Category Archives: Fără categorie

Application of Two Direct Optimization Methods on a SMES Device by DOE and FEM: Method by Zooms and Method by Slidings of Plans

Fără categorie

Abstract 

The Design of Experiments (DOE) applied to electrical systems modeled by the finite element method (FEM) has become a useful strategy to solve many optimization problems. In this paper, two direct optimization methods by DOE and 2-D FEM were applied on a Superconducting Magnetic Energy Storage (SMES) device with modular toroid coil, in order to optimize its storage capacity: the method by zooms without computation of models and the method by slidings of plans without computation of models. Two parameters that characterize the geometric torus shape were chosen to minimize the volume of the superconducting material with a maximum stored magnetic energy: the coil inner diameter ratio and the coil thickness ratio. The 2-D FEM implementation uses an equivalent rectangular cross section toroid, conserving the inductance of the system. The optimization results by the two methods are obtained with less than 2% error of objective function value and they are comparable between them and better than previous approximate values determined by simple numerical tests. images

Utilization of Phase Margin for Analyzing Stability of Asynchronous Motors Supplied by Frequency Converters

Fără categorie

Abstract 

This paper analyzes a few aspects regarding the dynamic regime operation of the asynchronous motors supplied by variable frequency. The starting point is the conclusion that the stability is a quantitative feature of systems associated to their dynamic behaviour and that has imposed a method for the stability analysis, presented in this paper. The method has as a starting point the mathematical model of the motor written in per unit values. This model has been processed with the help of the Laplace transform. There has been obtained a block scheme with negative reaction which has been used for carrying out a Matlab program for stability analysis. With the help of the program there have been obtained some amplitude-pulsation, phase–pulsation, amplitude-phase characteristics and some hodographs corresponding to a low power asynchronous motor. Comparing the characteristics obtained when some motor parameters have been modified, the conclusions detailed in the final part of the paper have resulted. The notion of phase margin has had a special place for finalizing the analysis. This quantity shows the stability reserve of the machine until the stability limit is reached. The simulations have shown that the phase margin increases when the stator resistance value increases. On the other hand, when the rotor resistance value decreases, the phase margin decreases. images

The Synchronous Fundamental dq Frame Theory Application for the Active Filtering

Fără categorie

Abstract 

 

One of the methods that have been used for the analysis of three phase systems is the rotating fundamental dq frame. Although it was especially used for the analysis of three phase machines, because it is a time domain method is also suitable for the compensating current computation in the active filtering. In fact, it was already been used for the computation of the current fundamental, and if desired, for the computation of some of the upper harmonics. This way the compensator could eliminate from the power grid current all or some of the harmonic content. But this is also, the limitation of this method, because it cannot intrinsically obtain the compensation of reactive power. This is because this method refers to currents and not powers so the reactive power is not defined. At the same time and for the same reasons, it could not obtain the compensated current to have the same shape as the grid voltage. If the compensation goal includes the reactive current compensation, this method must be adapted to compute beside the load current fundamental, the active component of the load current fundamental. Another adaptation of this method is the unity power factor compensation, which implies that the compensated current has the same shape and phase with the grid voltage, so the active power is transported not only on the voltage fundamental, but also on the voltage harmonics. images

Structure and Properties of Polyethylene-Based Magnetic Composites

Fără categorie

Abstract 

Magnetic polymer composite materials have very good rheological (that are characteristic for polymers used as matrix) and magnetic properties superior to those of polymers (due to their magnetic filler) making them useful in many power applications (electromagnetic shielding, permanent magnets etc.). In this paper the results of an experimental study regarding the manufacture and characterization of some composites which have low density polyethylene (LDPE) as matrix and neodymium (Nd) and neodymium-iron-boron (Nd-Fe-B) as filler are presented. The manufacture process (with mass content between 0 and 15 %) and their structure (obtained by electronic and optical microscopy) are presented. It is shown that the samples are inhomogeneous and isotropic and the filler particles form clusters of variable dimensions and distances between them. The rheological behavior of composites was analyzed and more rapid melting was observed for composites compared to neat polyethyleneThen, the first magnetization cycles obtained on neodymium (A) and neodymium-iron-boron (B) samples for three mass concentrations (5, 10 and 15 %) are presented. It is shown for both samples type (A and B) that the hysteresis area cycles and the hysteresis losses increase with filler content being greater for samples B than A. It is shown, also, that the magnetic permeability values increase with filler content, but decrease very quickly with the magnetic field strength. images

Effect Assessment of TCSC on Algerian Transmission Line Protected by IDMT Directional Overcurrent Relay

Fără categorie

Abstract 

 

The paper presents the effect of apparent reactance and injected voltage by series Flexible AC Transmission System (FACTS) i.e. Thyristor Controlled Series Capacitor (TCSC) on transmission line high voltage protected by an Inverse Definite Minimum Time (IDMT) Directional Overcurrent Relay (DOCR) based International Electrotechnical Commission (IEC) standard characteristic curve. The DOCR is used to protect a 400kV transmission line of the Algerian transmission power systems which belong to the Algerian Company of Electrical. The effects of TCSC on protected transmission line parameters (reactance and resistance) as well as fault current and operation time of the DOCR in the presence of phase to earth fault with fault resistance for three cases study is investigated. images

