A robust model-free controller for a three-phase grid-connected photovoltaic system based on ultra-local model

In this paper, a robust model-free controller for a grid-connected photovoltaic (PV) system is designed. The system consists of a PV generator connected to a three-phase grid by a DC/AC converter. The control objectives of the overall system are to extract maximum power from the PV source, to control reactive power exchange and to improve the quality of the current injected into the grid. The model-free control technique is based on the use of an ultra-local model instead of the dynamic model of the overall system. The local model is continuously updated based on a numerical differentiator using only the input–output behavior of the controlled system. The model-free controller consists of a classical feedback controller and a compensator for the effects of internal parameter changes and external disturbances. Simulation results illustrate the efficiency of the controller for grid-connected PV systems.     

Nonlocal PDE morphology: a generalized shock operator on graph

This paper presents an adaptation and extension of the shock filters on weighted graphs using the formalism of partial difference equations. This adaptation leads to new morphological operators that alternate between nonlocal dilation and nonlocal erosion filter type on graphs. Furthermore, this adaptation extends the shock filter applications to any data that can be represented by graphs. This approach is illustrated through image, data defined on region maps, and 3D point cloud processing.     

A sliding mode control and artificial neural network based MPPT for a direct grid‐connected photovoltaic source

A robust sliding mode controller for a grid‐connected photovoltaic source is proposed in this paper. The objective of the presented control scheme is to force both the output voltage of the photovoltaic PV source and the power factor at the inverter output to follow a certain trajectory reference. The main idea is to apply the robust sliding mode controller directly to the nonlinear state model of the system composed of the PV source and the inverter with its input and output filters. In order to operate the PV system at the maximum power point and to satisfy the environmental factors, such as solar irradiance and temperature, we included a rigorous maximum power point tracker based on an artificial neural network. Simulation results are presented to illustrate the performance of the proposed control scheme. In addition, we show that the grid current satisfies the harmonic limits of the IEEE standard for interconnecting distributed energy sources with electric power systems.     

Effects of plasma treatment on greenhouse polyethylene cover aged under sub‐Saharan conditions

The effects of natural ageing, in sub‐Saharan regions, on treated low density polyethylene by cold plasma are presented in this work. The data analysis is performed by comparing the changes of physical, mechanical and structural effects on the material surface induced by plasma treatment with regard to the natural abrasion effect due to sand wind. Plasma treatments for short durations are applied to neutral LDPE (low density polyethylene) films. Few seconds suffice to observe chemical changes on the samples. The treated samples are then subjected to natural ageing in the region of Ouargla (south of Algeria), characterized by very frequent sand wind. The characterization of the effects of plasma treatment and its combination with sand wind is performed using XPS (X‐ray Photoelectron Spectroscopy), FTIR (Fourier Transform Infrared spectrometry), and mechanical tensile testing. The results led to conclude a synthesis of new materials on the surface that significantly change the material surface properties and physico‐chemical properties of material, more particularly, optical, and mechanical properties are thus strongly affected. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Isomérisation du n‐hexane sur des catalyseurs Ni‐WOx/Al2O3‐SiO2

Isomerization of n‐hexane into bi‐ and tri‐branched products was studied at atmospheric pressure on Ni‐WO_x/Al₂O₃‐SiO₂ catalysts. Two groups of catalysts (A and B) were prepared by using the sol‐gel method. The objective of the present study is the selection of the catalyst having the best isomer (bi‐ and tri‐branched) yield under optimum operating conditions (reaction temperature, reduction temperature, flow duration, etc.). The results show that the introduction of tungsten (group B) modifies siginificantly the catalyst activity and that the optimum nickel amount in these catalysts is 15 wt. %. When a steady flow is achieved (100 min), the catalyst containing 15 % nickel and 10 % tungsten exhibits the highest and largest selectivity at a reaction temperature of 250°C and a reduction temperature of 430°C.     

Linear adaptive control of a class of SISO nonaffine nonlinear systems

This paper addresses the problem of linear adaptive control for a class of uncertain continuous-time single-input single-output (SISO) nonaffine nonlinear dynamic systems. Using the implicit function theory, the existence of an ideal controller which can achieve control objectives is firstly demonstrated. However, this ideal controller cannot be known and computed even if the system model is well known. The aim of our work is to construct this unknown ideal controller using a simple linear controller with the free parameters updated online by a stable adaptation mechanism designed to minimise the error between the unknown ideal controller and the used linear controller. Since the mathematical model of the system is assumed unknown in this work, the proposed control scheme can be regarded as a simple model free controller for the studied class of nonaffine systems. We prove that the closed-loop system is stable and all the signals are bounded. An application of the proposed linear adaptive controller for a nonaffine system is illustrated through the simulation results to demonstrate the effectiveness of the proposed control scheme.     

Performance analysis of Vernier slotted doubly salient permanent magnet generator for wind power

This paper presents the impact results of the variation of the rotor and the stator tooth pitches (Vernier effect), on the waveform of the back-electromotive force (EMF) generated by the low speed Doubly Salient Permanent Magnet machine (DSPM). The rotating electrical machines with and without Vernier effect are designed and optimized using genetic algorithms combined with finite element method. The optimization of machines parameters is focused on the maximization of the mass to torque ratio. The results show that the machine with Vernier effect has better performances. The obtained Vernier slotted doubly salient permanent magnet generator is then integrated into an autonomous wind energy conversion system. Simulations tests are carried out through Matlab/Simulink. The results show that the proposed machine is a valid and inexpensive alternative for directly coupled wind turbines.     

Thermal control influence on energy efficiency in domestic refrigerator powered by photovoltaic

This paper studies the importance of temperature control in household refrigerator on the environmental and economic plan. Refrigerator energy consumption is greatly affected by room temperature, door opening and thermostat regulation. A household refrigerator powered by photovoltaic energy was tested in laboratory to determine the effect of thermal regulation on energy consumption. Our investigation reveals that there is a difference in minimal average temperature between the thermostat and the evaporator for three different thermostat positions. This difference in temperature was justified by three parameters: the bad contact between the thermostat bulb and the surface of the evaporator, thermostat thermal inertia and the error due to the mechanical control of the thermostat. Finally, this work allows us an estimate of the energy saving by the kWh electricity price in the Middle East and North Africa region (MENA) Vs Europe region depending on the number of refrigerators. The energy optimization decreases the aggressive methods of electricity production. The Energy Efficiency and Solar Energy present an important alternative on the three planes Energy, Economic and Environmental (3E).     

A neuro-fuzzy-sliding mode controller using nonlinear sliding surface applied to the coupled tanks system

The aim of this paper is to develop a neuro-fuzzy-sliding mode controller （NFSMC） with a nonlinear sliding surface for a coupled tank system. The main purpose is to eliminate the chattering phenomenon and to overcome the problem of the equivalent control computation. A first-order nonlinear sliding surface is presented, on which the developed sliding mode controller （SMC） is based. Mathematical proof for the stability and convergence of the system is presented. In order to reduce the chattering in SMC, a fixed boundary layer around the switch surface is used. Within the boundary layer, where the fuzzy logic control is applied, the chattering phenomenon, which is inherent in a sliding mode control, is avoided by smoothing the switch signal. Outside the boundary, the sliding mode control is applied to drive the system states into the boundary layer. Moreover, to compute the equivalent controller, a feed-forward neural network （NN） is used. The weights of the net are updated such that the corrective control term of the NFSMC goes to zero. Then, this NN also alleviates the chattering phenomenon because a big gain in the corrective control term produces a more serious chattering than a small gain. Experimental studies carried out on a coupled tank system indicate that the proposed approach is good for control applications.