메뉴 건너뛰기




Volumn 58, Issue 9, 2011, Pages 4023-4038

Robust controller for DFIGs of grid-connected wind turbines

Author keywords

Doubly fed induction generator (DFIG); low voltage fault ride through capability (LVRT); reactive support; robust controller; wind turbine (WT)

Indexed keywords

CONTROLLER DESIGNS; DOUBLY FED INDUCTION GENERATORS; DOUBLY-FED INDUCTION GENERATOR; FAST DYNAMICS; FAULT OPERATION; FAULT RIDE THROUGH CAPABILITY; FLUX EQUATIONS; GRID-CONNECTED; LOW-VOLTAGE; NETWORK FAULTS; NOMINAL MODELS; REACTIVE SUPPORT; REFERENCE FRAME; ROBUST CONTROLLERS; UNBALANCED VOLTAGES;

EID: 80051771432     PISSN: 02780046     EISSN: None     Source Type: Journal    
DOI: 10.1109/TIE.2010.2098630     Document Type: Article
Times cited : (167)

References (54)
  • 3
    • 80051767530 scopus 로고    scopus 로고
    • International Wind Energy Development, World Market Update 2007, Forecast 2008-2012
    • Online
    • P. Krogsgaard and B. T. Madsen, "International Wind Energy Development, World Market Update 2007, Forecast 2008-2012", Ringkøbing, Denmark, BTM Consult ApS, 2008. [Online]. Available: http://www.btm.dk
    • (2008) Ringkøbing, Denmark, BTM Consult ApS
    • Krogsgaard, P.1    Madsen, B.T.2
  • 4
    • 70349614159 scopus 로고    scopus 로고
    • Adaptive observer for sensorless control of stand-alone doubly fed induction generator
    • Oct
    • D. Forchetti, G. Garcia, and M. Valla, "Adaptive observer for sensorless control of stand-alone doubly fed induction generator", IEEE Trans. Ind. Electron., vol. 56, no. 10, pp. 4174-4180, Oct. 2009.
    • (2009) IEEE Trans. Ind. Electron. , vol.56 , Issue.10 , pp. 4174-4180
    • Forchetti, D.1    Garcia, G.2    Valla, M.3
  • 5
    • 70349612250 scopus 로고    scopus 로고
    • A topology for multiple generation system with doubly fed induction machines and indirect matrix converter
    • Oct
    • R. Pena, R. Cardenas, E. Reyes, J. Clare, and P. Wheeler, "A topology for multiple generation system with doubly fed induction machines and indirect matrix converter", IEEE Trans. Ind. Electron., vol. 56, no. 10, pp. 4181-4193, Oct. 2009.
    • (2009) IEEE Trans. Ind. Electron. , vol.56 , Issue.10 , pp. 4181-4193
    • Pena, R.1    Cardenas, R.2    Reyes, E.3    Clare, J.4    Wheeler, P.5
  • 6
    • 70349614158 scopus 로고    scopus 로고
    • Modeling and control of a cascaded doubly fed induction generator dedicated to isolated grids
    • Oct
    • N. Patin, E. Monmasson, and J.-P. Louis, "Modeling and control of a cascaded doubly fed induction generator dedicated to isolated grids", IEEE Trans. Ind. Electron., vol. 56, no. 10, pp. 4207-4219, Oct. 2009.
    • (2009) IEEE Trans. Ind. Electron. , vol.56 , Issue.10 , pp. 4207-4219
    • Patin, N.1    Monmasson, E.2    Louis, J.-P.3
  • 8
    • 29244448716 scopus 로고    scopus 로고
    • Modeling and experimental verification of grid interaction of a DFIG wind turbine
    • DOI 10.1109/TEC.2005.853750
    • A. Petersson, T. Thiringer, L. Harnefors, and T. Petru, "Modeling and experimental verification of grid interaction of a DFIG wind turbine", IEEE Trans. Energy Convers., vol. 20, no. 4, pp. 878-886, Dec. 2005. (Pubitemid 41830065)
    • (2005) IEEE Transactions on Energy Conversion , vol.20 , Issue.4 , pp. 878-886
    • Petersson, A.1    Thiringer, T.2    Harnefors, L.3    Petru, T.4
  • 9
    • 21644452371 scopus 로고    scopus 로고
    • A DFIG wind-turbine ride-through system influence on the energy production
    • Mar
    • S. L. Andreas Petersson and T. Thiringer, "A DFIG wind-turbine ride-through system influence on the energy production", in Proc. NORDIC Wind Power Conf., Mar. 2004, pp. 1-7.
