Extremum Seeking Control for optimization of a feed-forward Pelton turbine speed controller in a fixed-displacement hydraulic wind turbine concept

With the sustained drive towards higher power ratings for offshore wind turbines, the size of the turbine rotor and drivetrain components scale accordingly. Compact hydraulic transmissions are widely applied in high-load systems and form a business case for application in multi-megawatt offshore turbines. The Delft Offshore Turbine (DOT) is a hydraulic wind turbine concept replacing conventional drivetrain components with a single seawater pump. In the DOT concept, pressurized seawater is directed to a Pelton turbine-generator combination, located at a central electricity generation platform. An in-field test campaign is performed using a prototype DOT turbine with a retrofitted 500 kW hydraulic drivetrain, consisting of fixed-displacement components. As a result of this configuration, a feed-forward Pelton speed controller is derived and implemented for operating the Pelton turbine at maximum efficiency. However, the controller tuning is based on estimations of physical system properties, of which the resulting optimality is unknown. For verification of the implementation, the model-free, gradient-based and data-driven Extremum Seeking Control (ESC) optimization scheme is employed. Results show fast convergence of the algorithm and an average maximum power increase of 3 %. The algorithm is well suited for application to real-world systems, due to its simplicity and ease of tuning.