This paper briefly describes direct power control methods for two- and threelevel AC/DC converters and their modified DPC 3H 2-? and the DPC 5H2-? algorithms. It also presents two new control methods DPC-3Am (direct power control 3 areas with modification) and the DPC-3L-3Am (direct power control 3 levels 3 areas with modification). The research results were used to compare the described methods. The comparison was based on an average value of switching frequency and current distortion coefficient. Experimental investigations into the methods have shown that the use of the modified DPC methods reduces the number of switchings by more than 70% compared with the standard DPC method.
In this paper a system of a grid side and a generator side converters, both working with a common capacitor, is presented. The 6-phase asymmetric inset-type SMPMSM generator is used. A large pole pair number of this generator enables a gearless wind turbine operation. The fundamental and 3rd harmonic cooperation is used to increase the generator performance. This is accomplished by means of the 3rd harmonic current injection. For that reason the generator side converter must have a neutral connection.
The paper presents an induction generator connected to the power grid using the AC/DC/AC converter and LCL coupling filter. In the converter, both from the generator and the power grid side, three-level inverters were used. The algorithm realizing pulse width modulation (PWM) in inverters has been simplified to the maximum. Control of the induction generator was based on the indirect field oriented control (IFOC) method. At the same time, voltage control has been used for this solution. The MPPT algorithm has been extended to the variable pitch range of the wind turbine blades. The active voltage balancing circuit has been used in the inverter DC voltage circuit. Synchronization of control from the power grid side is ensured by the use of a PLL loop with the system of preliminary suppression of undesired harmonics (CDSC).
Natalia Marek-Trzonkowska and Piotr Trzonkowski of the Medical University of Gdańsk talk about trust, coordination, and creative conflicts – in the first of a series of interviews with scientists who are partners both at work and in life.
Applications in geodesy and engineering surveying require the determination of the heights of the vertical control points in the national and local networks using different techniques. These techniques can be classified as geometric, trigonometric, barometric and Global Positioning System (GPS) levelling. The aim of this study is to analyse height differences obtained from these three techniques using precise digital level and digital level, total station (trigonometric levelling) and GPS which collects phase and code observations (GPS levelling). The accuracies of these methods are analysed. The results obtained show that the precise digital levelling is more stable and reliable than the other two methods. The results of the three levelling methods agree with each other within a few millimetres. The different levelling methods are compared. Geometric levelling is usually accepted as being more accurate than the other methods. The discrepancy between geometric levelling and short range trigonometric levelling is at the level of 8 millimetres. The accuracy of the short range trigonometric levelling is due the reciprocal and simultaneous observations of the zenith angles and slope distances over relative short distances of 250 m. The difference between the ellipsoidal height differences obtained from the GPS levelling used without geoid and the orthometric height differences obtained from precise geometric levelling is 4 millimetres. The geoid model which is obtained from a fifth order polynomial fit of the project area is good enough in this study. The discrepancy between the precise geometric and GPS levelling (with geoid corrections) is 4 millimetres over 5 km.
When conducting geodetic and gravimetric measurements, there is a problem of projecting them to the reference surface. Since the gravitational field is inhomogeneous under the real conditions, the problem arises of determining the corrections to the measured values of gravitational acceleration in order to use the obtained data for the subsequent solutions of projection problems. Currently, the solution to this problem is performed using a Bouguer reduction, which requires information about the internal structure of the upper layer of the earth’s surface, topography, etc. The purpose of this study is to develop a methodological approach that would allow to determine the reduction (projection) corrections for gravitational acceleration on technogenic and geodynamic polygons without using data about the distribution of surface layer density and topography. The research process is based on the use of mathematical analysis methods and a wide range of experimental geodetic and gravimetric measurements. In the course of the performed researches, an algorithm was obtained and a practical implementation of the determination of the corrections in the measured values of gravitational acceleration on the basis of geodetic and gravimetric measurements was carried out at the certain geodynamic polygon in order to bring all corrections to one level surface.
