1 Risø National Laboratory for Sustainable Energy, Technical University of Denmark2 Department of Electrical Engineering, Technical University of Denmark
The current report is part of the reporting of the work executed as part of the project 'Active Control and Wind Turbine Dynamics'. The project has been supported by the Danish Energy Agency under contract EFP91, ENS j.nr. 1364/91-0003. Projectparticipants were Vestas Wind Systems A/S, DTU (Technical Univ. of Denmark) and Risø National Laboratory. The objective of the project is to investigate the application of active control of a wind turbine and analyse the interaction with the wind turbinedynamics in order to optimise energy production, improve power control and minimise structural laods. Measurements and experiments have been conducted on a 400 kW WD34 pitch controlled wind turbine. The current report is about optimisation of thecontrollers, primarily with regard to improvement of power control. The controller optimisation is divided in three phases. In the first phase the performance of the existing PI-controller is investigated through measurements with respect to powercontrol. In the second phase a model for control purposes of a pitch controlled wind turbine is formulated. It is applied in the optimisation process of the PI-controllers. The results of optimisation are tested on the real wind turbine. In the thirdphase more advanced controllers are investigated. Both mesurements and simulations have shown that it is not possible to achieve significant improvements of the power control by optimising the PI-controllers. This is due shape of the transfer function.If the power control should be improved it requires a controller with a large differential part. Such a controller will make the system very sensitive to noise and parameter changes. The application of LQG-controllers could have improved the quality ofthe power control because such controllers are model based and therefore contain more knowledge about the system to be controlled. However, the same limitation in the shape of the transfer function applies to this design so that in order to havesufficient control bandwidth the system will be very sensitive to noise and model uncertainties. The results from the tests with the LQG-controllers have shown that it is very important to include robustness considerations in the design of these moreadvanced controllers. The model developed in the project can be applied in the design of controllers for variable speed wind turbines if a model of the frequency converted is included.
Vindenergi og atmosfæriske processer; Risø-R-1044; Risø-R-1044(DA)