Research On Carrier Communication Channel Model And Characteristics Of Medium Voltage Underground Cables

With the application of orthogonal frequency division multiplexing(OFDM)in the field of power line communicaiton(PLC),PLC has once again attracted wide attention and is expected to become an important part of smart grid communication system.In this paper,the medium-voltage(MV)underground cable widely used in urban distribution network is taken as the research object,its channel models are established,and its channel characteristics are analyzed.Firstly,the structure and related parameters of typical MV underground cable are introduced,which provides the basic parameters for the application of multi-conductor transmission line(MTL)theory.Second,by combining MTL model with loop analysis,four kinds of transmission modes and their transmission characteristics of MV underground cable are determined by improved modal decomposition.At the same time,based on the idea of modulus decomposition and superposition,an equivalent multimode transmission model with partial conductor grounding is established to solve the problems of shielding layer and steel armor grounding in the field.The reliability of the model is verified by numerical simulation.Then,from the reflection of carrier signal at the nudes of impedance discontinuity,carrier signals in MV underground cable are considered as the combination of incident waves and reflected waves,and then combined with general boundary conditions of nodes,BLT(Baum,Liu,Tesche)equation based MV underground cable carrier communication channel model are established,The credibility of the model is verified through comparing the results of proposed model and that of the existing model and simulation results using lumped parameters.The proposed model has simple form,good generality and is convenient to analysis and calculation.Finally,the multimode transmission characteristics and intrinsic impedance characteristics of underground cables with grounded shields and armors are analyzed.The results show that,generally speaking,in MV underground cables with grounded shields and armors,the forward and reverse modes are different,and the channel itself has two different intrinsic impediments of forward intrinsic impediment and reverse intrinsic impediment.In addition,the grounding of shields and armors will induce resonance,leading to multi-stop-band characteristic of attenuation constant of correlation modulus,and accompanied by oscillation phenomenon.The phase shift constant has nonlinear distortion,which may cause signal distortion.Resonance phenomenon also exists in the positive and negative intrinsic impediment of the channel.When the grounding conditions of shields and armors are taken into account,the transmission characteristics of carrier signals are almost unaffected if the carrier signal are injected between the core wires and shields.If the carrier signal are injected between the shields and the ground,the extent to which its transmission characteristics are affected is closely related to the type and value of the ground impedances.