PV power forecast using a nonparametric PV model

Forecasting the AC power output of a PV plant accurately is important both for plant owners and electric system operators. Two main categories of PV modeling are available: the parametric and the nonparametric. In this paper, a methodology using a nonparametric PV model is proposed, using as inputs several forecasts of meteorological variables from a Numerical Weather Forecast model, and actual AC power measurements of PV plants. The methodology was built upon the R environment and uses Quantile Regression Forests as machine learning tool to forecast AC power with a confidence interval. Real data from five PV plants was used to validate the methodology, and results show that daily production is predicted with an absolute cvMBE lower than 1.3%.

Contribución a la localización en interiores basada en comunicaciones inalámbricas

Determinar con buena precisión la posición en la que se encuentra un terminal móvil, cuando éste se halla inmerso en un entorno de interior (centros comerciales, edificios de oficinas, aeropuertos, estaciones, túneles, etc), es el pilar básico sobre el que se sustentan un gran número de aplicaciones y servicios. Muchos de esos servicios se encuentran ya disponibles en entornos de exterior, aunque los entornos de interior se prestan a otros servicios específicos para ellos. Ese número, sin embargo, podría ser significativamente mayor de lo que actualmente es, si no fuera necesaria una costosa infraestructura para llevar a cabo el posicionamiento con la precisión adecuada a cada uno de los hipotéticos servicios. O, igualmente, si la citada infraestructura pudiera tener otros usos distintos, además del relacionado con el posicionamiento. La usabilidad de la misma infraestructura para otros fines distintos ofrecería la oportunidad de que la misma estuviera ya presente en las diferentes localizaciones, porque ha sido previamente desplegada para esos otros usos; o bien facilitaría su despliegue, porque el coste de esa operación ofreciera un mayor retorno de usabilidad para quien lo realiza. Las tecnologías inalámbricas de comunicaciones basadas en radiofrecuencia, ya en uso para las comunicaciones de voz y datos (móviles, WLAN, etc), cumplen el requisito anteriormente indicado y, por tanto, facilitarían el crecimiento de las aplicaciones y servicios basados en el posicionamiento, en el caso de poderse emplear para ello. Sin embargo, determinar la posición con el nivel de precisión adecuado mediante el uso de estas tecnologías, es un importante reto hoy en día. El presente trabajo pretende aportar avances significativos en este campo. A lo largo del mismo se llevará a cabo, en primer lugar, un estudio de los principales algoritmos y técnicas auxiliares de posicionamiento aplicables en entornos de interior. La revisión se centrará en aquellos que sean aptos tanto para tecnologías móviles de última generación como para entornos WLAN. Con ello, se pretende poner de relieve las ventajas e inconvenientes de cada uno de estos algoritmos, teniendo como motivación final su aplicabilidad tanto al mundo de las redes móviles 3G y 4G (en especial a las femtoceldas y small-cells LTE) como al indicado entorno WLAN; y teniendo siempre presente que el objetivo último es que vayan a ser usados en interiores. La principal conclusión de esa revisión es que las técnicas de triangulación, comúnmente empleadas para realizar la localización en entornos de exterior, se muestran inútiles en los entornos de interior, debido a efectos adversos propios de este tipo de entornos como la pérdida de visión directa o los caminos múltiples en el recorrido de la señal. Los métodos de huella radioeléctrica, más conocidos bajo el término inglés “fingerprinting”, que se basan en la comparación de los valores de potencia de señal que se están recibiendo en el momento de llevar a cabo el posicionamiento por un terminal móvil, frente a los valores registrados en un mapa radio de potencias, elaborado durante una fase inicial de calibración, aparecen como los mejores de entre los posibles para los escenarios de interior. Sin embargo, estos sistemas se ven también afectados por otros problemas, como por ejemplo los importantes trabajos a realizar para ponerlos en marcha, y la variabilidad del canal. Frente a ellos, en el presente trabajo se presentan dos contribuciones originales para mejorar los sistemas basados en los métodos fingerprinting. La primera de esas contribuciones describe un método para determinar, de manera sencilla, las características básicas del sistema a nivel del número de muestras necesarias para crear el mapa radio de la huella radioeléctrica de referencia, junto al número mínimo de emisores de radiofrecuencia que habrá que desplegar; todo ello, a partir de unos requerimientos iniciales relacionados con el error y la precisión buscados en el posicionamiento a realizar, a los que uniremos los datos correspondientes a las dimensiones y realidad física del entorno. De esa forma, se establecen unas pautas iniciales a la hora de dimensionar el sistema, y se combaten los efectos negativos que, sobre el coste o el rendimiento del sistema en su conjunto, son debidos a un despliegue ineficiente de los emisores de radiofrecuencia y de los puntos de captura de su huella. La segunda contribución incrementa la precisión resultante del sistema en tiempo real, gracias a una técnica de recalibración automática del mapa radio de potencias. Esta técnica tiene en cuenta las medidas reportadas continuamente por unos pocos puntos de referencia estáticos, estratégicamente distribuidos en el entorno, para recalcular y actualizar las potencias registradas en el mapa radio. Un beneficio adicional a nivel operativo de la citada técnica, es la prolongación