Abstract
A nonlinear predictive controller is proposed for a variable speed wind turbine. The objective is power capture optimization and transient loads reduction. The controller acts only on low wind speed area. It consists of a doubly fed induction generator controller coupled with a model predictive aeroturbine controller. Unlike the majority of existing work on DFIG, the nonlinear controller deals directly with the generator model without any simplifying assumptions. This makes it possible to remove some assumptions on the DFIG model. The nonlinear DFIG controller achieves asymptotic torque and flux tracking. For the aeroturbine part, the model predictive controller uses predictions of the output to compute the optimal control sequence. It makes a compromise between power capture optimization and loads reduction. The controllers design procedure is detailed. The global controller is tested with the parameters of a real experimental variable speed wind turbine. It is compared with PID and LQG controllers. The simulations show satisfactory results in comparison with these schemes. The proposed controller achieves better power capture optimization and load reduction. It therefore allows a good achievement of the design objectives.
5. Conclusion
A global controller for both the generator and aeroturbine is proposed. It is applied for a variable speed wind turbine equipped with a DFIG generator. The controller is composed of a nonlinear controller for the DFIG and an MPC controller for the power capture optimization. The two controllers are interconnected using a two-loop control structure with suitable time constants. The simulations are made with the parameters of a real wind turbine and a realistic wind speed profile. They confirm the efficiency of the controller in terms of power capture optimization and control loads reduction. The good performance of the predictive controller are explained by the well adaptation of predictive control scheme for systems like wind turbines. The wind is considered as an filtered-input disturbance. The predictive behavior of the MPC controller allows a premature reaction of the controller for a smooth control of a inertial systems like wind turbine. The predictive controller achieves a good compromise between simplicity and efficiency. A whole controller is to be considered in future works. It will include full load area for high wind speed. It should also take into consideration the transition between power capture optimization and power regulation.
