Predictive control for voltage collapse avoidance using a modified discrete multi-valued PSO algorithm

Voltage stability is one of the most challenging concerns that power utilities are confronted with, and this paper proposes a voltage control scheme based on Model Predictive Control (MPC) to overcome this kind of instability. Voltage instability has a close relation with the adequacy of reactive power and the response of Under Load Tap Changers (ULTCs) to the voltage drop after the occurrence of a contingency. Therefore, the proposed method utilizes reactive power injection and tap changing to avoid voltage collapse. Considering discrete nature of the changes in the tap ratio and also in the reactive power injected by capacitor banks, the search area for the optimizer of MPC will be an integer area; consequently, a modified discrete multi-valued Particle Swarm Optimization (PSO) is considered to perform this optimization. Simulation results of applying the proposed control scheme to a 4-bus system confirm its capability to prevent voltage collapse.     

Systematic Modeling for Free Stators of Rotary Piezoelectric Ultrasonic Motors

This paper presents an equivalent circuit model with complex numbers that describes the free stator model of traveling-wave ultrasonic motors. The mechanical, dielectric, and piezoelectric losses associated with the vibrator are considered by introducing the imaginary part to the equivalent circuit elements. The determination of the complex circuit elements is performed by using a new, simple iterative method. The presented method uses information about five points of the stator admittance measurements. The accuracy of the model in fitting to the experimental data is verified by using the measurements of a recently developed piezoelectric motor and a well-known USR60     

Cu(acac)<Subscript>2</Subscript>–PVA composite nanofibers in catalysis of Michael addition of carbon nucleophiles to α,β-unsaturated carbonyl compounds

Copper (II) acetylacetonate containing nanofibers of polyvinyl alcohol (Cu(acac)₂–PVA) were prepared by electrospinning and characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, Fourier transform infrared spectroscopy, inductively coupled plasma (ICP) and diffuse reflectance spectroscopy. The obtained nanofibers were almost uniform and uniaxially aligned with their longitudinal axes oriented randomly and no entanglement was observed between them. It was also found that Cu(acac)₂ was embedded as distinct nanoparticles inside and over the walls of the nanofibers. The obtained nanocomposite was successfully used as a recoverable heterogeneous catalyst in the Michael addition reaction of carbon nucleophiles such as malononitrile, indole and 2-methylindole to various α,β-unsaturated carbonyl compounds. The Michael addition reaction proceeded smoothly at room temperature in dry THF. Under very mild reaction conditions, good to excellent yields of the desired products were obtained. Although one favorable feature of the catalyst was ease of recycling, a minor decrease in its efficiency during successive runs was observed. It was found that 7% decrease in efficiency after four successive runs may be due to the slight leaching of Cu(acac)₂ into the solution based on an ICP analysis of the recovered catalyst of the fourth run.     

Systematic experimental based modeling of a rotary piezoelectric ultrasonic motor

In this paper, a new method for equivalent circuit modeling of a traveling wave ultrasonic motor is presented. The free stator of the motor is modeled by an equivalent circuit containing complex circuit elements. A systematic approach for identifying the elements of the equivalent circuit is suggested. The Levenberg-Marquardt parameter estimation algorithm is used to model the alteration of the admittance after placing the rotor on the stator. Thereafter, theoretical assessments and experimental measurements are used to account for the speed reduction that is caused by placing the rotor on the stator and applying the load torque. Finally, the effects of temperature changes and the resultant response of the motor are computed. Results of the experiments and measurements are used to verify and validate the precision of the new modeling method.     

Second modification of a polyamide membrane surface

The aim of this study was to develop the water flux and antifouling properties of a polyamide (PA) nanofiltration membrane. A nascent PA membrane was prepared with an interfacial polymerization technique and modified with 2,5‐diaminobenzene sulfonic acid (2,5‐DABSA) as a second modification. The effects of the 2,5‐DABSA monomer concentration and the modification time on the membrane performance were investigated. The chemical structure, morphology, roughness, hydrophilicity, molecular weight cutoff, and antifouling properties of the membranes were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force spectroscopy, contact angle measurement, poly(ethylene glycol) tracers, and cetyl trimethyl ammonium bromide filtration, respectively. The PA membrane with optimized performance was shown to have a greater than 44% higher water permeate flux with a change in the salt rejection in the order RNa₂SO₄ > RCaCl₂ > RNaCl to RNa₂SO₄ > RNaCl > RCaCl₂. The improvement of the hydrophilicity led to excellent antifouling properties in the new PA membranes and illustrated a promising and simple method for the fabrication of high‐performance PA membranes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43583.     

Role of Organic Acids in Flux Enhancement of Polyamide Nanofiltration Membranes

A novel thin‐film composite (TFC) nanofiltration membrane containing hydrophilic organic additives was fabricated via interfacial polymerization. Three organic acids, i.e., lactic, maleic, and citric acid, served as aqueous‐phase additives and their role in membrane structure and nanofiltration membrane flux enhancement was investigated. Fourier transform‐infrared (FT‐IR) analysis confirmed the presence of organic acids in the polyamide (PA) layer. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses were applied to investigate the membrane morphology. The more carboxylic functional groups present in the additive resulted in higher hydrophilicity and porosity and flux was enhanced significantly compared to the neat PA membrane, while salt rejection was influenced only to a minor extent.     

