Method for collecting power consumption data, terminal equipment and storage medium

Methods of collecting electricity consumption data, terminal equipment, and storage media technical fields

[0001] The present invention relates to the technical field of power data collection, and in particular, to a method, terminal equipment, and computer readable storage medium for collecting power data.

Background technique

[0002] With the advancement of the digitization of power distribution systems, more and more power data needs to be effectively aggregated from end-side devices to the cloud. The current power data convergence channel is composed of two parts, namely, the north channel: the channel from the edge-side equipment to the cloud; the south channel: the channel from the end-side equipment to the edge-side equipment. Among them, the northbound channel is dominated by 4G networks and will be upgraded to 5G networks in the future. There is no bottleneck in data transmission, while the southbound channel is dominated by HPLC (wideband power line carrier), and the bandwidth and reliability of HPLC are far inferior to 4G networks. At present, there have been cases in which only part of the power data can be selectively transmitted due to insufficient bandwidth, and the failure of individual nodes due to the instability of the carrier network and user load interference, and the data cannot be effectively transmitted. In the future, as the power data needs to be transmitted further With growth, these problems will become more serious. In order to solve these problems, on the one hand, it is necessary to improve the performance of HPLC itself, on the other hand, it is also necessary to apply the HPLC network more efficiently according to the characteristics of the electric power industry.

[0003] Among them, the power consumption collection system is a typical application system in the power industry. Edge-side devices (concentrators or energy controllers, etc.) read data from end-side devices (smart meters or other power sensing devices) through HPLC. , The edge measurement equipment uploads the data to the cloud (master station) through the 4G network. Smart meters as end-side devices are stored in a meter box. There are often several or a dozen smart meters in a meter box. On the one hand, these smart meters communicate with the concentrator through HPLC, and on the other hand, these smart meters also have a 485 bus. Local communication capabilities such as, infrared, Bluetooth, etc., then, how to use this local communication capability to replace HPLC communication to a certain extent, so that HPLC network can be applied more efficiently, has become a key issue that needs to be solved urgently in the power industry. In addition, when applying local communication capabilities, because multiple smart meters usually communicate in multicast mode, how to solve the conflict problem in the broadcast, how to automatically obtain the address of each electric energy meter and select the communication agent, these It will be a problem that needs to be solved in the next step.

Summary of the invention

[0004] The present invention provides a method for collecting electricity consumption data, terminal equipment, and computer-readable storage medium to solve the problem of insufficient bandwidth, instability, and user load interference in the existing HPLC network. Technical issues of effective transmission.

[0005] According to one aspect of the present invention, there is provided a method for collecting electricity consumption data, including the following steps:

[0006] Step S1: construct a local alliance of smart meters in a specified time period, and select a proxy node from each node of the local alliance, the local alliance of smart meters includes a plurality of nodes that communicate through multicast;

[0007] Step S2: During the non-alliance construction period, the proxy node broadcasts the data aggregation request information to each node in the local alliance one by one, and each node in the local alliance responds to the electricity consumption data collected by itself, and the proxy node sends each node in the local alliance The collected electricity consumption data is aggregated and sent to the edge-side equipment in a unified manner;

[0008] Step S3: The edge-side device transmits the received power consumption data to the cloud.

[0009] Further, in the step S1, a local alliance of the smart watch is constructed during a specified period of time, and each of the local alliances

The process of selecting a proxy node from the nodes includes the following steps:

[0010] Step S11: Select an alliance construction period;

[0011] Step S12: The alliance construction period is sequentially divided into election time slots, election results release time slots, address collection time slots, and agent appointment time slots, and only corresponding message communication is allowed in each time slot;

[0012] Step S13: Select multiple nodes that can communicate directly in a local area and build a local alliance;

[0013] Step S14: each node performs message communication in multiple time slots. After the alliance convener is elected, the alliance convener designates the proxy node of the local alliance.

[0014] Further, in the election time slot, each node needs to publish an election message, and the first node to publish the election message is elected as the convener of the alliance;

[0015] In the election result release time slot, only the elected convener of the alliance is allowed to release election result messages;

[0016] In the address collection time slot, nodes that are not in the known address list included in the election result message need to publish an address collection message to announce their address to the convener of the alliance;

[0017] In the agent appointment time slot, only the convener of the alliance is allowed to issue an agent appointment message containing the address of the agent node.

