Optimization of Economic Dispatch in Three-Phase Unbalanced Microgrid System with Distributed Generation

Priya Thekkumparambath Mana

The future of the electric power grid is envisioned to include distributed sources of energy. Distributed sources including renewable generation can promote emission reduction and resiliency in the grid. Microgrids provide an ideal platform for realization of these goals. This thesis aims to promote microgrid penetration in the conventional electric power grid through optimization of economic dispatch at the microgrid level. The solutions explored here aid the microgrid operator at Microgrid Systems Central Controller (MGCC) in balancing demand and supply of real power within a microgrid system while minimizing operational costs. An optimizer was developed based on the principles of Particle Swarm Optimization (PSO) algorithm. This was used to calculate economic dispatch which involved decisions regarding how much each generator should produce (set-points) and how much power should be purchased from the bulk grid. The simulations were implemented on a microgrid system developed from IEEE 13-bus test feeder with three-phase unbalanced load and generation. The optimizer set-points were dispatched to the microgrid system every 15 minutes. The validity of the optimizer output for 15 minutes duration was checked against power flow simulation per second in the microgrid system. In the presence of varying loads and renewable generation, a difference of less than 200 kW was observed between the optimizer set-points and the actual system output in grid-connected mode. In islanded mode of operation, the optimizer was focused mainly on maintaining power balance because of the unavailability of bulk grid backup. The dispatch decisions including battery storage system charging/discharging and load curtailment taken by the optimizer kept the microgrid running even during islanded mode. The price of operating the microgrid in various grid-connected scenarios was compared. The least operating cost was observed when power was purchased from bulk grid during off-peak load hours and distributed generators like microturbines within the microgrid were used during peak-load hours. The mismatch of set-points and actual data during grid-connected mode can be fulfilled by the bulk grid. In islanded mode, battery storage system and diesel generators provide slack bus functionality in absence of the bulk grid. The performance and accuracy of optimizer with various objective functions such as cost minimization and self-sufficiency in grid-connected mode and reliable power during islanded mode was verified using 24-hour long simulations.

Optimization of Economic Dispatch in Three-Phase Unbalanced Microgrid System with Distributed Generation

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