TMR array with circular skeleton coil for high-current measurement

Abstract

DC high current measurement is one of the important supporting technologies of the power system. As an emerging current sensing technology, tunnel magnetoresistance (TMR) has attracted more and more attention due to its advantages of high sensitivity and good linearity. But the TMR sensor is not suitable for high current measurement, and its accuracy can be further improved. Aiming at these problems, this paper proposes a TMR array with a circular skeleton coil for high current measurement. Eight TMR chips are evenly installed on the circular skeleton coil to measure the magnetic field generated by the primary current carrying conductor, and the output of the feedback amplifier generates a compensation current to the feedback winding to generate a compensation magnetic field, so that the magnetic flux in the sensor is almost zero. The circular structure can reduce measurement errors caused by wire offset and external interference. Since there is no iron core, the nonlinear errors are also avoided. Simultaneously, the feedback loop designed based on zero magnetic flux principle can reduce the hysteresis error and expand the measurement range, making the sensor suitable for DC high current measurement. This paper proposes a new TMR array current sensor model, builds a prototype and compares it with a closed-loop TMR current sensor with an iron core. Experimental results proved that the TMR array sensor’s DC measurement error could be lower than 0.01%, compared to 0.32% of the closed-loop current sensor. Moreover, the proposed current sensor consistently has higher measurement accuracy in the full range of primary current.