Power Regulation and Load Mitigation of Fixed-Bottom Offshore Wind Turbines via Adaptive Dynamic Programming

Due to the uncertainty of the wind-wave environment and the low damping characteristic of the in-plane direction, the lateral direction of monopile offshore wind turbines (MOWTs) frequently experiences significant structural loads, which will shorten the service life of MOWTs. To solve this issue, an optimal pitch control method based on adaptive dynamic programming (ADP) is proposed for MOWTs, which comprehensively considers both power generation and load mitigation performance. First, the motion equation of the tower together with monopile under wind-wave environment is constructed on the foundation of the Euler–Lagrange equation. For the convenience of the controller design, a novel nonlinear affine MOWT mathematical model is presented, and an ADP-based optimal pitch controller is proposed to solve the multiobjective optimal control problem. Then, the uniformly ultimately bounded (UUB) stability of the system is proved by the Lyapunov theory. Finally, to validate the feasibility of the proposed control method, a national renewable energy laboratory (NREL) 5-MW offshore code comparison collaborative (OC3) MOWT has been emulated using the OpenFAST platform developed by the NREL.