| Due to the good economy and convenient, the power line communication (PLC) technologies are often used for smart grid communication. Ring topology and mesh topology would appear in the smart distribution grid to improve the power supply reliability, and all kinds of distributed generation would be connected to the smart distribution grid, which will change the impedance characteristics of the grid. All of the changes will affect the PLC channel transmission characteristics. Therefor it is necessary to establish a PLC channel modling method for arbitrary topology. The impedance characteristics and the effect to PLC system also should been studied.The paper has proposed the concept of information nodes, and then the power line channel modeling method for arbitrary topology has established. Firstly, taken each power line as a subnetwork and obtain the power line transmission relationship of each power line, and then obtain the voltage-current relationship of conneting nodes between power line, load and source by the basic circuit theory, lastly obtain the transmission characteristics from the signal launching point to the signal receiving point. The effectiveness and universal applicability of this method are verified by actual measurement.Using the channel modeling method based on information nodes, the simulation has carried out to analyze the influence of line length, load impedance and topology to channel transmission characteristics and input impedance characteristics in tree topology and ring topology. Simulation results show the trunk line length and branch line length has heavy effect on amplitude-frequency characteristics and phase-frequency of channel respectively. The number of branch has heavy effect on the notchs and phase-frequency characteristics. The input impedance changes greatly with topology, but the input impedance of amplitude-frequency characteristics peak pointes maintained in a fixed value. The paper also has analyzed the difference channel transmission characteristics of symmetric ring topology in closed ring operational mode and open ring operational mode. Simulation results show the peaks frequency points in closed ring operational mode are also the peaks in open ring mode.The paper has analyzed the influence of the single-phase photovoltaic systems connect to the power line communication system. It is summarized that the filter is the junction device between photovoltaic systems and power system. And basis on this summary, the influence of the single-phase photovoltaic systems connect to the power line communication system has simulinked in the paper. Simulation results show the photovoltaic system equivalent to open-circuit in power line communication network. The high frequency impedance model of the asynchronous motor has been analyzed in the paper, and the influence of the asynchronous motor connect to the power line communication system has been analyzed in the paper. Analysis results show that the asynchronous motor load equivalent to open-circuit in low frequency and short-circuit in high frequency. The paper has established the impedance characteristics model of coaxial communication cables. The open circuit impedance and short-circuit impedance of the cable are measured by open short-circuit impedance method, and then the characteristic impedance and propagation constant of cables are obtained basis the measure results. The correctness of the cables model is verified by the comparison of measure results and the simulink results. The above work is the basis of improving the accuracy of channel transmission characteristics.According to serious impact of the power line channel noise, the paper has analyzed the type and characteristics of the power line channel noise, and established the model of periodic impulse noise asynchronous to the mains freauency. These impulse noises are abundant in the smart distribution network. Aim to analysis the noise characteristes and time variation of power line channel, the paper has measured the lower frequency and high frequency power line channel noise in our laboratory at different time points. |
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