A flywheel energy storage system (FESS) with a permanent magnet bearing (PMB) and a pair of hybrid ceramic ball bearings is developed. A flexibility design is established for the flywheel rotor system. The PMB is located at the top of the flywheel to apply axial attraction force on the flywheel rotor, reduce the load on the bottom rolling bearing, and decrease the friction power loss. The magnetic force of the PMB is analyzed through finite element method, and the force with the air gap of the PMB is verified experimentally. A squeeze film damper (SFD) is introduced to support the bottom rolling bearing, suppress lateral vibration, and enhance the stability of the flywheel rotor system. A dynamic model of FESS is established through transfer matrix method, Jones-Harris rolling bearing theory, and a finite length bearing dynamic model for SFD, which is verified by measuring the amplitude-frequency response. The effect of SFD radial clearance and unbalanced mass distribution on the dynamics of FESS is discussed. A spin-down test for the FESS prototype is conducted in a moderate vacuum. Results show that the hybrid bearing and flexibility design for the rotor system allow for the use of a small rolling bearing to reduce the power loss of FESS caused by friction. The developed FESS is simple in structure, stable without active control, low in cost, and convenient in maintenance.

Flywheel energy storage system with a permanent magnet bearing and a pair of hybrid ceramic ball bearings

Because of the complicated running condition and many unpredicted factors such as unmodelled dynamics and external disturbances, the fault analysis of the high-speed motorized spindle is proved difficult. In this paper, a novel experimental method is proposed to research the vibration characteristics of the running high-speed motorized spindle. The method consists of four steps. Firstly, the vibration signal measurement and processing system are built according to data collector and signal analysis software, and then, the vibration signal of the spindle extracted from sophisticated experimental environment is studied by using harmonic wavelet transform for its advantages, such as ultra-narrow band, high resolution detection and ability of extracting weak signal. After that, local frequency domain zooming technique of harmonic wavelet packet is employed to study the vibration spectrum of the spindle at eight different rotating speeds. Furthermore, the axis orbit of the rotor is purified successfully, which can serve as verification basis for subsequent on-site fault diagnosis. Finally, a comparative analysis of eight different vibration signals under the same load but different speeds condition is carried out, the spectral components are classified into two types: the repeated ones and the regular ones. The accordance between experimental results and theoretical analysis suggests that the proposed method in this paper is effective.

A novel experimental research on vibration characteristics of the running high-speed motorized spindles

Mechanics analysis on the composite flywheel stacked from circular twill woven fabric rings

Suppression of low-frequency vibration for rotor-bearing system of flywheel energy storage system

A flywheel battery, composed from commercially available low-cost materials, can be designed as an additional energy storage system for further increasing the energy efficiency of vehicles, driven mainly in cities with frequent speed changes. Increasing demands from European Union on additional reduction of CO 2 emissions in near future will offer better conditions for commercially successful serial production of hybrid and electric vehicles. Sufficient short-term power for the acceleration of a passenger vehicle in the city as well as efficient accumulation of vehicle kinetic energy during braking for several minutes can be reached even from a flywheel battery of energy capacity of about 200Wh. In combination with traction motor/generator of around 20kW and voltage 48V, the flywheel battery represents an interesting additional retrofit for conventional drives with combustion engines with positive influence on reduction of fuel consumption and therefore, also CO 2 emissions. Such solution contributes to energy smart management in frame of smart city systems.

Flywheel energy storage retrofit system for hybrid and electric vehicles

The strength study of the flywheel is important to the flywheel energy storage. The motor and bearing are the key challenges for the high-speed flywheel spin test device in vacuum. By using a small stiffness pivot-jewel bearing and a spring squeeze film damper as the lower support of the flywheel, a simple spin system was designed at a low cost and is suitable for longtime operation. The auxiliary sup- port at the top was not removed until the flywheel passed the first critical speed. The flywheel that kept its rigid state in sub-critical state was tested at the high speed without the top support. The dynamic model of the flywheel-bearing-damper was built by means of the La- grangian equation to calculate critical speeds, mode shapes and modal damping ratios at different speeds. The lower damper's effects on the modal damping ratios and forced vibration were discussed. The vibrations of the flywheel-bearing-damper system were measured at the different damping coefficients in the experiment. When the lower damper was adjusted to be overdamped, the flywheel ran up to 50000 r/min steadily, and the experimental result was in agreement with the theoretical assumption. The sub-critical rotor dynamics de- sign and pivot-jewel bearing proved to be good solutions to the spin test for the composite flywheel.

http://www.j-mst.org/On_line/admin/files/04-J2011-1861_2669-2677_2648%B9%E9_.doc.pdf

Xing-Jian Dai

Papers

Rotor dynamics analysis and experiment study of the flywheel spin test system