[0018] Further, after the convener of the alliance collects the addresses and phases of the nodes in the local alliance, each of the three phases A, B, and C is selected as a proxy node.

[0019] Further, in the step S12, the keep-alive time slot and the keep-alive dispute time slot are also split before the election time slot. In the keep-alive time slot, only the convener of the alliance is allowed to release keep-alive messages, and other ordinary members Only receive keep-alive messages. When only one alliance convener releases the keep-alive message, the keep-alive message is successful, and the alliance is not disputed. When at least two alliance conveners release the keep-alive message, or the keep-alive message is superimposed due to communication conflicts If the verification fails together, the keep-alive fails, and the alliance is disputed;

[0020] In the keep-alive dispute time slot, when the alliance has no dispute, there is no message transmission in this time slot. When the alliance has a dispute, other ordinary members send a keep-alive dispute message to notify the convener of the alliance that there is a dispute in the alliance. After the convener receives the keep-alive dispute message in this time slot or the message overlay verification fails due to communication conflicts, the identity of the convener of the alliance is changed to an ordinary member, and a new convener is re-elected in the subsequent election time slot .

[0021] Further, when multiple nodes need to publish messages in the same time slot, the message publishing time of each node is set based on the following process:

[0022] Select the starting time T0 of the corresponding time slot, on this basis, the delay does not exceed the number of minutes of the time slot duration, and then the delay does not exceed the number of seconds of minutes, by selecting different minutes and seconds to get the difference between each node The moment the news was released. [0023] Further, the number of minutes and seconds that each node is delayed is determined by the following process:

[0024] Select the character string of the node address individually, or select the concatenated character string of the node address and the current day-level timestamp and/or the current time point, convert the character string into a long integer by the Hash algorithm, and use the long integer to The remaining minutes of the time slot duration are obtained by taking the remainder operation to obtain the number of minutes of delay, and the remaining seconds are obtained by taking the remaining operation on 60 seconds using the long integer.

[0025] Further, in the election result release time slot, if there is a dispute about the election result, the alliance construction process will be restarted in the alliance construction period of the next day.

[0026] In addition, the present invention also provides a terminal device, including a processor and a memory, the memory is stored with a computer program, the processor by calling the computer program stored in the memory, for executing the above The steps of the described method.

[0027] In addition, the present invention also provides a computer-readable storage medium for storing a computer program for collecting electricity consumption data, and the computer program executes the steps of the method described above when running on a computer.

[0028] The present invention has the following effects:

[0029] The method of collecting electricity consumption data of the present invention firstly constructs a local alliance based on multiple nodes that can communicate directly in a local area and selects a proxy node, and the construction of the alliance is carried out within a specified time period, and the data collection process It is carried out during the non-alliance construction period to avoid communication conflicts, and then the agent node broadcasts the data aggregation request information to each node in the alliance one by one, and each node responds to the electricity consumption data collected by itself, which further avoids the inter-node communication in the alliance. In the case of communication conflicts, the proxy node aggregates the power consumption data of each node and sends it to the edge-side device through HPLC. Finally, the edge-side device transmits the received power consumption data to the cloud, which greatly reduces the difference between the end-side device and the edge-side device. The number of times of communication and the amount of communication data, which greatly improves the transmission capacity of power data on the HPLC, can also solve the problem of the failure of individual HPLC nodes that cause the power data to be unable to be effectively transmitted.

[0030] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. Hereinafter, the present invention will be described in further detail with reference to the drawings.

Description of the drawings

[0031] The drawings constituting a part of the present application are used to provide a further understanding of the present invention, and the exemplary embodiments and descriptions of the present invention are used to explain the present invention, and do not constitute an improper limitation of the present invention. In the attached picture:

[0032] FIG. 1 is a schematic flowchart of a method for collecting electricity consumption data according to a preferred embodiment of the present invention.

[0033] FIG. 2 is a schematic diagram of a sub-flow of step S1 in FIG. 1.

Detailed ways

[0034] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention can be implemented in a variety of different ways defined and covered below.

