Torque ripple attenuation in permanent magnet synchronous motors

The authors study the torque ripple attenuation of permanent magnet synchronous motors caused by EMF harmonics and cogging torque. First, the magnet arc influence upon these variables is analyzed. Next, the impact on the harmonic contents caused by attenuation methods such as stator slot skewing, permanent magnet shifting and combinations of the two are presented. The last method makes it possible, using results of the simplest case (nonskewed slots and aligned magnets), to obtain the waveform of the EMF and cogging torque in more complex cases. The best combinations of the magnet arc and harmonic attenuation methods for minimizing electric torque harmonics and cogging torque are suggested. An analysis of cogging torque sensitivity to errors in the slot skewing angle is discussed.<>