TMR Busbar Current Sensor With Good Frequency Characteristics

Busbar current sensor without magnetic core is used more and more in compact power electronic equipment due to its small size and lightweight. The differential measurement technique is generally adopted to resist external magnetic interference. The sensitivity of busbar current sensors varies with the frequency of the sensed current due to the skin effect in the busbar. Traditional coreless busbar current sensors can accurately measure dc current, but the measurement error increases when sensing high-frequency ac current. A coreless sensor configuration based on four tunneling magnetoresistance (TMR) chips is proposed in this article with high measurement accuracy for both dc and high-frequency ac currents while eliminating the effect of magnetic stray field. An optimization method is introduced for the layout of the TMR chips around the busbar in order to obtain a current error below 1.5% up to 1 kHz. The effectiveness of the proposed sensor configuration and layout optimization method are verified by finite element simulation and prototype tests.