• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.422.2-422.2
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• 2016

스마트폰, 태블릿 등의 디바이스의 발전에 따라 휴대성이 매우 중요해졌다. 디바이스의 크기, 두께, 유연성에 관한 연구가 활발히 진행되고 있으며, 그 중에서도 energy storage device의 flexibility를 향상시키는 연구가 주목 받고 있다. Energy storage device의 성능 향상을 위해서는 power density를 높여야 하며 flexibility를 위해서는 전극판과 전극소재 간의 부착력을 증가시켜야 한다. 본 연구에서는, power density와 소재 간의 부착성을 개선시키기 위해 기존 graphene보다 표면적이 넓으며 power density가 좋고 전극판과의 부착성이 좋은 hybrid GNP-CNT를 사용하였다. 그리고 Ag NWs/CNT PET film 을 사용하여 전도성이 있는 flexible한 전극판을 사용하였다. SEM 측정을 통해 표면 분석을 하였고, sample에 패턴을 하고 Bending test를 하여 부착성을 확인하였다. 또한, CV curve를 측정하여 supercapacitor의 특성을 확인하였다. 향후, $MnO_2$ NWs를 hybrid GNP-CNT에 합성시킴으로 energy storage device의 energy density를 더욱 향상시키는 연구를 진행할 것이다.

• Composites Research
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• v.31 no.6
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• pp.355-364
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• 2018

Flexible energy-storage devices (FESDs) have been studied and developed extensively over the last few years because of demands in various fields. Since electrochemical performance and mechanical flexibility must be taken into account together, different framework from composition of conventional energy-storage devices (ESDs) is required. Numerous types of electrodes have been proposed to implement the FESDs. Herein, we review the works related to the FESDs so far and focus on free-standing electrodes and, especially substrate-based ones. The way to utilize carbon woven fabric (CF) or carbon cloth (CC) as flexible substrates is quite simple and intuitive. However, it is meaningful in the point of that the framework exploiting CF or CC can be extended to other applications resulting in multifunctional composites. Therefore, summary, which is on utilization of carbon-based material and conductive substrate containing CF and CC for ESDs, turns out to be helpful for other researchers to have crude concepts to get into energy-storage multi-functional composite. Moreover, polymer electrolytes are briefly explored as well because safety is one of the most important issues in FESDs and the electrolyte part mainly includes difficult obstacles to overcome. Lastly, we suggest some points that need to be further improved and studied for FESDs.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.392.1-392.1
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• 2016

Nowadays, research interest in developing the wearable devices are growing remarkably. Portable consumer electronic systems are becoming lightweight, flexible and even wearable. In fact, wearable electronics require energy storage device with thin, foldable, stretchable and conformable properties. Accordingly, developing the flexible energy storage devices with desirable abilities has become the main focus of research area. Among various energy storage devices, supercapacitors have been considered as an attractive next generation energy storage device owing to their advantageous properties of high power density, rapid charge-discharge rate, long-cycle life and high safety. The energy being stored in pseudocapacitors is relatively higher compared to the electrochemical double-layer capacitors, which is due to the continuous redox reactions generated in the electrode materials of pseudocapacitors. Generally, transition metal oxides/hydroxide (such as $Co_3O_4$, $Ni(OH)_2$, $NiFe_2O_4$, $MnO_2$, $CoWO_4$, $NiWO_4$, etc.) with controlled nanostructures (NSs) are used as electrode materials to improve energy storage properties in pseudocapacitors. Therefore, different growth methods have been used to synthesize these NSs. Of various growth methods, electrochemical deposition is considered to be a simple and low-cost method to facilely integrate the various NSs on conductive electrodes. Herein, we synthesized amorphous $NiWO_4$ NSs on cost-effective conductive textiles by a facile electrochemical deposition. The as-grown amorphous $NiWO_4$ NSs served as a flexible and efficient electrode for energy storage applications.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.597-597
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• 2012

A simple solution-based method is developed to deposit crystalline ultrathin (2 nm) nickel hydroxide on vertically grown ZnO nanowires to achieve high specific capacitance and long-term life for flexible and wearable energy storage devices. Ultrathin crystalline $Ni(OH)_2$ enables fast and reversible redox reaction to improve the specific capacitance by utilizing maximum number of active sites for the redox reaction while vertically grown ZnO nanowires on wearable textile fiber effectively transport electrolytes and shorten the ion diffusion path. Under the highly flexible state $Ni(OH)_2$ coated ZnO nanowires electrode shows a high specific capacitance of 2150 F/g (based on pristine $Ni(OH)_2$ in 1 M LiOH aqueous solution with negligible decrease in specific capacitance after 1000 cycles. The synthesized energy-storage electrodes are easy-to-assemble which can provide unprecedented design ingenuity for a variety of wearable and flexible electronic devices.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.12
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• pp.1096-1101
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• 2008

