Abstract

This paper makes an analytical study, a numerical and an experimental analysis of the magnetic forces which act in magnetic liquids during the experiment called Quincke’s effect. Quincke’s effect consists in the rise of the magnetic liquid between the poles of an electromagnet. In ferrohydrodynamics theory, the forces acting in the magnetic liquid are not always treated in a uniform manner. The main goal of this paper is to give a consistent macroscopic view, pointing out the importance of the magne-tostriction in the force localization understanding. If the absence of the magnetostrictive term in the forces expres-sion leads to an exclusively superficial localization of the forces, the presence of this term leads both to a superficial localization of forces as well as their presence in the mag-netic liquid volume. Moreover, in the magnetic liquid rise, the volume forces have a significant contribution than the surface forces, so the magnetostrictive term shall not be neglected. In this analysis, the magnetic liquid will be considered as a linear and nonconducting medium placed in a stationary (or quasistationary) field. In order to support the analytical study, a numerical analysis of the magnetic forces and some qualitative experiments were made. The value of the magnetic field forces which act in the magnetic liquid were established in Matlab using the magnetic field strength established by FEM analysis. Analyzing the numerical results and the magnetic liquid deformation obtained by ex-periments, the main conclusion consists in the fact that the magnetostrictive term has an important contribution in the localization of the forces, so it shall be taken into consideration.

Abstract

The paper presents the synthesis of the battery charging system of an electric stand-alone locomotive. The traction converter as boost rectifier is used together with a dedicated control strategy in order to obtain the unity power factor on the grid. Two objectives, often contradic-tory, that can be tracked in the choice of the control mode for the PWM rectifier are highlighted: increasing the per-formance, in order to obtain a rectifier with the best power factor, the best-controlled load current, acceptable switch-ing frequencies for common power transistors, a stable op-eration of the control system, etc.; reducing the complexity and price of the converter by giving up certain elements of the control system, such as the multiplication circuit, the voltage loop, and the use of specialized integrated circuits. A patented structure which responds better to the require-ments and particularities of autonomous vehicles is used. In the control part, direct current control method is adopted and it was implemented by two control loops. The external loop is dedicated to charging current control and the inter-nal loop is dedicated to grid current control. In order to the performance determination, the entire system is analyzed under Simulink environment and the energetic perform-ances are determined. Also, the influence of switching fre-quency is analyzed.

Abstract

This paper contains a theoretical and experimen-tal study on rotary magnetostrictive motor, performed with the purpose of determining the optimal conditions of opera-tion. The two main types of magnetostrictive motors known from the literature, inchworm respectively resonance pre-sent the advantage of large and accurately controlled devel-oped torques for low speed values. The electromagnetic torque developed by the rotary magnetostrictive motor be-ing proportional to the frequency of the current circulating through its inductor, became the subject of frequency con-trol methods. This fact lead to the idea of controlling the torque by controlling the frequency of the current, with direct implication in the domain of torque-controlled drives. Although the actuator represents the central part of any magnetostrictive device, the entire magnetic circuit configu-ration determines the position of the permanent magnet operating point on the linear portion of the magnetostrictive characteristic. The paper includes two different methods, applied for the permanent magnet operating point alloca-tion. The magnetostrictive torque was determined and ex-pressed as function of time, for the full cycle of the periodi-cal current carried by the actuator’s coil. The cycle of the magnetostrictive torque is identical with the cycle of the periodical current circulating through the coil of the actua-tor. The analytical mathematical model developed and pre-sented in the paper considers both regimes, starting and running, making possible the tracking of the operation point. Furthermore, was possible to determine the moment of separation between the rotor disk and the flexible friction element. Several acquired data, recorded at different values of power supply frequency, demonstrate a good correlation between the theory and experiment.

Abstract

The paper presents a method of calculation of LC parameters of reactive balancing compensators of linear time-invariant (LTI) loads supplied with a nonsinusoidal and asymmetrical voltage. The method is based on the Cur-rents’ Physical Components (CPC) – based power theory. Complete compensation of the reactive and unbalanced cur-rents in the presence of the supply voltage harmonics can require compensators of very high complexity. The paper presents a method of calculation of LC parameters of reac-tive balancing compensators with a reduced complexity. The method is illustrated with a numerical example.