Robust H(∞) control of uncertain switched systems defined on polyhedral sets with Filippov solutions

This paper considers the control problem of a class of uncertain switched systems defined on polyhedral sets known as piecewise linear systems where, instead of the conventional Carathéodory solutions, Filippov solutions are studied. In other words, in contrast to the previous studies, solutions with infinite switching in finite time along the facets and on faces of arbitrary dimensions are also taken into account. Firstly, established upon previous studies, a set of linear matrix inequalities are brought forward which determines the asymptotic stability of piecewise linear systems with Filippov solutions. Subsequently, bilinear matrix inequality conditions for synthesizing a robust controller with a guaranteed H(∞) performance are presented. Furthermore, these results has been generalized to the case of piecewise affine systems. Finally, a V-K iteration algorithm is proposed to deal with the aforementioned bilinear matrix inequalities. The validity of the proposed method is verified through the analysis of two simulation examples.     

Analysis,modeling, and implementation of a new transformerless semi-quadratic Buck–boost DC/DC converter

This paper presents a novel transformerless semi-quadratic buck-boost converter (SQBuBoC). In the proposed SQBuBoC, two power switches with simultaneous operation are used and a higher step-up/step-down voltage conversion ratio is achieved compared with the traditional buck-boost, Cuk, single-ended primary-inductor converter, and Zeta converters. The positive polarity of the output voltage, along with low ripple continuous input current and common ground between the source and the output voltages, are some features that make the suggested topology more suitable for many applications with wide range of output voltage such as photovoltaic systems. Moreover, the total voltage stress across the power switches in this converter is lower than the cascade boost, and the traditional buck-boost converters led to power MOSFETs selection with lower drain-source ON resistance (R_ds) and efficiency improvement. All the steady-state analysis and comparisons in continuous conduction mode (CCM) are discussed in details. In addition, to study the low frequency behavior of the SQBuBoC by means of the state-space averaging technique, the small and large signal models of this converter in CCM are presented. Finally, the SQBuBoC analysis is justified using experimental results of a 50 W step-up 25 V to 120 V and a 28 W step-down 25 V to 14 V laboratory prototypes.     

Preparation and characterization of a novel positively charged nanofiltration membrane based on polysulfone

The goal of this study was to prepare positively charged nanofiltration (NF) membranes to remove cations from aqueous solutions. A composite NF membrane was fabricated by the modification of a polysulfone ultrafiltration support. The active top layer was formed by the interfacial crosslinking polymerization of poly(ethylene imine) (PEI) with p‐xylene dichloride (XDC). Then, it was quaternized by methyl iodide (MI) to form a perpetually positively charged layer. The chemical and morphological changes of the membrane surfaces were studied by Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy. To optimize the membrane operation, the PEI solution concentration, PEI coating time, XDC concentration, crosslinking time, and MI concentration were optimized. Consequently, high water flux (5.4 L m^?2 h^?1 bar^?1) and CaCl₂ rejection (94%) values were obtained for the composite membranes at 4 bars and 30°C. The rejections of the NF membrane for different salt solutions, obtained from pH testing, followed the order Na₂SO₄ < MgSO₄ < NaCl < CaCl₂. The molecular weight cutoff was calculated by the retention of poly(ethylene glycol) solutions with different molecular weights, and finally, the stoke radius was calculated as 1.47 nm. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41988.     

Fault ride-through capability improvement in a DFIG-based wind turbine using modified ADRC

In this paper, an overview of several strategies for fault ride-through (FRT) capability improvement of a doubly-fed induction generator (DFIG)-based wind turbine is presented. Uncertainties and parameter variations have adverse effects on the performance of these strategies. It is desirable to use a control method that is robust to such disturbances. Auto disturbance rejection control (ADRC) is one of the most common methods for eliminating the effects of disturbances. To improve the performance of the conventional ADRC, a modified ADRC is introduced that is more robust to disturbances and offers better responses. The non-derivability of the fal function used in the conventional ADRC degrades its efficiency, so the modified ADRC uses alternative functions that are derivable at all points, i.e., the odd trigonometric and hyperbolic functions (arcsinh, arctan, and tanh). To improve the efficiency of the proposed ADRC, fuzzy logic and fractional-order functions are used simultaneously. In fuzzy fractional-order ADRC (FFOADRC), all disturbances are evaluated using a nonlinear fractional-order extended state observer (NFESO). The performance of the suggested structure is investigated in MATLAB/Simulink. The simulation results show that during disturbances such as network voltage sag/swell, using the modified ADRCs leads to smaller fluctuations in stator flux amplitude and DC-link voltage, lower variations in DFIG velocity, and lower total harmonic distortion (THD) of the stator current. This demonstrates the superiority over conventional ADRC and a proportional-integral (PI) controller. Also, by changing the crowbar resistance and using the modified ADRCs, the peak values of the waveforms (torque and currents) can be controlled at the moment of fault occurrence with no significant distortion.