• Journal of Power Electronics
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• v.15 no.4
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• pp.1006-1017
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• 2015

This paper presents a finite control set model predictive control (FCS-MPC) strategy for the AC/DC matrix converter used in grid-connected battery energy storage system (BESS). First, to control the grid current properly, the DC current is also included in the cost function because of input and output direct coupling. The DC current reference is generated based on the dynamic relationship of the two currents, so the grid current gains improved transient state performance. Furthermore, the steady state error is reduced by adding a closed-loop. Second, a Luenberger observer is adopted to detect the AC input voltage instead of sensors, so the cost is reduced and the reliability can be enhanced. Third, a switching state pre-selection method that only needs to evaluate half of the active switching states is presented, with the advantages of shorter calculation time, no high dv/dt at the DC terminal, and less switching loss. The robustness under grid voltage distortion and parameter sensibility are discussed as well. Simulation and experimental results confirm the good performance of the proposed scheme for battery charging and discharging control.

• Proceedings of the KIEE Conference
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• 1998.07c
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• pp.1244-1246
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• 1998

This paper present a variety fault problem brought out with the multifunctional Battery Energy Storage System [MBESS] expected to be practical in the short future interconnected to power distribution system. Multifunctional BESS model and interconnection model to power system is simply configured, the problems of protection coordination and operation is studied. A line fault in the power distribution system are discussed such as line to ground and three phase fault in order to show the impact on power utilities, demand-side and BESS-side. In order to simulate a variable transient phenomenon due to 2 the BESS interconnection operation to power distribution system, in this paper, PSCAD/EMTDC simulation tools is used.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.2
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• pp.281-289
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• 1992

In an attempt to simulate the flows in the computer hard disk storage system, flow visualization and quantification by image processing technique were applied. Model geometry was constructed while the dynamic similitude was maintained. Circumferential velocities were mapped out in the transient spin-up phase. During the spin-up phase, fluid close to the rotating inner hub approached the solid body rotation, while the fluid in the outer region showed the velocity deficit compared to the rotating speed of the disks. Effects of presence of read/write head arm assembly between the gap were studied by changing the location of the head. The experimental results could serve as a benchmark for the alidation of numerical codes.

• International Journal of Air-Conditioning and Refrigeration
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• v.6
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• pp.14-26
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• 1998

This paper deals with approximate analytical solutions for the two-region one-dimensional model describing the charging process of stratified thermal storage tanks at variable inlet temperature with momentum-induced mixing. An arbitrarily increasing inlet temperature is decomposed into inherent step changes and intervals of continuous change. Each continuous interval is approximated as a finite number of piecewise linear functions, which admits an analytical solution for perfectly mixed region. Using the Laplace transform, the temperature profiles in plug flow region with both the semi-infinite and adiabatic ends are successfully derived in terms of well-defined functions. The effect of end condition on the solution proves to be negligible under the practical operating conditions. For a Quadratic variation of inlet temperature, the approximate solution employing a moderate number of pieces agrees excellently with the exact solution.

• Journal of the Korean Society of Groundwater Environment
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• v.4 no.2
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• pp.95-102
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• 1997

So far, several fractal models of fluid flow in a fractured aquifer have been developed. In this study, a new fractal model is derived that considers transient flow in the dual-porosity aquifer with the fracture skin between the fissure and the block, and the storage capacity and the wellbore skin on the pumping well. Constant-head upper boundary is specified in the block. This model is a generalized one which comprises both modified Hantush equation (1960) and Boulton-Streltsova equation (1978). Type curves are plotted for different flow dimensions (0.5, 1, 1.5, 2, 2.5 and 3) with various values of the leakage factor and the fracture skin. They show dimensionless drawdown in the pumping well and observation wells located either in the fissure system or in the matrix block.

