A Generalized Power-Flow Model of VSC-Based Hybrid AC–DC Systems Integrated With Offshore Wind Farms

Abstract

This paper presents a unified power-flow model of ac power systems incorporating voltage-sourced converter (VSC) based multi-terminal high voltage direct current (MTDC) grids. Offshore wind farms (OWFs) are appropriately interfaced with the MTDC grid(s). Pulsewidth modulation control is employed for the VSCs. In the proposed model, the VSC modulation indices are considered as unknowns. The proposed model employs realistic grid control strategies like nonlinear distributed dc voltage control. The power-flow solution is carried out using the Newton–Raphson method. The convergence properties of the proposed algorithm are investigated vis-a-vis varying terminal end active and reactive power specifications of the VSCs and the rectifying power injections of the OWFs, in light of different MTDC control strategies employed. Corresponding to nonlinear dc voltage droop control, five different operating points are considered to observe the sharing of power among the dc terminals with changes in the operating point specifications. The results validate the model.