Petre Marian Nicolae

Real-time analysis using discrete wavelet transform in power systems

The paper is concerned with the analysis based on the Discrete Wavelet Transform (DWT) of (non)stationary regimes in power systems under real-time operation constraints. Different techniques (some original, other provided by Matlab) are employed to perform decompositions using trees with 10 levels for a signal in stationary regime and respectively in a complex non-stationary regime, when most of the signals parameters are affected (shape, periodicity, magnitude etc). Power indices are calculated in both regimes with different methods, correlating the results with the energetic evaluations. The abilities of different methods to detect faults and respectively to deal with severe asymmetries are analyzed in various situations. Considering the results and other important criteria (run time, memory consumptions, perfect reconstruction), practical recommendations are made with respect to the selection of the fastest reliable DWT algorithm depending on the operating conditions.

Analysis and simulation of line notching attenuation for a static excitation system in a power system

This paper presents measurements of power quality indices for a static excitation system composed of a transformer and a controlled rectifier bridge in a power system generator group and the corresponding MATLAB/Simulink simulation. Replacing the old auxiliary excitation generator eliminates the disadvantage of using electrical machines with inertial moving masses and wear over time, but with the price of facing two important problems: the line voltage notching due to thyristor switching and the line current distorting. Theoretical aspects of line notching and several solutions for compensation strategies (and their limitations) are discussed. The MATLAB/Simulink model made possible the implementation of the solution selected to deal with these problems and to evaluate its effectiveness based on the results.

Designing and simulation of an active filter using MATLAB / SIMULINK

The paper deals with a solution for the compensation of a distorting regime from a distribution station for urban transport using a power active filter. Firstly the distorting regime is analyzed with a data acquisition system that provides the input data for the MATLAB/SIMULINK program used to size the active filter. The calculated parameters are afterward validated in MATLAB/SIMULINK. Experimental data obtained on stand validate the proposed solution.

Direct-Flux Vector Control of induction motor for light traction

The paper presents a Direct-Flux Vector Control (DFVC) scheme suitable for induction motors employed in light traction applications. In such applications, deep flux weakening is required, and the maximum torque production must be obtained under current and voltage constraints. The mathematical model of the control scheme is discussed and the implementation issues are analysed. Experimental results are presented for a small power induction motor, showing the feasibility of the proposed control, with a particular focus on the robust flux-weakening operation.

Practical aspects on the improved DC driving system used in electric urban traction

The paper presents some practical considerations and experimental results obtained by the exploitation of a tram that has an electric driving system with an improved technological solution. One presents the technological solution using chopper that substitutes the initial accelerators of the tram. Some aspects concerning the operation in running and respectively in braking regimes in the new configuration (including the regenerative braking regime) are discussed. Some considerations with respect to the electromagnetic compatibility problems and modalities to improve it are made. The recordings of the current and voltage waveforms, during the normal running stage, when the tram climbs a ramp and respectively goes down on a slope are presented and explained. The experimental determinations revealed that the system was designed correctly, in order to support all the operational conditions that could appear in its exploitation.

Ensuring the security of the energy system by predetermining the size of inrush current at power transformers coupling

The current shock occurring when connecting the transformers to the mains can lead to electrical and mechanical stress in transformers, which can cause failures compromising the reliability of the power system the equipment (transformer) is part of. In order to prevent the occurrence of major failure at the level of the power system, the project we propose aims at detecting the size and the time of occurrence of the transient current as early as the design stage. Aimed at ensuring the reliability of the power system, for predetermining the size of the transient current occurring when connecting the transformers to the mains, a mathematical model of the transformer was developed, which was validated through tests (simulations, measurements) in order to determine the electrical stress of the transformer. The test was carried out on a 15 MVA, 10.5/6.3 kV transformer, starting from its magnetization parameter. The modeling of the phenomenon occurring when connecting the transformer to the supplying network was achieved using MATLAB software, and the results obtained thereof were similar to those obtained from laboratory experimental measurements.

Analysis of a parabolic antenna with fed

This paper comes to support choosing a type of parabolic antenna for RF distributors. To do that, authors was done a series of analysis on the paper with purpose of finding an optimum solution. One of those analysis was to find a distance from the LNB to antennas reflector. This distance was varied from 0 to 1m. On the same analysis was done another analysis, to determine that are the most favorable design for parabolic antenna (from concave to off-set). The distance that was varied was from 50 mm to 300 mm and the diameter remains constant, 1200 mm. As compared results was set gain and return loss. The frequencies of the antenna was also varied from 10 to 14 GHz. At the end, results was validated with dates from a local supplier of RF services. To accomplish those analysis, authors used ANSYS 14.5 with the latest modules such ANSYS HFSS 15 and ANSYS Design Modeler. For optimization was used ANSYS Optimetrics and ANSYS Design Exploration. All those products could be brought together with ANSYS WORKBENCH, the common environment for all ANSYS products.

Analysis and simulation of distorting regime compensation for a static excitation system in a power system through passive filtering

This paper presents measurements of power quality indices for a static excitation system composed of transformer and controlled rectifier bridge in a power system generator group and the corresponding MATLAB/Simulink simulation. Replacing the old auxiliary excitation generator eliminates the disadvantage of using electrical machines with the mass in motion inertia and wear over time, but with the price of facing two important problems: the line voltage notching due to thyristor commutation and also the distorting of line current. Theoretical aspects of line notching and several solutions for compensation strategies and their limitations are discussed. The MATLAB/Simulink model allows us to implement the solution we chosen to deal with these problems and observe its effectiveness based on the results.

2D electromagnetic transient and thermal modeling of a three phase power transformer

The purpose of this study is to validate an already designed three phase power transformer with some advanced ANSYS modules, such ANSYS Maxwell 2D and ANSYS Mechanical, for three types of charging (minus tap position - rated parameters, medium tap position - 50% and maxim tap position - 100%). On the same time, it can be seen the 2D magnetic nonlinear behaviour of this three phase power transformer and thermal effects for the ferromagnetic core. Also it can be found the magnitude of B field, the regions with problems and the value of the total core losses for the same transformer. It has used the latest versions from ANSYS, Workbench 14.5, ANSYS Mechanical and Maxwell 2D v.16.

Direct flux vector control for dual-three phase induction motor drives

The paper deals with the analysis, design and implementation of a field-oriented vector control system for a dual-three-phase induction motor for low DC link voltage applications. The issues addressed in this paper include: the advantages of dual-three-phase induction motors, the modeling of dual-three-phase induction motor, Pulse-Width Modulation (PWM) techniques for Voltage Source Inverters (VSI); Field Oriented Control (FOC) and Direct Torque Control (DTC) strategies for dual-three-phase induction motors. The experimental results, obtained for a dual-three-phase induction motor drive in a test laboratory, are included in the paper.