Active Power Control and Load Suppression for Wind Turbines Based on a Variable-Degree-of-Freedom Framework

Structural load suppression of wind turbines is one of the important means to improve the economic efficiency of wind farm operation. However, wind turbines are complex systems coupled with multiple control variables. There is no comprehensive solution for the flexible and coordinated control of multiple controllable degrees of freedom. The main difficulty lies in the greater optimization burden of multi-degree-of-freedom systems. This paper proposes a variable degree-of-freedom control system for wind turbines, and uses multivariable model predictive control to design collaborative controllers for generator torque, pitch angle and yaw angle. To avoid the increase in complexity caused by the continuous intervention of yaw control, a yaw control cut-in/cut-out strategy is set, and the non-disturbance of switching is theoretically proved. Simulation results show that the proposed variable degree-of-freedom control system can effectively realize active power control and structural load suppression of wind turbines in a large wind speed range. Note to Practitioners—This paper focuses on efficiently using wind turbines’ control degrees of freedom to achieve better structural load suppression. The control strategy of existing commercial wind turbines is decentralized. This paper innovatively considers the organic coordination of generator torque, pitch, and yaw angles, and designs two- and three-degree-of-freedom controllers using model predictive control methods. Considering that the yaw angle control should be reduced in practical applications, this paper designs a switching strategy that can achieve disturbance-free switching between two- and three-degree-of-freedom. These works can provide a new development idea for the control framework of wind turbines and better serve the structural load suppression during the operation of wind turbines.