Research On Impedance Matching Methods And Impedance Matching Couplers In DC Power Line Communications

Power line Communication(PLC)refers to the technology that uses power lines as the transmission medium for data transmission and information exchange.Power lines,which were primitively designed for transmitting energy at 50 or 60 Hz,may not be an ideal transmitting channel for higher frequency carrier signal.To achieve effective and reliable communication over the PLC channels,there are some challenges that need to be overcome.For example,the signal interference caused by impulse noise introduced by various electrical components connected in the power line network should be taken into account.In addition,the access impedance at different access points varies with location and time since the electrical components removed randomly from the power line network,which will lead to the impedance mismatch between PLC transmitter/receiver and power line channel(network).Impedance mismatch will reduce the signal power transfer which will thus affect the reliability of communication.Therefore,to improve the signal power transfer and the reliability of the communication,impedance matching technology is the key solution.As there are significant differences between DC-PLC and AC-PLC,the traditional AC-PLC impedance matching methods and couplers(have some limitations)cannot be directly applied in the DC-PLC.In this work,we attempts to design effective impedance matching couplers and adaptive impedance matching systems for DC-PLC from four aspects as follows:1.We established a DC-PLC system model and a lumped parameter model for DC power line channel.Also,we deduced the mathematical relationship between the optimal winding ratio of a coupling transformer and the power line impedance.Based on the coupling transformer,we designed a modifiable impedance matching coupler for low voltage narrowband DC-PLC.Through simulations and prototype tests,it is found that the modifiable impedance matching coupler can select an optimal winding ratio according to the power line impedance,thus achieving the dynamic impedance matching between the PLC transmitter/receiver and the power line channel,which significantly improves the signal power transfer as well as the reliability and stability of the communication.2.To reduce the implementation cost and the size of the coupling transformer,we built the characteristic parameter model of power line channel,simplified the approximate calculation of power line impedance and designed a low-cost band-pass matching coupler for low/extra-low voltage narrowband DC-PLC.It is shown that the impedance matching circuit which was designed based on the accurate power line channel impedance(instead of an average value)can improve the accuracy of impedance matching circuit.Besides,we found that the band-pass matching coupler obtained 1 d B-4 d B gains in simulations and prototype tests compared with the coupler without impedance matching.3.As there the two-element L-shaped network has forbidden regions,the component values of three-element(?-shaped and T-shaped)networks cannot be solved uniquely with the only two equations provided by the complex conjugate matching method.Therefore,we illustrated a complex impedance matching method for the T-shaped network based on series resonance characteristic.Also,we designed a simple-structure and low-cost T-shaped impedance matching coupler for Vehicular Power Line Communication(VPLC).According to the simulation results it is shown that the designed T-shaped impedance matching coupler had maximum power transfer at the matching frequency which obtained 2.2 d B and 0.35 d B for the transmitter-matching and the receiver-matching respectively.4.The VPLN(Vehicular Power Line Network)access impedance is a complex quantity that varies with location and time.In light of the complex circuit structures and adaptive control logics of the L-shaped adaptive impedance matching system,a T-shaped adaptive impedance matching system is designed on the basis of the resonance-and absorption-based complex impedance matching method.In this system,the component values of the T-shaped matching network are dynamically adjusted,which helps to achieve the adaptive impedance matching between the VPLC transmitter/receiver and the VPLN.According to the simulation results,we found that the designed T-shaped matching network(T-shaped adaptive impedance matching system)obtains 0.4 d B-3 d B and 0.2 d B-1.0 d B power gains for the transmitter-matching and the receiver-matching respectively,which is better than the system without impedance matching.In short,compared with the L-shaped adaptive impedance matching system,the T-shaped adaptive impedance matching system which has the advantages of a simple circuit structure and adaptive control logic achieves impedance matching without changing the structure of the matching network.