Academic literature on the topic 'Online control technique'

This paper presents an application of the MRAC (Model Reference Adaptive Control) techniques to achieve the attitude stabilization in an unmanned aerial vehicle (UAV) type quadrotor when there exists disturbances and/or uncertainties in the parameters due to changes in the payload, variations in battery voltage during flight, etc. This is achieved by performing an online adaptation of the controller parameters, which are obtained by showing the stability property of the closed loop control system using Lyapunov theory. Simulation results using Matlab-Simulink platform are presented to demonstrate the convergence of the controller parameters.

Modeling and simulation of chaotic system with dynamic control have been extensively presented in the past decades. Several control techniques have been proposed for the control of chaos. One technique that has not been sufficiently explored for the control of nonlinear systems is the controller identification technique. This technique is based on the evaluation of controllers even if they are not online. This technique does not use a priori knowledge of the plant parameters. In this work, we propose a class of controllers candidates to follow desired trajectories. Simulation results are presented for the control of chaotic systems.

Whereas power-electronics-based power systems are expected to enable more integration of renewable energy sources, they could pose crucial challenges including stability issues due to the Thévenin impedance seen by inverters. Such problems could be mitigated by enabling the inverters to estimate the grid impedance by including a grid impedance estimation technique into their control loop. However, one aspect which has been overlooked thus far is that the accuracy of such grid impedance estimation techniques is significantly affected by various grid conditions. For instance, the unbalance in three-phase power systems causes unwanted oscillations at double the fundamental frequency in the inverters control loops. Therefore, this paper proposes a simple and reliable online estimation of the grid impedance under unbalanced conditions. The technique is based on wide-band impedance estimation incorporated into the control loop of the positive sequence of a three-phase grid-connected inverter equipped with a positive- and negative-sequence control (PNSC) strategy. Additionally, complex curve fitting is utilized to obtain parametric models of the grid impedance. To demonstrate the efficacy of the proposed grid impedance estimation technique, extensive case studies are performed. These include: (1) unbalanced operations of both resistive-inductive (RL) and resistive-inductive-capacitive (RLC) models of the grid, (2) background harmonics, and (3) asymmetrical impedances of the network.

The study aimed to determine: (1) the effect of online inquiry learning methods on increasing the knowledge of basic soccer techniques for class XI students and (2) differences in knowledge of basic soccer techniques for class XI students between the experimental group and the control group. The method uses a “pre-test post-test control group design" experiment. The sampling technique is simple random sampling, totaling 33 students in the experimental class with the inquiry learning method treatment and 34 students in the control class. The instrument used is an essay test. Data analysis used a t-test with a significance level of 5%. The study results: (1) There is a significant effect of the online inquiry learning method on increasing the knowledge of basic soccer techniques for class XI students, the t value is 12.158 > t table is 1.693, and the significance is 0.000 < 0.05. (2) There is a significant difference in the knowledge of basic football techniques of class XI students between the experimental group and the control group; the t-count value is 9.617 > t-table 1.668, and the significance is 0.000 < 0.05.

AbstractOnline control of industrial processes by lean principle increases productivity and yields higher product quality. Polysaccharides are dissolved in liquids, such as water, in many industrial products, like paints, cosmetics and culinary products. In these products, it is important to control viscosity or create thixotropy and yield stress for product functionality. Electromagnetic field and electrical conductivity techniques were applied to a meter polysaccharide dissolution process online up to a 0.5 wt% concentration, and the resultant solution was also further tested by UV–Vis spectrophotometry. The electromagnetic field technique measures changes in the local electrical permittivity of the liquid and the interest in this research were to find out whether the changes correlate to the concentration changes during the dissolution of polymer polysaccharide. The results that were obtained showed good consistency, suggesting the feasibility of the electromagnetic field technique in online monitoring of a polysaccharide suspension concentration. Moreover, this technique gives the advantage of instant monitoring of a polysaccharide dissolution for improved process control. Graphic abstract

This dissertation summarises the study of different aspects of the aerosol-assisted chemical vapour deposition (AACVD) technique for the production of multi-wall carbon nanotubes (MWCNTs). Upscaling the synthesis while retaining the quality of MWCNTs has been a prime objective throughout the work. A key aspect of this work was the study of different growth parameters and their influence on the homogeneity of the products across the reactor. The effect of the precursor composition on the yield and quality of MWCNTs were also investigated. It was shown that the synthesis rate can be significantly (60 – 80 %) increased by tuning the composition of the precursor. Moreover, by optimising the synthesis recipe and using a larger reactor, the synthesis rate and efficiency of the precursor were increased fivefold (up to 14 g/hr) and twice (up to 88 %) respectively. Large area (up to 90 cm²), mm-thick carpets of MWCNTs which were both free-standing and on substrate were produced. The carpets could withstand normal handlings without tearing apart, making them suitable for macroscopic characterisations and applications. By in-situ qualitative and quantitative gas analysis of the atmosphere of the reactor, the thermocatalytic cracking behaviour of 25 precursors was investigated and a mechanism for successive formation of different hydrocarbon fragments inside the reactor was proposed. A number of dedicated gas analysis methods and apparatuses such as a probe for zone-by-zone gas analysis of reactor and a heated chamber for preparation of standard gas analysis samples were developed to explore some of the least investigated aspects of the thermocatalytic cracking of precursors. Mapping the reactor revealed that some single-wall and double-wall carbon nanotubes (SWCNTs and DWCNTs) were also produced near the exhaust of the reactor. The SWCNTs were partly covered by fullerene-like species and resembled different forms of carbon nanobuds. In addition, the effect of the electron beam on the interaction of the SWCNTs and the fullerene-like species was studied in situ using high-resolution transmission electron microscopy (HRTEM).