CPC-Based Reactive Compensation of Linear Loads Supplied with Asymmetrical
Nonsinusoidal Voltage – Leszek S. Czarnecki

The Rotary Magnetostrictive Motor: a Promising Solution for Low Power Actuators – Alexandru Dalea, Mircea Ignat, Sorin Deleanu, Mihai Iordache, Neculai Galan

Synthesis of the Battery Charging System of a Stand-Alone Electric Locomotive – Alexandru Bitoleanu, Mihaela Popescu, Vlad Constantin Suru, Mihail Rădulescu

How to Design a Passive Damped LCL Coupling Filter for an Active DC-Traction Substation – Mihaela Popescu, Alexandru Bitoleanu, Mircea Dobriceanu, Florin Alexandru Teodorescu

Analytical Study, Numerical Modelling and Experimental Results of the Forces which Act in the Magnetic Liquid Placed between the Poles of an Electromagnet – Daniela Vesa

Application of Direct Optimization Method by Zooms to Improve the Performances of AC Electromagnet – Alin-Iulian Dolan

Controller for BLDC Motors – Florin Ravigan, Laurenţiu Alboteanu, Marius Dumitriu, Ionuţ Zglimbea

An Improved Numerical Model of Heat Transfer Coefficient Corresponding to a Through Connector – Constantin Florin Ocoleanu, Ioan C. Popa

Automatic Sorting and Handling Station Actuated by Pneumatic Drive – Laurenţiu Alboteanu, Gheorghe Manolea, Florin Ravigan

The Resistive Tubular Heater – Mathematical and Simulation Model – Mitică Iustinian Neacă

Simulation of Idle Running Operating Characteristics for Low-Power
Asynchronous Motors – Raluca-Cristina (Presură) Nicolae

Disturbance Analysis for Power Systems Based on LabVIEW Real-Time and Reconfigurable FPGA Modules Using Wavelet Transform – Marcel Nicola, Claudiu-Ionel Nicola, Sebastian Popescu, Dumitru Sacerdoţianu, Marian Duţă

Single/Three-Phase Transformer with Variable Frequency for Electric Locomotives – Berzan Vladimir, Ermurachi Iurie, Ivanov Sergiu

Continuous Monitoring and SCADA Integration of the Sag of Overhead Electricity
Transmission Cables Based on the Measurement of their Slope – Dumitru Sacerdoţianu, Marcel Nicola, Claudiu-Ionel Nicola, Iulian Hurezeanu, Florica Lăzărescu

Implementation of Virtual Instrumentation for Testing of Induction Motors – Gheorghe-Eugen Subţirelu

Analysis of Losses in Brushless Direct Current Motors and Their Influence upon Operation Characteristics – Monica-Adela Enache, Aurel Campeanu, Ion Vlad, Sorin Enache

Current Aspects in the Conception and Performance of Dispatching Manoeuvres
in the National Electric Power Transmission System – Silvia-Maria Digă, Nicolae Digă, Cristian Bratu, Adelaida-Mihaela Duinea

Diagnosis with Analytic Model of a Rectifier for Faults of the Rectifier Control – Virginia Ivanov, Maria Brojboiu, Sergiu Ivanov

Modeling Three-Phase Short-Circuits for Radial Distribution Systems – Horia Bălan, Mircea Ion Buzdugan, Liviu Neamţ

Graphical User Interface to Extrapolate the Ideal Covering Factor of the Polar Step – Gabriela Dana Petropol Şerb , Ion Petropol Şerb

Power line Compromising Emanations Analysis – Vlad Butnaru, Bogdan Trip, Andrei Macovei, Georgiana Roşu, Alexandru Boitan, Simona Halunga

Indirect Current Control Algorithm Implementation and Validation, for Active Filtering Using Constant Switching Frequency Hysteresis Controllers – Mihaita Lincă, Constantin Vlad Suru, Cristina Alexandra Preda

Analysis of the Phaseportrait for the Lü Dynamical System in a Particular Case – Adela Ionescu, Florian Munteanu

Abstract

In this paper there are presented a few aspects regarding the operation of the direct current power supply system of cars. The operation of the electronic voltage con-troller is specially approached. Theoretical aspects of the problem are presented. In the second part of the paper there are presented a series of experimental determinations car-ried out on a modern stand. The results have been con-firmed by measurements with a car. In order to analyze the rectifier defects there have been viewed the output voltage waveforms for five situations of defect of the diodes. In or-der to analyze the voltage control, there have been obtained the waveforms of the excitation current for three particular situations. In the last part of the paper there are presented the conclusions obtained following the researches. It is em-phasized that: damaging one or more diodes of the rectifier can be identified by viewing, by means of an oscilloscope, the waveform of the output voltage of the alternator; when one of all the diodes is functional, the waveform is symmet-rical, waved and with small variations; for the same number of damaged diodes, the distortion degree of the voltage also depends on their position in the rectifying bridge (e. g. the distortion is higher when two positive diodes are damaged than in case when a positive diode and a negative one are damaged); an existing fault situation can be identified by viewing the output voltage of the alternator.

