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

• Current Assignee: Donald L. Watrous
• Original Assignee: Donald L. Watrous
• Inventors: Watrous, Donald L.
• Application Number:
  US04/751,489
• Time in Patent Office: 1,082 Days
• US Class Current: 318/809
• CPC Class Codes: H02P 25/04 Single phase motors, e.g. capacitor motors
• CPC Class Codes: H02P 25/14 Universal motors H02P25/12 takes precedence

Abstract

An adjustable speed capacitor run or polyphase AC induction motor energized by phase controlled voltage is stabilized by an AC phase control circuit whose timing is referenced to the zero crossing of the capacitor voltage in an RC circuit and supplies gating signals to a thyristor in series with the motor, characterized by a degenerative feedback circuit comprising an impedance element connected to modify the capacitor voltage in such manner that the cessation of thyristor conduction modulates the timing of the next gating signal.

Claims

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.

2. A stabilized adjustable speed drive system comprising a capacitor run alternating current induction motor including two stator windings effectively connected in parallel circuit relationship and a capacitor connected in series circuit relationship with one of the windings, bidirectional conducting thyristor means connected in series circuit relationship with said induction motor, the power circuit comprising said induction motor and thyristor means being connected between a pair of power supply terminals in which appears an alternating current electric potential, a phase control circuit connected to supply gating signals to render conductive said thyristor 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 series circuit falls below the holding current of said thyristor means, said phase control circuit including the series combination of a resistor and capacitor connected between said power supply terminals, wherein the capacitor voltage across said last mentioned capacitor serves as a timing reference for the production of the gating signals, and degenerative feedback means comprising an impedance element effectively coupled between the junction of said induction motor and thyristor means and the junction of the series connected resistor and capacitor for changing the capacitor voltage as a function of the period of conduction of said thyristor means in a previous half cycle, to thereby change the timing reference, whereby the periods of conduction of the thyristor means and the phase angles of the gating signals are substantially equal and the motor is stabilized.

3. A system as set forth in claim 2 wherein the impedance element in said degenerative feedback means is a resistor, and the timing reference is provided by the passage through zero of the capacitor voltage, and the degenerative feedback means changes the zero crossing of the capacitor voltage in a leading sense with respect to the power supply terminal electric potential.

4. A system as set forth in claim 2 wherein said bidirectional conducting thyristor means comprises a triac device, and the impedance element in said degenerative feedback means is a resistor connected directly between the aforesaid junction points.

5. A system as set forth in claim 2 wherein the timing constant of the series connected resistor and capacitor in said phase control circuit is relatively short and the timing reference capacitor voltage is substantIally in phase with the power supply terminal electric potential, and said phase control circuit further includes a gating circuit connected across said last mentioned capacitor which in turn includes timing means arranged to commence the timing of the production of the gating signals upon the passage through zero of the timing reference capacitor voltage.

6. A system as set forth in claim 2 wherein the timing constant of the series connected resistor and capacitor in said phase control circuit is relatively short and the timing reference capacitor voltage is substantially in phase with the power supply terminal electric potential, and said phase control circuit further includes a monolithic integrated gating circuit connected across said last mentioned capacitor, said gating circuit in turn comprising timing means arranged to commence timing upon the passage through zero of the timing reference capacitor voltage, means for producing an output signal at the preselected phase angle, and a switching device coupled between said thyristor means and last mentioned capacitor which is turned on by said output signal to thereby apply the gating signal to said thyristor means.

7. A stabilized adjustable speed drive system comprising a power circuit including an alternating current induction motor connected in series circuit relationship with bidirectional conducting controlled solid state switching means between power supply terminals in which appear an alternating current electric potential, a phase control circuit connected to supply gating signals to render conductive said solid state switching means at a selected 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, said phase control circuit including the series combination of a charging capacitor and charging means therefor, wherein the voltage across said charging capacitor serves as a timing reference for the production of gating signals, and a degenerative feedback impedance effectively coupled between the junction of said charging capacitor and charging means and the junction of said induction motor and solid state switching means to provide an additional path for charging said charging capacitor, during intervals of nonconduction of said solid state switching means, as a function of the period of conduction of said solid state switching means in a previous half cycle, to thereby stabilize the motor.

8. A system as set forth in claim 7 wherein the series combination of said charging capacitor and charging means in connected between said power supply terminals, and said charging means comprises a resistor, and said degenerative feedback impedance is a resistor connected directly between the aforesaid junction points.