• Journal of Electrical Engineering and Technology
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• v.12 no.4
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• pp.1442-1448
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• 2017

Recently, electric power systems have been operating with tight margins and have reached their operational limits. Many researchers consider a microgrid as one of the best solutions to relieve that problem. The microgrid is generally powered by renewable energies that are connected through power converters. In contrast to the rotational machines in the conventional power plants, the converters do not have physical rotors, and therefore they do not have rotational inertia. Consequently, a stand-alone microgrid has no inertia when it is powered by the only converter-based-generators (CBGs). As a result, the relationship between power and frequency is not valid, and the grid frequency cannot represent the power balance between the generator and load. In this paper, a superconducting flywheel energy storage system (SFESS) is applied to an inertia-free stand-alone (IFSA) microgrid. The SFESS accelerates or decelerates its rotational speed by storing or releasing power, respectively, based on its rotational inertia. Then, power in the IFSA microgrid can be balanced by measuring the rotor speed in the SFESS. This method does not have an error accumulation problem, which must be considered for the state of charge (SOC) estimation in the battery energy storage system (BESS). The performance of the proposed method is verified by an electromagnetic transient (EMT) simulation.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.305-309
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• 1999

This paper presents an high efficiency energy conversion system for very high-speed flywheel energy storage system using high Tc superconducting bearings. Main configuration of power convertor is designed to replace of the conventional battery with EMB(Electro Mechanical Battery). PMSM(Permanent Magnet Synchronous Motor) using Halbach array is used as the energy conversion system of motor and generator. Some PWM methods for the high frequency inverter is described and the power factor effects to the torque characteristics and efficiency of the motor and generator is analyzed. As the results, it is verified that the inverter output current is well regulated to be in-phase or inverse-phase sinusoidal waveform to have the wide operational range from 2,500rpm to 42,000rpm. Proposed circuit is designed to obtain the very high speed, high efficiency and stable rotational characteristics, and to be applied to1.2r[kW]/65[Wh] system.

• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.5
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• pp.433-441
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• 1999

This paper presents a S-FES(Superconducting magnetic becuing Flywheel Energy Storage System) for the p purpose of replacing battery used to store the energy. Especially, the design elements of FES, such as the b beming, wheel mateηaI, and power converter, etc., are described. The design and manufacturing techniques of t the controllable IXlwer converter are proposed to generate the sinusoidal output current in the high speed operation and to get the const빠synchronous motor with halbach cuTay of high coesive I\d-Fe-B permanent magnet is used as the driver of F FES. The proposed S-FES system shows the stable rotation characteristics at high speed range about l 10,000[rpm]. To verify the validity of proposed system, the comparative study with the conventional ball b beming s~rstem is proceeded and it is well confirmed with the result of the lower friction losses of S-FES S system.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.606-607
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• 2007

This paper is about optimal flywheel capacity estimation for Ullueng-do power system. The power system of Ullueng-do has some differences with other island power system in Korea. It includes wind generator, hydro-generators as well as diesel generators. There are some problems on 600kW wind generator. Because of frequent drop of wind generator, the Ulleung-do power system have been threatened on frequency. The power frequency is 60Hz, and it should be between 59.9 and 60.1Hz. However, since the electrical inertia is small and the weight of wind generation is relatively high, generator drop of wind generation might make the power frequency out of boundary. In this paper, the flywheel energy storage system is assumed to be installed on Ulleung-do power system. Then, the maximum wind generation capacity and the optimal superconducting flywheel energy storage system capacity is estimated by the transient stability simulations.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.6
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• pp.820-827
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• 2014

Since a microgrid has renewable energy sources, imbalance between power supply and power demand occurs in the islanded mode. In order to solve the imbalance, several energy storage systems (ESSs) such as bettary energy storage system (BESS), EDLC (electric double layer capacitor), flywheel, and SMES (superconducting magnetic energy storage) are generally used. Especially, their electrical characteristics are different. For efficient use of them, a coordinated control scheme is required. In this paper, a coordinated control scheme for using a Lead-acid BESS, a Lithium BESS, and a EDLC is designed to efficient frequency control for a microgrid in the islanded mode. The coordinated frequency control strategy is designed based on their electrical characteristics. The feasibility of the proposed coordinated frequency control strategy is verified through the simulation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.343.2-343
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• 2002

Squeeze film dampers(SFDs) are designed and analyzed for radial superconducting bearings. The designed SFDs are mounted on the superconductors submerged in liquid nitrogen such that the dampers should supply additional damping to the relatively underdamped superconducting bearing support. Basic theory of SFD with superconducting bearing are introduced. Rotordynamic simulations are provided to support the feasibility of the superconducting magnetic bearings mounted on SFDs for a horizontal flywheel energy storage system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.399-403
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• 2002

Squeeze film dampers (SFDs) are designed and analyzed for radial superconducting bearings. The designed SFDs are mounted on the superconductors submerged in liquid nitrogen such that the dampers should supply additional damping to the relatively underdamped superconducting bearing support . Basic theory of SFD assembled with superconductors is introduced. Rotordynamic simulations are provided to support the feasibility of the superconducting bearings mounted on SFDs for a horizontal flywheel energy storage system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.04a
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• pp.88-95
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• 2002

Recent development in the field of RE-Ba-Cu-O (REBCO, RE: Y or rare earth elements) bulk high-Tc superconductors (HTS) is reviewed in the present paper. After the fatal weak link problem of sintered REBCO superconductors has been overcome by melt processing, this field has been greatly advanced during last ten years. The critical current density $J_c$ at 77 K has been enhanced by introducing effective flux pinning sites into the $REBa_2Cu_3O_y$ (RE123) superconducting matrix. Large melt-textured REBCO bulk crystals have been fabricated with the TSMG(top-seeded melt growth) technique. Mechanical properties of REBCO bulks have been improved by using the Ag additive or epoxy resin. Real bulk applications such as current lead, fault current limiter, flywheel energy storage system, magnetic field source, magnetic separation system, and etc., surely come true near future.

• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.2
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• pp.215-222
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• 1999

Integrating energy storage into electlic power system has long been recognized as a way to maximize a utility's g generation and transmission capacity, Electlic power can be stored during off-peak periods and then recovered during p peak conditions to offset the need for larger generation and transmission capacity, Currently large-scale SMES for the p purpose of energystorage which can be also se$\pi$ed by battery storage or flywheel system has been developed, and near f future it will be integrated into power grids, This paper presents an investment analysis on large-scale SMES which c can determine its optimal size in power systems, In operation model. least generation cost for energy storage in SMES a and its mar밍nal capacity cost can be calculated using the discreteness of probability distribution for power availability I Investment decisions are made by the maximum p디nciple and the case study shows the optimal operation and realistic i information on the proper size of large-scale SMES in power systems.