Category Archives: Fără categorie

Computing of Phase Shift for Coupled Oscillators through a Two-Port Passive Network

Abstract 

Voltage controlled microwave oscillators are used in digital communication systems. Pairs of coupled and synchronized voltage controlled oscillators are used to control the phase in microwave antenna arrays as an alternative to other methods. A particular phase shift can be obtained by choosing the free-running frequencies of the oscillators in the array. The aim of this paper is to analyze such a pair of coupled oscillators by targeting the phase shift between their output voltages, the coupling circuit being a passive two-port passive network. For this purpose, we use our computer-aided analysis tool ANCSYAP (ANalog Circuit Symbolic Analysis Program) capable to build the symbolic expressions of desired network functions or global parameters (as input/output/transfer impedances and admittances, fundamental or hybrid parameters) and to find the resonant frequencies of any two-port network as function of global parameters. The analysis is performed both in time domain and in frequency domain and in this way we can compute the shift phase analytic expression. To prove the procedure, we include two relevant examples. images

Harmonics Analysis Using DFT

Abstract 

Harmonics analysis is established by international standards as well as national norms [6], [7]. There are also definitions and calculus relationships for the indicators considered representative for this non quality aspect of the electric power. Among the harmonics analysis methods, the authors have dealt with application of DFT, given the fact that were to be analyzed acquired waves experimentally, using data acquisition boards. Experiences in using DFT, difficulties and highlighted errors as well are materialized in this paper, which is of great use to practitioners in this field.

Next, there is made a distinction between the a.c. and d.c. current waves in defining the harmonics indicators, which gives accuracy and expressivity to the harmonic analysis.

images

A Geometrical and Numerical Study of the Main Sizes of the Lotka-Volterra Models

Abstract 

The blend of geometry and numerical analysis that is taking place in the present material produces a subject with can gives a lots of detail and richness for the case of dynamical models arising in mathematics, science and engineering. The goal of this paper is the geometrical and numerical study of the main sizes of the mathematical models of the multispecies interactions which are important in determining long-time dynamics, based on the application of various notions from the theory of  dynamical systems to the numerical approximation of initial value problems over long-time intervals.  The numerical methods are widely used for the study of complicated temporal behavior of dynamical systems, in order to approximate different types of invariants sets or invariant manifolds and also to extract statistical information on the dynamical behavior in the computation of natural invariant measures or almost invariants sets. The present study is a interplay between dynamical systems geometrical theory and computational calculus of dynamical systems, knowing that the theory provides a framework for interpreting numerical observations and foundations for efficient numerical algorithms. We perform a computational study for the case of four important examples: prey-predator 2D Lotka-Volterra system, Bailey model for the evolution of epidemics, classical Kermack-McKendrick model of evolution of epidemics and the  prey-predator 3D Lotka-Volterra system. images

Improving the Shunt Active Power Filter Control Methods under Distorted and Unbalanced Grid Voltages

Abstract 

For a proper operation of the shunt active power filters, the current reference detection method must be robust. This means it must extract correctly the fundamental frequency even if the grid has distorted and unbalanced voltages at the point of common connection. The most used reference current detection methods for shunt active power filters are analyzed and compared in this article, theoretically and through simulations in MATLAB/Simulink. One used criteria like settling time, transient performance, THD of reference and compensated grid current, overshoot and unbalance. Some practical aspects of hardware implementation and shunt active power filter design considerations are also discussed. Measured data, acquired with a dedicated data acquisition system provides the parameters required for a non-ideal real system simulation, namely a static excitation system of a power generator group. The simulated system consists of a transformer which feeds a Silicon Controlled Rectifier bridge. The Matlab/Simulink models allows for testing of the reference current detection methods implementation and improvement for dealing with problems arising with distortion and unbalance of mains voltages. Because the active power filter is a complex system, the reference current detection methods are studied with their dependencies, for example the different strategy to deal with voltage distortion and unbalance. The current controller and hardware setup are preserved. The study contributes to the existing comparisons in specialized literature by testing their weaknesses in distorted and unbalanced PCC voltages and may be useful in future hardware implementation. images

Coupled Magneto-Thermal Model for an Encapsulated Busbars System Using QuickField

Abstract 

In this paper, we propose an approach for the magnetic and thermal modeling of an encapsulated busbars system, in three-phase execution, for high voltage using QuickField software. The paper proposes a numerical model developed by coupling of the magnetic field problem with the stationary and transient heat field problems for the geometry of a three-phase execution busbars system with common shield. The coupling of problems is realized by importing specific losses from the magnetic field problem as heat sources for thermal field problem. The magnetic field problem is also coupled to the electrical circuit. The electrodynamic forces that occur between conductors in the presence of the ferromagnetic shield have different values compared to those that occur in an unshielded system. In the model it was taken into account the variation of electrical conductivity with the temperature. The global heat transfer coefficient by convection and radiation used in thermal model was estimated using the power losses computed by magnetic model. When evaluating the global heat transfer coefficient was taken into account the temperature dependence of the physical properties of the air. There is a good agreement between numerical and analytical temperature values. The paper analyzes the results for two materials used to build the shield, iron and aluminum. The presented model can be used for analysis, design and optimization of three-phase busbars system with common shield. images

Improving Efficiency of DWT Analysis through Faster Interpolation Methods and Multithreading Techniques