del tiempo de usabilidad fiable del sistema, bajando la frecuencia en la que se requiere volver a capturar el mapa radio de potencias completo. Las mejoras anteriormente citadas serán de aplicación directa en la mejora de los mecanismos de posicionamiento en interiores basados en la infraestructura inalámbrica de comunicaciones de voz y datos. A partir de ahí, esa mejora será extensible y de aplicabilidad sobre los servicios de localización (conocimiento personal del lugar donde uno mismo se encuentra), monitorización (conocimiento por terceros del citado lugar) y seguimiento (monitorización prolongada en el tiempo), ya que todos ellas toman como base un correcto posicionamiento para un adecuado desempeño. ABSTRACT To find the position where a mobile is located with good accuracy, when it is immersed in an indoor environment (shopping centers, office buildings, airports, stations, tunnels, etc.), is the cornerstone on which a large number of applications and services are supported. Many of these services are already available in outdoor environments, although the indoor environments are suitable for other services that are specific for it. That number, however, could be significantly higher than now, if an expensive infrastructure were not required to perform the positioning service with adequate precision, for each one of the hypothetical services. Or, equally, whether that infrastructure may have other different uses beyond the ones associated with positioning. The usability of the same infrastructure for purposes other than positioning could give the opportunity of having it already available in the different locations, because it was previously deployed for these other uses; or facilitate its deployment, because the cost of that operation would offer a higher return on usability for the deployer. Wireless technologies based on radio communications, already in use for voice and data communications (mobile, WLAN, etc), meet the requirement of additional usability and, therefore, could facilitate the growth of applications and services based on positioning, in the case of being able to use it. However, determining the position with the appropriate degree of accuracy using these technologies is a major challenge today. This paper provides significant advances in this field. Along this work, a study about the main algorithms and auxiliar techniques related with indoor positioning will be initially carried out. The review will be focused in those that are suitable to be used with both last generation mobile technologies and WLAN environments. By doing this, it is tried to highlight the advantages and disadvantages of each one of these algorithms, having as final motivation their applicability both in the world of 3G and 4G mobile networks (especially in femtocells and small-cells of LTE) and in the WLAN world; and having always in mind that the final aim is to use it in indoor environments. The main conclusion of that review is that triangulation techniques, commonly used for localization in outdoor environments, are useless in indoor environments due to adverse effects of such environments as loss of sight or multipaths. Triangulation techniques used for external locations are useless due to adverse effects like the lack of line of sight or multipath. Fingerprinting methods, based on the comparison of Received Signal Strength values measured by the mobile phone with a radio map of RSSI Recorded during the calibration phase, arise as the best methods for indoor scenarios. However, these systems are also affected by other problems, for example the important load of tasks to be done to have the system ready to work, and the variability of the channel. In front of them, in this paper we present two original contributions to improve the fingerprinting methods based systems. The first one of these contributions describes a method for find, in a simple way, the basic characteristics of the system at the level of the number of samples needed to create the radio map inside the referenced fingerprint, and also by the minimum number of radio frequency emitters that are needed to be deployed; and both of them coming from some initial requirements for the system related to the error and accuracy in positioning wanted to have, which it will be joined the data corresponding to the dimensions and physical reality of the environment. Thus, some initial guidelines when dimensioning the system will be in place, and the negative effects into the cost or into the performance of the whole system, due to an inefficient deployment of the radio frequency emitters and of the radio map capture points, will be minimized. The second contribution increases the resulting accuracy of the system when working in real time, thanks to a technique of automatic recalibration of the power measurements stored in the radio map. This technique takes into account the continuous measures reported by a few static reference points, strategically distributed in the environment, to recalculate and update the measurements stored into the map radio. An additional benefit at operational level of such technique, is the extension of the reliable time of the system, decreasing the periodicity required to recapture the radio map within full measurements. The above mentioned improvements are directly applicable to improve indoor positioning mechanisms based on voice and data wireless communications infrastructure. From there, that improvement will be also extensible and applicable to location services (personal knowledge of the location where oneself is), monitoring (knowledge by other people of your location) and monitoring (prolonged monitoring over time) as all of them are based in a correct positioning for proper performance.

