Grid requirements, monitoring, synchronization and control of wind turbines under grid faults

LVRTcan be implemented with resistive crow-bar and reactive power injection to existing wind farms. Variable speed wind turbines can do LVRT as they are capable of quickly reduce the torque of the generator and inject reactive power. The capability of the system to allow ride-through grid disturbances is strictly related to the inverter rating (maximum voltage and current at the ac-side) as well as its dc-link energy storage (maximum/minimum voltage at the dc-side). A robust control strategy for the grid inverter should ride-through transient faults avoiding under-/over-voltage trip in the dc-bus and output overcurrents due to distortion and imbalance reactive power injection is helping the grid voltage to recover. Several strategies for reference current generations. Over-current and under/over voltage should be avoided to ride-through transient faults. Different power delivery strategies under fault are also presented. New grid codes with even more restrictions during grid faults are expected in the future an more advanced control strategies have to be developed.