Artículos de revistas

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https://repositorio.uc.cl/handle/11534/1156

Esta colección incluye artículos de revistas de profesores de la Pontificia Universidad Católica de Chile, publicados en revistas nacionales y extranjeras.

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23-Level Inverter for Electric Vehicles Using a Single Battery Pack and Series Active Filters
(IEEE, 2012) Pereda Torres, Javier Eduardo; Dixon, Juan
Cascaded H-bridge (CHB) multilevel inverters have been conceived as an alternative to reduce total harmonic distortion (THD) in medium-voltage drives. The reduced THD makes them useful for electric vehicle (EV) applications, but the main problem with the CHB is the large amount of isolated power sources required to feed each of the H-bridges. An improved variant known as the asymmetrical CHB (ACHB) inverter uses H-bridges of different sizes and then needs fewer isolated power sources than the CHB. However, in battery-powered EVs, only one power supply (fuel cell or battery pack) is desirable. This work presents a solution to solve the problem, operating some of the small H-bridges (Aux-bridges) as series active filters and using a small high-frequency link (HFL). With this solution, only one dc source is required to feed the inverter, and if the control is adjusted to work at particular switching points, more than 98% of power is transferred through the larger H-bridges (MAIN bridges). The proposed ACHB topology can produce any number of levels, and the M AIN bridges always commutate at fundamental frequency. As the number of levels must remain constant for all output voltages, a variable dc source is required to control the amplitude of the motor voltage. This work shows some simulations and experiments on a 2-kW 27-level ACHB working with only 23 levels. The concept is being implemented in a small EV with an ACHB drive of 18 kW.
3D Quantification of Wall Shear Stress and Oscillatory Shear Index Using a Finite-Element Method in 3D CINE PC-MRI Data of the Thoracic Aorta
(2016) Sotelo Parraguez, Julio Andrés; Urbina, Jesus; Valverde, Israel; Tejos Nunez, Cristian Andres; Irarrázaval Mena, Pablo; Andia Kohnenkampf, Marcelo Edgardo; Uribe Arancibia, Sergio A.; Hurtado Sepúlveda, Daniel
Several 2D methods have been proposed to estimate WSS and OSI from PC-MRI, neglecting the longitudinal velocity gradients that typically arise in cardiovascular flow, particularly on vessel geometries whose cross section and centerline orientation strongly vary in the axial direction. Thus, the contribution of longitudinal velocity gradients remains understudied. In this work, we propose a 3D finite-element method for the quantification of WSS and OSI from 3D-CINE PC-MRI that accounts for both in-plane and longitudinal velocity gradients. We demonstrate the convergence and robustness of the method on cylindrical geometries using a synthetic phantom based on the Poiseuille flow equation. We also show that, in the presence of noise, the method is both stable and accurate. Using computational fluid dynamics simulations, we show that the proposed 3D method results in more accurate WSS estimates than those obtained from a 2D analysis not considering out-of-plane velocity gradients. Further, we conclude that for irregular geometries the accurate prediction of WSS requires the consideration of longitudinal gradients in the velocity field. Additionally, we compute 3D maps of WSS and OSI for 3D-CINE PC-MRI data sets from an aortic phantom and sixteen healthy volunteers and two patients. The OSI values show a greater dispersion than WSS, which is strongly dependent on the PC-MRI resolution. We envision that the proposed 3D method will improve the estimation of WSS and OSI from 3D-CINE PC-MRI images, allowing for more accurate estimates in vessels with pathologies that induce high longitudinal velocity gradients, such as coarctations and aneurisms.
A clean four-quadrant sinusoidal power rectifier using multistage converters for subway applications
(2005) Dixon, Juan; Morán, Luis
A special 27-level four-quadrant rectifier for subway applications is analyzed. The arrangement uses only three H-bridges per phase, common dc bus, and independent input transformers for each H-bridge. The transformers allow galvanic isolation and power escalation to obtain high-quality voltage waveforms, with total harmonic distortion of less than 1%. Some advantages of this 27-level rectifier are: 1) only one of the three H-bridges, called the main converter, manages more than 80% of the total active power in each phase and 2) it switches at fundamental frequency, reducing the switching losses at a minimum value. The rectifier analyzed in this paper is a current-controlled voltage-source type, with a conventional feedback control loop. Some simulations in a rectifier substation, including power reversal at full load are displayed (750 Vdc, 1200 A). The rectifier shows the ability to produce clean ac and dc waveforms without any ripple, and fast reversal of power. Some experimental results with a small prototype, showing voltage and current waveforms, are finally displayed.
