• Progress in Superconductivity
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• v.13 no.3
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• pp.195-202
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• 2012

In this paper, we designed Active Magnetic Bearing (AMB) for large scale Superconductor Flywheel Energy Storage System (SFESS) and PD controller for AMB. And we experimentally evaluated SFESS including hybrid type AMB. The radial AMB was designed to provide force slew rate that was sufficient for the unbalance disturbances at the maximum operating speed. The thrust AMB is a hybrid type where a permanent magnet carries the weight of the flywheel and an electromagnetic actuator generates the dynamic control force. We evaluated the design performance of the manufactured AMB through comparison of FEM analysis and the results of experimental force measurement. In order to obtain gains of PD controller and design a notch filter, the system identification was performed through measuring frequency response including dynamics for the AMBs, a power amp and a sensor using a sine swept test method after levitating the flywheel. Through measuring the current input of the AMBs and the orbit of a flywheel according to rotational speed, we verified excellent control performance of the AMBs with small amount current for the large scale SFESS.

• Advances in Energy Research
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• v.4 no.1
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• pp.47-68
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• 2016

A well designed hybrid power system (HPS) can deliver electrical energy in a cost effective way. In this paper, model for HPS consisting of photo voltaic (PV) module and wind mill as renewable energy sources (RES) and solar lead acid battery as storage device connected to unidirectional grid is developed for peak demand reduction. Life time energy cost of the system is evaluated. One year hourly site condition and load pattern are taken into account for analysing the HPS. The optimal HPS is determined for least life time energy cost subject to the constraints like state of charge of the battery bank, dump load, renewable energy (RE) generation etc. Optimal solutions are also found out individually for PV module and wind mill. These three systems are compared to find out the most feasible combination. The results show that the HPS can deliver energy in an acceptable cost with reduced peak consumption from the grid. The proposed optimization algorithm is suitable for determining optimal HPS for desired location and load with least energy cost.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.488.1-488.1
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• 2014

As the society demands the high performance energy storage devices, development of efficient and renewable energy storage materials has been a topic of interest. Here, we report pseudocapacitive behaviors of biopolymer (lignin) that was confined onto reduced graphene oxides (RGOs) for a renewable energy storage system. The strong surface confinement of quinone groups onto the electroconductive RGOs created the renewable hybrid electrodes for supercapacitors (SCs) with fast and reversible redox charge transfer. As a result, the pseudocapacitors fabricated with the hybrid electrodes of lignin and RGO presented the outstanding electrochemical performances of remarkable rate and cyclic performances:~4% capacitance drop after 3000 cycles and a maximum capacitance of 432 F g-1.

• Journal of Hydrogen and New Energy
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• v.29 no.6
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• pp.606-619
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• 2018

This study focuses on the performance of hydrogen energy based hybrid system in terms of system reliability of electricity generation. With this aim to evaluate the off-grid system of photovoltaic (PV), wind turbine, electrolyzer, fuelcell, $H_2$ tank and storage batteries, 14 different sites in South Korea are simulated using HOMER. Performance analysis includes simulation on the different sites, verification of operational behaviors on regional and seasonal basis, and comparison among a control group. The result shows that the generation performance of hydrogen powered fuelcell is greatly affected by geographical change rather than seasonal effect. In addition, as the latitude of the hybrid systems location decrease, renewable power output and penetration ratio (%) increase under constant electrical load. Therefore, the hydrogen based hybrid system creates the stability of electricity generation, which best suits in the southern part of South Korea.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.2
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• pp.247-252
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• 2015

The majority of electric power in the domestic manned islands with off-grid power system is supplied by the diesel generators. However, in the case of off-grid islands the fuel cost is more expensive to inland areas and difficult to transport them to islands. So the development of renewable energy system using natural resource have been recently introduced. But renewable energy that depend on the natural environment, it is necessary to organized the hybrid system with existing diesel engine because the energy is difficult to maintain stable electric power. This paper presents the results of a feasibility study of hybrid system with energy storage system such as wind, solar, battery and diesel engine. The study included off-grid island as the Seogeochado islands located in Jeolanamdo Province. And, the paper proposed a optimal capacity of hybrid system configuration to maintain carbon free with minimum investment cost. the analysis of economic adaptability performed by HOMER program.

