Optimization of Wind Power Curtailment by OPF in Hybrid AC/VSC-HVDC Systems With DC Voltage Constraints

Abstract

This paper proposes an optimization method for wind power output curtailment based on optimal power flow (OPF) analysis. The wind curtailment ratio is incorporated as a controllable variable in the OPF formulation. A voltage-source converter based high-voltage direct current (VSC-HVDC) system is installed in a power system model considering large-scale wind farm integration. Inertia emulation control (IEC) is implemented for the VSC-HVDC system. When a disturbance occurs, the VSC-HVDC system can participate in the AC grid frequency stabilization by supplying active power. However, the utilization of the active power in the VSC-HVDC system results in DC grid voltage fluctuation. This fluctuation can be reduced if the IEC frequency control can be replaced by wind-side frequency regulation. However, wind-based frequency control requires wind output suppression to obtain the reserve capacity. This is undesirable for minimizing the fuel cost objective function. In this context, the novel point of this paper is to determine the optimal wind output curtailment considering both the fuel cost objective function and the DC voltage constraints by the OPF analysis. Considering the DC voltage reference deviation occurred by the IEC, the deviation range of the DC voltage reference is limited as an inequality constraint to prevent infeasible DC voltage fluctuations. Based on this approach, the advantage of wind output suppression can be analyzed from the DC voltage perspective. Sensitivity analysis on the DC voltage constraints, wind power plant capacity, and VSC-HVDC system capacity is performed to prove the effectiveness of the proposed method.