Method of eliminating self oscillations of an induction motor powered from a frequency changer and means for effecting same

摘要

A method of eliminating self-oscillations of an induction motor powered from a thyristor frequency changer, differing from those known in the prior art in that it provides for forming a signal proportional to a first derivative of the low frequency component of the motor reactive current oscillations which signal is applied as a positive feedback, in sequence with a main control, signal to an output frequency control circuit of the thyristor frequency changer.PPA control system provided comprising a power supply and a power circuit energized by the former to produce an a.c. output voltage whose amplitude and frequency are proportionally regulated, and a control circuit energized by the power supply to control the power circuit. The latter circuit includes a three-phase rectifier bridge and an independent inverter. The control circuit includes respective means for controlling the amplitude and the frequency of the inverter output voltage. The latter means includes a frequency regulator, a controlled reference voltage circuit which determines the output frequency of the inverter under steady-state conditions. The improvement of the invention resides in that a feedback circuit is provided to produce a voltage proportional to the low- frequency component of the reactive current oscillations of the motor the frequency regulator being supplied with the reference voltage plus the feedback voltage, thus providing for control of the inverter output frequency under transient conditions.