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Ibrahim A.O.,University of Waterloo | Nguyen T.H.,Yeungnam University | Lee D.-C.,Yeungnam University | Kim S.-C.,Korea Western Power Co.
IEEE Transactions on Energy Conversion | Year: 2011

This paper proposes a low-voltage ride-through technique of a doubly fed induction generator (DFIG) wind turbine system using a dynamic voltage restorer (DVR). For effective control of the DVR, digital all-pass filters are used for extracting the positive-sequence component from the unbalanced grid voltage since they have the advantages of giving a desired phase shift and no magnitude reduction over conventional low- or high-pass filters. Using the positive-sequence component, the phase angles for the positive- and negative-sequence components of the grid voltage are derived. A control algorithm for the DVR that is dual voltage controllers only is implemented for the two sequence components in the dq synchronous reference frame. In order to achieve the power rating reduction of the DVR, the stator power reference for the DFIG is reduced during faults. In addition, a control scheme of pitch angle system is applied to stabilize the operation of the wind turbine system in the event of grid faults. PSCAD/EMTDC simulations show the effectiveness of the proposed technique and a feasibility of reducing the power rating of DVR for the fault ride-through capability of DFIG. The validity of the proposed control scheme for the DVR has also been verified by experimental results. © 2011 IEEE.

Sung Y.,Imperial College London | Sung Y.,Pusan National University | Lee S.,Pusan National University | Kim C.,Korea South East Power Corporation | And 4 more authors.
Experimental Thermal and Fluid Science | Year: 2016

Hybrid technologies combining fuel blending and air-staging processes have been applied to a pulverized coal fired furnace to reduce NOx emissions. In this study, an Australian bituminous coal (Whitehaven), an Indonesian sub-bituminous coal (Adaro), and an Indonesian woody biomass were selected as fuel with blending ratio of 10%, 20%, and 30% of the low-rank fuels, and the air-staging levels were set to 235mm, 390mm, 585mm, and 760mm. The purpose of this study was to investigate the synergistic effect of woody biomass co-firing on the level of NOx emissions and the degree of carbon burnout under air-staged conditions. For single coals, sub-bituminous coal was more favorable than that for bituminous coal to reduce NOx emissions due to low fuel-N composition. This tendency was more dominant with increasing the air staging levels. In the co-firing of woody biomass with coal, as the biomass is highly volatile but has a low carbon content, it could be successfully applied to low-NOx combustion under air-staged conditions. In addition, the degree of carbon burnout and the flame temperature both increased. As a result of this research, we determined that hybrid NOx reduction technologies have the potential to reduce exhaust gas emissions and enhance combustion performance. A dominant synergistic effect on NOx reduction and carbon burnout was observed when woody biomass co-firing with coal was applied to air-staged combustion. © 2015 Elsevier Inc.

Namkung H.,Ajou University | Xu L.-H.,Institute for Advanced Engineering | Kang T.-J.,Ajou University | Kim D.S.,Korea Western Power Co. | And 2 more authors.
Applied Energy | Year: 2013

Coal gasification was carried out in order to verify the coal fouling tendency in the drop tube furnace (DTF), which can simulate an entrained-bed gasifier. Thirteen pulverized coal samples, in the range of bituminous and sub-bituminous, were utilized, and compared, with predictions using a wide range of empirical indices. Large discrepancies were noted in most cases, with respect to experimental results, ash deposition rates, and different indices. Some indices used for anticipating fouling tendency are not co-related with the results of this experiment. A newly approached index, which is especially important considering the diffusivity parameter, looks at the ratio of acid and alkali mineral matters injected into gasifier and heat flux, indicates that traditional expressions are modified to account for other parameters which influence the ash deposition phenomenon. The alternative index resulted in improved correlations between predictions and experimental observations. © 2012 Elsevier Ltd.

Oh T.,Gyeongsang National University | Lim J.,Gyeongsang National University | Choi J.,Gyeongsang National University | Cha J.,Daejin University | And 2 more authors.
Midwest Symposium on Circuits and Systems | Year: 2011

The maintenance of generating units is implicitly related to power system reliability and has a tremendous bearing on the operation of the power system. A technique using a fuzzy search method which is based on fuzzy multi-criteria function has been proposed for GMS (generator maintenance scheduling) in order to consider multi-objective function. In this study, a new technique using combined fuzzy set theory and genetic algorithm (GA) is proposed for generator maintenance scheduling. The effectiveness of the proposed approach is demonstrated by the simulation results on a practical size test systems. © 2011 IEEE.

Choi J.,Gyeongsang National University | Park J.,Gyeongsang National University | Baek U.,Korea Western Power Co. | Ku B.,Daejin University | Cha J.,Daejin University
2010 IEEE 11th International Conference on Probabilistic Methods Applied to Power Systems, PMAPS 2010 | Year: 2010

A technique using a fuzzy search method which is based on fuzzy multi-criteria function has been proposed for GMS(generator maintenance scheduling) in order to consider uncertainties of forced outage rate of generators and multiobjective function. This paper evaluates the results of maintenance scheduling of the seven generation company obtained by the previous proposed method. Especially this paper focus on the GMS of Korea Western Power Co. The probabilistic reliability evaluation method was used to calculate production cost and used as criterion. © 2010 IEEE.

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