[0035] As shown in FIG. 1, a preferred embodiment of the present invention provides a method for collecting electricity consumption data, including the following steps: [0036] Step S1: Build a local alliance of smart meters at a specified time period, and start from each of the local alliances A proxy node is selected from the nodes, and the local alliance of the smart table includes a plurality of nodes that communicate in a multicast manner;

[0037] Step S2: During the non-alliance construction period, the proxy node broadcasts the data aggregation request information to each node in the local alliance one by one, and each node in the local alliance responds to the electricity consumption data collected by itself, and the proxy node sends each node in the local alliance The collected electricity consumption data is aggregated and sent to the edge-side equipment in a unified manner;

[0038] Step S3: The edge-side device transmits the received power consumption data to the cloud.

[0039] It can be understood that the method of collecting electricity consumption data in this embodiment first constructs a local alliance based on multiple nodes that can communicate directly in a local area and selects a proxy node, and the construction of the alliance is carried out within a specified time period. , And the data collection process is carried out during the non-alliance construction period to avoid communication conflicts. Then the agent node broadcasts the data aggregation request information to each node in the alliance one by one, and each node responds to the electricity data collected by itself, which further avoids Communication conflicts between nodes in the alliance. The proxy node aggregates the power consumption data of each node and sends it to the edge-side equipment through HPLC. Finally, the edge-side equipment transmits the received power consumption data to the cloud, which greatly reduces the end-side equipment. The number of communications and the amount of communication data with edge-side devices have greatly improved the transmission capacity of power data on the HPLC, and at the same time, it can solve the problem of ineffective transmission of power data due to the failure of individual HPLC nodes.

[0040] It can be understood that in the step S1, the smart watch local alliance is composed of multiple nodes that can directly communicate in a local area, and these nodes may be all smart meters in a meter box that communicate through infrared modules. It can also be all smart meters in an area that communicate through wireless modules such as 485 bus or Bluetooth. In addition, as shown in Figure 2,

In the step S1, the process of constructing a local alliance of smart tables in a specified time period and selecting a proxy node from each node of the local alliance includes the following steps:

[0041] Step S11: Select an alliance construction period;

[0042] Step S12: The alliance construction period is divided into election time slots, election results release time slots, address collection time slots, and agent appointment time slots in turn, and only corresponding message communication is allowed in each time slot;

[0043] Step S13: Select multiple nodes that can communicate directly in a local area and build a local alliance;

[0044] Step S14: Each node performs message communication in multiple time slots. After the alliance convener is elected, the alliance convener designates the proxy node of the local alliance.

[0045] Wherein, in the step S11, in order to avoid communication conflicts, the process of alliance building can be performed in a designated time period, for example, 1:00 to 2:00 in the morning.

[0046] In the step S12, the alliance construction period is sequentially divided into election time slots, election results release time slots, address collection time slots, and agent appointment time slots, and only corresponding message communication is allowed in each time slot. For example, the election time slot only allows the sending of election messages, the election result release time slot only allows the release of election result messages, the address collection time slot only allows the release of address collection messages, and the agent appointment time slot only allows the release of agent appointment messages. By splitting the alliance construction period into multiple time slots, and only allowing corresponding message communication in each time slot, the multi-node communication content in the alliance can be effectively managed and communication conflicts within the alliance can be avoided.

[0047] It can be understood that in one or more of the time slots, there may be situations in which multiple nodes publish messages. At this time, it is necessary to consider the problem of communication conflicts between nodes in each time slot. When there are multiple nodes that need to publish messages in the same time slot, set the message publishing time of each node based on the following process, so that each node publishes the message in the corresponding time slot at a different time, so as to avoid Communication conflicts between nodes occur in the time slot.

[0048] Select the starting time T of the corresponding time slot₀On this basis, the delay does not exceed the number of minutes of the time slot duration, and then the delay does not exceed the number of seconds of minutes. By selecting different minutes and seconds, different message release times for each node are obtained. [0049] Wherein, the number of minutes and seconds that each node is delayed is determined by the following process:

[0050] Select the character string of the node address individually, or select the concatenated character string of the node address and the current day-level timestamp and/or the current time point, convert the character string into a long integer by the Hash algorithm, and use the long integer to The remaining minutes of the time slot duration are obtained by taking the remainder operation to obtain the number of minutes of delay, and the remaining seconds of 60 seconds are obtained by using the long integer to obtain the remaining number of seconds.