Abstract

The aim of this paper is the design and implementation of the control algorithm of a PWM boost rectifier capable to handle bidirectional energy flow. For this goal, the boost rectifier control loops must be tuned for the proper operation of absorbing active power from the power grid and transfer it to the dc load at constant output voltage, and also to give the rectifier the ability to generate back to the power grid the energy intake from the dc-link, using the dc-link capacitor as intermediary energy tank. It will be proved that the transition between rectifier operation and inverter operation is done automatically, without the intervention of the human operator or of a specially designed system. The correct implementation and tuning of the control algorithm was validated on a complete Matlab Simulink model which includes in detail all the sections of the rectifier system. The simulation and experimental results proved the correct answer of the tuned dc-link voltage controller and the overall operation of the system for a step changing active load. Because the boost rectifier control algorithm is similar to shunt active filters control algorithm, the indirect current control approach was adopted, which is the most suitable for this purpose.

Abstract

The investments in units of electricity production from the renewable energy sources have an increasing trend in the European Union countries. The production of elec-tricity from renewable energy sources and cogeneration is promoted by various support mechanisms. The quota obli-gation system and tradable green certificates was imple-mented in Romania. In the case of biomass, the support scheme provides two green certificates for each MWh deli-vered to the public electricity network and additional one green certificate if the electricity is produced in high effi-ciency cogeneration. For cogeneration plants, demand for useful heat is the essential condition in the qualification of electricity production in high efficiency cogeneration. A solution to provide the demand for useful heat and compen-sation of load variations over time is the storage of thermal energy. The paper presents the technical and economic analysis of the heat storage systems integration for a coge-neration unit with organic Rankine cycle (ORC) and bio-mass fuel. The use of thermal energy storage in the heating network of the ORC unit may allow connection of new con-sumers without disrupting the operation of current consum-ers. The increased heat consumption delivered of the coge-neration unit will allow the qualify for a larger amount of electricity in high efficiency cogeneration.

Abstract

A frequently used method for monitoring and fault diagnosis of the electric equipment is the one based on the analytic model. The paper applies the diagnosis method based on the analytic model by investigating the waveforms of the currents and voltages specific to a transport and dis-tribution line when interruption fault occurs. This method can be used when the system behavior is compared with the results of the mathematical model which reproduces the system in normal operation conditions. For identifying the fault, the waveforms corresponding to different faults are stored in an information database and compared with the ones corresponding to the normal operation. The paper presents a microcontroller based system used to control switching of interruption fault for transport and distribu-tion lines. In order to reduce the breaker stress due to the commutation overvoltage, the paper presents an analysis of the optimum instant when a long line must be disconnected. Similarly, an analysis is performed on the instants of the long lines reconnection. The both analyses are performed taking into account the specific parameters and the length of the lines. The focused magnitudes during the transients are both the maximum values and the slopes of the overvoltage and the maximum values of the currents.

Abstract

Nowadays the efficiency of aerodynamics profiles placed in a supersonic flow represents a permanent goal of the human civil transportation or military equipments. Present paper intends to present an optimization method of their shapes, taking into account the Navier-Stokes flow equations, applied for thin layers. Generally, in supersonic flow, the cross-sections of the wings are thin profiles, sym-metric as to reduce the drag force coefficient and maximize the lift coefficient. It is presented a method of the shape cal-culation for aerodynamic profiles with small curvature, based on integral equations Fredholm of the second kind, with a good behavior in the supersonic flows. Some aspects referring to the unsteady flows and air compressibility are also mentioned. There were selected four aerodynamic air-foils with characteristics dedicated to high velocities, with different characteristics, having as main purpose the identi-fication of essential aspects needed to be considered in the numerical modeling. From these four profiles, two are de-duced by theoretical assessments, and two are special known as super-sonic aerodynamic profiles. They were first tested into a subsonic wind channel for incidences between 00 – 40 at different values of wind velocity and secondly into a su-personic wind tunnel, at same incidences, as to better ana-lyze the main factors who influence the aerodynamic of shapes curvature and to assure an optimization of their be-havior. The purpose of testing these profiles was to improve the main characteristics, especially into the trailing and leading edges. The effect of the angle of attack, the influence of velocity and viscosity, the shape curvature on the vortex development were also considered. The obtained results assure a better functioning in the supersonic flow regime, eliminating the adverse pressure gradient and the boundary layer separation, assuring an optimum behavior. Finally are mentioned some conclusions and references.