Digital Integrator for Rogowski Coil Current Sensing
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Solution Overview
Problem
Current Rogowski coil-based current sensing circuits face challenges in accurately measuring current due to small output voltages and susceptibility to noise, especially under large temperature variations, which affect precision in metering and control applications.
Innovation Solution
A digital integrator is introduced in the current sensing circuit, which includes input terminals for the Rogowski coil output voltage, filtering elements, an amplifier, an analog-to-digital converter, a digital integrator implementing a discrete-time transfer function, and a direct current blocker filter to produce a digital current output signal proportional to the primary current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an analog integrator is used in the current sensing circuit, then the circuit can integrate the Rogowski coil output voltage, but the output voltage becomes even smaller and more susceptible to noise
Solution Approach 1:
The patent replaces the analog integrator (electronic circuit) with a digital integrator implemented through software algorithms on a microprocessor. The Rogowski coil output is amplified, converted to digital signals via ADC, and then integrated using digital computation methods. This substitution eliminates the noise amplification issues inherent in analog integrators while maintaining the integration function, thereby improving measurement precision without increasing noise susceptibility.
Solution Approach 2:
The patent introduces an analog-to-digital converter (ADC) as an intermediary between the analog Rogowski coil output and the digital processing stage. This ADC converts the analog voltage signal to digital form before integration, allowing the system to benefit from both analog signal conditioning and digital processing advantages. The digital domain acts as an intermediary that preserves signal integrity while enabling precise integration without noise contamination.
2Volume of moving object
If the current sensing circuitry is integrated with the Rogowski coil, then the overall device size is reduced, but temperature variations cause component property changes that affect measurement accuracy
Solution Approach 1:
The patent implements temperature compensation through feedback mechanisms. Temperature sensors monitor the thermal conditions of the integrated circuitry, and the microprocessor uses this feedback information to adjust measurement parameters or apply correction algorithms. This feedback loop compensates for temperature-induced component drift, maintaining measurement accuracy despite the compact integrated design that exposes components to varying temperatures.
Solution Approach 2:
The patent employs parameter changes to counteract temperature effects. The system dynamically adjusts electronic parameters (such as gain, sampling rate, or integration constants) based on detected temperature conditions. By changing these parameters in response to temperature variations, the system maintains consistent measurement accuracy across different thermal environments while preserving the compact integrated structure.
3Object-affected harmful factors
If ferrite beads are used to suppress high frequency noise, then noise filtering is improved, but the circuit complexity increases
Solution Approach 1:
The patent replaces passive analog filtering components (ferrite beads and RC filters) with active digital filtering implemented in software. The microprocessor applies digital filter algorithms to the ADC output signals, eliminating the need for additional passive filtering components. This substitution maintains effective noise suppression while significantly reducing circuit complexity and component count.
Solution Approach 2:
The patent extracts the noise filtering function from the analog domain and relocates it to the digital domain. Instead of using ferrite beads and analog RC filters in the signal path, the system takes out these passive components and implements equivalent filtering functionality through digital signal processing algorithms. This extraction simplifies the analog circuitry while maintaining or improving noise rejection performance.
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
The digital integrator enhances signal precision and noise resistance, enabling accurate current measurement across varying temperatures and improving performance in protection, metering, and monitoring applications.
Implementation Method 1
The Rogowski coil 2 includes coils wound over a non-magnetic core... The output of the Rogowski coil 2 is a voltage v R (t) between its output terminals 4,6
Implementation Method 2
Ferrite beads 14, 16 are electrically connected to the terminals 10, 12 and suppress high frequency noise in the voltage v R (t)
Data Source
Figure 1
Figure 2~3
Figure 4~6
AI summary
A current sensing circuit (100) for use with a Rogowski coil (2) arranged around a conductor having a primary current includes input terminals (102,104) structured to receive an output voltage of the Rogowski coil, an analog to digital converter (112) structured to convert a differential voltage to a digital differential voltage signal, a digital integrator (114) structured to receive the digital differential voltage signal, to implement a discrete-time transfer function that is a transform of a transfer function of an analog integrator, and to output a digital integrator output signal, and a direct current blocker filter (116) structured to remove a direct current bias from the digital integrator output signal and to output a digital current output signal that is proportional to the primary current in the conductor.