In the first part of the paper we propose a complete nonlinear dynamic model of a magnetic bearing. The bearing is made up to two controlled axes and three passive axes. This model takes into account the changeover of the power between the two coils of each controlled axis in order to control each axis without exciting currents. In this case, the model is not linear anymore. In the second part we compute a linear regulator taking into account the nonlinearity of the model. For that, we use the lsquo;lsquo;describing function approachrsquo;rsquo; (the nonlinearity is approximated by a complex gain which is a function of the magnitude of the input signal). The stability of the control is assumed first by using the frequency response of the linear part of the model and second by using the describing function of the nonlinearity. In the third part, the regulator is implemented on a digital computer with a sampling period of 0.4 ms. The matching between simulation results and experimental trials shows the accuracy of both the model and the control. Trials on the plant show the good performances of the control law especially during the crossing of critical frequencies.
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