Comparison between unipolar and bipolar single phase grid-connected inverters for PV applications

An inverter is essential for the interfacing of photovoltaic panels with the AC network. There are many possible inverter topologies and inverter switching schemes and each one will have its own relative advantages and disadvantages. Efficiency and output current distortion are two important factors governing the choice of inverter system. In this paper, it is argued that current controlled inverters offer significant advantages from the point of view of minimisation of current distortion. Two inverter switching strategies are explored in detail. These are the unipolar current controlled inverter and the bipolar current controlled inverter. With respect to low frequency distortion, previously published works provide theoretical arguments in favour of bipolar switching. On the other hand it has also been argued that the unipolar switched inverter offers reduced switching losses and generates less EMI. On efficiency grounds, it appears that the unipolar switched inverter has an advantage. However, experimental results presented in this paper show that the level of low frequency current distortion in the unipolar switched inverter is such that it can only comply with Australian Standard 4777.2 above a minimum output current. On the other hand it is shown that at the same current levels bipolar switching results in reduced low frequency harmonics

Effect of proofreading on mechanics and structure of writing--grades four, five, six

Thesis (M.A.)--Boston Universit

The development and evaluation of exercises in meaningful word practice in first grade,

Research chapter for this study will be found in Ash, Dorothea: "Development and evaluation of silent reading exercises in grade one" Thesis (M.A.)--Boston Universit

Real-time wavefront reconstruction from intensity measurements

We propose an efficient approximation to the nonlinear phase diversity method for wavefront reconstruction from intensity measurements. The new method, iterative linear phase diversity (ILPD), assumes that the residual phase aberration is small and makes use of a first order Taylor expansion of the point spread function (PSF) performed for an arbitrary (large) diversity in order to optimize the phase retrieval. For static aberrations, ILPD makes use of two images collected at each iteration of the algorithm. In each step, the residual phase aberrations are estimated by solving a linear least squares problem, followed by the use of a deformable mirror to correct for the aberrations. A further contribution of the paper is the extension of the static ILPD to the case of dynamic wavefront reconstruction for which a computationally efficient H2 controller is presented.Delft Center for Systems and ControlMechanical, Maritime and Materials Engineerin

Polymer Nanocomposite Materials Based on Carbon Nanotubes

(Invited Book Chapter

Influence of SiO2, TiO2 and Fe2O3 nanoparticles on the properties of fly ash blended cement mortars

This study explores the effects of different types of nanoparticles, namely nano-SiO2 (NS), nano-TiO2 (NT), and nano-Fe2O3 (NF) on the fresh properties, mechanical properties, and microstructure of cement mortar containing fly ash as a supplementary cementitious material. These nanoparticles existed in powder form and were incorporated into the mortar at the dosages of 1%, 3%, and 5% wt.% of cement. Also, fly ash has been added into in mortars with a constant dosage of 30% wt.% of cement. Compressive and flexural strength tests were performed to evaluate the mechanical properties of the mortar specimens with different nanoparticles at three curing ages, 7, 14, and 28 days. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) tests were conducted to study the microstructure and the hydration products of the mortars. To elucidate the effects of nanoparticles on the binder phase, additional experiments were performed on accompanying cement pastes: nanoindentation and open porosity measurements. The study shows that, if added in appropriate amounts, all nanoparticles investigated can result in significantly improved mechanical properties compared to the reference materials. However, exceeding of the optimal concentration results in clustering of the nanoparticles and reduces the mechanical properties of the composites, which is accompanied with increasing the porosity. This study provides guidelines for further improvement of concretes with blended cements through use of nanoparticles

Implementation of the Walrasian Correspondence by Market Games

In this paper we present a set of axioms guaranteeing that, in exchange economies with or without indivisible goods, the set of Nash, Strong and active Walrasian Equilibria all coincide in the framework of market games.Market Games, Implementation

Choral reading

Thesis (Ed.M.)--Boston Universit

The relationship of the knowledge of letter names and reading achievement in grade one.

Thesis (Ed.M.)--Boston Universit