Patent ID: 8710775

Claim:
An electric power steering apparatus comprising: an inverter for supplying three-phase AC electric power to three phases of an electric motor; a current coordinate converting unit for converting currents flowing in the three phases of the electric motor into d-q coordinate currents including a d-axis current as an exciting current component and a q-axis current as a torque current component; a voltage coordinate converting unit for converting three-phase voltages applied to the electric motor into a d-axis voltage and a q-axis voltage; an abnormal phase detecting unit for determining a combination of phases whose interphase voltage is of nearly zero volts in a state where the q-axis current is equal to or smaller than a first threshold value though the q-axis voltage is being applied, and detecting a phase other than the combination of phases as an abnormal phase; and a rotational speed detecting unit for detecting a rotational speed of the electric motor; wherein the abnormal phase detecting unit is operated when the rotational speed is equal to or smaller than a second threshold value, wherein the second threshold value comprises a threshold value for determining whether the electric motor is generating an excessive counter-electromotive force which makes accuracy of detecting the abnormal phase by the abnormal phase detecting unit inadequate.