Category Archives: Fără categorie

Monitoring and Analysis of the Electrical Parameters for an Industrial Consumer using LabVIEWEnvironment

14 December 2016Fără categoriecburada

Abstract

This paper presents a case study for monitoring the quality of electric energy in an industrial consumer. The measurements were carried in the power supply point where the quality of the electric energy is influenced by the activity of the manufacturer, the transmission and distribution provider, the supplier as well as the electric power consumer activity. Transients occur at this limiting point, with negative effects on the consumer, as well as on the electric power supply network. There are two types of electric energy quality indicators, depending on the point of occurrence. Primary quality indicators are given by the production, transport and distribution of electric energy. Secondary indicators are given by the disruptive operation of industrial consumers. The data processing was achieved using LabVIEW software in terms of the two types of quality indicators. Based on the data obtained from the measurements and using the interface created in LabVIEW, it was possible to carry out the analysis of the average hourly consumption, the power factor, the wave forms of the current and voltage, the analysis of the current and voltage harmonics. The software application enables creation of customized reports with varying ease of use and flexibility. Using the software application developed in LabVIEW, full quality analysis of electric energy can be done at the user’s premises.

Simulation and Implementation of Sensorless Control Using Estimators in Electric Drives with HighDynamic

14 December 2016Fără categoriecburada

Abstract

In this article we’ll tackle the control of electric drive with high dynamic, with rapid changes in torque and speed, where the control strategy is FOC (Field Oriented Control). In the surface mining industry, from which the electric drive application for this article is selected, the general trend is toward using asynchronous motors with shortcircuit rotor, due to the advantages of this motor both in terms of design and operation. In order to achieve the variable speed, must be used the static frequency converters. Simulations were carried out using a converter with FOC control strategy and a 45kW motor. The simulations also followed the direction from simple to complex in order to emphasize both qualitative and quantitative elements with respect to the overall dynamic behavior. Simulations were carried out both in the case where the overall structure contains an encoder for speed information, and where the sensorless approach is used the implementation of an estimator is strictly necessary. Such cases were dealt with where speed is measured directly with an encoder, compared with the case of sensorless control, where speed is estimated using a Model References Adaptive Control Estimator. Simulations were carried out in MATLAB/Simulink environment, highlighting the control structures and comparative results achieved for a drive application commonly used in surface mining industry. Following these directions a functional application was implemented and tested.

Improving the Power Quality and Controllability of PV Power Plants for Microgrids Integration

14 December 2016Fără categoriecburada

Abstract

This paper deals with the implementation of the control strategy for a three-phase voltage source inverter (VSI) system with the purpose of improving the power quality and controllability of photovoltaic (PV) system for microgrids (MGs) integration by means of energy storage system. The proposed model comprises of a PV power plant with an energy storage system coupled to the grid by means of a VSI. The PV system and the battery storage are integrated with the help of DC-DC and DC-AC converters in such a way that bidirectional flow of active and reactive powers can be achieved. The required power for the connected loads can be effectively delivered and supplied by the proposed PV system and energy storage systems, subject to an appropriate control method. The ultimate goal of any power system is to maintain a balance between demand and supply of active power at any set point in time. Controllers integrating energy sources respond to the received signals and attempt to fulfil the grid demand. The system response is almost instantaneous and thus can be very helpful in grid frequency and voltage support. The grid voltage harmonic generation influences the PI current controller and generates current harmonics; the used harmonic compensator is effective for both positive and negative sequence fifth and seventh harmonics. The proposed control system is validated by means of simulation results.

