Dissertations / Theses on the topic 'Stability Enhancement'
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1
Houghton, Timothy Oliver. "Axial compressor stability enhancement." Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/252194.
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Aircraft jet engines must operate in a stable manner at all times. One source of instability is compressor stall. Stall problems can be reduced by machining cavities into the compressor casing adjacent to the rotor blades. This ?casing treatment? is the focus of the present work. Two treatment configurations are tested: circumferential grooves cut into the casing above the rotor blades, and axial slots cut into the casing adjacent to the rotor blade leading edges. The performance of a single casing groove is measured at different axial locations over the blade tips. For the first time, it is shown that there are two locations where compressor stability is maximised; near the leading edge and near mid-chord. The interaction between the groove and the compressor flow field is then studied. It is found that when located near the leading edge, the groove has a strong interaction with the near-casing flow and tip leakage vortex, but when located near mid-chord, the interaction is more subtle and less damaging to efficiency. Since the groove works well in both locations, it is concluded that manipulating the tip leakage vortex is not critical for improving compressor stability. Different groove numbers and cross-sections are then tested. For multiple grooves, the effi- ciency reduction is the sum of the constituent grooves, while the stall margin improvement is less than this sum. A simple square-section groove is found difficult to improve on, although in certain circumstances, a new ?intermittent groove? geometry is beneficial. The performance of axial slots is then investigated. Different slot shapes are tested and the results added to previous work to suggest an optimum slot geometry. A computational flow study shows that large variations in blade loading occur as the blades pass the slots, which could cause noise and vibration. It is found that while the flow inside the slot is principally a quasi-steady recirculation, the interaction between the slots and blades is highly unsteady, and this unsteadiness should not be neglected in design. In general, it is found that casing treatments that generate large stability improvements cause large efficiency losses. It is shown for the first time that the performance of casing grooves can be seriously reduced by changes in the stall inception mechanism. Maximum performance is achieved when the treated compressor stalls with a spike inception. Models from the literature are tested, but do not predict the stall inception mechanism well, which makes predicting the performance of casing grooves in a given compressor hard. Finally, it is shown that designing the blades and casing treatment as a unit may improve compressor performance.
2
朱太秀 and Tai-xiu Zhu. "Knowledge-based assessment and enhancement of voltage stability." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B31236455.
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Zhu, Tai-xiu. "Knowledge-based assessment and enhancement of voltage stability /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B18061680.
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Cao, Qiang. "Stability control and throughput enhancement for slotted ALOHA networks." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265329.
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Voolapalli, Ravi Kumar. "Stability enhancement of anaerobic digestion through intermediate product regulation." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390626.
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Zhang, Tan. "Adaptive Energy Storage System Control for Microgrid Stability Enhancement." Digital WPI, 2018. https://digitalcommons.wpi.edu/etd-dissertations/190.
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Microgrids are local power systems of different sizes located inside the distribution systems. Each microgrid contains a group of interconnected loads and distributed energy resources that acts as a single controllable entity with respect to the grid. Their islanding operation capabilities during emergencies improve the resiliency and reliability of the electric energy supply. Due to its low kinetic energy storage capacity, maintaining microgrid stability is challenging under system contingencies and unpredictable power generation from renewable resources. This dissertation highlights the potential benefits of flexibly utilizing the battery energy storage systems to enhance the stability of microgrids. The main contribution of this research consists in the development of a storage converter controller with an additional stability margin that enables it to improve microgrid frequency and voltage regulation as well as its induction motor post-fault speed recovery. This new autonomous control technique is implemented by adaptively setting the converter controller parameters based on its estimated phase-locked loop frequency deviation and terminal voltage magnitude measurement. This work also assists in the microgrid design process by determining the normalized minimum storage converter sizing under a wide range of microgrid motor inertia, loading and fault clearing time with both symmetrical and asymmetrical fault types. This study evaluates the expandability of the proposed control methodologies under an unbalanced meshed microgrid with fault-induced feeder switching and multiple contingencies in addition to random power output from renewable generators. The favorable results demonstrate the robust storage converter controller performance under a dynamic changing microgrid environment.
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Ali, Muhammad. "Power System Stability Enhancement through Data Center Ancillary Services." Diss., North Dakota State University, 2015. https://hdl.handle.net/10365/27636.
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The primary objective of a control system is stability and steady-state performance under varying dynamics, such as faults and disturbances. The stable power system should continue to function properly in case of faults and disturbances. Stability of the power systems find applications in various domains, such as power delivery through Permanent Magnet Synchronous Generator (PMSG), Doubly-Fed Induction Generator (DFIG), and data centers. The goal of this dissertation is to design a robust control for a power system. We propose a hybrid Fault-Ride-Through (FRT) strategy for DFIG and two new PMSG grid-interfaced models, named PMSG Boost and PMSG Rectifier-Inverter. We analyze the aforesaid system using symmetrical and asymmetrical grid faults and observe the following parameters: (a) voltage support, (b) active and reactive power support, (c) stringent grid-code conduct, (d) overvoltage and overcurrent protection of rotor and stator, and (e) damped rotor oscillations in current and voltage. On the other side, we also propose a bi-directional model for power system and data centers. The goal of this research work is to increase the steady-state performance of the power system through computational capabilities of the data centers. Enormous energy consumption of data centers has a major impact on power systems by significantly increasing the electrical load. Due to the increase in electrical load, power systems are facing demand and supply miss-management problems. Therefore, power systems require fast and intelligent ancillary services to maintain robustness, reliability, and stability. Power system jobs will make this situation even more critical for data centers. In our work, we seek an Ancillary Services Model (ASM) to service data centers and power systems. In ASM, we find an optimal job scheduling technique for executing power systems? jobs on data centers in terms of low power consumption, reduced makespan, and fewer preempted jobs. The power systems? jobs include Optimal Power Flow (OPF) calculation, transmission line importance index, and bus importance index. Furthermore, a Service Level Agreement (SLA) between data centers and power systems is shown to provide mutual benefits.
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Qiu, Xiao. "Self-esteem, motivation, and self-enhancement presentation on WeChat." Scholar Commons, 2018. http://scholarcommons.usf.edu/etd/7221.
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The purpose of the present study was to analyze whether self-esteem stability moderated the association between self-esteem level and the forms of self-enhancement strategies. Previous research has found that self-esteem level can predict the forms of self-enhancement, whereas the advances in the conceptualization of self-esteem recommend that the self-esteem stability is another essential variable in terms of analyzing the relationship between self-esteem and self-enhancement. Depending on the relevant researches on use and gratification theory, which indicate that people use social media for self-enhancement and fulfilling their inner needs. This research focused on examining the forms of individual’s self-enhance on WeChat Circle of Friends (COF) and how it influenced by the interaction between self-esteem level and self-esteem stability by analyzing 305 participants in China. The results of the study show that both self-esteem level and stability was positively correlated with direct self-enhancement, but negatively correlated with indirect self-enhancement. Furthermore, the findings also show that self-esteem stability moderated the association between self-esteem level and direct self-enhancement such that individuals with stable high self-esteem reported higher levels of frequency in direct self-enhancement. However, the findings also revealed the self-esteem stability failed to moderate the association between self-esteem level and indirect self-enhancement presentation. These results suggest that self-esteem level and self-esteem stability will interact to impact the forms of self-enhancement. The importance of considering both stability and level of self-esteem in analyses of self-enhancement presentation on social media is discussed.
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Wu, Nancy Y. (Nancy Yue). "Stability enhancement of atomic timekeeping using Raman adiabatic rapid passage." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/119294.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 83-85).
Current state-of-the-art atomic clocks span the range from large accurate fountain clocks such as the NIST-F2 to relatively small inaccurate chip scale clocks. Small clocks with higher accuracy could greatly expand the range of applications for precision timekeeping, and enable cheaper implementation of existing applications. This type of clock may be realized by use of optical Raman interferometry based on pulsed interrogation of cold atoms. However, this method suffers from serious systematic error sources, e.g., AC Stark shift and Zeeman shift, which alter the atomic resonance frequency. A new method based on adiabatic rapid passage (ARP) has been recently demonstrated at Draper which has significantly reduced phase sensitivity to differential AC Stark shift. It is found that compared to standard Raman, use of ARP enhances timekeeping stability by a factor of three with stability of 2 x 10⁻¹² at 100 seconds. Increasing data rate may also improve short term stability. With all of the above improvements, ARP enhances short term fractional stability to 7 x 10⁻¹² at one second.
by Nancy Y. Wu.
S.M.
10
Weichert, Stephanie April. "Tip clearance flows in axial compressors : stall inception and stability enhancement." Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/243400.
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The flow in the rotor tip clearance gap in an axial compressor influences the loss levels and the stall onset point. The role of tip clearance flows in the stall inception process is still debated, though. The aim of this thesis is to improve the fundamental understanding of the tip clearance flow field and its role in the stall inception process. The knowledge gained is used to develop a new casing treatment for an aero-engine core compressor. Detailed static pressure, total pressure, and velocity measurements were made in the rotor tip clearance gap at design and near stall flow conditions. The resulting overtip flow maps showed the flow field in more detail than previously possible. Flow variations around the annulus and among blade passages were analyzed and found to increase as stall is approached. This increase was not uniform around the annulus or among passages; instead, some blade passages exhibited unique behaviour compared to all the other passages. The flow variations in the unique passages were linked to small physical irregularities in compressor blading. Detailed overtip measurements were also made at stall inception to investigate the formation of the spike disturbance. These measurements, the first of their kind, showed that the disturbance which initiates the formation of the spike destabilizes the boundary between the reversed flow and incoming flow. After destabilization, reversed flow increasingly dominates the passage until the neighbouring passage is affected. The spike was found to originate most often from those regions in the compressor where the flow variations are highest and was not, as suggested by some research, associated with the forward movement of the tip leakage vortex. A new casing treatment for axial compressors was proposed and tested. The casing treatment extracts air from over the rotor blade tips and re-injects it upstream of the rotor blade leading edges into the tip region through discrete re-circulation loops. The overtip location of air extraction is unique and enables self-regulation of the amount of flow re-circulated: a minimum amount of air is re-circulated at compressor design conditions (thus minimizing any loss of efficiency) and a maximum amount of air is re-circulated near the stability limit (thus maximizing stall margin). Modest stall margin improvements (2%) were achieved without any loss of compressor efficiency at design conditions.