    • (2004) Proc. NORDIC Wind Power Conf. , pp. 1-7
    • Petersson, S.L.A.1    Thiringer, T.2
  • 10
    • 70349617246 scopus 로고    scopus 로고
    • Predictive current control of doubly fed induction generators
    • Oct
    • L. Xu, D. Zhi, and B. Williams, "Predictive current control of doubly fed induction generators", IEEE Trans. Ind. Electron., vol. 56, no. 10, pp. 4143-4153, Oct. 2009.
    • (2009) IEEE Trans. Ind. Electron. , vol.56 , Issue.10 , pp. 4143-4153
    • Xu, L.1    Zhi, D.2    Williams, B.3
  • 11
    • 70349625590 scopus 로고    scopus 로고
    • Direct virtual torque control for doubly fed induction generator grid connection
    • Oct
    • J. Arbi, M.-B. Ghorbal, I. Slama-Belkhodja, and L. Charaabi, "Direct virtual torque control for doubly fed induction generator grid connection", IEEE Trans. Ind. Electron., vol. 56, no. 10, pp. 4163-4173, Oct. 2009.
    • (2009) IEEE Trans. Ind. Electron. , vol.56 , Issue.10 , pp. 4163-4173
    • Arbi, J.1    Ghorbal, M.-B.2    Slama-Belkhodja, I.3    Charaabi, L.4
  • 12
    • 70349628410 scopus 로고    scopus 로고
    • Reactive power control design in doubly fed induction generators for wind turbines
    • Oct
    • B. Rabelo, W. Hofmann, J. da Silva, R. de Oliveira, and S. Silva, "Reactive power control design in doubly fed induction generators for wind turbines", IEEE Trans. Ind. Electron., vol. 56, no. 10, pp. 4154-4162, Oct. 2009.
    • (2009) IEEE Trans. Ind. Electron. , vol.56 , Issue.10 , pp. 4154-4162
    • Rabelo, B.1    Hofmann, W.2    Da Silva, J.3    De Oliveira, R.4    Silva, S.5
  • 13
    • 70349617244 scopus 로고    scopus 로고
    • Stator-flux-oriented vector control for brushless doubly fed induction generator
    • Oct
    • S. Shao, E. Abdi, F. Barati, and R. McMahon, "Stator-flux-oriented vector control for brushless doubly fed induction generator", IEEE Trans. Ind. Electron., vol. 56, no. 10, pp. 4220-4228, Oct. 2009.
    • (2009) IEEE Trans. Ind. Electron. , vol.56 , Issue.10 , pp. 4220-4228
    • Shao, S.1    Abdi, E.2    Barati, F.3    McMahon, R.4
  • 14
    • 34250829966 scopus 로고    scopus 로고
    • Alberta Elect. Syst. Operator-AESO, Calgary, AB, Canada, Online. Available
    • Wind Power Facility-Technical Requirements, Alberta Elect. Syst. Operator-AESO, Calgary, AB, Canada, 2004. [Online]. Available: http://www.aeso.ca
    • (2004) Wind Power Facility-technical Requirements
  • 16
    • 84870608828 scopus 로고    scopus 로고
    • Bundesverband der Energie und Wasserwirtschaft e. V. BDEW, Berlin, Germany, Online. Available
    • Generating Plants Connected to the Medium Voltage Network, Bundesverband der Energie und Wasserwirtschaft e. V. (BDEW), Berlin, Germany, 2008. [Online]. Available: http://www.bdew.de
    • (2008) Generating Plants Connected to the Medium Voltage Network
  • 17
    • 20444427743 scopus 로고    scopus 로고
    • E. ON Netz GmbH, Bayreuth, Germany, Online. Available
