Tiberiu Tudorache

Methods for cogging torque reduction of directly driven PM wind generators

This paper deals with several methods for the reduction of cogging torque in case of low speed permanent magnets wind generators. The first analyzed method consists in asymmetrical spacing of the permanent magnets on the rotor outer surface. The second method consists in using close stator slots that determines a nearly isotropic magnetic stator structure. The last investigated method consists in stator skewing. The smallest cogging torque results however were obtained by combining closed stator slots with the other two studied methods. The proposed solutions for cogging torque reduction are analyzed by means of 2D/3D finite element models developed using the professional Flux software package. The numerical results are discussed and compared with experimental measurements.

Permanent-Magnet Synchronous Machine Cogging Torque Reduction Using a Hybrid Model

An optimally designed permanent magnet synchronous machine (PMSM) is characterized by low cogging torque (CT) peak value. The reduction of this quantity requires in many cases a series of optimization calculations for finding the best geometrical configuration of the machine. A coupling between optimization algorithms and finite element (FE) analysis for optimizing the PMSM geometry is a very time consuming task. This paper presents a time saving model called “hybrid” (numerical-analytical model) combined with optimization algorithms to reduce CT peak values of a given PMSM. After implementing the proposed optimization procedure in Matlab environment, it is successfully used for the CT reduction of a given PMSM equipped with asymmetrically spaced permanent magnets.

Finite Element Analysis of Self-Excited Induction Generator for Isolated Small Power Wind Turbines

This paper deals with the field-circuit type finite element analysis of the dynamic regimes of the three-phase squirrel cage induction generator used in the isolated small power wind conversion systems. The numerical analysis of the squirrel cage induction generator using circuit models may lead to inaccurate results due to the usual simplifying hypotheses. This paper proposes a field-circuit model of the machine that is much more elaborated, being able to successfully take into account the complex specific phenomena such as: magnetic saturation, skin effect in the rotor bars, teeth harmonics etc. Among the dynamic regimes specific to the operation of the induction generator integrated in the isolated wind conversion systems, this paper is focused on the following aspects: self excitation phenomenon in case of open-circuit, three-phase short-circuit and dynamic response of the generator in case of load variations.

Magneto‐thermal‐motion coupling in transverse flux heating

Purpose – This paper aims to deal with the 3D finite element analysis of metallic sheets heating in translating motion through the air gap of an inductor of transverse flux type.Design/methodology/approach – This study presents two finite element based motion coupling techniques used to analyze the transient temperature field of moving metallic sheets heated by induction.Findings – The numerical results obtained by the two different magneto‐thermal – translating motion coupling techniques proposed in this paper are in good agreement with each other being validated also by experimental measurements.Practical implications – The proposed numerical techniques can be used for the design and optimization of transverse flux induction heating systems.Originality/value – An original solution to improve the transversal thermal profile of the metallic sheet based on the magnetic shielding is proposed and analyzed. The numerical results of the thermal field are validated by experimental measurements.

3D Finite Element thermal analysis of a small power PM DC motor

The paper presents a 3D numerical analysis of the thermal behavior of a small permanent magnet DC motor, performed by Finite Element Method (FEM). The accuracy of the computed temperatures was confirmed by comparison with experimental results; a prototype of the motor was tested in the steady-state in order to calibrate the numerical model. The motor was subsequently analyzed using a transient heat transfer numerical model, under various load conditions. Given the diverse applications and demanding operating conditions, small DC servo motors must be precisely designed and rated, especially with regard to the maximum heating of their windings and sometimes in connection with special thermal restrictions set on the mounting system. Numerical simulation of the heat transfer process proves to be a valuable tool that provides a great flexibility in studying the temperature distribution inside such motors, under various load conditions.

Numerical simulations of continuous induction heating of magnetic billets and sheets

The relative motion between the inductor and the work‐piece to be heated, the magnetic non‐linearity and the dependence of physical properties on temperature are considered in the numerical simulations of continuous transverse flux induction heating of metallic sheets and scanning type induction heating of billets. Using the translating air‐gap technique, the transient and the steady state electromagnetic and thermal fields are evaluated.

Numerical evaluation of electromagnetic field effects in electric arc furnaces

This paper presents a 3D numerical modeling of electromagnetic and thermal fields in three‐phase electric arc furnaces. The thermal effect of the foamy slag is studied in the first part of the paper. The Joule power density is calculated with an AC electromagnetic analysis and is transferred to the steady state thermal problem as heat source. The second part of the paper presents a numerical analysis of new electromagnetic stirring methods.

Influence of design parameters on a line start permanent magnet machine characteristics

This paper presents the design of a Line Start Permanent Magnets Synchronous Machine (LSPMSM) and the analysis of its starting capability. A preliminary sizing of the machine is carried out using an analytical procedure and the obtained solution is finally refined and completed by 2D Finite Element (FE) analysis. The effect of modifying the geometrical configuration of PMs, rotor bars and flux barriers on the LSPMSM starting capability is analyzed using the FLUX software package. This study is proved to be useful for the optimal design of the machine with the purpose of improving its start-up capability, one of the most sensible points of LSPMSM.

Three phase line start claw poles permanent magnet motor with pole changing winding

A new concept of three phase synchronous motor with permanent magnets and additional squirrel cage in the rotor is presented from both manufacturing and experimental point of view. The permanent magnets have ring shape with axially magnetization and are imbedded in the claw pole ferromagnetic modular pieces. The main characteristics of the manufactured motor are presented and the experimental results regarding the starting and rated load running are fully interpreted in the paper.

Eddy currents in thin plates modelled as surface regions

This paper analyses the conditions for which the results of eddy currents computation in thin regions modelled by surface regions are concordant with those obtained using volume finite elements. The concepts of geometrically thin or thick region, electromagnetically thin or thick region, 2D or 3D problem, transverse or longitudinal flux problem are used to characterise the limits of the surface model. The computation of eddy currents in sheets heated in transverse flux inductors and of the eddy current losses in metallic casing of an induction furnace highlights the surface finite element applicability.