A Sliding Mode Control of a Hybrid Magnetic Bearing for Wayside Flywheel Energy Storage Systems

Recently, rail transportation agencies have been giving great interest to installing wayside energy storage systems (WESS) to store (for a short period of time) and recycle back the energy generated from regenerative braking systems. For economical and technical purposes, it is important to look for facilities to store energy for longer terms. Although a flywheel energy storage system is a promising technology for short period applications, the self-discharge problem impedes them from being applied in keeping energy for long periods. Magnetic bearings could be a good solution to improve the storability of FESS. However, they themselves could be a source for power loss. Thus hybrid magnetic bearings (HMB) are optimal solution for long-term FESS. To compensate the non-linear behavior of HMB, a sliding mode controller is proposed for stabilizing a rotor-HMB systems. Simulation results and a comparison to the decentralized PID controller with respect to the attenuation of rotor unbalance vibrations are presented.