Losses in an optimized 8-pole radial AMB for Long Term Flywheel Energy Storage

In this paper, we will study the effect of losses (non including losses in the power electronic) of an optimized eight pole radial AMB on the discharge time of a no-load Long Term Flywheel Energy Storage (LTFES). Load capacity is the main parameter of an Active Magnetic Bearings (AMB) design. This parameter has to take into account the external disturbance force which may be constant, synchronous with the rotor angular velocity or completely general. To relatively simplify this study, we restricted the effect of external disturbance to a constant unbalance force only. The latter plays a high part on the size of bearing system. Before optimizing the AMB design, we have built and validated an Excel theoretical model with 2-D Finite Element Method (FEM). Several optimizations have been made in order to seek the minimum of both copper and iron losses we could obtain for a given load capacity. Then, evolution of losses functions of angular velocity speed of rotor has been drawn. Flywheel discharge time has been computed to pass from 9000 rpm to 4500 rpm and evolution of this time versus mass of AMB has been shown for different values of unbalance forces.