電力系統在經歷異常情況時，諸如短路故障或是干擾導致的電力傳輸中斷等情形，這些情形下會產生劇烈的波動，嚴重者會大量損害電力系統的供電部分。為了防止故障產生或者將故障後果最小化，因此需要設計安裝和調整相應的保護系統。保護系統由具有不同特性的和不同類型的保護電驛模塊組成。通過採用不同特征的故障分量來進行不同的故障判別是一些常用的辦法。通過對故障特征進行計算然後判斷出不同的故障類型，進而由保護模塊採取相應的動作來切除故障以穩定電路，從而對系統進行保護。
由於DFIG傳輸線路故障輸出特性的變化，基於常規方向元件的繼電保護不能正確判斷故障方向。本文提出了基於PSCAD / EMTDC的雙饋風電場模擬模型，分析了DFIG風電場故障電壓和電路的輸出特性。傳統方向元件判據研究進一步證明，當風電場送出線三相短路時，方向分量可以正常工作，而在電網短路時，方向分量不能正常工作。基於短路方向與判斷結果精度的關係，提出了一種基於正序極化電壓相位比較的新型方向元件判據，並分析了故障前轉速等不同故障條件下的保護動作，如撬棒保護，線路長度和故障定位。此外，本文還研究了常規分量測量的一些相應標準，病通過模擬結果表明，新的標準可以保證各種故障情況下方向元件的可靠性。


關鍵詞：雙饋風電場、故障特徵、方向元件、正序極化電壓

Electric power systems experience abnormal conditions like faults and disturbances which lead to power interruptions, loss of stability and blackouts. To prevent or at least minimize the fault consequences, a protection system is designed, installed and adjusted. Protection system consists of different types of relays that have different characteristics and functions. Here, the directional component is taken into consideration and compared with the proposed method. Whereas the conventional directional component may not identify the fault accurately when there is a variation of line fault output characteristics in a transmission line with DFIG. This thesis analyzes the output characteristics of fault voltage and circuit of DFIG-based wind farm by proposing the simulation model of doubly-fed Wind Farm using PSCAD/EMTD. Further, this thesis also studies the criterion for conventional directional component, which can operate only when there is a three phase short circuit from wind farm outgoing line and not with a short circuit from power grid. Based on the relationship between the results obtained from the direction of short circuit, the new criterion for the directional component is proposed. The criterion is based on the positive sequence polarization voltage phase comparison and the analysis for protection under various fault conditions such as rotational speed before the fault, crowbar protection, line length and fault location. The simulation results show cases that the new criterion guarantees the reliability of the directional component under various fault conditions of a transmission line with a DFIG.

Table of Contents
Abstract II
摘要 III
Acknowledgements IV
Chapter1 Introduction 1
1.1 Research motivation and literature review 1
1.2 Contribution 3
1.3 Organization of the thesis 4
Chapter2 Overview of DFIG and the equivalent modelling and analysis of faults 5
2.1 The structure and working principle of DFIG 5
2.1.1 The structure of DFIG 5
2.1.2 Operational and controlling characteristics of DFIG with energy storage 6
2.2 Simulation modeling of DFIG with energy storage 7
2.2.1 Mathematical model of wind turbines 7
2.2.2 Mathematical model of wound induction motor 9
2.3 Equivalent modeling of wind turbines 12
2.3.1 Equivalent modeling of doubly-fed wind farms 13
2.3.2 Equivalent method of DFIG 15
2.3.3 The comparison of the simulation model of wind turbines before and after the equivalence 16
2.4 Analysis on the fault characteristics of wind farm outgoing Lines 18
2.5 Summary 20
Chapter3 Principle of the Fault Protection 22
3.1 Adaptability analysis on directional element in conventional distance protection 22
3.2 Simulation of traditional distance protection direction components 24
3.3 Analysis of fault characteristics of feed - out line of doubly - fed wind farms and calculation of phase angle difference 28
3.3.1 The frequency of the rotor is not close to the Industrial Frequency before the fault 28
3.3.2 The rotor frequency close to the frequency before the fault 34
3.4 Summary 37
Chapter4 Simulation verification of the new method for fault simulation protection 38
4.1 New criteria for directional elements of wind farms 38
4.2 Simulation verification 41
4.2.1 Analysis of influencing factors 41
4.3 Simulation of directional elements 44
4.4 summary 50
Chapter5 Conclusions and Future Scopes 51
5.1 Conclusion 51
5.2 Future Scopes 52
References 53

