Esteban Velilla | Universidad de Antioquia (original) (raw)

Papers by Esteban Velilla

Lecturas de Economía, 2018

An electronic prototype was developed and implemented with the aim to evaluate solar panel perfor... more An electronic prototype was developed and implemented with the aim to evaluate solar panel performance on outdoor condition. The prototype obtains the panel IV-curve by charging a capacitive circuit. Voltage and current signal acquisition was achieved using a National Instruments card (NI-DAQ-USB6009), controlled by Labview software. The diode model was used to fit acquired signals in order to reduce electrical noise. The prototype results were validated with AMPROBE SOLAR600 analyzer using tree different panels in situ (two of 10W with similar characteristics and other of 55W). In uniform irradiance conditions, both devices showed similar performance on the IV curve, open circuit voltage and short circuit current measurements. However, the prototype presented shorter acquisition time and lower sensibility at transient irradiance variations caused by clouds.

International Journal of Energy Economics and Policy, 2018

This study aims to predict electricity prices in the Colombian electricity market. To achieve thi... more This study aims to predict electricity prices in the Colombian electricity market. To achieve this goal, conventional time series econometrics analysis and one alternative technique based on artificial intelligence algorithms have been implemented. We use autoregressive-moving-average models (ARMAX) and non-linear autoregressive neural networks (NARX). After estimating a hybrid model that combines ARMAX and ARNX models, including exogenous inputs, we forecasted an electricity price time series in a horizon of 12 months ahead (May 2017). Results show that NARX model's performance is not significantly better than ARMAX's. After applying a Diebold-Mariano test for forecasting accuracy, the null hypothesis is not rejected. This suggests no significant difference in predictive accuracy between the competing methodologies.

Evaluacion de compensadores estaticos en la estabilidad transitoria de sistemas eolicos con gene... more Evaluacion de compensadores estaticos en la estabilidad transitoria de sistemas eolicos con generadores de induccion en redes de distribucion En la actualidad la mayoria de los parques eolicos utilizan generadores de induccion para su operacion. Debido a su naturaleza, estos generadores normalmente son equipados con elementos de compensacion que pueden ser de naturaleza estatica o dinamica. En este articulo se presenta una evaluacion del uso de compensadores estaticos en la estabilidad de sistemas eolicos equipados con generadores de induccion. Para el estudio se utilizo un sistema base sobre el cual se simula una falla trifasica que desestabiliza la red. Posteriormente, para estabilizar la red y evitar una eventual desconexion o dano del parque eolico, se consideraron tres alternativas de compensacion: condensadores, STATCOM y SVC. Las simulaciones fueron realizadas en la herramienta Simulink de MATLAB@, mostrando resultados satisfactorios para las alternativas de compensacion est...

Revista Facultad De Ingenieria-universidad De Antioquia, 2005

Resumen es: Uno de los efectos de gran importancia en lineas de transmision (LT) es el efecto cor... more Resumen es: Uno de los efectos de gran importancia en lineas de transmision (LT) es el efecto corona, y es a raiz de este que se desarrollan fenomenos tales como la ...

Cuadernos de Economía, 2018

Los componentes estacionales se encuentran en los precios de la mayoría de los commodities, en lo... more Los componentes estacionales se encuentran en los precios de la mayoría de los commodities, en los cuales los precios se determinan, en gran medida, por la anticipación de la estacionalidad en la oferta y la demanda. Este artículo presenta una metodología para determinar precios estacionales en forwards en mercados de generación de electricidad. Un juego de Cournot se considera para caracterizar este mercado. Los precios forward se construyen de acuerdo con la elasticidad de la demanda a los forward y el precio spot por medio de un diferencial que representa el premio por riesgo en los forward actuales más una heterogeneidad no observable. La distribución de estas cantidades en contratos estacionales se realiza mediante la teoría clásica de portafolio. Esta metodología se aplica al caso colombiano, mostrando que es más rentable para los generadores vender los forward hídricos estacionales propuestos.

The behavior and response of power systems grounding, is determined by the variations of differen... more The behavior and response of power systems grounding, is determined by the variations of different parameters related with the type and magnitude of the injected current, the type of soil and the configuration of the grounding electrodes. In the specific case of power transmission lines, counterpoises are commonly used to decrease the low frequency resistance, without taking into account the characteristics that the impedance acquires once a lightning stroke reaches the grounding system. In this work the behavior of the overvoltage on the transmission tower and on the grounding system is analyzed, facing the variation of the main parameters that influence the response to slow and fast impulses.

