Optimal control of the magnetic bearings for a flywheel energy storage system

With the advances of high strength/light weight composite material, high performance magnetic bearings, and power electronics technology, flywheel energy storage systems (FESS) with magnetically assisted bearings are becoming an exciting alternative to traditional battery systems. One of the challenging problems for such systems is to stabilize the sensitive rotor due to disturbances and plant uncertainties. In this paper, an optimal control system is proposed by incorporating cross-coupling technology into the control architecture, so that the synchronization performance of the rotor in the radial direction can be improved. The control scheme is based on minimization of a new quadratic performance index in which the synchronization errors in the radial direction are embedded. Stability of the control scheme is investigated through Linear Quadratic Gaussian (LQG) optimal control technique. It has been shown that with adequate control parameters the closed-loop stability can be guaranteed theoretically, and the resulting control system can provide satisfactory synchronization performance. Simulations on a compact and efficient FESS with integrated magnetic bearings demonstrate that the proposed approach is very effective to suppress the gyroscopic effort caused by the outside disturbances and model uncertainties.