The ‘Drive Train’ block in Fig. 2 represents the WT drive train, modelled by the
two inertia equivalent shown in Fig. 3. The two inertias correspond to the rotor and
generator and are interconnected through an elasticity element with internal damping.
An external damping coefficient is also associated with each rotating mass. Using
this simplified two-body equivalent, the first torsional mode of the drive train, which
is generally the most important, can be taken into account.
Expressing all variables in p.u., the gearbox transfer ratio is eliminated from the
Fig. 3.drive train mechanical equivalent equations, which are well known and have the
following form in the Laplace domain: