General Electric Company

Herbert W Weiss

Loren H Walker

James W Sember

Leland C Tupper

Paul M Espelage

David L Lippitt

A system for controlling a polyphase electric motor, particularly at low speeds, using a load commutated inverter includes the generation of half sine wave signals within a range of desired frequencies which are subsequently converted to single phase alternating current power for application to selected windings of the motor. In a single channel polyphase embodiment, motor starting is achieved using zero current commutation and normal phase control. A two channel embodiment results in what amounts to two phase operation of the motor.

Method and apparatus for controlling an alternating current motor

A system for controlling the operation of an alternating current induction motor having windings supplied by electrical power from the polyphase alternating current source includes a load commutated inverter circuit which is connected between the power source and the induction motor for furnishing electrical power to the motor. Controllers responsive to a command signal and a feedback signal indicative of motor operating parameters control the operation of said load commutated inverter circuit. There is further provided a fixed capacitor circuit connected between the windings of the motor for supplying reactive volt amperes (VARs) to said load commutated inverter circuit and said motor. Finally, there is provided a variable VAR generator connected between the motor windings for supplying VARs to said load commutated inverter circuit and said motor in response to the output of a third feedback control path which is also responsive to a command signal and prescribed operating parameter(s) of said load and/or said commutated inverter.

Flux control for induction motor drive using load commutated inverter

Induction motor drive using load commutated inverter circuit

Excitation current control for induction motor drive using load

A load commutated inverter synchronous motor drive system wherein a thyristor firing control of the inverter is determined by the amplitude of pesudo flux waveforms which are derived from the integral of the line voltages coupling the inverter to the motor being driven. A firing strategy is provided based on the premise that optimum thyristor firing in a load commutated inverter operating at a leading power factor occurs at a point just below the peak of the forthcoming pseudo flux waveform which point comprises an amount of volt-seconds necessary to effect current commutation plus a nominal safety margin. The determination and control is implemented, preferably, in a software phase lock loop but can, when desirable, be implemented in hardware.

Flux feedback firing control for a load commutated inverter

A plurality of controlled current inverter circuits each including a plurality of electrical current conducting legs having controlled rectifiers and associated commutating capacitors are connected in parallel and individually controlled to collectively supply an alternating current motor load with electrical power. At high speed, low required torque conditions, less than the total number of inverter circuits are maintained operative to thereby maintain sufficient current within the effective inverter circuit or circuits to sustain effective inverter commutation.

Method and apparatus for controlling an alternating current motor load

A method of controlling the thyristors of an a.c. to d.c. bridge converter, having neutral connected thyristors, at relatively low power levels by gating each phase leg thyristor conductive for a predetermined minimum period within the electrical separation between adjacent line to neutral phase voltages and immediately gating the respective neutral leg thyristor conductive for the remainder of the period such that there are no intervals in the cycle when both neutral leg thyristors are in conduction. In a three phase bridge converter system, this requires at least 60 electrical degrees minimum conduction for each phase leg thyristor followed by a 60.degree. conduction of the neutral leg thyristors. In any event, the sum of the phase leg conduction and the neutral leg conductions is always equal to 120.degree. in a three phase system. This control method improves the response to a reverse command voltage by assuring that a phase leg thyristor is conductive, thus making a transition from the first to fourth quadrant operation at maximum possible speed.

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Salem, VA, United States of America

Herbert W Weiss