Patent ID: 8115442

Claim:
An electric motor drive system for driving an electric motor at variable rotational speeds comprising: a current detecting section for detecting the current flowing into the electric motor; a speed variation calculating section for calculating the speed variation estimating value for the electric motor in accordance with the current detected by the current detecting section and the current command value for the electric motor; and a compensatory calculating section for delivering a value that serves to compensate the amplitude, frequency and phase of the voltage applied to the electric motor in accordance with the speed variation estimating value calculated by the speed variation calculating section, wherein the compensatory calculating section delivers the value that serves to compensate the amplitude, frequency and phase of the voltage applied to the electric motor in such a manner that the phase of the speed variation estimating value calculated by the speed variation calculating section leads by an amount represented by an equation of −π/4+tan −1 (Lσ·ω/rσ), wherein ω, Lσ and rσ denotes the angular frequency of the speed variation, motor stray inductance of the electric motor and motor resistance respectively.