Litton Industrial Products, Inc.

Magnetek, Inc.

Charles E Rettig

Stanley L Mann

A voltage limit circuit for phase controlled rectifiers avoids shoot-through and limit cycling conditions by limiting the d.c. output voltage of the rectifier bridge. The circuitry follows a voltage reference signal as long as the reference signal is less than an input derived from the a.c. voltage applied to the bridge, reduced by the volt-seconds required for commutation. Should the reference signal exceed the a.c. derived input, the a.c. derived input limits the maximum available d.c. voltage. To this end, a voltage reference signal provides an output signal corresponding to the desired output voltage of the bridge. A slew limit circuit limits the rate by which the output signal may be changed. A magnitude limit circuit is coupled to the output of the slew limit circuit and provides a reference signal for the firing circuit of the rectifier bridge. The magnitude limit circuit receives the a.c. voltage derived limiting signal for limiting the reference signal to a magnitude not greater than that established by the limiting signal. The limiting signal is obtained in a commutating volt-seconds subtraction circuit that reduces an appropriately scaled a.c. voltage by an amount necessary to establish the volt-seconds required for commutation of the controlled rectifiers.

Voltage limit protection circuit for phase controlled rectifiers

A commutation sensor circuit for a DC-to-DC silicon controlled rectifier (SCR) chopper circuit to protect against commutation failure by determining the commutation capability of the chopper. This determination is made by testing two conditions, first, the applied voltage is measured and used to predict the commutation voltage available after a main SCR has been gated on and a commutating capacitor charged, and second, the available commutation voltage is measured after the main SCR has been gated on and the commutating capacitor charged. The first test allows the chopper to turn on if the predicted voltage when compared to the current flowing is sufficient to commutate the chopper. The second test initiates a commutation if the current flowing in the chopper reaches the maximum commutating ability of the chopper.

Commutation sensor circuit for a DC-to-DC silicon controlled rectifier

A DC-to-DC chopper circuit has a first switch that is selectively actuated to supply load current to a regulated bus and bus voltage to a resonating circuit which increases the applied voltage to approximately twice the value of the bus voltage, and a second switch selectively actuated so that the current on the bus flows through the resonating circuit discharging the increased voltage stored therein to zero whereupon a freewheeling circuit permits the established current to freewheel until the next chopper cycle.

DC-to-DC chopper circuit

A method for controlling the output torque condition of an induction motor includes the steps of generating a slip frequency in the motor proportional to the desired output torque condition while simultaneously establishing the magnitude and phase displacement of the stator current at preselected values. The invention also obtains the speed control of self excited alternating current motors.

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Brookfield, WI, United States of America

Charles E Rettig