Design and control of a ring-type flywheel battery system with hybrid Halbach magnetic bearings

In this study, the system consists of 5-DOF magnetic bearing and a built-in motor/generator. The magnetic bearing is of hybrid type, with passive axial magnetic bearing and active radial magnetic bearing. For the passive magnetic bearing (PMB), a pair of ring-type Halbach arrays of permanent magnets are arranged vertically to support the weight of rotor and flywheel. For the active magnetic bearing (AMB), a set of ring-type Halbach array is placed on the rotor side, which will correspond to a coil set on the stator side. The AMB can produce both attraction and repulsion forces on the radial direction, depending on the direction of the coil currents. Furthermore, fabrication of ring-type permanent magnets will be discussed, and it mainly consists of arc-shaped permanent magnet and bonding them with adhesives, so it probably causes the existence of eccentricity. On other hand, a polygon structure with cuboid permanent magnets is considered and equivalent to a ring-type permanent magnet when the analysis of magnetic force is conducted. When driven by an active feedback control system operating in conjunction with a position sensor, the actuator can produce appropriate magnetic force to balance the radial forces which are caused by the PMB and to achieve stable levitation. In the AMB, the differential winding mode is applied, which can result in a linear force-current relation. In order to achieve higher reliability, the variation of rotating speed will be considered in the dynamics of the system, because it is very important and related to resonance and natural frequency. At last, the controller is designed by integral sliding mode control (ISMC) to overcome the effects of uncertainty and to achieve good steady-state accuracy. Moreover, numerical simulation results verify the effectiveness of the controller.