Research On Non-contacting DC Current Transformer Based On Tunnel Magnetoresistance(TMR)

In the context of the energy revolution,the demand for electrical measurement of DC distribution network is complex due to high proportion of distributed new energy and high proportion of power electronic equipment.High-performance non-contacting current measurement has become the focus of attention for reliable grid information monitoring.As a new generation of magnetic sensing element,tunnel magnetoresistance has superior performance and holds great promises in meeting the complex electrical measurement technical requirements.This paper conducts research on the non-contacting DC current transformer based on the tunnel magnetoresistance sensing element.The research content includes:The current sensor modules based on tunnel magnetoresistance were analyzed.The interference situations were analyzed and error models were constructed based on electrical models of various modules.For the characteristics of temperature drift,hysteresis of tunnel magnetoresistance,which restrict the measurement performance,the self-compensation scheme was explored.The tunnel magnetoresistance current sensor based on the closed-loop operation was mathematically analyzed,and an equivalent circuit simulation model was built in TINA to verify the theoretical analysis.Regarding the spatial variation of the conductor that affects the measurement performance,a current sensor design scheme with dual air gaps and dual sensing elements was proposed to decreasing the susceptibility of spatial deviation and reduce the centrifugal error effectively.To ensure the consistency of the magnetic field environment in the air gap where each sensor chip is located when the dual air gap structure is adopted,from the perspective of magnetic circuit optimization,finite element analysis is used to reasonably design the magnetic core to optimize magnetic field distribution and improve measurement performance.A test prototype of a current sensor with a rated measurement current of ±50A and a measurement range of 0～±75A was built.The tests of DC measurement performance,AC measurement performance and step response performance were carried out on test platform.The direct comparison method was used to calibrate the accuracy of the prototype.The results show that the prototype can achieve high-precision measurement of DC current.