Digital Power Metering Resampling to Reduce Spectral Leakage
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Solution Overview
Problem
Digital power metering systems face spectral leakage issues due to non-integer sample rates, leading to false spectral components when determining power signal frequencies, as the adjustable sample clock lacks precision to set the required frequency for all input frequencies.
Innovation Solution
The system measures the fundamental frequency of the power signal, determines if the sampling rate is coherent, and if not, resamples the signal using interpolation to produce coherent resample values, allowing for accurate frequency domain transformation and reduction of false spectral components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the sampling rate is set to a fixed value determined by hardware clock, then the system operation is simple, but spectral leakage occurs when the sampling rate is not an integer multiple of the signal frequency
Solution Approach 1:
The system dynamically adjusts the sampling rate based on the measured fundamental frequency of the power signal. Instead of using a fixed sampling rate, the system calculates the required sampling rate as an integer multiple of the measured frequency and adjusts the digital clock accordingly to achieve coherent sampling, thereby eliminating spectral leakage while maintaining operational simplicity.
Solution Approach 2:
The system changes the sampling rate parameter dynamically to match the signal characteristics. By measuring the fundamental frequency and setting the sampling rate to an integer multiple (e.g., 64x, 128x) of this frequency, the system ensures that an integer number of cycles are captured during each FFT window, preventing spectral leakage and improving measurement precision.
2Measurement precision
If the digital clock frequency is adjusted to achieve coherent sampling, then spectral leakage is reduced, but the clock precision is insufficient for all input frequencies
Solution Approach 1:
Instead of trying to achieve precise continuous frequency adjustment of the clock, the system transitions to a discrete approach by selecting from predefined integer multiples (64x, 128x, 256x, etc.) of the measured fundamental frequency. This dimensional change from continuous to discrete frequency selection resolves the precision limitation of the hardware clock while maintaining coherent sampling.
Solution Approach 2:
The system introduces an intermediate calculation step that determines the required sampling rate as an integer multiple of the measured frequency. This intermediary approach allows the system to work within the hardware clock's precision limitations while achieving the desired coherent sampling by selecting the closest available integer multiple.
3Measurement precision
If resampling is performed using interpolation, then coherent sampling is achieved, but computational overhead increases
Solution Approach 1:
The system performs preliminary frequency measurement and determines the appropriate integer multiple factor before conducting the FFT analysis. By pre-calculating the required sampling rate adjustment based on the measured fundamental frequency, the system avoids complex real-time resampling operations and reduces computational overhead while maintaining spectral analysis accuracy.
Data Source
AI summary
A digital power metering system reduces spectral leakage when determining the frequencies present in a power signal by a technique that includes sampling the signal and performing a transformation from the time domain to the frequency domain. The system initially measures the fundamental frequency of the power signal, and samples the power signal at a known sampling rate to produce digital sample values representing the power signal. The system then determines whether the known sampling rate is within a preselected range of a rate that is coherent with the measured fundamental frequency. If the answer is negative, then the system resamples the signal at a rate that is coherent with the measured fundamental frequency to produce resample values representing the signal, so that the frequencies present in the power signal can be determined from the resample values.