A fuzzy expert system for loss reduction and voltage control in radial distribution systems

In this paper, two methods for improving voltage profile and minimizing total system losses in radial distribution feeders are presented. The first method concerns with the capacitor allocation problem. Fuzzy expert system (FES) is used to select the best candidate nodes for capacitors to be installed in order to maximize total loss reduction and total net savings. The second method illustrated the voltage regulator problem. In this method, the location and the tapping ratio of the voltage regulators are determined in order to minimize total system losses while keeping the voltage within specified limits. The two methods have been applied to two test feeders. Comparison with other techniques is included to ensure methods validity and superiority.     

An accurate fault location scheme for connected aged cable lines in double-fed systems

This paper presents an adaptive fault location scheme for aged power cables using synchronized phasor measurements from both ends of the cable. The proposed fault location scheme is derived using the two-terminal synchronized measurements incorporated with distributed line model, modal transformation theory and Discrete Fourier Transform. The proposed scheme has the ability to solve the problem of cable changing parameters, especially the change of the relative permittivity over its age and thus for the operating positive, negative, and zero-sequence capacitance changes. Extensive simulation studies are carried out using Alternative Transients Program ATP/EMTP. The simulation studies show that the proposed scheme provides a high accuracy in fault location calculations under various system and fault conditions. The results show that the proposed scheme responds very well to any fault insensitive to fault type, fault resistance, fault inception angle and system configuration. The proposed scheme solves the problem of aged cables with the change of the electric parameters. In addition to, it gives an accurate estimation of the fault resistance.     

Thermo-mechanical finite element model of friction stir welding of dissimilar alloys

A thermo-mechanical finite element model is developed based on Coupled Eulerian Lagrangian method to simulate the friction stir welding of dissimilar Al6061-T6 and Al5083-O aluminum alloys using different tool pin profiles. The model is validated using published measured temperatures and weld microstructure. The finite element results show that maximum temperatures at the weld joint were below the materials’ melting point. Placing the harder alloy (Al6061-T6) at advancing side led to a decrease in maximum process temperature and strain rate, but increased tool reaction loads. Featured tool pin produced better material mixing resulting in enhanced joint quality with reduced volumetric defects.     

Decomposing global solar radiation into its diffuse and direct normal radiation

ABSTRACT

This work presents a model based on Radial Basis Function (RBF) to estimate the diffused solar radiation (DSR) and direct normal radiation (DNR) fractions of solar radiation from global solar radiation in a semiarid area in Algeria based on a database measured between 2013 and 2015. The data has been collected at Applied Research Unit for Renewable Energies, (URAER) at Ghardaia city situated in the south of Algeria. The experimental results show that RBF model estimates DNR and DSR with high performance. The difference between the measured and the predicted values show a normalised Root Mean Square Error (nRMSE) of 0.033 and 0.065 for DNR and DSR, respectively. The obtained values of Determination Coefficient (R²) and Correlation Coefficient (R) are: 97.3%, 98.60%, respectively for DNR and 88.89%, 91.12% For DSR.

However, the obtained results are very plausible and showed that RBF model estimates the DSR and DNR with good accuracy.     

Study of the effect of finned tube adsorber on the performance of solar driven adsorption cooling machine using activated carbon–ammonia pair

Solar refrigeration represents an important application of solar energy due to the excellent matching between the high sunshine and the refrigeration needs. Solar adsorption refrigeration devices are among the significant techniques used to meet the needs for cooling requirements. Several solar refrigeration systems have been proposed and are under development such as sorption systems including liquid/vapor, solid/vapor absorption, adsorption, vapor compression and others. The purpose of this paper is to identify the influence of a cylindrical adsorber on the performances of a solar adsorption refrigerating machine. The adsorber heated by solar energy contains an activated carbon–ammonia pair; it is composed by many cylindrical tubes welded using external fins. A model based on the conservation equations of energy and mass in the adsorber has been developed and well described. Using real solar irradiance data as well as many initial conditions, the model computes for each point and in the considered time interval during the day, the temperature, the adsorbed mass, the pressure inside the adsorber and the solar performance coefficient (COP). The results show that the optimal diameter of the adsorber with fins is greater than the one without fins. Moreover the mass cycled in the case of an adsorber equipped with external fins is more significant than the one without fins, and the maximal temperature reached in the adsorber with fins attains 97 °C while in the adsorber without fins reaches 77 °C. Thus, the performances of the solar adsorption refrigerating machine with an adsorber equipped with fins are higher than the machine without fins.     

Stability analysis of delayed fuzzy Cohen-Grossberg neural networks with discontinuous activations

In this article, we investigate the dynamical behavior of a class of delayed fuzzy Cohen-Grossberg neural networks (FCGNNs) with discontinuous activation functions subject to time delays and fuzzy terms. By using the inequality analysis technique and the M-matrix theory, sufficient and proper conditions are given in order to establish the existence, convergence, and global exponential stability of equilibrium point of the system. In particular, we discuss the impact of discontinuous neuron activations on the existence and exponential stability of equilibrium point for FCGNNs. Two numerical examples are provided to substantiate the theoretical results.     

A New Strategy for Selection of Switching Instant to Reduce Transformer Inrush Current in a Single-phase Grid-connected Photovoltaic System

Photovoltaic energy integration with the power system is increasing with the lack of fossil resources and developments in photovoltaic technology. Magnetizing inrush current occurs due to switching the transformer into service. Inrush current leads to shortage in the transformer lifetime and/or the operation of protection devices disconnecting the transformer. This article studies the impact of existing photovoltaic energy on the reduction of transformer inrush current. Photovoltaic power is utilized to reduce the inrush current by applying an opposite flux on the transformer, then connecting the transformer with the power network at a suitable switching instant of grid voltage waveform. The switching instant depends upon the flux produced in the transformer primary winding by the photovoltaic system. This article introduces a new strategy to determine the switching instant for reducing the transformer inrush current. The proposed method depends upon the monitoring of total harmonic distortion at different switching instants. The proposed method is appropriate for real-time applications. The proposed procedure is applied to a single-phase example and simulated in MATLABR2013a/SIMULINK (MathWorks, Natick, Massachusetts, USA). The simulation results show the suitable instant of switching to reduce the magnetizing inrush current and the corresponding total harmonic distortion.