PURPOSE: To prevent an induction motor against the generation of torque ripple affected by a dead time by selecting a prearranged instantaneous space vector by means of the calulated primary flux phase and by controlling an inverter.

CONSTITUTION: A coordinate conversion section 6 separates output currents Iu, Iv and Iw for each phase of an inverter 2 into exciting portion current Id and torque portion current Iq. A comparison section 7 compares the exciting portion current Id with exciting portion command Id*, while a comparison section 8 compares the torque portion current command Iq*. The primary flux phase operation section 9 works out the primary flux phase λ by means of the exciting protion current command Id*, the torque portion command Iq*, an output angle frequency command Ws*, and an induction motor constant. An instantaneous space vector selector 10 selects an instantaneous space vector stored a memory, etc., in advance from each comparison result and the primary flux phase λ and dperfoms a PWM output.