Research On Channel Impedance Matching Method For Medium Voltage Power Line Carrier Communication

Smart grid is different from the traditional power grid,it can achieve automatic regulation and protection control of the power network,so that all levels of the system of the power grid form an organic whole,improve the safety and reliability of the power grid.At present,all countries in the world are actively developing smart grid.However,the construction of smart grid is inseparable from the development of communication technology.The establishment of high-speed,two-way,real-time and integrated communication system is the basis of realizing the functions of smart power grid.The communication modes of power system in China are mainly optical fiber communication,microwave communication and wireless communication.However,power line carrier communication still serves as an important auxiliary communication mode because it does not need to set up special communication lines and has incomparable economic advantages in cost saving.At the same time,power line carrier communication technology has been widely used in automatic meter transcription,remote control of relay protection device and automatic distribution network.Therefore,it is still of great significance to study power line carrier communication technology and improve the transmission performance of carrier communication.Based on the transmission line theory,this paper first solves the telegraph equation of the transmission line,and obtains the expression of voltage and current at any point from the boundary condition.The relationship between the input impedance and the input power of the power line with the line length and the carrier frequency is shown in a three-dimensional diagram.The results show that when the carrier frequency is the same,the amplitude of the input impedance changes in a wavy shape with the line length.When the length of the line is the same,the amplitude of the input impedance fluctuates with the carrier frequency.Then two methods of carrier communication channel modeling are described: top-down method and bottom-up method.The top-down method introduces the basic principle of the classical multipath model as an example.The bottom-up method firstly introduces the dispersion matrix modeling method,and builds the actual distribution network model of baoding huazhuang station and danyang station based on this method.Then the two-port matrix modeling method is introduced,and the influence of line length,line parameters and number of branch nodes on signal transmission characteristics is analyzed.Two-port modeling method is used to convert each module of carrier communication into a transmission matrix,which provides a basic platform for further research on impedance matching of carrier communication coupling devices.Finally,in view of the carrier communication impedance mismatch caused by the problem of large amplitude attenuation of signal,is proposed based on band-pass filter characteristic impedance matching method,according to the principle of maximum power transfer of the circuit,the characteristic impedance of the band-pass filter and characteristic impedance of the circuit are equal,the characteristic impedance of the line can be calculated by line parameters,and the characteristics of the band-pass filter impedance is also known.Then,the circuit of the fixed K-type band pass filter can be obtained.Structure and corresponding inductance and capacitance parameters.The simulation results show that the attenuation amplitude of the matched signal is reduced by about 2d B before matching,which improves the transmission characteristics of carrier communication.