US 4,065,704 AGranted

Static speed control circuit for polyphase induction motors

AssigneeGeneral Electric Company

InventorFrancis M. Bailey

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Abstract

A modified three-phase bridge circuit, incorporating resistors and thyristors connected in specific configuration in one leg of each phase circuit and diodes in a second leg, is adapted for connection to the motor rotor. A speed control signal, modulated with a triangular waveform of predetermined frequency, below the instantaneous rotor frequency, is applied to a plurality of AND circuits acting as pulse width modulators. Each AND circuit has an output coupled to the gate of one thyristor in each phase circuit. Changes in speed control signal representative of calls for increasing speed produce sequentially, on successive outputs, a train of pulses increasing in pulse width to full turn on. Additional thyristors are thus gated on in each phase circuit to modify the effective resistance presented by the resistors in each leg so as to smoothly decrease the resistance of the bridge circuit.

Claims18

Dependent claims

A rotor current control circuit adapted to modify the speed of a wound rotor motor by modifying the effective resistance of a polyphase network comprising a plurality of interconnected phase circuits adapted to be connected to the multiple phase rotor windings of the motor, comprising:

a. each of said phase circuits comprising a plurality of parallel connected series networks;
b. each of said series networks comprising resistance means and thyristor means connected to be self-commutated by the phase signals induced in the phase windings of the rotor windings;
c. a source of speed control signal whose magnitude is representative of the desired speed of said wound rotor motor;
d. control means comprising an input coupled to said source, and a plurality of outputs;
e. gating means coupled from each of one of said outputs to gate on the thyristor means in a specified one of said series networks of each phase circuit;
and
f. said control means being constructed to sequentially produce signals on consecutive ones of said outputs responsive to magnitude changes of said speed control signal representative of calls for increasing motor speed to consecutively gate on the thyristor means of additional ones of said parallel connected networks of each phase circuit so that the resistance means of additional ones of said parallel connected series networks are inserted in parallel in each phase circuit.

4 more elements

A rotor current control circuit for modifying the speed at a three phase full wave bridge whose three phase terminals are adapted to be connected to the terminals of the motor rotor windings, comprising:

a. a first leg of each of the three phase circuits of said bridge comprising unilaterally conducting means;
b. a second leg of each of the three phase circuits of said bridge comprising a plurality of resistance means and a plurality of thyristor means connected between first and second end terminals of said second leg;
c. each phase terminal of said bridge being connected to one terminal of said unilaterally conducting means and to one end terminal of the second leg of one of said phase circuits;
d. means for interconnecting the other terminal of all of said unilaterally conducting means and the other end terminal of each second leg;
e. said thyristor means and resistance means being connected such that conduction of additional ones of said thyristor means of the second leg incrementally reduces the resistance between said first and second end terminals;
f. said unilaterally conducting means being poled in one direction and the thyristor means of each second leg being poled in the opposite direction such that current flow between any phase terminal and its first phase leg is in opposing direction to current flow between said phase terminal and its second phase leg;
g. a source of speed control signal whose magnitude is representative of the desired speed of said wound rotor motor;
h. control means comprising an input coupled to said source and a plurality of outputs;
i. gating means coupled from each of said plurality outputs and connected to gate on a specified one of said thyristor means of the second leg in each of the three phase circuits;
and
j. said control means being constructed to sequentially produce signals on consecutive ones of said outputs responsive to magnitude changes of said speed control signal representative of calls for increasing motor speed to consecutively gate on additional ones of said thyristor means in each of the three phase circuits so that the resistance between said first and second end terminals of each second leg is reduced.

8 more elements

Dependencies are inferred from the claim text.