Hierarchical Voltage/VAR security boundaries and margin assessments in Multi-HVDC infeed systems

Abstract

Operational security issues such as a lack of voltage/VAR support and cascading failures triggered by an initial fault present crucial challenges and issues in systems with multiple high-voltage direct current (HVDC) infeeds with both line-commutated converter (LCC) and voltage-source converter (VSC) links. Due to the complexity of the switching strategy for the filter banks in the converter stations, the modeling of the voltage control process inside converter stations is also complex; however, this complexity is not considered in the existing methods, leading to low calculation accuracy. Therefore, this paper proposes an approach based on hierarchical voltage/VAR security boundaries (HVVSBs) and margin assessments for multi-HVDC infeed systems to ensure high calculation accuracy and speed. The voltage/VAR control characteristics of LCC/VSC stations are appropriately formulated by means of a stepwise search method and boundary information, and an HVVSB-based method of dynamic reactive power reserve evaluation is proposed that is suitable for extreme scenarios. Finally, the proposed method is tested in a modified IEEE-118 system to verify its accuracy and effectiveness.