Gradiometric Current Sensor for Skin Effect Compensation
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Solution Overview
Problem
Current sensors face challenges in accurately measuring AC currents with high frequency components due to the skin effect, which increases the effective resistance of electrical conductors, making it difficult to achieve precise measurements across a wide frequency range.
Innovation Solution
A current sensor system utilizing a gradiometric sensor device positioned at a specific 'sweet zone' relative to the busbar, measuring the magnetic field gradient, which is substantially proportional to the AC current amplitude, independent of frequency from 100 Hz to 2000 Hz, allowing for improved accuracy without frequency compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If magnetic sensors are used to measure AC currents, then galvanic separation and compact size are achieved, but measurement accuracy deteriorates due to the skin effect at high frequencies
Solution Approach 1:
The patent changes the spatial parameters of the sensor system by positioning two magnetic sensors at specific locations relative to the busbar (at a distance of 0.5mm to 4.0mm from the busbar surface and spaced 0.5mm to 4.0mm apart). This geometric configuration creates a differential measurement that compensates for skin effect-induced errors, maintaining measurement accuracy across frequencies from 100 Hz to 2000 Hz while preserving galvanic separation
Solution Approach 2:
The patent divides the measurement function into two separate magnetic sensors instead of using a single sensor. By segmenting the measurement into two spatially separated sensing points, the system can compute the magnetic field gradient, which provides frequency-independent AC current measurement accuracy while maintaining galvanic isolation
2Ease of operation
If conventional current sensors are used, then measurement simplicity is maintained, but measurement accuracy deteriorates for high frequency AC currents due to skin effect
Solution Approach 1:
The patent modifies the measurement approach by using a differential configuration with two sensors positioned at specific distances from the busbar. The evaluation unit calculates the magnetic field gradient based on the difference between the two sensor readings, which inherently compensates for skin effect without requiring complex frequency-dependent calibration or compensation circuits, thus maintaining operational simplicity while improving accuracy
3Device complexity
If single sensor measurement is used, then device complexity is reduced, but measurement accuracy worsens due to frequency dependence
Solution Approach 1:
The patent employs two magnetic sensors instead of one, segmenting the measurement function spatially. This segmentation enables the system to measure the magnetic field gradient, which provides frequency-independent accuracy for AC currents up to 2000 Hz. The additional sensor and gradient calculation add minimal complexity while achieving the desired measurement precision across the full frequency range
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 system provides accurate measurement of AC currents with minimal processing power, requiring only a single sample period, and maintains high accuracy across the specified frequency range, even for currents with multiple harmonics, by using a predefined constant factor for calculation.
Implementation Method 1
each configured for measuring a magnetic field component oriented in a second direction perpendicular to the first direction (e.g., in the thickness direction of the busbar)
Implementation Method 2
the sensor device being configured for determining a magnetic field difference or a magnetic field gradient along the first direction based on these magnetic field components
Data Source
Figure 1(a)~1(c)
Figure 2(a)~2(c)
Figure 3(a)~3(c)
AI summary
A current sensor system (200) for measuring an AC electrical current, comprising: a busbar (201) having a thickness (T) and a width (W); a sensor device (202) comprising two sensor elements (H1, H2) spaced apart (dx) along a first direction (X) for measuring two magnetic field components (Bz1, Bz2) oriented in a second direction (Z); the sensor device configured for determining a magnetic field difference (ΔBz), and for determining the AC current based on said difference. The sensor device (202) is positioned relative to the busbar (201) such that a reference point (R) in the middle between the two sensor elements (H1, H2) is located at a first distance (ds) from a side (S) of the busbar from 70% to 110% or from 70% to 95% of the width (W) of the busbar, and is located at a second distance (Zs) from 0.5 to 4.0 mm from the busbar.