A multifunctional dynamic voltage restorer for power quality improvement

Power quality is a major concern in electrical power systems. The power quality disturbances such as sags, swells, harmonic distortion and other interruptions have an impact on the electrical devices and machines and in severe cases can cause serious damages. Therefore it is necessary to recognize and compensate all types of disturbances at an earliest time to ensure normal and efficient operation of the power system. To solve these problems, many types of power devices are used. At the present time, one of those devices, Dynamic Voltage Restorer (DVR) is the most efficient and effective device used in power distribution systems. In this paper, design and modeling of a new structure and a new control method of multifunctional DVRs for voltage quality correction are presented. The new control method was built in the stationary frame by combining Proportional Resonant controllers and Sequence-Decouple Resonant controllers. The performance of the device and this method under different conditions such as voltage swell, voltage sag due to symmetrical and unsymmetrical short circuit, starting of motors, and voltage distortion are described. Simulation result show the superior capability of the proposed DVR to improve power quality under different operating conditions and the effectiveness of the proposed method. The proposed new DVR controller is able to detect the voltage disturbances and control the converter to inject appropriate voltages independently for each phase and compensate to load voltage through three single-phase transformers.Web of Science116art. no. 135

THE TAX COMPLIANCE RISK FOR BANK PAYMENT TRANSACTIONS IN THE TAX ADMINISTRATION CONTEXT IN VIETNAM

The article provides the reference on tax compliance risk for bank transactions payments by businesses in the context of developing countries such as Vietnam, as tax departments are gradually modernizing the tax administration, the use of taxpayer data between tax department and banks are not good. The review of the materials examines the issues involved in the field of tax compliance risk management and to identify gaps in the study of a tax compliance risk

Effective Interactions in a Graphene Layer Induced by the Proximity to a Ferromagnet

The proximity-induced couplings in graphene due to the vicinity of a ferromagnetic insulator are analyzed. We combine general symmetry principles and simple tight-binding descriptions to consider different orientations of the magnetization. We find that, in addition to a simple exchange field, a number of other terms arise. Some of these terms act as magnetic orbital couplings, and others are proximity-induced spin-orbit interactions. The couplings are of similar order of magnitude, and depend on the orientation of the magnetization. A variety of phases, and anomalous Hall effect regimes, are possible.Comment: 10 pages, 3 figures, 3 table

Corruption: Case Studies of Vietnam and Italy

Corruption is morally and legally wrong. Despite many governmental policies and strategies designed to combat corruption, it still persists in most parts of the world. To understand why corruption is so persistent and pervasive, it is necessary to recognize the perceptions of the beneficiaries and victims of the issue and to comprehend the extent to which cultural biases influence individuals’ decisions to give in to corruption. Acquiescence to dishonest and fraudulent behavior can foster political corruption in many countries. Vietnam and Italy were selected as case studies for this paper. Using the case studies of these two different countries will provide an explanation of how different cultural and social contexts can influence the prevalence of corruption. This paper also endeavors to give some practical recommendations to policy makers and to activists to ponder upon

Advanced Control of the dynamic voltage restorer for mitigating voltage sags in power systems

The paper presents a vector control with two cascaded loops to improve the properties of Dynamic Voltage Restorer (DVR) to minimize Voltage Sags on the grid. Thereby, a vector controlled structure was built on the rotating dq-coordinate system with the combination of voltage control and the current control. The proposed DVR control method is modelled using MATLAB-Simulink. It is tested using balanced/ unbalanced voltage sags as well as fluctuant and distorted voltages. As a result, by using this controlling method, the dynamic characteristics of the system have been improved significantly. The system performed with higher accuracy, faster response and lower distortion in the voltage sags compensation. The paper presents real time experimental results to verify the performance of the proposed method in real environments

Quantum Geometric Oscillations in Two-Dimensional Flat-Band Solids

Two-dimensional van der Waals heterostructures can be engineered into artificial superlattices that host flat bands with significant Berry curvature and provide a favorable environment for the emergence of novel electron dynamics. In particular, the Berry curvature can induce an oscillating trajectory of an electron wave packet transverse to an applied static electric field. Though analogous to Bloch oscillations, this novel oscillatory behavior is driven entirely by quantum geometry in momentum space instead of band dispersion. While the orbits of Bloch oscillations can be localized by increasing field strength, the size of the geometric orbits saturates to a nonzero plateau in the strong-field limit. In non-magnetic materials, the geometric oscillations are even under inversion of the applied field, whereas the Bloch oscillations are odd, a property that can be used to distinguish these two co-existing effects.Comment: 6 + 7 pages, 2 figures. Comments are greatly appreciated

Boundary Modes from Periodic Magnetic and Pseudomagnetic Fields in Graphene

Single-layer graphenes subject to periodic lateral strains are artificial crystals that can support boundary spectra with an intrinsic polarity. These are analyzed by comparing the effects of periodic magnetic fields and strain-induced pseudomagnetic fields that respectively break and preserve time-reversal symmetry. In the former case, a Chern classification of the superlattice minibands with zero total magnetic flux enforces {\it single} counter-propagating modes traversing each bulk gap on opposite boundaries of a nanoribbon. For the pseudomagnetic field, pairs of counter-propagating modes migrate to the {\it same} boundary where they provide well-developed valley-helical transport channels on a single zigzag edge. We discuss possible schemes for implementing this situation and their experimental signatures.Comment: 5+12 pages; 3+6 figures; version accepted to Physical Review Letter

Protected Fermionic Zero Modes in Periodic Gauge Fields

It is well-known that macroscopically-normalizable zero-energy wavefunctions of spin-$\frac{1}{2}$ particles in a two-dimensional inhomogeneous magnetic field are spin-polarized and exactly calculable with degeneracy equaling the number of flux quanta linking the whole system. Extending this argument to massless Dirac fermions subjected to magnetic fields that have \textit{zero} net flux but are doubly periodic in real space, we show that there exist \textit{only two} Bloch-normalizable zero-energy eigenstates, one for each spin flavor. This result is immediately relevant to graphene multilayer systems subjected to doubly-periodic strain fields, which at low energies, enter the Hamiltonian as periodic pseudo-gauge vector potentials. Furthermore, we explore various related settings including nonlinearly-dispersing band structure models and systems with singly-periodic magnetic fields.Comment: 9 pages, 1 figure. Comments are very appreciate

Effects of Frequency and Mass of Eccentric Balls on Picking Force of The Coffee Fruit for The As-Fabricated Harvesting Machines

Currently, Vietnam ranks second about the coffee export in the world. To match that position, the use of coffee harvesting tools/machines according to the automatic trend is essential. However, the most common forms of coffee harvesting in Vietnam are manual, improved manual-coffee picking machines that are imported from foreign countries. The above harvesting forms have low productivity and have some disadvantages such as labor cost, labor hiring, high labor cost, and long harvesting time, low harvesting, and post-harvesting quality. Studies of scientists around the world have applied the principle of vibration to produce the picking force for coffee fruits, and the picking force is known to be different from many factors in every region of the world growing coffee. The paper presents the method of design and manufacturing an automatic coffee harvesting machine based on the evaluation of picking force for coffee in Vietnam. The influences of eccentric ball mass and vibrating frequency on the magnitude of the picking force are carefully calculated. On that basis, the experimental programming is applied to find the optimal working point of the picking machine for coffee. The results showed that the eccentric ball mass of 8.5 kg, the rotation speed of the eccentric ball from 480 to 574 rpm would produce the picking force by the coffee fruit of Vietnam