Demands in the area of electrical energy generation and distribution, as a result of energy policies, are leading to far reaching changes in the structure of the energy supply, which is characterised, on the one hand, by the substitution of conventional power stations by renewable energy generation, a decision which has already been made, and, on the other hand, by the changeover from centralised to decentralised energy generation. From an electrical engineering point of view, a new situation will arise for consumers concerning security of supply and power quality, which calls for further technical measures by the grid operators to ensure that the increasingly stringent supply criteria can be met. This article describes a new power electronics based approach which allows a grid compatible integration of predominantly renewable electricity generators even in weak grids making them appear to be electromechanical synchronous machines. As a consequence, all the proven properties of this type of machine which have so far defined the grid continue to do so, even when integrating photovoltaic or wind energy. These properties include, for instance, interaction between grid and generator as in a remote power dispatch, reaction to transients as well as the full electrical effects of a rotating mass. In addition, this new development can be operated in such a way that it provides primary reserve allowing, from a grid point of view, electricity generators such as wind and PV to be regarded as conventional power stations.
Local relief models (LRM) are proposed as a new tool for archaeological prospection. A data processing approach is presented which produces LRM from LiDAR-derived high-resolution digital elevation models (DEMs). The LRM represents local, small-scale elevation differences after removing the large-scale landscape forms from the data. The LRM greatly enhances the visibility of small-scale, shallow topographic features irrespective of the illumination angle and allows their relative elevations as well as their volumes to be measured directly. This makes the LRM an improved basis for spatially extensive archaeological prospection over a wide range of landscapes. The LRM raster map of local positive and negative relief variations can be used for the mapping and prospection of archaeological featuressuchasburialmounds, linearand circularearthworks, sunkenroads, agriculturalterraces, ridgeandfurrow fields, kiln podia and mining/quarrying sites.This approach is currently being used in a project aimed at the complete archaeologicalmappingandprospection ofthe state Baden-Wˇrttemberg (Germany), coveringan area of 35 751km 2 .The goal oftheprojectistheverificationandextensionofthe existingarchaeologicaldata base.Anobject-basedlocalrelief vector layer is produced as a by-product; however, due to the common amalgamation of natural and anthropogenic features this cannot be used efficiently for archaeological prospection at present.
Virtual Synchronous Machine also called VISMA [1] is a control algorithm to make an inverter operated as a conventional electromechanical synchronous machine. It is a promising solution to overcome the problems of the grid stability and quality, which have been exacerbated by increasing integration of distributed generation units into the grid. Compared to the conventional power plants, in which the synchronous machine dominate, the distributed generation units have either significantly smaller or no rotating mass and damping effect. These weaknesses can be compensated by using the VISMA concept and thus the power system quality will be improved. Furthermore, the penetration level of the DG sources won't be restricted any more.Up to now the VISMA was implemented by using a voltage-tocurrent model on a hysteresis controlled inverter [1][2] [3]. This method will be called VISMA-Method 1 here. Since the most products of inverters in the market are PWM controlled, the VISMA-Method 1 cannot be easily applied on these inverters. Therefore, a new method is developed to implement the VISMA by using a current-to-voltage model on the currently widely applied PWM controlled inverter. This new method is called VISMA-Method 2 in this paper and will be compared with the VISMA-Method 1 by simulation results.
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