Application of a multiobjective minimization technique for reducing the torque ripple in permanent-magnet motors

The main design parameters of a permanent-magnet motor, which reduce the total torque ripple, are determined. A two-step design procedure is utilized. First the geometry of the permanent-magnet rotor is derived by a one-dimensional field analysis coupled to a multiobjective minimization technique. The objective function of the minimization is defined as a combination of the electromotive force harmonic components induced in the stator and of the harmonic components of the air-gap magnet permeance. As a second step, a two-dimensional numerical model, solved through a finite element method, is adopted to further improve the analysis of the magnetic field. This allows the optimization of the magnet arc width and the minimization of the cogging torque. The method described has been used for the design of a three-phase, six-pole, permanent-magnet synchronous motor. Experimental tests have been carried out to verify the results obtained by the design procedure