Abstract: According to the repeated electromagnetic locking device based on the self-locking principle for magnetic bearing flywheel, the electromagnetic and mechanics characteristics of primary explicit electromagnet are analyzed. It is concluded that the minimum unlocking residual force is much too large, while the adoption of the implicit electromagnet can get rid of it and increase the unlocking reliability. The equivalent magnetic circuit method is applied to magnetic analysis of implicit electromagnet, and its mechanics model under four statuses including carrying out locking/unlocking and keeping locking/unlocking is got. The electromagnetic numerical analysis method is used for a solid example design for the implicit electromagnet. Additionally, to verify the protective effect of the improved locking device for the flywheel system during satellite launch, the swept-sine vibration and random vibration are carried out. The results show that the minimum unlocking residual force of locking device is 0.25 N, far smaller than that of explicit electromagnet about 29.5 N. Moreover, the maximum vibration displacement between the flywheel stator and rotor is 70 μm and its maximum amplitude is 10 μm. Both of them are less than the flywheel system protective gap of 100 μm. This indicates that the improved implicit electromagnet can effectively carry out the locking protection function to the flywheel system while raising the unlocking reliability.

Key words: Electromagnet, Equivalent magnetic circuit, Finite element method, Locking device, Magnetic bearing flywheel