A Compact Answer Set Programming Encoding of Multi-Agent Pathfinding
(IEEE, 2021) Gómez Araya, Rodrigo Nicolás Teófilo; Hernández, Carlos; Baier Aranda, Jorge Andrés
Multi-agent pathfinding (MAPF) is the problem of finding k non-colliding paths connecting k given initial positions with k given goal positions on a given map. In its sum-of-costs variant, the total number of moves and wait actions performed by agents before they definitely reach the goal is minimized. Not surprisingly, since MAPF is combinatorial, a number of compilations to Boolean Satisfiability (SAT) and Answer Set Programming (ASP) exist. In this article, we describe in detail the first family of compilations to ASP that solve sum-of-costs MAPF over 4-connected grids. Compared to existing ASP compilations, a distinguishing feature of our compilation is that the number of total clauses (after grounding) grow linearly with the number of agents, while existing compilations grow quadratically. In addition, the optimization objective is such that its size after grounding does not depend on the size of the grid. In our experimental evaluation, we show that our approach outperforms search-based sum-of-costs MAPF solvers when grids are congested with agents. We also show that our approach is competitive with a SAT-based approach when follow conflicts are taken into account. We also explore the potential of our solver when finding makespanoptimal solutions, in which makespan is minimized first and then cost is minimized. Our results show that makespan-optimal solutions are slightly suboptimal in most benchmarks. Moreover, our MAPF solver, when run in that mode, is faster and scales better.
A delicate balance in South America
(2008) Rudnick, Hugh; Barroso, Luiz; Mocarquer, Sebastian; Bezerra, Bernardo
This article deals with the challenges of balancing the need for hydroelectricity with the impact on the environment. Economic efficiency, energy security, and environmental sustainability are concerns that must be considered in any energy policy in any given country. These key aspects remain challenged currently in South America. High energy consumption growth worldwide rising fossil fuels prices, strong environmentalist pressure toward reducing greenhouse gas effects, and promotion of renewable energy production have been a common challenge in South American energy markets. The development of vast unexploited hydroelectric resources is also at the center of attention, where its renewable character is being confronted with its environmental impact.
A Framework for Transmission Expansion Planning: A Complex Problem Clouded by Uncertainty
(IEEE, 2016) Velásquez Guerino, Constantin Sebastián Klaus; Watts Casimis, David; Rudnick van de Wyngard, Hugh; Bustos Sölch, Cristián Pablo
Transmission Expansion Planning (TEP), a complex problem that is vital to ensure the proper functioning of restructured electricity markets, is clouded by uncertainties. Timely and cost-effective transmission expansion is necessary for providing secure and reliable electricity service to customers, enhancing competition, and ensuring market efficiency in electricity markets. Given the irreversibility and long lifetimes of transmission investments, TEP requires addressing uncertainties on future system conditions several years ahead. Because of these fundamental properties of transmission, the importance of developing tools and models to assist power system planning under uncertainty has long been recognized. As any decision under uncertainty is made before the uncertainty is revealed, addressing uncertainties allows hedging against risks caused by the outcomes of decisions taken under uncertainty.
A fuzzy-controlled active front-end rectifier with current harmonic filtering characteristics and minimum sensing variables
(1999) Dixon Rojas, Juan; Contardo, J. M.; Morán, L. A.
A control strategy which allows conventional voltage-source current-controlled (VSCC) pulsewidth modulation (PWM) rectifiers to work simultaneously as active power filters is presented. The proposed control strategy also allows compensating the system power factor and compensating unbalanced loads. The measurement and/or calculation of the harmonics and reactive power are not required, making the proposed control scheme very simple. The active front-end rectifier acts directly on the mains line currents, forcing them to be sinusoidal and in phase with the mains voltage supply. To improve the dynamic of the system, the amplitude of the current is controlled by a fuzzy system, which adjusts the DC-link voltage of the PWM rectifier. The strategy is based on connecting all the polluting loads between the PWM rectifier and their input current sensors. The main advantages of this approach are the following: (1) there is no need to install a specially dedicated active power filter; (2) it also works simultaneously as a power factor compensator; and (3) no special and complicated calculations are required for harmonic elimination. The viability of the proposed active front-end rectifier is proved by simulation and with experimental results obtained from a 2 kVA PWM prototype.
