Control of Hybrid Active Power Filter Based on Switching Function Coefficients

A pulse width modulation (PWM)-based control method for a three-level, four-wire neutral point clamped (NPC) inverter employed in a hybrid active power filter (HAPF) is proposed in this paper. The control method is based on switching function coefficients (SFCs) for harmonic compensation. An interior loop is also proposed for control and balancing of the DC-link voltages. In the proposed control system, one carrier signal is employed in the PWM unit in order to simplify its hardware as compared with traditional PWMs. Based on Fourier decomposition technique, mathematical analysis of the proposed control method is also presented. To decrease the NPC inverter rated power, passive power filters (PPFs) are designed to eliminate fifth and seventh order harmonic currents and to compensate source reactive currents. The proposed control system is implemented by a digital signal processing (DSP) in a laboratory prototype. The experimental results confirmed the validity of the proposed control method in compensation of harmonic currents under non-linear conditions     

Non-polynomial spline method for solving Bratu's problem

Smooth approximate solutions of the one-dimensional Bratu's problem are developed by using non-polynomial spline function. The inverse of some tridiagonal matrices are obtained which are required in proving the convergence analysis of the presented method. By considering the maximum absolute errors in the solution at grid points and tabulated in tables for different choices of step size we conclude that our presented method produces more accurate results in comparison with those obtained by B-spline, Laplace and decomposition methods.     

Toward wafer-scale patterning of freestanding intermetallic nanowires

Individual metal alloy nanowires of constant diameter and high aspect ratio have previously been self-assembled at selected locations on atomic force microscope (AFM) probes by the method reported in Yazdanpanah et al (2005 J. Appl. Phys. 98 073510). This process relies on the room temperature crystallization of an ordered phase of silver-gallium. A parallel version of this method has been implemented in which a substrate, either an array of micromachined tips (similar to tips on AFM probes) or a lithographically patterned planar substrate, is brought into contact with a continuous, nearly planar film of melted gallium. In several runs, freestanding wires are fabricated with diameters of 40-400 nm, lengths of 4-80 μm, growth rates of 80-170 nm s( - 1) and, most significantly, with yields of up to 97% in an array of 422 growth sites. These results demonstrate the feasibility of developing a batch manufacturing process for the decoration of wafers of AFM tips and other structures with selectively patterned freestanding nanowires.     

Scanning gate microscopy on graphene: charge inhomogeneity and extrinsic doping

We have performed scanning gate microscopy (SGM) on graphene field effect transistors (GFET) using a biased metallic nanowire coated with a dielectric layer as a contact mode tip and local top gate. Electrical transport through graphene at various back gate voltages is monitored as a function of tip voltage and tip position. Near the Dirac point, the response of graphene resistance to the tip voltage shows significant variation with tip position, and SGM imaging displays mesoscopic domains of electron-doped and hole-doped regions. Our measurements reveal substantial spatial fluctuation in the carrier density in graphene due to extrinsic local doping from sources such as metal contacts, graphene edges, structural defects and resist residues. Our scanning gate measurements also demonstrate graphene's excellent capability to sense the local electric field and charges.     

Luminescence properties of monoclinic Cu4I4(Piperidine)4

A new modification of Cu₄I₄Pip₄ has been synthesized under hydrothermal conditions. X-ray crystallography revealed that this compound crystallized in the monoclinic system and consists of a tetrahedral core with composition Cu₄I₄, in which each Cu atom is coordinated by a piperidine molecule via the N atom. In contrast to a previously reported modification of Cu₄I₄Pip₄, the present modification shows luminescent properties when exposed to UV-light. In addition, we have used time-dependent density functional theory calculations to characterize both compounds in term of both absorption and emission.     

Using an active resistive damper in hybrid active power filter to avoid resonance over-voltage

This paper presents a hybrid active power filter (HAPF) comprising an active resistive damper (ARD). The ARD consists of three resistances connected to the grid through three bi-directional electronic switches (IGBTs). The ARD can rapidly damp over voltages or over currents under resonance conditions, when the active part (inverter) of the HAPF is disconnected from the grid due to electrical or non-electrical failures. To drive the bi-directional electronic switches of the ARD, a control method is presented in this paper. The control method is based on comparison of resonance over voltage magnitude with a reference voltage (voltage protection level) to control the bi-directional electronic switches. Also the magnitude–frequency characteristics and the control method of the HAPF based on source current detection strategy are analyzed in detail in this paper. Performance of the HAPF with and without the ARD is analyzed in this paper and the results are compared with each other. Finally, the simulation results are provided to validate the proposed topology.     

Existence and numerical simulation of solutions for nonlinear fractional pantograph equations

In this paper a method based on Sinc approximation is developed for the numerical solution of a nonlinear fractional pantograph equation. In order to use Sinc approximation, the problem needs to have an analytic solution. So we investigated the existence and uniqueness of analytic solutions in the proposed domain. Single and double exponential transformations are used to approximate the solution. Some test problems are given to demonstrate the efficiency and applicability of the methods. The results are compared with some other existing numerical methods to show the performance and good accuracy of the methods. The numerical orders of convergence show that the method has exponential rate of convergence.     

Three-dimensional solution of low-velocity impact on sandwich panels with hybrid nanocomposite face sheets

In this article, a three-dimensional solution based on Fourier's series and the generalized differential quadrature method is presented to model the low-velocity impact on sandwich panels with hybrid nanocomposite face sheets. Navier's equations are derived and displacements are substituted by their corresponding Fourier's series. The contact force is considered as a Fourier's series of impactor displacement and deflection of contact point. To verify the theoretical model, experiments are performed on a polyurethane foam-cored sandwich panel with epoxy/woven-fiberglass/nanosilica hybrid nanocomposite face sheets. Contact force and lateral displacement of contact point histories are compared with the theoretical model.     

A neuro‐based approach to designing a Wilkinson power divider

In this paper, a new neuro‐based approach using a feed‐forward neural network is presented to design a Wilkinson power divider. The proposed power divider is composed of symmetrical modified T‐shaped resonators, which are a replacement for quarter‐wave transmission lines in the conventional structure. The proposed technique reduces the size of the power divider by 45% and suppresses unwanted bands up to the fifth harmonics. To verify the concept, a prototype of the power divider has been fabricated and tested, exhibiting good agreement between the predicted and measured results. The results show that the insertion loss and the isolation at the center frequency are about 3.3 ± 0.1 dB and 23 dB, respectively.     

A bootstrap test for symmetry based on ranked set samples

To test the hypothesis of symmetry about an unknown median we propose the maximum of a partial sum process based on ranked set samples. We discuss the properties of the test statistic and investigate a modified bootstrap ranked set sample bootstrap procedure to obtain its sampling distribution. The power of the new test statistic is compared with two existing tests in a simulation study.