Center-Tapped Rogowski Coil Common-Mode Rejection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current electricity metering technologies face challenges in achieving high accuracy over a large range due to susceptibility to errors from DC magnetic fields and AC signal coupling, particularly in Rogowski coil current sensors, which are prone to noise and require costly compensation methods.
Innovation Solution
A Rogowski coil current sensor with a center-tap configuration and coupled to a common-mode rejection circuit, allowing for improved rejection of external AC fields and interface with an inexpensive single op-amp differential integrator, enhancing accuracy and reducing production costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Rogowski coil is used for current measurement, then immunity to DC current and permanent magnets is achieved, but sensitivity to AC signal coupling increases causing offset errors
Solution Approach 1:
A differential amplifier is introduced as an intermediary component between the Rogowski coil and the measurement system. The differential amplifier rejects common-mode AC signals coupled capacitively to the coil while amplifying the differential signal representing the actual current, thus eliminating offset errors caused by AC coupling sensitivity
Solution Approach 2:
The patent changes the electrical parameters of the measurement system by using a differential measurement approach instead of single-ended measurement. This parameter change transforms the system's response to AC coupling, converting what would be offset errors into rejected common-mode signals, thereby improving measurement accuracy
2Measurement precision
If additional compensation windings and precision circuits are added to CT designs, then measurement accuracy is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts the measurement function from the complex compensated CT design and implements it using a simple Rogowski coil connected to a differential amplifier. By taking out the measurement function and implementing it separately with simpler components, the system achieves high accuracy without the complexity of multiple compensation windings and precision circuits
Solution Approach 2:
The patent replaces expensive, complex compensated CT designs with a simpler, more economical Rogowski coil system. The Rogowski coil with differential amplifier provides comparable or superior accuracy at lower cost, effectively substituting expensive components with cheaper alternatives that achieve the same or better 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 solution effectively reduces noise interference from external AC fields, improving the accuracy of current measurements while minimizing production costs by leveraging a center-tapped Rogowski coil with a differential integrator circuit for enhanced common-mode rejection.
Implementation Method 1
The Rogowski coil's output is a low level voltage (VRC) that is directly proportional to the derivative of the primary side input current (Ip). The output voltage is then integrated to recover the phase and amplitude of the primary current.
Implementation Method 2
The output voltage is then integrated to recover the phase and amplitude of the primary current.
Implementation Method 3
Nearby AC voltages (VAC) may couple capacitively through Ce. This capacitively coupled VAC induces an error current that will result in an offset error out the integrator output.
Data Source
AI summary
A sensor includes a non-magnetic core having a first winding wrapped thereon. The first winding has a center tap dividing the first winding into a first winding portion and a second winding portion. The center tap is coupled to a reference voltage. The first winding portion and the second winding portion are configured to sense first AC signals, and have a balanced susceptibility to second AC signals. The differential integrating circuit is configured to provide common mode rejection of the second AC signals. The differential integrator circuit is operably coupled to the first winding portion and the second winding portion.