Influence of Stator Asymmetry on Cogging Torque of Permanent Magnet Brushless Machines

Dept. of Electron. & Electr. Eng., Univ. of Sheffield, Sheffield
IEEE Transactions on Magnetics (Impact Factor: 1.21). 12/2008; DOI: 10.1109/TMAG.2008.2001322
Source: IEEE Xplore

ABSTRACT The paper investigates the influence of stator asymmetry on the cogging torque of permanent magnet brushless motors. It shows that high localized magnetic saturation due to such asymmetry can significantly increase the magnitude of the cogging torque and introduces cogging components which have an order lower than the least common multiple between the stator slot number and the rotor pole number. The findings are confirmed by both finite element analyses and measurements on an 18-slot, 6-pole prototype motor.

  • [Show abstract] [Hide abstract]
    ABSTRACT: This study proposes a systematic process of a multi-objective optimal design of an axial-flux permanent-magnet motor for electric scooters. The preliminary design uses a zero-dimensional (0D) model to determine the number of slots and poles and initial sizes of the motor according to the driving requirements of the scooter. The optimal design process uses a 1D magnetic circuit model with an effective air-gap distribution function, whereas searching for a set of motor parameters that minimise or maximise motor performance indices such as torque, torque density and torque ripple. The final design is verified and refined by the 3D finite element method. The resulting prototype motor features high torque density of 8.94 Nm/kg and electronic gearshifts between low and high gears. According to their efficiency maps, the driving-cycle efficiency is estimated as 57% for the electric scooter to operate on the driving cycle ECE-40.
    IET Electric Power Applications 01/2014; 8(1):1-12. DOI:10.1049/iet-epa.2013.0026 · 1.31 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: One of the main challenges in permanent magnet electrical machine design is cogging torque reduction. In this article, the magnet segmentation method is used for cogging torque reduction. For this end, each surface permanent magnet is divided into eight parts, and a symmetrical structure with equal angular widths and considering the angular gaps between them is used for minimizing a number of optimization parameters. In this article, three optimization algorithms—response surface methodology, genetic algorithm, and particle swarm optimization—are used to determine the optimal values of optimization parameters. Finally, the result is obtained that the optimum values of response surface methodology are more efficient than of those of the genetic algorithm and particle swarm optimization in cogging torque reduction, because the objective function of the response surface methodology is cogging torque that is calculated using the finite-element method, whereas the objective function in the genetic algorithm and particle swarm optimization is based on the analytical methods. However, the main objection of the magnet segmentation method is the simultaneous reduction of average torque with cogging torque.
    Electric Power Components and Systems 09/2014; 42(12). DOI:10.1080/15325008.2014.893548 · 0.66 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The problem of evaluating the impact on the efficiency consequent to the adoption of bonded magnets in substitution of ferrites in small permanent-magnet machines is faced. That is necessary for the development of the main object of this paper: The evaluation of the obtainable performances of a specific brushless dc motor fractional motor through simple substitution of bonded magnets proposed by the authors to the ferrite magnets used up to now. The final aim is to make clear the practical adoptability of the proposal. Several prototypes produced in the authors' laboratories have been tested, and a long experimental activity has been carried on. In particular, the focus of the work has been the identification and separation of the iron losses, both hysteresis and eddy currents, from the contribution of the bearings. The corresponding torques have been calculated, and the energetic behaviors of the original machine with ferrites and the prototypes with phenolic bonded magnets have been analyzed. The satisfactory impact on the efficiency and the improvement of the output power of the motor with bonded magnets let possible to consider the analyzed solution as realistically adoptable.
    IEEE Transactions on Industry Applications 09/2014; 50(5):3249-3257. DOI:10.1109/TIA.2014.2306978 · 2.05 Impact Factor