Dissertação para obtenção do Grau de Mestre em Engenharia Electrotécnica e de Computadores<br>The main goal of this thesis will be focused on developing an adaptative closed loop control solution, using fuzzy methodologies. A positive theoretical and experimental contribution, regarding modelling and control of fuzzy and neuro fuzzy systems, is expected to be achieved. Proposed non-linear identification solution will use for modelling and control, a recurrent neuro fuzzy architecture. Regarding model solution, a state space approach will be considered during fuzzy consequent local models design. Developed controller will be based on model parameters, being expected not only a stable closed loop solution, but also a static error with convergence towards zero. Model and controller fuzzy subspaces, will be partitioned throughout process dynamical universe, allowing fuzzy local models and controllers commutation and aggregation. With the aim of capturing process under control dynamics using a real time approach, the use of recursive optimization techniques are to be adopted. Such methods will be applied during parameter and state estimation, using a dual decoupled Kalman filter extended with unscented transformation. Two distinct processes one single-input (SISO) other multi-input (MIMO), will be used during experimentation. It is expected from experiments, a practical validation of proposed solution capabilities for control and identification. Presented work will not be completed, without first presenting a global analysis of adopted concepts and methods, describing new perspectives for future investigations.

Time-optimal solutions provide us with the fastest means to regulate a system in presence of input constraints. This advantage of time-optimal control solutions is offset by the fact that their real-time implementation involves computationally intensive iterative techniques. Moreover, time-optimal controls depend on the initial state and have to be recalculated for even the slightest perturbation. Clearly time-optimal controls are not good candidates for online regulation. Consequently, the search for alternatives to time-optimal solutions is a very active area of research. The work described here is inspired by the simplicity of optimal-aim concept. The "optimal-aim strategies" provide online regulation in presence of bounded inputs with minimal computational effort. These are based purely on state-space geometry of the plant and are inherently adaptive in nature. Optimal-aim techniques involve aiming of trajectory derivative (or the state velocity vector) so as to approach the equilibrium state in the best possible manner. This thesis documents the efforts to develop an online regulation algorithm for systems with input constraints. Through a number of hypotheses focussed on trying to reproduce the exact time-optimal solution, the diffculty associated with this task is demonstrated. A modification of optimal-aim concept is employed to develop a novel regulation algorithm. In this algorithm, aim directions are chosen in a special manner to generate the time-optimal control approximately. The control scheme thus developed is shown to be globally stabilizing for systems having eigenvalues in the CLHP (closed left half-plane). It is expected that this method or its modifications can be extended to higher dimensional systems as a part of future research. An alternative control algorithm involving a simple state-space aiming concept is also developed and discussed.

