Méthode de Caractérisation Electromagnétique In Situ et Large Bande des Ferrites Anisotropes pour l'Aide à la Conception de Circulateurs

National audienceCe travail décrit l'analyse dynamique d'une structure de propagation de type microruban dont la section transversale est partiellement remplie du matériau magnétique anisotrope à caractériser. L'approche théorique retenue est basée sur l'analyse modale des différentes régions de la structure et, aux discontinuités, du raccordement des champs associés à chaque mode. Une méthode particulière de recherche, en variable complexe, des racines de l'équation caractéristique a été développée. Les diagrammes de dispersion et les paramètres S traduisant le caractère non-réciproque de la structure sont présentés. Il s'agit de la première étape dans la mise en oeuvre d'une méthode de mesure large bande et " in situ " (environnement E.M. réel) des composantes du tenseur de perméabilité et de la permittivité des ferrites aimantés utilisés pour réaliser des circulateurs

Generalized Measurement Method for the Determination of the Dynamic Behavior of Magnetic Materials in Any Magnetization State

International audienceA broad-band characterization method based on the junction of the full-wave analysis of a nonreciprocal strip transmission line with a predictive permeability tensor model is presented. The aim of this method is the direct measurement of the permeability tensor components spectra of magnetized thick samples, whatever their magnetization state is. The propagation constants of the dominant transverse electromagnetic (TEM) and higher order modes inside the measurement cell are obtained along with its scattering parameters (S-parameters). The apparition of magnetostatic modes and the nonreciprocal nature of the structure are probed. Procedures based on the use of this method to find accurate values of gyromagnetic resonance and the resonance line width DH are proposed. The direct analysis is validated by comparison of the calculated S-parameters with those obtained with an electromagnetic field simulator based on finite element methods (FEM)

Broadband permeability measurement method for ferrites at any magnetization state: Experimental results

International audienceThis paper describes the experimental results obtained by a broadband permeability measurement method based on the full-wave electromagnetic (EM) analysis of a non-reciprocal transmission line. The method offers a new experimental tool for measuring the broadband dynamic behavior of ferrites whatever their magnetization state. The methodology and experimental setup are presented with the aim of extracting both the permittivity and the two components (diagonal µ and off-diagonal k) of the permeability tensor. Experimental data on commercial ferrites set in different magnetization states are presented and discussed. Furthermore, this method opens perspectives for the determination of other useful magnetic parameters such as resonance linewidth DH. This quantity can be then measured at different frequencies, where conventional resonant methods give a value at a fixed frequency

Forecasting Solar Irradiance by looking at clouds from above and below

The energy meteorology measurement network Eye2Sky is a cloud monitoring system covering roughly 110x100 km in north-west Germany. It is equipped with 38 cloud cameras, solar radiation measurement stations and individual Lidar based cloud altitude measurements distributed throughout the region around Oldenburg. The system collects high-resolution information on solar radiation, tracks the variability at different locations and outputs forecasts for very short time scales. It covers a resolution range of fewer than 100 metres and less than 1 minute and supports forecasts of up to one hour (depending on the prevailing cloud height). A second data source for this region is given by images from the geostationary satellite MSG. With these images longer forecast horizons are achieved in a coarser resolution. The hybrid use of both data sources has only just begun in the community. This allows the development of new models with an improved quality of predictions. The presentation gives an overview on Helmholtz AI collaboration of DLR VE and AI collaboration with institutes DLR SP and DLR SF

Impact of tropical convective conditions on solar irradiance forecasting based on cloud motion vectors

Intra-day forecasts of global horizontal solar irradiance (GHI) are widely produced by displacing existing clouds on a geo-stationary satellite image to their future locations with cloud motion vectors (CMVs) derived from preceding images. The CMV estimation methods assume rigid cloud bodies with advective motion, which performs reasonably well in mid-latitudes but can be strained for tropical and sub-tropical climatic zones during prolonged periods of seasonal convection. We study the impact of the South Asian monsoon time convection on the accuracy of CMV based forecasts by analysing 2 years of forecasts from three commonly used CMV methods—Block-match, Farnebäck (Optical flow) and TV-L1 (Optical flow). Forecasted cloud index (CI) maps of the entire image section are validated against analysis CI maps for the period 2018–2019 for forecast lead times from 0 to 5.5 h. Site-level GHI forecasts are validated against ground measured data from two Baseline Surface Radiation Network stations—Gurgaon (GUR) and Tiruvallur (TIR), located in hot semi-arid and tropical savanna climatic zones respectively. The inter-seasonal variation of forecast accuracy is prominent and a clear link is found between the increase in convection, represented by a decrease in outgoing longwave radiation (OLR), and the decrease in forecast accuracy. The GUR site shows the highest forecast error in the southwest monsoon period and exhibits a steep rise of forecast error with the increase in convection. The highest forecast error occurs in the northeast monsoon period of December in TIR. The impact of convection on the number of erroneous time blocks of predicted photovoltaic production is also studied. Our results provide insights into the contribution of convection to errors in CMV based forecasts and shows that OLR can be used as a feature in future forecasting methods to consider the impact of convection on forecast accuracy

High resolution hybrid forecast based on the combination of satellite and an all sky imager network forecasts

