Sampling Rate Conversion Using PLLs for Jitter-Resistant Energy Metering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing energy metering systems face complications in energy measurement due to non-integer multiple sampling rates and line frequency jitter, necessitating complex compensation and being sensitive to line frequency deviations.
Innovation Solution
A method and device for converting sampling rates using Fast Fourier Transform (FFT) and phase-locked loops to track the fundamental frequency, enabling accurate and efficient energy measurements by resampling digital poly-phase signals, independent of ADC sampling rates and immune to line frequency jitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the sampling rate of ADC is set to be an integer multiple of the line frequency, then the calculation of energy measurements is simplified, but the system becomes sensitive to line frequency deviations and jitter
Solution Approach 1:
The patent implements a dynamic resampling system where the sampling rate is continuously adjusted to track the fundamental frequency of the power signal. The system uses frequency detection and phase-locked loops to dynamically modify the resampling rate, ensuring that the sampling rate remains synchronized with the actual line frequency despite deviations or jitter. This dynamic adaptation resolves the contradiction by maintaining measurement accuracy while keeping calculation simplified through coherent sampling.
Solution Approach 2:
The system employs feedback mechanisms through phase-locked loops and frequency detectors that continuously monitor the fundamental frequency and adjust the resampling rate accordingly. This feedback ensures that the sampling rate adapts to line frequency variations, maintaining both measurement accuracy and calculation simplicity by keeping the sampling rate as an integer multiple of the actual line frequency.
2Reliability
If the sampling rate is not an integer multiple of the line frequency, then the system is immune to line frequency jitter, but complex compensation is needed for fractional portions
Solution Approach 1:
The system dynamically adjusts the resampling rate to track the fundamental frequency, ensuring that the output sampling rate is always an integer multiple of the detected fundamental frequency. This dynamic resampling eliminates the need for complex fractional portion compensation while maintaining immunity to frequency variations through continuous adaptation.
Solution Approach 2:
The patent introduces an intermediate resampling stage that acts as a mediator between the fixed ADC sampling rate and the variable line frequency. This resampler with variable output rate converts the ADC samples to a new sampling rate that is an integer multiple of the fundamental frequency, simplifying subsequent calculations while maintaining measurement accuracy.
3Adaptability or versatility
If the sampling rate tracks the fundamental frequency dynamically, then the system is independent of ADC sampling rate and immune to line frequency jitter, but additional processing stages are required
Solution Approach 1:
The resampling system performs multiple functions: it converts from ADC sampling rate to a rate that is an integer multiple of the fundamental frequency, tracks frequency variations dynamically, and prepares signals for coherent energy measurement calculations. This multi-functional approach achieves independence from ADC sampling rate while managing processing complexity through integrated design.
Solution Approach 2:
The patent replaces traditional mechanical frequency synchronization methods with digital signal processing techniques, including Fast Fourier Transform for frequency detection and digital phase-locked loops for tracking. This substitution enables dynamic adaptation to frequency variations without mechanical components, achieving independence from fixed ADC sampling rates through software-based frequency tracking.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A method of processing power signals is provided. The method includes: receiving an analog poly-phase signal associated with power delivered using alternating current (AC); converting the analog poly-phase signal to a digital poly-phase signal sampled at a first sampling rate; detecting a fundamental frequency of the analog poly-phase signal; determining a second sampling rate, wherein the second sampling rate is based on and tracks the fundamental frequency; resampling the digital poly-phase signal at the second sampling rate; for each cycle of the resampled digital poly-phase signal: transforming the resampled digital poly-phase digital signal to a frequency-domain signal; calculating a phase angle of the reference voltage component; adjusting the resampled digital poly-phase signal by compensating the calculated phase angle; and transforming the adjusted resampled digital poly-phase signal to an updated frequency-domain signal using FFT; and calculating one or more measurements based on the updated frequency-domain signal.