Waveform library for characterizing an AC power line spectrum
First Claim
1. An apparatus coupled to an alternating current power line for characterizing an alternating current power line voltage or current frequency spectrum comprising:
- a. means for acquiring a power line voltage or current waveform and converting it into an acquired time-domain representation, coupled to the alternating current power line;
b. means for comparing the acquired waveform to a library of previously stored waveforms, the library having a digital time-domain representation and a corresponding frequency-domain representation for each waveform stored;
c. means for retrieving the corresponding frequency-domain representation, if there is a waveform stored in the library which corresponds to the acquired time-domain representation within a difference threshold;
d. means for converting the acquired time-domain representation into an acquired frequency-domain representation, if there is no waveform stored in the library which corresponds to the acquired time-domain representation within a difference threshold; and
e. means for storing the acquired frequency-domain representation in the waveform library, if there is no waveform stored in the library which corresponds to the acquired time-domain representation within a difference threshold.
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Abstract
An apparatus and method for characterizing an alternating current power line which uses a library of waveforms and associated spectra of digitally sampled alternating current power system voltage or current waveforms. The library of waveforms is built as new waveforms are measured from the alternating current power line. A measured waveform that is not found in the library will be converted to frequency-domain representation, using a Discrete Fourier Transform, that will then be stored in the library. When the library becomes full, the frequency domain representation of the new waveform will be stored in place of the least used waveform currently stored in the library.
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Citations
21 Claims
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1. An apparatus coupled to an alternating current power line for characterizing an alternating current power line voltage or current frequency spectrum comprising:
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a. means for acquiring a power line voltage or current waveform and converting it into an acquired time-domain representation, coupled to the alternating current power line; b. means for comparing the acquired waveform to a library of previously stored waveforms, the library having a digital time-domain representation and a corresponding frequency-domain representation for each waveform stored; c. means for retrieving the corresponding frequency-domain representation, if there is a waveform stored in the library which corresponds to the acquired time-domain representation within a difference threshold; d. means for converting the acquired time-domain representation into an acquired frequency-domain representation, if there is no waveform stored in the library which corresponds to the acquired time-domain representation within a difference threshold; and e. means for storing the acquired frequency-domain representation in the waveform library, if there is no waveform stored in the library which corresponds to the acquired time-domain representation within a difference threshold. - View Dependent Claims (2, 3, 4)
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5. An apparatus coupled to an alternating current power line for characterizing an alternating current power line voltage or current frequency spectrum comprising:
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a. means for acquiring sampled values of a power line voltage or current waveform at a predetermined interval of time forming an acquired signal, the means for acquiring coupled to the alternating current power line; b. first means for converting the sampled values into digital values forming a digital time-domain representation of the waveform; c. second means for converting the digital time-domain representation into a corresponding frequency-domain representation; d. first means for storing a plurality of the digital time-domain representations and their corresponding frequency domain representations, forming a waveform library; e. means for comparing a digital time-domain representation of a subsequent measured waveform with each of the plurality of digital time-domain waveforms stored in the waveform library for determining if the subsequent measured waveform representation corresponds to any of the plurality of waveform representations stored in the waveform library within a difference threshold; f. means for retrieving the corresponding frequency-domain representation of the corresponding digital time-domain representation, if there is a waveform representation stored in the waveform library which corresponds to the subsequent measured waveform within the difference threshold; and g. second means for storing a frequency=domain representation of the subsequent measured waveform if there is no waveform representation stored in the waveform library which corresponds to the subsequent measured waveform within the difference threshold wherein the difference threshold determines how closely the subsequent measured waveform must match a digital time-domain representation of a waveform stored in the waveform library and further wherein the difference threshold is adjusted according to whether or not the frequency-domain representation of the subsequent measured waveform is approaching any one of predetermined threshold limits on voltage or current Total Harmonic Distortion or predetermined limits on individual current harmonics.
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6. An apparatus coupled to an alternating current power line for characterizing an alternating current power line voltage or current frequency spectrum comprising:
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a. means for acquiring sampled values of a power line voltage or current waveform at a predetermined interval of time forming an acquired signal, the means for acquiring coupled to the alternating current power line; b. first means for converting the sampled values into digital values forming a digital time-domain representation of the waveform; c. second means for converting the digital time-domain representation into a corresponding frequency-domain representation; d. first means for storing a plurality of the digital time-domain representations and their corresponding frequency-domain representations, forming a waveform library; e. means for comparing a digital time-domain representation of a subsequent measured waveform with each of the plurality of digital time-domain waveforms stored in the waveform library for determining if the subsequent measured waveform representation corresponds to any of the plurality of waveform representations stored in the waveform library within a difference threshold; f. means for retrieving the corresponding frequency-domain representation of the corresponding digital time-domain representation, if there is a waveform representation stored in the waveform library which corresponds to the subsequent measured waveform within the difference threshold; and g. second means for storing a frequency-domain representation of the subsequent measured waveform if there is no waveform representation stored in the waveform library which corresponds to the subsequent measured waveform within the difference threshold. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13)
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14. A method of determining a frequency spectrum of an alternating current power line voltage or current waveform comprising the steps of:
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a. acquiring sampled values of the power line voltage or current waveform at a predetermined interval of time; b. convering the sampled values into digital values forming an acquired digital time-domain representation of the waveform; c. comparing the acquired digital time-domain representation with each of a plurality of stored digital time-domain representations stored in a waveform library, the waveform library having a corresponding stored frequency-domain representation for each stored digital time-domain representation, to determine if the acquired digital time domain representation matches any of the stored digital time-domain representations within a difference threshold; d. retrieving a corresponding stored frequency-domain representation from the waveform library if the acquired digital time-domain representation matches one of the stored digital time-domain representations; e. converting the acquired digital time-domain representation into a corresponding acquired frequency domain representation if there is no match; and f. storing the corresponding acquired frequency domain representation in the waveform library if the acquired digital time-domain representation does not match any of the stored digital time-domain representations wherein the difference threshold determines how closely the digital time-domain representation must match a stored digital time-domain representation and further wherein the difference threshold is adjusted according to whether or not the frequency-domain representation of the waveform is approaching predetermined threshold limits on voltage or current Total Harmonic Distortion or predetermined limits on individual current harmonics.
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15. A method of determining a frequency spectrum of an alternating current power line voltage or current waveform comprising the steps of:
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a. acquiring sampled values of the power line voltage or current waveform at a predetermined interval of time; b. converting the sampled values into digital values forming an acquired digital time-domain representation of the waveform; c. comparing the acquired digital time-domain representation with each of a plurality of stored digital time-domain representations stored in a waveform library, the waveform library having a corresponding stored frequency-domain representation for each stored digital time-domain representation, to determine if the acquired digital time-domain representation matches any of the stored digital time-domain representations within a difference threshold; d. retrieving a corresponding stored frequency-domain representation from the waveform library if the acquired digital time-domain representation matches one of the stored digital time-domain representations; e. converting the acquired digital time-domain representation into a corresponding acquired frequency-domain representation if there is no match; and f. storing the corresponding acquired frequency-domain representation in the waveform library if the acquired digital time-domain representation does not match any of the stored digital time-domain representations. - View Dependent Claims (16, 17, 18, 19, 20, 21)
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Specification