Measurement of Small-Magnitude Direct Current Mixed With Alternating Current by Tunneling Magnetoresistive Sensor

Measurement of small-magnitude direct current (dc) mixed with alternating current (ac) is crucial in the power systems in which large-scale renewable energy and power electronics are used. This research proposes a method to design a nonintrusive surface-mount current sensor that can measure milliampere dc mixed with ac of different amplitudes based on the tunneling magnetoresistive (TMR) sensors. A sensor module configuration that uses a high-sensitivity TMR sensor to detect small-magnitude dc and ac was proposed. Moreover, because the high-sensitivity TMR sensor was susceptible to saturation, a medium-sensitivity TMR sensor was used to detect the large-magnitude ac. A signal processing framework was built, in which the mean and standard deviation of the detected waveforms were calculated to obtain the dc and ac components of the current under measurement, and the measurement error due to the TMR sensor saturation was also reduced by a compensation algorithm. The results showed that the sensor could accurately measure dc lower than 40 mA mixed with the root-mean-square ac ranging from 100 mA to 2 A.