No description available.

No description available.

Malaria, a preventable disease caused by a mosquito-transmitted parasitic infection, continues to be a prominent public health problem today. Progress has been made in the last decade demonstrated by malaria mortality reductions primarily attributed to current vector control strategies. However, the continuing threat of resistance, both resistance of mosquitoes to insecticides and parasites to antimalarial medicines, requires the development of new and improved strategies to supplement those already in place. Housing improvements such as screening doors and windows, closing eaves, patching cracks in walls, and installing ceilings are one such intervention that help stop contact between malaria vectors and humans, and therefore, help stop malaria transmission. Historically considered successful in helping fight malaria, housing improvements are being looked to again today.

Simulation is a powerful tool for developing electric drive systems. Simulations allow the designer to experiment with control algorithms and hardware systems in a safe environment. To this end simulation is becoming increasingly popular. On'-line simulation does have its limitations in that the controller developed during the simulation period has eventually to be transferred to the target processor which will operate in the actual drive system. If, however, a real-time simulation environment could be realised, then the actual controller running in the actual target processor could be included in the simulation. Therefore no translation of code would be required once the controller had been developed and tested within the simulation. This would obviously lead to a reduction in development time and eliminate any possibility of introducing errors due to the translation between the simulated and actual controllers. This thesis describes the development of such a system using a multiple digital signal processing environment. The real-time simulated drive is operated in parallel with an experimental drive to allow a direct comparison between the two. The ability of the multiple processing system to operate in real-time has allowed the whole concept of simulation to be taken a stage further by the development of a real-time power level simulator. This simulator is capable of emulating a machine and load in real-time with real level of voltage and current. It is designed to replace a real machine during the development and testing stages of drive manufacture. This Virtual Machine is a controllable source/sink which is driven by the real-time simulation, and because of this the Virtual Machine takes on the characteristics of any choice of model within the real-time simulation. Moreover, because of its ability to handle bi-directional power flow, the Virtual machine can be programmed to emulate motors or generators. The Virtual Machine also includes the emulation of loads, thus making it extremely flexible and of interest to applications such as machine tools, electric vehicles, and wind generators, to name but a few.

Thesis (M.Nurs.)--University of Hong Kong, 2008. / Includes bibliographical references (p. 96-107)

published_or_final_version / Nursing Studies / Master / Master of Nursing

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No description available.

No description available.

Voltage Source Converter (VSC) applications include but are not limited to HVDC, Flexible AC Transmission System (FACTS) devices such as STATCOM, SSSC, UPFC and Wind generators and active filters. The VSC based HVDC system is a feasible option for bulk power transmission over long or short distances and the grid integration of renewable energy sources in existing transmission and distribution systems. The main requirement in a power transmission system is the precise control of active and reactive power flow to maintain the system voltage stability. The VSC operating with the specified vector control strategy can perform independent control of active/reactive power at both ends. This ability of VSC makes it suitable for connection to weak AC networks or even dead networks i.e. without local voltage sources. For power reversal, the DC voltage polarity remains the same for VSC based transmission system and the power transfer depends only on the direction of the DC current. This is advantageous when compared to the conventional Current Source Converter (CSC) based HVDC system. Furthermore, in case of VSC, the reactive power flow can be bi-directional depending on the AC network operating conditions. In this thesis, a 3-phase, 2-level, 6-switch VSC connected to an active but weak AC system at both ends of the HVDC link is developed using EMTP-RV. The VSC-HVDC transmission system model is developed using both direct control and vector control techniques. The direct control method is an approximate method in which the active power, AC voltages at both ends of HVDC link and DC link voltage are controlled directly by using PI-controllers. In vector control method, closed loop feed-forward control system is used to control the active power, reactive power at both ends and DC voltage. By comparing the simulation results, it is concluded that the vector control method is superior to the direct control because of the removal of the coupling between control variables to achieve the independent control of active and reactive powers at both ends of the HVDC link. / UOIT