Christopher Lusty

Flywheel Energy Storage Systems are interesting solutions for energy storage, featuring advantageous characteristics when compared to other technologies. This has motivated research effort focusing mainly on cost aspects, system reliability and energy density improvement. In this context, a novel shaftless outer-rotor layout is proposed. It features a semi-hard magnetic FeCrCo 48/5 rotor coupled with two bearingless hysteresis drives. The novelty lies in the use of the semi-hard magnetic material, lending the proposed layout advantageous features thanks to its elevated mechanical strength and magnetic properties that enable the use of bearingless hysteresis drives. The paper presents a study of the proposed layout and an assessment of its energetic features. It also focuses on the modeling of the radial magnetic suspension, where the electromagnets providing the levitating forces are modeled through a one-dimensional approach. The Jiles–Atherton model is used to describe the magnetic hysteresis of the rotor material. The proposed flywheel features a mass of 61.2 kg, a storage capability of 600 Wh at the maximum speed of 18,000 rpm and achieves an energy density of 9.8 Wh/kg. The performance of the magnetic suspension is demonstrated to be satisfactory and the influence of the hysteresis of the rotor material is highlighted.

This paper demonstrates vibration reduction in a hollow rotating shaft by means of internal-stator active magnetic actuators, which are resiliently mounted. This problem requires further consideration over and above classic rotor / magnetic bearing systems on account of the flexible behavior of the magnetic actuator support structure. The paper presents an experimental facility conforming to the proposed topology, with a particular focus on the control problem such a system presents. The unique challenges are discussed, and a solution is presented in the form of H-infinity based control. Ultimately, experimental results demonstrate the system to be capable of substantial rotor vibration suppression, including while passing the first rotor critical speed, which was not obtainable with simpler classical control techniques. This means the top achievable rotor speed was increased from approximately 3000 rpm without magnetic actuator vibration suppression to over 9000 rpm with vibration suppression active. At the rotor critical speed, the magnetic actuators effect a reduction in rotor vibration amplitude of over 70% compared to the rotor supported purely on mechanical bearings, while simultaneously avoiding excessive excitation of the flexible AMB support structure.

A topology composed of a hollow-shaft rotor on rolling element bearings coupled with internal-stator magnetic bearings mounted on independently supported flexible shafts is considered for the purposes of vibration reduction. Details of a bespoke test rig constructed to assess this topology are presented. The rig makes use of customdesigned internal-stator magnetic bearings fabricated from Soft Magnetic Composite material. Results from standard numerical analysis of the rig are given to demonstrate the expected behaviour of the system, with a particular focus on its potential to reduce synchronous vibration seen in the rotor while passing critical speeds. These behaviours are then confirmed via a series of experimental tests. These results show that the proposed topology can be used effectively to alter the system vibration behaviour

A novel rotor topology is proposed with the goal of reducing vibration in high speed rotor systems. Reduction in vibration at critical speeds is targeted. In essence, the novel topology consists of a hollow tube rotor coupled to a secondary non-rotating shaft located concentrically within the primary rotor. The two shafts are linked via a number of actively managed magnetic couplings. The topology is provided, along with an analysis comparing the out-of-balance vibration response of the proposed rotor to a comparable simple passive rotor. Designs for a test rig based on this topology are presented, together with an outline of anticipated testing and development of the idea. Special consideration is given to the design of the magnetic bearings, which form the system couplings. An internal-stator homopolar bearing design fabricated from soft magnetic composite is presented. The qualities of soft magnetic composite as a bearing core material are shown to be comparable with a standard laminated core with the added advantage of minimal eddy current losses within the primary rotor.