Power line communication impedance profiling and matching for broadband applications.

Masters Degree. University of KwaZulu-Natal, Durban.Power line communication(PLC) is a wired communication technology that has recently re- ceived a lot of attention due to its attractive prospects towards home and /or neighborhood network applications as well as smart grid technologies. It allows establishing digital com- munications without any additional wiring requirements. Effectively, one’s home and/or neighborhood wiring contributes into a smart grid to deploy various data services. It is well known that the power grid is one of the most pervasive infrastructure built to provide electricity to customers, therefore, utilizing this infrastructure for digital communications will only result in an ubiquitous telecommunications network. It is common practice to use wires to establish a physical connection in many telecommunications channels, but most electronic devices already have a pair of wires connected to the power lines. Therefore, these wires can be used to simultaneously establish digital communications. Thus, power line communications can be used as an alternative solution to more established technologies such as wireless, coaxial and optical communications. As a promising technology, PLC has attracted a lot of research and has become an active area of research which continues to evolve over time. Notwithstanding its advantages, PLC has issues, namely, severe noise at low frequencies and varying characteristic impedance. This is primarily because the power line channel was not originally designed to be used for communications, thus, it remains a harsh channel. Other challenges arise from the fact that there are different wiring practices around the world, unpredictable loading characteristics as well as differential- and common-mode characteristic impedance. As a result, there is a considerable amount of noise signal attenuation during data transmission. Loss of signal can be addressed by increasing the power at the transmitter, noise reduction and/or reducing channel attenuation to improve the signal-to-noise ratio. However, PLC modems are subject to legislation that impose a limit with regards to the signal levels in the lines. Power lines are good radiators at high frequencies which makes them behave like large antennas with the ability to intercept other radiations in the same frequency range. The radiated signal is proportional to the currents in the line, thus, increasing line currents will not solve the problem but would rather lead to violation of electromagnetic compatibility (EMC) regulations. In this work, an alternative solution is provided which seeks to address the issue of signal attenuation caused by the changing input impedance of a typical power line channel. The deleterious effects of noise are not considered since this work focuses on broadband PLC in the 1–30 MHz frequency range. The objective of this work was to design and build an impedance adaptive coupler to mitigate effects of channel attenuation caused by varying impedance. In this way, the propagating signal will “see” a uniform impedance and as a result the data output will be improved. The work was facilitated by measuring several impedance profiles of PLC channels in the band of interest. Typically, the network topology of PLC networks is not known and the building architectural blueprints are not always readily available. To overcome this issue,this work was performed on power line test-beds designed to mimic varied typical PLC network topologies. Moreover, there is an additional benefit in that it is possible to relate the output impedance profile to the network topology. The channel input impedance characteristics were determined in a deterministic manner by considering a power line network as a cascade of parallel resonant circuits and applying transmission line theory to develop the model. The model was validated by measurements with good agreement over the frequency range was considered. Several measurements were then used to determine the minimum, average and maximum input impedance that a signal will experience as it traverses the channel. It was found that, regardless of the network size (in terms of number of branches), the average input impedance is 354 ± 1.1 % Ω in the 1-30 MHz frequency band. Due to the unpredictable nature of the input impedance of the power line network, an impedance adaptive bidirectional coupler for broadband power line communications was designed. The impedance matching is achieved by using typical L-section matching networks in the 1–30 MHz band. The matching section of the coupler has the characteristics of a lowpass filter while the coupling section is a highpass filter, effectively forming a bandpass network. The simulated transfer characteristics of the designed coupler performs very well for impedances starting around 150 Ω and the performance improves a great deal as the impedance increases. The coupler can still be improved to accommodate much lower input impedances (as low as 50 Ω). However, based on the measured results of input impedance, it was observed that the power line channel impedance is statistically higher than 200 Ω most of the time which makes the presented design acceptable

Adaptive impedance matching circuit for narrowband power line communication

The noise level and impedance mismatch are still the main concerns in the narrowband power line communication (NB-PLC) technology. The low voltage power line network has impedances that are time and location variant. So it is difficult to achieve maximum power transfer all the time. Thus two new adaptive impedance matching circuits are proposed for NB-PLC. These methodologies are derived from the RLC and LCRC circuit model to achieve simpler configuration and higher matching resolution

