TMCnet News
A Novel Multi-network Convergence Communication Mechanism for Electricity Information Acquisition System Test Platform [Sensors & Transducers (Canada)](Sensors & Transducers (Canada) Via Acquire Media NewsEdge) Abstract: Electricity Information Acquisition System (EIAS) test platform is used to evaluate the communication performance of the different communication methods. For realizing the reliable and quick information interaction in the test terminal, a hierarchical structure multi-network convergence communication mechanism is designed. The convergence communication mechanism is divided into the communication interface convergence layer, the core convergence layer and the business convergence layer to realize the information interaction among the Ethernet communication, power line carrier communication, RS-485 communication and wireless communication. Combined with the tunnel transmission mechanism, the buffer pool mechanism, the communication check mechanism and the timeout control mechanism, the multi-network convergence communication mechanism can effectively improve the communication performance of the test terminal. The test results show that the mechanism can satisfy the real-time and reliability requirements for the electricity information acquisition system test platform. Copyright © 2014 IFSA Publishing, S. L. Keywords: Electricity information acquisition system, Multi-network convergence communication, Hierarchical structure, Information interaction, Test platform. 1. Introduction With the rapid development of smart grid technology and only single communication method is difficult to accommodate the practical applications in the Electricity Information Acquisition System (EIAS), more and more communication methods are used in the electricity information acquisition system [1]. There are four kinds of comparatively extensive communication methods which are currently used in the system, namely optical fiber Ethernet communication, Power Line Communication (PLC), wireless communication and RS485 communication respectively. The optical fiber communication technology used the light wave as the carrier has the large communication capacity, long transmission distance, strong anti-interference, good transmission quality and other advantages, but the defects of the invariant line laying and maintenance and the high costs are existing [2]. The power-line communication (PLC) technology is a mean of communication which uses the existing 380V/220V low voltage power line infrastructure for the communication purposes. PLC without needing to rebuild the network can be transmitted by the existing power line as the medium. However, the harmonic noise and pulse noise interferences are inherently present in the PLC environment, so the quality of the communication is very poor [3]. RS485 communication has good anti-interference, long transmission distance, low cost, but the defects of the poor adaptability and the weak self-protection ability exist in it [4], Short-range wireless communication network is convenient, low power consumption and low cost. However, it is easy to be interfered by the other microwave noises and its transmission speed is very low, so the communication performance is not reliable [5]. In view of the environment differences of smart grid application, effective evaluating and selecting an appropriate communication method which is used for the electricity information acquisition system are important issues for many electric power enterprises. The smart grid test platform of the electricity information acquisition system is used to test and evaluate the comprehensive performance for the different communication methods. The test platform of the electricity information acquisition system consists of the test station and the test terminal. In order to gain the different communication performances, the test terminal is needed to support the different communication methods or communication interfaces. However, the communicating protocols of the different communication methods are different, how to realize fast and reliable information interaction between the different communication methods in test terminal is a main challenge. Information interaction between the different communication methods is always defined as a multi-network convergence communication mechanism [6]. Multi-network communication convergence of China is usually indicated as the convergence of the similar networks or the two specific network convergence or three networks which included the telecommunication network, cable TV network and the Internet. In recent years, many multi-network communication convergence mechanisms have been proposed to improve the communication performance or communication usability. In the Ref [7], a communication convergence method based on MPLS (Multi-Protocol Label Switching) used to build the ATM backbone network for the IP business was proposed to realize the communication convergence among the computer network, cable television network and telecommunication network. The data transmission of communication convergence method was completed in LSP (Layered Service Provider) network tunnel. In the Ref [8], a front agent method has been constructed in the edge of TCP/IP for sensor networks. Thus, the communication vulnerability of the single point can be reduced, and the safety and simplicity of the connection can be improved. In the Ref [9], a communication network convergence method based on the industrial Ethernet integrating multi-field bus technology has been presented to realize seamless information interaction between the control network and the enterprise information network. These communication convergence technologies have a positive role to improve the communication performance. In the smart electricity information acquisition system, the wireless and the wired communication methods are generally coexisting, so the information interaction and the data stream service