transmitted from the master 100 to the master 100. The response packet includes battery information required by the command packet.

[0069] The watchdog timer 240 is operably coupled to the control unit 230 and/or the wireless communication circuit 220. The watchdog timer 240 is provided to repeatedly monitor whether the slave 200 is malfunctioning.

[0070] The control unit 230 outputs an initialization signal to the watchdog timer 240 in response to the reception of the command packet. A time count of the watchdog timer 240 is initialized by the initialization signal. The time count of the watchdog timer 240 indicates a period of time that has passed from the time at which the time count was initialized last.

[0071] In a situation where the command packet from the master 100 cannot be received by the slave 200 due to a malfunction of the control unit 230 and/or the wireless communication circuit 220, the time count may reach a timeout. The watchdog timer 240 outputs a rest signal to the control unit 230 and/or the wireless communication circuit 220 each time the time count reaches a predetermined timeout.

[0072] The timeout may be equal to or less than the reference time or the threshold time. Accordingly, when the command packet from the master 100 is not received by the control unit 230 for the standby period, the watchdog timer 240 outputs the reset signal at least once for the standby period.

[0073] The slave 200 is reset by the reset signal. Resetting the slave 200 may refer to resetting the control unit 230 and/or the wireless communication circuit 220. Each time the slave 200 is reset by the watchdog timer 240, the control unit 230 may increase the reference signal strength for wireless transmission of the response packet by a predetermined value.

[0074] FIG. 3 is a timing chart for describing a process of collecting the battery information through wireless communication of the master 100 of FIG. 1 with the plurality of slaves 200_1200_N.

[0075] In FIG. 3, a time point T10 denotes a start time of a cycle, a time point T20 denotes a start time of the next cycle, T.sub.ref denotes the reference time, T.sub.th denotes the threshold time, and T.sub.out denotes the timeout. T.sub.ref or T.sub.th is divided into N or more time slots, and among them, assume that N time slots are sequentially allocated to the plurality of slaves 200_1200_N.

[0076] The threshold time T.sub.th may be equal to or less than of the reference time T.sub.ref. In FIG. 3, the threshold time T.sub.th is of the reference time T.sub.ref, and the timeout T.sub.out is shorter than the threshold time T.sub.th.

[0077] At the time point T10, the master 100 wirelessly transmits a main command packet CP1 to the plurality of slaves 200_1200_N. The master 100 may wirelessly transmit the main command packet CP1 with a predetermined first signal strength. The main command packet CP1 may be transmitted to the plurality of slaves 200_1200_N simultaneously through a broadcasting method. The main command packet CP1 may include first data D11 and second data D12, and may further include third data D13. The first data D11 indicates whether or not the corresponding command packet was initially transmitted by the master 100 at the current cycle (i.e., whether the corresponding command packet is a main command packet or a sub command packet). For example, the first data D11 being a first value (for example, 0) indicates that the corresponding command packet is a main command packet. The second data D12 includes a request for the plurality of slaves 200_1200_N. The request is for requesting a slave belonging to the second group to perform a specific function (for example, voltage measurement, cell balancing). The third data D13 includes the IDs of all of the plurality of slaves 200_1200_N.

[0078] Each of the plurality of slaves 200_1200_N wirelessly transmits the response packet RP at the time slot allocated to each slave 200_1200_N when wirelessly receiving the main command packet CP1. That is, where i=1N, the slave 200_i wirelessly transmits the response packet RP at the i.sup.th time slot among N or more time slots.

[0079] The master 100 scans the response packet RP from the plurality of slaves 200_1200_N during the threshold time T.sub.th from the time point T10.

[0080] Assume that the master 100 received the response packet RP from the slave 200_1, 200_3200_N-2, 200_N within the threshold time T.sub.th from the time point T10, but did not receive the response packet RP from the slave 200_2, 200_N-1.

[0081] Then, the master 100 may set the slaves 200_1, 200_3200_N-2, 200_N to which the IDs included in the response packet RP are allocated as the first group, and the remaining slaves 200_2, 200_N-1 as the second group.

[0082] When the timeout T.sub.out is equal to or less than the threshold time T.sub.th, each of the slaves 200_2, 200_N-1 of the second group may be reset by the watchdog timer 240 before a time point T11.

[0083] At the time point T11, only two slaves 200_2, 200_N-1 are set as the second group. At the time point T11, the master 100 wirelessly transmits a sub command packet CP2. The sub command packet CP2 may include first data D21, second data D22 and third data D23. The first data D21 has a second value (for example, 1), and this indicates that the corresponding command packet is the sub command packet for requesting the response packet of the second group. The second data D22 includes a request for the slave 200_2, 200_N-1 of the second group. The third data D23 includes the ID of each of the slaves 200_2, 200_N-1 of the second group.