Drawing on in-depth interviews with Romanian workers posted in the German construction and meat-pro-cessing industries, with representatives of German unions and with migrant advisers, and on ethno-graphic work, this study examines precarity in posted employment. Firstly, the paper describes the precarious circumstances of Romanians posted in the construction and meat-industry sectors in Ger-many. Secondly, analysing the Romanians’ own perspectives, it shows that low wages in the country of origin, often associated with insecurity and poor working conditions, drive these workers to engage in posted work. Their lack of knowledge of the German language prevents them from finding and carrying out standard jobs in Germany and, thus, determines that they remain in posted employment. Finally, the paper argues that posted workers experience different layers of precarity in the country of destination. It shows that those under contract with various companies for short periods of time are more precarious than de facto posted workers and workers with long-term informal agreements with one single employer.
One of the fundamental problems in evolutionary sciences is the direction of evolution at different levels of matter organization. According to traditional teleological interpretations, the evolving systems should develop toward a final state—a goal. However, in most cases such a goal is not determinable—scientists do not know it. However, they can reveal a general tendency or a series of changes in time: a teleonomy or a directness based mainly upon an internal pattern of the evolving system although modified also by external influences. Teleonomical processes are responsible for all evolutionary processes including transitions from one level of organization to another.
The article aims at demonstrating that authority is a complex and multifaceted phenomenon. An overview of numerous definitions and theories of authority serves as a point of departure that leads to the reconstruction of the typologies of authority existing in social sciences and to qualifying the functions of authority. The place of the phenomenon in social life is revealed by the analysis of its key operation mechanisms and impact areas. Theoretical definitions and typologies form the background for concentrating on authority in local communities, since its social role (e.g. inspirational, regulatory and integrative) at this level is exceptionally important from the perspective of social order maintenance and local communities’ development.
In this study, several variants create and choose of a local quasi-geoid model in Poland have been considered. All propositions have a source in European Gravimetric Geoid models – EGG2008 and EGG2015, which are purely gravimetric models of reference surface. In the course of this work, each model has been analyzed in various ways: without any corrections, by parallel shifting of residuals, by the 7-parameter conformal transformation and by fitting residuals by 4- and 5-parameter trigonometric polynomials. Eventual corrections were based on points of national GNSS/levelling networks (EUVN, EUVN_DA, POLREF, EUREF and ASG-EUPOS eccentric points). As a final result of this study, a comparison of the accuracy of selected models has been carried out by RMSE statistics and maps showing spatial distribution of residuals and histograms. Validation has shown that the maximum achievable accuracy of the EGG models is approximately 2 cm for the ETRF2000 reference system and approximately 8 cm for ETRF89. In turn, fitting with the use of different mathematical methods results in an improvement of the standard deviation of residues to the level of 1.3–1.4 cm. The conclusions include an evaluation of considerations for and against the use of models based only on EGG realizations and, on the other hand, fitted to the points of Polish vertical network. Its usefulness is strictly connected with needs of the definition of up to date quasi-geoid model for the new realization of heights system in Poland, based on EVRF2007 frame.
The paper analyzes the monthly day equivalent levels, Lday (06–22 h) and night equivalent levels, Lnight (22–06 h) values observed in year 2015 and 2016 for the 70 locations whereby continuous noise monitoring is conducted under the National Ambient Noise Monitoring Network (NANMN). The study exclusively analyzes the ambient noise data acquired for 25 locations in commercial zone, 12 in industrial, 16 in residential and 17 in silence zones. The analysis of (Lday–Lnight) for 70 locations under observations reveals that 10 dB night time adjustment in day-night average sound level descriptor is not appropriate in such a scenario and as such it is recommended to use day-night average sound level and day-eveningnight average sound level descriptors without any 10 dB night time adjustment or 5 dB evening time adjustments. The analysis and conclusions of the present study shall be very useful for developing single value noise descriptor correlating the noise annoyance and health effects in Indian perspectives.
Noise is one of the most significant factors which not only disturbs working conditions, but has a large impact on workers’ health. This problem has existed in industries since the beginning and, despite technical and other solutions, it has not been solved. There is a large number of papers, supported with very detailed analyses, that investigate noise levels in industry or contain questionnaires about the impact of noise on workers’ overall health and work abilities. The purpose of this paper is to contribute to the global picture of sustainability and the development of strategies for improving the quality of working environment, with special attention to the generation of noise in different production processes in thirteen different industries in Novi Sad, Serbia. The paper also seeks to examine the advantages and drawbacks of the implemented protective methods and to provide some recommendations for their better implementation in order to contribute to solving this significant problem of today.