Mihail Popescu

Three phase tooth-concentrated multiple-layer fractional windings with low space harmonic content

The possibility of obtaining lower space harmonic content for the fractional-slot, tooth-concentrated windings by multiplying the number of coils, leading to bigger number of layers in the armature slots is presented. By using multiple layer windings it is possible to reduce or even to cancel some space sub-harmonics having as final result lower eddy current losses induced by the armature reaction in the iron structure of the rotor. The general method of doubling (or trebling) the winding and relatively shifting by one (or more) slots is presented in the paper. Two examples of three phase concentrated windings are presented and analyzed as primitive windings, 12 slots/10poles and 9 slots/8 poles. In the first case the only existing space sub-harmonic is reduced firstly from 35.9% (from fundamental wave) to 9.6% and finally it is canceled by using different number of turns per coils. In the second case the two existing sub-harmonics are reduced and balanced by using the developed method.

Adjustable Flux Three-Phase AC Machines With Combined Multiple-Step Star-Delta Winding Connections

In this paper, a complete theory and analysis method for combined star-delta three-phase windings from the point of view of magnetomotive force spatial harmonics content and equivalent winding factors calculation is developed. The method allows for any spatial angle and any coils percentage distribution between star and delta balanced winding systems. It is proven that connecting the inner delta in the clockwise or counterclockwise direction leads to two different space angles between the star and delta systems and two different steps in the flux level control. It means that, compared to what is known and applied up to now, using n winding sections in each phase, it is possible to obtain 2 n steps (instead of n + 1) in the flux level. To check the analysis validity, two experimental tests are reported on both squirrel-cage, integer-winding, induction motor, and permanent magnet, low-speed, fractional-winding, synchronous generator with a specially designed stator winding, allowing multiple-step air-gap flux regulation.

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.

Three phase tooth-concentrated interspersed windings with low space harmonic content

The paper presents a new possibility of obtaining lower space harmonic content for the fractional-slot, tooth-concentrated windings by interspersing the phase windings. By using multiple layer windings it is possible to reduce or even to cancel some space sub-harmonics having as final result lower eddy current losses induced by the armature reaction in the iron structure of the rotor. The general method of multiplying the winding and relatively shifting by one (or more) slots is presented in the paper. The application of the method is developed for the general case of the windings having Z=2p±1 where, instead of double layers winding, the partial three or even four layers winding is obtained. The example of application is given for 15 slots, 14 poles, three phase concentrated windings which is presented and analyzed as primitive windings.

Adjustable flux three phase a.c. machines with combined multiple-step star-delta winding connections

In the paper it is developed a complete theory and analysis method of combined star-delta three-phase windings from the point of view of MMF spatial harmonics content and equivalent winding factors calculation. The method allows for any space angle and coils percentage distribution between the star and delta balanced winding systems. It is proven that connecting the inner delta in the CW or CCW direction leads to two different space angle between the star and delta systems and two different steps in the flux level control. It means that, compared to what is known and applied up to now, using n winding sections in each phase, it is possible to obtain 2n steps (instead of n+1) in the flux level. To check the analysis validity, two experimental tests are reported on both squirrel cage integer winding induction motor and PM low speed fractional synchronous generator with a specially designed stator winding, allowing multiple-step air-gap flux regulation.

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.

Design and implementation of an autonomous Wind/PV/Diesel/Battery power system

This paper deals with the design, implementation and experimental analysis of a complex hybrid power system based on renewable energy sources. The optimal design of the Wind/PV/Diesel/Battery power system of 5kW peak power was carried out using Homer software package. The system implementation includes important contributions related to the execution and systemic integration of various components such as: pure sine-wave inverter with galvanic isolation, electronic unit for batteries charging from Diesel-electric generator, intelligent control unit that turns on/off the Diesel-electric generator depending on the battery State Of Charge (SOC), wind turbine emulator composed of a vector control induction motor drive system and a special designed PM synchronous generator, etc.

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 ®.

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.