Load Mitigation and Power Tracking Control for Multi-Rotor Turbines

A model-based feasible control strategy for multi-rotor systems is presented, pursuing two control objectives simultaneously: Mechanical loads on the main tower are to be mitigated, and an externally determined power change is to be followed to obtain fast power reference response in power systems. For this purpose, a scalable control strategy consisting of two levels is proposed: The first level consists of the decentralized control of each rotor unit. By using an LPV formalism, it is shown how the nonlinearities of the controlled system are considered in the design using a decentralized wind speed observer of each rotor to improve the overall closed-loop performance. To mitigate the lateral loads on the multi-rotor main tower caused by asymmetric rotor thrust forces, a higher-level controller is introduced. Finally, the applicability of the controller structure is demonstrated by simulation studies.