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Nazari, Hamid. "Enhancement of operational stability of glucose oxidase by immobilization on nylon." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0010/NQ41480.pdf.
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Ahmed, Faisal Mahmood. "Estimated Droop Control for Parallel Connected Voltage Source Inverters : Stability Enhancement." Thesis, Karlstads universitet, Avdelningen för fysik och elektroteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-30794.
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Renewable Energy Sources (RES) are considered as the replacement of conventionalenergy sources. These RES can use wind energy, solar light, bio waste and can alsobe in the form of small hydro power units. These RES has very poor power qualityand contains voltage uctuations and variable frequency. These factors make RES astability risk for the main utility grid. As a solution, currently inverters with dierentdesign techniques are being used as an interface between RES and main utility grid. Thecurrent study proposed a new technique "estimated droop control" for inverter design.The conventional droop control technique which was already used in inverter design, hasdiculty in synchronizing parallel connected inverters with dierent droop gains and lineimpedances. The proposed "estimated droop control" does not use any predened droopvalues for inverters and all inverters are responsible for the estimation of their own droopvalues with respect to their output power. Therefore, inverters are not bound to usesame and static droop values which are considered as a vital communication link. Theproposed design methodology has made inverters independent from this only virtual linkof communication due to which the reliability of a system has increased. The proposeddesign technique has given very good results in a simulation run. When the Simulinkmodel was run in parallel connected inverter with dierent line impedances, it was asuccess as both inverters started operating with same droop values as they were sharingan equal load. The most important test was with dierent line impedances because inconventional droop control it is dicult for inverters to keep their synchronism withdierent line impedances and an unequal load sharing make inverters to deviate fromtheir nominal values and to generate dierent tracking signals for each set. This problemhas been successfully solved with estimated droop control as in this method each inverterset its droop gains according to its output power, which helps an inverter to operate atnominal values with dierent droop gains and line impedance.
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Lakkireddy, Jahnavi. "Steady State Voltage Stability Enhancement Using Shunt and Series FACTS Devices." ScholarWorks@UNO, 2014. http://scholarworks.uno.edu/td/1881.
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It is specifically important to focus on voltage stability analysis of the power system to avoid worst case scenarios such as voltage collapse. The purpose of this thesis is to identify methods for enhancing the steady-state voltage stability using FACTS devices and determining their impact on real and reactive power losses, improvement of bus voltage magnitude, and transmission line loadability. To achieve this, FACTS devices such as Static VAR Compensator (SVC), Static Synchronous Compensator (STATCOM), and Thyristor Controlled Series Capacitor (TCSC) are used in the test system as three separate test cases. The results obtained assist in drawing conclusions on the effectiveness of each FACTS devices at generator, load and swing buses, on lines between two load buses, and between a load bus and a generator bus, in terms of metrics such as voltage magnitude profile, PV curves, and active and reactive power losses.
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Gade, Prasad V. N. "Performance Enhancement and Stability Robustness of Wing/Store Flutter Suppression System." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30339.
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In recent years, combat aircraft with external stores have
experienced a decrease in their mission capabilities due to
lack of robustness of the current passive wing/store flutter
suppression system to both structured as well as unstructured
uncertainties. The research program proposed here is to
investigate the feasibility of using a piezoceramic wafer
actuator for active control of store flutter with the goal
of producing a robust feedback system that demonstrates
increased performance as well as robustness to modeling
errors. This approach treats the actuator as an active
soft-decoupling tie between the wing and store, thus isolating
the wing from store pitch inertia effects. Advanced control
techniques are used to assess the nominal performance and
robustness of wing/store system to flutter critical
uncertainties.
NOTE: (10/2009) An updated copy of this ETD was added after there were patron reports of problems with the file.Ph. D.
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Juanuwattanakul, Parachai. "Bus voltage ranking and voltage stability enhancement for unbalanced multiphase networks." Thesis, Curtin University, 2012. http://hdl.handle.net/20.500.11937/301.
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Voltage instabilities and subsequent system collapses are considered as growing concerns in modern multiphase distribution networks as they are progressively forced to operate closer to their stability limits due to many factors such as increasing load level, lack of reactive power sources, high installation of single-phase shunt capacitors and reverse action of voltage control devices. System operators must be able to quickly identify trouble spots and take corrective steps to avoid critical voltage collapses. To achieve this, suitable indices must be defined to assess system security and take corrective control actions when predefined thresholds are reached. In this regard, the identification and ranking of weak buses in a power system is an important research area.The existing conventional bus voltage ranking indices are only defined for single-phase and balanced three-phase networks. This thesis proposes a new bus voltage ranking index (VRI) to identify the weakest single-, two- and three-phase buses of multiphase distribution networks. Then, applications of the proposed bus ranking index will be tested for enhancing the voltage stability of unbalanced multiphase distribution networks.In the first part of this thesis, the definition of conventional voltage ranking indices are modified and generalized to also include unbalanced and multiphase networks using symmetrical components. For the first time, the method of symmetrical components is applied to the three-phase voltages computed from three-phase power flow. The new index is defined as the ratio of the (fundamental) positive-sequence voltage at the point of voltage collapse to the positive-sequence voltage at the base-load source. The former voltage level is determined by increasing the active power of all loads while keeping power factor constant until the point of voltage collapse is reached.In the second part of this thesis, the new VRI is validated through the calculation of grid losses and PV curves based on positive-sequence voltage. Extensive simulations of the IEEE 13 and 34 node test feeders are performed using the DIgSILENT PowerFactory to further validate and compare the performance of the new VRI with three well-known conventional ranking indices.In the third part of the thesis, the new VRI is used to identify the weakest three-phase buses in unbalanced three-phase distribution networks. Then, the index is utilized to place compensation devices at the weakest buses of the modified unbalanced three-phase 13 node test feeder to improve voltage stability and increase the maximum loading factor (MLF) under unbalanced three-phase operating conditions.In the fourth part of the thesis, static analyses are carried out to demonstrate applications of the proposed VRI in increasing MLF and improving voltage stability of multiphase networks under unbalanced loading and/or network conditions. Then, dynamic simulations are performed to further validate the accuracy of the proposed VRI and improving voltage stability under dynamic operating conditions.In the fifth part of the thesis, an online application of the proposed bus ranking is introduced to identify the weakest buses in multiphase smart grids with plug-in electric vehicle (PEV) charging stations.Finally, the proposed voltage ranking and stability enhancement approach are utilized to improve the performance of multiphase distribution networks by proper placement and sizing of distributed generator (DG) units such as doubly-fed induction generators (DFIGs) and single-phase capacitors. An iterative algorithm is proposed for the placement and sizing of DG units and single-phase capacitors in multiphase networks to reduce grid losses and increase MLF while keeping all bus voltages within acceptable limits. The approach consists of utilizing the positive- sequence voltage ratio Vcollapse/Vbase-load to identify the weakest three-phase and single-phase buses for the installation of DG units and shunt capacitors, respectively. DG penetration levels are increased (e.g., 40%) by evaluating their impacts on voltage profile, grid losses, and voltage stability margin while considering the voltage limits at all buses. The impacts of DIFG on voltage profile, active power loss, MLF and voltage unbalance factor are highlighted.
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Salih, Embaiya. "Superconducting magnetic energy storage for power system stability and quality enhancement." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2018. https://ro.ecu.edu.au/theses/2084.
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The stability of power systems has become the most critical issue affecting their quality and performance. Concerns over climate change are now moving the energy sector into a new era of modern power grids. To sustain the reliable operation of power systems and improve the quality of power generation, several instability issues that affect the quality of the operation of power systems are addressed in this thesis. The first is the fluctuations in generated power due to variations in wind velocity in wind power systems. The fluctuation in the wind, which is the main energy source in a wind power system, leads directly to voltage and frequency fluctuations in both generation and load and affects the stability of power systems. In microgrids, a long period of transient, which occurs after the switching operation of microgrid (MG) and load demand changes, is the second issue addressed. The third instability issue is the impact of instability on the power load because of voltage and frequency variations.
Therefore, as a contribution to overcoming the impacts of these instability issues on power systems, this thesis proposes to apply a superconducting magnetic energy storage (SMES)-based neural network (NN) control strategy to enhance the quality of the wind power supply, increase the stability of the MG, and protect critical power loads. In this research, as a method, NNs and the adaptive control method are proposed and applied to control the power flow via its power conversion system. NNs are applied to forecast renewable energy as a short-term prediction of wind power fluctuations. The backpropagation function is used for training the NNs on wind speed variations and then NN is used as a predictive controller. To increase the stability of wind power systems, the proposed SMES-based NN is connected to a wind power system for stabilising wind power fluctuations. SMES-based NN is also applied to an MG to reduce the transient period that occurs after switching of the MG and because of the load demand changes. Furthermore, SMES is operated as an uninterruptible power supply (UPS) to reduce the fluctuations in generated power to protect the critical loads.