Rev. fac. ing. univ. Antioquia, 2009

In order to classify the corrosivity of the different Colombian atmospheres, as part of an extens... more In order to classify the corrosivity of the different Colombian atmospheres, as part of an extensive research project [1], plates of carbon steel were placed in 21 stations spread along the country electrical infrastructure (transmission lines and substations). There were measured ...

Thin Films Photovoltaics, 2021

In the case of emerging photovoltaic technologies such as perovskite, most published works have f... more In the case of emerging photovoltaic technologies such as perovskite, most published works have focused on laboratory-scale cells, indoor conditions and no international standards have been fully established and adopted. Accordingly, this chapter shows a brief introduction on the standards and evaluation methods for perovskite solar minimodules under natural sunlight conditions. Therefore, we propose evaluating the outdoor performance in terms of power, following the international standard IEC 61853–1 to obtain the performance according to the power rating conditions. After some rigorous experimental evaluations, results shown that the maximum power (Pmax) evolution for the analyzed minimodules could be correlated with one of the three patterns commonly described for degradation processes in the literature, named convex, linear, and concave. These patterns were used to estimate the degradation rate and lifetime (T80). Moreover, ideality factor (nID) was estimated from the open-circu...

This paper presents a methodology to develop direct current sources using BJT transistors on the ... more This paper presents a methodology to develop direct current sources using BJT transistors on the linear region (active region). This region depends on the saturation voltage, maximum power and polarization voltage of the element; from these parameters it is obtained the load resistance range that ensures a constant current. The methodology is used to develop a DC current source prototype of 2A and the range of the load resistance is defined by the transistor characteristics. The temperature and power constrains are taking into account.

Energies

With the aim to determine the photo-generated current, diode saturation current, ideality factor,... more With the aim to determine the photo-generated current, diode saturation current, ideality factor, shunt, and series resistances related to the one-diode model for p-i-n planar perovskite solar cells, reference cells with active area of approximately 1 cm2 and efficiencies ranging between 4.6 and 12.2% were fabricated and characterized at standard test conditions. To estimated feasible parameters, the mean square error between the I-V curve data of these cells and the circuital model results were minimized using a Genetic Algorithm combined with the Nelder-Mead method. When considering the optimization process solutions, a numerical sensitivity analysis of the error as a function of the estimated parameters was carried out. Based on the errors behavior that is showed graphically through maps, it was demonstrated that the set of parameters estimated for each cell were reliable, meaningful, and realistic, and being related to errors lower than 9.1 × 10−9. Therefore, these results can b...

Lecturas de Economía

This paper presents an estimation of the reaction of electricity demand to changes in price level... more This paper presents an estimation of the reaction of electricity demand to changes in price levels of forward contracts in the manufacturing industry of Colombia. To that end, a structural vector autoregressive (SVAR) model was developed, considering several economic activities at different voltage levels. The industrial sectors under study showed an electricity demand not significantly sensitive to price variations. However, the food and drink sectors, plastic and rubber manufacturing, as well as retail trade turned out to be more sensitive to price shocks than the chemical industry or textile manufacturing. Such inelasticity could be softened if information concerning prices and quantity demanded were of common knowledge, or if the forward curve were observable.

Solar Energy Materials and Solar Cells

Solar Energy Materials and Solar Cells

Revista Facultad De Ingenieria Universidad De Antioquia, Feb 1, 2010

Proyecto académico sin fines de lucro, desarrollado bajo la iniciativa de acceso abierto *

Información tecnológica, 2016

En este artículo se presenta una propuesta de función de adaptación y manejo de restricciones apl... more En este artículo se presenta una propuesta de función de adaptación y manejo de restricciones aplicada al problema de flujo de potencia óptimo reactivo. Este problema tiene como objetivo la reducción de pérdidas mediante el control de tensiones de generadores, bornes en transformadores (taps), y bancos desconectables de capacitores y reactores. La función de adaptación consiste en un producto de subfunciones que representa los límites de las variables del sistema e incluye una meta específica de reducción de pérdidas. La principal ventaja de la función de adaptación propuesta consiste en que se puede conocer el óptimo global del problema con antelación. La función propuesta fue implementada y comparada con una función de adaptación tradicional mediante un algoritmo genético para tres casos de prueba IEEE: de 57, 118 y 300 barras. Se encontró que esta función presenta un mejor desempeño que la tradicional, garantizando la operación del sistema dentro de la región factible.

