Dynamic Response of grid Connected Wind Turbine with DFIG during Disturbances Abram Perdana, Ola Carlson Dept. of Electric Power Engineering Chalmers University of Technology Jonas Persson Dept. of Electrical Engineering Royal Institute of Technology

Contents of Presentation 1. Background & objectives 2. Model of WT with DFIG 3. Simulation a. Fault and no protection action b. Fault in super-synchronous operation + protection action c. Fault in sub-synchronous operation + protection action 4. Effect of saturation 5. Conclusions

Objectives Background Possibilities and constraints for designing fault ride through strategy  safe for both WT and the grid Presentation of DFIG’s behavior during grid disturbances in different cases Background DFIG accounts for 50% of market share Tightened grid connection requirements  immunity of DFIG to external faults is becoming an issue

Model Structure

Wound rotor induction generator Saturation Generator Model Reactive power controller Active power controller Rotor Side Converter Controller

Turbine Model tip-speed ratio pitch angle Pitch Controller

Drive-train Model Grid Model

Case 1: Small disturbance, no protection action Rfault = 0.05 pu Avg. wind speed = 7.5 m/s

Case 1: Small disturbance, no protection action active & reactive power turbine & generator speed rotor current stator current terminal voltage

Case 2: Protection action during super-synchronous speed Rfault = 0.01 pu Avg. wind speed = 11 m/s

Case 2: Protection action during super-synchronous speed Sequence: A. Fault occurs B. If ir > 1.5 pu: converter is blocked & rotor is short-circuited C. Generator is disconnected D. Fault is cleared

Case 2: Protection action during super-synchronous speed terminal voltage active power reactive power stator current Insertion of external rotor resistance

Case 2: Protection action during super-synchronous speed no disconnection generator & turbine speed disconnection + acting of pitch angle generator & turbine speed pitch angle

Case 3: Protection action during sub-synchronous speed Rfault = 0.01 pu Avg. wind speed = 9 m/s

Case 3: Protection action during sub-synchronous speed terminal voltage stator current active power reactive power turbine & generator speed

Effect of Saturation in the Model saturation curve Effect of Saturation in the Model stator current rotor current

Conclusions DFIG provides a better terminal voltage recovery compared to SCIG during (small) disturbance when no converter blocking occurs, for severe voltage dips DFIG will be disconnected from the grid (with conventional strategy) converter blocking during super-synchronous operation causes high reactive power consumption, converter blocking during sub-synchronous operation causes high reactive and active power absorption and abrupt change of rotor speed Saturation model predicts higher value of stator & rotor currents, therefore it is important to include in designing protection