Wireless visual sensor network is an emerging field which has proveduseful in many applications, including industrial control and monitoring,surveillance, environmental monitoring, personal care and the virtual world.Traditional imaging systems used a wired link, centralized network, highprocessing capabilities, unlimited storage and power source. In manyapplications, the wired solution results in high installation and maintenancecosts. However, a wireless solution is the preferred choice as it offers lessmaintenance, infrastructure costs and greater scalability.The technological developments in image sensors, wirelesscommunication and processing platforms have paved the way for smartcamera networks usually referred to as Wireless Visual Sensor Networks(WVSNs). WVSNs consist of a number of Visual Sensor Nodes (VSNs)deployed over a large geographical area. The smart cameras can performcomplex vision tasks using limited resources such as batteries or alternativeenergy sources, embedded platforms, a wireless link and a small memory.Current research in WVSNs is focused on reducing the energyconsumption of the node so as to maximise the life of the VSN. To meet thischallenge, different software and hardware solutions are presented in theliterature for the implementation of VSNs.The focus in this thesis is on the exploration of energy efficientreconfigurable architectures for VSNs by partitioning vision tasks on software,hardware platforms and locality. For any application, some of the vision taskscan be performed on the sensor node after which data is sent over the wirelesslink to the server where the remaining vision tasks are performed. Similarly,at the VSN, vision tasks can be partitioned on software and the hardwareplatforms.In the thesis, all possible strategies are explored, by partitioning visiontasks on the sensor node and on the server. The energy consumption of thesensor node is evaluated for different strategies on software platform. It isobserved that performing some of the vision tasks on the sensor node andsending compressed images to the server where the remaining vision tasks areperformed, will have lower energy consumption.In order to achieve better performance and low power consumption,Field Programmable Gate Arrays (FPGAs) are introduced for theimplementation of the sensor node. The strategies with reasonable designtimes and costs are implemented on hardware-software platform. Based onthe implementation of the VSN on the FPGA together with micro-controller,the lifetime of the VSN is predicted using the measured energy values of theplatforms for different processing strategies. The implementation resultsprove our analysis that a VSN with such characteristics will result in a longerlife time.

The wireless visual sensor network is an emerging field which is formed by deploying many visual sensor nodes in the field and in which each individual visual sensor node contains an image sensor, on board processor, memory and wireless transceiver. In comparison to the traditional wireless sensor networks, which operate on one dimensional data, the wireless visual sensor networks operate on two dimensional data which requires higher processing power and communication bandwidth. Research focus within the field of wireless visual sensor networks has been on two different extremes, involving either sending raw data to the central base station without local processing or conducting all processing locally at the visual sensor node and transmitting only the final results.This research work focuses on determining an optimal point of hardware/software partitioning at the visual sensor node as well as partitioning tasks between local and central processing, based on the minimum energy consumption for the vision processing tasks. Different possibilities in relation to partitioning the vision processing tasks between hardware, software and locality for the implementation of the visual sensor node, used in wireless visual sensor networks have been explored. The effect of packets relaying and node density on the energy consumption and implementation of the individual wireless visual sensor node, when used in a multi-hop wireless visual sensor networks have also been explored.The lifetime of the visual sensor node is predicted by evaluating the energy requirement of the embedded platform with a combination of the Field Programmable Gate Arrays (FPGA) and the micro-controller for the implementation of the visual sensor node and, in addition, taking into account the amount of energy required for receiving/forwarding the packets of other nodes in the multi-hop network.Advancements in FPGAs have been the motivation behind their choice as the vision processing platform for implementing visual sensor node. This choice is based on the reduced time-to-market, low Non-Recurring Engineering (NRE) cost and programmability as compared to ASICs. The other part of the architecture of the visual sensor node is the SENTIO32 platform, which is used for vision processing in the software implementation of the visual sensor node and for communicating the results to the central base station in the hardware implementation (using the RF transceiver embedded in SENTIO32).

M.Ing. / Inverters are daily used in industry, and to a large extent, as induction motor drives. Power levels of inverters vary from a few watt to several megawatt. The most common part of inverters is a phase arm or a pole, consisting of two power electronic switches and two freewheeling diodes. The hard switched phase arm is the standard in industry due to simplicity and cost. Regenerative snubbing is often used at larger power levels to reduce losses in the inverter. Some aspects of the non-linear resonant pole inverter, such as regenerative snubbing and zero voltage switching, are investigated. It is obtained by utilising a non-linear resonant tank. Low current stresses permit the optimal use of the power electronic switches. The non-linear resonant pole inverter can replace the hard switched inverter, with no restriction with respect to power levels. Experimental and analytical modelling was employed to investigate some aspects, such as controllability, losses and feasibility.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, infulfilment of the requirements for the degree of Master of Science in Engineering Johannesburg, 1989 / T his dissertation examines simple Meteor Burst Communication (M B C) out-starioL * i-^nas. The eSect o f illum ination gain, beam w idth and orientation was studied using computer ^vr.t-iation. Sim ilarly, the performance o f M B C links using a half-wave dipole, a quarter-wave rnonopole, a square loop, a long w ue and a 5-elements Yagi-Uda antennas was determined. The performance o f these links are related to the antennas’ sky i l l umination. This investigation provides designers some bench-mark results which indicate the role played by the antennas ’ radiation patterns in M B C. A value system was formulated to provide practical and electrical trade-offs fo r m obile andmanpack antennas in the meteor scatter environment. Simulated results indicate that simple antennas cause degraded communications due to their reduced size and complexity. The conclusion is that the directional master station should provide adequate sky illumination. I t is recommended that the results obtained be validated by measurements and further work concentrate on master station antennas.