Lecturas de Economía, 2018

An electronic prototype was developed and implemented with the aim to evaluate solar panel perfor... more An electronic prototype was developed and implemented with the aim to evaluate solar panel performance on outdoor condition. The prototype obtains the panel IV-curve by charging a capacitive circuit. Voltage and current signal acquisition was achieved using a National Instruments card (NI-DAQ-USB6009), controlled by Labview software. The diode model was used to fit acquired signals in order to reduce electrical noise. The prototype results were validated with AMPROBE SOLAR600 analyzer using tree different panels in situ (two of 10W with similar characteristics and other of 55W). In uniform irradiance conditions, both devices showed similar performance on the IV curve, open circuit voltage and short circuit current measurements. However, the prototype presented shorter acquisition time and lower sensibility at transient irradiance variations caused by clouds.

International Journal of Energy Economics and Policy, 2018

This study aims to predict electricity prices in the Colombian electricity market. To achieve thi... more This study aims to predict electricity prices in the Colombian electricity market. To achieve this goal, conventional time series econometrics analysis and one alternative technique based on artificial intelligence algorithms have been implemented. We use autoregressive-moving-average models (ARMAX) and non-linear autoregressive neural networks (NARX). After estimating a hybrid model that combines ARMAX and ARNX models, including exogenous inputs, we forecasted an electricity price time series in a horizon of 12 months ahead (May 2017). Results show that NARX model's performance is not significantly better than ARMAX's. After applying a Diebold-Mariano test for forecasting accuracy, the null hypothesis is not rejected. This suggests no significant difference in predictive accuracy between the competing methodologies.

Evaluacion de compensadores estaticos en la estabilidad transitoria de sistemas eolicos con gene... more Evaluacion de compensadores estaticos en la estabilidad transitoria de sistemas eolicos con generadores de induccion en redes de distribucion En la actualidad la mayoria de los parques eolicos utilizan generadores de induccion para su operacion. Debido a su naturaleza, estos generadores normalmente son equipados con elementos de compensacion que pueden ser de naturaleza estatica o dinamica. En este articulo se presenta una evaluacion del uso de compensadores estaticos en la estabilidad de sistemas eolicos equipados con generadores de induccion. Para el estudio se utilizo un sistema base sobre el cual se simula una falla trifasica que desestabiliza la red. Posteriormente, para estabilizar la red y evitar una eventual desconexion o dano del parque eolico, se consideraron tres alternativas de compensacion: condensadores, STATCOM y SVC. Las simulaciones fueron realizadas en la herramienta Simulink de MATLAB@, mostrando resultados satisfactorios para las alternativas de compensacion est...

Revista Facultad De Ingenieria-universidad De Antioquia, 2005

Resumen es: Uno de los efectos de gran importancia en lineas de transmision (LT) es el efecto cor... more Resumen es: Uno de los efectos de gran importancia en lineas de transmision (LT) es el efecto corona, y es a raiz de este que se desarrollan fenomenos tales como la ...

Cuadernos de Economía, 2018

Los componentes estacionales se encuentran en los precios de la mayoría de los commodities, en lo... more Los componentes estacionales se encuentran en los precios de la mayoría de los commodities, en los cuales los precios se determinan, en gran medida, por la anticipación de la estacionalidad en la oferta y la demanda. Este artículo presenta una metodología para determinar precios estacionales en forwards en mercados de generación de electricidad. Un juego de Cournot se considera para caracterizar este mercado. Los precios forward se construyen de acuerdo con la elasticidad de la demanda a los forward y el precio spot por medio de un diferencial que representa el premio por riesgo en los forward actuales más una heterogeneidad no observable. La distribución de estas cantidades en contratos estacionales se realiza mediante la teoría clásica de portafolio. Esta metodología se aplica al caso colombiano, mostrando que es más rentable para los generadores vender los forward hídricos estacionales propuestos.

The behavior and response of power systems grounding, is determined by the variations of differen... more The behavior and response of power systems grounding, is determined by the variations of different parameters related with the type and magnitude of the injected current, the type of soil and the configuration of the grounding electrodes. In the specific case of power transmission lines, counterpoises are commonly used to decrease the low frequency resistance, without taking into account the characteristics that the impedance acquires once a lightning stroke reaches the grounding system. In this work the behavior of the overvoltage on the transmission tower and on the grounding system is analyzed, facing the variation of the main parameters that influence the response to slow and fast impulses.

Rev. fac. ing. univ. Antioquia, 2009

In order to classify the corrosivity of the different Colombian atmospheres, as part of an extens... more In order to classify the corrosivity of the different Colombian atmospheres, as part of an extensive research project [1], plates of carbon steel were placed in 21 stations spread along the country electrical infrastructure (transmission lines and substations). There were measured ...

