Rogowski Coil Equalisation for Saturation-Free Current Measurement
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Solution Overview
Problem
Current measurement systems using Rogowski coils or similar sensors face challenges with signal saturation and poor signal-to-noise ratio due to the positioning of the corner frequency of the analog filter outside the frequency range of interest, leading to inaccurate measurements and increased costs for high dynamic range ADCs.
Innovation Solution
Analog filters with corner frequencies positioned within the frequency range of interest, combined with digital equalizers that compensate for changes in group delay and magnitude response, ensuring a constant gain and group delay across the frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the corner frequency of the analog filter is positioned outside the frequency range of interest, then signal saturation is avoided, but signal-to-noise ratio deteriorates and measurement accuracy decreases
Solution Approach 1:
The filtering function is segmented into two parts: an analog filter with corner frequency within the frequency range of interest to maintain good signal-to-noise ratio, and a digital equalizer to compensate for the filter's frequency response characteristics. This segmentation allows each component to operate optimally without requiring the analog filter corner frequency to be positioned outside the measurement band.
Solution Approach 2:
A digital equalizer is introduced as an intermediary component that compensates for the frequency response changes introduced by the analog filter. The equalizer adjusts the frequency response to maintain measurement accuracy while allowing the analog filter to operate with its corner frequency within the frequency range of interest, thus avoiding signal saturation while preserving measurement precision.
2Measurement precision
If the corner frequency of the analog filter is positioned within the frequency range of interest, then signal-to-noise ratio improves, but gain and group delay become non-constant across the frequency range
Solution Approach 1:
The system uses digital signal processing with equalization that effectively implements feedback to compensate for the analog filter's frequency response variations. By measuring or characterizing the filter's frequency response and applying compensating gains through the digital equalizer, the system maintains constant overall gain across the frequency range of interest while allowing the analog filter to operate with optimal signal-to-noise ratio.
3Measurement precision
If high dynamic range ADCs are used to avoid clipping, then measurement accuracy is maintained, but system cost and power consumption increase
Solution Approach 1:
The analog filter performs preliminary action by attenuating high-frequency components that could cause clipping in the ADC, while its corner frequency is positioned within the frequency range of interest to maintain good signal-to-noise ratio. This preliminary filtering action allows the use of lower dynamic range ADCs without sacrificing measurement accuracy, thereby reducing system cost and power consumption.
Data Source
AI summary
Various current measurement systems and methods of signal processing are disclosed. In one example, there is a current measurement system that includes a filter with a corner frequency within the operating frequency range of the current measurement system. This provides a system with good SNR, whilst also preventing or reducing the likelihood of output saturation during large di/dt spikes. The system further includes an equaliser arranged to compensate for the phase and/or magnitude response of the filter within the operating frequency range.