Device for diagnosing electric motor, method for diagnosing electric motor, and device for inferring indication of abnormality in electric motor

A diagnosis device for electric motor, comprising:

• a current detection circuit for detecting current of an electric motor driven by an inverter;
• and
• a calculation processor which receives an output of the current detection circuit and performs determination for winding short-circuit abnormality of the electric motor, wherein
• the calculation processor includes
• an operation state determination circuitry which calculates a current effective value from the current of the electric motor and performs determination for an operation state,
• an inverter driving frequency calculation circuitry which calculates an inverter driving frequency,
• an initial negative-phase-sequence current analysis circuitry which analyzes initial negative-phase-sequence current in a normal state in accordance with the calculated inverter driving frequency,
• an evaluation value analysis circuitry which calculates an evaluation value for winding short-circuit from a difference between negative-phase-sequence current calculated from the current of the electric motor during driving and the initial negative-phase-sequence current corresponding to the inverter driving frequency calculated during driving, and
• a winding short-circuit determination circuitry which performs determination for winding short-circuit of the electric motor through comparison between the calculated evaluation value and a predetermined evaluation threshold.