José Roberto Cardoso

Identification of the Jiles–Atherton model parameters using random and deterministic searches

Abstract The five parameters of the Jiles–Atherton (J–A) model are identified using a simple program based on the Matlab platform which identifies the J–A parameters automatically from experimental B – H hysteresis curves of magnetic cores. This computational tool is based on adaptive adjustment of the J–A model parameters and conjugates its parametric non-linear coupled differential equations with techniques of simulated annealing.

Coupling electric circuit and 2D-FEM model with Dommel's approach for transient analysis [of EM devices]

Dommels approach applied to simulate the electrical parameters in a transient analysis of electromagnetic devices, such as electrical machines and transformers, is presented in this paper. Equations of electric circuit and equations of magnetic fields are taken into account by simultaneously coupling nodal analysis and 2D FEM. The inductances and capacitances are treated like one-dimensional finite elements leading to a symmetrical matrix solved by a step-by-step technique. The formulation was validated by comparing numerical results and experimental data.

FEM modelling of grounded systems with unbounded approach

This paper presents a GROUND-3D update which allows the modelling of grounded systems by 3D-FEM. We have developed a formulation in order to represent the remote point without shortening the domain as in the traditional approach. Accuracy is improved, and the number of unknowns arising from the FEM formulation is significantly reduced as well. We can model large substation grounded meshes with microcomputers by using the mapping presented here. >

Control strategies of doubly fed induction generators to support grid voltage

The use of wind power has been increasing very fast in the last 10 years. Many new projects for the next 10 years including offshore and onshore wind farms are been developed and planned. The fast growing of the use of wind power has brought new challenges to the Transmission System Operators (TSO) in regions where wind power has reached significant penetration levels like Denmark, United Kingdom, Spain and Germany. According to new grid code requirements wind turbines must remain connected to the grid during grid disturbances and, moreover, they must also contribute to voltage support during and after grid faults. Dynamic models of doubly fed induction generator (DFIG) were developed to investigate the behavior off different converter control and protection strategies of the back-to-back IGBT-based converters during grid fault. The results have showed that reactive power injection by DFIG-based wind farms is limited when the rotor side converter is blocked.

Modified nodal analysis applied to electric circuits coupled with FEM in the simulation of a universal motor

In the last few years, several papers considering the finite element method coupled with electric circuits were published. Many of these works have been used the theory of mesh analysis to analyze the electric circuit. However, when we use a circuit with many current and voltage sources, it is not always easy to use this analysis. Aiming to avoid this problem, this paper presents the application of the modified nodal analysis in the analysis of coupled circuits, as a continuation of the previously presented work, where the use of nonlinear ferromagnetic devices was not considered. The analysis of a universal motor at stall is presented to validate this new approach.

The element-free Galerkin method applied to the study of fully developed magnetohydrodynamic duct flows

In this paper, the meshless method is introduced to magnetohydrodynamics. A numerical scheme based on the element-free Galerkin method is used to solve the laminar steady-state two-dimensional fully developed magnetohydrodynamic flow in a rectangular duct. Accurate and convergent solutions are achieved for low to moderately high Hartmann numbers.

Design Considerations for Achieving High Radial Stiffness in an Attraction-Type Magnetic Bearing With Control in a Single Direction

In past work, the authors have proposed a radial magnetic bearing architecture where the rotor was kept suspended only by means of magnetic forces produced by permanent magnets working in attraction mode and the rotor was actively controlled only in one degree of freedom (d.o.f.), i.e., its axial direction. Although the presented architecture is simpler than those bearings with active control in two or more d.o.f., it presented limitations mainly of low radial stiffness. So, in this context this paper discusses ways to enhance the radial stiffness in this kind of bearing and presents simplified analytical methods used to find magnets and actuator optimal dimensions that gives both ring magnets radial stiffness and actuator force/current ratio maximum intensities.

Analysis of a Three-Phase LSPMM by Numerical Method

Line-start permanent magnet motor (LSPMM) is a very attractive alternative to replace induction motors due to its very high efficiency and constant speed operation with load variations. However, designing this kind of hybrid motor is hard work and requires a good understanding of motor behavior. The calculation of load angle is an important step in motor design and can not be neglected. This paper uses the finite element method to show a simple methodology to calculate the load angle of a three-phase LSPMM combining the dynamic and steady-state simulations. The methodology is used to analyze a three-phase LSPMM.

Optimization of grounding grids by response surfaces and genetic algorithms

In this paper, we use an optimization technique based on the creation of response surfaces and the application of genetic algorithms to minimize the number of conductors of grounding grids, guaranteeing the safety levels defined by the maximum touch potential.

Finite element analysis of anisotropic optical waveguide with arbitrary index profile

This work presents the application of a scalar finite element formulation for E/sup x/ (TE-like) modes in anisotropic planar and channel waveguides with diagonal permittivity tensor, diffused in both transversal directions. This extended formulation considers explicitly both the variations of the refractive index and their spatial derivatives inside of each finite element. Dispersion curves for E/sup x/ modes in planar and channel waveguides are shown, and the results compared with solutions obtained by other formulations.