Abstract illustration of wind turbines with network nodes.

Advanced ancillary services from wind farms

Ancillary services are supporting services required by the power system operators to maintain correct
functionality of the power system. Future power systems with higher share of renewables will be characterised by lower inertia and potentially weaker frequency regulation. Provision of ancillary services from large wind farms will therefore be even more crucial.

A virtual synchronous machine (VSM) is a common implementation scheme to provide grid forming capabilities and synthetic inertia. A VSM can be applicable in wind farms controlling the power according to the maximum power point tracking (MPPT) during normal conditions. However, as a reaction to disturbances, it can add virtual inertia by extracting energy from the wind turbine rotating inertia.

The power reference tracking in a VSM-based control is in general poorer compared to a classical grid following scheme. The VSM has a slow reaction speed to power production variations since power from the VSM is linked to the virtual rotor position and the virtual inertia acts like a low-pass filter.

Improving the power reference tracking is critical for a wind turbine to avoid needing to oversize the DC bus capacitor. A power feed-forward (PFF) strategy scheme for improving the tracking without affecting grid forming and inertia support has been developed in earlier projects. The PFF was at TRL 3 in Q4 2021 and has been further developed within NorthWind to reach TRL 4. The control scheme originally published has been modified with an additional compensation term to allow a more precise and faster correction. Moreover, the scheme has been implemented in a small scale converter prototype and tested in the National Smartgrid Laboratory. The test results confirm the expected improvements in performance of the VSM-based control concerning power reference tracking.