AC Measurement Channel Calibration for Frequency-Dependent Error Correction
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Solution Overview
Problem
Existing methods for measuring electric-power network quantities, particularly frequency measurement, suffer from significant errors due to frequency differences, especially when the sampling frequency does not match the measured frequency, leading to inaccuracies in both magnitude and phase-angle calculations.
Innovation Solution
A method that calibrates the non-linearity of each measurement channel at different frequencies and creates a frequency-dependent correction function, using a matrix of correction values for discrete frequencies, which are interpolated to correct magnitude and phase-angle values, thereby eliminating errors across a wide frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fixed frequency sampling is used, then device complexity is reduced, but measurement precision deteriorates due to frequency differences
Solution Approach 1:
The patent implements dynamic sampling frequency adjustment where the sampling frequency is automatically adapted to match the measured signal frequency. The system continuously monitors the input signal frequency and adjusts the sampling rate accordingly, transforming a static sampling system into a dynamic one that maintains measurement accuracy across varying frequencies without requiring complex manual configuration
Solution Approach 2:
The patent changes the sampling frequency parameter based on the detected signal frequency. By dynamically modifying this key parameter, the system ensures that the sampling frequency remains synchronized with the measured frequency, thereby maintaining high measurement precision for magnitude and phase-angle calculations across different operating conditions
2Measurement precision
If frequency-dependent sampling is used, then measurement precision improves, but measurement errors increase due to component non-linearity
Solution Approach 1:
The patent performs preliminary calibration measurements at multiple discrete frequencies before actual operation. During calibration, the system measures the non-linearity errors of analog components at each frequency point and stores correction factors. When operating, these pre-calculated correction factors are applied to compensate for frequency-dependent errors, thereby improving reliability without sacrificing measurement precision
Solution Approach 2:
The patent implements a feedback mechanism where measured frequency information is used to select appropriate correction factors from calibration data. The system continuously monitors the input frequency, retrieves corresponding correction factors, and applies them to compensate for non-linearity errors, creating a closed-loop system that maintains high reliability across the frequency range
3Measurement precision
If calibration at multiple frequencies is performed, then measurement precision improves across wide frequency range, but device complexity increases
Solution Approach 1:
The patent divides the frequency range into discrete calibration points rather than attempting continuous calibration across the entire range. By segmenting the frequency spectrum into specific measurement points, the system achieves wide frequency-range accuracy while keeping the calibration process manageable and the data structure organized, reducing overall system complexity
Data Source
AI summary
A method and system for measuring alternating-current system quantities through measurement connections producing frequency-dependent errors, in which method the analog signal of at least one measurement channel is sampled at a selected an approximately measured frequency fm at a multiple frequency fs, creating a base series depicting a period on each measurement channel, from each base series the fundamental frequency and the magnitude or phase-angle values or both of at least one harmonic frequency component are calculated with the aid of Fourier analysis or similar, each of which is corrected with the aid of a calibrated frequency-dependent function k(f), when the selected quantities are calculated from the calibrated values.