Induction motor speed determination by flux spectral analysis
First Claim
1. Apparatus for determining the rotational speed of an AC induction motor, supplied from an AC power source with a line frequency, having a predetermined number of poles, and having a synchronous speed which is two times the line frequency divided by the number of poles, said apparatus comprising:
- a magnetic flux transducer for sensing magnetic flux generated by the motor during operation, producing magnetic flux signals; and
a data processing system including;
a spectrum analyzer receiving signals from said magnetic flux transducer for generating a flux frequency spectrum having a set of peaks each characterized by a frequency and an amplitude,means for searching the flux frequency spectrum for a plurality of sets of particularly defined families of peaks, each set potentially including at least one family of peaks satisfying the particular family definition, having a family score and indicative of a possible rotational speed, and selecting for each set that includes at least one family the possible speed having the highest family score as a candidate speed, andmeans for determining whether there is a candidate speed with an overall score which exceeds a predetermined threshold and, if so, determining the motor rotational speed as that candidate speed.
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Abstract
Apparatus for determining the rotational speed of an AC induction motor based on a spectrum analysis of a magnetic flux signal. For a Phase I analysis, which is usually sufficient, three sets of families of peaks indicative of possible rotational speeds are defined, and the flux frequency spectrum is searched for peaks meeting the family definitions to determine candidate speeds, and to assign scores. If there is a candidate speed with an overall score which exceeds a predetermined threshold, the motor rotational speed is determined as that candidate speed. A Phase II analysis, employing a more exhaustive set of five additional family definitions, is applied when Phase I fails to reach a result.
52 Citations
17 Claims
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1. Apparatus for determining the rotational speed of an AC induction motor, supplied from an AC power source with a line frequency, having a predetermined number of poles, and having a synchronous speed which is two times the line frequency divided by the number of poles, said apparatus comprising:
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a magnetic flux transducer for sensing magnetic flux generated by the motor during operation, producing magnetic flux signals; and a data processing system including; a spectrum analyzer receiving signals from said magnetic flux transducer for generating a flux frequency spectrum having a set of peaks each characterized by a frequency and an amplitude, means for searching the flux frequency spectrum for a plurality of sets of particularly defined families of peaks, each set potentially including at least one family of peaks satisfying the particular family definition, having a family score and indicative of a possible rotational speed, and selecting for each set that includes at least one family the possible speed having the highest family score as a candidate speed, and means for determining whether there is a candidate speed with an overall score which exceeds a predetermined threshold and, if so, determining the motor rotational speed as that candidate speed. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method of determining the rotational speed of an AC induction motor, said motor producing leakage flux during operation, the method comprising the steps of:
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producing magnetic flux signals representative of the magnetic flux generated by the motor; generating a flux frequency spectrum from the magnetic flux signals, the spectrum having a set of peaks where each peak is characterized by a frequency and an amplitude; searching the flux frequency spectrum for a plurality of sets of particularly defined families of peaks, each set potentially including at least one family of peaks satisfying the particular family definition, having a family score and indicative of a possible rotational speed; selecting for each set that includes at least one family the possible speed having the highest family score as a candidate speed; determining whether there is a candidate speed with an overall score which exceeds a predetermined threshold; and if a candidate speed is determined to have an overall score that exceeds the predetermined threshold, defining the motor rotational speed as that candidate speed. - View Dependent Claims (17)
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Specification