Research Of GMM Fiber Current Sensor

With the good insulation and wide dynamic range,optical current sensor has be used to the development of the new generation of power system online monitoring,digital power grid.Take advantages of the high reliability of fiber Bragg grating and the high magnetostrictive coefficient,fast response speed of giant magnetostrictive material Terfenol-D.The current transformer,composed of the fiber Bragg grating and giant magnetostrictive material,can meet the specific requirement of digital power system.For the problems of cross sensitivity of fiber Bragg grating counter stress and temperature in GMM-FBG current sensor,a new differential current sensor is put forward,the sensing head of this kind of sensor is composed of two combination of FBG and GMM,which are placed in two symmetrical magnetic circuit of the adjacent air gap and was applied the same size and opposite direction's bias magnetic field.When the measured current is applied to the two magnetic circuits,the two sensing heads will feel different direction of magnetic field,obtaining differential mode signal.But under the influence of temperature,obtaining common mode signal.the system automatically suppress common mode signal to eliminate the influence of temperature on the measurement.The differential current sensor realize the measurement of alternating current.The influence of the hysteresis nonlinearity caused by the gaint magnetostrictive material in the GMM-FBG current sensor is studied,first modeling of GMM materials by J-A model and preisach model is studied respectively,in the modeling process,it is found that the parameters of these models are complicated to solve and the real-time correction of nonlinear hysteresis is difficult to implement.Therefore,we propose two kinds of hysteresis nonlinear compensation methods based on graphics law,namely ratio and vertex coordinates fitting,through analysis of the law of these known hysteresis loops,which is adopted to predict the unknown input currentcorresponding to the hysteresis curve mathematical model,and by using the inverse model correct the hysteresis nonlinearity of voltage signal which is obtained by the sensor,the signal of the input current can be obtained.Finally,through the correction of alternating current prove that the input current signal can be reconstructed accurately with the correction method.Comparing with no correction,the instantaneous error and amplitude error can be reduced in the measurement range.For the problems of low resolution in differential current sensor,a kind of high resolution current sensor based on Fabry-Perot interferometer principle is proposed,cavity length of interferometer is tuned by current to be measured,which have the same frequency with output signal,and is proportional to output signal in amplitude.A quadrature intensity demodulation method based on narrow-band distributed feedback laser is used to achieve demodulation of cavity length of Fabry-Perot interferometer.Finally the experimental results show that resolution of current sensor based on Fabry-Perot interferometer raised nearly 16 times comparing with differential GMM-FBG current sensor.