A novel dynamic inertial control of wind turbines based on event size estimation

High penetration of variable renewable energy sources causes volatile grid frequency movements in low inertia systems. Large-scale wind turbines (WTs) are stipulated to participate in frequency control upon occurring a disturbance event. This paper proposes a novel inertial control scheme aimed at improving the frequency nadir based on frequency event size (FES) estimation. Upon occurring a frequency event, the WTs immediately inject a stepwise active power into the grid, and its corresponding frequency deviation is measured to estimate the FES using mean absolute error solution of a sinusoidal exponential function regression. Subsequently, an inertial control is developed to mitigate the frequency movements taking into account the available kinetic energy in rotating masses of WTs and estimated FES. To ensure a safe rotor speed recovery to its maximum power point tracking mode within this scheme, the rotor speed recovery time, and the second frequency drop can be flexibly adjusted. The WTs overproduction and recovery stages are dynamically adapted to wind speed fluctuations based on the defined modifications and rules. Additionally, the scheme considers the latency of communication delay during FES estimation. The proposed method is validated using a large-scale wind farm integrated into IEEE 9bus and 39-bus test systems in Digsilent PowerFactory. Comparison results with existing methods in the literature demonstrate that the proposed scheme achieves better frequency nadir improvement across various types and sizes of events and wind speeds. Furthermore, it exhibits robust performance against communication latencies. Finally, the experimental results support the findings in terms of FES estimation.