In this research, an NN controller is built and trained to predict and track the fluctuations of wind power. This NN controller as a reference model, along with the adaptive control strategy, is implemented and applied as a control system for SMES. The behaviour of the proposed system is verified to decrease the voltage and frequency fluctuations in wind power supply with variations of wind speed. The results show that with a high dynamic response, the proposed NN controller based SMES maintains the voltage and frequency within acceptable limits and stabilises its generating power significantly. Also, the reliability of the SMES-NN for stabilising an MG is investigated. The results verify that the MG was stabilised under the proposed power controller. Moreover, the system’s ability to protect and support the loads during power interruptions and instability events affecting the quality of the supply is tested. The results show that as a short-term storage system, the UPS-SMES efficiently protects the loads by injecting power into the system when it is needed.
Consequently, this research with the developed techniques of reducing instability impacts on power systems could underpin the reliability of renewable power sources as well as supporting and protecting equipment and power loads from such critical issues.
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Kanchanaharuthai, Adirak. "Small-Signal Stability, Transient Stability and Voltage Regulation Enhancement of Power Systems with Distributed Renewable Energy Resources." Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1321988036.
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Cai, Hui. "Enhancement of power system dynamic stability using electric vehicles and distributed generation." Thesis, Queen's University Belfast, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602450.
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This thesis proposes a method to establish the accurate parameters of stabilisers in the context of power systems with increasing penetration of Doubly Fed Induction Generators (DFIGs), Solid Oxide Fuel Cells (SOFCs) and Photovoltaic (PVs) using a hierarchical coordinated strategy and localised design. The performance of the tuned stabilisers is verified using modal analysis results and non-linear simulation. This thesis proposes that by using regulated stabilisers, the dynamic stability of a power system with large-scale Distributed Generation (DG) integration can be maintained. SmartParks have been proposed in published literature to support emergent electric vehicle charging. In practice, a SmartPark can be configured as an adjustable load, in charging mode, or a regulated generator, in a discharging mode using a voltage control strategy. In this thesis, damping torque analysis (DTA) has been used to investigate the impact on dynamic stability of the joint operation of SmartParks in power systems with conventional synchronous machines. The analysis reveals that in terms of the local damping ratio, optimal charging and local capacity is best considered during SmartPark design. According to a Phillips-Heffron model developed for a multi-machine system with SmartPark, active and reactive power stabiliser can be incorporated into the SmartPark control loops to improve the damping of the system. Finally, this thesis considers the economic operation of micro-grids by proposing a combined EV charging/discharging model which incorporates stochastic uncertainties in vehicle travel patterns and initial battery state of charge (SOC). The model includes provision of energy storage and renewable generation infeed is used to establish an economic basis for micro-grid operation based on market revenues.
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Alsafih, Hamza A. "Transmission stability enhancement using Wide Area Measurement Systems (WAMS) and critical clusters." Thesis, University of Bath, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607141.
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Due to the on-going worldwide trend towards investment in de-regulated electricity markets driven by political, economic and environmental issues, increasing interconnection between modern power systems has made power system dynamic studies much more complex. The continuous load growth without a corresponding increase in transmission network capacities has stressed power systems further and forced them to operate closer to their stability limits. Large power transfers between utilities across the interconnections stress these interconnections. As a result, stability of such power systems becomes a serious issue as operational security and reliability standards can be violated. On the other hand, the evolving technology of Wide-Area Measurement Systems (WAMS) has led to advanced applications in Wide-Area Monitoring, Protection and Control (WAMPAC) systems, which offer a cost-effective solutions to tackle these challenging issues. The main focus of this research project was to develop a wide-area based stability enhancement control scheme for large interconnected power systems. A new method to identify coherent clusters of synchronous generators involved in wide area system oscillations was the initial part of the work. The coherent clusters identification method was developed to utilise measurements of generators speed deviation signals combined with measurements of generators active power outputs to extract coherency property between system's generators. The obtained coherency property was then used by an agglomerative clustering algorithm to group system's generators into coherent clusters. The identification of coherent clusters was then taken as a base to propose a new structure of a WAMS based stability control scheme. The concept of WAMS and a nonlinear control design approach (fuzzy logic theory) was used to provide a comprehensive new control algorithm. The objectives of the developed control scheme were to enhance and improve the control performance of modern power systems. Thus, allowing improved dynamic performance under severe operation conditions. These objectives were achieved by means of enhanced damping of power system oscillations, enhanced system stability and improved transfer capabilities of the power system allowing the stability limit to be approached without threatening the system security and reliability.
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Hassan, Faiza. "Heterogeneous catalysis in supercritical fluids : the enhancement of catalytic stability to coking." Thesis, University of Birmingham, 2011. http://etheses.bham.ac.uk//id/eprint/3166/.
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Catalytic deactivation caused by coking was studied in ZSM5 and zeolite Y catalysts during the isomerisation of 1-hexene under sub and supercritical conditions. The effects of varying temperature and pressure, from 220–250 °C and 10-70 bar respectively, on conversion and coke deposition were studied in both zeolites. TGA, DRIFTS, nitrogen sorption isotherms for fresh and coked catalysts and catalyst acidity measurements were compared. In ZSM5 the catalyst was stable for 96 hours. TGA and DRIFTS results show coke deposits were mainly polyolefinic and the amount decreases considerably from 18.8 wt% in the subcritical region to 10 wt% in the supercritical region. In zeolite Y, decay in conversion was observed with the rate of deactivation being slower at supercritical conditions at 235 °C and 40 bar. Naphthalene hydrogenation on NiMo/γ-Al2O3 catalyst was also studied. The effect of temperature, pressure, varying naphthalene feed concentration and operating in sub and supercritical conditions were studied. Coke deposit decreased by 38 wt% in the supercritical region. SC CO2 (Tc 31.04 °C, Pc 73.8 bar) was also used to re-activate the coked catalysts. This resulted in recovering 93% of the catalytic activity and 37% of the coke was effectively extracted by SC CO2.
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Hsiao, Hui-Chun. "ANTHOCYANIN COLOR ENHANCEMENT BY USING CATECHIN AS COPIGMENTS AND STABILITY DURING STORAGE." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397748937.
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Elkington, Katherine. "On the Use of Wind Power for Transient Stability Enhancement of Power Systems." Thesis, KTH, Elektriska energisystem, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-118931.
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This report deals with the impact of doubly fed induction generators on the stability of a power system. The impact was quantified by means of detailed numerical simulations. The report contains a full description of the simulation, and details of the small signal analysis performed to analyse the system. Before the simulation results are presented, a foundation is laid, explaining the theory required to understand the models used and the calculations performed in the simulation. The derivation of a model of a doubly fed induction generator is presented, along with a description of the model of a synchronous generator. These are used in the simulation and analysis of a multi-machine power system, consisting of both of these types of generators. An explanation of how dynamic simulations of power systems can be performed is also put forward. This is useful, not only for understanding the simulation performed for this report, but as a guide to performing simulations of this type. This is true also for a description of linearisation and small signal analysis contained in this report. The software package MATLAB is used to perform the simulations, and the small signal analysis. Since the method described in this report is very general, it can be used to perform similar power system simulations for other power systems, and with other software. Numerical simulations reveal that the addition of doubly fed generators, such as those in wind parks, to a power system improves the response of the system after small disturbances, but can worsen it after larger disturbances.
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Fu, Le. "Voltage stability monitoring and enhancement in electrical power systems using transformer tap changers." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.506484.
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GREENHALGH, ANGELA BARBOSA. "VOLTAGE STABILITY ENHANCEMENT IN THE OPERATION OF POWER SYSTEMS THROUGH AN OPTIMIZATION MODEL." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1998. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8943@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORMuito tem sido feito para que se possa entender os mecanismos que levam o sistema a uma situação de instabilidade de tensão e até mesmo ao colapso, assim como também para se suprir a necessidade de ferramentas analíticas capazes de prever e avaliar a proximidade do colapso de tensão em sistemas complexos, identificando as áreas susceptíveis à instabilidade de tensão. Uma vez detectada a inconveniente proximidade a uma condição de operação susceptível ao colapso de tensão, é necessária a identificação de grandezas-chave e sensibilidades, que forneçam entendimento suficiente, para ajudar no desenvolvimento de metodologias para reforçar as condições de estabilidade de tensão. Tendo isto como objetivo, este trabalho trata do problema de reforço da estabilidade de tensão através da mudança do perfil de tensão, utilizando como ferramenta computacional um algoritmo de otimização. Há no sistema variáveis de controle que interferem diretamente no perfil de tensão, tais como, tensão base nos geradores e compensadores, taps de transformadores, e capacitadores e reatores usados para compensação de potência reativa. Entretanto, quando as condições de estabilidade já se encontram deterioradas, as ações de controle do perfil de tensão podem levar a resultados insatisfatórios, podendo mesmo agravar o problema. Neste trabalho é apresentada uma metodologia, baseada em algoritmo de otimização, que fornece a lista de variáveis de controle mais eficientes para o reforço da estabilidade de tensão, e a direção em que os controles devem ser acionados. O interesse é obter um ponto de operação viável mais robusto, do ponto de vista de estabilidade de tensão, e não necessariamente um ponto de operação ótimo.
Much hás been done for the understanding of the voltage instabilitu mechanisms and to supply the necessity of analytical tools, which should have the ability tom predict and evaluate the proximity of voltage collapse in complex systems, identifying the critical áreas susceptible to voltage istability. Once the inconvenient proximity to an operating condition susceptible to voltage collapse is identified, it is necessary to look for the key factors and sensitivities that provide the reinforcement of the voltage stability conditions. Having it as a goal, this work treats the problem of reinforcing the voltage stability conditions, through changes of the voltage profile, using an optimal algorithm as a computational tool. There are control variables in the system which directly interfere on the voltage profile, such as, voltage set point on generators and compensators, transformer taps, capacitors and reactors. However, when the voltage stability conditions are already deteriorated, the voltage profile control actions may lead to unsatisfactory results, and may even aggravate the problem. It is presented a methodology based on an optimal, that provides the list of the most efficient control variables for the reinforcement of voltage stability, and the corresponding direction of movement. The search is for a feasible operating point, more robust in relation to voltage stability, and not necessarily for an optimal operating point.