A low-cost altitude control system for the Kadet Senior radio-controlled airplane
(2003) Abusleme Hoffman, Ángel Christian; Cipriano, Aldo; Guarini Hermann, Marcelo Walter
In automatic control education, real examples always improve students' learning and motivation. Considering this fact, a hardware-in-the-loop, low-cost altitude control system for a radio-controlled (RC) airplane has been developed to improve automatic control education. This system constitutes a high-impact demonstrator for teaching automatic control topics, applied to a real-life problem. The airplane has an altitude sensor; students can safely remotely control this variable in a computer real-time environment. This paper addresses the system analysis and description, controller design, and real demonstrations. This device was tested in a basic automatic control course for undergraduate electrical engineering students and received good results; students reacted with curiosity and enthusiasm and encouraged the lecturers to design more experiences like this one.
A Principal-Agent Approach to Transmission Expansion-Part I: Regulatory Framework
(IEEE, 2013) Molina Castro, Juan David; Contreras, J.; Rudnick van de Wyngard, Hugh
Different regulatory frameworks have implemented competitive mechanisms to increase efficiency in transmission, a natural monopoly. Conflicts of interest and hidden costs make necessary to define methods to obtain an appropriate valuation of new transmission assets. This paper is the first one of a two-paper series and presents the fundamentals of transmission project valuation and cost allocation. We show the fundamentals of non-cooperative game theory, different concepts of game equilibria (Nash, Stackelberg, and Berge), and solutions to the bilateral negotiation problem (Nash bargaining solution, Kalai-Smorodinsky, and Rubinstein). In addition, the design of mechanisms, the information revelation principles, and incentive compatibility issues are described. We propose a model composed of three elements: valuation of a transmission project based on a linear contract, a principal-agent model to determine the optimal effort of an agent developing the transmission project, and the optimal bilateral negotiation of right-of-way costs. We define a method to evaluate the offers to build a transmission line project as a function of the number of agents bidding for it. The value of the project is a function of both the incentives and the valuation of the right-of-way costs. In part two of this series, we present two case studies: the IEEE 24-bus RTS and the Sistema Interconectado Central (SIC) in Chile, where we apply the methodology to a real network.
A Principal-Agent Approach to Transmission Expansion-Part II: Case Studies
(IEEE, 2013) Molina Castro, Juan David; Contreras, J.; Rudnick van de Wyngard, Hugh
This paper is the second of a two-paper series and presents a model to assess and promote investment projects defined in a plan of expansion of the transmission. We propose a model that consists of three main elements: valuation of a project based on the design of a linear contract, a principal-agent model to assess the optimal effort of an agent, and the right-of-way negotiating cost. We also define a model to evaluate bids by the agents. The value of the project depends on the number of competitors, the incentives to invest, and the right-of-way costs. The right-of-way cost is approached from the perspective of a bilateral bargaining problem.
An Efficient Forecasting-Optimization Scheme for the Intraday Unit Commitment Process Under Significant Wind and Solar Power
(2018) Cordova, Samuel; Rudnick, Hugh; Lorca Galvez, Álvaro Hugo; Martinez Aranza, Victor Julio
Due to their uncertain and variable nature, the large-scale integration of wind and solar power poses significant challenges to the generator scheduling process in power systems. To support this process, system operators require using repeatedly updated forecasts of the best possible quality for renewable power. Motivated by this, the present work aims to study the benefits of incorporating spatiotemporal dependence and seasonalities into probabilistic forecasts for the intraday unit commitment (UC) process. With this purpose, a highly efficient forecasting-optimization scheme is proposed, which is composed of a detrended periodic vector autoregressive model and a technology-clustered interval UC model. The proposed approach is tested on a 120-GW power system with 210 conventional generators using real wind and solar measurements and compared to existing deterministic and stochastic UC techniques alongside standard forecasting methods. Extensive computational experiments show that the incorporation of spatiotemporal dependence and seasonalities into forecasts translates in a reduction of up to 1.55% in operational costs for a daily UC relative to standard practice, the application of intraday instead of daily UC runs further reduces operational costs in up to 1.51%, and the proposed forecasting-optimization scheme takes less than 10 h to simulate a whole year.
