Research On Signal Demodulation System In All Fiber-optical Current Transformer

Reflected-Sagnac interferometer fiber-optic current transformer is a kind ofoptical fiber current transformer.Being compared with the traditional currenttransformer based on electromagnetic effect, it has many merits: small size and lightvolume, wide measurement frequency band, and be out of ferromagnetic saturation andoily contamination. Thus, more and more researchers at home and abroad focus on it,The research on reflective Sagnac interferometric fiber-optic current transformer inDomestic is also more and more. In this article we will introduce include the principleof the fiber-optic current transformer, the system composition and structures,anti-jamming algorithm, and finally we build a reflective Sagnac interferometricfiber-optic current transformer having high anti-jamming capability. Firstly, thisarticle introduce the generation of all-optical fiber-optic current sensor non-reciprocalphase difference principle, the theory of wave optics, use the Bessel functionderivation method, establishment of a theoretical model of this system, focusing onanalysis of the system phase modulation errors, pointed out that the high-frequencycarrier signal modulation interference impact on system performance.Secondly, introduce the basic principles and the classification of the all-fibercurrent transformer, so that readers can have a preliminary understanding of theall-optical fiber current transformer, the reflection-type all-fiber current transformererror theory, in order to improve the all-fiber the current measurement accuracy of thecurrent transformer, for sinusoidal modulation schemes proposed an improved signaldemodulation method. Expression of the effective modulation depth, Analysis the threesources of outside interference under the effective modulation depth in practicalengineering applications. In order to overcome these disturbances, we use high-orderharmonic component solutions of the modulation depth values in real time, in order toachieve the modulation phase of the disturbance compensation. Phase modulation ofthe adaptive compensation algorithm, and the realization of the principle of thealgorithm is explained.Again, in order to verify the feasibility of the phase modulation of the adaptivecompensation algorithm, this paper put forward the all-fiber current transformer signal detection and processing, analysis, screening finalize the data acquisition card+LabVIEW program implementation, and from hardware, software, algorithms conducta detailed analysis of the program, to prepare for the follow-up validation of thealgorithm and experimental.Finally, reflective Sagnac interferometric fiber-optic current transformer systemprototype testing, experimental results show that the measured current from200A to1500A range, the improved algorithm of the system anti-jamming performanceincreased by30times, the system measures the relative deviation to maintain below0.2%, to meet the requirements of high-precision current measurement.In this paper, the innovation lies in:1. the laboratory demodulation system adaptive the intelligent correction modulationdepth change, dependent objects can effectively control demodulation, the eliminationof parasitic amplitude modulation.2. after extensive testing, the data show that the interference intensity of the phasemodulator within the range of from0.1%to20%, the compensation algorithmcompared to the traditional algorithm, greatly improve the stability of the measurementaccuracy to meet the0.2measurement requirements.