Abstract 

The paper deals with techniques to accelerate the DWT power quality analysis. A brief description of a non-spline interpolation schematic is provided firstly. It is used for the evaluation of the first components near the right border of the signal. Comparisons were made between power quality indices, shape of details waveforms and runtimes, considering data acquired on stand, corresponding to a driving system using chopper and DC motor and respectively waveforms acquired from the secondary winding of the excitation system used to supply a generator. FFT and 3 distinct original functions were used for comparison. Similar results were generated by all methods. The spline-free interpolation technique, which used mean slopes, proved to be a better option when the analyzed signal’s periodicity is questionable, because it exhibited halved runtimes as compared to the spline interpolation technique. Two multithreading techniques, relying on a horizontal and respectively on an interleaved schematic, were afterward analyzed considering their performances relative to the DWT decomposition and respectively re-composition of single-phase currents or voltages. The analyzed filters had different lengths: 4, 6 and 8. 10 sets of 300 consecutive decompositions of signals consisting in 36864 samples were used as input data. Our Java programs implementing the horizontal technique revealed the diminishing of runtimes for all analyzed filters during the decompositions by 16%…23%, the technique being more efficient for shorter filters. Another multi-threading technique, relying on an interleaving schematic, was considered for the reconstruction of signals. It proved to be non-effective, revealing increases of runtimes in the range 19%…23%. Similar results were obtained with the horizontal technique. Finally a multithreading technique, relying on a vertical schematic is presented. Using it, savings of 45% of runtimes were revealed by tests made on three-phase systems.

images

Experimental Evaluation of Induction Heating Systems with Phase-Shift Voltage Resonant Inverter

Abstract 

This paper is devoted to the synthesis of the power control loop for a single-phase resonant inverter controlled by phase shift and used in an induction heating system. It starts from the assumption that, if the inverter control frequency is close to the resonance frequency of the assembly consisting of the compensation capacitor, inductor and heating piece, the current supplied by the inverter contains almost only the active component that determines directly the power transmitted to the inductor. After establishing the structural scheme and highlighting the transfer function, a PI controller is adopted for the control of the current through the inverter. The inverter active current is achieved by a Proportional-Integral controller tuned in accordance with the Modulus Optimum criterion in Kessler variant. Next, different experimental tests are presented in order to determine the performances of the induction heating system. The objectives of the tests were: the verification of the proper operation of the current through inverter control loop, the achievement of zero-current switching, the  control of the power transmitted to the load by adjusting the inverter frequency and the determining the efficiency of the  converter-inductor-pipe system. images

Magneto-Thermal Model for Crimped Connections

Abstract 

In this paper numerical results coresponding to thermal regime of two types of superposed crimped connections has been obtained. The samples studied use copper wire crimped by two methods: the first method uses one crimp indents and the second method is with two crimp indents. The ferrule is a parallel one type. A 2D model of crimped connections has been created in QuickField Professional to obtain the numerical results. For obtaining temperature values, a coupled problem AC Magnetics – Steady-State Heat Transfer was solved. Numerical simulations were made considering the next values for electrical current intensity: 510 A,  682 A, 855 A, until the steady state regime is established. First, the AC Magnetics problem was solved to obtain the specific Joule heat. Then, the source term was imported in steady state heat transfer problem to solve it. Joule Heat and temperature values are presented and discussed. An important parameter in numerical simulations is heat transfer coefficient which depends on overtemperature. Knowing heat transfer coefficient law and using in numerical simulation can be obtained the real numerical temperature values. The temperature dependence of global heat transfer coefficient has been taking into account into numerical simulations. Finally, obtained numerical results are discussed and proposals are made. images

Control of a Single-Phase Active Filter Using Triangular Carrier and Hysteresis Switching in MATLAB/Simulink

Abstract 

The paper deals with MATLAB/Simulink models of single-phase active filters used for reducing the harmonic level and electromagnetic interference and to get compliance with the power quality standards. Four cases are modeled and studied in order to design and tune the best configuration for the active filter. Two of them are determined by the configuration of the load, which consists of a single-phase rectifier which feeds a resistive load, having a capacitive dc filter as a first setup and an inductive dc filter as the second setup. The single-phase active filtering system is based on a single-phase Voltage Source IGBT inverter with dc-link capacitor and a complete current control system that uses two different pulse-width modulation techniques. The two switching techniques, triangular carrier and hysteresis, determine the third and the fourth cases. The power quality and the existing standards are discussed, including the disturbances in a power system for a single-phase rectifier. The harmonics, how they are generated, and what problems they may introduce in the power system, are presented. The reference current for the power active filter is generated by the means of a resonant sinusoidal signal integrator filter implemented with a transfer function block. All simulations performed in MATLAB/Simulink validate the theoretical considerations but not all of them reveal a good agreement with the existing standards. The sinusoidal signal integrator integral coefficient it’s tuned in order to obtain a good compromise between grid THD current and transient response to load change. The results are interpreted and centralized so they can be useful in possible hardware implementation.

images

Power Control Assessment in Induction Heating Systems with Voltage Source Inverter and Resonant L-LC Load

Abstract 

The attention in this paper is directed to the power control in an induction heating system for seamless pipes consisting of a single-phase voltage source inverter with L-LC resonant load supplied by a three-phase full controlled bridge rectifier. The maximal power transfer from the inverter output to the work piece is ensured by the proper design of the matching inductor. The power control is achieved through the inverter output current by making use of a Proportional-Integrator-Derivative controller designed according to the Modulus Optimum criterion in Kessler variant. An experimental platform based on dSPACE DS1103 control board is used for the practical implementation of the control system. It works together with Matlab/Simulink environment and the conceived graphical user interface allows interacting with the experiment. The experimental setup of the induction heating system is presented and the assessment of the control system performance under different tests is performed. Depending on the prescribed value of the inverter output current and the imposed operating frequency, different situations may occur. The possibilities of diminishing the switching losses through zero-current switching and of increasing the power when the operating frequency is over the resonance value are also pointed out. All the results illustrate the proper operation and good performance of the control system. images