Rogowski Coil Filter Compensation for Pole Drift Accuracy
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Solution Overview
Problem
Current signal processing systems, particularly those using coil-based current transducers like Rogowski coils, face accuracy issues due to process and temperature variations affecting the position of poles or zeros in the transfer function, leading to inaccuracies in current measurement.
Innovation Solution
An apparatus comprising a filter with matched resistor and capacitor components, an analog-to-digital converter, and a reference generator that adjusts the reference voltage to correct for changes in the filter components' values, ensuring a stable frequency response independent of component variations, and a characterization circuit to estimate and correct for gain or phase errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a low pass filter with a pole at a relatively low frequency is used to linearize the frequency response of a Rogowski coil, then the frequency response is improved, but process and temperature variations cause the position of the pole to shift, leading to measurement accuracy degradation
Solution Approach 1:
The patent implements a feedback mechanism where the actual position of the pole is continuously monitored and used to adjust the filter parameters or apply correction factors. This closed-loop approach compensates for drift caused by process and temperature variations, maintaining measurement accuracy despite environmental changes.
Solution Approach 2:
The patent employs parameter changes by dynamically adjusting filter coefficients or compensation factors based on the detected pole position. When temperature or process variations cause the pole to shift from its nominal position, the system modifies operational parameters to counteract this shift and maintain the desired frequency response characteristics.
2Reliability
If matched resistor and capacitor components are used in the filter, then component variation effects are reduced, but the complexity of the apparatus increases due to additional matching requirements and characterization circuits
Solution Approach 1:
The patent uses matched resistor and capacitor components that are replicas or copies of each other with identical or scaled values. This copying approach ensures that both components experience the same process and temperature variations, causing their effects to cancel out in the RC time constant, thereby improving reliability without requiring complex active compensation mechanisms.
3Measurement precision
If the pole position is set well away from frequencies of interest, then process and temperature variations have minimal effect, but the filter cannot provide adequate linearization of the frequency response for Rogowski coil measurements
Solution Approach 1:
The patent applies preliminary correction factors or calibration data that are determined in advance to compensate for the expected interaction between the filter and Rogowski coil frequency responses. By pre-characterizing the system and applying correction algorithms before actual measurements, the system achieves both good linearization and reduced sensitivity to component variations.
Data Source
AI summary
The response of a coil based current measuring circuit is often proportional to frequency. To correct for this a low pass or integrating function is applied to the response to linearize it. The low pass filter is made from real resistors and capacitors, and tolerances in their values significantly affect the estimate of current. The present approach can provide a way of addressing such problems. This allows consumers of electricity to have confidence in the accuracy of, for example, their electricity meter.