convergence of the peer to peer network and the vertical network are the very important technologies. The above proposed communication network convergence schemes are difficult to achieve seamless access over the wireless and the wired communication methods. In order to meet the requirement of the communication performance for the smart electricity information acquisition system, a hierarchical communication structure-based multi-network communication convergence mechanism of the test terminal is designed in this paper. The communication convergence mechanism is divided into the communication interface convergence layer, the core layer and the business convergence layer to realize the reliable and fast information interaction among the Ethernet communication, power line carrier communication, RS-485 communication and wireless communication. Thus, the test terminal can provide the exact performance parameters to the test platform which is used to evaluate the combination performances of the different communication methods. 2. Model of Multi-network Convergence Communication for EIAS 2.1. Structure of Electricity Information Acquisition System Test Platform The electricity information acquisition system test platform is mainly used to evaluate the communication performance of the local communication method, and it consists of three parts, the test master station, the test terminal and the acquisition terminal device (or the collector). The structure diagram of the electricity information acquisition system test platform is as shown in Fig. 1. In Fig. 1, the test terminal receives the acquisition data sent by the acquisition terminal through different communication methods such as PLC, wireless or RS485. The multi-network convergence function of the test terminal acts on the correlative processing task and realize the reliable and fast information interaction among the Ethernet communication, PLC, RS-485 communication and wireless communication. At last, the test master station analyzes the communication performance of the different communication methods according to the received the parameters sent by the test terminal. 2.2. Basic Model of Multi-network Convergence Communication The communication networks of the electricity information acquisition system test platform are composed of the backbone communication network and the access network. The backbone communication is used to connect the test terminal and the master station, which is needed to meet the network bandwidth and the high speed transmission without error. So the optical fiber Ethernet communication method is adopted in our design. The access communication network refers to the communication work between the testing terminal and the local acquisition terminals, which includes the traditional Ethernet communication, PLC, RS485 communication and wireless communication. The hierarchical model convergence architecture of the multi-network for the test platform of the electricity information acquisition system is shown in Fig. 2. In Fig. 2, information of the local acquisition terminal is sent through Ethernet, PLC, RS485 or wireless to the test terminal. Then, the test terminal analyzes the communication types, the data types and the check information of the received data. If the check information of the data is correct, the test terminal rapidly extracts the data and loads the data into the different layer such as the communication interface convergence layer, the core layer and the business convergence layer according to the different data types. After the communication convergence is completed, the integrated data packet would be sent to the master station. The right of Fig. 2 is the basic model of our multinetwork communication convergence mechanism. The OSI seven layers model is generally followed by the existing protocols of the open system, the protocol differences in same layer and the communication similarity in the inter layer are existing in the above four kinds of communication methods. In order to reduce the complexity of the information interaction implementation, a multinetwork convergence communication model based on the OSI model is proposed in this paper. The multinetwork convergence communication of the test terminal is divided into the interface communication layer, the core convergence layer and the business convergence layer corresponding to the physical layer, the data link layer, the network layer, the transport layer, the session layer, the presentation layer and the application layer. A variety of communication methods are used in the test terminal and the local acquisition terminals, so the simultaneous communication of the two more terminals may be existed in the test operation. In order to improve the communication reliability, the buffer pool mechanism, avoidance strategy, and access convergence mechanism are respectively used to prevent the network congestion and the data collision. The uniform communication interface protocol is offered by the access layer and the core convergence layer, which realizes the data transition between the access convergence layer and the core convergence layer through the tunnel mechanism. The check mechanism is used to analyze whether the communication information is correct or not. During the operation, the test terminal must be responded timely according to the commands sent by the master station. The timeout mechanism is used to judge the end of the data transmission or the fault of the communication between the test terminal and the master station, and the feedback information would be sent to the master station if the timeout of the test terminal is reached. 2.3. Components of Multi-network Convergence Communication Mechanism According to the basic model of the multinetwork convergence, and combining with the communication performance requirements of the electricity information acquisition system test platform, the communication interface convergence layer, the core convergence layer and the business convergence layer of the test terminal act on the following functions respectively. 