Controller for AC induction motors
First Claim
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1. A controller for an AC induction motor coupled to an AC power source, said controller comprising:
- a circuit for providing a voltage signal in phase with voltage applied to said motor from said AC power source;
a triac coupled between said motor and said AC power source, said triac having a gate and being switchable from a non-conductive state to a conductive state in response to a control signal applied to said gate, said triac remaining in said conductive state until current flowing through said triac becomes zero; and
a microcontroller coupled to said circuit and to said gate, and responsive to said voltage signal and the voltage at said gate of said triac during at least the time that said motor is to be operated after an initial start period for determining a time during each AC cycle that said triac is rendered conductive to couple said AC power source to said motor and to generate said control signal in accordance with said time.
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Abstract
A controller for use with AC induction motors utilizes a microcontroller in conjunction with a triac to control the duty cycle of the AC power applied to the motor. A voltage sensing circuit provides signals to the microcontroller. The microcontroller is also coupled to the gate of a triac. The microcontroller automatically selects the appropriate parameters for most efficient motor operation based upon the motor power factor as determined by the time at which the voltage across the motor crosses zero and the voltage at the triac gate crosses zero.
83 Citations
11 Claims
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1. A controller for an AC induction motor coupled to an AC power source, said controller comprising:
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a circuit for providing a voltage signal in phase with voltage applied to said motor from said AC power source; a triac coupled between said motor and said AC power source, said triac having a gate and being switchable from a non-conductive state to a conductive state in response to a control signal applied to said gate, said triac remaining in said conductive state until current flowing through said triac becomes zero; and a microcontroller coupled to said circuit and to said gate, and responsive to said voltage signal and the voltage at said gate of said triac during at least the time that said motor is to be operated after an initial start period for determining a time during each AC cycle that said triac is rendered conductive to couple said AC power source to said motor and to generate said control signal in accordance with said time. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A controller for an AC induction motor coupled to an AC power source, comprising:
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a circuit coupled to said motor to provide a voltage signal indicating when AC voltage applied to said motor crosses zero; a triac coupled between said motor and said AC power source, said triac having a gate and being switchable from a non-conductive state to a conductive state in response to a control signal applied to said gate, said triac remaining in said conductive state until current flowing through said triac goes to zero whereupon said triac switches to said nonconductive state; and a microcontroller connected to said circuit and to said gate of said triac for monitoring said voltage signal and said gate voltage, said microcontroller generating said control signals at least during the time that said motor is operated after an initial start up period such that the duration of time during each AC cycle that the triac connects power to said motor is varied in inverse proportion to the difference in phase between said gate voltage and said voltage signal. - View Dependent Claims (10)
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11. Apparatus comprising:
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an AC induction motor; a controller for said motor, said controller comprising; a triac coupled between said motor and an AC power source, said triac having a gate and being switchable from a non-conductive state to a conductive state in response to a control signal at a gate terminal; a circuit for providing a voltage signal indicative of when the voltage applaud to said motor crosses zero; and a microcontroller coupled to said circuit and to said gate to receive said voltage signal and the voltage at said gate, and coupled to said gate for supplying said control signal thereto during at least the time said motor is operated after an initial start up period such that the duration of time during each AC cycle that said triac is in said conductive state is varied in accordance with a predetermined relationship between said voltage signal and said gate voltage.
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Specification