Design of a Mobile Flywheel Energy Storage driven by a Switched Reluctance Machine

The rising number of hybrid and fully electrical driven cars requires more powerful short term energy storages to recover the breaking energy, especially in urban traffic. This paper presents a mobile flywheel energy storage system (FESS) designed for the use in mobile applications like passenger cars. The system is equipped with a carbon fiber composite flywheel connected to two switched reluctance machines which both can operate as motor and generator. The storage capacity is 190Wh at an overall weight of 64kg. The peak power of the system is 24kW. The construction of the flywheel will be outlined considering a stress distribution up to 30 000rpm as well as rotordynamic concerns including the bearing concept. The system carries hybrid super precision roller bearings in a paired (tandem) configuration equipped with adjustable preloading and direct water cooling. Switched reluctance machines (SRMs) show great advantages in flywheel applications such as wide speed range, high reliability, and a robust rotor structure. The modelling process for the driving SRMs will be presented including the simulation workflow as well as results for key operation points.