Simplified approach for the optimal number of rotors and support structure design of a multi rotor wind turbine system

Abstract

In this study different multi rotor wind turbine systems (MRSs) are designed in such a way that the space frame, forming the connection between rotor nacelle assemblies (RNAs) and tower, will be modeled and dimensioned as an ideal truss work. The main focus is on multi digit MRSs (MD-MRS) with a high number of rotors. To dimension the tube diameters and wall thicknesses, a simplified load case is used with an adjusted safety factor for loads. Parameters that are varied are the number of rotors, depth of the space frame, as well as the location of the fixed bearing for the yaw system. As such, the simplified approach is a preliminary step helping to choose a good design parameter combination for a more detailed and comprehensive analysis. Buckling is a main design driver, as well as the thrust forces. For a high number of rotors, a fixed bearing position and therefore tower height, halfway through the space frame height seems favorable regarding the cost.

Yaw control strategies for 20 MW multi-rotor systems

“…The MRS and the 20 MW single rotor turbines are scaled and based on the 10 MW DTU reference turbine [15]. The design is based on concept studies done in [16] and [17] and is shown in Figure 1. Figure 2 shows the numbering of the rotors and the position of the yaw bearing.…”

“…Figure 2 shows the numbering of the rotors and the position of the yaw bearing. In [16] and [17] different concepts for the yaw bearing of an MRS are shown, whereby the twin-bearing approach with fixed and floating bearing was considered. The modelling of such a twin-bearing in Bladed is not possible at the moment, which is why a central yaw bearing is assumed for both simulations.…”