Research On Low Voltage Power Line Carrier Communication Channel Model Based On OFDM

The low voltage power line communication system ensures the safety and reliable operation of Smart Grids and promotes the integration and informatization of generator sets and transmission lines.It is of great significance to economize social resources by using the existing power line as the medium of communication and transmission.However,the transmission environment of power line channel is very bad,the noise interference is serious,and the signal decays rapidly with the transmission distance increasing.The complex topological structure of power network,unsteady impedance at the load end,mismatching and frequent switching,as well as aging and heating of the line,external weather and other factors,make the power line channel to have time-varying attenuation and frequency selectivity.For the above problems,this paper is aim to measure channel characteristic of the real low voltage electric power environment,through measuring data established the low-voltage power line carrier communication channel model that simulate the real power environment,to find the right load impedance matching and to grasp the rule of the power line attenuation changes for avoiding signal attenuation effectively,confirming the noise interference band resisting noise,and thus improving the power and the rate of signal transmission,etc.The thesis mainly completes the following contents:First of all,to measure and to sample the low-voltage line at field,and then according to measurement scheme of the impedance characteristics,attenuation characteristics,and noise characteristic,gather the waveform and analyze data,in order to draw the input impedance frequency diagram and time-domain attenuation characteristic figure,simulate frequency attenuation characteristic figure,different types of noise figure,the time domain waveform figure with noise under the different sampling rate and the frequency domain power spectrum diagram of different degree of noise respectively.As following,the potential law of measured data is studied,the causes of impedance,attenuation and noise characteristics of field power lines are analyzed,and the carrier communication channel characteristics of low-voltagepower lines are summarized.Second,according to the measured impedance characteristics and attenuation characteristics,and the theory of low voltage power transmission line,the carrier communication channel model of low-voltage power line based on ABCD transmission matrix is established in the frequency domain.The attenuation characteristic model fitted with Multisim software to simulate and measure the environment is compared with the multipath channel model in modeling ideas and simulation performance,which proves that the model established in this paper can fully reflect the transmission characteristics of power channel and facilitate the operation and observation.According to the measured noise interference data,the models of LSTV background noise and MCA pulse noise are established.By superimposing the two noise models,the noise time-domain waveform and power spectrum are simulated.Compared with the measured environmental data,the random probability distribution parameters are consistent.Finally,based on the established low-voltage power line channel model,it is proposed that an OFDM non-progressive stacking adaptive bit power algorithm with optimal transmission rate.Simulation is used to test the performance of OFDM optimization algorithm,such as transmission rate and signal-to-noise ratio.The research of this paper shows that the study of low-voltage power line carrier channel model can improve the performances of simulating real low-voltage power line environment,such as transmission characteristics,transmission rate,stable output of power and so on.