• Proceedings of the KIPE Conference
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• 2011.11a
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• pp.44-45
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• 2011

Research on photovoltaic (PV) generation is taking a lot of attention due to its infinity and environment-friendliness with decrease of price per PV cell. While central inverters connect group of PV modules to utility grid in which maximum power point tracking (MPPT) for each module is difficult, micro inverter is attached on each module so that MPPT for individual modules can be easily achieved. Moreover, energy generation and consumption efficiency can be much improved by employing direct current (DC) distribution system. In this paper, a digitally controlled PV micro converter interfacing PV to DC distribution system is proposed. Boundary conduction mode (BCM) is utilized to achieve zero voltage switching (ZVS) of active switch and eliminate reverse recovery problem of passive switch. A 120W prototype boost PV micro converter is implemented to verify the feasibility and experimental results show higher than 98% efficiency at peak power and 97.29% of European efficiency.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.1
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• pp.42-48
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• 2009

Microgrid supplies loads with power interconnected grid. And it is defined a independent power system compounded micro sources over two devices which have enough capacity to operate independently, storage devices and loads. The energy sources of micro source have different dynamic characteristics corresponding to classes and application skills. However their transient responses are various from a few seconds to minutes. Therefore it is limitation for understanding operation characteristics of microsource modeling constant voltage source or constant current source. This paper shows that we designed EMTP/RV model of micro source which is microturbine based energy source. And we performed dynamic analysis of micro source corresponding to operation mode of microgrid.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2788-2793
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• 2008

A numerical analysis has been conducted for flow characteristics and performance of a micropump with piezodisk and MHD(Magnetohydrodynamics) fluid. Various micro systems which could not be considered in the past have been recently growing with the development of MEMS(Micro Electro Mechanical System) and micro machining technology. Especially, micropumps, essential part of micro fluidic devices, are being lively studies by many researchers. In the present study, the piezo electric micropump with electromagnetic resistance for electrically conducting fluids is considered. The prescribed grid deformation method is used for the displacement of the membrane. The change of the performance of the micropump and flow characteristics of the electrically conducting fluid with the magnitude of the magnetic fields, duct size, the position of the inlet and outlet duct are investigated in the present study.

• Journal of Power Electronics
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• v.8 no.2
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• pp.156-162
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• 2008

This paper proposes a low-cost power converter for micro wind turbine systems using permanent magnet synchronous generators (PMSG). The proposed converter consists of a two-leg three-phase PWM inverter for the generator control and a single-phase half-bridge PWM converter which is connected to the utility grid. For the two separate DC-link voltages, a balancing control is added and the adverse effect of the DC-link voltage ripples on the inverter output voltage is compensated. The control performance of the proposed converter topology for the micro wind turbine system is shown by the simulation results using PSIM software.

• Journal of Welding and Joining
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• v.24 no.5
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• pp.22-28
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• 2006

A spacer grid assembly, which is an interconnected array of slotted grid straps and is welded at the intersections to form an egg crate structure, is one of the main structural components of the nuclear fuel assembly for Pressurized Water Reactors (PWRs). The weld quality of spacer grids in PWRs fuel is extremely important for the fuel assembly performance in the nuclear renter. The spacer grid welds are currently evaluated mainly by the metallographic examination although it reveals only cross-points which are welded by the laser beam. This experiment is also to compare the weldability of Zircaloy-4 spacer grids using by the GTA and LB. The effect of node geometries of spacer grids for the GTAW and LBW has been studied and optimum conditions of spacer grid welding have been found. Microstructures and micro-hardness of the GTA and LB welded zones have been also compared.

• Journal of Power Electronics
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• v.18 no.1
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• pp.185-194
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• 2018

Interaction among multiple grid-connected inverters has a negative impact on the stable operations and power quality of a power grid. The interrelated influences of inverter inductor-capacitor-inductor filters constitute a high-order power network, and consequently, excite complex resonances at various frequencies. This study first establishes a micro-grid admittance matrix, in which inverters use deadbeat control. Multiple resonances can then be evaluated via modal analysis. For the active damping method applied to deadbeat control, the sampling frequency and the stable domain of the virtual damping ratio are also presented by analyzing system stability in the discrete domain. Simulation and experimental results confirm the efficiency of modal analysis and stable domain calculation in multi-inverter grid-connected systems.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.12
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• pp.1337-1344
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• 2015

Formation process through charge/discharge operation is needed in manufacturing Li-ion battery. In the process battery is discharged by a load resistor of discharger. Here, energy losses happen. Therefore, in this paper, the efficient energy operation of battery is studied in the charge/discharge system based on DC ${\mu}-Grid$. A result of computer simulation shows that if in the charge/discharge system based on DC ${\mu}-Grid$, the number of discharge batteries in comparison with three charge battery sets exceeds 133%, voltage fluctuation that occurs while the grid voltage stabilizes, which makes the system fatal. Therefore, it was demonstrated that a remarkable energy saving effect could be achieved when the number of discharge battery set is maintained to be 133% in comparison with three charge battery sets.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.6
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• pp.8-16
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• 2003

Aerodynamic characteristics over Micro Aerial Vehicle(MAV) in low Reynolds number regime are numerically studied using 3-D unsteady, incompressible Navier-Stokes flow solver with single partitioning method for multi-block grid. For more efficient computation of unsteady flows, this flow solver is parallel-implemented with MPl(Message Passing Interface) programming method. Firstly, MAV wing with not complex geometry is considered and then, we analyze aerodynamic characteristics over full MAV configuration varying the angle of attack. Present computational results show a better agreement with the experimental data by MACDL(Micro Aerodynamic Control and Design Lab.), Seoul National University. We can also find the conceptually designed MAV by MACDL has the static stability.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1139_1141
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• 2009

Distributed Generation (DG) is predicted to play a important role in electric power system in the near future. insertion of DG system into existing distribution network has great impact on real-time system operation and planning. It is widely accepted that micro turbine generation (MTG) systems are currently attracting lot of attention to meet customers need in the distributed power generation market In order to investigate the performance of MT generation systems, their efficient modeling is required. This paper presents the modeling and simulation of a MT generation system suitable for grid-connected operation. The system comprises of a permanent magnet synchronous generator driven by a MT. A brief description of the overall system is given, and mathematical models for the MT and permanent magnet synchronous generator are presented. Also, the use of power electronics in conditioning the power output of the generating system is demonstrated. Simulation studies with MATLAB/Simulink have been carried out in grid-connected operation mode of a DG system. The control strategies for grid connected operation mode of DG system is also presented.

• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.3
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• pp.264-271
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• 2014

Virtual synchronous generator (VSG) in single-phase to interface distributed renewable energy resources is investigated in this paper. Mathematical models and numerical analysis are utilized to illustrate the features of the VSG. Enhanced control strategy is presented to ensure the performance of the VSG. Besides, a second order generalized integer (SOGI) is employed to calculate the instantaneous output power of the VSG in virtual ${\alpha}{\beta}$ frame. By the means of a phase-locked loop based scheme, the VSG can seamlessly transform between islanded and grid-tied modes, which can meet the requirements of micro-grid. At last, the validation and the proposed approach are verified by the simulated results using PSCAD/EMTDC.