Andres Pantoja | Universidad de los Andes (Colombia) (original) (raw)

Papers by Andres Pantoja

2021 IEEE 5th Colombian Conference on Automatic Control (CCAC)

This paper presents a data-based discrete-time linear model for a coffee fermentation process. Th... more This paper presents a data-based discrete-time linear model for a coffee fermentation process. The selected state variables (Brix degrees, Hydrogen potential (pH), and intank temperature) are easily measured in real process and properly reproduce a simple model with the ambient temperature as input. The parameter identification is performed using Particle Swarm Optimization (PSO) to find the best fitting for experimental data. Two models are analyzed with complete and reduced parameters to validate the performance, obtaining best results for the reduced model.

La UPME con otros actores centrales y locales (entre ellos, Universidad de Narino), inicio el des... more La UPME con otros actores centrales y locales (entre ellos, Universidad de Narino), inicio el desarrollo de una estrategia regional en el 2012,basada en el analisis de los elementos locales relevantes en materia de energizacion, productividad y emprendimiento que permitan plantear el mapa de ruta energetico de la region de estudio y desarrollar el catalogo de proyectos integrales identificado, para un periodo de minimo 15 anos. Este mecanismo denominado Planes de Energizacion Rural Sostenible –PERS- es el resultado de un esquema de trabajo regional interinstitucional con el proposito de unir esfuerzos en busqueda del fortalecimiento de las regiones y la descentralizacion del conocimiento, con el liderazgo, en lo posible, de la Academia. Con esta estrategia, se garantiza que los proyectos integrales incluidos en el catalogo cumplan con los objetivos de sostenibilidad y aprovechamiento de la energia como insumo de produccion, para el desarrollo de las comunidades rurales.

El presente articulo es producto de investigacion del proyecto “Analisis de oportunidades energet... more El presente articulo es producto de investigacion del proyecto “Analisis de oportunidades energeticas con fuentes alternativas en el departamento de Narino –Alternar–”, ejecutado desde el 2014 hasta inicios del 2016, por la Universidad de Narino, en cooperacion con la Universidad de los Andes y ASC Ingenieria S. A. E. S. P., con el apoyo de la Gobernacion de Narino, y financiado por el Sistema General de Regalias durante el 2014, en Colombia. El objetivo de la investigacion fue proponer un esquema de aprovechamiento integral y sostenible de los recursos locales para la generacion de energia, investigando las tecnologias de redes inteligentes y microrredes aplicadas a zonas no interconectadas zni. Metodologia: los estudios se llevaron a cabo en dos poblaciones de la region Pacifica narinense, donde los indices de cobertura energetica son muy bajos (2-5 horas/dia). Para determinar el potencial energetico de cada zni, se realizaron los siguientes pasos: caracterizacion geografica y soc...

2016 XXI Symposium on Signal Processing, Images and Artificial Vision (STSIVA), 2016

The identification of solar potentials in remote areas represents an opportunity to provide renew... more The identification of solar potentials in remote areas represents an opportunity to provide renewable energy solutions to population isolated from the main electric grid. For this, a methodology to estimate the solar irradiation is proposed, taking into account free satellite images from Landsat 7 and MODIS projects. The method includes the image processing and regression models to obtain high-resolution solar irradiance maps. To prove the application of the methodology, the process is performed over a zone in Southwest Colombia and the resulting maps are presented in a website with georeferencing tools.

Ingeniería e Investigación

The sum of squares (SOS) decomposition technique allows numerical methods such as semidefinite pr... more The sum of squares (SOS) decomposition technique allows numerical methods such as semidefinite programming to be used for proving the positivity of multivariable polynomial functions. It is well known that it is not an easy task to find Lyapunov functions for stability analysis of nonlinear systems. An algorithmic tool is used in this work for solving this problem. This approach is presented as SOS programming and solutions were obtained with a Matlab toolbox. Simple examples of SOS concepts, stability analysis for nonlinear polynomial and rational systems with uncertainties in parameters are presented to show the use of this tool. Besides these approaches, an alternative stability analysis for switched systems using a polynomial approach is also presented.

