Active Magnetic Bearings for 10kWh Flywheel Energy Storage System

As the demand for electric power has been increasing steadily, a flywheel energy storage system (FESS) using magnetic bearings is needed in order to level daily load of electric power. We have succeeded to suspend a flywheel of 385kg in total weight which has a 1,000ram diameter carbon fiber reinforced plastics (CFRP) rotor performing as 10kWh FESS by means of 5 axis controlled active magnetic bearings (A.M.B.). This paper presents the A.M.B. used in the above system controlled by digital signal processor (DSP). The switching power amplifiers of the A.M.B. can supply maximum current of 8A per channel driven by 300V supply voltage. The radial electromagnets were designed as so called homopolar type in order to reduce rotational loss due to eddy current. The decentralized controller was designed for upper and lower radial beatings using bias current system linearization. On the other hand, an axial electromagnet was designed as a permanent magnet biased (non-linear) actuator. It is possible not only to monitor the displacement of the rotor and control currents in the electromagnet but also to change control parameters of each axis from personal computer by means of serial communication, including telephone line with modem, accessing directly to the DSP. The paper also reports the system information of the FESS and measured data during stand still and rotation by means of above mentioned serial communication.