Total transfer capability assessment of HVDC tie‐lines in asynchronous grids

Abstract

This paper discusses how frequency-stable operational decision-making of asynchronous grids with intensive high-capacity HVDC tie-lines, can be achieved leveraging a novel total transfer capability (TTC) evaluation approach. This problem is formulated as a hierarchical optimization model with multiple decision-makers, in which the master problem is solved by the coordinator to determine the base case maximum acceptable transmission power of each HVDC tie-line, while the sending- and receiving-end grid's local TSO each autonomously solves a frequency constrained optimal power flow sub-problem. Coordinated fast and slow frequency arrest strategies are fully integrated into the TTC assessment framework, which not only ensure that last-resort protections are not triggered following the HVDC bi-pole block contingency, but also take advantage of the potential control capability of the sending- and receiving-end grids and would therefore increase the TTC of HVDC tie-lines. A decentralized algorithm based on accelerated analytical target cascading is developed to solve the formulated model. Case studies on a modified two-area RTS-96 system and a practical large-scale system demonstrate the effectiveness of the proposed approach.