Category Archives: Fără categorie

Contributions to the Development of Complementary Equipment for the Romanian Anti-Hail System

29 January 2018Fără categoriecburada

Abstract

The method used in Romania for combating hail is the sowing of the clouds method, with missiles launched from the ground. This paper presents contributions of the University of Craiova, Center for Innovation and Technol-ogy Transfer in the development Hail Suppression System. The primary contribution was the complementary equip-ment that was necessary for developing the anti-hail system in Romania. Two of the systems that contain the anti-hail complementary equipment are showcased: the photovoltaic panels power supply system and the automatic positioning system for missiles launch ramp, respectively. The configu-ration of the accomplished photovoltaic system provides the power for the 12V, 24V, and 48V DC consumers and the 220V AC consumers as well. Likewise, this system can also function independently, interconnected with other energy sources (such as wind turbines, diesel generators, etc.), or synchronized with the national power grid. An energy man-agement system was created, to secure the energy required to launch the anti-hail missiles (high priority consumers). The energy management system controls and monitors the energy flow from the photovoltaic panels to the consumers, using a hierarchy of consumers algorithm. The automatic positioning system for anti-hail missiles launch ramps con-tains intelligent motor drives and a touchscreen human in-terface. Credited to the research work and the accomplished complementary equipment, the University of Craiova – In-novation and Technology Transfer Centre became part of “General designer of the anti-hail Romanian system”.

Design Optimization of an Asynchronous Motor Used in Light Railway Traction

29 January 2018Fără categoriecburada

Abstract

The appropriateness of this work is provided by highlighting some aspects insufficiently treated in the areas of designing and dimensioning of asynchronous traction motors associated with light traction static converters. The traction system is aimed for the light railway vehicles. Through the usage of asynchronous motors supplied by independent converters, the performances concerning the traction and the electric braking system are improved, while the maintenance expenses are reduced. The newly designed motor is aimed for the traction system of a locomotive driv-ing a multiple unit train, while the parameters necessary for the analysis of the regenerative braking system are also ac-counted for. An algorithm for the optimal design of the asynchronous motor is developed, considering the main parameters as the electric and magnetic quantities, the manufacturing and operating costs. The motor dimensions are computed starting from the values of the electromagnet-ic quantities resulted in the optimization process. The opti-mization algorithm is realized in Mathcad, any parameter modification leading to a new motor model. The main objec-tive of the paper is to optimally design the asynchronous traction motor directly rotating the drive wheel of the elec-tric train. The motor design takes into account the statio-nary rated regime, with the speed adjustment within wide limits, frequent starts and stops.

Aspects Regarding Operation of Power Supply System of Cars

29 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.

Dynamic State of Low Power Asynchronous Motors in Direct-on-Line Starting

29 January 2018Fără categoriecburada

Abstract

The research opportunity is explained by the results obtained in modelling and simulation of asynchronous motors, in the purpose of increasing their technical and economic performances when they operate in dynamic states. The study of the dynamic state is compulsory for low and very low power asynchronous motors which are used for driving industrial robots. In order to have simulation results, which are to be close to reality (those established experimentally), it is necessary to know the main inductance and the leakage inductance of the windings, their dependence upon the machine load, so upon the magnetic saturation. In this paper there are presented results, simulations and experimental tests are carried out in order to establish the errors which occur, for correcting the mathematical model used. With the help of the mathematical model presented in this paper, much complex dynamic states can also be studied, caused by the variation of the voltage, of the resistant torque, of the inertia moment etc. The starting characteristics have been computed considering magnetic saturation and current pressing, the results being: starting current Ip=4.208*IN, starting time tp=0.17s. It is considered that this study of asynchronous motor starting is justified, with an eye to obtaining some indications for their optimum construction and operation.

Estimation of Certain Power in Single-phase Network and DC Circuits

29 January 2018Fără categoriecburada

Abstract

Requirement of electrical energy is in order to operate various domestic and industrial devices like ap-pliances, equipment and machinery. Electrical energy per time unit represents electrical power transferred. Well knowing the electrical power is very important because of economical aspects. Electrical power, an important element of an energy system, which considers elements like harmon-ics and phase between voltage and current, influence the cost and elements component of electrical power grid. This paper presents the evaluation of mark-space method of elec-trical power system. This method represents a mathematical approach, simulation, and analog implementation solving the power measurement suitable for single-phase network and DC circuits. The schematics developed consist of well-known electronic circuits like the pulse width modulation (PWM), filtering with operational amplifier, and absolute value of signal. This approach avoids multiplying operations that aid error generating. The main purposes are to track the performance of such a circuit in different operating sit-uations and present the schematic. Thus, influence of phase between voltage and current, influence of waveform shape regarding result using analyzed method, and characteristic linearity are example of tests perform. The results con-firmed the theoretical principle being analyzed using specif-ic simulation programs like LTSpice or Scilab, but not re-stricted to them.

Hybrid Systems Modeling Approach with Petri Nets

29 January 2018Fără categoriecburada

Abstract

The purpose of this paper is to present the achievement of the Hybrid Petri Nets techniques used for modeling and behavioral analysis of a class of hybrid systems. In our sense, a dynamic hybrid system contains at least two distinct subsystems which interact: a continuous subsystem (linear, or not) and a discrete subsystem with a finite number of states. In this context, after a brief introduction to the basic elements of Hybrid Petri Nets modeling, two hybrid systems, consisting of liquid level control of one and two interconnected tanks were analyzed in different specific scenarios. The analysis starts with the synthesis of a Hybrid Petri Net model for each system, followed by their refinement and validation by simulation of their behavioral properties, in order to achieve and implement a command – control structure (the sequential controller) of the process. For the models synthesis and for their validation, Modified Hybrid Petri Nets were used. Such structure is a extinction of the classical topology of a generalized Hybrid Petri Nets model, achieved by assignation to every continuous transition a firing speed as a algebraic relation whose variables depend of different marking of continuous places, arbitrary or not. The synthesis of the models and their validation was obtained using Visual Object Net++ tool.

