Back to results
US 4,409,533 AGranted
Method of restarting induction motor and apparatus for carrying out the same
AssigneeMitsubishi Denki Kabushiki Kaisha
InventorTakao Kawabata
Life of this patent
Estimating the term…
Loading patent…
Loading patent…
AssigneeMitsubishi Denki Kabushiki Kaisha
InventorTakao Kawabata
Estimating the term…
A frequency detector produces a pulse train from an emf generated across a three-phase induction motor in the decelerating mode with its pulse repetition frequency proportional to the speed of the motor. A phase locked loop synchronizes this frequency with that of a variable frequency oscillator for a variable frequency inverter and the synchronization is maintained by the phase locked loop and a ramp generator controlled with the signal from the detector. When the detected frequency equals a command frequency from a reference circuit, the inverter starts to operate the motor. When the start operation has been completed, the phase locked loop is disabled while the ramp generator is connected to the reference circuit to change the frequency of the inverter to the command frequency to complete the restart operation of the motor.
A method of restarting an induction motor in the decelerating mode by a variable frequency electric source, comprising the steps of detecting a residual electromotive force across said induction motor, synchronizing the frequency of said variable frequency electric source with the frequency of said residual electromotive force to thereby supply electric power to said induction motor from said variable frequency source while maintaining the frequency of said variable frequency electric source in synchronism with the speed of said induction motor, and then changing said frequency of said variable frequency electric source to a predetermined value to thereby place said induction motor in a predetermined operating state.
An apparatus for restarting an induction motor in the decelerating mode by a variable frequency electric source, comprising a variable frequency electric source for powering said induction motor, a frequency detector for detecting a residual electromotive force across said induction motor and for detecting the frequency thereof, a variable frequency oscillator for driving said variable frequency electric source, a synchronization control circuit for synchronizing the frequency of said variable frequency oscillator with a frequency signal from said frequency detector, and a control circuit for causing said variable frequency electric source to supply electric power to said induction motor while the frequency of the output from said variable frequency electric source is maintained in synchronism with the speed of said induction motor by said synchronization control circuit, and for changing said frequency of said variable frequency electric source to a predetermined value after the initiation of said supplying of power to thereby accelerate said induction motor to a predetermined speed.
Dependencies are inferred from the claim text.