1) The communication interface convergence layer realizes the data transmission between the physical layer and the link layer, and the seamless access task for the Ethernet communication, PLC, wireless communication and the RS-485 communication. 2) The core convergence layer realizes the data interface uniform, access switch, data mapping, data convergence and protocol conversion functions. 3) The business convergence layer is responsible for transmitting data come from the core convergence layer and processing the service function of the application layer. In the electricity information acquisition system test platform, the service function main consists of the data acquisition command, the communication control command, the communication performance test type and the fault location of the communication link failure. Furthermore, the business layer receives, extracts and seals the core convergence layer information according to the protocol of application layer protocol, and effective information extraction and encapsulation, and test results and test results, the test results of performance or communication connection response message to the test station, and sends the link response information and the test results of the performance parameters to the master station. Each layer has its own relatively independent task, and the information interface can only be transferred between two adjacent layers. The core convergence layer plays the connection role of the bridge between the communication interface layer and the business convergence layer. The diagram of the hierarchical structure multi-network convergence communication mechanism is shown in Fig. 3. The communication protocols of the electricity information acquisition system in the physical layer and the link layer are different. The general protocol of the Ethernet is IEEE802.3. In the Ethernet communication, the received data stream information is processed through the data link layer, such as the data stream check and the data stream discard. In PLC communication, the bit stream information is modulated or demodulated through the power line. Now the narrowband PLC has an operating range of 3-500 kHz, and its operating range includes CENELEC, ARIB and FCC specified bands. The protocols of the physical layer and the link layer for the narrowband PLC work on the recommendations and standards by IEC14908-3, IEC14543-3-5, IEC61334-3-1, IEC61334-5-1, etc [10]. At present, the related data processing algorithms and the communication protocols of the most PLC products are realized in the link layer. The MODBUS protocol is always used in the RS485 communication. In the MODBUS protocol, the tunnel mechanism is used to encapsulate and transmit for the received data frame according to the uniform network lay protocol. The protocol of the most short-range wireless communication such as ZigBee or Wi-Fi is formed IEEE802.15.4 or 802.11. The communication interface convergence layer of the multi-network convergence mechanism is used to complete the data reception for the different network interfaces, and analysis and transfer the data frames based on the respective physical layer and link layer protocols to achieve the seamless access. The core convergence layer is used for the access switch, the data mapping, the data convergence and the protocol conversion according to the uniform interface. In order to meet the rapid and reliable information interaction, the specific buffer pool mechanism is adopted in the core convergence layer. The buffer pool can temporarily save the data frames which not be processed in time into the particular storage space. The buffer pool is worked with the linked list mechanism, which makes the subsequent operations be executed orderly and can reduce the network congestion risk for the massive data transmit-receive. The data stream would be changed when the communication method is switched. So a vertical switching method [11] is adopted to keep the communication connection when the networks are switched. In order to improve the information transmission reliability and reduce the risk of the communication link failure which is caused by the environment disturbances, transmission channel interference or other factors, a timeout mechanism and the check mechanism are used in the core convergence layer. If there is no packet transmission during a specified time, the end of the data frame transmission or the communication fault would be analyzed by the core convergence layer. The check mechanism is used to analyze that the data frame transmission is correct or not according to the special flag information of the data source and CRC check method. In the test platform of the electricity information acquisition system, the business convergence layer realizes the transmissions for the acquisition instructs, the controlling instructs, the communication performance test and the fault location of the communication link. Furthermore, the business convergence layer is formed with its own application layer protocols, and it extracts the received information come from the core convergence layer, and then sends the test results or the connection responding information to the test master station. 3. Implementation of Multi-network Convergence Mechanism As a very important part of the electricity information acquisition system test platform, the test terminal can support different communication methods and realize the reliable and quick information interaction. 