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This paper talks about some design issues for spoke type interior permanent magnet (IPM) motor for low voltage high current servo applications. After initial motor design, several analyses to improve the motor's torque quality have been carried out using Finite Element Analysis (FEA). Effect of skewing and segmented rotors has also been explored and the goal of improved torque quality has been realized. A prototype IPM motor has been built, tested and experimentally verified.

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This article proposes a new magnet step-skew approach for surface mounted permanent magnet (PM) motors in order to reduce the cogging torque and torque pulsations as well as to increase the output torque quality. The proposed approach based on semi finite element analysis (FEA) relies on varying both the length of the magnet segments and the angle between the rotor segments. The proposed method targets to optimize the magnet length and the skew angle so as to achieve minimum torque pulsations as opposed to the conventional magnet step-skew approach in which the magnet length and the skew angle are kept the same. Semi-2D-FEA based simulations with an optimization algorithm are completed to attain the optimum magnet geometries as well as the skew angles. 3D-FEAs are also performed for optimized design to check the reliability of the proposed approach. A prototype motor is developed using the proposed design approach, tested and verified. A detailed comparison between the proposed novel approach and the test data are also provided. It is confirmed that the new approach provides very practical results and performs well compared to conventional step-skew approach.INDEX TERMS Permanent magnet motor, step-skew, different skew angle, different magnet length, 2D and 3D FEA.

This paper discusses cogging torque minimization techniques in surface-mounted, axial-flux, multirotor permanent magnet synchronous disc motors in order to eliminate cogging components and obtain sinusoidal back-EMF for low-speed applications. Cogging torque minimization techniques are examined in detail with a focus on magnet skewing and pole and rotor shifting in order to obtain zero cogging. Some magnet shape and rotor design alternatives with conventional skew planar magnets were investigated based on 3D finite element analysis (FEA). Improvements compared to unskewed reference axial-flux permanent magnet (AFPM) motor design are presented. A prototype AFPM motor was built and tested based on the analyses. Results obtained from FEA and experimental study are well matched and it was shown that zero cogging and sinusoidal back-EMF can be obtained even for integer slot axial-flux PM motors with the proposed low-cost cogging torque minimization methods.