[0084] Since the sub command packet CP2 includes only the IDs of the two slaves 200_2, 200_N-1 belonging to the second group, the slaves 200_1, 200_3200_N-2, 200_N classified as the first group may not respond to (ignore) the sub command packet CP2. For example, the slaves 200_1, 200_3200_N-2, 200_N may erase the sub command packet CP2 from their memory devices.

[0085] In contrast, when receiving the sub command packet CP2, each slave 200_2, 200_N-1 of the second group may determine a relative rank of the slave's ID to all the IDs included in the sub command packet CP2. The slave 200_2 determines the rank of the slave's ID as highest since there is no ID having a higher rank than the ID of slave 200_2 among all the IDs included in the third data D23. The slave 200_N-1 may determine the slave's ID as second highest since only one of the IDs included in the third data D23 has a higher rank than the ID of the slave 200_N-1.

[0086] The slave 200_2 wirelessly transmits the response packet RP at a timing (for example, the first time slot) associated with the relative rank of the ID of the slave 200_2. The slave 200_N-1 wirelessly transmits the response packet RP including the ID of the slave 200_N-1 at the timing (for example, the second time slot) associated with the relative rank of the slave's ID.

[0087] During the threshold time T.sub.th from the time point T11, the master 100 scans the response packet RP from the slave 200_2, 200_N-1 of the second group. Assume that the master 100 received the response packet RP from the slave 200_2, but did not receive the response packet RP from the slave 200_N-1, within the threshold time T.sub.th from the time point T11. Then, the master 100 sets the slave 200_2 as the first group from the second group, while maintains the slave 200_N-1 as the second group.

[0088] The slave 200_N-1 of the second group is reset by the watchdog timer 240 before a time point T12.

[0089] At the time point T12, the master 100 wirelessly transmits a sub command packet CP3. The sub command packet CP3 may include first data D31, second data D32 and third data D33. The first data D31 of the sub command packet CP3 may have a second value. The second data D32 includes a request for the slave 200_N-1 of the second group. The third data D33 includes the ID of the slave 200_N-1 of the second group.

[0090] Since the sub command packet CP3 includes only the ID of the slave 200_N-1 of the second group, the slave 200_1200_N-2, 200_N set as the first group may ignore the sub command packet CP3. The slave 200_N-1 may determine a relative rank of the slave's ID to all the IDs included in the sub command packet CP3. Since the third data D33 includes only the ID of the slave 200_N-1, the slave 200_N-1 determines the rank of the slave's ID as highest. Accordingly, the slave 200_N-1 transmits the response packet RP to the master 100 at the timing (for example, the first time slot) associated with the relative rank of the slave's ID.

[0091] During the threshold time T.sub.th from the time point T12, the master 100 scans the response packet RP from the slave 200_N-1 of the second group. When the master 100 receives the response packet RP from the slave 200_N-1 within the threshold time T.sub.th from the time point T12, the master 100 classifies the slave 200_N-1 as the first group from the second group. Then, since the number of members of the second group is 0, the master 100 does not wirelessly transmit an additional sub command packet and stands by before the time point T20 arrives.

[0092] Meanwhile, the slave 200 may wirelessly transmit the response packet RP with a predetermined second signal strength. Alternatively, each slave 200 may wirelessly transmit the response packet RP with the slave's reference signal strength. For example, for the slave 200_i-1, when the number of times the slave 200_i-1 was reset is x, the reference signal strength of the slave 200_i-1 may equal the sum of a product obtained by multiplying a predetermined value by x and the predetermined second signal strength.

[0093] FIG. 4 is a flowchart showing a wireless battery management method according to a first embodiment of the present disclosure. The method of FIG. 4 may be performed every reference time T.sub.ref.

[0094] Referring to FIGS. 1 to 4, in step S410, the master 100 wirelessly transmits the main command packet CP1. The main command packet CP1 may be wirelessly transmitted with the predetermined first signal strength. When receiving the main command packet CP1, each slave 200 may wirelessly transmit the response packet RP including the slave's ID with the predetermined second signal strength or the slave's reference signal strength. When receiving the main command packet CP1, each slave 200 may initialize the time count of the watchdog timer 240 provided in the slave 200.

[0095] In step S420, the master 100 scans the response packet RP from the plurality of slaves 200_1200_N during the threshold time T.sub.th.

[0096] In step S430, the master 100 classifies each slave 200 to which the ID included in each response packet RP received within the threshold time T.sub.th is allocated as the first group, and each slave 200 not classified as the first group as the second group.

[0097] In step S440, the master 100 determines whether at least one of the plurality of slaves 200_1200_N is classified as the second group. When a value of the step S440 is Yes, step S450 is performed. When the value of the step S440 is No, the method may end.

