This paper shows a comparison about dynamic behavior of a rotating shaft when it is suspended by 4-axis radial active magnetic bearing system. The active magnetic suspension is obtained by two different controllers which realize the robust stability and robust performance. The control systems used are \ub5-synthesis and loop shaping design procedure.
Each of these controllers is characterized by fourinput and four output signals and the
introduction of uncertainties on displacement gain and current gain is justified by the simple fact that during the time the component which constitutes these gains can be subjected to torn and worn which can lead the entire system to instability phenomena. The inputs are the
feedbacks of four displacement components relative to the four axis of radial active magnetic bearing while the outputs are the control current injected in the plant in order to provide the control of position of two section under the monitoring of ideal sensors. An ideal sensor here is meant to be able to capture small displacements and without presence of noise. The advantages of a four input controller is the absence of velocity components which are present
in the state vector such that no observer and speedsensors are need to build a feedback. The comparison of the performances is made through the introduction of same weighting function for the two control system. The weighting functions are introduced in order to define the required performances for the position and control signals. The results are produced by simulations tracking of reference and disturbance rejection are tested in order to provide elements useful to implement the goal of this paper. All simulations and results are performed by MATLab
