Algorithms for Optimal Power Flow in Isolated Distribution Networks Using Different Battery Energy Storage Models

Battery energy storage systems (BESS) are crucial for remote communities operating isolated distribution networks (IDNs) that are transitioning from dependence on diesel generators to renewable energy sources for their energy needs. Since renewable energy sources are variable, these isolated communities still depend on diesel generators during periods when the output of renewable resources are lower than the demand or not available. In order to minimize the dependence on high-cost diesel fuel it is necessary to accurately model the BESS for grid optimization in IDNs. This paper employs existing BESS models, including linear, convex nonlinear, and nonlinear, in a 17 bus test system extracted from the IEEE-123 bus feeder model with the inclusion of network constraints. The optimal power flow problem formulated with each of the three BESS models shows that convex relaxation of the non-convex equation for a non-linear BESS model significantly reduces the computation time with comparable results.