Thesis (MScEng)--Stellenbosch University, 2001.<br>ENGLISH ABSTRACT: The worldwide trend for systems is to become more complex. This leads to the need for new ways to control these complex systems. A relatively new approach for controlling systems, called on-line planning and control, poses many potential benefits to a variety of end-users, especially in the manufacturing environment. Davis [3J developed a framework for on-line planning and control that is currently incomplete. This project aims to fill one of the gaps in the framework by automating one of the functions, eliminating the need for a human observer. This function, the real-time compromise analysis function, does the comparison of the statistical performance estimates to select a control policy for implementation in the system being controlled (the realworld system) at the current moment in time. In this project, two techniques were developed to automate the function. The first technique is based on a common technique for statistically comparing two systems, the paired-t confidence interval technique. The paired-t confidence interval technique is used to compare the control policies by building confidence intervals of the expected differences for the respective performance criteria and testing the hypothesis that the statistical performance estimates of the one control policy are better than those of the other control policy. The results of these comparisons are then consolidated into a compromise function that is used to determine the control policy to be implemented currently in the real-world system. The second developed technique is derived, but differs greatly, from Davis's [3J dominance probability density function approach, and it includes principles of the paired-t confidence interval technique. It compares the control policies by determining the probability (confidence level) with which one can assume that the performance criterion of the one control policy will provide a performance value that is better than the other's and vie-ursa. These confidence levels are then aggregated into a single compromise function that is used to determine the control policy to be implemented currently in the real-world system. After the techniques were developed, it was not possible to determine their efficiency mathematically, because their statistical base is suspect. The techniques needed to be implemented before they could be evaluated and it was decided to develop an emulator of the on-line planning and control process in accordance with the framework given by Davis [3J to implement them. This Emulator is in essence a Visual Basic" program that uses Arena" models. However, this Emulator needed certain deviations from the framework to make it possible. Firstly, while the systems that will be controlled with the on-line planning and control process will be complex systems, the system controlled in the Emulator is only a straightforward MlM/l/FIFO/OO / 00 system. This allowed for the conditions that have not been addressed sufficiently, e.g. the initialising of the system models, to be bypassed. Secondly, the Emulator does not include all parts of the framework, and parts for which the technology does not currently exist have been excluded. Thirdly, the real-world system is replaced with a model, because a real-world system was not available for the study. Finally, concurrent operations are actually done sequentially, but in a way that makes it seem that they were done concurrently, as not to influence the results. This Emulator was used to analyse both techniques for two different traffic intensities. The first part of the analysis consisted of an off-line non-terminating analysis of the individual control policies of the system. This was used as a base line against which the on-line planning and control process of the Emulator was evaluated. The findings of the evaluations were that, at the traffic intensities evaluated, the techniques provided results that were very similar to the results of the best individual control. From these results, it was speculated that at different traffic intensities, different control policies would be better than the techniques themselves, while the techniques will only give slightly worse results. In addition, because the on-line planning and control process attempts to respond to changing conditions, it can be assumed that the techniques will excel in those conditions where the input distribution is changing continuously. It is also speculated that the techniques may be advantageous in cases where it is not possible to determine beforehand which of the individual control policies to use because it is impossible to predict the input distribution that will occur. It is expected that the techniques will give good (but unfortunately, not necessarily the best) results for any input distribution, while an individual control policy that may give the best results for one input distribution, may prove disastrous for another input distribution. Three important conclusions can be made from the project. Firstly, it is possible to automate the real-time compromise analysis function. Secondly, an emulator can be developed to evaluate the techniques for the real-time compromise analysis. The greatest advantage of this Emulator is that it can run significantly faster than real-time, enabling the generation of enough data to make the significant statistical comparisons needed to evaluate the techniques. The final conclusion is that while initial evaluations are inconclusive, it can be shown that the techniques warrant further study. Three important recommendations cart be made from the project. Firstly, the techniques need to be studied further, because they cannot be claimed to be perfect, or that they are the only possible techniques that will work. In fact, they are merely techniques that may work and other techniques may still prove to be better. Secondly, because it would be foolhardy to assume that the Emulator is complete, the Emulator needs to be improved with the most critical need to develop the Emulator in a programming language and simulation package that allows concurrent operations and effortless initialisation. This will enable the Emulator to be much faster and a lot more flexible. The final recommendation is that the techniques need to be evaluated with other parameters in other increasingly complex systems, culminating in the evaluation of the on-line planning and control process with the techniques included in a real-world flexible manufacturing system. Only then can there be decided conclusively on whether the techniques are efficient or not. It is hoped that this project will form a valuable building block that will facilitate making on-line planning and control a viable alternative to controlling complex systems, enabling them to respond better to changing conditions that are currently becoming the norm.<br>AFRIKAANSE OPSOMMING: Wêreldwyd is stelsels besig om meer ingewikkeld te raak. Dit bring mee dat nuwe metodes benodig word om hierdie ingewikkelde stelsels te beheer. Gekoppelde beplanning en beheer ("On-line planning and control") is 'n relatiewe nuwe metode om stelsels te beheer en het baie moontlike voordele vir 'n verskeidenheid van gebruikers, veral in die vervaardigingsomgewing. Davis [3] het 'n raamwerk ontwikkel vir gekoppelde beplanning en beheer, maar die raamwerk is tans onvolledig. Hierdie projek het gepoog om een van die gapings in die raamwerk te vul deur een van die funksies te outomatiseer en sodoende die behoefte vir 'n menslike waarnemer te elimineer. Hierdie funksie, die intydse-kompromie-analise-funksie ("real-time compromise analysis function"), is verantwoordelik vir die vergelyking van die statistiese prestasieskattings om 'n beheerbeleid te kies wat geïmplementeer moet word in die stelsel wat beheer word (die regtewêreld -stelsel). Die projek het twee tegnieke ontwikkel om die funksie te outomatiseer. Die eerste tegniek is gebaseer op 'n algemene tegniek om twee stelsels statisties met mekaar te vergelyk, naamlik die gepaarde-t vertrouensinterval-tegniek. Die gepaarde-t vertrouensinterval-tegniek word gebruik om die beheerbeleide te vergelyk deur vertrouensintervalle te bou van die verwagte verskille vir die verskillende vertoningskriteria en om die hipotese te toets dat die statistiese prestasieskattings van die een beheerbeleid beter is as dié van 'n ander beheerbeleid. Die resultate van hierdie vergelykings word dan gekonsolideer in 'n kompromiefunksie wat gebruik word om te bepaal watter beheerbeleid tans geïmplementeer moet word in die regte-wêreld-stelsel. Die tweede ontwikkelde tegniek is afgelei, maar verskil baie, van Davis [3] se oorheersende waarskynlikheidsdigtheid-funksie ("dominance probability density function") -benadering en gebruik ook idees van die gepaarde-t vertrouensinterval-tegniek. Dit vergelyk die beheerbeleide deur die waarskynlikheid (vertrouensvlak) te bereken waarmee aanvaar kan word dat die vertoningskriterion van een van die beheerbeleide 'n beter vertoningswaarde sal hê as die ander, en omgekeerd. Hierdie vertrouensvlakke word dan gekonsolideer in 'n kompromiefunksie wat gebruik word om te bepaal watter beheerbeleid tans géimplementeer moet word in die regte wêreld stelsel. Nadat die tegnieke ontwikkel is, was dit nie moontlik om hulle effektiwiteit wiskundig te evalueer nie, want hulle statistiese basis is verdag. Dus moes die tegnieke geïmplementeer word voordat hulle geëvalueer kon word. Daar is besluit om 'n emuleerder van die proses van gekoppelde beplanning en beheer te ontwikkel volgens die raamwerk wat deur Davis [3] ontwikkel is sodat die tegnieke geïmplementeer kan word. Hierdie Emuleerder is 'n Visual Basic* program wat Arena" modelle gebruik. Om die Emuleerder moontlik te maak, was sekere afwykings van die raamwerk nodig. Die eerste hiervan is dat die stelsels wat beheer word met gekoppelde beplanning en beheer, komplekse stelsels is, maar dat die stelsel wat deur die Emuleerder beheer word, slegs 'n eenvoudige MIMI l/EIEBI 00 I 00 sisteem is. Dit maak dit moontlik om aspekte wat nog nie genoegsaam aangespreek is nie, byvoorbeeld die inisiëring van die stelselmodelle, te omseil. Tweedens bevat die Emuleerder nie al die dele van die raamwerk nie en dele waarvoor die tegnologie tans nog nie bestaan nie, is uitgelaat. Derdens, die regte wêreld stelsel is vervang met 'n model, want 'n regte wêreld stelsel was nie beskikbaar nie. Laastens is operasies wat eintlik gelyktydig gedoen moes word, sekwensieel gedoen, maar op so 'n marrier dat dit lyk asof hulle gelyktydig gedoen is, sodat die resultate nie beïnvloed word nie. Die Emuleerder is gebruik om beide tegnieke te analiseer vir twee verskillende verkeersdigthede. Die eerste deel van die analise het bestaan uit 'n nie-terminerende analise van die individuele beheerbeleide van die stelsel. Dit is gebruik as 'n basislyn waarteen die Emuleerder se proses van gekoppelde beplanning en beheer geëvalueer is. Die bevindinge van die evaluasie was dat vir die verkeersdigthede wat geëvalueer is, die tegnieke resultate lewer wat vergelykbaar is met die van die beste individuele beheerbeleide. Oor hierdie resultate is daar gespekuleer dat by verskillende verkeersdigthede, verskillende beheerbeleide beter sal vaar as die tegnieke, terwyl die tegnieke slegs marginale swakker resultate sal lewer. En omdat gekoppelde beplanning en beheer poog om te reageer op veranderende omstandighede, kan dit aanvaar word dat die tegnieke sal presteer in omstandighede waar die toevoerverdeling die heeltyd verander. Dit word ook beweer dat die tegnieke tot voordeel sal wees in gevalle waar dit nie moontlik is om vooraf te bepaal watter van die individuele beheerbeleide om te gebruik nie, omdat dit onmoontlik is om te voorspel watter toevoerverdeling gerealiseer gaan word. Dit word verwag dat die tegnieke goeie (maar ongelukkig nie noodwendig die beste nie) resultate saliewer vir enige toevoerverdeling, terwyl 'n individuele beheerbeleid wat moontlik die beste resultate vir die een toevoerverdeling sal gee, katastrofies kan wees vir 'n ander toevoerverdeling. Drie belangrike gevolgtrekkings kan gemaak word van die projek. Eerstens, dit is moontlik om die intydse-komprornie-analise-funksie te outomatiseer. Tweedens, 'n emuleerder kan ontwikkel word om die tegnieke vir die intydse-komprornie-analise te evalueer. Die grootste voordeel van die Emuleerder is dat dit heelwat vinniger as reële tyd kan opereer, wat dit moontlik maak om genoeg data te genereer om die betekenisvolle statistiese vergelykings te maak wat benodig word om die tegnieke te evalueer. Die laaste gevolgtrekking is dat, alhoewel die aanvanklike evaluasie nie beslissend is nie, dit gewys kan word dat die tegnieke verdere studie verdien. Drie belangrike aanbevelings kan gemaak word vanuit die projek. Eerstens, die tegnieke moet nog verder bestudeer word, omdat daar nie beweer kan word dat hulle perfek is of dat hulle die enigste tegnieke is wat kan werk nie. Om die waarheid te sê, hulle is slegs tegnieke wat moontlik kan werk en ander tegnieke kan steeds bewys word om beter te wees. Tweedens sou dit onsinnig wees om te beweer dat die Emuleerder volledig is, en moet die Emuleerder nog verbeter word. Die mees kritiese vereiste is om die Emuleerder te ontwikkel in 'n programmeringstaal en simulasiepakket wat gelyktydige operasies en moeitelose inisiëring toelaat. Dit sal die Emuleerder toelaat om baie vinniger en meer buigsaam te wees. Die laaste aanbeveling is dat die tegnieke geëvalueer moet word met ander parameters in ander stelsels van stygende kompleksiteit, wat die hoogtepunt bereik in die evaluasie van die proses van gekoppelde beplanning en beheer met die tegnieke ingesluit in 'n regte-wêreld buigbare vervaardigingstelsel ("flexible manufacturing system"). Slegs dan sal dit moontlik wees om onomwonde te sê of die tegnieke effektief is of nie. Daar word gehoop dat hierdie projek 'n waardevolle boublok sal vorm wat sal bydra om gekoppelde beplanning en beheer 'n uitvoerbare alternatief te maak vir die beheer van komplekse stelsels, omdat dit hulle sal toelaat om beter te reageer op die veranderende omstandighede wat deesdae die norm is.

