Development Of Coupe Filter For Power Line Communication Based On Impedance Matching

Medium-voltage distribution network carrier communication technology is an economical and doable communication technology. With high economic returns and social benefits, nowadays it receives more and more widespread attention. However, at present, using the medium-voltage distribution network to set up the data access still has many difficulties, mainly in these respects: large-signal attenuation, the noise level of the medium-voltage distribution network is high, and the impedance will change unpredictable without any forecast. The medium-voltage network systems with a large number of branch lines which are also unable to build resistance filter, so the interface impedance in line usually can not be matched, which will seriously affect the quality of communications. Therefore, how to overcome the above problems and increasing the stability of the signal transmission is the key to realize the network communications technology.In view of the communication problems which caused by the impedance changes on signal access points of the medium-voltage distribution network, the author has done an in-depth study on the medium-voltage distribution network communication coupe technology. It involves three main aspects: The analysis of the impedance of the medium-voltage distribution network, the design of the medium-voltage distribution network with k-band-pass filter and the design of the automatic impedance matching system.When analyzing the impedance of the medium-voltage distribution network, the author summarized the impedance test methods, analyzed the testing principle of the precision impedance analyzer (Agilent 4294A) and the test method of the impedance of the medium-voltage distribution network, analyzed the impedance change of the medium-voltage distribution network which caused by the architecture of the medium-voltage distribution network. At last, through testing the medium-voltage distribution network and analyzing the test results of the impedance on each communications site, the author summarized the characteristics of the impedance of the medium-voltage distribution network.In designing the K type band-pass filter for medium-voltage distribution network, the author analyzed the concept, purpose and methods of the impedance matching; on this basis, raised the K type band-pass filter design ideas and the design steps, then put forward the concrete K type band-pass filter design, made the simulation test of pass band by MATLAB on the designed K type band-pass filter, made the impedance matching tests on it.In designing the automatic impedance matching system, on the basis of analysis on the impedance of the medium-voltage distribution network and research on the K type band-pass filter, the author raised one kind of model for the automatic impedance matching system, then designed the hardware electric circuit which used AD5933 and AVR chip, studied the following key parts: the band-pass filter, the impedance measurement, the calculation control, the reactance compensation and the resistance transformation, Then designed the program of the automatic impedance matching system and did actual test. In the end, the author did the experimental confirmation to the impedance test and the impedance matching results of the entire automatic impedance matching system.