University of Macau / Faculty of Science and Technology. / Department of Electrical and Computer Engineering

The interconnection of multiple oshore renewable energy sources to form a network and maximise their availability requires a method for controlling the transportation of bulk electrical energy. For the distances considered, and as a result of the capacitive nature of HVAC cables, HVDC is the most likely technology for meeting these bulk transport requirements. This research investigates the development of an MMC based Dual Active Bridge (DAB) for interfacing two different parts of a HVDC network. Computational tools are developed in order to design and evaluate such a power electronics structure as well as to support the design process of the transformer required for scaling and matching voltages between the two parts of the network. Linear control techniques are applied to control the converter to operate at the required average capacitor voltage level and power transmission. Simulation results, supported by experimental data from a low voltage MMC prototype are presented to validate the approaches.

The key motivation of this study is to investigate the potential of graphene/metal oxides nanocomposites as electrodes for electrochemical capacitor applications. It is envisioned that the positive synergistic effect between graphene and metal oxides (where novel graphene material acts as a highly conductive platform for ease of ion transfer kinetics and metal oxide acts as spacers to avoid the restacking of graphene sheets to make available more active surface areas) results in excellent electrode material for high performance electrochemical capacitor. In this thesis, a series of hybrid composites comprising of graphene and low cost transition metal oxides were synthesised and characterised for their potential as electrode for electrochemical capacitor applications. In order to achieve this, the graphene used in the preparation of the hybrid composites was successfully synthesised from highly pyrolytic graphene in a proper ratio of ethanol and water before the integration of the metal oxides via a solvothermal route. A parametric study was carried out in a step by step approach to validate the success of the composite synthesis before the electrochemical stage. X-ray Diffraction, Field emission and Transmission scanning electron microscopy, energy-dispersive X-ray and Raman spectroscopy, cyclic voltammetry and galvanostatic charge/discharge tests were used to verify the integrity of the as-produced graphene/metal oxide composites and their applicability to electrochemical capacitors. Upon the completion of the experimental work, the electrochemical tests demonstrated that the introduction of graphene to the metal oxide improved the electrochemical performance in-terms of capacitance, energy density, power density, equivalent series resistance and cycling stability. The results also indicated that the ratio of graphene to metal-oxide plays a significant role in the electrochemical performance of the composite. In comparison with the different graphene/Zinc oxide (ZnO) nanocomposites studied, the electrode material with a weight ratio of 1:8 (graphene: ZnO) displayed a specific capacitance of 236 F/g at a scan rate of 10 mV/s with energy and power densities of 11.80 Wh/kg and 42.48 kW/kg respectively. The specific capacitance of the graphene-Manganese oxide (MnO2) composite electrode material with a weight ratio of 1:16 (graphene: MnO2) demonstrated the best performance of 380 F/g at a scan rate of 5 mV/s among the four ratios studied. The G1Co4 composite electrode with a weight ratio of 1:8 (graphene: Co3O4) demonstrated a superior specific capacitance of 384 F/g at a current density of 0.3 A/g coupled with retention of 80% of its capacitance after 1000 cycles among the graphene-cobalt composites. The Graphene-Nickel cobaltite composite electrode with weight ratio of 1:8 (graphene: NiCo2O4) labelled G-8NC2 displayed a superior specific capacitance (698 F/g at a current density of 0.5 A/g) and good cycling stability (74% capacity retention after 5000 cycles at current density of 1 A/g). The 1:8 ratio exhibited well attached Nickel molybdate nanorods on the surface and edges of the graphene sheets with the highest specific capacitance of 670 F/g at 0.3 A/g, as compared to other tested composites. The significance of these findings details a synthesis route that provides an effective, simple and practical method of preparing graphene-metal oxide composite materials for electrochemical capacitor applications.

No description available.

In this work, a computationally efficient solution for constraint management of square multi-input multi-output (MIMO) systems is presented. The solution, referred to as the Decoupled Reference Governor (DRG), maintains the highly-attractive computational features of scalar reference governors (SRG) compared to Vector Reference Governor (VRG) and Command Governor (CG). This work focuses on square MIMO systems that already achieve the desired tracking performance. The goal of DRG is to enforce output constraints and simultaneously ensure that the degradation to tracking performance is minimal. DRG is based on decoupling the input-output dynamics of the system so that every channel of the system can be viewed as an independent input-output relationship, followed by the deployment of a bank of scalar reference governors for each decoupled channel. We present a detailed set-theoretic analysis of DRG, which highlights its main characteristics. A quantitative comparison between DRG, SRG, and the VRG is also presented in order to illustrate the computational advantages of DRG. Finally, a distillation process is introduced as an example to illustrate the applicability of DRG.

In automakers' never-ending quest to reduce emissions and improve performance, the turbocharger represents a major step in advancing these goals. By repurposing waste exhaust and compressing the air intake, they are able to increase overall power. One critical control loop in the turbocharger is control of boost pressure via the wastegate. This is a highly nonlinear process and experimental data has shown that a gain-scheduled PID (proportional integral derivative) controller developed with IMC (internal model control) tuning methodology is an effective means to control boost pressure. Motivated by this successful implementation of IMC-PID tuning in the automotive world, this work hopes to extend and analyze that framework. Traditionally, the success of an IMC controller depends on the accuracy of the plant model. This research challenges this view and investigates using IMC with a gain-integrator-delay (GID) model identified at a critical frequency, regardless of the actual plant. The GID model is useful because of its simplicity to characterize and its ability to be translated to the ubiquitous PID controller easily. Three design techniques are developed: (1) design for post-hoc tuning, (2) design for closed loop bandwidth, and (3) design for phase margin. In addition, these techniques are investigated via a Monte Carlo simulation to determine efficacy for when there exists plant/model mismatch. Finally, the three techniques are applied to control the speed of an inertia disk on the Quanser Servo 2 device.