Hardware Implementation of 3-level Inverter using Microcontroller for Single Phase Induction Motor

<p>The conventional two level inverter has many limitations for high voltage &amp; high power applications. The term multilevel began with the three-level inverter. Subsequently, several multilevel inverter topologies have been developed. However, the elementary concept of a multilevel inverter to achieve higher power is to use a series of power semiconductor switches with several lower voltage dc sources to perform the power conversion by synthesizing a staircase voltage waveform. Output voltage of 3 level inverter consists of 3 levels, which results smoother output. And hence the THD will be reduced. In this paper Simulink of 3 level inverter and the hardware implementation of micro controller based control of multilevel inverter for single phase Induction motor are presented.</p>

Effects of Implementing Adaptable Channelization in Wi-Fi Networks

The unprecedented increase of wireless devices is now facing a serious threat of spectrum scarcity. The situation becomes even worse due to inefficient frequency distribution protocols, deployed in trivial Wi-Fi networks. The primary source of this inefficiency is static channelization used in wireless networks. In this work, we investigate the use of dynamic and flexible channelization, for optimal spectrum utilization in Wi-Fi networks. We propose optimal spectrum sharing algorithm (OSSA) and analyze its effect on exhaustive list of essential network performance measuring parameters. The elementary concept of the proposed algorithm lies in the fact that frequency spectrum should be assigned to any access point (AP) based on its current requirement. The OSSA algorithm assigns channels with high granularity, thus maximizing spectrum utilization by more than 20% as compared to static width channel allocation. This optimum spectrum utilization, in turn, increases throughput by almost 30% in many deployment scenarios. The achieved results depict considerable decrease in interference, while simultaneously increasing range. Similarly signal strength values at relatively longer distances improve significantly at narrower channel widths while simultaneously decreasing bit error rates. We found that almost 25% reduction in interference is possible in certain scenarios through proposed algorithm.

Eurocodes for bridge design versus mechanics

Regulations on which designers base their process of designing of any engineer structures should include and combine mechanics, loads and dimensioning. It is not always the case as far as eurocodes are concerned. Ambiguities appear everywhere, which sometimes leads to incorrect understanding of a norm. The authors meticulously analysed basic mechanical terms. Their digressions began with the concepts of strain and deformation that have discrepant definitions in sources from other countries. The next part of article discusses the concept of „shear lag”. It is treated as an elementary concept in the eurocodes, although is has not been defined yet. Other sources define it as cooperating width and shear strain in the beam flanges or as stretching. Polish translation mentions the effect of „wide stripes”. The authors focused also on dynamics – especially while discussing first natural frequencies denoted as “n0”. They scrutinised the norm EN 1991-2 in which dynamic problems of bridges are understood as effects of service load when the environmental impact is not included. As always, in a situation when there is a doubt, it is possible apply the to accurate mechanics rules. To sum up, Polish versions of bridge eurocodes should be corrected to be unambiguous and useful in a design.

Microcontroller Based Less Switches Topology and Digital Gating Technique for Single-Phase Five-Level Inverter

The multilevel inverter is the idea of connecting such distributed DC energy sources (solar and fuel cells in addition to rectified output of wind turbines) to a power grid. Multilevel pulse width modulation (PWM) inverters have gained importance in high performance power applications without requiring high ratings on individual devices. The elementary concept of a multilevel converter to achieve higher power is to use a series of power semiconductor switches with several lower voltage DC sources to perform the power conversion by synthesizing a staircase voltage waveform. In the present paper we introduce a power circuit for single-phase five-level inverter which contains a very lower number of switches and the technique for the generation of required signals to control the operation of the inverter switches. The presented technique is implemented via microcontroller ATmega16. The simulation and practical results are presented.

ON THE BURNSIDE SEMIGROUPS xn = xn+m

In this paper we prove that the congruence classes of A* associated to the Burnside semigroup with |A| generators defined by the equation xn=xn+m, for n≥4 and m≥1, are recognizable. This problem was originally formulated by Brzozowski in 1969 for m=1 and n≥2. De Luca and Varricchio solved the problem for n≥5 in 90. A little later, McCammond extended the problem for m≥1 and solved it independently in the cases n≥6 and m≥1. Our work, which is based on the techniques developed by de Luca and Varricchio, extends both these results. We effectively construct a minimal generator Σ of our congruence. We introduce an elementary concept, namely the stability of productions, which allows to eliminate all hypothesis related to the values of n and m. A substantial part of our proof consists of showing that all productions in Σ are stable, for n≥4 and m≥1. We also show that Σ is a Church-Rosser rewriting system, thus solving the word problem, and show that the semigroup is finite [Formula: see text]-above. We prove that the frame of the ℛ-classes of the semigroup is a tree. We characterize and calculate the ℛ-classes, ℋ-classes and the [Formula: see text]-classes of the semigroup, regular or not, and prove that its maximal subgroups are cyclic of order m whenever all productions of Σ are stable. Recently Guba extended the cases in which the conjecture holds to n≥3 and m≥1. Using his work we obtain the stability of the productions of Σ for n=3 and m≥1 too and, hence, all properties about the semigroup structure hold in this case.

Facetten der Macht

Social power has many facets. This paper aims to illuminate some of these. First of all, it considers the general conceptual framework in which the concept of power is embedded. The author then elaborates on an analysis of the elementary concept of social power resulting in a proposal how to define power. Furthermore, the article deals with complex networks of power relations, namely constellations and structures of power. Another section focuses on some special aspects of the dynamics of power structures. Finally, the author discusses the problem of legitimation of power.