A Novel Current Sensing Method for Multicore Cables Using Tunnel-Magnetoresistance Sensor Array

This article proposed a novel method for current sensing of multicore cables utilizing a tunnel-magnetoresistance (TMR) sensor array. In fact, multicore cables belong to multi-conductor systems. A trans-impedance is built to describe the mathematical relationship between the current phasors of the multi-conductor system and the output voltage phasors of all the magnetic sensors, based on which the current phasors can be recovered by simply performing matrix multiplication. The determination of the trans-impedance is dependent on the identification of the geometry parameters of the conductors (i.e., positions and tilt angles). Based on the output voltage phasors of the magnetic sensors at fundamental frequency, these conductor parameters can be identified by solving over-determined equations which are formulated in a form of one nonlinear least square (NLLS) problem. The value of the gain factor of the designed TMR sensor is almost a constant and the value of the corresponding phase shift is approximately zero. A real trans-impedance matrix can be obtained converted from the complex one, based on which real time current waveforms reconstruction can be achieved. Simulation study and laboratory experiments are conducted to verify the validation of the proposed current sensing method. From the simulation study, it is found that a value of lower than 5% for the maximum relative current amplitude error and the corresponding value of less than 4° for the maximum phase error can be achieved though the tilt angles of the conductors are arbitrarily varied. A probe-like current sensor is fabricated and experimentally characterized. Laboratory experiments including current phasor measurement at fundamental frequency and real-time current waveforms reconstructing are conducted. For both balanced and unbalanced three-phase cases, the testing results for current phasor measurement at fundamental frequency show that a value of lower than 8.24% for the maximum relative current amplitude error and a value of smaller than 4.46° for the corresponding maximum phase error can be achieved. Meanwhile, the current waveforms for three-phase currents having plenty of harmonics are successfully recovered in real time through experiments.