Measurements, Models, Systems and Design

531 s.

HVDC Control and operation for the integration of extremely high-RES systems with focus on permanent DC faults

This master thesis presents the control and analysis of a DC fault on a zero inertia offshore grid integrating multiple Voltage Source Converters. The system analyzed consists in an offshore grid which includes two wind power plants and two offshore converter platforms. These two offshore converter platforms are connected to two different onshore grids through High Voltage Direct Current (HVDC) point-to-point connections. First, the modeling and control of Voltage Source Converters for offshore wind energy HVDC systems are presented. Two control strategies are described for them depending on their operating mode which can be grid-forming or grid-following. Then, the complete model of the system, including the onshore grids, is presented. For simulation purposes an aggregated model is used for the WPPs. Further, two control methods for power reduction for the system to be able to perform correctly under DC faults are proposed. Finally, a simulation of the modelled system under a pole-to-pole DC fault on one of the HVDC transmission links is performed and evaluated by means of time domain simulations using Matlab Simulink®.Outgoin

DIRBE External Calibrator (DEC)

Under NASA Contract No. NAS5-28185, the Center for Space Engineering at Utah State University has produced a calibration instrument for the Diffuse Infrared Background Experiment (DIRBE). DIRBE is one of the instruments aboard the Cosmic Background Experiment Observatory (COBE). The calibration instrument is referred to as the DEC (Dirbe External Calibrator). DEC produces a steerable, infrared beam of controlled spectral content and intensity and with selectable point source or diffuse source characteristics, that can be directed into the DIRBE to map fields and determine response characteristics. This report discusses the design of the DEC instrument, its operation and characteristics, and provides an analysis of the systems capabilities and performance

Precision measurement of carbon isotope ratio in exhaled breath for the detection of helicobacter pylori

The utility of breath trace compounds as bio-markers for various physiological conditions has long been exploited for the diagnosis of various diseases. Urea breath tests have been adopted as the gold standard for the detection of Helicobacter pylori which is a primary cause for acute gastritis and peptic ulcers. In these tests, small changes in the ratio of stable CO2 isotopomers, 13CO2 and 12CO2, present in exhaled breath are measured precisely and this is conventionally done by using anIsotope Ratio Mass Spectrometer. However, the huge cost and complexity involved in operating these instruments has restricted their widespread use. A viable and low cost alternative is offered by instruments employing non-dispersive infrared absorption techniques. The feasibility of such an instrument has been explored in this work.The instrument presented here is a two channel isotope ratiometer that performs whole band integrated absorption measurements. Detection is based on a novel feedback mechanism whereby an imbalance in the channel absorptions causes the pathlength along one of the channels to be altered in order to bring the system back to balance. This change in ratio of pathlengths is directly related to thechange in the 13CO2/12CO2 concentration. Significant amount of work has already been done to investigate the effects of interferences from coincident absorption bands and other spectral effects that can lead to spurious results.A comprehensive description of the overall system design, development and performance evaluation of the first prototype instrument has been presented here. This involved significant computer modeling and simulations and the results were verified experimentally. These results provided sufficient evidence to suggest the feasibility of such an instrument as a diagnostic tool. It was also concluded that some design improvements were required to circumvent issues related to pathlength variation and a list of recommendations has been provided for this purpose. On the basis of the results obtained as part of this research endeavour, it was concluded that the non-dispersive instrument design presented here can form the basis for a low cost commercial alternative for performing carbon isotope ratio breath tests.</p

Methods for Determining Blood Flow Through Intact Vessels of Experimental Animals Under Conditions of Gravitational Stress and in Extra-terrestrial Space Capsules Final Report, 1 Nov. 1960 - 31 Dec. 1964

Electromagnetic blood flow meter to determine blood flow through intact vessels of test animals in gravitational stress and in extraterrestrial space capsule

Progress of analog-hybrid computation

Review of fast analog/hybrid computer systems, integrated operational amplifiers, electronic mode-control switches, digital attenuators, and packaging technique

DC microgrid power coordination based on fuzzy logic control

The power coordination in DC microgrids has a vital role in enhancing the performance and management of multi generation units. Renewable Energy Sources (RES) are limited to their available power with intermittent nature. Battery-based energy storage sources have limitations in the charging and discharging capabilities to avoid depleting the battery and preserve the State of Charge (SOC) within its satisfactory limits. The battery balances the power difference between RES and loads. However, in severe cases where the SOC is very low, load shedding is crucial. In this paper, a Fuzzy Logic Controller (FLC) has been proposed to coordinate the power flow of PV unit and battery to satisfy the load by full use of the available PV power. It controls the PV’s output power and keeps the SOC and charging / discharging power of the battery within their required margins regardless of the variations in load. Furthermore, load shedding of low priority load has been implemented when the battery couldn’t balance the microgrid power flow. Simplicity in managing multi input-multi output system by FLC is the main merit. Matlab/Simulink results are presented to validate the performance of the proposed controller

