DFT Frequency Measurement Using Positive-Sequence Angle Change
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Solution Overview
Problem
Conventional frequency measurement methods in power systems, such as those used in intelligent electronic devices, face challenges in accurately measuring frequency changes due to spectral leakage and frequency aliasing, leading to errors and inadequate response times for fast frequency changes.
Innovation Solution
A frequency measurement method employing an open-loop structure that uses Discrete Fourier Transform (DFT) calculations to directly obtain frequency-related measurement values, including frequency and frequency change rate, by calculating the positive-sequence voltage angle change, which suppresses harmonics and allows for quick response to frequency changes without iterative calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If digital phase-locked loop principle is used for frequency measurement, then measurement accuracy of electric quantities is ensured, but frequency response time is extended and cannot meet fast frequency change requirements
Solution Approach 1:
The patent segments the frequency measurement process into distinct functional modules: sampling module, positive-sequence voltage calculation module, frequency offset calculation module, and frequency-related measurement value calculation module. This segmentation eliminates iterative calculations by enabling direct computation of frequency parameters from sampled signals, thereby reducing response time while maintaining measurement accuracy.
Solution Approach 2:
The patent performs preliminary action by pre-calculating the positive-sequence voltage angle change amount using DFT on sampled signals before frequency calculation. This preliminary computation of angle changes enables direct derivation of frequency offset and frequency values without requiring iterative phase-locked loop convergence, thus accelerating the frequency response.
2Device complexity
If conventional DFT algorithms are used for phasor measurement, then calculation is simplified, but spectral leakage and frequency aliasing cause large errors in frequency and phase parameters
Solution Approach 1:
The patent changes the parameter of interest from direct phasor magnitude to positive-sequence voltage angle change amount. By calculating the angle difference between consecutive DFT results and multiplying by frequency, the patent derives accurate frequency offset values without suffering from spectral leakage effects that plague conventional magnitude-based phasor measurement methods.
3Measurement precision
If iterative calculation and successive approximation algorithms are used in digital phase-locked loop, then frequency measurement accuracy is improved, but frequency response time is extended
Solution Approach 1:
The patent replaces the mechanical iterative adjustment mechanism of phase-locked loops with a direct computational approach using DFT-based angle change calculation. This substitution eliminates the need for successive approximation iterations, enabling instantaneous frequency calculation from sampled signals and thereby dramatically improving frequency response speed while preserving measurement accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides high accuracy and rapid response to frequency changes, reducing errors and ensuring reliable measurements even under harmonic interference and external disturbances.
Implementation Method 1
obtaining a positive-sequence voltage angle change amount for a predetermined operation interval time by using a sampling sample obtained by the sampling and based on a Discrete Fourier Transform (DFT) calculation
Data Source
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AI summary
A frequency measurement method is provided, which comprising: sampling a voltage to be measured with a fixed sampling frequency; obtaining a positive-sequence voltage angle change amount for a predetermined operation interval time by using a sampling sample obtained by the sampling and based on a discrete Fourier transform (DFT) calculation; obtaining a frequency offset amount by using the positive-sequence voltage angle change amount; and obtaining a frequency-related measurement value by using the frequency offset amount. This frequency measurement method does not require iterative calculations, and directly obtains frequency-dependent measurement values, thereby responding quickly to frequency changes. In addition, a frequency measurement apparatus is also provided.