Concentric Winding BLDC Motor Design

Concentric winding method is preferred for low cost permanent magnet (PM) motors applicable to home appliances. The MMF of the concentric winding looks like a square function so that it has severe space harmonics. To minimize the torque ripple, special effort needs to be applied to reduce the rotor field harmonics, since they make EMF harmonics in conjunction with the MMF harmonics. In this work, the relation between EMF harmonics and rotor field harmonics is derived for a given rectangular winding function. Also, as a means to reduce the harmonics, arc shaped air gap bridge is added on the top surface of the rotor magnet. FEM simulations were repeated by changing the arc radius. In choosing the optimal one, average air gap field density B
_ave
, as well as the field harmonic is considered