Inertial response with improved variable recovery behaviour provided by type 4 WTs

Requirements for inertial response (IR) from wind turbines (WTs) have been implemented or drafted by power systems (PSs) operators worldwide. This is a response to the replacement of conventional power plants using synchronous generators by non-synchronous, power electronics-based generation and the resulting effect on frequency dynamics in the case of contingency events. The additional active power provided during operation in IR mode must be drawn from the rotating masses. A re-acceleration accompanied by reduced active power output follows the activation phase. The allowed depth and duration of the post-inertial recovery will be regulated in future versions of grid codes, e.g. in Quebec and Ireland. This study describes an improved version of an IR control system that enables a more PSs-friendly provision of such short-term frequency support. The new controls allow adjusting the duration of the recovery period. Potential negative effects of IR from WTs on the PS in the form of a second frequency nadir during the recovery phase can be minimised. The outcome of simulations and of field testing will be presented. All results shown in this study include the initial and the future inertia emulation performance which allows easy comparison of the two controls.