Investigation On Electromagnetism Of An Arc-Linear Axial Flux Permanent-Magnet Synchronous Machine

Electric machine is a mechanical device which can convert the electric energy into mechanical energy.Most of the electric machines in the traditional application are rotary direct-current machines or alternationg-current machines which can always complete a 360 degree circular motion.Among these rotary machines,the permanent magnet synchronous machines have attracted more and more attention due to its higher power density and efficiency.However,in some specific areas,such as large telescope driving system and robot joint,the load only rotates within a limited angle.Considering the high torque density of the axial flux permanent magnet synchronous machines,a kind of arc-linear axial flux permanent-magnet synchronous machine(AL-AF-PMSM)for direct-drive scanning system is proposed in this paper.Aiming at how to eliminate the AL-AF-PMSM’s torque ripple,the electromagnetic properties of the AL-AF-PMSM is researched:In order to avoid the use of 3-D finite-element method(FEM),a new equivalent 2-D calculating method using the Complex Simpson integral formula is proposed in this paper.This new method transformes the AL-AF-PMSM’s 3-D FEM model into a series of 2-D FEM linear-motor models.After comparing to the 3-D FEM’s result,the correctness of this proposed method is validated.A new structure with reversed slot for arc-linear machine is proposed to reduce the cogging torque and the new structure is adopted in the AL-AF-PMSM.What’s more,two compensation windings are added to the AL-AF-PMSM to optimize the distorted back EMF caused by the reversed slots.Two steps are adopted to optimize the end effect torque:1)adjusting the primary angle of each stator and 2)shifting the phase of each stator’s end torque to compensate each other.As the stator core and the rotor core of the AL-AF-PMSM both have finite length,the torque ripple is still very large when rotor edge is closing to stator edge,which makes the smooth operating range decrease.In order to improve the smooth operating range,a new shape of the edge permanent magnet is proposed.The correctness of the above theoretical analysis is verified by experiment.