Method and apparatus for quiet variable motor speed control
First Claim
1. An apparatus for controlling the speed of an AC motor to be driven from an AC supply voltage from an AC source, comprising:
- a first series capacitor adapted to be coupled in series electrical connection between the AC source and the AC motor;
a shunt switch adapted to be coupled in shunt electrical connection across the AC motor, the switch having a control input; and
a control circuit coupled to the control input for controlling the conduction time of the shunt switch;
whereby the motor speed is controllable in dependence upon the conduction time of the shunt switch and wherein the control circuit causes the shunt switch to become conductive when the voltage across the motor is approximately zero volts.
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Accused Products
Abstract
An apparatus for controlling the speed of an AC motor comprising a switch adapted to be coupled in parallel with power terminals for the AC motor; a capacitor coupled in series with the parallel combination of the switch and the motor; the capacitor adapted to provide an AC supply voltage from an AC source to the parallel circuit comprising the motor and the switch; and a control circuit for controlling the conduction time of the switch in order to vary the speed of the motor. The switch is preferably pulse-width modulated at a frequency twice the line frequency of the AC supply voltage, and the switch is turned on when the voltage across the AC motor is zero volts. The apparatus is operable to provide for continuously variable control of the motor speed while minimizing acoustic noise in the motor.
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Citations
34 Claims
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1. An apparatus for controlling the speed of an AC motor to be driven from an AC supply voltage from an AC source, comprising:
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a first series capacitor adapted to be coupled in series electrical connection between the AC source and the AC motor; a shunt switch adapted to be coupled in shunt electrical connection across the AC motor, the switch having a control input; and a control circuit coupled to the control input for controlling the conduction time of the shunt switch; whereby the motor speed is controllable in dependence upon the conduction time of the shunt switch and wherein the control circuit causes the shunt switch to become conductive when the voltage across the motor is approximately zero volts. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A method for controlling the speed of an AC motor driven from an AC supply voltage from an AC source, comprising the steps of:
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coupling a first capacitor in series electrical connection between the AC source and the AC motor; coupling a shunt switch in shunt electrical connection across the AC motor, the shunt switch having a control input for controlling the conduction time of the shunt switch; and controlling the conduction time of the shunt switch to vary the speed of the motor; whereby the motor speed is controllable in dependence upon the conduction time of the shunt switch and wherein the step of controlling causes the shunt switch to become conductive when the voltage across the motor is approximately zero volts. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
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Specification