Common Mode Suppression in Tunneling Magnetoresistive DC Residual Current Sensor with Conductor Geometry Optimization

With the rapid deployment of low-voltage direct current (LVDC) systems, DC residual currents have become an increasingly critical issue in distributed power networks, electric vehicle charging infrastructure, and industrial power systems, which cannot be reliably detected by conventional residual current sensors. Tunneling magnetoresistive (TMR) sensors are well suited for weak current detection due to the high sensitivity and low power consumption. However, the presence of interfering magnetic fields makes it difficult for TMR sensors to detect weak residual currents under large common mode currents. In this work, we propose a geometrically optimized conductor to suppress common mode interference. Finite element simulations reveal that the optimized conductor reduces common mode magnetic fields by 80% compared to conventional long straight conductors. A prototype DC residual current sensor is fabricated, integrating the optimized conductor and a low-noise signal processing circuit. Experimental results show a measurement error below 0.7%, a resolution of 48.5 μ A, the noise of sensor is 330 nV/√Hz and the detection limit for residual current is 1 mA under a DC common-mode current of 35 A. The DC residual current sensor demonstrating potential for applications in distributed power grids, electric vehicles, and industrial power systems.