Ovidiu Craiu

A new 4/6 pole-changing double layer winding for three phase electrical machines

The paper presents a new double layer three phase 4 to 6 pole-changing winding, with 48 slots and 6 terminals. In order to obtain a higher fundamental winding factor when winding is 6-pole connected, a degree of asymmetry is accepted for the winding when 4-pole connected. The new winding is compared with a well known two-layer winding presented in literature. An experimental motor equipped with the new winding was built on a 4-pole base and frame 100 (2.2/1.5 kW) and tested. At the same time, 2D FEM field-circuit models were developed to simulate the operation of the experimental model equipped with the newly proposed winding, and model equipped with the well known two-layer winding.

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.

Claw-pole line-start permanent-magnet synchronous motor design and development

A new concept of three-phase permanent-magnet synchronous motor with rotor embedded starting squirrel-cage is presented. The rotor has been equipped with ring shaped inner permanent magnets axially-magnetized and placed between consecutive claw poles built as ferromagnetic modular pieces. The start and the steady operation of the manufactured prototype have been experimentally tested. Results such as static and dynamic torque, efficiency and power factor have been determined and discussed in the paper. A numerical analysis of the prototype has been also conducted using a 3-D FEM-based software.

Finite element analysis of a wind generator with two counter-rotating rotors

This paper presents a 2D finite element analysis of a counter-rotating permanent magnet wind generator. The studied device is a two in one electrical machine used for counter-rotating dual rotor wind turbines used to convert the wind energy into electricity. The purpose of this study is to design the machine and to estimate its behaviour using the finite element based software package Flux ®.

The equivalent winding — A solution to a unified approach for the magnetic force inside round airgaps of electrical machines

The electromagnetic complex phenomena inside electrical machines make the determination of specific mathematical models rather laborious. Often, the electrical machine analysis is made based on simplified assumptions according to which iron losses are neglected and iron permeability is considered infinite. Thereby, the whole magnetic energy, on which is based the entire electromechanical conversion, is considered located only in the air gap, between the two armatures. The paper presents the advantages of using the air gap magneto motive force (MMF) as an intermediate quantity between ampere-turns produced by a field coil and the space variation of the magnetic field produced by the field current. The MMF in the air-gap along a field line does not depend on the air-gap length and superposition of magnetic waves is possible. The space-time variation of the magnetic force in the air-gap depends on the field coil and the way conductors are distributed in the slots around the armature. In order to achieve a unified and consistent approach regarding distribution of the magnetic force inside electrical machine air-gaps, the authors are introducing the concept of the equivalent winding placed on an equivalent surface attached to the main field armature. The constructive elements, the characteristics of the equivalent windings and the features of the equivalent surface are presented. Examples are provided to underline the advantages of the equivalent winding concept.

Design and development of a hybrid excited claw pole synchronous machine

The paper presents a new contactless hybrid excited claw pole synchronous machine. The excitation field is produced by both NdFeB permanent magnets mounted on the rotor, and two fixed coils embedded within machine shields, and fed from a controlled DC source. A 3-D numerical model based on the Finite Element Method (FEM) that takes into account the magnetic circuit nonlinearity and movement of the armature is used to demonstrate the principle of the new excitation system. The no-load and magnetization characteristics, as well as the e.m.f. time dependence are calculated. The main operating characteristics of the manufactured machine have been determined experimentally for motor and generator regimes.

Numerical and experimental analysis of two permanent magnet claw poles wind generators

The paper presents numerical and experimental results of a 1.6 KW and 3 kW wind generators with permanent magnet claw poles. A 3D model based on finite element method (FEM) considering the nonlinearity of the magnetic circuit and the movement of armatures was used to calculate the generators characteristics at load and no-load. Experimental tests were conducted in order to validate the numerically computed characteristics.

Evaluation of local and integral magnitudes in metal sheets inductive levitation device by FEM electromagnetic field modeling

This paper presents a numerical computation of a device for the horizontal casting of the inductive levitated metallic sheets. Local and integral magnitudes of electromagnetic field values are computed by means of FEM, using the FLUX-2D software and the dedicated program LEVITA. The influences of the supply frequency, magnetic saturation, and device configuration on the levitation force, induced power and transverse variation of the levitation force density are studied. Some experimental proof of the calculated magnitudes is also presented.