Energetic Analysis of the Drying Process of Cur-rent Transformers from 110 kV Ciungetu Power Station

14 December 2016Fără categoriecburada

Abstract

Currently, at company Hidroserv Râmnicu Vâlcea, the drying of current transformers used in power transformer stations is done by a combination between induction and conduction heating at the frequency of 50 Hz. Obviously, this solution is outdated in terms of technology and the performed energetic analysis proves it. In order to achieve the design of a multifunction static system intended to replace the existing one, so as to respond as best as possible to the specific needs, it is necessary to analyze the drying process from energetic point of view. The knowledge of the equivalent parameters of the loads is needed too. To substantiate the feasibility of this new technical solutions, the goal of the paper is the analysis of the actual technology from energetic point of view. Considering that the current transformer of the 110 kV power station Ciungetu is the typical load, experimental determinations relating to the its drying process have been performed. Two heating coils are used, of 33 turns and 38 turns, respectively. In order to determine the associated parameters for both coils, the current and voltage across the equivalent induc tor have been recorded by using an oscilloscope Tektronix TDS3000. It is obvious, and the performed energetic analysis demonstrates this, the solution currently used is outdated in terms of technology.

Development of a Barrier Structure Actuated by Three Shape Memory Alloy Springs

14 December 2016Fără categoriecburada

Abstract

In this paper, the authors present an experimental analysis in order to highlight the behavior of a barrier structure model, actuated by three shape memory alloy (SMA) helical springs. The authors have developed this new barrier structure to increase the performances of conventional barriers, based on SMAs unique properties and their advantages. SMAs are advantageous for actuation because of their light weight, silent operation and flexibility. SMAs began to be increasingly present in industrial applications as well because they display high reliability and can replace the functions that make the motors or complex gears despite their simple construction. The actuator used in our model works as a linear actuator, contracting itself with great strength and speed, thus exerting the necessary force to lift the barrier arm when the SMA springs are heated by carrying an electric direct current. The designer can control the direction of actuation, the amount of force generated and the stroke of the actuator through various combinations that he can achieve with these three SMA springs. After a description of the accomplished model and of how it works, the authors present an experimental analysis of the behavior displayed by the SMA springs-based barrier structure. The experiments consisted in the determination of the SMA spring functioning time periods at constant value of the SMA spring activating electric current, and while maintaining the barrier arm stroke and weight constant.

Some Considerations Concerning Radiated Emissions Produced by a Board Display

14 December 2016Fără categoriecburada

Abstract

The paper presents some considerations related to the radiated emissions from automotive area of interest. Firstly the equipment used for tests dedicated to radiated emissions is presented. Afterward some considerations on the test equipment, used in a semianechoic chamber are made. Characteristics of the horn antenna used to accomplish tests dedicated to radiated emissions within the range 0.8…1.6 GHz, along with some aspects related to design and simulation are also presented. The analysis of the electric field in the antenna and respectively of the electric field distribution in the remote field area was performed for three different frequencies (1.2GHz, 1.4GHz, 1.6GHz). Tests conditions are also described. Discussions are made with respect to the recorded data. The results of tests concerning the radiated emissions for a board display are presented, both for the horizontal and respectively vertical polarizations. Tests were made firstly for the initial hardware structure and problems related to the vertical polarization were noticed. Measures to improve the display operation are analyzed. Results of tests after the application of improvement measures are presented. Conclusions related to the improvement of the board display operation are deduced.

Power Control and Energetic Performances of an Induction Heating System Destined for Drying of Current Transformers

14 December 2016Fără categoriecburada

Abstract

This paper is concerned with the design of the power control system for a single-phase voltage source inverter feeding a parallel resonant induction heating load and the analyse of its energetic performances. The control of the inverter output current, meaning the active component of the current through the induction coil when the control frequency is equal or slightly exceeds the resonant frequency, is achieved by a Proportional-Integral-Derivative controller tuned in accordance with the Modulus Optimum criterion in Kessler variant. The control system response, in terms of the rms current at the inverter output when a prescribed step current is applied, shows that the dynamic and static performances are very good. In the second part, the paper presents the energetic performances of a proposed system for drying of current transformer from 110 kV Ciungetu power station. First, based on the actual technical solution and experimental recording of voltage and current, the equivalent parameters of the load circuit have been determined. In the proposed solution, the drying process is based on an induction heating system that contains a halfcontrolled rectifier and a voltage source inverter that operates with resonant load. The energetic performances have been determined in order to ensure zero-current switching of the inverter.

