Daily Archives: 22 February 2021

Annals of the University of Craiova, Series : Electrical Engineering - 2020

The Use of Helmholtz Coils Designed for 50 Hz at Higher Frequencies – Georgiana Roşu, Ionel Dumbravă, Ion Pătru, Aurelia Scornea, Octavian Baltag, Andrei Marinescu

Wireless Remote Control for the Anti-Hail Missiles Launch Ramp Positioning System – Sorin Stepan, Gheorghe Manolea

Influence of Synchronized Measurement Errors on the Results of Identification of the Transmission Line Parameters – Murdid Ecaterina, Boris Jingan, Dobrea Ina, Vasilos Elena

Metamaterials – Current and Future Trends – Elena Helerea, Lia- Elena Aciu

Virtual Instrumentation for Study of Shape Memory Alloys Strip while Bending – Gheorghe-Eugen Subţirelu, Sonia Degeratu

Aspects Regarding the Impact of Electrical Vehicles’ Charging on Power Quality – Denisa Ruşinaru, Gabriel Cosmin Buzatu, Leonardo Geo Mănescu, Claudiu Popirlan

‘Open Ended’ Laboratory to Study the Influence of Unit’s Weight on Axle Torque in Railway Traction – Petropol Şerb Gabriela Dana, Petropol Şerb Ion

Constructive Dimensions Optimization for Asynchronous Motors used in Coal Mills – Raluca-Cristina Presură (Nicolae), Sorin Enache, Ion Vlad, Marian-Ștefan Nicolae

Program for Monitoring Operation Regimes of Low-Power Electrical Machines – Sorin Enache, Ion Vlad, Monica-Adela Enache

Contributions Regarding the Monitoring in the Command Center of the Anti-Hail Launch Pads – Sorin Stepan, Gheorghe Manolea

Modeling of Thermal Comfort Parameters in Residential Buildings – Radu-Cristian Dinu, Daniela Popescu, Ioana-Gabriela Sîrbu, Dan-Gabriel Stănescu

Studies on the Command of Single-Phase Rectifiers Using the Scalar Control Technique – Florin Alexandru Teodorescu

ANNALS OF THE UNIVERSITY OF CRAIOVA – Electrical Engieneering Series, no. 44, vol. 44, Issue 1, 2020 (click to download)

Studies on the Command of Single-Phase Rectifiers Using the Scalar Control Technique


One of the important problems of power supply systems consists in ensuring the quality of energy supplied to consumers. In this issue, the reduction of the harmonic spectrum of the supplied voltage and current has a key role. As electronic power converters are now increasingly used by consumers, the problem of reducing the harmonic spectrum of the current absorbed by the power supply by these consumers is becoming more and more pronounced. For this, there is the problem of using consumers with a power factor as close as possible to the unit, which also ensures the increase of the efficiency of these consumers. The present paper focuses on the study of single-phase rectifier configurations provided with power factor control (PFC) structures. Among the multiple techniques and methods of power factor control, the scalar power factor control technique was applied to a boost type power converter, in two variants. The first variant is that of a single-phase rectifier in fully controlled bridge. The second is that of a single-phase rectifier in uncontrolled bridge. In both cases, the study of the scalar PFC technique was based on the Matlab/Simulink modeling of the two mentioned configurations. Achieving these models allowed the study of the correction mechanism of the power factor under the influence of the various functional parameters of the approached configurations. images

Modeling of Thermal Comfort Parameters in Residential Buildings


At the level of residential buildings, current studies and research are focused on issues that have as a main priority, the energy of buildings. Energy efficiency of buildings involves, in addition to technical regulations and energy rehabilitation works, an economic optimization of energy in buildings. This optimization must not be done at random, but we must ensure that the conditions of thermal comfort inside the building are met at all times. In this paper, the object of the study is a room located in the middle of a condominium building in Craiova. The building of which the studied room is part is located inside the locality and has constructive structure of the tire elements, characterized by specific thermal resistances of the construction materials used. The mathematical model involves determining the values of thermal comfort parameters (indoor temperature, average radiation temperature, etc.) and their implementation in the calculation of the thermal comfort index, B. The results obtained for the three categories of rooms, allow the feeling of comfort to be included in one of the seven levels. Between the three types of studied rooms there are differences of the calculated interior temperatures, due to the temperature differences on the faces of the construction elements. images

Contributions Regarding the Monitoring in the Command Center of the Anti-Hail Launch Pads


This paper describes an Internet-connected radio remote control designed for the positioning system of the launching pad of anti-hail missiles used by the Romanian Anti-Hail System. The remote control works on the ISM band of 433 MHz and was successfully tested on a small size experimental model of the launch pad. The azimuth and elevation position can be locally controlled by the operator, with the possibility of monitoring and even controlling the launch pad from the Command Center, over the Internet. The remote control uses a touch screen display on the opera-tor side and a PLC connected to the launch pad. The commands on the touch screen are grouped into three pag-es: manual positioning, automatic positioning, and a list of recorded events. Sending the coordinates to the launch pad and firing the missiles are considered events, automatically recorded on an SD card or USB flash drive attached to the remote control. Communication between the touch screen and the PLC is realized by two RF transceivers using LoRa modulation. The touch screen display is connected to the Internet, making it possible to remotely monitor and control the launch pad using an Internet-connected computer. The access to the remote control is password protected and can be disabled by the local operator. images

