What causes torque ripple in electric motors and how is it reduced?

Torque ripple (periodic torque variation during rotation) is caused by: Cogging torque (magnetic interaction between permanent magnets and stator slots), harmonic content in the back-EMF waveform, current harmonic distortion from the inverter, and mechanical tolerances. Reduction strategies include skewed rotors or stators, optimized magnet pole arc, fractional slot windings, higher switching frequency, current harmonic injection, and improved control algorithms. Torque ripple affects NVH and smoothness; targets are typically <5% of rated torque. More demanding in premium vehicles.