Patent ID: 7005828

Claim:
A control device for an electric motor, comprising: an inverter circuit connected to a direct-current power source to convert a power from the direct-current power source to an alternating current power, thereby driving the electric motor by the alternating current power; a control unit for controlling the operation of the inverter circuit on the basis of a target torque; a superimposing unit for superimposing a superimposed current on a drive current for driving the electric motor, the superimposed current having a frequency different from a frequency of the drive current; a feature target generating unit for calculating a target value of a feature based on at least one of the length of a long axis of a current vector locus and the length of a short axis thereof, corresponding to the target torque; a separating unit for separating the superimposed current from the drive current supplied to the electric motor; an actual feature detecting unit detecting an actual value of the feature based on at least one of the length of the long axis of a current vector locus of the superimposed current separated by the separating unit and the length of the short axis thereof; and a phase angle detecting unit for detecting a phase angle of the electric motor on the basis of the target value calculated by the feature target generating unit and the actual value detected by the actual feature detecting unit, wherein the control unit controls the operation of the inverter circuit on the basis of the phase angle detected by the phase angle detecting unit.