Integrated Micro -Flywheel Concept and Design: A Massively Micro Modularity Approach

In this paper, we propose a new flywheel energy storage approach using micro -rotors that is safe and free of gyroscopic effects. Moreover, due to the micro size of the rotor, it will have higher specific energy/power and energy/power density than previously proposed flywheel systems and offers many advantages such as flexibility in size, shape and en ergy output characteristics. Thus, its application could range from small consumer electronics to automobile and aerospace applications. We call this Massively Micro Modularity (MMM) approach. In MMM approach, the storage device consists of many independe ntly controlled tiny cells insulated from one another and thus is safer and more robust than one big flywheel. In each cell, energy is stored kinetically in tiny spherical or cylindrical rotor rotating at high speed and suspended by electrostatic instead o f magnetic bearings. Energy is drawn from the rotating magnetic field emanating from the magnetized rotor side. The key to the advantages described above is the small size of the rotor. We show by analyses that as the size of the rotor decrease; the moment um that causes gyroscopic effect and stresses on the surrounding container reduces dramatically. Thus, the specific energy/power is closer to the flywheel theoretical limit due to a reduction in the weight of the structure needed to contain the rotor. Anot her consequence of the small rotor size is that it is more robust to environmental disturbances thanks to the use of electrostatic bearings. Unlike magnetic force that is proportional to volume, electrostatic force is proportional to surface area. As the r otor volume reduces, the control authority, defined as the ratio between the suspension force and the weight of the rotor, increases dramatically in the electrostatic bearing. To demonstrate the feasibility of such suspension concept, we successfully suspe nded a small rotating cylindrical rotor in one axis using electrostatic force while generating enough power from its permanent magnet to light up an LED for about 1 second. Finally, we discuss the various challenges as well as promises of this new technol ogy and suggest future research directions.