An Industrial Internet Application for Real-Time Fault Diagnosis in Industrial Motors
(IEEE, 2020) Langarica Chavira, Saúl Alberto; Ruffelmacher, Christian; Nuñez, Felipe
Being able to detect, identify, and diagnose a fault is a key feature of industrial supervision systems, which enables advance asset management, in particular, predictive maintenance, which greatly increases efficiency and productivity. In this paper, an Industrial Internet app for real-time fault detection and diagnosis is implemented and tested in a pilot scale industrial motor. Real-time fault detection and identification is based on dynamic incremental principal component analysis (DIPCA) and reconstruction-based contribution (RBC). When the analysis indicates that one of the vibration measurements is responsible for the fault, a convolutional neural network (CNN) is used to identify the unbalance or bearing fault type. The application was evaluated in its three functionalities: fault detection, fault identification, and fault identification of vibration-related faults, yielding a fault detection rate over 99%, a false alarm rate below 5%, and an identification accuracy over 90%.
An Overview of Microgrids Challenges in the Mining Industry
(2020) Gómez, Juan S.; Rodriguez, Jose; Garcia, Cristian; Tarisciotti, Luca; Flores-Bahamonde, Freddy; Pereda Torres, Javier Eduardo; Nuñez Retamal, Felipe Eduardo; Cipriano, Aldo; Salas, Juan Carlos
The transition from fossil fuels to renewable energies as power sources in the heavy industries is one of the main climate change mitigation strategies. The carbon footprint in mining is related to its inherent extraction process, its high demand of electric power and water, and the use of diesel. However, considering its particular power requirements, the integration of microgrids throughout the whole control hierarchy of mining industry is an emergent topic. This paper provides an overview of the opportunities and challenges derived from the synergy between microgrids and the mining industry. Bidirectional and optimal power flow, as well as the integration of power quality have been identified as microgrid features that could potentially enhance mining processes. Recommendations pertaining to the technological transition and the improvement of energy issues in mining environments are also highlighted in this work.
Analysis of Key Comparisons Incorporating Knowledge About Bias
(2012) Lira Canguilhem, Ignacio; Chunovkina, Anna; Elster, Clemens; Woger, Wolfgang
A method is proposed for analyzing key comparison data. It is based on the assumption that each laboratory participating in the comparison exercise obtains independent and consistent estimates of the measurand and that, in addition, each laboratory provides an estimate of the quantity that collects all systematic effects that the laboratory took into account. The unknown value of the latter quantity, subtracted from its estimate, is defined as the laboratory's bias. The uncertainties associated with the estimates of the measurand and with the vanishing biases' estimates are also assumed to be reported. In this paper, we show that the information provided in this way may be of help for judging the performances of the laboratories in their correction of systematic effects. This is done by developing formulas for the final (consensus) estimates and uncertainties of the measurand and of the biases. Formulas for the final estimates and uncertainties of the pairwise differences between the biases are also developed. An example involving simulated key comparison data makes apparent the benefits of the proposed approach.
Assessment of Three Spectroscopic Techniques for Rapid Estimation of Calcite in Copper Ore
(IEEE, 2010) Escarate, P.; Guesalaga Meissner, Andrés; Albertini, Valerio Rossi; Bailo, Daniele
This paper presents the assessment of three spectroscopic techniques, i.e., Raman spectroscopy (RS), ultraviolet fluorescence (UVF) spectroscopy, and energy-dispersive X-ray diffraction (ED-XRD), for measuring calcite (CaCO3) concentration in copper ore. The results for the three methods are compared in terms of their correlation coefficient R2 and prediction error (root-mean-square error of prediction, RMSEP). These approaches substantially shorten the measurement time with respect to current laboratory procedures from 300 min down to 1,15, and 9 min for RS, ED-XRD, and UVF, respectively, while preserving a good accuracy level (RMSEP <
Asymmetrical Multilevel Inverter for Traction Drives Using Only One DC Supply
(2010) Dixon Rojas, Juan; Pereda Torres, Javier Eduardo; Castillo Tamayo, Carlos Ignacio; Bosch Castro, Sebastián Andrés
The main advantage of asymmetrical multilevel inverters is the optimization of levels with a minimum number of power supplies. However, this optimized multilevel system still needs a large number of isolated and floating dc supplies, which makes these converters complicated to implement in electric vehicles (EVs), because the system will require many independent battery packs. In this paper, a very simple scheme, based on a small and cheap high-frequency link (HFL), allows the utilization of only one power supply for the complete multilevel inverter drive, with an inherent regulation of the voltages supplied among the H-bridges. It also allows voltage control with the full number of levels if the dc source is of a variable voltage characteristic. This paper is focused on a 27-level asymmetric inverter, but the strategy, using only one power supply, can be applied to converters with any number of levels. In particular, an asymmetrical 27-level converter needs nine isolated power supplies, and the proposed system reduces these nine sources to only one: the battery car. The topology also permits full regenerative braking working as a three-level converter. The proposed system is intended for application in EVs from power ratings up to 150 kW. Simulations and experimental results show the feasibility to implement this â€œone-sourceâ€ multilevel system.
