PLC Overview
PLC is a communication method that uses power line transmission data and voice signals. It has a history of decades of development. On the mid -to -high voltage transmission network, data or voice through the use of lower frequencies (9-490kHz) through the electric wire carrier is one of the main forms of power line communication technology applications. In the low -voltage field, PLC technology is first used in load control, remote metering and home automation. Its transmission rate is generally 200bit/ s or lower, called low -speed PLC. In recent years, high -speed PLC technology that uses low -voltage power line transmission rates above 1Mbit/ s has been carried out at home and abroad, which can transmit data with up to 45Mbit/ s, and can transmit data, voice, videos, and electricity at the same time. New trend of "unity.
The above picture shows a typical PLC system application. The main PLC station is located at the low -voltage circuit end of the power distribution transformer. The power cable is connected through a capacitor or inductor coupler to inject and extract high -frequency PLC signals. The other side is connected to the Internet through traditional communication methods. The computer on the side is connected to the PLC modem through the Ethernet interface or USB interface. The ordinary telephone is connected to the PLC modem through the RJ11 interface, and the PLC modem was directly inserted into the wall socket. If the PLC high -frequency signal is large or the interference is large, you can install a relayr at the appropriate place to amplify the signal.
PLC uses the transmission line as the transmission medium of the signal, which can transmit telephones, telegrams, data and remote protection signals. The power line has high mechanical strength and good reliability, and does not require the infrastructure investment and daily maintenance costs of the line. Therefore Information transmission has played an important role. At the same time, PLC can easily provide communication links for various .
Related artcle : Low-Power Wireless Communication
PLC key technology
The modulation technology adopted by high -speed PLC internationally includes expansion spectrum technology and orthogonal frequency duplication (OFDM) technology. OFDM technology has become one of the most attractive technologies because of its unique advantages in broadband and high -speed PLC, which has successfully solved many problems in PLC technology.
OFDM technology is a parallel data transmission system that can transmit data on different bandwidth channels on the same power line. This technology uses discrete Fourier transformation to achieve the process of modulation and demodulation. It does not require a beam filter group to achieve relatively simple. The use of digital signal processor technology and fast Fourier transformation algorithm can achieve a communication bandwidth up to 200Mbit/s, and at the same time, it can obtain higher data transmission rate and more effective spectrum utilization rate.
Read here about "data transmission"
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LoRa module and DTU, Long-range Wireless data Transmission
The characteristics of PLC
(1) High -voltage carrier routing is reasonable and low investment
The route direction of the high -voltage power line is usually from the terminal station to the hub station, and then to the schedule. This routing is a reasonable routing required by the power scheduling communication, and it is also the basic communication method of power communication. Because the carrier channel construction does not need to consider line investment, it has become a very favorable way to communicate. In addition, the power line carrier channel is usually completed in the construct of the substation first, which is also very helpful for the communication of the new power station.
(2) Frequent bands are limited, and the capacity is small
In the case of today's communication business has been greatly developed, the channel capacity of the carrier channel has become the "bottleneck" of its further application. Although the random insertion method, division method, group segmentation method, frequency blocking method, map color method and computer frequency distribution software were studied in the distribution of carrier spectrum, and high -frequency is required to be built between electric lines of different voltage levels. The bridge road makes the load frequency reuse as much as possible, but still cannot meet the needs. In recent years, the development of optical fiber communication and the emergence of all -digital power line carriers have slightly alleviated the tension of carriers.
(3) High reliability requirements
The power line carrier transmits important scheduling information and the personal safety needs of voltage isolation in the power system, so it requires high reliability. In order to ensure the quality of the product, the power line carrier must be treated with high temperature aging treatment before leaving the factory, and the final inspection of safety inspection projects must be performed. Since the 1980s, the General Administration of Quality Supervision, Inspection and Quarantine has implemented a mandatory production license management of the power line carrier (class) products. The current management scope has included various voltage level carrier, relay protection receipt, carrier, carriers, and carriers. Data transmission device and power line Internet modem. Most high -voltage and medium -voltage power line carrier manufacturers have established a relatively complete quality system in accordance with the requirements of the production license.
(4) Large line noise
The noise interference brought by the power line as a communication medium is much larger than that of telecommunications lines. On high -voltage power routes, the noise generated by free discharge dizziness, insulators dirty lightning, switching operations, etc., especially the high level of noise has a high level.
(5) Interference to the outside world
The high -voltage power line carrier band should be limited to 40-500kHz. Control the harmonic and interference interference of the transmitted transmission of the carrier can avoid interference to the outside world. In order to achieve high -speed data communication, the expansion wire access device often occupies a frequency band of 30MHz or even more. When transmitting data with frequency bands of 2 to 30MHz, it will affect the short -wave radio broadcasting of the frequency band. When establishing the power line data communication standard in my country, further research and restricting this degree of interference should be restricted.
(6) Network application requirements are higher
Modern communication's requirements for power line carrier pay more attention to the network aspect. It is necessary to expand the concept of the original passage into the concept of the network. In the past, the electric line carrier depended on the automatic disk and the sound rotation interface to achieve a small -scale network. Considering the carrier and scheduling machine, the network application application of the carrier coordinated substation scheduling machine, and the appropriate setting of the data acquisition transmitter that can be able to with the communication network monitoring system interface should be considered in recent years. The application of the low -voltage line in the electric line carrier is based on the network application.
Pay attention when applying PLC
Traditional PLC uses high -voltage electrical lines as the transmission channel for high -frequency signals, which can no longer meet the requirements of broadband development. At present, it is developing in the direction of large capacity and high transmission rate. Various businesses such as electric line calls and Internet access. Foreign abroad is also conducting research and tests of low -voltage distribution network communication, such as the "Home Plug Powerline Alliance". my country is also conducting experimental research using electricity online. In the future, PLC should be able to achieve the comprehensiveization of communication business, broadband of transmission capacity, and intelligent network management, and can achieve seamless connections with the remote network. But at the same time, you need to pay attention to the following issues:
In terms of hardware platform selection, you need to consider the reasonable choice of communication methods and optimization of communication network structure. For the frequency expansion method, OFDM technology, and multi -dimensional grid encoding methods, comparison and analysis need to be performed to determine which method is suitable for low -voltage networks. In addition, you can also consider using the idea of software radio to provide a unified platform for these three methods. With the complex structure of the power network and the ever -changing network topology, how to optimize the network structure of the communication network is also a question that needs in -depth research.
We need to further study the PLC communication theory and improve signal processing technology and coding technology to adapt to the special environment of PLC. In addition to studying the modulation and coding technologies suitable for PLC, it is also necessary to study technologies such as adaptive channel balance, echo cancer, adaptive gain adjustment, etc. These technologies are particularly important for low -voltage PLC to ensure communication.
Low -voltage power cables can realize remote automatic reading data, electricity, and gas meter data, and build a security monitoring system and medical emergency system. The use of electricity cables can transmit data, voice, video, and electricity to achieve the "four networks". Any electrical appliances in the home can be connected to the network and connect to the backbone network. To achieve seamless connections of the four networks and the complex network management problems brought about by this require further research.
