Digital power metering system

Abstract

Methods and systems for identifying the frequencies present in a power signal are provided. The systems and methods sample power signals and perform a transformation from the time domain to the frequency domain.

What is claimed is: 
     
         1 . A method for identifying harmonic and inter-harmonic information present in a power signal in a digital power meter, the method comprising:
 digitally sampling sensor data yielding digital sampled data;   performing a calibration on the digital sampled data yielding calibrated digital sampled data;   filtering the calibrated digital sampled data to yield calibrated and filtered sampled data;   detecting n consecutive zero-crossing events in the calibrated and filtered sampled data;   identifying all calibrated digital sampled data points in the range between the first zero-crossing event and the nth zero-crossing event;   storing all of the identified calibrated digital sampled data points;   resampling the stored calibrated sampled data points yielding a set of resampled calibrated sampled data points.   
     
     
         2 . The method according to  claim 1 , wherein the step of resampling insures that the total number of data points in the set of resampled calibrated data points is an integer power of 2. 
     
     
         3 . The method according to  claim 1 , wherein the number of detected zero-crossing events is 24. 
     
     
         4 . The method according to  claim 1 , further including a step of determining the frequencies present in the power signal by performing a Fast Fourier Transform (FFT) on the set of resampled calibrated sampled data points. 
     
     
         5 . The method according to  claim 1 , wherein the sensor data comprises sensed line voltages and currents. 
     
     
         6 . A digital power metering system for identifying harmonic and inter-harmonic information present in a power signal, the system comprising:
 a microprocessor programmed to perform a calibration on sampled data yielding calibrated sampled data;   a digital signal processor programmed to filter the calibrated sampled data to yield calibrated and filtered sampled data;   the microprocessor configured to detect n consecutive zero-crossing events in the calibrated and filtered sampled data;   a storage element configured to store each calibrated sampled data point in the range of the n consecutive zero-crossing events yielding a stored set of calibrated and filtered sampled data points;   the microprocessor further configured to resample the stored set of calibrated sampled data points yielding a resampled set of calibrated and filtered sampled data points.   
     
     
         7 . The digital power metering system of  claim 6 , further including an analog-to-digital converter for digitally sampling sensor data yielding sampled data. 
     
     
         8 . The digital power metering system of  claim 6 , wherein said microprocessor is programmed to resample by linear interpolation. 
     
     
         9 . The digital power metering system of  claim 6 , wherein said microprocessor is programmed to determine the frequencies present in said power signal by use of said resampled values in a Fast Fourier Transform.