Hybrid HVAC/DC transmission capacity expansion planning considering large-scale renewable-based energy storage systems to mitigate network-associated flexibility insufficiency

This paper presents a new multi-period hybrid high-voltage alternating/direct current (HVAC/DC) model for transmission capacity expansion planning to address network-associated flexibility (NAF) insufficiency. For this purpose, the proposed model, from a new viewpoint, allows the reinforcement and/or installation of HVAC and multiterminal voltage source converter-based HVDC transmission lines, as well as the deployment of composite solar and wind farms (S&WFs) across the transmission network. Additionally, to offset the intermittency of composite S&WFs, large-scale compressed-air and subsurface hydrogen energy storage systems (C&HESSs) are integrated in coordination with these renewable farms. On this basis, two incommensurable objective functions, namely the net present values of the total investment and operation costs, as well as the congestion-caused NAF insufficiency measure, are considered, which are to be minimized simultaneously subject to a set of technical, operational, discrete logical, and financial constraints. The resulting non-convex mixed-integer nonlinear optimization problem is solved using a two-stage posterior implementation procedure, comprising a multi-objective symphony orchestra search algorithm to obtain the Pareto-front solutions, and a combination of fuzzy entropy weight and affiliation degree techniques to find the most preferred solution. The newly developed model is tested on the Iranian 400-kV transmission network, and its effectiveness and practicality are confirmed through comprehensive simulation studies.