When we design a controller for the active magnetic bearings that support a large rotor, it is important to have an accurate model of the rotor. For the case of the flywheel that is used to store energy, an accurate rotor model is especially important because the dynamics change with respect to the running speed due to gyroscopic effects. In this paper, we present a procedure of obtaining an accurate rotor model of a large flywheel energy storage system using finite-element method. The model can predict the first and the second bending mode which match well with the experimental results obtained from a prototype flywheel energy storage system.

• Journal of Electrical Engineering and Technology
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• v.6 no.4
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• pp.447-458
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• 2011

In this paper, a novel flywheel energy storage device, called the flexible power conditioner, which integrates both the characteristics of the flywheel energy storage and the doubly-fed induction machine, is proposed to improve power system stability. A prototype is developed and its principle, composition, and design are described in detail. The control system is investigated and the operating characteristics are analyzed. The test results based on the prototype are presented and evaluated. The test results illustrate that the prototype meets the design requirement on power regulation and starting, and provides a cost-effective and effective means to improve power system stability.

• Journal of Biomedical Engineering Research
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• v.19 no.5
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• pp.519-530
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• 1998

In this paper, the basic study on the design of the flexible keel of the energy-storage prosthetic foot was performed in order to Improve the walking performance and Increase the activities of the below knee amputees. Based on the analysis of the anthropometric data and the normal gait on two dimensional sagittal plane available In the literature, we presented a model of the basic structure of the flexible keel of the prosthetic foot. The model of the basic structure was composed of the simple beams, and linear rotational spring and damper. Laminated carbon fiber-reinforced composites were selected as the material of the basic structure model of the flexible keel In order to apply the high strength and light weight materials to the basic structure of the flexible keel of the prosthetic foot. The recoverable strain energy In response to the change of beam shape was calculated bur the finite element analysis and it was suggested that the change of beam shape could be the design variable in flexible keel design. The simulation process was systematically designed by using orthogonal array table in order to design the flexible keel structure which could store the more recoverable strain energy. finite element analysis was carried but according to the design of simulations by using the finite element program ABAQUS and the flexible keel structure of the energy-storage prosthetic foot was obtained from the analysis of variance(ANOVA). The dynamic simulation model of the prosthetic walking using the flexible keel structure was made and the dynamic analysis was carried but during one walk cycle. Based on the above results, an effective design process was presented for the development of the prosthetic fool system.

• Journal of Power Electronics
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• v.19 no.4
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• pp.858-868
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• 2019

With the widespread use of modern clean energy, lithium-ion batteries have become essential as a more reliable energy storage component in the energy Internet. However, due to the difference in monomers, some of the battery over-charge or over-discharge in battery packs restrict their use. Therefore, a novel multiphase interleaved converter for reducing the inconsistencies of the individual cells in a battery pack is proposed in this paper. Based on the multiphase converter branches connected to each lithium battery, this circuit realizes energy transferred from any cell(s) to any other cell(s) complementarily. This flexible interlaced converter is composed of an improved bi-directional Buck-Boost circuit that is presented with its own available control method. A simulation model based on the PNGV model of fundamental equalization is built with four cells in PSIM. Simulation and experimental results demonstrate that converter and its control achieve simple and fast equalization. Furthermore, a comparison of traditional methods and the HNFABC equalization is provided to show the performance of the converter and the control of lithium-based battery stacks.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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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.

• Tunnel and Underground Space
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• v.19 no.2
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• pp.77-85
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• 2009

Flexible and lined segment air-tight tunnelling technology for Compressed Air Energy Storage-Gas Turbine(CAES-G/T) power generation was introduced. The distinguished characteristics of the air-tight tunnel system can be summarized by two facts. One is that the high inner pressure due to compressed air is sustained by surrounding rock mass with allowing sufficient displacement of lining segment. The other is that the air-tightness of storage tunnel was enhanced by adopting a specially designed rubber sheet. The flexible lined air-tight underground tunnel can be constructed at a comparatively shallow depth and near urban area so that the locally distributed CAES-G/T power generation can be accomplished. In addition, this air-tight tunnelling technology can be applied to a variety of energy underground storage tunnels such as Compressed Natural Gas(CNG), Liquifed Petroleum Gas(LPG), DeMethyl Ether(DME) etc.