Temperature Adaptive FBG-GMM Current Sensor

In order to ensure the safe and stable operation of the smart grid and avoid the occurrence of disaster accidents,it is urgent to study the current detection technology with high security,high stability,high sensitivity,large range,long life,simple structure,small volume and low cost.It becomes a new hotspot to explore the new scientific current detecting methods,especially the fiber optical current sensing technology.The FBG-GMM current sensor,which combines the giant magnetostrictive material(GMM)with the fiber grating(FBG),has attracted much attention because of its simple structure and high sensitivity.However,the current sensor needs to overcome the cross-sensitivity to temperature.In order to solve this problem,the FBG-GMM current sensor,which combines FBG-GMM sensor head with magnetic circuit system,is proposed.The temperature is eliminated by using the different responses of FBG-GMM to magnetic field and the same responses to temperature.In addition,magnetic circuit system can improve the current sensitivity by focusing magnetic field on the sensor head.FBG-GMM current sensor based on single magnetic loop system and cross-type sensor head is researched.The cross-type sensor head was designed and placed in the opening of the C-type magnetic circuit.The radial direction of the sensing FBG was parallel to the direction of the magnetic field,while the radial direction of the reference FBG was perpendicular to the direction of the magnetic field,resulting in the different magnetic field responses of sensing FBG and reference FBG.Considering the same temperature responses of the sensing FBG and the reference FBG,current demodulation and temperature compensation are realized by dual grating matched demodulation.The influence of the length of GMM rod,cross-sectional area of GMM rod,and the gap width of magnetic circuit on the magnetic flux density at sensor head is analyzed by ANSYS Maxwell software,and the results show that the magnetic field increases with the gap decreasing,the cross-section reducing,and the length of GMM rod shortening.Experimental results show that the sensing FBG and the reference FBG have the same temperature response.The output varies linearly with ampere-turn current from 1.0 A to 138.2 Awith a measurement accuracy of 16.0 m V/A.The peak-to-peak distortion of the AC current is less than 2.2% in the linear variation range.FBG-GMM current sensor based on double magnetic loop system is researched.Two C-type magnetic circuits,which are parallel to each other,are designed.There is a FBG-GMM sensor head in each magnetic circuit.The two magnetic circuits are applied to the opposite bias magnetic fields.When the measured magnetic field is simultaneously applied to the double magnetic circuits.The GMM rod in one magnetic circuit elongates and that in the other magnetic circuit shrinks,causing one FBG shifting to the long wavelength,while the other FBG shifting to the short wavelength.Considering that the same temperature response of the two FBGs,the demodulation of current and temperature compensation are realized by dual FBG matching demodulation.In order to increase the linear range and sensitivity of matching demodulation,flat-top FBGs are used.ANSYS Maxwell simulation is used to analyze the influence of interference between the two magnetic circuits.The simulation results show that with rising the distance of the two magnetic circuits,their mutual influence reduces gradually and the magnetic field passing through GMM bars increases gradually.And when the distance is larger than 20 mm,the mutual influence can be ignored.Experimental results show that the sensor output changes linearly with the ampere-turn current in the range of 0.6 A to 159.8 A with the measurement accuracy of 30 m V/A.Temperature can be compensated automatically in the range of 20~80?.The peak-to-peak distortion of the AC current is less than 1.8% in the linear variation range.