Strength Analysis Of Fiber-enforced Flywheel And Design Of High Effective PMB

High energy density and high power density are two directions in flywheel energy storage systems (FESS) development. There is a trend of including these two advantages into better high-speed high-power flywheels. In-depth theoretical study and a great deal of experimental research on flywheel rotor and bearing technology has been done for improving the energy density and power rating of the tested FESS.Through strength analysis of composite flywheel rotors made by fiber winding: (1) The concept was introduced for thermal residual stress generated in normal curing and cooling phase of fiber winding process. Comparison of theoretical calculation with experiment result has shown that, this stress is an important factor that influences flywheel safety and performance. An improved fabrication process was proposed which could increase the rotor performance by 37%. (2) Tensioning winding with in-situ curing, which is a new rotor fabrication technology is also proposed to enhance rotor radial strength by producing radial prestress. The theory and calculation method of thick-wall cylinder winding is developed and completed. The dissertation also shows how to define and calculate a set of fiber tensioning force for certain radial prestress. With same material and structure size, the new prestressed flywheel can reach an energy density as high as 140Wh/kg. An effective calculation method that can solve most of the mechanics problems met during the manufacture and use of fiber-enforced flywheel is developed.An upper permanent magnetic bearing (PMB) was designed for high-power vertical energy storage flywheels. The bearing consists of a radial two PM-ring stator and an alloysteel magnetic-conducting rotor which allow it to work at super high speed and to avoid thermal impact from flywheel rotor. With minimized bearing size and magnetic leakage, the bearing has an axial unloading force of kNs at working gap of 1 mm.Intensive experiments have been done to improve the energy density and power rating of FESS. Spin tests of high speed flywheel rotors achieve ultimate speed 905r/s, circumferential speed 796m/s and energy density 48Wh/kg. Failure analysis was done to the rotor. A new 20kW FESS was set up. After effective finite element analysis simulation and plenty of spin tests, the rotor system behavior is fairly understood, which is helpful and necessary to improve the design.