Impact of wind variation on the measurement of wind turbine inertia provision

Wind turbine (WT) control is being adapted to enable inertia provision that supports network frequency on short timescales. Measuring the inertia contribution from wind turbines is critical to asses the provision of the service as well as understand the WT operation. However, inertia measurement methods disagree on the impact of the wind and how to approximate its effects. This paper uses data from a Scottish Power Renewables (SPR) test of a grid connected wind farm to highlight that wind can impact inertia provision and that external network power measurements are unable to measure the inertia. Two proposals are made to improve inertia measurements. First, the International Electrotechnical Commission (IEC) industrial standard for WT inertia measurement is adapted, and secondly, an alternate method using system identification is proposed that considers characteristics of the WT's dynamic response. The measurement methods from the literature and the proposals are assessed using the output of time-domain WT models to find the sensitivity of their accuracies to variations in the wind, frequency, and control-setting conditions. The methods from the literature are inaccurate during variable wind conditions but the proposed approaches improve the accuracy. The findings of the sensitivity study are then validated by applying the measurement methods to the SPR wind farm experimental data and confirm that the proposed system identification method is the most accurate measurement approach.