• Journal of Korean Society on Water Environment
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• v.25 no.4
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• pp.589-596
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• 2009

The spectroscopic characteristics and chemical oxygen demand (COD) oxidation efficiencies were investigated for dissolved organic matters (DOM) from diverse sources, which may indirectly affect the concentrations and the quality of DOM found in watersheds. The DOM investigated for this study showed a wide range of the percent distributions of refractory organic matter (R-OM) from 8 to 100%. Relatively high R-OM distributions were observed for the DOM with the source of head water, sediments, paddy soils, field soils, and treated sewage whereas the DOM from livestock waste, reed, weeds, algae, and attached algae exhibited lower R-OM percent distributions. The percent distribution of R-OM had positive correlations with specific UV absorbance (SUVA) and humidification indices (HIX) of DOM. The investigated DOM was classified into four different source groups (i.e., biota, vegetables, soils, sediments) by comparing the synchronous fluorescence spectra. The DOM group from biota source was characterized by a prominent presence of protein-like fluorescence (PLF) whereas fulvic-like fluorescence (FLF) was additionally observed for vegetable-source DOM. FLF became significant for the DOM from both soils and sediments although no PLF was found for soil-derived DOM. A range of COD oxidation efficiency was observed for the various DOM, ranging from 36 to 94% and from 65 to 125% for $COD_{Mn}$ and $COD_{Cr}$, respectively. The results indicate that $COD_{Cr}$ reflects the higher OM concentration than $COD_{Mn}$. However, 95% confidence intervals of the COD oxidation efficiencies were similar for the two types of COD, suggesting that $COD_{Cr}$ may not be the superior OM index to $COD_{Mn}$ in terms of the variability of the oxidation efficiency. No significant correlations were obtained between COD oxidation efficiencies and the spectroscopic characteristics of DOM for this study.

• Journal of the Korea Society of Computer and Information
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• v.14 no.2
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• pp.157-168
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• 2009

In this paper, a photovoltaic system is designed with a step up chopper and single phase PWM(Pulse Width Modulation) voltage source inverter. Where proposed Synchronous signal and control signal was processed by one-chip microprocessor for stable modulation. The step up chopper operates in continuous mode by adjusting the duty ratio so that the photovoltaic system tracks the maximum power point of solar cell without any influence on the variation of insolation and temperature because solar cell has typical voltage and current dropping character. The single phase PWM voltage source the inverter using inverter consists of complex type of electric power converter to compensate for the defect, that is, solar cell cannot be developed continuously by connecting with the source of electric power for ordinary use. It can cause the effect of saving electric power. from 10 to 20[%]. The single phase PWM voltage source inverter operates in situation that its output voltage is in same phase with the utility voltage. In order to enhance the efficiency of photovoltaic cells, photovoltaic positioning system using sensor and microprocessor was design so that the fixed type of photovoltaic cells and photovoltaic positioning system were compared. In result, photovoltaic positioning system can improved 5% than fixed type of photovoltaic cells. In addition, I connected extra power to the system through operating the system voltage and inverter power in a synchronized way by extracting the system voltage so that the phase of the system and the phase of single-phase inverter of PWM voltage type can be synchronized. And, It controlled in order to provide stable pier to the load and the system through maintaining high lurer factor and low output power of harmonics.

• Journal of Sensor Science and Technology
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• v.15 no.2
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• pp.77-83
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• 2006

A monitoring apparatus for pulse shapes of human heartbeats has been developed using an amorphous MI(Magnetic Impedance) sensor. The pulse shapes are successfully obtained from voltage signals due to the variations of magnetic impedance in the amorphous MI sensor, which is attached to a patient's wrist. This voltage signal was fed into a signal processing module to extract the pulse shapes of heartbeats. The signal processing module, which is proposed to detect a weak variations of impedance in MI sensor under a noisy measurement environment, consists of a high frequency current source, an amplifier stage and a synchronous detection circuit. To evaluate the characteristics of a newly developed apparatus, various experiments were performed. The experimental results show that the developed apparatus could be used as a diagnosis tool for traditional Korean medicine with further systematic clinical studies.

• Journal of Electrical Engineering and Technology
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• v.12 no.1
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• pp.225-229
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• 2017

This paper describes the loss analysis based on load conditions of the air conditioning compressor motors using variable dc-link voltage. The losses of PMSM (Permanent Magnet Synchronous Motor) should be analyzed by the PWM (Pulse Width Modulation) output of inverter. The harmonic loss by the PWM cannot consider that using the current source analysis of the inverter. In addition, when the voltage of dc-link is variable with the condition of variable speed and load conditions in motor, the losses of motor are also changeable, however it is hard to analyze those losses by only electromagnetic finite element method (FEM). Therefore, this paper proposes the analysis method considering the carrier frequency of the inverter and the varying state of the dc-link voltage through the FEM-control coupled analysis. Using proposed analysis method, additional core loss and eddy current loss of permanent magnet caused by PWM could be analyzed. Finally, the validity of the proposed analysis method is verified through the comparison the result of coupled analysis with experiment.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.3
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• pp.238-248
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• 2016