Power absorption measurements during NMR experiments

The heating produced by the absorption of radiofrequency (RF) has been considered a secondary undesirable effect during MRI procedures. In this work, we have measured the power absorbed by distilled water, glycerol and egg-albumin during NMR and non-NMR experiments. The samples are dielectric and examples of different biological materials. The samples were irradiated using the same RF pulse sequence, whilst the magnetic field strength was the variable to be changed in the experiments. The measurements show a smooth increase of the thermal power as the magnetic field grows due to the magnetoresistive effect in the copper antenna, a coil around the probe, which is directly heating the sample. However, in the cases when the magnetic field was the adequate for the NMR to take place, some anomalies in the expected thermal powers were observed: the thermal power was higher in the cases of water and glycerol, and lower in the case of albumin. An ANOVA test demonstrated that the observed differences between the measured power and the expected power are significant.

Monolithic master oscillator power amplifier at 1.58 µm for lidar measurements

Nowadays the interest in high power semiconductor devices is growing for applications such as telemetry, lidar system or free space communications. Indeed semiconductor devices can be an alternative to solid state lasers because they are more compact and less power consuming. These characteristics are very important for constrained and/or low power supply environment such as airplanes or satellites. Lots of work has been done in the 800-1200 nm range for integrated and free space Master Oscillator Power Amplifier (MOPA) [1]-[3]. At 1.5 ?m, the only commercially available MOPA is from QPC [4]: the fibred output power is about 700 mW and the optical linewidth is 500 kHz. In this paper, we first report on the simulations we have done to determine the appropriate vertical structure and architecture for a good MOPA at 1.58 ?m (section II). Then we describe the fabrication of the devices (section III). Finally we report on the optical and electrical measurements we have done for various devices (section IV).

Novel method to improve the signal-to-noise ratio in the far-field results obtained from planar near-field measurements

A method to reduce the noise power in far-field pattern without modifying the desired signal is proposed. Therefore, an important signal-to-noise ratio improvement may be achieved. The method is used when the antenna measurement is performed in planar near-field, where the recorded data are assumed to be corrupted with white Gaussian and space-stationary noise, because of the receiver additive noise. Back-propagating the measured field from the scan plane to the antenna under test (AUT) plane, the noise remains white Gaussian and space-stationary, whereas the desired field is theoretically concentrated in the aperture antenna. Thanks to this fact, a spatial filtering may be applied, cancelling the field which is located out of the AUT dimensions and which is only composed by noise. Next, a planar field to far-field transformation is carried out, achieving a great improvement compared to the pattern obtained directly from the measurement. To verify the effectiveness of the method, two examples will be presented using both simulated and measured near-field data.