Argonne National Laboratory Reports

Many of Argonne National Laboratory`s (ANL`s) scientific staff members were very active in R & D work related to accelerator-based spoliation sources in the 1970s and early 1980s. In 1984, the Seitz/Eastman Panel of the National Academy of Sciences reviewed U.S. materials science research facilities. One of the recommendations of this panel was that the United States build a reactor-based steady-state source, the Advanced Neutron Source (ANS), at Oak Ridge National Laboratory. Subsequently, R & D activities related to the design of an accelerator-based source assumed a lower priority. The resumption of pulsed-source studies in this country started simultaneously with design activities in Europe aimed at the European Spallation Source (ESS). The European Community funded a workshop in September 1991 to define the parameters of the ESS. Participants in this workshop included both accelerator builders and neutron source users. A consortium of European countries has proposed to build a 5-MW pulsed source, and a feasibility study is currently under way. Soon after the birth of the ESS, a small group at ANL set about bringing themselves up to date on pulsed-source information since 1984 and studied the feasibility of upgrading ANL`s Intense Pulsed Neutron Source (IPNS) to 1 MW by means of a rapidly cycling synchrotron that could be housed, along with its support facilities, in existing buildings. In early 1993, the Kohn panel recommended that (1) design and construction of the ANS should be completed according to the proposed project schedule and (2) development of competitive proposals for cost-effective design and construction of a 1-MW pulsed spallation source should be authorized immediately

Maximum power point tracking algorithm for photovoltaic home power supply.

Thesis (M.Sc.Eng)-University of KwaZulu-Natal, Durban, 2011.Solar photovoltaic (PV) systems are distributed energy sources that are an environmentally friendly and renewable source of energy. However, solar PV power fluctuates due to variations in radiation and temperature levels. Furthermore, when the solar panel is directly connected to the load, the power that is delivered is not optimal. A maximum peak power point tracker is therefore necessary for maximum efficiency. A complete PV system equipped maximum power point tracking (MPPT) system includes a solar panel, MPPT algorithm, and a DC-DC converter topology. Each subsystem is modeled and simulated in a Matlab/Simulink environment; then the whole PV system is combined with the battery load to assess the overall performance when subjected to varying weather conditions. A PV panel model of moderate complexity based on the Shockley diode equation is used to predict the electrical characteristics of the cell with regard to changes in the atmospheric parameter of irradiance and temperature. In this dissertation, five MPPT algorithms are written in Matlab m-files and investigated via simulations. The standard Perturb and Observe (PO) algorithm along with its two improved versions and the conventional Incremental Conductance (IC) algorithm, also with its two-stage improved version, are assessed under different atmospheric operating conditions. An efficient two-mode MPPT algorithm combining the incremental conductance and the modified constant voltage methods is selected from the five ones as the best model, because it provides the highest tracking efficiencies in both sunny and cloudy weather conditions when compared to other MPPT algorithms. A DC-DC converter topology and interface study between the panel and the battery load is performed. This includes the steady state and dynamic analysis of buck and boost converters and allows the researcher to choose the appropriate chopper for the current PV system. Frequency responses using the state space averaged model are obtained for both converters. They are displayed with the help of Bode and root locus methods based on their respective transfer functions. Following the simulated results displayed in Matlab environment for both choppers, an appropriate converter is selected and implemented in the present PV system. The chosen chopper is then modeled using the Simulink Power Systems toolbox and validates the design specifications. The simulated results of the complete PV system show that the performances of the PV panel using the improved two-stage MPPT algorithm provides better steady state and fast transient characteristics when compared with the conventional incremental conductance method. It yields not only a reduction in convergence time to track the maximum power point MPP, but also a significant reduction in power fluctuations around the MPP when subjected to slow and rapid solar irradiance changes

Parity violation in polarized cold neutron capture

The longitudinal asymmetry in photons emitted during radiative neutron-proton capture depends cleanly on the neutral current contribution to the weak nucleonnucleon interaction. The NPDGamma experiment is an eort to measure this asymmetry with precision ten parts per billion, which is 10% of its range of predicted values. In 2006 the NPDGamma collaboration acquired its rst production dataset at the Los Alamos Neutron Science Center. A pulsed beam of polarized slow neutrons is incident on a 16 L parahydrogen target; capture photons are observed in current mode in a cylindrical array of CsI scintillators. In this initial experiment, roughly 730 hours running with 50-55% neutron polarization, we set a new upper limit of 210 parts per billion for the size of the NPDGamma asymmetry, a modest improvement over the existing limit. In the next stage of the experiment this limit will be greatly reduced with the increased neutron ux at the Spallation Neutron Source