Inductive load current harmonic injection

Induction motor audible noise can be related to the frequency content present in the stator winding currents. These currents produce time varying air gap fluxes which in turn produce exciting forces resulting in vibrations in the mechanical structure. By adding harmonics into the winding currents, additional frequencies can be added to the air gap flux and audible noise. If the additional frequencies can be made to mask the switching related noise components, a motor drive combination will be less annoying than an unmasked combination. This paper shows results obtained by using a wait-hop strategy to extend the range of frequencies obtainable by using a look-up table, and a multiple index implementation for signal construction.