Program for Monitoring Operation Regimes of Low-Power Electrical Machines


In this paper there are presented details about a program for monitoring steady states and dynamic regimes of low-power electrical machines. The program allows viewing the variation waves of the main electrical quantities, their harmonic content and the relative position of the characteristic phasors. The program advantages are mentioned and there have exemplified some data acquisitions, carried out for a few concrete situations. The main work windows from the Instrument menu are detailed. There have also been presented the results obtained by monitoring the operation of two motors, a three-phase asynchronous motor with single-phase supply and a single-phase asynchronous motor. A part of the conclusions obtained could be mentioned as follows: a) for the case of three-phase asynchronous motor with single-phase supply, we noticed that a voltage increase leads to an increase of the inductive phase shift of the current I1, the phase shift of the current I2 (measured on the phase in series with the capacitor) remains practically unchanged, the capacitive phase shift of the current I3 increases and the distortion degree of the current I1 decreases; b) for the case of the single-phase asynchronous motor we noticed that in load operation (at rated voltage) a decrease of the phase shift between the current and voltage corresponding to the main winding occurs and the current distortion degree increases when the load increases. The paper ends with conclusions and references. images

Constructive Dimensions Optimization for Asynchronous Motors used in Coal Mills


The high operating cost, owed to the large consumption of active and reactive power, led to the optimization of the design and construction of asynchronous motors used in driving the coal mills. The reduction of the operating cost is a difficult problem, because the motor usually lies in a closed enclosure, with provided gauge dimensions, and with specific requirements imposed by the type of drive in use. Using this information, while keeping the existing electromagnetic stresses (for heating reasons), the optimal construction dimensions can be established by design, so as to reduce the operating cost. The optimization is substantiated by the decrease of the operating cost of such a motor with 26100 euros, as compared to the existing version. images

‘Open Ended’ Laboratory to Study the Influence of Unit’s Weight on Axle Torque in Railway Traction


The aim of the paper is to propose a scenario and a test bench to study, in a trans-disciplinary way, how the operation of a traction unit with asynchronous motor is influenced by the railway channel. The main issue of the experiment is to find how the weight of the motor unit can influence the axle torque. The topics involved are: 1. ‘How to calculate the train resistance to forward movement’ (expected results: calculation and plot in Matlab) and 2. ‘How to calculate the force needed to move the train and the traction characteristic at the startup of the train’ (expected results: data acquisition and plotting in LabView). The design of the scenario follows the guideline of an ‘Open Ended’ laboratory. The advantages of this approach are: the study can have an inter- and trans- disciplinary approach, the lab could be developed in a hybrid way: in presence in lab, individual for the-oretical research and in team to solve and disseminate the results. Regarding IT communication, the research needs to use different software packages as Matlab, LabView. images

Aspects Regarding the Impact of Electrical Vehicles’ Charging on Power Quality


A major problem with the increased penetration of electric vehicles is the preparation of the power supply system to accommodate the increasing number of charging stations. Possible problems include exceeding the rated power of distribution equipment and electrical systems components, changing the voltage profile and altering the quality parameters of electricity. In these scenarios it is important for the grid operators to have an accurate information on present grid status, as well as the effects of EVs charging facilities interaction with the hosting grid. This knowledge will help the operators to more efficiently manage their grids while the e-mobility is expanding. This paper addresses issues related to the challenges of large-scale implementation of electric vehicles in Romania and especially their estimated impact on the power quality in current distribution networks. The authors present some of the results of a monitoring and analysis study of the power quality parameters in the coupling buses of some electric vehicle models during their charging cycle. The results of the study are included in a database used as a reference for a larger project aimed at developing intelligent solutions for PQ-based control of load units. images

Virtual Instrumentation for Study of Shape Memory Alloys Strip while Bending


In this paper, using LabVIEW graphical pro-gramming environment and the portable reconfigurable input/output (RIO) device from National Instruments (myRIO-1900), the concept of virtual instrumentation is implemented. Thus, it is created a hardware and software system that is used to study the nickel and titanium shape memory alloy (NiTi SMA) strip during bending under the influence of electric current. The SMA strip is caught in cantilever mode (fixed at one end only). For this study, the following quantities are measured: the deformation of the strip (using a created electronic transducer around an oper-ational amplifier and a piezoelectric effect sensor), the volt-age applied to its ends and the current flowing through it (with LEM transducers). The evolution of the electrical re-sistance as well as the bending of the SMA band at different values of the electric current, during and due to the heating process is reported using this system. The values of the measured quantities are presented in graphical and numeri-cal form. Thus, the evolution on time intervals of the order of seconds can be followed with precision with the help of horizontal and vertical cursors, respectively. Amplitude values can also be accurately determined. The results ob-tained with the proposed system are useful in practical ap-plications of cantilever SMA strip for development of sim-ple, more compact and reliable actuators or sensors. images

Metamaterials – Current and Future Trends


Recently, metamaterials have attracted considerable attention due to their feasibility and multiple applications. As man-made artificial structures, metamate-rials possess properties that are not yet highlighted in the natural world, such as perfect lensing, negative refraction, and backward propagation. These properties are obtained by the proper design of the structure of metamaterials, with the periodic arrangement of unit cells, ”meta-atoms”, which have dimensions below the order of magnitude of the inci-dent wavelength, at which resonance processes can be estab-lished. Thus, the electric and magnetic response of the met-amaterial can be flexibly tailored to meet the desired macro-scopic properties, in terms of effective electric permittivity and magnetic permeability. In this paper, a review of the state of research and development of metamaterials is made, highlighting the new challenges and ways to improve and to apply these new synthetic structures in electromagnetics and optics. There are analyzed the processes and structures of metamaterials used in various applications. Based on the actual researches, new classification of metamaterials with the criterion of the capabilities and flexibilities in controlling electromagnetic waves is described and analyzed. images