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STABILIZING PHASE CONTROLLED AC INDUCTION MOTORS

  • US 3,596,158 A
  • Filed: 08/09/1968
  • Issued: 07/27/1971
  • Est. Priority Date: 08/09/1968
  • Status: Expired due to Term
First Claim
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1. A stabilized adjustable speed drive system comprising a power circuit including an alternating current induction motor and at least one bidirectional conducting controlled solid state switching means connected in series circuit relationsHip between power supply terminals in which appears an alternating current electric potential, a phase control circuit connected between said power supply terminals and to said switching means including timing means for timing the production of gating signals to render conductive said switching means at a preselected phase angle of each half cycle of the electric potential for a period of conduction that terminates when the current in said power circuit falls to approximately zero, and degenerative feedback means comprising an impedance element effectively coupled to a junction between said induction motor and switching means for modifying said timing means as a function of the period of conduction of said switching means in a previous half cycle, whereby the periods of conduction of the switching means and the phase angles at which the gating signals are produced are substantially equal and the motor is stabilized, wherein said phase control circuit includes a series connected resistor and capacitor connected between said power supply terminals which has a time constant that is relatively short so that the voltage across said capacitor and the power supply terminal electric potential are substantially in phase, and said timing means is provided by gating circuit means fabricated as a monolithic integrated circuit and connected across said capacitor such that the capacitor voltage is a timing reference for the timing means.

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