High temperature superconducting levitation flywheel system and its control

A simple and stable flywheel system with high temperature superconducting levitation is presented, in which a control is not needed for levitation. In order to have stable levitation, a superconductor and a permanent magnet are used, and three permanent magnets support the top of the shaft. In the part of drive system, eight-poles cylindrical permanent magnet and eight cylindrical coils are used to drive the rotor, in which magnetic forces in the direction perpendicular to the shaft axis are cancelled. Hence, vibration force due to the driving is zero in this system. A coil-type electromagnetic damper is presented which works in the magnetic field of levitation permanent magnet. It consists of four coils. The dampers lie at both ends of the shaft. When the shaft vibrates in the direction perpendicular to the shaft axis, current flows in the damper coil. It generates the electromagnetic force. The force is in proportion to vibration frequencies of the shaft when the velocity feedback is performed, so that the force behaves like damping forces. Using this system, a control like the sensor less control can be performed by using sensors consisting of coils only. Analytical expressions are obtained for the torque for our cylindrical-type motor, and a method for accelerating the shaft is presented by controlling the voltage of the coil based on the expressions. Experimental tests have been carried out. It is clarified that our system has stable levitation, and vibrations are extremely suppressed.