Hierarchical Reserve Power Dispatching Strategy of Wind Farms for Grid Frequency Support

Abstract

Wind turbine (WT) is required to support grid frequency in some cases usually by decelerating the rotor speed. However, the available adjustment capacity is limited and short-lasting, requiring reserve power for more capacity. For wind farms (WFs), reserve power dispatching is important both at steady state and during dynamic grid frequency support process, as it influences the lifespan and cost of WFs. Moreover, power dispatching at steady state and during dynamic grid frequency support process may have a mutual impact on their performance. For this regard, this paper proposes a hierarchical reserve power dispatching (HRPD) strategy of WFs for grid frequency support. The hierarchical concept is reflected on the WF and the WT control layers spatially, as well as on the steady-state layer and the dynamic grid frequency support layer temporally. First, the central controller of WF determines the reserve power command of each WT at the steady-state layer according to the total reserve power requirement, where the total fatigue of WFs and the fatigue distribution among WTs are considered to reduce the operating fatigue of the WF and maintain the consistency of WTs. Meanwhile, the WT controller assesses the real-time grid frequency support capability of each WT at the dynamic grid frequency support layer, according to the available kinetic energy of rotor and the real-time pitch angle to optimize the utilization of regulation capacity while maintaining the performance of grid frequency support. Based on this, the central controller adjusts and assigns a dynamic frequency droop coefficient to each WT. Case studies validate the performance of the proposed HRPD strategy in total fatigue reduction, fatigue distribution restriction, and grid frequency support.