Efficient and Robust Power Flow Algorithm for Asynchronous Grids Coupled Through a VSC-MTDC System and Its Probability Analysis

Abstract

With the interconnection of asynchronous ac grids through a voltage source converter-based multiterminal direct current (AGs/VSC-MTDC) system and the large-scale integration of renewable energy, it is important to resolve the power flow calculation problems efficiently and robustly for secure and economic operation of such system under stochastic context. Therefore, an improved sequential algorithm for deterministic power flow (DPF) of AGs/VSC-MTDC system is proposed first. This enhances the conventional manner of updating power losses of VSCs, which leads to a one-shot DPF solution of the ac/dc grid, thus boosting the efficiency; while the coupling of ac/dc systems is considered to remain high accuracy. In combination with the efficient DPF method for each sample, probabilistic power flow (PPF) analysis of the AGs/VSC-MTDC system is performed by using Zhao's three-point estimate method (Z-3PEM) with much fewer samples, thus achieving a higher efficiency with good accuracy. In addition, the PPF analysis of AGs/VSC-MTDC systems being more prone to the poor robustness in stochastic scenarios is effectively addressed, benefitting from the decreased nonconvergence of improved DPF and fewer extreme samples of Z-3PEM. Finally, the effectiveness and performance of works are verified through the results on an 11-terminal VSC-MTDC system with three asynchronous ac grids modified from different IEEE test systems.