Development of 10kWh Flywheel Energy Storage System

We have designed and manufactured a flywheel energy storage system (FESS). The system has a flywheel made of carbon fiber reinforced plastics (CFRP) of the diameter of lm supported by active magnetic bearings (AMB) of low energy loss. The flywheel rotor can be accelerated to 17,200rpm by a synchronous motor. The rated capacity of the energy storage system is 10kWh. The energy loss of AMB is measured by using a test rig, which is designed to minimize the energy loss of AMB. Results obtained by free-running tests up to 12,000rpm show that the energy loss of the homopolar AMB is smaller than that of the heteropolar AMB. The energy loss of the homopolar AMB is found to be about 75W for one unit of the AMB with the bias current of 1.5A at 12,000rpm. The present paper shows details of the energy loss of the test rig equipped with three types of the AMB, and also presents some of the measured data of the 10kWh FESS.