Analysis of Deloaded Wind Power in Hybrid AC/HVDC Systems by Frequency Stability Constrained Optimal Power Flow

This paper investigates the relationship between the frequency support by voltage-source converter based high-voltage direct current (VSC-HVDC) systems and the deloaded wind power operation considering the frequency stability constraints. The frequency stability is incorporated as additional constraints in the optimal power flow (OPF) analysis. The reserve capacity of the wind power plants should be provided for frequency support, which requires wind power output suppression during the steady-state. On the contrary, this wind output curtailment is unnecessary if the frequency stability constraints can be satisfied by the fast frequency controller of the VSC-HVDC system. The optimal wind power deload ratio can be determined by the OPF calculation. A hybrid AC/VSC-HVDC system model is designed based on the IEEE 39-bus system. The inertia emulation control (IEC) method is applied to the slack converter for the primary frequency support. Sensitivity analysis on the frequency stability constraints, and the capacities of wind power plants and HVDC systems are carried out. It is validated that the primary frequency support of VSC-HVDC systems can reduce the wind power output suppression.