• 전력전자학회논문지
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• 제21권4호
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• pp.335-342
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• 2016

This paper proposes an energy storage-assisted, series-connected module-integrated power conversion system that integrates a photovoltaic power conditioner and a charge balancing circuit. In conventional methods, a photovoltaic power conditioner and a cell-balancing circuit are needed for photovoltaic systems with energy storage devices, but they cause a complex configuration and high cost. Moreover, an imbalanced output voltage of the module-integrated converter for PV panels can be a result of partial shading. Partial shading can lead to the fault condition of the boost converter in shaded modules and high voltage stresses on the devices in other modules. To overcome these problems, a bidirectional buck-boost converter with an integrated magnetic device operating for a charge-balancing circuit is proposed. The proposed circuit has multiple secondary rectifiers with inductors sharing a single magnetic core, which works as an inductor for the main bidirectional charger/discharger of the energy storage. The secondary rectifiers operate as a cell-balancing circuit for both energy storage and the series-connected multiple outputs of the module-integrated converter. The operating principle of the cell-balancing power conversion circuit and the power stage design are presented and validated by PSIM simulation for analysis. A hardware prototype with equivalent photovoltaic modules is implemented for verification. The results verify that the modularized photovoltaic power conversion system in the output series with an energy storage successfully works with the proposed low-cost bidirectional buck-boost converter comprising a single magnetic device.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1999년도 전력전자학술대회 논문집
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• pp.427-430
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• 1999

This paper presents a S-FES(Superconducting magnetic bearing Flywheel Energy Storage System) for the purpose of replacing battery used to store the energy. Especially, the design elements of FES, such as the bearing, wheel material, and power converter, etc., is described. The design and manufacturing techniques of the controllable power converter are proposed to generate the sinusoidal output current in the high speed operation and to get the constant DC voltage in the regeneration mode. The cylindrical permanent magnet synchronous motor with halbach array of Nd-Fe-B permanent magnet which is the high coercivity material is used as the driver of FES. The proposed S-FES system shows the stable rotation characteristics at high speed range about 10,000 rpm. To verify the validity of proposed system, the comparative study with the conventional ball bearing system is proceeded and it is well confirmed with the result of the lower friction loss of S-FES system.

• KEPCO Journal on Electric Power and Energy
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• 제1권1호
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• pp.157-162
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• 2015

대용량 초전도 에너지저장장치(Superconducting Magnetic Energy Storage, SMES)용 초전도 권선을 제작하기 위해서는 높은 자장특성을 가고 있는 2세대 고온초전도 (2nd Generation High-Temperature Superconductor, 2G HTS) 선재를 사용하는 것이 효율적이다. 자기에너지 저장 밀도를 높이기 위해서는 권선에 높은 전류밀도를 인가해야 하는데, 도체의 평면에 수직 방향으로 인가되는 자속밀도가 커지면 임계전류가 작아지는 2세대 HTS 선재의 특성상 토로이드 형태의 권선을 구성하는 것이 일반적이다. 이러한 고온초전도 권선을 설계하기 위해서는 권선 특성의 정확한 해석이 필요한데 이를 위해 유한요소법을 사용한 프로그램을 이용하여 해석이 가능하나 토로이드 형태의 권선은 대칭성의 문제로 3차원 해석을 해야만 하며, 이는 모델링에 많은 어려움과 높은 컴퓨터 사양, 그리고 매우 긴 계산 소요시간이 필요함을 의미한다. 본 논문에서는 이러한 문제점을 해결하기 위해 분석적이고 통계적으로 고온 초전도 코일에서 작용하는 최대 수직자장과 저장된 에너지를 결정하는데 이해하기 쉽고 효율적으로 계산하는 방법을 제시했다. 이 방법은 현저한 시간단축과 효율적인 설계를 할 수 있는 새로운 계산 방법으로 기존의 유한요소법에 의해 소요되는 계산 시간에 비해 1/1000정도로 계산시간 단축을 할 수 있었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2009년도 추계학술대회 논문집
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• pp.258-263
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• 2009

This paper describes an analysis of the stability and performance of a large-capacity flywheel energy storage system (FESS) supported by active magnetic bearings. We designed and manufactured the system that can store up to 5kWh of usable energy at the maximum speed of 18,000 rpm. In order to analyze the stability of the systems accurately, we derived a rigid body rotor model, flexible rotor model using finite-element method, and a reduced-order model using modal truncation. The rotor model is combined with those of active magnetic bearings, amplifiers, and position sensors, resulting in a system simulation model. This simulation model is validated against experimental measurements. The stability of the system is checked from the pole locations of the closed-loop transfer functions. We also investigated the sensitivity function to quantify the robustness of the systems to the disturbances such as mass imbalance and sensor noises.