[0051] For example, the number of minutes can be selected as HASH(ADDR||DATE) %T_mOr HASH(ADDR||TIME) %T_nWait, the number of seconds can be HASH(ADDR) %60 or HASH(ADDR||DATE||TIME) %60, etc. Among them, HASH represents a hash algorithm, which is used to convert a character string into a long integer. Specifically, MD5 algorithm, SHA1 algorithm, SHA256 algorithm, etc. can be used. T_mIt is the minute duration of the time slot. For a 5-minute time slot, it is 5, ADDR represents the node address, DATE represents the day-level timestamp, such as "20201216" represents December 16, 2020, and TIME represents the current time point, usually in seconds For example, "222222" means twenty-two twenty-two minutes and twenty-two seconds, | | means a string splicing operation, and% means a remainder operation, which is used to ensure that the delay in minutes does not exceed the time slot minutes Duration, the number of seconds of delay is less than 60s. If the node address is "12345" and the day-level timestamp is "20201216", then ADDR||DATE is "1234520201216". The purpose of adding the day-level timestamp is to avoid conflicts in the calculation of the day and avoid the calculation of the next day. The same conflict arises. Therefore, as a preference, the present invention preferably adopts the splicing of the node address and the day-level timestamp or the character string of the current time point to calculate the message publishing time of each node.

[0052] Since the addresses of each node are different, the values converted by the Hash algorithm are also different. After taking the remainder of the time slot minutes, the number of minutes will be delayed. The number of minutes depends on the size of the time slot minutes. Smaller chance of coincidence,

This value also has a small coincidence probability for the number of seconds to be delayed after taking the remainder of 60. However, the sending time of each node is the start time of the time slot + the number of minutes after the delay + the number of seconds after the delay, the number of minutes and the delay The probability that the delay seconds overlap at the same time is very small, so the communication conflict problem between nodes in each time slot can be basically solved. In addition, the day-level timestamp or the current time point and the node address can be combined with the node address before the Hash algorithm conversion. Even if the number of delayed minutes and the number of delayed seconds coincide with each other at the same time, in the calculation of the next day, the new Day-level timestamps will eliminate this overlap.

[0053] It can be understood that in the election time slot, each node needs to publish an election message. The content of the election message includes the message type, the sender's node address, phase, identity, and CRC check value. The message type is used for Indicates that the message is an election message, the sender's node address is used to record the sender's address, the phase is used to record the sender's phase, the identity is used to identify itself as the convener of the alliance or an ordinary member, and the CRC check value is used for verification Election news. In addition, the first node that publishes the election message is elected as the convener of the alliance. After the first election message is sent, the remaining nodes need to accept the result. In the subsequent election messages sent by the remaining nodes, their identities are changed to ordinary members, and the first election message is sent. The identity of a node that sends an election message is the convener of the alliance. The convener of the alliance receives election messages sent by other nodes, verifies and records its address. In the election time slot, the election of the convener of the alliance and the information collection of ordinary members can be completed. In addition, since each node needs to send election messages in the election time slot, it is necessary to avoid communication conflicts in this time slot, and the above process can be effective to calculate the time when each node sends election messages in the election time slot. Avoid communication conflicts between nodes. Among them, the duration of the election time slot can be set to 35 minutes.

[0054] In the election result release time slot, only the elected alliance convener is allowed to release the election result message. When only one alliance convener sends the election result message first, then the node is successfully elected. If there are at least two alliance conveners both Send the election result message, that is, at least two nodes are the first to send the election message at the same time in the election time slot, which means that the election result is disputed, and the alliance construction process will be restarted in the next day's alliance construction period, that is, the next day's election The new day-level timestamp is used in the time slot to re-elect a new convener of the alliance. It can be understood that the election result message is a message issued by the elected convener of the alliance, which includes the message type, the node address of the sender, the number of known node addresses, the known node addresses, a random day-level timestamp, CRC check value, where the message type is used to indicate that the message is an election result release message, the senders node address is used to record the node address of the sender, the convener of the alliance, and the number of known node addresses is used to indicate the presence of the convener of the alliance The number of node addresses that have been collected during the election phase. Known node addresses are used to indicate the node addresses that the convener of the alliance has collected during the election phase. The random day-level timestamp needs to be different from the timestamp of the day, which is used in the next The time slot (that is, the address collection time slot) replaces the day-level time stamp of the day. Multiple nodes that have already experienced communication conflicts in the election time slot need to use this random time when calculating their own message sending time in the address collection time slot. The day-level time stamp is used to avoid sending time conflicts again, and the CRC check value is used to verify the election result release message. Among them, the length of the time slot for issuing election results can be set to 5 minutes.