3.1. Hardware Structure of the Test Terminal The hardware of the test terminal is mainly composed of three parts: MCU control module, the communication module and the power supply module. The communication modules include optical fiber Ethernet communication, twisted -pair Ethernet, wireless communication, RS-485 communication and PLC communication. The hardware structure of the test terminal is shown in Fig. 4. The microprocessor module is the core of the test terminal, which includes CPU, reset circuit, clock circuit and multi-communication interfaces. It is connected with the different communication modules and used to control and manage all communication tasks, and analyze the received data frame. The PLC data communication unit is connected with the CPU through the UART. The wireless communication module and the RS-485 communication module are connected with the CPU through the expansion serial port. The physical map of the test terminal is shown in Fig. 5. 3.2. Software Structure of the Test Terminal The terminal can be used to test the communication performance of ELAS, such as the basic communication parameters and the operational parameters. The software of the test terminal is divided into three parts which include the driver software, the development library and the application software. The driver software is used to control the device's initialization operation and the operation of the data translation between in the kernel and the hardware. As a bridge between the application software and the driver software, the development library packages are used to control the interface operation for the hardware registers and provide the interface functions for the application software. The application software completes the test terminal communication and business function. The work mechanism of the multi-network convergence is mainly achieved in this part. The software structure diagram of the test terminal is shown in Fig. 6. 3.3. Workflow of Multi-network Convergence Communication Mechanism When the communication connection between the test terminal and the master station is established, the port selection instructions would be sent to the terminal devices by the test master station. If the terminal devices receive the test commands, the acquire data frames of the terminal devices would be sent to the test terminal. After the source flag being added to the received data frame by the test terminal, the access convergence layer starts to the unified protocol encapsulate and transmit the initial processed data according to the tunnel mechanism. According to the length of the data packets or the number of the received data frame, the core convergence layer judges whether write the data to the buffer pool or not. During the receiving data, the core convergence layer judges the end of the data transmission and the fair failure of the communication link based on the timeout mechanism. After the data transmission is successfully completed, the core convergence layer starts to analyze the data frame such as the data frame check and extracts the data source information. After the protocol conversion and the data processing are completed by the core convergence layer, the business convergence layer starts to test and analyze the communication performance and send the test results to the master station. The flow chart of the test terminal' task is shown in Fig. 7. 4. Test and Analysis of Performance 4.1. Test Environment To illustrate the performance of the proposed multi-network convergence mechanism, the actual environmental information samples provided by the Chongqing Electric Power CORP. of China are used to construct the testing environment. In order to simulate the data flow of the electricity information acquisition system, the appropriate data packet with the special length is formed according to the specification provided by the State Grid Corp. of China. The evaluation software can be used to display the test results and evaluate the communication performance of the different communication methods. The graphical interface of the evaluation and management software is shown in Fig. 8. In Fig. 8, the communication performance evaluation results of each communication method are comprehensively analyzed according to the reference value, the measured value and the evaluation value of the performance parameters. The reference value refers to the relevant standard protocols, and the measured value is the value of actual measurement based on the test platform, and the evaluation value is calculated in accordance with the reference value and the measured value. 4.2. Test and Analysis of Packet Loss Rate In order to evaluate the packet loss rate of the test terminal based on the multi-network convergence communication mechanism, the different test terminal devices are connected with the test terminal, and the point to point tests and the retransmit tests are adopted to test the reliability of the basic communication performance and the retransmit communication function. In the point to point test, one of the four communication methods such as the twisted -pair Ethernet, 2.4 GHz wireless, PLC and RS-485 communication is selected as the data acquisition terminal device, and the optical fiber Ethernet works as the backbone network between the test terminal and the master station. The communication cycle is set as 50 ms, and the total number of test times is 2000. The packet loss rate statistical program is used to analyze the statistics and calculation of packet loss rate. The calculation formula can be expressed as Eq. (1). P, = (l-P/Ps)xl00% (1) In Eq. (1), Pr denotes the number of the received correct frame sent by the data acquisition terminal device. Ps denotes the number of the test frames sent by the transition terminal device. The test results of the average packet loss rate (/> ) for the point to point communication are shown in Table 1. In the retransmit communication test, a terminal device whose communication method is one of the four communication methods is selected as the data sending source, and the other devices receive the data frame retransmitted by the test terminal. The test sketch map is shown as Fig. 9. In order to improve the accuracy of the statistical results, the response message is used between the test terminal and the terminal communication. The statistical results of the average packet loss rate for the retransmit communication are shown in Table 2. The test results of Table 1 and Table 2 show that the average packet loss rate for the point to point communication and the retransmit communication are very low and they are smaller than far 5 % which is a mandatory requirement in Q/GDW 378.3 - power user electricity information acquisition system design guidelines [12]. 