Study of the Halbach magnetization in small PM electrical machines adopting the bonded magnets

Abstract

In the recent past the authors dedicated much work to small PM motor adopting permanent bonded magnets, and to the magnetization problems. Now it is largely proposed the so-called Halbach magnetization, presenting the directions of the magnetic induction variable along the magnet; its constitutes a tentative of sinusoidality for the magnetic induction component orthogonal to the magnet surface. It was decided to try to realize a motor prototype through the realization of the magnets by accosting small sectors, each with a magnetization direction different, and aiming to obtain an Halbach magnetization. In this paper a FEM simulation activity is presented to select the proper choice of the number and characteristics of the elementary sectors. At first the simulation instrument reliability has been tested through a confrontation between simulated and experimental results for some typical situations. Then the analysis was devoted to compare the windings rms voltage value and the cogging torque amplitude; the selected reference case is the one providing a radial magnetization. The analyzed solutions provide some hypothetical composed magnets, having different number of sectors and different angular amplitudes. Such activity allowed interesting considerations and a criterion useful for the choice of the magnets characteristics and for the number of the elementary sectors to be adopted for the motor prototype. The negative effect of the Halbach solution on the cogging torque amplitude is considered too.