Legendre Sequence Pulse Signal for Insulation Resistance Measurement
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Solution Overview
Problem
Existing methods for determining insulation resistance and leakage capacitance in ungrounded electrical networks face challenges with interference, particularly in systems like solar systems with inverters, where measuring disturbances is impractical, leading to inaccurate results due to unknown interference signals.
Innovation Solution
A method using a novel 3-valued periodic time signal represented by Legendre sequences, with pulse values of 0, 1, and -1, applied in a pattern corresponding to a prime number period, allowing for spectral decomposition and determination of ohmic and capacitive insulation resistance, while filtering out deviating values to reduce interference influence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sinusoidal measurement signal is used, then measurement precision is improved under ideal conditions, but measurement reliability deteriorates when interference signals are present at the test frequency
Solution Approach 1:
The patent applies a periodic pulse train measurement signal instead of a sinusoidal signal. This periodic action with multiple discrete frequency components allows the measurement system to probe the insulation resistance across a spectrum of frequencies, making it possible to identify and exclude frequency components affected by interference through spectral analysis.
Solution Approach 2:
The measurement signal is segmented into multiple frequency components through spectral decomposition. By analyzing the response at each frequency component separately and identifying outliers, the method segments the measurement problem to eliminate the influence of interference at specific frequencies while maintaining overall measurement accuracy.
2Reliability
If a periodic pulse train with multiple frequency components is used, then measurement reliability is improved under interference, but device complexity increases due to spectral decomposition requirements
Solution Approach 1:
The patent replaces complex hardware filtering mechanisms with signal processing algorithms. Instead of using physical filters to eliminate interference, the method uses digital spectral analysis and statistical evaluation to identify and exclude affected frequency components, reducing hardware complexity while maintaining reliability.
Solution Approach 2:
The method changes the measurement approach by using a periodic pulse train with specific characteristics (prime number periods, Legendre sequences) that facilitate spectral decomposition. This parameter change enables the use of computational methods rather than complex hardware, managing device complexity through intelligent signal design.
3Measurement precision
If spectral decomposition and outlier filtering are applied, then measurement precision is maintained under interference, but loss of time increases due to additional processing steps
Solution Approach 1:
The patent performs preliminary spectral decomposition and outlier identification during the measurement process itself, rather than as a separate post-processing step. By integrating the filtering logic into the measurement acquisition phase, the method minimizes additional processing time while ensuring measurement precision is maintained.
Data Source
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AI summary
The invention relates to a method for determining the insulation resistance in an ungrounded DC or AC electrical network, wherein the DC or AC network has an ohmic (Rf) and capacitive (Cf) insulation resistance between the network and earth, wherein a periodically repeating sequence of voltage pulses is applied to the DC or AC network to be monitored via an ohmic network coupling (Ri) between the network and earth, characterized in that the sequence of voltage pulses is formed with three different, predefined pulse voltage values, wherein the number of voltage pulses applied in one period corresponds to a prime number, and wherein the amplitude of the pulse voltage values is defined by a Legendre sequence.