    • Grid Code, High and Extra High Voltage, E. ON Netz GmbH, Bayreuth, Germany, 2006. [Online]. Available: http://www.eon.de
    • (2006) Grid Code, High and Extra High Voltage
  • 20
    • 80051714371 scopus 로고    scopus 로고
    • Operador Nacional do Sistema ONS, Santa Catarina, Brazil, Requisitos Técnicos, May, Online. Available
    • Procedimentos de Rede PROREDE, Operador Nacional do Sistema (ONS), Santa Catarina, Brazil, Requisitos Técnicos, May 2002. [Online]. Available: http://www.ons.org.br
    • (2002) Procedimentos de Rede PROREDE
  • 21
    • 33947634098 scopus 로고    scopus 로고
    • Short-circuit current of wind turbines with doubly fed induction generator
    • DOI 10.1109/TEC.2006.889615, Special Issue on Wind Power
    • J. Morren and S. de Haan, "Short-circuit current of wind turbines with doubly fed induction generator", IEEE Trans. Energy Convers., vol. 22, no. 1, pp. 174-180, Mar. 2007. (Pubitemid 46487490)
    • (2007) IEEE Transactions on Energy Conversion , vol.22 , Issue.1 , pp. 174-180
    • Morren, J.1    De Haan, S.W.H.2
  • 23
    • 70349616088 scopus 로고    scopus 로고
    • Current sensor fault detection, isolation, and reconfiguration for doubly fed induction generators
    • Oct
    • K. Rothenhagen and F. Fuchs, "Current sensor fault detection, isolation, and reconfiguration for doubly fed induction generators", IEEE Trans. Ind. Electron., vol. 56, no. 10, pp. 4239-4245, Oct. 2009.
    • (2009) IEEE Trans. Ind. Electron. , vol.56 , Issue.10 , pp. 4239-4245
    • Rothenhagen, K.1    Fuchs, F.2
  • 24
    • 70349616083 scopus 로고    scopus 로고
    • Ride through of wind turbines with doubly fed induction generator under symmetrical voltage dips
    • Oct
    • J. Lopez, E. Gubia, E. Olea, J. Ruiz, and L. Marroyo, "Ride through of wind turbines with doubly fed induction generator under symmetrical voltage dips", IEEE Trans. Ind. Electron., vol. 56, no. 10, pp. 4246-4254, Oct. 2009.
    • (2009) IEEE Trans. Ind. Electron. , vol.56 , Issue.10 , pp. 4246-4254
    • Lopez, J.1    Gubia, E.2    Olea, E.3    Ruiz, J.4    Marroyo, L.5
  • 26
    • 0035674621 scopus 로고    scopus 로고
    • Mechanical stresses in fixed-speed wind turbines due to network disturbances
    • DOI 10.1109/60.969476, PII S0885896901100616
    • S. Papathanassiou and M. Papadopoulos, "Mechanical stresses in fixed-speed wind turbines due to network disturbances", IEEE Trans. Energy Convers., vol. 16, no. 4, pp. 361-367, Dec. 2001. (Pubitemid 34035510)
    • (2001) IEEE Transactions on Energy Conversion , vol.16 , Issue.4 , pp. 361-367
    • Papathanassiou, S.A.1    Papadopoulos, M.P.2
  • 27
    • 0016503772 scopus 로고
    • Calculation of negative-sequence losses and negative-sequence resistance of turbogenerators
    • May
    • I. Canay, "Calculation of negative-sequence losses and negative-sequence resistance of turbogenerators", IEEE Trans. Power App. Syst., vol. PAS-94, no. 3, pp. 764-773, May 1975.
