System and Method for Operating a Wind Turbine Power System During Low Wind Speeds to Improve Efficiency

A wind turbine power system configured to supply real and reactive power to a grid, the wind turbine power system comprising:

• a wind turbine comprising:
• a rotor comprising a hub and a plurality of blades coupled to the hub,
• a generator coupled to the rotor, and
• a power converter coupled to the generator;
• and
• a controller for controlling operation of the wind turbine, the controller comprising at least one processor configured to perform a plurality of operations, the plurality of operations comprising:
• operating the generator of the wind turbine up to a first speed limit;
• monitoring a wind speed at the wind turbine;
• when the wind speed drops below a predetermined threshold, reducing the first speed limit of the generator to a reduced speed limit of the generator, wherein the reduced speed limit ranges from about 85% to about 95% of the first speed limit;
• and
• operating the generator at the reduced speed limit for as long as the wind speed remains below the predetermined threshold so as to optimize a tip-speed-ratio of the wind turbine during low wind speeds, thereby increasing power production of the wind turbine at low wind speeds.

A method for operating a wind turbine power system that supplies real and reactive power to a grid, the wind turbine power system including a doubly fed induction generator (DFIG) coupled to a power converter, the method comprising:

• monitoring a wind speed at the wind turbine power system;
• when the wind speed drops below a predetermined threshold, reducing a speed limit of the DFIG by a predetermined amount;
• maintaining the reduced speed limit for as long as the wind speed remains below the predetermined threshold so as to reduce a tip-speed-ratio of the wind turbine power system during low wind speeds, thereby increasing power production of the wind turbine power system at low wind speeds,
• wherein reducing the speed limit of the DFIG by the predetermined amount further comprises transferring at least a portion of the reactive power to a reactive power compensation device.