Thin Films Photovoltaics, 2021

In the case of emerging photovoltaic technologies such as perovskite, most published works have f... more In the case of emerging photovoltaic technologies such as perovskite, most published works have focused on laboratory-scale cells, indoor conditions and no international standards have been fully established and adopted. Accordingly, this chapter shows a brief introduction on the standards and evaluation methods for perovskite solar minimodules under natural sunlight conditions. Therefore, we propose evaluating the outdoor performance in terms of power, following the international standard IEC 61853–1 to obtain the performance according to the power rating conditions. After some rigorous experimental evaluations, results shown that the maximum power (Pmax) evolution for the analyzed minimodules could be correlated with one of the three patterns commonly described for degradation processes in the literature, named convex, linear, and concave. These patterns were used to estimate the degradation rate and lifetime (T80). Moreover, ideality factor (nID) was estimated from the open-circu...

This paper presents a methodology to develop direct current sources using BJT transistors on the ... more This paper presents a methodology to develop direct current sources using BJT transistors on the linear region (active region). This region depends on the saturation voltage, maximum power and polarization voltage of the element; from these parameters it is obtained the load resistance range that ensures a constant current. The methodology is used to develop a DC current source prototype of 2A and the range of the load resistance is defined by the transistor characteristics. The temperature and power constrains are taking into account.

Energies

With the aim to determine the photo-generated current, diode saturation current, ideality factor,... more With the aim to determine the photo-generated current, diode saturation current, ideality factor, shunt, and series resistances related to the one-diode model for p-i-n planar perovskite solar cells, reference cells with active area of approximately 1 cm2 and efficiencies ranging between 4.6 and 12.2% were fabricated and characterized at standard test conditions. To estimated feasible parameters, the mean square error between the I-V curve data of these cells and the circuital model results were minimized using a Genetic Algorithm combined with the Nelder-Mead method. When considering the optimization process solutions, a numerical sensitivity analysis of the error as a function of the estimated parameters was carried out. Based on the errors behavior that is showed graphically through maps, it was demonstrated that the set of parameters estimated for each cell were reliable, meaningful, and realistic, and being related to errors lower than 9.1 × 10−9. Therefore, these results can b...

Lecturas de Economía

This paper presents an estimation of the reaction of electricity demand to changes in price level... more This paper presents an estimation of the reaction of electricity demand to changes in price levels of forward contracts in the manufacturing industry of Colombia. To that end, a structural vector autoregressive (SVAR) model was developed, considering several economic activities at different voltage levels. The industrial sectors under study showed an electricity demand not significantly sensitive to price variations. However, the food and drink sectors, plastic and rubber manufacturing, as well as retail trade turned out to be more sensitive to price shocks than the chemical industry or textile manufacturing. Such inelasticity could be softened if information concerning prices and quantity demanded were of common knowledge, or if the forward curve were observable.

Solar Energy Materials and Solar Cells

Solar Energy Materials and Solar Cells

Revista Facultad De Ingenieria Universidad De Antioquia, Feb 1, 2010

Proyecto académico sin fines de lucro, desarrollado bajo la iniciativa de acceso abierto *

Información tecnológica, 2016

En este artículo se presenta una propuesta de función de adaptación y manejo de restricciones apl... more En este artículo se presenta una propuesta de función de adaptación y manejo de restricciones aplicada al problema de flujo de potencia óptimo reactivo. Este problema tiene como objetivo la reducción de pérdidas mediante el control de tensiones de generadores, bornes en transformadores (taps), y bancos desconectables de capacitores y reactores. La función de adaptación consiste en un producto de subfunciones que representa los límites de las variables del sistema e incluye una meta específica de reducción de pérdidas. La principal ventaja de la función de adaptación propuesta consiste en que se puede conocer el óptimo global del problema con antelación. La función propuesta fue implementada y comparada con una función de adaptación tradicional mediante un algoritmo genético para tres casos de prueba IEEE: de 57, 118 y 300 barras. Se encontró que esta función presenta un mejor desempeño que la tradicional, garantizando la operación del sistema dentro de la región factible.

Currently, most wind power plants use induction generators in their operation. Due to their natur... more Currently, most wind power plants use induction generators in their operation. Due to their nature, these generators are usually equipped either with static or dynamic compensation devices. This paper presents an assessment of the use of static compensators in the stability of wind induction generators. To perform the study, a base case was used in which a three-phase fault that destabilizes the network is simulated. Then, to stabilize the network and avoid an eventual disconnection or damage of the wind power farm, three compensation alternatives were considered: capacitors, STATCOM and SVC. The effectiveness and performance of each of these alternatives were evaluated. Simulations were carried out in Simulink of MATLAB@, showing satisfactory results for the compensation alternatives under study. The performed simulations identified the STATCOM with IGBT as the most effective compensation under eventual contingencies. On the other hand, it was found that all the studied alternatives are equally effective for voltage compensation in steady state conditions.