Continuous-time tube-based explicit model predictive control for collective pitching of wind turbines

Abstract

This paper introduces an extension to continuous time model predictive control to take care of time varying systems by adopting a tube-based approach. The proposed controller can be formulated as a multi-parametric quadratic program that can be solved offline. Therefore, the computational time is reduced. The proposed controller is used to control the pitch angles of large wind turbines in order to regulate the generator speed and power while operating above the turbines rated wind speeds. The proposed controller has two merits. First, it has a fast execution time due to its explicit nature. Second, it is robust against the uncertainties due to the system nonlinearities (as it adopts a tube-based approach). The performance of the proposed controller is compared to a gain-scheduled PI controller which is commonly adopted in industry. Simulation results, based on a benchmark of a typical 5-MW offshore wind turbine, demonstrate the superiority of the proposed predictive controller.