Abstract
The present paper proposes a refined nonlinear axial bearing model not too complex for real-time applications, which may potentially improve the estimator quality of modulation-based self-sensing. Measurements show that the AC component (ripple) of the bearing current is an underlinear function of the AC excitation voltage, which causes the bearing admittance amplitude ¦Y(jω, iac)¦ to considerably increase at low amplitudes of iac. The non-consideration of this effect might explain the poor dynamic performance observed in former implementations of modulation-based self-sensing. The model proposed in this paper includes a dynamic (rate dependent) hysteresis model of the Bertotti type, where the magnetic H field is a nonlinear function of the time derivative of flux density dB/dt. Eddy currents are modelled by a linear lumped RL ladder network (Cauer type). The proposed model gives encouraging results and is able to reproduce the observed phenomena.
