Improved Low Voltage Ride-Through Capability of DFIG with ESO Controller under Unbalanced Network Conditions
AbstractUnder unbalanced grid condition, in a Doubly-Fed Induction Generator (DFIG), voltage, current, and flux of the stator become asymmetric. Therefore, active-reactive power and torque will be oscillating. In DFIG controlling Rotor Side Converter (RSC) aims to eliminate power and torque oscillations. However, simultaneous elimination of the power and torque oscillations is not possible. Also, Grid Side Converter (GSC) aims to regulate DC-Link voltage. In this paper, in order to regulate DC-Link voltage, an Extended State Observer (ESO) based on a Generalized Proportional-Integral (GPI) controller, is employed. In this controlling method, DC-Link voltage is controlled without measuring the GSC current, and due to using the GPI controller, the improved dynamic response is resistant against voltage changes, and the settling time is reduced. To improve the transient stability and Low Voltage Fault Ride Through (LVRT) capability of DFIG, Statistic Fault Current Limiter (S-FCL) and Magnetic Energy Storage Fault Current Limiter (MES-FCL) are proposed in this paper. The proposed FCL does not only limit the fault current but also fasten voltage recovery. The simulations are implemented by MATLAB software in the synchronous positive and negative sequence reference (d-q).
 Z. Xue-guang and X. Dian-guo, “Research on control of DFIG with active crowbar under symmetry voltage fault condition,” Electr. Mach. Control, vol. 13, no. 1, pp. 99– 103, 2009.
 C. Wessels and F. W. Fuchs, “Fault Ride through of DFIG Wind Turbines during symmetrical voltage dip with Crowbar or Stator Current Feedback Solution,” IEEE Energy Convers. Congr. Expo. pp. 2771–2777, 2010.
 M. E. Elshiekh, D. E. A. Mansour, and A. M. Azmy, “Improving fault ride-through capability of DFIG-based wind turbine using superconducting fault current limiter,” IEEE Trans. Appl. Supercond., vol. 23, no. 3, Jun. 2013, Art. ID. 5601204.
W.Guo, L.Xiao, Sh.Dai, and et al, “Evaluation of the Performance of BTFCLs for enhancing LVRT capability of DFIG,” IEEE Trans. Power Electronics, vol. 30, no. 7, pp. 3623–3637, 2014.
 I. Ngamroo and T. Karaipoom, “Cooperative control of SFCL and SMES for enhancing fault ride through capability and smoothing power fluctuation of DFIG wind farm,” IEEE Trans. Appl. Supercond., vol. 24, no. 5, Oct. 2014, Art. ID. 5400304.
 A.M, and R.R, “Power System Stability Enhancement and Improvement of LVRT Capability of a DFIG Based Wind Power System by Using SMES and SFCL,” International Journal of Electrical and Computer Engineering, vol. 3, no. 5,pp. 618-628, 2013.
 O. Abdel-Baqi and A. Nasiri, “Series voltage compensation for DFIG wind turbine low-voltage ridethrough
Solution,” IEEE Trans. Energy Convers. vol. 26, no. 1, pp. 272–280, 2011.
 M.Fazli, N.Talebi, “A New Method for Uninterrupted Operation of Wind Turbines Equipped With DFIGs During Grid Faults Using FCL,” in Proc Environment and Electrical Engineering, pp. 33–36, 2010.
 B. Mukhopadhyay and R. K. Mandal, “Voltage compensation using PSO-PI controlled STATCOM in a DFIG-based grid-connected wind energy system,” Int. Conf. Electr. Power Energy Syst. ICEPES 2016, pp. 88– 93, 2017.
 I. Erlich, W. Winter, and a. Dittrich, “Advanced grid requirements for the integration of wind turbines into the German transmission system,” 2006 IEEE Power Eng.Soc. Gen. Meet., pp. 1–7, 2006.
 J.Lu , S.Golestan , M.Savaghebi, JC.Vasquez, JM.Guerrero,A.Marzabal , “An enhanced State observer for DC-Link voltage control of three-Phase AC/DC converters,“ IEEE Transactions on Power lectronics,vol.33,no.2,pp.936-942,2018.
 J.Yang, H.Cui, S.Li, A.Zolotas, “ Optimized active disturbance rejection control for DC-DC buck onverters with uncertainties using a reduced-order GPI observer, “IEEE Transactions on Circuits and Systems ,vol. 65,no.2,pp.832 – 841,2018.
 G.Wenyong, X.Liye,D. Shaotao, and al et, “LVRT Capability Enhancement of DFIG With Switch-Type Fault Current Limiter,” IEEE Trans. Industrial Electronics, vol. 62, no.1, pp. 332-342,2015.
 I. Ngamroo and T. Karaipoom, “Improving Low-Voltage Ride-Through Performance and Alleviating Power Fluctuation of DFIG Wind Turbine in DC Microgrid by Optimal SMES With Fault Current Limiting Function,” vol. 24, no. 5, 2014.
 F.Wei, D.M. Vilathgamuwa and Ch.S.Shing, “Design of mode switching scheme for low-voltage ride-through of doubly fed induction generators,” Published in IET Renewable Power Generation, vol. 9, no. 2, pp. 109-119, 2015