Dynamics of a CRAFT : A simulation study on a Counter Rotating vertical Axis Floating Tilting wind turbine

Abstract: In this thesis the Counter Rotating vertical Axis Floating Tilting wind turbine (CRAFT) has been explored by creating a simulation model in the program Simulink. The CRAFT prototype is a new type of wind turbine under development by World Wide Wind and Uppsala University with the aim to produce a large scale floating vertical axis wind turbine (VAWT) with two cone shaped counter rotating turbines. The objective of this thesis is to study the required size of the secondary generator in the CRAFT. The generator is required in order to keep both of the turbines rotating with the same but opposite rotational speed, even when the turbines are experiencing different wind loads. Further areas that are investigated are if certain parameters have a specifically high impact on the need for the secondary generator.  The objective was reached by creating a model of the prototype and implementing control algorithms for both the secondary and main generator in order to control the rotational speed of the turbines. The behaviour of the CRAFT was then simulated with different wind loads and varying parameters such as the size of the main load, the size of the power output to the secondary generator and the wing length of the lower turbine. The simulations showed that it is possible to keep the rotational speed of the two turbines equal and opposite even during turbulent wind loads with the chosen control algorithm. The simulation also showed that if a small deviation in the turbine's rotational speed is allowed, a secondary generator of only 1 kW is needed instead of the currently used 5 kW generator. It was also shown that the elongating of the lower turbine wings had a small and positive effect on the energy output of the CRAFT.