Modeling, Analyzing, and Suppression of EMI Effects in Eddy Current Sensors of Active Magnetic Bearings

The displacement sensor is of vital importance for the levitation control of the active magnetic bearing (AMB). For the most widely used eddy current sensor (ECS), it is easy to be affected by electromagnetic interference (EMI) produced by the high-frequency switching of the AMB drive converter. This phenomenon has been sophisticatedly researched in this article. The circuit model of the ECS along with its conditioning circuits have been constructed to predict the conducted EMI in the sensor up to 30 MHz. The mechanism of the EMI on sensor signals have been analyzed. The impact of high-frequency EMI on low-frequency closed-loop control has also been explained. The suppression methods of the EMI effect on the ECS have been proposed based on either high-frequency or low-frequency mechanism. The experiment results have shown that the constructed model can well predict the effect of EMI in the ECS, and the proposed suppression method can significantly improve the measurement accuracy of the ECS.