• New & Renewable Energy
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• v.6 no.1
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• pp.12-19
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• 2010

In Korea, experiences in wind farm operation are limited and the foundation for setting standards in electrical system connection is still weak in comparison to the operation experience in connection of wind power to the electrical system of other countries around the world. Therefore, standards that are being applied in various countries for connection and optimal operation in wind farms need to be examined, and in addition, procedures for the assessment of the effects on the system are needed for setting connection standards and optimal operation plans in accordance with Korean electrical system characteristics. In this study, procedures for the assessment of effects of wind power connection to the electrical system are presented.

• Journal of Power Electronics
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• v.16 no.4
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• pp.1455-1468
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• 2016

This paper presents a grid-connected dual stator-winding induction generator (DWIG) wind power system suitable for wide wind speed ranges. The parallel connection via a unidirectional diode between dc buses of both stator-winding sides is employed in this DWIG system, which can output a high dc voltage over wide wind speed ranges. Grid-connected inverters (GCIs) do not require booster converters; hence, the efficiency of wind energy utilization increases, and the hardware topology and control strategy of GCIs are simplified. In view of the particularities of the parallel topology and the adopted generator control strategy, we propose a novel excitation-capacitor optimization solution to reduce the volume and weight of the static excitation controller. When this excitation-capacitor optimization is carried out, the maximum power tracking problem is also considered. All the problems are resolved with the combined control of the DWIG and GCI. Experimental results on the platform of a 37 kW/600 V prototype show that the proposed DWIG wind power system can output a constant dc voltage over wide rotor speed ranges for grid-connected operations and that the proposed excitation optimization scheme is effective.

• Geomechanics and Engineering
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• v.35 no.6
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• pp.617-626
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• 2023

In this study, three-dimensional numerical parametric study was conducted to explore deformation mechanisms of grouped piled-raft-foundation due to lateral load in clays. Effects of load intensity, loading angle, soil stiffness, pile diameter, pile spacing and pile length on foundation deformations were explored. It is found that the smallest and largest movements of pile foundation are induced when the loading angles are 0° and 30°~60°, respectively. By increasing loading angle from 0° to 30°~60°, the resultant horizontal movements and settlements increase by up to 20.0% and 57.1%, respectively. Since connection beams can substantially increase integrity of four piled raft foundation, resultant horizontal movements, settlements and bending moments induced in the piled raft foundation decrease by up to 54.0%, 8.8% and 46.3%, respectively. By increasing soil stiffness five times, resultant horizontal movements and settlements of pile foundation decrease by up to 61.7% and 13.0%, respectively. It is indicated that effects of connection beam and soil stiffness on settlements of pile foundation are relatively small. When pile diameter is less than 1.4 m, deformations of piled raft foundation decrease substantially as a reduction in the pile diameter. Two dimensional groups are proposed to develop calculation charts of horizontal movements and settlements of pile foundation. The proposed calculation charts can directly estimate movements of piled raft foundation under arbitrary loading, ground and pile conditions.

• 전기의세계
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• v.60 no.11
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• pp.56-63
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• 2011

In the face of global warming and resource depletion, a smart grid has been suggested as one way of contributing to abating the environment problems and increasing energy efficiency. Smart grids utilize renewable energy which has intermittent and irregular output power depending on weather conditions. In order to maintain stability and reliability of the power system, smart grids need to have complementary measures for the possible unstable system conditions. Cogenerating systems such as Combined Heat and Power(CHP) can be one good solution as it has capability of instantly increasing or decreasing output power. Therefore, this paper investigates the connectivity between Combined Heat and Power systems and smart grid technologies. The smart grid national roadmap formulated by South Korea Ministry of Knowledge and Economy and 'IEC Smart Grid Standardization Roadmap' are analyzed to extract related components of the smart grid for the CHP connection. Also, case studies on demonstration projects for smart grids with CHP systems completed or currently being implementing in the world are presented.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.5
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• pp.1093-1101
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• 2017

Microgrid as a unit component consisting a smart grid is an isolated system, which has a decentralized power supply system. This paper proposes an electrical isolation of the microgrid from the utiliy grid based on a power conditioning system, and also proposes an operation method maintaining the isolated state efficiently using diverse distributed energy resources such as renewable energy sources and energy storage system. The proposed system minimizes the influence of the grid connection on the internal load though a phase detection and synchrnoization to the utiligy grid and the microgrid can be stable even if the grid is failed.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1554-1565
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• 2019

When grid voltage is unbalanced, the grid-connected output current and power of Virtual Synchronous Generators (VSGs) are distorted and quadratic. In order to improve the power quality of a grid connected to a VSG when the grid voltage is unbalanced, a comprehensive coordinated control strategy is proposed. The strategy uses the positive sequence current reference command obtained by a VSG in the balanced current control mode to establish a unified negative sequence current reference command analytical expression for the three objectives of current balance, active power constant and reactive power constant. In addition, based on the relative value of each target's volatility, a comprehensive wave function expression is established. By deriving the comprehensive wave function, the corresponding negative sequence current reference value is obtained. Therefore, the VSG can achieve the minimum comprehensive fluctuation under the premise that the three targets meet the requirements of grid connection, and the output power quality is improved. The effectiveness of the proposed control strategy is verified by simulation and experimental results.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.151_152
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• 2009

The capacity constraints of tie-lines in production cost analysis are very important issues in the operation and planning of MicroGrid power systems. This paper presents the Harmony Search(HS) algorithm to solve the Economic Dispatch (ED) problem with tie-line capacity limits in MicroGrid system. The applied HS algorithm has achieved efficient and accurate solutions for three-area MicroGrid systems with renewable power units.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.12
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• pp.2402-2409
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• 2009

This paper proposed a simple and helpful analysis model of voltage variation in order to predict the voltage variation at PCC (Point of Common Coupling), when a wind turbine is connected in an isolated grid. The PCC voltage flucuates when the wind turbine outputs active power to an isolated grid. This voltage variation is proportional to the product of the line impedance from the ideal generator to the PCC and the wind turbine output current. And It is different according as where wind turbine is connected. To solve the problem of voltage variation, this paper proposed the reactive power control. To verify the proposed analysis model, this paper utilized PSCAD/EMTDC Simulation and the field measurement data of the voltage variation during the wind power generation.

• Journal of Power Electronics
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• v.9 no.1
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• pp.85-92
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• 2009

This paper studies the method to predict voltage variation that can be presented in the case of operating a small-sized wind turbine in grid connection to the isolated small-sized power system. In order to do this, it makes up the simplified simulation model of the existing power plant connected to the isolated system, load, transformer, and wind turbine on the basis of PSCAD/EMTDC and compares them with the operating characteristics of the actual established wind turbine. In particular, it suggests a simplified model formed with equivalent impedance of the power system network including the load to analytically predict voltage variation at the connected point. It also confirms that the voltage variation amount calculated by the suggested method accords well with both simulation and actually measured data. The results can be utilized as a tool to ensure security and reliability in the stage of system design and preliminary investigation of a small-sized grid connected wind turbine.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1759-1761
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• 2005

The exploitation of the resource wind energy is a rapidly growing area world-wide. The number of installed units is continuously increasing, and therefore, it is important to respect and to deal with the impact of wind power generation system. From the view of an electric grid utility, there is a major problem with the impact of the wind system on the voltage of the electric grid, to which a turbine in connected. The problem is rather common in the connection of a wind power system to an already existing grid, since the grid is very seldom designed for the transmission of additional power. In this paper, it is investigated the voltage impact of distribution line, to which wind power generation system is connected.