Development of high efficiency flywheel energ storage system for power load-leveling

This paper introduces the performance of a power leveling system with a 3.0-MJ, 3315-r/min flywheel energy storage. In terms of cost reduction, this system uses low cost ball bearings and general purpose induction motor. Therefore, such a system configurations occurs large loss during standby mode. In order to overcome this problem, low loss design algorithm that focuses on the mechanical loss is applied to the design of the flywheel. From the experimental results, it is confirmed that the charge and discharge efficiency of the mechanical part of the proposed flywheel system is 95.2% (charge 97.9%, discharge 97.5%). Moreover, charging and discharging efficiency are measured to evaluate the prototype flywheel system. In addition, a design approach of the outer rotor type motor for improving the efficiency and the energy density is discussed. From the analysis, it is confirmed that the loss of the PMSM at the rated output is reduced by 71.7% as compared with the induction machine. As a result, it is confirmed that the charging efficiency is 93.3% and the discharging efficiency is 93.1% if the outer rotor PMSM drives the flywheel.