Patent ID: 7759888

Claim:
An AC motor controller, comprising: an AC motor; an inverter for driving the AC motor with three phase motor currents each through a motor cable; a motor current detector for detecting the three phase motor currents each flowing in the motor cable connected to the AC motor; and a processor operatively associated with the motor current detector and configured to detect while the motor is still running the occurrence of an abnormal state of the motor cable, which abnormal state is a disconnected or unconnected state, based on the three phase motor currents detected by the motor current detector and identify the phase of the motor cable in which the abnormal state occurs, wherein said processor detects the abnormal state of the motor cable when a motor current command value computed based on a torque instruction value of said AC motor is still not less than a predetermined value, and a driving current of said motor computed based on the three phase motor currents is smaller than the predetermined value, and a sampling time in said processor of the motor current data is at least a half cycle of the motor driving frequency.