A method to combine a highly resolved All sky imager (ASI) network forecast with a satellite based forecast was developed. The ASI network forecast input is based on the data from the DLR's Eye2Sky network. This network is installed in NortWest Germany and includes 29 ASIs, 10 Rotating Shadowband Irradiometers (RSIs) and 2 reference meteorological stations (based on thermal irradiometers) in an extent of 100 km2. This forecast was developed by our colleges from DLR-SF (Publication in preparation). It has a forecast horizon of 30 minutes and a step of 1 min with an update of 30 seconds on a domain of 40 km2. The satellite based input forecast is based on our operational satellite forecast at DLR-VE and has a horizon of 6 hours with a step and update of 15 minutes. The satellite domain is reduced to the same 40 km2 area. The method consists on 3 blocks, forecasts homogenization, regression and prediction. In the homogenization block the satellite forecast is interpolated in space and time to the resolutions of the ASI network forecast. We applied linear interpolation for both resolutions as first test case. In the second block, a linear regression is applied to find the optimal weights of the linear combination of the forecast inputs, including a bias term. The regression is based on timeseries extracted from the historical forecasts (features) where the reference are taken from the historical timeseries of ground measurements (samples). Historical data is used in order to indirectly characterize the mean actual local weather conditions on the domain. It is important to note that the regression is performed independently for every lead time. In the third block, we use the optimized weights and biases along with the present (not historical) forecasts to produce the hybrid forecasts. The hybrid forecasts resolutions are the same as the ASI based forecast. The output product can be given as maps or timeseries. For the test case, we are limited from the ASI network side to a dataset of 2 full months of forecasts (July and August 2020). The highly resolved hybrid forecast was validated against the individual input sources and satellite persistence. We found that this newly developed forecast outperforms the RMSE of persistence and the individual input forecasts for all lead times calculated. It shows an improvement on RMSE of 5.07% to 13.97% with respect to satellite forecasts and 7.55% to 15.09% with respect to the ASI network forecast on lead times going from 5 to 30 minutes. It also shows a lower RMSE under high variability conditions

A network of all sky imagers (ASI) enabling accurate and high-resolution very short-term forecasts of solar irradiance

The Eye2Sky network is a measurement network in north-western Germany consisting of multiple all-sky imagers (ASI), meteorological and solar irradiance measurements. The network provides high temporal and spatial resolution data for meteorological and especially solar energy related applications. With increasing photovoltaic (PV) capacity in electrical grids fluctuations in solar irradiance due to changing cloud cover may have adverse effects on the grid stability. Within Eye2Sky, new technologies and methodologies facing the demand for more accurate solar irradiance forecasts are being developed. The ASIs used in Eye2Sky record 180° field of view hemispherical sky images from fish-eye lensed cameras. Accompanied with local measurements of solar irradiance components (global, direct and diffuse) a very short-term forecast of the solar resource is possible. These nowcasts provide minutely updated information up to 20 minutes ahead with 1-minute temporal and 50 m x 50 m spatial resolution. This approach shows more precise forecasting results for the next minutes ahead compared to traditional and less detailed methods based on satellite or numerical weather prediction models. In the network, multiple ASIs are used to enlarge the spatial coverage and the forecast horizon requested by many applications. Moreover, the forecast error can be reduced with a network of cameras. In this article, the Eye2Sky network, its research results and applications are introduced

Forecasting Solar Irradiance by looking at clouds from above and below

The energy meteorology measurement network Eye2Sky is a cloud monitoring system covering roughly 110x100 km in north-west Germany. It is equipped with 38 cloud cameras, solar radiation measurement stations and individual Lidar based cloud altitude measurements distributed throughout the region around Oldenburg. The system collects high-resolution information on solar radiation, tracks the variability at different locations and outputs forecasts for very short time scales. It covers a resolution range of fewer than 100 metres and less than 1 minute and supports forecasts of up to one hour (depending on the prevailing cloud height). A second data source for this region is given by images from the geostationary satellite MSG. With these images longer forecast horizons are achieved in a coarser resolution. The hybrid use of both data sources has only just begun in the community. This allows the development of new models with an improved quality of predictions

Comparison of short-term (hour-ahead) solar irradiance forecasts from all-sky imagers and satellite images

The all sky imagers (ASI) network Eye2Sky has been used for short-term solar irradiance forecasting in the urban area of the city of Oldenburg, in northwest Germany. Eye2Sky is a network of ASI and meteorological measurement instruments operated by DLR. This network is the basis for very short-term, high resolution and accurate predictions of solar irradiance in the upcoming minutes (nowcast). A high density of ASI with low spatial distances between cameras in the urban area allow an almost full coverage of the city (about 10x12 km). On the other hand, ASI-based solar irradiance nowcasts lack long forecast horizons due to their limited field of view (typically 15 minutes for single cameras). With a network of ASIs not only the coverage is increased but also the forecast horizon. Forecasting methods based on satellite images or numerical weather prediction (NWP) models are use as the standard for solar power forecasts. They provide larger spatial coverages and longer forecast horizons compared to ASI forecasts. On the contrary, due to their limited resolution and update rates the accuracy for short-term horizons and single sites is reduced. Here, we demonstrate the value of a network of ASI inside an urban environment for the spatial coverage and forecast horizon. Moreover, we show a comparison of forecast accuracy between the ASI nowcasts and the reference forecasts from satellite and a NWP model. These studies are the basis for a seamless forecasting strategy covering always finer spatial and temporal scales for intra-day applications. The main objective is to provide the highest available accuracy based on the hybridization of multiple data sources. We are looking for an intensive exchange with research and industry on the application of short-term solar forecasting in modern renewable energy driven energy systems, e.g. the use of short-term forecasts in the operation of large PV plants. Any feedback from stakeholders on their needs and requirements will support us to adapt nowcasting strategies to specific applications