D.Ing. / The technique of using a live power cable to simultaneously transport a communication signal, has been practiced since the early 1900’s. In most cases, power-line communications has been implemented as a retrofit technology, with its main benefit being the utilization of a ‘free’ existing network. This driving force of power-line communications is typical for high-, medium-, and low-voltage distribution networks, as well as intra-building networks currently targeted for home automation and home networking. Researchers have thus focused on the optimum use of these existing power-line channels, often accepting the inherent drawbacks of this hostile communication channel. Apart from unpredictable noise sources, two main disadvantages of the low-voltage powerline network as a communication channel, are i) the unknown power cable characteristics and topology and ii) time-dependent fluctuation of the power-line impedance level as loads are unpredictable switched into, and out of the network. These two factors have obscured the requirements for proper coupling and impedance adaptation to the degree that most researchers and manufacturers have merely accepted this typical ≈ 20-dB coupling loss as one of the inherited disadvantages of the power-line channel. Most researchers and manufacturers have thus defaulted to a guessed power-line impedance level, and have used one fixed coupler winding ratio under all circumstances, regardless of power-line conditions. This study has shown that proper coupling and impedance adaptation can yield significant transmission gains even with limited (qualitative) knowledge of a power-line channel and its topology. After formulating design steps for an impedance-adapting coupler that facilitates bidirectional transmission, the impact of the fluctuating power-line impedance on coupler bandwidth was investigated. Next, impedance adaptation strategies were considered and the tradeoff between series cable requirements and parallel load requirements was explored. A model of sufficient simplicity was developed to facilitate qualitative description and classification of power outlets – functioning as communication nodes. Very interesting simulation results were obtained and these were verified using a laboratory setup of characterized power cables and calibrated loads. Next, these simulation results were employed to improve power-line transmission over a live, uncharacterized 220-V residential network by means of i) classifying typical residential rooms qualitatively in order to choose proper coupler winding ratios and ii) using an innovative dual coupler for dedicated on-off switching with harsh loads, thereby mitigating the fluctuating impact of said loads on low-voltage power-line communications.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:8314 |
| Date | 28 April 2009 |
| Creators | Janse van Rensburg, P. A. |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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