Drive control apparatus and method of alternating current motor

A drive control apparatus for driving an AC motor by applying a rectangular wave voltage thereto, comprising:

• a torque estimating unit that obtains an estimated torque of a rotor of the AC motor;
• a torque deviation detecting unit that detects a torque deviation as a difference between the estimated torque and a torque command value representing a required torque of the AC motor;
• and
• a rectangular wave voltage controller that controls a state of the rectangular wave voltage applied to the AC motor, through torque feedback control based on the torque deviation, so that a torque of the rotor approaches the torque command value, thereby controlling the AC motor without the use of a rotor position sensor,
• wherein the rectangular wave voltage controller comprises:
• a rotation speed detector that detects a current rotation speed of the AC motor;
• a rectangular wave voltage phase switching unit that switches, in a predetermined order, a plurality of predetermined rectangular wave voltage states corresponding to different phase values of the rectangular wave voltage;
• and
• a switching timing controller that sets a switching timing of the rectangular wave voltage states to a timing that deviates from a reference timing determined based on the current rotation speed, by a length of time corresponding to the torque deviation.