| The signals are carried and distributed by the wiring system in power line communication(PLC).It is a promising technology which uses the existing system and has the advantages of simple network,free wiring,low cost,easy to implement and so on.However,the design of power line channel mainly considers the transmission of power and the transmission of signals over power lines,which poses challenges for many technologies.Impedance mismatch is one of the important factors that influence the development of power line carrier communication.Therefore,This paper firstly introduces the basic composition and characteristics of power line carrier communication,and summarizes the current research situation in relevant fields both at home and abroad.In this paper,On the basis of this,the impedance matching problem is deeply studied,the impedance matching method is proposed for the impedance matching with the frequency variation of impedance.In order to understand the channel characteristics,this paper takes the medium voltage power line channel as an example,first introduces the basic theory of the power line channel,and then based on these theories,the mathematical model of the impedance characteristics of the medium voltage power line channel is established by the method of branch addition.The network carrier channel model is used to analyze the influence of these factors on the voltage transfer function and input impedance of the channel.In the research of impedance matching method,for the fixed impedance mode,the traditional impedance matching network inserts a fixed passive network between signal source and power network,which is widely used in wireless communication.Because the research of impedance matching method of power line carrier communication is still in the initial stage,the impedance of point-to-point communication of power line carrier communication does not change greatly in the frequency domain.Therefore,literature do not consider the change of impedance in frequency domain However,the fixed passive matching network can not be adjusted flexibly and even exist a restricted area when the impedance changes over time,In order to solve this problem,the Smith chart and the principle of circuit transformation are utilized.this paper proposes a modified L-structure adaptive impedance matching circuit to adjust the input impedance and avoids the problem that the traditional L-type network has a matching restricted area Aiming at solving the parameters in matching network,an analytical algorithm is proposed,and the calculation method of parameters is analyzed and deduced theoretically.the closed solutions of the corresponding regions and parameters of different impedance types are given,the effectiveness of the method is verified by simulation.Finally,the effectiveness of the method of calculating parameters is verified by simulation.The equivalent input impedance of the actual channel changes greatly with the frequency in the narrow band by modeling the channel of medium voltage power line.The actual channel is not just for a point-to-point communication but in a band transmission,which requires us to consider the overall transmission of the entire band rather than concerned about a certain frequency.In order to be able to be close to the actual network,this paper consider the channel equivalent input impedance changes with the frequency.The principle of transformer is used to transform the impedance of the network first so that the impedance of the network is within a small impedance range,and then the matching network is selected for impedance matching.Finally,the particle swarm optimization algorithm is used to optimize the parameters of the matching network so that the overall transmission efficiency is maximized. |
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