4.3. Communication Delay Test and Analysis The communication delay test for the point to point communication and the retransmit communication are used to evaluate the communication real-time of the test terminal based on the convergence communication mechanism. The testing environment is same as that of the packet loss rate test. The communication total delay (Ta) indicates the delay time between the source communication acquisition terminal device and the test terminal, and it includes the received delay time of the source communication acquisition terminal ( Tr ), the queue buffer delay time (T ), and the target transmission delay time the source communication acquisition terminal ( Ts ), The calculation formula of the delay is as Eq. (2). T=T+T+ T (2) The communication delay test results are shown in Table 3 and Table 4. In Table 3, it is shows that the communication real-time of Ethernet acted as a communication method in the acquisition terminal device is the best. The Table 4 shows that the retransmission delay time is less than 1 s. And the time delay is less than 5 s required in the Q/GDW_378.3. The test results show that the communication delay of the test terminal can meet the requirement for evaluating the communication performance of the different communication methods in the electricity information acquisition system. 5. Conclusion In this paper, a hierarchical structure multinetwork convergence communication mechanism consisted of the communication interface convergence layer, the core convergence layer and the business convergence layer is designed to evaluate the communication performance of the different communication methods in the electricity information acquisition system. With different convergence layers, the reliable and fast information interaction among the Ethernet communication, power line carrier communication, RS-485 communication and wireless communication can be realized. The test results shows that the packet loss rate and the communication delay of the test terminal is below 5 % and 0.924 s respectively with this convergence communication mechanism, and its communication performance can meet the communication real-time and reliability evaluating requirements for the electricity information acquisition system test platform. Acknowledgements This work was supported by Science Project of State Grid Corporation of China (Research on Electric Marketing Management and Service of Intelligent Power Utilization Technology), Natural Science Foundation Project of cstc2013jcyjA40002, and Chongqing Municipal Engineering Technology Research Center Construction Project of cstc201 lpt-gc40001. References [1] . V. C. Gungor, F. C. Lambert. A survey on communication networks for electric system automation, Computer Networks, Vol. 50, Issue 7, 2006, pp. 877-897. [2] Wang Chengyi, Wang Hui, Wei Dunkai, et al., Realization of multichannel signal sampling and duplex optical fiber communication system, Chinese Journal of Scientific Instrument, Vol. 28, No. 9, 2007, pp. 1677-1682. [3] . Zhang Jinming, Cui Lin, Du Bin, The application of power line carrier and 485 bus in remote power meter system, Chinese Journal of Scientific Instrument, Vol. 22, No. 4,2001, pp. 247-248. [4] . Ling Guoping, Zhou Xinjian, How to improve RS485 communication reliability in measure and control system, Chinese Journal of Scientific Instrument, Vol. 26, No. 8,2005, pp. 471-476. [5] Lv Tao, Zhou Yanmei, Zheng Qiliang, Zhang Renjie, Design of a 2.4 GHz wireless transmission module using in detection system, Chinese Journal of Scientific Instrument, Vol. 27, Issue 3, 2006, pp. 2062-2063. [6] . Zhao Junhua, Wen Fushuan, Xue Yusheng, et al., Modeling analysis and control research framework of cyber physical power systems, Automation of Electric Power Systems, Vol. 35, Issue 16,2011, pp. 1-8. [7] . Bi Yongjun, Yi Chuanping, Lin Xiangkang, Current situation and development trend of communication network, Automation of Electric Power Systems, Vol. 25, Issue 1,2001, pp. 71-74. [8] . Liu Yuan'an, Ye Liang, Shao Qianming, et al., Integrating wireless sensor networks with the TCP/IP networks, Journal of Beijing University of Posts and Telecommunications, Vol. 29, No. 6,2006, pp. 1-4. [9] . Zheng Jianbin, Tan Tao, Li Wei, The research of the control network and the convergence technology of multi-fieldbuses based on Ethernet, Industrial Control Computer, Vol. 16, Issue 7,2003, pp. 4-6. [10] . Ahmad Usman, Sajjad Haider Shami, Evolution of communication technologies for smart grid applications, Renewable and Sustainable Energy Reviews, Vol. 19,2013, pp. 191-199. [11] . Fang Fei, Li Yun, An algorithm for vertical handoff in heterogeneous wireless networks, Communications Technology, Vol. 43, Issue 6,2010, pp. 137. [12] . Q/GDW_378.3-2009 Design Guidelines of Power User electricity information acquisition system: Technical Solution Design Guidelines, China Electric Power Press, 2010. 1,2 Min XIANG,1,2 Ling LUO,1,2 Ping WANG,3 Jianjun HUANG, 3 Xingzhe HOU 1 Key Laboratory of Industrial Internet of Things & Networked Control, Ministry of Education, Chongqing University of Posts and Telecommunications, Chongqing 400065, China 2 Chongqing Internet of Things engineering technology research center, Chongqing 400065, China 3 Chongqing Electric Power CORP, Chongqing 400000, China 1 Tel: +86-23-62461770, fax: +86-23-62461601 E-mail: [email protected], [email protected] Received: 27December 2013 /Accepted: 28 February 2014 /Published: 31 March 2014 (c) 2014 International Frequency Sensor Association |