Heliyon

In this paper, we present the first study of the long-term climate-change impact on photovoltaic ... more In this paper, we present the first study of the long-term climate-change impact on photovoltaic power potential in Nariño, Colombia. In this region, more than half of the territory does not have a constant electricity supply, but it has great potential for solutions with renewable energy sources. Based on the Coordinated Regional Downscaling Experiment (CORDEX), we assess the change in photovoltaic power potential towards the end of this century, considering two climate change scenarios, one optimistic and the other pessimistic. Our results suggest that changes in photovoltaic power potential, by the end of the century, will have a maximum decrease of around 2.49% in the central zone of Nariño, with some non-affected areas, and a maximum increase of 2.52% on the southeastern side with respect to the pessimistic climate change scenario.

2019 IEEE 4th Colombian Conference on Automatic Control (CCAC)

The management of urban traffic is a challenging task due to its complexity and importance in mod... more The management of urban traffic is a challenging task due to its complexity and importance in modern cities. This work propoeses two control strategies for a study case developed in a co-simulation platform between a specialized traffic simulator (VISSIM) and Matlab to implement the control methods. The proposed strategies (Particle Swarm Optimization and Replicator Dynamics) are compared with a fixed-time technique (Webster) to analize the influence of the adaptive methods on some performance indexes such as queue lenghts, vehicle fluxes, and fuel consumption in a real network.

Tecnura, 2021

Context: This work presents different models based on artificial neural networks, among them NNAR... more Context: This work presents different models based on artificial neural networks, among them NNARX, for estimating global solar radiation from UV index measurements. The objective is to determine the efficiency of the models studied to estimate global solar radiation in terms of the coefficient of determination (R2), the root-mean-square error (RMSE), and the mean absolute error (MAE). Methodology: It is divided into four stages: i) conformation of the training dataset (in this case, it uses a training set of 213.019 data collected over five years in the city of Pasto, Colombia, with the Davis Vantage Pro 2.0 station); ii) pre-processing of data to remove erroneous and unusual data; iii) definition of models based on recurrent and conventional artificial neural networks according to an analysis of topologies, e.g. NNFIR and NNARX; iv) training of the models and evaluation of the estimation efficiency through metrics such as R2, RMSE, and MAE. To validate the model, a new dataset col...

2019 IEEE 4th Colombian Conference on Automatic Control (CCAC), 2019

Most of the wireless networks in use today, such as WiFi and LTE, use multicarrier communication ... more Most of the wireless networks in use today, such as WiFi and LTE, use multicarrier communication techniques. These systems divide the available bandwidth into a set of orthogonal subchannels. Performance in this type of systems is optimized by appropriately assigning power to each subchannel such that a total power constraint is satisfied. In this paper, we propose a dynamic resource allocation scheme based on replicator dynamics to achieve maximum spectral efficiency in a multicarrier system. We demonstrate that the population-based technique obtains the optimal water-filling solution. We illustrate the algorithm application with numerical simulations for a single-user power allocation in a common WiFi scenario. The results show the optimality and low computational cost of the proposed strategy, which can be used in the future to design resource allocation schemes in multiuser settings.

2017 IEEE 3rd Colombian Conference on Automatic Control (CCAC), 2017

Consensus protocols, used in multiagent systems to achieve agreements, are affected by inherent i... more Consensus protocols, used in multiagent systems to achieve agreements, are affected by inherent issues into the communication networks. An interesting research problem is the effect of time delays in the process, which could prevent the system to obtain the desired agreement equilibrium. In this work we propose to use the Lambert W function to analyze the input time delays in a system of interacting agents, assuming directed graphs to represent a network with simple-integrator dynamics in each agent. Then, a closed-form for the marginally-stable delay is obtained and tested with simulations in a study case.

2017 IEEE 3rd Colombian Conference on Automatic Control (CCAC), 2017

The design of attitude controllers for UAVs is a challenging problem due to the high nonlineariti... more The design of attitude controllers for UAVs is a challenging problem due to the high nonlinearities of the plant and its inherent instability. This work presents the development of a nonlinear controller based on Lyapunov theory in order to achieve a robust tracking for the orientation of a quadcopter. Based on a typical model, the inclusion of error integrals in the Lyapunov functions allow the UAV to achieve the desired set points without steady state error despite of changes in plant parameters and sensors noise. The results are compared in simulations to another nonlinear controller to show the robustness of the proposed strategy to disturbance in plant and outputs.

