Control Design and Data-Driven Parameter Optimization for the DOT500 Hydraulic Wind Turbine

Control Design and Data-Driven Parameter Optimization for the DOT500 Hydraulic Wind Turbine

Jager, S.M.

Mulders, S.P. (mentor)
van Wingerden, J.W. (mentor)

Mechanical, Maritime and Materials Engineering

Delft Center for Systems and Control

2017-01-03

In an effort to reduce the Levelized Cost Of Energy (LCOE) of offshore wind energy to a market competitive level, a new wind turbine prototype with hydraulic drive train has been introduced by the start-up company Delft Offshore Turbine (DOT). In the DOT concept, a seawater pump is directly connected to the rotor shaft. The pump pressurizes sea water, which is transferred to a hydro-power station at sea level. There, the hydraulic power is converted to electric power by means of a Pelton turbine, which is mechanically connected to an electric generator. In below-rated wind conditions, practically all commercial wind turbines regulate the rotor speed by adjusting the generator torque demand. However, due to the decoupling of the rotor and generator in the DOT concept, conventional below-rated torque control is no longer possible. With the hydraulic drive train concept considered in this thesis, an alternative torque control strategy is designed and implemented, where fluid pressure is regulated to vary the system torque. The developed hydraulic torque control strategy is integrated in the turbine control system, which includes e.g. yaw, pitch and supervisory control. Functionality of the derived strategy is validated through field trials, performed on a 500 kW prototype of the DOT wind turbine. A second-hand Vestas V44 wind turbine was retrofitted with hydraulic components and installed on the Maasvlakte II for this purpose (see Figure 1). Since the required seawater pump for the ideal DOT concept is not yet commercially available on the market, an intermediate hydrostatic oil transmission was used as a hydraulic gearbox between rotor and water pump. However, the operating principles of the control strategy remain identical for both the ideal and intermediate DOT scenario. Results show that below-rated speed regulation is possible with the derived hydraulic torque controller. The developed strategy enables operation along the theoretical optimal tip-speed ratio for attaining the maximum (rotor) power coefficient. The blade fine-pitch angle, which leads to maximum rotor power extraction in the below-rated region, was subsequently found with the direct data-driven Extremum Seeking Control (ESC) algorithm. Finally, the ESC method was implemented to find the generator speed feedforward control gain. Results indicate an instant generator power increase and led to the detection of a malfunctioning sensor. Therefore, ESC appeared to be a valuable tool to deal with modelling and measurements uncertainties.

http://resolver.tudelft.nl/uuid:17e2bfcf-7d30-472c-95df-d6d7adb8cad3

2018-01-03

Student theses

master thesis

(c) 2017 Jager, S.M.