Design of Broadband Coupling Circuits for Power- Line Communication

One of the most critical components of any Power Line Communication (PLC) system is its interface circuit (or coupling circuit) with the power distribution network. This is by no means a simple unit considering the challenging characteristics of the PLC channel. Due to high voltages, varying impedances, high amplitudes and time dependent disturbances, coupling circuits need to be carefully designed to provide both the specific signal transmission with the appropriate bandwidth, and the safety level required by the applicable domestic or international standard. This paper presents various aspects on practical coupling circuit design. We investigate inductive coupling, capacitive coupling and some hybrid designs. We present measurements of the coupling circuits in terms of transfer function and PLC channel measurements under practical power line noise and impedance loading. We demonstrate the influence of coupling circuit in measurements and show how to compensate its effects in order to measure the actual scattering parameters of the power lines. We compare and comment the various coupling circuit designs in order to define their applicability in practical power line communication systems.