Research On The Principle Of Temperature Compensation Of GMM-FBG Current Sensor Based On All-fiber MZI

Current parameters are key parameters that reflect the operating conditions of electrical equipment and power systems.Therefore,the device Current Transformer(CT)used for current detection has an important position in the power system,and it is a key device that reflects the operating status of the power system and ensures its safe operation.However,when the traditional electromagnetic CT detects high voltage and large current,due to its own ferromagnetic coil structure,large volume,electrical connection between the high and low voltage sides,oil-filled and other structural characteristics,it is difficult to expose high-voltage insulation,and ferromagnetic is easy to appear.Problems such as saturation make it difficult to achieve safe detection of large currents.Therefore,researching a new type of current transformer that can overcome the shortcomings exposed by electromagnetic CT in large current measurement is particularly important for realizing current safety detection.At present,the new type of current transformer researched in our country is mainly an Optical Current Transformer(OCT).Because OCT adopts optical fiber material,which has the characteristics of small volume,good insulation performance and strong anti-interference ability.It can work in a small working space where traditional electromagnetic CT is difficult to work,and in special environments such as high current detection,so as to solve the difficult work of electromagnetic CT.Among several types of OCT,the GMM-FBG current sensor composed of GMM and FBG has an important research position in OCT,because FBG is wavelength coding,it not only has strong anti-interference ability and is easy to reuse,but also can overcome the influence of linear birefringence on the magneto-optical OCT based on Faraday effect,so it has an important research position in OCT.However,the temperature-strain cross sensitivity of FBG will reduce the measurement accuracy of GMM-FBG current sensor.The demodulation accuracy and cost of GMM-FBG current sensor are affected by the great difficulty of FBG wavelength coded signal demodulation and the high cost of demodulation equipment.The all-fiber Mach-Zehnder Interferometer(MZI)has good performance such as low manufacturing cost,low insertion loss,uniform output pulse,and easy multiplexing.Therefore,this thesis mainly studies the temperature compensation of GMM-FBG current sensor and the light intensity demodulation of FBG center wavelength with all-fiber MZI as the front device.The main research contents are as follows:(1)Based on the FBG sensing mechanism,through the analytical derivation and simulation analysis of the FBG reflection spectrum.Analyze the influence of different parameters on the reflection spectrum of FBG,and grasp the mechanism of temperature and strain sensing by FBG.(2)According to the classic J-A model,a magnetic-force-thermal coupling J-A model that can accurately predict the hysteresis characteristics of GMM is derived,and it is numerically solved by matlab to study the magnetostrictive strain-magnetic field and stress and temperature of GMM Relationship.Grasp the principle of magnetostrictive strain produced by giant magnetostrictive materials,the influence of temperature on the magnetostrictive strain-magnetic field curve of GMM is analyzed and mastered.,and conclude that when GMM works in the linear range of the strain-magnetic field curve,the influence of temperature is very small and can be ignored.(3)Aiming at the problem that the measurement accuracy of GMM-FBG current sensor is reduced by the influence of temperature,the principle of single and double difference compensation is mainly discussed.Considering that in the single and double difference compensation system,two FBG have the same temperature response,the temperature compensation can be realized by detecting the change of light intensity in the overlap region of double FBG antispectral.Theoretical analysis shows that the sensitivity of wavelength offset of dual-difference compensation system to current is 2 times that of single-difference compensation system.The feasibility of the dual-difference temperature compensation system is verified by the simulation analysis of the current sensing characteristics of GMM-FBG with bias magnetic field.(4)In order to solve the problem of demodulation accuracy and demodulation cost,an all-fiber MZI is proposed as the pre-device of the demodulation system.The light intensity demodulation of GMM-FBG current sensing with all-fiber MZI for desensitization temperature compensation structure,single-difference temperature compensation structure and dual-difference temperature compensation structure were explored respectively,and analyzed by simulation.The simulation results shows that the use of the all-fiber MZI output pulse to select the FBG wavelength and the demodulation method that converts the FBG wavelength change to the light intensity change can improve the demodulation accuracy.It can also use the MZI multiple output pulses to multiple GMM-FBG current sensor performs demodulation,which can reduce the demodulation device.