Investigation on the degree of controllability of wind turbines for the maximum power point tracking

Based on the simplified aerodynamic and motion equations of wind turbines, a linear model is derived for the maximum power point tracking (MPPT). With this model, the expressions of the controllability degree as a function of the aerodynamic/structural parameters of wind turbines are deduced. It is found that the two types of controllability degree both increase with the decrement of rotor inertia. Meanwhile, the variation of the controllability degree versus the performance of MPPT control is investigated by simulations. It is observed that when using the same MPPT control, the higher efficiency of wind energy capture can be achieved by the wind turbine with small rotor inertia and little optimum tip-speed ratio. This implies that the better control performance can be obtained by the wind turbine with the larger controllability degree. This study shows that it is feasible to consider the controllability degree as an indicator that reflects the impacts of structural parameters on the control performance. And, the controllability degree can be further applied to the design and optimization of the structural parameters with a view of control.