Analysis on the fundamental properties of active magnetic bearing control systems by a transfer function approach

The fundamental properties of active magnetic bearing controllers are investigated from the standpoint of output regulation in the presence of deterministic disturbances. A transfer function approach is used in the analysis. The variable to be regulated is selected from rotor displacement, coil current and bearing force. The treated disturbance is stepwise or harmonic; the latter is caused by rotor unbalance. The essential properties of the controller achieving output regulation for step disturbances are derived. Those for unbalance disturbance are also shown by using complex-variable representation, which makes the procedure of analysis similar to that for constant disturbances. The derived controllers for unbalance compensation are converted into two types of real-variable representation: state equation and convolution integral. It clarifies the equivalence between the independently developed unbalance compensation controllers. It is also shown that the obtained results can be utilized in designing controllers.