• The Transactions of the Korean Institute of Power Electronics
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• v.5 no.6
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• pp.610-619
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• 2000

This paper presents an off-line UPS using the high temperature superconductive magnetic bearing. FES(Flywheel Energy Storage) system has good advantages in compare with lead acid battery. So, high efficiency FES using high temperature SMB(superconductive magnetic bearing) was composed in this paper. The outer rotor type of PMSM(Permanent Magnet Synchronous Motor) as motor/generator was used for the experiment, and square wave current and sinusoidal wave control methods was compared for high efficiency operation of motor/generator. The circuit for in phase sinusoidal wave current control with EMF in the full speed range was designed and the proposed flywheel energy storage system was applied in single phase off-line UPS system. As the stable operation characteristics of prototype system was confirmed, the its excellence as energy storage device in Off-line UPS was proved.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.879-884
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• 2007

Flywheel energy storage systems have advantages over other types of energy storage devices in such aspects as unlimited charge/discharge cycles and environmental friendliness. In this paper we propose a millimeter scale flywheel energy storage device. The flywheel is supported by a pair of passive magnetic bearings and rotated by a toroidally wound electric motor/generator. The geometry of the bearings is optimized for the maximum dynamic performance.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.8
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• pp.717-726
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• 2010

For the application into a 1 kWh flywheel energy storage system(FESS), this paper presents the design scheme of radial and axial hybrid magnetic bearings which use bias fluxes generated by permanent magnets. In particular, the axial hybrid magnetic bearing is newly proposed in this paper, in which a permanent magnet is arranged in axial direction so that it can support the rotor weight as well as provide a bias flux for axial magnetic bearing. Such hybrid magnetic bearings consume very low power, compared with conventional electromagnetic bearings. In this paper, to stably support a 140 kg flywheel rotor without contact, design process is explained in detail, and magnetic circuit analysis and three-dimensional finite element analysis are carried out to determine the design parameters and predict the performance of the magnetic bearings.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.7
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• pp.1045-1052
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• 2013

In this study we deal with design procedures for the flywheel energy storage system that has the capacity to store the regenerative energy produced from the railway vehicles. The flywheel energy storage system (FESS) stores the regenerative electrical energy into the high speed rotational flywheel, by conversion the electrical energy into the mechanical rotational energy. Thus the FESS is composed of the energy conversion components, such as the motor and generator, mechanical support components, such as the rotational rotor, the magnetic bearings to support the rotor, and the digital controller to control the air gap between the rotor and the magnetic bearings. In this paper the design procedures for the rotor operating at the rigid mode and the magnetic bearings to support the rotational rotor without contact are presented.

• 한국초전도학회:학술대회논문집
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• 2008.08a
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• pp.93-93
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• 2008

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.176-181
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• 2009

In this article, excitation forces due to unbalance mass in a flywheel energy storage system will be discussed, which mainly consists of a composite flywheel and active magnetic bearings and a motor/generator. Unbalance mass causes moments as well as centrifugal forces to the center of the flywheel when the flywheel rotates. The moment excites the flywheel to revolve in the shape of conical revolution and in real operation, the flywheel shows an aspect that conical revolution is a main mode when system failure occurs. Although there are several excitation sources to the flywheel including unbalance mass, an excitation from motor and control issues of the magnetic bearings, we could infer unbalance mass is the main cause of the failure from a comparison between a composite flywheel and a steel flywheel in the same condition. In this of view, excitation forces and moments induced by unbalance mass should be carefully considered in dynamics of the flywheel so that the energy storage system can be operated in more stable conditions.

• Transactions of the Society of Information Storage Systems
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• v.3 no.2
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• pp.86-93
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• 2007

In this paper we explain why future probe storage systems will use patterned media. As a model system, magnetic patterned media will be discussed, even though their data density is limited to about $7Tbit/in^2$. The first results on magnetic probe storage on patterned media are presented, and the problem of switching field distribution is discussed in detail. Finally we will present the first steps into two-dimensional coding for patterned media.

• Proceedings of the Korean Magnestics Society Conference
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• 2007.05a
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• pp.179.2-179.2
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• 2007

• Journal of the Korean Society for Precision Engineering
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• v.15 no.2
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• pp.170-177
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• 1998

The purpose of superconducting magnetic bearing flywheel energy storage system(SMB-FESS) is to store unused nighttime electricity as kinetic energy and convert it to electricity during daytime. The SMB-FESS is proposed as an efficient energy storage system because there is no mechanical problems, such as friction and wear The flywheel over SMB is rotated at a high speed, 50,000rpm. The major source of energy loss in the SMB-FESS is vibration of flywheel. Therefore, the vibration characteristics of SMB-FESS should be identified. In this study, the axial/radial stiffness and damping coefficient of SMB are measured by a vibration test. Natural frequencies and natural modes of flywheel and magnet are analyzed by a finite element method. The modal analysis of system is performed using the modal parameters of each component and the measured stiffness/damping coefficient. So, natural at frequencies and mode shapes of the joined system can be obtained. According to critical speed analysis, the system has two rigid conical modes in the low speed range. Nevertheless, the system has not been affected by the critical speed in the main operating range.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.9
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• pp.104-109
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• 1999

The flywheel energy storage system using superconducting magnetic bearings is a device to store electrical energy as rotatioal kinetic energy by motor and to convert it to electrical energy by generator when it is necessary. The rotordynamic analysis should be performed with an adequate analytical model and equations of motion to identify the stable driving condition and the dynamic behavior. The critical speed and the unbalance response of superconducting magnetic bearings-flywheel system are studied in this paper. The analytical results show that the system has one forward whirling mode and two backward whirling models below 500rpm. The maximum displacement 0.75mm is detected at the first forward mode (385rpm)through unbalance response analysis. The analytical results are compared with the experimental result by the spin-down test. The experimental result shows that the maximum displacement is 0.7mm at 370rpm.