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Composite control for soft start and dynamic braking of a three-phase induction motor

  • US 4,482,853 A
  • Filed: 08/24/1981
  • Issued: 11/13/1984
  • Est. Priority Date: 08/24/1981
  • Status: Expired due to Term
First Claim
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1. A soft start control circuit for a three phase induction motor conveniently modifiable so as to provide a dynamic braking function comprising:

  • a source of three phase power having a first, second and third supply line;

    a selector circuit providing for operator selection of RUN and BRAKE modes;

    a three phase voltage controller having silicon controlled rectifiers connected in said supply lines for connecting said source of three phase power to said motor;

    another silicon controlled rectifier connected between two terminals of said three phase induction motor;

    means to control the firing of said another silicon controlled rectifier;

    means for providing an adjustable positive ramp signal;

    means for providing a sawtooth wave form signal for and synchronized with each of said first, second and third supply lines; and

    a first, second and third phase control circuit means for controlling the firing angles of said silicon controlled rectifiers;

    said first, second and third phase control circuit means being responsive to said positive ramp signal and said sawtooth waveform signal for controlling the firing angles of said silicon controlled rectifiers to provide a soft start for said motor; and

    means to provide an adjustable brake torque signal;

    means to provide an adjustable brake timer signal determining the duration of said brake torque signal;

    means to provide a second timer signal to become active at the termination of said brake timer signal;

    said first phase control circuit means being responsive to said brake torque signal for controlling the firing angle of said silicon controlled rectifier in said first supply line to provide a dynamic brake for said motor; and

    means responsive to said second timer signal to discontinue said supply of three phase power on said first, second and third supply lines.

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