Using a Shape Memory Alloy Spring Actuator to Increase the Performance of Solar Tracking System

Fără categorie

Abstract 

The exclusive properties (e.g. one way and two way shape memory effect, superelasticity, etc.) exhibited by shape memory alloys (SMAs) offer the possibility of producing smart sun tracking mechanisms for photovoltaic panels (PV panels). This article presents an experimental model, conceived by authors, of an active solar panel tracking system, actuated by two SMA springs working against each other. The shape memory effect enables any SMA spring to work as linear actuator by contracting with great strength and speed when heated. This translating motion is converted into a rotation motion of the photovoltaic panel so that it will be appropriately tilted to directly face the sun during the day time. On one hand, the authors make a brief description of the tracking mechanism, and, on the other hand, they comprehensively explain how the automatic orientation of the photovoltaic panel is controlled. The authors also explain how a SMA spring actually works emphasizing the advantages such a device really exhibits in using it as actuator. The active shape-change control of SMA spring the miniaturization possibilities, easy integration into the system structure, automatic orientation of PV panel (using a programmable logic controller) are underlying an effective increase in the efficiency of such smart sun tracking mechanisms. images

Power Electronic Converters – New Trends in Power Quality of Low Voltage Power Grids

Fără categorie

Abstract 

Power quality problems are of high actuality. Voltage and current harmonics compensation as well as control or compensation of power factor in low voltage grids can be today performed by using intelligent power electronic converters, instead of using high cost, environment unfriendly capacitors and passive filters. Active filter based configurations are used for harmonic compensation introduced by nonlinear consumers. For the active power factor conditioning, PWM controlled voltage converters can be used. To achieve both harmonics and power factor compensation, we need complex conditioning using intelligent controlled double sided voltage converters. The exponential evolution of increased performances of power electronic switching devices (high power, high switching frequency, low size) and the inverse exponential draw of costs for power electronic devices and power electronic converters makes solutions presented in this paper as a possible and desired trend in power quality problems.

 images

Modern AC Drive System with Induction Machine

Fără categorie

Abstract 

The induction machine is widespread in AC drive system. The energy efficiency of the induction machine during dynamic regimes is up to 40%. Therefore, for the electrical drives with frequent dynamics (starting, breaking or reversing) the energy efficiency becomes a serious problem. The regenerative drive system is a solution to improve the energy efficiency in an elegant manner. This method requires of using an active front end rectifier instead of the uncontrolled rectifier, as in the conventional AC drives system. The authors proposed in this paper, a modern way to increase the energy efficiency of the drive system through the regeneration process. The power supply converter of the three-phase induction machine is designed in a modular manner, consisting of a series active power rectifier (APR), DC link, and three-phase power inverter. As regarding the DC link, the braking resistor is not necessary, the recovered energy during the braking process being delivered to the grid. Moreover, due to the used power control, DC link voltage control and current control in the grid side power converter, both the power quality and DC link capacitor minimization are ensured. The load side contains three phase voltage source inverter (VSI) in order to supply the three phase induction motor connected to the load. Through the Matlab/Simulink environment software, the obtained performances of the modular AC drive system and motoring and regenerating operation modes are shown. images

Practical Considerations Concerning Conducted Electromagnetic Interferences for a PC

Fără categorie

Abstract 

The paper refers to theoretical and practical considerations concerning conducted electromagnetic interferences (IEM). The standards used for measuring of conducted emissions (CE) are presented and discussed.  FCC and CISPR standards are approached. A line impedance stabilization network (LISN) must be inserted between the AC power cord of the device under test and the commercial power outlet. Due to the difference in the regulated frequency ranges between the FCC and CISPR 22 Standards, the LISNs for both of them have similar layouts, but the component values are different. Standards used for test setup CE measurements are presented to understand the test procedures used to measure CE. Test instruments used for measuring CE are presented. A laptop was selected as the equipment under test (EUT). It is basically a noisy source containing a switched mode power supply. The standard requirements for CE and configuration of the test set-up measurements were investigated in this case. Also the test instruments used for accurate measurements and suitable comparison to the limits provided in the required standards are discussed. The equipment used for the measurements were: a LISN, a measuring EMI receiver and specialized software – EMC32. In fact the conducted disturbance voltages were measured by using the methods required by CISPR 22, that was applied considering the frequency range from 150 kHz to 30 MHz. The results for the CE measurement are presented. The quasi-peak and average values during testing do not exceed the allowed limits and comply with the standard required. The tests revealed that the values obtained with the EMC32 software comply with the standards, therefore the equipment tested can be validated. images

Increasing Frequency Capability of PMSM Vector Controlled Drive for Pumped Storage

Fără categorie

Abstract 

The subject of this paper is a comparative study between two supply modes of a permanent magnet synchronous motor (PMSM). The goal is to obtain a better efficiency for a hydraulic pump drive system. The machine (PMSM) is operated in vector control mode. The inverter is controlled with a sinusoidal pulse-width modulation (SPWM) technique. The study will allow to increase the root mean square (RMS) of the voltage and hence speed, avoiding over-modulation. The comparison is also made between third harmonic injection and over-modulation.

 images