# Two Stage Fractional Order Control Approach to Design an Optimal Controller for A Small Size Rotor Having Internal Dissipation

TL;DR: This approach not only eases out the implementation of digital/analog realization of a Fractional Order PID (FOPID) controller with its integer order but at the same time it also preserves the advantages of fractional order controller.

Abstract: Rotating machines and its applications directly affect the basic economic issues and deals very closely with human life. Its safe operation is hence an absolute necessity. Rotors with speed higher than a specific threshold value become unstable due to rotating damping forces produced by the dissipation in rotor material, couplings or due to friction in tool-tips and splines. Some techniques do exist for stabilizing rotors however they are not well suited for small, micro and mini rotor systems. Orbital response function and 2-stage sub-optimal controller tuning methodology in rotor system actuated by a piezo actuator for providing adequate damping force has been used to keep the rotor stable. The approximated integer order PID gains thus obtained from conformal mapping-based FO method of stage 2 tuning pushes the closed loop poles of the system towards greater damping as compared to stage 1. This approach not only eases out the implementation of digital/analog realization of a Fractional Order PID (FOPID) controller with its integer order but at the same time it also preserves the advantages of fractional order controller. Simulation is done on MATLAB & SIMULINK. The analysis of the performances for both the cases are discussed.

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