Category Archives: Fără categorie

Aspects Regarding Operation of Power Supply System of Cars

30 January 2018Fără categoriecburada

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.

The Implementation and Validation of a Bidirectional PWM Boost Rectifier Control Algorithm

29 January 2018Fără categoriecburada

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.

Technical and Economic Analysis of Thermal Energy Storage in the Biomass CHP Plants with ORC Technology

29 January 2018Fără categoriecburada

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.

Monitoring System for Reducing the Electric Equipment Stress in Transport and Distribution Lines

29 January 2018Fără categoriecburada

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.

Optimization of the Aerodynamics Airfoils Placed in Supersonic Viscous Flow

29 January 2018Fără categoriecburada

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.

Theoretical and Practical Aspects Regarding Radiated Emission Testing in Semi-Anechoic Chambers

29 January 2018Fără categoriecburada

Abstract

This paper presents some theoretical and practical aspects on measurements of radiated emission from a Portable computer. The used Standards are presented and discussed. The measurements were carried out in a Semi-Anechoic Chamber (SAC) in accordance with EN 55022 (CISPR 22) Standard. The test arrangement was in accordance with IEC 61000-4-3 Standard and the following equipment was included: reception antenna, signal generator and emission antenna. The measurements were made at a distance of 3 meters, according to the generic Standard IEC 61000-6-3. The radiated electromagnetic interference (EMI) was assessed in the frequency domain, for the frequency range of 30 MHz – 1 GHz, in compliance with CISPR 22 Standard. The test was performed to verify if the tested item (EUT) – in our case a Portable computer – is operating according to the radiated emission limits imposed by the product Standard of the class in which the equipment is framed: IEC 61000-6-1. Analyzing the values obtained for Quasi-peak during the test period, we noted that none of them exceeded the maximum allowed. The results were in satisfactory agreement with the limits imposed by CISPR 22 Standard, and have demonstrated that the equipment – in our case a Portable computer – works in optimal parameters, passing the radiated emission test.

The Influence of the Output Current Deforming Regime on the Input Current Harmonics for a Three-Phase Rectifier Bridge

29 January 2018Fără categoriecburada

Abstract

The present paper was created based on the desire of the author to realize a systemic approach of static converters in general and especially of rectifiers. Looked as system from energetic point of view, a rectifier could be represented “as a black box” without internal energetic sources. It is connected to external environment with an electric DC load and a power supply (mono-phase or three-phase). On the other side the electric current represents an ordered movement of electric charge carriers. In order to supply a certain current to the DC load, the electrons must be “transferred” by the static converter from power supply. Thus, a certain wave form of the current at the output can be obtained only based on some wave forms of the currents from the supply phases. The present paper answers to two questions: (1): does the modification of the spectrum of the load current produces the modification of the spectrum of the currents from the supply phases; (2):if yes, how it modifies the spectrum of the current from the supply phase, only in the magnitude of the basic harmonics, or it appears new harmonics? The paper proves the fact that the spectrum of the currents from the supply phases of the three-phased bridge rectifier depends on the harmonic spectrum of the output current. This dependence is materialized only on the change of the components of basic harmonic spectrum, without some visible new harmonics.

Control of Flow and Pressure in the Cooling Water Circuit of a Thermal Power Plant Using Fuzzy Logic

29 January 2018Fără categoriecburada

Abstract

Optimum operation of cooling water systems means minimum use of water while maintaining proper temperatures to limit algae growth and cool all equipment properly. Combined, the application of inverters and cooling water pumps brings us not only good energy-saving benefits but some new problems, such as inverter configuration and overload etc. The objective of this paper is to find a suitable solution by designing the intelligent controller for frequency control of cooling water systems, such as fuzzy logic and to investigate the controllability of this model under various changes of static head system. Based on the mathmatical model of puming systems with or without static head, the paper discusses some issues in detail, such as pressure and flow rate regulation. In fuzzy logic control, Mamdani model is used to control the system. The suggested system uses the concept of fuzzy logic system where the fuzzy rule base consists of a collection of fuzzy IF–THEN rules. The fuzzy inference engine uses these fuzzy IF–THEN rules to determine a mapping from fuzzy sets in the input universe of discourse to fuzzy sets in the output universe of discourse based on fuzzy logic principles. The fuzzy model can be successfully used for the variable speed control of hydraulic systems, when the Affinity Lows not observe exactly.

Analysis of Direct Current Motors in Dynamic Regimes Using Numerical Techniques

29 January 2018Fără categoriecburada

Abstract

The electromechanical converters and the electric drive systems where they are parts are generally nonlinear systems due to the nonlinear properties of the materials they are built from, as well as the multiple dependencies between their electrical, magnetical and mechanical parameters. However, under certain conditions (e.g. operation on the linear part of the characteristics), some simplifying hypo-theses are accepted, which allow the treatment of systems as linear systems. This simplifies their analysis and solutions could be obtained with acceptable errors. So the electrome-chanical converters and the electric drive systems can be analyzed as linear or nonlinear systems, depending on their properties and on the equations that govern them. Thus, analytical or numerical solving techniques can be used in order to obtain the solution, i.e. the variation in time of some electric, magnetic or mechanic quantities. In this paper a separately excited direct current motor that drives a me-chanical load is analyzed. The transient processes due to startup or sudden change of torque are analyzed both ana-lytically and numerically. Two techniques – namely numeri-cal solving using a Runge-Kutta method and respectively using an equivalent electrical scheme corresponding to the entire driving system – were used. By comparing the ob-tained numerical and analytical results a very good correla-tion between the different solving methods was proved. Thus, this paper offers alternative and viable analysis tech-niques, suitable for the dynamic regimes of the driving sys-tems with direct current motors.

Synthesis of the PID Algorithm for Control the Thermal Regime in the 3D Printer

29 January 2018Fără categoriecburada

Abstract

In this paper it is described the automatic system for formation the small pieces from polymer, based on the principle of thermoplastic extrusion and it is proposed the graph – analytical algorithm for identification the mathematical model of the control object first and second order inertia of the industrial process by the experimental curve of the transient process as response at the step signal applied to the entrance of the system.The procedure of calculation the approximation of the control object is based on the experimental curve of the process for which the output level is determined at the value of 0.632k and the respectively time. As control object is used the thermal stabilization regime in the extruder of 3D printer. The obtained results of identification are compared with results obtained in case of identification in MATLAB. For the obtained identified models was synthesized the PID control algorithm by the analytical methods and auto-tuning regime.