Leonard Melcescu

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.

Low Speed Directly Driven Permanent Magnet Synchronous Generators for Wind Energy Applications

The paper is evaluating the main performances of the low speed, multi-pole permanent magnet synchronous generator provided with fractional winding. The constructive aspects versus running characteristics as cogging torque and full load/no-load voltage are compared for surface mounted and claw-pole inner embedded permanent magnets generators. The armature reaction mmf is analyzed and experimental facts are reported for the small power synchronous up to 10 kW/240 rpm.

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.

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.

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.

Induction motors with changeable pole windings in the ratio 1:4

The paper presents a new three phase 4 to 16 pole-changing winding for an induction motor with 36 stator slots and 6 terminals. The principle of design is explained and the space harmonics are calculated for both of polarities. In order to obtain a higher fundamental winding factor and lower space harmonic content for 16-pole winding, a degree of non-uniformity was accepted for the slot filling factor. The winding is developed partially in single layer and partially in double layers and contains two types of coils wound by different wire diameter. An experimental motor with the new winding was built on a 6-pole base motor in the IEC frame 132 having the rated power of 4 kW for 4-poles (double star) and 1 kW (single star) for 16-poles. The test results have shown the validity of the design. The manufactured motor was modeled using 2D FEM field-circuit method in order to simulate the operation characteristics in the both speeds.

Computation of the characteristics eddy current electromagnetic brake for a bicycle, by the finite element method 3D

The paper presents numerical and experimental study of the eddy current brakes, used to produce braking torque of a medical bike. Complex structure and lack of symmetry plane parallel geometry required the development of 3D numerical models to calculate the magnetic field. They allow determination of overall brake performance and design optimization to increase braking torque and to reduce volume. 3D numerical models developed on the basis of finite element method are models of transient magnetic system for determining induced currents in the disk. In solving problems field, it was used the formula TФ-Фr. Thus in the region of the disk were used electric vector potential T and total magnetic scalar potential Ф, in regions of the core magnetic total scalar magnetic potential Ф, and in areas of air forms in Фr reduced scalar magnetic potential.

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.

Numerical modeling using 2D FEM for a low power DC brushless motor

The paper presents a numerical and experimental study of an electronic switched DC motor with permanent magnets used to power fans in household appliances. The starting point is the symmetry and periodicity of the stators and rotors magnetic cores which lead to the development of a 2D numeric model for the magnetic field. This analysis establishes the overall motor performance and design optimization in order to reduce its volume and lower the cogging torque. The 2D numerical models developed based on finite element methods are studied in transient regime and the problems generated by the computation of the magnetic field in conjunction with the electric circuit are discussed.

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 ®.