• 정보저장시스템학회논문집
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• 제5권2호
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• pp.53-57
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• 2009

This study is concerned with the design of a camera iris-shutter device for producing force. The camera iris-shutter with yoke should have a smaller size and a bigger magnetic force than the previous model. Since the induced magnetic force operates shutter movement, the magnetic force maximization for a given input current is an important issue. To achieve the goal, new system is designed by the topology optimization method. The design is refined through the design of experiments to find the detail camera iris shutter design satisfying design constraints.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권6호
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• pp.411-420
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• 2000

The energy storage systems are being widely researched for the high quality of the electric power. The FES(flywheel energy system) is especially, on the center of the research because it does not make any pollution and its life is long. The FES converts the electrical energy into the mechanical kinetic energy of the flywheel and reconverts the mechanical energy into the electrical energy. In order to store as much energy as possible, the flywheel is supposed to be rotated with very high speed. The motor/generator of the FES should be high efficient at high speed, and generate constant torque with respect to the rotation. In this paper, a motor/generator employing a Halbach array of permanent magnets is designed and constructed to meet the requirements, and its characteristics are examined. The magnetic field is analysed by using the magnetic surface charge method. The armature winding is designed for the harmonic components to be minimized by using the FFT. The sinusoidal current for the motor driving are generated by the hysteresis current controller. A sample superconducting flywheel energy storage system is constructed with a duralumin flywheel which has a maximum rotating speed of 40,000[rpm] and a stored energy of 240[Wh] and its validity is examined through the experiment.

• 비파괴검사학회지
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• 제22권1호
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• pp.38-44
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• 2002

누설자속법은 신뢰성과 경제성을 충족시키면서 정성적인 결과를 제공하는 비파괴시험법이다. 특히 저장탱크바닥판의 검사에 효과적으로 적용될 수 있음을 보여주었다. 이전에 저장탱크 qkekrvis의 검사에 사용되었던 초음파탐상법은 검사속도가 느리고, 적용에 따른 어려움으로 국부검사에 한정되어 왔다. 본 연구팀은 이러한 초음파탐상의 단점을 극복하고자 누설자속탐상법을 개발하였다. 개발된 시스템의 주요부분은 누설자속 발생부, 어레이센서, crawler 및 운용프로그램으로 구성되어 있고, 최종적으로 개발된 시스템이 6mm강판에서 ${\psi}3.2mm,\;d\;1.2mm$와 같은 인공결함을 검출할 수 있음을 보여주었다.

• Progress in Superconductivity
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• 제13권1호
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• pp.40-46
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• 2011

A superconductor flywheel energy storage system (SFES) is an electro-mechanical battery which transforms electrical energy into mechanical energy for storage, and vice versa. A 10 kWh class flywheel energy storage system (FESS) has been developed to evaluate the feasibility of a 35 kWh class SFES with a flywheel $I_p/I_t$ ratio larger than 1. The 10 kWh class FESS is composed of a main frame, a composite flywheel, active magnetic dampers (AMDs), a permanent magnet bearing, and a motor/generator. The flywheel of the FESS rotates at a very high speed to store energy, while being levitated by a permanent magnetic bearing and a pair of thrust AMDs. The 10 kWh class flywheel is mainly composed of a composite rotor assembly, where most of the energy is stored, two radial and two thrust AMD rotors, which dissipate vibration at critical speeds, a permanent magnet rotor, which supports most of the flywheel weight, a motor rotor, which spins the flywheel, and a central hollow shaft, where the parts are assembled and aligned to. The stators of each of the main components are assembled on to housings, which are assembled and aligned to the main frame. Many factors have been considered while designing each part of the flywheel, stator and frame. In this study, a 10 kWh class flywheel energy storage system has been designed and constructed for test operation.

• 한국컴퓨터정보학회논문지
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• 제21권5호
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• pp.1-10
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• 2016

Magnetic disks have been used for decades in auxiliary storage devices of computer systems. In recent years, the use of NAND flash memory, which is called SSD, is increased as auxiliary storage devices. However, NAND flash memory, unlike traditional magnetic disks, necessarily performs the erase operation before the write operation in order to overwrite data and this leads to degrade the system lifetime and performance of overall NAND flash memory system. Moreover, NAND flash memory has the lower endurance, compared to traditional magnetic disks. To overcome this problem, this paper proposes EPET (Enhanced Prediction and Elapsed Time) wear leveling technique, which is especially efficient to portable devices. EPET wear leveling uses the advantage of PET (Prediction of Elapsed Time) wear leveling and solves long-term system failure time problem. Moreover, EPET wear leveling further improves space efficiency. In our experiments, EPET wear leveling prolonged the first bad time up to 328.9% and prolonged the system lifetime up to 305.9%, compared to other techniques.

• 한국초전도ㆍ저온공학회논문지
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• 제16권4호
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• pp.57-61
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• 2014

Output fluctuation which is generated in wind power farm can hinder stability of total power system. The electric energy storage (EES) reduces unstable output, and superconducting magnetic energy storage (SMES) of various EESs has the proper performance for output compensation of wind power farm since it charges and discharges large scale power quickly with high efficiency. However, because of the change of current within SMES, the electromagnetic losses occur in the process of output compensation. In this paper, the thermal effect of the losses that occur in SMES system while compensating in wind power farm is analyzed. The output analysis of wind power farm is processed by numerical analysis, and the losses of SMES system is analyzed by 3D finite element analysis (FEA) simulation tool.