In recent years, the automotive industry has been characterized by a growth in the field of electronics. This growth concerns many aspects in the car design such as energy efficiency, safety, x-by-wire systems, connectivity and comfort. For this reason, while in the past electronic power consumption was negligible with respect to the total car energy consumption, a particular attention is paid nowadays to the efficiency of these devices. Furthermore, there is a political and social pressure to reduce CO2 emissions that results in penalties and taxes for those companies who do not comply with the limits imposed by national and international targets. It is clear that failure to meet these standards causes a loss of competitiveness and profit. Therefore many efforts have been made during the last years by the automotive industry to find affordable solutions to improve the energy efficiency of each part of the vehicle. For small power devices such as safety systems (airbag, adaptive cruise control, collision avoidance etc...), vehicle networking, body (windows drivers, led driver etc...) the state of the art technologies belong to the class Smart Power Technology (SPT). Such class of technologies allows to include in the same chip die low voltage digital and analog devices like MOSFET and bipolar transistors (smart part) and power devices like high voltage DMOS (power part). The smart part of the technology is used by designers to implement systems like over temperature, short circuit protection and over voltage management circuits, while the power part is used to implement the power stage. The most widespread class of power stages is so far represented by linear regulators because of their relative simplicity, low noise, small size and low cost. The major weakness, however, is their typically poor efficiency. As a consequence, although linear regulators still represent the main source of profit, the automotive silicon industry is investing more in highly efficient solutions such as switching converters. The main reasons that obstruct the diffusion of switched-mode power supplies in low power automotive applications are the additional costs and additional area consumption caused by the need to include bulky inductors. Goal of this Ph.D. research is to explore on the fly efficiency optimization strategies, also known as online efficiency optimization techniques, in which the converter is dynamically brought to its maximum efficiency operating point regardless of the specific operating conditions. This research activity is conducted through the collaboration between Infineon Technologies Italia and the Department of Information Engineering (DEI) of the University of Padova within the framework of a contract of Apprenticeship in Higher Education and Research, and focuses on modeling and design of efficiency optimization techniques for high-frequency dc-dc converters in automotive applications. Part of the research activity has been developed during a six months visiting period at the Colorado Power Electronics Center of the University of Colorado at Boulder, under the supervision of Prof. Dragan Maksimovic. The approach followed during the research activity aims to transfer the hardware complexity from the power stage, that is typically the most expensive part, to the control stage. In this regard, the digital control appears a natural choice enabling the possibility to explore advanced control strategies and modulation schemes that exploit the degrees of freedom offered by the converter for purpose of regulation and efficiency optimization. Moreover, being the compactness one of the major issues, the soft switching capability become a crucial aspect allowing to thereby increase the switching frequency without compromise the converter efficiency and to reduce the passive component size. The thesis is organized as follows. First of all, a general overview of the automotive power electronics is presented in order to clarify the motivation of this research. The first part of the thesis focuses on the steady state analysis of the Dual Half Bridge converter with particular regard to the efficiency characterization. Such topology is considered, in both its resonant and non-resonant versions, because of its degrees of freedom inherently available in the converter modulation space. Control strategy are proposed that allow to accomplish the output voltage regulation and an online efficiency optimization. In systems like the one under consideration, the controller moves the converter from one operating point to a new one every time a new event occurs (for example a load step or battery line variation). For this reason, a wide area of the control space can be potentially spanned during the normal operations, therefore an accurate dynamic analysis is mandatory to ensure the stability of the system throughout the entire control space. For this reason another important topic analyzed in this thesis is the dynamic study of digitally controlled Dual Active Bridge converters. The dynamics introduced by uniformly sampled phase shift modulators and combined phase shift and pulse width modulators is analyzed in detail and incorporated into a multi-harmonic small-signal model valid for both the resonant and non resonant dual half-bridge topologies. All the results presented in this thesis are validated both via simulations and experiments made on discrete components prototype.<br>Negli ultimi anni si è assistito ad un rapido sviluppo nell'ambito dell'elettronica di potenza applicata all'industria automobilistica. Questa evoluzione riguarda molti aspetti nella progettazione dell'automobile, ad esempio l'efficienza energetica, la sicurezza, l'introduzione di sistemi x-by-wire, connettività e confort. Per questa ragione, mentre in passato il consumo di potenza associato ai dispositivi elettronici era trascurabile rispetto al consumo totale dell'auto, oggi si presta molta attenzione all'efficienza di ciascun dispositivo. Vi sono inoltre pressioni sociali e politiche che spingono verso la riduzione delle emissioni di CO2. Queste si traducono in sanzioni e tasse aggiuntive per le aziende inadempienti nei confronti dei limiti imposti dalle normative nazionali e internazionali, e in un conseguente danno di immagine delle stesse. È perciò chiaro che non rispettare questi standard causa una perdita di profitto e competitività. Perciò, negli ultimi anni, sono stati fatti molti investimenti finalizzati a trovare soluzioni economicamente realizzabili con lo scopo di migliorare l'efficienza energetica di ogni parte del veicolo. A questo proposito, il progetto di sistemi di alimentazione ad alta efficienza è di cruciale importanza. Per sistemi di alimentazione di dispositivi a bassa potenza quali i sistemi di sicurezza (airbag, sistemi anti-collisione etc...), connettività e illuminazione, lo stato dell'arte prevede l'utilizzo di circuiti di potenza appartenenti alla classe Smart Power Technology (SPT). Questa tecnologia permette di includere nello stesso chip, componenti analogici, digitali e transistori di potenza. Il punto di forza più importante di questa tecnologia è la possibilità di includere nello stesso circuito integrato oltre che al convertitore, sistemi di anti-surriscaldamento, protezione da cortocircuiti e sovratensioni e implementare sistemi di gestione intelligente dell'energia. Per molto tempo, la classe di convertitori di potenza più utilizzata è rappresentata dai regolatori lineari. Le caratteristiche principali di questi convertitori sono la loro bassa complessità dell'hardware e la riduzione dei costi e dimensioni. Per contro, risultano poco efficienti dal punto di vista energetico poiché la regolazione della tensione di uscita avviene dissipando la potenza in eccesso nel convertitore stesso. Di conseguenza, benché i regolatori lineari rappresentino ancora la maggior fonte di profitto, l'industria automobilistica sta investendo in soluzioni più efficienti come ad esempio i convertitori a commutazione. Le ragioni più importanti che hanno ostacolato la diffusione di questa classe di convertitori nell'ambito dei sistemi a bassa potenza sono i costi tipicamente più elevati e l'ingombro causato dall'impiego di componenti esterni quali induttori e condensatori di filtro. Questa attività di ricerca di dottorato si inquadra quindi nell'ambito dello sviluppo di tecniche di ottimizzazione online dell'efficienza, ossia sistemi nei quali il convertitore è mantenuto nel suo punto operativo di massima efficienza a prescindere dalle condizioni in cui esso si trova. L'attività di ricerca è svolta in cotutela con Infineon Technologies Italia Srl nell'ambito di un contratto di Apprendistato in Alta Formazione e Ricerca dal titolo “Studio e progetto di architetture e topologie circuitali innovative per convertitori DC/DC ad alta efficienza e ad alta frequenza di commutazione per applicazioni nel campo dell'industria automobilistica”. Una parte dell'attività è stata svolta durante un periodo di studio di sei mesi presso il Colorado Power Electronics Center dell'Università del Colorado a Boulder, sotto la supervisione del Prof. Dragan Maksimovic. L'approccio seguito mira a trasferire la complessità dell'hardware dal convertitore al controllo con un impatto minimo sul costo complessivo del sistema. A questo proposito, l'implementazione digitale del controllore rende possibile lo sviluppo di strategie di controllo avanzate e schemi di modulazione che sfruttano i gradi di libertà del convertitore per motivi di regolazione e ottimizzazione dell'efficienza. Un esempio è la possibilità di utilizzare tecniche soft-switching le quali consentono di aumentare notevolmente la frequenza di commutazione senza compromettere l’efficienza del convertitore e, in aggiunta, di ridurre le dimensioni dei componenti passivi. In particolare la ricerca è focalizzata sullo studio dei convertitori a doppio mezzo ponte, nelle loro versioni risonante e non risonante. Questa classe di convertitori è stata scelta per la bassa complessità dell'hardware e per il numero dei gradi di libertà che possono essere utilizzati per finalità di controllo. La prima parte della tesi tratta il tema della modellizzazione di questi convertitori dal punto di vista statico con particolare attenzione agli aspetti che riguardano la caratterizzazione dell'efficienza. Sulla base dei risultati ottenuti, sono proposte delle tecniche di controllo multivariabile e ottimizzazione online dell’efficienza. In sistemi di questo tipo, il convertitore si porta da un punto operativo all'altro ogni volta che si verifica un evento (ad esempio una variazione del carico o della tensione di batteria). Per questo motivo, durante il normale funzionamento, il punto operativo del convertitore può attraversare un'ampia porzione dello spazio di controllo quindi è richiesta un'accurata analisi dinamica per garantire la stabilità del sistema. Un'importante tematica affrontata in questa tesi, è lo studio dinamico dei convertitori a doppio mezzo ponte con controllo digitale multivariabile. In dettaglio, sono stati approfonditi aspetti riguardanti la modellistica della dinamica introdotta dai modulatori a sfasamento digitale a campionamento uniforme e dai modulatori a sfasamento e larghezza d'impulso a campionamento uniforme. Tali modelli sono stati impiegati al fine di costruire un modello ai piccoli segnali di tipo multi-armonica per il convertitore a doppio mezzo ponte con controllo digitale multivariabile. Tutti i risultati presentati in questa tesi sono validati tramite simulazioni e misure sperimentali fatte su prototipi a componenti discreti.

