Inertial Response with Improved Variable Recovery Behaviour Provided by Type 4 Wind Turbines
Presenter (Affiliation): Sönke Engelken (WRD GmbH, Germany)

Requirements for inertial response from wind turbines (WTs) have been implemented or drafted by a number of power systems 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. Previous publications have shown operational experiences with inertial response provided by WTs that have been in commercial operation for more than two years. One of the outcomes of the assessment was that the recovery period is a critical aspect for the electric network. The additional active power provided during operation in inertial response mode must be drawn from the energy stored in the rotating masses. This slows down the WT rotor speed and hence leads to a lower active power output during the recovery period compared to before the activation of the inertial response. The allowed depth and duration of the post-inertial recovery will be regulated in greater detail in future versions of grid codes, e.g. in Québec and the Republic of Ireland. This paper describes an improved version of an inertial response control system that enables a more power systems-friendly provision of such short-term frequency support. It introduces a less pronounced reduction in output power during the recovery period. The new controls allow adjusting the duration of the recovery period, and therefore the re-acceleration phase can be stretched over relatively long time intervals (e.g. one minute). This approach results in small reductions in the output power compared to aggressive re-acceleration over only several seconds. Potential negative effects of inertial response from WTs on the power system in the form of a second frequency nadir during the recovery phase can be minimized. Besides a description of the control system achieving this improved inertial response, the proposed paper contains simulations and experimental results for a Type 4 WT showing the effectiveness of the system.

Reference number:
Wind Integration Workshop
SESSION 6a: Inertia and Frequency Issues