[0055] In the address collection time slot, nodes that are not in the known address list included in the election result message need to publish an address collection message to announce their address to the convener of the alliance. The address collection message includes the message type, the senders node address, phase, and CRC check value, where the message type is used to indicate that the message is an address collection message, and the senders node address is used to record the senders node address, The phase is used to record the phase of the sender, and the CRC check value is used to check the address collection message. Among them, the length of the address collection time slot can be set to 5 minutes. In addition, although different delay minutes and seconds can be used to set the message sending time of each node in the election time slot, there is still the possibility of overlap. When there are at least two ordinary members in the election time slot Since the message sending time is the same and the election messages overlap, the election messages sent by the at least two ordinary members cannot be obtained by the convener of the alliance, and the address information of the at least two ordinary members will not appear in the known address list. At this time, in the address collection time slot, communication has already occurred in the previous election time slot

When multiple conflicting nodes recalculate their own message sending time, they need to use the random day-level timestamp contained in the election result message to replace the day-level timestamp of the day to avoid communication conflicts appearing again in the election time slot Case.

[0056] In the agent appointment time slot, only the convener of the alliance is allowed to issue an agent appointment message containing the address of the agent node. Specifically, after collecting the addresses and phases of the nodes in the local alliance, the convener of the alliance selects one node in each of the three phases A, B, and C as a proxy node, and then issues a proxy appointment message, which includes message type, sending The node address of the party, the number of proxy nodes, the address of the proxy node, and the CRC check value. The message type is used to indicate that the message is a proxy appointment message. The senders node address is used to record the senders node address and the number of proxy nodes. Represents the number of alliance agent nodes selected this time. The address of the agent node represents the address of each agent node. The number of addresses is the number of the above agent nodes, and the CRC check value is used to verify the agent appointment message. In this time slot, only one convener of the alliance publishes a message, so there is no communication conflict, and the duration of the time slot appointed by the agent can be set to 5 minutes. In addition, the selection of proxy nodes is random.

[0057] It can be understood that the first construction process of the smart watch local alliance is composed of election time slots, election result release time slots, address collection time slots, and proxy appointment time slots, where the duration of each time slot can be set as needed. set.

[0058] Preferably, in the step S12, the keep-alive time slot and the keep-alive disputed time slot are split before the election time slot. The keep-alive time slot is used for the keep-alive of the existing alliance. Only the convener of the alliance is allowed to release keep-alive messages, and other ordinary members only receive keep-alive messages. When only one convener of the alliance releases keep-alive messages, no communication conflicts will occur, and the keep-alive is successful. The alliance is not disputed. At least two alliance conveners release keep-alive messages, or if the messages are superimposed together and the verification fails due to communication conflicts, the keep-alive fails, and the alliance is disputed. After each alliance is successfully created, only one node will be the alliance convener. When at least two local alliances are merged, or the alliance convener in other alliances is included in the alliance, the updated alliance will There are at least two alliance conveners. At this time, the updated alliance is in dispute, and a new alliance convener needs to be re-elected in the subsequent election time slots. In addition, after receiving the keep-alive message, each ordinary member needs to check whether the convener of the alliance has a dispute, that is, whether it has received the keep-alive message issued by at least two conveners of the alliance. The keep-alive dispute time slot publishes keep-alive dispute news. At the same time, each ordinary member also needs to check whether their information needs to be updated. After receiving an undisputed keep-alive message, nodes that are not in the known address list and nodes whose information has changed need to publish address collection in the address collection time slot. Eliminate Information in order to notify the convener of the alliance of his own address and information changes. Among them, the duration of the keep-alive time slot can be set to 5 minutes.

