Patent ID: 7005825

Claim:
An electric motor control system comprising: a 3-phase/2-phase converting means for converting output current from an inverter section that inverts dc power to ac power into mutually perpendicular 2-phase signals that are a d-axis current component signal and a q-axis current component signal; a current phase commanding means for outputting, in restarting after an instantaneous power failure being restored, mutually perpendicular 2-phase signals that are the d-axis current component commanding signal and the q-axis current component commanding signal, and phase angles of the d-axis current component commanding signal and the q-axis current component commanding signal; a d-axis current control means for amplifying a difference signal of the d-axis current component, the difference signal of the d-axis current component being the difference between the d-axis current component commanding signal and the d-axis current component signal, and for outputting a d-axis component of a 2-phase-voltage command that controls output current from the inverter section in such a manner that the difference signal is zero; a q-axis current control means for amplifying a difference signal of the q-axis current component, the difference signal of the q-axis current component being the difference between the q-axis current component commanding signal and the q-axis current component signal, and for outputting a q-axis component of a 2-phase-voltage command that controls output current from the inverter section in such a manner that the difference signal is zero; an induction-motor-rotation-status detecting section for receiving the d-axis component of the 2-phase-voltage command outputted from the d-axis current control means, and the q-axis component of the 2-phase-voltage command outputted from the q-axis current control means, and for calculating a rotating frequency and a rotating direction of a coasting induction motor; and a phase-reversal-timing detecting means for detecting as a phase-reversal timing a specific phase at which an amplification factor of ripple components superposed on the d-axis component of the 2-phase-voltage command outputted from the d-axis current control means is maximal, the current phase commanding means turning each phase of the d-axis and q-axis current component commanding signals by 180 degrees according to the specific phase outputted from the phase-reversal-timing detecting means.