ABSTRACT Voltage instability has become a major concern in power systems. Many blackouts have been reported where the main cause is voltage instability. This thesis deals with two specific areas of voltage stability in on-line power system security assessments: small-disturbance (long-term) and large-disturbance (short-term) voltage stability assessment. For each category of voltage stability, both voltage stability analysis and controls are studied. The overall objective is to use the learning capabilities of computational intelligence technology to build up the comprehensive on-line power system security assessment and control strategy as well as to enhance the speed and efficiency of the process with minimal human intervention. The voltage stability problems are quantified by voltage stability indices which measure the system for the closeness of current operating point to voltage instability. The indices are different for small-disturbance and large-disturbance voltage stability assessment. Conventional approaches, such as continuation power flow or time-domain simulation, can be used to obtain voltage stability indices. However, these conventional approaches are limited by computation time that is significant for on-line computation. The Artificial Neural Network (ANN) approach is proposed to compute voltage stability indices as an alternative to the conventional approaches. The proposed ANN algorithm is used to estimate voltage stability indices under both normal and contingency operating conditions. The input variables of ANN are obtained in real-time by an on-line measurement system, i.e. Phasor Measurement Units (PMU). This thesis will propose a suboptimal approach for seeking the best locations for PMUs from a voltage stability viewpoint. The ANN-based method is not limited to compute voltage stability indices but can also be extended to determine suitable control actions. Load shedding is one of the most effective approaches against short-term voltage instability under large disturbances. The basic requirement of load shedding for recovering voltage stability is to seek an optimal solution for when, where, and how much load should be shed. Two simulation based approaches, particle swarm optimization (PSO) algorithm and sensitivity based algorithm, are proposed for load shedding to prevent voltage instability or collapse. Both approaches are based on time-domain simulation.

