The Research On Signal Processing Technology Of All Fiber Optical Current Transducer

With the rapid development of electric power industry， powertransmission system capacity increases. Under this kind of high voltageand high current environment, the traditional electromagnetic currenttransducer can not meet the needs of the modern electric power industrybecause the exposed defects. All fiber optical current transducer (AFOCT)has advantages, such as small size, light weight, high security and highmeasurement precision. Considerable development in the research ofAFOCT has been made since the1960s.This paper focuses on the research of AFOCT signal processingtechnology. Signal processing technology is divided into two classes,which are known as polarization detection type and interference detectiontype signal processing technology, according to the AFOCT signaldetection methods. The architecture of the reflective AFOCT based on the interference detection type signal processing technology is established.This paper analyzes theoretical basis of the AFOCT, includingpolarized light theory, Jones matrix and the Faraday effect. Thearchitecture of the reflective AFOCT is analyzed in this paper. Themathematical analysis in light signal transmission is carried out usingJones matrix. The mathematical form of the receiving signal is obtained.The methods of the first harmonic and harmonic division are advanced.The harmonic division is established as the research object of this paperthrough the comparative analysis.This paper discusses the design and realization of signal transmissionend and receiving and processing end of the reflective AFOCT signalprocessing in detail. The design of the signal transmission end includes thegeneration and modulation of light signal, the setting of phase modulatorworking point and the generation of modulation signal and local oscillatorsignal. The method of laser control, the design of laser drive circuit and thedesign of TEC temperature control are discussed in detail. The setting ofthe phase modulator working point is carried out according to themaximum system sensitivity criterion. The DDS technique based on FPGAis used to generate modulation signal and local oscillator signal. Thedesign of the receiving and processing end includes receiving and amplification of the light signal, coherent demodulation, analog to digitalconversion, the realization of harmonic division based on FPGA and thedesign of output interface. Photoelectric conversion and signalamplification circuit and the design of8-pole active low pass filter arediscussed in this paper. FPGA is used to realize the harmonic divisionalgorithm because of its high precision and high speed calculation. Noprecision loss of FPGA calculation is the guarantee of the high precision ofthe system. The design of the output interface is carried out according tothe demands of the merging unit.In this work we finish the design and implementation of the AFOCTsignal processing. The effects of phase modulation depth, harmonicdemodulation balance and phase deviation on the AFOCT are analyzedtheoretically and experimentally. The optimization method is proposedaccording to the analyzing result. The optimized AFOCT can measure thecurrent in the range of2~2000A. The relative measurement error is within0.5%. It reaches the performance of class0.5S.