Rogowski Coil Integration Using High-Pass Filter
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Solution Overview
Problem
Existing energy metering systems using Rogowski coils face challenges in accurately measuring current and energy due to approximation errors in analog integration and mapping errors in digital implementations, especially at higher frequencies, which affect the accuracy of metering higher order harmonics.
Innovation Solution
The method involves using a high-pass filter function with at least one zero at s=0 for the current channel and a high-pass filter function with a flat amplitude response to eliminate approximation errors in analog integration, and employing a higher order digital integration function to cancel out poles on the unit circle, thereby reducing mapping errors in digital implementations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an ideal analog integration function is used, then measurement accuracy is improved, but system stability deteriorates due to the pole at the origin
Solution Approach 1:
The patent introduces a high-pass filter as an intermediary component between the Rogowski coil and the integrator. This filter has a transfer function with a zero at the origin that cancels the pole at the origin of the integrator, thereby eliminating the stability issue while preserving the measurement accuracy of the ideal integration function.
Solution Approach 2:
The patent modifies the integrator's transfer function by changing the system parameters - specifically, it transforms the ideal integration function (with pole at origin) into a modified version where the pole is cancelled by introducing a zero at the same location through the high-pass filter, thus changing the system's stability characteristic without sacrificing accuracy.
2Stability of the object's composition
If a lossy integration function is used to improve stability, then system stability is improved, but measurement accuracy deteriorates due to approximation errors
Solution Approach 1:
The high-pass filter acts as a mediator that allows the system to use the ideal integration function without introducing approximation errors. By cancelling the pole at the origin, it enables accurate measurement while maintaining stability, avoiding the need for lossy integration approximations.
3Measurement precision
If digital implementation is used to improve integration accuracy, then measurement accuracy is improved, but new errors are introduced due to mapping and approximation errors
Solution Approach 1:
The patent replaces the problematic digital integration approach with an analog solution using a high-pass filter and ideal integrator combination. This substitution eliminates mapping errors (which occur in digital-to-analog conversion) and approximation errors (which occur in digital pole placement), achieving accurate measurement without these harmful factors.
4Measurement precision
If higher order digital integration functions are used to reduce mapping errors, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent substitutes complex higher-order digital integration functions with a simple analog high-pass filter followed by an ideal integrator. This replacement achieves the same accuracy improvement without increasing device complexity, as the analog filter can be implemented with simple RC circuits rather than complex digital signal processing.
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
This approach ensures stable and accurate measurement of the root-mean-square (rms) value of current and energy by eliminating approximation errors and minimizing mapping errors, resulting in precise metering of energy without amplitude or phase distortion across the frequency band of interest.
Implementation Method 1
The changes in the magnetic flux density passing through a conductor loop generate an electromotive force (EMF) between the two ends of the loop. The EMF is a voltage signal proportional to the di/dt of the current.
Data Source
AI summary
Devices and methods for accurately realizing the integration functions, in particular for energy metering systems using a Rogowski coil, are disclosed. In this regard, exemplary embodiments of the present invention may be constructed as two stable filters for the current (I) and voltage (U) channel. In the analog realization form, the transfer function of the voltage channel may be constructed as a high-pass filter function with at least one zero at the origin, while the transfer function of the current channel may be constructed as the multiplication of the high-pass filter function of the voltage channel and the ideal analog integration function. In the digital realization form, the transfer function of the filter for the voltage channel may be constructed as a high-pass filter function with zero(s) at the same location(s) as the pole(s) of the digital integration function, while the transfer function of the filter for the current channel is the multiplication of the high-pass filter function of the voltage channel and the digital integration function.