Study On Current Sensing Technology Based On Tunnel Magnetoresistance Effect

With the deployment and advancement of smart grid and ubiquitous power Internet of things,power system has put forward higher demands on current sensing technology.There are many types of currents that power system need to measure,and it is difficult to fully meet the technical requirements of power system current measurement using existing single current sensors.The tunnel magnetoresistance(TMR)current sensor has many advantages,such as high sensitivity,high response frequency,simple structure and low price.It is a potential product for power system current measurement.This thesis studies the tunnel magnetoresistance current sensor technology.Firstly,the thesis analyzes the current measurement method of TMR sensor,and proposes a current sensor using a combination of a magnetic ring structure and a closed-loop feedback structure.The transfer function is used to analyze the characteristics of the open-loop structure and the closed-loop structure TMR current sensor.The representative magnetic sensor products at home and abroad are researched and compared,and the test platform of TMR sensor chip is built to test the characteristics of the selected TMR2503 chip.The structure of TMR current sensor is designed.The measurement sensitivity of the single conductor without magnetic ring is low,and the deviation of the conductor will bring great errors,so it is difficult to meet the measurement requirements.The error caused by the position deviation of conductor and TMR chip can be solved by introducing the concentrating ring structure.The relationship between the permeability of the concentrating ring and the shielding efficiency is analyzed.The concentrating ring structure has a certain shielding effect on stray magnetic field,and the same shielding efficiency as the shielding shell can be achieved by increasing the permeability of the concentrating ring ring.The air gap width of the magnetic concentrating ring is 5 mm.The thesis designs the signal processing circuit of TMR current sensor.The two-stage amplifying circuit of the three-op amp circuit and inverting amplifier circuit is designed to amplify the mV-level output voltage signal of the TMR chip to the V-level;the inherent offset cancellation circuit and the temperature compensation circuit of the TMR current sensor are designed,to reduce the influence of external factors on TMR current sensor and improve the measurement accuracy.The parameters and performance of the TMR current sensor are tested.The experimental platform is built to test the static characteristics and AC characteristics of the TMR current sensor.The comparison test between the TMR current sensor and other current sensors is carried out.The TMR current sensor can accurately measure the current and meet the requirements of accurate current measurement.