    • (1975) IEEE Trans. Power App. Syst. , vol.PAS-94 , Issue.3 , pp. 764-773
    • Canay, I.1
  • 29
    • 12744262671 scopus 로고    scopus 로고
    • Evaluation of current control methods for wind turbines using doubly-fed induction machines
    • DOI 10.1109/TPEL.2004.839785
    • A. Petersson, L. Harnefors, and T. Thiringer, "Evaluation of current control methods for wind turbines using doubly-fed induction machines", IEEE Trans. Power Electron., vol. 20, no. 1, pp. 227-235, Jan. 2005. (Pubitemid 40154864)
    • (2005) IEEE Transactions on Power Electronics , vol.20 , Issue.1 , pp. 227-235
    • Petersson, A.1    Harnefors, L.2    Thiringer, T.3
  • 30
    • 33947313847 scopus 로고    scopus 로고
    • Dynamic modeling and control of DFIG-based wind turbines under unbalanced network conditions
    • DOI 10.1109/TPWRS.2006.889113
    • L. Xu and Y. Wang, "Dynamic modeling and control of DFIG-based wind turbines under unbalanced network conditions", IEEE Trans. Power Syst., vol. 22, no. 1, pp. 314-323, Feb. 2007. (Pubitemid 46437741)
    • (2007) IEEE Transactions on Power Systems , vol.22 , Issue.1 , pp. 314-323
    • Xu, L.1    Wang, Y.2
  • 31
    • 44449142859 scopus 로고    scopus 로고
    • Coordinated control of DFIG's rotor and grid side converters during network unbalance
    • DOI 10.1109/TPEL.2008.921157
    • L. Xu, "Coordinated control of DFIG's rotor and grid side converters during network unbalance", IEEE Trans. Power Electron., vol. 23, no. 3, pp. 1041-1049, May 2008. (Pubitemid 351756681)
    • (2008) IEEE Transactions on Power Electronics , vol.23 , Issue.3 , pp. 1041-1049
    • Xu, L.1
  • 32
    • 80051768784 scopus 로고    scopus 로고
    • Controle do gerador de inducão duplamente alimentado durante distúrbios na rede elétrica: Crowbar ativo e suporte de reativos
    • Sep
    • J. P. da Costa, J. R. Massing, and H. Pinheiro, "Controle do gerador de inducão duplamente alimentado durante distúrbios na rede elétrica: Crowbar ativo e suporte de reativos", in Proc. XVII Brazilian Conf. Automatica, Sep. 2008, pp. 01-07.
    • (2008) Proc. XVII Brazilian Conf. Automatica , pp. 01-07
    • Da Costa, J.P.1    Massing, J.R.2    Pinheiro, H.3
  • 34
    • 33947430524 scopus 로고    scopus 로고
    • Control of a doubly fed induction generator in a wind turbine during grid fault ride-through
    • DOI 10.1109/TEC.2006.875783
    • D. Xiang, L. Ran, P. Tavner, and S. Yang, "Control of a doubly fed induction generator in a wind turbine during grid fault ride-through", IEEE Trans. Energy Convers., vol. 21, no. 3, pp. 652-662, Sep. 2006. (Pubitemid 46445154)
    • (2006) IEEE Transactions on Energy Conversion , vol.21 , Issue.3 , pp. 652-662
    • Xiang, D.1    Ran, L.2    Tavner, P.J.3    Yang, S.4
  • 35
    • 57749193475 scopus 로고    scopus 로고
    • FPGA-based real-time power converter failure diagnosis for wind energy conversion systems
    • Dec
    • S. Karimi, A. Gaillard, P. Poure, and S. Saadate, "FPGA-based real-time power converter failure diagnosis for wind energy conversion systems", IEEE Trans. Ind. Electron., vol. 55, no. 12, pp. 4299-4308, Dec. 2008.
    • (2008) IEEE Trans. Ind. Electron. , vol.55 , Issue.12 , pp. 4299-4308
    • Karimi, S.1    Gaillard, A.2    Poure, P.3    Saadate, S.4
  • 36
    • 0042658183 scopus 로고    scopus 로고
    • A novel doubly-fed induction wind generator control scheme for reactive power control and torque pulsation compensation under unbalanced grid voltage conditions
    • Jun
    • T. Brekken and N. Mohan, "A novel doubly-fed induction wind generator control scheme for reactive power control and torque pulsation compensation under unbalanced grid voltage conditions", in Proc. IEEE 34th Annu. Power Electron. Spec. Conf., Jun. 2003, vol. 2, pp. 760-764.
    • (2003) Proc. IEEE 34th Annu. Power Electron. Spec. Conf. , vol.2 , pp. 760-764
    • Brekken, T.1    Mohan, N.2
  • 37
    • 70849095406 scopus 로고    scopus 로고
    • Small-signal stability analysis of a DFIG-based wind power system under different modes of operation
    • Dec
    • Y. Mishra, S. Mishra, F. Li, Z. Y. Dong, and R. C. Bansal, "Small-signal stability analysis of a DFIG-based wind power system under different modes of operation", IEEE Trans. Energy Convers., vol. 24, no. 4, pp. 972-982, Dec. 2009.
