Development of flywheel energy storage system with multiple parallel drives

This paper introduces performance of a power leveling system with a 3.0-MJ, 2900-r/min of flywheel energy storage for multiple parallel operations. In terms of cost reduction and improvement efficiency, this system uses low cost ball bearings at the low speed. Moreover, the system is composed by not a large capacity flywheel but many flywheels with small energy capacity but the cost reduction of the flywheel system. As a result, the cost reduction can be achieved by mass production. The proposed flywheel system is designed by a low-loss design method that focuses on the mechanical loss aspect. 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%). In addition, the suitable drive system with permanent magnet synchronous motors (PMSMs) are developed for the multiple parallel flywheels system. The PMSMs which consist of a main winding and a damping winding are driven by a single main inverter and small auxiliary inverters. From the experimental results, the validity of the parallel drives control method using two PMSMs is confirmed.