System and method for evaluating back electromotive force in a motor
First Claim
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1. A method for determining back electromotive force (EMF) in a polyphase motor, comprising:
- obtaining samples of back EMF values of said motor at regular intervals;
obtaining a first back EMF value from said samples at a first time;
at a second time subsequent to the first time, obtaining a second back EMF value from said samples;
determining a difference between the first back EMF value and the second back EMF value; and
evaluating the back EMF for the motor for purposes of next sector commutation only after a predetermined back EMF event occurs relating to the first and second back EMF values and after the prior sector commutation of the motor.
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Abstract
Methods for evaluating back electromotive force (EMF) in a polyphase motor is described. The methods include monitoring back EMF in the motor after a commutation of the motor, and evaluating the back EMF only after a back EMF event occurs after the commutation of the motor. The methods may also include monitoring a total current appearing on all phase windings of the motor after a rotor of the motor begins to rotate, and evaluating back EMF only after the total current is within a predetermined margin of the current supplied to the motor. Systems implementing the methods are also described.
89 Citations
22 Claims
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1. A method for determining back electromotive force (EMF) in a polyphase motor, comprising:
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obtaining samples of back EMF values of said motor at regular intervals; obtaining a first back EMF value from said samples at a first time; at a second time subsequent to the first time, obtaining a second back EMF value from said samples; determining a difference between the first back EMF value and the second back EMF value; and evaluating the back EMF for the motor for purposes of next sector commutation only after a predetermined back EMF event occurs relating to the first and second back EMF values and after the prior sector commutation of the motor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A system for determining back electromotive force (EMF) in a polyphase motor, comprising:
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sense circuitry for sampling back EMF values in said motor at regular intervals and for monitoring back EMF in the motor after a commutation of the motor; and a motor controller for receiving the back EMF and evaluating the back EMF only after a predetermined back EMF event occurs after the commutation of the motor, wherein the sense circuitry obtains a first back EMF value at a first time from said samples and obtains at a second time subseauent to the first time a second back EMF value from said samples; and the motor controller utilizes a difference between the first back EMF value and the second back EMF value to evaluate the back EMF. - View Dependent Claims (11, 12, 13, 14, 15)
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16. A method for evaluating observed back electromotive force (EMF) in a polyphase motor, comprising:
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monitoring a total current appearing on all phase windings of the motor after a rotor of the motor begins to rotate; and evaluating back EMF only after the total current is within a pre-determined margin of the current demanded of the motor, wherein the current supplied to the motor is provided to the phase windings of the motor by a bridge circuit connected to the phase windings, and the monitoring the total current includes obtaining the current appearing across the bridge circuit. - View Dependent Claims (17, 18, 19, 20)
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21. A system for evaluating observed back electromotive force (EMF) in a polyphase motor, comprising:
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sense circuitry for monitoring a total current appearing on all phase windings of the motor after a rotor of the motor begins to rotate; and a motor controller for receiving the total current and evaluating back EMF only after the total current is within a pre-determined margin of the current demanded of the motor, wherein; the current supplied to the motor is provided to the phase windings of the motor by a bridge circuit connected to the phase windings, and the monitoring the total current by the sense circuitry includes obtaining the current appearing across the bridge circuit; the pre-determined margin is selected so that the back EMF is evaluated only after an error component of the total current has decayed below a negligible value as signified by the total current being with the pre-determined margin of the current demanded of the motor; the motor controller controls the current demanded of the motor is controlled in a closed loop fashion; the motor is a three-phase motor; and the motor controller includes a digital signal processor. - View Dependent Claims (22)
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Specification