Optimal Region 2 operation of a distributed wind turbine with time-varying weightings to smooth torque variation

Maximizing energy capture during wind turbine operation plays a crucial role in increasing wind energy´s economic viability and its penetration in the grid. Variable speed operation enables the turbine to extract more energy during partial load operation or Region 2 operation. Various control algorithms have been developed to maximize the benefit of using variable ratio operation. However, the existing control methods cannot provide the knowledge of the maximum wind energy that can be captured and the efficiency gap between an optimal control design and these methods. Therefore, it is necessary to explore the application of optimal control methods. This paper presents a numerical optimal control (NOC) technique to maximize wind energy capture for Region 2 operation of a wind turbine system. Mitigating turbine torque variation, thus reducing the fatigue loading of a turbine drivetrain, is also considered in the control design. Furthermore, an approach of incorporating time-varying weightings into developing the optimal controller is introduced to seek further improvement on turbine torque reduction. The performance of the proposed control technique is compared to traditional control strategies in a simulation environment.