• Korean Journal of Hydrosciences
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• v.2
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• pp.13-24
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• 1991

The governing partial differential equation of flow in porous media is developed on the bases of the continuity equation of fluid for transient flow through a saturated-unsaturated zone, and substitution of Dercy's law. The numerical solution is obtained by the Galerkin finite element method based on the principle of weighted residuals. The analysis is carried out by using the unsteady storm data observed and the functional relationships between the hydraulic conductivities, capillary pressure heads, and volumetric water contents under saturated-unsaturated conditions. As the results the hydraulic conductivities, rates of change of storage and initial moisture conditions are significantly influened on the responses of subsurface flow on a hillslope.

• Tunnel and Underground Space
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• v.14 no.1
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• pp.16-25
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• 2004

As underground caverns have many advantages such as safety and operation, they can also be used for gas storage purpose. When liquefied gas is stored underground, the cryogenic temperature of the gas affects the stability of the storage cavern. In order to store the liquefied gas successfully, it is essential to estimate the exact temperature distribution of the rock mass around the caverns. The main purpose of this study is the development of theoretical solution to be able to estimate the temperature distribution around storage caverns and the assessment of the solution. In this study, a theoretical solution and a conceptual model for estimating two and three dimensional temperature distribution around the storage caverns are suggested. Based on the multi-dimensional transient heat transfer theory, the theoretical solution is successfully derived by assuming the caverns shape as simplified geometry. In order to assess the theoretical solution, by performing numerical experiments with this multi-dimensional model, the temperature distribution of the theoretical solution is compared with that of numerical analysis. Furthermore, the effects of the caverns size are investigated.

• Journal of Power Electronics
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• v.14 no.2
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• pp.392-401
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• 2014

A fast-transient repetitive control strategy for a three-phase shunt active power filter is presented in this study to improve dynamic performance without sacrificing steady-state accuracy. The proposed approach requires one-sixth of the fundamental period required by conventional repetitive control methods as the repetitive control time delay in the synchronous reference frames. Therefore, the proposed method allows the system to achieve a fast dynamic response, and the program occupies minimal storage space. A proportional-integral regulator is also added to the current control loop to eliminate arbitrary-order harmonics and ensure system stability under severe harmonic distortion conditions. The design process of the corrector in the fast-transient repetitive controller is also presented in detail. The LCL filter resonance problem is avoided by the appropriately designed corrector, which increases the margin of system stability and maintains the original compensation current tracking accuracy. Finally, experimental results are presented to verify the feasibility of the proposed strategy.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.1 no.1
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• pp.9-20
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• 1989

This paper presents an analysis to predict thermal behaviors of water in ice storage tank during the coldness release process. To deal with complicated transient phenomena due to ice-water phase change and the density inversion, a theoretical model which consists of initial perfectly mixed, stratified and thermal diffusion state was introduced and a criterion on the growth of thermal boundary layer was developed. The analysis includes considerations on the type of ice-making heat exchanger, refrigerator on/off and tank arrangement. Also, discussions on the various parameters and operating conditions which have influence on the performance of the system were made. Finally, simulated results were shown, which agreed with experiments in trends reasonably.

• Nuclear Engineering and Technology
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• v.30 no.2
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• pp.91-98
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• 1998

Time history analysis is usually performed to characterize the nonlinear seismic behavior of a spent fuel storage rack(SFSR). In the past, the seismic analyses of the SFSR were performed with two-dimensional planar models, which could not account for torsional response and simultaneous multi-directional seismic input In this study, three-dimensional seismic analysis methodology is developed for the single SFSR using the ANSYS code. The 3D- Model can be used to determine the nonlinear behavior of the rack, i.e., sliding, uplifting, and impact evaluation between the fuel assembly and rack, and rack and the pool wall, This paper also reviews the 3-D modeling of the SFSR and the adequacy of the ANSYS for the seismic analysis. AS a result of the adquacy study, the method of ANSYS transient analysis with acceleration time history is suitable for the seismic analysis of highly nonlinear structure such as an SFSR but it isn't appropriate to use displacement time history of seismic input.