Apparatus for controlling a.c. motor.

摘要

A first PWM inverter (1) for converting the acvoltage of an ac power source (AC) to a devoltage is connected through a dc circuit with a second PWM inverter (2) for driving an ac motor (3). A smoothing capacitor (15) is provided in the dc circuit. The firing angles of the first inverter (1) are so controlled that the voltage in the dc circuit may be kept at a predetermined value and the second inverter (2) is controlled in accordance with the speed instruction signalforthe acmotor(3), whereby the ac motor (3) can operate a regenerative operation without inducing higher harmonic components