Integrated Impedance-Matching Coupler for Smart Building and Other Power-Line Communications Applications

Power-line communications is a promising technology to help automate buildings, since 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 or physical size. In this paper, a novel approach is followed: 1) a suitable dual-function bandpass matching circuit is designed for ordinary electronics, whereafter 2) the specifications of this bandpass matching circuit are 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 bandpass 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.