METHOD OF CONTROLLING AC MOTOR.

摘要

A method of controlling an AC motor capable of preventing or decreasing fluctuation of the output torque of the AC motor when it operates at low speeds. When an electric motor (6) operates at a low speed, a combination of a second pulse coder (PC2) that detects the rotational position of the motor (6) with high resolution and a second table (T2) storing sinusoidal data for determining current instruction with high resolution is selected by a processor comprising switching means (20) and switches (SW1, SW2). Sinusoidal data of each of the phases are read from a second table according to a phase angle ( THETA ) of a primary current of the motor determined based on an actual rotational speed of the motor detected according to the number of pulses (FP2) supplied from the second pulse coder, the motor is controlled based on the current instructions of phases calculated based on these data with high resolution, and the output torque of the motor is prevented from fluctuating.