[1] A. K. Pradhan and G. Joos, "Adaptive distance relay setting for lines connecting wind farms," IEEE Transactions on Energy Conversion, vol. 22, no. 1, pp. 206-213, March 2007.
[2] B. H. Zhang et al., "Configuration, cooperation and existing problems of wind farm relay protection," 2012 11th International Conference on Environment and Electrical Engineering, Venice, 2012, pp. 1038-1042.
[3] V. P. Mahadanaarachchi and R. Ramakuma, "Impact of distributed generation on distance protection performance - A review," 2008 IEEE Power and Energy Society General Meeting - Conversion and Delivery of Electrical Energy in the 21st Century, Pittsburgh, PA, 2008, pp. 1-7.
[4] M. Khoddam and Hosein Kazemi Karegar, "Effect of wind turbines equipped with doubly-fed induction generators on distance protection," 2011 International Conference on Advanced Power System Automation and Protection, Beijing, 2011, pp. 1349-1353.
[5] M. Khoddam and Hosein Kazemi Karegar, "Effect of wind turbines equipped with doubly-fed induction generators on distance protection," 2011 International Conference on Advanced Power System Automation and Protection, Beijing, 2011, pp. 1349-1353.
[6] G. H. Li et al., "Wind farm electromagnetic dynamic model and outgoing line protection relay RTDS testing," Universities' Power Engineering Conference (UPEC), Proceedings of 2011 46th International, Soest, Germany, 2011, pp. 1-6.
[7] A. Hooshyar, M. A. Azzouz and E. F. El-Saadany, "Distance protection of lines connected to induction generator-based wind farms during balanced faults," IEEE Transactions on Sustainable Energy, vol. 5, no. 4, pp. 1193-1203, Oct. 2014.
[8] M. M. Eissa, "Current directional protection technique based on polarizing current," International Journal of Electrical Power & Energy Systems, vol. 44 (1), 2013, pp. 488-494.
[9] M. Petit, X. Le Pivert and L. Garcia-Santander, "Directional relays without voltage sensors for distribution networks with distributed generation: Use of symmetrical components," Electric Power Systems Research, vol. 80 (10), 2010, pp. 1222-1228.
[10] A. Hooshyar, M. A. Azzouz and E. F. El-Saadany, "Three-Phase Fault Direction Identification for Distribution Systems With DFIG-Based Wind DG," IEEE Transactions on Sustainable Energy, vol. 5, no. 3, pp. 747-756, July 2014.
[11] C. Abbey and G. Joos, "A doubly-fed induction machine and energy storage system for wind power generation," Canadian Conference on Electrical and Computer Engineering 2004 (IEEE Cat. No.04CH37513), 2004, pp. 1059-1062 Vol.2.
[12] P. M. Anderson and A. Bose, "Stability simulation of wind turbine systems," IEEE Power Engineering Review, vol. PER-3, no. 12, pp. 32, Dec. 1983.
[13] Andreas Petersson, “Analysis, modeling and control of doubly-fed induction generators for wind turbines,” International symposium on physical design, Chalmers University of Technology, 2005.
[14] N. W. Miller, J. J. Sanchez-Gasca, W. W. Price and R. W. Delmerico, "Dynamic modeling of GE 1.5 and 3.6 MW wind turbine-generators for stability simulations," 2003 IEEE Power Engineering Society General Meeting (IEEE Cat. No.03CH37491), 2003, pp. 1977-1983, Vol. 3.
[15] Lianwei Jiao, G. Joos, C. Abbey, Fengquan Zhou and Boon-Teck Ooi, "Multi-terminal DC (MTDC) system for wind farms powered by doubly-fed induction generators (DFIGs)," 2004 IEEE 35th Annual Power Electronics Specialists Conference (IEEE Cat. No.04CH37551), 2004, pp. 1413-1418 Vol.2.
[16] Dawei Xiang, Li Ran, P. J. Tavner and S. Yang, "Control of a doubly fed induction generator in a wind turbine during grid fault ride-through," IEEE Transactions on Energy Conversion, vol. 21, no. 3, pp. 652-662, Sept. 2006.
[17] L. Qu and W. Qiao, "Constant power control and fault-ride-through enhancement of DFIG wind turbines with energy storage," 2009 IEEE Industry Applications Society Annual Meeting, Houston, TX, 2009, pp. 1-8.
[18] J. Morren and S. W. H. de Haan, "Ridethrough of wind turbines with doubly-fed induction generator during a voltage dip," in IEEE Transactions on Energy Conversion, vol. 20, no. 2, pp. 435-441, June 2005.
[19] Baohui Zhang, Jin Wang and Guanghui Li, "Analysis on fault features of wind turbine generators concentratedly connected to power grid," in Power System Technology (07), 2012, pp. 176-183.
[20] L. Qin-hao, Z. Yong-jun, Y. Wei-peng and L. Feng, "A study on influence of wind power on positive sequence voltage polarized impedance relay," 2012 Power Engineering and Automation Conference, Wuhan, 2012, pp. 1-4.
[21] X. Kong and Z. Zhang, "Fault-current study of the wind-turbine-driven doubly-fed induction generator with the crowbar protection,” Elektrotehniski Vestnik Electrotechnical Review, vol.81 (1-2), 2014, pp. 57-63.
[22] Zhai Jiajun, Zhang Buhan, Wang Kui, and Shao Wen, "Three-phase symmetrical short circuit current characteristic analysis of doubly fed induction generator with crowbar protection," IEEE PES Innovative Smart Grid Technologies, Tianjin, 2012, pp. 1-5.
[23] H. Geng, C. Liu, and G. Yang, "LVRT capability of DFIG-based WECS under asymmetrical grid fault condition," IEEE Transactions on Industrial Electronics, vol. 60, no. 6, pp. 2495-2509, June 2013.
[24] M. Kheshti, Xiaoning Kang, Guobing Song and Zaibin Jiao, "Modeling and fault analysis of doubly fed induction generators for Gansu wind farm application," Canadian Journal of Electrical and Computer Engineering vol. 38.1, 2015, pp. 52-64.
[25] Z. P. Wei, T. Zheng and J. Li, "Short circuit current analysis of DFIG with crowbar under unsymmetrical grid fault," 2nd IET Renewable Power Generation Conference (RPG 2013), Beijing, 2013, pp. 1-4.
[26] Lie Xu and P. Cartwright, "Direct active and reactive power control of DFIG for wind energy generation," in IEEE Transactions on Energy Conversion, vol. 21, no. 3, pp. 750-758, Sept. 2006.
[27] T. Brekken, N. Mohan and T. Undeland, "Control of a doubly-fed induction wind generator under unbalanced grid voltage conditions," 2005 European Conference on Power Electronics and Applications, Dresden, 2005, pp. 10 pp.-P.10.
[28] A. K. Saxena, A. M. Rawool and T. C. Kaushik, "Crowbar scheme based on plasma motion for pulsed power applications," in IEEE Transactions on Plasma Science, vol. 41, no. 10, pp. 3058-3062, Oct. 2013.