The Charles Stark Draper Laboratory, Inc.

William E Stanton

George A Oberbeck

David B Eisenhaure

Robert D Drescher

Kenneth Fertig

Andrew W Stewart

An optimum efficiency control system for a variable torque/speed rotary a.c. induction machine including means for varying the frequency and magnitude of the excitation voltage/current supplied to the machine in three optimum efficiency regions of operation, a first fixed slip frequency region, a second flux saturation region, and a third voltage saturation region; and means for commanding the means for varying in the first fixed slip frequency region of operation with an excitation frequency command signal derived from the machine rotor speed and unconstrained maximum efficiency slip frequency, and an excitation voltage/current command signal derived from the difference between the commanded torque/speed of the machine and its actual torque/speed; in the second flux saturation region of operation with an excitation frequency command signal derived from the machine rotor speed and slip frequency command signal derived from the machine rotor speed and slip frequency which is a function of the difference between the commanded torque/speed of the machine and its actual torque/speed; and an excitation voltage/current command signal derived from the difference between the saturation flux and actual flux in the machine; and in the third voltage saturation region of operation with the saturation voltage and an excitation frequency command signal derived from the machine rotor speed and slip frequency which is a function of the difference between the commanded torque/speed and actual torque/speed of the machine.

Optimum efficiency control system

A power conversion system for converting between electrical power at different frequencies, including a rotary electrical machine including a rotor, a stator, first and second independently controllable field windings, and at least one armature winding for each phase; a switching circuit including a plurality of switching devices and having first terminal means interconnected with the armature winding which carries a high frequency signal established by the machine, and a second terminal for interconnection with an impedance establishing a lower frequency signal; the first field control circuit for monitoring the machine to sense phase difference between the optimum zero crossings and actual zero crossings of the higher frequency signal for driving the first field winding to adjust the phase of the higher frequency signal to minimize the phase difference; a second field control circuit for modulating the higher frequency signal carried by the armature winding with the lower frequency signal and for monitoring the second terminal means to sense amplitude difference between a selected one of the voltage and current parameters of the lower frequency signal and a reference level for driving the second field winding to adjust that parameter towards the reference level; and a switch firing circuit responsive to the machine voltage and one of the voltage and current parameters of the lower frequency signal at the second terminal means for selectively triggering to the on state and self-commutating to the off state the switching devices synchronously with the zero crossings of the higher frequency signal for transferring power between the higher and lower frequency signals through the switching circuit.

Rotary electric machine and power conversion system using same

A saturable reactor device for limiting alternating and direct current in an external electric circuit. In one form, the required magneto-motive force (mmf) bias for the saturable reactor is provided by a controllable flux bias element in order to minimize the required bias power. A current sensor provides a control signal representative of the alternating or direct current passing between the source and the load. This signal is used to control the magnitude of the bias so that the mmf provided by the bias element is a function of the current driving the load, permitting a current limiting threshold at a predetermined percentage of the current applied to the load. In an alternate form, the device may be adapted to limit bipolar current in the external circuit. In this form, the device includes an input circuit and an associated direct current saturable reactor limiter. In response to direct current of either positive or negative polarity passing through the external circuit, unidirectional current is driven through the input coil of the direct current limiter. The magnitude of the unidirectional current passing through the input coil is proportional to the magnitude of the current provided by the source. When the unidirectional current exceeds a predetermined threshold, the direct current limiter effectively provides a relatively high current-limiting impedance between the source and load of the external electric circuit. When the unidirectional current is below that threshold, the direct current limiter has minimal effect on the external electric circuit.

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Newton, MA, United States of America

William E Stanton