Power System Frequency Estimation Using Interpolated DFT Phasors
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Solution Overview
Problem
Existing methods for determining the frequency of an electrical power system are inaccurate, especially under conditions of rapid frequency changes and low frequency stability, which can lead to detrimental system fluctuations and fault handling challenges.
Innovation Solution
A method and device that estimate the frequency of an electrical power system by interpolating discrete Fourier transform (DFT) phasors using sampling times before and after the desired time, with the frequency interval depending on an approximated frequency, and applying a correction function to adjust the phasor estimates, thereby improving the accuracy of frequency determination and phasor estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard DFT methods are used to determine frequency, then the method is simple to implement, but the frequency determination accuracy deteriorates under rapid frequency changes and low frequency stability
Solution Approach 1:
The patent applies preliminary action by estimating a second DFT phasor at a first time interval before the first time using interpolation, before the actual frequency calculation is performed. This preliminary estimation allows the method to account for frequency changes that occur between sampling points, improving accuracy without requiring complex real-time processing during the main frequency determination step
Solution Approach 2:
The patent uses an intermediary approach by introducing an estimated DFT phasor as a mediator between the actual sampled phasor and the frequency calculation. This estimated phasor, obtained through interpolation at a previous time point, serves as an intermediate value that helps bridge the gap caused by frequency variations, enabling more accurate frequency determination while maintaining a relatively simple computational structure
2Measurement precision
If frequency determination is performed without interpolation, then the computational process is fast, but the accuracy deteriorates when frequency varies from nominal
Solution Approach 1:
The patent applies partial action by performing interpolation only for the second DFT phasor estimation at a previous time point, rather than interpolating all phasors. This selective application of interpolation provides sufficient accuracy improvement for frequency determination while avoiding the excessive computational overhead that would result from interpolating every phasor in the sequence
Solution Approach 2:
The interpolation operation is performed in advance to estimate the second DFT phasor before the main frequency calculation. This preliminary computation allows the system to prepare accurate reference values ahead of time, reducing the computational burden during the critical frequency determination phase and minimizing real-time processing delays
3Reliability
If DFT phasors are used directly without correction, then the processing is straightforward, but the accuracy is insufficient under severe system contingencies
Solution Approach 1:
The patent implements feedback by using the determined frequency to update the approximation of the system frequency for subsequent calculations. This feedback mechanism allows the system to adapt to changing conditions in real-time, improving reliability under severe contingencies by continuously refining the frequency estimates based on the most recent measurements and interpolated values
Solution Approach 2:
The system performs preliminary frequency determination using the interpolated phasors before applying fault handling measures. This preliminary action ensures that accurate frequency information is available in advance for decision-making processes, improving system reliability during contingencies without requiring complex real-time adjustments during the actual fault response
Data Source
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AI summary
A method for providing a frequency of an electrical quantity in an electrical power system comprises obtaining (30), with respect to a first time, a first discrete Fourier transform, DFT, phasor of an electrical quantity in the electrical power system, estimating (32) a second DFT phasor at a time interval before the first time, where the time interval depends on an approximated frequency, and determining (34) the frequency at the first time based on the first and the second DFT phasor.