METHOD AND APPARATUS FOR CONTROLLING VARIABLE SPEED, CONTROLLED CURRENT INDUCTION MOTOR DRIVE SYSTEMS

摘要

20-TT-611ABSTRACTA new induction motor control method and system utilizes one ormore electric power inverters each supplying a separate induction motorwith alternating current excitation power. The respective inverters pre-ferably comprise auto-sequential commutated controlled current inverters.Direct current is supplied to each inverter in the system from a commondirect current power supply preferably comprising a phase controlled rec-tifier circuit with individual current smoothing inductors connected in thedirect current link to each power inverter for isolation purposes. A com-mon operator controlled power level control module is provided for con-trolling the magnitude of the output current supplied from the commonphase controlled rectifier to all of the inverters in parallel. Respectivemotor flux sensing means are provided for each induction motor for de-riving individual feedback control signals representative of the flux de-veloped by the respective induction motors. The flux feedback signal issummed with an input command value of a flux control signal in a suitablesumming circuit, and the error signal is supplied through a suitable com-pensating circuit for regulating the flux level of the respective inductionmotors by individually controlling the frequency of the excitation currentsupplied to the stator windings of the motor by its associated inverter. Ina preferred embodiment the actual electro-magnetic flux produced acrossthe induction motor stator-rotor gap is sensed and fed back to the summingcircuit for control purposes. This sensed actual value of motor flux signalalso is utilized to derive an actual value of torque feedback control signalthat is employed in controlling the magnitude of the direct current suppliedby the common phase controlled rectifier to all of the inverters in parallel.20-TT-611It is also preferred to employ a phase lock-loop converteras the compensating circuit in the frequency control.