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Behbehani, Hussain M. "Enhancement of power system stability using fuzzy logic based supervisory power system stabilizer." Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/10778.
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Maintaining power system stability has become a challenging task for engineers. A consequence of such factors is that power system damping of electro-mechanical oscillations is often reduced which could sometimes destabilise the power systems if the electro-mechanical oscillations are poorly/lightly damped. Decentralised power system stabilisers are often used to increase damping of local oscillation modes and to some extent to increase damping of inter-area oscillation modes. However, damping of inter-area oscillations modes by the local PSS is not quite effective as for local oscillation modes. Therefore, it is necessary to implement a new control strategy to enhance damping of inter-area oscillation modes. With today’s advancement of phasor measurement units (PMUs), global information, which contains valuable information about the existence of inter-area oscillation modes, could be possibly used as inputs to mitigate inter-area oscillations as the literature suggests. The aim of this thesis is to propose supervisory power system stabilisers (SPSS) which are based on Fuzzy Logic to improve damping of such electro-mechanical oscillations in particular inter-area oscillation modes. Three different structures of supervisory power system stabilisers are presented in this thesis. The inputs to the proposed supervisory damping controllers will use global signals, speeds and their derivatives; however, the structure of the inputs to the supervisory power system stabilisers is different depending on the structural design of SPSS. The uniqueness of each SPSS type proposed is that they all make use of the same control rules regardless to which power system is applied. The robustness of such control rules and proposed SPSS are verified on three different test systems as the results of the case studies demonstrate. The time domain simulations will highlight the impact of each SPSS type on the system response.
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Almutairi, Abdulaziz. "Enhancement of power system stability using wide area measurement system based damping controller." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/enhancement-of-power-system-stability-using-wide-area-measurement-system-based-damping-controller(7d98d164-8051-4662-ad18-374620d28a00).html.
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Contemporary power networks are gradually expanding incorporating new sources of electrical energy and power electronic based devices. The major stability issue in large interconnected power systems is the lightly damped interarea oscillations. In the light of growth of their incidents there are increased concerns about the effectiveness of current control devices and control systems in maintaining power system stability. This thesis presents a Wide Area Measurement System (WAMS) based control scheme to enhance power system stability. The control scheme has a hierarchical (two-level) structure comprising a Supplementary Wide-Area Controller (SWAC) built on top of existing Power System Stabilisers (PSSs). The SWAC's focus is on stabilising the critical interarea oscillations in the system while leaving local modes to be controlled entirely by local PSSs. Both control systems in the two levels work together to maintain system stability. The scheme relies on synchronised measurements supplied by Phasor Measurement Units (PMUs) through the WAMS and the only cost requirement is for the communication infrastructure which is already available, or it will be in the near future. A novel linear quadratic Gaussian (LQG) control design approach which targets the interarea modes directly is introduced in this thesis. Its features are demonstrated through a comparison with the conventional method commonly used in power system damping applications. The modal LQG approach offers simplicity and flexibility when targeting multiple interarea modes without affecting local modes and local controllers, thus making it highly suitable to hierarchical WAMS based control schemes. Applicability of the approach to large power systems is demonstrated using different scenarios of model order reduction. The design approach incorporates time delays experienced in the transmission of the SWAC's input/output signals. Issues regarding values of time delays and required level of detail in modelling time delays are thoroughly discussed. Three methods for selection of input/output signals for WAMS based damping controllers are presented and reviewed. The first method uses modal observability/controllability factors. The second method is based on the Sequential Orthogonalisation (SO) algorithm, a tool for the optimal placement of measurement devices. Its application is extended and generalised in this thesis to handle the problem of input/output signal selection. The third method combines clustering techniques and modal factor analysis. The clustering method uses advanced Principal Component Analysis (PCA) where its draw backs and limitations, in the context of power system dynamics' applications, are overcome. The methods for signal selection are compared using both small signal and transient stability analysis to determine the best optimal set of signals. Enhancement of power system stability is demonstrated by applying the proposed WAMS based control scheme on the New England test system. The multi-input multi-output (MIMO) WAMS based damping controller uses a reduced set of input/output signals and is designed using the modal LQG approach. Effectiveness of the control scheme is comprehensively assessed using both small signal and transient stability analysis for different case studies including small and large disturbances, changes in network topology and operating condition, variations in time delays, and failure of communication links.
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Sagha, Hossein. "Development of innovative robust stability enhancement algorithms for distribution systems containing distributed generators." Thesis, Queensland University of Technology, 2015. https://eprints.qut.edu.au/91052/1/Hossein_Sagha_Thesis.pdf.
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This project was a step forward in improving the voltage profile of traditional low voltage distribution networks with high photovoltaic generation or high peak demand. As a practical and economical solution, the developed methods use a Dynamic Voltage Restorer or DVR, which is a series voltage compensator, for continuous and communication-less power quality enhancement. The placement of DVR in the network is optimised in order to minimise its power rating and cost. In addition, new approaches were developed for grid synchronisation and control of DVR which are integrated with the voltage quality improvement algorithm for stable operation.
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Bricker, Garrett Demyan. "Analytical Methods of Testing Solid Waste and Leachate to Determine Landfill Stability and Landfill Biodegradation Enhancement." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/35162.
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This was a study undertaken to investigate municipal solid waste (MSW) landfill stability parameters and landfill leachate properties to determine how solid waste and leachate characteristics can be used to describe stability. The primary objective was to determine if leachate properties could be used to determine stability of the overlying refuse. All landfills studied were engineered landfill bioreactors giving insight to how leachate recirculation affects stability.
This study investigated the correlation between cellulose, lignin, volatile solids, and biochemical methane production (BMP). These parameters can been used to characterize landfill stability. The BMP tests indicate that a saturated waste can produce methane. Cellulose is an indicator of landfill stability. Wastes high in cellulose content were found to have high BMP. Paper samples studied indicated gas production from high-cellulose paper was higher compared to low-cellulose samples. Lignin has been found to correlate fairly well with BMP. Increasing cellulose to lignin ratios correlate well with increasing BMP levels, further supporting the use of the BMP test to indicate solid waste stability.
In the BMP test for leachate, a mixture of the standard growth medium (less 80% distilled water) and 80% v/v leachate incubated for 15 days produced the most consistent BMP results. Leachate cellulose and BMP correlated well. The chemical oxygen demand (COD) and biochemical oxygen demand (BOD) also had some correlation to BMP tests. Leachate COD was found to decrease over time in landfill bioreactors. The use of leachate rather than MSW to determine stability would be more efficient.Master of Science
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VEGA, JORGE LEONIDAS LAFITTE. "VOLTAGE STABILITY ASSESSMENT AND ENHANCEMENT IN VOLTAGE-CONTROLLED BUSES BY SYNCHRONOUS GENERATORS AND COMPENSATORS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2009. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=14009@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOApós a incidência de alguns colapsos de tensão em sistemas de transmissão de energia a nível mundial, a segurança de tensão tornou-se um assunto de muito interesse nos últimos anos devido à importância do seu impacto. O fenômeno de estabilidade de tensão deve-se a fluxos de potência ativa e reativa excessivos na rede de transmissão e está associado às restrições ambientais e econômicas que impedem a expansão da rede. Atualmente, sabese da existência de uma máxima carga que pode ser alimentada pela rede e é a manifestação mais conhecida do fenômeno mas, também, é possível que o problema manifeste-se pela existência de uma máxima injeção de potência ativa e reativa na rede por geradores e compensadores síncronos. E mais, em situações de carregamento elevado da rede, é possível que ações de controle de tensão tenham efeito oposto ao usual. É apresentado um método seqüencial iterativo de avaliação e reforço para as condições de carregamento da rede em barras de tensão controlada, embora na literatura somente as barras de carga são analisadas. A verificação do comportamento do gerador e compensador síncrono como dispositivo de controle torna-se necessária já que, se funcionar de forma inversa, poderá levar o sistema ao colapso por problemas de tensão. Uma vez que a avaliação do carregamento da rede de transmissão detectou uma barra de geração crítica em um determinado ponto de operação, o reforço consiste do cálculo de ações de controle para aumentar a distância ou margem de potência entre a geração daquela barra e o novo máximo permitido. Muitas vezes isso pode ser conseguido através da alteração do perfil de tensão com a conseqüente redução nas perdas. Muitas outras vezes, o redespacho de potência ativa torna-se necessário. As etapas do método são: identificar a barra crítica, identificar a sub-rede utilizada para transmitir potência ativa dessa barra para as cargas, nessa sub-rede determinar o caminho e ramo mais carregados e, desviar o fluxo de potência do ramo mais carregado para outros. A seqüência é repetida até que as novas margens de potência sejam consideradas aceitáveis. Exemplos numéricos ilustrativos reais com o sistema brasileiro são apresentados. É verificado que o método proposto realmente produz os resultados desejados.
