A robust controller for an AC induction motor is designed using principal gains method to govern stator currents. State space equations of an AC induction motor in α-β stator fixed frame are nonlinear with respect to rotor speed. Nonlinear equations are rewritten to parameter from describing dependency on rotor speed which is assumed to be known by measurement or by estimation. A nominal model (ω=0rd/s) is considered for synthesis, and all regimes dependent of ω are considered perturbed regimes at output multiplicative uncertainty. The singular values of uncertainty are quantified. Robust conditions of stability and performances are given. It is showed, from the results in frequency and time domain, that the principal gains method can be successfully applied to induction motor. 