This paper investigates the magnetic saturation problem of self-sensing electromagnetic levitation system and presents a novel self-sensing scheme. The proposed approach employs a demodulation technique. By superimposing a high frequency voltage, the resulting electromagnet coil currents have ripples that can be used for gap sensing. This paper shows the effect of magnetic saturation on the gap sensing and the gap length is not uniquely determined when using the relation between the ripple, control current and the gap in simulations. The results imply that the constraint conditions are to be determined to solve the problem. The proposed approach utilizes the dynamical motion model of the electromagnetic levitation system to uniquely identify the gap. By using the system behavior information, the gap can be uniquely estimated. To incorporate the dynamical model with the gap sensing algorithm, the unscented Kalman filter is employed. The proposed estimator is demonstrated in simulations. The results show that it is possible to deal with magnetic saturation by using the proposed gap sensing scheme. The estimator has a good accuracy in wide gap range compared to the conventional method.
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