2017 IEEE 3rd Colombian Conference on Automatic Control (CCAC), 2017

Path planning and motion control are primary goals in mobile robotics since they are the basis of... more Path planning and motion control are primary goals in mobile robotics since they are the basis of autonomous navigation. This work presents a quantitative methodology to compare different algorithms that solve the path-planning problem, taking into account their basic concepts and results obtained in three simulation scenarios. The resulting trajectories are smoothed by Spline and B-Spline interpolation methods in order to propose a solution to the non-holonomic constraints of a differential-traction robot with a tracking controller. The comparison is based on simulations to calculate indexes and evaluate different performance criteria.

Renewable Energy, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

IFAC-PapersOnLine, 2020

We present a novel distributed heterogeneous multi-population evolutionary dynamics approach, whi... more We present a novel distributed heterogeneous multi-population evolutionary dynamics approach, which can be used in diverse engineering applications as a distributed optimizationbased algorithm. We also provide stability certificates of Nash equilibria under the proposed approach. Finally, over the end of this paper, an example illustrates the performance of the aforementioned multi-population evolutionary dynamics.

International Journal of Electrical Power & Energy Systems, 2019

Sweden is a country with abundant hydro power and has expectations to include more renewable ener... more Sweden is a country with abundant hydro power and has expectations to include more renewable energy sources, namely from wind power, into its electrical system. Currently, in order to improve the frequency response requirements of its electrical system, the country is considering upgrading its hydro-governors. This effort is part of maintaining the system frequency and reaction within their limits following any disturbance events. To partially compensate for increased frequency fluctuations due to an increased share of renewables on its system, the frequency response of hydro-governors should be improved. This paper proposes an innovative network control system, through a supplementary control, for the improvement of the hydro-governor's action. This supplementary control allows having more flexibility over the control action and improves the primary frequency control, and thereby the overall system frequency response. The proposed supplementary control, based on an evolutionary game theory strategy, uses remote measurements and a hierarchical dynamic adjustment of the control. Additionally, in order to guarantee an optimal response, a Simulated Annealing algorithm is combined with the supplementary control. This paper illustrates the analysis and design of the proposed methodology, and is tested on two power systems models: (i) an aggregated model that represents the frequency response of Sweden, Norway and Finland, and (ii) The Nordic 32 test system.

Journal of the Franklin Institute, 2018

In a multi-agent framework, distributed optimization problems are generally described as the mini... more In a multi-agent framework, distributed optimization problems are generally described as the minimization of a global objective function, where each agent can get information only from a neighborhood defined by a network topology. To solve the problem, this work presents an information-constrained strategy based on population dynamics, where payoff functions and tasks are assigned to each node in a connected graph. We prove that the so-called distributed replicator equation (DRE) converges to an optimal global outcome by means of the local-information exchange subject to the topological constraints of the graph. To show the application of the proposed strategy, we implement the DRE to solve an economic dispatch problem with distributed generation. We also present some simulation results to illustrate the theoretic optimality and stability of the equilibrium points and the effects of typical network topologies on the convergence rate of the algorithm.

2015 20th Symposium on Signal Processing, Images and Computer Vision (STSIVA), 2015

Dimensionality reduction (DR) methods represent a suitable alternative to visualizing data. Nonet... more Dimensionality reduction (DR) methods represent a suitable alternative to visualizing data. Nonetheless, most of them still lack the properties of interactivity and controllability. In this work, we propose a data visualization interface that allows for user interaction within an interactive framework. Specifically, our interface is based on a mathematic geometric model, which combines DR methods through a weighted sum. Interactivity is provided in the sense that weighting factors are given by the user via the selection of points inside a geometric surface. Then, (even non-expert) users can intuitively either select a concrete DR method or carry out a mixture of methods. Experimental results are obtained using artificial and real datasets, demonstrating the usability and applicability of our interface in DR-based data visualization.

