Research On GMR Wide-band DC Current Sensor Based On Gradient Field Detection

DC power equipment is very common in power electronics systems.Real-time and reliable DC current detection has a significant role in the safe and stable operation of the system.With the application of wide-band gap semiconductor devices of Si C and Ga N materials in electrical equipment,the dynamic current frequency continues to increase,so increasing the detection frequency of current sensors has become a research topic for many scholars.This paper presents a Giant Magnetoresistance(GMR)DC current sensor based on gradient magnetic field detection.Compared with traditional DC sensors,it has the characteristic of wide detection frequency bandwidth.The application of GMR chips based on gradient magnetic field detection in gear coding has been widely known,but there is no precedent for current detection in the survey literature.This article introduces in detail the detection principle,internal structure,and chip characteristics of the magnetic gradient magneto GMR chip,and provides a theoretical basis for its application in current detection.Subsequently,the current sensing method of GMR sensors is analyzed,and a GMR current sensing scheme based on gradient magnetic field detection is proposed.Compared with other types of current sensors,it has the characteristic of wide detection frequency bandwidth.Because the adopted GMR chip is sensitive to the gradient magnetic field and not sensitive to the absolute magnetic field,it is necessary to establish a design method of the GMR current sensor based on the gradient magnetic field detection.This article gives a detailed design process and design method for the proposed current sensor,including three parts: structural design,magnetic design,and hardware circuit design.In the structural design,this article considered the requirements of insulation and GMR detection position adjustment to achieve the device fixation.In the part of magnetic design,this article gives the complete reference steps of magnetic design,constructs the gradient magnetic field at the position of the magnetic ring gap,and gives the mathematical derivation of the optimal boundary of the magnetic ring gap.The NSGA2-?algorithm is used for optimization.According to the excellent results,the optimal working point was selected according to the processing difficulty and magnetic saturation,so the design of the magnetic field at the gap of the core was completed.In the hardware circuit design part,in order to meet the requirements of most application scenarios,this article has amplified the GMR output signal.In order to make the full use to the wide-band detection capability of the GMR chip and enable the current sensor to meet the needs of high frequency,the high frequency anti-interference design of the hardware circuit was analyzed in detail,from the aspects of eliminating inductive coupling noise and avoiding circuit oscillation,theoretical derivation and circuit simulation.Based on the observation of experimental phenomena,a magnetic coupling noise model was established,and this theory was applied to PCB layout.The method of laminated wiring was used to eliminate the magnetic coupling noise.In order to avoid amplifier oscillation,an amplifier oscillation model considering parasitic parameters is established,the influence of parasitic parameters on the amplifier is analyzed,and a reference for the compensation is given.During the simulation,the PCB board's parasitic parameters were considered,and the parasitic parameters were brought into the circuit for simulation,so as to judge the rationality of the anti-interference design of the PCB board.Due to the characteristics of analog circuits that are sensitive to parasitic effects at higher frequencies,in order to give a reference design for high-frequency current sensors to avoid unknown circuit oscillations,this article also includes op amp circuits built with discrete devices and op amps built with integrated chips.The two schemes of the circuit were simulated and compared experimentally.The results show that the integrated op amp has good input and output characteristics,is not easy to oscillate,and is easy to debug.However,the op amp built with discrete devices has better bandwidth,but it is difficult to debug,and it is easy to be affected by parasitic parameters.With the use of filters,both schemes achieve the detection of wideband DC current.