• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.1
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• pp.54-60
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• 2006

A power limiting algorithm is proposed for stable operation of grid-connected inverter in case of grid voltage unbalance considering the operation limit of inverter. During the voltage unbalance the control performance of Inverter. is degraded and the output power contains 120Hz ripple due to the negative sequence of voltage. In this paper, conventional dual sequence current controller is implemented to solve these problems using separated control of positive and negative sequence. Especially the maximum power limit which guarantees the maximum rated current of the inverter is automatically calculated as the instant grid voltage changes. As soon as the voltage recovers the proposed algorithm can return to the normal power control mode accomplishing low voltage ride through. Proposed algorithm is verifed using PSCAD/EMTDC simulations and tested experimentally at 4.4kW wind turbine simulator set-up.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.1
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• pp.39-46
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• 2006

PLL is a key item of power converter for power quality compensation and power flow control. This paper proposes a novel 3-phase PLL that is composed of ALC and PI controller. The operational principle was investigated through theoretical approach, and the performance was verified through computer simulations with MATLAB and experimental works with TMS320VC33 DSP board. The proposed 3-phase PLL shows accurate performance under the voltage disturbances such as sag, harmonics. phase-angle jump, and frequency change.

• Proceedings of the KIEE Conference
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• 1996.07b
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• pp.731-733
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• 1996

In this paper, a new time-domain reduction method for unbalanced 3 phase power systems will be represented. The impulse response of the system is used to identify a discrete-time equivalent filter model. The model is formulated directly in the phase domain. Each phase has a self-mode equivalent model and two mutual-mode equivalent models. The equivalent model is determined by the transfer function identification technique based on the Prony analysis. The model is implemented in EMTDC and tested with an unbalanced 3 phase network. The result of test showed that the equivalent model is accurate.

• Proceedings of the KIEE Conference
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• 1996.07b
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• pp.686-688
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• 1996

Network reconfiguration is performed by opening/closing two types of switches, tie and sectionalizing switches. A whole feeder, or part of a feeder, may be served from another feeder by closing a tie switch linking the two while an appropriate sectionalizing switch must be opened to maintain radial structures. In loss reduction, the problem is to identify tie and sectionalizing switches that should be closed and opened, respectively, to achieve a maximum loss reduction. In this paper, it is introduced to propose the reconfiguration plan for loss reduction by using the Civanlar's loss reduction formular.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.281-283
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• 2003

In the rower systems of Korea, there is little chance of the separation of power systems as well as a blackout due to the large disturbance. However, that possibility shouldn't be ignored, and always exists. In this paper, we present the results of the analysis of transient stabilities for the case of contingencies of power systems separation in the isolated power systems where the regional concentration of supply and demand exists.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.31-33
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• 2003

Power system restoration following a partial or complete blackout starts with energizing of primary transmission lines. Because system changed rapidly during early restoration process, transformer energization and load pickup is executed to maintain the power system stability. However unexpected problem such as harmonic overvoltage may be arisen during energizing transformer. The reason of harmonic overvoltage is known as transformer saturation and magnetizing in-rush current and so on, but it is difficult to estimate the condition of occurrence. This paper describes the analysis of the harmonic overvoltage while unloaded transformer is energized using PSCAD/EMTDC.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.190-192
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• 2003

When generators trip on the occurrence of disturbance, the power system frequency declines by the amount of difference between demand and supply due to the imbalance between power generation and load. Even though the power system is operated with the same grid structure, generating capacity, and load, the resulting frequency decline and its recovery slope show different aspects according to the inertia constants of generators, spinning reserves, and the speed adjusting rates at the governors. From this point of view, we analysed differences of frequency decline at the various conditions in domestic power system.

• Proceedings of the KIEE Conference
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• 2004.11b
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• pp.119-121
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• 2004

This paper presents a methodology which can make alternatives of distribution system, and can calculate reliability costs, harmonics costs, and construction costs. And by using total cost of the system, decision maker can select the most economic and reasonable alternative. As a result, not only we can decide most economical and reasonable result, but we can get proper reliability and harmonics level. The usefulness of the method is verified by applying it to the test system.

• Proceedings of the Korean Society of Grassland Science Conference
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• 2005.06a
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• pp.186-187
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• 2005

• Animal Systematics, Evolution and Diversity
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• no.nspc2
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• pp.25-36
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• 1988

The Korean scleractinians examined in the present study are seven species in five families . They have six kinds of cnidae ; atrichous isorhizas, basitrichous isorhizas, holotrichous isorhizas, microbasis p-mastigophores, microbasic b-mastigophores and spirocysts, of which the holotrichous isorhizas, microbasic p-mastigophores and spirocysts are distributed in all species. The atrichous and basitrichous isorhizas are present very rare in Korean scleractinians. Especially the microbasic p-mastigophores are common in most parts of all species.