Sensorless speed detection circuit and method for induction motors
First Claim
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1. A circuit for detecting rotational speed of a rotor in an induction motor, the motor including a phase winding connected to an AC power supply, the circuit comprising:
- switching means for selectably opening and closing the connection of the winding to the AC power supply, such that when the connection is closed, there is developed across the winding a periodic voltage waveform from the AC power supply, and such that when the connection is subsequently opened, there is developed across the winding a residual periodic voltage waveform induced by the rotor.amplitude rejection circuit means for extracting the frequency component of the periodic voltage waveform, creating a square wave with edges corresponding to the zero-crossing points of the periodic voltage waveform;
controller means for controlling the duty cycle of the switching means and for measuring the time interval between selected edges of the square wave.
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Abstract
The present invention provides a sensorless circuit for detecting rotational speed of a rotor in an induction motor. The circuit includes a switch between the AC source driving the motor and a motor phase winding. When the switch is closed, there is developed across the phase winding a voltage waveform from the AC source. When the switch is subsequently opened, there is developed across the winding a residual voltage waveform induced by the rotor. The speed of the motor is determined by measuring a time interval between selected points on the voltage waveform.
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Citations
18 Claims
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1. A circuit for detecting rotational speed of a rotor in an induction motor, the motor including a phase winding connected to an AC power supply, the circuit comprising:
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switching means for selectably opening and closing the connection of the winding to the AC power supply, such that when the connection is closed, there is developed across the winding a periodic voltage waveform from the AC power supply, and such that when the connection is subsequently opened, there is developed across the winding a residual periodic voltage waveform induced by the rotor. amplitude rejection circuit means for extracting the frequency component of the periodic voltage waveform, creating a square wave with edges corresponding to the zero-crossing points of the periodic voltage waveform; controller means for controlling the duty cycle of the switching means and for measuring the time interval between selected edges of the square wave. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13)
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12. An improved motor of the type including a rotor driven by an AC power supply connected to a phase winding, the improvement comprising:
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switching means for opening and closing the connection of the winding to the AC power supply, such that when the connection is closed, there is developed across the winding a periodic voltage waveform induced by the AC source, and such that when the connection is subsequently opened, there is developed across the winding a residual periodic voltage waveform induced by the rotor; amplitude rejection circuit means for extracting the frequency component of the periodic voltage waveform, creating a square wave with edges corresponding to the zero-crossing points of the periodic voltage waveform; controller means for controlling the duty cycle of the switching means and for measuring the time interval between selected edges of the square wave.
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14. A method for detecting rotational speed of a rotor in an induction motor, the motor including a phase winding connected to an AC power supply, the method comprising:
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providing switching means for opening and closing the connection of the winding to the AC power supply, such that when the connection is closed, there is developed across the winding a periodic voltage waveform from the AC power supply, and such that when the connection is subsequently opened, there is developed across the winding a residual periodic voltage waveform induced by the rotor; extracting the frequency component of the periodic voltage waveform, thereby creating a square wave with edges corresponding to the zero-crossing points of the periodic voltage waveform; controlling the duty cycle of the switching means and measuring the time interval between selected edges of the square wave. - View Dependent Claims (15, 16, 17, 18)
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Specification