Analysis of a Shaftless Semi-Hard Magnetic Material Flywheel on Radial Hysteresis Self-Bearing Drives

Abstract

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.Actuators 2018, 7, 87 2 of 22 lower component count and more compact layout than common solutions with separate electric motor and bearing system.FESSs provide various advantages compared to other energy storage technologies, including high power rating, long lifetime, fast recharging, short response time and high power density. These devices require little periodic maintenance, have a very low environmental impact, their charge/discharge cycles do not degrade storage capacity, and their state of charge is easily obtained by measuring the rotational speed [17]. The use of self-bearing drives in flywheel applications lends the system more compactness, higher reliability, lower component count and mass saving, thus strengthening the FESS advantages [18][19][20][21]. On the other hand, one of the main drawbacks of FESSs is the low energy density when compared to other storage technologies [1]. This aspect has motivated a research effort devoted to investigating higher energy density layouts. One solution is represented by flywheels made of composite materials, which achieve higher energy density compared to high-strength steel flywheels thanks to their light-weight, along with the very large mechanical strength permitting very high rotational speeds. A rim made of composite material can be much lighter than a steel flywheel when storing a comparable amount of energy. In this configuration, the rotor is usually in the shape of a hollow cylinder made of composite material such as carbon fiber reinforced plastic.Since the energy density depends directly on the mass of the whole FESS, it can be improved by designing as much mass of the system to contribute to storing energy. The index allowing quantif...

A review of flywheel energy storage systems: state of the art and opportunities

“…Sandia National Lab [111,112] is working on improving flywheel energy density with graphene to increase the flywheel's strength. Circosta et al [113] present a semi-hard magnetic FeCrCo 48/5 rotor that enables the use of bearingless hysteresis drives. Low-cost materials, such as concrete, are also being used.…”

Vibration Analysis and Active Control of Rotor Shaft in Magnetically Suspended Air-Blower

“…The FESS with self-bearing hysteresis drive was proposed for the satellite energy system, and the vibration performance of the satellite flywheel rotor was tested. The results showed that the magnetic suspension system could satisfy performance at the maximum speed of the flywheel rotor [12]. However, the effective vibration control method of the rotor shaft was not designed for the FESS.…”

Internal Rotor Actuation and Magnetic Bearings for the Active Control of Rotating Machines

“…Combining the actuation and rotor support, Active Magnetic Bearings (AMBs) can be used to mitigate vibrations for high speed machines, offering improved performance, even though they require the inclusion of amplifiers and sensors to control the rotor levitation. Indeed, AMBs have a much higher life expectancy compared to rolling element bearings, together with having a lubrication-free architecture particularly well suited to wide temperature ranges [22], operation in a vacuum and very high speed applications, such as flywheels [23,24]. The closed loop nature of AMB levitation allows tailoring of the controller to suit a given application, for example, with custom stiffness, damping and unbalance rejection [25,26].…”