A Multi-objective Transmission Expansion Planning Strategy: A Bilevel Programming Method

This paper describes a methodology for transmission expansion planning (TEP) within a deregulated electricity market. Two objective functions including investment cost (IC) and congestion cost (CC) are considered. The proposed model forms a bi-level optimization problem in which upper level problem represents an independent system operator (ISO) making its decisions on investment while in the lower level, the market clearing problem is formulated. ISO tries to minimize the investment cost on new transmission capacity to be installed and to minimize the congestion cost. Minimizing the CC can facilitate the competition between market participants. Locational marginal prices (LMPs) which are necessary to be calculated for the congestion cost are obtained at the lower level. The LMP of buses are dual variables of the corresponding active power balance equation. Lower problem is replaced by its Karush-Kuhn-Tucker (KKT) conditions resulting in a one-level optimization problem which can be efficiently solved by commercial existing solvers. The formulated multi-objective mathematical programming is solved by augmented ε-constraint method which is able to produce the Pareto-optimal solutions. The presented framework is applied to a simple 3-bus power system and also IEEE 24-bus reliability test system (RTS). Results from these illustrative examples are reported and thoroughly discussed. The results show the effectiveness of the presented work.