Abstract
Power-line communications is a promising
technology to help automate buildings, as it utilizes the in-situ
power cabling as a communications channel. However, couplers
are required to inject and extract the communication signal from
the power grid. Most power-line communications couplers make
use of a small transformer to adapt impedance levels while also
providing galvanic isolation. The cost and size of these
transformers have been hindrances in the quest for compact,
economic couplers. Previous attempts to eliminate this coupling
transformer, while maintaining impedance adaptation, have not
been successful in reducing component cost nor physical size. In
this paper, a novel approach is followed: (1) a suitable dualfunction
band-pass matching circuit is designed as for ordinary
electronics, whereafter (2) the specifications of this band-pass
matching circuit is upgraded to function safely in the power-grid
environment as a coupler. Therefore a matching circuit is
transformed into a compact power-line coupler, which further
exhibits band-pass filtering and excellent impedance-adapting
performance. Simulations as well as laboratory measurements
are shown which confirm the accuracy of the design. Finally,
practical 220-V measurements in an office block are presented,
which prove the versatility of this novel coupler when power-grid
conditions fluctuate.