    • (2009) IEEE Trans. Energy Convers. , vol.24 , Issue.4 , pp. 972-982
    • Mishra, Y.1    Mishra, S.2    Li, F.3    Dong, Z.Y.4    Bansal, R.C.5
  • 39
    • 68349150311 scopus 로고    scopus 로고
    • Impact of increased penetration of DFIG-based wind turbine generators on transient and small signal stabilityof power systems
    • Aug
    • D. Gautam, V. Vittal, and T. Harbour, "Impact of increased penetration of DFIG-based wind turbine generators on transient and small signal stabilityof power systems", IEEE Trans. Power Syst., vol. 24, no. 3, pp. 1426-1434, Aug. 2009.
    • (2009) IEEE Trans. Power Syst. , vol.24 , Issue.3 , pp. 1426-1434
    • Gautam, D.1    Vittal, V.2    Harbour, T.3
  • 40
    • 70849089427 scopus 로고    scopus 로고
    • LQG design for megawatt-class WECS with DFIG based on functional models fidelity prerequisites
    • Dec
    • E. B. Muhando, T. Senjyu, A. Uehara, T. Funabashi, and C.-H. Kim, "LQG design for megawatt-class WECS with DFIG based on functional models fidelity prerequisites", IEEE Trans. Energy Convers., vol. 24, no. 4, pp. 893-904, Dec. 2009.
    • (2009) IEEE Trans. Energy Convers. , vol.24 , Issue.4 , pp. 893-904
    • Muhando, E.B.1    Senjyu, T.2    Uehara, A.3    Funabashi, T.4    Kim, C.-H.5
  • 41
    • 70349612968 scopus 로고    scopus 로고
    • Stability analysis of a wind energy conversion system based on a doubly fed induction generator fed by a matrix converter
    • Oct
    • R. Cardenas, R. Pena, G. Tobar, J. Clare, P. Wheeler, and G. Asher, "Stability analysis of a wind energy conversion system based on a doubly fed induction generator fed by a matrix converter", IEEE Trans. Ind. Electron., vol. 56, no. 10, pp. 4194-4206, Oct. 2009.
    • (2009) IEEE Trans. Ind. Electron. , vol.56 , Issue.10 , pp. 4194-4206
    • Cardenas, R.1    Pena, R.2    Tobar, G.3    Clare, J.4    Wheeler, P.5    Asher, G.6
  • 42
    • 70349620384 scopus 로고    scopus 로고
    • Doubly fed induction generator model-based sensor fault detection and control loop reconfiguration
    • Oct
    • K. Rothenhagen and F. Fuchs, "Doubly fed induction generator model-based sensor fault detection and control loop reconfiguration", IEEE Trans. Ind. Electron., vol. 56, no. 10, pp. 4229-4238, Oct. 2009.
    • (2009) IEEE Trans. Ind. Electron. , vol.56 , Issue.10 , pp. 4229-4238
    • Rothenhagen, K.1    Fuchs, F.2
  • 43
    • 70049083223 scopus 로고    scopus 로고
    • Improving stability of a DFIG-based wind power system with tuned damping controller
    • Sep
    • Z. Dong, M. Tripathy, N. Senroy, Y. Mishra, and S. Mishra, "Improving stability of a DFIG-based wind power system with tuned damping controller", IEEE Trans. Energy Convers., vol. 24, no. 3, pp. 650-660, Sep. 2009.
    • (2009) IEEE Trans. Energy Convers. , vol.24 , Issue.3 , pp. 650-660
    • Dong, Z.1    Tripathy, M.2    Senroy, N.3    Mishra, Y.4    Mishra, S.5
  • 44
    • 77952951957 scopus 로고    scopus 로고
    • Integral sliding-mode direct torque control of doubly-fed induction generators under unbalanced grid voltage
    • Jun
    • S. Z. Chen, N. Cheung, K. C. Wong, and J. Wu, "Integral sliding-mode direct torque control of doubly-fed induction generators under unbalanced grid voltage", IEEE Trans. Energy Convers., vol. 25, no. 2, pp. 356-368, Jun. 2010.