Power Measurement Methodology for FPGA Devices

The efficiency of power optimization tools depends on information on design power provided by the power estimation models. Power models targeting different power groups can enable fast identification of the most power consuming parts of design and their properties. The accuracy of these estimation models is highly dependent on the accuracy of the method used for their characterization. The highest precision is achieved by using physical onboard measurements. In this paper, we present a measurement methodology that is primarily aimed at calibrating and validating high-level dynamic power estimation models. The measurements have been carefully designed to enable the separation of the interconnect power from the logic power and the power of the clock circuitry, so that each of these power groups can be used for the corresponding model validation. The standard measurement uncertainty is lower than 2% of the measured value even with a very small number of repeated measurements. Additionally, the accuracy of a commercial low-level power estimation tool has been also assessed for comparison purposes. The results indicate that the tool is not suitable for power estimation of data path-oriented designs.

From irradiance to output power fluctuations: the pv plant as a low pass filter

The power generated by large grid-connected photovoltaic (PV) plants depends greatly on the solar irradiance. This paper studies the effects of the solar irradiance variability analyzing experimental 1-s data collected throughout a year at six PV plants, totaling 18 MWp. Each PV plant was modeled as a first order filter function based on an analysis in the frequency domain of the irradiance data and the output power signals. An empiric expression which relates the filter parameters and the PV plant size has been proposed. This simple model has been successfully validated precisely determining the daily maximum output power fluctuation from incident irradiance measurements.

Broadband Channel Long Delay Cluster Measurements and Analysis at 2.4GHz in Subway Tunnels

The delay caused by the reflected ray in broadband communication has a great influence on the communications in subway tunnel. This paper presents measurements taken in subway tunnels at 2.4 GHz, with 5 MHz bandwidth. According to propagation characteristics of tunnel, the measurements were carried out with a frequency domain channel sounding technique, in three typical scenarios: line of sight (LOS), Non-line-of-sight (NLOS) and far line of sight (FLOS), which lead to different delay distributions. Firstly IFFT was chosen to get channel impulse response (CIR) h(t) from measured three-dimensional transfer functions. Power delay profile (PDP) was investigated to give an overview of broadband channel model. Thereafter, a long delay caused by the obturation of tunnel is observed and investigated in all the scenarios. The measurements show that the reflection can be greatly remained by the tunnel, which leads to long delay cluster where the reflection, but direct ray, makes the main contribution for radio wave propagation. Four important parameters: distribution of whole PDP power, first peak arriving time, reflection cluster duration and PDP power distribution of reflection cluster were studied to give a detailed description of long delay characteristic in tunnel. This can be used to ensure high capacity communication in tunnels

Characterization of thin film PV modules under standard test conditions: Results of indoor and outdoor measurements and the effects of sunlight exposure

Photovoltaic modules based on thin film technology are gaining importance in the photovoltaic market, and module installers and plant owners have increasingly begun to request methods of performing module quality control. These modules pose additional problems for measuring power under standard test conditions (STC), beyond problems caused by the temperature of the module and the ambient variables. The main difficulty is that the modules’ power rates may vary depending both on the amount of time they have been exposed to the sun during recent hours and on their history of sunlight exposure. In order to assess the current state of the module, it is necessary to know its sunlight exposure history. Thus, an easily accomplishable testing method that ensures the repeatability of the measurements of the power generated is needed. This paper examines different tests performed on commercial thin film PV modules of CIS, a-Si and CdTe technologies in order to find the best way to obtain measurements. A method for obtaining indoor measurements of these technologies that takes into account periods of sunlight exposure is proposed. Special attention is paid to CdTe as a fast growing technology in the market.

Relativistic high-current electron-beam stopping-power characterization in solids and plasmas: collisional versus resistive effects.

We present experimental and numerical results on intense-laser-pulse-produced fast electron beams transport through aluminum samples, either solid or compressed and heated by laser-induced planar shock propagation. Thanks to absolute K� yield measurements and its very good agreement with results from numerical simulations, we quantify the collisional and resistive fast electron stopping powers: for electron current densities of � 8 � 1010 A=cm2 they reach 1:5 keV=�m and 0:8 keV=�m, respectively. For higher current densities up to 1012 A=cm2, numerical simulations show resistive and collisional energy losses at comparable levels. Analytical estimations predict the resistive stopping power will be kept on the level of 1 keV=�m for electron current densities of 1014 A=cm2, representative of the full-scale conditions in the fast ignition of inertially confined fusion targets.

