Patent ID: 8531148

Claim:
A control apparatus for an AC electric motor including: a DC power supply; an inverter having a plurality of switching devices to convert DC electric power from the DC power supply into AC electric power; an inverter control circuit to PWM control the plurality of switching devices; an AC electric motor supplied with electric power from the inverter; and a current detector to detect DC bus current flowing through the inverter, the control apparatus comprising: current sampling means to sample the DC bus current produced by the current detector plural times at predetermined intervals during first and second predetermined periods; first integration operation means to integrate sampled current values during the first and second periods; second integration operation means to integrate sine and cosine functions of output voltage phase of the inverter at the sampling moment during the first and second periods; and current estimation means to estimate reactive and active currents flowing through the AC electric motor on the basis of integrated values of the first and second integration operation means, wherein the current estimation means multiplies vectors having integrated values of sampled current values during the first and second periods by an inverse matrix having integrated values during the first and second periods, of sine and cosine functions of output voltage phase of the inverter at sampling moment to thereby estimate reactive and active currents flowing through the AC electric motor.