博士<br>南臺科技大學<br>電機工程系<br>107<br>This dissertation proposes direct torque control (DTC) based on constant voltage per frequency (V/F) control technique (DTC-CVFC), that is another control method for three-phase induction motor (IM). To reduce the torque and stator flux ripples and achieve the constant switching frequency, the nonlinear hysteresis comparators and look-up switching table in classical DTC are replaced by the proportional and integral (PI) controllers and space vector modulation (SVM) technique. This method uses the torque error and the stator flux magnitude error to generate the stator voltage magnitude reference and the stator phase angle reference for controlling IM based on constant V/F control principle. This control scheme is simple and similar to the classical DTC. Full-order observer is adopted to estimate stator flux and cope the problems from drift and initial condition from using the pure integrator in practical implementation. Its feedback gains are designed by simple manner to improve the rate of convergence of the stator flux estimation, especially in low speed range. The necessary conditions for the stability are introduced as well. Furthermore, an artificial neural network (ANN) based speed estimator is proffered. For the speed estimation, a weight in ANN, which relates to the speed, is adjusted by using Widrow-Hoff learning rule to minimize the sum of squared errors between the measured stator current and the estimated stator current. The consequence of using this method leads to the ability of online speed estimation and simple ANN structure. The simulation and experimental results show that the offered control scheme has good dynamic and steady-state Responses. The full-order observer with the proposed feedback gains has stable operation and can estimate the stator flux accurately over high and low speed ranges. The proffered ANN speed estimator has small estimation errors in dynamic and steady-state operations in both high and low speed ranges. These results have confirmed the effectiveness and validity of the introduced concepts.

