Optimal distributed generation planning in distribution networks: A comparison of transmission network models with FACTS

In Distributed Generators (DG) optimal planning solutions, transmission section is modelled as an ideal voltage-controlled bus at 1.0 pu., this ignores the impacts of Flexible Alternating Current Transmission Systems (FACTS). However, modern transmission networks include optimally placed FACTS for improved power quality. Moreover, voltages at Point of Common Coupling (PCC) between transmission and distribution networks varies with FACTS control operations. Hence, these can result in local optimal DG planning solutions. In this paper, a two-bus Thevenin’s equivalent model of transmission section to account for FACTS is proposed. Hybrid line voltage stability indices and particle swarm optimization (LVSI-PSO) obtain a reduced search space, location and sizes of FACTS at transmission section, while Particle Swarm Optimization (PSO) is used to locate and size DG in the distribution section of the test system. The test system is an integrated transmission-distribution network; with modified IEEE 9 bus as transmission section and IEEE 16 node as distribution section. Modification of driving point and transfer impedance of Zbus matrix account for Thyristor Controlled Series Compensator (TCSC) and Static Var Compensator (SVC). Results show that solutions obtained with transmission network modelled as an ideal voltage-controlled bus is a local optimal solution compared with integrated transmission-distribution network model and Thevenin’s equivalent model. The Proposed Thevenin’s equivalent model through parameter estimations Eth and Zth closely matches results from the integrated test system.