• Advances in Energy Research
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• v.4 no.1
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• pp.87-106
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• 2016

In this research, optimum design of the combined solar collector, geothermal heat pump and thermal seasonal storage system for heating and cooling a sample greenhouse is studied. In order to optimize the system from technical point of view some new control strategies and functions resulting from important TRNSYS output diagrams are presented. Temperatures of ground, rock bed storage, outlet ground heat exchanger fluid and entering fluid to the evaporator specify our strategies. Optimal heat storage is done with maximum efficiency and minimum loss. Mean seasonal heating and cooling COPs of 4.92 and 7.14 are achieved in series mode as there is no need to start the heat pump sometimes. Furthermore, optimal parallel operation of the storage and the heat pump is studied by applying the same control strategies. Although the aforementioned system has higher mean seasonal heating and cooling COPs (4.96 and 7.18 respectively) and lower initial cost, it requires higher amounts of auxiliary energy either. Soil temperature around ground heat exchanger will also increase up to $1.5^{\circ}C$ after 2 years of operation as a result of seasonal storage. At the end, the optimum combined system is chosen by trade-off between technical and economic issues.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 1999.02a
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• pp.121-124
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• 1999

A horizontal axle-type superconductor flywheel energy storage system has many great features such as extensibility and stability compared to the traditional vertical axle-type flywheel systems. In this paper, a prototype flywheel device with a horizontal axle is presented briefly, and the hybrid construction as an essential supplement in superconductor journal bearing design against the levitation drift is proposed.

• Journal of the Korean Institute of Intelligent Systems
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• v.26 no.5
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• pp.351-360
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• 2016

Rapid population growth with high living standards and high electronics use for personal comfort has raised the electricity demand exponentially. To fulfill this elevated demand, conventional energy sources are shifting towards low production cost and long term usable alternative energy sources. Hybrid renewable energy systems (HRES) are becoming popular as stand-alone power systems for providing electricity in remote areas due to advancement in renewable energy technologies and subsequent rise in prices of petroleum products. Wind and solar power are considered feasible replacement to fossil fuels as the prediction of the fuel shortage in the near future, forced all operators involved in energy production to explore this new and clean source of power. Presented paper proposes fuzzy logic based Energy Management System (EMS) for Wind Turbine (WT), Photo Voltaic (PV) and Diesel Generator (DG) hybrid micro-grid configuration. Battery backup system is introduced for worst environmental conditions or high load demands. Dump load along with dump load controller is implemented for over voltage and over speed protection. Fuzzy logic based supervisory control system performs the power flow control between different scenarios such as battery charging, battery backup, dump load activation and DG backup in most intellectual way.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.3
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• pp.279-286
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• 2006

The present study concerns the annual performance evaluation of a hybrid-renewable energy system with geothermal and solar heat sources for hot water, heating and cooling of the residential buildings. The hybrid energy system consists of ground source heat pump of 2 RT for cooling, solar collectors of $4.8m^2$, storage tank of 250 liters and gas fired backup boiler of 11.6 kW. The averaged coefficients of performance of geothermal heat pump system during cooling and heating seasons are measured as 4.1 and 3.5, respectively. Also solar fraction for hot water is measured as 35 percent. Overall, the results shows that the hybrid-renewable energy system satisfactorily operated under all climatic conditions.

• Applied Chemistry for Engineering
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• v.23 no.4
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• pp.359-366
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• 2012

Zn-Air energy storage cell is an attractive type of batteries due to its theoretical gravimetric energy density, cost-effective structure and environmental-friendly characteristics. The chargeability is the most critical in various industrial applications such as smart portable device, electric vehicle, and power storage system. Thus, it is necessary to reduce large overpotential of oxygen reduction/evolution reaction, the irreversibility of Zn anode, and carbonation in alkaline electrolyte. In this review, we try to introduce recent studies and developments of bi-functional air cathode, enhanced charge efficiency via modification of Zn anode structure, and blocking side reactions applying hybrid organic-aqueous electrolyte for high power density rechargeable Zn-Air energy storage cells.