Patent ID: 7948205

Claim:
A multi-phase AC motor driving device comprising: an inverter circuit including pairs of upper and lower arms providing in association with respective phases of the motor, the inverter circuit being constituted such that the respective arm has a switching device for driving the multi-phase AC motor and a reflux diode connected in parallel to the switching device, and a voltage for driving the motor is extracted from a connection point of the upper and lower arms of the respective phases; a current detecting section, arranged in the lower arm of the respective phase of the inverter circuit, for detecting a phase current of the motor; a control section for controlling ON/OFF operation of each switching device of the inverter circuit with the predetermined duty ratio; a first determining occurrence of a failure based on a current value detected by the current detecting section; the multi-phase AC motor driving device further comprising; and a second determining section for determining whether or not all ON-duty ratios of the switching devices of the upper arms of the inverter circuit are smaller than a predetermined value, wherein the first determining section does not make a determination on the occurrence of the failure if the second determining section determines that the ON-duty ratios are not smaller than the predetermined value, wherein the first determining section makes a determination on the occurrence of the failure if the second determining section determines that the ON-duty ratios are smaller than the predetermined value, and wherein when determining that the ON-duty ratios are not smaller than the predetermined value, the second determining section compares an absolute value of the current value of one phase and an absolute value of a sum of current values of the other phases if only the ON-duty ratio of the switching device of the upper arm of one phase if the absolute value of the current value of the one phase is larger than the absolute value of the sum of the current values of the other phases.