Differential Evolution for Optimal Siting and Sizing of Flexible AC Transmission System Devices on the IEEE 30-Bus System with Techno-Economic Assessment

The optimal siting and sizing of Flexible AC Transmission System devices is a non-linear, non-convex optimal power flowproblem in which technical benefit must be balanced against high capital cost. This study allocates two static var compensatorsand two thyristor-controlled series capacitors on the IEEE 30-bus system using Differential Evolution, benchmarked against aGenetic Algorithm and Particle Swarm Optimisation under an identical evaluation budget. Each candidate design is evaluatedwith a Newton-Raphson power flow written in MATLAB, and a 24-hour Simulink model links the selected designs to energyloss, net present value and payback. Under the standard voltage limits, a design that ignores cost reduced voltage deviation by 56 percent but reduced loss by only 0.20 percent at a cost of about 6.4 million dollars, whereas a cost-aware design cost about 1.0 million dollars and had a negative net present value because the base case already exceeds the upper voltage limit at two buses. With the upper limit relaxed slightly, the cost-aware solution was a series-compensator-only design costing about 135,000 dollars, with 0.30 percent loss reduction and a payback of 6.4 years. Differential Evolution matched or beat the other algorithms in every case and was significantly better than Particle Swarm Optimisation in all three. When generator voltages and active power were also optimised, loss fell by 72 percent and no compensator was selected, so most of the achievable loss reduction in this model comes from generator re-dispatch rather than from the compensators.