Active magnetic bearings (AMB) are currently under consideration for application to energy storage flywheels (ESFs). These bearings quite often suffer from high operating losses due to the rotation of the magnetic bearing journal in the stator’s magnetic field. Such losses may provide a significant obstacle to the application of AMBs to ESFs unless very unorthodox, new approaches are employed. Another impediment to the application of AMBs for this application are the significant effects that gyroscopic forces have upon the rotor’s natural frequencies and modeshapes. The speed-dependence of the rotor’s behavior greatly complicates the design of feedback controllers for the stable magnetic suspension of the rotor.
Our research seeks to develop the theory and practical knowledge for the employment of gain-scheduled, nonlinear controllers for the minimization of rotating losses so as to achieve stable and robust magnetic suspension of high-speed, flexible rotors. Such controllers should intelligently tune themselves as a function of rotor speed to account for gyroscopic effects.
Our approach to design the nonlinear feedback controllers takes advantage of the recent breakthroughs in the theory of gain-scheduled control. Using Linear Matrix Inequality (LMI) methods, robust, feedback control algorithms can be synthesized that are a continuous function of time-varying parameters. This eliminates the need for large controller look-up tables and the interpolation between entries in these tables. This method also guarantees performance even with quickly varying parameters, unlike earlier gain scheduling approaches based on look-up tables. Most importantly, these techniques can be applied to the development of controller for nonlinear systems via a quasi-LPV formulation.