[0059] Wherein, the keep-alive message includes the message type, the node address of the convener of the alliance, the number of proxy nodes, the address of the proxy node, the number of known node addresses, the known node address and phase, and the CRC check value , The message type is used to indicate that the message is a keep-alive message. The node address of the convener of the alliance is used to verify whether the convener has a dispute. If multiple keep-alive messages from different addresses are received during the period, the convener has a dispute and the proxy node The number is the number of communication agents in the alliance. The address of the agent node is used to record the address of each agent node. The number of addresses is the number of the above agent nodes. The number of known node addresses is the number of known node addresses in the alliance. The node address and phase are the known node addresses and phases in the alliance. The CRC check value is used to verify whether the message is correct. If the received message is incorrect, the convener of the alliance has a dispute. Further, when a keep-alive message is received keep-alive messages and non-controversial, collected at the address within the slot, and information that are not known to the node address list node needs to send the address change occurs collection message, which employs day day Level timestamp to calculate.

[0060] In the keep-alive dispute time slot, when the alliance has no dispute, there is no message transmission in this time slot. When the alliance has a dispute, other ordinary members send a keep-alive dispute message to notify the convener of the alliance that there is a dispute in the alliance. After the alliance convener receives the keep-alive dispute message in this time slot or the message overlay verification fails due to communication conflicts, the identities of all the alliance conveners are changed to ordinary members, and new ones will be re-elected in the subsequent election time slots. Convener of the alliance. The keep-alive dispute resolution

The information includes the message type, the senders node address, and the CRC check value. The message type is used to indicate that the message is a keep-alive dispute message, the senders node address is used to record the senders node address, and the CRC check value is used for the check. Check and keep live disputes. Among them, the duration of the keep-alive disputed time slot can be set to 5 minutes. In addition, as a preference, in the keep-alive dispute time slot, as long as the original convener of the alliance receives a message, regardless of whether the message is verified correctly, it means that the alliance is in dispute, and the identity of the convener of the alliance becomes an ordinary member to ensure that the appointed agent The uniqueness of the node avoids communication conflicts during the data collection process.

[0061] It can be understood that after the establishment of the alliance is completed, the process required for the daily operation of the alliance only includes keep-alive time slots, and when a new table is added or the table phase is changed, the required process only includes keep-alive time slots and address collection time. For a new table or a table whose phase has changed, it is necessary to publish an address collection message in the address collection time slot, and inform the convener of the alliance of its address or phase. When a communication conflict occurs, the required process includes keep-alive time slot, Keep-alive dispute time slot, election time slot, election result release time slot, address collection time slot, and agent appointment time slot. Therefore, as long as there is a communication conflict in the alliance, all processes will be restarted, and a new alliance convener will be elected, and then the new alliance convener will choose a new proxy node, and the time when each node sends a message in a different time slot will follow. When the day-level timestamp is updated and updated, the chance of coincidence is very small, which can effectively solve the problem of communication conflicts between nodes in the alliance.

[0062] In addition, in the step S3, the edge-side device may simultaneously receive the power consumption data sent by the proxy nodes of multiple local alliances, and then uniformly send it to the cloud storage.

[0063] In addition, the present invention also provides a terminal device, including a processor and a memory, the memory is stored with a computer program, the processor by calling the computer program stored in the memory for executing the above The steps of the described method.

[0064] In addition, the present invention also provides a computer-readable storage medium for storing a computer program for collecting electricity consumption data, and the computer program executes the steps of the above method when running on a computer.

[0065] The general form of computer readable media includes: floppy disk, flexible disk, hard disk, magnetic tape, any other magnetic media, CD-ROM, any other optical media, Punch cards, paper tape, any other physical media with holes in the pattern, random access memory (RAM), programmable read-only memory (PROM), erasable programmable only Read memory (EPROM), flash erasable programmable read-only memory (FLASH-EPROM), any other memory chips or cassettes, or any other media that can be read by a computer. The instruction can be further transmitted or received by a transmission medium. The term transmission medium can include any tangible or intangible medium that can be used to store, encode, or carry instructions for execution to a machine, and include digital or analog communication signals or intangible media that facilitate the communication of the above instructions. Transmission media include coaxial cables, copper wires, and optical fibers, which include the wires of a bus used to transmit a computer data signal.

[0066] The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.