After the incidence of some voltage collapses in the energy transmission systems in the world, the voltage security became an issue of great interest in the last years due to the importance of its impact. The phenomenon of voltage stability is due to the excessive active and reactive power flow in the electrical transmission network and has been associated with environment questions and lack of financial resources for transmission system expansion. Nowadays, it is well-known that there is a maximum power that the network can transmit to a load bus and is the best known manifestation of the phenomenon, but, is not familiar to many that there is a maximum power that can be injected by generators and synchronous compensators into the network. Moreover, in heavy loading conditions is possible that voltage control actions would have the inverse effect. It is shown a sequential iterative method for assessment and voltage security reinforcement in voltage-controlled buses, although the literature only the load buses are analyzed. The verification of the behaviour of the generator and synchronous compensator as control device becomes necessary since, if it works in an inverse way, it can take the system to the voltage collapse. Once the assessment is performed and is detected one generation critical bus in some operating point, the objective of the reinforcement function is to calculate adequate control actions in order to increase the distance or power margin between the actual generation and the new maximum power flow. Several times this may be achieved by voltage profile changes and consequent loss reduction. Sometimes that procedure is not enough and active generation rescheduling is recommended. The stages of the method are: identify the critical bus, identify the sub-network used to transmit active power flow from this bus to load buses, in this sub-network the critical transmission path and critical branch are determined and redirect the power flow from the branch more loaded to others. The sequence is repeated until resultant power margins are judged suitable. Illustrative real life numerical examples with the Brazilian system are provided. It is verified that the proposed method really produces the desired results.
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Chen, Yu-Jen. "The solubility enhancement and the stability assessment of rifampicin, isoniazid and pyrazinamide in aqueous media." Thesis, Rhodes University, 2000. http://hdl.handle.net/10962/d1005009.
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Tuberculosis (TB) is a highly contagious disease caused by the bacterium known as Mycobacterium tuberculosis which is widely spread in South Africa, especially in the rural areas of the Western Province. Rifampicin, isoniazid and pyrazinamide are the three most effective drugs against this organism. However, most of the current commercial anti-TB formulations are inconvenient to administrate. This results in patient non-compliance which has increased with incomplete tuberculosis treatment and further has intensified the mortality rate. The matter is especially severe amongst the paediatric and geriatric patients. Therefore, creating a "user-friendly" but non-alcoholic liquid formulation should improve the whole situation. The key to a successful formulation relies on sufficient concentrations of the drugs within the formulation together with acceptable stability of these drugs. Therefore, during the pre-formulation stage, the solubility and stability studies of rifampicin, isoniazid and pyrazinamide are to be conducted. Rifampicin, isoniazid and pyrazinamide were fully characterized and identified by means of spectroscopic and thermal techniques. A HPLC method for simultaneous analysis of the three drugs was developed and validated. This HPLC method was employed for all the solubility and stability assessments. Unbuffered HPLC water of pH value 7.01 was chosen as the aqueous solvent. This was decided after the stability of rifampicin, isoniazid and pyrazinamide was studied at a pH range of 2 to 10. The solubility and the stability studies of rifampicin, isoniazid, pyrazinamide, rifampicin with isoniazid, rifampicin with pyrazinamide, isoniazid with pyrazinamide and rifampicin combined with both isoniazid and pyrazinamide were performed in the presence of various agents. These agents can be categorized into three groups: the surfactants (poloxamer 188, poloxamer 407 and sorbitol) which could increase the intrinsic solubility or the drugs by altering the surface tensions of the aqueous solution medium, the suspending agents (carbopol 934 and carbopol 974P) which could enable the amount of dosage required to be homogeneously suspended in the formulation without considering the low intrinsic solubility factor of the drugs, and the complexing agents (ß-cyclodextrin, hydroxypropyl-ß-cyclodextrin and -cyclodextrin) which could initiated the inclusion complex between the host cyclodextrin and the drugs, thus further enhance the solubility of the drugs . The stability assessments were performed after 7-days stability trail with the HPLC method developed. Each drug/combination of drugs were stored in closed ampoules and subjected to 25, 40 and 60° C with or without nitrogen flushing while in the presence of the above mentioned agents. While assessing the solubility/stability of the drugs in the presence of the above mentioned surfactants, the phase-solubility curves indicate that both rifampicin and pyrazinamide fail to achieve the desired concentration. Moreover, the stability-time plots clearly indicate that these surfactants fail to enhance the general stabilities of the drugs. When the stabilizing effects of the above mentioned suspending agents were investigated, it was found that although the desired concentration could be easily accomplished by suspending the drug in the aqueous carbopol solutions, the stabilities of the different drug combinations were still below the regulatory level. Cyclodextrins are well known to form inclusion complexes with less polar drug molecules. The inclusion complexation could enhance both the solubility and the stability of the included drug molecules. The computer force field generated models of the cyclodextrin-drug were used to predict the complexation sites. The results indicated the all the inclusion complexation between the drugs and the cyclodextrins were favourable, but do not necessary protect the potential degradation sites of the drugs. The stability results confirmed the above findings as the cyclodextrins did not enhance the stability of the drugs. Various drug-drug interaction pathways were also predicted from the experimental observations which clearly indicated the stability reductions of these drugs in combination. This leads to the conclusion that a liquid formulation combining rifampicin, isoniazid and pyrazinamide should not initiate the use of aqueous solutions as the protic ions of the solution are able to initiate the degradation of these drugs.
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Joseph, Tibin. "Operation and control of voltage source converters in transmission networks for AC system stability enhancement." Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/111498/.
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The rapid expansion in power transmission for the integration of large-scale renewables is foreseen in the future. This will be complemented by infrastructure reinforcements in the form of series compensation and high-voltage direct current (HVDC) links. These changes will bring forth new operability challenges to grid operators. The stability issues pertained to such reinforcements: potential threat of subsynchronous resonance (SSR) and frequency regulation will be investigated in this thesis. Utilising the existing and future voltage source converters (VSC) based HVDC links to support the AC system by proving ancillary services will be of significant importance in the coming decades. The research work presented in this thesis is aimed to address these challenges, in particular, the technical barriers associated with AC/DC interaction and to propose measures to avoid any potential instability. The main contributions of this research work comprise of four parts, namely, (1) analysis of interactions in-terms of SSR in AC/DC grids, (2) design of SSR damping (SSRD) controllers, (3) experimental demonstration of SSRD schemes, and (4) assessment and improvement of frequency regulation in a wind-thermal bundled AC/DC grid. An VSC-HVDC connected series-compensated AC system resembling the Great Britain (GB) power system has been used as the test network to evaluate the operability challenges pertained to the reinforcements. A state-space representation has been formulated and an eigenvalue analysis has been performed to assess the impact of VSC-HVDC on the torsional modes of nearby connected thermal generation plants. This is followed by damping torque investigation for SSR screening with the results compared against time-domain simulations for testing the accuracy of the small-signal models for SSR studies. A series of SSRD schemes is presented which have been integrated with the VSC-HVDC to damp SSR in the series-compensated GB power system. In addition, this thesis proposes an adaptive SSRD method based on the real-time estimation of the subsynchronous frequency v Abstract component present in series-compensated transmission lines–key information for the optimal design of HVDC subsynchronous damping controllers. Furthermore, the combined AC/DC GB network has been implemented in a real-time digital simulator and connected to a VSCHVDC scaled-down test-rig to performhardware-in-the-loop tests. The efficacy and operational performance of the AC/DC network while providing SSR damping is tested through a series of experiments. In order to provide frequency support in a wind-thermal bundled AC/DC system a dualdroop controlmethod is presented. The scheme binds the system frequency with the DC voltage of an HVDC network. For completeness, the performance of the proposed method is compared to conventional frequency regulation schemes. Sensitivity studies and eigenvalue analyses are conducted to assess the impact that wind penetration and changes in the dual-droop coefficient have on grid stability. Experimental validation is performed using a real-time hardware-inthe- loop test-rig, with simulation and experimental results showing a good agreement and evidencing the superior performance of the proposed frequency support scheme.
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麥禮安 and Lai-on Mak. "Fuzzy logic statcom controller design with genetic algorithm application for stability enhancement of interconnected power systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B42128699.
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Mak, Lai-on. "Fuzzy logic statcom controller design with genetic algorithm application for stability enhancement of interconnected power systems." Click to view the E-thesis via HKUTO, 2000. http://sunzi.lib.hku.hk/hkuto/record/B42128699.
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Kim, Yuan Hwan. "Lactate dehydrogenase regulation of the metmyoglobin reducing system to improve color stability of bovine muscles through lactate enhancement." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2966.
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Pham, Ngoc Duy. "Efficiency enhancement in solution-processed organic-inorganic perovskite solar cells." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/133985/1/Ngoc%20Duy_Pham_Thesis.pdf.
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Organic-inorganic lead halide perovskite is a promising candidate in the photovoltaic field due to the combined merits of impressive power conversion efficiencies and relatively cost-effective solution processes. Despite its remarkable success, there is still room for further improvement. This thesis aims to investigate the impacts of morphological microstructure and elemental composition of organic-inorganic lead halide perovskite light absorber on power conversion efficiency, stability and current-voltage hysteresis behaviour of perovskite solar cells.
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Wijenayaka, A. K. Lahiru Anuradha. "Improved theoretical prediction of nanoparticle stability and the synthesis, characterization, and application of gold nanopartticles of various morphology in surface-enhanced infrared spectroscopy." Diss., University of Iowa, 2015. https://ir.uiowa.edu/etd/1931.
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The overarching objective of the investigations discussed herein is the development of a model experimental system for surface-enhanced infrared absorption (SEIRA) spectroscopy, with potential applicability in higher order infrared spectroscopic techniques, specifically, surface-enhanced two-dimensional infrared (SE-2D IR) spectroscopy.
Theoretical predictions that accurately predict the stability of functionalized nanoparticles enable guided design of their properties but are often limited by the accuracy of the parameters used as model inputs. Hence, first, such parameterization limitations for the extended DLVO (xDLVO) theory are overcome using a size-dependent Hamaker constant for gold, interfacial surface potentials, and tilt angles of self-assembled monolayers (SAMs), which collectively improves the predictive power of xDLVO theory for modeling nanoparticle stability. Measurements of electrical properties of functionalized gold nanoparticles validate the predictions of xDLVO theory using these new parameterizations illustrating the potential for this approach to improve the design and control of the properties of functionalized gold nanoparticles in various applications.
