A New Control Strategy for Photovoltaic System Connected to the Grid via Three-Time-Scale Singular Perturbation Technique with Performance Analysis

This chapter addresses the problem of controlling single-phase grid-connected photovoltaic system through a full bridge inverter with L-filter. The control objectives are threefold: (i) forcing the voltage in the output of photovoltaic panel to track a reference. This reference has been obtained from the maximum power point tracking strategy; (ii) guaranteeing a tight regulation of the DC-link voltage; and (iii) ensuring a satisfactory power factor correction (PFC) at the grid such as the currents injected must be sinusoidal with the same frequency and the same phase as the grid voltage. The considered control problem entails several difficulties including: (i) the high dimension and strong nonlinearity of the system; (ii) the changes in atmospheric conditions. The problem is dealt with by designing a synthesized nonlinear multi-loop controller using singular perturbation technique, in which a three-time-scale dynamics is artificially induced in the closed-loop system. A formal analysis based on the three-time-scale singular perturbation technique and the averaging theory is developed to proved that all control objectives are asymptotically achieved up to small harmonic errors (ripples). The performance of the proposed approach and its strong robustness with respect to climate changes are evaluated based on the various simulations results carried out under Matlab/Simulink software

Isolation and X-ray crystal structure of tetrahydroisoquinoline alkaloids from Calycotome villosa Subsp. intermedias

Two tetrahydroisoquinoline alkaloids were extracted from the alkaloid fraction of a methanol extract of the seeds of Calycotome Villosa Subsp. intermedia. Their structures were established as (R)-1-hydroxymethyl-7-8-dimethoxy-1,2,3,4-tetrahydro- isoquinoline (1) and (S)-7-hydroxymethyl-2-3-dimethoxy-7,8,9,10-tetrahydroisoquinoline chloride (2) by spectroscopic techniques and X-ray diffraction analysis

Main individual factors influencing the learning approaches: The first-year students’ perspective

Currently, the quality of student learning i.e. in-depth learning is essential in any planned reform. The massification phenomenon is one of the challenges facing this quality. This study explored the student characteristics influencing the learning process in an open access faculty, namely, the Dhar El Mahraz Faculty of Science in Fez, Morocco. Semi-structured interviews were conducted on 15 freshmen who enrolled in Earth and Universe Sciences and Life Sciences (EUS/LIS) program and presented a dominance of a surface learning approach. The main factors encouraging surface learning emerged were the learning habits and strategies, language competencies, motivational aspects and gender. The findings serve as an input for the design and implementation of actions to enhance deep learning

Diammonium tris­[hexa­aqua­magnesium(II)] tetra­kis­[hydrogenphosphate(III)], (NH4)2[Mg(H2O)6]3(HPO3)4

The framework of the title compound is made up of discrete Mg(H2O)6 octa¬hedra, and HPO3 and NH4 tetra¬hedra, which are organized in planes parallel to (010). Strong hydrogen bonding between the building units stabilizes the structure. The hydrogenphosphate(III) tetra¬hedra, the ammonium tetra¬hedron and one of the two Mg atoms lie on positions with m symmetry, whereas the second Mg atom is located on a position with 2/m symmetry

Crystal structure of NaCd(H2PO3)3·H2O and spectroscopic study of NaM(H2PO3)3·H2O, M= Mn, Co, Ni, Zn, Mg and Cd

NaCd(H2PO3)3·H2O was synthesized in solution and its structure was studied by single-crystal X-ray diffraction. It crystallizes in the orthorhombic system (Pbca, Z = 8) with the cell parameters: a = 9.2895(14) Å, b = 15.124(2) Å, c = 15.0592(12) Å. Final residual factors R/Rw are 0.0297/0.0790. Both Na+ and Cd2+ are octahedrally coordinated, [NaO6] and [CdO6] share edges to form zigzag chains along [1 0 0]. The 3D framework is build upon these chains which are interconnected by H2PO3 pseudo-pyramids and an intricate network of weak hydrogen bonds. NaCd(H2PO3)3·H2O belongs the series of isostructural phosphites NaM(H2PO3)3·H2O (M = Mn, Co, Ni, Zn and Mg). IR spectroscopic studies show the bands confirming the presence of the phosphite H2PO32− anion in the whole series NaM(H2PO3)3·H2O, M = Mn, Co, Ni, Zn, Mg and Cd. The UV–Vis spectroscopy was used for characterizing the d–d transitions in the Mn, Co and Ni phosphites.The financial support from Centre National de Recherche Scientifique et Technique (CNRST) (Morocco) (URAC 19). The institutional research plan No. AVOZ10100521 of the Institute of Physics and the grant “Praemium Academiae” of the Academy of Sciences of the Czech Republic

Dilead(II) hydrogen­phosphite dinitrate

In the title compound, Pb2(HPO3)(NO3)2, the two distinct Pb2+ ions (both with site symmetry m) adopt irregular PbO10 coordination polyhedra. The structure is completed by two distinct nitrate groups (in which one O atom and the N atom have m site symmetry for both ions) and an HPO3 2− anion (in which one O atom and the P and H atoms have m site symmetry). The connectivity of the PbO10, NO3 and HPO3 units in the crystal structure results in a three-dimensional network

Ortho­rhom­bic polymorph of (6,7-dimeth­oxy-1,2,3,4-tetra­hydro­isoquinolin-1-yl)methanol

The asymmetric unit of the title compound, C12H17NO3, contains two mol­ecules with different conformations. It is a polymorph of the monoclinic form [El Antri et al. (2004 ▶). Mol­ecules, 9, 650–657]; the samples were crystallized at different temperatures from the same solvent. In both structures, mol­ecules are linked by O—H⋯N hydrogen bonds, forming chains. The conformations of the chains and their packing differ markedly in the two polymorphs

Dicaesium magnesium bis­(dihydrogen phosphate(V)) dihydrate

The title compound, Cs2Mg(H2P2O7)2·2H2O, is isostructural with the related known isoformular phosphates. The crystal framework consists of corner-sharing MgO6 and H2P2O7 polyhedra, leading to tunnels parallel to the b-axis direction in which Cs+ ions are located. The H2P2O7 unit shows a bent eclipsed conformation. The Mg2+ ion lies on an inversion center. The water molecules form hydrogen bonds to O atoms of two different dihydrogenphosphate ions, which are further hydrogen bonded to symmetry-equivalent dihydrogenphosphate ions