2021 IEEE 5th Colombian Conference on Automatic Control (CCAC)

This paper presents a data-based discrete-time linear model for a coffee fermentation process. Th... more This paper presents a data-based discrete-time linear model for a coffee fermentation process. The selected state variables (Brix degrees, Hydrogen potential (pH), and intank temperature) are easily measured in real process and properly reproduce a simple model with the ambient temperature as input. The parameter identification is performed using Particle Swarm Optimization (PSO) to find the best fitting for experimental data. Two models are analyzed with complete and reduced parameters to validate the performance, obtaining best results for the reduced model.

La UPME con otros actores centrales y locales (entre ellos, Universidad de Narino), inicio el des... more La UPME con otros actores centrales y locales (entre ellos, Universidad de Narino), inicio el desarrollo de una estrategia regional en el 2012,basada en el analisis de los elementos locales relevantes en materia de energizacion, productividad y emprendimiento que permitan plantear el mapa de ruta energetico de la region de estudio y desarrollar el catalogo de proyectos integrales identificado, para un periodo de minimo 15 anos. Este mecanismo denominado Planes de Energizacion Rural Sostenible –PERS- es el resultado de un esquema de trabajo regional interinstitucional con el proposito de unir esfuerzos en busqueda del fortalecimiento de las regiones y la descentralizacion del conocimiento, con el liderazgo, en lo posible, de la Academia. Con esta estrategia, se garantiza que los proyectos integrales incluidos en el catalogo cumplan con los objetivos de sostenibilidad y aprovechamiento de la energia como insumo de produccion, para el desarrollo de las comunidades rurales.

El presente articulo es producto de investigacion del proyecto “Analisis de oportunidades energet... more El presente articulo es producto de investigacion del proyecto “Analisis de oportunidades energeticas con fuentes alternativas en el departamento de Narino –Alternar–”, ejecutado desde el 2014 hasta inicios del 2016, por la Universidad de Narino, en cooperacion con la Universidad de los Andes y ASC Ingenieria S. A. E. S. P., con el apoyo de la Gobernacion de Narino, y financiado por el Sistema General de Regalias durante el 2014, en Colombia. El objetivo de la investigacion fue proponer un esquema de aprovechamiento integral y sostenible de los recursos locales para la generacion de energia, investigando las tecnologias de redes inteligentes y microrredes aplicadas a zonas no interconectadas zni. Metodologia: los estudios se llevaron a cabo en dos poblaciones de la region Pacifica narinense, donde los indices de cobertura energetica son muy bajos (2-5 horas/dia). Para determinar el potencial energetico de cada zni, se realizaron los siguientes pasos: caracterizacion geografica y soc...

2016 XXI Symposium on Signal Processing, Images and Artificial Vision (STSIVA), 2016

The identification of solar potentials in remote areas represents an opportunity to provide renew... more The identification of solar potentials in remote areas represents an opportunity to provide renewable energy solutions to population isolated from the main electric grid. For this, a methodology to estimate the solar irradiation is proposed, taking into account free satellite images from Landsat 7 and MODIS projects. The method includes the image processing and regression models to obtain high-resolution solar irradiance maps. To prove the application of the methodology, the process is performed over a zone in Southwest Colombia and the resulting maps are presented in a website with georeferencing tools.

Ingeniería e Investigación

The sum of squares (SOS) decomposition technique allows numerical methods such as semidefinite pr... more The sum of squares (SOS) decomposition technique allows numerical methods such as semidefinite programming to be used for proving the positivity of multivariable polynomial functions. It is well known that it is not an easy task to find Lyapunov functions for stability analysis of nonlinear systems. An algorithmic tool is used in this work for solving this problem. This approach is presented as SOS programming and solutions were obtained with a Matlab toolbox. Simple examples of SOS concepts, stability analysis for nonlinear polynomial and rational systems with uncertainties in parameters are presented to show the use of this tool. Besides these approaches, an alternative stability analysis for switched systems using a polynomial approach is also presented.