Next, a series of experiments were conducted to elucidate the behavior of various infrared active molecules in the presence of spherical gold nanoparticles of average diameter ∼20 nm. Here, the spectroscopic anomalies, specifically the shifted vibrational frequency and the dispersive lineshape observed in the infrared spectra for SCN- in the presence of gold nanoparticles provide direct evidence of SIERA.
Nevertheless, it was evidenced that nanomaterial with plasmonic properties that extends into the infrared wavelengths are imperative in observing efficient infrared enhancements. Hence, nanomaterial indicating plasmonic properties extending into the infrared wavelengths were synthesized via a straightforward, seedless, one-pot synthesis. The gold nanostars prepared here indicated plasmonic behavior clearly extending into the near infrared, with simple plasmonic tunability via changing the buffer concentration used during synthesis.
The systematic understanding achieved here in terms of theoretical prediction of nanoparticle stability, origin of infrared spectral anomalies in the presence of nanomaterials, and the preparation of infrared plasmonic material, collectively provides a resilient framework for the further investigation of surface-enhanced infrared spectroscopic techniques including SEIRA and SE-2D IR spectroscopies.
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Musa, Aysar [Verfasser], Antonello [Akademischer Betreuer] Monti, and Albert [Akademischer Betreuer] Moser. "Advanced control strategies for stability enhancement of future hybrid AC/DC networks / Aysar A. Aydan Musa ; Antonello Monti, Albert Moser." Aachen : Universitätsbibliothek der RWTH Aachen, 2019. http://d-nb.info/1210929228/34.
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Strasunske, Kristina. "Automatic monitoring systems for trace metals in natural and waste water : Nafion coated solid metal electrodes for sensitivity enhancement and stability improvement." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for kjemi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-11245.
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Voltammetry is one of a few analytical methods, suitable for on-line monitoring of trace metals and is sufficiently sensitive in the low μg/L range for this purpose. The advantages of in-situ use of voltammetry are low cost and no or minimal sample change, since the sample is taken automatically and analysis is performed immediately without a need to collect a sample manually risking contamination and metal loss. Automatic monitoring is essential to record the natural variations of metal concentration in natural or industrial water and registration of accident due to natural or anthropogenic reasons. Remote monitoring of trace metals is of special importance due to their biological role. For that reason extensive research has been carried out internationally to develop suitable monitoring methods. The introduction of the innovative solid silver amalgam and other solid metal electrodes made the use of voltammetry suitable for remote monitoring without the use of toxic electrode materials. An automatic trace metal system (ATMS) in combination with solid silver amalgam electrode has been applied for long time monitoring of zinc and iron in waste water. The system worked automatically with manual maintenance every five days. Sample taking, addition of electrolyte solution, stirring, chemical analysis, electrode cleaning and cell draining were carried out automatically, while electrode polishing, filter changing and calibration were carried out manually every five days. For comparison, verification and to provide a better insight into the complex waste water matrix manual samples have been taken regularly and analyzed with ICP-MS. From data obtained from those two analytical methods a speciation study was performed. The automatic voltammetric system for continuous monitoring of trace metals has been applied in three different locations for monitoring of trace metals in different water samples. River water and drainage water has been used as complex natural water matrixes. A solid silver amalgam electrode has been used as a working electrode. The systems have been fully automated to measure the labile concentration of trace metals for a long time monitoring and store the collected data. Manual maintenance has been performed to calibrate the systems and to clean the working electrodes. Additionally, random samples have been collected manually and analyzed by ICP-MS for the total dissolved metal concentration for data verification and getting better insight into sample matrix. Development of the ATMS has provided an opportunity to monitor earthquake precursor in ground water. A monitoring station has been installed in Husavik, Northern Iceland, for monitoring of trace metals in a ground water. The monitored concentration of metals clearly indicated changes in the ground water prior to the earthquake. The results revealed increased electrolabile concentrations of zinc, iron and copper 7-8 days before the earthquake. The increased concentrations lasted until the occurrence of the earthquake and were possible to monitor by the ATMS. The characterization and application of a Nafion coated solid silver amalgam electrode has been tested for the determination of trace metals by differential pulse anodic stripping voltammetry (DPASV). Effect of model surfactants, commonly presented in natural water sources has also been investigated. It has been found that Nafion coated electrode is useful in surfactant containing samples. The performance of the Nafion coated silver amalgam electrode has been investigated and compared to uncoated silver amalgam electrodes. The modification of the electrode yields higher sensitivity. Moreover, the long time use of Nafion film and practical application has been tested by the use of DPASV in polluted river water sample and has shown to work optimal for 2 weeks. New electrodes made of silver germanium and silver antimony have been tested and found to be suitable for determination of metals by DPASV with very good linearity. This type of electrodes extends potential window to both positive and negative direction. Additionally, very good sensitivity for cadmium has been observed. The practical application has been tested for applying the electrodes in monitoring station to monitor zinc concentration in polluted river water. Moreover, Nafion coating has been applied and has been found to be advantageous considering electrode stability. The aim of this work has been to test silver amalgam and other solid metal electrodes for application in natural and environmental water samples for use in long time online monitoring in field. The papers included in this thesis prove successful applications of these electrodes in different environmental matrixes. The results provide positive evidence about the ability of voltammetry in combination with solid metal electrodes (bare and modified with Nafion) as a working electrodes to be employed in automatic monitoring of trace metals in polluted water with minimal sample pretreatment and minimal maintenance of the system. The use of solid metal electrodes avoids the use of liquid mercury in voltammetric analyses, and offers an environmental friendly alternative suitable for use in field. Due to ease to use, nontoxic fabrication materials, wide cathodic potential window, long time stability, and good sensitivity these electrodes can be applied for continuous online monitoring in various environmental and industrial solutions. They are also easy to modify and this extends the application even further. Several experimental projects at different locations and in different water samples (river-, sea-, ground-, drainage- and waste water) have shown sufficiently long time stability without the need for physical presence for maintenance. These results strongly indicate that further developed and improved method may in future be used as a commercial warning system for environmental pollution accidents.
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Gmuender, Christopher. "On black-and-white paper image-stability enhancement effectiveness of toning treatments on silver gelatin prints determined by the hydrogen peroxide fuming test /." Online version of thesis, 1992. http://hdl.handle.net/1850/10950.
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Rajaguru, Mudiyanselage Thilanki Maneesha Dahigamuwa. "Enhancement of Rainfall-Triggered Shallow Landslide Hazard Assessment at Regional and Site Scales Using Remote Sensing and Slope Stability Analysis Coupled with Infiltration Modeling." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7562.
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Landslides cause significant damage to property and human lives throughout the world. Rainfall is the most common triggering factor for the occurrence of landslides. This dissertation presents two novel methodologies for assessment of rainfall-triggered shallow landslide hazard. The first method focuses on using remotely sensed soil moisture and soil surface properties in developing a framework for real-time regional scale landslide hazard assessment while the second method is a deterministic approach to landslide hazard assessment of the specific sites identified during first assessment. In the latter approach, landslide inducing transient seepage in soil during rainfall and its effect on slope stability are modeled using numerical analysis.
Traditionally, the prediction of rainfall-triggered landslides has been performed using pre-determined rainfall intensity-duration thresholds. However, it is the infiltration of rainwater into soil slopes which leads to an increase of porewater pressure and destruction of matric suction that causes a reduction in soil shear strength and slope instability. Hence, soil moisture, pore pressure and infiltration properties of soil must be direct inputs to reliable landslide hazard assessment methods. In-situ measurement of pore pressure for real-time landslide hazard assessment is an expensive endeavor and thus, the use of more practical remote sensing of soil moisture is constantly sought. In past studies, a statistical framework for regional scale landslide hazard assessment using remotely sensed soil moisture has not been developed. Thus, the first major objective of this study is to develop a framework for using downscaled remotely sensed soil moisture available on a daily basis to monitor locations that are highly susceptible to rainfall-
triggered shallow landslides, using a well-structured assessment procedure. Downscaled soil moisture, the relevant geotechnical properties of saturated hydraulic conductivity and soil type, and the conditioning factors of elevation, slope, and distance to roads are used to develop an improved logistic regression model to predict the soil slide hazard of soil slopes using data from two geographically different regions. A soil moisture downscaling model with a proven superior prediction accuracy than the downscaling models that have been used in previous landslide studies is employed in this study. Furthermore, this model provides satisfactory classification accuracy and performs better than the alternative water drainage-based indices that are conventionally used to quantify the effect that elevated soil moisture has upon the soil sliding. Furthermore, the downscaling of soil moisture content is shown to improve the prediction accuracy. Finally, a technique that can determine the threshold probability for identifying locations with a high soil slide hazard is proposed.
On the other hand, many deterministic methods based on analytical and numerical methodologies have been developed in the past to model the effects of infiltration and subsequent transient seepage during rainfall on the stability of natural and manmade slopes. However, the effects of continuous interplay between surface and subsurface water flows on slope stability is seldom considered in the above-mentioned numerical and analytical models. Furthermore, the existing seepage models are based on the Richards equation, which is derived using Darcy’s law, under a pseudo-steady state assumption. Thus, the inertial components of flow have not been incorporated typically in modeling the flow of water through the subsurface. Hence, the second objective of this study is to develop a numerical model which has the capability to model surface, subsurface and infiltration water flows based on a unified approach, employing fundamental fluid dynamics, to assess slope stability during rainfall-induced transient seepage conditions. The developed model is based on the Navier-Stokes equations, which possess the capability to model surface, subsurface and infiltration water flows in a unified manner. The extended Mohr-Coulomb criterion is used in evaluating the shear strength reduction due to infiltration. Finally, the effect of soil hydraulic conductivity on slope stability is examined. The interplay between surface and subsurface water flows is observed to have a significant impact on slope stability, especially at low hydraulic conductivity values. The developed numerical model facilitates site-specific calibration with respect to saturated hydraulic conductivity, remotely sensed soil moisture content and rainfall intensity to predict landslide inducing subsurface pore pressure variations in real time.
