Signal-Processing Circuit for Lightning Current Measurement
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Solution Overview
Problem
Current signal processing circuits using Rogowski coils struggle with high accuracy when measuring currents with large dynamic ranges and steep signal edges, leading to integration errors, particularly with lightning currents, which are not accurately represented or distorted, limiting their application due to the need for costly and bulky shunt resistors.
Innovation Solution
A signal processing circuit combining a first passive integrator, a non-inverting active integrator, and a second passive integrator with a differentiating element, which attenuates steep-edged signals, reducing the slew rate processed by the active integrator and compensating for the frequency response of the second passive integrator, allowing accurate measurement of highly dynamic currents like lightning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a non-inverting active integrator is used to process signals from a Rogowski coil, then the circuit can handle large voltage swings, but integration errors occur when signals have very high edge steepness or slew rate (greater than 10 kA/μs)
Solution Approach 1:
The signal processing circuit is divided into multiple stages: a first passive integrator stage, a non-inverting active integrator stage, and a second passive integrator stage. Each stage handles specific aspects of signal processing, with the first stage preparing the signal and the second stage finishing the integration, thereby preventing integration errors from high slew rate components while maintaining voltage swing handling capability.
Solution Approach 2:
A differentiating element is introduced as an intermediary component between the active integrator and the output. This differentiating element compensates for the frequency response effects of the second passive integrator and ensures accurate reproduction of the integrated signal, particularly for high slew rate components.
2Measurement precision
If shunt resistors are used to measure lightning currents, then accurate measurement of high dynamic range currents is achieved, but the systems become voluminous, complex, and permanently installed
Solution Approach 1:
The patent replaces the mechanical/shunt resistor-based measurement system with an electronic signal processing system using Rogowski coils and integrated circuitry. This substitution eliminates the need for bulky shunt resistors and complex installation infrastructure, enabling portable and easily installable lightning current measurement systems.
Solution Approach 2:
The circuit uses carefully selected time constants and frequency responses in the passive integrators to optimize performance for lightning current measurement. The first passive integrator has a time constant optimized for preparing the signal, while the second passive integrator has a time constant optimized for final integration, both working together to accurately capture lightning current waveforms.
3Measurement precision
If the second passive integrator is added to attenuate steep-edged signals, then the active integrator processes signals with lower slew rate, but the frequency response is affected
Solution Approach 1:
The differentiating element provides a form of feedback compensation by counteracting the frequency response changes introduced by the second passive integrator. This ensures that the overall frequency response of the signal processing circuit remains accurate across the relevant bandwidth, particularly for high-frequency components of lightning currents.
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 configuration enables accurate measurement of highly dynamic currents, reducing the complexity and cost of lightning current measurement systems, making them more applicable for widespread use, especially in exposed systems like wind turbines, thereby enhancing safety and knowledge about lightning effects.
Implementation Method 1
A Rogowski coil outputs the differential of the measured current as a voltage at its output
Implementation Method 2
Both active and passive circuits for integrating a signal are known
Implementation Method 3
it is therefore necessary to prepare such a measurement signal using subsequent integration
Data Source
Figure 1~3
AI summary
The invention relates to a signal-processing circuit (1), comprising at least one signal path (2) between an input (3) and an output (4) of the signal-processing circuit (1), wherein: the signal path (2) has a first passive integrating element (5) and an active integrator (6); the active integrator (6) is designed as a non-inverting active integrator (6); the first passive integrating element (5) and the active integrator (6) are connected in series within the signal path (2). According to the invention, the signal path (2) additionally has a second passive integrating element (7) and a differentiating element (20).