Linearization of Force Characteristics of Active Magnetic Bearings for the FPGA-based LQ-controller

This paper discusses a linear-quadratic (LQ) control and nonlinearities compensation of a rotor suspended by Active Magnetic Bearings (AMBs). The control structure is based on a state-space controller with additional integrative feedback, current estimator and disturbance estimator. An effective compensation of performance variations in dynamic force characteristics of AMBs is performed using two nonlinear principles. Firstly, the usage of the inverse nonlinearity, a well-known method in control engineering is studied. Secondly, the novel model reference based method is introduced and validated. It is shown that the proposed compensation provides certain advantages over conventional linearized model based controllers. The overall control is tested with the flexible rotor model and the nonlinear AMBs. Finally, we present an integration of the proposed compensation into the digital controller. Accurate modeling of the AMB nonlinearities in a Field Programmable Gate Array (FPGA) based controller is achieved by using multivariable interpolation and look-up table.