Patent ID: 8350516

Claim:
An electric motor drive device, comprising: an electric power conversion device for generating an AC voltage through a switching operation of a power semiconductor device; an electric motor having a coil winding to which the AC voltage from said electric power conversion device is applied; and a control device for controlling the switching operation of said electric power conversion device, and said control device setting a lower limit value of the AC voltage when partial discharge may occur in a space between said coil windings in reversal of polarity of said AC voltage to a first prescribed value, in accordance with relation between said AC voltage and life until dielectric breakdown of said coil winding of said electric motor, and controlling the switching operation of said electric power conversion device such that a voltage variation rate in reversal of polarity of said AC voltage is relatively lower, when said AC voltage exceeds said first prescribed value, than when said AC voltage is lower than said first prescribed value.