New Aspects on the Frequency Splitting and Bifurcation Phenomena in Wireless Power Transfer Systems

14 December 2016Fără categoriecburada

Abstract

This paper focuses on the frequency splitting and bifurcation phenomena that appear in the wireless power transfer systems. These two phenomena are analyzed for different possible configurations of the magnetically coupled circuits of the system, through electric circuit methods and mathematical calculus. Considering two printed spiral coils with similar geometrical properties, the study started with a calculus of the splitting frequency. It was made for the series-series connection, but also for series-parallel, parallelseries and parallel-parallel connections. The graphical representations of the load voltage as function of the frequency revealed that this phenomenon is visible only for the series-series and series-parallel connections; even if one or two peaks appear in all cases they are not directly connected to the frequency splitting phenomena, respectively to the spitting factor. The bifurcation phenomenon is analyzed starting from the bifurcation equation defined for the input admittance of the wireless power transfer system. The four types of configurations are analyzed from the graphical representations of the imaginary part of the admittance as function of the frequency. Because an important factor in the frequency splitting and bifurcation phenomena appearance is the ratio between the input resistance and the load resistance, in the last part of the paper the splitting coupling factor as function of the input resistance – load resistance ratio is depicted. The paper brings new contributions in the field through a comparative study on the frequency splitting and bifurcation phenomena for all the four types of configuration of the wireless power transfer systems. Through mathematical calculations, formulas for estimating the frequency (angular frequency) of occurrence of each phenomenon are obtained. The results are validated by comparative simulations related to a system of identical spiral coupled coils. The results of the analysis were commented comparatively and some conclusions could be drawn.

On the Implementation of FBD-Theory Concepts in the Control of Active DC-Traction Substations

14 December 2016Fără categoriecburada

Abstract

This paper is focused on the transformation of a classical DC-traction substation with twelve-pulse uncontrolled rectifier into an active traction substation by adding a dedicated system for active filtering and regeneration called SISFREG. The connection of SISFREG to the ACside is performed in the primary of the traction transformer via a passive coupling filter and a recovery transformer, whereas an active separating circuit ensures the connection to the DC-traction line. The new functions added to the DCtraction substation lead to the increasing the energy efficiency of the whole system in both traction and braking regimes of the vehicles’ traction motors. The control of the current provided by the shunt active filter, which is the main component of SISFREG, is achieved in indirect mode, by means of the current upstream the point of common coupling. In the generation of the set current, the concepts of the Fryze-Buchholz-Depenbrock theory are implemented. Thus, an active current is always imposed at the power supply side and the current control loop guarantees almost sinusoidal current and global unity power factor. A complex Simulink model of the whole system, including facilities for energetic analysis, has been developed and the simulation results show good performances in both steady-state and dynamic regimes.

Evaluating RMS of Linearly Variable Magnitude Waveforms by Using FFT and WPT. Theory and Practice

14 December 2016Fără categoriecburada

Abstract

The paper deals with the evaluation of the Root Mean Square (RMS) indices of signals with linearly variable magnitude by using Wavelet Packet Transform (WPT) and Fast Fourier Transform (FFT). Firstly there is presented a synthesis of employed techniques and previous results of the authors with respect to synthetically generated singleharmonic signals. The signals had linearly decreasing/increasing magnitude M. M varies according to a constant slope G. The studied absolute difference between the final and initial values of M belongs to the set {2,5, 5, 7.5 and 10}% from the initial M. Results of the RMS evaluation by using both FFT and WPT in a single harmonic approach are recalled, focusing on the maximum absolute values of percent relative errors. New studies are presented now, firstly considering randomly generated synthetic multiharmonic signals. Three cases are considered, corresponding to harmonic orders belonging to 3 distinct ranges: 3…9, 31…39 and respectively 3…40. The errors associated to the use of FFT and WPT are evaluated for them. Two real multi-harmonic signals are afterward analyzed. Small differences were noticed between the values yielded by FFT and WPT for the total RMS as compared to those computed with Riemann sums. The differences between the RMS yielded by FFT and WPT are also evaluated and discussed.