Control of hubless flywheel system

The increasing global adoption of renewable energy and electric vehicles (EVs) necessitates the development of efficient energy storage systems to stabilize power grids under fluctuating demand and supply. Conventional lithium-ion batteries, though prevalent, face limitations in applications requiring frequent charge-discharge cycles, such as EV charging stations. Flywheel energy storage systems (FESS), with their rapid response, high efficiency, and minimal degradation, present a viable alternative. This study examines the design, modeling, and control of a high-speed, hubless flywheel system supported by radial active magnetic bearings (AMBs). The flywheel utilizes a carbon fiber rotor, which offers high tensile strength and lightweight properties, enabling high angular speeds and improved energy storage density. The system incorporates a vertical rotor design with passive magnetic axial support and active radial control via AMBs. A model-based control approach is employed to manage the cross-coupled system efficiently. The system is modeled using a linearized dynamic plant model that incorporates actuator bandwidth and time delay components. Robust control is achieved using the Glover-McFarlane method, allowing for frequency response shaping and disturbance rejection. Experimental validation was conducted following system commissioning, with a focus on ensuring compliance with ISO 14839 for output sensitivity. A resonance issue caused by foundation dynamics was addressed by incorporating a resonance model into the control synthesis. Post-tuning results demonstrated improved stability margins within standard limits. The study confirms the effectiveness of model-based robust control in managing the dynamic behavior of high-speed, hubless flywheel systems with radial AMBs. These results support the feasibility of deploying such systems for grid support and EV charging applications in areas with limited peak power availability.