Patent ID: 8148937

Claim:
A control apparatus for an alternating-current motor in which applied current is controlled by an inverter, comprising: a current detector that detects current flowing between the inverter and the alternating-current motor; a position detector that detects a rotational position of the alternating-current motor; and a rectangular wave voltage control portion that generates a control command for the inverter such that rectangular wave voltage that has been phase-controlled to make the alternating-current motor operate according to an operation command is applied to the alternating-current motor, wherein the rectangular wave voltage control portion includes i) a torque estimating portion that estimates the output torque of the alternating-current motor based on the output of the current detector and the output of the position detector, ii) a voltage phase controlling portion that determines the phase of the rectangular wave voltage according to a difference between the torque estimated by the torque estimating portion and a torque command value, and iii) a voltage controlling portion that controls a voltage conversion in the inverter such that rectangular wave voltage according to the phase determined by the voltage phase controlling portion is applied to the alternating-current motor, and wherein every predetermined first electrical angle that is set in advance, the torque estimating portion executes an angle interruption that samples the phase currents of the alternating-current motor based on the output of the current detector and converts the sampled phase currents into a d-axis current and a q-axis current, and the predetermined first electrical angle is set such that the number of angle interruptions varies according to the rotation speed of the alternating-current motor.