Basic Design of 1kWh Class Compact Flywheel Energy Storage System -Application of Active Magnetic Bearings with Zero-power Nonlinear Control Method-

For the development of a 1kWh flywheel energy storage system (FESS) that provides a rated power of 300 W for three hours, mechanical and electrical losses of the FESS become a crucial point. Therefore, this paper presents the specifications in terms of losses for active magnetic bearings (AMB) and motor/generator. The total loss of a conventional FESS and the methods to reduce it almost by a quarter are presented. The improvement is mainly due to the AMB using the zero-power nonlinear control. This control method avoids bias current, which causes the rotational losses and losses in the AMB controller. Additionally the dynamic of the rotor, which consists of a shaft and flywheel, is analyzed in order to guarantee stable rotation up to the rated rotational speed. The conclusion is that the unexpected vibration of the rotor caused by bending mode natural frequencies will not occur. The basic design of the 1kWh class compact flywheel energy storage system (ComFESS), that is able to supply the energy of 300 W for three hours, has been completed.