Assessment of grid-connected wind turbines with an inertia response by considering internal dynamics

This paper presents a small-signal analysis of different grid side controllers for full power converter wind turbines with inertia response capability. In real wind turbines, the DC link controller, the drivetrain damping controller and the inertial response might present contradictory control actions in a close bandwidth range. This situation might lead to reduced control performance, increased component stress and non-compliance of connection agreements. The paper presents an analysis of the internal wind turbine dynamics by considering different grid-side converter control topologies: standard current control used in the wind industry, standard current control with inertia emulation capabilities and virtual synchronous machines. Comments are made on the similarities between each topology and the negative effects and limits, and possible remedies are discussed. Finally, the conclusion poses that the inclusion of a DC link voltage controller reduces the ability of a converter to respond to external frequency events without energy storage. The degradation increases with the DC link voltage control speed.