Influence of Stator Asymmetry on Cogging Torque of Permanent Magnet Brushless Machines
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.
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ABSTRACT: The influence of various design parameters on the cogging torque developed by permanent magnet machines is investigated. It is shown that the slot and pole number combination has a significant effect on the cogging torque, and influences the optimal value of both skew angle and magnet arc, as well as determining the optimal number of auxiliary teeth/slots. A simple factor, which is proportional to the slot number and the pole number and inversely proportional to their smallest common multiple, has been introduced to indicate the “goodness”β of the slot and pole number combination. In general, the higher the “goodness” factor the larger the cogging torqueIEEE Transactions on Energy Conversion 01/2001; · 2.43 Impact Factor
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ABSTRACT: A variety of techniques are available to reduce cogging torque in permanent-magnet brushless DC motors. Theoretically, all the techniques are quite effective for minimizing the cogging torque. This paper presents the efficacy of these methods in mass production subject to manufacturing tolerances/variations. The cogging torque minimization becomes a challenging task when the requirement is very stringent in applications such as electric power steering and robotics. Some of the known techniques for reducing the cogging torque are the magnet pole design, skewing, step skewing, and dummy slots in the stator lamination. They will be discussed in this paper considering manufacturing tolerances/variations when used in mass production. Finite-element analysis is carried out to determine the worst case scenarios. The research demonstrates that the cogging torque amplitude and frequency are highly sensitive to magnet shapes, dimensions, locations and magnetization pattern, as well as slot/pole combination. In reality, the cogging torque may not be eliminated completely but minimized to a satisfactory level depending on the application requirements.IEEE Transactions on Industry Applications 06/2004; · 1.67 Impact Factor
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ABSTRACT: A simple analytical technique is proposed to synthesize the cogging-torque waveform of a permanent-magnet brushless machine from the cogging torque, which is associated with a single stator slot. An analytical expression is derived, which reveals the relationship between the two. It is then applied to two motors, which have a fractional number of slots per pole. It is shown that the resultant cogging-torque waveform can be synthesized to a high accuracy, as confirmed by both finite-element analysis and measurements. It is also shown that not all the cogging-torque harmonics that exist in the cogging-torque waveform due to a single slot will be present in the resultant cogging torque, and that the most significant components can be identified analytically.IEEE Transactions on Industry Applications 06/2006; · 1.67 Impact Factor