    • (2010) IEEE Trans. Energy Convers. , vol.25 , Issue.2 , pp. 356-368
    • Chen, S.Z.1    Cheung, N.2    Wong, K.C.3    Wu, J.4
  • 45
    • 33847646777 scopus 로고    scopus 로고
    • Ride-through analysis of doubly fed induction wind-power generator under unsymmetrical network disturbance
    • DOI 10.1109/TPWRS.2006.882471
    • S. Seman, J. Niiranen, and A. Arkkio, "Ride-through analysis of doubly fed induction wind-power generator under unsymmetrical network disturbance", IEEE Trans. Power Syst., vol. 21, no. 4, pp. 1782-1789, Nov. 2006. (Pubitemid 46357779)
    • (2006) IEEE Transactions on Power Systems , vol.21 , Issue.4 , pp. 1782-1789
    • Seman, S.1    Niiranen, J.2    Arkkio, A.3
  • 46
    • 77249175320 scopus 로고    scopus 로고
    • Direct power control of doubly-fed-induction-generator-based wind turbines under unbalanced grid voltage
    • Feb
    • G. Abad, M. Rodriguez, G. Iwanski, and J. Poza, "Direct power control of doubly-fed-induction-generator-based wind turbines under unbalanced grid voltage", IEEE Trans. Power Electron., vol. 25, no. 2, pp. 442-452, Feb. 2010.
    • (2010) IEEE Trans. Power Electron. , vol.25 , Issue.2 , pp. 442-452
    • Abad, G.1    Rodriguez, M.2    Iwanski, G.3    Poza, J.4
  • 47
    • 77249131236 scopus 로고    scopus 로고
    • Model-based predictive direct power control of doubly fed induction generators
    • Feb
    • D. Zhi, L. Xu, and B. Williams, "Model-based predictive direct power control of doubly fed induction generators", IEEE Trans. Power Electron., vol. 25, no. 2, pp. 341-351, Feb. 2010.
    • (2010) IEEE Trans. Power Electron. , vol.25 , Issue.2 , pp. 341-351
    • Zhi, D.1    Xu, L.2    Williams, B.3
  • 48
    • 72949097448 scopus 로고    scopus 로고
    • Improved direct power control of a DFIG-based wind turbine during network unbalance
    • Nov
    • P. Zhou, Y. He, and D. Sun, "Improved direct power control of a DFIG-based wind turbine during network unbalance", IEEE Trans. Power Electron., vol. 24, no. 11, pp. 2465-2474, Nov. 2009.
    • (2009) IEEE Trans. Power Electron. , vol.24 , Issue.11 , pp. 2465-2474
    • Zhou, P.1    He, Y.2    Sun, D.3
  • 49
    • 77956056188 scopus 로고    scopus 로고
    • Minimum-threshold crowbar for a fault-ride-through grid-code-compliant DFIG wind turbine
    • Sep
    • G. Pannell, D. Atkinson, and B. Zahawi, "Minimum-threshold crowbar for a fault-ride-through grid-code-compliant DFIG wind turbine", IEEE Trans. Energy Convers., vol. 25, no. 3, pp. 750-759, Sep. 2010.
    • (2010) IEEE Trans. Energy Convers. , vol.25 , Issue.3 , pp. 750-759
    • Pannell, G.1    Atkinson, D.2    Zahawi, B.3
  • 50
    • 76649127421 scopus 로고    scopus 로고
    • Rotor voltage dynamics in the doubly fed induction generator during grid faults
    • Jan
    • F. Lima, A. Luna, P. Rodriguez, E. Watanabe, and F. Blaabjerg, "Rotor voltage dynamics in the doubly fed induction generator during grid faults", IEEE Trans. Power Electron., vol. 25, no. 1, pp. 118-130, Jan. 2010.
    • (2010) IEEE Trans. Power Electron. , vol.25 , Issue.1 , pp. 118-130
    • Lima, F.1    Luna, A.2    Rodriguez, P.3    Watanabe, E.4    Blaabjerg, F.5
  • 52
    • 67649364552 scopus 로고    scopus 로고
    • Instantaneous reactive power theory: A reference in the nonlinear loads compensation
    • Jun
    • R. Herrera and P. Salmeron, "Instantaneous reactive power theory: A reference in the nonlinear loads compensation", IEEE Trans. Ind. Electron., vol. 56, no. 6, pp. 2015-2022, Jun. 2009.
    • (2009) IEEE Trans. Ind. Electron. , vol.56 , Issue.6 , pp. 2015-2022
    • Herrera, R.1    Salmeron, P.2


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.