Frequency regulation strategy of over-speed wind turbines considering power deficit and system reserve capacity

The integration of large-scale renewable energy sources has led to a reduction in the equivalent inertia of the power grid and insufficient primary frequency regulation capability. To address this issue, a frequency regulation strategy for over-speed wind turbines based on power deficit and reserve capacity is proposed. Firstly, the modified system frequency response model with primary frequency regulation of wind turbines is established, and the time domain expression of the system frequency response following a disturbance is derived based on the modified model. Subsequently, the initial rate of change of frequency following a disturbance is used to roughly estimate the system's power deficit, which is compared with the system reserve capacity. When the reserve capacity is sufficient, the frequency regulation strategy of wind turbines is designed to optimize the comprehensive dynamic frequency indicators of the system. When the reserve capacity is insufficient, the frequency regulation strategy of wind turbines is designed to maximize the time at which the system frequency reaches its lowest frequency limit. Finally, when the reserve capacity is sufficient, the steady-state frequency after the completion of primary frequency regulation is used to accurately calculate the system power deficit. A secondary power increase for wind turbines is then designed to further enhance the system final frequency. Case study analysis demonstrates that the proposed frequency regulation strategy of over-speed wind turbines, which takes into account the system varying power deficits and reserve capacities, can improve the dynamic frequency indicators of the system, delay the time at which the frequency reaches its lowest frequency limit and can even achieve zero-error frequency regulation.