Low-voltage power line carrier communication is a special communication mode that uses low-voltage distribution lines as information transmission media to transmit data or voice. The extensive coverage of power line network determines that it has considerable potential use value. This research abroad has a history of nearly a hundred years and has absolute advantages in theory and technology. The research on this technology abroad began very early and has achieved considerable results so far. China's power network is unique, and the research on this technology has only begun in recent years, which determines the urgency for us to actively study this technology. This paper will focus on the basic principle of low-voltage power carrier communication, communication channel characteristics and modeling, networking of low-voltage power carrier communication system, and make a comparative analysis of various key technologies and various carrier chips and modules.
Keywords: low-voltage power line; Carrier communication; technology application
Design strategy of 1 low voltage power line communication system
The quality of low-voltage power line carrier communication is affected by many factors in actual operation, among which the two most important aspects include the impedance characteristics and attenuation of communication channels and noise interference. Impedance will directly restrict the transmission distance of signals, while noise interference will seriously affect the communication quality. It can be said that these two factors directly determine the success or failure of the communication system. Only by targeted analysis and research on these two aspects can the low-voltage power communication system be designed comprehensively. According to these characteristics, the following aspects should be fully considered in the design of communication system: 1) Because the design of power line impedance and the application of materials determine that its impedance is generally small, the impedance of the transmitter and receiver of communication system should be controlled as much as possible, so as not to lose too much energy during transmission due to impedance mismatch;
2) High-frequency signals will be attenuated to a great extent during indoor power line transmission. And when signals are transmitted through power lines, time-varying interference and noise are common. Therefore, it is necessary to use indoor power lines as communication channels. In order to realize the communication system with small signal-to-noise ratio, it must have strong anti-interference ability. The commonly used technologies in power line carrier communication system are spread spectrum technology and orthogonal frequency division multiplexing technology, which can obtain higher receiving signal-to-noise ratio under the condition of small signal-to-noise ratio, while orthogonal frequency division multiplexing technology has the advantages of resisting frequency selective fading and multipath interference in addition to the above advantages.
3) The selection of wave frequency and bandwidth of communication should be reasonable enough, and the attenuation of signal in frequency domain and noise spectral density should be analyzed according to the actual situation. In view of this, we should choose a lower frequency band. On the contrary, if the noise factor is considered first, we should choose a higher frequency band, so we should compare these two aspects in reality and make a comprehensive comparison.
4) There are many branches in general household power grid. At the same time, due to impedance mismatch, standing wave, reflection and other phenomena, when the signal finally reaches the receiving end through different dry wells, it may produce strong multipath interference. Rake receiver can not only effectively resist multipath fading, but also play the role of signal energy diversity and reduce the bit error rate.
5) Because the distance of the noise source has the greatest influence on the communication quality, when the distance cannot be changed, a wave arrester with better isolation should be installed at the communication receiving place;
6) Using convolutional codes with appropriate code length can further reduce the bit error rate;
7) Due to the strong time-varying attenuation performance of low-voltage power line communication signals, enough attention should be paid to the adaptive ability in the design of communication system, so that it can automatically adjust the transmitter power and receiver sensitivity according to the actual attenuation situation, thus ensuring the communication quality;
8) In the design of low-voltage power line carrier communication system, long data packets should be avoided as much as possible. If necessary, they can be repackaged to shorten the length of data packets. Due to the existence of pulse interference, the shorter the data packet, the better, which can reduce the amount of data interfered by pulse accordingly and ensure the data transmission speed.
2 the specific application in China.
Developed power supply network lines provide a broad platform for the development of low-voltage power line carrier communication technology, which has unparalleled advantages such as not occupying wireless channel resources, saving wiring, reducing engineering quantity and simple maintenance. At the same time, with the development of science and technology and the gradual opening of China's power network, low-voltage power carrier communication technology has been widely used in China. Typical examples include home intelligence, automatic meter reading and new intelligent residential areas.
2. 1 Home Intelligence
Intelligent home network refers to connecting various microcontrollers distributed in residential buildings and PCs into a home network, which can realize intelligent management of equipment and unlimited internet access as long as there are sockets.
Because there is no need to lay signal lines, the advantage of networking project is that it does not destroy the original furniture environment. At the same time, it can also ensure the stability of the system, and its engineering cost is relatively easy to control.
Usually, the power broadband Internet access system consists of power modems, PLC devices, PCs, switches and routers. When the low-voltage power line is used for network connection, the PC signal is converted into a special power signal through the power modem, and then the power signal is transmitted to the PLC equipment through the power line. At the same time, the equipment converts the power signal into the original data signal, and then enters the Internet through the switch and router, so as to achieve the purpose of power line access to the network.
2.2 Automatic meter reading system
China's automatic meter reading industry rose in the 1980s, but its development was relatively slow. It was not until 2003 that it gradually entered the promotion, and it entered the period of rapid growth from 2006. Now it is in the golden stage of the development of power carrier meter reading. The automatic meter reading technology of low-voltage power line carrier communication is gradually moving towards the practical application stage, so that the meter reading work is not limited by time and space, residents will also be able to inquire about their electricity consumption at any time, and power management departments will also be able to obtain electricity consumption data accurately at any time.
Research on power carrier communication network networking
Low-voltage distribution lines have physical topology and certain time-varying, and the change of logical topology is closely related to channel quality, which seriously affects the reliability of low-voltage power line carrier communication. Some scholars propose to explore and study the networking mode and network model of high-speed power line communication, so as to find appropriate algorithms to optimize the routing of power line communication network and improve the reliability of power communication. The selection, establishment and automatic routing of narrow-band power line communication data logical links in low-voltage distribution network are studied and discussed, and a dynamic routing algorithm and network reconfiguration algorithm based on non-overlapping clustering are proposed to ensure the effectiveness of communication network. Some scholars have proposed that the network self-organization reconfiguration technology can be used in power line carrier communication of low-voltage distribution network, automatically detect the logical nodes and optimal relay nodes that can be communicated, dynamically adjust the routing and configure relay information, and automatically identify the input or deletion of nodes, thus realizing point-to-point and point-to-multipoint reliable communication of low-voltage distribution network.
4 conclusion
Low-voltage power carrier communication technology has gradually become the focus of technical research in the field of communication with its unique advantages. It can be said that low-voltage power carrier communication technology has broad application prospects and available value. However, the particularity of China's low-voltage power grid determines that it is difficult to analyze and model the communication channel, and it is impossible to directly use foreign mature technologies and products. However, with the attention of domestic research institutions and related companies, China's low-voltage power carrier communication is also gradually developing. The development of power carrier chip with independent intellectual property rights marks a substantial breakthrough in this technical field in China. However, there is still a big gap with foreign heavyweight research institutions and companies. We should gradually strengthen the research and application of this technology. The specific application direction of low-voltage power carrier communication technology is not only in the fields of remote automatic meter reading, home intelligence and new intelligent community, but also in the monitoring of agricultural water-saving irrigation and the informationization of agricultural products circulation process.
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