Heliyon

In this paper, we present the first study of the long-term climate-change impact on photovoltaic ... more In this paper, we present the first study of the long-term climate-change impact on photovoltaic power potential in Nariño, Colombia. In this region, more than half of the territory does not have a constant electricity supply, but it has great potential for solutions with renewable energy sources. Based on the Coordinated Regional Downscaling Experiment (CORDEX), we assess the change in photovoltaic power potential towards the end of this century, considering two climate change scenarios, one optimistic and the other pessimistic. Our results suggest that changes in photovoltaic power potential, by the end of the century, will have a maximum decrease of around 2.49% in the central zone of Nariño, with some non-affected areas, and a maximum increase of 2.52% on the southeastern side with respect to the pessimistic climate change scenario.

2019 IEEE 4th Colombian Conference on Automatic Control (CCAC)

The management of urban traffic is a challenging task due to its complexity and importance in mod... more The management of urban traffic is a challenging task due to its complexity and importance in modern cities. This work propoeses two control strategies for a study case developed in a co-simulation platform between a specialized traffic simulator (VISSIM) and Matlab to implement the control methods. The proposed strategies (Particle Swarm Optimization and Replicator Dynamics) are compared with a fixed-time technique (Webster) to analize the influence of the adaptive methods on some performance indexes such as queue lenghts, vehicle fluxes, and fuel consumption in a real network.

Tecnura, 2021

Context: This work presents different models based on artificial neural networks, among them NNAR... more Context: This work presents different models based on artificial neural networks, among them NNARX, for estimating global solar radiation from UV index measurements. The objective is to determine the efficiency of the models studied to estimate global solar radiation in terms of the coefficient of determination (R2), the root-mean-square error (RMSE), and the mean absolute error (MAE). Methodology: It is divided into four stages: i) conformation of the training dataset (in this case, it uses a training set of 213.019 data collected over five years in the city of Pasto, Colombia, with the Davis Vantage Pro 2.0 station); ii) pre-processing of data to remove erroneous and unusual data; iii) definition of models based on recurrent and conventional artificial neural networks according to an analysis of topologies, e.g. NNFIR and NNARX; iv) training of the models and evaluation of the estimation efficiency through metrics such as R2, RMSE, and MAE. To validate the model, a new dataset col...

2019 IEEE 4th Colombian Conference on Automatic Control (CCAC), 2019

Most of the wireless networks in use today, such as WiFi and LTE, use multicarrier communication ... more Most of the wireless networks in use today, such as WiFi and LTE, use multicarrier communication techniques. These systems divide the available bandwidth into a set of orthogonal subchannels. Performance in this type of systems is optimized by appropriately assigning power to each subchannel such that a total power constraint is satisfied. In this paper, we propose a dynamic resource allocation scheme based on replicator dynamics to achieve maximum spectral efficiency in a multicarrier system. We demonstrate that the population-based technique obtains the optimal water-filling solution. We illustrate the algorithm application with numerical simulations for a single-user power allocation in a common WiFi scenario. The results show the optimality and low computational cost of the proposed strategy, which can be used in the future to design resource allocation schemes in multiuser settings.

2017 IEEE 3rd Colombian Conference on Automatic Control (CCAC), 2017

Consensus protocols, used in multiagent systems to achieve agreements, are affected by inherent i... more Consensus protocols, used in multiagent systems to achieve agreements, are affected by inherent issues into the communication networks. An interesting research problem is the effect of time delays in the process, which could prevent the system to obtain the desired agreement equilibrium. In this work we propose to use the Lambert W function to analyze the input time delays in a system of interacting agents, assuming directed graphs to represent a network with simple-integrator dynamics in each agent. Then, a closed-form for the marginally-stable delay is obtained and tested with simulations in a study case.

2017 IEEE 3rd Colombian Conference on Automatic Control (CCAC), 2017

The design of attitude controllers for UAVs is a challenging problem due to the high nonlineariti... more The design of attitude controllers for UAVs is a challenging problem due to the high nonlinearities of the plant and its inherent instability. This work presents the development of a nonlinear controller based on Lyapunov theory in order to achieve a robust tracking for the orientation of a quadcopter. Based on a typical model, the inclusion of error integrals in the Lyapunov functions allow the UAV to achieve the desired set points without steady state error despite of changes in plant parameters and sensors noise. The results are compared in simulations to another nonlinear controller to show the robustness of the proposed strategy to disturbance in plant and outputs.