Diminishing the Computational Burden when Analyzing Electrical Signals with Long Wavelet Filters

29 January 2018Fără categoriecburada

Abstract

Wavelet analysis is characterized by filters with irrational coefficients and runtimes increasing with filters order. The terminal nodes of Wavelet Packet decomposition trees exhibit good harmonics’ selectivity when implemented with Daubechies wavelet mothers with filters of length 28 and respectively of length 40 (denoted in MATLAB by ‘db14’ and ‘db20’). Therefore they can be used for power quality (PQ) analysis of electric signals. When rounded to 4 decimal places, certain coefficients from these filters become 0. In the “rounded” context, the number of iterations sup-porting the convolution products involved by the Wavelet analysis is restricted. Based on the number of neglected co-efficients and length of wavelet filter, a formula is deduced for the percent runtime savings strictly associated to the wavelet decompositions. Statistical evaluations (considering sets of 20 consecutive programs executions) were performed considering full operational contexts, where all types of studied wavelets were involved in complex operations like evaluating PQ indices and harmonic spectra. The mean runtime savings proved to be 20.4% for ‘db14’ and respec-tively 23.2% for ‘db20’. The impact of rounding over the PQ analysis’s accuracy was evaluated considering three-phase waveforms acquired from a power group. The follow-ing quantities were considered: harmonic spectra and ener-gies of the Wavelet Packet tree’s terminal nodes, instanta-neous values corresponding to the fundamental frequency, vectors of details and approximations yielded by the Dis-crete Wavelet Transform and signals reconstructed from the vectors of details and approximations. Highly acceptable small errors were obtained, recommending the rounding to 4 decimal places of the analyzed wavelet filters as a faster reliable wavelet based analysis method.

Static Force Characteristic and Thermal Field for a Plunger-Type AC Electromagnet

29 January 2018Fără categoriecburada

Abstract

In this paper we propose an approach for the de-termination of static force characteristic of a plunger-type AC electromagnet using 2D numerical model developed in QuickField software and the determination of the thermal field. The attraction electromagnetic force is calculated us-ing Maxwell stress tensor method. The magnetic numerical model is an AC magnetics problem coupled with the coil electric circuit. The magnetic numerical model has been experimentally validated. The thermal field is determined in steady-state regime. The source term in the thermal model equation is calculated from the magnetic model data.

DC-Traction Substation with Improved Power Quality and Regeneration Capability

29 January 2018Fără categoriecburada

Abstract

In the DC-traction substations, the diode rectifi-ers are commonly used to provide the needed DC-voltage for vehicles. Unfortunately, they attract important issues of power quality, of which the most significant is the injection of harmonic currents into the AC power supply. Withal, the feedback of the recovered braking energy into the power supply is not possible. This paper is focused on the trans-forming a DC-traction substation with six-pulse uncon-trolled rectifier into an active substation, leading to substan-tially improved power quality and energy efficiency. These effects are obtained through an IGBT-based voltage source inverter with a proper control, connected between the DC-traction line and the power supply via a dedicated trans-former and specific interfacing circuits. The indirect current control is based on the concepts of the p-q theory of the powers and intermediate use of the synchronous reference frame, so that perfect harmonic cancellation is imposed even under distorted supply voltages. The conceived Matlab-Simulink model of the system for active filtering and regen-eration is presented and the simulation results illustrate very good performance in both operating regimes of the system. Experiments on a 30 kVA reduced-scale laboratory setup controlled and monitored by a dSPACE 1103 based platform verify the feasibility and effectiveness of the pro-posed scheme. Both the harmonic distortion of the current upstream the point of common coupling and the power fac-tor are significantly improved.

Testing a Filtering and Regeneration System on a Recuperative Stand

29 January 2018Fără categoriecburada

Abstract

The paper has three main objectives: the presen-tation of a laboratory model of a system for active filtering and regeneration (SISFREG) developed through an applied research collaborative project in the frame of Partnerships in priority area programme during 2014-2016; the presenta-tion of the methodology and design of recuperative testing structure and the presentation of few experimental results. SISFREG allows the conversion of the DC traction substa-tions into “active substations”. The laboratory model is composed of one configurable voltage source inverter (input voltage range 200-560 V DC; output voltage 3×400 V AC; rated power 30 kVA) adequately interfaced with the DC-line and properly controlled in closed loop. The control algo-rithm was implemented on the dSPACE 1103 system that allows the monitoring of the system too. The methodology and the testing structure configuration started from the actual conditions existed in a substation for DC traction. The experimental structure is based on the equipment avail-able in the laboratory and it contains: the equivalent of the transformer-rectifier traction group; the equivalent of the DC traction motors; the possibility of system to be con-nected, on the one hand, in the connection point of the trac-tion transformer, and, on the other hand, with the DC line (equivalent catenary). Finally, the paper presents several experiments conducted in accordance with the testing pro-tocol, the analysis of the experimental results and the re-sulted performance of the system, during both active filter-ing and regeneration operation modes.