• Journal of the Korean Institute of Telematics and Electronics B
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• v.33B no.10
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• pp.148-156
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• 1996

Increasing the switching frquency is essential to achieve the high density of switched mode power supplies, but this leads to the increase of switching losses. A number of new soft switching converters have been presented ot reduce switching losses, but most of them may have some demerits, such as the increase of voltage/current stresses and high conduction losses. To overcome these problems, the ZVT-PWM converter has recently been presented. in this paper, the operation characteristics of the ZVT-PWM boost converter is analyzed, and the steady-states (DC) and small-signal model of this converter are derived and analyzed, and then the transfer functions of this converter are derived. The transfer functions of ZVT-PWM boost converter are similar to those of the conventional PWM boost converter, but the transfer characteristics are affecsted by te duty ratio and the switching frequency.

• Journal of Electrical Engineering and Technology
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• v.13 no.2
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• pp.699-703
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• 2018

Flux-switching permanent magnet machines (FSPMM) have doubly-salient and simple structures making it cost effective and suitable for mass production. In addition, it is possible to increase the rotor rotating speed and concentrate the flux of the permanent magnet on the air-gap. Due to these merits, the FSPMM can be applied to the various industry applications. To improve the performance, various design variables need to be studied in terms of design techniques. In this paper, we especially concentrate on the distribution of iron losses using a two-dimensional finite-element method (2D FEM). As a result, we can get an information for high efficiency FSPMM design.

• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.834-836
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• 2000

The round HTS wire is easier to handle than the rectangular HTS tape. This paper describes the coupling losses of the round HTS wires by finite element method. Effect of filament arrangement and filament size of the round HTS wire are considered. Three types of filaments arrangement, one and double layer radial filaments and Multi-filament, are considered. Calculation results show that coupling losses of the one layer filaments round HTS wire vary only a little with the direction of external magnetic field.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1551-1553
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• 2000

Superconducting power cable is one of the most promising energy application of high-$T_c$ superconductors (HTS). A prototype HTS cable have been constructed multi-layer cable using Bi-2223 tape and tested. The result shows that the total transport current of HTS cable in $LN_2$ was 475[A], and transport current passed through almost the outer layer (2-layer). Also, AC transport losses in outer layer of HTS cable was proportion to $I^2$ and higher than losses of inner layer. As magnetic distribution were concentrated on outer layer.

• Proceedings of the KIEE Conference
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• 1998.07c
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• pp.1111-1113
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• 1998

A robust economic dispatch algorithm involving transmission losses is proposed and investigated for a possibility of on-line applications. In this paper, the penalty factors are calculated directly from transposed Jacobian of load flow analysis with advantages of superiority to B-coefficients method based on its computation time and suitability for real time application since the approach is based on a current system condition. The proposed algorithm is systematically handling the generation capacity constraints with transmission losses. Implementation of the algorithm for IEEE systems and EPRI Scenario systems shows that computation time is enough to apply on-line economic dispatch to large power system and production cost is saved compared with the crude classical economic dispatch algorithm without considering transmission losses.

• Proceedings of the KIEE Conference
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• 1998.07a
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• pp.340-342
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• 1998

This paper presents the ac losses simulation in the rotor having an high-Tc superconducting field winding using Ag sheathed Bi-2223. The analysis was conducted with an equivalent model of the high-Tc superconducting motor under transition condition during the load that varies from 250watt to 500watt. The simulation results show that the transient state lasts for about 2 seconds, and the ac losses decreased exponentially from the initial value above 2 watts.

• Proceedings of the KIEE Conference
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• 1999.07a
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• pp.262-264
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• 1999

The AC losses of BSCCO-2223 multifilamentary superconducting tapes were measured using magnetization method and compared with the results of theoretically calculated values. In general, AC losses in multifilamentary superconducting tapes could be quantitatively explained by the simple sum of the Hysteresis and Coupling Loss. As a result of experiment, We found that AC losses of multifilamentary superconducting tape increase rapidly in large magnetic field region.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.260-262
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• 2003

AC loss is an important issue in the design of high-T$_{c}$, superconducting power cables which consist of a number of Bi-2223 tapes wound on a cylindrical former. In this paper, the ac loss characteristics in the 3-conductor have investigated experimentally. The loss test results indicate that the ac loss is not related to the arrangement of Bi-2223 tapes, contact position and applied frequency. The measured losses in face-to-face arrangement are larger than those in edge-to-edge arrangement. The measured losses in the 3-conductor also agree well with the sum of the transport losses measured in each Bi-2223 tape.e.

• Journal of the Korean Solar Energy Society
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• v.37 no.3
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• pp.23-32
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• 2017

This paper presents losses comparison and analysis results for different types of fault modes of grid-connected photovoltaic system generated for long-term operation. The approach of losses comparison and analysis by faults is to identify relationship between measured and estimated values of five loss factors which are quantified from irradiance to system output power. This paper presents the symptom results for faults such as snow, shading, sensor defect, blackout, soiling and so on from three years or more monitored data. These results will indicate that it is useful to develop fault detection and diagnosis tool to enhance capacity factor and save operation and maintenance cost of grid-connected photovoltaic system in the field.

• Water Engineering Research
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• v.7 no.1
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• pp.29-41
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• 2006

The Imha watershed is vulnerable to severe erosion due to the topographical characteristics such as mountainous steep slopes. Sediment inflow from upland area has also deteriorated the water quality and caused negative effects on the aquatic ecosystem of the Imha reservoir. The Imha reservoir was affected by sediment-laden density currents during the typhoon 'Maemi' in 2003. The RUSLE model was combined with GIS techniques to analyze the mean annual erosion losses and the soil losses caused by typhoon 'Maemi'. The model is used to evaluate the spatial distribution of soil loss rates under different land uses. The mean annual soil loss rate and soil losses caused by typhoon 'Maemi' were predicted as 3,450 tons/km2/year and 2,920 ton/km2/'Maemi', respectively. The sediment delivery ratio was determined to be about 25% from the mean annual soil loss rate and the surveyed sediment deposits in the Imha reservoir in 1997. The trap efficiency of the Imha reservoir was calculated using the methods of Julien, Brown, Brune, and Churchill and ranges from 96% to 99%.