2017 IEEE 3rd Colombian Conference on Automatic Control (CCAC), 2017

Path planning and motion control are primary goals in mobile robotics since they are the basis of... more Path planning and motion control are primary goals in mobile robotics since they are the basis of autonomous navigation. This work presents a quantitative methodology to compare different algorithms that solve the path-planning problem, taking into account their basic concepts and results obtained in three simulation scenarios. The resulting trajectories are smoothed by Spline and B-Spline interpolation methods in order to propose a solution to the non-holonomic constraints of a differential-traction robot with a tracking controller. The comparison is based on simulations to calculate indexes and evaluate different performance criteria.

Renewable Energy, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

IFAC-PapersOnLine, 2020

We present a novel distributed heterogeneous multi-population evolutionary dynamics approach, whi... more We present a novel distributed heterogeneous multi-population evolutionary dynamics approach, which can be used in diverse engineering applications as a distributed optimizationbased algorithm. We also provide stability certificates of Nash equilibria under the proposed approach. Finally, over the end of this paper, an example illustrates the performance of the aforementioned multi-population evolutionary dynamics.

International Journal of Electrical Power & Energy Systems, 2019

Sweden is a country with abundant hydro power and has expectations to include more renewable ener... more Sweden is a country with abundant hydro power and has expectations to include more renewable energy sources, namely from wind power, into its electrical system. Currently, in order to improve the frequency response requirements of its electrical system, the country is considering upgrading its hydro-governors. This effort is part of maintaining the system frequency and reaction within their limits following any disturbance events. To partially compensate for increased frequency fluctuations due to an increased share of renewables on its system, the frequency response of hydro-governors should be improved. This paper proposes an innovative network control system, through a supplementary control, for the improvement of the hydro-governor's action. This supplementary control allows having more flexibility over the control action and improves the primary frequency control, and thereby the overall system frequency response. The proposed supplementary control, based on an evolutionary game theory strategy, uses remote measurements and a hierarchical dynamic adjustment of the control. Additionally, in order to guarantee an optimal response, a Simulated Annealing algorithm is combined with the supplementary control. This paper illustrates the analysis and design of the proposed methodology, and is tested on two power systems models: (i) an aggregated model that represents the frequency response of Sweden, Norway and Finland, and (ii) The Nordic 32 test system.

Journal of the Franklin Institute, 2018

In a multi-agent framework, distributed optimization problems are generally described as the mini... more In a multi-agent framework, distributed optimization problems are generally described as the minimization of a global objective function, where each agent can get information only from a neighborhood defined by a network topology. To solve the problem, this work presents an information-constrained strategy based on population dynamics, where payoff functions and tasks are assigned to each node in a connected graph. We prove that the so-called distributed replicator equation (DRE) converges to an optimal global outcome by means of the local-information exchange subject to the topological constraints of the graph. To show the application of the proposed strategy, we implement the DRE to solve an economic dispatch problem with distributed generation. We also present some simulation results to illustrate the theoretic optimality and stability of the equilibrium points and the effects of typical network topologies on the convergence rate of the algorithm.

2015 20th Symposium on Signal Processing, Images and Computer Vision (STSIVA), 2015

Dimensionality reduction (DR) methods represent a suitable alternative to visualizing data. Nonet... more Dimensionality reduction (DR) methods represent a suitable alternative to visualizing data. Nonetheless, most of them still lack the properties of interactivity and controllability. In this work, we propose a data visualization interface that allows for user interaction within an interactive framework. Specifically, our interface is based on a mathematic geometric model, which combines DR methods through a weighted sum. Interactivity is provided in the sense that weighting factors are given by the user via the selection of points inside a geometric surface. Then, (even non-expert) users can intuitively either select a concrete DR method or carry out a mixture of methods. Experimental results are obtained using artificial and real datasets, demonstrating the usability and applicability of our interface in DR-based data visualization.