In this study, an automatic command mode transition strategy of direct power control (DPC) is proposed for permanent magnet synchronous generators (PMSGs) medium-voltage (MV) offshore wind turbines (WTs). Benchmarking against the control methods are performed based on a three-level neutral-point-clamped (NPC) back-to-back type voltage source converter (VSC). The ramping rate criterion of complex power is utilized to select the switching vector in DPC for a three-level NPC converter. With a grid command and an MPPT mode transition strategy, the proposed control method automatically controls the generated output power to satisfy a grid requirement from the hierarchical wind farm controller. The automatic command mode transition strategy of DPC is confirmed through PLECS simulations based on Matlab. The simulation result of the automatic mode transition strategy shows that the proposed control method of VOC and DPC achieves a much shorter transient time of generated output power than the conventional control methods of MPPT and VOC under a step response. The proposed control method helps provide a good dynamic performance for PMSGs MV offshore WTs, thereby generating high quality output power.

• Journal of Power Electronics
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• v.10 no.5
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• pp.477-484
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• 2010

A pulse width modulation-voltage source inverter (PWM-VSI) is used for variable speed permanent magnet synchronous motor (PMSM) drives. The PWM-VSI fed PMSM has two major disadvantages. Firstly, the PWM-VSI DC-link voltage limits the magnitude of the PMSM terminal voltage. As a result, the motor speed is restricted. Secondly, in a low speed range, the PWM-VSI modulation index declines. This is caused by a high DC-link voltage and a low terminal voltage ratio. As a result, the distortion of the voltage command and the stator current are increased. This paper proposes an optimal pulse amplitude modulation (PAM) control which can adjust the inverter DC-link voltage by using a buck-boost DC-DC converter. At a low speed range, the proposed system can reduce the distortion of the voltage command, which improves the stator current waveform. Also, the allowable speed range is extended. In order to verify the proposed method, experimental results are provided to confirm the simulation results.

• Korean Journal of Remote Sensing
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• v.33 no.4
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• pp.391-400
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• 2017

Geo-based application services linked with the Open Geospatial Consortium (OGC) Web Processing Service (WPS) protocol have been regarded as an important standardized framework for of digital earth building in the web environments. The WPS protocol provides interface standards for analysis functionalities within geo-spatial processing in web-based service systems. Despite its significance, there is few performance tests of WPS applications. The main motivation in this study is to perform the comparative performance test on WPS standards. Test system, which was composed of WPS servers, WPS framework, data management module, geo-based data processing module and client-sided system, was implemented by fully open source stack. In this system, two kinds of geo-based image processing functions such as cloud detection and gradient magnitude computation were applied. The performance test of different server environments of non-WPS, synchronous WPS 1.0 and asynchronous WPS 2.0 was carried out using 100 threads and 400 threads corresponds client users on a web-based application service. As the result, at 100 threads, performance of three environments was within an adjacent range in the average response time to complete the processing of each thread. At 400 threads, the application case of WPS 2.0 showed the distinguished characteristics for higher performance in the response time than the small threads cases. It is thought that WPS 2.0 contributes to settlement of without performance problems such as time delay or thread accumulation.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1053_1054
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• 2009

A significant number of renewable energy systems have been connected to the grids as supplement power source. The renewable energy systems require control algorithm to maintain the power-supply reliability and quality. This paper proposes a novel control algorithm for smart Power Conditioning System (PCS) with harmonics and reactive power compensation. The smart PCS is used to feed Photovoltaic (PV) power to utility and compensate harmonics and reactive power at the same time. The experimentation is carried out on the proposed grid-connected PV generation system, and controlled by digital signal processor. The grid-connected PV generation system injects PV energy into the grid and performs as Active Filter (AF) and Static Synchronous Compensator (STATCOM) without additional devices. The experiment results show that the proposed control algorithm is effective for smart PCS with harmonics and reactive power compensation.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.10
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• pp.1796-1801
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• 2008

In this paper, a new current based maximum power point tracking (CMPPT) method is proposed for a single phase photovoltaic power conditioning system and the current based MPPT modifies incremental conductance method. The current based MPPT method makes the entire control structure of the power conditioning system simple and uses an inherent current source characteristic of solar cell array. In addition, digital phase locked loop using an all pass filter is introduced to detect phase of grid voltage as well as peak voltage. Controllers about dc/dc boost converter, dc-link voltage, dc/ac inverter is designed for a coordinated operation. Furthermore, PI current control using a pseudo synchronous d-q transformation is employed for grid current control with unity power factor. 3kW prototype photovoltaic power conditioning system is built and its experimental results are given to verify the effectiveness of the proposed control schemes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.6
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• pp.1158-1168
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• 1994

The paper proposes a distributed control self-healing algorithm for a line failure to improve the restoration time. This proposed self-healing algorithm acquired the fast restoration time by reducing the number of control messages and the queueing delay. And the reduction of queueing delay was attained by the ASC_NULL(Available Spare Channel_NULL) message which informs neighbor nodes that a source node has no available spare channel to reduce the waste of time during the rerouting. It is difficult for this proposed self-healing algorithm to be compared with other self-healing algorithms, because each self-healing algorithm has different simulation conditions. So, the performance of the proposed self-healing algorithm was compared with only NETRATS(NETwork Restoration Algorithm for Telecommunication Systems). The results of the simulation showed that the proposed self-healing algorithm was better than NETRATS in the restoration time.