In recent years, Power Line Communication (PLC) technology has become a new research hotspot in communication systems, and it is regarded as an important field device bus communication technology in the future. However, as a communication method with bright prospects, power carrier communication has many inherent problems in the specific application due to its inherent characteristics such as time-varying and frequency selectivity.
Power carrier communication characteristics
1. Overview of power line carrier communication technology
Power line carrier communication (PLC) refers to the technique of modulating a signal with a dedicated modem and then loading the signal into an existing power line for communication. As early as the 1920s, power carrier communication began to be applied to l0kV distribution network line communication, using power carrier and wave blocker to transmit voice, control commands and system status and other information in the medium and high voltage distribution network. Relevant international and national standards. For low-voltage distribution networks, many emerging digital technologies, such as spread spectrum communication technology, digital signal processing technology and computer control technology, have greatly improved and improved the availability and reliability of power carrier communication in low-voltage distribution networks. Carrier communication technology has a more attractive application prospect. To this end, the FCC of the United States Federal Communications Commission stipulates that the power line bandwidth is 100-450 kHz; the EN50065-1 of the European Electrical Standards Committee (CENELEC) specifies a power carrier frequency band of 3 to 148.5 kHz. The establishment of these standards has made a significant contribution to the development of power carrier technology. Despite this, many problems in power line carrier communication in low-voltage distribution networks have not been well resolved. At the same time, with the promotion and expansion of power carrier application fields, a series of problems such as low-cost distribution network power carrier communication cost issues, protocol (standard) issues, and security issues have begun to surface. The practical application of power line carrier communication in low-voltage distribution networks is still facing many challenges.
2. Power line carrier communication characteristics
For low-voltage distribution networks, power line carrier communication generally has the following characteristics:
(1) Time-varying of the communication channel For the carrier signal, the low-voltage power line is a non-uniform distribution transmission line, and various types of power loads are randomly input and disconnected at any position of the low-voltage distribution network to make the channel performance A strong time-varying.
(2) The frequency selectivity of the communication channel is precisely due to the fact that the load condition in the low-voltage distribution network is very complicated, the load variation range is large, the noise type is strong and strong, and the impedance of each node is not matched, and the signal is easy to generate reflection and standing wave. The phenomenon of resonance, etc., makes the attenuation of the signal extremely complicated, resulting in a strong frequency selectivity of the power carrier communication channel.
(3) Strong noise interference and large signal attenuation Generally speaking, there are three main types of noise affecting power communication, namely background noise, periodic noise and burst noise. The background noise is generally distributed throughout the communication band; periodic noise includes periodic continuous interference and periodic pulse interference; sudden noise is generally generated by the input or disconnection of the powered device. Research shows that pulse interference has the greatest impact on the quality of low-voltage power line carrier communication, and the signal attenuation can reach 40dB. It is precisely because of the above characteristics that power carrier communication has been facing the test of usability and reliability in practical application.
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