POWER OUTPUT FLUCTUATION ASSESSMENT OF A LARGE-SCALE WIND TURBINE-GENERATOR SYSTEM UNDER WIND SPEED FLUCTUATION

Power output fluctuation of 2 MW-wind turbine-generator systems, which apply fixed speed operation and variable speed operation separately, is analyzed through numerical simulation carried out by using an observed field wind data. The fixed speed operation has two levels of operating rotational speeds in response to the wind speed. The variable speed operation has two operation modes: a constant tip speed ratio operation mode at low wind speeds and constant speed operation mode at high wind speeds. For any operation, the pitch angle is controlled to maintain rated electric power output at high wind speeds. The simulation result shows that the variable speed operation can reduce the power output fluctuations with both long and short periods as compared with the fixed speed operation due to rotational inertia of the rotor. Furthermore, it is revealed that the pitch angle control is effective to reduce the power output fluctuation with long periods for any operation.