Traditionally OUP relied on travellers to promote and sell its books in the UK and branch staff to do so overseas; these activities were managed from the Sales Department at Ely House. Feedback from the branches and UK travellers on customer preferences did not reliably reach editors in Oxford and London. Following the reorganization of the Press in the 1970s, publishing divisions took control of marketing their own books and a greater priority was given to market preferences in decisions about design, format, pricing, timing of publication, and projected sales. The chapter chronicles the changes in marketing policy and sales techniques, offering examples of the impact of market analysis, customer feedback, and promotional campaigns on particular titles. The chapter also considers the way the Press reacted to changes in the retail book sales with the growth of chain stores, book clubs, and the online marketplace.

Research over the last decade has identified Internet addiction as a new and often unrecognized clinical disorder that impacts a user’s ability to control online use to the extent that it can cause relational, occupational, and social problems. Symptoms of problem Internet use are compared to the criteria used to diagnose other addictions. In particular, pathological gambling is compared to problematic Internet use because of overlapping criteria. As new cases of problem Internet use are being documented, this chapter describes the diagnostic and treatment implications of the disorder. As computers are used with great frequency, detection and diagnosis of Internet addiction are often difficult. Symptoms of a possible problem may be masked by legitimate use of the Internet, and clinicians may not ask questions about computer use because problem Internet use is still a new and often unrecognized condition. This chapter outlines diagnostic conceptualizations of problem Internet use including the DSM-V proposed criteria for Pathological Computer Use, assessment techniques, and treatment considerations.

This book presents an in-depth deliberation on optical networks in four parts, capturing the past, present, and ensuing developments in the field. Part I has two chapters presenting an overview of optical networks and the enabling technologies. Part II has three chapters dealing with the single-wavelength optical networks: optical LANs/MANs, optical access networks using passive optical network architecture, SONET/SDH, optical transport network and resilient packet ring. Part III consists of four chapters on WDM-based optical networks, including WDM-based local/metropolitan networks (LANs/MANs) using single and multihop architectures over passive-star couplers, WDM/TWDM access networks as an extension of PONs with WDM transmission, WDM metro ring networks covering circuit-switched (using point-to-point WDM and wavelength-routed transmission) plus packet-switched architectures and WDM long-haul backbone networks presenting the offline and online design methodologies using wavelength-routed transmission. Part IV deals with some selected topics in six chapters. The first deals with transmission impairments and power-consumption issues in optical networks, while the next three chapters deal with the survivable optical networks, network control and management techniques, including GMPLS, ASON, and SDN/SDON, and datacenter networks using electrical, optical, and hybrid switching techniques. The final two chapters present elastic optical networks using flexible grid for better utilization of the optical-fiber spectrum and optical packet and burst-switched networks. The three appendices present the basics of the linear programming techniques, noise processes encountered in the optical communication systems, and the fundamentals of queuing theory and its applications in telecommunication networks. (238 words)

AbstractThe study aims to examine digital piracy using the Theory of Planned Behavior (TPB), religious theory, and deterrence theory by adding economic and hedonic benefits. This study used a non-probability sampling technique. The questionnaire was distributed through an online platform and obtained from 214 respondents. The data acquired from the respondents used SPSS 23 and AMOSS 21 to process the Structural Equation Model (SEM). This study shows that attitude toward digital piracy and perceived behavioral control positively influence consumer intention to commit digital piracy. The results also reveal that attitude toward digital piracy is positively influenced by hedonic benefit and negatively influenced by extrinsic religiousness. According to this study, the government and the film industry must change the way Indonesian consumers perceive digital piracy so that the number of digital piracies in Indonesia can decrease.

