Document Type: Original Research Paper


Faculty of Engineering and Technology, Shahrekord University, Shahrekord, Iran



Background and Objectives: Cascaded doubly fed induction generators (CDFIGs) can directly connected to isolated load or power grid without any brushes which are needed in conventional DFIGs. Output control targets before grid connection of CDFIGs are voltage and frequency control and after that are active and reactive power control. In control aspect, output control of CDFIG is a multi-input multi-output (MIMO) subject. In this paper, Relative Gain Array (RGA) methodology, as a MIMO interaction index, is used to show the degree of relevance between the control inputs and output targets, in both voltage control mode (before grid connection) and active-reactive power control mode (after grid connection). Based on RGA results, conventional PI controllers cannot be used to decouple control of generator outputs in grid connected mode. So, a powerful method based on sliding mode approach is proposed to generate the proper control voltages for output control of CDFIG in both islanded and grid connected mode. Simulation and experimental results using Matlab and TMS320F28335 based prototype of CDFIG are provided to demonstrate the effectiveness and robustness of the proposed method.
Methods: A mathematical method based on RGA matrix is used to evaluate the amount of interactions between output targets and input control variables in CDFIGs in islanded and grid connected mode.
Results: Conventional PI controller is a proper method to control the output voltage of Power Machine (PM) in CDFIG but is not a suitable technique for active and reactive power control in grid-tied mode.
Conclusion: Sliding mode control can be used to decouple control of CDFIGs in both before and after grid connection. As well as, robustness against the wind speed variation and parameters uncertainties is proved via both simulation and experimental tests.


Main Subjects

[1] F. Blaabjerg, M. Liserre, K. Ma, “Power electronics converters for wind turbine systems,” IEEE Trans. Ind. Appl., 48(2): 708–719, 2012.

[2] B. Hopfensperger, D. J. Atkinson, R. A. Lakin, “Stator flux oriented control of a cascaded doubly-fed induction machine,” Proc. Inst. Elect. Eng.—Elect. Power Appl., 146(6): 597–605, 1999.

[3] T. D. Strous, H. Polinder, J. A. Ferreira, "Brushless doubly-fed induction machines for wind turbines: developments and research challenges," in IET Electric Power Applications, 11(6): 991-1000, 2017.

[4] E. Abdi, R. McMahon, P. Malliband, S. Shao, M. E. Mathekga, P. Tavner, S. Abdi, A. Oraee, T. Long, M. Tatlow, “Performance analysis and testing of a 250 kw medium-speed brushless doubly-fed induction generator,” IET Renew. Power Gener., 7(6): 631–638, 2013.

[5] M. Achkar, R. Mbayed, G. Salloum, S. Le Ballois, E. Monmasson, “Generic study of the power capability of a cascaded doubly fed induction machine,” International Journal of Electrical Power & Energy Systems, 86: 61-70, 2017.

[6] S. Ademi, M. G. Jovanović, M. Hasan, "Control of Brushless Doubly-Fed Reluctance Generators for Wind Energy Conversion Systems," in IEEE Transactions on Energy Conversion, 30(2): 596-604, 2015.

[7] Y. Tang, H. He, Z. Ni, J. Wen, X. Sui, “Reactive power control of grid-connected wind farm based on adaptive dynamic programming”, Neurocomputing, 125: 125–133, 2014.

[8] J. Chen, W. Zhang, B. Chen, Y. Ma, “Improved vector control of brushless doubly fed induction generator under unbalanced grid conditions for offshore wind power generation,” Energy Conversion, IEEE Transactions on, 31(1): 293-302, 2015.

[9] J.d.D.N. Ndongmo, G. Kenné, R.K. Fochie, A. Cheukem, H.B. Futsin, F.L. Lagarrigue, “A simplified nonlinear controller for transient stability enhancement of multimachine power systems using SSSC device”, Int. J. Electr. Power Energy Syst., 54: 650–657, 2014.

[10] G. Wang, R. Wai, Y. Liao, "Design of backstepping power control for grid-side converter of voltage source converter-based high-voltage dc wind power generation system," in IET Renewable Power Generation, 7(2): 118-133, 2013.

[11] H. E. Medouce, H. Benalla, A. Mehdi, A. Reama, "Sensorless direct power regulation by sliding mode approach of DFIG generator based wind energy system," in Proc. 2015 IEEE 15th International Conference on Environment and Electrical Engineering (EEEIC), Rome: 1880-1885, 2015.

[12] Z. TIR, H. Rajeai, R. Abdessemed, “Analysis and vector control of a cascaded doubly fed induction generator in wind energy applications”. Revue des Energies Renouvelables: 347-358, 2010.

[13] M. E. Achkar, R. Mbayed, G. Salloum, N. Patin, S. Le Ballois, E. Monmasson, "Modeling and control of a stand alone cascaded doubly fed induction generator supplying an isolated load," 2015 17th European Conference on Power Electronics and Applications (EPE'15 ECCE-Europe), Geneva: 1-10, 2015.

[14] Z. S. Du, T. A. Lipo, "Dynamics and vector control of wound-rotor brushless doubly fed induction machines," in Proc. 2014 IEEE Energy Conversion Congress and Exposition (ECCE), Pittsburgh, PA: 1332-1339, 2014.

[15] J. Hu, J. Zhu, D. G. Dorrell, "A New Control Method of Cascaded Brushless Doubly Fed Induction Generators Using Direct Power Control," in IEEE Transactions on Energy Conversion, 29(3): 771-779, 2014.

[16] K. C. Wong, S. L. Ho, K. W. E. Cheng, “Direct voltage control for grid synchronization of doubly-fed induction generators,” Electr. Power Compon. Syst., 36(9): 960–976, 2008.

[17] M. Sadrnia, “A novel method for decoupling of non-minimum phase MIMO systems”: 475-480, 2006.

[18] S. Z. Chen, N. C. Cheung, Y. Zhang, M. Zhang, X. M. Tang, “Improved Grid Synchronization Control of Doubly Fed Induction Generator Under Unbalanced Grid Voltage,” in IEEE Transactions on Energy Conversion, 26(3): 799-810, 2011.

[19] S. Z. Chen, N. C. Cheung, K. C. Wong, J. Wu, “Grid Synchronization of Doubly-fed Induction Generator Using Integral Variable Structure Control,” in IEEE Transactions on Energy Conversion, 24(4): 875-883, 2009.