A TMR DC current sensor based on dual air-gaps and multistage magnetic ring

With the deep digital and intelligent advancement of smart grids, current sensors—key secondary equipment—must satisfy wide frequency response, miniaturized deployment, and strong anti-electromagnetic interference (EMI) capability. However, traditional TMR current sensors are susceptible to stray magnetic fields under strong EMI, suffering from attenuated accuracy and significant temperature drift, restricting their reliable application in power systems. This study establishes the non-contact measurement principle based on the Biot-Savart law and TMR effect, designs a multistage magnetic ring (alternating high-permeability permalloy and high-conductivity aluminum) with symmetric dual air-gaps to suppress common-mode interference, analyzes the effects of magnetic ring stages (N=1-5) and TMR deployment via COMSOL Multiphysics simulation, and develops a signal conditioning circuit integrating two-stage amplification, second-order Butterworth filtering, bias zero-adjustment, and hardware temperature compensation. Simulation results show that when N=3, the air-gap magnetic field uniformity (H) reaches 0.787-0.837 and the coefficient of variation (CV) is 0.053- 0.062, achieving an optimal balance between magnetic concentration and uniformity. It effectively offsets external EMI and reduces errors from temperature drift and bias voltage, providing a low-cost, high-stability technical solution for accurate DC current detection in smart distribution networks.