Research On Key Technologies Of Medium Voltage Power Line Communication

In recent years, with the rapid development of smart distribution network, there are more and more demands for communication system. Since distribution network in China has the characteristics of wide coverage and complex structure, the appropriate communication technologies must be chose to suit the local conditions. Among them, the medium voltage power line communication (MVPLC) technology has its own unique advantages and broad prospects. Whereas there are still a number of technical problems need to be further improved and solved. The thesis is combined with the subject 'Research on key technologies of medium voltage power line communication oriented to smart grid'which is supported by the National Natural Science Foundation of China (Grant No.61172075). The modeling of MVPLC channel and related communication technologies are studied and a feeder automation system which is based on MVPLC is designed and implemented. The main innovative achievements are presented as follows:1. Based on the theory of multi-conductor transmission lines, the transmission and impedance models of overhead medium voltage power lines are proposed. Combined with a typical line structure the signal propagation characteristics of each mode in the three-phase line are analyzed, which shows that the Clarke matrix can be used as phase mode transformation matrix in the whole frequency band. This method reduces the difficulty of channel modeling. The characteristics of phase to ground and phase to phase impedance are analyzed. The simplified calculation formulas are proposed for calculating the transmission attenuation of a uniform three-phase power lines in the manner of phase to ground and phase to phase coupling, which revel the relationship of mutual coupling of different modes, then the calculation method of matching resistor in the manner of phase to phase coupling is proposed.2. Based on measured data of several distribution transformers, the impedance characteristics of MV terminals are analyzed in the power line communication frequency band. Applying the symmetry of input impedance matrix, a simplified transformer port modeling is proposed.3. The systematic model of MVPLC channel is proposed. The field test of impedance and attenuation data proves the validity of the model. The effects of modeling parameters on the results are discussed, which further simplifies the complexity of the model. A wideband macromodel of medium voltage power line input impedance is proposed, which can be employed to the design of impedance matching circuit in the laboratory.4. The wideband impedance matching method of medium voltage power line is proposed by direct optimization and simplified real frequency techniques, which can effectively improve the signal power into the power line. The online power line impedance detection system is proposed by lock-in amplifier, which has strong ability of noise suppression and measurement of the real and imaginary part of the input impedance. In order to verify the effect of impedance matching, a scheme is designed that replaced the detection object of amplifier output current by DC power supply current.5. A feeder automation system based on integrated intelligent10kV switch is designed, which is applied to distribution network firstly. The key technologies with the independent intellectual property of MVPLC, measurement and protection are analyzed. Aiming at the hostile channel environments of power line communication, an adaptive channel selection strategy is employed and the corresponding communication protocol is designed. The field operation data of a feeder automation system has proved that the MVPLC technologies can achieve stable and reliable communication service for distribution automation system. According to the data of communication signal strength, the general law of channel attenuation and noise are analyzed. Then the channel characteristics of distribution network are summarized, which verified the feasibility of modeling method. These data can be referenced by the related researchers.