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Mecke R.,Hochschule Harz University of Applied Sciences
2013 15th European Conference on Power Electronics and Applications, EPE 2013

The paper presents the energy saving potential of induction machines by using variable rotor flux instead of commonly used constant flux. The efficiency optimized rotor flux depends on the actual load and speed of the motor. At low load it has to be decreased with reference to a pre-calculated lookup table. This table can be included in a field oriented speed control structure as reference value of the rotor flux. The calculation of optimal rotor flux curves includes the non-linear main inductance, the frequency-dependent rotor resistance and rotor leakage inductance, the speed-dependent iron, friction and windage losses and the motor frequency. This distinguishes this paper from former scientific works. The calculations and measurements are carried out at an 11 kW high-efficiency (efficiency classification IE2) asynchronous machine with 2 pole pairs. An increase in efficiency can be reached below 2/3 of rated torque. The maximum increase is about 35 % in motor and 45 % in generator operation mode. The average efficiency improvement is 4,5 % in motor and 6,0 % in generator mode. Additionally, the power factor can be improved over the whole load range and the current consumption can be reduced. Energy saving with variable rotor flux is possible in the whole speed range from 10 to 100 Hz. © 2013 IEEE. Source

Stolzenburg F.,Hochschule Harz University of Applied Sciences
Spatial Cognition and Computation

Three of the major problems in building autonomous mobile robots are localization, exploration, and navigation. This paper investigates how well different qualitative methods based on angle information, most of them originally invented for representation of spatial knowledge, are suited for addressing these problems. It combines results from discrete and computational geometry with methods from qualitative spatial reasoning, gaining some new insights on the complexity of robot navigation. It turns out that essentially only with panoramas (special roundviews) the qualitative localization problem can be solved in a satisfactory manner. The exploration problem (qualitative map building), remains difficult for all considered approaches. © Taylor & Francis Group, LLC. Source

Krauser J.,Hochschule Harz University of Applied Sciences | Nix A.-K.,University of Gottingen | Gehrke H.-G.,University of Gottingen | Hofsass H.,University of Gottingen | And 2 more authors.
New Journal of Physics

Electrically conducting ion tracks are produced when high-energy heavy ions pass through a layer of tetrahedral amorphous carbon (ta-C). The tracks are embedded in the insulating ta-C matrix and have a diameter of about 8 nm. Earlier studies showed that the electrical currents through individual tracks produced with Au and U projectiles exhibit rather large track-to-track fluctuations. In striking contrast, 30 MeV C60 cluster ions are shown to generate conducting tracks of very narrow conductivity distributions. Their current-versus-voltage curves are linear at room temperature. We also investigated ta-C films doped with B, N, Cu and Fe at a concentration of 1 or 2 at.%. In particular, Cu- and Fe-doped samples show increased ion track conductivity. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Source

Mecke R.,Hochschule Harz University of Applied Sciences
2015 17th European Conference on Power Electronics and Applications, EPE-ECCE Europe 2015

Multilevel inverter topologies are an alternative for a wide range of low voltage electrical drives. They can reduce power semiconductor losses, voltage transients at the motor windings, harmonic losses in the cables and common mode disturbance currents. In the voltage range below 1000 V highly optimized switches with lower losses are available. The paper compares the component losses (power semiconductor losses in the frequency inverter, losses of the output filter, harmonic cable and motor losses) and the efficiency of a drive system with two-level and different multilevel NPC inverters. Higher inverter levels reduce the power losses of the inverter and the output filter. For a 22 kW induction motor a losses reduction of 800 W is simulated, if a five-level inverter is used. A five-level inverter requires power semiconductor devices with 300 V blocking voltage. New wide-bandgap semiconductors (SiC, GaN) with low blocking voltage have the potential to reduce the conduction and switching losses in multilevel inverters. This would lead to a reduction of cooling effort and to smaller inverter size. Moreover, the sine filter at the inverter output can be chosen smaller which is accompanied by lower power losses inside the filter. The application of multilevel inverters also in the so called low voltage range can make a contribution to efficiency improvement in electrical drives. © 2015 EPE Association and IEEE. Source

Spangenberg T.,Hochschule Harz University of Applied Sciences
Information Technology and Tourism

GPS tracking is a common empirical research method to gain information about human mobility behavior. Based on the recorded GPS trajectories it is possible to analyze and explain motion spatially, and temporally. More comprehensive explanations of specific movement patterns require the coupling with other survey techniques such as trip diaries, interviews, and questionnaires, which are widespread data acquisition methods in tourism research. However, GPS-based surveys require a high effort in the preparation and post-processing of the data, and expertise in both, information technologies and tourism research. In order to prepare the data for the analysis in geographic information systems a number of steps with different tools is necessary. In this paper the GimToP Toolkit (GTK) is presented that integrates the methodological approach and the technology in an easy-to-handle manner. The GTK combines trajectory data with digital questionnaires based on a mobile application that is used for the data collection and preprocessing tasks. Connected to a server, which offers a service-oriented architecture, the GTK has the ability to process the survey data and to provide interoperability for the analysis in other applications. This paper presents the components of the GTK and shows its usage during two field studies, which are carried out in the city of Wernigerode and the Harz National Park in Germany. The results offer new insights in the movement behavior of the tourists and can be used to support a more sustainable development of the destinations. © 2014, Springer-Verlag Berlin Heidelberg. Source

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