[0098] In step S450, the master 100 wirelessly transmits the sub command packet CP2 including the ID of each slave 200 classified as the second group. The sub command packet CP2 may be wirelessly transmitted with the predetermined first signal strength. Each slave 200 of the second group wirelessly transmits the response packet RP including the slave's ID with the predetermined second signal strength or the slave's reference signal strength when receiving the sub command packet CP2.

[0099] In step S460, the master 100 scans the response packet RP from each slave 200 of the second group during the threshold time T.sub.th.

[0100] In step S470, the master 100 classifies each slave 200 of the second group to which the ID included in each response packet RP received within the threshold time T.sub.th is allocated as the first group. Each of the remaining slaves 200 of the second group is maintained as the second group. After the step S470, the method may move to the step S440.

[0101] FIG. 5 is a flowchart showing a wireless battery management method according to a second embodiment of the present disclosure, and FIG. 6 shows a look up table for the second embodiment. The method of FIG. 5 may be performed every reference time T.sub.ref.

[0102] Referring to FIGS. 1 to 3, 5 and 6, in step S510, the master 100 wirelessly transmits the main command packet CP1. The main command packet CP1 may be wirelessly transmitted with the predetermined first signal strength. When receiving the main command packet CP1, each slave 200 may wirelessly transmit the response packet RP including the slave's ID with the predetermined second signal strength or the slave's reference signal strength. When receiving the main command packet CP1, each slave 200 may initialize the time count of the watchdog timer 240 provided in the slave 200.

[0103] In step S520, the master 100 scans the response packet RP from the plurality of slaves 200_1200_N during the threshold time T.sub.th.

[0104] In step S530, the master 100 classifies each slave 200 to which the ID included in each response packet RP received within the threshold time T.sub.th is allocated as the first group, and each slave 200 not classified as the first group as the second group.

[0105] In step S540, the master 100 determines whether at least one of the plurality of slaves 200_1200_N is classified as the second group. When a value of the step S540 is Yes, step S545 is performed. When the value of the step S540 is No, the method may end.

[0106] In step S545, the master 100 determines an amplified signal strength. In detail, the master 100 determines a gain value from the look up table 600 based on the lowest ranked ID among the IDs of all the slaves 200 classified as the second group. The look up table 600 stores a plurality of gain values A.sub.1A.sub.N associated with the IDs S.sub.1S.sub.N of the plurality of slaves 200_1200_N in a one-to-one relationship. The minimum value of the plurality of gain values A.sub.1A.sub.N is greater than 1. In the look up table 600, a larger gain value is associated with a lower ranked ID. That is, A.sub.1<A.sub.2, . . . . A.sub.N-1<A.sub.N. For example, as shown in FIG. 3, when the slave 200_2 and the slave 200_N-1 belong to the second group, the lowest ranked ID is S.sub.N-1, and thus A.sub.N-1 determined as the gain value, and the amplified signal strength is determined to be equal to the multiplication of the predetermined first signal strength by the gain value A.sub.N-1.

[0107] In step S550, the master 100 wirelessly transmits the sub command packet CP2 including the ID of each slave 200 classified as the second group. The sub command packet CP2 may be wirelessly transmitted with the amplified signal strength determined in the step S545. Each slave 200 of the second group wirelessly transmits the response packet RP including the slave's ID with the predetermined second signal strength or the slave's reference signal strength when receiving the sub command packet CP2.

[0108] In step S560, the master 100 scans the response packet RP from each slave 200 of the second group during the threshold time T.sub.th.

[0109] In step S570, the master 100 classifies each slave 200 of the second group to which the ID included in each response packet RP received within the threshold time T.sub.th is allocated as the first group. Each of the remaining slaves 200 of the second group is maintained as the second group. After the step S570, the method may move to the step S540.

[0110] The embodiments of the present disclosure described hereinabove are not implemented only through the apparatus and method, and may be implemented through programs that perform functions corresponding to the configurations of the embodiments of the present disclosure or recording media having the programs recorded thereon, and such implementation may be easily achieved by those skilled in the art from the disclosure of the embodiments previously described.

[0111] While the present disclosure has been hereinabove described with regard to a limited number of embodiments and drawings, the present disclosure is not limited thereto and it is obvious to those skilled in the art that various modifications and changes may be made thereto within the technical aspects of the present disclosure and the equivalent scope of the appended claims.

[0112] Additionally, as many substitutions, modifications and changes may be made to the present disclosure described hereinabove by those skilled in the art without departing from the technical aspects of the present disclosure, the present disclosure is not limited by the above-described embodiments and the accompanying drawings, and some or all of the embodiments may be selectively combined to allow various modifications.