Torque ripple

The fluctuating part of the torque generated by a rotating motor. There are at least three causes.
(1) Cogging torque
(2) In a brushless motor, the back emf has a sinusoidal waveform. However, the current displays a distorted waveform which is non-sinusoidal. The distorted portion is a type of torque ripple.
(3) Even when the current displays a sinusoidal waveform, the back emf waveform may contain fifth and seventh harmonics, which are forms of torque ripple.