Fault Ride-Through of a DFIG Wind Turbine Using a Dynamic Voltage Restorer During Symmetrical and Asymmetrical Grid Faults

ABSTRACT:

 The application of a dynamic voltage restorer (DVR) connected to awind-turbine-driven doubly fed induction generator (DFIG) is investigated. The setup allows the wind turbine system an uninterruptible fault ride-through of voltage dips. The DVR can compensate the faulty line voltage, while the DFIG wind turbine can continue its nominal operation as demanded in actual grid codes. Simulation results for a 2 MW wind turbine and measurement results on a 22 kW laboratory setup are presented, especially for asymmetrical grid faults. They show the effectiveness of the DVR in comparison to the low-voltage ride-through of the DFIG using a crowbar that does not allow continuous reactive power production.

 KEYWORDS:

  1. Doubly fed induction generator (DFIG)
  2. Dynamic voltage restorer (DVR)
  3. Fault ride-through and wind energy

 SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fault Ride-Through of a DFIG

Fig. 1. Schematic diagram of DFIG wind turbine system with DVR.

 EXPECTED SIMULATION RESULTS:

 

Fig. 2. Simulatin of DFIG performance with crowbar protection during 37 % two-phase voltage dip. (a) Line voltage. (b) DVR voltage. (c) Stator voltage. (d) Stator current. (e) RSC current. (f) Crowbar current. (g) Mechanical speed. (h) Active and reactive stator power. (i) Active and reactive DVR power.

Fig. 3. Simulation of DFIG performance with DVR protection during 37 % two-phase voltage dip. (a) Line voltage. (b) DVR voltage. (c) Stator voltage. (d) Stator current. (e) RSC current. (f) Crowbar current. (g) Mechanical speed. (h) Active and reactive stator power. (i) Active and reactive DVR power.

Fig. 4. Measurement results for DFIG with crowbar protection: (a) stator

voltages, (b) stator currents, and (c) rotor currents.

Fig. 5. Measurement results for DFIG with DVR protection: (a) line voltages, (b) DVR voltages, (c) stator voltages, (d) stator currents, and (e) rotor currents.

CONCLUSION:

The application of a DVR connected to a wind-turbine-driven DFIG to allow uninterruptible fault ride-through of grid voltage faults is investigated. The DVR can compensate the faulty line voltage, while the DFIG wind turbine can continue its nominal operation and fulfill any grid code requirement without the need for additional protection methods. The DVR can be used to protect already installed wind turbines that do not provide sufficient fault ride-through behavior or to protect any distributed load in a microgrid. Simulation results for a 2 MW wind turbine under an asymmetrical two-phase grid fault show the effectiveness of the proposed technique in comparison to the low-voltage ridethrough of the DFIG using a crowbar where continuous reactive power production is problematic. Measurement results under transient grid voltage dips on a 22 kW laboratory setup are presented to verify the results.

REFERENCES:

[1] M. Tsili and S. Papathanassiou, “A review of grid code technical requirements for wind farms,” Renewable Power Generat., IET, vol. 3, no. 3, pp. 308–332, Sep. 2009.

[2] R. Pena, J. Clare, and G. Asher, “Doubly fed induction generator using back-to-back pwm converters and its application to variable-speed windenergy generation,” Electr. Power Appl., IEE Proc., vol. 143, no. 3, pp. 231–241, May 1996.

[3] S.Muller,M.Deicke, andR.DeDoncker, “Doubly fed induction generator systems for wind turbines,” IEEE Ind. Appl.Mag., vol. 8, no. 3, pp. 26–33, May/Jun. 2002.

[4] J. Lopez, E. Gubia, P. Sanchis, X. Roboam, and L. Marroyo, “Wind turbines based on doubly fed induction generator under asymmetrical voltage dips,” IEEE Trans. Energy Convers., vol. 23, no. 1, pp. 321–330, Mar. 2008.

[5] M. Mohseni, S. Islam, and M. Masoum, “Impacts of symmetrical and asymmetrical voltage sags on dfig-based wind turbines considering phaseangle jump, voltage recovery, and sag parameters,” IEEE Trans. Power Electron., to be published.

Inner Control Method and Frequency Regulation of a DFIG Connected to a DC Link

 

ABSTRACT:

In this paper, an inner loop for the control and frequency regulation of the doubly fed induction generator connected to a dc link through a diode bridge on the stator is presented. In this system, the stator is directly connected to the dc link using a diode bridge, and the rotor is fed by only a pulse width-modulated (PWM) converter. If compared to the DFIG connected to an ac grid, this system uses one PWM inverter less and a much less expensive diode bridge. Thus, the cost of power electronics is reduced. The application in mind is for dc networks such as dispersed generation grids and microgrids. These networks use several elements that should work together. Usually, these elements are connected with each other by power electronic devices in a common dc link. This paper presents a control system for the inner control loop in order to regulate the torque and the stator frequency. Simulation and experimental results show that the system works properly and is able to keep the stator frequency near the rated value of the machine.

 KEYWORDS:

  1. Control
  2. Dc link
  3. Dc microgrids
  4. Doubly fed induction generator

 SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

 Fig. 1. Structure of the DFIG-DC. Diode bridge on the stator, PWM converter on the rotor.

EXPECTED SIMULATION RESULTS:

Fig. 2. Torque, stator flux, frequency error, and sinδ.

Fig. 3. Stator and rotor currents in closed loop.

Fig. 4. Torque, stator flux, frequency error, and sinδ.

 Fig. 5. Response to a voltage dip down to 0.5 p.u.

Fig. 6. Twelve-pulse rectification curves. Six-pulse stator currents, torque,

and equivalent three-phase current using 12 pulse and torque.

CONCLUSION:

This paper presents a control method for the DFIG connected to a dc link through a diode rectifier on the stator windings. Simulation and experimental results show that it is possible to drive the stator flux at the rated frequency of the machine by using a simple controller that adjusts the rotor d-axis current reference in order to annihilate the orientation error. The method converges to the field orientation and the steady-state frequency error is zero.Agood dynamics is achieved in the electromagnetic torque. The waveforms of the stator current are not sinusoidal, due to the presence of the diode bridge, but have an acceptable harmonic content. The industrial application of this system could be implemented using a 12-pulse rectifier, which reduces not only the torque ripple but also the harmonic content in the rotor currents.

REFERENCES:

[1] S. Chowdhury, S. P. Chowdhury, and P. Crossley “Microgrids and active distribution networks,” in IET Renewable Energy (Series 6). London, U.K.: The Institution of Engineering and Technology, 2009.

[2] J. A. Pec¸as Lopes, C. L. Moreira, and A. G. Madureira, “Defining control strategies for microgrids islanded operation,” IEEE Trans. Power Syst., vol. 21, no. 2, pp. 916–924, May 2006.

[3] F.Blaabjerg, Z. Chen, and S. B. Kjaer, “Power electronics as efficient interface in dispersed power generation system,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1184–1194, Sep. 2004.

[4] F. Blaabjerg, R. Teodorescu, M. Liserre, and A. V. Timbus, “Overview of control and grid synchronization for distributed power generation systems,” IEEE Trans. Ind. Electron., vol. 53, no. 5, pp. 1398–1409, Oct. 2006.

[5] D. Salomonsson and A. Sannino, “Low-voltage DC distribution system for commercial power systems with sensitive electronic load,” IEEE Trans. Power Del., vol. 22, no. 3, pp. 1620–1627, Jul. 2007.