Bumpless Transfer-Based Inter-Region Controller Switching of Wind Turbines for Reducing Power and Load Fluctuation

For wind turbine operation, wind variations around the rated wind speed can lead to frequent controller switching actions, which may result in significant fluctuation in power output and structural load. This paper presents a bumpless transfer scheme for the inter-region controller switching for variable-speed variable-pitch wind turbines, which aims to reduce the associated power fluctuation and fatigue load. The study follows a typical partition of Region 2 (maximum power capture control), Region 2.5 (rotor speed regulation), and Region 3 (constant power control) around the rated wind speed. Two relatively simple bumpless transfer techniques, i.e., 1) the conditioning technique and 2) the linear quadratic (LQ) technique, respectively, are employed for different situations of inter-region controller switching. The conditioning bumpless transfer approach is adopted for switching between Regions 2 and 2.5 via generator torque control. The LQ bumpless transfer technical is applied to the switching between Regions 2.5 and 3, when the generator torque is saturated at its rated value, the pitch controller takes over so as to limit the load of wind turbine. The simulation results demonstrated the effectiveness of the proposed scheme of inter-region switching, with significant reduction of power flicker and structural load.