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Eck, Michael [Verfasser], and Michael [Akademischer Betreuer] Krüger. "Performance enhancement of hybrid nanocrystal-polymer bulk heterojunction solar cells : : aspects of device efficiency, reproducibility, and stability = Verbesserung der Leistung von hybriden Nanokristall-Polymer Heteroübergangs-Solarzellen : Aspekte der Solarzellen-Effizienz, -Reproduzierbarkeit und -Stabilität." Freiburg : Universität, 2014. http://d-nb.info/1123481768/34.
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Li, Tianya. "Electromechanical wave propagation phenomenon and its control implications in power systems." Thesis, Queensland University of Technology, 2016. https://eprints.qut.edu.au/95962/1/Tianya_Li_Thesis.pdf.
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This thesis investigates advanced control methods and strategies to enhance the transient stability of a power system which is affected by the electromechanical wave propagation phenomenon. The characteristics of the travelling wave phenomenon and its impact on system separation during first swing are investigated in detail. This thesis identifies four innovative control implications for power system stability and proposes an improved method to enhance power system transient stability. By designing better control of existing equipment, this research achieves increased maximum power transfer under contingencies in a cost efficient and readily implemented way.
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Kelly, Ryan J. "Solid Waste Biodegradation Enhancements and the Evaluation of Analytical Methods Used to Predict Waste Stability." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/32484.
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Conventional landfills are built to dispose of the increasing amount of municipal solid waste (MSW) generated each year. A relatively new type of landfill, called a bioreactor landfill, is designed to optimize the biodegradation of the contained waste to stabilized products. Landfills with stabilized waste pose little threat to the environment from ozone depleting gases and groundwater contamination. Limited research has been done to determine the importance of biodegradation enhancement techniques and the analytical methods that are used to characterize waste stability. The purpose of this research was to determine the effectiveness of several biodegradation enhancements and to evaluate the analytical methods which predict landfill stability.
In the first part of this study leachate recirculation, and moisture and temperature management were found to significantly affect the biodegradation of MSW. Leachate recirculation, increased moisture, and higher temperatures increased the first order degradation rates of cellulose and volatile solids. Of the three enhancements, temperature was shown to have the biggest impact on the biodegradation of waste, but sufficient moisture is critical for degradation. Plastic material was also shown to significantly impact the measurements for volatile solids and lignin, which is important if these measurements are used to establish waste stability.
In the second part of the study the analytical methods used to characterize waste were evaluated to determine if relationships existed between the methods and which methods were the best predictors of waste stability. Volatile solids and cellulose were found to be the best parameters to monitor waste in landfills. These parameters correlate well with each other, age of the waste, and other parameters. Volatile solids and cellulose are also relatively easy to determine, quick, and show little variation.Master of Science
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Shah, Rakesh K. "Enhancements of Mechanical, Thermal Stability, and Tribological Properties by Addition of Functionalized Reduced Graphene Oxide in Epoxy." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc699889/.
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The effects of octadecylamine-functionalized reduced graphene oxide (FRGO) on the frictional and wear properties of diglycidylether of bisphenol-A (DGEBA) epoxy are studied using a pin-on-disk tribometer. It was observed that the addition of FRGO significantly improves the tribological, mechanical, and thermal properties of epoxy matrix. Graphene oxide (GO) was functionalized with octadecylamine (ODA), and then reduction of oxygen-containing functional groups was carried out using hydrazine monohydrate. The Raman and x-ray photoelectron spectroscopy studies confirm significant reduction in oxygen-containing functional groups and formation of ODA functionalized reduced GO. The nanocomposites are prepared by adding 0.1, 0.2, 0.5 and 1.0 wt % of FRGO to the epoxy. The addition of FRGO increases by more than an order of magnitude the sliding distance during which the dynamic friction is ≤ 0.1. After this distance, the friction sharply increases to the range of 0.4 - 0.5. We explain the increase in sliding distance during which the friction is low by formation of a transfer film from the nanocomposite to the counterface. The wear rates in the low and high friction regimes are approximately 1.5 x 10-4 mm3/N·m and 5.5 x 10-4 mm3/N·m, respectively. The nanocomposites exhibit a 74 % increase in Young’s modulus with 0.5 wt. % of FRGO, and an increase in glass transition and thermal degradation temperatures.
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Кунченко, Тетяна Юріївна. "Параметрична оптимізація умовно стійких електромеханічних систем методом діаграм якості керування." Thesis, НТУ "ХПІ", 2016. http://repository.kpi.kharkov.ua/handle/KhPI-Press/21345.
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Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.09.03 – електротехнічні комплекси та системи. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2016.
Дисертація присвячена визначенню і дослідженню задач оптимізації параметрів астатичних регуляторів багатократноінтегруючих систем з використанням мінімаксних критеріїв оптимізації. Виконано аналіз способів параметричної оптимізації та підвищення ефективності керування умовно стійкими багатократноінтегруючими електромеханічними системами (ЕМС) методом діаграм якості керування. Теоретично обґрунтовано існування оптимального рішення для керування такими ЕМС на основі комплексного критерія якості керування – максимуму добротності та запасу стійкості (МДС). Розроблені комп'ютерні методики побудови та аналізу діаграм якості керування (ДЯК) систем у часовій і частотних областях, на яких виділені області підвищеної добротності та запасу стійкості (ПДС). Обґрунтована інженерна методика застосування діаграм якості керування до задачі оптимізованого синтезу по критерію МДС систем з астатизмом другого і третього порядків. Виконано параметричну оптимізацію за критерієм МДС різноманітних умовно стійких ЕМС з послідовною та паралельної корекцією з урахуванням особливостей структури об'єкта керування, включаючи до її складу немінімально-фазові ланки. Розглянуті конкретні приклади підвищення ефективності керування ЕМС методом ДЯК з оптимізацією їх параметрів за мінімаксним критерієм МДС. Доказано можливість збільшення добротності систем у межах 20% і при заданій добротності збільшення запасу стійкості на 10%.The dissertation for the degree of technical sciences candidate by specialty 05.09.09 – electrical complexes and systems. – NTU "KhPI". – Kharkiv, 2016. The dissertation is devoted to researching and solving parameter optimization problems for multiple-integration system astatic regulators with minimax criterion application. Parametric optimization and control efficiency enhancement methods are analyzed as applied to conditionally stable multiple-integration electromechanical systems through control quality diagram technique. Existence of the optimal solution for conditionally stable electromechanical system control on the basis of a complex control efficiency criterion – Q-factor maximum and stability margin - is theoretically substantiated. Computer-aided techniques are worked out to develop and analyze conditionally stable system control quality diagrams in time and frequency domains in which zones of enhanced Q-factor and stability margin are marked. An engineering technique is validated for control quality diagram application to optimization synthesis of systems with astatism of the 2nd and 3rd order using the control quality diagram technique criterion. Control quality diagram technique criterion based parametric optimization of different conditionally stable electromechanical systems with series and parallel compensation is performed taking into account the control object structure features, including nonminimum phase links as its components. Specific examples of electromechanical system control enhancement via the control quality diagram technique application are considered with the system parameter optimization on the control quality diagram technique minimax criterion. Feasibility of 20% system Q-factor enhancement and 10% increase in the stability margin for a given Q is proved.
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Кунченко, Татьяна Юрьевна. "Параметрическая оптимизация условно устойчивых электромеханических систем методом диаграмм качества управления." Thesis, НТУ "ХПИ", 2016. http://repository.kpi.kharkov.ua/handle/KhPI-Press/21350.
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Диссертация на соискание ученой степени кандидата технических наук по специальности 05.09.03 – Электротехнические комплексы и системы. – Национальный технический университет "Харьковский политехнический институт", Харьков, 2016 г.
Диссертация посвящена исследованию и решению задач оптимизации параметров астатических регуляторов многократноинтегрирующих систем с использованием минимаксных критериев оптимизации. Выполнен анализ способов параметрической оптимизации и повышения эффективности управления условно устойчивыми многократно интегрирующими электромеханическими системами методом диаграмм качества управления. Теоретически обосновано существование оптимального решения для управления условно устойчивыми электромеханическими системами (ЭМС) на основании комплексного критерия качества управления – максимума добротности и запаса устойчивости (МДУ). Разработаны компьютерные методики построения и анализа ДКУ условно устойчивых систем во временной и частотной областях, на которых выделены области повышенной добротности и запаса устойчивости (ПДУ). Обоснована инженерная методика применения диаграмм качества управления к решению задач оптимизационного синтеза по критерию МДУ систем с астатизмом второго и третьего порядков. Выполнена параметрическая оптимизация по критерию МДУ различных условно устойчивых ЭМС с последовательной и параллельной коррекцией с учетом особенностей структуры объекта управления, включая в ее состав неминимально-фазовые звенья. Использование результатов работы при минимальных затратах позволяет переналадить работающие МИС ЭП, что будет способствовать повышению точности их работы, росту качества выпускаемой продукции. При разработке новых систем целесообразно расчет астатических регуляторов осуществлять на основании разработанной инженерной методики, основанной на ДКУ и линии МДУ.The dissertation for the degree of technical sciences candidate by specialty 05.09.09 – electrical complexes and systems. – NTU "KhPI". – Kharkiv, 2016. The dissertation is devoted to researching and solving parameter optimization problems for multiple-integration system astatic regulators with minimax criterion application. Parametric optimization and control efficiency enhancement methods are analyzed as applied to conditionally stable multiple-integration electromechanical systems through control quality diagram technique. Existence of the optimal solution for conditionally stable electromechanical system control on the basis of a complex control efficiency criterion – Q-factor maximum and stability margin - is theoretically substantiated. Computer-aided techniques are worked out to develop and analyze conditionally stable system control quality diagrams in time and frequency domains in which zones of enhanced Q-factor and stability margin are marked. An engineering technique is validated for control quality diagram application to optimization synthesis of systems with astatism of the 2nd and 3rd order using the control quality diagram technique criterion. Control quality diagram technique criterion based parametric optimization of different conditionally stable electromechanical systems with series and parallel compensation is performed taking into account the control object structure features, including nonminimum phase links as its components. Specific examples of electromechanical system control enhancement via the control quality diagram technique application are considered with the system parameter optimization on the control quality diagram technique minimax criterion. Feasibility of 20% system Q-factor enhancement and 10% increase in the stability margin for a given Q is proved.