Improving skills in rounding off the whole number

This study was conducted to address teaching and learning skills in rounding off a whole number. This study consisted of 15 years 4 students from the Kong Nan Chinese Primary School, Parit Raja, Johor, Malaysia. Initial survey to identify this problem was carried out by analyzing the exercise books and exercises in pre-test. Based on these analyses, a large number of students were not proficient in relevant skills. A ‘q’ technique was introduced as an approach in teaching and learning to help students master the skills of rounding whole numbers. In summary, this technique helps students to remember the sequence of processes and process in rounding numbers. A total of four sessions of teaching and learning activities that take less than an hour have been implemented specifically to help students to master this technique. Results of the implementation of these activities have shown very positive results among the students. Two post tests were carried out to see the effectiveness of techniques and the results shows that 100% of students were able to answer correctly at least three questions correctly. The t-test analysis was clearly showed the effectiveness of ‘q’ technique. This technique also indirectly helps to maintain and increase student interest in learning Mathematics. This is shown with the active involvement of students in answering questions given by the teacher

A Study on the Optimal Receiver Impedance for SNR Maximization in Broadband PLC

We consider the design of the front-end receiver for broadband power line communications. We focus on the design of the input impedance that maximizes the signal-to-noise ratio (SNR) at the receiver. We show that the amplitude, rather than the power, of the received signal is important for communication purposes. Furthermore, we show that the receiver impedance impacts the amplitude of the noise term. We focus on the background noise, and we propose a novel description of the noise experienced at the receiver port of a PLC network. We model the noise as the sum of four uncorrelated contributions, that is, the active, resistive, receiver, and coupled noise components. We study the optimal impedance design problem for real in-home grids that we assessed with experimental measurements. We describe the results of the measurement campaign, and we report the statistics of the optimal impedance. Hence, we study the best attainable performance when the optimal receiver impedance is deployed. We focus on the SNR and the maximum achievable rate, and we show that power matching is suboptimal with respect to the proposed impedance design approach

Design and Construction of a Liquid-Cooled Solid-State Digital Television Transmitter

With the advent of terrestrial digital broadcasting, new and improved digital transmitter technologies are required since existing analog transmitter technology is, for the most part, unable to adequately transmit a decodable digital television signal. This study focuses on the design and construction of a solid-state, liquid-cooled UHF digital television transmitter. Emphasis is placed on the design of the amplifier module including the amplifier card, Wilkinson splitter and combiner, input and output matching circuits, DC bias network and the system mask filter. The results of this research are also presented for two television transmitters that are installed and continue to be in use today, including analyses of specific failures that have occurred while in the field. The overall objective of this study is not only to document the research that is behind the design of this system, but also to document the construction of the transmitter for reference in system maintenance and repair as well as a basis for future design

Design and Construction of a Liquid-Cooled Solid-State Digital Television Transmitter

With the advent of terrestrial digital broadcasting, new and improved digital transmitter technologies are required since existing analog transmitter technology is, for the most part, unable to adequately transmit a decodable digital television signal. This study focuses on the design and construction of a solid-state, liquid-cooled UHF digital television transmitter. Emphasis is placed on the design of the amplifier module including the amplifier card, Wilkinson splitter and combiner, input and output matching circuits, DC bias network and the system mask filter. The results of this research are also presented for two television transmitters that are installed and continue to be in use today, including analyses of specific failures that have occurred while in the field. The overall objective of this study is not only to document the research that is behind the design of this system, but also to document the construction of the transmitter for reference in system maintenance and repair as well as a basis for future design

Design and Experimental Characterization of a Combined WPT - PLC System

In this contribution, the authors perform the design and show the experimental results relative to a prototype of a combined wireless power transfer (WPT)–power line communications (PLC) system, in which the WPT channel is interfaced to a PLC environment to allow data transfer when the cabled connection is no longer available. The main rationale behind this idea stays in the fact that PLC communication is now a popular choice to enable communications, for instance, in smart grids and in home automation, while WPT devices start to be available in the market (i.e. for mobile phones) and soon they will be a reality also for higher power (i.e. vehicle battery charging). In particular, theoretical insights about the requirements of the system are given; a two coils system has been implemented and a measurement campaign, together with simulations, show that the system is of great potentiality and could be used in applications where both wireless power and data transfer are needed (such as vehicles battery charging), achieving maximum power transfer and good data rate in order to transmit high-speed signals

Application of Advanced Early Warning Systems with Adaptive Protection

This project developed and field-tested two methods of Adaptive Protection systems utilizing synchrophasor data. One method detects conditions of system stress that can lead to unintended relay operation, and initiates a supervisory signal to modify relay response in real time to avoid false trips. The second method detects the possibility of false trips of impedance relays as stable system swings “encroach” on the relays’ impedance zones, and produces an early warning so that relay engineers can re-evaluate relay settings. In addition, real-time synchrophasor data produced by this project was used to develop advanced visualization techniques for display of synchrophasor data to utility operators and engineers