Robustness of Self-Sensing Magnetic Bearing

Self-sensing magnetic bearings work without position sensors. The position measurement, which is required by the controller, can be deduced from the electromagnetic interaction between stator and rotor. The self-sensing method discussed in this paper is based on controlling the voltage over the coils and measuring the current through the coils. This method can be realized with a minimal amount of hardware and therefore with low costs. On the other hand several earlier experiments have shown, that this method needs a complicated adjustment procedure of the controller. Furthermore with optimum adjustment the system robustness is low. The goal of this paper is to analyze the sensitivity of a self-sensing magnetic bearing to the controller parameters. It will be shown, that stability within the whole air gap can only be achieved at the expense of system robustness. The low system robustness is characterized by one or two low frequency poles of the closed-loop.