Mains Frequency Detection Using Phase Interval Analysis
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Solution Overview
Problem
Mains analyzers face difficulties in accurately determining the mains frequency in voltage signals with high harmonic levels, often resorting to nominal frequencies which compromise measurement accuracy.
Innovation Solution
A method involving the calculation of two phases using the discrete Fourier transform and a window function to derive the mains frequency, allowing for precise determination even in signals with high harmonics, by adjusting the sample frequency through iterations until the desired accuracy is achieved.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage zero crossings are evaluated to derive mains frequency, then frequency detection is possible, but additional zero crossings from harmonics make it difficult to derive the period duration accurately
Solution Approach 1:
The patent extracts only the fundamental frequency component from the voltage signal by using Fourier transform to separate it from harmonic components. This allows accurate period duration derivation by focusing exclusively on the fundamental frequency's zero crossings, eliminating the interference from additional zero crossings caused by harmonics.
Solution Approach 2:
The patent performs preliminary Fourier transform analysis to identify and isolate the fundamental frequency component before deriving the period duration. This preliminary separation of the fundamental frequency from harmonics enables accurate frequency detection without the confusion of multiple zero crossings.
2Productivity
If a nominal frequency is taken as a basis for data capture when harmonics are present, then measurement process continues, but the accuracy of actual measurements is harmed
Solution Approach 1:
The patent implements a feedback mechanism where the measured fundamental frequency is continuously updated and used to adjust the measurement process. Instead of relying on a fixed nominal frequency, the system measures the actual fundamental frequency through Fourier transform and uses this feedback to maintain both productivity and accuracy even in the presence of harmonics.
Solution Approach 2:
The patent dynamically changes the frequency parameter from a fixed nominal value to a dynamically measured fundamental frequency. By using Fourier transform to continuously determine the actual fundamental frequency and adjusting measurements accordingly, the system maintains measurement accuracy while ensuring continuous operation.
3Measurement precision
If Fourier transform is used to separate fundamental frequency from harmonics, then accurate frequency detection is achieved, but computational complexity increases
Solution Approach 1:
The patent applies partial Fourier transform analysis by focusing only on the frequency range relevant to the fundamental frequency (50Hz ± a small deviation range). Instead of performing a complete spectral analysis of all frequency components, the method selectively analyzes only the necessary portion of the spectrum, reducing computational complexity while maintaining accurate fundamental frequency detection.
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
Enables reliable and accurate determination of mains frequency in voltage signals with high harmonic levels, improving measurement precision and reliability.
Implementation Method 1
a first phase φ1(X) is ascertained on the basis of the formula [Fourier transform formula] where l=0, 1, . . . and w (n) is a window function
Data Source
AI summary
A method for ascertaining a mains frequency from a voltage signal which has a particularly high proportion of harmonics includes stipulating a sample frequency for a sample collection, polling a voltage signal at equidistant times during periods of the sample oscillation. A discrete Fourier transform may be used to calculate two phases, and a phase interval between these two phases is used to infer the mains frequency.