Design and development of an innovative controller for small wind turbines

Recent demand for decentralized renewable energy on a small scale has led to the advancement of micro-wind turbines and customized control systems. In this work, the arising need for an innovative control system for small scale wind turbines particularly suited to a low wind speed urban environment has been addressed.
This work focuses on the stand-alone application of a vertical-axis wind turbine (VAWT)
cross-flow prototype with the prospect of being able to grid-tie the system without any major modification to the control system. This constraint has led to the inclusion of a
magnetic brake with various advantages over conventional braking methods which are addressed in the literature review of this thesis. Furthermore, the latter revealed lack of
computerized models for the setup described, therefore it has been decided in this work to
focus on software-based controller development utilizing models which have been validated
by various experiments.
In the first development stage, a novel test bench prototype has been developed for prior
evaluation of the brake characteristics. The prototype has been utilized for deriving a model
dedicated to the low-speed region and for developing an efficient design strategy to be able to customize control systems for future small scale wind turbines.
The second development stage has been dedicated to the development of a suitable model
for the wind turbine. Different modelling strategies are evaluated, i. e. the use of look-up tables (LUT), analytical models and CFD models, and the most suitable selected. This work
uses an analytical model based on experimental data.
The third and last development stage leads to a software-based controller development
approach with emphasis on two control modes common in variable speed wind turbine control: a. braking to a reference speed once the maximum allowable rotor speed has been reached or exceeded and b. braking to track the maximum power point when a turbine has not yet reached its rated power. A supervisory control template is given for future development for use in an embedded microcontroller design.