Loss In Rotor Magnets Research Articles

Advantages and Characteristic Analysis of Slotless Rotary PM Machines in Comparison With Conventional Laminated Design Using Statistical Technique

Slotless permanent magnet (PM) machines have been the considerable research subject for electric vehicles application due to their obvious merits. As opposed to conventional laminated PM machines, such machines can offer zero cogging torque, sinusoidal torque curve angle yielding a machine with very smooth rotation, no laminated core loss, and negligible eddy current losses in rotor magnets. This paper presents the mathematical model and the characteristics analysis of slotless rotary PM machines compared to a conventional laminated design. An explicit analytical expression of slotless rotary machines is developed to calculate the electromagnetic torque on both the ${q}$ - and ${d}$ -axis current injections. The validity of an analytical calculation is confirmed by the finite element analysis. Subsequently, the performance comparisons of slotless and laminated designs are carried out using a statistical technique. The key results derived from the comparative study are expected to be a useful reference resource for decision makers who should make a comparative judgment.

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.

Analytical Prediction of 3-D Magnet Eddy Current Losses in Surface Mounted PM Machines Accounting Slotting Effect

This paper presents a novel analytical technique for predicting three-dimensional (3-D) magnet eddy current losses accounting the slotting effect of any pole–slot combinations for a surface mounted permanent magnet machine under any conditions of load. The slotting effect is incorporated from a subdomain model and the 3-D boundary conditions are imposed with the current vector potential to represent the 3-D eddy currents circulating in the magnets. The proposed model in polar coordinate system is demonstrated on a fractional slot rare-earth permanent magnet machine by analyzing its magnet losses as functions of axial and circumferential segmentations. The results have shown an excellent match with 3-D numerical calculations. The analytical prediction has also been validated by experimental tests. The interaction of the armature reaction field with the slotting harmonics is analyzed and their effect on eddy current loss in rotor magnets is established. The proposed technique is employed to evaluate the effect of slotting on magnet loss with increase in field weakening angle.

Prediction of 3-D High-Frequency Eddy Current Loss in Rotor Magnets of SPM Machines

This paper proposes a computationally efficient method for accurate prediction of 3-D high-frequency eddy current loss in the rotor magnets of surface mounted permanent magnet machines, employing the imaging method. 2-D finite element analysis (FEA) is used to generate the information on radial and tangential 2-D magnetic field variations (eddy current sources) within the magnet. The diffusion of eddy current sources along the axial plane of the magnet computed analytically is incorporated in the imaging method to establish the 3-D eddy current source variations within the magnet. The modified method is validated with results from 3-D time-stepped FEA for an 8-pole, 18-slot permanent magnet machine, evaluating its magnet loss considering axial and circumferential segmentation.

Improved Eddy-current Field Loss Model and Scaling Index for Magnets of Permanent Magnet Synchronous Motors

The paper gives detailed systematic researches on the mechanism and key factors of eddy-current losses in rotor magnets of high power-density permanent magnet synchronous motors(PMSMs). Firstly, this paper establishes quantitative mathematic model of eddy-current losses for surface-mounted PMSM based on eddy current field model and Maxwell equations. Then, a scaling index is put forward to weigh the key factors relevant to the eddy-current losses in magnets. At the same time, the principles of eddy-current losses in prototype PMSM are analyzed by the finite element analysis (FEA) software. The contents researched in the paper have practical reference values for design and reliability analysis of PMSMs.