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In order to increase the torque performance of the conventional surface-inset Halbach machines, a surface-inset Halbach machine with trapezoidal mixed grade magnets is proposed and investigated. Based on a layered and linear superposition method, the air-gap magnetic fields are analytically obtained from solution of matrix equations. In addition, the dimensions of mid-magnet and the remanences of Halbach magnets are analytically optimized. In order to show its advantages, the optimized performances of the proposed machine model are compared with those of the conventional Halbach and trapezoidal equal grade Halbach machines. The prediction shows that the proposed optimized machine model has the largest electromagnetic torque and the lowest torque ripple. The demagnetization performance is also investigated. Finally, the finite element analysis (FEA) results verify the analytical predictions.

This paper presents a mixed grade magnet model for surface-inset machines considering the magnet thickness. In the polar coordinates, on the basis of the Laplace/quasi-Poisson equations and boundary conditions, the constructed matrix equations are solved and the air gap magnetic field in the machine is derived. Taking an 8-pole/12-slot surface-inset motor as an example, through the presented optimization process, the air gap field is optimized considering the magnet thickness, remanence and magnetization angle. In addition, the back-EMF and electromagnetic torque are analytically obtained. The optimized results show that the proposed mixed grade magnet model has larger electromagnetic torque and smaller torque ripple than the conventional one. Finally, the analytical predictions are evaluated by finite element analysis (FEA).

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