Interferometric Voltage Sensor Error Compensation
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Solution Overview
Problem
Optical voltage sensors face systematic errors due to Faraday rotation angle deviations and mechanical misalignments, which affect measurement accuracy, especially in high-voltage DC applications, where existing compensation methods are not applicable.
Innovation Solution
A method and device that corrects interference contrast and phase shift measurements by calculating calibrated values using a complex compensation formula, accounting for errors caused by misalignments and non-45° rotations in the Faraday rotator, allowing for accurate voltage determination across a wide range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a 45° Faraday rotator is used to achieve polarization mode swapping, then the scale factor and zero point stability are improved, but systematic errors due to Faraday rotation angle deviation and mechanical misalignment occur
Solution Approach 1:
The patent applies preliminary action by performing calibration measurements at multiple known voltage points before actual voltage measurement. The system pre-determines calibration parameters (including Faraday rotation angle and alignment deviations) through these initial measurements, which are then used to correct subsequent measurements. This preliminary calibration phase captures and stores the systematic error characteristics of the specific hardware configuration, enabling accurate compensation during operation.
Solution Approach 2:
The patent employs parameter changes by measuring calibration parameters at multiple different voltage points and using these varying conditions to determine optimal compensation parameters. The system changes the operating parameters (voltage levels) during calibration to capture the full range of systematic errors, then uses these parameter variations to calculate correction factors that improve measurement accuracy across the entire measurement range.
2Adaptability or versatility
If the unambiguous voltage measurement range is extended to ±500 kV using interference-contrast-based period disambiguation, then the measurement range is improved, but the complexity of the measurement system increases
Solution Approach 1:
The patent applies feedback by using the measured interference contrast to determine the phase shift period and combining this information with the principal value measurement. The system continuously monitors the interference contrast and uses this feedback to resolve period ambiguity, enabling the extended measurement range. The feedback mechanism allows the system to adapt to different voltage levels and correctly interpret the phase measurements across the full ±500 kV range.
Solution Approach 2:
The patent uses another dimension by introducing interference contrast measurement as an additional measurement dimension alongside the principal phase value. This extra dimension (interference contrast) provides the necessary information to resolve the period ambiguity that limits the measurement range. By measuring in this additional dimension, the system can uniquely determine voltages across the extended range without increasing physical system complexity.
3Measurement precision
If calibration is performed at multiple voltage points, then the accuracy of error compensation is improved, but the calibration time and complexity increase
Solution Approach 1:
The patent applies partial action by performing calibration at a selected number of discrete voltage points rather than continuously across the entire range. The system determines the minimum necessary calibration points needed to accurately characterize the systematic errors, performing calibration only at these essential points. This approach achieves sufficient compensation accuracy without the excessive time requirement of continuous calibration, optimizing the trade-off between accuracy and calibration time.
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 provides high accuracy with errors less than 0.2%, suitable for measuring high-voltage DC applications, including HVDC systems, by compensating for systematic errors and ensuring precise voltage measurement.
Implementation Method 1
A 45° Faraday rotator inserted between the polarization-maintaining (PM) fiber and the electro-optic crystal in the voltage sensor
Implementation Method 2
into a first end of Pockels effect crystal 5, which is being exposed to the electrical field from the voltage to be measured
Implementation Method 3
At the second end of the crystal, the waves are reflected by a reflector 6 and sent back through the components 1-5
Implementation Method 4
The two returning polarizations are brought to interference in MPD optoelectronics module 1, which gives rise to a signal with a basically periodic dependence of the voltage to be measured
Data Source
AI summary
In order to measure a voltage, an electro-optic element is placed in an electrical field generated by the voltage, and light is passed from a light source through a Faraday rotator and the electro-optic element onto a reflector and from there back through the electro-optic element and the Faraday rotator, thereby generating a voltage-dependent phase shift between two polarizations of the light. The interference contrast as well as a principal value of the total phase shift between said polarizations are measured and converted to a complex value having an absolute value equal to the contrast and a phase equal to the principal value. This complex value is offset and scaled using calibration values in order to calculate a compensated complex value. The voltage is derived from the compensated complex value.