Influence of slot harmonics on radial magnetic forces in low-speed PM machine with concentrated windings

In this paper, influence of slot harmonics on magnetic vibrational forces are studied in a 120slot/116pole low-speed PM machines in no-load. Different cases including open slots, semi-closed slots and semi-magnetic wedges are discussed. Magnetic flux distribution in the airgap is computed using time-stepping finite element method. Spatial harmonics due to slotting are investigated in different cases. Maxwell´s stress tensor is employed to calculate radial force density in the airgap. Spatial distribution of the total forces on the teeth and also time-dependent force waveform on one tooth are analyzed and discussed for different cases. It is shown how the amplitude of the lowest mode of vibration is reduced in the case of using semi-closed slots and semi-magnetic wedges. Tangential force density distribution and torque production capability of open and semi-closed slots are also discussed.