A 5MW direct-drive generator for floating spar-buoy wind turbine: Development and analysis of a fully coupled Mechanical model

Abstract

This work forms the first of a two-part investigation aimed at identifying the challenges and opportunities of implementing a direct-drive generator for a spar-buoy type floating wind turbine. Preliminary specifications are presented for a fully coupled aero-hydro-servo-elastic model of a floating wind turbine with a 5 MW direct-drive generator. The drivetrain model uses a low-speed, high-torque radial flux permanent magnet generator supported by two main-shaft bearings. The mechanical properties of the drive-train, including the main dimensions, mass of major nacelle equipment and details for the hub/nacelle assembly are presented. The rationale behind the adjustments to the tower and platform properties and the motivation to selection of best arrangement that is appropriate for supporting the developed system is explained. A discussion on the development of the variable speed-variable pitch control system suitable for the directdrive system including modifications to avoid negative damping and blade-pitch instability are presented. Fully coupled simulations for the developed aero-hydro-servo elastic model were carried out in HAWC2 for the normal operating conditions of the wind turbine. The aerodynamic response of the model was verified and compared with that of a geared floating wind turbine system. Some initial results comparing the main shaft loads of the land-based and floating versions of the direct-drive wind turbine suggest satisfactory dynamic behaviour of the drive-train. The results prompt further research using a detailed drive-train model to verify the internal response, loading and durability of the components to assess their compatibility with a floating wind turbine system.

The effect of the rotor adjustment on the vibration behaviour of the drive-train system for a 5 MW direct-drive wind turbine

“…The rotor displacement and bearing forces are discussed under different operating conditions. In performing numerical simulations, the parameters of the drive-train system are selected from the designed DDPMG of a 5 MW NREL wind turbine, 2,28 and are given in Table 1. It is known that the DDPMG would operate at a low rotating speed, normally in the range of 5 to 30 r/min.…”

“…2,15,25,26 Figure 2 shows the main structure of the rotor nacelle of a 5 MW direct-drive wind turbine. 2 The stator is assumed to be fixed and constrained in all directions. The rotor system is held by two different bearings, which are fixed with the stator.…”

“…Assume that the unbalanced CG has the eccentricity e and the skew angle . Equations (2) and 3can be rewritten by using the relationship 34…”

“…1 The direct-drive wind turbines have greater reliability than the indirect-drive wind turbines due to their fewer rotating parts and wear components. 2 Polinder et al 3 compared five different systems of direct-drive and geared generators in terms of cost and annual energy yield. For geared generators, the doubly fed induction generator with threestage gearbox is the most widely used in onshore wind turbines due to its lowest weight and cost; however, there are high energy losses in the gearbox.…”

Structural Reliability Analysis of Wind Turbines: A Review

“…Because the damage development of the mechanical components is influenced by the operational conditions including unsteady wind, braking, generator misalignment, lubricants and grid faults [147], there is a need to address the uncertainties related to these factors. In addition to the traditional gear transmission, other types of drivetrain technologies including direct drive [148] and hydraulic transmission [149,150] have also appeared on the market, and the reliability of these novel technologies remains an open question.…”