Methods for noise reduction in far-field patterns obtained from cylindrical near-field antenna measurements

Two different methods to reduce the noise power in the far-field pattern of an antenna as measured in cylindrical near-field (CNF) are proposed. Both methods are based on the same principle: the data recorded in the CNF measurement, assumed to be corrupted by white Gaussian and space-stationary noise, are transformed into a new domain where it is possible to filter out a portion of noise. Those filtered data are then used to calculate a far-field pattern with less noise power than that one obtained from the measured data without applying any filtering. Statistical analyses are carried out to deduce the expressions of the signal-to-noise ratio improvement achieved with each method. Although the idea of the two alternatives is the same, there are important differences between them. The first one applies a modal filtering, requires an oversampling and improves the far-field pattern in all directions. The second method employs a spatial filtering on the antenna plane, does not require oversampling and the far-field pattern is only improved in the forward hemisphere. Several examples are presented using both simulated and measured near-field data to verify the effectiveness of the methods.

Indoor characterization at production sccale: 200 kWp of CPV solar simulator measurements

In order to complement ISFOC’s characterization capabilities, a Helios 3198 CPV Solar Simulator was installed in summer 2010. This Solar Simulator, based on a parabolic mirror and a high-intensity, small area Xenon flash lamp was developed by the Instituto de Energía Solar in Madrid [1] and is manufactured and distributed by Soldaduras Avanzadas [2]. This simulator is used not only for R&D purposes, but as a quality control tool for incoming modules that are to be installed in ISFOC’s CPV plants. In this paper we will discuss the results of recent measurements of close to 5000 modules, the entire production of modules corresponding to a small CPV power plant (200 kWp). We scrutinize the resultant data for signs of drift in the measurements, and analyze the light quality before and after, to check for changes in spectrum or spatial uniformity.)

Application of postprocessing techniques methods for noise reduction in cylindrical near field antenna measurements

Three different methods to reduce the noise power in the far-field pattern of an antenna when it is measured in a cylindrical near field system are presented and compared. The first one is based on a modal filtering while the other two are based on spatial filtering, either on an antenna plane or either on a cylinder of smaller radius. Simulated and measured results will be presented.

Evaluation of the Grounding Circuit Measurements for Stator Ground-Fault Location of Synchronous Generators

Locating stator-winding ground faults accurately is a very difficult task. In this paper the grounding circuit measurements are evaluated in order to obtain information about the stator ground-fault location in synchronous generators. In power generators grounded through a high impedance, the relation between the neutral voltage and the phase voltage provide a first estimation of the fault location. The location error by using this ratio depends on the fault resistance and the value of the capacitance to ground of the stator winding. However, the error added by ignoring the value of the fault resistance is the most relevant term. This location estimation and the location error have been evaluated through the data of a real synchronous machine.

Simplified small-signal stability analysis for optimized power system architecture

The optimization of power architectures is a complex problem due to the plethora of different ways to connect various system components. This issue has been addressed by developing a methodology to design and optimize power architectures in terms of the most fundamental system features: size, cost and efficiency. The process assumes various simplifications regarding the utilized DC/DC converter models in order to prevent the simulation time to become excessive and, therefore, stability is not considered. The objective of this paper is to present a simplified method to analyze small-signal stability of a system in order to integrate it into the optimization methodology. A black-box modeling approach, applicable to commercial converters with unknown topology and components, is based on frequency response measurements enabling the system small-signal stability assessment. The applicability of passivity-based stability criterion is assessed. The stability margins are stated utilizing a concept of maximum peak criteria derived from the behavior of the impedance-based sensitivity function that provides a single number to state the robustness of the stability of a well-defined minor-loop gain.