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Awan, Faisal Ur Rahman. "Electrokinetic investigation of coal fines in fractured and porous media." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2022. https://ro.ecu.edu.au/theses/2523.
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Coal seams are unconventional subsurface formations that host methane and are weaker (relative to conventional subsurface) formations. Coal seams are prone to coal fines generation within the fractured porous space throughout the life of the reservoir. These coal fines damage the permeability, deliverability and productivity of coal seams. Furthermore, the coal fines mobility/blockage in the hydraulically induced fractures and proppant packs negatively impacts the proppant conductivity. In this work, a comprehensive study has been conducted to augment the understanding of coal fines and their behaviour within porous and proppant pack systems. Systematic experiments were conducted to address the coal fines by developing various approaches presented in this work. The approaches adopted to achieve the study objectives were: i) streaming zeta potential on coal and sandstone, ii) nano-treated proppant surface modification for coal fines adsorption, and iii) coal fines mobility/attachment in the proppant packs.
One of the electrokinetic parameters that is crucial in releasing/mobilising coal fines is coal’s zeta potential. The coal surface is generally hydrophobic and possesses negative zeta potential. Researchers have used the electrophoretic zeta potential technique to indicate charge identification of coal particles, denoting repulsion or attraction of the particle. In chapter 3, a robust study investigates streaming zeta potential measurements of an in-situ sub-bituminous coal core saturated with saline water of 0.1, 0.3 and 0.6 mol.dm-3 NaCl salinities. Thus, the novel study determines the charge carried by percolating fluid when passing through coal rock. The zeta potential is directly proportional to saline water salinity. The trends found in the research were consistent with reported zeta potential measured using other techniques, while the magnitude varied. The findings reported in the study apply to subsurface coal seams at salinity up to 0.6 mol.dm-3 NaCl.
Coal seams are hydraulically fractured for commercial production, and sand-based proppants occupy the fractured space. Before understanding the electrokinetics of coal fines, the behaviour of these sand-based proppants should be determined. Sand-based proppants are predominantly silica, and so are sandstones. Furthermore, the selection of sandstone was further motivated by two reasons, i) for comparison and benchmarking, and ii) correlation with coals (as sandstone and coal both are negatively charged). The research presented in chapter 4 considered clay-rich (i.e. clay ≥ 5 wt.%) sandstones for the first time (as coal can have clay ingredients). Specifically, streaming potential measurements were conducted on Bandera Grey sandstone (clay-rich and -poor) saturated with saline water in pressurised environments. Additionally, the streaming potential was determined at identical conditions for the effect of two surfactants, sodium dodecylbenzene sulfonate (SDBS) and cetrimonium bromide (CTAB), at concentrations of 0.01 and 0.1 wt. % on the clay-poor sample. Moreover, a comparison of electrophoretic and streaming zeta potentials was conducted. Accordingly, the work analyses the effects of mineralogy and surfactants within this process. Clay-rich sandstone possessed lower zeta-potentials than clay-poor sandstone at the two tested salinities. SDBS reduced zeta-potential and yielded higher repulsive forces rendering the rock more hydrophilic. Additionally, electrophoretic zeta-potentials were higher when compared to streaming zeta-potentials. Mechanisms for the observed phenomena are also provided.
Following the observations from the two studies, proppant column experiments with glass bead proppant and high volatile bituminous were conducted and are presented in chapter 5. One of the approaches to handling coal fines is its dispersal within the aqueous suspension. Proppant column experiments were conducted to test various schemes. It was found that coal zeta potential using SDBS reaches a maximum, and regardless of the pH, it effectively delivers the maximum output of coal fines in the effluent. Thus, a 0.001 wt.% SDBS could effectively disperse coal fines suspension through proppant packs.
Nano-treated proppant surface modification was developed to investigate coal fines mobility/attachment within the proppant packs. Succinctly, four (alumina, magnesia, silica and zirconia) nanoparticles (NPs) were adsorbed onto synthetic porous media (glass bead) using a robust pseudo-continuous fixed-bed (PCFB) adsorption method in work presented in chapter 6. A wide range of salinity (0 to 10.5 wt.% NaCl), temperature (298.15 to 348.15 K), NPs loading (0.01 to 0.2 wt.%), and injection rate (1 to 50 mL.min-1) were tested. Results showed that PCFB adsorption of NPs with higher specific surface area resulted in faster adsorption (adsorbed in ~25 mins) with > 99% immobilisation of NPs on the proppant pack. Adsorption kinetics showed reasonable conformity with the pseudo-first-order model, where isothermal adsorption followed the Sips model. The adsorption capacity of magnesia NPs (specific surface area 50 to 80 m2.g-1, 7 wt.% NaCl) at 298.15 K was higher than silica NPs. Accordingly, the newly developed PCFB method can be used for onsite treatment of proppants with nanoparticles, which can then be injected into a fractured formation to achieve multiple objectives such as fines fixation, wettability alteration and sand control.
In this work, another study explored the application of nano-treated proppant packs on the adsorption of coal fines, presented in chapter 7. In this study, the objective was to identify silica nano-formulations (0 – 0.1 wt.%), and coal fines concentration of 0.1 to 1 wt.% were examined to determine the fixation of coal fines within the glass bead synthetic proppant pack. The quantitative results showed that the proppant pack with nanoparticle treatment strongly affects the fixation ability of coal fines. The non-NP treated pack yielded 30% adsorption, whilst the NP treated pack yielded 74% adsorption. It was noted that greater adsorption is also related to the higher zeta potential of silica NPs (i.e. nearer to iso-electric point).
A set of laboratory experiments on industrial-grade proppants was conducted as the definitive work, presented in chapter 8. The work involved sensitivity experiments as a function of coal rank, pH, salinity, and surfactants. These conductivity results were compared with established analytical models to interpret the mechanistic coal-proppant interaction in the presence of an electrolyte. It was found that fines dispersion and its mobility within the proppant pack is easier at high pH, low salinity, temperature, anionic surfactants, and lower concentration of coal fines. However, fines mobility is reduced at neutral pH, high salinity, temperature, and cationic surfactants.
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Cheng, Yu-Chia, and 鄭玉佳. "The enzymatic stability enhancement by supercritical carbon dioxide pretreatment." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/73206109240644497772.
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碩士國立臺灣大學
化學工程學研究所
88
Bacillus subtilis alpha-amylase (EC 3.2.1.1) losses over 80% activity at low concentrations in deionized water. This study mainly investigated the stability enhancement of alpha-amylase caused by supercritical carbon dioxide (SC-CO2) pretreatment. The alpha-amylase powder is pretreated for 1 hour in SC-CO2 at certain pressure and temperature. Moreover, the denaturation of pretreated lysozyme (EC 3.2.1.17) was also evaluated to examine the effect of the SC-CO2 pretreatment. Experimental results indicated that the stability enhancement was observed when the SC-CO2 conditions are set to 50℃ with 2000 or 2500psi and 60℃, 3000psi. The optimal SC-CO2 condition for the alpha-amylase is found to be 60℃, 3000psi and the pretreated alpha-amylase maintained the 33% activity compared the original one only 20%. Besides, the 60℃-3000psi- (SC-CO2) pretreated alpha-amylase increased 2 times in the solution stability. The results also showed that SC-CO2 pretreatment also applied to stabilize lysozyme (EC 3.2.1.17). Compared with the original lysozyme lost 60~75% activity in an hour when denatured by urea, the lysozyme pretreated by 40℃, 2500psi SC-CO2 maintained 60~80% activity after 2 hour. The result means that the stability enhancement by SC-CO2 is not specific to -amylase and other enzyme can also adapt to this method. The results of the experiment provide a novel method to improve the enzymatic stability.
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Sun, San-Yung, and 孫善勇. "The Dynamic Stability Enhancement of Power System Incorporating STATCOM." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/35875516783495588832.
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碩士輔仁大學
電子工程學系
89
This paper solves the problem of power system stabilization by using the advanced static VAR compensator (STATCOM) to increase the damping of the electromechanical mode of the power system. The dynamic oscillations are repressed by the proposed STATCOM controller, which is an output feedback controller designed by the strip poles assignment method. The controller is reliable and can guarantee a vertical strip that the electromechanical mode will fall into. We will study the effect of this component in single machine and multi-machine power system and design an output feedback controller for measurable signals and a decentralize controller of local machine signals, respectively. Finally we can prove that the power systems incorporating STATCOM and its controller can increase the damping of electromechanical mode and repress the low frequency oscillation effectively.
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Liu, Chuan Sheng, and 劉傳聖. "Excitation system identification and power system dynamic stability enhancement." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/44995610095729487814.
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