Modeling and Coordinated Control Design for Brushless Doubly-Fed Induction Generator-Based Wind Turbine to Withstand Grid voltage Unblance

ABSTRACT:

Induction Generator Grid codes require wind turbines to have capability to withstand a certain grid voltage unbalance without tripping. However, existing controls for brushless doubly-fed induction generator (BDFIG) based wind turbine under grid unbalance have many problems such as difficulty in realizing decoupling control, involvement with flux or current estimations, and complex control structure. Moreover, the existing studies only focused on the control of machine side converter (MSC)

MSC

but the coordinated control between MSC and grid side converter (GSC) and the control objectives of overall BDFIG wind turbine system have not yet been addressed so far. To overcome these problems and improve the control capability, this paper proposes a coordinated control strategy by considering MSC and GSC together. First, the enhanced control objectives for overall BDFIG wind turbine system are determined. Second, the simple single current closed-loop controllers without involving with any flux or current estimations are designed for MSC and GSC, respectively.

BDFIG

Meanwhile, in current loops, all the disturbances and cross-coupling terms on dq axes are derived and used for feedforward control so as to achieve decoupling control and improve system dynamic response. Further, a fast sequence decomposition approach is employed to enhance the control characteristics of the whole system. Finally, the effectiveness of proposed control is validated through case studies for a 2 MW BDFIG based wind generation system. The results demonstrate that the proposed control can effectively achieve the control objectives of overall wind turbine system under grid voltage unbalance and provide excellent dynamic and stable performance.

KEYWORDS:

  1. Brushless doubly-fed induction generator (BDFIG)
  2. Voltage unbalance
  3. Decoupling control
  4. Wind turbine
  5. Sequence decomposition

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig.1. configuration of BDFIG-based wind turbine system

EXPECTED SIMULATION RESULTS:

Figure 2. Sequence Decomposition Results Of Grid Voltage With Notch Filter And Fast Decomposition Algorithm. (A) Grid Voltage Vgabc (P.U.). (B) Positive Sequence Component In __ Reference Frame (P.U.) (C) Negative Sequence Component In  Reference Frame (P.U.). (D) Positive Sequence Component In (Dq)C Reference Frame (P.U.). (E) Negative Sequence Component In (Dq)􀀀 Reference Frame (P.U.). (A) Decomposition Method With Notch Filter. (B) Fast Sequence Decomposition Algorithm

Figure 3. Waveforms With Elimination Of Torque Oscillations And Three Selectable Control Objectives Under 10% Grid Voltage Unbalance (!R D 0:7 P.U., ” D 10%). (A) Total Output Current (P.U.). (B) Gsc D- Axis And Pw Q- Axis Currents (P.U.). (C) Gsc Q- Axis And Pw D-Axis Currents (P.U.). (D) Gsc Dc Axis And Qc Axis Currents (P.U.). (E)Total Output Active Power (P.U.). (F) Pw And Gsc Active Power (P.U.). (G) Total Output Reactive Power (P.U.). (H) Pw And Gsc Reactive Power (P.U.). (I) Electromagnetic Torque (P.U.). (J) Dc Link Voltage (P.U.).

Figure 4. Waveforms With Two Control Modes Under ” D 10% Grid Voltage Unbalance (!R D 1:2 P.U.). (A) Total Output Current (P.U.). (B) Pw Voltage (P.U.). (C) Gsc Current (P.U.). (D) Cw Current (P.U.). (E) Total Output Active Power (P.U.). (F) Pw And Gsc Active Power (P.U.). (G) Total Output Reactive Power (P.U.). (H) Pw And Gsc Reactive Power (P.U.). (I) Bdfig Electromagnetic Torque (P.U.). (J) Dc Link Voltage (P.U.). (A) Control Mode 1. (B) Control Mode 2.

Figure 5. Waveforms With Variation Of Rotating Speed Under ” D 10% Grid Voltage Unbalance. (A) Total Output Current (P.U.). (B) Cw Current (P.U.). (C) Total Output Active Power (P.U.). (D) Pw And Gsc Active Power (P.U.) (E) Total Output Reactive Power (P.U.). (F) Pw And Gsc Reactive Power (P.U.). (G) Mechanical Torque And Electromagnetic Torque (P.U.). (H) Rotor Rotating Speed (P.U.). (I) Dc Link Voltage (P.U.).

CONCLUSION:

In this paper, the mathematical model of BDFIG based wind turbine system under grid voltage unbalance is derived in detail. Based on such model, a coordinated control strategy by considering MSC and GSC together is proposed. Compared to existing controls, proposed control for MSC is greatly simplified and more applicable and has much better parameter robustness due to adopting single current loop control structure without involving with PW flux, CW flux, and rotor current estimations.

GSC

Meanwhile, in current loop, all the cross-coupling terms and disturbances are derived and used for feedforward control, thus decoupling controls for the d-axis and q-axis currents as well as the average PW active and reactive power can be achieved. On the other hand, GSC is used to realize coordinated control with MSC so as to achieve three selectable enhanced control objectives, i.e., eliminating unbalanced total output current, oscillations of the total output active or reactive power.

PLL

Further, a fast sequence decomposition approach instead of notch filers and enhanced PLL for MSC and GSC are employed to improve the control characteristics of the whole system. The effectiveness of proposed control is verified by means of theoretical analysis and case studies. The results demonstrated that the proposed control can improve the capability of withstanding grid voltage unbalance significantly and provide excellent dynamic and stable performance.

REFERENCES:

[1] W. Xu, M. G. Hussien, Y. Liu, M. R. Islam, and S. M. Allam, “Sensorless voltage control schemes for brushless doubly-fed induction generators in stand-alone and grid-connected applications,” IEEE Trans. Energy Convers., vol. 35, no. 4, pp. 1781_1795, Dec. 2020.

[2] Z. Li, X. Wang, M. Kong, and X. Chen, “Bidirectional harmonic current control of brushless doubly fed motor drive system based on a fractional unidirectional converter under a weak grid,” IEEE Access, vol. 9, pp. 19926_19938, 2021.

[3] Y. Cheng, B. Yu, C. Kan, and X.Wang, “Design and performance study of a brushless doubly fed generator based on differential modulation,” IEEE Trans. Ind. Electron., vol. 67, no. 12, pp. 10024_10034, Dec. 2020.

[4] F. Zhang, S. Yu, Y. Wang, S. Jin, and M. G. Jovanovic, “Design and performance comparisons of brushless doubly fed generators with different rotor structures,” IEEE Trans. Ind. Electron., vol. 66, no. 1, pp. 631_640, Jan. 2019.

[5] I. A. Gowaid, A. S. Abdel-Khalik, A. M. Massoud, and S. Ahmed, “Ride-through capability of grid-connected brushless cascade DFIG wind turbines in faulty grid conditions_A comparative study,” IEEE Trans. Sustain. Energy, vol. 4, no. 4, pp. 1002_1015, Oct. 2013.

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