The time and space characteristics of magnetomotive force in the cascaded linear induction motor

To choose a reasonable mode of three-phase winding for the improvement of the operating efficiency of cascaded linear induction motor, the time and space characteristics of magnetomotive force were investigated. The ideal model of the cascaded linear induction motor was built, in which the B and C-phase windings are respectively separated from the A-phase winding by a distance of d and e slots pitch and not overlapped. By changing the values of d and e from 1 to 5, we can obtain 20 different modes of three-phase winding with the different combinations of d and e. Then, the air-gap magnetomotive forces of A-, B-, and C-phase windings were calculated by the magnetomotive force theory. According to the transient superposition of magnetomotive forces of A-, B-, and C-phase windings, the theoretical and simulated synthetic fundamental magnetomotive forces under 20 different arrangement modes were obtained. The results show that the synthetic magnetomotive force with d = 2 and e = 4 is close to forward sinusoidal traveling wave and the synthetic magnetomotive force with d = 4 and e = 2 is close to backward sinusoidal traveling wave, and their amplitudes and wave velocities are approximately constant and equal. In both cases, the motor could work normally with ahigh efficiency, but under other 18 arrangement modes （d= 1, e=2; d= 1, e=3; d= 1, e=4;...）, the synthetic magnetomotive force presents obvious pulse vibration and moves with variable velocity, which means that the motor did not work normally and had high energy loss.

Design of a hybrid magnetomotive force electromechanical valve actuator

We propose a novel axis-symmetric modified hybrid permanent magnet(PM)/electromagnet(EM) magnetomotive force actuator for a variable valve timing camless engine. The design provides a large magnetic force with low energy consumption, low coil inductance, PM demagnetization isolation, and improved transient response. Simulation and experimental results confirm forces of about 200 N(in the presence of coil current) at the equilibrium position and 500 N(in the absence of coil current) at the armature seat. We compared our proposed design with a double solenoid valve actuator(DSVA). The finite element method(FEM) designs of the DSVA and our proposed valve actuator were validated by experiments performed on manufactured prototypes.

Magnetomotive Force Harmonic Reduction Techniques for Fractional-Slot Non-Overlapping Winding Configurations in Permanent-Magnet Synchronous Machines

Compared to conventional distributed winding configurations,the fractional-slot non-overlapping(concentrated)windings exhibit advantages such as short end-winding length,high copper packing factor(particularly with segmented stator structure),low cogging torque,good field weakening capability owing to relatively large d-axis inductance,and better fault tolerant capability due to low mutual inductance.However,one of the key problems of employing concentrated windings in Permanent-magnet Synchronous Machines(PMSMs)is the high eddy-current losses in rotor magnets and/or rotor iron due to the presence of a large number of lower and higher order space harmonics in the stator Magneto-Motive Force(MMF).These MMF harmonics also result in other undesirable effects,such as acoustic noise and vibrations,and localized core saturation which tend to reduce reluctance torque.This paper reviews the current state-of-the-art of the MMF harmonic reduction techniques for concentrated winding configurations in PMSMs,including winding split and shift,delta-star connected windings,multiple 3-phase windings,multilayer windings,uneven turn numbers,and stator flux barriers.Their concepts,advantages and disadvantages are presented and assessed.

Simplified modeling of electromagnets for dynamic simulation of transient effects for a synchronous electric motor

This study aims to show an approach for the dynamic simulation of a synchro-nous machine.The magnetic forces in the air gap are calculated efficiently using simplified approaches without neglecting important effects.For the modeling of the magnetic forces,an equivalent magnetic circuit is constructed in which the magnetic saturation and the leakage flux are taken into account and coupled with the electrical circuit at the end.The calculated magnetic forces are then passed to a mechanical model of the motor.Together with a predefinable load torque,the resulting motor rotation and the forces in the bearings are identified.The presented model is then investigated in a small example.This novel ap-proach is intended to provide a method of calculating dynamically the forces transmitted from the shaft to the motor housing and to create the basis for evaluating electric motors for vibrations,noise,and harshness under varying loads and input voltages.