Professor Nikolaos Gatsis at ECE Spring 2024 Colloquium

Modeling and optimization of electric distribution grids

Electric distribution grids have undergone major transformation, driven by the need to enable novel interactions with the end-user, accommodate electrified transportation, and integrate inverter-based resources that interface renewable energy generation. This talk features recent advances in modeling, analysis, and optimization of three-phase electricity distribution networks. Various practical models for distribution grid components are presented, followed by a three-phase power flow solver called the Z-Bus method. The method amounts to fixed-point iteration on the network nodal voltages and its convergence is established. A consequence is that the power flow problem in three-phase distribution networks has a unique solution over a region that can be explicitly calculated from the network parameters. The talk proceeds with extending the Z-Bus method for short-circuit analysis of distribution networks with grid-following inverters. The latter is well motivated because integration of inverter-based resources into distribution systems impacts the fault currents in the network and the coordination of protection devices. Modern grid codes call for inverter dynamic reactive current control and oftentimes require that the inverter injects both positive and negative sequence currents during faults. The short circuit analysis is coupled with inverter controls modeled in the direct-quadrature (dq) reference frame, which represents their typical implementation. The talk wraps up with review of optimal power flow routines that coordinate various distribution network assets, including step voltage regulators.