Asymmetrical Triangular Current Mode (ATCM) for Bidirectional High Step Ratio Modular Multilevel Dc–Dc Converter
(IEEE, 2020) Pineda Fornerod, Cristian Andrés; Pereda Torres, Javier Eduardo; Rojas, Félix; Cerda, Carlos; Zhang, Xiaotian; Watson, Alan J.
Direct current (Dc) networks have proven advantages in high voltage direct current (HVDC) transmission systems, and now they are expanding to medium- and low-voltage distribution networks. One of the major challenges is to develop reliable dc-dc voltage transformation achieving high efficiency and performance, especially at high voltage and high step ratio. New resonant modular multilevel topologies have arisen as an alternative, mainly because of advantages such as optional use of transformers, natural voltage balance, simple control, and soft-switching capability. However, this type of operation generates a high peak current, does not allow control of power flow in all power range, and has a limited range of voltage variation. This article proposes an asymmetrical triangular current mode applied to high step ratio modular multilevel dc-dc converters. The proposed modulation increases the efficiency and achieves bidirectional control of the power, soft-switching, and a natural balance of the voltage in the cell capacitors. The experimental results show the bidirectional operation and the capacitor voltage balance of the converter under different operating conditions with higher efficiency (97.72%) and lower peak current compared to previous reports of this topology using resonant operation.
Auction mechanisms for long-term electricity contracts: Application to the Colombian market
(IEEE, 2014) Caicedo Beltrán, Germán Alberto.; Rudnick van de Wyngard, Hugh; Sauma Santis, Enzo Enrique
Electricity contracts are long-term supply assurance mechanism still in critical conditions, encourage competition and mitigate the risk of price volatility. However, it is necessary to evaluate design alternatives that balance contracts market versus expectations of the producers and the planner and/or regulator of the system. In this paper an international referencing is made, the formation of long-term price is analyzed, as well as market risks and their management. It implements a market simulation model, applying auction theory and descending clock auction. Contracting strategies are simulated, with product sensitivities, clearance mechanism, supply restriction and payment allocation, considering also the expectation of the buyer. For this, the demand function is estimated, the willingness to pay, and the maximum offer utility by sub-optimal allocations of opportunity cost and efficient frontier. Results show that the descending auction clears at more suitable prices against closed envelope auction and promotes competition under certain characteristics of the demand function. Best results are obtained with a standardized product, but in blocks of no more than 1% of the amount auctioned. A larger size creates infeasible solutions, increasing the closing price that contrasts when considering a supply pivotal constraint, obtaining lower closing prices. The proposed method offers a more suitable solution regarding intervention or handling mechanisms of the demand function.
Automatic Control on Batch and Continuous Distillation Columns
(IEEE, 2018) Díaz Quezada, Simón Diego; Pérez C., José Ricardo; Fernandez-Fernandez, Mario Alberto
Distillation is fundamental in Chemical Engineering. It is a highly complex and non-linear process. Therefore, developing intelligent control systems for distillation columns is challenging. These control techniques are based on previous knowledge and intuitive rules. In this work, several control strategies, such as IMC, Gain Scheduling, Expert, Fuzzy (Mamdani and Sugeno) and Neural-Network Control are applied to control a simulated distillation column for batch and continuous processes, and their performance is compared with a traditional PI controller. The controlled variable was the distillate molar fraction using as manipulated variable the reflux ratio. All control strategies were tested with respect set-point changes in two scenarios: without and with disturbances. The best control strategy was the Neural-Network, using a NARMA-L2 controller. This control has a good disturbance rejection and a fast set-point tracking with a smooth control action.
Balance of power
(2009) Mocarquer, Sebastian; Barroso, Luiz; Rudnick, Hugh; Bezerra, Bernardo; Pereira, Mario
This paper discusses the challenges in the procurement of electricity. The primary challenge faced by the countries in Latin America is to ensure sufficient capacity and investment to reliably serve their growing economies. The turn of the century brought different challenges to the energy supply in the region and to its market policy emphasis, coupled with a worldwide rocketing up of fuel prices.

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