AbstractOur physical world is being projected into online cyberspace at an unprecedented rate. People nowadays visit different places and leave behind them million-scale digital traces such as tweets, check-ins, Yelp reviews, and Uber trajectories. Such digital data are a result of social sensing: namely people act as human sensors that probe different places in the physical world and share their activities online. The availability of massive social-sensing data provides a unique opportunity for understanding urban space in a data-driven manner and improving many urban computing applications, ranging from urban planning and traffic scheduling to disaster control and trip planning. In this chapter, we present recent developments in data-mining techniques for urban activity modeling, a fundamental task for extracting useful urban knowledge from social-sensing data. We first describe traditional approaches to urban activity modeling, including pattern discovery methods and statistical models. Then, we present the latest developments in multimodal embedding techniques for this task, which learns vector representations for different modalities to model people's spatiotemporal activities. We study the empirical performance of these methods and demonstrate how data-mining techniques can be successfully applied to social-sensing data to extract actionable knowledge and facilitate downstream applications.

Abstract Non-intrusive continuous wall thickness monitoring systems are fast becoming industry best practice for online detection and monitoring of corrosion and erosion. Challenges with localized corrosion have been knowing where to deploy online monitoring sensors and also being able to quickly and easily interpret the data that is delivered. The authors will demonstrate that deploying only a modest number of point measurement devices in an area of elevated localized corrosion risk will provide the best possible combination of probability of detection (POD) as well as ongoing wall thickness monitoring for localized corrosion attack. Recent advances in ultrasonic signal processing that takes advantage of specific historic data that is recorded by the online wireless wall-thickness monitoring system has been instrumental in separating the effects of wall-thickness loss from changes to internal surface morphology at the measurement locations. These advances make the data from the online monitoring system considerably easier to understand and interpret when the corrosion mechanism that is occurring is creating a rough internal surface at the measurement location – i.e., as per many localized corrosion mechanisms. Specific field examples from the ~10,000 installed sensors worldwide are presented to demonstrate the improvements of the new signal processing technique.

Abstract Changes in design and operational practice have resulted in a number of failures of copper-nickel components in seawater systems that have been attributed to exposure to sulfide-polluted, stagnant seawater during shutdowns. This has generated interest in the development of online corrosion monitors for these systems. In order to assess electrochemical frequency modulation for this role, 90/10 and 70/30 copper-nickel specimens were exposed to flowing seawater until protective films were developed. Some specimens were then buried in decaying organic debris at the bottom of the tank. These specimens were re-exposed to flowing seawater after remaining in the sediment for 55 days. Corrosion rates were monitored throughout the experiment using three different electrochemical techniques. Electrochemical frequency modulation confirmed earlier work showing that copper-nickel alloys experienced high corrosion rates in clean seawater after exposure to decaying organic debris. The technique, supported by electrochemical impedance measurements, also indicated that the corrosion rate was generally not under diffusion control. The corrosion rate was found to be profoundly influenced by the amplitude of the applied voltage. However, the technique highlighted changes in the corrosive environment and changes in the corrosion mechanism, indicating that it has potential as an online monitoring technique.

Abstract Quality control in district heating systems to keep uniform corrosion rates low and localized corrosion minimal is based on water quality control. Side-stream units equipped with carbon steel probes for online monitoring were mounted in district heating plants to investigate which techniques would be applicable, and if on-line monitoring could improve the quality control. Water quality monitoring was applied as well as corrosion rate monitoring with linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), electrical resistance (ER) technique, mass loss and a crevice corrosion cell for localized corrosion risk estimation. Important variations in corrosion rate due to changes in make-up water quality were detected with the continuous monitoring provided by ER and crevice cell, while LPR gave unreliable corrosion rates. The acquisition time of two-three days for EIS measurements was too long for real time data, and reliable mass loss data could only be obtained after 6 months exposure. It was furthermore found that localized corrosion events detected by the carbon steel crevice corrosion cell correlated with oxygen peaks of even a few hours duration.

Abstract Online Continuous Non-Intrusive Corrosion Monitoring is fast becoming industry best-practice in the Refining Industry globally. This technique involves wireless battery-powered sensors placed in the process units which deliver high-quality data directly to the desk of the corrosion engineer. This paper will present a case study and learnings from various refineries from the deployment of non-intrusive ultrasonic wall thickness monitoring systems in HF alkylation units. Online non-intrusive automated corrosion monitoring of HF alkylation units is valuable due to the safety risks associated with inspection inside these units, as well as the high probability of corrosion events and grave consequences of leakages. The technology discussed in this paper was developed using information from around 300 thickness monitoring sensors installed across 12 HF alkylation units globally. Traditional expectation is that iron fluoride scale layers that build up will not affect ultrasonic thickness results. However, through monitoring using permanently installed ultrasonic sensors, it was observed that the scale layer did negatively affect the ultrasonic signal. Our field experience has led to the development of an advanced signal processing algorithm, designed to be less affected by the effects of ultrasonic distortion due to the scale build-up. Data examples will be presented to explain this effect and comparisons between traditional signal processing methods and the advanced methods developed for this application. We close with a case study from a refinery who, via online monitoring of their HF alkylation unit, were able to detect elevated corrosion rates and take action to bring the corrosion under control, before any danger.

On 28 December 2022, the Spanish government announced a temporary Value Added Tax (VAT) rate reduction for selected products. VAT rates were cut on 1 January 2023 and are expected to go back to their previous level by mid-2024. Using a web-scraped dataset, we leverage machine learning techniques to classify each product. Then we study the price effects of the temporary VAT rate reduction, covering the daily prices of roughly 10,000 food products sold online by a Spanish supermarket. To identify the causal price effects, we compare the evolution of prices for treated items (that is, subject to the tax policy) against a control group (food items outside the policy’s scope). Our findings indicate that, at the supermarket level, the pass-through was almost complete. We observe differences in the speed of pass-through across different product types.